Description:TECHNICAL FIELD
[0001] The present disclosure generally relates to a field of polymer recycling and waste management. More specifically, the present disclosure relates to a method for upcycling thermoplastic polyolefin wastes.
BACKGROUND
[0002] Thermoplastic polyolefin (TPO) waste constitutes one of the largest fractions of global plastic waste streams, with post-consumer polyolefins, such as polypropylene (PP), polyethylene (PE), and related derivatives representing approximately 60 wt% of municipal plastic waste. Recycling of TPOs remains highly challenging as conventional recycling methods for TPOs primarily rely on thermal reprocessing through melting and remolding at elevated temperatures. Repeated exposure to such conditions across multiple recycling cycles accelerates polymer chain degradation, including chain scission and thermal oxidation, which progressively reduce molecular weight and weaken the polymer backbone. Consequently, recycled polyolefins exhibit deterioration in mechanical properties, including reduced tensile strength, decreased elongation at break, and increased brittleness. The resulting loss of performance weakens the structural reliability and practical utility of recycled TPOs, thereby restricting the large-scale adoption in sustainable plastic waste management solutions.
[0003] Certain attempts have been made to address degradation in recycled polyolefins, such as incorporating antioxidant and thermal stabilizers during reprocessing and optimizing processing conditions to reduce thermal exposure. However, such attempts provide only limited protection against degradation effects, such as reduction in tensile strength, decrease in elongation at break, and the like during multiple recycling cycles. In addition, conventional recycling methods for polyolefins often fail to maintain both mechanical strength and flexibility, resulting in recycled polyolefins with compromised performance. Thus, there exists a technical problem of how to prevent mechanical property degradation while maintaining flexibility across multiple reprocessing cycles during the recycling of the post-consumer polyolefins.
[0004] Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks.
SUMMARY
[0005] The present disclosure provides a method for upcycling thermoplastic polyolefin wastes. The present disclosure provides a solution to the technical problem of how to prevent mechanical property degradation while maintaining flexibility across multiple reprocessing cycles during the recycling of the post-consumer polyolefins. 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 recycling thermoplastic polyolefins through chemical functionalization and dynamic crosslinking that enable multiple recycling cycles while retaining mechanical strength and flexibility.
[0006] 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.
[0007] In one aspect, the present disclosure provides a method for upcycling thermoplastic polyolefin wastes, which comprises functionalizing post-consumer recycled polyolefins with maleic anhydride and styrene in the presence of a radical initiator to obtain grafted polyolefins, crosslinking the grafted polyolefins with a vitrimeric ionic liquid crosslinker at elevated temperature to form a crosslinked polymer network and obtaining a crosslinked material with a dual crosslinking system comprising reversible ionic domains and covalent adaptive networks.
[0008] Advantageously, the method for upcycling thermoplastic polyolefin wastes is utilized to enhance the recyclability, mechanical performance, and environmental sustainability of post-consumer polyolefins, such as by maintaining tensile strength and flexibility across multiple reprocessing cycles. The incorporation of vitrimeric ionic liquid crosslinkers with maleic anhydride-grafted polyolefins, results in a dual crosslinking that provides enhanced elongation at break and stable tensile strength during recycling. Moreover, the utilization of reversible ionic domains prevents molecular degradation during repeated thermal processing, thereby enhancing the long-term stability of the recycled polymers. Furthermore, the controlled reactive extrusion process provides precise crosslinking that achieves high elongation at break while maintaining yield strength, thereby optimizing the balance between flexibility and mechanical integrity. The vitrilomer network enables recycling of post-consumer polyolefin wastes for up to three cycles without any significant property loss, ensuring recovery of tensile strength and elongation in order to provide a sustainable and high-performance recycling solution for thermoplastic waste management.
[0009] 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.
[0010] 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
[0011] 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 to scale. Wherever possible, like elements have been indicated by identical numbers.
