1. A method of processing a polystyrene comprising: performing a first extrusion (102) of a first polystyrene and a maleic anhydride in presence of a free radical initiator at a temperature in a range of 200 to 240 °C to form a maleated polystyrene, wherein the first polystyrene and the maleic anhydride are present in a weight ratio of 9:1 to 49:1; and performing a second extrusion (104) of the maleated polystyrene and a dynamic crosslinker in presence of a Lewis acid catalyst at a temperature in a range of 200 to 240 °C to form a polystyrene product comprising a polystyrene vitrimer, wherein the dynamic crosslinker comprises a polyol that reacts with the maleated polystyrene to form the polystyrene vitrimer comprising ester linkages configured to undergo transesterification.

2. The method as claimed in claim 1, wherein performing the second extrusion (104) comprises extruding in presence of a second polystyrene, wherein the polystyrene product comprises a blend of the second polystyrene and the polystyrene vitrimer.

3. The method as claimed in claim 1, wherein the first polystyrene is a virgin polystyrene or a recycled polystyrene, and wherein the first polystyrene is selected from a group of general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), and any combinations thereof.

4. The method as claimed in claim 2, wherein the second polystyrene is a virgin polystyrene or a recycled polystyrene, and wherein the second polystyrene is selected from a group of general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), expandable polystyrene (EPS), styrene-butadiene rubber (SBR), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-ethylene/butylene-styrene (SEBS), and any combinations thereof.

5. The method as claimed in claim 1, wherein the polyol is selected from a group of aliphatic diols, aromatic diols, aliphatic triols, aliphatic tetrols, polyether polyols, and any combinations thereof.

6. The method as claimed in claim 5, wherein the polyol comprises ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, cyclohexanedimethanol, glycerol, trimethylolpropane, pentaerythritol, sorbitol, polyethylene glycol, polypropylene glycol, polyglycerols, or a combination thereof.

7. The method as claimed in 2, wherein a concentration of the second polystyrene is varied to modify a property of the polystyrene product, wherein the property comprises one or more of a mechanical property, a thermal property, a tensile strength, or an elongation at yield.

8. The method as claimed in 2, wherein the maleated polystyrene and the second polystyrene are extruded in a weight ratio of 9:1 to 1:1.09.

9. The method as claimed in claim 1, wherein the maleated polystyrene and the dynamic crosslinker are extruded in a weight ratio of 9:1 to 49:1.

10. The method as claimed in claim 1, wherein the first extrusion (102) and the second extrusion (104) are performed in a twin-screw extruder at a screw speed of 80 to 120 rotations per minute (rpm) and at a residence time of 1 to 10 minutes.

11. The method as claimed in claim 1, wherein the free radical initiator comprises benzoyl peroxide, lauryl peroxide, dicumyl peroxide (DCP), or combinations thereof.

12. The method as claimed in claim 1, wherein the Lewis acid catalyst comprises triazobicyclodecene, triphenylphosphine, zinc acetylacetonate, or combinations thereof.

13. The method as claimed in claim 1, wherein the method of processing the polystyrene comprises upcycling the polystyrene, recycling the polystyrene, or modifying a property of the polystyrene, or combinations thereof.

14. A polystyrene product obtained by a method, the method comprising: performing a first extrusion (102) of a first polystyrene and a maleic anhydride in presence of a free radical initiator at a temperature in a range of 200 to 240 °C to form a maleated polystyrene, wherein the first polystyrene and the maleic anhydride are present in a weight ratio of 9:1 to 49:1, wherein the first polystyrene comprises a virgin polystyrene or a recycled polystyrene, selected from a group of general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), and any combinations thereof; and performing a second extrusion (104) of the maleated polystyrene and a dynamic crosslinker in presence of a Lewis acid catalyst at a temperature in a range of 200 to 240 °C to form the polystyrene product comprising a polystyrene vitrimer, wherein the dynamic crosslinker comprises a polyol that reacts with the maleated polystyrene to form the polystyrene vitrimer comprising ester linkages configured to undergo transesterification.

15. The polystyrene product as claimed in claim 14, comprising a second polystyrene, the second polystyrene is a virgin polystyrene or a recycled polystyrene, and wherein the second polystyrene is selected from a group of general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), expandable polystyrene (EPS), styrene-butadiene rubber (SBR), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-ethylene/butylene-styrene (SEBS), and any combinations thereof.

16. An article comprising the polystyrene product as claimed in any of the claims 1-15.

Description:BACKGROUND

FIELD OF THE DISCLOSURE
[0001] Various embodiments of the present disclosure relate generally to processing commercial-grade polystyrene. More specifically, various embodiments of the disclosure relate to recycling/upcycling polystyrene via vitrimerization to produce polystyrene vitrimers.

RELATED ART
[0002] Polystyrene (PS) and its major commercial variants, such as general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), and expanded polystyrene (EPS) are widely used commodity plastics due to their versatility and performance. The global demand for PS across grades is projected to increase steadily, driven primarily by the rapid expansion of packaging, consumer electronics, and construction industries.
[0003] GPPS finds widespread use in disposable dinnerware, stationery, medical ware, insulation foams, and oriented PS films. HIPS, owing to its enhanced impact resistance, toughness, and excellent surface gloss, is an essential material for appliance housings, consumer electronics, toys, automotive components, and various injection-moulded and extruded articles. Special HIPS grades are tailored for demanding applications such as refrigerator cabinet liners, air-conditioner aesthetic panels, washing-machine components, and business-machine housings. EPS foams, known for their cushioning and thermal-insulation properties, are extensively used in packaging, building insulation, cold-chain logistics, and lightweight civil-infrastructure applications.
[0004] Correspondingly, the volume of PS-based post-consumer waste is rising rapidly, contributing substantially to landfill load and incineration streams. Due to the inherently low density of PS, its waste occupies disproportionately large volumes, making collection and recycling logistics challenging. Conventional mechanical recycling of PS often results in deterioration of mechanical properties, reduced impact strength, and poor surface quality, limiting the ability to reuse these materials in high-value applications. This challenge becomes even more pronounced for post-consumer recycled (PCR) PS, where contamination, degradation, and shrinkage restrict effective reuse.
[0005] To overcome these limitations, there is a growing interest in chemical recycling and upcycling routes that can recover or enhance material performance. Vitrimer technology has emerged as a promising approach for imparting recyclability and reprocessability to traditionally non-recyclable thermoset-like polymers and has since been extended to thermoplastic polymers such as polystyrenes.
[0006] Polystyrene and other high-styrene-content polymers possess rigid, inert hydrocarbon backbones, which make chemical functionalization and subsequent vitrimerization inherently challenging. Commercial grade polystyrenes, including GPPS and HIPS are typically high molecular weight materials and may also contain rubbery or copolymer components, further increasing melt viscosity and limiting chain mobility. High molecular weight PS grades generally exhibit melt viscosities on the order of about 10³–10⁵ Pascal second (Pa.s) under conventional processing temperatures, with even higher viscosities observed at low shear rates or in impact-modified grades. Commercial PS exhibits processing temperatures generally between about ~180 to 240 °C, beyond which thermal degradation and chain scission tend to occur (commonly above ~300 °C). The inert chemical structure of PS significantly restricts the vitrimerization process since there are no functional groups to react with chemical moieties to undergo exchange reactions.
[0007] Most reported vitrimerization strategies for polystyrene, such as those involving boronic esters, vinylogous urethanes, or other associative dynamic covalent chemistries, have therefore been carried out in solution. Such methods are inherently time-consuming, as they rely on extended reaction times to achieve sufficient grafting yields and require solvent as a carrier, rather than enabling direct, efficient melt-processing. Notably, the majority of published work employs laboratory-synthesized or purified PS, with fewer studies addressing the vitrimerization of commercial PS such as HIPS. Despite these advances, there remains a need for an energy-efficient, continuous, and faster recycling processing methods for commercial polystyrene waste streams.
[0008] Limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of described systems with some aspects of the present disclosure, as set forth in the remainder of the present application and with reference to the drawings.

