WO2025128188A1 - Curable resins containing pvc - Google Patents

Abstract

A PVC-containing resin for additive manufacturing, comprising polyvinyl chloride (PVC) dissolved in a liquid base resin, and methods of making and using the same.

Description

CURABLE RESINS CONTAINING PVC

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority to U.S. Provisional Application No. 63/609,069, filed December 12, 2023, which is incorporated by reference herein in its entirety.

GOVERNMENT SUPPORT CLAUSE

[0002] This invention was made with government support under Grant No. 2132133 awarded by the National Science Foundation. The Government has certain rights in the invention.

BACKGROUND

[0003] Recycling of polyvinyl chloride (PVC) faces significant hurdles due to the complex composition of post-consumer products and limited collection of PVC. PVC, the third most manufactured plastic in the world, requires recycling methods that rely on energy intensive processes and contaminate recycling streams. A lack of widespread markets for recycled PVC materials further hinders its sustainability as plastic material. As such, there exists a need for improved methods for the reuse and recycling of PVC. These needs and others are at least partially satisfied by the present disclosure.

SUMMARY

[0004] Disclosed herein are PVC-containing resins suitable for use on photocuring (SLA) 3D printers or in other additive/conventional manufacturing techniques (e.g., injection molding). Organic solvents are used to formulate and customize 3D printing resins to achieve new combinations of desirable properties. This provides a low-cost, safe, and environmentally- friendly approach to recycling PVC materials and expands the utility of SLA and other additive manufacturing resins.

[0005] In an aspect, provided is a PVC-containing resin for additive manufacturing, including polyvinyl chloride (PVC) dissolved in a liquid base resin.

[0006] In another aspect, provided is a method of additive manufacturing (e.g., 3D printing, injection molding) an article, the method including: a) providing any of the disclosed PVC- containing resins; and b) curing the PVC-containing resin to form an article. [0007] In another aspect, provided is a solid article formed by any of the disclosed methods of additive manufacturing.

[0008] In another aspect, provided is a method of preparing a PVC-containing resin for additive manufacturing, the method including: a) contacting a quantity of PVC with an organic solvent to form a PVC extract including a soluble fraction of PVC and the organic solvent; and b) dissolving at least a portion of the PVC extract into a liquid base resin to form a PVC- containing resin including PVC.

[0009] Other systems, methods, features and/or advantages will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features and/or advantages be included within this description and be protected by the accompanying claims.

BRIEF DESCRIPTION OF DRAWINGS

[0010] FIGURE 1 depicts an overview of PVC-containing resin formulation and 3D printing workflow.

[0011] FIGURE 2 depicts 3D printed dogbone samples containing 12.5% by mass PVC (left); dogbones in mechanical testing instrument (middle); stress-strain curves for dogbones with 0 - 50% PVC by mass (right).

[0012] FIGURE 3 depicts High resolution 3D prints from PVC-containing SLA resin. Left: ring, OD = 22 mm, ID = 20 mm, h = 4 mm; Right: UA logo, A = 50 mm x 50 mm area, h = 12 mm.

[0013] FIGURE 4 is an illustration of the single-step and sequential fractionation of PVC in this work.

[0014] FIGURE 5 is a photograph of PVC pipe trimmings (left) and PVC pellets (right).

[0015] FIGURE 6 is an FTIR spectra of PVC pipe, and PVC pipe cleaned via dissolution, centrifuge and precipitation.

[0016] FIGURE 7 is an FTIR spectra of PVC pellet, plasticizer (DINP) extracted by soaking PVC pellets in a 60% Ace - 40% MeOH solvent mixture, and PVC pellet cleaned via dissolution, centrifuge and precipitation.

[0017] FIGURE 8 depicts a comparison between solvent-based recovery of “whole” plastic and solvent-based fractionation of specific plastic “grades.” Note that the recovery method can be reversed, with the recovered material being the insoluble (In fractionation terminology, recovery of the soluble = solvent extraction, recovery of the insoluble = fractional precipitation). [0018] FIGURE 9 depicts the weight average molecular weight (M_w, log scale) of (A) PVC K-50 single-step, ( • ) PVC K-50 sequential and (■) commercial PVC sequential fractionations in different solvent systems. Bottom X: content of solvent systems. Top X: Hansen Solubility Parameter (HSP) Distance Ra (MPa^1/2) of corresponding solvent system.

[0019] FIGURE 10 depicts the ratio of surface area for PVC in Ace-MeOH and THF- MeOH mixes at different MeOH % and at different npvc.

[0020] FIGURES 11A-11C depict FTIR spectra for PVC K-50 single-step fractionation (FIG. HA), PVC K-50 sequential fractionation (FIG. 11B) and sequential commercial fractionation (FIG. 11C).

[0021] FIGURE 12 depicts predicted T_g values using the Flory-Fox Equation. A Single- step PVC K-50 fractions, • Sequential PVC K-50 fractions, ■ sequential commercial PVC fractions , * other fractions (individually labeled).

[0022] FIGURE 13 depicts solution dynamic viscosity (p) of acetone fractions of PVC K- 50 and K-65. Solution concentration: 100 mg PVC per 1 mL solvent (THF).

[0023] FIGURES 14A-14B depict volume of mixing (cm³/kg) (FIG. 14A) and Flory- Huggins interaction parameter

(FIG. 14B) for PVC in Ace-MeOH and THF-MeOH mixes at different MeOH % and at different npvc.

[0024] FIGURE 15 depicts Hansen Solubility Parameter (HSP) Distance Ra (MPa^1/2) between PVC and Ace-MeOH and THF-MeOH mixtures at different % MeOH.

DETAILED DESCRIPTION

[0025] It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate aspects, can also be provided in combination with a single aspect. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single aspect, can also be provided separately or in any suitable subcombination. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure.

[0026] In this specification and in the claims that follow, reference is made to a number of terms, which shall be defined to have the following meanings:

[0027] Throughout the description and claims of this specification, the word “comprise” and other forms of the word, such as “comprising” and “comprises,” means including but not limited to, and are not intended to exclude, for example, other additives, segments, integers, or steps. Furthermore, it is to be understood that the terms comprise, comprising, and comprises as they relate to various aspects, elements, and features of the disclosed invention also include the more limited aspects of “consisting essentially of’ and “consisting of.”

[0028] As used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a “polymer” includes aspects having two or more such polymers unless the context clearly indicates otherwise.

[0029] Ranges can be expressed herein as from “about” one particular value and/or to “about” another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It should be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. In some aspects, about can be ± 5% of the stated value, e.g., ± 1, 2, 3, 4, or 5 % of the stated value.

[0030] As used herein, the terms “optional” or “optionally” mean that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

[0031] For the terms “for example” and “such as,” and grammatical equivalences thereof, the phrase “and without limitation” is understood to follow unless explicitly stated otherwise. [0032] As used herein, the terms “resin” or “liquid base resin” refer to a liquid composition which can be converted into a polymer (e.g., cured, hardened, etc.). Such resins can include polymer precursors (e.g., monomers, oligomers), polymerization initiators, hardeners, dyes, pigments, or any other suitable additives which are known in the art.

PVC-CONTAINING RESINS AND SOLID ARTICLES

[0033] In an aspect, provided is a PVC-containing resin for additive manufacturing, including polyvinyl chloride (PVC) dissolved in a liquid base resin.

[0034] In some aspects, the liquid base resin can include monomers, oligomers, polymerization initiators, dyes, pigments, or any combination thereof. In some aspects, the liquid base resin can include monomers and/or oligomers of polypropylene, acrylonitrile butadiene styrene (ABS), polyethylene, polystyrene, acrylic, polycarbonate, polyethylene terephthalate, polyurethane, epoxy, or any combination thereof. [0035] In some aspects, the PVC can be present in an amount of from about 1 wt% to about 50 wt%, or from about 5 wt% to about 45 wt%, or from about 10 wt% to about 40 wt%, or from about 15 wt% to about 35 wt%, or from about 20 wt% to about 30 wt%, or from about 1 wt% to about 25 wt%, or from about 5 wt% to about 20 wt%, or from about 10 wt% to about 15 wt%, or from about 25 wt% to about 50 wt%, or from about 30 wt% to about 45 wt%, or from about 35 wt% to about 40 wt % relative to the total weight of the PVC-containing resin.

[0036] In some aspects, the PVC can have an average molecular weight of from about 1,000 g/mol to about 100,000 g/mol, or from about 10,000 g/mol to about 90,000 g/mol, or from about 20,000 g/mol to about 80,000 g/mol, or from about 30,000 g/mol to about 70,000 g/mol, or from about 40,000 g/mol to about 60,000 g/mol, or from about 1,000 g/mol to about 50,000 g/mol, or from about 10,000 g/mol to about 40,000 g/mol, or from about 20,000 g/mol to about 30,000 g/mol, or from about 50,000 g/mol to about 100,000 g/mol, or from about 60,000 g/mol to about 90,000 g/mol, or from about 70,000 g/mol to about 80,000 g/mol, or from about 1,000 g/mol to about 10,000 g/mol, or from about 2,000 g/mol to about 10,000 g/mol, or from about 3,000 g/mol to about 10,000 g/mol, or from about 4,000 g/mol to about 10,000 g/mol, or from about 5,000 g/mol to about 10,000 g/mol.

[0037] In some aspects, the PVC can have a poly dispersity index (PDI) of from about 1 to about 2, or from about 1.05 to about 1.95, or from about 1.1 to about 1.9, or from about 1.15 to about 1.85, or from about 1.2 to about 1.8, or from about 1.25 to about 1.75, or from about 1.3 to about 1.7, or from about 1.35 to about 1.65, or from about 1.4 to about 1.6, or from about 1.45 to about 1.55, or from about 1 to about 1.5, or from about 1.05 to about 1.45, or from about 1.1 to about 1.4, or from about 1.15 to about 1.35, or from about 1.2 to about 1.3, or from about 1.5 to about 2, or from about 1.55 to about 1.95, or from about 1.6 to about 1.9, or from about 1.65 to about 1.85, or from about 1.7 to about 1.8.

[0038] In some aspects, the PVC can have a glass transition temperature (T_g) of from about 40°C to about 90°C, or from about 45°C to about 85°C, or from about 50°C to about 80°C, or from about 55°C to about 75°C, or from about 60°C to about 70°C, or from about 40°C to about 65°C, or from about 45°C to about 60°C, or from about 50°C to about 55°C, or from about 65°C to about 90°C, or from about 70°C to about 85°C, or from about 75°C to about 80°C.

[0039] In some aspects, the PVC can be sufficiently uniformly dispersed in the liquid base resin.

[0040] In some aspects, the PVC-containing resin can include one or more copolymers of PVC. For example, in some aspects, the PVC-containing resin can include PVC-acetate. In some aspects, the PVC-containing resin can include PVC and one or more copolymers of PVC. In other aspects, the PVC containing resin can include only copolymers of PVC.

[0041] In another aspect, provided is a method of additively manufacturing (e.g., 3D printing, injection molding) an article, the method including: a) providing any of the disclosed PVC-containing resins; and b) curing the PVC-containing resin to form an article. In some aspects, the method can further include heating the PVC-containing resin, for example, before, during, or after step a). In some aspects, heating the PVC-containing resin can increase the solubility of the PVC in the liquid base resin. In some aspects, heating the PVC-containing resin can decrease the viscosity of the PVC-containing resin to facilitate additive manufacturing.

[0042] In some aspects, step b) can include irradiating the PVC-containing resin with a light source; and the light source can polymerize the resin into a solid plastic, thereby forming the solid article. In some aspects, step b) can include heating the PVC-containing resin. In some aspects, step b) can include altering the pH of the PVC-containing resin.

[0043] In another aspect, provided is a solid article formed by any of the disclosed methods of additive manufacturing. In some aspects, the PVC can be sufficiently uniformly dispersed in the solid plastic.

[0044] In some aspects, the solid article can have an elastic modulus that is from about 1% to about 90% lower than a reference solid article made from the liquid base resin without PVC, or from about 5% to about 85% lower, or from about 10% to about 80% lower, or from about 15% to about 75% lower, or from about 20% to about 70% lower, or from about 25% to about 65% lower, or from about 30% to about 60% lower, or from about 35% to about 55% lower, or from about 40% to about 50% lower, or from about 1% to about 50% lower, or from about 5% to about 45% lower, or from about 10% to about 40% lower, or from about 15% to about 35% lower, or from about 20% to about 30% lower, or from about 50% to about 90% lower, or from about 55% to about 85% lower, or from about 60% to about 80% lower, or from about 65% to about 75% lower.

