DESC:TECHNICAL FIELD
[0001] The present disclosure relates to polymer recycling technology, in particular, the present disclosure relates to a method for co-upcycling post-consumer recycled polyolefins and recyclable polymer compositions with enhanced mechanical properties and recyclability.
BACKGROUND
[0002] In the plastics industry, there is a growing demand for sustainable alternatives to traditional mechanical recycling due to increasing concerns over environmental degradation, property deterioration, and resource depletion. The sustainable alternatives include co-upcycling methods, which act as an eco-friendly alternative to the traditional single-polymer recycling approaches. Moreover, the co-upcycling has suitable mechanical properties, enhanced recyclability, improved property retention, and a reduced environmental footprint compared to traditional mechanical recycling methods. However, one of the challenges limiting the widespread use of polyolefin co-recycling is the phenomenon of incompatibility. The incompatibility manifests as poor mechanical properties and phase separation that form when different polyolefin waste streams are processed together. The incompatibility affects the performance of the recycled material. The incompatibility forms from the fundamental differences in chemical structure and processing characteristics between polymers such as polyethylene and polypropylene when exposed to thermal processing conditions. Thus, there exists a technical problem of how to develop a compatible co-upcycling method for mixed polyolefin waste streams.
[0003] Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks.
SUMMARY
[0004] The present disclosure provides a method for co-upcycling post-consumer recycled polyolefins and a recyclable polymer composition with enhanced mechanical properties. The present disclosure addresses the technical problem of how to develop a compatible co-upcycling method for mixed polyolefin waste streams while maintaining mechanical properties and recyclability over multiple processing cycles. An aim of the present disclosure is to provide a solution that overcomes at least partially the problems encountered in the prior art and provides an improved method for co-upcycling post-consumer recycled polyolefins and an improved recyclable polymer composition featuring a vitrimer matrix formation and mechanical interlocking that enables enhanced mechanical properties while maintaining recyclability with property retention.
[0005] One or more objectives of the present disclosure is achieved by the solutions provided in the enclosed independent claims. Advantageous implementations of the present disclosure are further defined in the dependent claims.
[0006] In one aspect, the present disclosure provides a method for co-upcycling post-consumer recycled polyolefins comprising functionalizing post-consumer recycled polypropylene (PCR PP) by melt grafting a polar functional monomer in the presence of a vinyl aromatic stabilizer and a radical initiator to form grafted PCR PP having enhanced grafting efficiency and reduced chain degradation. Furthermore, the method provides crosslinking the grafted PCR PP with a dynamic crosslinker containing reversible covalent bonds to form a vitrimer network, and mechanically interlocking post-consumer recycled polyethylene (PCR PE) within the vitrimer network through melt blending to form a co-upcycled blend having enhanced mechanical properties compared to individual components and recyclability with property retention over multiple processing cycles.
[0007] Advantageously, the method for co-upcycling post-consumer recycled polyolefins is used to provide a combination of enhanced mechanical properties and recyclability by incorporating a vinyl aromatic stabilizer during functionalization and forming a vitrimer network through dynamic crosslinking. The method is used to create a co-upcycled blend that mechanically interlocks PCR PE within a vitrimerized PCR PP matrix. The method is used to provide a dual-mechanism behavior for efflorescence control through chemical binding and physical entanglement. During normal processing conditions, the vitrimer network provides enhanced mechanical properties with yield strengths exceeding individual components, delivering exceptional strength and dimensional stability compared to conventional polymer blends. When subjected to thermomechanical recycling, the dynamic covalent bonds undergo controlled bond exchange reactions, enabling property retention and even improvement over multiple processing cycles while maintaining overall structural integrity. Unlike existing recycling methods, which suffer from progressive property degradation, the co-upcycled blend can be repeatedly processed, maintaining or exceeding original mechanical properties without sacrificing the performance characteristics associated with high-quality polymer materials.
[0008] In another aspect, the present disclosure provides a recyclable polymer composition comprising a vitrimer matrix derived from post-consumer recycled polypropylene having grafted polar functional groups crosslinked with dynamic covalent bonds, and post-consumer recycled polyethylene mechanically interlocked within the vitrimer matrix without chemical modification. Moreover, the composition exhibits yield strength greater than individual components and maintains or improves mechanical properties upon thermomechanical recycling.
[0009] Advantageously, the recyclable polymer composition provides a combination of mechanical performance and enhanced recyclability by incorporating a vitrimer matrix derived from functionalized post-consumer recycled polypropylene with mechanically interlocked post-consumer recycled polyethylene. The composition creates a unique hybrid structure that combines the benefits of dynamic covalent networks with physical entanglement mechanisms. During thermomechanical recycling, the dynamic covalent bonds enable controlled bond exchange while the mechanically interlocked PCR PE maintains structural stability without undergoing irreversible chemical modification.
[0010] In yet another aspect, the present disclosure is configured to provide a functionalized post-consumer recycled polypropylene comprising a polypropylene backbone derived from post-consumer waste, polar functional groups grafted onto the backbone in the presence of vinyl aromatic stabilizer resulting in enhanced grafting yield compared to direct grafting, and reactive sites capable of forming dynamic covalent networks with multifunctional crosslinkers.
[0011] Advantageously, the functionalized post-consumer recycled polypropylene provides a combination of enhanced grafting efficiency and reduced polymer degradation by incorporating polar functional groups through vinyl aromatic stabilizer-assisted grafting. The functionalized polymer creates reactive sites distributed along the polypropylene backbone that enable subsequent dynamic network formation.
[0012] It is to be appreciated that all the aforementioned implementation forms can be combined. All steps that are performed by the various entities described in the present application, as well as the functionalities described to be performed by the various entities, are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. It will be appreciated that features of the present disclosure are susceptible to being combined in various combinations without departing from the scope of the present disclosure as defined by the appended claims.
[0013] Additional aspects, advantages, features, and objects of the present disclosure would be made apparent from the drawings and the detailed description of the illustrative implementations construed in conjunction with the appended claims that follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not too scale. Wherever possible, like elements have been indicated by identical numbers.
[0015] Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:
FIG.1 is a flowchart illustrating a method for co-upcycling post-consumer recycled polyolefins, in accordance with an embodiment of the present disclosure;
FIG. 2 is a diagram illustrating the overall process flow for co-upcycling post-consumer recycled polyolefins, in accordance with an embodiment of the present disclosure;
FIG. 3A is a flowchart illustrating a reaction mechanism for functionalization of post-consumer recycled polypropylene relevant to creating a functionalized post-consumer recycled polypropylene for vitrimer formation, in accordance with an embodiment of the present disclosure;
FIG. 3B is a diagram illustrating the formation of a recyclable polymer composition through vitrimer network formation from the functionalized post-consumer recycled polypropylene, in accordance with an embodiment of the present disclosure;
FIG. 4 is a graphical representation illustrating Fourier transform infrared (FTIR) spectroscopy analysis of different polymer formulations in the co-upcycling process, in accordance with an embodiment of the present disclosure;
FIG. 5 is a graphical representation illustrating a detailed view of Fourier transform infrared (FTIR) spectroscopy analysis focusing on specific functional group regions of polymer formulations, in accordance with an embodiment of the present disclosure;
FIG. 6 is a graphical representation illustrating gel fraction analysis of various polymer formulations, in accordance with an embodiment of the present disclosure;
FIG. 7 is a graphical representation illustrating mechanical property comparison of different polymer formulations, in accordance with an embodiment of the present disclosure; and
FIG. 8 is a graphical representation illustrating recycling performance recovery rates after three processing cycles, in accordance with an embodiment of the present disclosure.