SUMMARY

[0009] According to embodiments of the present disclosure, a method of processing a polystyrene is provided. The method comprises performing a first extrusion of a first polystyrene, and a maleic anhydride in presence of a free radical initiator at a temperature in a range of 200 to 240 °C to form a maleated polystyrene. The first polystyrene and the maleic anhydride are present in a weight ratio of 9:1 to 49:1. The method further comprises performing a second extrusion of the maleated polystyrene and a dynamic crosslinker in presence of a Lewis acid catalyst at a temperature in a range of 200 to 240 °C to obtain a polystyrene product comprising a polystyrene vitrimer. The dynamic crosslinker comprises a polyol that reacts with the maleated polystyrene to form the polystyrene vitrimer comprising ester linkages configured to undergo transesterification.
[0010] In another embodiment of the present disclosure, a polystyrene product obtained by a method is provided. The method comprises performing a first extrusion of a first polystyrene, and a maleic anhydride in presence of a free radical initiator at a temperature in a range of 200 to 240 °C to form a maleated polystyrene. The first polystyrene and the maleic anhydride are present in a weight ratio of 9:1 to 49:1. The method further comprises performing a second extrusion of the maleated polystyrene and a dynamic crosslinker in presence of a Lewis acid catalyst at a temperature in a range of 200 to 240 °C to obtain the polystyrene product comprising a polystyrene vitrimer. The dynamic crosslinker comprises a polyol that reacts with the maleated polystyrene to form the polystyrene vitrimer comprising ester linkages configured to undergo transesterification.
[0011] In yet another embodiment, an article comprising the polystyrene product is provided.

BRIEF DESCRIPTION OF DRAWINGS

[0012] FIG. 1 is a flow chart that illustrates a method of processing a polystyrene, in accordance with an exemplary embodiment of the disclosure;
[0013] FIG. 2 is a reaction scheme in accordance with an exemplary embodiment of the disclosure;
[0014] FIG. 3 depicts FTIR spectra comparing virgin high-impact polystyrene (HIPS), functionalized HIPS and vitrimerized HIPS samples, in accordance with an exemplary embodiment of the disclosure; and
[0015] FIG. 4 depicts FTIR spectra of HIPS and HIPS vitrimers containing varying amounts of a crosslinker, in accordance with an exemplary embodiment of the disclosure.
[0016] Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description of exemplary embodiments is intended for illustration purposes only and is, therefore, not intended to necessarily limit the scope of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

