Regenerated thermally stable polystyrene composition and method for providing excellent thermal stability in mechanical recovery of polystyrene

Abstract

The invention relates to a regenerated thermally stable polystyrene composition P, comprising a regenerated polystyrene composition A, which comprises at least one polystyrene A-1, which is produced by thermally initiated and / or 1, 1-bis (tert-butylperoxy)-3, 3, 5-trimethylcyclohexane-initiated radical polymerization, and at least one sterically hindered phenolic antioxidant as component B. The invention also relates to a method for producing the regenerated polystyrene composition P, comprising a regenerated polystyrene composition A, which comprises at least one polystyrene A-1, which is produced by thermally initiated and / or 1, 1-bis (tert-butylperoxy)-3, 3, 5-trimethylcyclohexane-initiated radical polymerization, and at least one sterically hindered phenolic antioxidant. The invention also relates to a method for providing excellent thermal stability in mechanical recovery of polystyrene. In addition, a regenerated thermally stable polystyrene composition P, a process for preparing the regenerated thermally stable polystyrene composition P and the use of the regenerated thermally stable polystyrene composition P for preparing molded articles are described.

Description

Technical Field

[0001] The present invention relates to a regenerated heat-stable polystyrene composition and a method for providing excellent thermal stability in polystyrene mechanical recycling. In addition, the present invention also relates to a method for preparing the regenerated heat-stable polystyrene composition. Compared with conventional polystyrene (PS) compositions, the regenerated heat-stable polystyrene composition P contains and releases a reduced amount of residual monomers. Background Art

[0002] Products made of or containing plastic 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. Some of the most common polymer types in waste plastic materials derived from recycled items are high impact polystyrene (HIPS), acrylonitrile butadiene styrene copolymer (ABS), polypropylene (PP), and polycarbonate (PC).

[0003] The desired grade of polystyrene composition for low residual monomer content is that monomers, such as styrene, will not be released due to degradation of the polystyrene during processing. Processing of polystyrene compositions generally results in degradation of the polystyrene due to a combination of mechanical stress, thermal decomposition and oxidation. High temperatures significantly promote the generation of styrene monomers. 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. It has been reported that thermally initiated polystyrene is more stable than free radical initiated polystyrene (M. Singh, US Naudi, J. Polym, Sci. Polym. Lett., 17, 121, 1979).

[0004] It is known that so-called "weak links" in the polymer chain play an important role in initiating thermal degradation of polystyrene. It is also known that the initial degradation rate is a function of the initiation mechanism (anion vs. free radical) and, for free radical initiated polystyrene, a function of the specific initiator. Graeme Moad, David H. Solomon and R. Ian Willing (Division of Applied Organic Chemistry, Melbourne, Australia) reported on the properties of initiator derived end groups in polystyrene prepared with benzoyl peroxide as initiator and speculated on the possible role of these end groups in the thermal and photochemical degradation of the polymer (Macromolecules 21, pp. 855-857, 1988).

[0005] Study of the NMR spectra of the degraded polymers showed that after only 10 minutes, all resonances due to secondary benzoate end groups disappeared, while the primary benzoate resonances remained essentially unchanged in both appearance and relative intensity. Thus, end groups formed by monomer head addition, transfer to initiator, or termination of primary free radicals are far less thermally stable than end groups formed by ordinary tail addition.

[0006] However, no information is given on how to replace benzoyl peroxide by initiation methods that result in superior thermal stability. Furthermore, methods for improving the performance of polystyrene compositions for reuse in post-consumer recycled food packaging, with respect to the content of residual monomers, have so far been unclear.

[0007] In order to use the recycled polystyrene composition in, for example, food packaging, it is inevitable to minimize the residual styrene content in the recycled polystyrene composition, since the styrene monomer may be transferred from the packaging material, for example, into the food. The recycled polystyrene composition tends to contain and / or release a greater amount of residual styrene monomer due to repeated thermal and / or mechanical treatments during the recycling process.

[0008] Surprisingly, thermally stable polystyrene compositions P can be obtained if recycled polystyrene produced by free-radical polymerization initiated thermally and / or with 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane is used and further mixed with at least one sterically hindered phenolic antioxidant. Furthermore, it has been found that the processing properties, such as viscosity, can be improved by the present invention. Summary of the invention

[0009] The present invention relates to a recycled heat-stable polystyrene composition P, which comprises (or consists of): A: At least one recycled polystyrene composition as component A, comprising: A-1: at least one polystyrene as component A-1, wherein the polystyrene A-1 is obtained by free radical polymerization initiated thermally and / or by 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane; A-2: Optionally, at least one impact-modified polymer as component A-2 comprises at least one selected from styrene, 1,3-butadiene, isoprene, acrylonitrile, ethylene, C3 to C 12 Polymer particles of monomers of alpha-olefins and combinations thereof; and A-3: optionally at least one additive as component A-3; B: at least one sterically hindered phenolic antioxidant as component B; and C: Optionally, as component C, at least one additive.

[0010] According to the invention, component A-1 can be a polystyrene component which was originally obtained (long ago) by free radical polymerization initiated thermally and / or by 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, used for a period of time in polymer products and then reused in a new process for the preparation of a recycled heat-stable polystyrene composition P.

[0011] Preferably, the recycled heat-stable polystyrene composition P comprises (or consists of): A: 95-99.9% by weight of at least one recycled polystyrene composition as component A, based on the recycled heat-stable polystyrene composition P; B: 0.1% to 1% by weight of at least one sterically hindered phenolic antioxidant as component B, based on the recycled heat-stable polystyrene composition P; and C: Based on the recycled heat-stable polystyrene composition P, 0% to 4% by weight of at least one additive as component C.