[0045] In some aspects, the solid article can stretch from about 120% to about 200% of its original length, or from about 130% to about 190%, or from about 140% to about 180%, or from about 150% to about 170%, or from about 120% to about 160%, or from about 130% to about 150%, or from about 160% to about 200%, or from about 170% to about 190%. In some aspects, the solid article can stretch more than 200% of its original length. METHODS OF PREPARING PVC-CONTAINING RESINS

[0046] In an aspect, provided is a method of preparing a PVC-containing resin for additive manufacturing, the method including: a) contacting a quantity of PVC with an organic solvent to form a PVC extract including a soluble fraction of PVC and the organic solvent; and b) dissolving at least a portion of the PVC extract into a liquid base resin to form a PVC- containing resin including PVC.

[0047] In some aspects, the PVC in the PVC-containing resin can be sufficiently uniformly dispersed in the liquid base resin.

[0048] In some aspects, the method of preparing a PVC-containing resin can start from virgin PVC (i.e., without additives), formulated PVC (e.g., PVC pellets which may have additives but have not been processed), or commercial PVC products (e.g., “rigid” PVC pipe, pipe fittings, shower liners, cladding, siding) of the form that could be obtained from a concentrated waste management program focused on construction sites. In some aspects, the method of preparing a PVC-containing resin can start from post-consumer PVC (e.g., packaging, containers, tubing) where any number of other components/additives may be present. In still further aspects, by “PVC” is also meant related chlorinated plastics such as CPVC, CPE, and PVDC. In some aspects, the PVC can be cut into smaller pieces, e.g., using grinding, chopping, or shredding. In some aspects, the method of preparing a PVC-containing resin can start from any combination of the above-mentioned types of PVC.

[0049] In some aspects, the method of preparing a PVC-containing resin can start from PVC having a K value of from about 50 to about 75, or from about 50 to about 70, or from about 50 to about 65, or from about 50 to about 60, or from about 50 to about 55, or from about 55 to about 70, or from about 60 to about 65.

[0050] In some aspects, the method of preparing a PVC-containing resin can start from one or more copolymers of PVC. For example, in some aspects, the method of preparing a PVC- containing resin can start from PVC-acetate. In some aspects, the method of preparing a PVC- containing resin can start from PVC and one or more copolymers of PVC. In other aspects, the method of preparing a PVC-containing resin can start from only copolymers of PVC.

[0051] In some aspects, the organic solvent can include ethyl acetate, acetone, methyl acetate, tetrahydrofuran (THF), methanol, methyl ethyl ketone, 2-methyltetrahydrofuran (2- MeTHF), cyclohexanone, or any combination thereof.

[0052] In some aspects, the PVC extract can further include an insoluble fraction of PVC, and step a) can further include removing said insoluble fraction of PVC from the PVC extract. In some aspects, the insoluble fraction of PVC can be removed via filtration. In other aspects, the insoluble fraction of PVC can be removed via decantation.

[0053] In some aspects, the method can further include at least partially evaporating the organic solvent from the PVC extract before step b). In some aspects, the method can further include at least partially evaporating the organic solvent from the PVC-containing resin during or after step b).

[0054] In some aspects, step a) can further include: i) contacting the quantity of PVC with a first organic solvent to form a first PVC extract including a first soluble fraction of PVC and the first organic solvent; ii) at least partially precipitating the soluble fraction of PVC; and iii) dissolving the precipitated PVC in a second organic solvent to form a second PVC extract including a second soluble fraction of PVC and the second organic solvent; and the second PVC extract can be used as the PVC extract in step b).

[0055] In some aspects, step ii) can include at least partially evaporating the first organic solvent from the first PVC extract and/or adding a non-solvent to the first PVC extract. In some aspects, the non-solvent can include water, methanol, alkanes, or any combination thereof.

[0056] It is understood that the above description of the organic solvent may also describe the first and second organic solvents. For example, in some aspects, each of the first organic solvent and the second organic solvent can independently include ethyl acetate, acetone, methyl acetate, tetrahydrofuran (THF), methanol, methyl ethyl ketone, 2-methyltetrahydrofuran (2- MeTHF), cyclohexanone, or any combination thereof. In some aspects, the first organic solvent can have a same composition as the second organic solvent. In other aspects, the first organic solvent can have a different composition than the second organic solvent.

[0057] In some aspects, the first PVC extract can further include a first insoluble fraction of PVC and/or the second PVC extract can further include a second insoluble fraction of PVC, and step a) can further include removing the first insoluble fraction of PVC from the first PVC extract and/or removing the second insoluble fraction of PVC from the second PVC extract. In some aspects, the first insoluble fraction of PVC and/or the second insoluble fraction of PVC can be removed via filtration. In other aspects, the first insoluble fraction of PVC and/or the second insoluble fraction of PVC can be removed via decantation.

[0058] In some aspects, the second soluble fraction of PVC can have a lower molecular weight and/or a lower poly dispersity index (PDI) than the first soluble fraction of PVC.

[0059] In some aspects, step a) can further include repeating steps ii) and ii) any number of times, for example, 1 time, 2 times, 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, or more, and the final PVC extract produced in the final repetition can be used as the PVC extract in step b).

[0060] In some aspects, each repetition of step ii) can include at least partially evaporating each organic solvent from some or all of the PVC extracts and/or adding a non-solvent to some or all of the PVC extracts. In some aspects, the non-solvent can include water, methanol, alkanes, or any combination thereof. In some aspects, each non-solvent can have a same composition. In other aspects, each non-solvent can have a different composition.

[0061] It is understood that the above description of the organic solvent may also describe any of the organic solvents in any of the repetitions. For example, in some aspects, each of the organic solvents can independently include ethyl acetate, acetone, methyl acetate, tetrahydrofuran (THF), methanol, methyl ethyl ketone, 2-methyltetrahydrofuran (2-MeTHF), cyclohexanone, or any combination thereof. In some aspects, each organic solvent can have the same composition. In other aspects, each organic solvent can have a different composition. In some such aspects, each subsequent organic solvent can increase the amount of at least one component (for example, by about 1%, about 2%, about 3% about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, or about 25%) and decrease the amount of at least one other component by the same amount. By means of specific example, in some specific aspects, each subsequent organic solvent can increase the amount of acetone and/or THF (for example, by about 1%, about 2%, about 3% about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, or about 25%) and decrease the amount of methanol by the same amount.

[0062] In some aspects, some or all of the PVC extracts can further include an insoluble fraction of PVC, and step a) can further include removing each insoluble fraction of PVC from some or all of the PVC extracts. In some aspects, each insoluble fraction of PVC can be removed via filtration. In other aspects, each insoluble fraction of PVC can be removed via decantation.

[0063] In some aspects, each soluble fraction of PVC can have a lower molecular weight and/or a lower poly dispersity index (PDI) than the preceding soluble fraction of PVC.

[0064] In some aspects, the liquid base resin can include monomers, oligomers, polymerization initiators, dyes, pigments, or any combination thereof. [0065] In some aspects, the liquid base resin can include monomers and/or oligomers of polypropylene, acrylonitrile butadiene styrene (ABS), polyethylene, polystyrene, acrylic, polycarbonate, polyethylene terephthalate, polyurethane, epoxy, or any combination thereof.

[0066] In some aspects, the PVC-containing resin can include from about 1 wt% to about 50 wt% PVC, or from about 5 wt% to about 45 wt% PVC, or from about 10 wt% to about 40 wt% PVC, or from about 15 wt% to about 35 wt% PVC, or from about 20 wt% to about 30 wt% PVC, or from about 1 wt% to about 25 wt% PVC, or from about 5 wt% to about 20 wt% PVC, or from about 10 wt% to about 15 wt% PVC, or from about 25 wt% to about 50 wt% PVC, or from about 30 wt% to about 45 wt% PVC, or from about 35 wt% to about 40 wt % PVC relative to the total weight of the PVC-containing resin.

[0067] In some aspects, the PVC in the PVC-containing resin can have an average molecular weight of from about 1,000 g/mol to about 100,000 g/mol, or from about 10,000 g/mol to about 90,000 g/mol, or from about 20,000 g/mol to about 80,000 g/mol, or from about 30,000 g/mol to about 70,000 g/mol, or from about 40,000 g/mol to about 60,000 g/mol, or from about 1,000 g/mol to about 50,000 g/mol, or from about 10,000 g/mol to about 40,000 g/mol, or from about 20,000 g/mol to about 30,000 g/mol, or from about 50,000 g/mol to about 100,000 g/mol, or from about 60,000 g/mol to about 90,000 g/mol, or from about 70,000 g/mol to about 80,000 g/mol, or from about 1,000 g/mol to about 10,000 g/mol, or from about 2,000 g/mol to about 10,000 g/mol, or from about 3,000 g/mol to about 10,000 g/mol, or from about 4,000 g/mol to about 10,000 g/mol, or from about 5,000 g/mol to about 10,000 g/mol.

[0068] In some aspects, the PVC in the PVC-containing resin can have a poly dispersity index (PDI) of from about 1 to about 2, or from about 1.05 to about 1.95, or from about 1.1 to about 1.9, or from about 1.15 to about 1.85, or from about 1.2 to about 1.8, or from about 1.25 to about 1.75, or from about 1.3 to about 1.7, or from about 1.35 to about 1.65, or from about 1.4 to about 1.6, or from about 1.45 to about 1.55, or from about 1 to about 1.5, or from about 1.05 to about 1.45, or from about 1.1 to about 1.4, or from about 1.15 to about 1.35, or from about 1.2 to about 1.3, or from about 1.5 to about 2, or from about 1.55 to about 1.95, or from about 1.6 to about 1.9, or from about 1.65 to about 1.85, or from about 1.7 to about 1.8.

[0069] In some aspects, the PVC in the PVC-containing resin can have a glass transition temperature (T_g) of from about 40°C to about 90°C, or from about 45°C to about 85°C, or from about 50°C to about 80°C, or from about 55°C to about 75°C, or from about 60°C to about 70°C, or from about 40°C to about 65°C, or from about 45°C to about 60°C, or from about 50°C to about 55°C, or from about 65°C to about 90°C, or from about 70°C to about 85°C, or from about 75°C to about 80°C. [0070] In some aspects, the method can produce any of the disclosed PVC-containing resins described above.

EXAMPLES

Example 1: Synthesis of Resin

[0071] Translucent AB S-like photopolymer resin (UV wavelength 405nm) from ELEGOO was used as a parent solution. Two types of PVC-containing solutions were used to form a PVC extract. The PVC extract was dissolved in either tetrahydrofuran (THF) with 0.25 g PVC in 1 mL of THF, or in ethyl acetate (EA) with 0.875 g PVC in 1 mL of EA. The weight% of PVC (actual extracted PVC dissolved in THF or EA) was varied from 0, 5, 15, 25 and 50.

[0072] In order to homogeneously mix and distribute the extracted PVC in the ABS-like resin, it was first dissolved in THF or EA solvents, and then those solutions were mixed with appropriate concentrations. The amounts of ingredients were taken such that the final blend of PVC-resin was around 30 g or ~30 mL.

[0073] For THF, the first appropriate amount of ABS-like resin was weighed in a beaker along with 25 wt% PVC (e.g., 7.5 g of PVC in 22.5 g of ABS-like resin). To get 7.5 g of dissolved PVC in the blend, about 30 mL of PVC-THF solution was added into the resin. The blend was then covered with a UV-blocking lid to rule out photopolymerization of blended resin. The blend was stirred overnight at 200 rpm at room temperature in order to eliminate the THF from the blend. The stirring not only allowed homogeneous mixing of the PVC particles in the resin, but also upped the evaporation rate of THF.

[0074] The weight of PVC-resin blend was measured before and after stirring overnight. The blend was not kept stirring for long time to avoid evaporating the other solvents in the ABS-like resin itself. Once the desired amount of THF was eliminated, the PVC-containing resin was then transferred into the resin tray of SLA 3D printer (MARS 2P from ELEGOOO) and allowed to sit there for 10 min. The resin tray and the build plates were initially cleaned thoroughly with IPA and dried. The leveling of the build plate was performed.

[0075] Similar steps were performed for the PVC-EA solution. In the case of EA, less quantity of PVC-EA solution was required because of a higher dissolved concentration of PVC in EA. For 25 wt%, only 8.57 mL of PVC-EA solution was required to mix 7.5 g PVC in the ABS-like resin.