[0017] The following description illustrates some exemplary embodiments of the disclosed disclosure in detail. Those of skill in the art will recognize that there are numerous variations and modifications of this disclosure that are encompassed by its scope. Accordingly, the description of a certain exemplary embodiment should not be deemed to limit the scope of the present disclosure.
[0018] The term “comprising” as used herein is synonymous with “including,” or “containing,” and is inclusive or open-ended and does not exclude additional, unrecited elements, or process steps.
[0019] As used herein, the term “or combinations thereof” means that the listed components may be used individually or in any combination thereof.
[0020] All numbers expressing quantities of ingredients, property measurements, and so forth used in the specification are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained.
[0021] These and other features and advantages of the present disclosure may be appreciated from a review of the following detailed description of the present disclosure, along with the accompanying figures in which like reference numerals refer to like parts throughout.
[0022] As used herein, the term “polystyrene” refers to polymers obtained by the polymerization of styrene monomers, including homopolymers of styrene, copolymers comprising styrene, and blends thereof. Polystyrene comprises various commercial grades, including general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), expandable polystyrene (EPS), and other styrenic variants. Polystyrene typically exhibits a glass transition temperature (Tg) of about 95 to 105 °C and is characterized by a rigid, glassy character.
[0023] The term “commercial grade polystyrene”, as used herein
refers to polystyrene materials manufactured for industrial, packaging, consumer, or engineering applications. Such grades generally possess higher molecular weight and broader molecular weight distribution relative to laboratory-synthesized polystyrene, and may contain additives, stabilizers, fillers, rubber phases, or other contaminants. Commercial grades include but are not limited to GPPS, HIPS, and EPS.
[0024] As used herein, the term “copolymer” refers to a polymer derived from more than one species of monomer, where the copolymer includes repeating units of each of the monomers.
[0025] As used herein, the term “blend” refers to a mixture of two or more polymers or copolymers that have been blended together to create a new material with different physical properties.
[0026] The term “general-purpose polystyrene” or “GPPS”
refers to unmodified polystyrene obtained by polymerizing styrene monomers without rubber modification. GPPS is typically transparent, rigid, and brittle.
[0027] As used herein, the term “high-impact polystyrene” or “HIPS”
refers to rubber-modified polystyrene containing dispersed elastomeric domains, typically polybutadiene rubber, introduced to enhance impact strength and toughness. HIPS may include varying levels of rubber content and different rubber morphologies.
[0028] As used herein, the term “expandable polystyrene” or “EPS”
refers to polystyrene made by using a physical blowing agent (e.g., pentane) capable of expanding into closed-cell foams. EPS is characterized by low density, high cushioning performance, and thermal insulation properties.
[0029] As used herein, the term “styrene–ethylene–butylene–styrene” or “SEBS”
refers to a hydrogenated styrenic block copolymer derived from styrene–butadiene–styrene (SBS). The hydrogenation of the midblock renders the polymer more thermally and oxidatively stable. SEBS exhibits elastomeric behaviour with improved durability.
[0030] As used herein, the term “styrene–butadiene–styrene” or “SBS”
refers to a triblock copolymer comprising polystyrene end-blocks and a polybutadiene midblock. SBS exhibits elastomeric properties, high flexibility, and good processability.
[0031] As used herein, the term “styrene–isoprene–styrene” or “SIS”
refers to a triblock copolymer comprising polystyrene end-blocks and a polyisoprene midblock, characterized by high elasticity and tackiness.
[0032] As used herein, the term “styrene–butadiene rubber” or “SBR”
refers to a random copolymer of styrene and butadiene synthesized via emulsion or solution processes. SBR exhibits good abrasion resistance and aging stability.
[0033] Functionalization of a polymer generally refers to the introduction of specific functional groups (for example, hydroxyl, carboxyl, amine, or anhydride) onto a polymer chain, for example by grafting such functional groups or functional moieties onto the polymer backbone. Functionalizing the polymer modifies its chemical properties by altering structure, reactivity, adhesion, or compatibility with other materials.
[0034] The term “crosslinking” of a polymer generally refers to the formation of covalent bonds between polymer chains, leading to a formation of three-dimensional network structure. The polymer formed through this process is referred to as a “crosslinked polymer”. Crosslinking improves the mechanical and thermal properties of the polymer without significantly altering its chemical properties.
[0035] As used herein, the term “covalent adaptive network” (CAN) encompasses crosslinked polymer networks in which the covalent bonds between polymer chains are reversible or exchangeable upon application of external stimuli. Exemplary external stimuli include heat, pH, and light. In such networks, the polymer retains a crosslinked structure while permitting bond-exchange reactions that enable network rearrangement.
[0036] A “vitrimer” is a specific class of CAN that undergoes associative bond-exchange reactions, in which network connectivity of CAN is maintained during bond exchange, thereby preserving the crosslinked topology. Unlike conventional thermoplastics, which soften upon heating, and thermosets, which are permanently crosslinked, vitrimers maintain a crosslinked network capable of network rearrangement via bond-exchange reactions upon application of the external stimuli. As a result, the vitrimer exhibits solid-like behaviour at service temperatures and viscoelastic flow at elevated temperatures, enabling reprocessability, recyclability, and stress relaxation, while retaining the advantageous properties of thermoset polymers. In the present disclosure, dynamic covalent bond exchange and network reconfiguration occur in the presence of heat. In the context of vitrimers, “service temperature” refers to a temperature or temperature range below the activation temperature for dynamic covalent bond exchange, at which the vitrimer exhibits solid-like behaviour and maintains its crosslinked network.
[0037] FIG. 1 is a flow chart 100 that illustrates a method of processing a polystyrene through exemplary steps 102 through 104, according to embodiments of the present disclosure. The term “processing a polystyrene”, as used herein, refers to recycling the polystyrene, upcycling the polystyrene, treating the polystyrene to modify a property of the polystyrene, or a combination thereof.
[0038] As used herein, the term “recycling” refers to processing a polystyrene or a polystyrene-containing material to recover or repurpose the material for reuse, according to embodiments of the present invention. In certain embodiments, recycling may comprise vitrimerization of polystyrene and/or blending polystyrene with a polystyrene vitrimer.
[0039] The term “upcycling,” as used herein, refers to processing a polystyrene or a polystyrene-containing material to obtain a resultant material exhibiting improved performance in one or more mechanical properties relative to the starting material, according to embodiments of the present invention. The improvement in one or more mechanical properties may be demonstrated using any suitable test method as known in the art. The mechanical properties may include, but are not limited to, ultimate tensile strength, elongation at break, stiffness, toughness, durability, ductility, flexibility or a combination thereof. In certain embodiments, upcycling may comprise vitrimerization of polystyrene and/or blending polystyrene with a polystyrene vitrimer.
[0040] As used herein, the term “ultimate tensile strength” (UTS) is defined as the maximum stress a material can withstand while being stretched or pulled before breaking in a tensile test. The term “elongation at break” is defined as the percentage increase in length a material undergoes before fracturing in a tensile test. UTS measures a material's resistance to breaking under tension, and elongation at break quantifies its ductility or flexibility. As used herein, the term “stiffness” refers to the resistance of a material to elastic deformation under an applied load. As used herein, the term “toughness” refers to the ability of a material to absorb energy and undergo deformation before failure. As used herein, the term “durability” refers to the ability of a material to retain its mechanical performance over time under conditions of use, including resistance to degradation, fatigue, or damage.
[0041] As used herein, the term “modifying a property” refers to altering one or more mechanical properties, thermal properties of a polymer relative to its initial state, including increasing, decreasing, or otherwise tuning the property, without requiring an overall improvement in performance. The mechanical properties may include, but are not limited to, ultimate tensile strength, elongation at break, stiffness, toughness, durability, ductility, flexibility or a combination thereof. The thermal properties may include, but are not limited to, glass transition temperature (Tg), and thermal degradation temperature. In certain embodiments, modifying the property of the polystyrene may comprise vitrimerization of polystyrene and/or blending polystyrene with a polystyrene vitrimer.
[0042] At step 102, a first extrusion of a first polystyrene and a maleic anhydride is performed in the presence of a free radical initiator at a temperature in a range of 200 to 240 °C to form a maleated polystyrene.
[0043] The first polystyrene comprises GPPS, HIPS or a combination thereof. The first polystyrene may be virgin polystyrene or recycled polystyrene. The term “recycled polystyrene,” as used herein, refers to polystyrene material that has been previously produced and subsequently recovered and reprocessed for reuse, including, without limitation, post-consumer recycled (PCR) and post-industrial recycled (PIR) polystyrene. Post-consumer recycled (PCR) polystyrene refers to polystyrene waste generated by consumers, or in other words, after-use polystyrene products. The composition of PCR polystyrene can vary significantly due to the diverse mix of polymers and additives used by different manufacturers. The variation in composition makes recycling of PCR polystyrene more complex and challenging when compared to PIR polystyrenes. In contrast, post-industrial recycled (PIR) polystyrene is derived from polystyrene waste produced during industrial and manufacturing processes. PIR plastics are generally easier to recycle as they typically originate from a single source and are of known composition.
[0044] In embodiments where the polystyrene is recycled polystyrene, the recycled polystyrene is washed to remove any contaminants or residues and dried to remove moisture before processing. In one embodiment, the recycled polystyrene is washed with an aqueous detergent solution. The washing is followed by drying in a vacuum oven at a temperature in a range of 50°C to 80°C for a time period of 1 to 10 hours before use to remove moisture. Once the recycled polystyrene is washed and dried, it is cut into smaller pieces for the first extrusion.
[0045] The first polystyrene as used herein may be provided in any suitable physical form, including but not limited to film, granules, flakes, powders, pellets, beads or combinations thereof. Before adding the polystyrene into an extruder, it may be suitably sized into desirable dimensions of the order of a few millimetres (mm).
[0046] The first extrusion results in the formation of the maleated polystyrene. As used herein, the term “maleated polystyrene” refers to a polystyrene polymer in which one or more maleic anhydride moieties are covalently attached as pendant groups to the carbon–carbon (C-C) backbone of the polystyrene. In embodiments where the first polystyrene is GPPS, maleic anhydride moieties are grafted onto the carbon–carbon backbone of the GPPS, resulting in maleated GPPS comprising pendant succinic anhydride functionalities, while the aromatic styrene rings remain substantially intact. In embodiments where the first polystyrene comprises high-impact polystyrene (HIPS), grafting of maleic anhydride occurs under free-radical conditions on both the polystyrene component and the rubber component of the HIPS, as schematically illustrated in FIG. 2.
[0047] The grafting makes the otherwise inert C-C backbone of the polystyrene polar thus making it amenable for further functionalization and reaction with other functional groups. A grafting yield of the maleated polystyrene may provide a quantitative measure of the extent of maleic anhydride moieties grafted onto the C-C backbone. As used herein, the term “grafting yield” refers to the extent of maleic anhydride moieties grafted onto the first polystyrene relative to the first polystyrene before grafting, expressed as a relative or normalized value indicative of the degree of grafting, as determined by spectroscopic, titrimetric, or gravimetric analysis. In some embodiments, the grafting yield is determined by Fourier Transform Infrared (FTIR) spectroscopy, based on the relative intensity or integrated area of characteristic absorption bands corresponding to the maleic anhydride moieties and the polystyrene. In some embodiments, the grafting yield is in a range of 3% to 26%.
[0048] A weight ratio of the first polystyrene and the maleic anhydride is in a range of 9:1 to 49:1 for the first extrusion. In one embodiment, the weight ratio of the first polystyrene and the maleic anhydride is 9:49.
[0049] The first extrusion, at step 102, is performed in presence of the free radical initiator. The free radical initiator generates free radicals for initiating a chemical reaction between the first polystyrene and the maleic anhydride. Examples of free radical initiators comprise benzoyl peroxide, lauryl peroxide, dicumyl peroxide (DCP), or combinations thereof. In one embodiment, the free radical initiator is dicumyl peroxide (DCP).
[0050] A concentration of the free radical initiator for the first extrusion is in a range of 0.1 weight percent (wt%) to 1 wt%.
[0051] The first extrusion is performed in an extruder such as a single-screw extruder, or a twin-screw extruder. The processing parameters of the extruder may be varied to facilitate reactive extrusion of the polystyrene and the maleic anhydride, in the presence of the free radical initiator by optimizing one or more of flowing of the first polystyrene, homogeneous mixing of the first polystyrene, maleic anhydride, and the free radical initiator, and efficient reaction between the first polystyrene and maleic anhydride. Examples of such process parameters include, but are not limited to, type of extruder, geometrical design of the extruder, screw speed, residence time of material in the extruder, feed rate of the material into the extruder, temperature, and die geometry through which a product is extruded. In one embodiment, the extruder is a twin-screw extruder that facilitates enhanced mixing of the first polystyrene, maleic anhydride, and the free radical initiator, when compared to a single-screw extruder. The first extrusion may be performed at a temperature corresponding to the processing temperature of the first polystyrene. In some embodiments, the residence time is in a range of 1 to 10 minutes, preferably 2 to 7 minutes. In some embodiments, screw speed is in a range of 80 to 120 rotations per minute (rpm) in a twin-screw extruder. The first extrusion, in one embodiment, is performed in a twin-screw extruder at a temperature of 220°C and screw speed of 100 rotations per minute (rpm) for a residence time of 5 minutes.