[0016] In the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item to which the arrow is pointing.
DETAILED DESCRIPTION OF EMBODIMENTS
[0017] Generally, polyethylene (PE) remains difficult to vitrimerize due to side reactions such as chain scission and uncontrolled self-crosslinking during peroxide-mediated functionalization, which exhaust functional groups essential for dynamic bond formation. The peroxide-mediated grafting process in PE systems leads to ß-scission reactions that degrade the polymer backbone, reducing molecular weight and creating structural instability. Furthermore, the uncontrolled crosslinking consumes reactive sites before they can participate in controlled dynamic bond exchange mechanisms, preventing the formation of the reversible covalent networks characteristic of vitrimer materials. To address this fundamental limitation, the present disclosure provides a novel approach involving the blending of PCR PE, derived from widely used single-use milk pouches, with a preformed PCR polypropylene (PP) vitrimer matrix. The method is used to prevent a direct vitrimerization of PE by mechanically interlocking the PCR PE chains within an established vitrimer network, thereby preserving the PE's inherent chemical stability while benefiting from the dynamic crosslinking capabilities of the functionalized PP matrix. The present disclosure enables the incorporation of PE into recyclable vitrimer systems without subjecting the polyethylene to the harsh chemical modifications that would otherwise compromise its structural integrity and processing characteristics.
[0018] The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practicing the present disclosure are also possible.
[0019] FIG.1 is a flowchart illustrating a method for co-upcycling post-consumer recycled polyolefins, in accordance with an embodiment of the present disclosure. With reference to FIG. 1, a method 100 includes steps 102 to 106.
[0020] At step 102, the method 100 includes functionalizing post-consumer recycled polypropylene (PCR PP) by melt grafting a polar functional monomer in the presence of a vinyl aromatic stabilizer and a radical initiator to form a grafted PCR PP. The PCR PP refers to a polypropylene polymer collected from post-consumer sources such as used food containers, buckets, and packaging waste. The polypropylene is a hydrocarbon-based thermoplastic polymer characterized by high crystallinity and non-polarity.
[0021] The melt grafting refers to a reactive extrusion method in which the polypropylene is first melted and then chemically modified by covalently attaching functional molecules to its molecular structure. The polymer chain structure of polypropylene, hereinafter referred to as the “polypropylene backbone”, consists of saturated carbon-carbon bonds that form the main molecular chain to which chemical groups may be attached. The melt grafting is carried out by heating the polypropylene above its melting point, for example, at a processing temperature of 180 degrees Celsius, and introducing reactive additives into the melt phase.
[0022] In an implementation, the polar functional monomer includes glycidyl methacrylate (GMA). The GMA is a bifunctional monomer comprising an epoxy ring and a methacrylate group. The methacrylate group undergoes radical-initiated reactions while the epoxy ring remains unreacted during the melt grafting. The methacrylate group is chemically bonded to the polypropylene backbone via a process known as free radical-initiated grafting. The free radical-initiated grafting involves generation of free radicals that abstract hydrogen atoms from the polypropylene chains, resulting in reactive macroradicals that form covalent bonds with the methacrylate group of the GMA.
[0023] In an implementation, the vinyl aromatic stabilizer includes styrene. The styrene comprises a vinyl group and an aromatic ring. The vinyl group enables chemical grafting onto the polypropylene backbone, and the aromatic ring stabilizes radical intermediates through resonance. The styrene participates in a co-grafting mechanism with the GMA. The styrene and the GMA are simultaneously or sequentially grafted onto the same polypropylene backbone. The co-grafting enhances the grafting efficiency of the GMA and reduces beta-chain scission. The beta-chain scission refers to the degradation of the polypropylene chains caused by cleavage at the beta-position of the radical center. The degradation of the polypropylene chains reduces molecular weight and mechanical strength of the polypropylene chain.
[0024] In an implementation, the radical initiator includes dicumyl peroxide (DCP). The DCP decomposes thermally to form free radicals. The free radicals initiate hydrogen abstraction from the polypropylene backbone, forming polypropylene macroradicals. The polypropylene macroradicals undergo coupling with the methacrylate group of the GMA and the vinyl group of the styrene. The presence of the styrene leads to the formation of stabilized styryl radicals. The styryl radicals enhance reaction control and enable the formation of branched graft structures. The use of styrene leads to the formation of grafted polypropylene chains with the GMA and styrene moieties.
[0025] The melt grafting is carried out under controlled shear using a co-rotating twin-screw micro-extruder equipped with a recirculation loop. The micro-extruder allows precise control over residence time, thermal exposure, and shear intensity. In an implementation, other extrusion systems such as counter-rotating twin-screw extruders or single-screw reactive extruders may also be used to perform the melt grafting.
[0026] A grafted polypropylene (g'-PCR PP) is produced after grafting. The grafted polypropylene includes pendant epoxy groups available for dynamic crosslinking. In an implementation, the weight ratio of the GMA to the styrene is maintained at approximately 1:1 to achieve an optimal balance between grafting efficiency and structural stability of the polypropylene. In another implementation, an antioxidant such as Irganox 1010 is added in an amount of 0.5 weight percent during melt grafting to suppress oxidative degradation of the polypropylene chains during thermal processing. For the functionalization, the PCR PP is modified using a carefully balanced formulation comprising the PCR PP with 79 weight percent, the GMA with 10 weight percent, the styrene with 10 weight percent, the DCP with 0.5 weight percent, and the Irganox 1010 antioxidant with 0.5 weight percent to produce the g'-PCR PP. The balanced formulation maintains a 1:1 ratio of the GMA to the styrene to optimize grafting efficiency while minimizing chain degradation, where the low concentrations of DCP (0.5 weight percent) and Irganox (0.5 weight percent) provide controlled radical initiation and oxidative protection without compromising the functionalization process. The crosslinking step involves combining g'-PCR PP (85 weight percent) with AFD crosslinker (15 weight percent) to form the V'-PCR PP vitrimer matrix. The formulation uses approximately 15 weight percent AFD crosslinker to achieve suitable gel content while maintaining dynamic bond exchange capabilities essential for recyclability. The final co-upcycled blends are prepared using two comparative formulations: a conventional PCR PP/PCR PE blend (70:30 weight percent) and the innovative V'-PCR PP/PCR PE blend (70:30 weight percent). These compositions demonstrate the preferred 70:30 ratio that balances mechanical properties with processability, where the vitrimer matrix provides structural integrity while the mechanically interlocked PCR PE contributes to enhanced toughness and recyclability. The systematic progression from unmodified PCR PP through functionalization, crosslinking, and final blending enables the transformation of post-consumer waste into high-performance recyclable materials.
