Method for improving degradation stability of polystyrene composition in recovery process

Abstract

The invention relates to a method for improving degradation stability of a polystyrene composition P in a recovery process. The invention also relates to the use of less than 0.4% by weight of a stabilizer component for improving the degradation stability of a polystyrene composition in a recovery process, and to a polystyrene composition having improved degradation stability.

Description

Technical Field

[0001] The present invention relates to a method for improving the degradation stability of a polystyrene (PS) composition in a recycling process. The present invention relates to the use of a stabilizer component for improving the degradation stability of a polystyrene composition in a recycling process, and a polystyrene composition with improved degradation stability. Background Art

[0002] Products made of or containing plastic components are part of many workplaces or home environments. Most of these plastics are virgin polymers produced from petroleum. In recent years, there has been a strong trend towards recycling and reusing petrochemical products such as plastics, in addition to metal materials. Recycling plastics from waste plastic materials has many benefits compared to producing virgin plastics from petroleum, such as less energy required, less need to dispose of waste, and reduced use of finite geological resources such as petroleum. Typically, waste plastic materials include post-consumer and post-industrial waste and plastic waste, including polymer types such as general-purpose polystyrene (GPPS) and high-impact polystyrene (HIPS).

[0003] The processing of polystyrene compositions, for example in recycling processes, generally results in polystyrene degradation due to a combination of mechanical stress, thermal cracking and oxidation. Due to the severe degradation of polystyrene during processing, high temperatures promote the formation of monomers, such as styrene monomer. The ceiling behavior of commercial polystyrene materials generally results in residual monomer contents of 400 ppm styrene monomer at 220°C and 1500 ppm styrene monomer at 260°C.

[0004] In order to use the recycled polystyrene composition, especially in food packaging, it is inevitable to minimize the residual styrene content in the recycled styrene composition because the styrene monomer can be transferred from the packaging material to the food. The recycled polystyrene composition tends to contain and / or release a larger amount of residual styrene monomer due to repeated thermal and / or mechanical treatments in the recycling process.

[0005] Polystyrene with a low residual monomer content is sought, especially after post-consumer recycling, and the desired grade is one that does not form styrene monomers during processing. Processing can lead to polystyrene degradation due to a combination of mechanical stress, thermal decomposition and oxidation (W. Loth "Kinetik und Mechanismus des Abbaus", H. Gausepohl and R. Gellert, eds. "Polystyrol", Kunsttoff-Handbuch 4, Hanser Verlag, Munich, 1996).

[0006] In everyday applications, low residue levels are particularly important in the food packaging sector. In this paper, semi-impact resistant HIPS or GPPS / HIPS blends are used. Literature results show that stabilization of HIPS also helps to reduce the residue content.

[0007] Therefore, there is a high demand for polystyrene compositions with low residual monomer content and reduced release of monomers such as styrene due to the degradation of polystyrene during processing.

[0008] Surprisingly, it was found that increasing the amount of stabilizer component leads to an increase in the formation of styrene monomer during the processing of high impact polystyrene. This result was confirmed for a large number of different stabilizer components. After extensive research, the inventors of the present invention have discovered a method for improving the degradation stability of polystyrene compositions as described herein. Summary of the invention

[0009] The present invention relates to a method for improving the degradation stability of a polystyrene composition P in a recycling process, wherein the method comprises mixing at least one polystyrene component as component A with 0.01% to less than 0.4% by weight, preferably 0.02% to 0.3% by weight, typically 0.03% to 0.2% by weight, for example 0.04% to 0.15% by weight of at least one stabilizer component as component B and optionally at least one additive as component C, based on the total weight of the polystyrene composition P; Wherein, at least one polystyrene component A comprises: A-1: at least one impact-modified polystyrene as component A-1; and / or A-2: at least one non-impact-modified polystyrene as component A-2; And, wherein at least one stabilizer component B comprises at least one component selected from: B-1: at least one sterically hindered phenolic antioxidant as component B-1; B-2: optionally at least one phosphorus-containing co-stabilizer as component B-2; and B-3: Optionally at least one sulfur-containing co-stabilizer as B-3 component.

[0010] Preferably, the polystyrene composition P comprises (or consists of): (i) at least one impact-modified polystyrene A-1 and at least one sterically hindered phenolic antioxidant B-1; or (ii) at least one impact-modified polystyrene A-1 and at least two sterically hindered phenolic antioxidants B-1; or (iii) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1 and at least one phosphorus-containing co-stabilizer B-2; or (iv) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1 and at least one sulfur-containing co-stabilizer B-3; or (v) at least one non-impact modified polystyrene A-2 and at least one sterically hindered phenolic antioxidant B-1.

[0011] It has been found that when the amount of typical heat stabilizers including stabilizer component B is 0.4% by weight and above, the polystyrene composition P containing impact-modified polystyrene component A-1 such as high impact polystyrene (HIPS) performs poorly during heat treatment. Good stabilization effects can be obtained even with small amounts of heat stabilizers. For example, amounts as low as 0.04% to 0.15% by weight of heat stabilizer B are generally sufficient to obtain good degradation stability during heat treatment.

[0012] If only non-impact-modified polystyrene component A-2, such as general-purpose polystyrene (GPPS), is present, at least one sterically hindered phenolic antioxidant B-1 is generally sufficient to improve its degradation stability in the recycling process. However, also for the non-impact-modified polystyrene component A-2, the presence of more than one sterically hindered phenolic antioxidant B-1, or at least one phosphorus-containing costabilizer B-2 and / or at least one sulfur-containing costabilizer B-3 in combination with at least one sterically hindered phenolic antioxidant B-1 is suitable and is an embodiment of the present invention.

[0013] The present invention also comprises polymer blends of an impact-modified polystyrene component A-1 and a non-impact-modified polystyrene component A-2. According to the present invention, these blends require the presence of at least one sterically hindered phenolic antioxidant B-1. The at least one sterically hindered phenolic antioxidant B-1 is preferably used in combination with at least one other sterically hindered phenolic antioxidant B-1, at least one phosphorus-containing costabilizer B-2 and / or at least one sulfur-containing costabilizer B-3.

[0014] If a polymer blend of the impact-modified polystyrene component A-1 and the non-impact-modified polystyrene component A-2 is prepared, it is usually sufficient to mix the non-impact-modified polystyrene component A-2 with the impact-modified polystyrene component A-1 that already contains sufficient stabilizer component B. Although it is possible, it is not necessary to mix the non-impact-modified polystyrene component A-2 with the stabilizer component B before blending with the impact-modified polystyrene component A-1.

[0015] Therefore, according to one embodiment, the present invention relates to a method for improving the degradation stability of a polystyrene composition P in a recycling process, wherein at least one polystyrene component A is selected from: A-1: at least one impact-modified polystyrene as component A-1; Provided that the polystyrene composition comprises (or consists of): (i) at least one impact-modified polystyrene A-1 and at least one sterically hindered phenolic antioxidant B-1; or (ii) at least one impact-modified polystyrene A-1 and at least two sterically hindered phenolic antioxidants B-1; or (iii) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1 and at least one phosphorus-containing co-stabilizer B-2; or (iv) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1 and at least one sulfur-containing co-stabilizer B-3.

[0016] According to an alternative embodiment, the invention relates to a method for improving the degradation stability of a polystyrene composition P in a recycling process, wherein at least one polystyrene component A is selected from: A-2: at least one non-impact-modified polystyrene as component A-2; Provided that the polystyrene composition comprises (or consists of): (i) at least one non-impact modified polystyrene A-2 and at least one sterically hindered phenolic antioxidant B-1.

