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US-20260125494-A1 - METHOD FOR IMPROVING THE DEGRADATION STABILITY OF POLYSTYRENE COMPOSITIONS IN RECYCLING PROCESSES

US20260125494A1US 20260125494 A1US20260125494 A1US 20260125494A1US-20260125494-A1

Abstract

The invention relates to a method for improving the degradation stability of a polystyrene composition in recycling processes. The invention also relates to the use of less than 0.4 wt.-% of stabilizer components for improving the degradation stability of polystyrene compositions in recycling processes and to polystyrene compositions with improved degradation stability.

Inventors

  • Norbert Niessner
  • Frank Eisentraeger

Assignees

  • INEOS STYROLUTION GROUP GMBH

Dates

Publication Date
20260507
Application Date
20230717
Priority Date
20220718

Claims (20)

  1. 1 - 15 . (canceled)
  2. 16 . A method for improving the degradation stability of a polystyrene composition P in recycling processes including repeated extrusion steps at elevated temperatures, wherein the method comprises: admixing at least one polystyrene component A with 0.01 to less than 0.4 wt.-%, based on the total weight of the polystyrene composition P, of at least one stabilizer component B and optionally at least one additive component C, wherein the at least one polystyrene component A comprises: A-1: at least one impact-modified polystyrene A-1; and A-2: optionally at least one non-impact modified polystyrene A-2, and wherein the at least one stabilizer component B comprises at least one component selected from the group consisting of: B-1: at least one sterically hindered phenolic antioxidant B-1; B-2: optionally at least one phosphor-containing co-stabilizer B-2; and B-3: optionally at least one sulfur-containing co-stabilizer B-3.
  3. 17 . The method of claim 16 , wherein the method further comprises: a) providing the at least one impact-modified polystyrene A-1 and optionally the at one least non-impact modified polystyrene A-2 as the at least one polystyrene component A; b) providing the at least one sterically hindered phenolic antioxidant B-1, optionally at least one further sterically hindered phenolic antioxidant B-1, optionally the at least one phosphor-containing co-stabilizer B-2, and optionally the at least one sulfur-containing co-stabilizer B-3 as the at least one stabilizer component B, wherein the at least one further sterically hindered phenolic antioxidant B-1 is different from the first at least one sterically hindered phenolic antioxidant B-1; c) optionally providing the at least one additive component C; d) admixing the at least one polystyrene component A with 0.01 to less than 0.4 wt.-%, based on the total weight of the polystyrene composition P, of the at least one stabilizer component B, and optionally the at least one additive component C to obtain the polystyrene composition P; and e) optionally extruding and cooling the obtained polystyrene composition P.
  4. 18 . The method of claim 16 , wherein the polystyrene composition P comprises: (i) at least one impact-modified polystyrene A-1, and at least one sterically hindered phenolic antioxidant B-1; (ii) at least one impact-modified polystyrene A-1, and at least two sterically hindered phenolic antioxidants B-1; (iii) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1, and at least one phosphor-containing co-stabilizer B-2; (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.
  5. 19 . The method of claim 16 , wherein the at least one polystyrene component A is admixed with 0.02 to 0.3 wt.-%, based on the total weight of the polystyrene composition P, of at least one stabilizer component B and optionally at least one additive component C.
  6. 20 . The method of claim 16 , wherein the at least one polystyrene component A is admixed with 0.03 to 0.2 wt.-%, based on the total weight of the polystyrene composition P, of at least one stabilizer component B and optionally at least one additive component C.
  7. 21 . The method of claim 16 , wherein the at least one polystyrene component A is admixed with 0.04 to 0.15 wt.-%, based on the total weight of the polystyrene composition P, of at least one stabilizer component B and optionally at least one additive component C.
  8. 22 . The method of claim 16 , wherein the at least one sterically hindered phenolic antioxidant B-1 is selected from compounds of a general formula (I): wherein R1 to R5 independently represent hydrogen atoms or alkyl groups having 1 to 70 carbon atoms, wherein the alkyl groups optionally comprise at least one hetero atom selected from O and S, wherein at least one of the substituents R1 and R5 represents a hydrocarbon group having at least 3 carbon atoms, wherein R6 independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and wherein the alkyl group of R6 forms a 5- to 6-membered ring structure with at least one of the carbon atoms of the alkyl groups of the adjacent substituents R1 and/or R5.
  9. 23 . The method of claim 16 , wherein the phosphor-containing co-stabilizer B-2 is a phosphite component of a general formula (II): wherein R1 to R3 independently represent aryl groups, which are optionally substituted with hydrocarbon groups having 1 to 20 carbon atoms.
