WO2025029197A1

WO2025029197A1 - Magnetic induction processing of thermoplastics, their composites, and production thereof

Info

Publication number: WO2025029197A1
Application number: PCT/SG2024/050489
Authority: WO
Inventors: Terry William Joseph STEELE; Raju V. RAMANUJAN
Original assignee: Nanyang Technological University
Current assignee: Nanyang Technological University
Priority date: 2023-08-01
Filing date: 2024-08-01
Publication date: 2025-02-06
Anticipated expiration: 2026-02-01

Abstract

Disclosed herein are a method of conducting in-situ frontal polymerisation of one or both of a thermoplastic resin precursor and a thermoset resin precursor, and a thermoplastic polymeric composite material comprising a solid thermoplastic polymeric material, and Curie nanoparticles having a Curie temperature of from 90 to 400 ºC homogeneously distributed throughout the solid thermoplastic polymeric material. Also disclosed herein are methods of forming the thermoplastic polymeric composite material, laminating two or more sheets of a thermal insulating foam together, delaminating two or more sheets of a thermal insulating foam so as to separate the two or more sheets, consolidating a plurality of thermoplastic sheets together, and consolidating a plurality of thermoplastic semipreg sheets together.

Description

MAGNETIC INDUCTION PROCESSING OF THERMOPLASTICS, THEIR COMPOSITES, AND PRODUCTION THEREOF

Field of Invention

The present invention generally relates to thermoplastics, their composites, and production thereof, and more particularly relates to magnetic induction processing of thermoplastics, their composites, and production thereof.

Background

The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.

Current composites based on thermoset/fiber prepregs are not recyclable and are a landfill hazard at a current production rate of 4 Mkg.y¹. Thermoplastic composites have considerable benefits over thermoset composites in terms of material properties and sustainability. However, scalable, automated production platforms for thermoplastic composites have not reached the same level as that of thermoset composites, thus limiting their usage.

Thermoplastic composites are composed of a thermplastic matrix (e g. polyether ether ketone- PEEK, poly-ether sulfone-PES, polyphenylene sulfide-PPS, polyphthalamide-PPA, polyetherimide-PEI, styrene acrylonitrile-SAN, polycarbonate-PC, polyamide 6/6 -PA66, polyamide 6-PA6, polyamide 12-PA12, polybutylterephthalate-PBT, polyoxymethylene-POM, polypropylene-PP) and a reinforcing material, fabric or fibre (e g. glass, carbon, synthetic, aramid, metal, basalt, flax, hybrids, and braided). Thermoplastic composites are available in a number of manufacturing stages, such as semipregs, prepregs, and organosheets.

Semipregs are fabrics with a thermoplastic matrix powder that has been partially melted or coated to the fabric surface. The semipreg is still flexible (drape) and can be easily formed, cut, and manipulated. Prepreg is the subsequent processing stage of semipreg, which becomes fully impregnated with matrix, forming a relatively stiff fabric. Organosheets combine semipregs or prepegs into a thermal fabric stacking process that fully consolidates and impregnates the multilayer sheets. Current production lines for consolidation of semipregs and prepregs are limited to a layer by layer process (Automated Tape Laying, ATL or Advanced Fiber Placement, AFP) because rapid surface heating can only be done via direct energy sources, such as lasers and ultrasound. The latter methods are limited to single layers of composite consolidation since these methods of direct energy application cannot be evenly applied to multi-layer fabrics. A method of multi-layer composite consolidation is an unmet industrial need where 3-10 layers or more are often required within a finished organosheet. Another unmet industrial need is a process that allows reversible consolidation of composites in order to address recycling and sustainability mandates.

Thermoplastics need to be heated nearer above their glass transition temperature (Tg) before they can be shaped, formed, or consolidated. Thermal conduction or radiation based heating is inefficient for processing materials that have low thermal conductivity (e.g. 0.01 - 1 W.m LK ¹) or materials that are opaque, such as foams, laminates, and most thermoplastic resins. These methods are not capable of volumetric heating and are limited to finite surface heating applications. Radiation based heating offers a method of heat transfer via electromagnetic waves and is generally easier to control with respect to spatial and dynamic production processes. However, most radiation heating is limited to thin films (<1 mm) as light wavelengths from UV (200 nm) to infrared waves (10,000 nm) have limited penetration depths in most fibre or solid materials. Lasers/infrared lamps or other methods of surface heating such as hot gases require expensive hardware and consumables, lack temperature control, and are best suited for uniform resins. These devices cannot be used for mixed materials, multi-laminate designs, or delamination. Microwave wavelengths range from 30 to 0.03 cm. The transducers that produce these wavelengths lack a method of uniform surface and volume exposure. Penetration is attenuated by certain type of fibers employed in composites. For example, some carbon fibres geometries reflect the microwave radiation and others absorb it. Variable frequency microwaves (VFM) require parti cl es/fibers as field-to-heat energy transducers. For example, VFM relies on activated carbon (AC) particulates to convert E- Fields to heat, known as the microwave absorption heating element (MAHE). However, the MAHE particles required for VFM application has no method of temperature self-regulation, thus requiring expensive feedback temperature sensors and assumes known risks of resin deterioration from particle overheating and hot spots (pyrolysis). Carbon fibre is a known MAHE that causes detrimental arcing and thus local damage when used to produce carbon fibre/resin composites. VFM’s reliance on microwaves leads to limited penetration depths. This limitation prevents production of multilayer carbon fibre composites with homogenous heating. Temperature gradients between layers have previously been shown. VFM also has known occupational hazards, e g. published warnings suggests the technology has fire hazards with previous observations of ignition of soot vapors via VFM (Hubbard, J. W. et al., ACS Appl. Mater. Interfaces 2013, 5 (21), 11329-11335). Ultrasonic heating is limited due to the horn size/geometry available (< 50 mm contact width) and best suited for narrow width advanced fibre placement designs. There is no current technology that allows homogenous volumetric heating with a heating source that can be tuned for a preset self-regulating temperature.

Thermoplastic elastomers combine the advantages of vulcanized rubber material properties with the positive attributes of thermoplastics. Thermoplastic elastomers (e.g. TPU) are designed to replace thermoset resins (e g. silicone rubbers and isobutylene) as they have a better environmental profile (recyclable, reusable) and offer a method of debonding interfaces after production through temperature elevation at substrate interfaces. One example is Copolyester Elastomers (COPES) with hard segments of polyester, polybutylene terephthalate and polyether soft segments. Some of the known positive attributes include excellent resistance to flexural fatigue, high impact resistance, high abrasion resistance, excellent adhesion to both plastics and metals, low moisture absorption, and excellent dimensional stability. COPES is ideal for applications and parts that require excellent flexural strength in a wide temperature range of use. Some example applications include electrical & mechanical sectors, electric cars, sporting goods, boots, air ducts, water seals, foam adhesives, gaskets, belts, hoses, wire coatings, cable insulation, railpads, diaphragms, valves, caps, and closures.

In-situ frontal polymerization is a process of activating reactive monomers by exploiting exothermic chemical reactions where a sufficient balance of heat is generated to propagate polymerization within a thin film. Choice of monomer and polymerization chemistry can lead to either thermoset or thermoplastic polymers. Continuous initiation and propagation of the reactive monomers requires the resin to exceed a temperature or activation energy threshold. However, creation of too much energy within a defined volume leads to exothermic runaway that leads to resin volatilization and subsequent creation of gas pockets and foams. Homogenous resin polymerization requires the correct balance of exothermic Joule heating (watts in) and heat dissipation by substrate thermal conductivity (watts out). The right dynamic energy balance results in a stable cure of resin with the monomer majority consumed while free from gas pockets. Partial curing (initiation, but incomplete monomer consumption) results if activation energy, temperature, or both is too low. Overcuring occurs when the heat produced exceeds the heat removed by the adjacent resin, substrate, endothermic reactions, or combination thereof causing a local rapid temperature rise that leads to resin volatilization. The latter process yields foamed heterogenous resins with numerous voids and trapped gas pockets whose bulk mechanical properties are relatively weak compared to stable cured resins.