[0017] The present invention also relates to a method for improving the degradation stability of a polystyrene composition P in a recycling process, wherein at least one polystyrene component A is selected from: A-1: at least one impact-modified polystyrene as component A-1; and A-2: at least one non-impact-modified polystyrene as component A-2; Provided that the polystyrene composition comprises: (i) at least one sterically hindered phenolic antioxidant B-1; or (ii) at least two sterically hindered phenolic antioxidants B-1; or (iii) at least one sterically hindered phenolic antioxidant B-1 and at least one phosphorus-containing co-stabilizer B-2; or (iv) at least one sterically hindered phenolic antioxidant B-1 and at least one sulfur-containing co-stabilizer B-3.

[0018] The method for improving the degradation stability of a polystyrene composition P in a recycling process preferably comprises the following steps: a) providing at least one impact-modified polystyrene A-1 and / or at least one non-impact-modified polystyrene A-2 as component A; b) providing as component B at least one sterically hindered phenolic antioxidant B-1, optionally at least one further sterically hindered phenolic antioxidant B-1 which is different from the first sterically hindered phenolic antioxidant B-1, optionally at least one phosphorus-containing co-stabilizer B-2 and / or optionally at least one sulfur-containing co-stabilizer B-3; c) optionally providing at least one additive as component C; d) mixing component A with 0.01% to less than 0.4% by weight, preferably 0.02% to 0.3% by weight, typically 0.03% to 0.2% by weight, for example 0.04% to 0.15% by weight of component B and optionally component C, based on the total weight of the polystyrene composition P, to obtain a polystyrene composition P; e) optionally extruding and cooling the polystyrene composition P obtained.

[0019] The mixing step c) can be carried out by methods known per se. For example, extruders, such as co-rotating or counter-rotating single-screw or twin-screw extruders, or other conventional kneading equipment, such as continuous or intermittent kneaders, Brabender mixers or Banbury mixers, can be used for the mixing step. The kneading elements should ensure sufficient homogeneity of the components to ensure micromixing.

[0020] The process according to the invention can comprise mixing and homogenizing components A, B and C by conventional methods of plastics technology, wherein the sequence of adding the components can vary.

[0021] As used herein, the term "polystyrene" refers to a polymer containing monomer residues of one or more monomers selected from styrene, p-methylstyrene, t-butylstyrene, dimethylstyrene, nuclear brominated or chlorinated derivatives thereof, and combinations thereof.

[0022] As used herein, the term "monomer residue" or "polymer made from a specific monomer" or "polymer comprising a specific monomer" refers to the monomer repeating unit in a polymer derived from polymerization of a specific monomer containing a polymerizable unsaturated group. As used herein, the term "polymer" is intended to include homopolymers, copolymers, and graft copolymers.

[0023] Components A, B and C, and suitable amounts thereof, are further defined below. Impact-modified polystyrene as component A-1

[0024] The method according to the invention uses at least one impact-modified polystyrene as component A-1. The at least one impact-modified polystyrene A-1 generally comprises (or consists of): A-1.1: at least one polystyrene as component A-1.1; A-1.2: at least one impact-modifying polymer as component A-1.2; and A-1.3: Optionally at least one additive as component A-1.3.

[0025] According to a preferred embodiment, based on the polystyrene A-1.1, the polystyrene A-1.1 contains at least 30% by weight, more preferably at least 60% by weight, and particularly preferably at least 85% by weight of one or more monomers selected from styrene, p-methylstyrene, tert-butylstyrene, dimethylstyrene, their nuclear brominated or chlorinated derivatives, and combinations thereof. Preferably, based on the polystyrene A-1.1, the polystyrene A-1.1 contains at least 30% by weight, more preferably at least 60% by weight, and particularly preferably at least 85% by weight of styrene.

[0026] In a preferred embodiment, the polystyrene A-1 is selected from high impact polystyrene (HIPS).

[0027] The preparation, structure and properties of polystyrene are generally described in detail in the literature, for example in Echte, Haaf, Hambrecht in Angew. Chen. (Int. Ed. Engl.) 20, pp. 344-361, 1981; and in Kunststoffhandbuch, edited by Vieweg and Daumiller, Volume 4, "Polystyrol", Carl-Hanser-Verlag, Munich, 1996.

[0028] The term "high impact polystyrene" or "HIPS" as used herein refers to a rubber-modified polystyrene comprising polystyrene A-1 as a base material and at least one impact-modified polymer A-1.2 as described below as an elastomeric material. For example, HIPS can be prepared by adding polybutadiene rubber or other elastomeric materials to styrene monomers during the polymerization process, so that it can be chemically combined with polystyrene to form a graft copolymer, which helps to incorporate the impact-modified polymer A-1.2 into the final resin composition.

[0029] As used herein, the term "elastomeric material" refers to a material that deforms when stress is applied and returns to its original structure when the stress is removed.

[0030] Typically, the elastomeric material that can be used to make high impact polystyrene (HIPS) is one or more elastomeric materials selected from styrene, 1,3-butadiene, isoprene, acrylonitrile, ethylene, C3 to C 12Impact-modified polymer A-1.2 comprising monomer residues of alpha olefins and combinations thereof.

[0031] In some embodiments of the present invention, the impact-modified polymer A-1.2 may be a rubber polymer containing ethylenically unsaturated structures. In some cases, the impact-modified polymer A-1.2 may be one or more C 4-6 Copolymers or homopolymers of conjugated dienes (such as polybutadiene).

[0032] In some specific embodiments, the polystyrene component A-1 is selected from high impact polystyrenes comprising polystyrene A-1.1 and at least one impact-modifying polymer A-1.2 selected from butadiene rubber (BR) and styrene-butadiene rubber (SBR).

[0033] Butadiene rubber is low, medium or high cis polybutadiene, especially medium high cis polybutadiene. Generally, based on polybutadiene, polybutadiene contains not less than 10%, preferably not less than 70%, most preferably not less than 90% by weight, and in some cases more than about 93% by weight of cis-configured monomer units. In many cases, based on polybutadiene, the cis content of medium cis polybutadiene is about 30% to 50% by weight, and in some cases about 35% to 45% by weight.

[0034] Suitable butadiene rubbers useful in the present invention include those commercially available from a variety of sources; for example, Buna CB 550 available from Arlanxeo Corporation (Pittsburgh, Pennsylvania, USA); PB 5800-Schkopau available from Trinseo LLC (Berwyn, Pennsylvania, USA); and PTFE 500 available from Firestone Polymers LLC (Akron, Ohio, USA). 55AC15 and 70AC15.

[0035] Furthermore, the impact-modifying polymer A-1.2 can be selected from structurally modified specific butadiene rubbers, for example, butadiene rubbers partially modified in 1,4-cis and / or 1,4-trans or partially modified in 1,2 and 1,4 bonds relative to conventional rubbers.

[0036] Furthermore, instead of butadiene rubber, other diene rubbers may be used, elastomers of the ethylene propylene diene copolymer (EPDM rubber) type may be used, and hydrogenated diene rubber may be used as the impact-modifying polymer A-1.2.