[0012] In one embodiment of the present invention, the recycled heat-stable polystyrene composition P preferably comprises (or consists of): A: Based on the recycled heat-stable polystyrene composition P, 97.5% to 99.9% by weight of at least one recycled polystyrene composition as component A, comprising: A-1: at least one polystyrene as component A-1, wherein the polystyrene A-1 is produced by thermally initiated free radical polymerization; A-2: at least one impact-modifying polymer as component A-2, which comprises at least one selected from styrene, 1,3-butadiene, isoprene, acrylonitrile, ethylene, C3 to C 12 Polymer particles of monomers of alpha-olefins and combinations thereof; and A-3: optionally at least one additive as component A-3; B: Based on the recycled heat-stable polystyrene composition P, 0.1% to 0.5% by weight of at least one sterically hindered phenolic antioxidant as component B, 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), and mixtures thereof; and C: Based on the recycled heat-stabilized polystyrene composition P, 0% to 2% by weight of at least one additive as component C.

[0013] For the purposes of the present invention, recycled polystyrene refers to polymers from the polystyrene type, including general-purpose polystyrene (GPPS) and high-impact polystyrene (HIPS), which are usually obtained from waste plastic materials, especially from recycled items, during recycling and separation processes.

[0014] For the purposes of the present invention, "recycled articles" are articles such as packaging materials, in particular food packaging materials, household appliances, machinery, sports equipment, consumer electronics and automobiles.

[0015] In the context of the present invention, recycled polymers (such as recycled polystyrene A) are defined as polymers whose origin comes from polymer products that are recovered and reprocessed at the end of their useful life. The treatment of the obtained recycled polymers can be accomplished by different methods known in the industry, such as R. (2014): “Recycling of waste plastics using advanced electrochemical technology”, in DG Karl J. Thomacei-kozmiensky (ed.), Recycling and Recycling, Volume 7 (pp. 379-400), TK Verlag Karlthomacei-kozmiensky, Neuruppin, Germany.

[0016] The recycled polystyrene A is characterized in that it has been processed into an article (e.g., a molded article) at least once after its production as a primary polymer (virgin polymer). Therefore, the recycled polystyrene A is generally different from the primary polymer (virgin polymer), in particular in that the recycled polymer has undergone at least one separate thermal compounding step, such as an extrusion process or an injection molding process, before being used in the recycled heat-stable polystyrene composition P according to the present invention.

[0017] Thus, unlike the primary polymer (virgin polymer), the recycled polystyrene A typically undergoes at least one thermal compounding step at a temperature above the melting temperature of the recycled polystyrene A, for example in a temperature range of 180°C to 320°C, typically in a temperature range of 200°C to 300°C, for example in a temperature range of 220°C to 280°C, as determined according to ISO 294, and / or is mechanically stressed by mixing, in particular by shear forces, for example in an extruder, such as a single-screw or twin-screw extruder, or in other conventional plasticizing devices, such as a Brabender mixer or a Banbury mixer.

[0018] Furthermore, the recycled polystyrene A may have been subjected to further processing steps in which the recycled polymer was subjected to mechanical stresses at temperatures below the melting temperature range, such as calendering.

[0019] The composition of the recycled heat-stable polystyrene composition P, in particular components A, B and C, are further defined below. Recycled polystyrene composition (component A)

[0020] The polystyrene composition P comprises as component A a recycled polystyrene composition comprising: A-1: at least one polystyrene as component A-1; A-2: optionally at least one impact-modifying polymer as component A-2, and A-3: Optionally, at least one additive may be used as component A-3.

[0021] At least one polystyrene A-1 included in the recycled polystyrene composition A is prepared by free radical polymerization initiated by heat and / or 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane.

[0022] Preferably, the recycled polystyrene composition A is a recycled material obtained from post-consumer items, preferably selected from food packaging, office supplies, cosmetic packaging, automotive equipment, household appliances and electrical equipment.

[0023] In a preferred embodiment, the recycled polystyrene composition A comprises (or consists of): A-1: at least one polystyrene A-1; A-2: at least one impact-modified polymer A-2, comprising at least one selected from styrene, 1,3-butadiene, isoprene, acrylonitrile, ethylene, C3 to C 12 Polymer particles of monomers of alpha-olefins and combinations thereof; and A-3: Optionally, at least one additive may be used as component A-3.

[0024] In one embodiment of the present invention, polystyrene A-1 is prepared by a thermally initiated free radical polymerization process.

[0025] In one embodiment of the present invention, polystyrene A-1 is prepared by a free radical polymerization process initiated by 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane.

[0026] In one embodiment of the present invention, polystyrene A-1 is prepared by a thermally initiated free radical polymerization process, and is initiated by 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane.

[0027] 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.

[0028] According to a preferred embodiment, based on polystyrene A-1, polystyrene A-1 contains at least 30% by weight, more preferably at least 60% by weight, 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 styrene A-1, polystyrene A-1 contains at least 30% by weight, more preferably at least 60% by weight, particularly preferably at least 85% by weight of styrene.

[0029] According to one embodiment, the recycled polystyrene composition A can be selected from ordinary polystyrene (also known as general purpose polystyrene GPPS). In this embodiment, polystyrene A-1 is selected from ordinary polystyrene, and there is no impact-modified polymer A-2. Optionally, the recycled polystyrene composition A can include at least one additive as component A-3.

