RU2540273C1 - Oxo-decomposing additive for polyolefins - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: oxo-decomposing additive for polyolefins includes metal carboxylates or mixtures of metal carboxylates deposited on an inert support; the metal carboxylates used are, for example, 2-ethylhexanoates of zinc or zirconium. The inert support used can be calcium carbonate.

EFFECT: oxo-decomposing additive is capable of initiating oxidative breakdown of polyolefin chains in small concentrations.

3 cl, 4 dwg, 2 tbl, 14 ex

Description

The invention relates to technologies for creating biodegradable polymeric materials, in particular to additives that increase the biodegradability of polyolefins, and can be used to create materials and products from them that are capable of undergoing accelerated biodegradation in natural conditions.

Modern megacities are faced with the urgent need to dispose of giant landfills of solid household waste, a significant part of which falls on packaging waste and other waste products that have a short service life, including disposable products and polyolefin-based polymeric materials, which are highly resistant to the environment.

Known technical solutions in which to increase the ability of polyolefins to biodegrade, they introduce natural polymer fillers, such as cellulose, starch, etc. [RU 2480495 C2, publ. 04/27/2013, RU 2446191 C1, publ. 03/27/2012, RU 2408621 C2, publ. 01/10/2011 and others.]. However, it is obvious that for the production of large-tonnage materials for short-term use, the use of valuable products used in the food industry, feed production and other industries is not economically feasible. For this purpose, it is more justified to use cheap, non-food and feed value fillers. According to the invention [RU 2363711 C1, publ. 08/10/2009] the biodegradable thermoplastic composition as a polymer base contains industrial and / or household waste polyethylene, technological additives, and as a biodegradable additive - waste food industry - rice husk. A biodegradable composition is known, including a polyethylene-containing polymer base, a binding agent is a copolymer of ethylene and vinyl acetate and a biodegradable additive is a lignocellulosic filler, for example flax fire, sunflower husk, sodium lignosulfonate, as well as plant objects, for example foliage or straw [RU 2473578 C2, opub . 01/27/2013].

A common drawback of the approach based on the use of natural polymer products as biodegradable additives is the difficulty in obtaining material with standard, reproducible properties, satisfactory physical and mechanical characteristics and the ability to withstand the effects of microorganisms during the established periods of their storage and useful use.

This drawback lacks an approach based on the use of biodegradable additives of chemical origin, characterized by an adjustable and reproducible quantitative and qualitative composition. A photodegradable composition based on polyolefins (high or low density polyethylene, polypropylene, copolymers of ethylene with polypropylene, higher olefins, vinyl acetate, etc.), which contains alkyloxy-silylferrocene as a photosensitizing additive [RU 94023952, A, publ. May 27, 1997]. The presence of ferrocene derivative in the material limits the possibilities of its application, in particular, for the production of products intended for contact with food products and other household items. In [JP 2007177083 A, publ. 12.07.2007] describes a light-destructible polymer composition containing a mixture of polyethylene and polypropylene, and as an additive - 40-65 mass. % calcium carbonate, 3-5 wt. % stearin and 1-3 mass. % stearic acid.

One of the modern approaches to the creation of environmentally destructible materials based on polyolefins is based on the use of oxo-biodegradable additives that increase the ability of polymeric materials to degrade under natural conditions. Under the influence of light and heat in the presence of oxidation initiators contained in the additives, chemical reactions occur in the polymer matrix, leading to the breaking of long chains of polyolefin molecules. These processes lead to a gradual decrease in the molecular weight of the polymer up to the fragmentation of the material. In this case, the hydrophilicity of the polymer increases, microcracks form on the surface, and, thus, conditions are created to facilitate the penetration of microorganisms utilizing short fragile molecules into the polymer matrix. In the process of life, microorganisms secrete weak acids (acetic, formic), which contributes to the speedy decomposition of the material. In order for the polymeric materials to maintain the necessary operational properties during the period of their storage and use and only then undergo decomposition, additional components are introduced into the composition of additives, including antioxidants that “delay” the onset of oxidative decomposition of the polymer.