[0037] Preferably, the impact-modified polystyrene A-1 comprises a high-impact polystyrene, which comprises 80 to 99% by weight, preferably 85 to 98% by weight, of polystyrene A-1.1 as a styrene matrix, and 1 to 20% by weight, preferably 2 to 15% by weight, of at least one impact-modifying polymer A-1.2, preferably polybutadiene and / or a styrene-butadiene copolymer, whose at least one glass transition temperature Tg is less than 0° C., preferably less than −40° C., most preferably less than −60° C. The glass transition temperature Tg is determined according to ISO 11357-1 / -3 at a heating rate of 10 K / min.

[0038] The impact-modified polymer A-1.2 is typically in the form of particles, typically having an average particle size of at least about 0.25 μm (measured by conventional methods), in some cases at least about 0.5 μm, and in other cases at least about 1 μm. Preferably, the average particle size of the impact-modified polymer A-1.2 particles can be up to about 12 μm, in some cases up to about 11 μm, and in other cases up to about 10 μm. Typically, the average particle size of the impact-modified polymer A-1.2 particles can be in the range of 1 μm to 10 μm, for example 2, 4 or 7 μm. The average particle size of the impact-modified polymer A-1.2 particles can be any value or any range between any of the above values. The (volume-based) average particle size of the impact-modified polymer A-1.2 is typically measured by analyzing a spectrum obtained by light scattering of a solution of the particles in a polystyrene solvent (such as methyl ethyl ketone or ethyl acetate). Instruments suitable for this measurement include Horiba's Model LA-920 or Beckman Coulter's LS13 320.

[0039] Generally, the weight average molecular weight (M) of polystyrene A-1.1 is w ) ranges from 30,000 to 500,000 g / mol, preferably from 50,000 to 250,000 g / mol, and more preferably from 70,000 to 240,000 g / mol. Specifically, the weight average molecular weight (M w ) ranges from 80,000 to 400,000 g / mol, preferably from 120,000 to 300,000 g / mol, and more preferably from 150,000 to 250,000 g / mol. Specifically, the weight average molecular weight (M w) ranges from 100,000 to 500,000 g / mol, preferably from 130,000 to 360,000 g / mol, and more preferably from 150,000 to 350,000 g / mol. Molecular weight values ​​are typically determined using gel permeation chromatography (GPC) using tetrahydrofuran (THF) as eluent and appropriate polystyrene standards. Unless otherwise indicated, molecular weight values ​​referred to herein are mass average molecular weight (M w ).

[0040] Typically, the viscosity number VN (measured in accordance with DIN 53726) of the impact-modified polystyrene A-1 is in the range from 50 to 120 ml / g, preferably in the range from 60 to 100 ml / g.

[0041] In particular, high impact polystyrene (HIPS) which already contains one or more additives A-1.3, such as mineral oil (e.g. medical white oil), lubricant (e.g. metal stearate), stabilizer, antistatic agent, flame retardant or wax, can be used as impact-modified polystyrene A-1. Suitable additives are known in the art and can be selected from the additives described below as component C.

[0042] In one embodiment of the present invention, at least one impact-modified polystyrene A-1 comprises (or consists of): A-1.1: 80% to 99% by weight, preferably 85% to 98% by weight, of at least one polystyrene A-1.1, based on the total impact-modified polystyrene A-1; A-1.2: 1 to 20% by weight, preferably 2 to 15% by weight, based on the total impact-modified polystyrene A-1, of optionally at least one impact-modifying polymer A-1.2; and A-1.3: 0 to 7% by weight, preferably 0 to 5% by weight, of at least one additive A-1.3, based on the total impact-modified polystyrene A-1. Non-impact modified polystyrene A-2

[0043] The method according to the invention uses at least one non-impact-modified polystyrene as component A-2. The at least one non-impact-modified polystyrene A-2 generally comprises (or consists of): A-2.1: at least one polystyrene as component A-2.1, and A-2.2: Optionally at least one additive as component A-2.2.

[0044] At least one polystyrene component A-2.1 can be selected from the above-mentioned polystyrene components A-1.1, but does not include impact-modified polymers. Suitable standard polystyrenes or also called general-purpose polystyrenes (GPPS) are prepared by anionic or free radical polymerization methods of styrene or styrene derivatives as described above. Preferably, GPPS is prepared by polymerization of styrene or a mixture of styrene and any other copolymerizable monomers. Preferably, GPPS is prepared by polymerization of styrene or a mixture of styrene and one or more monomers selected from p-methylstyrene, tert-butylstyrene, dimethylstyrene, their nuclear brominated or chlorinated derivatives and combinations thereof. In general, the inhomogeneity of the polymer may be affected by the polymerization method, but in the present invention the effect is minimal.

[0045] Generally, the weight average molecular weight (M) of polystyrene A-2.1 is w ) ranges from 50,000 to 500,000 g / mol, preferably from 100,000 to 450,000 g / mol, and more preferably from 150,000 to 400,000 g / mol. Specifically, the weight average molecular weight (M w ) ranges from 200,000-375,000 g / mol, preferably 250,000 to 350,000 g / mol, more preferably about 300,000 g / mol-350,000 g / mol.

[0046] Molecular weight values ​​are typically determined using gel permeation chromatography (GPC) using tetrahydrofuran (THF) as the eluent and appropriate polystyrene standards. Unless otherwise stated, molecular weight values ​​referred to herein are mass average molecular weight (Mw).

[0047] Typically, the viscosity number VN (measured in accordance with DIN 53726) of the non-impact-modified polystyrene A-2 is in the range from 50 to 130 ml / g, preferably in the range from 60 to 120 ml / g.

[0048] In particular, general-purpose polystyrene (GPPS) which already contains one or more additives A-2.2, such as mineral oil (e.g. medical white oil), lubricant (e.g. metal stearate), stabilizer, antistatic agent, flame retardant or wax can be used as non-impact-modified polystyrene A-2. Suitable additives are known in the art and can be selected from the additives described below as component C.

[0049] In one embodiment of the present invention, at least one non-impact modified polystyrene A-2 comprises (or consists of): A-2.1: 93% to 100% by weight, preferably 95% to 100% by weight, of at least one polystyrene as component A-2.1, based on the total non-impact-modified polystyrene A-2, and A-2.2: 0 to 7% by weight, preferably 0 to 5% by weight, of at least one additive A-2.2, based on the total non-impact-modified polystyrene A-2. Stabilizer component B

[0050] According to the invention, at least one stabilizer component B comprises at least one component selected from: B-1: at least one sterically hindered phenolic antioxidant as component B-1; B-2: optionally at least one phosphorus-containing co-stabilizer as component B-2; and B-3: Optionally at least one sulfur-containing co-stabilizer as component B-3. Sterically hindered phenolic antioxidant (component B-1)

[0051] The sterically hindered phenolic antioxidant component B-1 is preferably selected from antioxidants of the general formula (I-1) and mixtures thereof: wherein R1 to R5 represent a hydrogen atom or an alkyl group having 1 to 70 carbon atoms, wherein the hydrocarbon group optionally contains at least one heteroatom selected from O and S, and wherein at least one of the substituents R1 and R5 represents a hydrocarbon group having at least 3 carbon atoms; and R6 represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, wherein the hydrocarbon group forms a 5-6 membered ring structure with at least one carbon atom of the hydrocarbon group of the adjacent substituents R1 and / or R5. Preferably, R6 represents a hydrogen atom.

[0052] In a preferred embodiment, the sterically hindered phenolic antioxidant component B-1 is selected from the phenolic antioxidants of the general formula (I-2) and mixtures thereof: wherein R1 to R5 each represent a hydrogen atom or an alkyl group having 1-70 carbon atoms, wherein the hydrocarbon group optionally contains at least one heteroatom selected from O and S, and wherein at least one of the substituents R1 and R5 represents a hydrocarbon group having at least 3 carbon atoms.