[0052] At step 104, a second extrusion of the maleated polystyrene and a dynamic crosslinker in presence of a Lewis acid catalyst is performed at a temperature in a range of 200 to 240 °C to obtain a polystyrene product comprising a polystyrene vitrimer. The term “polystyrene product”, as used herein, refers to a material obtained by the disclosed method and comprises a polystyrene vitrimer, either alone or in combination with one or more additional components, including but not limited to a second polystyrene, additives present in a starting material, or combinations thereof. The dynamic crosslinker comprises a polyol that reacts with the maleated polystyrene through ester formation to form the polystyrene vitrimer configured to undergo transesterification. As used herein, “configured to undergo transesterification” refers to a polymer network comprising ester linkages that undergo associative bond exchange when subjected to external stimuli such as temperature. The polyols described herein may have a hydroxyl functionality of at least 2, or above, depending on the desired degree of esterification or crosslinking. The reaction between the maleated polystyrene and the polyols results predominantly in ring opening of the maleic anhydride moiety via esterification, forming ester functionalities covalently bonded to the polystyrene backbone.
[0053] The polyol is selected from a group of aliphatic diols, aromatic diols, aliphatic triols, polyether polyols, aliphatic tetrols, and any combinations thereof. The term “combinations thereof” refers to mixtures or blends of two or more of the foregoing polyols, selected to tailor the balance of rigidity, flexibility, polarity, and crosslink density in the modified polystyrene. Aliphatic diols are dihydric alcohols comprising two hydroxyl (–OH) groups attached to aliphatic carbon atoms and capable of reacting with an anhydride functionality to form mono- or di-ester linkages. Non-limiting examples of aliphatic diols include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, cyclohexane dimethanol, neopentyl glycol, and diethylene glycol. Aromatic diols are dihydric alcohols comprising two hydroxyl (–OH) groups associated with an aromatic ring and capable of reacting with an anhydride functionality to form aromatic ester linkages. Non-limiting examples of aromatic diols include bisphenol A, bisphenol F, hydroquinone, resorcinol, and catechol. Aliphatic triols are trihydric alcohols comprising three hydroxyl (–OH) groups attached to aliphatic carbon atoms. Non-limiting examples of aliphatic triols include glycerol, trimethylolpropane, trimethylolethane, and 1,2,6-hexanetriol. Polyether polyols are polyhydric alcohols comprising repeating ether linkages and two or more hydroxyl (–OH) groups. Non-limiting examples include polyethylene glycol (PEG), polypropylene glycol (PPG), polyglycerols, polytetramethylene ether glycol (PTMEG), ethylene oxide–propylene oxide copolyols. Aliphatic tetrols are tetrahydric alcohols comprising four hydroxyl (–OH) groups attached to aliphatic carbon atoms. Exemplary aliphatic tetrols include, but are not limited to, erythritol, threitol, pentaerythritol, and combinations thereof. In some embodiments, the polyol comprises ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, cyclohexanedimethanol, glycerol, trimethylolpropane, pentaerythritol, sorbitol, polyethylene glycol, polypropylene glycol, polyglycerols, or a combination thereof.
[0054] It is to be understood that a composition of the polystyrene product may vary depending on the nature of the starting polystyrene. When the process utilizes virgin polystyrene, the polystyrene product predominantly comprises the polystyrene vitrimer. When recycled polystyrene is used, as the recycled polystyrene may further comprise additional components, including fillers, dyes, or other polymers, in such embodiments, the polystyrene product comprises the polystyrene vitrimer in combination with one or more of the additional components present in the recycled polystyrene. In embodiments employing maleated high-impact polystyrene (HIPS), the polystyrene product comprises a vitrimerized HIPS composition, wherein dynamic covalent bonds are formed through maleated functional groups present on both the polystyrene component and allylic carbon atoms of the rubber component. If the maleated HIPS is made from PCR HIPS starting material then the polystyrene product may further comprise additional components originally present in the starting PCR HIPS material.
[0055] In some embodiments, the second extrusion 104 is performed in the presence of a second polystyrene. The second polystyrene comprises a virgin polystyrene or a recycled polystyrene. The second polystyrene is selected from a group of general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), expandable polystyrene (EPS), styrene-butadiene rubber (SBR), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-ethylene/butylene-styrene (SEBS), and any combinations thereof.
[0056] Generally, expanded polystyrene (EPS) is difficult to recycle due to its low bulk density and high volume. It is a particular advantage of the present invention that EPS can be recycled through the method as illustrated in FIG. 1. In such embodiments, the polystyrene product comprises a blend of the second polystyrene (EPS) and the polystyrene vitrimer. Further, a concentration of the second polystyrene is varied to modify a property of the obtained polystyrene product. The property comprises one or more of a mechanical property, a thermal property, a tensile strength, an elongation at yield, a glass transition temperature and thermal degradation temperature.
[0057] In some embodiments, the maleated polystyrene and the second polystyrene are extruded in a weight ratio of 9:1 to 1:1.09.
[0058] In one embodiment, the maleated polystyrene and the dynamic crosslinker are extruded in a weight ratio of 9:1 to 49:1. A concentration of the dynamic crosslinker extruded with the maleated polystyrene is in a range of 0.5 to 15% by weight. In another embodiment, concentration of the dynamic crosslinker in the polystyrene vitrimer is in a range of 0.5 to 5% by weight. The concentration of the dynamic crosslinker may be decided based on a desired property of the resultant polystyrene vitrimer. For example, by varying the concentration of the dynamic crosslinker mechanical properties of the polystyrene vitrimer, such as ultimate tensile strength and/or elongation at break may be varied.
[0059] The second extrusion is performed in the presence of a Lewis acid catalyst. Examples of Lewis acid catalysts include triazobicyclodecene, triphenylphosphine, zinc acetylacetonate, or combinations thereof. In one embodiment, the Lewis acid catalyst is zinc acetylacetonate.
[0060] A concentration of the Lewis acid catalyst in the polystyrene vitrimer is in a range of 0.5 wt% to 2 wt%.
[0061] The second extrusion 104, like the first extrusion 102, is performed in an extruder such as a single screw extruder, or a twin-screw extruder. The processing parameters of the extruder may be varied to facilitate reactive extrusion of the maleated polystyrene and the dynamic crosslinker, as discussed with reference to the first extrusion. In one embodiment, the extruder is a twin-screw extruder that facilitates enhanced mixing between the maleated polystyrene and the dynamic crosslinker when compared to a single-screw extruder. The second extrusion may be performed at a temperature corresponding to the processing temperature of the polystyrene. In some embodiments, the processing temperature is in a range of 200 to 240°C. In some embodiments, the residence time is in a range of 1 to 10 minutes, preferably 2 to 7 minutes. The second extrusion, in one embodiment, is performed in a twin-screw extruder at a temperature of 220°C, at screw speeds in a range of 80 to 120 rpm and at a residence time of 5 minutes.
[0062] The extruded polystyrene product obtained at step 104 may be immediately quenched in a water bath and pelletized. Such pellets can be used for subsequent molding, or shaping. The polystyrene product of the present disclosure may be shaped in the form of films, sheets, foams, particles, granules, beads, rods, plates, strips, stems, tubes, etc. via any process known to those skilled in the art. Examples of such processes include extrusion, casting, compression molding and the like.
[0063] In some embodiments, the first extrusion (step 102) and the second extrusion (step 104) may be performed in presence of additives commonly used during polymer processing such as UV stabilizers, heat stabilizers and the like. Examples of suitable additives include phenolic antioxidants and thioesters, such as pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox® 1010), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 3,3′,3′,5,5′,5′-hexa-tert-butyl-α,α′,α″-(mesitylene-2,4,6-triyl)tri-p-cresol, 4,4′-thiobis(3-methyl-6-tert-butylphenol), 2,2′-thiobis(6-tert-butyl-p-cresol), 2,2′-thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], distearyl thiodipropionate, dilauryl thiodipropionate, pentaerythritol tetrakis(β-laurylthiopropionate) or combinations thereof. Suitable UV stabilizers include hindered amine light stabilizers (HALS), benzotriazole-based UV absorbers, and benzophenone-based UV absorbers, such as bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, 2-(2′-hydroxy-5′-tert-octylphenyl)benzotriazole, and 2-hydroxy-4-octoxybenzophenone, or combinations thereof.
[0064] The formation of the polystyrene vitrimer, according to the flow chart 100 illustrated in FIG. 1, can be better understood through a representative reaction scheme 200, as shown in FIG. 2, in accordance with the embodiments of the disclosure. The reaction scheme 200 illustrates one possible mechanism by which the reaction may proceed. It is understood that alternative pathways, intermediates, or mechanisms could also account for the observed results, and the invention is not limited to the mechanism depicted below.
[0065] In the representative reaction 200, as shown in FIG. 2, the free radical initiator is dicumyl peroxide (DCP). The first polystyrene is HIPS having styrene as well as rubber components. Referring to FIG. 2, without wishing to be bound by any particular theory, the initiator (for example, dicumyl peroxide) undergoes homolytic cleavage to generate free radicals, which abstract hydrogen atoms from the polystyrene backbone and/or allylic C-C backbone of the rubber component to produce macroradicals. The maleic anhydride reacts with the macroradicals to form maleated polystyrene, as shown by structure [II]. The resulting maleated polystyrene possesses pendant anhydride group (maleic anhydride moieties) suitable for subsequent reactions with nucleophilic functional groups, such as hydroxyls. During the second extrusion with the dynamic crosslinker, the maleated polystyrene (structure [II]) reacts with the dynamic crosslinker, glycerol, through esterification to form the polystyrene vitrimer (structure [III]) configured to undergo transesterification.
[0066] According to embodiments of the present disclosure, a polystyrene product obtained by a method is provided. The method comprises performing a first extrusion of a first polystyrene, and a maleic anhydride in presence of a free radical initiator at a temperature in a range of 200 to 240 °C to form a maleated polystyrene. The first polystyrene and the maleic anhydride are present in a weight ratio of 9:1 to 49:1. The first polystyrene comprises a virgin polystyrene or a recycled polystyrene, selected from a group of general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), and any combinations thereof. The method further comprises performing a second extrusion of the maleated polystyrene and a dynamic crosslinker in presence of a Lewis acid catalyst at a temperature in a range of 200 to 240 °C to obtain a polystyrene product comprising the polystyrene vitrimer. The dynamic crosslinker comprises a polyol that reacts with the maleated polystyrene to form the polystyrene vitrimer comprising ester linkages configured to undergo transesterification.
[0067] Prior art vitrimerization processes have typically been carried out in solution phase for custom-made polystyrenes. Such prior art methods are generally ineffective for processing commercial-grade polystyrenes, including general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), and expanded polystyrene (EPS). In contrast, the process disclosed herein is less time-consuming and less energy-intensive compared to solution-phase methods. Furthermore, the disclosed process may be operated in batch, semi-continuous, and/or continuous modes, thereby offering improved scalability and industrial applicability. The solvent-free nature of thel disclosed method provides environmental and sustainability advantages over solvent-based processes.
[0068] The polystyrene product comprising the polystyrene vitrimer, alone or in combination with the second polystyrene, as disclosed herein, exhibits mechanical properties that are comparable to, or superior to, the mechanical properties of the parent polystyrene (first polystyrene) from which it is derived. The inventive process and the resulting polystyrene vitrimers provide, in at least one embodiment, an upcycling of polystyrene materials. In certain embodiments, difficult-to-recycle polystyrenes, including EPS and other polystyrenes, such as the disclosed second polystyrene, may be advantageously recycled and/or upcycled. In embodiments incorporating a second polystyrene, one or more properties of the parent polystyrene may be modified. Further, the content of the second polystyrene may be varied to tune the mechanical and/or physical properties of the resulting polystyrene product.
[0069] The reprocessability of the polystyrene vitrimers disclosed herein overcomes key challenges associated with recycling polystyrene plastic waste. In some embodiments, the disclosed process enables transformation of polystyrene waste into mechanically stronger polystyrene materials while retaining other desirable properties that contribute to the versatility of polystyrenes. The polystyrene product of the present disclosure may be reprocessed multiple times without significant degradation of mechanical properties when compared to conventionally processed polystyrene. Multiple times, as used herein, refers to more than once, preferably more than 3 times. A particular advantage of the present disclosure is that, irrespective of the presence of additives in the polystyrene, the material may be reprocessed using the disclosed method to yield recycled and/or upcycled post-consumer recycled (PCR) polystyrene.
[0070] In some embodiments, an article comprising the polystyrene product of the present disclosure is provided. The article may be formed by molding, blow molding, injection molding, filament winding, continuous molding or film-insert molding, infusion, pultrusion, RTM (resin transfer molding), RIM (reaction-injection molding), 3D printing, or any other method known to those skilled in the art.