  10. 24 . The method of claim 16 , wherein the sulfur-containing co-stabilizer B-3 is a carboxylic acid ester of the general formula (III): wherein R1 is independently selected from hydrocarbon groups having 1 to 30 carbon atoms and optionally comprising oxygen atoms, wherein R2 is independently selected from hydrocarbon groups having 1 to 30 carbon atoms, and wherein m independently represents an integer from 1 to 8.
  11. 25 . A polystyrene composition P for multiple recycling cycles including repeated extrusion steps at elevated temperatures, wherein the polystyrene composition P comprises: A: at least one polystyrene component A comprising: A-1: at least one impact-modified polystyrene A-1; and A-2: optionally at least one non-impact modified polystyrene A-2; B: 0.01 to less than 0.4 wt.-%, based on the total weight of the polystyrene composition P, of at least one stabilizer component B selected from the group consisting of: B-1: at least one sterically hindered phenolic antioxidant B-1; B-2: optionally at least one phosphor-containing co-stabilizer B-2; and B-3: optionally at least one sulfur-containing co-stabilizer B-3; and C: optionally at least one additive component C, wherein A, B, and C sum up to 100 wt.-% of the polystyrene composition P.
  12. 26 . The polystyrene composition P of claim 25 , wherein the polystyrene composition P comprises: (i) at least one impact-modified polystyrene A-1, and at least one sterically hindered phenolic antioxidant B-1; (ii) at least one impact-modified polystyrene A-1, and at least two sterically hindered phenolic antioxidants B-1; (iii) at least one impact-modified polystyrene A-1, at least one sterically hindered phenolic antioxidant B-1, and at least one phosphor-containing co-stabilizer B-2; (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.
  13. 27 . The polystyrene composition P of claim 25 , wherein the polystyrene composition P comprises: A: >89.6 to 99.99 wt.-%, based on the total weight of the polystyrene composition P, of at least one polystyrene component A; B: 0.01 to <0.4 wt.-%, based on the total weight of the polystyrene composition P, of at least one stabilizer component B; and C: 0 to 10 wt.-%, based on the total weight of the polystyrene composition P, of at least one additive C; wherein A, B, and C sum up to 100 wt.-% of the polystyrene composition P.
  14. 28 . The polystyrene composition P of claim 25 , wherein the at least one stabilizer component B comprises: B-1: 0.01 to <0.4 wt.-%, based on the total weight of the polymer composition P, of at least one sterically hindered phenolic antioxidant B-1; B-2: 0 to 0.39 wt.-%, based on the total weight of the polymer composition P, of at least one phosphor-containing co-stabilizer B-2; and B-3: 0 to 0.39 wt.-%, based on the total weight of the polymer composition P, of at least one sulfur-containing co-stabilizer B-3, wherein the total amount of the at least one stabilizer component B sums up to 0.01 to <0.4 wt.-% based on the total weight of the polymer composition P.
  15. 29 . The polystyrene composition P of claim 28 , wherein the at least one stabilizer component B comprises: B-1: 0.01 to 0.3 wt.-%, based on the total weight of the polymer composition P, of the at least one sterically hindered phenolic antioxidant B-1; B-2: 0 to <0.39 wt.-%, based on the total weight of the polymer composition P, of the at least one phosphor-containing co-stabilizer B-2; and B-3: 0 to <0.39 wt.-%, based on the total weight of the polymer composition P, of the at least one sulfur-containing co-stabilizer B-3, wherein the total amount of the at least one stabilizer component B sums up to 0.01 to <0.3 wt.-% based on the total weight of the polymer composition P.
  16. 30 . The polystyrene composition P of claim 28 , wherein the at least one stabilizer component B comprises: B-1: 0.01 to 0.2 wt.-%, based on the total weight of the polymer composition P, of the at least one sterically hindered phenolic antioxidant B-1; B-2: 0 to 0.29 wt.-%, based on the total weight of the polymer composition P, of the at least one phosphor-containing co-stabilizer B-2; and B-3: 0 to 0.29 wt.-%, based on the total weight of the polymer composition P, of the at least one sulfur-containing co-stabilizer B-3, wherein the total amount of the at least one stabilizer component B sums up to 0.01 to <0.2 wt.-% based on the total weight of the polymer composition P.
  17. 31 . The method of claim 23 , wherein R1 to R3 independently represent aryl groups, which are optionally substituted with hydrocarbon groups having 3 to 10 carbon atoms.
  18. 32 . The method of claim 24 , wherein R1 is independently selected from linear hydrocarbon groups having 5 to 20 carbon atoms and optionally comprising carboxyl groups, wherein R2 is independently selected from linear hydrocarbon groups having 10 to 20 carbon atoms, and wherein m independently represents an integer from 2 to 4.
  19. 33 . The polystyrene composition P of claim 25 , wherein the weight percentage of the at least one stabilizer component B is 0.02 to 0.3 wt.-%, based on the total weight of the polystyrene composition P.
  20. 34 . The polystyrene composition P of claim 25 , wherein the weight percentage of the at least one stabilizer component B is 0.03 to 0.2 wt.-%, based on the total weight of the polystyrene composition P.