It should be noted that the quantitative and qualitative composition of most currently known commercial products positioned as oxo-biodegradable additives is not fully disclosed in publicly available information sources. For example, about Wells Plastics Ltd. additives sold under the Reverte ^tm trademark, it is known that, as components that activate the ability of polymer chains to undergo decomposition under the influence of natural factors (photo- and thermal destruction), they contain metal ions and also include additional components that enhance the biodegradation of the polymer in the subsequent stages of the decomposition process. Additive D ₂ W ^® manufactured by Symphony Environmental Technologies plc. and is used in many countries in the production of products from polyethylene and polypropylene; it contains transition metal salts (cobalt, iron, manganese, copper, zinc, cerium, nickel). The EPI ENVIRONMENTAL PRODUCTS INC oxo-biodegradable additive includes cobalt stearate, citric acid, and may further include calcium oxide [US 5854304 A, publ. 12/29/1998]. According to the patent of the same company [US 5565503 A, publ. 10/15/1996], polyolefin biodegradable films contain from 25 to 60 mass. % of fillers selected from inorganic carbonates, synthetic carbonates, nepheline, talc, magnesium and aluminum hydroxides, diatomaceous earth, mica, natural or synthetic silicas and calcined clays or mixtures thereof, and further include stearates of metals such as iron, cobalt, cerium and magnesium. From [RU 2352597 C1, publ. 04/20/2009] a biodegradable composition is known, which along with technological additives (thermal stabilizers, antioxidants, etc.) also contains cobalt stearate, citric acid or its salts, calcium oxide. In the application [US 20060280923 A1, publ. December 14, 2006] a multilayer film is described, one of the layers of which is made of a polyolefin containing 0.1-10 mass. % degrading additives - metal carboxylate and at least one aliphatic polyhydroxycarboxylic acid.

As a prototype taken the invention described in [CA 2821357 A1, publ. 07/05/2012]. Declared not containing natural components, a composite additive that reports the biodegradability property of polyolefin materials after the end of their useful life. The additive includes a pro-oxidant (15-30 wt.%), Which is used as one or more metal stearates selected from the group including manganese, iron and cobalt, one or more phenolic antioxidants (10-20 wt.%), Filler - calcium carbonate and / or titanium dioxide and a polymer base (polyethylene or polypropylene). The additive is introduced into the base polymer in an amount of 1-5 mass. % A common disadvantage of using salts of higher fatty acids, in particular stearates, as pro-oxidants is the relatively low content of catalytically active metal ions in the total weight of the additive, which necessitates the use of high concentrations of these salts.

The closest analogue to the proposed additive is one of the options for additives proposed in [US 3797690 A, publ. 03/19/1974], to accelerate the biodegradation of polyolefins, namely cobalt 2-ethylhexanoate. The additive is applied to the surface of the polymer as a coating composition, which may contain or be mixed with other components. For the manifestation of the oxo-decomposing effect, the additive must penetrate from the outer layer into the thickness of the polymer, contributing to the acceleration of its destruction under the influence of natural factors.

We have shown that cobalt 2-ethylhexanoate has a relatively low pro-oxidant activity compared to salts of several other transition metals. The effect of the additive is significantly reduced due to its inefficient uncontrolled penetration from the surface coating layer into the polymer thickness. This requires the use of high concentrations of the agent, which is uneconomical and creates an additional burden on the environment.

An object of the present invention is to provide an oxo-decomposing additive capable of initiating oxidative disruption of polyolefin chains in low concentrations and, thus, increasing the biodegradability of polyolefin-based polymeric materials after the end of their useful life

In accordance with the invention, an oxo-degrading additive to polyolefin-based polymer compositions is described comprising metal carboxylates or metal carboxylate mixtures supported on an inert carrier, characterized in that zinc and zirconium 2-ethylhexanoates are used as metal carboxylates.