[0027] In an implementation, the vinyl aromatic stabilizer captures polymer radicals to form stable aromatic radicals. The stable aromatic radicals facilitate grafting of the polar functional monomer while suppressing ß-chain scission of the PCR PP backbone. The vinyl aromatic stabilizer, specifically styrene, functions by intercepting primary and secondary polypropylene radicals formed during DCP decomposition and converting them into resonance-stabilized benzyl radicals through radical addition across the vinyl double bond. For example, when PCR PP macroradicals are generated at 180 degrees Celsius, the styrene molecules preferentially react with these radicals at rates 10-50 times faster than competing ß-scission reactions, forming styryl-terminated polymer chains that resist further degradation. This radical capture mechanism is performed to prevent the formation of low molecular weight degradation products and volatile compounds that would otherwise reduce the grafting efficiency of GMA and compromise the mechanical properties of the functionalized polymer. The stabilization results in preserved molecular weight distribution of the PCR PP backbone while enabling controlled attachment of polar functional groups through subsequent GMA grafting reactions.
[0028] At step 104, the method 100 includes crosslinking the grafted polypropylene (g'-PCR PP) with a dynamic crosslinker to form a vitrimer network. A vitrimer, as used herein, refers to a covalently crosslinked polymer network comprising reversible bond exchange capabilities under elevated temperatures. The behaviour of the vitrimer allows the material to be thermally reprocessed while maintaining the structural integrity of the material.
[0029] In an implementation, the dynamic crosslinker includes 4,4’-diaminodiphenyl disulfide (AFD). The AFD is an aromatic disulfide compound comprising two amine functional groups and a central disulfide linkage. The amine groups of the AFD react with the epoxy groups of the g'-PCR PP via a nucleophilic ring-opening reaction. The reaction between the amine and epoxy functionalities results in the formation of secondary amine linkages, while the disulfide group remains embedded within the network. The disulfide linkage enables dynamic exchange of covalent bonds at elevated processing temperatures, contributing to the vitrimer characteristics of the crosslinked polypropylene. The disulfide-based dynamic crosslinking facilitates reversible bond exchange through thermally activated cleavage and reformation of the S–S bonds, which allows for melt reprocessing and recyclability of PCRPP.
[0030] In an implementation, the crosslinking is performed by melt blending the g'-PCR PP with the AFD in a reactive extrusion system. The blend is processed at a temperature of approximately 180 degrees Celsius under shear to initiate the epoxy-amine ring-opening reaction and to distribute the crosslinker uniformly throughout the polymer melt. In an implementation, the reactive extrusion is carried out using a co-rotating twin-screw extruder. In another implementation, alternative processing equipment such as a batch mixer or counter-rotating twin-screw extruder may also be used to perform the crosslinking reaction. In an implementation, the AFD is added in an amount of 15 weight percent relative to the g'-PCR PP to achieve a crosslink density sufficient for vitrimer formation.
[0031] In an implementation, the dynamic crosslinker forms reversible bonds selected from disulfide bonds, transesterification bonds, or transcarbamoylation bonds that enable bond exchange at processing temperatures while maintaining network integrity at service temperatures. The dynamic crosslinker, specifically AFD (4,4'-diaminodiphenyl disulfide), creates disulfide bonds through nucleophilic ring-opening of epoxy groups by primary amine functionalities, forming secondary amine linkages with pendant disulfide bridges embedded within the polymer network. For example, at processing temperatures of 180 degrees Celsius, the disulfide bonds undergo thermal activation enabling metathesis reactions where S-S bonds cleave and reform with neighboring disulfide groups, facilitating stress relaxation and bond rearrangement without permanent network degradation. This reversible bonding mechanism is employed to enable thermomechanical reprocessing and recycling while maintaining crosslink density and mechanical performance at ambient service temperatures below 100 degrees Celsius. The dynamic bond exchange provides the vitrimer 100 with self-healing capabilities and enables multiple recycling cycles with property retention or improvement due to network reorganization during each reprocessing event.
[0032] Additionally, the crosslinking is performed using g'-PCR PP (85 weight percent) and AFD (15 weight percent) under processing conditions of 180 degrees Celsius, 150 rpm for 2 minutes. The crosslinking efficiency is confirmed by gel content analysis, where the pure V'-PCR PP vitrimer achieves 58 percent gel content, confirming successful crosslinking. The FTIR analysis of V'-PCR PP shows an additional peak at 3374 cm?¹ (O–H stretch) confirming successful AFD crosslinker incorporation within the PCR PP matrix and formation of dynamic covalent bonds. The crosslinked vitrimer obtained is referred to as vitrimerized polypropylene (V'-PCR PP), which exhibits melt reprocessability and mechanical stability suitable for subsequent blending with other recycled polymers.
[0033] At step 106, the method 100 includes mechanically interlocking post-consumer recycled polyethylene (PCR PE) within the vitrimerized polypropylene (V'-PCR PP) network through melt blending to form a co-upcycled polymer blend. The PCR PE refers to polyethylene obtained from post-consumer waste streams such as single-use milk pouches and packaging films. The polyethylene is a saturated polyolefin characterized by high flexibility, low surface energy, and chemical inertness. The mechanical interlocking refers to the physical entrapment of polyethylene chains within the vitrimer matrix without the formation of covalent bonds between the polyethylene and the crosslinked polypropylene.
[0034] In an implementation, the mechanical interlocking occurs through physical interpenetration and polymer chain entanglement facilitated by dynamic bond exchange during melt processing, creating interfacial adhesion without covalent bonding between PCR PE and the vitrimer network. The mechanical interlocking is achieved by blending PCR PE with the V'-PCR PP vitrimer matrix 200 at temperatures where the dynamic disulfide bonds undergo exchange reactions, allowing temporary network relaxation that accommodates penetration of polyethylene chains into the crosslinked structure. For example, during melt blending at 180 degrees Celsius and 150 rpm for 2 minutes, the dynamic covalent bonds in the vitrimer undergo controlled cleavage and reformation, creating transient openings in the three-dimensional network that allow PCR PE chains to interpenetrate and become physically trapped upon cooling. This interlocking mechanism is utilized to avoid chemical modification of the polyethylene phase while achieving intimate mixing and stress transfer between the two immiscible polymer phases. The physical entanglement creates a composite structure where the PCR PE contributes ductility and impact resistance while the vitrimer matrix provides structural rigidity and recyclability through dynamic crosslinking.
[0035] In an implementation, the PCR PE is derived from single-use packaging waste including milk pouches, and the co-upcycled blend is processable into articles suitable for 3D printing, injection molding, or extrusion applications with circular economy compatibility. The PCR PE is obtained from post-consumer low-density polyethylene (LDPE) milk pouches and linear low-density polyethylene (LLDPE) packaging films that are collected, cleaned, and granulated through mechanical recycling processes before incorporation into the vitrimer blend. For example, the V'-PCR PP/PCR PE blend with 70:30 weight ratio demonstrates melt flow characteristics suitable for fused deposition modeling (FDM) 3D printing with extrusion temperatures of 200-220 degrees Celsius, injection molding with cycle times of 30-60 seconds, and profile extrusion for structural applications. This processing versatility is achieved to enable direct replacement of virgin polymers in existing manufacturing equipment while providing enhanced end-of-life value through repeated recyclability. The circular economy compatibility results from the ability to repeatedly reprocess the co-upcycled blend without significant property degradation, enabling closed-loop recycling systems where waste materials are continuously converted back into high-value products.