[0076] Meanwhile, the object to be printed (Tensile bars or PVC molecular structure or ring or Alabama Roll Tide A logo) was sliced using CHITUBOX proprietary software (from ELEGOO) with appropriate UV-exposure time and fed to the 3D printer when the PVC-resin blend was ready (without any air bubbles). [0077] After the objects were 3D-printed, they were thoroughly washed with IPA before being removed from the build plate. Once removed, they were again rinsed in IPA and finally cured in a UV-curing machine (ELEGOO Mercury Plus) to further photocure any remnant semi-solid resin of the printed object.

Example 2: Photocurable PVC-Containing Liquid Resin for 3D Printing

[0078] Polyvinyl chloride (PVC), widely used plastic in day-to-day life, is difficult to recycle because of its high chlorine content. One of the ways to mitigate it as waste is to reuse/upcycle it by blending it with other 3D-printing resins not only to reduce the overall resin cost but also to improve the desired properties of the end-product. The PVC resins (from which PVC products are made) are classified by their K-value (range: 50-75), an empirical parameter closely related to intrinsic viscosity (indirectly to flowability), an indicator of the molecular weight and the degree of polymerization. In general, high K-value comes with high molecular weight resin for strength, and low K-values offer easier processing.

[0079] Incorporating PVC directly into SLA 3D printing resins (e.g., acrylonitrilebutadiene- styrene (ABS)-like liquid resin) is challenging as they both do not have a common solvent to mix. Hence, from the 3D-printing point of perspective, the lowest concentration of PVC (lower molecular weight) in the form of extract was utilized by dissolving in a volatile solvent as means of dissolving PVC into the resin. A study was conducted in which two different commercial PVC resin powders, K-50 and K-65 (obtained from a major US supplier), were utilized to obtain the PVC extracts. K-50 is used for some demanding applications, like blending resins, to reduce the costs and are easier to process. K-65 has a good balance of mechanical property and processibility. The preparation of PVC extracts involved a process in which about 300 g of PVC resin powder was mixed with ~2.5 L of solvent (ethyl acetate or acetone) in a container. The mixture was gently agitated to promote mixing and then allowed to settle. Then, the mixture was vacuum-filtered and the liquid volume from the filtration was reduced via rotary evaporation by around 80-90%. The resulting solution was then kept in a large beaker, and ~2.5 L of methanol was added to this to precipitate PVC. The solution was stirred for 2-3 days. Finally, the precipitate was obtained by vacuum-filtration and then dried in a vacuum oven for 2 days. The dried precipitate is the desired extract that was then used to dissolve in a solvent of interest for further processing.

[0080] The extraction of K-50 and K-65 PVC resins was performed using two solvents such as ethyl acetate (EtOAc) and acetone (Ace), respectively. EtOAc and Ace were also used as the transition solvents to blend PVC extracts into the ABS-like photopolymer liquid resin (density = 1.1 g/cm³), polymerizable at ultraviolet (UV) wavelength of 405 nm. The concertation of PVC extract in the transition solvent was appropriately adjusted just enough to blend well with ABS-like liquid resin. The K-50 PVC extract (PVCE-50) concentration in EtOAc was 0.350 g/mL (70 g in 200 mL) while K-65 PVC extract (PVCE-65) concentration in Ace was 0.244 g/mL (36.67 g in 150 mL). First, the content of PVCE-50 in ABS-like resin was varied from 0, 5, 12.5, 25, and 50 wt.%. Each mixture was stirred under UV-protection cover for several hours to evaporate EtOAc. Homogeneous mixing is a key to getting the perfectly 3D-printed parts. The air-bubbles produced in the resin mixture during stirring were removed by agitation/sonication for few minutes and then the resin was transferred to the resin vat for 3D-printing using stereolithography (SLA) 3D printer (ELEGOO MARS 2P) and allowed to sit and settle there for 10 min. The resin tray and the build plates were initially cleaned thoroughly with isopropyl alcohol (IP A) and dried completely. The leveling of build plate was also performed beforehand. Meanwhile, the object to be printed (tensile dog-bone specimens) was sliced using CHITUBOX proprietary software (from ELEGOO) with appropriate UV-exposure time and fed to the 3D printer when the PVCE-ABS resin blend is ready (free from any air bubbles). After the specimens are 3D-printed, they are thoroughly washed with IPA before detaching from the build plate. Once removed, they were again rinsed in IPA and finally cured in UV-curing machine (ELEGOO Mercury Plus) to photopolymerize any remnant semi-solid resin of the printed object. At least four dog-bone shaped specimens for UV exposure time of 6 or 12 s were 3D-printed to test the effect of PVCE content on their mechanical properties. The elongation tests were performed on the dog-bone specimens at ambient temperature using a compact table-top electromechanical-driven universal test machine (Newton, Test Resources, MN, USA) equipped with a 1.1 kN load cell controlled by easily customizable Newton software. The mechanical studies (stress-strain curves) reveal that pristine sample (ABS-PVCE-50-0) has the highest maximum tensile strength (avg. 19.18 MPa). The strength decreases to as low as 2.73 MPa for the highest PVCE-50 content. However, the elasticity of the dog-bone specimens improved with elongation at break increasing from avg. 42.84% to avg. 72.72% from 0 wt.% to 5 wt.% PVCE-50, after which it drops to avg. 40.78 % for 25 wt.% PVCE-50. This suggests that the rigid ABS-like resin becomes more flexible (70% increase) upon incorporation of certain amount of PVC extract while retaining almost 50% of the tensile strength of pristine ABS resin. Generally, plasticizers are added to make the rigid plastics softer. In that context, PVC extract acts as a plasticizer for the ABS-like resin as the addition of PVC extracts makes the relatively rigid dog-bones softer and more elastic. [0081] In a similar fashion, the content of PVCE-65 in ABS-like resin was varied from 0, 5, and 10 wt.%. Each mixture was stirred under UV-protection cover for relatively less duration to evaporate the Ace solvent. In the case of Ace transition solvent, the resin mixture of PVCE- 65 and ABS resulted in a lot of whitish air-bubbles unlike EtOAc. The air-bubbles were eventually all removed. However, it was noticed that the viscosity of the resin mixture increased even with 5 wt.% PVCE-65, understandably because of using relatively high K-value PVC extract. It was attempted to make 20 wt.% PVCE-65 resin mixture. However, the resin mixture was not suitable to 3D-printing as it became more viscous. However, warming it up at 50°C did help decrease its viscosity making it suitable for 3D-printing. However, its temperature still needs to be maintained at 50°C while 3D-printing and that required some additional engineering control of attaching a thermal heater around the resin vat inside the 3D- printer. This kind of approach can also help incorporate high molecular weight PVC into the ABS-like resin. Almost identical processing steps were followed to get the dog-bone specimens with UV exposure time of 6s for the tensile testing studies. The stress-strain curves suggest that addition of 5 wt.% PVCE-65 decreased the maximum tensile strength of pristine sample (ABS- PVCE-65-0) by only 13.5% (avg. 19.18 MPa vs. avg. 16.59 MPa) unlike PVCE-50, which is quite interesting. The tensile strength decreased further to almost 45% for higher PVCE-65 (10 wt.%). However, the elasticity of the specimens improved slightly for 5 wt.% PVCE-65 with elongation at break increasing from avg. 42.84% to avg. 45.68%, went on to extend the elongation slightly more to avg. 58.16 % for 10 wt.% PVCE-65 (only 36 % increase). This implies that the rigid ABS-like resin maintains the rigidity at the cost of decreased elasticity. Hence, it can be concluded from these two case studies that there is a trade-off between the tensile strength and the elasticity based on the choice of PVC K-value irrespective of the use of volatile transition solvents such as EtOAc or Ace as their end-goal was to help mix the PVC extract into the ABS-like resin.

Example 3: Formulating PVC-containing Resins for SLA 3D Printing

[0082] Extraction and Characterization of PVC: A major task is extracting PVC from the bulk and understanding the relationships between the soluble fractions of PVC and solvent nature. Here, the focus can be on virgin PVC resins (e.g., K-50, K-65, etc.) obtained from US suppliers. The extractions of PVC can focus on screening low cost, commonly available green (or “greener”) solvents including EtOAc, methyl acetate (MeOAc), isopropyl acetate (iPrOAc), t-butyl acetate (tBuOAc), acetone, and 2-methyl tetrahydrofuran (2-MeTHF). Work on solvent extractions can assess the fraction of PVC that can be extracted from a given source (e.g., mass extracted PVC/total mass of PVC) relative to temperature, separation of additives, and the compatibility of the resins when mixed with the PVC + solvent. The PVC extracted in this manner can be characterized for molecular weight (using gel permeation chromatography, GPC), thermal properties such as glass transition temperature (using differential scanning calorimetry, DSC), viscosity (rheology), and mechanical properties (using tensile testing and dynamic mechanical analysis (DMA)). These data can help provide understanding as to the properties/qualities of PVC that are being mixed into the resins, and guide resin formulations with optimal PVC content and resins with overall properties that behave as close to conventional PVC products as possible.

[0083] Resin Formulations: Using the PVC extracts and solvent compositions, PVC can then be dissolved at varying mass fractions in commercial resins (e.g., 5 - 50 wt%), and the behaviors and properties of the uncured resins can be assessed after removal of solvent(s). For this work, the baseline resin can be the Elegoo ABS-like resin (TABLE 1) and at least 2-3 other resins from the list provided in TABLE 2.

TABLE 1. Composition of Elegoo ABS-like resin as provided by the manufacturer.

TABLE 2. List of some commercially available 3D printing resins with compositions possibly amenable to incorporating PVC.

[0084] Using this knowledge, customized resins can be formulated that can have enhanced compatibility with PVC and/or contain mass fractions of PVC > 50%. Additional components (e.g., additives recovered from PVC recycling streams) can also be considered for use in resin formulations, as SLA 3D printing can be performed even with opaque resins. This process can utilize the pigments, stabilizers, plasticizers, and other additives in PVC products for recycling into 3D printing resins.

[0085] 3D Printing of Resins Containing PVC: Using consumer-level 3D printers (e.g., Elegoo Mars, Elegoo Saturn, etc.) 3D printing of the PVC-containing resins that contain PVC at up to 50 wt% PVC can be demonstrated. The 3D printing can serve multiple purposes: [0086] 1) Overall viability of using PVC within existing SLA-based resins for 3D printing, including controlling physical, mechanical, and thermal properties with respect to PVC content.

[0087] 2) High-level technoeconomic assessment (e.g., inputs, costs, profits). [0088] 3) Produce high quality parts (e.g., dogbones) for mechanical, thermal, and other forms of testing, including long-term observations of color/uniformity.

[0089] 4) Produce high quality objects for demonstrations and that promote interest in the use of PVC in 3D printing.

[0090] Similar 3D printing work can be performed with customized resins or other commercial resins. Furthermore, the PVC-containing resins can be demonstrated on more advanced printers. The more advanced printers provide functionalities which can print more viscous resins (i.e., higher mass fractions of PVC) effectively by heating the resin tub, as well as use gradients of light to control/vary properties throughout a print. These are key advantages which will help get the most traction and uptake for the PVC-containing resins.

[0091] Thermal, Mechanical, and Other Testing of 3D Prints: Among the key properties of the PVC-containing 3D printed resins are thermal and mechanical properties. Here DSC and thermogravimetric analysis (TGA) can be used to measure the thermal behaviors and decomposition temperatures of the cured resins. Mechanical properties will be measured using an Instron-type machine and DMA. Properties such as clarity (light transmission), contact angle with water, and behavior (e.g., swelling/degradation) of 3D printed parts in the presence of solvents can also be measured. X-ray diffractometry (XRD) can also be utilized to gather information as to the orientation of PVC (e.g., coiled, extended) within the 3D prints (which will influence properties), which can provide key information on PVC-solvent and PVC-resin interactions that are “frozen” in the 3D print.