The inventive additive that performs the function of an oxidation initiator, a pro-oxidant, can be introduced directly into the base polymer or can be used as a component of the masterbatch designed to be introduced into the base polymer based on polyolefins (polyethylene, polypropylene, their copolymers) to give made of it products with the ability to accelerate biodegradation in natural conditions.

In the following embodiments, calcium carbonate is used as an inert carrier in the additive, but this does not exclude the possibility of using other neutral fillers of natural and chemical origin as an inert carrier. The quantitative content of the inert carrier in the composition of the additive should, on the one hand, provide the technical possibility of applying the required amounts of metal salts to it, and on the other hand, should not adversely affect the physicomechanical characteristics of the polymers containing the additive. Based on this, in practice it is convenient to use from 80 to 90 masses. % filler while maintaining high pro-oxidative activity of the additive.

A significant difference between the proposed technical solution from the known analogues and prototype is that as the metal carboxylates in the oxidation initiator, individual 2-ethylhexanoates (2-EG) of zinc and zirconium are used, as well as mixtures of these salts. The main advantage of salts of 2-ethylhexanoic acid over stearates is a relatively small acid residue, which contributes to their more uniform distribution in the polymer matrix and increase the efficiency of the initiation of oxidative rupture of polymer molecules, in particular due to an increase in the additive relative mass fraction of metal ions.

It is known that 2-ethylhexanoates of transition and some non-transition metals (including cobalt, zinc, zirconium salts) are catalysts for oxidative polymerization of vegetable oils and are part of desiccants used to accelerate the film formation of oil-containing paints and varnishes. Desiccants promote the transfer of oxygen interacting with methylene groups located in the α-position to the double bonds of unsaturated acids, with the formation of hydroperoxides. At the stage of initiation of radical polymerization, metals participate in the decomposition of hydroperoxides with the formation of radicals. As shown below, these same substances also exhibit catalytic activity with respect to the free radical processes of thermo- and photooxidative destruction of carbon bonds in long-chain polyolefin molecules, which lead to a decrease in molecular weight and increase the hydrophilicity of the material due to the formation of terminal oxygen-containing functional groups, which increases its availability for exposure to microorganisms.

In the examples below, the ability of polyolefins to oxo-decompose is characterized by the dynamics of changes in the ratio of the intensity of the absorption bands D1720 _rel = D1720 / D3640 depending on the exposure time under experimental conditions. The optical band of 1720 cm ^-1 corresponds to carbonyl groups, the accumulation of which indicates the occurrence of a process of oxidation of samples under experimental conditions. An optical band of 3640 cm ⁻¹ is an internal standard for samples; assignment to it allows one to exclude the influence of the sample thickness on its IR absorption spectrum.

As samples in examples 1-10, films with a thickness of 80-100 μm were used, prepared from model samples of masterbatch containing 50 mass. % polyolefin and the inventive additives, including calcium carbonate and individual 2-ethylhexanoates of cobalt, zinc or zirconium (examples 1-3), as well as double (examples 4-6) or ternary (examples 7-10) mixtures of these salts. Example 1, including individual cobalt 2-ethylhexanoate, is given as an example of a comparison showing the pro-oxidative activity of the prototype additive in comparison with the additives of the present invention. In examples 11 to 14, similar films were prepared as samples prepared from a base polyolefin — low density polyethylene (LDPE) grade 15803-020 (examples 11, 12, 14) or polypropylene grade 01130 (example 13), containing 1 to 3 masses . % of model masterbatch samples, including mixtures of 2-ethylhexanoates of zinc and zirconium, obtained according to example 6, as well as a mixture of 2-ethylhexanoates of cobalt, zinc and zirconium, obtained according to examples 9 and 10. As a means of 2-ethylhexanoates of metals and mixtures thereof, desiccants of the company LLC "INDLAC", which are solutions of individual salts or mixtures thereof in white spirit.