[0030] Suitable ordinary polystyrene or general purpose polystyrene (GPPS) is prepared by a free radical polymerization process of styrene or the above-mentioned styrene derivatives, initiated by heat and / or 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane. Preferably, GPPS is prepared by polymerization of styrene or a mixture of styrene and any other copolymerizable monomers mentioned above. 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 heterogeneity of the polymer may be affected by the polymerization process, but the heterogeneity of the polymer is not important in the present invention.

[0031] According to an alternative embodiment, the recycled polystyrene composition A can be selected from high impact polystyrene (also called HIPS). In this embodiment, polystyrene A-1 can be selected from ordinary polystyrene, and at least one impact-modified polymer A-2 is present. Optionally, the recycled polystyrene composition A can contain at least one additive as component A-3. In one embodiment, the recycled polystyrene composition A consists of 100% by weight of HIPS, based on the recycled polystyrene composition A.

[0032] According to another embodiment, the recycled polystyrene composition A may include a mixture of high impact polystyrene (HIPS) and general purpose polystyrene (GPPS).

[0033] In a preferred embodiment, the recycled polystyrene composition A is selected from high impact polystyrene (HIPS). The preparation, structure and properties of said polystyrene are generally described in detail in the literature, for example Echte, Haaf, Hambrecht in Angew. Chem. (Int. Ed. Engl.) Vol. 20, pp. 344-361, 1981; and in Kunststoffhandbuch, edited by Vieweg and Daumiller, Vol. 4 "Polystyrol", Carl-Hanser-Verlag, Munich, 1996.

[0034] As used herein, the term "high impact polystyrene" or "HIPS" refers to a rubber-modified polystyrene comprising polystyrene A-1 as a matrix material and at least one impact-modified polymer A-2 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 bonded with polystyrene to form a graft copolymer, which helps to incorporate the impact-modified polymer A-2 into the final resin composition. According to the present invention, polymerization is carried out by a free radical polymerization method of styrene or the above-mentioned styrene derivatives in the presence of at least one impact-modified polymer A-2, initiated by heat and / or 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane.

[0035] As used herein, the term "elastomeric material" refers to a material that deforms when stress is applied and returns to its original configuration when the stress is removed.

[0036] Typically, the elastomeric material that can be used to make high impact polystyrene (HIPS) is one or more impact-modified polymers A-2, which contain styrene, 1,3-butadiene, isoprene, acrylonitrile, ethylene, C3 to C 12 Monomer residues of alpha olefins and combinations thereof.

[0037] 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.

[0038] In some embodiments of the present invention, the impact-modified polymer A-2 may be a rubber polymer containing an ethylenically unsaturated structure. In some cases, the impact-modified polymer A-2 may be one or more C 4-6 Copolymers or homopolymers of conjugated dienes (such as polybutadiene).

[0039] In some specific embodiments, the polystyrene composition A is selected from high impact polystyrene, which comprises polystyrene A-1 and at least one impact-modifying polymer A-2 selected from butadiene rubber (BR) and styrene-butadiene rubber (SBR).

[0040] Butadiene rubber is especially medium-high cis polybutadiene. Typically, high cis polybutadiene contains not less than 90% by weight, and in some cases more than 93% by weight of monomer units of cis configuration based on polybutadiene. In many cases, the cis content of medium cis polybutadiene is about 30%-50% by weight, and in some cases, about 35%-45% by weight based on polybutadiene.

[0041] 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); SE PB 5800-Schkopau available from Trinseo LLC (Berwyn, Pennsylvania, USA); and PTFE 500 available from Lion Elastomers LLC (Orange, Texas, USA). 55AC15 and KBR 710S available from Kumho Petrochemical Co. (Seoul, Korea).

[0042] Furthermore, the impact-modifying polymer A-2 may 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.

[0043] Furthermore, instead of butadiene rubber, other diene rubbers may be used, ethylene propylene diene copolymer (EPDM rubber) type elastomers may be used, and hydrogenated diene rubbers may be used as the impact-modifying polymer A-2.

[0044] Recycled polystyrene A can be obtained by recycling polystyrene previously prepared by polymerizing one or more styrene monomers selected from styrene, p-methylstyrene, tert-butylstyrene, dimethylstyrene, their nuclear brominated or chlorinated derivatives and combinations thereof, optionally in the presence of impact-modified polymer A-2, provided that: (i) The polymerization reaction is thermally initiated; (ii) the polymerization reaction is initiated by free radicals using 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane as initiator; or (iii) The polymerization reaction was initiated thermally and by free radicals using 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane as initiator.

[0045] Thermal initiation can be achieved by subjecting a reaction mixture containing one or more of the above-mentioned styrene monomers (selected from styrene, p-methylstyrene, tert-butylstyrene, dimethylstyrene, their core brominated or chlorinated derivatives and combinations thereof), optionally in the presence of the impact-modified polymer A-2, to high temperature induction, for example, a temperature of 100° C. to 180° C., preferably 110° C. to 150° C. At this temperature, the polymerization reaction is initiated without the addition of an initiator.

[0046] If 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane is used as the initiator, the amount of the initiator used is preferably 50 ppm to 500 ppm, more preferably 100 ppm to 250 ppm, based on the total reaction mixture.

[0047] For example, the preparation methods are disclosed in US2011 / 0054123, US 5543461 (see column 5, lines 3-42), US 5861455 (see column 3, line 42 to column 4, line 17), and US 6613837 (see column 3, line 55 to column 4, line 23), the relevant parts of which are incorporated herein by reference.