[0036] In an implementation, the mechanical interlocking is achieved by blending the V'-PCR PP and the PCR PE under molten conditions at a processing temperature of approximately 180 degrees Celsius. The melt blending allows the V'-PCR PP and the PCR PE, which are thermodynamically immiscible, to partially interpenetrate. In addition, the dynamic nature of the vitrimeric bonds in the V'-PCR PP enables conformational rearrangements during mixing. Upon cooling, the vitrimer bonds become kinetically stable, and the entangled polyethylene chains become mechanically locked within the vitrimer network. Moreover, specific blend ratios with the optimal V'-PCR PP/PCR PE blend ratio being 70:30 by weight, processed at 180 degrees Celsius, 150 rpm for 2 minutes is used to provide the mechanical interlocking.
[0037] In an implementation, the blend ratio of V'-PCR PP to PCR PE is selected from 30:70, 50:50, or 70:30 by weight depending on the desired mechanical performance. In an implementation, the blending is performed in a co-rotating twin-screw extruder or a melt mixer to ensure uniform dispersion of the polyethylene phase. In another implementation, the vitrimer blend is processed into molded articles using injection molding or extrusion techniques. The co-upcycled polymer blend obtained from step 106 demonstrates enhanced mechanical strength, thermal resistance, and recyclability compared to unmodified PCR PE or PCR PP alone. The vitrimer matrix provides a structurally robust network, while the embedded polyethylene contributes to improved toughness and strain hardening behaviour.
[0038] FIG. 2 is a diagram illustrating the overall process flow for co-upcycling post-consumer recycled polyolefins, in accordance with an embodiment of the present disclosure. FIG. 2 is described in conjunction with elements from FIG. 1. With reference to FIG. 2, there is shown a process flow 200 representing the complete lifecycle of polyolefin waste processing and upcycling such as by depicting the transformation of household plastic waste streams through collection, processing, and manufacturing stages. The discarded milk packets and household PP waste being collected and processed through mechanical systems at 180 degrees Celsius and 150 rpm for 2 minutes. The diagram 200 illustrates the formation of PCR PP and PCR PE through shredding and granulation processes, followed by vitrimer formation and mechanical interlocking to create V'-PCR PP/PCR PE blends. The final products include 3D printed applications and mechanically interlocked polymer structures, with chemical structures and dynamic crosslinks represented at the molecular level to demonstrate the co-upcycling mechanism. As a result, the method 100 is used for transforming mixed polyolefin waste into high-value applications through controlled processing conditions and vitrimer network formation that provides direct conversion of household waste streams into functional products while maintaining chemical compatibility and mechanical performance through dynamic crosslinking mechanisms.
[0039] FIG. 3A is a flowchart illustrating a reaction mechanism for functionalization of post-consumer recycled polypropylene relevant to creating a functionalized post-consumer recycled polypropylene for vitrimer formation, in accordance with an embodiment of the present disclosure. FIG. 3A is described in conjunction with FIGs. 1 to 2. With reference to FIG. 3A, there is shown a flowchart 300A that includes a series of operations from 302A to 306A for producing the functionalized post-consumer recycled polypropylene.
[0040] At operation 302A, the PCR PP macroradicals are generated from the polypropylene backbone derived from post-consumer waste through initiation with the DCP (dicumyl peroxide) under Irganox stabilization at 180 degrees Celsius, 150 rpm for 2 minutes. The DCP acts as the radical initiator that decomposes at elevated temperatures to generate free radicals along the polypropylene backbone. The Irganox functions as the antioxidant stabilizer that prevents unwanted oxidative degradation during the radical generation process. The radical initiation occurs through thermal decomposition of the peroxide bond in the DCP, leading to the formation of reactive sites along the polypropylene backbone derived from post-consumer waste.
[0041] At operation 304A, the PCR PP macroradicals react with the styrene to form styryl macroradicals through radical addition reactions. The styrene acts as the vinyl aromatic stabilizer that captures PCR PP radicals to form stable styryl macroradicals, resulting in enhanced grafting yield compared to direct grafting approaches. The styrene is an aromatic vinyl monomer containing a benzene ring attached to a vinyl group (CH2=CH-). The styryl macroradicals are formed when the reactive PCR PP radicals add across the vinyl double bond of the styrene. The styrene addition occurs under the processing conditions of 180 degrees Celsius, 150 rpm for 2 minutes with Irganox stabilization. The styryl groups provide stabilization to the polymer radicals and create attachment points for subsequent grafting of polar functional groups.
[0042] At operation 306A, the styryl macroradicals undergo grafting with GMA (glycidyl methacrylate) to produce functionalized g'-PCR PP containing polar functional groups grafted onto the backbone. The GMA is a bifunctional monomer containing both a methacrylate vinyl group and an epoxy ring that provides the polar functional groups. The grafting reaction occurs through radical addition of the styryl macroradicals to the vinyl group of GMA under the same processing conditions. The epoxy rings in the grafted GMA serve as reactive sites capable of forming dynamic covalent networks with multifunctional crosslinkers. The functionalized g'-PCR PP contains both styryl groups for radical stabilization and epoxy groups as polar functional groups for dynamic crosslinking, completing the functionalization pathway necessary for creating the functionalized post-consumer recycled polypropylene.
[0043] FIG. 3B is a diagram illustrating the formation of a recyclable polymer composition through vitrimer network formation from the functionalized post-consumer recycled polypropylene, in accordance with an embodiment of the present disclosure. FIG. 3B is described in conjunction with elements from FIGs. 1 to 3A. With reference to FIG. 3B, there is shown a reaction scheme 300B representing the second step of creating the recyclable polymer composition through crosslinking of the polar functional groups with dynamic covalent bonds. The reaction between the functionalized g'-PCR PP and AFD (aromatic disulfide crosslinker) at 180 degrees Celsius, 150 rpm for 2 minutes forms the vitrimer matrix derived from post-consumer recycled polypropylene. The formation of dynamic covalent bonds through disulfide bond exchange mechanisms creates the vitrimer matrix with a three-dimensional network structure containing reversible crosslinks. The vitrimer matrix provides the foundation for the recyclable polymer composition that maintains mechanical properties during recycling. As a result, the method 100 is used to provide controlled functionalization and crosslinking pathways that preserve the polypropylene backbone derived from post-consumer waste while introducing polar functional groups and reactive sites for dynamic network formation, which enables precise control over grafting efficiency and crosslink density, resulting in a recyclable polymer composition with dynamic covalent bonds that maintain mechanical properties during thermomechanical recycling.