Description

The present invention relates to a method for improving the degradation stability of a polystyrene (PS) composition in a recycling process. The invention describes the use of stabilizer components for improving the degradation stability of polystyrene compositions in recycling processes and to polystyrene compositions with improved degradation stability. Products made from or incorporating plastic components are part of many work places or home environment. Most of these plastics are virgin polymers that are produced from petroleum. In recent years, there has been a strong movement towards recycling and reuse of petrochemical products, such as plastics, in addition to metallic material. Recycling plastic from waste plastic materials has a variety of benefits compared to producing virgin plastic from petroleum, e.g. less energy is required, the need for disposing waste material is reduced, and the use of limited geological resources, such as petroleum, is reduced. Often, waste plastic materials include post-consumer and post-industrial waste materials and plastic scrap, including polymer types such as general purpose polystyrene (GPPS) and high impact polystyrene (HIPS). Processing of polystyrene compositions, e.g. during recycling processes, often leads to polystyrene degradation due to a combination of mechanical stress, thermolysis and oxidation. Elevated temperatures promote the generation of monomers, e.g. styrene monomers, due to degradation of the polystyrene during processing considerably. The ceiling behavior of commercial polystyrene materials typically leads to residual monomer contents of 400 ppm styrene monomer at 220° C. and 1500 ppm styrene monomer at 260° C. In order to use recycled polystyrene compositions in particular in food packaging, it is inevitable to minimize the residual styrene content in the recycled styrene composition since styrenic monomers can migrate from the packaging material into food. Recycled polystyrene compositions are prone to comprise and/or emit increased amounts of residual styrenic monomers due to the repeated thermal and/or mechanical processing they undergo during the recycling process. The quest for polystyrenes with low residual monomer content, especially after post-consumer recycling, requires grades that do not build up styrene monomers during processing. Processing leads to polystyrene degradation due to a combination of mechanical stress, thermolysis and oxidation (W. Loth “Kinetik und Mechanismus des Abbaus”, H. Gausepohl und R. Gellert Eds. “Polystyrol”, Kunsttoff-Handbuch 4, Hanser Verlag, München 1996). In day-to-day applications, low residual levels are especially important in the food packaging sector. Here, semi-impact HIPS or GPPS/HIPS blends are used. Literature results indicate that a stabilization of HIPS can help reducing residual content as well. Thus, there is a high demand of polystyrene compositions with low residual monomer content and reduced emission of monomers, e.g. styrene, due to degradation of the polystyrene during processing. It was surprisingly found that increased amounts of stabilizer components can lead to an increase in styrene monomer formation during processing of high impact polystyrene. This result was confirmed with a multitude of different stabilizers components. After extensive studies, the inventors of the present invention found a method for improving the degradation stability of polystyrene compositions as described herein. DETAILED DESCRIPTION OF THE INVENTION The invention relates to a method for improving the degradation stability of a polystyrene composition P in recycling processes, wherein the method comprises admixing at least one polystyrene component as component A with 0.01 to less than 0.4 wt.-%, preferably 0.02 to 0.3 wt.-%, often 0.03 to 0.2 wt.-%, for example 0.04 to 0.15 wt.-%, based on the total weight of the polystyrene composition P, of at least one stabilizer component as component B and optionally at least one additive as component C, wherein the at least one polystyrene component A comprises:A-1: at least one impact-modified polystyrene as component A-1; and/orA-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 phosphor-containing co-stabilizer as component B-2; andB-3: optionally at least one sulfur-containing co-stabilizer as component B-3. 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 antioxidants 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 phosphorous-con