[0048] In one embodiment, the recycled polystyrene composition A is a high impact polystyrene, which comprises 80%-99%, preferably 85%-98% by weight of a styrene matrix (polystyrene A-1), preferably polystyrene, and 1%-20%, preferably 2%-15% by weight of at least one impact-modifying polymer A-2, preferably polybutadiene and / or a styrene-butadiene copolymer.

[0049] The impact-modified polymer A-2, if present, is typically in the form of particles, typically having an average particle size (measured by conventional methods) of at least about 0.25 μm, in some cases at least about 0.5 μm, and in other cases at least about 1 μm. Preferably, the average particle size (based on volume) of the impact-modified polymer A-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-2 particles can be between 1 μm and 10 μm, for example 2, 4 or 7 μm. The average particle size of the impact-modified polymer A-2 particles can be any value or range between any of the above values.

[0050] The particle size of the impact-modified polymer A-2 is usually measured by analyzing the spectrum obtained by light scattering of a solution of the particles in a polystyrene solvent such as methyl ethyl ketone or ethyl acetate. Suitable instruments for this measurement include Horiba's Model LA-960V2 or Beckman Coulter's LS13 320.

[0051] Generally, the weight average molecular weight (M) of polystyrene A-1 is w ) ranges from 50,000 to 500,000 g / mol, preferably from 120,000 to 250,000 g / mol, and more preferably from 130,000 to 240,000 g / mol. Specifically, the weight average molecular weight (M w ) is in the range of 170,000-250,000 g / mol, preferably 180,000-207,000 g / mol, and more preferably about 190,000 g / mol. Specifically, the weight average molecular weight (M) of polystyrene A-1 is w ) ranges from 120,000 to 240,000 g / mol, preferably from 132,000 to 207,000 g / mol, and more preferably about 165,000 g / mol. Molecular weight values ​​are typically determined using gel permeation chromatography (GPC) using appropriate polystyrene standards. Unless otherwise indicated, molecular weight values ​​shown herein are weight average molecular weight (M w ).

[0052] Typically, the recycled polystyrene composition A may comprise (or consist of) GPPS or HIPS, the viscosity number VN of which (measured according to DIN 53726) is in the range of 50-100 ml / g, preferably 60-80 ml / g.

[0053] Specifically, GPPS and / or HIPS that already contains one or more additives A-3 (usually unknown because the source of the recycled items is usually unknown), such as mineral oil (such as medical white oil), lubricant (such as metal stearate), stabilizer, antistatic agent, flame retardant or wax can be used as the recycled polystyrene composition A. Phenolic antioxidant (component B)

[0054] According to the present invention, the polystyrene composition P comprises at least one sterically hindered phenolic antioxidant B. The phenolic antioxidant component B is preferably selected from the group consisting of sterically hindered phenolic antioxidants of the general formula (I) 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.

[0055] 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.

[0056] In one embodiment, at least one of the substituents R2, R3 and R4 represents a hydrogen atom.

[0057] In one embodiment, at least one of the substituents R2, R3 and R4 represents a hydrocarbon group having at least 1 carbon atom.

[0058] 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 hydrogen atoms; and one of the substituents R2, R3 and R4 represents a hydrocarbon group having at least 1 carbon atom.

[0059] In one embodiment, the at least one sterically hindered phenolic antioxidant B is selected from compounds of formula (Ia): 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, wherein at least one of the substituents of R2, R3 and R4 is not hydrogen.

[0060] In one embodiment of the present invention, the 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.

[0061] 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.

[0062] In one embodiment of the present invention, component B includes (or consists of) 2,6-di-tert-butyl-p-cresol (CAS No. 87-97-8), a hindered phenolic antioxidant of the following formula (Ib):

[0063] In one embodiment of the present invention, component B includes (or consists of) 2-(1,1-dimethylethyl)-6-[(3-(1,1-dimethylethyl)-2-hydroxy-5-methylphenyl]methyl-4-tolyl acrylate (CAS No.: 61167-58-6), a hindered phenol antioxidant of the following formula (Ic):

[0064] 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), a hindered phenolic antioxidant of the following formula (Id):

[0065] In one embodiment of the present invention, component B comprises a mixture of hindered phenolic antioxidants of formula (Ib), (Ic) and / or (Id).

[0066] Preferably, the thermal stability of the polystyrene composition P is improved by mixing the recycled polystyrene composition A with 0.01% to 5% by weight, more preferably 0.1% to 2% by weight, typically 0.1% to 1% by weight, based on the total recycled thermally stable polystyrene composition P, of at least one sterically hindered phenolic antioxidant B. Additives (Component C)

[0067] The recycled heat stable polystyrene composition P may comprise up to 10% by weight, preferably up to 5% by weight, of one or more further additives C different from component B, based on the total recycled heat stable polystyrene composition P.

[0068] Preferably, the recycled heat-stable polystyrene composition P may contain 0.01%-10%, preferably 0.1%-5%, more preferably 0.1%-2.5% by weight of one or more additives C, based on the total recycled heat-stable polystyrene composition P. Additive C may be mixed with the polystyrene composition A and the sterically hindered phenolic antioxidant B during the preparation of the recycled heat-stable polystyrene composition P.

[0069] However, typically the recycled polystyrene composition A contains a large amount of additive A-3, which may be the same as additive C. In this case, no further addition of additive C is required, or only the amount of additive C needs to be reduced, respectively. Thus, the recycled heat-stable polystyrene composition P may contain the well-known additive A-3 derived from the recycled polystyrene composition A, but it is not included in the amount stated for additive C.