To simulate thermal oxidation, film samples are thermostated in air at 90 ° C for 15 hours, controlling the spectrometric accumulation of carbonyl groups. To simulate photooxidation, a film sample is first thermostated at 90 ° C for an hour, and then subjected to ultraviolet radiation (UV lamp VL-6 / LC, 254 nm) at room temperature for 300 hours, controlling the spectrometric accumulation of carbonyl groups. Spectrometric measurements are carried out on a Spectrum 100 Perkin Elmer IR Fourier spectrometer at Τ = 23 ± 2 ° C in transmitted light in the wavelength range of 4600≤ν≤450 cm ^-1 .

In FIG. 1 shows the dynamics of changes in D1720 _rel during thermal oxidation of the samples obtained in examples 1-3.

In FIG. 2 shows the dynamics of changes in D1720 _rel during thermal oxidation of the samples obtained in examples 4-10.

In FIG. Figure 3 shows the dynamics of changes in D1720 _rel during thermal oxidation of samples obtained according to examples 11-14 in comparison with a sample prepared from polypropylene grade 01130 with the addition of 2 mass. % commercial product D ₂ W ^® .

The correspondence of the curve numbers in FIG. 1-3 specific embodiments of the invention are indicated in tables 1 and 2.

In FIG. 4 shows the dynamics of changes in D1720 _rel during the photooxidation of the samples obtained in examples 11 (curve 1) and 14 (curve 3), in comparison with the pure base polymer (curve 2).

The invention is as follows.

Preparation of oxo-degrading additives

Calcium carbonate crushed in a ball mill (particle size 70 - 90 nm) is thoroughly mixed with a solution of salt or a mixture of salts in white spirit until a homogeneous pasty mass is obtained. The resulting mass is dried at a temperature of 90 ° C for 24 hours until the solvent is completely removed and crushed to obtain a homogeneous friable powder (80-100 nm).

Cooking a Model Masterbatch

Prepare a model masterbatch containing 50 mass. % oxo-degradable additives and polyolefin base, which is selected depending on the melting temperature of the base polymer, to add to which the masterbatch is intended. For low melting polyethylene, a masterbatch based on polyethylene is used, and for polymers containing polypropylene, a masterbatch based on polyethylene or polypropylene can be used. The calculated amount of polymer is melted in a Brabender type laboratory mixer (20-30 rpm) at a temperature exceeding the polymer melting by 15-20 ° C, after which an equal weight amount of the additive prepared as described above is added to the melt and stirring is continued in for 6-10 minutes until complete homogenization of the mixture. The material is cooled to room temperature, mechanically crushed to a size of 2-3 mm and used to prepare films or to add to the base polymer.

To prevent premature oxidative decomposition of the polyolefin base during storage of the masterbatch, intended for industrial use, it is necessary to introduce antioxidants into it. In the conditions of model experiments in which the masterbatch is used immediately after preparation, the introduction of antioxidants is not required.

Preparation of the base polymer with the addition of masterbatch

LDPE grade 15803-020 or PP grade 01130 were used as base polymers. Masterbatch content in the base polymer is 1-3 wt. % The calculated amount of the base polymer is melted in a Brabender type laboratory mixer (20-30 rpm) at 140 ± 2 ° С in the case of LDPE or at 190 ± 2 ° С in the case of PP, after which the required weight amount of the masterbatch prepared is added to it as described above, and stirring is continued until the mixture is completely homogenized (6-8 minutes). The material is cooled to room temperature, mechanically crushed to a particle size of 2-3 mm and used to prepare films.

Preparation of polyolefin films

Samples of films with a thickness of 80 - 100 μm are obtained by extrusion using an extruder with a slit head at the melting temperature of the polymer.

In the examples below (see Tables 1 and 2), not exhaustive of all the possibilities of carrying out the invention, the composition and characteristics of polyolefin films obtained using the inventive additive are shown.

Table 1. The composition of the model masterbatch

The results presented in Table. 1 and in FIG. 1 show that the individual 2-ethylhexanoates of zinc and zirconium on an inert carrier in the composition of the masterbatch containing 50 mass. % of the polymer base (examples 2 and 3) exhibit pronounced pro-oxidant activity with respect to the polyolefin chain. It is noteworthy that cobalt 2-ethylhexanoate, shown as a comparative example (curve 1 in Fig. 1,), is significantly inferior to zinc and zirconium salts (curves 2 and 3 in Fig. 1) in their ability to catalyze free radical thermooxidative processes destruction of carbon bonds in polyolefin molecules.