EXAMPLES
[0071] The present disclosure will now be described in greater detail by the
following non-limiting examples. It is understood that one skill in the art will envision additional embodiments consistent with the disclosure provided herein.

EXAMPLE 1
Preparation of maleated polystyrenes
[0072] Maleated polystyrene samples were prepared from various polystyrene materials, including post-consumer recycled high-impact polystyrene (PCR-HIPS), virgin high-impact polystyrene (HIPS), and post-consumer recycled general-purpose polystyrene (PCR-GPPS). The polystyrene materials were heat conditioned for 2 hours at 70-80°C in a hot air oven to remove surface moisture.
[0073] Reactive extrusion was carried out with each of the polystyrene materials and maleic anhydride (MA) in the presence of dicumyl peroxide (DCP) in a DSM Explore twin-screw extruder operated in tandem with a DSM Explore Manual Injection Moulding Machine equipped with a tensile dumbbell mould conforming to ASTM D638 Type V dimensions. The extruder had a 15 cm³ capacity and comprised a co-rotating conical screw configuration with a recirculating chamber to control residence time. Extrusion was conducted at a temperature in the range of 220–240 °C, a screw speed of 100 rpm, and a residence time of 5 minutes. Table 1 presents the composition of the components used to prepare the maleated polystyrene samples, where the composition is expressed in terms of weight percent (wt%). The dicumyl peroxide content was maintained at 0.5 wt%, while the amounts of the polystyrene materials and maleic anhydride (MA) were varied.