Commercial monomer formulations to achieve reactive resins are available with low viscosities (< 100 mPa.s) for complete in-situ polymerization and impregnation within fiber matrices. Elium® is one such liquid resin based on a proprietary methacrylate/peroxide (thermoplastic) formulation that is marketed to replace epoxy resins (thermoset) that have a poor sustainability profile. Elium® targets sustainable manufacturing of thermoplastic prepregs, organosheets, and finished composites within the wind power, sailing, concrete reinforcement, and hydrogen storage industries. Current Elium® resins cure like a thermoset in 20-30 minutes at 80 °C. The composite matrix, once cured, behaves like a thermoplastic (PMMA, poly-methylmethacrylate) that can be thermoformed into any shape and induction welded to other thermoplastics. Sustainable recycling are thus possible since the resin can be melted, demanufactured, removed, or combination thereof from the composite fibers.

Magneto-composite technology offers a non-contact method of consolidating prepregs and semipregs based on magnetic induction. The nanotechnology is based on paramagnetic particles that have no remnant magnetization at room temperature. The particles only have magnetic properties and associated interactions if external magnetic fields are applied. This prevents magnetic agglomeration of the particles when suspended in fluids under zero-field conditions unlike permanent magnets that suffer from particle agglomeration due to attractive magnetic forces. A few studies have been initiated to develop alternating magnetic field (AMF) mediated in-situ heating (induction) for the production of composites. Previous studies have investigated activation of thermoset resins based on FeCo epoxy composites (Miller, K. J. et al., J. Appl. Phys. 2009, 105 (7), 07E714). Induction curing of thiol-acrylate and thiol-ene composite systems were demonstrated with Cobalt and Nickel particles (Ye, S. et al., Macromolecules 2011 , 44, 4988-4996). However, FeCo nanoparticles have Curie temperatures (T_c) exceeding 900 °C, which exceeds the degradation temperature of all epoxy resins, which generally occurs above 300 °C. The Curie temperatures (T_c) refers to the temperature point where the magnetic material loses its magnetic properties and no longer interacts with the magnetic field, thus allowing a method of self- regulating temperature. Polymerization of cyanate ester using Fe₃O4 (T_c 570°C) as an induction-based heat source was demonstrated, but cyanate esters have a degradation temperature above 400 °C (Hubbard, J. W. et al., ACS Appl. Mater. Interfaces 2013, 5 (21), 11329-11335). Induction curing was also studied with nickel nanoparticles (T_c s 350°C) for bonding of the composite, however nickel particles are ferromagnetic and naturally aggregate due to attractive magnetic forces, preventing distribution in liquid resins (Suwanwatana, W. etal., Compos. Sci. Technol. 2006, 11-12 (66), 1713-1723). Nickel particles also rapidly oxidize, which results in limited shelf stability and loss of induction heating parameters. Nickel materials also have many toxicity concerns and are thus generally avoided if possible. In-situ polymerization has been demonstrated with iron oxide nanochains (T_c s 570 °C) (Ma, M. et al., J. Colloid Interface Sei. 2012, 1 (374), 339-344). Magsilica formulations that have a core-shell nanoparticle are known, where the core is magnetite (T_c 2 570°C) and the shell is a thin layer of silica on the order of a few nanometers thick, which aids in dispersion. All the paramagnetic particles employed to date lack the ability to self-regulate temperature within the known temperature range of thermoplastic processing, which is generally from 80 - 400 °C.

EP1326741 B1 discloses the temperature-controlled induction heating of polymeric materials. EP1326741B1 presents the induction heating of thermoplastic polymeric materials by adding ferromagnetic particles. Ferromagnetic hexagonal ferrite particles are, for example, SrFe^Oig, Co2Ba₂Fei₂O22, Mg₂Ba₂Fei2O22, ZniMgiBa₂Fei₂O22 and ZniCoiBa₂Fei₂O22. Loading of these materials into thermoplastics was varied from 1% to 50% by volume and explored at a magnetic field frequencies of 275 kHz and 4 MHz. Ferromagnetic particles cannot be employed in liquid resins due magnetic induced aggregation, preventing homogenous distribution and application of volumetric heating.

W02019090067A1 discloses the adhesive/sealant materials filled with metallic particles for induction heating. The metallic filler is required to be 30% - 70% by weight of the adhesive/sealant material. Dendritic shaped fern-like particles of pure iron was mostly explored.

The drive for lightweight/energy-efficient designs and sustainability requires dramatic changes within manufacturing lines and material choices. Replacing unsustainable thermoset composites is the major market driving factor toward the implementation of thermoplastic composites, as the latter incorporate numerous mechanical and sustainable benefits. However, thermoset materials are currently far more advanced in their reproducibility, shear strength (resin impregnation), and manufacturing output. Modern thermoplastic composite manufacturing relies on indirect heating methods such as stamping, press forming, and autoclaves. These operations are not only laborious/inefficient, but time consuming with heating cycles taking tens of minutes to hours. Market forces are pushing for innovations focused on direct energy methods that can rapidly (0.5 - 5s) heat the thermoplastics above the glass transition temperature but below the degradation temperature (T_fl < T_proCess < Tdeg). The directed energy sources include microwaves, laser/hot gas heating, and ultrasound to obtain in-situ consolidation. The latter signifies bonding between prepregs and impregnation within the thermoplastic prepregs filled with carbon, glass, or aramid fibres. These directed energy methods are restricted as the heat transfer cannot be uniformly applied volumetrically across multiple prepreg layers - thus existing industry tooling is limited to layer-by-layer consolidation. Other specific impediments are known; microwave energy fields are rarely uniform and carbon fibres reflect the radiation - this method is best suited for glass fibre composites. Lasers/infrared lamps/hot gas have expensive hardware and consumables, lack temperature control, and best suited for uniform resins - cannot be used for mixed materials, multi-laminate designs, or delamination. Ultrasonic heating is limited due to the horn size/geometry available (< 50 mm contact width) and best suited for narrow width advanced fibre placement designs. Previous applications of magnetic induction have employed ferromagnetic materials that aggregate in liquid states or applied paramagnetic particles whose Curie temperature is above the resin degradation temperature.

Therefore, there exists a need for an improved and environmentally friendly process for prepreg and semipreg consolidation, in-situ polymerization of thermoplastic matrices, and methods to recycle composites which will ameliorate the drawbacks of prior art processes.

Summary of Invention

Aspects and embodiments of the invention are provided in the following numbered clauses.

1. A method of conducting in-situ frontal polymerisation of one or both of a thermoplastic resin precursor and a thermoset resin precursor, the method comprising the steps of:

(a) providing a mixture comprising: one or both of a monomeric and/or oligomeric thermoplastic resin precursor and a monomeric and/or oligomeric thermoset resin precursor; at least one initiator suitable for initiating polymerisation of the monomeric and/or oligomeric thermoplastic resin precursor and the monomeric and/or oligomeric thermoset resin precursor;

Curie nanoparticles having a Curie temperature of from 90 to 400 °C; and

(b) subjecting the mixture to an alternating magnetic field to provide one or both of a thermoplastic resin and a thermoset resin, wherein the Curie nanoparticles are provided in an amount of from 1 to 10 wt% relative to the weight of the resin precursor(s) present in the mixture.

2. The method according to Clause 1 , wherein the Curie nanoparticles are provided in an amount of: (ai) from 4 to 10 wt% (e g. from 5 to 10 wt%) relative to the weight of the resin precursor(s) present in the mixture, where only monomeric and/or oligomeric thermoplastic resin precursors are present if an over-cured resin is desired;

(aii) from 1 to 3 wt% (e.g. from 1 to 2 wt%) relative to the weight of the resin precursor(s) present in the mixture, where only monomeric and/or oligomeric thermoplastic resin precursors are present if complete curing, without overcuring, is desired;

(aiii) from 1 .5 to 2.5 wt% (e.g. 2 wt%) relative to the weight of the resin precursor(s) present in the mixture, where only monomeric and/or oligomeric themoset resin precursors are present.