[0092] The properties of the PVC-containing 3D prints vary using the custom-designed resins can also be considered. These properties of 3D prints of the resins can also be considered. [0093] PVC Functionalization to Modify Resin Properties: PVC is an advantageous and versatile plastic for upcycling given that it can be dehydrochlorinated (forming “DHPVC”) through conjugated chains of C=C double bonds are introduced. Successful and efficient methods have been developed to functionalize these C=C bonds via hydrogenation and/or hydroacylation. The C=C bonds have also been used as points for cleaving DHPVC into smaller PVC oligomers using olefin metathesis reactions. PVC functionalization through these reactions can be considered for modifying resin mechanical and thermal properties (e.g., hydrogenation and hydroacylation) and/or increasing the amount of PVC in resin formulations (i.e., via olefin metathesis to shorter chains). It has been observed that hydrogenation and hydroacylation of DHPVC can be used to make materials more flexible (lowering glass transition) and make them more soluble (easier to process, dissolve more PVC into solvents/resins). Olefin metathesis can break down DHPVC into smaller PVC chains which can be more readily dissolved in solvents/resins and tailor resin properties. An overview of methods in this area are outlined U.S. Patent No. 11,685,796, U.S. Patent Application Publication No. 2023/0279160, and U.S. Patent Application No. 18/508,719, which are hereby incorporated by reference in their entireties.

[0094] A simple reaction, hydrogenation of DHPVC to “H2-DHPVC”, can be used to study the impact of modified PVC on resin formulation and properties. Hydroacylation and olefin metathesis can also be pursued as complementary strategies for SLA resin formulations using PVC. Breaking down PVC chains through scission of C=C double bonds using olefin metathesis (e.g., Grubbs catalysts with ethylene gas) can present a facile way to process PVC to smaller chains and thereby increasing its solubility in resins, and modification of resin properties. Furthermore, producing smaller PVC chains with terminal C=C bonds via these olefin metathesis methods can allow for formulation of an SLA resin that minimizes/eliminates the need for acrylates and a resin formulation that approaches 100% PVC (excluding initiator, additives, etc.) for SLA 3D printing. This could further incentivize the use of PVC (and collection/recycling) and achieve an advance in 3D printing of a commodity plastic.

[0095] The key science used to formulate PVC-containing resins for SLA 3D printing is that the acrylate molecules/prepolymers in the resins also blend well with PVC. Knowledge of polymer-solvent interactions can be applied to develop PVC-containing resins for SLA. These efforts can drive new uses for PVC (and ultimately incentivize PVC collection and recycling) as the extraction and formulation processes can handle essentially any source of PVC, with the option to remove/recover additives (e.g., pigments, stabilizers, plasticizers) which themselves can be used within the resins or applied elsewhere.

[0096] Preliminary work has focused on extraction of PVC from commercial samples (virgin K-50 and K-65 provided by a major US PVC resin supplier) as well as a formulated product (Sylvin™ 9684-95C) purchased through a major online retailer. The extractions have utilized low cost “green” (i.e., non-toxic, biodegradable) solvents, particularly ethyl acetate (EtOAc) and acetone. This work has shown that at room temperature, -18% by mass of K-50 PVC was readily soluble in EtOAc, with -46% by mass of K-50 PVC was soluble in acetone. For K-65 virgin PVC, the relative mass extracted at room temperature was -7% and 11% for EtOAc and acetone, respectively. These results are contrary to guidelines which would suggest that solvents of choice for PVC are the conventional petroleum-derived solvents: tetrahydrofuran (THF), cyclohexanone, dichloromethane (DCM), and methyl ethyl ketone (MEK). [0097] Molecular weight analysis of this extracted fraction of PVC shows that it is lower than the bulk, meaning that there is at least a portion of PVC that can easily be solubilized (and optionally stripped of additives) using common, inexpensive, green solvents such as EtOAc, acetone, or blends of these two. This finding has been a key result that is enabling many of the efforts at UA in upcycling and depolymerization of PVC as these highly soluble PVC fractions are able to be modified (e.g., via dehydrochlorination) and further processed via hydrogenation/hydrofunctionalization, and even broken down to smaller chains under controlled reaction conditions. The fraction of PVC that is insoluble in EtOAc or acetone can also be utilized by using more commonly used solvents (e.g., THF). The soluble portion of PVC is more easily processed, and the soluble PVC fractions can be formulated into 3D printing resins for SLA. Extractions of PVC from the bulk commercial samples can scaled up as needed. The EtOAc and acetone used are recoverable via distillation, and separation and recovery of plasticizers from the Sylvin product (using hexanes as a solvent, where PVC is fully insoluble) can also be achieved.

[0098] It is recognized that EtOAc (ester) and acetone (ketone) have molecular structures that are similar to acrylate components that are used in SLA 3D printing resins. As such, the possibility that the soluble fractions of PVC might also readily dissolve into these resins has been considered. Initial attempts sought to dissolve PVC directly into a commercially available resin (Elegoo ABS-Like Resin) purchased from Amazon.com. Direct mixing of PVC extracts with commercially available resin met with mixed results in preliminary studies, particularly because of the resin viscosity. Instead, better results were achieved by adding the PVCZEtOAc solution to the resin and then gently evaporating EtOAc or acetone, at which point the PVC remained fully solubilized within the resin. In this manner, so far up to 50 wt% PVC has been dissolved in the commercial SLA resins, although the room temperature viscosity of 50 wt% PVC resins can limit the 3D printing process. This can be overcome in the future by acquiring an SLA 3D printer with a heated resin tank.

[0099] These PVC-containing SLA resins were then successfully printed using an inexpensive Elegoo Mars 3D printer (FIG. 1) without needing to modify any parameters for the resin. The initial prints of the PVC (25 wt%) resin were made as ASTM standard “dogbones” (FIG. 1) (approximately 7” long) which is a conventional form for performing mechanical testing.

[0100] FIG. 2 illustrates the mechanical testing of the 3D printed dogbones from the Elegoo ABS-like resin containing various amounts of PVC. [0101] The graph in FIG. 2 illustrates that the addition of PVC extracted from the K-50 PVC to the Elegoo 3D printing resin yielded finished products which have much greater elasticity than when no PVC is added. Adding just 5% by mass PVC to the resin created a remarkably different stress-strain curve where the dogbone stretched to -180% of its original length before breaking. For comparison, the resin with no PVC added could stretch only 110% before breaking. Increasing amounts of PVC showed a similar slope (i.e., elastic modulus) in the stress-strain curve, although achieving less elongation. This may be due to the dilution of the acrylates within the resin, and further research is needed to understand the relationship between PVC mass fraction, properties, and the nature of the microscopic polymer network within the 3D printed parts.

[0102] Furthermore, 3D printing of more complex objects, such as a ring and the UA ‘Script A” logo (FIG. 3), has also been demonstrated using the same PVC-containing SLA resin as for the dogbones.

[0103] These methods and compositions for SLA resin formulations can prove to be highly valuable in the 3D printing market as they can bring PVC-containing materials to commercialization in a rapid and profitable manner. At scale, it is estimated that it will cost < $l/kg to extract PVC from virgin resins, which can then be directly used to formulate 3D printing resins with any number of current products and/or future resins that can be designed specifically to maximize the amount of PVC and optimizing the overall properties of the final products. Consumer-level SLA resins such as the Elegoo resin already retail for $30-40/kg or more, while specialty resins can cost $149/kg or more. The value proposition of adding low- cost virgin PVC to these resins will undoubtedly incentivize PVC recycling as another source of PVC and additives for resin formulations.

[0104] The composition of the Elegoo ABS-like Resin has also been analyzed (TABLE 1). This information helped elucidate how the components present in these resins can solubilize/blend with PVC. The information obtained was also useful for identifying a range of other commercial resin offerings for SLA 3D printing which can also be compatible with PVC and these methods.

[0105] As seen in TABLE 1, the Elegoo ABS-like resin contains 93% by mass of acrylate- containing small molecules (#1, 2) and acrylate-functionalized polymers (#3) which are the organic species that form a homogenous blend with the extracted PVC. The remaining components are the photoinitiator (#4) and small amounts of inorganics (#5, 6). Using the information in TABLE 1, a wide range of other commercially available SLA resins was then examined, and a list was compiled (TABLE 2) of current consumer-level offerings as additional candidate resins with compositions (e.g., > 70% by mass acrylates) into which the extracted PVC can be added as a means of modifying resin properties. This list is meant to illustrate that there is already a wide range of products into which PVC can be introduced (and therefore many possible outlets for the products of this project). However, it is not intended to be a fully comprehensive survey of all viable current products, and it is worth noting that new resins offerings are constantly being brought to market.

[0106] As previously mentioned, the work on integrating PVC into resins for SLA-based 3D printing used virgin K-50 and K-65 PVC resins from a major US supplier as well as a commercial Sylvin™ resin obtained from an online retailer. Given the results described earlier for EtOAc and acetone, there are substantial amounts of PVC that can be very easily introduced to 3D printing resin formulations. Of course, PVC is found in in many different products with a wide range of additives, and as such the amount of PVC that can be very easily recycled using green solvents needs to be further assessed by testing various grades of virgin PVC formulated resins of known compositions, and consumer products (e.g., pool floats, shower curtains) which may constitute much of the flexible PVC waste available when considering recycling PVC for the formulation of 3D printing resins. As EtOAc and acetone are just two possible green solvents, the recyclability of PVC using other options such as MeOAc, 2-MeTHF, etc. and the use of other green solvents (e.g., methanol, ethanol) to assist in extraction/ processing of additives found in PVC can also be assessed. Recyclability of a range of PVC products/waste streams through these processing methods can also be assessed.

[0107] The methods and process disclosed herein represent a path to bringing recycled PVC products to market. While 3D printing is emphasized as a primary application for this recycled PVC given the growth of this industrial sector (and the demand for a PVC product in 3D printing, but lack of supply) the reality is that these methods allow for extracted PVC to be recycled and repurposed into any application where the properties of the extracted PVC meet product needs. Furthermore, resins containing PVC are not limited to 3D printing, as these formulations could find use in conventional manufacturing processes as well. The PVC fraction that was not extracted into EtOAc, acetone, or other green solvents would effectively be “cleaned” by this process and could be recycled into other products through reformulation with additives and conventional plastic processing. In this case, PVC could be 100% recyclable when fractionated in this manner. Example 4: Tuning Solvent Strength Can Fractionate PVC into Ultra-low Molecular Weight Material with Low Dispersity

[0108] The undeniable impact plastic pollution has on the planet has charged world governments with renewed enthusiasm in dealing with end-of-life plastics. The United Nations Environment Programme and many governments around the world (Matthews, C. et al., A review on European Union’s strategy for plastics in a circular economy and its impact on food safety. Journal of Cleaner Production, 2021. 283: p. 125263) (Zhu, J., et al., Efforts for a Circular Economy in China: A Comprehensive Review of Policies. Journal of Industrial Ecology, 2019. 23(1): p. 110-118) have already planned or taken measures toward managing plastic waste. Industry is playing its role towards a solution as well. Academic interest in end- of-life plastics has also grown exponentially, perhaps as a response to the mainstream interest or a progenitor of it. Research into the “circular economy” of plastics can be generalized by the development of new recyclable polymers (Tang, X. and E.Y.X. Chen, Toward Infinitely Recyclable Plastics Derived from Renewable Cyclic Esters. Chem, 2019. 5(2): p. 284-312) (Shieh, P., et al., Cleavable comonomers enable degradable, recyclable thermoset plastics. Nature, 2020. 583(7817): p. 542-547) or products, development of sustainable (biobased) monomer production methods (Rosenboom, J.-G., et al., Bioplastics for a circular economy. Nature Reviews Materials, 2022. 7(2): p. 117-137) (Bhubalan, K., et al., Leveraging blockchain concepts as watermarkers of plastics for sustainable waste management in progressing circular economy. Environmental Research, 2022. 213: p. 113631) (Benyathiar, P., et al., Polyethylene Terephthalate (PET) Bottle-to-Bottle Recycling for the Beverage Industry: A Review. Polymers, 2022. 14(12): p. 2366) (Sheldon, R.A. and M. Norton, Green chemistry and the plastic pollution challenge: towards a circular economy. Green Chemistry, 2020. 22(19): p. 6310-6322), and the development of recycling/upcy cling methods (open-loop and closed-loop) (Nicholson, S.R., et al., The Critical Role of Process Analysis in Chemical Recycling and Upcycling of Waste Plastics. Annual Review of Chemical and Biomolecular Engineering, 2022. 13(Volume 13, 2022): p. 301-324) (Horodytska, O., et al., Plastic flexible films waste management - A state of art review. Waste Management, 2018. 77: p. 413-425).