Sample name Polystyrene material employed Polystyrene material (wt%) MA (wt %) DCP (wt%)
m-HIPS HIPS 97.5-89.5 2-10 0.5
m-PCR HIPS PCR HIPS 97.5-89.5 2-10 0.5
m-GPPS GPPS 97.5-89.5 2-10 0.5
m-PCR GPPS PCR GPPS 97.5-89.5 2-10 0.5

Table 1

EXAMPLE 2
Preparation of polystyrene product comprising polystyrene vitrimers
[0074] The maleated HIPS polymer sample (m-HIPS), maleated PCR HIPS (m-PCR HIPS) sample and maleated PCR GPPS sample of Example 1 were weighed and mixed with the catalyst zinc acetylacetonate (about 99% purity) and the crosslinker glycerol (about 98% purity) in predetermined amounts, as shown in Table 2. The glycerol content was varied from 2 wt% to 10 wt%, while the zinc acetylacetonate catalyst concentration was maintained constant at 1 wt%. All materials were obtained from commercial sources and were used as received, without further purification.
[0075] The resulting mixture was fed into the extruder through a hopper and subjected to reactive extrusion under the following conditions, a temperature of 220 °C maintained across all zones, a screw speed of 100 rpm, and a residence time of 5 minutes. After extrusion, the molten compound was directly transferred to the injection-moulding barrel maintained at 220 °C and injection-moulded at an injection pressure of 14 bar.
[0076] As shown in Table 2, HIPS-2V, HIPS-4V, HIPS-6V, HIPS-8V and HIPS-10V correspond to polystyrene vitrimers obtained from m-HIPS with 2 wt%, 4 wt%, 6 wt%, 8 wt% and 10 wt% of crosslinker glycerol, respectively. The PCR HIPS-2V corresponds to polystyrene vitrimer obtained from m-PCR HIPS with 2 wt% of glycerol. PCR GPPS-V2 and PCR GPPS-V5, correspond to polystyrene vitrimer obtained from m-PCR GPPS maleated with 2 wt% and 5 wt% of maleaic anhydride, respectively.
Sample name Maleated polymer (wt%) Glycerol
(wt%) Zinc acetyl acetonate (wt%)
HIPS-2V 97 2 1
HIPS-4V 95 4 1
HIPS-6V 93 6 1
HIPS-8V 91 8 1
HIPS-10V 89 10 1
PCR HIPS-2V 97 2 1
PCR GPPS-V2 97 2 1
PCR GPPS-V5 97 2 1

Table 2

[0077] In addition to glycerol as the crosslinker, a sample employing ethylene glycol as the crosslinker was prepared. Specifically, sample HIPS-2V-EG was prepared using 97 wt% maleated HIPS, 2 wt% ethylene glycol as the crosslinker, and 1 wt% zinc acetylacetonate.

Infrared (IR) study of polystyrene product comprising the polystyrene vitrimers
[0078] FIG. 3 illustrates FTIR spectra 300 of HIPS, maleated HIPS (m-HIPS), and a HIPS vitrimer corresponding to sample HIPS-2V. The FTIR spectrum 304 of the maleated HIPS (m-HIPS) exhibits a characteristic peak at 1780 cm⁻¹ corresponding to the cyclic maleic anhydride group, which is absent in the IR spectrum 302 of HIPS. Upon crosslinking with glycerol, the maleic anhydride ring undergoes ring opening to form β-hydroxy ester linkages, which are dynamic in nature and capable of undergoing transesterification reactions at elevated temperatures. The ring opening of the maleic anhydride group results in ester formation, accompanied by the generation of hydroxyl groups. The structural changes are evidenced by the appearance of a broad O–H stretching band at approximately 3400 cm⁻¹ and an ester C=O stretching band at approximately 1740 cm⁻¹ in FTIR spectrum 306 of HIPS vitrimer (HIPS-2V).
[0079] FIG. 4 illustrates FTIR spectra 400 of HIPS and HIPS vitrimer with varying content of crosslinker glycerol corresponding to samples HIPS-2V, HIPS-4V, HIPS-6V, HIPS-8V, HIPS-10V, respectively. As shown in FIG. 4, with an increase in concentration of glycerol from HIPS-2V sample to HIPS-10V, the intensity of the ester C=O band at 1740 cm⁻¹ increases, while the intensity of the anhydride band at 1780 cm⁻¹ decreases, along with a corresponding increase in the O–H stretching band at approximately 3400 cm⁻¹. These spectral changes confirm the occurrence of the crosslinking reaction and the formation of the vitrimer network.

Mechanical testing of polystyrene product comprising the vitrimers
[0080] The stress-strain properties of the samples were measured according to ASTM D638 (type V) using a Tinius Olsen 1ST Universal Testing Machine at room temperature using Test Parameters of Load Cell: 5 kN; Preload Force: 0.1 N; Cross Head Speed: 50mm/minutes; Gauge Length: 15mm; Number of Samples: 5 per batches for consistency; and Sample Dimension: 50 mm length x 4.1 mm width x 2.1 mm thickness.
[0081] The samples were placed between clamps of the Universal Testing Machine - Tensile Testing Module such that the edges of the samples were parallel to the direction of the load. The grips were tightened to hold the samples securely within the jig. The test samples were then pulled apart at a tensile speed of 50 mm/minute until they broke. Table 3 provides the mechanical testing data of HIPS and HIPS vitrimers.