[0053] In another preferred embodiment, at least one of the substituents R1 and R5 represents a hydrocarbon group having 3 to 6 carbon atoms, preferably isopropyl, sec-butyl, tert-butyl, neopentyl and / or cyclohexyl.

[0054] In one embodiment, at least one of the substituents R2, R3 and R4 represents a hydrogen atom.

[0055] In one embodiment, at least one of the substituents R2, R3 and R4 represents a hydrocarbon group having at least 1 carbon atom.

[0056] In one embodiment, at least one of the substituents R1 and R5 represents a tert-butyl group; at least two of the substituents R2, R3 and R4 represent a hydrogen atom; and one of the substituents R2, R3 and R4 represents a hydrocarbon group having at least 1 carbon atom.

[0057] In one embodiment, the at least one sterically hindered phenolic antioxidant B comprises at least one component B-1.1 selected from compounds of the general formula (I-3): wherein R3 represents a hydrocarbon group having 1-70 carbon atoms, wherein the hydrocarbon group optionally contains at least one heteroatom selected from O and S; and R2, R4 and R5 represent a hydrogen atom or an alkyl group having 1-4 carbon atoms, respectively, and at least one of the substituents R2, R3 and R4 is not hydrogen.

[0058] In one embodiment of the present invention, at least one sterically hindered phenolic antioxidant B is selected from octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (CAS No.: 2082-79-3, 1076), 2,6-di-tert-butyl-p-cresol (CAS No. 87-97-8, TBK), 2-(1,1-dimethylethyl)-6-[(3-(1,1-dimethylethyl)-2-hydroxy-5-methylphenyl]methyl-4-tolyl acrylate (CAS No.: 61167-58-6, 3052), and mixtures thereof.

[0059] Other examples of compounds that can be used as component B include oxygen free radical scavengers such as pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (CAS No.: 6683-19-8, 1010, BASF SE), tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate]methane (CAS No.: 6683-19-8, 1010, Songwon), 2,6-di-tert-butyl-4-(4,6-dioctylthio-1,3,5-triazine-2-yl)aminophenol (CAS No.: 991-84-4, 565, BASF SE), and mixtures thereof; carbon radical scavengers, such as 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate (CAS No.: 123968-25-2, GS, Sumitomo), 2-(1,1-dimethylethyl)-6-[[3-(1,1-dimethylethyl)-2-hydroxy-5-methylphenyl]-methyl]-4-methylphenyl acrylate (CAS No.: 61167-58-6, GM, Sumitomo), and mixtures thereof.

[0060] In one embodiment of the present invention, component B comprises or consists of: octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (CAS No.: 2082-79-3, 1076) as component B-1.1, is a hindered phenol antioxidant of the following formula (Ia):

[0061] In one embodiment of the present invention, component B comprises or consists of: 2-methyl-4,6-bis(octylthiomethyl)phenol (CAS No.: 110553-27-0, 1520) as component B-1.2, is a hindered phenol antioxidant of the following formula (Ib):

[0062] In one embodiment of the present invention, component B comprises a mixture of a hindered phenolic antioxidant of formula (Ia) as component B-1.1 and a hindered phenolic antioxidant of formula (Ib) as component B-1.2, preferably the weight ratio of B-1.1 to B1.2 is 1:2 to 2:1, more preferably 1:1.5 to 1.5:1.

[0063] The amount of at least one hindered phenolic antioxidant B-1 may be 0.01% to less than 0.4% by weight, preferably 0.02% to 0.3% by weight, typically 0.03% to 0.2% by weight, for example 0.04% to 0.15% by weight, based on the total weight of the polystyrene composition P. Provided that the total amount of the stabilizer component B does not exceed 0.4% by weight, based on the total weight of the polystyrene composition P, Phosphorus-containing co-stabilizer (component B-2)

[0064] Specific suitable phosphorus-containing co-stabilizers include phosphite components of general formula (II): Wherein R1 to R3 represent an aryl group, which is optionally substituted by a hydrocarbon group having 1 to 20 carbon atoms, preferably 3 to 10 carbon atoms. In a preferred embodiment, R1, R2 and R3 represent a phenyl group, which has 1 to 3 alkyl groups containing 3 to 10 carbon atoms as substituents. Particularly preferred phosphorus-containing costabilizers include tris (4-nonylphenyl) phosphite (TNPP, CAS No.: 3050-88-2), tris (2,4-di-tert-butylphenyl) phosphite (CAS No. 31570-04-4, from BASF SE, Germany), and mixtures thereof.

[0065] The phosphorus-containing co-stabilizer or the sulfur-containing co-stabilizer may be used alone or in combination with each other.

[0066] Based on the total weight of the polystyrene composition P, the amount of at least one phosphorus-containing co-stabilizer B-2 can be 0.01% to less than 0.4% by weight, preferably 0.02% to 0.3% by weight, typically 0.03% to 0.2% by weight, for example 0.04% to 0.15% by weight, provided that the total amount of stabilizer component B does not exceed 0.4% by weight, based on the total weight of the polystyrene composition P. Sulfur-containing co-stabilizer (component B-3)

[0067] Suitable sulfur-containing co-stabilizers include carboxylic acid esters of the general formula (III): wherein R1 is independently selected from a hydrocarbon group having 1-30 carbon atoms, preferably a linear hydrocarbon group having 5-20 carbon atoms, optionally containing oxygen atoms, especially oxygen atoms in the form of carboxyl functional groups; R2 is independently selected from a hydrocarbon group having 1-30 carbon atoms, preferably a linear hydrocarbon group having 10-20 carbon atoms; and M independently represents an integer between 1-8, preferably an integer between 2-4, especially 2.

[0068] In one embodiment, suitable sulfur-containing co-stabilizers include dicarboxylic acid esters of the general formula (III-a): wherein R1 and R2 are independently selected from hydrocarbon groups having 1 to 30 carbon atoms, preferably linear hydrocarbon groups having 10 to 20 carbon atoms; and n and m independently represent integers of 1 to 8, preferably integers of 2 to 4, especially 2. Particularly preferred sulfur-containing co-stabilizers of formula (III-a) include didodecyl thiodipropionate (Irganox PS 800, BASF SE), ditetradecyl thiodipropionate (CAS No.: 123-28-4; Irganox PS 801, BASF SE), distearyl thiodipropionate (CAS No.: 693-36-7; Irganox PS 802, BASF SE), and mixtures thereof.

[0069] In another embodiment, suitable sulfur-containing co-stabilizers include carboxylic acid esters of the general formula (III-b): wherein R1 is selected from a hydrocarbon group having 1 to 30 carbon atoms, preferably a linear hydrocarbon group having 5 to 15 carbon atoms; and m represents an integer of 1 to 8, preferably an integer of 2 to 4, especially 2. Particularly preferred sulfur-containing co-stabilizers of formula (III-b) include 2,2-bis[[3-(dodecylthio)-1-propionyloxy]methyl]propane-1,3-diyl-bis[3-(dodecylthio)propionate] (CAS No.: 29598-76-3, 412S, Li’anlong, China).