[0044] The recyclable polymer composition comprises a vitrimer matrix derived from post-consumer recycled polypropylene having grafted polar functional groups crosslinked with dynamic covalent bonds. The vitrimer matrix is formed by crosslinking the functionalized g'-PCR PP with AFD (aromatic disulfide crosslinker) through nucleophilic attack of amine groups on epoxy rings, creating disulfide linkages that undergo reversible bond exchange at elevated temperatures. For example, the crosslinking reaction occurs at 180 degrees Celsius, 150 rpm for 2 minutes, where the epoxy groups from the grafted GMA react with the amine functionalities of AFD to form a three-dimensional network. The crosslinking is performed to create dynamic covalent bonds that enable reprocessability while maintaining structural stability, resulting in a vitrimer network that can undergo controlled bond rearrangement during recycling without permanent degradation.
[0045] The post-consumer recycled polyethylene is mechanically interlocked within the vitrimer matrix without chemical modification. The mechanical interlocking is achieved through melt blending of PCR PE with the vitrimerized PCR PP matrix under the processing conditions of 180 degrees Celsius, 150 rpm for 2 minutes, where the PCR PE chains become physically entangled within the crosslinked network structure without forming covalent bonds. For instance, the PCR PE maintains the original chemical structure while being trapped within the three-dimensional vitrimer network through physical entanglement and interfacial interactions.
[0046] In an implementation, repeated recycling induces additional crosslinking between unreacted functional groups, resulting in progressive enhancement of mechanical properties over multiple processing cycles. The additional crosslinking occurs when residual epoxy groups from the initial GMA grafting reaction encounter unreacted amine functionalities from AFD crosslinker during subsequent thermomechanical reprocessing at 180 degrees Celsius. For example, after three recycling cycles, the V'-PCR PP/PCR PE blend 800 achieves yield strength recovery rates exceeding 100 percent (30±0.45 MPa compared to initial 27±0.59 MPa) and elongation recovery rates above 100 percent (24±0.91% compared to initial 23±0.29%), demonstrating property improvement rather than degradation. This progressive enhancement mechanism is enabled by the dynamic nature of the crosslinked network that allows bond rearrangement and optimization during each reprocessing cycle while simultaneously forming new crosslinks from previously unreacted sites. The cumulative crosslinking results in densification of the vitrimer network and improved load transfer efficiency between the polymer phases, creating a recyclable material system that becomes stronger with each use cycle.
[0047] In an implementation, the vitrimer matrix exhibits gel fraction indicating crosslink density and activation energy consistent with dynamic covalent bond exchange mechanisms. The vitrimer matrix demonstrates gel fraction values of 58 percent for pure V'-PCR PP 610 and 38 percent for the V'-PCR PP/PCR PE blend 608, measured through solvent extraction in xylene at 120 degrees Celsius for 24 hours to determine the insoluble crosslinked fraction. For example, dynamic mechanical analysis reveals activation energy values of 120-150 kJ/mol for the disulfide bond exchange process, which falls within the typical range for thermally activated covalent bond metathesis reactions and confirms the dynamic nature of the crosslinked network. This characterization is performed to distinguish the vitrimer behavior from conventional thermoset materials that exhibit permanent crosslinks with activation energies exceeding 200 kJ/mol for bond breaking. The measured gel fraction and activation energy values confirm the formation of a covalently crosslinked network that can undergo controlled bond rearrangement at processing temperatures while maintaining structural integrity at service temperatures.
[0048] The functionalized post-consumer recycled polypropylene comprises polar functional groups grafted onto the backbone in the presence of vinyl aromatic stabilizer resulting in enhanced grafting yield compared to direct grafting. For example, the styrene stabilization prevents chain scission during radical formation and provides controlled attachment points for GMA grafting, achieving enhanced grafting efficiency. The stabilized grafting approach is utilized to minimize polymer backbone degradation while maximizing functional group incorporation, resulting in functionalized g'-PCR PP with preserved molecular weight and homogeneous distribution of reactive epoxy sites.
[0049] The reactive sites capable of forming dynamic covalent networks with multifunctional crosslinkers are provided by the epoxy rings in the grafted GMA units. The epoxy functionality serves as nucleophilic attack sites for amine-containing crosslinkers such as AFD, enabling ring-opening reactions that form stable yet reversible covalent bonds through disulfide exchange mechanisms. For instance, each epoxy ring can react with primary or secondary amines to form hydroxyl-amine linkages that subsequently participate in dynamic bond exchange at elevated temperatures. The reactive sites are incorporated to enable subsequent vitrimer network formation with multifunctional crosslinkers, allowing the functionalized PCR PP to undergo controlled crosslinking while maintaining the ability to rearrange bonds during thermomechanical processing for enhanced recyclability.
[0050] In an implementation, the polar functional groups comprise epoxy groups, anhydride groups, or carboxyl groups capable of ring-opening reactions or condensation reactions with crosslinkers containing complementary functional groups. The polar functional groups are introduced through melt grafting of reactive monomers including glycidyl methacrylate (GMA) for epoxy functionality, maleic anhydride for anhydride groups, or acrylic acid for carboxyl groups, each providing distinct reaction pathways for subsequent crosslinking with multifunctional compounds. For example, epoxy groups from GMA undergo nucleophilic ring-opening with primary or secondary amines to form hydroxyl-amine linkages, while anhydride groups react with hydroxyl or amine functionalities through condensation reactions to create ester or amide bonds with the release of water or alcohol byproducts. This diversity of polar functional groups is incorporated to enable compatibility with various crosslinking chemistries and processing requirements depending on the desired vitrimer properties and application needs. The multiple functionalization pathways provide flexibility in network design and allow optimization of dynamic bond exchange kinetics, crosslink density, and thermal stability for specific end-use applications while maintaining the fundamental vitrimer characteristics of reversible covalent bonding.
[0051] FIG. 4 is a graphical representation illustrating Fourier transform infrared (FTIR) spectroscopy analysis of different polymer formulations in the co-upcycling process, in accordance with an embodiment of the present disclosure. FIG. 4 is described in conjunction with elements from FIGs. 1 to 3B. With reference to FIG. 4, there is shown a graphical representation 400 depicting the absorption of infrared light by different polymer samples at different wavelengths. The transmittance percentage is represented on the ordinate axis. The wavenumber is measured in centimeters inverse (cm?¹) on the abscissa axis. Transmittance percentage quantifies the amount of light that passes through a polymer sample, expressed as a percentage of the original light intensity. The wavenumber is defined as the number of wavelengths per unit distance. The graphical representation 400 includes a curve 402 depicting the spectral behaviour of V'-PCR PP. Further, the graphical representation 400 includes a curve 404 representing the spectral behaviour of g'-PCR PP. The graphical representation 400 includes a curve 406 representing the spectral behaviour of PCR PP. The graphical representation 400 includes a curve 408 representing the spectral behaviour of PCR PE. Further, the graphical representation 400 includes a region 410 approximately ranging between 2700-3200 cm?¹.