[0012] 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 upcycling thermoplastic polyolefin wastes, in accordance with an embodiment of the present disclosure;
FIG. 2 is a flowchart for synthesizing vitrilomer from post-consumer recycled polyolefins, in accordance with an embodiment of the present disclosure;
FIG. 3 is a graphical representation illustrating Fourier Transform Infrared (FTIR) spectroscopic analysis of post-consumer recycled polyolefin and vitrilomer formulations, in accordance with an embodiment of the present disclosure;
FIG. 4 is a graphical representation illustrating mechanical properties comparison between post-consumer recycled polyolefin and various vitrilomer formulations, in accordance with an embodiment of the present disclosure;
FIG. 5A is a graphical representation illustrating differential scanning calorimetry (DSC) thermal analysis of post-consumer recycled polyolefin and vitrilomer formulations, in accordance with an embodiment of the present disclosure;
FIG. 5B is a graphical representation illustrating thermogravimetric analysis (TGA) of post-consumer recycled polyolefin and vitrilomer formulation, in accordance with an embodiment of the present disclosure;
FIG. 6A is a graphical representation illustrating rheological analysis of post-consumer recycled polyolefin and vitrilomer formulation, in accordance with an embodiment of the present disclosure;
FIG. 6B is a graphical representation illustrating rheological analysis of post-consumer recycled polyolefin and vitrilomer formulation, in accordance with an embodiment of the present disclosure; and
FIG. 7 is a graphical representation illustrating reprocessability comparison between post-consumer recycled polyolefin and vitrilomer formulation across multiple recycling cycles, in accordance with an embodiment of the present disclosure.
[0013] 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 at which the arrow is pointing.
DETAILED DESCRIPTION OF EMBODIMENTS
[0014] 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.
[0015] FIG. 1 is a flowchart illustrating a method for upcycling thermoplastic polyolefin wastes, in accordance with an embodiment of the present disclosure. With reference to FIG. 1, there is shown a flowchart illustrating the method 100 for upcycling thermoplastic polyolefin wastes. The method 100 includes steps 102 to 106.
[0016] There is provided the method 100 for upcycling thermoplastic polyolefin wastes. The method 100 includes functionalizing post-consumer recycled polyolefins with maleic anhydride and styrene in the presence of a radical initiator to obtain grafted polyolefins. In an implementation, the functionalization is carried out through reactive extrusion at a temperature range of about 180 °C to 220 °C for 1 to 3 minutes at a screw speed of about 100 to 150 rpm. Moreover, the method 100 includes crosslinking the grafted polyolefins with vitrimeric ionic liquid crosslinkers, such as bis(2-hydroxyethyl) dimethylammonium chloride, to form a crosslinked polymer network. The incorporation of the ionic liquid crosslinker in an amount of about 1 to 30 wt% with the grafted polyolefins creates a dual crosslinking system comprising reversible ionic domains and covalent adaptive networks. Furthermore, the method 100 includes obtaining a crosslinked polymer network that exhibits enhanced elongation at break while maintaining tensile strength, thereby enhancing the recyclability, flexibility, or long-term stability of post-consumer polyolefins across multiple reprocessing cycles. Unlike conventional vitrimer systems that rely solely on dynamic covalent bonds and suffer from poor mechanical properties when applied to degraded polyolefins, or ionomer systems that provide only ionic clustering without dynamic bond exchange capability, the method 100 integrates both mechanisms within a single polymer matrix. This dual crosslinking provides unexpected synergistic benefits by maintaining tensile strength and flexibility simultaneously, thereby ensuring consistent performance and recyclability of post-consumer polyolefins across multiple processing cycles.
[0001] At step 102, the method 100 includes functionalizing post-consumer recycled polyolefins with maleic anhydride and styrene in the presence of a radical initiator to obtain grafted polyolefins. The post-consumer recycled polyolefins may include, but are not limited to, polypropylene, polyethylene, and blends thereof, which undergo reactive extrusion under controlled thermal and mechanical conditions. In an implementation, the post-consumer recycled polyolefins are pretreated by washing with an aqueous detergent solution, followed by repeated rinsing with cold water and drying in a vacuum oven at approximately 70 °C for six hours. The dried polyolefins are then chopped into small pieces to ensure uniform feeding and consistent processing during reactive extrusion. The grafting reaction introduces functional groups onto the polymer backbone through incorporation of maleic anhydride, thereby forming grafted polyolefins with reactive sites suitable for subsequent crosslinking.