[0070] The amount of at least one sulfur-containing co-stabilizer B-3 may be 0.01% to less than 0.4% by weight, preferably 0.02% to 0.3% by weight, typically 0.03% to 0.2% by weight, for example 0.04% to 0.15% by weight, based on the total weight of the polystyrene composition P. Provided that the total amount of stabilizer component B does not exceed 0.4% by weight, based on the total weight of the polystyrene composition P, Additives (Component C)

[0071] According to the method of the present invention, the polystyrene composition P may contain up to 10% by weight, preferably up to 5% by weight, of one or more additional additives C different from component B, based on the total polystyrene composition P. Preferably, the polystyrene composition P may contain 0.01% to 10% by weight, preferably 0.1% to 5% by weight, more preferably 0.1% to 2.5% by weight of one or more additives C, based on the total polystyrene composition P.

[0072] During the preparation of the polystyrene composition P, the additives C can be admixed with at least one polystyrene component A and / or with at least one stabilizer component B.

[0073] The additional additive C is usually selected from commonly known additives for polystyrene and its copolymers and compositions. Substances that can be used as additives or auxiliary agents are polymer additives known to those skilled in the art and described in the prior art (e.g., Plastics Additives Handbook, edited by Schiller et al., 6th edition, 2009, Hanser Press). Additives and / or auxiliary agents can be added before or during the compounding process (mixing of polymer components A and B in the molten state).

[0074] The polystyrene composition P may contain as component C up to 10% by weight, typically 0.01% to 5% by weight, of conventional additives such as processing aids, stabilizers, oxidation inhibitors, UV absorbers, lubricants, flame retardants, colorants, pigments and plasticizers.

[0075] Examples of oxidation inhibitors and heat stabilizers are sterically hindered phenols other than component B-1, various substitutions of these groups and mixtures thereof in concentrations of up to 1% by weight, based on the total polystyrene composition P.

[0076] UV stabilizers may be used in an amount of up to 2% by weight, based on the total polystyrene composition P, and are various substituted resorcinols, salicylates, benzotriazoles and benzophenones different from component B. The amount of the above stabilizers is preferably 0.01% to 0.5% by weight, more preferably 0.1% to 0.3% by weight, based on the total polystyrene composition P.

[0077] An example of a processing aid is a homogeneously miscible oil or oil mixture, which can be used in an amount of 0.1% to 5% by weight, preferably 0.5% to 4% by weight, based on the total polystyrene composition P, and is particularly selected from mineral oil (medical grade mineral oil), natural plant oil (also known as vegetable oil) and silicone oil. Specifically, medical grade mineral oil (e.g. DAB 70) can be used as additive C in an amount of 1% to 4% by weight based on the polystyrene composition P.

[0078] Preferred lubricants can be selected from long-chain fatty acids, such as stearic acid or behenic acid, fatty acid salts (such as calcium stearate or zinc stearate), fatty acid esters (such as stearic acid esters or pentaerythritol stearate), amide derivatives of fatty acids (such as ethylene bis stearamide, erucic acid amide, ), phosphates (such as tricalcium phosphate), hydrocarbon waxes, such as microcrystalline wax and paraffin wax (such as ) and fumed silica (such as Generally, fatty acids are linear or branched, saturated or unsaturated C5-C 25 Alkyl chain carboxylic acid.

[0079] The additive C mentioned can be used alone or in combination of two or more additives C. Uses and Applications

[0080] The method according to the invention can be used to improve the degradation stability of a polystyrene composition P in a recycling process. The method according to the invention allows the polystyrene composition P obtained, for example in a recycling process, to be subjected to multiple mechanical processing, including repeated extrusion steps at high temperatures, for example in a temperature range of 180° C. to 400° C., preferably 200° C. to 300° C., typically 210° C. to 270° C., while the decomposition of the polystyrene component A and the formation of styrene monomers are significantly reduced. Repeated extrusion steps at high temperatures are typical conditions to which polymer materials are subjected in recycling processes.

[0081] In another aspect of the present invention, the present invention relates to the use of at least one stabilizer component B selected from the group consisting of: B-1: at least one sterically hindered phenolic antioxidant as component B-1; B-2: optionally at least one phosphorus-containing co-stabilizer as component B-2; and B-3: optionally at least one sulfur-containing co-stabilizer as component B-3; The polystyrene composition P comprises at least one polystyrene component A, which comprises (or consists of): A-1: at least one impact-modified polystyrene as component A-1; and / or A-2: at least one non-impact modified polystyrene as component A-2; and Provided that, based on the total weight of the polystyrene composition P, the polystyrene composition P comprises 0.01% to less than 0.4% by weight, preferably 0.02% to 0.3% by weight, typically 0.03% to 0.2% by weight, for example 0.04% to 0.15% by weight of the at least one stabilizer component B.

[0082] Preferably, the polystyrene composition P comprises (or consists of): (i) at least one impact-modified polystyrene A-1 and at least one sterically hindered phenolic antioxidant B-1; or (ii) at least one impact-modified polystyrene A-1 and at least two sterically hindered phenolic antioxidants B-1; or (iii) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1 and at least one phosphorus-containing co-stabilizer B-2; or (iv) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1 and at least one sulfur-containing co-stabilizer B-3; or (v) at least one non-impact modified polystyrene A-2 and at least one sterically hindered phenolic antioxidant B-1.

[0083] As described above and further demonstrated by the following examples, mixing 0.01% to less than 0.4% by weight of stabilizer component B and optionally at least one additive C with polystyrene component A, based on the total weight of the polystyrene composition P, can provide a polystyrene composition P having improved degradation stability in a recycling process. That is, during multiple mechanical processing of the obtained polystyrene composition P, such as in a recycling process, the degradation of the polystyrene component A is reduced and the styrene monomer formed due to polymer degradation is reduced, including repeated extrusion steps at high temperatures, such as in a temperature range of 160°C to 400°C, preferably 180°C to 300°C, and typically in a temperature range of 200°C to 280°C. Polystyrene composition P for multiple recycling cycles

[0084] In another aspect, the present invention relates to a polystyrene composition P for multiple recycling cycles, wherein the polystyrene composition P comprises (or consists of): A: at least one polystyrene component A, comprising: A-1: at least one impact-modified polystyrene as component A-1; and / or A-2: at least one non-impact-modified polystyrene as component A-2; and B: 0.01% to less than 0.4% by weight, preferably 0.02% to 0.3% by weight, typically 0.03% to 0.2% by weight, for example 0.04% to 0.15% by weight, based on the total weight of the polystyrene composition P, of at least one stabilizer component B selected from: B-1: at least one sterically hindered phenolic antioxidant as component B-1; B-2: optionally at least one phosphorus-containing co-stabilizer as component B-2; and B-3: optionally at least one sulfur-containing co-stabilizer as component B-3; and C: optionally at least one additive as component C, The total amount of A, B and C is 100% by weight of the polystyrene composition P.

[0085] Preferably, the polystyrene composition P comprises (or consists of): (i) at least one impact-modified polystyrene A-1 and at least one sterically hindered phenolic antioxidant B-1; or (ii) at least one impact-modified polystyrene A-1 and at least two sterically hindered phenolic antioxidants B-1; or (iii) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1 and at least one phosphorus-containing co-stabilizer B-2; or (iv) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1 and at least one sulfur-containing co-stabilizer B-3; or (v) at least one non-impact modified polystyrene A-2 and at least one sterically hindered phenolic antioxidant B-1.