[0109] Closed loop recycling is usually represented by the circularity of post-industrial and post-consumer plastic regrind. Nonetheless, perhaps the most straightforward closed-loop recycling process is solvent-based recovery. In simple and general terms, solvent-based recovery is the use of solvents for (selective) recovery of plastics from waste (Zhao, Y.-B., et al., Solvent-based separation and recycling of waste plastics: A review. Chemosphere, 2018. 209: p. 707-720). This is done using a “strong solvent” for the dissolution of plastic from waste and an “anti-solvent,” or filtration of insoluble materials, for the selective recovery of clean plastic(s). The same concept can be applied to leaching just the additives from waste plastics, effectively “washing” the plastic (Ugdiiler, S., et al., Challenges and opportunities of solventbased additive extraction methods for plastic recycling. Waste Management, 2020. 104: p. 148- 182). Although not a new concept (Sperber, R.J. and S.L. Rosen, Recycling of thermoplastic waste: Phase equilibrium in polystyrene-PVC-polyolefin solvent systems. Polymer Engineering & Science, 1976. 16(4): p. 246-251), interest in solvent-based recovery has recently grown. This resurgence brought modern technologies (Wang, L., et al., Recycling of phosphorus-containing plastic based on the dual effects of switchable hydrophilicity solvents. Chemosphere, 2020. 259: p. 127402) (Yousef, S., et al., Sustainable green technology for recovery of cotton fibers and polyester from textile waste. Journal of Cleaner Production, 2020. 254: p. 120078) and techniques (Walker, T.W., et al., Recycling of multilayer plastic packaging materials by solvent-targeted recovery and precipitation. Science Advances, 2020. 6(47): p. eaba7599) to the field, with a “green” emphasis on existing (Samori, C., et al., Recycling of multilayer packaging waste with sustainable solvents. Resources, Conservation and Recycling, 2023. 190: p. 106832) (Gil-Jasso, N.D., et al., A methodology for recycling waste expanded polystyrene using flower essential oils. Fuel, 2022. 307: p. 121835) or new (Qian, S., et al., Properties of symmetric 1,3-diethers based on glycerol skeletons for CO2 absorption. Fluid Phase Equilibria, 2020. 521 : p. 112718) (Soyemi, A. and T. Szilvasi, Calculated Physicochemical Properties of Glycerol-Derived Solvents to Drive Plastic Waste Recycling. Industrial & Engineering Chemistry Research, 2023. 62(15): p. 6322-6337) solvents for such processes.

[0110] Compared to mechanical recycling, solvent recovery not only promises a cleaner and more consistent (Pin, J.-M., et al., Recyclability of Post-Consumer Polystyrene at Pilot Scale: Comparison of Mechanical and Solvent-Based Recycling Approaches. Polymers, 2023. 15(24): p. 4714) product, but also more options for controlling the form or morphology of the product obtained. Powder and pellets can be obtained using precipitation (Cavalcante, J., R. Hardian, and G. Szekely, Antipathogenic upcycling of face mask waste into separation materials using green solvents. Sustainable Materials and Technologies, 2022. 32: p. e00448), films can be obtained using blow spinning (Singhal, R., et al., Integrated Polymer Dissolution and Solution Blow Spinning Coupled with Solvent Recovery for Expanded Polystyrene Recycling. Journal of Polymers and the Environment, 2019. 27(6): p. 1240-1251) or solvent casting (Pulido, B.A., et al., Recycled Poly(ethylene terephthalate) for High Temperature Solvent Resistant Membranes. ACS Applied Polymer Materials, 2019. 1(9): p. 2379-2387) (Ramirez-Martinez, M., et al., Bio-based solvents for polyolefin dissolution and membrane fabrication: from plastic waste to value-added materials. Green Chemistry, 2023. 25(3): p. 966- 977). Yet, solvent recovery is not without limitations and challenges. Most methods of solvent based recovery of plastics focus on the recovery of the whole plastic with separation of additives. However, unless “take-back” arrangements are made between producer and endusers) for specific products, simple solvent recovery methods are not likely to yield desirable results for mixed products of the same plastic. This is because dissolving two or more products made from the same plastic but with different molecular weight distributions will yield a material with a much higher dispersity (D) (also known as poly dispersity index, PDI), which may render the recovered “pure” material much less useful. It is best to think of this method as complementary rather than competitive. Ideally, certain plastics would be sorted into their own “best” way of recovery (i.e. chemical recycling of PET (Barnard, E., et al., Chemolytic depolymerisation of PET: a review. Green Chemistry, 2021. 23(11): p. 3765-3789) or polyolefins (Faust, K., et al., Recent Advances in Catalytic Chemical Recycling of Polyolefins. ChemCatChem, 2023. 15(13): p. e202300310), and so on). To save on solvent use, solventbased recovery can work as a complementary method to mechanical recycling (Nordahl, S.L., et al., Complementary roles for mechanical and solvent-based recycling in low-carbon, circular polypropylene. Proceedings of the National Academy of Sciences, 2023. 120(46): p. e2306902120), where pure products are desired, or with tough-to-recycle wastes. While solvent-based recovery of plastic mixes may seem ideal, it may be an outdated way of thinking of plastic mixes, especially with the fast-developing technology of plastic sorting (Gundupalli, S.P., et al., A review on automated sorting of source-separated municipal solid waste for recycling. Waste Management, 2017. 60: p. 56-74) (Cimpan, C., et al., Central sorting and recovery of MSW recyclable materials: A review of technological state-of-the-art, cases, practice and implications for materials recycling. Journal of Environmental Management, 2015. 156: p. 181-199), which can facilitate single plastic recycling/upcycling.

[0111] Amongst the plastics that would benefit from isolation from mixed plastics is polyvinyl chloride (PVC). PVC is ’’anti -synergistic” (i.e., problematic) in mixed plastic recycling (Yan, S., et al., New insight into the synergistic reactions involved in the hydrothermal co-liquefaction of synthetic polymer wastes by molecular dynamics and DFT methods. Journal of Hazardous Materials, 2023. 449: p. 131032) (Chen, L., et al., Efficient and selective dual-pathway polyolefin hydro-conversion over unexpectedly bifunctional M/Ti02- anatase catalysts. Applied Catalysis B: Environmental, 2023. 335: p. 122897) and special treatment may be needed (Kots, P.A., et al., A two-stage strategy for upcycling chlorine- contaminated plastic waste. Nature Sustainability, 2023. 6(10): p. 1258-1267) to prevent potential complications that may arise from the presence of PVC in mixed waste that is thermomechanically recycled (Sadat-Shojai, M. and G.-R. Bakhshandeh, Recycling of PVC wastes. Polymer Degradation and Stability, 2011. 96(4): p. 404-415) (Ait-Touchente, Z., et al., Recent advances in polyvinyl chloride (PVC) recycling. Polymers for Advanced Technologies, 2024. 35(1): p. e6228). Due to these complications and given the common presence of additives in PVC (Babinsky, R., PVC additives: a global review. Plastics, Additives and Compounding, 2006. 8(1): p. 38-40), solvent-based recovery is particularly well-suited to PVC and has already been explored for large-scale operation. The VinyLoop process was introduced by Solvay in 2003. Despite its closure in 2018 (due to EU phthalate regulation), VinyLoop showed the potential of recycling by dissolution, which lead to its recent development and re-emergence under INEOS Inovyn. Although rarely mentioned, solvent-based recovery of PVC has a significant hill to climb, and it is not the potential of residual additive (which can be remedied (Ugdiiler, S., et al., Challenges and opportunities of solvent-based additive extraction methods for plastic recycling. Waste Management, 2020. 104: p. 148-182)). Commercial PVC products are rarely made from the same source PVC resin. Rather, varying grades (referred to by their K-value), or blends of grades are used for certain products (Wypych, G., 4 - THE PVC FORMULATIONS, in PVC Formulary (Third Edition), G. Wypych, Editor. 2020, ChemTec Publishing, p. 95-363). This fact would undoubtedly complicate PVC recovery from mixed products (using solvents, or mechanically), as the resulting recycled product would likely result in much larger D. Hence, a method for a fractional recovery of PVC becomes a very interesting option.

[0112] Fractionation is commonly used for lignins (Gigli, M. and C. Crestini, Fractionation of industrial lignins: opportunities and challenges. Green Chemistry, 2020. 22(15): p. 4722- 4746), however rarely applied to plastic, at least not recently. The still developing, yet mature, field of lignin fractionation gave rise to many fractionation methods, like fractional precipitation, pH dependent precipitation, membrane fractionation, and most commonly solvent extraction (single and sequential) (Gigli, M. and C. Crestini, Fractionation of industrial lignins: opportunities and challenges. Green Chemistry, 2020. 22(15): p. 4722-4746). Much like lignin products (Ma, Q. and X. Zhang, An integral method for determining the molecular composition of lignin and its application. Scientific Reports, 2022. 12(1): p. 19136), PVC exhibits a broad distribution curve. In previous works by Pepperl (Pepperl, G., Molecular weight distribution of PVC blends from resins with different K values. Journal of Vinyl and Additive Technology, 2000. 6(4): p. 181-186) (Pepperl, G., Molecular weight distribution of commercial PVC. Journal of Vinyl and Additive Technology, 2000. 6(2): p. 88-92), it was shown that all PVC grades contain chains at both ends of the curve. This suggests the existence of low molecular weight chains potentially accessible by weak solvents, and large molecular weight only accessible by strong solvents.

[0113] Herein, a study was conducted which demonstrates that solvent extraction of PVC can be used as a means of obtaining products with targeted molecular weight distributions and can yield fractions with very narrow D values (as low as —1.1). Solvent extraction was performed in both single-step and multi-step (i.e., sequential) process using a weak solvent (acetone (Ace)), a weak solvent + nonsolvent blend (Ace and methanol (MeOH)), and a strong solvent + nonsolvent blend (tetrahydrofuran (THF) and MeOH). Single-step solvent blend extraction methods show that virgin PVC resin (K-50) can be fractionated to obtain molecular weight ranges that correspond to solvent “strength”, while sequential solvent blend extractions shows that PVC of low D can be fractionated from the bulk polymer (FIG. 4). Further, the study illustrates the viability of this method in fractionating and cleaning for commercial PVC samples (plasticized PVC and PVC pipe), which shows its potential as a recycling route for PVC. These results suggest that solvent fractionation of PVC can offer unique opportunities as the solubility of the low molecular weight fractions produced using this method can provide well-defined feedstocks for chemical modification and/or depolymerization of PVC (Alshaikh, A., et al., PVC Modification through Sequential Dehydrochlorination-Hydrogenation Reaction Cycles Facilitated via Fractionation by Green Solvents. ACS Applied Polymer Materials, 2024) or back into PVC blends as melt rheology modifiers (Pepperl, G., Molecular weight distribution of PVC blends from resins with different K values. Journal of Vinyl and Additive Technology, 2000. 6(4): p. 181-186), while the remaining (i.e., insoluble) recovered clean PVC can be readily routed back as feedstock to existing applications.

Experimental

[0114] Materials'. Virgin PVC (K-50 and K-65 grades) were generously provided by a major US vinyl producer. Plasticized PVC pellets (Sylvin 9684-95) used in this work were purchased in 10 lb batches from eBay seller “The Freight Adoption Agency, ” and received as transparent flexible pellets with a purple hue. Schedule 40 PVC pipe was recovered from leftover construction materials.

[0115] Ethanol (EtOH, > 99.5%), methanol (MeOH, > 99.8%), hexane (mixture of isomers, > 98.5%), and acetone (Ace, > 99.5%) were purchased from VWR through the University of Alabama Chemistry Stockroom. Tetrahydrofuran (THF, > 99.0%) was bought from VWR. [0116] Single-step PVC K-50 fractionation'. PVC K-50 (1 g) was added to a polypropylene centrifuge tube (15 mL), followed by a solution of Ace-MeOH or THF-MeOH (10 g) prepared according to the pre-determined concentrations (TABLE 3). Solvent blends are referred to as wt%THF/Ace:wt%MeOH going forward (e.g., A 50 wt% acetone and 50 wt% methanol blend is 50Ace:50MeOH). The contents of the tube were mixed using a vortex mixer (VWR) for 30 s . The tube was then moved to an ultrasonic bath (VWR) and sonicated for 1.5 h, mixed using a vortex mixer, then sonicated again for 1.5 h. Once the sonication period was completed, the tubes were placed in a centrifuge (VWR) and centrifuged for 30 min at 6500 rpm. The liquid phase in the tube was then decanted into a pre-weighed beaker inside a hood and the solvent was allowed to evaporate (~ 24-48 h). Once the solvent was evaporated, the beaker was weighed again to determine the yield of the fractionation. Each fractionation was done thrice simultaneously, and the solutions were combined prior to evaporation.