3. The method according to Clause 1 or Clause 2, wherein a preset temperature or a desired preset temperature profile are maintained through a dynamic feedback control on an induction field strength of the alternating magnetic field.

4. The method according to any one of the preceding clauses, wherein:

(i) the monomeric and/or oligomeric thermoplastic resin precursor is selected from one or more of the group consisting of acrylates, urethanes, lactones, silanes, and amides, wherein said materials are presented in the form of one or both of monomers and oligomers;

(ii) the monomeric and/or oligomeric thermoset resin precursor is selected from one or more of the group consisting of epoxy, oxetane, di-acrylates, tri-acrylates, tetra-acrylates, vinyl carbonates, vinyl carbamates, latex, isoprene, butyl diene, and styrene, wherein said materials are presented in the form of one or both of monomers and oligomers, as well as condensation oligomers and monomers; and

(iii) the at least one initiator is selected from one or more of the group consisting of azoradicals, diazirines, peroxy, diperoxy, carbonates, diacyl peroxides, peroxyketals, peroxyesters, dialkyl peroxides, hydroperoxides, triazines, persulfates, iodonium salts, and sulfonium salts.

5. A thermoplastic polymeric composite material comprising: a solid thermoplastic polymeric material; and

Curie nanoparticles having a Curie temperature of from 90 to 400 °C homogeneously distributed throughout the solid thermoplastic polymeric material.

6. The thermoplastic polymeric composite material according to Clause 5, wherein one or both of the following apply:

(aai) the Curie nanoparticles are present in an amount of from 1 to 20% wt/wt (e.g. from 5 to 15% wt/wt, such as about 10 % wt/wt) relative to the solid thermoplastic polymeric material; and (aaii) the solid thermoplastic polymeric material is selected from one or more of the group consisting of polyacrylates, polyurethanes, polylactones, polysilanes, polyamides and copolymers thereof.

7. A method of forming the thermoplastic polymeric composite material according to Clause 5 or Clause 6, the method comprising the steps of:

(bi) providing a mixture comprising a solid thermoplastic polymeric material and Curie nanoparticles having a Curie temperature of from 90 to 400 °C, where the solid thermoplastic polymeric material and Curie nanoparticles are provided as separate, non-unitary components; and

(bii) subjecting the mixture to an alternating magnetic field to provide the thermoplastic polymeric composite material according to Clause 5 or Clause 6.

8. A method of laminating two or more sheets of a thermal insulating foam together, the method comprising the steps of:

(ci) providing at least two sheets of a thermal insulating foam and at least one sheet of a thermoplastic polymeric composite material according to Clause 5 or Clause 6, where each sheet of thermal insulating foam is separated from each other sheet of thermal insulating foam by a sheet of the thermoplastic polymeric composite material; and

(cii) subjecting the mixture to an alternating magnetic field to provide a laminated product.

9. A method of delaminating two or more sheets of a thermal insulating foam so as to separate the two or more sheets, the method comprising the steps of:

(ci) providing a laminate construct comprising at least two sheets of a thermal insulating foam and at least one sheet of a thermoplastic polymeric composite material according to Clause 5 or Clause 6, where each sheet of thermal insulating foam is separated from each other sheet of thermal insulating foam by a sheet of the thermoplastic polymeric composite material, and where the thermoplastic polymeric composite material is adhered to each of the thermal insulating foam sheets; and

(cii) subjecting the mixture to an alternating magnetic field to enable separation of the laminate construct to provide a delaminated product through the removal of the two or more sheets of thermal insulating foam from the thermoplastic polymeric composite material.

10. A method of consolidating a plurality of thermoplastic sheets together, the method comprising the steps of:

(di) providing n thermoplastic sheets where each sheet has a first surface and a second surface diametrically opposed to the first surface, and either: n-1 of the sheets have a first surface that is coated with Curie nanoparticles having a Curie temperature of from 90 to 400 °C and the sheets are arranged such that each coated first surface is in contact with an uncoated second surface of a directly neighbouring thermoplastic sheet; or when n is a multiple of three, one of the thermoplastic sheets is coated on the first and second surfaces with Curie nanoparticles and is sandwiched between two uncoated sheets; and

(dii) subjecting the mixture to an alternating magnetic field to provide a consolidated product, wherein n is from 2 to 30.

11. A method of consolidating a plurality of thermoplastic semipreg sheets together, the method comprising the steps of:

(di) providing a stack of m thermoplastic semipreg sheets under compression, where each sheet has a first surface and a second surface diametrically opposed to the first surface, where when a first surface of a first sheet is brought into contact with a second surface of a second sheet, they together form a mating surface, where each mating surface is coated with Curie nanoparticles having a Curie temperature of from 90 to 400 °C; and

(dii) subjecting the stack of m thermoplastic semipreg sheets under compression to an alternating magnetic field to provide a consolidated product, wherein m is from 2 to 30.

12. The method according to any one of Clauses 1 to 4, the thermoplastic polymeric composite material according to Clause 5 or Clause 6, the method according to Clause 7, the method according to Clause 8, the method according to Clause 9, the method according to Clause 10 or the method according to Clause 11 , wherein the Curie nanoparticles are selected from one or more of the group consisting of Mi._xZn_xFe₂O4 and NaFeO₂, where:

M represents Mn, Co or Ni; and x represents 0 to 0.6 (e.g. from 0.01 to 0.6, such as from 0.1 to 0.6).

13. The methods and composite material according to Clause 12, wherein the Curie nanoparticles are selected from one or more of the group consisting of Mno 4ZnoeFe₂04, Mno 5Zno.5Fe₂04, Mno eZno.4Fe₂04, Mno.?Zno 3Fe₂04, Mno.8Zno ₂Fe₂04, Mno.gZno.iFe₂04, Coo.g. Zno iFe₂C>4, MnFe₂O4, and NaFeO₂.

14. The methods and composite material according to Clause 12 or Clause 13, wherein the Curie nanoparticles have a surface that is coated in an organic material. 15. The methods and composite material according to Clause 14, wherein the organic material is a surfactant, optionally wherein the organic material is a fatty acid having from 15 to 20 carbon atoms, further optionally wherein the fatty acid is oleic acid.

16. The methods and composite material according to Clause 14 or Clause 15, wherein the organic material further comprises one or both of bisphenol A diglycidyl ether, copolyester (COPES) and polycaprolactone.

Drawings

Fig. 1 depicts initiation of in-situ frontal polymerization resins and ring opening polymerization. (A) 2.5 wt% loading of CNP in resin. Rapid heating leads to exothermic volatization of resin, known as overcuring. (B) 2.0 wt% loading of CNP in resin. Moderate heating leads to a balanced exothermic reaction with complete curing of resin. (C) 1.5 wt% loading of CNP in resin. Insufficient heating leads to incomplete crosslinking reaction, or partial curing of resin. The magnetic field had a field strength of 200 Oersted (Oe) and frequency of 400 kHz. Mno 9Zn₀.iFe204 nanoparticles were used.

Fig. 2 depicts initiation of Elium® (Arekema) thermoplastic precursors and free radical polymerization. (A) 5 and 10 wt% loading of CNP in Elium®. The composite was brought to activation temperature (> 60 °C) within 4 minutes. Continuous heating leads to exothermic volatization of resin, known as overcuring. (B) 1 and 2 wt% loading of CNP in Elium®. Moderate heating leads to a balanced exothermic reaction with complete curing of resin, or partial curing of resin. The magnetic field has a field strength of 200 Oe and frequency of 400 kHz. Mno9Zno iFe₂04 nanoparticles were used.