[0086] Preferably, the polystyrene composition P comprises (or consists of): A: based on the total polystyrene composition P, > 89.6% to 99.99% by weight, preferably 91.7% to 99.97% by weight, typically 94.8% to 99.87% by weight, for example 95.85% to 99.76% by weight of at least one polystyrene component A; B: 0.01% to <0.4% by weight, preferably 0.02% to 0.3% by weight, typically 0.03% to 0.2% by weight, for example 0.04% to 0.15% by weight, of at least one stabilizer component B, based on the total polystyrene composition P; and C: 0 to 10% by weight, preferably 0.01 to 8% by weight, typically 0.1 to 5% by weight, for example 0.2 to 4% by weight, of at least one additive C, based on the total polystyrene composition P; The total amount of A, B and C is 100% by weight of the polystyrene composition P.

[0087] Components A, B and C are as described above. The polymer composition P disclosed herein, especially the specific amounts of A, B and C, can be used in the method for improving degradation stability according to the present invention.

[0088] The at least one polystyrene component A comprises (or consists of): at least one impact-modified polystyrene A-1, at least one non-impact-modified polystyrene A-2 or a mixture thereof. The polymer blend of at least one impact-modified polystyrene A-1 and at least one non-impact-modified polystyrene A-2 may comprise: A-1: 1% to 99.9% by weight, preferably 50% to 99.5% by weight, and typically 85% to 99% by weight of at least one impact-modified polystyrene A-1, based on the total polystyrene component A; and A-2: Based on the total polystyrene component A, 0.1 to 99% by weight, preferably 0.5 to 50% by weight, typically 1 to 15% by weight of at least one non-impact-modified polystyrene A-2.

[0089] The polystyrene composition P comprises at least one stabilizer component B, preferably a mixture of components B-1, B-2 and / or B-3, specifically comprising (or consisting of): B-1: 0.01% to <0.4% by weight, preferably 0.01% to 0.3% by weight, typically 0.01% to 0.2% by weight, for example 0.04% to 0.15% by weight, of at least one sterically hindered phenolic antioxidant B-1, based on the polymer composition P; B-2: 0% to 0.39% by weight, for example 0% to <0.39% by weight, preferably 0% to 0.29% by weight, typically 0% to 0.19% by weight, for example 0% to 0.14% by weight, of at least one phosphorus-containing co-stabilizer B-2, based on the polymer composition P; and B-3: 0% to 0.39% by weight, for example 0% to <0.39% by weight, preferably 0% to 0.29% by weight, typically 0% to 0.19% by weight, for example 0% to 0.14% by weight, of at least one sulfur-containing co-stabilizer B-3, based on the polymer composition P; This presupposes that the total amount of stabilizer component B, based on the polymer composition P, is 0.01% to <0.4% by weight, preferably 0.01% to 0.3% by weight, typically 0.01% to 0.2% by weight.

[0090] If the phosphorus-containing costabilizer B-2 is present in the polymer composition P, it is generally used in an amount of 0.01 to 0.2% by weight, based on the polymer composition P, typically 0.05 to 0.1% by weight.

[0091] If the sulfur-containing co-stabilizer B-3 is present in the polymer composition P, its amount, based on the polymer composition P, is generally 0.01 to 0.2% by weight, typically 0.05 to 0.1% by weight.

[0092] If phosphorus-containing co-stabilizer B-2 and sulfur-containing co-stabilizer B-3 are present in the polymer composition P, the total amount of components B-2 and B-3 is generally in the range of 0.01% to 0.2% by weight, typically 0.05% to 0.1% by weight, based on the polymer composition P.

[0093] If additives C are also admixed, the total amount of component C is generally in the range of 0 to 10% by weight, preferably 0 to 8% by weight, and typically 0 to 5% by weight, based on the total polystyrene composition P. The polystyrene composition P may generally contain 0.01 to 8% by weight, preferably 0.1 to 5% by weight, and more preferably 0.1 to 2.5% by weight of at least one component C, based on the total polystyrene composition P.

[0094] In one embodiment, the polystyrene composition P comprises (or consists of): A: based on the total polystyrene composition P, > 89.6 to 99.99% by weight, preferably 91.7 to 99.97% by weight, typically 94.8 to 99.87% by weight, for example 95.85 to 99.76% by weight of at least one polystyrene component A; B-1: 0.01% to <0.4% by weight, preferably 0.02% to 0.3% by weight, typically 0.03% to 0.2% by weight, for example 0.04% to 0.15% by weight, of at least one stabilizer component B, based on the total polystyrene composition P; and C: 0 to 10% by weight, preferably 0.01 to 8% by weight, typically 0.1 to 5% by weight, for example 0.2 to 4% by weight, of at least one additive C, based on the total polystyrene composition P; The total amount of A, B and C is 100% by weight of the polystyrene composition P.

[0095] In one embodiment, the polystyrene composition P comprises (or consists of): A-1: > 89.6% to 99.99% by weight, preferably 91.7% to 99.97% by weight, typically 94.8% to 99.87% by weight, of at least one impact-modified polystyrene A-1, based on the total polystyrene composition P; B-1.1: 0.005% to 0.395% by weight, for example 0.005% to <0.395% by weight, preferably 0.01% to 0.29% by weight, typically 0.015% to 0.185% by weight, of a first sterically hindered phenolic antioxidant as component B-1.1, based on the polymer composition P; B-1.2: 0.005% to 0.395% by weight, for example 0.005% to <0.395% by weight, preferably 0.01% to 0.29% by weight, typically 0.015% to 0.185% by weight, based on the polymer composition P, of a second sterically hindered phenolic antioxidant as component B-1.2; C: 0 to 10% by weight, preferably 0.01 to 8% by weight, typically 0.1 to 5% by weight, of at least one additive C, based on the polymer composition P; Wherein, components B1.1 and B1.2 are different from each other; Provided that the total amount of stabilizer component B is 0.01% to <0.4% by weight, preferably 0.01% to 0.3% by weight, typically 0.01% to 0.2% by weight, based on the polymer composition P, and The total amount of A-1, B-1.1, B-1.2 and C is 100% by weight of the polystyrene composition P.

[0096] In one embodiment, the polystyrene composition P comprises (or consists of): A-2: > 89.6% to 99.99% by weight, preferably 91.63% to 99.97% by weight, typically 94.67% to 99.87% by weight of at least one non-impact modified polystyrene A-2; B-1: 0.01% to <0.4% by weight, preferably 0.02% to 0.37% by weight, typically 0.03% to 0.33% by weight, based on the polymer composition P, of at least one sterically hindered phenolic antioxidant B-1; C: 0 to 10% by weight, preferably 0.01 to 8% by weight, typically 0.1 to 5% by weight, of at least one additive C, based on the polymer composition P; The total amount of A-2, B-1 and C is 100% by weight of the polystyrene composition P.

[0097] The process for preparing the polymer composition P is known per se in the art and is as described above. Typically, the process mixes components A, B and C in given amounts.

[0098] The present invention is further illustrated by the following examples and claims. DETAILED DESCRIPTION Example Conventional methods

[0099] According to Tables 1.1, 2.1, 2.2 and 3.1, commercial polystyrene components were compounded with different stabilizers.

[0100] The following extruder conditions were used: Extruder: ZSK 30 Temperature: 220℃ or 260℃ Speed: 200[1 / min] Production capacity: 10kg / h No degassing

[0101] The details are as follows.

[0102] Styrene monomer levels were determined by capillary gas chromatography using the headspace technique and a styrene-based calibration curve.

[0103] The viscosity number VN is determined in accordance with DIN 53726.