[0002] At step 104, the method 100 includes crosslinking the grafted polyolefins with a vitrimeric ionic liquid crosslinker at elevated temperature, such as about 180 °C to 220 °C, to form a crosslinked polymer network. The vitrimeric ionic liquid crosslinker may include, but is not limited to, bis(2-hydroxyethyl) dimethylammonium chloride, benzyl dimethyl(2-(2-(octyloxy)ethoxy)ethyl) ammonium chloride, or 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Furthermore, the ionic liquid crosslinker is incorporated with the grafted polyolefins, thereby forming a dual crosslinking network comprising reversible ionic domains and covalent adaptive networks. The dual crosslinking system enables the formation of a polymer network that maintains mechanical properties across multiple recycling cycles, while the covalent adaptive networks provide structural stability of the polymer network. The resulting crosslinked polymer network demonstrates enhanced elongation at break while maintaining tensile strength, thereby ensuring enhanced recyclability and flexibility of post-consumer polyolefins.
[0003] At step 106, the method 100 includes obtaining a crosslinked polymer network with a dual crosslinking system comprising reversible ionic domains and covalent adaptive networks. The dual crosslinking system enables repeated reprocessing of post-consumer polyolefins while maintaining mechanical performance. In an implementation, the crosslinked polymer network exhibits gel formation and maintains both yield strength and elongation after multiple reprocessing cycles. The presence of reversible ionic domains contributes to flexibility, while the covalent adaptive networks ensure structural integrity of the polymer matrix. As a result, the obtained crosslinked polymer network maintains tensile strength and elongation across multiple recycling cycles, thereby providing a recyclable, stable, and high-performance method for upcycling thermoplastic polyolefin waste.
[0004] In accordance with an embodiment, the post-consumer recycled polyolefins are selected from polypropylene, polyethylene, or blends thereof. The selection of these polyolefins is based on the abundance in municipal waste streams, where approximately 60 wt% of total plastic waste comprises polyolefins, including high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), and the like. The selected polyolefins are processed through maleic anhydride grafting to introduce reactive sites onto a polymer backbone, with polypropylene in particular containing tertiary carbon atoms that facilitate radical-mediated grafting reactions. Furthermore, the grafted polyolefins provide functionalized polymer matrices that enable crosslinking with vitrimeric ionic liquid crosslinkers in order to form dual crosslinking systems comprising reversible ionic domains and covalent adaptive networks. As a result, the selection and functionalization of post-consumer recycled polyolefins ensures a sustainable feedstock that accommodates efficient grafting and crosslinking, thereby ensuring stable recyclability performance during reprocessing cycles.
[0005] In accordance with an embodiment, the vitrimeric ionic liquid crosslinker is present in an amount ranging from 1 to 30 wt% based on the total weight of the composition, and the grafted polyolefins comprise 70 to 99 wt% of the total composition. In an example, the vitrimeric ionic liquid crosslinker is present in an amount of 1 wt%. In another example, the vitrimeric ionic liquid crosslinker is present in an amount of 15 wt%. In yet another example, the vitrimeric ionic liquid crosslinker is present in an amount of 30 wt%. In an implementation, the grafted polyolefins may be present in amounts of about 70 wt%, 85 wt%, or 99 wt% of the total composition. The formulation containing 10 wt% ionic liquid crosslinker and 90 wt% grafted polyolefins provides optimal performance, exhibiting an elongation at break of 383% while maintaining a tensile strength of 28 MPa. The incorporation of the vitrimeric ionic liquid crosslinker within the defined range enables the formation of dual crosslinking systems comprising reversible ionic domains and covalent adaptive networks, while the grafted polyolefins provide the functionalized polymer matrix for effective crosslinking. The ability to adjust the relative proportions of the crosslinker and the grafted polyolefins allows control over crosslinking density and polymer chain mobility. As a result, the defined composition ensures recyclability with consistent mechanical performance during reprocessing.
[0006] In accordance with an embodiment, the post-consumer recycled polyolefins are functionalized with maleic anhydride in an amount ranging from 5 to 20 wt%, styrene in an amount ranging from 5 to 20 wt%, and dicumyl peroxide as a radical initiator in an amount ranging from 0.1 to 2 wt%. In an implementation, the functionalization may be carried out with 10 wt% maleic anhydride, 10.62 wt% styrene, and 0.5 wt% dicumyl peroxide, resulting in a grafting yield of 2.25% compared to 0.38% without styrene. The maleic anhydride acts as the primary grafting agent to introduce functional groups onto the polymer backbone, while styrene functions as a co-grafting agent that reacts with polyolefin-derived macroradicals to form stable styryl macroradicals. Such styryl macroradicals subsequently copolymerize with maleic anhydride, thereby enhancing grafting efficiency while simultaneously suppressing chain degradation of the polymer backbone. The dicumyl peroxide initiates the radical reaction at a processing temperature of about 180 °C, enabling effective initiation without excessive polymer degradation. As a result, the specific formulation establishes a functionalized polymer matrix with improved grafting efficiency and controlled functionalization, thereby preventing the mechanical property degradation.