[0052] The curve 402 exhibits characteristic absorption features confirming successful formation of the vitrimer matrix derived from post-consumer recycled polypropylene having grafted polar functional groups crosslinked with dynamic covalent bonds. The curve 402 includes multiple absorption peaks in the region 410, with distinct peaks corresponding to O-H stretching vibrations from hydroxyl groups formed during the crosslinking reaction between epoxy groups and amine functionalities of AFD. The curve 402 shows additional peaks in the region 410 representing N-H stretching vibrations from the amine-epoxy reaction products, confirming the formation of dynamic covalent bonds in the recyclable polymer composition. In an implementation, the spectral characteristics in the region 410 confirm that the PCR PE maintains its original chemical structure during mechanical interlocking in the recyclable polymer composition. Comparative analysis shows that PCR PE and PCR PP individually exhibit zero gel fraction, and conventional PCR PP/PCR PE blends also show zero gel fraction, confirming that physical mixing alone cannot create the crosslinked networks necessary for enhanced performance.
[0053] The curve 404 exhibits absorption characteristics confirming the presence of polar functional groups grafted onto the polypropylene backbone derived from post-consumer waste. The curve 404 includes peaks in the region 410 corresponding to C-H stretching vibrations from both aliphatic groups and aromatic groups from grafted styrene units. The curve 404 shows distinct absorption features representing the successful functionalization of the post-consumer recycled polypropylene with reactive sites capable of forming dynamic covalent networks with multifunctional crosslinkers.
[0054] The curve 406 includes absorption characteristics representing the baseline polypropylene backbone derived from post-consumer waste before functionalization. The curve 406 exhibits peaks in the region 410 corresponding to aliphatic C-H stretching vibrations characteristic of the unmodified polypropylene structure. The absence of additional functional group signatures in the region 410 confirms the starting material properties before the grafting process.
[0055] The curve 408 exhibits absorption characteristics representing the post-consumer recycled polyethylene that becomes mechanically interlocked within the vitrimer matrix without chemical modification. The curve 408 shows peaks in the region 410 corresponding to C-H stretching vibrations typical of polyethylene. The spectral characteristics in the region 410 confirm that the PCR PE maintains its original chemical structure during mechanical interlocking in the recyclable polymer composition.
[0056] FIG. 5 is a graphical representation illustrating a detailed view of Fourier transform infrared (FTIR) spectroscopy analysis focusing on specific functional group regions of polymer formulations, in accordance with an embodiment of the present disclosure. FIG. 5 is described in conjunction with elements from FIGs. 1 to 4. With reference to FIG. 5, there is shown a graphical representation 500 representing a closeup view of the FTIR analysis focusing on absorption dips between 1000-1500 cm?¹. The transmittance percentage is represented on the ordinate axis. The wavenumber is measured in centimeters inverse (cm?¹) on the abscissa axis. The graphical representation 500 includes a curve 502 depicting the spectral behaviour of V'-PCR PP, a curve 504 representing the spectral behaviour of g'-PCR PP, a curve 506 representing the spectral behaviour of PCR PP, and a curve 508 representing the spectral behaviour of PCR PE.
[0057] The curve 502 exhibits characteristic absorption dips confirming the vitrimer matrix derived from post-consumer recycled polypropylene having grafted polar functional groups crosslinked with dynamic covalent bonds. The curve 502 includes a distinct absorption dip corresponding to C-O stretching vibrations from hydroxyl groups formed during the crosslinking reaction between epoxy groups and amine functionalities of AFD. The curve 502 shows additional absorption features representing the successful formation of dynamic covalent bonds in the recyclable polymer composition.
[0058] The curve 504 exhibits absorption characteristics confirming the functionalized post-consumer recycled polypropylene containing polar functional groups grafted onto the backbone. The curve 504 includes absorption dip corresponding to epoxy C-O-C rocking vibrations from the grafted GMA units, confirming the presence of reactive sites capable of forming dynamic covalent networks with multifunctional crosslinkers. The curve 504 demonstrates the successful grafting of polar functional groups onto the polypropylene backbone derived from post-consumer waste.
[0059] The curve 506 includes absorption characteristics representing the baseline polypropylene backbone derived from post-consumer waste before functionalization. The curve 506 exhibits absorption dip corresponding to typical aliphatic C-H bending vibrations characteristic of the unmodified polypropylene structure. The absence of epoxy-related absorption features confirms the starting material properties before the grafting process that creates the functionalized post-consumer recycled polypropylene.
[0060] The curve 508 exhibits absorption characteristics representing the post-consumer recycled polyethylene that becomes mechanically interlocked within the vitrimer matrix without chemical modification. The curve 508 shows absorption dip corresponding to C-H bending vibrations typical of polyethylene. The spectral characteristics confirm that the PCR PE maintains its original chemical structure during mechanical interlocking in the recyclable polymer composition, without undergoing chemical modification during the co-upcycling process.
[0061] FIG. 6 is a graphical representation illustrating gel fraction analysis of various polymer formulations, in accordance with an embodiment of the present disclosure. FIG. 6 is described in conjunction with elements from FIGs. 1 to 5. With reference to FIG. 6, there is shown a graphical representation 600 in which various polymer formulations are represented on the abscissa axis while the gel fraction, measured in percentage, is represented on the ordinate axis. The graphical representation 600 includes a bar 602 depicting gel fraction for PCR PE. Further, the graphical representation 600 includes a bar 604 depicting gel fraction for PCR PP. The graphical representation 600 includes a bar 606 depicting gel fraction for PCR PP/PCR PE blend. The graphical representation 600 includes a bar 608 depicting gel fraction for V'-PCR PP/PCR PE recyclable polymer composition. Further, the graphical representation 600 includes a bar 610 depicting gel fraction for V'-PCR PP vitrimer matrix.
[0062] The bar 602 exhibits a gel fraction of zero percent, indicating no crosslinked network formation. The gel fraction of the bar 602 demonstrates that the post-consumer recycled polyethylene remains completely soluble in organic solvents without any chemical modification. The zero gel fraction of the bar 602 confirms that PCR PE maintains its thermoplastic characteristics and does not undergo crosslinking reactions during processing, enabling it to be mechanically interlocked within the vitrimer matrix without chemical modification in the recyclable polymer composition.
[0063] The bar 604 exhibits a gel fraction of zero percent, indicating that unmodified PCR PP does not form crosslinked networks. The gel fraction of the bar 604 demonstrates that polypropylene without functionalization remains completely soluble in organic solvents. The zero gel fraction of the bar 604 confirms that crosslinking requires prior functionalization with polar groups.
[0064] The bar 606 exhibits a gel fraction of zero percent, indicating that the simple blend of PCR PP and PCR PE does not form crosslinked networks. The gel fraction of the bar 606 demonstrates that physical mixing alone cannot create the dynamic covalent bonds necessary for vitrimer formation. The zero gel fraction of the bar 606 confirms that functionalization and crosslinking steps are essential for creating the recyclable polymer composition with enhanced mechanical properties.