[0104] The melt volume flow rate (MVR, 200°C / 5kg) was determined according to ISO 1133. 1. Example of impact-modified polystyrene at 220°C extrusion temperature

[0105] According to the components given in Table 1.1, a commercial high impact modified polystyrene component (PS 486M, INEOSStyrolution) was compounded with different stabilizers. The following materials were used: Impact modified polystyrene component A: A-1: High impact polystyrene HIPS (PS 486M, INEOS Styrolution) Sterically hindered phenolic antioxidant B-1: B-1.1: Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate ( 1076, CAS No.: 2082-79-3) B-1.2: 2-methyl-4,6-bis(octylthiomethyl)phenol ( 1520, CAS No.: 110553-27-0) Phosphorus-containing co-stabilizer component B-2: B-2.2: Tris(nonylphenyl)phosphite (TNPP, CAS No.: 26523-78-4) Table 1.1: Test compositions and styrene levels measured after 5 extrusions

[0106] The compositions of Comparative Examples 1-5 and Example 1 were extruded 5 times at an extrusion temperature of 220°C and then the styrene monomer level was measured. Surprisingly, it was found that the HIPS composition with the lowest total stabilizer concentration exhibited the best degradation stability during extrusion and the styrene monomer accumulation formed by polystyrene degradation showed the lowest total styrene level of 373 ppm (see Example 1). 2. Example of impact-modified polystyrene at 260°C extrusion temperature

[0107] Commercial high impact polystyrene (HIPS) (PS 486M, INEOSStyrolution) was compounded with different stabilizers according to the components given in Tables 2.1 and 2.2. The following materials were used: Impact modified polystyrene component A: A-1: High impact polystyrene HIPS (PS 486M, INEOS Styrolution) Sterically hindered phenolic antioxidant B-1: B-1.1: Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate ( 1076, CAS No.: 2082-79-3) B-1.2: 2-methyl-4,6-bis(octylthiomethyl)phenol ( 1520, CAS No.: 110553-27-0) Phosphorus-containing co-stabilizer component B-2: B-2.1: Tris(2,4-di-tert-butylphenyl)phosphite ( 168, CAS No. 31570-04-4) B-2.2: Tris(nonylphenyl)phosphite (TNPP, CAS No.: 26523-78-4) Sulfur-containing co-stabilizer component B-3: B-3.1: Didodecyl-3,3'-thiodipropionate (Irganox PS 800, CAS No.: 123-28-4) Reference stabilizer components (reference example): Reference Example 1: IPPD-80 (RheinChemie), according to the product specifications, contains: 80% by weight of N-isopropyl-N'-phenyl-1,4-phenylenediamine and 20% by weight of an elastomeric binder and dispersant (CAS No.: 101-72-4) Reference Example 2: MBI-80 (RheinChemie), according to the product specifications, contains: 80% by weight of 2-mercaptobenzimidazole and 20% by weight of elastomeric binder and dispersant Reference Example 3: Reference 1,3,5-Triepoxypropyl isocyanurate ( PT 810 (HuntsmanAdvanced Materials), CAS number: 2451-62-9) Reference Example 4: 4,4'-bis(phenylisopropyl)diphenylamine ( CAS No.: 10081-67-1) Reference Example 5: trans-β-nitrostyrene (CAS No.: 5153-67-3) Reference Example 6: α-Tocopherol (CAS No.: 10191-41-0) Table 2.1: Compositions containing HIPS

[0108] A composition comprising HIPS as the A component and a commercially available reference stabilizer was further prepared: Table 2.2: Compositions containing HIPS and reference stabilizers

[0109] The compositions according to Example 2 and Comparative Examples 6-15 were extruded 5 times at an extrusion temperature of 260° C. After 5 extrusions, the styrene monomer content of the extruded compositions was measured. The test data are summarized in Table 2.1 and Table 2.2.

[0110] From the data given in Table 2.1, it can be seen that the HIPS composition with a stabilizer B-1 content of less than 0.4% by weight shows the lowest residual styrene formation after five extrusions, with a total styrene content of 395 ppm (Example 2). Surprisingly, the combination with other commercial stabilizers in an amount exceeding 0.4% by weight (Comparative Examples 6-15) leads to a decrease in the degradation stability of the HIPS composition (see Tables 2.1 and 2.2). 3. Examples of GPPS and extrusion at different extrusion temperatures

[0111] According to the components shown in Table 3.1, commercial general purpose polystyrene (GPPS) (polystyrene 168N, INEOSStyrolution) was compounded with different stabilizers. The following materials were used: Non-impact modified polystyrene component A-2 A-2: General purpose polystyrene GPPS (polystyrene 168N, INEOS Styrolution) Sterically hindered phenolic antioxidant B-1: B-1.1: Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate ( 1076, CAS No.: 2082-79-3) Table 3.1: Prepared GPPS compositions Composition P (component unit % weight percentage) Example 3 Comparative Example 16 A-2 99.7 100 B-1.1 0.3 ---

[0112] The compositions according to Example 3 and Comparative Example 16 were extruded 5 times at extrusion temperatures of 220° C. and 260° C., respectively. After 5 extrusions, the styrene monomer level, melt volume flow rate and viscosity number of the extruded compositions were measured. The test data are summarized in Table 3.2. Table 3.2: Styrene levels after extrusion at 220°C and 260°C

[0113] The data obtained from Example 3 and Comparative Example 16 show that 0.3% by weight of sterically hindered phenolic antioxidant can stabilize GPPS well.

[0114] Even at an extrusion temperature of 260° C., the styrene monomer content in the extruded polymer composition was low at 372 ppm after the fifth extrusion. In contrast, the styrene monomer content of GPPS without added stabilizer increased to 721 ppm.

[0115] The melt volume flow rate and viscosity number VN measurements further confirmed that the increase in styrene monomer concentration in the composition is directly related to the degradation of the polystyrene chains.

Claims

1. A method for improving the degradation stability of a polystyrene composition P in a recycling process, characterized in that: The method comprises mixing at least one polystyrene component as component A with 0.01% to less than 0.4% by weight of at least one stabilizer component as component B and optionally at least one additive as component C, based on the total weight of the polystyrene composition P; wherein the at least one polystyrene component A comprises: A-1: at least one impact-modified polystyrene as component A-1; and / or A-2: at least one non-impact-modified polystyrene as component A-2; And, wherein the at least one stabilizer component B comprises at least one component selected from: B-1: at least one sterically hindered phenolic antioxidant as component B-1; B-2: optionally at least one phosphorus-containing co-stabilizer as component B-2; and B-3: Optionally at least one sulfur-containing co-stabilizer as B-3 component.

2. The method for improving the degradation stability of a polystyrene composition P in a recycling process according to claim 1, characterized in that: The method comprises the following steps: a) providing at least one impact-modified polystyrene A-1 and / or at least one non-impact-modified polystyrene A-2 as component A; b) providing as component B at least one sterically hindered phenolic antioxidant B-1, optionally at least one further sterically hindered phenolic antioxidant B-1 different from the first sterically hindered phenolic antioxidant B-1, optionally at least one phosphorus-containing co-stabilizer B-2 and / or optionally at least one sulfur-containing co-stabilizer B-3; c) optionally providing at least one additive as component C; d) mixing component A with 0.01% to less than 0.4% by weight of component B and optionally component C, based on the total weight of the polystyrene composition P, to obtain the polystyrene composition P; e) optionally extruding and cooling the polystyrene composition P obtained.