Fig. 3 depicts induction melting and remelting of CoPES thermoplastic elastomer nurdles. (A) Temperature profile of CoPES nurdles with 10 wt% CNP/CoPES when exposed under a field strength of 200 Oe and frequency of 400 kHz. Mno.9Zno iFe₂04 nanoparticles were used. (B) Shear and loss modulus of neat CoPES and CoPES/CNP composite via a thermal rheometry sweep, where temperature sweep starts from 120 °C to 25 °C. (C) Complex viscosity of neat CoPES and CoPES/CNP composite via a thermal rheometry sweep, where temperature sweep starts from 120 °C to 25 °C. The complex shear modulus, which is defined as G* = ^ , with T being the complex shear stress and Y being the shear strain, is the measure of the material’s overall resistance to deformation. The complex viscosity, defined

measures the resistance to flow as a function of angular frequency. Fig. 4 depicts bonding of thermal insulating foam by CoPES thermoplastic elastomers. Black line: induction bonding with 10 wt% CNP/CoPES. Grey line: control sample.

Fig. 5 depicts (A) AMF melting and remelting of PCL thermoplastic polymer. Melting of PCL raw nurdles at 5.8 min to reach the Tm of 60 °C. Remelting of CNP/PCL composite, 3.9min@60 °C. Assuming relatively linear heating within the first minute, the corresponding temperature kinetics are 0.130, 0.137, and 0.146 °Cs-¹. This shows remelted specimens have increased dispersion as the bulk heating is more effective than the surface heating. Mno 9Zno.iFe204 CNPs were used to melt PCL nurdles under AMF strength of 200 Oe and frequency of 400 kHz. Magnetic coil diameter was 32 mm. (B) PCL nurdles (3 mm diameter) before (left), after (middle) physical mixing with CNP powder, and after induction melting (right). (C) Shear and loss modulus of neat PCL and 10 wt% CNP/PCL composite via a thermal rheometry sweep, where temperature sweep starts from 120 °C to 25 °C. (D) Complex viscosity (G7w) of neat PCL and 10 wt% CNP/PCL composite via a thermal rheometry sweep, where temperature sweep starts from 120 °C to 25 °C. (E) (Left) PCL formed and cut into sheets. (Center) PCL sheets coated with CNP at a surface concentration of 0.5 mg. erm². (Right) Induction-activated consolidation of PCL thermoplastic sheets with a field strength of 200 Oe and frequency of 400 kHz. Mno 9Zn₀.iFe₂04 nanoparticles were used.

Fig. 6 depicts thermoplastic polymers processing temperature compared to the Curie temperature (T_c) of particles with elemental composition of Mni._xZn_xFe2O4. Polycaprolactone, PCL. Polyurethane, TPU. Acrylonitrile butylstyrene, ABS. Polymethyl methacrylate, PMMA. Low density polyethylene, LDPE. High density polyethylene, HDPE. Polycarbonate, PC. polyvinyldiene chloride, PVDC. polyamide-6, PA6. Polyacetostyrene, SAN. polyethylene terephthalate, PET. Polytetrafluoroethylene, PTFE. polyether ketone, PEEK.

Fig. 7 depicts (A) consolidation of semipreg fabrics through induction. (Left) 60 mm induction coil with insertion of consolidation jig. (Right) Consolidation that applies a compressive force on 3 layers of semipreg fabric. Interface between fabric was coated with CNP 0.5 mg. erm² surface concentration. (B) Temperature of multilayer composite under induction (CF47 + CNP) with a field strength of 110 Oe and frequency of 400 kHz. Control experiments (CF47) generated a minimal temperature when CNP is not present. (C) Photographs of multilayer organosheets prepared under induction. Multilayer organosheets could be delaminated through subsequent exposure to induction and applying a peel force of > 1 N.mm within 30 seconds of induction heating. Fig. 8 depicts (A) induction curing of Elium150-15wtCNP-2wtBPO on three sheets of glass fiber cloth composite. (B) Temperature profile during cure. The specimen surpassed the 80 °C temperature set point in less than two minutes. Manufacturer recommends this temperature for optimal curing of the resin.

Fig. 9 depicts (A) foam substrates were bonded through thermoplastic melting of CNP/COPES. (B) Foam sandwich was attached to a non-metallic wood rod. (C) Exposure of the foam sandwich to induction field for 5 min. (D) Foam sandwich can be easily delaminated by hand with no damage to the foam substrates. Foam substrates can be recycled for sustainable manufacturing initiatives.

Fig. 10 depicts (A) determination of the onset temperature (95-105 °C) of three samples of CE + 1 mol% iodonium salt + 1 mol% BPO + 10 wt%CNP uncured resin via thermal Dynamic Scanning Calorimetry (DSC). (B) Dynamic field strength display temperature control at 95 ± 2 °C. (C) Dynamic field strength display temperature control at 102 ± 2 °C. (D) Dynamic field strength display temperature control at 107 ± 2 °C.

Description

It has been surprisingly found that the present invention provides non-contact consolidation of thermoplastic, semipreg, and prepreg matrices, and non-contact interfacial debonding of organosheets and consolidated thermoplastic composites. Further, the present invention provides a balance of heat (watts) input to achieve programmable temperature profiles suited to any desired resin activation temperature and curing profile.

Thus, in a first aspect of the invention, there is provided a method of conducting in-situ frontal polymerisation of one or both of a thermoplastic resin precursor and a thermoset resin precursor, the method comprising the steps of:

Curie nanoparticles having a Curie temperature of from 90 to 400 °C; and

In embodiments herein, the word “comprising” may be interpreted as requiring the features mentioned, but not limiting the presence of other features. Alternatively, the word “comprising” may also relate to the situation where only the components/features listed are intended to be present (e.g. the word “comprising” may be replaced by the phrases “consists of” or “consists essentially of”). It is explicitly contemplated that both the broader and narrower interpretations can be applied to all aspects and embodiments of the present invention. In other words, the word “comprising” and synonyms thereof may be replaced by the phrase “consisting of’ or the phrase “consists essentially of’ or synonyms thereof and vice versa.

When used herein, the term “frontal polymerisation” refers to a polymerization process for converting monomer into polymer in a localized reaction zone which could self-propagate in the bulk monomer.

Any suitable monomeric and/or oligomeric thermoplastic resin precursor may be used herein. Examples of monomeric and/or oligomeric thermoplastic resin precursors that may be mentioned herein include, but are not limited to acrylates, urethanes, lactones, silanes, amides, and combinations thereof. In certain embodiments that may be mentioned herein, the monomeric and/or oligomeric thermoplastic resin precursors may be presented in the form of one or both of monomers and oligomers.

Any suitable monomeric and/or oligomeric thermoset resin precursor may be used herein. Examples of monomeric and/or oligomeric thermoset resin precursors that may be mentioned herein include, but are not limited to epoxy, oxetane, di-acrylates, tri-acrylates, tetra-acrylates, vinyl carbonates, vinyl carbamates, latex, isoprene, butyl diene, styrene, and combinations thereof. In certain embodiments that may be mentioned herein, the monomeric and/or oligomeric thermoset resin precursors may be presented in the form of one or both of monomers and oligomers, and condensation oligomers and monomers.

Any suitable initiator may be used herein. Examples of initiators that may be mentioned herein include, but are not limited to azo-radicals, diazirines, peroxy(di), carbonates, diacyl peroxides, peroxyketals, peroxyesters, dialkyl peroxides, hydroperoxides, triazines, persulfates, iodonium salts, sulfonium salts, and combinations thereof. When used herein, the term “Curie nanoparticles” refers to nanoparticles that are paramagnetic and interact with alternating magnetic fields, resulting in heat generation by the Curie nanoparticles; the heat is dissipated and transferred to the surrounding environment.

Any suitable Curie nanoparticles may be used herein. In some embodiments that may be mentioned herein, the Curie nanoparticles may be selected from one or more of the group consisting of Mi._xZn_xFe2O4 and NaFeCh, where:

In further embodiments that may be mentioned herein, the Curie nanoparticles may be selected from one or more of the group consisting of Mno 4Zno.6Fe204, Mno.sZno 5Fe204, Mno.6- Zno.4Fe2C>4, Mno.7Zno 3Fe204, Mno 8Zno.2Fe204, Mno.gZno.iFe204, Coo 9Zno.i Fe204, MnFe2C>4, and NaFeCh. For example, the Curie nanoparticles may be Mn_o gZno iFe₂O4.