[0070] The additional additive C is usually selected from known additives for polystyrene and its copolymers and compositions. Substances that can be used as additives or auxiliary agents are polymer additives well known to those skilled in the art and are described in the prior art (e.g., Plastics Additives Handbook, edited by Schiller et al., 6th edition, 2009, Hanser Publishers). 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).

[0071] The recycled heat-stable polystyrene composition P may contain as component C 0.01% to 5% by weight of common additives such as processing aids, stabilizers, oxidation inhibitors, UV absorbers, lubricants, flame retardants, colorants, pigments and plasticizers.

[0072] Examples of oxidation inhibitors and heat stabilizers are sterically hindered phenols, various substitutes of these groups and mixtures thereof may be present in concentrations up to 1% by weight, based on the total regenerated heat-stabilized polystyrene composition P.

[0073] The amount of UV stabilizer used is usually up to 2% by weight, based on the total recycled heat-stabilized polystyrene composition P, which is different from various substituted resorcinols, salicylates, benzotriazoles and benzophenones of component B. In addition, auxiliary stabilizers such as tris (2,4-di-tert-butylphenyl) phosphite (CAS No.: 31570-04-4, From BASF SE, Germany). The auxiliary stabilizer is commercially available. Based on the total polystyrene composition P, the amount of the above stabilizer is preferably 0.01% to 0.5%, more preferably 0.1% to 0.3% by weight.

[0074] An example of a processing aid is a homogeneously miscible oil or oil mixture, in particular selected from mineral oil (medical grade mineral oil), natural plant oil (also known as vegetable oil) and silicone oil, which is used in an amount of 0.1% to 5% by weight, preferably 0.5% to 4% by weight, based on the recycled heat-stable polystyrene composition P. Specifically, medical grade mineral oil (e.g. DAB 70) can be used as additive C, and its amount is 1% to 4% by weight based on the recycled heat-stable polystyrene composition P.

[0075] 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.

[0076] In one embodiment of the present invention, the regenerated heat-stable polystyrene composition P may include as additive C 4,4'-(1,6-hexamethylenebis(formylamino))bis(2,2,6,6-tetramethyl-1-oxypiperidinyl), a polymerization inhibitor of the general formula (II-a) (commercially available from BASF) 4040P):

[0077] In one embodiment of the present invention, the regenerated heat-stable polystyrene composition P may include 5,7-bis(1,1-dimethylethyl)-3-[2,3-dimethylphenyl]-2(3H)-benzofuranone (CAS No.: 201815-03-4) as an additive C, an antioxidant of the general formula (II-b) (commercially available from BASF) HP-136):

[0078] In one embodiment of the present invention, the recycled heat-stable polystyrene composition P may include 2,3-dimethyl-2,3-diphenylbutane (CAS No.: 1889-67-4) as an additive C, a flame retardant synergist of the general formula (II-c) (commercially available from AkzoNobel) 30):

[0079] In one embodiment of the present invention, the regenerated heat-stable polystyrene composition P may include N-butyl-5,15-di(2,4,4-trimethylpentane-2-yl)-9,11-dioxo-2-thio-10-nickeltricyclo[10.4.0.0 3,8 ] hexadecyl-1(16),3,5,7,12,14-hexaen-10-amine (N-butyl-5,15-bis(2,4,4-trimethylpentan-2-yl)-9,11-dioxa-2-thia-10-nickelatricyclo[10.4.0.03,8]hex adeca-1(16),3,5,7,12,14-hexaen-10-aminium) (CAS No. 14516-71-3), a light stabilizer of general formula (II-d) (commercially available from BASF N-705):

[0080] In one embodiment of the present invention, the regenerated heat-stable polystyrene composition P may include as additive C a mixture of components of the general formula (IIa), (II-b), (II-c) and / or (II-d).

[0081] Preferably, the amount of components of formula (IIa), (II-b), (II-c) and / or (II-d) is 0% to 2% by weight, more preferably 0% to 1% by weight, based on the total recycled heat-stable polystyrene composition P. Method for providing excellent thermal stability in mechanical recycling of polystyrene compositions

[0082] The present invention also relates to a method for providing excellent thermal stability in the mechanical recycling of polystyrene, wherein the method comprises the following method steps: (i) Regeneration of a polystyrene composition A comprising at least one polystyrene as component A-1 and optionally at least one impact-modifying polymer A-2 as component A-2, wherein the at least one polystyrene A-1 is obtained by free-radical polymerization initiated thermally and / or with 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane; (ii) mixing the recycled polystyrene composition A with at least one sterically hindered phenolic antioxidant as component B and optionally at least one other additive as component C; and (iii) extruding a blend of the obtained recycled polystyrene composition A, at least one sterically hindered phenolic antioxidant B and optionally at least one other additive C.

[0083] The recycling of the polystyrene composition A in process step (i) is preferably achieved by recycling polymer waste obtained from the recycling of post-consumer items, for example selected from food packaging, office supplies, cosmetic packaging, automotive equipment, household appliances and electrical equipment.

[0084] The waste is preferably separated into polymers to reduce the amount of polymers different from component A and optionally washed. Preferably, the separated polymer waste obtained is pretreated, for example by homogenization, grinding, comminution and / or micronization, before introduction into process step (ii) or (iii). Before use in the process according to the invention, the polystyrene composition A is usually subjected to one or more thermal compounding steps, for example an extrusion process or an injection molding process.