3. The method for improving the degradation stability of a polystyrene composition P in a recycling process according to claim 1 or 2, characterized in that: The polystyrene composition comprises (or consists of): (i) at least one impact-modified polystyrene A-1 and at least one sterically hindered phenolic antioxidant B-1; or (ii) at least one impact-modified polystyrene A-1 and at least two sterically hindered phenolic antioxidants B-1; or (iii) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1 and at least one phosphorus-containing co-stabilizer B-2; or (iv) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1 and at least one sulfur-containing co-stabilizer B-3; or (v) at least one non-impact modified polystyrene A-2 and at least one sterically hindered phenolic antioxidant B-1.

4. The method for improving the degradation stability of a polystyrene composition P in a recycling process according to any one of claims 1 to 3, characterized in that: The method comprises mixing at least one polystyrene component as component A with 0.02% to 0.3% by weight of at least one stabilizer component as component B and optionally at least one additive as component C, based on the total weight of the polystyrene composition P.

5. The method for improving the degradation stability of a polystyrene composition P in a recycling process according to any one of claims 1 to 4, characterized in that: The method comprises mixing at least one polystyrene component as component A with 0.03% to 0.2% by weight of at least one stabilizer component as component B and optionally at least one additive as component C, based on the total weight of the polystyrene composition P.

6. The method for improving the degradation stability of a polystyrene composition P in a recycling process according to any one of claims 1 to 5, characterized in that: The method comprises mixing at least one polystyrene component as component A with 0.04% to 0.15% by weight of at least one stabilizer component as component B and optionally at least one additive as component C, based on the total weight of the polystyrene composition P.

7. Use of at least one stabilizer component B for improving the degradation stability of a polystyrene composition P in a recycling process, the component being selected from: B-1: at least one sterically hindered phenolic antioxidant as component B-1; B-2: optionally at least one phosphorus-containing co-stabilizer as component B-2; and B-3: optionally at least one sulfur-containing co-stabilizer as component B-3; The polystyrene composition P comprises at least one polystyrene component A, which comprises: A-1: at least one impact-modified polystyrene as component A-1; and / or A-2: at least one non-impact modified polystyrene as component A-2; and Provided that the polystyrene composition P comprises from 0.01% to less than 0.4% by weight of the at least one stabilizer component B, based on the total weight of the polystyrene composition P.

8. The use of the stabilizer component B according to claim 7, characterized in that: The polystyrene composition comprises (or consists of): (i) at least one impact-modified polystyrene A-1 and at least one sterically hindered phenolic antioxidant B-1; or (ii) at least one impact-modified polystyrene A-1 and at least two sterically hindered phenolic antioxidants B-1; or (iii) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1 and at least one phosphorus-containing co-stabilizer B-2; or (iv) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1 and at least one sulfur-containing co-stabilizer B-3; or (v) at least one non-impact modified polystyrene A-2 and at least one sterically hindered phenolic antioxidant B-1.

9. The use of the stabilizer component B according to claim 8, characterized in that: The at least one sterically hindered phenolic antioxidant component B-1 is selected from compounds of the general formula (I): wherein R1 to R5 represent a hydrogen atom or an alkyl group having 1 to 70 carbon atoms, respectively, wherein the hydrocarbon group optionally contains at least one heteroatom selected from O and S, and wherein at least one of the substituents R1 and R5 represents a hydrocarbon group having at least 3 carbon atoms; and R6 represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, wherein the hydrocarbon group forms a 5-6 membered ring structure with at least one carbon atom of the hydrocarbon group of the adjacent substituents R1 and / or R5.

10. Use of the stabilizer component B according to claim 8 or 9, characterized in that: The phosphorus-containing costabilizer B-2 is a phosphite component of the general formula (II): Wherein R1 to R3 each represent an aryl group, which is optionally substituted by a hydrocarbon group having 1 to 20 carbon atoms, preferably 3 to 10 carbon atoms.

11. Use of the stabilizer component B according to any one of claims 8 to 10, characterized in that: The sulfur-containing co-stabilizer B-3 is a carboxylic acid ester of the general formula (III): wherein R1 is independently selected from a hydrocarbon group having 1-30 carbon atoms, preferably a linear hydrocarbon group having 5-20 carbon atoms, optionally containing oxygen atoms, especially oxygen atoms in the form of carboxyl functional groups; R2 is independently selected from a hydrocarbon group having 1-30 carbon atoms, preferably a linear hydrocarbon group having 10-20 carbon atoms; and M independently represents an integer between 1-8, preferably an integer between 2-4, especially 2.

12. A polystyrene composition P for multiple recycling cycles, characterized in that: The polystyrene composition P comprises (or consists of): A: at least one polystyrene component A, comprising: A-1: at least one impact-modified polystyrene as component A-1; and / or A-2: at least one non-impact-modified polystyrene as component A-2; and B: 0.01% to less than 0.4% by weight, preferably 0.02% to 0.3% by weight, typically 0.03% to 0.2% by weight, for example 0.04% to 0.15% by weight, based on the total weight of the polystyrene composition P, of at least one stabilizer component B selected from: B-1: at least one sterically hindered phenolic antioxidant as component B-1; B-2: optionally at least one phosphorus-containing co-stabilizer as component B-2; and B-3: optionally at least one sulfur-containing co-stabilizer as component B-3; and C: optionally at least one additive as component C, The total amount of A, B and C is 100% by weight of the polystyrene composition P.

13. The polystyrene composition P for multiple recycling cycles according to claim 12, characterized in that: The polystyrene composition P comprises (or consists of): (i) at least one impact-modified polystyrene A-1 and at least one sterically hindered phenolic antioxidant B-1; or (ii) at least one impact-modified polystyrene A-1 and at least two sterically hindered phenolic antioxidants B-1; or (iii) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1 and at least one phosphorus-containing co-stabilizer B-2; or (iv) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1 and at least one sulfur-containing co-stabilizer B-3; or (v) at least one non-impact modified polystyrene A-2 and at least one sterically hindered phenolic antioxidant B-1.

14. The polystyrene composition P for multiple recycling cycles according to claim 12 or 13, characterized in that: The polystyrene composition comprises: A: based on the total polystyrene composition P, >89.6% to 99.99% by weight of at least one polystyrene component A; B: 0.01% to <0.4% by weight of at least one stabilizer component B, based on the total polystyrene composition P; and C: 0% to 10% by weight of at least one additive C, based on the total polystyrene composition P; The total amount of A, B and C is 100% by weight of the polystyrene composition P.

15. The polystyrene composition P for multiple recycling cycles according to any one of claims 12 to 14, characterized in that: The polystyrene composition P comprises at least one stabilizer component B, which is a mixture of components B-1, B-2 and / or B-3, comprising: B-1: 0.01% to <0.4% by weight, preferably 0.01% to 0.3% by weight, typically 0.01% to 0.2% by weight, for example 0.04% to 0.15% by weight, of at least one sterically hindered phenolic antioxidant B-1, based on the polymer composition P; B-2: 0% to 0.39% by weight, for example 0% to <0.39% by weight, preferably 0% to 0.29% by weight, typically 0% to 0.19% by weight, for example 0% to 0.14% by weight, of at least one phosphorus-containing co-stabilizer B-2, based on the polymer composition P; and B-3: 0% to 0.39% by weight, for example 0% to <0.39% by weight, preferably 0% to 0.29% by weight, typically 0% to 0.19% by weight, for example 0% to 0.14% by weight, of at least one sulfur-containing co-stabilizer B-3, based on the polymer composition P; (i) The condition is that the total amount of the stabilizer component B is 0.01% to <0.4% by weight, preferably 0.01% to 0.3% by weight, and usually 0.01% to 0.2% by weight, based on the polymer composition P.

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