In some embodiments that may be mentioned herein, the Curie nanoparticles may have a surface that is coated in an organic material. In further embodiments that may be mentioned herein, the organic material may be a surfactant. For example, the organic material may be a fatty acid having from 15 to 20 carbon atoms (e g. oleic acid). In further embodiments that may be mentioned herein, the organic material may further comprise one or both of bisphenol A diglycidyl ether, copolyester (COPES) and polycaprolactone.

When used herein, the term “Curie temperature” refers to the temperature above which certain materials lose their permanent magnetic properties.

When used herein, the term “alternating magnetic field” refers to fields which amplitudes vary in time. The alternating magnetic field may be generated with an alternating magnetic field heating equipment which includes a F1 Driver, a magnetic coil that creates the alternating magnetic field, and optic fiber probes. Any suitable frequency and Oe field strength may be used for the alternating magnetic field used herein. For example, the alternating magnetic field may have a frequency of 400 kHz and field strength of 200 Oe.

As mentioned above, the Curie nanoparticles may be provided in an amount of from 1 to 10 wt% relative to the weight of the resin precursor(s) present in the mixture. The amount of Curie nanoparticles may be varied to provide partially cured, completely cured, and overly cured products of one or both of a thermoplastic resin and a thermoset resin. In some embodiments that may be mentioned herein, if an over-cured resin is desired, the Curie nanoparticles may be provided in an amount of from 4 to 10 wt% (e.g. from 5 to 10 wt%) relative to the weight of the resin precursor(s) present in the mixture, where only monomeric and/or oligomeric thermoplastic resin precursors are present.

In some embodiments that may be mentioned herein, if complete curing, without overcuring, is desired, the Curie nanoparticles may be provided in an amount of from 1 to 3 wt% (e.g. from 1 to 2 wt%) relative to the weight of the resin precursor(s) present in the mixture, where only monomeric and/or oligomeric thermoplastic resin precursors are present.

In some embodiments that may be mentioned herein, if a partially cured resin is desired, the Curie nanoparticles may be provided in an amount of from 1.5 to 2.5 wt% (e.g. 2 wt%) relative to the weight of the resin precursor(s) present in the mixture, where only monomeric and/or oligomeric thermoset resin precursors are present.

In some embodiments that may be mentioned herein, a preset temperature or a desired preset temperature profile may be maintained through a dynamic feedback control on an induction field strength of the alternating magnetic field.

As will be appreciated, a preset T_c temperature control allows a self-regulating temperature that avoids the limitations of prior art designs, which observed scorching - a detrimental property of other ferromagnetic nanoparticles and paramagnetic particles that cannot be tuned to the desired temperature required for thermoplastic melting or in-situ polymerization of reactive thermoplastic monomers.

In a second aspect of the invention, there is provided a thermoplastic polymeric composite material comprising: a solid thermoplastic polymeric material; and

Any suitable solid thermoplastic polymeric material may be used herein. Examples of solid thermoplastic polymeric materials that may be mentioned herein include, but are not limited to polyacrylates, polyurethanes, polylactones, polysilanes, polyamides and copolymers thereof, and combinations thereof. In some embodiments of the second aspect of the invention that may be mentioned herein, the Curie nanoparticles may be present in an amount of from 1 to 20% wt/wt (e.g. from 5 to 15% wt/wt, such as about 10 % wt/wt) relative to the solid thermoplastic polymeric material.

In a third aspect of the invention, there is provided a method of forming the thermoplastic polymeric composite material according to the second aspect of the invention, the method comprising the steps of:

(bii) subjecting the mixture to an alternating magnetic field to provide the thermoplastic polymeric composite material according to the second aspect of the invention.

In a fourth aspect of the invention, there is provided a method of laminating two or more sheets of a thermal insulating foam together, the method comprising the steps of:

(ci) providing at least two sheets of a thermal insulating foam and at least one sheet of a thermoplastic polymeric composite material according to the second aspect of the invention, where each sheet of thermal insulating foam is separated from each other sheet of thermal insulating foam by a sheet of the thermoplastic polymeric composite material; and

When used herein, the term “thermal insulating foam” refers to a foam that provides a thermal barrier around a component or between an interior space and a heat or cold source. Any suitable thermal insulating foam may be used herein. Examples of thermal insulating foams that may be mentioned here include, but are not limited to maleimide, polyamide, polyurethane, glass wool, and polyethylene.

In a fifth aspect of the invention, there is provided a method of delaminating two or more sheets of a thermal insulating foam so as to separate the two or more sheets, the method comprising the steps of:

(ci) providing a laminate construct comprising at least two sheets of a thermal insulating foam and at least one sheet of a thermoplastic polymeric composite material according to the second aspect of the invention, where each sheet of thermal insulating foam is separated from each other sheet of thermal insulating foam by a sheet of the thermoplastic polymeric composite material, and where the thermoplastic polymeric composite material is adhered to each of the thermal insulating foam sheets; and (cii) subjecting the mixture to an alternating magnetic field to enable separation of the laminate construct to provide a delaminated product through the removal of the two or more sheets of thermal insulating foam from the thermoplastic polymeric composite material.

In a sixth aspect of the invention, there is provided a method of consolidating a plurality of thermoplastic sheets together, the method comprising the steps of:

In a seventh aspect of the invention, there is provided a method of consolidating a plurality of thermoplastic semipreg sheets together, the method comprising the steps of:

As discussed above, semipregs are fabrics with a thermoplastic matrix powder that has been partially melted or coated to the fabric surface.

Any suitable compression methods may be used herein. For example, the stack of m thermoplastic semipreg sheets may be compressed with a 3D printed ABS jig.

Accordingly, the present invention provides a magneto-composite consolidation of thermoplastic composites through a modifier methodology, wherein multi-layers prepregs and semipregs can melt-bond simultaneously, and the peel strength of the demonstrated system may be in a range of 1-7 kN/m. The present invention includes:

1) allowing a method of volumetric heating and self-regulating temperatures at the interface of thermoplastic matrix, semipreg, prepreg, or multiple thermoplastic matrices, semipreg, prepreg interfaces;

2) in-situ polymerisation of reactive resin monomers that embody thermoplastic or thermoset matrices with Curie nanoparticles (CNP);

3) development of the magneto-composite in-situ polymerisation resins modifier methodology, using commercial one component resins and ring-opening polymerization resins, comprising the steps of: i. charging CNP and matrix in a ratio between 10 to 50 wt.%; ii. Elium® (purchased from Arkema) = 5-30 wt.%;

Hi. raising the AMF heating of magnetocomposite within 5 min; and iv. carrying out the in-situ polymerization for a period of 30-60 min to achieve complete consumption of reactive monomer;

4) joining a range of sheets, fabrics, and foams including semipreg, thermoplastic matrices, elastomers, and foams with low thermal conductivity (< 1 W.K. -¹m-¹);

5) rapidly melting thermoplastic matrices and elastomers to form homogeneous resins that melt and consolidate other plastic surfaces via polymer entanglement;

6) present invention of thermoplastic consolidation may be remotely controlled, and may provide rapid and localized heating, reduced processing cost and energy by applying induction frequency in the range of 100 - 800 kHz and a magnetic field strength in the range of 100 - 200 Oe. The melting temperature required for consolidation was reached within 5 min and initiates resin entanglement after exceeding the glass transition temperature. Therefore, it is perfectly suitable for a range of industries;

7) in-situ polymerization activation of commercial resins for semipreg consolidation is attained within 5 min under AMF. Therefore, our method is perfectly suitable for a range of industries where low viscosity reactive monomers need a rapid transition into macromolecular polymers; and

8) incorporation of Curie nanoparticles (CNP) that are paramagnetic with predefined, self-regulating Curie temperatures that are tuneable within the range of plastic processing temperatures. The latter is specific to the chosen resin, but is generally defined as above the glass transition temperature but below the onset of degradation temperature. See Table 1 for examples of a range of paramagnetic particle compositions listed by Curie temperature. Table 1. Curie temperatures of known paramagnetic materials.