[0007] In an implementation, the composition and functionalization parameters for the post-consumer recycled polyolefins are provided in Table 1 given below:
Sample Name PCR PO
(wt %) Maleic anhydride
(wt %) Styrene
(wt %) DCP
(wt %) Irganox
(wt %)
PCR PO 100 - - - -
m'-PCR PO 78.38 10
10.62 0.5 0.5
TABLE 1
[0008] As shown in the Table 1, the composition of post-consumer recycled polyolefin (PCR PO) and functionalized polyolefin (m'-PCR PO) obtained through reactive extrusion. The PCR PO represents an unmodified polymer with 100% recycled polyolefin. In contrast, the m'-PCR PO is obtained by functionalizing the recycled polyolefin with additives, including maleic anhydride (10 wt%), styrene (10.62 wt%), dicumyl peroxide (0.5 wt%), and Irganox 1010 (0.5 wt%). The inclusion of maleic anhydride and styrene enables grafting onto the polyolefin backbone, while dicumyl peroxide acts as the radical initiator and Irganox 1010 serves as an antioxidant stabilizer. Thus, the table 1 shows the functionalized compositions that are utilized in the method 100 for preparing grafted polyolefins that serve as intermediates for subsequent crosslinking with vitrimeric ionic liquid crosslinkers.
[0009] In accordance with an embodiment, the vitrimeric ionic liquid crosslinker is selected from bis(2-hydroxyethyl) dimethylammonium chloride, benzyl dimethyl(2-(2-(octyloxy)ethoxy)ethyl) ammonium chloride, or 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. In an implementation, bis(2-hydroxyethyl) dimethylammonium chloride functions as an effective crosslinker by forming ester bonds with maleic anhydride-grafted polyolefins through hydroxyl group reactivity with anhydride rings. Such ester bonds enable transesterification reactions under processing conditions, thereby establishing dynamic covalent networks, while the ionic liquid simultaneously creates reversible ionic domains through electrostatic interactions. The combined mechanism of covalent bond adaptability and ionic associations ensures network integrity and flexibility during repeated reprocessing. As a result, the use of such ionic liquid crosslinkers facilitates the formation of dual crosslinking systems that maintain structural stability of the polymer network, thereby enabling recyclability with sustained mechanical performance across multiple processing cycles.
[0010] In an implementation, the composition and crosslinking formulations for the vitrilomer polymer networks are provided in Table 2 given below:
Sample Name m'-PCR PO
(wt%) IL
(wt%)
IL-5 95 5
IL-10 90 10
IL-15 85 15
TABLE 2
[0011] As shown in the Table 2, the composition of vitrilomer formulations obtained by crosslinking functionalized polyolefin (m'-PCR PO) with ionic liquid crosslinker (IL) under specific thermal conditions. The three formulations demonstrate varying concentrations of bis(2-hydroxyethyl) dimethylammonium chloride as the vitrimeric ionic liquid crosslinker. The IL-5 formulation comprises 95 wt% m'-PCR PO and 5 wt% ionic liquid crosslinker, providing minimal crosslinking density. The IL-10 formulation contains 90 wt% m'-PCR PO and 10 wt% ionic liquid crosslinker, representing the optimal balance between crosslinking and flexibility. The IL-15 formulation incorporates 85 wt% m'-PCR PO and 15 wt% ionic liquid crosslinker, offering higher crosslinking density. The inclusion of ionic liquid crosslinker enables the formation of dual crosslinking systems comprising reversible ionic domains and covalent adaptive networks. The table therefore illustrates the systematic variation in crosslinker concentration used in the method 100 for creating vitrilomer networks with enhanced recyclability.