[0085] Typically, before use according to the process of the invention, the recycled polystyrene A is subjected to at least one thermal compounding step at a temperature above the melting temperature of the recycled polystyrene A, for example in a temperature range of 180° C. to 320° C., typically in a range of 200° C. to 300° C., for example in a range of 220° C. to 280° C., determined according to ISO 294. Optionally, before use according to the process of the invention, the recycled polystyrene A is subjected to mechanical stress by mixing, in particular by shear forces, for example in an extruder such as a single-screw or twin-screw extruder, or in other conventional plasticizing devices such as a Brabender mixer or a Banbury mixer.

[0086] Method steps (ii) and (iii) can be carried out separately or in combination with each other. Typically, components A and B and optionally component C are melt compounded at a temperature in the range of 180°C to 300°C, preferably 200°C to 280°C. Methods suitable for method steps (ii) and (iii) are known per se. For example, an extruder, such as a co-rotating or counter-rotating single or twin screw extruder, or other conventional kneading equipment, such as a continuous or intermittent kneader, a Brabender mixer or a Banbury mixer, can be used to prepare the recycled heat-stable polystyrene composition P. The kneading elements should ensure that the components are sufficiently uniform to ensure micro-mixing. The recycled heat-stable polystyrene composition P of the present invention can be obtained by mixing and homogenizing the components by conventional methods of plastics technology, wherein the order of adding the components can be changed.

[0087] By measuring and comparing the thermal stability of polystyrene products produced by the process described in the present invention with those produced by conventional polystyrene recycling processes, it is possible to discover features that provide excellent thermal stability in the mechanical recycling of polystyrene. As an example, by measuring the styrene level in the extruded product, it is possible to measure the re-monomerization caused by polymer structural degradation during the extrusion run (at high temperatures).

[0088] The present invention also relates to a process for providing a regenerated thermally stable polystyrene composition P, which process comprises process steps (i) to (iii).

[0089] The components used in the process according to the invention, in particular components A, B and C and their preferred embodiments, are as described above. Method for preparing a regenerated heat-stable polystyrene composition P

[0090] Furthermore, the present invention also relates to a method for preparing the regenerative heat-stable polystyrene composition P of the present invention. In particular, the present invention relates to a method for preparing the regenerative heat-stable polystyrene composition P described herein, wherein components A and B and optionally component C are melt compounded at a temperature in the range of 180°C to 300°C, preferably 200°C to 280°C.

[0091] The regenerated heat-stable polystyrene composition P can be prepared by methods known per se. For example, an extruder, such as a co-rotating or counter-rotating single or twin screw extruder, or other conventional kneading equipment, such as a continuous or intermittent kneader, a Brabender mixer or a Banbury mixer, can be used to prepare the regenerated heat-stable polystyrene composition P. The kneading element should ensure that the components are sufficiently homogeneous to ensure micromixing. The regenerated heat-stable polystyrene composition P of the present invention can be obtained by mixing and homogenizing the components by conventional methods of plastics technology, wherein the order of adding the components can be changed.

[0092] Preferably, before melt compounding with component B, the polystyrene composition A may be pretreated, for example, by homogenization, grinding, pulverization and / or micronization. Use of recycled heat-stable polystyrene composition P

[0093] In addition, the present invention also relates to the use of the recycled heat-stable polystyrene composition P of the present invention as described herein for preparing molded articles (molded articles) for various applications, such as applications in the automotive field, electronics, household goods, construction, health care products, packaging, sports and leisure products. The recycled heat-stable polystyrene composition P of the present invention can be used to produce any type of molded articles. These molded articles can be produced by injection molding, extrusion and blow molding processes. Another processing method is to produce molded articles by thermoforming the previously produced sheet or film, as well as a film coating molding process. Specifically, the recycled heat-stable polystyrene composition P of the present invention is used to form molded articles in an extrusion process. Examples of these molded articles include films, profiles, and any type of housing parts. Specifically, the recycled heat-stable polystyrene composition P is used to manufacture extruded sheets in an extrusion process.

[0094] The recycled heat-stable polystyrene composition P can be used alone as such or in combination with virgin materials (eg, virgin polystyrene compositions).

[0095] For example, in one embodiment of the present invention, the recycled heat-stable polystyrene composition P can be used in a polymer blend P*, which comprises 1%-99% by weight, preferably 2%-70% by weight, and typically 5%-50% by weight of the recycled heat-stable polystyrene composition P according to the present invention, based on the total weight of the polymer blend P*, and 1%-99% by weight, preferably 30%-98% by weight, and typically 50%-95% by weight of a virgin polymer composition containing polystyrene, high impact polystyrene and a mixture thereof, based on the total weight of the polymer blend P*.

[0096] Furthermore, in an alternative embodiment, the recycled heat-stable polystyrene composition P can be used to construct a layered structure S comprising at least two layers, preferably at least three layers, wherein at least one layer is composed of the recycled heat-stable polystyrene composition P according to the present invention, and at least one layer is composed of a polymer composition P' different from the recycled polymer composition P. In a preferred embodiment of the present invention, the layered structure is a three-layer extruded structure S with a layer sequence of P'-P-P', i.e., a three-layer structure S, wherein the recycled heat-stable polystyrene composition P constitutes a central layer, the central layer covers two extended surfaces, and at least one of the extended surfaces is composed of a polymer composition P' different from the recycled polymer composition P according to the present invention. Typically, the polymer composition P' is a virgin polymer composition P' comprising polystyrene, high impact polystyrene or a mixture thereof. Molded articles made from recycled heat-stabilized polystyrene composition P

[0097] In addition, the present invention also relates to molded articles made from the recycled heat-stable polystyrene composition P of the present invention as described herein. The molded articles can be selected from, for example, any type of molded articles described herein. Specifically, the molded articles can be, for example, packaging materials, especially packaging materials for food packaging, packaging materials for cosmetics, packaging materials for medicines, housings for electrical equipment, housings and coverings for medical equipment, children's toys, sheet wall components, insulated transport containers, molded articles for sanitary and bathing equipment.