As will be appreciated, the present invention provides improved and advantageous methods over existing methods, comprising:

1) a processing platform designed to allow non-contact consolidation of thermoplastic, semipreg, and prepreg matrices through exposure to suitable alternating magnetic field frequency and strength. CNPs are paramagnetic and interact with the alternating magnetic fields, resulting in heat generation by the CNPs; the heat is dissipated and transferred to the surrounding polymers chains;

2) CNPs with a chosen preset Curie temperature (T_c) may be synthesized by controlling the specific elemental composition of crystal grains within the nanoparticles. As will be appreciated, the T_c of the CNPs is a macro property - i.e. of the bulk material and not of the individual crystal grains. The CNPs are paramagnetic with the advantage of programmable temperature and power profiles capable of homogenous distribution;

3) preset T_c temperature control allows a self-regulating temperature that avoids the limitations of previous designs, which observed scorching — a detrimental property of other ferromagnetic nanoparticles and paramagnetic particles that cannot be tuned to the desired temperature required for thermoplastic melting or in-situ polymerization of reactive thermoplastic monomers;

4) dynamic heat (watts applied) control is obvious by the method(s) disclosed herein through formulation, chemical composition, and instrumental parameters including but not limited to CNP (surface/volume/mass) concentration, CNP elemental composition, AMF frequency, field strength, substrate thermal conductivity, and coil geometry. For example, a resin with a higher % CNP, various elemental compositions, and AMF frequency affects the specific absorption ratio or SAR that has units of watts applied per gram of CNP. SAR represents the efficiency of AMF energy converted to heat by CNP. Thus, by varying the frequency, field strength, or combination thereof, SAR can be dynamically controlled to specific temperature profiles desired. ;

5) volumetric heating (watts applied) control is possible since magnetic fields can pass through organic resins and inorganic fibre materials with little to no attenuation, facilitating control of most material and mechanical properties of thermoplastic composites, including but not limited to polymer entanglement, multi-layer consolidation, polymer crystallinity, and setup of preplanned interface failure sites upon specific magnetic exposure;

6) a magnetic induction platform is designed to allow non-contact interfacial debonding of organosheets and consolidated thermoplastic composites, wherein CNPs have been incorporated at preplanned interface failure sites;

7) a magnetic induction platform has been designed to overcome the current limitations of Automated Tape Laying (ATL) that are based on photo- or ultrasonic heat methods; and

8) AMF heating by CNP additives within in-situ frontal polymerization resins offers a method that balances heat (watts) input to achieve programmable temperature profiles suited to any desired resin activation temperature and curing profile, including partial curing (higher viscosity and adhesive tack), homogenous stable curing (no voids with complete propagation), and over-curing (excess exothermic heat that leads to volatilization and foams).

Further aspects and embodiments of the invention will now be discussed by reference to the following non-limiting examples.

Examples

Materials

3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (CE) epoxy, and 1 ,1 , 2, 2 - Tetraphenyl - 1 ,2 - ethanediol (TPED), solvents, and other raw materials were purchased from Sigma-Aldrich (Singapore). Example 1. CNP Nanoparticles with organic coatings

The CNP nanoparticles may be represented by a formula of A_xZ ._xFe₂O4; wherein A is cobalt, manganese, or nickel; and x has a value in the range of 0.4 to 0.99. In particular embodiments, the CNP nanoparticles may be Mn_xZni._xFe₂O4 (x = 0.4 to 0.9).

The organic coating may be a surfactant. In particular embodiments, the organic coating may be a fatty acid having 15 to 20 carbon atoms. In more particular embodiments, the organic coating may be oleic acid (OA).

Example 2. Synthesis of CNP Nanoparticles with organic coatings

CNPs were dispersed in deionized water and placed in a sonicating water bath. OA was added to the solution and sonicated. This solution was heated (e.g. at 80 °C for 1 hour) under mechanical stirring (e.g. at 400 rpm). The resultant solution was washed 3-4 times with ethanol and the OA-coated CNPs were separated using a permanent magnet. The oleic acid-coated particles (Mn_xZni._xFe₂O4/OA) were used as they are for the further functionalization with a monomer (e.g. bisphenol A diglycidyl ether, and polycaprolactone).

Mn_xZni._xFe₂O4/OA particles were dispersed into tetrahydrofuran (THF) and sonicated. After that, a solution of bisphenol A diglycidyl ether (BADGE) in THF was added to the above solution and sonicated again. This solution was kept until the surface of the nanoparticles was completely wetted with BADGE (e.g. for 16 hours). Next, Mn_xZni._xFe₂O4/OA/BADGE was obtained by washing with THF and acetone, separated using a permanent magnet and vacuum dried. Same procedure was repeated for the functionalization of Mn_xZni._xFe₂C>4/OA particles with polycaprolactone.

Example 3. Initiation of in-situ frontal polymerization resins and ring opening polymerization

CNP of composition MnogZno.iFe₂04 nanoparticles (T_c > 280°C) were synthesized via the hydrothermal method as previously described in DOI: 10.1016/j.apmt.2020.100824. Mm. _xZn_xFe₂O4 nanoparticles have a tuneable T_c that ranges from 80 - 400°C based on the elemental composition. CNP nanoparticles with organic coatings (see Example 1) were mixed within the following in-situ frontal polymerization resin of CE epoxy, lodonium salt, and TPED. The alternating magnetic field (AMF) heating equipment includes the F1 Driver, the S³² magnetic coil (3 cm, water cooled copper coil) that creates the AMF, and optic fiber probe to monitor the temperature of the composites (nB Biomaterials). CNP additives were thoroughly mixed with the thermosetting material in a 5 mL glass vial. The composite was then sonicated to improve the nanoparticles dispersion for 30 minutes. Afterwards, the composite was placed at the middle of a magnetic coil (110 mm length, 32 mm diameter) and optic fiber probes used to measure the temperature in-situ. An AMF of 400 kHz frequency and 200 Oe field strength was subjected to the sample for each magnetocuring experiment. Heating output (Specific Absorption Rate) of the composite with respect to CNP concentration was also calculated as previously published see: DOI: 10.1016/j.apmt.2020.100824 and these results are provided in Fig. 1.

Example 4. In-situ polymerization of thermoplastic reactive monomer and resin

Elium® resin was mixed with 1, 2, 5, and 10 wt% of CNP (composition of Mno gZno.iFe204) and dispersed within an ultrasonic bath. Magnetic induction resulted in variable heating rates and temperature plateaus dependent on the CNP wt%. At 1 and 2 wt%, partial curing (liquid to solid gelation, but still flexible) and complete curing (liquid to solid gelation, dense and inflexible) were observed (Fig. 2). These formulations would be ideal for substrates with low thermal conductivity. At 5 and 10 wt%, rapid heating led to rapid resin activation and exothermic heat evolution. The resin is described as over-curing; liquid to solid gelation occurs but with resin volatilization that yields a porous and inflexible matrix. These formulations would be ideal for substrates with high thermal conductivity or other situations where high thermal dissipation is needed. Induction parameters; magnetic coil (110 mm length, 32 mm diameter), AMF of 400 kHz frequency, and 200 Oe field strength (see Example 3 for the AMF heating equipment used).

Example 5. Induction melting of thermoplastic elastomer nurdles

COPES resin nurdles (0.5 g) of ~100 pm diameter were mixed with Mno.9Zno.iFe204 CNP at 10 w/w% by a vortex mixer. The mixture was placed in a 5 mL glass vial and exposed to an AMF (see Example 3 for the AMF heating equipment used). Temperature was constantly recorded until a viscous polymer melt was visibly observed (e g. flowed under gravity). AMF was switched off at intervals, during which the elastomer composite was allowed to solidify into homogenous composite elastomer, as shown in Fig. 3. Subsequent AMF exposure resulted in remelting of this thermoplastic in lesser time than the first heterogenous mixture. The corresponding temperature increase rates of the melting and remelting segments were 0.132 °Cs^-1, and 0.152 ^oCs ¹, thus the remelted resin had a 15% higher heating rate due to the homogenous CNP distribution. Rheology temperature sweep (Fig. 3B) found no significant change in the melting properties, as defined at the point where G’ = G”. The complex viscosity of the CNP composites was equal or less than that of neat COPES control (Figure 3C).