Sample Name Ultimate tensile strength (MPa) Elongation at break (%)
HIPS (virgin) 30.47 ± 0.29 4.01 ± 0.09
HIPS-2V 42.1 ± 0.43 3.76 ± 0.07
HIPS-4V 40.3 ± 0.95 3.65 ± 0.05
HIPS-6V 40.5 ± 0.55 3.81 ± 0.15
HIPS-8V 40.03 ± 2.05 3.71 ± 0.15
HIPS-10V 39.5 ± 1.17 3.72 ± 0.14
HIPS-2V-EG 41.06 ± 1.13 3.51 ± 0.18
PCR HIPS 30.47 ± 0.28 4.01 ± 0.08
PCR HIPS-2V 35.8 ± 0.43 3.87 ± 0.36

Table 3

[0082] An improvement in mechanical strength is observed for the vitrimer samples. Virgin HIPS (HIPS) exhibits a tensile strength of approximately 30 MPa, whereas the vitrimer samples, HIPS-2V, HIPS-4V, HIPS-6V, HIPS-8V and HIPS-10V, show an increase in tensile strength of about 10–12 MPa, as summarized in Table 3. This enhancement indicates effective upcycling of the HIPS polymer. Furthermore, PCR HIPS–based vitrimer sample (PCR HIPS-2V) exhibits higher tensile strength compared to PCR-HIPS, demonstrating that the disclosed process is also effective for upcycling post-consumer recycled HIPS.
[0083] Table 4 provides the mechanical testing data of GPPS and GPPS vitrimers.

Sample Name Ultimate tensile strength (MPa) Elongation at break (%)
PCR GPPS 39.6 ± 3 4.05 ± 0.08
PCR GPPS-V2 38 ± 1.1 3.29 ± 0.05
PCR GPPS-V5 38 ± 0.6 3.17 ± 0.07

Table 4

[0084] Although a marginal decrease in UTS is observed upon vitrimerization of PCR GPPS (PCR GPPS-V2 and PCR GPPS-V5), the resulting material retains mechanical strength within the range required for practical reuse and recycling, while additionally offering the benefit of reprocessability enabled by dynamic covalent bonding.
Recyclability test
[0085] Recyclability tests were conducted to evaluate the retention of mechanical properties upon repeated reprocessing. For recyclability testing, samples of HIPS and HIPS vitrimer (HIPS-2V) were cut into small pieces, re-extruded, and injection molded multiple times to simulate successive recycling cycles. Recyclability tests were conducted up to three cycles, with RP0 corresponding to samples derived from Example 2, and RP3 corresponding to the sample at the end of the third recycling cycle. Table 5 presents the percentage recovery of ultimate tensile strength (UTS) and elongation at break of the two samples after the third recycling cycle.

Samples Ultimate tensile strength (MPa)
RP0 RP3 Percentage retention
HIPS 30.47 ± 0.29 32.83 ± 3.86 100
HIPS-2V 42.1 ± 0.43 39.27 ± 1.16 93
Table 5

[0086] As observed from Table 5, the HIPS-2V vitrimer retained approximately 93% of its tensile strength (UTS) after reprocessing, whereas virgin HIPS exhibited 100% strength retention. Notably, the standard deviation for the UTS of virgin HIPS increased significantly after three reprocessing cycles (RP3), indicating greater variability in mechanical performance. In contrast, HIPS-2V exhibited relatively lower standard deviation upon reprocessing, suggesting improved consistency. Furthermore, the RP3 UTS values of HIPS-2V were higher than those of reprocessed virgin HIPS, demonstrating superior retention of mechanical properties upon multiple reprocessing cycles. The superior recovery performance of the polystyrene vitrimer is attributed to the presence of dynamic covalent bonds within its network, which enable reversible bond exchange reactions during reprocessing, thereby maintaining the material’s mechanical integrity over multiple recycling cycles.

EXAMPLE 3
Preparation of polystyrene product comprising polystyrene vitrimer and a second polystyrene
[0087] Maleated HIPS (m-HIPS) from Example 1 was weighed and mixed with the catalyst zinc acetylacetonate and the crosslinker glycerol, together with post-consumer recycled expanded polystyrene (PCR EPS), in a weight ratio of 1:1 (m-HIPS:PCR EPS), as shown in Table 6, to obtain polystyrene product HIPSV-EPS through extrusion. Similarly, styrene-ethylene-butylene-styrene (SEBS) was extruded with maleated HIPS (m-HIPS), catalyst zinc acetylacetonate and the crosslinker glycerol according to composition as shown in Table 7, to obtain the polystyrene product HIPSV-SEBS through extrusion.

Sample Name maleated polymer (wt%) glycerol
(wt%) zinc acetyl acetonate (wt%) PCR EPS (wt%)
HIPSV-EPS 48.5 1.0 0.5 50

Table 6

Sample Name maleated polymer (wt%) glycerol
(wt%) zinc acetyl acetonate (wt%) SEBS
HIPSV-SEBS 87.3 1.8 0.9 10

Table 7

[0088] The reaction mixture was fed into the extruder through a hopper and subjected to reactive extrusion under the following conditions: a temperature of 220 °C maintained across all zones, a screw speed of 100 rpm, and a residence time of 5 minutes. After extrusion, the molten compound was directly transferred to the injection-moulding barrel maintained at 220 °C and injection-moulded at an injection pressure of 14 bar.

Mechanical testing of polystyrene product comprising polystyrene vitrimer and the second polystyrene
[0089] Table 8 provides the mechanical testing data of PCR EPS and polystyrene product obtained by extruding maleated-HIPS with EPS (HIPSV-EPS).

Sample Name Ultimate tensile strength (MPa) Elongation at break (%)
PCR EPS 39 ± 1.8 3.46 ± 0.2
HIPSV-EPS 39.8 ± 1.3 3.62 ± 0.2

Table 8

[0090] PCR EPS and the HIPSV-EPS exhibit comparable ultimate tensile strength (UTS) values, while the elongation at break of the HIPSV-EPS was marginally higher. These results demonstrate the suitability of the disclosed method for recycling EPS and further indicate that the mechanical properties of the resulting polystyrene product can be tuned by varying the concentration of EPS during the secondary extrusion step. Notably, EPS is conventionally difficult to process and recycle due to its low density and high bulk volume; however, the present method enables effective incorporation and reprocessing of EPS without significant loss of mechanical performance.
[0091] Table 9 provides the mechanical testing data of polystyrene product (HIPS2V-SEBS) obtained by extruding maleated HIPS, zinc acetyl acetonate, glycerol and styrene-ethylene-butylene-styrene (SEBS).