TABLE 3. Summary of single-step fractionation experiments conducted and their designated entry IDs. ^a Source PVC data.

[0117] Sequential PVC K-50 fractionation'. Sequential fractionations were done using similar methods to single-step fractionation. However, once the solution was decanted, another 10 g solution of higher Ace content was added and the extraction process repeated similarly. Ace content was increased by increments of +10 wt%, until an extraction of 100% Ace was finished. The extractions were then repeated using THF-MeOH solutions starting with 50THF:50MeOH, until all the PVC was dissolved using a solution of 70THF:30MeOH.

[0118] Sequential Commercial PVC mixture fractionation'. PVC pipe was first cut into small trimmings (FIG. 5). PVC pipe trimmings and pellets were separately cleaned with water and soap, followed by washing with EtOH, and finally soaked in hexanes overnight to remove any freely soluble additives. PVC was then removed from hexane and allowed to dry for two hours. Washed PVC pipe trimmings (15 g) and PVC pellets (15 g) were then moved into a glass bottle (250 mL) equipped with a stir bar. A 50Ace:50MeOH solution (200 g) was then added to the bottle and stirred for 4 h. The solids were then allowed to settle, and the liquid phase was then carefully decanted into a funnel plugged by cotton to stop any solids from passing. The solution was then evaporated on a pre-weighed Pyrex dish inside a hood (~ 24-48 h). The extraction was then repeated similarly using solutions of increasing Ace content by increments of +10 wt%, until an extraction with 100% Ace was done. The extractions were then repeated using THF-MeOH solutions starting with 50THF:50MeOH, until all the PVC was dissolved using a solution of 90THF: lOMeOH.

[0119] Characterization'. Gel permeation chromatography multi-angle laser light scattering with simultaneous refractive index (GPC-MALS-RI) system was used to determine the absolute molecular weights of the PVC sources as well as the fractionation products. The measurements were performed on DAWN MALS (D8, Wyatt Technology Corporation, Santa Barbara, CA) detector in HPLC grade THF at a flow rate of 1.0 mL min'¹ with a polarized single frequency light of 662.9 nm in conjunction with the RI detector (Model 2414, Waters Technology, San Diego, CA) using Styragel HR 5E mixed bed column (300 mm x 7.8 mm x 5 pm) for separation. The weight-average molecular weight (Mw), the dispersity (D = MW/MN) and hydrodynamic radius (Rh) of each sample was determined by the Zimm plot using the RI increment (dn/dc) value of 0.1010 mL g'¹ (a standard value for PVC in THF). Astra and Empower software programs were used to run and analyze the GPC traces for MALS and RI detectors, respectively. THF was served as a mobile phase as wells as solvent for dissolving PVC samples with optimized concertation of 8.0 mg mL'¹ and the injection volume of 80 pL. The MALS detector was operated at room temperature while the RI detector, pump oven and column oven were maintained at 40 °C. The GPC system was calibrated by using narrow distribution polystyrene standards.

[0120] Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) was used to study the molecular structure of produced fractions, PVC sources, and additive; FTIR spectra were obtained using the PerkinElmer Spectrum 2 instrument. Scans were acquired between 4000-400 cm’¹ using a resolution of 4 cm’¹, and 64 accumulations.

[0121] Differential scanning calorimetry (DSC) measurements were carried out on PVC sources and fractionation products using Discovery DSC250 instrument (TA Instruments, New Castle, DE, USA) in an ultrapure (USP) N2 atmosphere (20 mL min'¹) at a ramp rate of 10°C min-1 with at least three heating/cooling cycles in the temperature range from -40°C to 150°C. Trios software (Waters Technology) was used to analyze the DSC traces to determine the thermal properties of samples such as the glass transition temperature (T_g).

[0122] The viscosity measurements were obtained using the ViscoQC 300L PTD 100 Cone-Plate measurement system with a CP40 bob. Viscosity samples were prepared on a 10:90 polymer sample to solvent (THF) weight ratio. The instrument was calibrated with a certified reference standard (Cannon Instrument) before use. The measurements were collected using a 0.5 mL polymer solution at a temperature of 20 ± 1°C and shear rates of 10 or 100 s'¹ for 5 min.

[0123] Computational Methods'. To provide molecular-scale insights into the fractionation of PVC in acetone (Ace)-methanol (MeOH) and tetrahydrofuran (THF)-MeOH solvent mixtures, molecular dynamics (MD) simulations were performed at varying MeOH % and number of PVC chains (npvc). TABLE 4 outlines the system compositions used in this study. The PVC120 model was employed, as it has been validated in previous studies (Olowookere, F.V., et al., Effects of chain length on the structure and dynamics of polyvinyl chloride during atomistic molecular dynamics simulations. Molecular Simulation, 2023. 49(15): p. 1401-1412) (Olowookere, F. V. and C.H. Turner, Predicting optimal chain lengths in atomistic simulations of solvated polymers. Molecular Simulation, 2024: p. 1-9) (Olowookere, F.V., et al., Characterizing polyvinyl chloride interactions with additives in traditional and bioderived solvents. Industrial & Engineering Chemistry Research, 2024. 63(2): p. 1109-1121) as a reliable chain length (120 repeat units) for atomistic solvated polymer simulations. While the model does not capture the full molecular weight distribution observed experimentally, it has been shown to sufficiently represent the fundamental physics of experimental systems.

TABLE 4. Summary of the simulated system compositions.

[0124] The MD simulations were conducted using the Gromacs 2021.1 package (Abraham, M.J., et al., GROMACS: High performance molecular simulations through multi-level parallelism from laptops to supercomputers. SoftwareX, 2015. 1 : p. 19-25). The OPLS-AA force field (Jorgensen, W.L., et al., Development and testing of the OPLS all-atom force field on conformational energetics and properties of organic liquids. Journal of the american chemical society, 1996. 118(45): p. 11225-11236) was applied to represent bonded and nonbonded interactions for PVC and the solvents. Atomic charges for PVC were derived using ab initio Hartree-Fock/STO-3G (Valatin, J., Generalized hartree-fock method. Physical Review, 1961. 122(4): p. 1012) in PolyParGen (YABE, M., et al., Development of PolyParGen software to facilitate the determination of molecular dynamics simulation parameters for polymers. Journal of Computer Chemistry, Japan-International Edition, 2019. 5: p. 2018- 0034), while solvent charges were obtained using B3LYP/6-31++(d,p) (Tirado-Rives, J. and W.L. Jorgensen, Performance of B3LYP density functional methods for a large set of organic molecules. Journal of chemical theory and computation, 2008. 4(2): p. 297-306). van der Waals interactions were captured using the Lennard-Jones potential with a 1.0 nm cutoff, and long- range electrostatics were calculated using the particle mesh Ewald (PME) method (Darden, T., et al., Particle mesh Ewald: An N- log (N) method for Ewald sums in large systems. The Journal of chemical physics, 1993. 98(12): p. 10089-10092) beyond the 1.0 nm cutoff. Geometric combination rules were applied for cross interactions.

[0125] The system configurations were built using the PACKMOL package (Martinez, L., et al., PACKMOL: A package for building initial configurations for molecular dynamics simulations. Journal of computational chemistry, 2009. 30(13): p. 2157-2164), followed by energy minimization via the steepest descent method. The systems were then equilibrated in the isothermal-isobaric (NPT) ensemble at 1 bar and 300 K for 10 ns with a time step of 1 fs, using the Parrinello-Rahman barostat (Nose, S. and M. Klein, Constant pressure molecular dynamics for molecular systems. Molecular Physics, 1983. 50(5): p. 1055-1076) and velocityrescaling thermostat (Bussi, G., et al., Canonical sampling through velocity rescaling. The Journal of chemical physics, 2007. 126(1)) to maintain pressure and temperature respectively. To ensure sufficient exploration of the phase space, an annealing protocol was applied, heating the system to 600 K and cooling to 300 K over 4 cycles of 40 ns. Afterward, the systems were further equilibrated for 20 ns. Production runs were performed for 20 ns, during which configurations were extracted every 30 ps for further analyses. Hydrogen bond lengths were constrained with the LINCS algorithm (Hess, B., et al., LINCS: a linear constraint solver for molecular simulations. Journal of computational chemistry, 1997. 18(12): p. 1463-1472), and periodic boundary conditions were applied in all dimensions.

[0126] Surface area (SA) values of the PVC molecules were obtained using the Gromacs tool gmx sasa, while the PVC radius of gyration (Rg) was calculated using the Plumed package (Tribello, G.A., et al., PLUMED 2: New feathers for an old bird. Computer physics communications, 2014. 185(2): p. 604-613). The Flory -Huggins (FH) interaction parameter was determined following previous protocol (Olowookere, F.V., et al., Characterizing polyvinyl chloride interactions with additives in traditional and bioderived solvents. Industrial & Engineering Chemistry Research, 2024. 63(2): p. 1109-1121), based on the Flory-Huggins solution theory (Flory, P.J., Thermodynamics of high polymer solutions. The Journal of chemical physics, 1942. 10(1): p. 51-61):

(Eq. SI)

where H^E is the enthalpy of mixing, R is the universal gas constant, T is the temperature, Ni is ✓C TV the number of solvent molecules, <t>₂ is the lattice volume fraction <t>₂ = — ~ , N2 is the number

of PVC 120 chains, each of which has x repeat units, and TV is the total number of sites (N = Ni + xNi). To calculate H^E, the study simulated PVC-solvent mixtures, individual solvents (Ace, THF, MeOH) and bulk PVC systems and used the following equation:

where H)_m is the ensemble average molar enthalpy of the mixture (with 1 mol of PVC corresponding to a PVC120 chain), and Xi,

and {V)i represent the mole fraction, enthalpy, and molar volume of zth compound in its liquid state, respectively. The volume of mixing (V^s) can be similarly obtained through Equation S3 :

where {V)_m represent the ensemble average molar volume of the mixture.

[0127] The Hansen solubility parameter (3nans) is calculated as the square root of the cohesive energy density (CED), expressed as the sum of contributions from different interactions (Hansen, C., Three dimensional solubility parameter and solvent diffusion coefficient. Importance in surface coating formulation. Doctoral Dissertation, 1967):

^SHans = ^Sd + ^Sp + ^Sh (Eq. S4) where 3d, 3_P, and 3h represent the dispersion (van der Waals), polar (dipole-dipole), and hydrogen bonding interactions, respectively. Since the OPLS-AA force field does not include an explicit hydrogen bond term, the polar and hydrogen bonding contributions cannot be separated. Therefore, 3_P and 3h are combined into a single electrostatic term 3_e, similar to Salehi et. al’s work (Salehi, H.S., et al., Computing solubility parameters of deep eutectic solvents from Molecular Dynamics simulations. Fluid Phase Equilibria, 2019. 497: p. 10-18):

5_e ²

(Eq. S5)

[0128] The HSP of the Ace-MeOH and THF-MeOH mixtures (in MPa^{1 2}) was calculated using the average potential energy of the liquid phase and gas phases as:

where k represents the Hansen components (k = dispersion and electrostatic), (... ) denotes a time-averaged ensemble, V_m is the molar volume of the mixture in cm³/mol, E_{k gas} and E_k n_q are the gas and liquid phase energies of the components (J/mol), xi and %2 represent the molar fractions of Ace/THF and MeOH, respectively. For bulk PVC, the MeOH contribution is zero:

[0129] The liquid phase simulations were performed in the NPT ensemble (averaged from three independent runs) using the aforementioned protocol for 50 ns, sampled every 10 ps. Gas phase simulations were run in the NVT ensemble for isolated Ace, THF, and MeOH molecules in a 100 A box to minimize periodic boundary conditions (PBC) effects. After 200 ps of equilibration (timestep = 0.1 fs), average energy values were taken from a 1 ns production run. These energies were used to calculate the HSP components and total HSP in Equation S8.

[0130] Finally, the HSP Distance Ra between PVC and the mixtures (Ace-MeOH and THF-MeOH) was calculated to assess their compatibility in solubility space. A smaller Ra indicates higher compatibility between components. The equation is:

where S_D1 and S_D2 are dispersion terms of PVC and solvent mixture, respectively, and <5_F1 and 8_E2 are the electrostatic terms of PVC and solvent mixture, respectively.