The complex shear modulus, which is defined as G* = , with r* being the complex shear

stress and Y(t) being the shear strain, is a measure of the material’s overall resistance to deformation. G*can be mathematically separated into the two phase components of the shear storage modulus, G’, and the shear loss modulus, G” through the equation G* = G’ + iG”. The

complex viscosity, defined as TJ* = measures the resistance to flow as a function of angular frequency. Induction parameters; magnetic coil (110 mm length, 32 mm diameter), AMF of 400 kHz frequency, and 200 Oe field strength.

Example 6. Bonding of thermal insulating foam by thermoplastic elastomers

The CNP/COPES elastomer composite from Example 4 was applied for melt bonding of fabric insulation (e.g. thermal/acoustic foam composed of a polyester resin). AMF heating of the 10 w/w% CNP/COPES composite was applied (~1 mg.cnr²) to bond two layers of the fabric insulation of dimensions: L x W x T = 3 x 1 x 1 cm (see Example 3 for the AMF heating equipment used ). The fabric sandwich was immobilized by tape. The material was subject to 400 kHz and 200 Oe AMF heating. Upon cooling, a subsequent T-peel test (conducted using a static tensile tester (MTS Model 42)) compared melt bonding with a conventional conduction melt bonding prepared from an external industrial supplier (Dotcoat Europe GMBH, Germany) .

The peel strength of the AMF sample had a higher adhesive strength, as judged by the failure mode and T-peel force analysis (Fig. 4) using a static tensile tester (MTS Model 42). AMF melt bonding underwent a substrate failure vs. conduction melt bonding observed interfacial failure at the adhesive/foam interface, as seen in Fig. 4. Induction parameters; magnetic coil (110 mm length, 32 mm diameter), AMF of 400 kHz frequency, and 200 Oe field strength.

Example 7. Induction melting and remelting of a thermoplastic polymer

AMF melting and remelting was demonstrated on polycaprolactone (PCL, 70 kDa, T_m= 60 °C), forming a thermoplastic homogenous composite, as shown in Fig. 5. Fig. 6 displays a range of thermoplastic polymers’ processing temperature, including PCL, compared to the Curie temperature (T_c) of particles with elemental composition of Mni._xZn_xFe₂C>4. A sample mixture of 10 w/w% CNP (Mno 9Zno.iFe204 nanoparticles)/PCL was stored in a 5 mL glass vial and placed at the center of the magnetic coil. An AMF was then applied, and the temperature of the composite was recorded until a viscous melt was observed that flowed under gravity (see Example 3 for the AMF heating equipment used). The melting temperature (Tm) of 4 mm nurdle pellets was achieved in less than 5 min. The corresponding temperature ramp rates of the melting and remelting (x2) segments are 0.130, 0.137, and 0.146 °Cs'¹, respectively. The homogenous dispersion of CNPs has a faster heat dispersion than surface heating on nurdles.

The complex shear modulus and complex viscosity of 10 w/w% CNP/PCL was compared to neat PCL and had similar values over the temperature range of 25 - 120 °C. The rheology data was collected from a temperature sweep from 120 °C to 25 °C. The complex shear modulus, which is defined as G* = , with T* being the complex shear stress and Y(t) being

the shear strain, is the measure of the material’s overall resistance to deformation. G* can be mathematically separated into the two phase components of shear storage modulus, G’, and shear loss modulus, G" through the equation G* = G’ + iG". The complex viscosity, defined as = ~ measures the resistance to flow as a function of angular frequency. Induction parameters; magnetic coil (110 mm length, 32 mm diameter), AMF of 400 kHz frequency, and 200 Oe field strength.

Example 8. Induction consolidation of thermoplastic sheets through dry CNP coatings

Thermoplastics coupons were shown to be melt bonded through induction heating, as displayed in Fig. 5. PCL sheets of L x W x T = 200 x 17 x 1 mm were brush coated with a thin layer of CNP (MnogZno.iFe204 nanoparticles), which was applied with a paint brush dipped in a stock solution of 5 w/w% CNP in denatured EtOH, and then evaporating off the EtOH. The coated CNP coupon was then sandwiched to an uncoated coupon and fixed together by clear cello tape, with the CNP coating in contact with both PCL coupons. The center portion of the sample (~50 mm in width) was then exposed to AMF (see Example 3 for the AMF heating equipment used) for 10 min to spatially selective melt bond the two thermoplastic specimens. The T-peel adhesion strength was then evaluated using a static tensile tester (MTS Model 42).

The spatially melt bonded coupon fractured across the tensile plane before completing the induction exposed section. Thus, the melt bonded coupon exceeded the tensile strength of the PCL coupon (< 24 MPa). Melt bonding via the AMF heating thus shows successful consolidation of the two thermoplastic coupons. (Fig. 5). Induction parameters; magnetic coil (110 mm length, 32 mm diameter), AMF of 400 kHz frequency, and 200 Oe field strength. Example 9. Volumetric heating and multi-layer consolidation of thermoplastic semipreg fabrics through CNP coatings

Tecatec SAN CF47 T245 CP V02 (provided by Ensinger, Germany) is a thermoplastic semipreg. Carbon fibre with a twill 2/2 fibre architecture was sputter coated with SAN, resulting in a flexible semipreg with 47% vol. fibre content that is easily draped across complex surfaces with a mass of 245 g.m ². SAN is a styrene (75 wt%) acrylonitrile (25 wt%) resin often used in place of polystyrene due to a better profile of thermal and chemical resistance, while retaining visible transparency. This semipreg targets the automotive, mechanical engineering, and sporting good industries. Tg and Tm are 110 °C and 220 °C, which defines the semipreg process range and overlaps with the Curie temperature of the CNPs chosen (180 °C).

Semipreg mating surfaces were coated with CNP (Mno.9Zno.iFe2C>4) at a surface concentration of 0.5 mg. cm ² as described in Example 8. Three layers of semipreg (70 x 20 x 0.55 mm) were compressed with a 3D printed ABS jig and exposed to AMF for 10 min, as shown in Fig. 7 . During induction, the surface temperature of the fabric was monitored by an optic fiber probe, where the semipreg surface temperature was shown to exceed the SAN’s Tg of 110 °C. Semipreg was observed to have consolidated into a stiff and inflexible organosheet. Induction could easily consolidate multilayer thermoplastic composite films in a single operation, whereas current technology only provides layer-by-layer production methods. Organo-sheet could be delaminated for recycling through subsequent induction heating due to the inherent CNP layer. Induction parameters; magnetic coil (110 mm length, 60 mm diameter), AMF of 400 kHz frequency, and 110 Oe field strength (see Example 3 for the AMF heating equipment used).

Example 10. Induction and in-situ polymerization of Elium150 thermoplastic composite

Infusible thermoplastic resins are commercially available (i.e., Elium®) and consist of proprietary acrylic resins for reactive processing. In-situ polymerization of the low viscosity thermoplastic resins allows vacuum assisted infiltration of fiber-based composites and reactive transfer molding (RTM) manufacturing techniques. This allows manufacture of thermoplasticbased composites while overcoming the high viscosity of thermoplastic melts. However, there currently is no method of volumetric heating of the resin or resin/fiber composite once infiltrated. The components of Elium® acrylic resin are 2-propenoic acid, 2-methyl-, methyl ester, or methylmethacrylate monomer (MMA), and acrylic copolymer. Before infusion, resin is mixed with initiator chemical(s) (e.g. peroxides) to vary the initiation temperature from ambient to 90 °C. Infusion open time varies with peroxide initiator, initiator ratio, and concentration which ranges from 1 .5% (slow reactivity) to 3% (higher reactivity). Open time is the amount of time during which the viscosity of the resin is low enough to inject or infiltrate the resin within fiber composites.