[0098] According to the present invention, in addition to such a recycled heat-stable polystyrene composition P, the molded article may also contain a polymer blend P*, which contains 1% to 99% by weight, preferably 2% to 70% by weight, typically 5% to 50% by weight of the recycled heat-stable polystyrene composition P according to the present invention, based on the total weight of the polymer blend P*, and 1% to 99% by weight, preferably 30% to 98% by weight, typically 50% to 95% by weight of a virgin polymer composition containing polystyrene, high impact polystyrene and mixtures thereof, based on the total weight of the polymer blend P*.

[0099] Furthermore, in an alternative embodiment, the molded article may be a layered structure S comprising at least two layers, preferably at least three layers, wherein at least one layer is composed of the recycled heat-stable polystyrene composition P according to the present invention, and at least one layer is composed of a polymer composition P' different from the recycled heat-stable polystyrene composition P. In a preferred embodiment of the present invention, the layered structure is a three-layer extruded structure S having a P'-P-P' layer sequence, i.e., a three-layer structure S, wherein the recycled heat-stable polystyrene composition P constitutes a central layer, the central layer covers two extended surfaces, and at least one of the extended surfaces is composed of a polymer composition P' different from the recycled polymer composition P according to the present invention.

[0100] Typically, the polymer composition P' is a virgin polymer composition P' comprising polystyrene, high impact polystyrene or a mixture thereof.

[0101] The present invention is further illustrated by the following examples and claims. DETAILED DESCRIPTION Example 1. Effect of initiation method on thermal stability of polystyrene compositions

[0102] High impact modified polystyrene (HIPS) is produced in a standard 2-vessel 2-tower polymerization cascade, where the first vessel is a prepolymerization vessel, to which polybutadiene rubber solution and styrene are added. The second vessel is the vessel where the final HIPS morphology phase transition occurs. The HIPS obtained contains polybutadiene rubber particles with an average diameter of 2 μm in a polystyrene matrix and a total polybutadiene content of 8% by weight.

[0103] Aggregation is triggered by different mechanisms: Example 1: Thermal initiation at a temperature of about 110°C - 140°C. Example 2: Free radical initiation using 180 ppm of 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane (CAS No.: 6731-36-8) as an initiator. Example 3 (Comparative Example): Free radical initiation using 180 ppm of benzoic peroxyanhydride (CAS No.: 94-36-0) as an initiator.

[0104] The HIPS obtained according to Examples 1-3 was further mixed with 600 ppm zinc stearate and 400 ppm octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (CAS No.: 2082-79-3, 1076, from BASF) mixed.

[0105] The regeneration of styrene monomer was then investigated by multiple extrusions at high temperature using a high shear screw. The harsh conditions allowed a good differentiation between the samples. The extrusion tests were carried out at high temperature and under shear, which promotes re-monomerization. This treatment simulates the conditions in the (re)cycling process of polymer waste. The following conditions were used: Extruder: Coperion ZSK 30 Temperature: 260℃ Speed: 200[1 / min] Production capacity 10kg / h No degassing

[0106] In order to determine the degradation of the polymer structure during the extrusion process, the viscosity number VN of each composition was determined before the first extrusion and after each extrusion. The viscosity number VN was determined in accordance with DIN 53726. Table 1

[0107] The experimental data in Table 1 show that in all HIPS polymer compositions, the viscosity number VN of the corresponding polymer composition solution at 0.5% by weight is reduced after several extrusions. However, compared with the free radical initiated HIPS product, the thermally initiated HIPS product of Example 1 is more stable. Among the free radical initiated HIPS products, the HIPS product of Example 2 initiated by 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane is advantageous from the perspective of thermal stability. 2. Effect of phenolic antioxidant B on thermal stability of polystyrene compositions

[0108] The polystyrene compositions shown in Table 2 were prepared using the following components: A: high impact polystyrene (HIPS), containing 8% by weight of polybutadiene, 89% by weight of styrene and 3% by weight of medical white oil (DAB 70). 180 ppm (based on the total weight of the reaction mixture) of 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane (CAS No.: 6731-36-8) was used as an initiator to initiate polymerization. Component A also includes 600 ppm of zinc stearate (i.e., 0.06% by weight based on the total weight of HIPS and medical white oil); B-1: Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (CAS No.: 2082-79-3, 1076, from BASF); B-2: 2,6-di-tert-butyl-p-cresol (CAS No.: 87-97-8, TBK).

[0109] The compositions according to Table 2 were produced using an extruder at an extrusion temperature of 260°C. Table 2: Compositions of Examples 4-6

[0110] The compositions described in Examples 4, 5 and 6 were repeatedly extruded. This treatment simulates the conditions in the (re)cycling process of polymer waste. The following conditions were used: Extruder: Coperion ZSK 30 Temperature: 260℃ Speed: 200[1 / min] Production capacity: 10kg / h No degassing

[0111] To determine the re-monomerization due to polymer structure degradation during the extrusion process, the styrene level of each composition was measured before the first extrusion and after the first, third and fifth extrusions. The styrene level was determined by capillary gas chromatography using the headspace technique and a calibration curve based on styrene. Table 3: Multiple extrusions of recycled HIPS; styrene levels (in ppm) Number of squeezes Example 4 (Comparative Example) Example 5 Example 6 0 170 160 150 1 230 230 230 3 280 270 280 5 300 290 290

[0112] The data in Table 3 show that the addition of the hindered phenolic antioxidant B according to the present invention reduces the formation and release of monomeric styrene during repeated extrusion.