[0012] In accordance with an embodiment, the crosslinked polymer network exhibits a gel content of at least 25% as measured by extraction in boiling xylene and maintains mechanical properties after multiple reprocessing cycles with yield strength recovery of at least 95% and elongation at break recovery of at least 95% of their respective first-cycle values. In an implementation, after three reprocessing cycles, the formulation maintains approximately 100% yield strength recovery and 97% elongation recovery. The defined gel content and retained mechanical properties demonstrate the effectiveness of the dual crosslinking system comprising covalent adaptive networks and reversible ionic domains in resisting chain scission and minimizing property loss during thermal reprocessing. Thus, the crosslinked polymer network ensures long-term durability, flexibility, and reliable recyclability of post-consumer polyolefins.
[0013] In accordance with an embodiment, the crosslinking the grafted polyolefins with a vitrimeric ionic liquid crosslinker is carried out at a range of 180°C to 220°C for 1-2 minutes at a range of 100 to 150 rpm, and the resulting crosslinked polymer network exhibits a melt flow index of 6-7 g/10 min. In an example the crosslinking of the grafted polyolefins with the vitrimeric ionic liquid crosslinker is carried out at 180°C. In another example the crosslinking of the grafted polyolefins with the vitrimeric ionic liquid crosslinker is carried out at 200°C. In yet another example the crosslinking of the grafted polyolefins with the vitrimeric ionic liquid crosslinker is carried out at 220°C. In an implementation, the crosslinking is performed under defined processing conditions by utilizing a DSM Xplore batch twin-screw micro compounder, resulting in the formation of stable crosslinked networks with controlled flow properties. The defined temperature, residence time, and screw configuration facilitate efficient crosslinking while preventing thermal degradation and ensuring complete reaction between the grafted polyolefins and the ionic liquid crosslinker. The resulting melt flow index of 6 to 7 g/10 min indicates stable processability compatible with conventional polymer processing equipment, thereby enabling the method 100 to be effectively implemented in industrial recycling applications.
[0014] In accordance with an embodiment, the crosslinked polymer network exhibits improved elongation at break in the range of 350% to 400% while maintaining a yield strength in the range of 25 MPa to 30 MPa. In an implementation, the optimal crosslinked formulation achieves elongation at break of 383% while maintaining a yield strength of 28 MPa, representing an enhancement compared to functionalized polyolefins. The combination of enhanced elongation and stable yield strength is attained through the dual crosslinking system, wherein reversible ionic domains impart flexibility under mechanical stress while covalent adaptive networks preserve structural integrity. Thus, the synergy of such mechanisms (i.e., ionic domains providing reversible flexibility and covalent adaptive networks ensuring structural stability) enables vitrilomer networks to deliver both flexibility and strength simultaneously, thereby overcoming the conventional limitation of recycled polyolefins, which typically enhance either strength or flexibility.
[0015] In an implementation, the mechanical performance data for pristine, functionalized, and crosslinked polyolefin samples are provided in Table 3 given below:

Sample name Tensile Strength (MPa) Elongation at break (%)

PCR PO
28 ± 0.35
100 ± 12

m'-PCR PO 28 ± 0.61 45 ± 10
IL-5
26± 0.51 61 ± 8
IL-10
28 ± 0.34 383 ± 5
IL-15 27 ± 0.64 105 ± 6
TABLE 3
[0016] In another implementation, the samples are prepared by injection molding under a pressure of approximately 16 bar at a temperature of 180 °C for 30 seconds. The controlled molding process ensures consistent structural configuration and uniform material distribution, thereby enabling reliable comparison of mechanical properties across different formulations.
[0017] As shown in Table 3, the comparative mechanical properties of pristine PCR PO, functionalized m'-PCR PO, and vitrilomer formulations were evaluated in accordance with ASTM D638 at room temperature. The pristine PCR PO exhibits a tensile strength of 28 ± 0.35 MPa with elongation at break of 100 ± 12%. The functionalized m'-PCR PO maintains a similar tensile strength of 28 ± 0.61 MPa but shows reduced elongation at break of 45 ± 10% due to grafting-induced stiffening of the polymer chains. The vitrilomer formulations exhibit tunable performance depending on the ionic liquid crosslinker concentration. The IL-5 formulation shows slightly reduced tensile strength of 26 ± 0.51 MPa and marginal enhancement in elongation at break to 61 ± 8%. The IL-10 formulation maintains tensile strength of 28 ± 0.34 MPa while achieving enhancement in elongation at break to 383 ± 5%, representing the optimal balance between strength and flexibility. The IL-15 formulation maintains tensile strength of 27 ± 0.64 MPa with moderate elongation recovery to 105 ± 6%. Thus, the Table 3 shows that the dual crosslinking system in vitrilomers enables enhanced flexibility while preserving structural integrity. Among the various formulations, IL-10 provides the greater combination of tensile strength and elongation, thereby providing reliable mechanical performance for upcycling post-consumer polyolefins.