Elium150 thermoplastic resin is an acrylate adhesive that cures at room temperature. E-glass fiber cloth is from Saertex, which has an areal weight of 151 g/m² and is unidirectional. Elium150® with 2 wt% benzoyl peroxide (BPO) and 10 wt% CNP (Mno gZno iFe204) was applied at a 1 :1 w/w ratio of resin and glass fiber and resin. The resin soaked fibers have an area of 2.5 x 2.5 cm² area. An uncured, three-layer laminate specimen was positioned within the center of a 3.2 cm-diameter induction coil, and the temperature of this section was monitored in-situ using an optic fiber probe under AMF field strength of 200 Oe and frequency of 400 kHz (see Example 3 for the AMF heating equipment used).

Results and discussion

Upon exposure to the induction field, the specimen surpassed the 80 °C temperature set point in less than two minutes. The manufacturer recommends this temperature for optimal curing of the resin (Fig. 8). After the 30 minutes under induction, the specimen was rigid, and displayed no touch tack profile. Incorporation of CNP into the Elium150® resin allows in-situ polymerization, demonstrating a method of manufacturing composites with unidirectional glass fibers. The finished material forms a thermoplastic composite material.

Example 11. Debonding of thermal insulating foams via CNP/COPES adhesive interface

Induction generator: AMF, D5 series, 640W F1 Driver, attached with a solenoid coil (S³²) operating ata field strength of 200 Oe and 400 kHz frequency. Foams are bonded with CoPES thermoplastic particles are mixed with 10 wt% CNP (Mno.gZno iFe204).

Results and discussion

Adhesive failure under room temperature conditions occurs via substrate failure. After 5 min of exposure to induction field strength 200 Oe, the tg was exceeded and the foam substrates can easily be separated by hand within one minute after removal of the induction field (Fig. 9). This shows a method of debonding and allows recycling of the undamaged foam substrates. Foam substrates can be recycled, reused, or repurposed for sustainable manufacturing initiatives.

Example 12. Determination of induction onset temperature and maintaining dynamic temperature of exothermic in-situ frontal polymerization Composition: CE + 1 mol% iodonium salt + 1 mol% BPO + 10 wt%CNP. 100 pL of the resin was added into an NMR tube (wall thickness = 0.42 mm). The instantaneous adjustment of the induction field allows dynamic control of temperature through the standard PID algorithm. A range of setpoints (95-107 °C) is determined through analysis via thermal Dynamic Scanning Calorimetry (DSC), which quantifies the onset temperature range of CE + 1 mol% iodonium salt + 1 mol% BPO + 10 wt%CNP resin composition. Real-time monitoring of the measured temperature will dynamically adjust the induction field strength to maintain the onset temperature range or other preprogrammed temperature profile.

DSC

DSC experiments were performed using a TA Instruments DSC Q10 system with a maximum temperature of 400 °C. For this analysis, each sample consists of no more than 6 mg resin to avoid excessive exothermic reactions that distort the exothermic peak. Each resin sample was tested in an aluminium hermetic pan, and three measurements were carried out for each controlled temperature. One DSC run comprises of two heating ramps: 1) the first ramp was from -50 °C to +200 °C at a rate of 10 °C/min to acquire the exothermic peak from induction- cured epoxy; and 2) the second ramp was from -50 °C to +200 °C at a rate of 10 °C/min to confirm that there are no more exothermic reactions from induction-cured epoxy. The data from this 2^nd ramp serves as the baseline for exothermic peak analysis.

An AMF generating system (D5 series, 640W F1 Driver) attached with a solenoid coil (S³²) operating at 200 Oe and 400 kHz was used in all experiments. Liquid resin samples with dispersed CNPs were stored inside of an NMR glass vial (0.42 mm-thick wall, Wilmad®), and the samples were positioned at the centre of the solenoid. In-situ temperature monitoring was conducted via an optic fibre sensor (Neoptix, T1S-01-PT15, USA) connected to the AMF generator that was submerged into the resin during cure. Prior to all experiments, samples were freshly prepared by dispersing CNPs into CE epoxy resin with sonication for 60 minutes.

Results and discussion

Dynamic adjustment of the induction field controlled the setpoint temperature within ± 2 °C. No other method of resin thermal curing allows volumetric heating while reaching and maintaining the setpoint temperature in less than two minutes. Thermal DSC analysis of samples T95, T102, and T107 (which all consist of CE + 1 mol% iodonium salt + 1 mol% BPO + 10 wt%CNP and were prepared at at 95 °C, 102 °C, and 107 °C, respectively) found a degree of conversion 75, 80, and 92%, respectively (Fig. 10).

Claims

Curie nanoparticles having a Curie temperature of from 90 to 400 °C; and

2. The method according to Claim 1, wherein the Curie nanoparticles are provided in an amount of:

(ai) from 4 to 10 wt% (e g. from 5 to 10 wt%) relative to the weight of the resin precursor(s) present in the mixture, where only monomeric and/or oligomeric thermoplastic resin precursors are present if an over-cured resin is desired;

3. The method according to Claim 1 or Claim 2, wherein a preset temperature or a desired preset temperature profile are maintained through a dynamic feedback control on an induction field strength of the alternating magnetic field.

4. The method according to any one of the preceding claims, wherein:

6. The thermoplastic polymeric composite material according to Claim 5, wherein one or both of the following apply:

(aai) the Curie nanoparticles are present in an amount of from 1 to 20% wt/wt (e.g. from 5 to 15% wt/wt, such as about 10 % wt/wt) relative to the solid thermoplastic polymeric material; and

(aaii) the solid thermoplastic polymeric material is selected from one or more of the group consisting of polyacrylates, polyurethanes, polylactones, polysilanes, polyamides and copolymers thereof.

7. A method of forming the thermoplastic polymeric composite material according to Claim 5 or Claim 6, the method comprising the steps of:

(bii) subjecting the mixture to an alternating magnetic field to provide the thermoplastic polymeric composite material according to Claim 5 or Claim 6.

(ci) providing at least two sheets of a thermal insulating foam and at least one sheet of a thermoplastic polymeric composite material according to Claim 5 or Claim 6, where each sheet of thermal insulating foam is separated from each other sheet of thermal insulating foam by a sheet of the thermoplastic polymeric composite material; and (cii) subjecting the mixture to an alternating magnetic field to provide a laminated product.

(ci) providing a laminate construct comprising at least two sheets of a thermal insulating foam and at least one sheet of a thermoplastic polymeric composite material according to Claim 5 or Claim 6, where each sheet of thermal insulating foam is separated from each other sheet of thermal insulating foam by a sheet of the thermoplastic polymeric composite material, and where the thermoplastic polymeric composite material is adhered to each of the thermal insulating foam sheets; and

12. The method according to any one of Claims 1 to 4, the thermoplastic polymeric composite material according to Claim 5 or Claim 6, the method according to Claim 7, the method according to Claim 8, the method according to Claim 9, the method according to Claim 10 or the method according to Claim 1 1 , wherein the Curie nanoparticles are selected from one or more of the group consisting of Mi._xZn_xFe2O4 and NaFeCk, where:

13. The methods and composite material according to Claim 12, wherein the Curie nanoparticles are selected from one or more of the group consisting of Mno 4ZnoeFe204,

14. The methods and composite material according to Claim 12 or Claim 13, wherein the Curie nanoparticles have a surface that is coated in an organic material.

15. The methods and composite material according to Claim 14, wherein the organic material is a surfactant, optionally wherein the organic material is a fatty acid having from 15 to 20 carbon atoms, further optionally wherein the fatty acid is oleic acid.

16. The methods and composite material according to Claim 14 or Claim 15, wherein the organic material further comprises one or both of bisphenol A diglycidyl ether, copolyester (COPES) and polycaprolactone.