[0131] Additives’. PVC pellets and pipe (FIG. 5) used in this work contained significant additive content. Through dissolution, filtration and precipitation, it was found that PVC pipe contained roughly 14% additives by mass which reasonably aligns with information on typical pipe formulations (Wypych, G., 4 - THE PVC FORMULATIONS, in PVC Formulary (Third Edition), G. Wypych, Editor. 2020, ChemTec Publishing, p. 95-363). Determination of additives in pipe (presumed to largely include CaCOs) is complicated and not necessary for the goals of this work. However, PVC pipe may contain mostly inorganic stabilizers and fillers that are easily removed via centrifuge or filtration when PVC is dissolved in a suitable solvent (FIG. 6). PVC pellet had a much larger additive content, roughly 29% by mass, but likely slightly larger as some residual additive can be seen in some fractionation products, albeit at low concentrations. The plasticizer used in PVC pellet was determined previously to be diisononyl terephthalate (DINT) (Alshaikh, A., et al., PVC Modification through Sequential Dehydrochlorination-Hydrogenation Reaction Cycles Facilitated via Fractionation by Green Solvents. ACS Applied Polymer Materials, 2024. 6(16): p. 9656-9662) (FIG. 7). Nonetheless, simply through dissolution, centrifuge/filtration and precipitation in hexane, followed by a MeOH wash, PVC pellets can be cleaned thoroughly (FIG. 7).

Results

[0132] PVC single-step fractionation by solvent-mix extraction'. Unlike most solvent-based plastic recovery, fractionation offers the opportunity for selective recovery of certain “grades” of a specific plastic, based on the solvent or solvent-mix used (FIG. 8). However, among commodity plastics which bear resin identification codes 1-6 which include polyolefins (HDPE, LDPE, PP, PVC, and PS) and PET (a polyester) only PVC and PS have any appreciable solubility in common organic solvents at or near ambient temperature (Zhao, Y.-B., et al., Solvent-based separation and recycling of waste plastics: A review. Chemosphere, 2018. 209: p. 707-720).

[0133] Recently, it was shown that PVC was readily fractionated using either pure ethyl acetate (EtOAc) or Ace (Alshaikh, A., et al., PVC Modification through Sequential Dehydrochlorination-Hydrogenation Reaction Cycles Facilitated via Fractionation by Green Solvents. ACS Applied Polymer Materials, 2024), which are considered to be relatively weak solvents for PVC due to their inability to dissolve bulk PVC. This led to the consideration of how solvent mixtures could be used to more finely fractionate PVC. To fractionate the lower molecular weight portions that are known to be present in K-50 and K-65 PVC (Pepperl, G., Molecular weight distribution of PVC blends from resins with different K values. Journal of Vinyl and Additive Technology, 2000. 6(4): p. 181-186) (Pepperl, G., Molecular weight distribution of commercial PVC. Journal of Vinyl and Additive Technology, 2000. 6(2): p. 88- 92), extractions using mixtures of a weak solvent (Ace) and a non-solvent (MeOH). For higher molecular weights (short of bulk), mixtures of a strong solvent (THF) and a non-solvent (MeOH) were examined. Choice of solvents was motivated by their low boiling point for ease of recovery, and/or their recommendation for green chemistry (Byrne, F.P., et al., Tools and techniques for solvent selection: green solvent selection guides. Sustainable Chemical Processes, 2016. 4(1): p. 7). While methyl ethyl ketone (MEK or 2-butanone) is likely a better choice in the long-term as the strong solvent when considering price and green chemistry recommendations (Byrne, F.P., et al., Tools and techniques for solvent selection: green solvent selection guides. Sustainable Chemical Processes, 2016. 4(1): p. 7), THF was chosen as the strong solvent for this study due to its lower boiling point and is very well-matched to PVC (per HSP) (Grause, G., et al., Solubility parameters for determining optimal solvents for separating PVC from PVC-coated PET fibers. Journal of Material Cycles and Waste Management, 2017. 19(2): p. 612-622).

[0134] Solvent extraction can be done as a single-step or sequential process (FIG. 4). Single-step solvent extraction is one of the most common fractionation methods owing to its simplicity. Experiments were conducted with PVC using different solvent systems (TABLE 3). Fractions showed a gradual increase in Mw, MN, and D with increase of weak solvent or strong solvent (FIG. 9, TABLE 3). In all cases PVC K-50 was used, although only a 100% Ace fractionation was performed for PVC K-65.

[0135] The weight-average molecular weight of the extracts of K-50 (Mw = 26.3 kDa) and K-65 (Mw = 35.7 kDa) for the 100% Ace were different, corresponding to the molecular weight distributions within the individual source material (TABLE 3). This seems reasonable, as source PVC with higher molecular weight would contain fewer low molecular weight chains soluble in Ace, thus shifting the average molecular weight of the associated Ace extracts. The yields of the Ace extracts reflect this as well (K-50 > K-65). Using Ace as the only solvent, 44.2% by mass was extracted from K-50 with D = 1.53, while only 17.2% by mass was extracted from K-65 with similar value of D = 1.53.

[0136] PVC sequential fractionation by solvent-mix extraction'. While single-step fractionation with Ace could be efficient for bulk recovery of the lower Mw PVC chains present in a given sample, sequential fractionation could offer the ability to fractionate low D fractions (< 1.5), which can be blended into specific grades when needed (Pepperl, G., Molecular weight distribution of PVC blends from resins with different K values. Journal of Vinyl and Additive Technology, 2000. 6(4): p. 181-186). Previous sequential fractionation methods of PVC have focused on fractional precipitation (Geerissen, H., et al., Continuous fractionation and solution properties of PVC, 1. Continuous fractionation, characterisation. Die Makromolekulare Chemie, 1985. 186(4): p. 735-751). Sequential solvent extraction fractionation was chosen here for rather logistical reasoning. In fractional precipitation, extra care needs to be placed while processing the solvent, to avoid any solvent loss, which could cause an inconsistency in further solvent mix ratios. Further, recovery of solvent is complicated during fractional precipitation, especially for Ace-MeOH blends due to the presence of an azeotrope (Xu, W., et al., Revealing the mechanism of adsorption and separation of acetone/methanol by porous carbon via experimental and theoretical calculations. Chemical Engineering Journal, 2023. 474: p. 145565). Hence the choice of sequential solvent extraction, as those issues are non-existent for it, making a more convenient choice for processing large volumes of PVC.

[0137] In the methods presented here, PVC is contacted with the weakest solvent mixture first (here, 50Ace:50MeOH). The mixture is then separated into its liquid and solid components. The residual undissolved PVC is then contacted by an incrementally stronger solvent mixture in increments of -10% MeOH until it is 100% Ace. The residual PVC is then extracted in THF-MeOH mixtures similarly.

[0138] Similar to single-step solvent extraction, fractions see a gradual rise in the average molecular weight with increase of weak/strong solvent content (FIG. 9). However, the D values of the fractions were remarkably lower, and are consistently < 1.4, excepting S10 which had a D of 1.73, but contained the remaining PVC as the last fraction.

[0139] Commercial samples of PVC (pipe and plasticized pellets) were also sequentially fractionated to simulate these methods on end-of-life plastics. Both products had relatively high, but slightly different molecular weights, with PVC pipe and plasticized pellets having an Mw = 115 and 105 kDa, with an MN = 64.8 and 57.1 kDa respectively (TABLE 5). Since the starting materials had relatively high molecular weights, no fractions were likely to be recovered for the Ace mixtures with 50%-30% MeOH. Nonetheless, these fractionations were attempted, and acted as selective additive extraction steps, which prevented significant contamination in subsequent fractions. The fractions produced here showed a similar trend to K-50 experiments, however, they did not have similar molecular weights. This can be attributed to the difference in molecular weight of the source materials, but also the product form. PVC pipe and pellets were extracted either as-is or after cutting to small cubes (FIG. 5), which would interfere with the extraction process. Further, the fused/gelled behavior of commercial extruded PVC (Summers, J.W., et al., Measurement of PVC fusion (gelation). Journal of Vinyl Technology, 1986. 8(1): p. 2-6) leads to even less surface area for dissolution. PVC K-50 was received as a fine powder, which increased the surface area during the extraction. During the Ace phase of extractions, commercial PVC only gradually swelled, and only broke into powders, likely also breaking fused particles, during the THF phase of extractions. This aligns well with theory, as the relation between swelling/surface area and dissolution as explained by the Flory-Huggins theory (FIG. 10).

TABLE 5. Summary of sequential fractionation experiments conducted and their designated entry IDs. ^a Source PVC data. ^b Full dissolution. ^c 50:50 mixture by weight of: PVC Pellet (M_w = 105 kDa, M_n = 57.1 kDa, D = 1.84, T_g = 81.9 °C) and PVC Pipe (M_w = 115 kDa, M_n = 64.8 kDa, D = 1.78, T_g = 84.7 °C). ^d Only additives extracted using less Ace content.

[0140] Structural Analysis'. From spectroscopic analyses, all fractions produced during this work were identical to virgin PVC resin. For solvent-based recovery methods, the thermal or chemical degradation of the products can be a concern. Since all extractions were run under ambient temperatures and pressures (energy introduced during sonification is likely negligible), it is highly unlikely that any thermal degradation would occur, as the degradation temperature of PVC is above 250°C (Yu, J., et al., Thermal degradation of PVC: A review. Waste Management, 2016. 48: p. 300-314). Thermal degradation of PVC typically occurs through dehydrochlorination, which releases HC1 and forms conjugated sequences of C=C bonds which can undergo further reactions, including crosslinking (Cruz, P.P.R., et al., Thermal dehydrochlorination of pure PVC polymer: Part I — thermal degradation kinetics by thermogravimetric analysis. Journal of Applied Polymer Science, 2021. 138(25): p. 50598). In all products made in this work, no sign of C=C bond formation was observed. In FTIR, C=C peaks are observed between 1600-1700 cm'¹ (vc=c), which are not present in any products (FIGS. 11A-11C)

[0141] Chemical degradation during solvent-based recovery usually occurs as solvolysis or due to presence of additives and contaminants, introducing new structural defects. In this case, the most likely defect would be the formation of double bonds through elimination, or the formation of alcohols or ketones through oxidation. Fortunately, neither degradation routes were observed. Oxidation of PVC would cause -OH or C=O peaks to appear in FTIR spectra around 3500 cm'¹ (VO-H) and 1700-1780 cm'¹ (vc=o) respectively. While no -OH peaks were observed in the products, a small broad C=O peak (sometimes as two neighboring peaks) can be seen in all products and virgin resin. This C=O peak seems to be native to the PVC resin used, and is common in most PVC resins, and can be attributed to many causes as the presence of structural defects, additive, or processing agents.

[0142] The products made from commercial samples were analyzed for the presence of residual additives. Prior to any extractions, the source commercial PVC was soaked briefly in hexanes and MeOH to extract freely soluble plasticizers, additives, or dyes. However, that does not guarantee complete or efficient removal of all additives. So, fractionation started at a 50Ace:50MeOH solvent system, despite it not extracting any PVC, with the goal of removing as much additive as possible prior to recovering PVC. The sequential fractionation methods done with commercial samples allows for most additives to be extracted during the first fractions, with progressively less additive present in subsequent fractions. This was clear by the presence of residual additive in Cl to C4, albeit progressively less each step. This can be seen by the FTIR C=O peak around 1740 cm'¹ (vc=o), indicating the presence of terephthalate (described as non-ortho phthalate by the vendor), and another additive peak around 1670 cm'¹ (Likely vconjugated c=o). The intensity and shape of the CH2 peaks around 2780-3000 cm^-1(vc-H), for all fractions are PVC-like (Unlike PVC pipe or PVC pellet, FIG. 6, FIG. 7). Which alludes to the existence of only trace amounts of additive in the contaminated fractions. Nonetheless, further purification via dissolution/precipitation may be required for complete removal of additives. Subsequent fractions, accounting for 76.9 wt% of the total weight of the source material, show much cleaner FTIR spectra, which were overwhelmingly similar to virgin PVC (FIG. 11C) [0143] Properties'. The glass transition temperatures (T_g) of the fractionation products were measured using DSC. The dependence of T_g on the molecular weight of (linear) polymers is well understood and can be described empirically by the Flory-Fox equation (Fox, T.G., Jr. and P.J. Flory, Second - Order Transition Temperatures and Related Properties of Polystyrene. I. Influence of Molecular Weight. Journal of Applied Physics, 1950. 21(6): p. 581-591). DSC scans of PVC fractions show that PVC follows this relationship as well, as can be seen in FIG. 12. The results agree well with calculated values obtained using estimates of the Flory-Fox equation parameters of PVC (T_goo = 351 K and K = 8 x 10⁴, 16.5 x 10⁴ (Lu, X. and B. Jiang, Glass transition temperature and molecular parameters of polymer. Polymer, 1991. 32(3): p. 471-478)). Of note is the agreement of lower molecular weight fractions of commercial PVC, C2 to C4, which were shown to contain amounts of plasticizers. The exception was Cl, which had a lower T_g than predicted, or observed in SI, which had a lower MN (8.28 kDa vs 3.36 kDa) but similar T_g. This general agreement shows that the leftover plasticizer had little to no effect on the T_g of C2 to C4, thus confirming their presence in trace amounts only.