[0018] In another implementation, the recyclability performance data for the optimal vitrilomer formulation across multiple reprocessing cycles are provided in Table 4 given below:
Sample name Tensile Strength (MPa) Elongation at break (%)
IL-10 28 ± 0.34 383 ± 5
IL-10 R3 28 ± 0.42 372 ± 9
TABLE 4
[0019] As shown in Table 4, the retention of mechanical properties for the IL-10 vitrilomer formulation evaluated after three complete reprocessing cycles (R1, R2, and R3), each cycle involving reactive extrusion followed by injection molding. The initial IL-10 sample exhibits a tensile strength of 28 ± 0.34 MPa and an elongation at break of 383 ± 5%. After three reprocessing cycles, the sample (IL-10 R3) maintains a tensile strength of 28 ± 0.42 MPa and an elongation at break of 372 ± 9%, corresponding to approximately 100% tensile strength retention and 97% elongation retention relative to the first-cycle values. The ability to retain mechanical performance after repeated reprocessing cycles shows the strength of the dual crosslinking system within the vitrilomer matrix. The dynamic covalent adaptive networks facilitate bond exchange and structural rearrangement at elevated temperatures, thereby preserving the network structure. Thus, the Table 4 shows that the IL-10 vitrilomer formulation provides stable mechanical properties with minimal degradation across multiple recycling cycles, thereby ensures reliable recyclability and upcycling potential for post-consumer polyolefins.
[0020] In accordance with an embodiment, the crosslinked polymer network exhibits thermal stability with a melting temperature of 162 °C and a crystallization temperature of 130 °C. The melting temperature of 162 °C maintains the crystalline structure of the recycled polyolefins even after multiple reprocessing cycles, while the crystallization temperature of 130°C enables controlled molecular rearrangement during cooling to prevent premature degradation or uncontrolled phase transitions. By retaining the melting and crystallization temperatures, the dual crosslinking system comprising covalent adaptive networks and reversible ionic domains preserves the crystalline characteristics of the polymer matrix. As a result, the crosslinked polymer network retains processability and structural integrity of the recycled polyolefins during recycling, thereby enabling reliable thermal reprocessing and sustainable upcycling of post-consumer polyolefins.
[0021] In accordance with an embodiment, the functionalization of post-consumer recycled polyolefins with maleic anhydride and styrene is carried out through reactive extrusion at a temperature range of 180 °C to 220 °C for 1 to 3 minutes at a screw speed in the range of 100 to 150 rpm. In an implementation, the functionalization is performed by utilizing the DSM Xplore batch twin-screw micro compounder with a 15 cm³ capacity. The equipment includes co-rotating conical screws and a recirculation system that enables accurate control over material residence time, while the twin-screw configuration ensures efficient mixing and heat transfer. The optimized thermal, mechanical, and equipment conditions facilitate the grafting reaction between maleic anhydride, styrene, and the polymer backbone, thereby introducing functional groups onto the polyolefin chains. The established functional groups provide active sites for subsequent crosslinking with ionic liquid crosslinkers. By operating within the defined processing parameters, the method 100 ensures uniform and efficient grafting while reducing degradation of the recycled polyolefins, thus providing the functionalized polymer matrix that enables formation of the stable crosslinked polymer network. Advantageously, the method for upcycling thermoplastic polyolefin wastes is utilized to enhance the recyclability, mechanical performance, and environmental sustainability of post-consumer polyolefins, such as by maintaining tensile strength and flexibility across multiple reprocessing cycles. The incorporation of vitrimeric ionic liquid crosslinkers with maleic anhydride-grafted polyolefins, results in a dual crosslinking that provides enhanced elongation at break and stable tensile strength during recycling. Moreover, the utilization of reversible ionic domains prevents molecular degradation during repeated thermal processing, thereby enhancing the long-term stability of the recycled polymers. Furthermore, the controlled reactive extrusion process provides precise crosslinking that achieves high elongation at break while maintaining yield strength, thereby optimizing the balance between flexibility and mechanical integrity. The vitrilomer network enables recycling of post-consumer polyolefin wastes for up to three cycles without any significant property loss, ensuring recovery of tensile strength and elongation in order to provide a sustainable and high-performance recycling solution for thermoplastic waste management.