Sample Name Ultimate Tensile strength (MPa) Ultimate strain (%) Elongation at break (%)
HIPS2V-SEBS 36 ± 0.8 4.47 ± 0.04 7.11 ± 0.07
Table 9

[0092] Virgin HIPS exhibits an ultimate tensile strength (UTS) of approximately 30 MPa, which increases to about 42 MPa upon vitrimerization. When the HIPS vitrimer is blended with SEBS during a secondary extrusion step, the resulting polystyrene product exhibits a UTS of approximately 36 MPa, demonstrating the suitability of the disclosed method for recycling and incorporating SEBS into polystyrene-based materials. The mechanical properties of the resulting compositions are tunable by adjusting the concentration of SEBS.
[0093] Specifically, the presence of SEBS in the polystyrene product results in enhanced elongation accompanied by a reduction in tensile strength, reflecting a transition from predominantly brittle failure to ductile failure behaviour. This trend is evident from the tensile strain data, wherein both the ultimate strain and the break strain increase with SEBS addition, with the break strain exceeding the ultimate strain. Such separation between ultimate strain and break strain is characteristic of post-yield plastic deformation and ductile failure.
[0094] As used herein, the term “ultimate strain” refers to the tensile strain corresponding to the maximum stress (ultimate tensile strength) during a tensile test, whereas the term “elongation at break” refers to the tensile strain at the point of material fracture. In ductile materials, the elongation at break typically exceeds the ultimate strain due to continued deformation after yielding, whereas in brittle materials these values occur at substantially similar strain levels. Consistent with this behaviour, vitrimer compositions without SEBS exhibit lower strain values with ultimate strain and elongation at break occurring at substantially similar levels, indicative of predominantly brittle fracture.
Recyclability test
[0095] Recyclability tests were conducted for one cycle, with RP0 corresponding to the samples, PCR EPS, and maleated-HIPS extruded with glycerol and EPS (HIPSV-EPS) derived from Example 3, and RP1 corresponding to the samples at the end of the first recycling cycle. Table 10 presents the percentage recovery of ultimate tensile strength (UTS) and elongation at break of the two samples after the third cycle.

Sample Name Ultimate tensile strength (MPa)
RP0 RP1 Percentage retention
PCR EPS 39 ± 1.8 36.2 ± 0.7 93
HIPSV-EPS 39.8 ± 1.3 38.8 ± 3.1 98
Table 10

[0096] The HIPSV-EPS sample retained approximately 98% of its ultimate tensile strength (UTS) after reprocessing, compared to PCR EPS, which exhibited a UTS retention of about 93%. Accordingly, the recyclability tests demonstrate superior retention of mechanical properties for the polystyrene product comprising EPS in the vitrimer matrix, whereas PCR EPS alone shows a comparatively greater deterioration in mechanical performance upon reprocessing.
[0097] It is to be understood that the above description is intended to be illustrative, and not restrictive. Furthermore, many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. Although the present disclosure has been described with reference to specific exemplary embodiments, it will be recognized that the disclosure is not limited to the embodiments described, but can be practiced with modification and alteration within the scope of the appended claims.
, Claims:CLAIMS

I/We Claim:
1. A method of processing a polystyrene comprising:
performing a first extrusion (102) of a first polystyrene and a maleic anhydride in presence of a free radical initiator at a temperature in a range of 200 to 240 °C to form a maleated polystyrene, wherein the first polystyrene and the maleic anhydride are present in a weight ratio of 9:1 to 49:1; and
performing a second extrusion (104) of the maleated polystyrene and a dynamic crosslinker in presence of a Lewis acid catalyst at a temperature in a range of 200 to 240 °C to form a polystyrene product comprising a polystyrene vitrimer, wherein the dynamic crosslinker comprises a polyol that reacts with the maleated polystyrene to form the polystyrene vitrimer comprising ester linkages configured to undergo transesterification.
2. The method as claimed in claim 1, wherein performing the second extrusion (104) comprises extruding in presence of a second polystyrene, wherein the polystyrene product comprises a blend of the second polystyrene and the polystyrene vitrimer.
3. The method as claimed in claim 1, wherein the first polystyrene is a virgin polystyrene or a recycled polystyrene, and wherein the first polystyrene is selected from a group of general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), and any combinations thereof.
4. The method as claimed in claim 2, wherein the second polystyrene is a virgin polystyrene or a recycled polystyrene, and wherein the second polystyrene is selected from a group of general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), expandable polystyrene (EPS), styrene-butadiene rubber (SBR), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-ethylene/butylene-styrene (SEBS), and any combinations thereof.
5. The method as claimed in claim 1, wherein the polyol is selected from a group of aliphatic diols, aromatic diols, aliphatic triols, aliphatic tetrols, polyether polyols, and any combinations thereof.
6. The method as claimed in claim 5, wherein the polyol comprises ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, cyclohexanedimethanol, glycerol, trimethylolpropane, pentaerythritol, sorbitol, polyethylene glycol, polypropylene glycol, polyglycerols, or a combination thereof.
7. The method as claimed in 2, wherein a concentration of the second polystyrene is varied to modify a property of the polystyrene product, wherein the property comprises one or more of a mechanical property, a thermal property, a tensile strength, or an elongation at yield.
8. The method as claimed in 2, wherein the maleated polystyrene and the second polystyrene are extruded in a weight ratio of 9:1 to 1:1.09.
9. The method as claimed in claim 1, wherein the maleated polystyrene and the dynamic crosslinker are extruded in a weight ratio of 9:1 to 49:1.
10. The method as claimed in claim 1, wherein the first extrusion (102) and the second extrusion (104) are performed in a twin-screw extruder at a screw speed of 80 to 120 rotations per minute (rpm) and at a residence time of 1 to 10 minutes.
11. The method as claimed in claim 1, wherein the free radical initiator comprises benzoyl peroxide, lauryl peroxide, dicumyl peroxide (DCP), or combinations thereof.
12. The method as claimed in claim 1, wherein the Lewis acid catalyst comprises triazobicyclodecene, triphenylphosphine, zinc acetylacetonate, or combinations thereof.
13. The method as claimed in claim 1, wherein the method of processing the polystyrene comprises upcycling the polystyrene, recycling the polystyrene, or modifying a property of the polystyrene, or combinations thereof.
14. A polystyrene product obtained by a method, the method comprising:
performing a first extrusion (102) of a first polystyrene and a maleic anhydride in presence of a free radical initiator at a temperature in a range of 200 to 240 °C to form a maleated polystyrene, wherein the first polystyrene and the maleic anhydride are present in a weight ratio of 9:1 to 49:1, wherein the first polystyrene comprises a virgin polystyrene or a recycled polystyrene, selected from a group of general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), and any combinations thereof; and
performing a second extrusion (104) of the maleated polystyrene and a dynamic crosslinker in presence of a Lewis acid catalyst at a temperature in a range of 200 to 240 °C to form the polystyrene product comprising a polystyrene vitrimer, wherein the dynamic crosslinker comprises a polyol that reacts with the maleated polystyrene to form the polystyrene vitrimer comprising ester linkages configured to undergo transesterification.
15. The polystyrene product as claimed in claim 14, comprising a second polystyrene, the second polystyrene is a virgin polystyrene or a recycled polystyrene, and wherein the second polystyrene is selected from a group of general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), expandable polystyrene (EPS), styrene-butadiene rubber (SBR), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-ethylene/butylene-styrene (SEBS), and any combinations thereof.
16. An article comprising the polystyrene product as claimed in any of the claims 1-15.