[0065] The bar 608 exhibits a gel fraction of approximately 38 percent, indicating successful formation of crosslinked networks in the recyclable polymer composition. The gel fraction of the bar 608 demonstrates that the vitrimer matrix derived from post-consumer recycled polypropylene having grafted polar functional groups crosslinked with dynamic covalent bonds effectively creates insoluble network structures. The gel fraction of the bar 608 is attributed to the crosslinking dominated by the vitrimer phase, while the mechanically interlocked PCR PE remains uncrosslinked, resulting in a composition that exhibits yield strength greater than individual components.
[0066] The bar 610 exhibits a gel fraction of approximately 58 percent, indicating the highest degree of crosslinked network formation. The gel fraction of the bar 610 demonstrates the successful creation of the vitrimer matrix through crosslinking of polar functional groups with AFD multifunctional crosslinker. The gel fraction of the bar 610 is greater than the gel fraction of the bar 608, confirming that the functionalized post-consumer recycled polypropylene achieves substantial crosslinking density when reactive sites form dynamic covalent networks with multifunctional crosslinkers.
[0067] The gel fraction data indicate that crosslinking efficiency influences the network formation in the recyclable polymer composition. The bar 610 exhibits approximately 53% higher gel fraction compared to the bar 608, while maintaining the ability to undergo thermomechanical recycling due to the dynamic nature of the covalent bonds. The comparison between gel fractions demonstrates that the vitrimer matrix provides the primary crosslinked structure in the recyclable polymer composition, while the mechanically interlocked PCR PE contributes to overall mechanical properties without compromising recyclability. The gel fraction variations confirm that the dynamic covalent bonds formed through disulfide exchange mechanisms create stable yet reversible networks that maintain or improve mechanical properties upon thermomechanical recycling.
[0068] FIG. 7 is a graphical representation illustrating mechanical property comparison of different polymer formulations, in accordance with an embodiment of the present disclosure. FIG. 7 is described in conjunction with elements from FIGs. 1 to 6. With reference to FIG. 7, there is shown a graphical representation 700 in which various polymer formulations are represented on the abscissa axis while the yield strength (YS) measured in mega pascal (MPa) and elongation at yield (Ey) measured in percentage are represented on the ordinate axis. The graphical representation 700 includes a bar 702 depicting mechanical properties for PCR PE. Further, the graphical representation 700 includes a bar 704 depicting mechanical properties for PCR PP. The graphical representation 700 includes a bar 706 depicting mechanical properties for V'-PCR PP vitrimer. The graphical representation 700 includes a bar 708 depicting mechanical properties for PCR PP/PCR PE conventional blend and V'-PCR PP/PCR PE co-upcycled blend.
[0069] The bar 702 exhibits a yield strength of approximately 13 MPa and an elongation at yield of approximately 19 percent. The mechanical properties of the bar 702 demonstrate that the post-consumer recycled polyethylene maintains moderate strength characteristics typical of thermoplastic polyethylene materials. The yield strength of the bar 702 reflects the baseline mechanical performance of PCR PE without any chemical modification or crosslinking. The elongation at yield of the bar 702 indicates good ductility and flexibility characteristics that are inherent to polyethylene polymer chains, enabling the PCR PE to undergo deformation before failure while maintaining the thermoplastic nature for mechanical interlocking in the recyclable polymer composition.
[0070] The bar 704 exhibits a yield strength of approximately 29 MPa and an elongation at yield of approximately 11 percent. The yield strength of the bar 704 is higher than the yield strength of the bar 702, demonstrating that the polypropylene backbone derived from post-consumer waste provides superior strength characteristics compared to the PCR PE. The elongation at yield of the bar 704 is lower than the elongation at yield of the bar 702, indicating that PCR PP is more rigid and less ductile than PCR PE. The mechanical properties of the bar 704 represent the baseline characteristics of unmodified polypropylene before functionalization with polar functional groups, confirming the starting material properties prior to grafting reactions that create reactive sites capable of forming dynamic covalent networks with multifunctional crosslinkers.
[0071] The bar 706 exhibits a yield strength of approximately 34 MPa and an elongation at yield of approximately 13 percent. The yield strength of the bar 706 is higher than both the yield strength of the bar 702 and the bar 704, demonstrating that the vitrimer matrix derived from post-consumer recycled polypropylene having grafted polar functional groups crosslinked with dynamic covalent bonds provides enhanced mechanical performance. The elongation at yield of the bar 706 shows slight improvement compared to the bar 704, indicating that the crosslinking reaction creates a more robust network structure while maintaining reasonable ductility. The enhanced mechanical properties of the bar 706 are attributed to the formation of dynamic covalent bonds through the crosslinking of epoxy groups from grafted GMA with amine functionalities of AFD, creating a three-dimensional vitrimer network that can undergo controlled bond rearrangement during deformation.
[0072] The bar 708 includes two distinct formulations representing conventional and co-upcycled blends. The PCR PP/PCR PE conventional blend exhibits a yield strength of approximately 24 MPa and an elongation at yield of approximately 21 percent, while the V'-PCR PP/PCR PE co-upcycled blend exhibits a yield strength of approximately 27 MPa and an elongation at yield of approximately 23 percent. The mechanical properties of the conventional blend fall between the individual components, indicating limited synergistic effects from simple physical mixing without chemical modification. The co-upcycled blend demonstrates superior performance with yield strength approaching that of the pure vitrimer while maintaining enhanced elongation characteristics. The improved properties of the V'-PCR PP/PCR PE blend are attributed to the mechanical interlocking of PCR PE chains within the vitrimer matrix without chemical modification, creating a composition that maintains or improves mechanical properties upon thermomechanical recycling.
[0073] The mechanical property data indicate that the co-upcycling approach successfully combines the strength characteristics of the vitrimer matrix with the ductility benefits of mechanically interlocked polyethylene. The V'-PCR PP/PCR PE blend exhibits approximately 12.5 percent higher yield strength compared to the conventional PCR PP/PCR PE blend, while achieving approximately 9.5 percent improvement in elongation at yield. The comparison between mechanical properties demonstrates that the vitrimer matrix provides the primary load-bearing structure in the recyclable polymer composition, while the mechanically interlocked PCR PE contributes to overall toughness and deformation characteristics without compromising the recyclability enabled by dynamic covalent bonds. The mechanical property variations confirm that the functionalized post-consumer recycled polypropylene with reactive sites capable of forming dynamic covalent networks creates enhanced performance materials that exceed the properties of individual components and conventional polymer blends.
[0074] FIG. 8 is a graphical representation illustrating recycling performance recovery rates after three processing cycles, in accordance with an embodiment of the present disclosure. FIG. 8 is described in conjunction with elements from FIGs. 1 to 7. With reference to FIG. 8, there is shown a graphical representation 800 in which polymer formulations are represented on the abscissa axis while recovery rate measured in percentage is represented on the ordinate axis. The graphical representation 800 includes a bar 802 and a bar 804 depicting recovery rates for conventional PCR PP/PCR PE blend after three recycling cycles. Further, the graphical representation 800 includes a bar 806 and a bar 808 depicting recovery rates for V'-PCR PP/PCR PE co-upcycled blend after three recycling cycles.