[0022] The steps 102 to 106 are only illustrative, and other alternatives can also be provided where one or more steps are added, one or more steps are removed, or one or more steps are provided in a different sequence without departing from the scope of the claims herein.
[0023] FIG. 2 is a flowchart for synthesizing vitrilomer polymer network from post-consumer recycled polyolefins, in accordance with an embodiment of the present disclosure. FIG. 2 is described in conjunction with elements of the method 100. With reference to FIG. 2, there is shown a flowchart 200 that includes a series of operations from 202 to 208.
[0024] In an implementation, the flowchart 200 represents the sequential process flow of functionalizing and crosslinking post-consumer recycled polyolefin (PCR PO) into a crosslinked vitrilomer network. At operation 202, the PCR PO with R groups representing methyl or hydrogen substituents on the polymer backbone is subjected to reactive extrusion with maleic anhydride, dicumyl peroxide as a radical initiator and styrene as a co-grafting agent that reacts with polyolefin-derived macroradicals in order to form a stable styryl macroradicals. At operation 204, the styryl macroradicals copolymerize with maleic anhydride, resulting in functionalized m′-PCR PO containing grafted maleic anhydride groups that act as reactive sites for subsequent crosslinking, thereby enhancing grafting efficiency while suppressing chain degradation of the polyolefin backbone. At operation 206, the functionalized m′-PCR PO is reacted with bis(2-hydroxyethyl) dimethylammonium chloride ionic liquid crosslinker. The hydroxyl groups of the ionic liquid crosslinker open the anhydride rings of the grafted maleic anhydride, forming ester linkages with the polymer chains while simultaneously introducing ionic domains within the matrix through electrostatic interactions. Finally, at operation 208, the reaction results in the formation of the crosslinked vitrilomer polymer network comprising covalent ester bonds and reversible ionic domains. The dual crosslinking system establishes covalent adaptive networks capable of bond exchange reactions while maintaining structural integrity and flexibility, thereby enabling recyclability of the crosslinked vitrilomer polymer network with reliable performance retention during multiple reprocessing cycles.
[0025] FIG. 3 is a graphical representation illustrating Fourier Transform Infrared (FTIR) spectroscopic analysis of post-consumer recycled polyolefin and vitrilomer formulations, in accordance with an embodiment of the present disclosure. FIG. 3 is described in conjunction with elements from Figs. 1 to 2. With reference to FIG. 3, there is shown a graphical representation of 300 depicting the infrared absorption behavior of different polymer compositions as a function of wavenumber. The transmittance is measured in percentage and represented on the ordinate axis. The wavenumber is measured in reciprocal centimeters (cm⁻¹) and represented on the abscissa axis, ranging from approximately 1000 cm⁻¹ to 4000 cm⁻¹.
[0026] The graphical representation 300 includes a curve 302 representing the infrared absorption behavior of post-consumer recycled polyolefin (PCR PO), showing characteristic C–H stretching and bending vibrations without additional peaks, confirming the baseline profile of untreated material. A curve 304 represents functionalized PCR PO (m′-PCR PO), displaying new absorption peaks that validate grafting of maleic anhydride and styrene onto the polymer backbone. A curve 306 represents the VIL-5 formulation with 5 wt% ionic liquid crosslinker, showing initial ester bond formation through reaction between grafted anhydride groups and ionic liquid hydroxyl functionalities. A curve 308 represents the VIL-10 formulation with 10 wt% ionic liquid crosslinker, showing optimal crosslinking with enhanced ester peak intensity at 1730 cm⁻¹. A curve 310 represents the VIL-15 formulation with 15 wt% ionic liquid crosslinker, showing maximum crosslinking density. The absorption peak 312 at 1780 cm⁻¹ corresponds to cyclic anhydride stretching, while the absorption peak 314 at 1730 cm⁻¹ corresponds to ester carbonyl stretching from crosslinking reactions. As a result, the FTIR analysis confirms the chemical transformation from pristine polyolefin to functionalized polymer to crosslinked vitrilomer, validating ester linkage formation and establishing spectroscopic evidence of successful network formation across varying ionic liquid concentrations.