[0144] The relationship between polymer molecular weight and polymer solution viscosity is well known (Dobrynin, A.V., et al., Viscosity of Polymer Solutions and Molecular Weight Characterization. ACS Macro Letters, 2023. 12(6): p. 773-779). This relationship obeys the power law, and is often described by the Mark-Houwink equation (Mark-Houwink equation, in Compendium of Chemical Terminology. 2019, International Union of Pure and Applied Chemistry (IUPAC)). Viscosity measurements of the acetone fractions follow this trend (FIG. 13). F65 and its source PVC K-65, had a solution dynamic viscosity (p) of 25.33 cP and 134.7 cP respectively; F6 and its source PVC K-50 had p of 13.9 cP and 32.27 cP respectively.

[0145] Computational Results'. To explore the structural changes of PVC with increasing MeOH present in the solvent blends, the radius of gyration (R_g) of PVC in Ace-MeOH and THF-MeOH was computed (TABLE 6). Generally, R_g decreases with higher MeOH concentrations and with increasing npvc. Additionally, the ratio of surface area (SA) of PVC in solvent mixtures to the SA of bulk PVC was calculated (FIG. 10). A consistent decrease with increasing MeOH was observed. For instance, for npvc = 5 in Ace-MeOH, the SA ratio drops from 2.45 at 0% MeOH to 1.86 at 80% MeOH. Higher npvc exhibits lower SA across all MeOH concentrations, indicating that as npvc increases, PVC chains pack more tightly, reducing solvent accessibility. The addition of MeOH likely leads to polymer chain contraction, further lowering the SA. TABLE 6. Density of PVC-ACE-MeOH and PVC-THF-MeOH systems with different npvc corresponding to TABLE 4, as well as R_g values of the PVC in these systems.

[0146] TABLE 6 shows that the density decreases with increasing MeOH concentrations in both PVC-Ace-MeOH and PVC-THF-MeOH mixtures. Increasing npvc results in increased density due to the higher PVC concentration. Given the high PVC concentration in this study, direct comparison of density with experiments may be challenging. However, previous work (Olowookere, F.V., et al., Effects of chain length on the structure and dynamics of polyvinyl chloride during atomistic molecular dynamics simulations. Molecular Simulation, 2023. 49(15): p. 1401-1412) using the same force field parameters and models showed excellent agreement with experimental density values.

[0147] The study calculated the V^E and H^E and used the latter to determine the Flory- Huggins (FH) interaction parameters shown in FIGS. 14A-14B. For all npvc in both mixtures, V^E (FIG. 14A) becomes less negative as % MeOH increases. Higher npvc shows more negative V^E, indicating stronger contraction during mixing in both mixtures. The Ace-MeOH mixture exhibits stronger contraction (more negative V^E) compared to the THF-MeOH mixture, particularly at low MeOH concentrations. However, the difference narrows as % MeOH increases.

[0148] The Hansen method was applied to predict PVC solubility in the mixtures. Molar volumes (Vm) and Hansen solubility parameters (HSP) values are shown in TABLE 7. The Vm and HSPs of pure Ace, pure THF and bulk PVC are in very good agreement with experimental data at 300 K, validating the simulations. Vm in both mixtures decreases by a factor of ~2 as MeOH % increases, indicating that THF or Ace mixtures become more compact with added MeOH. Moreover, the electrostatic term increases while the dispersion term decreases, making both mixtures more polar and less compatible with PVC. Ace-MeOH shows stronger electrostatic interactions and slightly weaker dispersion interactions than THF-MeOH, making it less favorable for dissolving PVC.

TABLE 7. Computed molar volumes (cm³/mol) and Hansen solubility parameters and various contributions (dispersion and electrostatic) in MPa^{1 2} of ACE-MeOH and THF-MeOH mixtures as well as bulk PVC at 300 K from MD simulations. The values in parentheses represent the experimental values of pure ACE, THF, and bulk PVC from Zeng, W., et al., Solubility parameters, in Physical properties of polymers handbook. 2007, Springer, p. 289- 303.

[0149] Overall, the total HSP increases with higher % MeOH, indicating reduced compatibility with PVC, as confirmed by heightened Ra values (FIG. 15). The HSP distance increases with increasing % MeOH, with THF-MeOH showing slightly smaller Ra values than Ace-MeOH.

Conclusion

[0150] PVC was successfully fractionated using weak solvent/nonsolvent and strong solvent/nonsolvent mixtures using commodity solvents, two of which (Ace and MeOH) are considered “green”. The fractionations were attempted using both single-step and sequential fractionation methods. Both methods showed a trend in increasing molecular weight of fraction with decrease of nonsolvent, MeOH, in solvent mixtures. Fractions obtained using sequential fractionation showed remarkable decrease in D, with fractions as low as D = 1.14. Further, no degradation was observed in any of the extracted samples. Commercial PVC-containing products were also used to illustrate the capability of this method in recovering clean PVC. Early fractions showed slight contamination, however, the bulk of the recovered polymer, 76.9 wt%, appears identical to the pristine virgin PVC. T_g values for the recovered fractions agreed with theoretical values, constant at high MN values but reduced greatly at low MN values. The T_g of the low molecular weight fractions also agreed with theoretical values, proving that the contamination (presence of plasticizers) was only in trace amounts.

[0151] The results of fractionation of PVC warrant further study. Of interest, is the study and experimentation with green solvents towards fractionation (Soyemi, A. and T. Szilvasi, Calculated Physicochemical Properties of Glycerol-Derived Solvents to Drive Plastic Waste Recycling. Industrial & Engineering Chemistry Research, 2023. 62(15): p. 6322-6337). Furthering the inspiration from the lignin fractionation field, sequential fractionation can be attempted using different solvents rather than solvent mixtures (Park, S.Y., et al., Fractionation of lignin macromolecules by sequential organic solvents systems and their characterization for further valuable applications. International Journal of Biological Macromolecules, 2018. 106: p. 793-802). The low D of the fractions inspires study of PVC’s physical properties, such as determining more accurate Flory -Fox parameters, especially at high molecular weights. [0152] The following patents, applications and publications as listed below and throughout this document are hereby incorporated by reference in their entirety herein.

Claims

What is claimed is:

1. A PVC-containing resin for additive manufacturing, comprising polyvinyl chloride (PVC) dissolved in a liquid base resin.

2. The PVC-containing resin of claim 1, wherein the liquid base resin comprises monomers, oligomers, polymerization initiators, dyes, pigments, or any combination thereof.

3. The PVC-containing resin of claim 2, wherein the liquid base resin comprises monomers and/or oligomers of polypropylene, acrylonitrile butadiene styrene (ABS), polyethylene, polystyrene, acrylic, polycarbonate, polyethylene terephthalate, polyurethane, epoxy, or any combination thereof.

4. The PVC-containing resin of any one of claims 1-3, wherein the PVC is present in an amount of from about 1 wt% to about 50 wt%.

5. The PVC-containing resin of any one of claims 1-4, wherein the PVC has an average molecular weight of from about 1,000 g/mol to about 100,000 g/mol.

6. The PVC-containing resin of any one of claims 1-5, wherein the PVC has a poly dispersity index (PDI) of from about 1 to about 2.

7. The PVC-containing resin of any one of claims 1-6, wherein the PVC has a glass transition temperature (T_g) of from about 40°C to about 90°C.

8. A method of additively manufacturing (e.g., 3D printing, injection molding) an article, the method comprising: a) providing the PVC-containing resin of any one of claims 1-7; and b) curing the PVC-containing resin to form an article.

9. The method of claim 8, further comprising heating the PVC-containing resin.

10. The method of any one of claims 8-9, wherein step b) comprises irradiating the PVC- containing resin with a light source; and wherein the light source polymerizes the resin into a solid plastic, thereby forming the solid article.

11. A solid article formed by the method of any one of claims 8-10.

12. The solid article of claim 11, wherein the solid article has an elastic modulus that is from about 1% to about 90% lower than a reference solid article made from the liquid base resin without PVC.

13. The solid article of any one of claims 11-12, wherein the solid article can stretch from about 120% to about 200% of its original length.

14. A method of preparing a PVC-containing resin for additive manufacturing, the method comprising: a) contacting a quantity of PVC with an organic solvent to form a PVC extract comprising a soluble fraction of PVC and the organic solvent; and b) dissolving at least a portion of the PVC extract into a liquid base resin to form a PVC-containing resin comprising PVC.

15. The method of claim 14, wherein the organic solvent comprises ethyl acetate, acetone, methyl acetate, tetrahydrofuran (THF), methanol, methyl ethyl ketone, 2- methyltetrahydrofuran (2-MeTHF), cyclohexanone, or any combination thereof.

16. The method of any one of claims 14-15, wherein the PVC extract further comprises an insoluble fraction of PVC, and wherein step a) further comprises removing said insoluble fraction of PVC from the PVC extract.

17. The method of any one of claims 14-16, further comprising at least partially evaporating the organic solvent from the PVC extract before step b).

18. The method of any one of claims 14-17, further comprising at least partially evaporating the organic solvent from the PVC-containing resin during or after step b).

19. The method of any one of claims 14-18, wherein step a) further comprises: i) contacting the quantity of PVC with a first organic solvent to form a first PVC extract comprising a first soluble fraction of PVC and the first organic solvent; ii) at least partially precipitating the soluble fraction of PVC; and iii) dissolving the precipitated PVC in a second organic solvent to form a second PVC extract comprising a second soluble fraction of PVC and the second organic solvent; wherein the second PVC extract is used as the PVC extract in step b).

20. The method of claim 19, wherein step ii) comprises at least partially evaporating the first organic solvent from the first PVC extract and/or adding a non-solvent to the first PVC extract.

21. The method of claim 20, wherein the non-solvent comprises water, methanol, alkanes, or any combination thereof.

22. The method of any one of claims 19-21, wherein the first organic solvent has a same composition as the second organic solvent.

23. The method of any one of claims 19-21, wherein the first organic solvent has a different composition than the second organic solvent.

24. The method of any one of claims 19-23, wherein the second soluble fraction of PVC has a lower molecular weight and/or a lower poly dispersity index (PDI) than the first soluble fraction of PVC.

25. The method of any one of claims 19-24, wherein step a) further comprises repeating steps ii) and iii) 1 time, 2 times, 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, or 10 times; and wherein a final PVC extract produced in a final repetition is used as the PVC extract in step b).

26. The method of any one of claims 14-25, wherein the liquid base resin comprises monomers, oligomers, polymerization initiators, dyes, pigments, or any combination thereof.

27. The method of claim 26, wherein the liquid base resin comprises monomers and/or oligomers of polypropylene, acrylonitrile butadiene styrene (ABS), polyethylene, polystyrene, acrylic, polycarbonate, polyethylene terephthalate, polyurethane, epoxy, or any combination thereof.

28. The method of any one of claims 14-27, wherein the PVC-containing resin comprises from about 1 wt% to about 50 wt % PVC.

29. The method of any one of claims 14-28, wherein the PVC in the PVC-containing resin has an average molecular weight of about 1,000 g/mol to about 100,000 g/mol.

30. The method of any one of claims 14-29, wherein the PVC in the PVC-containing resin has a poly dispersity index (PDI) of from about 1 to about 2.

31. The method of any one of claims 14-30, wherein the PVC in the PVC-containing resin has a glass transition temperature (T_g) of from about 40°C to about 90°C.

32. The method of any one of claims 14-31, wherein the quantity of PVC comprises virgin PVC, formulated PVC, commercial PVC, post-consumer PVC, or any combination thereof.

33. The method of any one of claims 14-32, wherein the quantity of PVC has a K value of from about 50 to about 75.

34. The method of any one of claims 14-33, wherein the method produces the PVC- containing resin of any one of claims 1-7.