[0113] Therefore, the recycled thermally stable polystyrene compositions and methods described herein can produce better quality polystyrene compositions and products, which can be used, for example, in food packaging. The method also has ecological advantages.

Claims

1. A recycled heat-stable polystyrene composition P, comprising: A: At least one recycled polystyrene composition as component A, comprising: A-1: at least one polystyrene as component A-1, wherein the polystyrene is obtained by free radical polymerization initiated thermally and / or by 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane; A-2: Optionally, at least one impact-modified polymer as component A-2 comprises at least one selected from styrene, 1,3-butadiene, isoprene, acrylonitrile, ethylene, C3-C 12 Polymer particles of monomers of alpha-olefins and combinations thereof; and A-3: optionally at least one additive as component A-3; B: at least one sterically hindered phenolic antioxidant as component B; and C: Optionally, as component C, at least one additive.

2. The regenerated heat-stable polystyrene composition P according to claim 1, characterized in that: Include: A: 95-99.9% by weight of at least one recycled polystyrene composition as component A, based on the recycled heat-stable polystyrene composition P; B: 0.1% to 1% by weight of at least one sterically hindered phenolic antioxidant as component B, based on the regenerated heat-stable polystyrene composition P; C: Based on the regenerated heat-stable polystyrene composition P, 0% to 4% by weight of at least one additive as component C.

3. The regenerated heat-stable polystyrene composition P according to claim 1 or 2, characterized in that: Based on the regenerated heat-stable polystyrene composition P, 0.1% to 0.5% by weight of at least one sterically hindered phenolic antioxidant selected from the compounds of the general formula (I) is contained as component B: 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.

4. The regenerated heat-stable polystyrene composition P according to any one of claims 1 to 3, characterized in that: Include: A: Based on the recycled heat-stable polystyrene composition P, 97.5% to 99.9% by weight of at least one recycled polystyrene composition as component A, comprising: A-1: at least one polystyrene as component A-1, wherein the polystyrene A-1 is prepared by thermally initiated free radical polymerization: A-2: At least one impact-modified polymer as component A-2, which comprises at least one selected from styrene, 1,3-butadiene, isoprene, acrylonitrile, ethylene, C3-C 12 Polymer particles of monomers of alpha-olefins and combinations thereof; and A-3: optionally at least one additive as component A-3; B: Based on the regenerated heat-stable polystyrene composition P, 0.1% to 0.5% by weight of at least one sterically hindered phenolic antioxidant as component B, selected from octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (CAS No.: 2082-79-3), 2,6-di-tert-butyl-p-cresol (CAS No. 87-97-8), and mixtures thereof; and C: Based on the recycled heat-stable polystyrene composition P, 0% to 2% by weight of at least one additive as component C.

5. A method for providing excellent thermal stability in the mechanical recycling of polystyrene and a method for providing a regenerated thermally stable polystyrene composition P, characterized in that The method comprises the following method steps: (i) regeneration of a polystyrene composition A comprising as component A-1 at least one polystyrene obtained by free-radical polymerization initiated thermally and / or with 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane; (ii) mixing the recycled polystyrene composition A with at least one sterically hindered phenolic antioxidant as component B and optionally at least one other additive as component C; and (iii) extruding the mixture of the obtained recycled polystyrene composition A, at least one sterically hindered phenolic antioxidant B and optionally at least one other additive C.

6. The method according to claim 5, characterized in that The polystyrene composition A comprises: A-1: at least one polystyrene as component A-1; A-2: optionally at least one impact-modifying polymer as component A-2, comprising polymer particles derived from at least one monomer selected from styrene, 1,3-butadiene, isoprene, acrylonitrile, ethylene, C3-C12 α-olefins, and combinations thereof; and A-3: Optionally, at least one additive may be used as component A-3.

7. The method according to claim 5 or 6, characterized in that: The at least one polystyrene A-1 is obtained by a thermally initiated free-radical polymerization process.

8. The method according to claim 5 or 6, characterized in that: The at least one polystyrene A-1 is obtained by a free radical polymerization process initiated by 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane.

9. The method according to any one of claims 5 to 8, characterized in that: The at least one sterically hindered phenolic antioxidant B is selected from compounds of general formula (I): 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.

10. The method according to any one of claims 5 to 9, characterized in that: The 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), 2,6-di-tert-butyl-p-cresol (CAS No. 87-97-8), 2-(1,1-dimethylethyl)-6-[(3-(1,1-dimethylethyl)-2-hydroxy-5-methylphenyl]methyl-4-tolyl acrylate (CAS No.: 61167-58-6), and mixtures thereof.

11. Use of the recycled heat-stable polystyrene composition P according to any one of claims 1 to 4 as a material for molded articles in an extrusion process.

12. Use of the recycled heat-stable polystyrene composition P obtained according to the process according to any one of claims 5 to 10 as a material for molded articles in an extrusion process.

13. Use according to claim 11 or 12 as material for mouldings in an extrusion process for the production of extruded sheets.

14. A method for preparing the regenerated heat-stable polystyrene composition P according to any one of claims 1 to 4, characterized in that: Components A and B and optionally component C are melt compounded at a temperature in the range of 180°C to 280°C.

15. A molded article made from the recycled heat-stable polystyrene composition P according to any one of claims 1 to 4.

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