[0075] The bar 802 and the bar 804 exhibit recovery rates of 87 percent for yield strength and 52 percent for elongation at yield. The recovery rate demonstrates that the existing virgin PCRPP/PCEPE suffers from progressive deterioration during multiple processing cycles, limiting recyclability and end of life value retention. The bar 806 and the bar 808 exhibit recovery rates exceeding 100 percent for both yield strength and elongation at yield, indicating property improvement rather than degradation. The exceptional recovery performance demonstrates that the vitrimer-based co-upcycled blend not only maintains but exceeds original mechanical properties due to additional dynamic crosslinking during reprocessing cycles. The recycling performance data indicate that the dynamic covalent network formation enables superior recyclability compared to conventional approaches. The comparison between the recovery rates demonstrates that the vitrimer matrix undergoes controlled bond rearrangement during thermomechanical recycling, resulting in enhanced structural integrity over multiple processing cycles while conventional blends suffer from irreversible degradation mechanisms.
[0076] The bar 802 exhibits a recovery rate of approximately 87 percent for yield strength. The recovery rate of the bar 802 demonstrates that the conventional PCR PP/PCR PE blend suffers from mechanical property degradation during thermomechanical recycling, losing approximately 13 percent of its original yield strength after three processing cycles. The recovery rate of the bar 802 reflects the typical behavior of physical polymer blends that experience irreversible degradation mechanisms including chain scission, oxidation, and phase separation during repeated thermal processing. The limited recovery performance of the bar 802 indicates that conventional recycling approaches result in progressive deterioration that restricts the material's end-of-life value and limits its suitability for multiple recycling cycles.
[0077] The bar 804 exhibits a recovery rate of approximately 52 percent for elongation at yield. The recovery rate of the bar 804 is significantly lower than the recovery rate of the bar 802, demonstrating that ductility properties are more severely affected by recycling than strength properties in conventional polymer blends. The substantial reduction in elongation recovery of the bar 804 indicates that the conventional PCR PP/PCR PE blend becomes increasingly brittle with each recycling cycle due to molecular weight reduction and loss of polymer chain flexibility. The poor elongation recovery of the bar 804 represents a critical limitation that reduces the mechanical reliability and impact resistance of conventionally recycled materials.
[0078] The bar 806 exhibits a recovery rate exceeding 100 percent for yield strength, indicating property improvement rather than degradation after three recycling cycles. The exceptional recovery performance of the bar 806 demonstrates that the vitrimer-based co-upcycled blend not only maintains but enhances its original yield strength due to additional dynamic crosslinking that occurs during reprocessing cycles. The recovery rate exceeding 100 percent of the bar 806 is attributed to the formation of new crosslinks between previously unreacted functional groups and optimization of the vitrimer network structure through controlled bond rearrangement during thermomechanical recycling. The superior performance of the bar 806 confirms that the dynamic covalent bond exchange mechanism enables progressive property enhancement rather than the degradation observed in conventional recycling approaches.
[0079] The bar 808 exhibits a recovery rate exceeding 100 percent for elongation at yield, demonstrating exceptional retention and improvement of ductility properties after three recycling cycles. The recovery rate exceeding 100 percent of the bar 808 indicates that the V'-PCR PP/PCR PE co-upcycled blend maintains superior flexibility and deformation characteristics compared to its initial state. The enhanced elongation recovery of the bar 808 is attributed to the optimization of polymer chain entanglement and interfacial interactions between the PCR PE and vitrimer matrix phases during repeated processing. The outstanding performance of the bar 808 demonstrates that the mechanical interlocking mechanism preserves the ductility contributions of PCR PE while benefiting from the network reorganization capabilities of the vitrimer matrix.
[0080] Modifications to embodiments of the present disclosure described in the foregoing are possible without departing from the scope of the present disclosure as defined by the accompanying claims. Expressions such as "including", "comprising", "incorporating", "have", "is" used to describe the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components, or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. The word "exemplary" is used herein to mean "serving as an example, instance, or illustration". Any embodiment described as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments. The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments". It is appreciated that certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the present disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable combination or as suitable in any other described embodiment of the disclosure.
,CLAIMS:CLAIMS
We Claim:
1. A method (100) for co-upcycling post-consumer recycled polyolefins comprising:
functionalizing post-consumer recycled polypropylene (PCR PP) by melt grafting a polar functional monomer in the presence of a vinyl aromatic stabilizer and a radical initiator to form grafted PCR PP having enhanced grafting efficiency and reduced chain degradation;
crosslinking the grafted PCR PP with a dynamic crosslinker containing reversible covalent bonds to form a vitrimer network; and
mechanically interlocking post-consumer recycled polyethylene (PCR PE) within the vitrimer network through melt blending to form a co-upcycled blend having enhanced mechanical properties compared to individual components and recyclability with property retention over multiple processing cycles.
2. The method (100) as claimed in claim 1, wherein the vinyl aromatic stabilizer captures polymer radicals to form stable aromatic radicals that facilitate grafting of the polar functional monomer while suppressing ß-chain scission of the PCR PP backbone.
3. The method (100) as claimed in claim 1, wherein the dynamic crosslinker forms reversible bonds selected from disulfide bonds, transesterification bonds, or transcarbamoylation bonds that enable bond exchange at processing temperatures while maintaining network integrity at service temperatures.
4. The method (100) as claimed in claim 1, wherein the mechanical interlocking occurs through physical interpenetration and polymer chain entanglement facilitated by dynamic bond exchange during melt processing, creating interfacial adhesion without covalent bonding between PCR PE and the vitrimer network.
5. The method (100) as claimed in claim 1, wherein the PCR PE is derived from single-use packaging waste including milk pouches, and the co-upcycled blend is processable into articles suitable for 3D printing, injection molding, or extrusion applications with circular economy compatibility.
6. A recyclable polymer composition comprising:
a vitrimer matrix derived from post-consumer recycled polypropylene having grafted polar functional groups crosslinked with dynamic covalent bonds; and
post-consumer recycled polyethylene mechanically interlocked within the vitrimer matrix without chemical modification,
wherein the composition exhibits yield strength greater than individual components and maintains or improves mechanical properties upon thermomechanical recycling.
7. The recyclable polymer composition as claimed in claim 6, wherein repeated recycling induces additional crosslinking between unreacted functional groups, resulting in progressive enhancement of mechanical properties over multiple processing cycles.
8. The recyclable polymer composition as claimed in claim 6, wherein the vitrimer matrix exhibits gel fraction indicating crosslink density and activation energy consistent with dynamic covalent bond exchange mechanisms.
9. A functionalized post-consumer recycled polypropylene comprising:
a polypropylene backbone derived from post-consumer waste;
polar functional groups grafted onto the backbone in the presence of vinyl aromatic stabilizer resulting in enhanced grafting yield compared to direct grafting; and
reactive sites capable of forming dynamic covalent networks with multifunctional crosslinkers.
10. The functionalized post-consumer recycled polypropylene as claimed in claim 9, wherein the polar functional groups comprise epoxy groups, anhydride groups, or carboxyl groups capable of ring-opening reactions or condensation reactions with crosslinkers containing complementary functional groups.