As can be seen from FIG. 2, two-component combinations (curves 1–3) and three-component combinations (curves 4–7), which, in addition to zinc and zirconium 2-ethylhexanoates, less active cobalt 2-ethylhexanoate, also exhibit pro-oxidative activity with respect to polyolefin chains. By choosing empirically quantitative proportions of the components, it is possible to balance the composition of the mixture so that high pro-oxidative activity is achieved at a lower consumption of the relatively expensive zirconium salt (compare, for example, curve 3 in Fig. 1 and curve 7 in Fig. 2).

In table 2 and in FIG. 3 presents data showing the effect of the inventive additives on the ability of base polymers to thermooxidative decomposition and on their physical and mechanical characteristics. Examples 11 and 13 relate to samples of a polyethylene film prepared with the addition of 1 and 3 masses, respectively. % masterbatch according to example 9 (i.e., the films contain 0.1 and 0.3 wt.%, respectively, of a three-component mixture of salts). Example 12 relates to a sample of a polypropylene film prepared with the addition of 2 mass. % masterbatch according to example 10 (i.e., the film contains 0.2 wt.% the same ternary mixture of salts). Example 14 relates to a sample of a polyethylene film prepared with the addition of 3 mass. % masterbatch according to example 6 (i.e., the film contains 0.3 wt.% a two-component mixture of 2-ethylhexanoates zinc and zirconium). For comparison, in FIG. 3 shows the dynamics of thermo-oxidative decomposition of polypropylene containing 2 mass. % of a well-known commercial product D2W ^® .

Table 2. Composition and physico-mechanical characteristics of base polymer film samples prepared with the addition of masterbatch model samples

The dynamics of the accumulation of carbonyl groups under the influence of thermo-oxidative rupture of polymer chains shown in FIG. 3, indicates that double and ternary mixtures of 2-ethylhexanoates of zinc, zirconium and cobalt with their total content in the base polymer in an amount of 0.1 - 0.3 mass. % exhibit a pronounced pro-oxidant effect, stronger than the action of the commercial product widely available on the market - the D2W® oxo-decomposing additive. Given in the table. 2, the data also show that the addition to the polymer in the indicated amounts of a mixture of salts deposited on an inert carrier does not significantly affect the physicomechanical characteristics of the base polymers.

In FIG. 4 shows the effect of the inventive additives on the ability of the polyolefin polymer to photooxidation. To simulate photooxidation, a film sample obtained from low density polyethylene grade 15803-020 containing 1 mass. % of the masterbatch prepared according to example 11, first thermostat at 90 ° C for one hour, and then subjected to ultraviolet radiation at room temperature for 300 hours. The figure shows that, compared with pure LDPE, which is almost not subjected to photooxidation under the experimental conditions (curve 2), samples containing 0.1 mass. % of a mixture of 2-ethylhexanoates of cobalt, zinc and zirconium (curve 1) and 0.3 wt. % of a mixture of 2-ethylhexanoates of zinc and zirconium (curve 3) are susceptible to destruction by UV irradiation.

Thus, the above results show that the inventive oxo-decomposing additive in low concentrations accelerates thermal and photo-oxidative breakdown of polyolefin chains and, thus, increases the biodegradability of polyolefin-based polymeric materials.

Claims (3)

1. Oxo-decomposing additive to polyolefins, including metal carboxylates or mixtures of metal carboxylates, supported on an inert carrier, characterized in that zinc and zirconium 2-ethylhexanoates are used as metal carboxylates. 2. Oxo-decomposing additive according to claim 1, characterized in that as an inert carrier contains calcium carbonate. 3. Oxo-decomposing additive according to claim 1, characterized in that it further comprises cobalt 2-ethylhexanoate.

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