[0027] FIG. 4 is a graphical representation illustrating mechanical properties comparison between post-consumer recycled polyolefin and various vitrilomer formulations, in accordance with an embodiment of the present disclosure. FIG. 4 is described in conjunction with elements from Figs. 1 to 3. With reference to FIG. 4, there is shown a graphical representation 400 depicting the mechanical performance characteristics of different polymer compositions. The yield strength is measured in megapascals (MPa) and represented on the left ordinate axis. The elongation at break is measured in percentage and represented on the right ordinate axis. Five polymer formulations, PCR PO, m'-PCR PO, VIL-5, VIL-10, and VIL-15, are represented on the abscissa axis.
[0028] The graphical representation 400 includes a bar 402 depicting the yield strength of post-consumer recycled polyolefin (PCR PO), showing approximately 28 MPa as the baseline mechanical performance. The graphical representation 400 further includes a bar 404 depicting the elongation at break of PCR PO, showing approximately 100%, representing the initial ductility of the recycled polyolefin before functionalization. The graphical representation 400 includes a bar 406 depicting the yield strength of functionalized post-consumer recycled polyolefin (m′-PCR PO), maintaining approximately 28 MPa, while a bar 408 depicts the elongation at break of m′-PCR PO, reduced to approximately 45% due to grafting-induced chain stiffening. The graphical representation 400 further includes a bar 410 depicting the yield strength of the VIL-5 formulation with 5 wt% ionic liquid crosslinker, showing approximately 26 MPa, and a bar 412 depicting elongation at break of approximately 61%, representing marginal enhancement over the functionalized polyolefin. A bar 414 depicts the yield strength of the VIL-10 formulation with 10 wt% ionic liquid crosslinker, showing approximately 28 MPa, while a bar 416 depicts elongation at break of approximately 383%, indicating optimal flexibility through dual crosslinking system formation. A bar 418 depicts the yield strength of the VIL-15 formulation with 15 wt% ionic liquid crosslinker, showing approximately 27 MPa, and a bar 420 depicts elongation at break of approximately 105%, reflecting restricted chain mobility at higher crosslinking density. The comparison between bars 408 and 416 demonstrates that the VIL-10 formulation achieves an enhancement in elongation at break from 45% to 383% while preserving yield strength at 28 MPa. As a result, the mechanical analysis confirms that vitrimer formation in the VIL-10 formulation with 10 wt% ionic liquid crosslinker provides the optimal balance between flexibility and strength, validates the effectiveness of the dual crosslinking mechanism, and establishes the superior performance of the optimized formulation for sustainable upcycling of post-consumer polyolefins.
[0029] FIG. 5A is a graphical representation illustrating differential scanning calorimetry (DSC) thermal analysis of post-consumer recycled polyolefin and vitrilomer formulations, in accordance with an embodiment of the present disclosure. FIG. 5A is described in conjunction with elements from Figs. 1 to 4. With reference to FIG. 5A, there is shown a graphical representation 500A depicting the heat flow behavior of different polymer compositions as a function of temperature. The heat flow is measured in watts per gram (W/g) and represented on the ordinate axis with endothermic transitions and exothermic transitions. The temperature is measured in degrees Celsius (°C) on the abscissa axis, ranging from approximately 40°C to 200°C.
[0030] The graphical representation 500A includes a curve 502 representing the thermal behavior of post-consumer recycled polyolefin (PCR PO), exhibiting a sharp endothermic melting peak at approximately 162 °C corresponding to the melting temperature of the polypropylene matrix present in the recycled polyolefin. The curve 502 demonstrates characteristic thermal transitions of pristine recycled polyolefin with well-defined crystalline structure and preserved thermal properties. The graphical representation 500A includes a curve 504 representing the thermal behavior of functionalized post-consumer recycled polyolefin (m′-PCR PO), showing an endothermic melting peak at approximately 163 °C with slightly modified peak characteristics resulting from maleic anhydride and styrene grafting reactions. The curve 504 indicates that the functionalization process maintains the fundamental thermal transitions of polypropylene while showing minor variations in crystalline structure. Additionally, the graphical representation 500A includes a curve 506 representing the thermal behavior of vitrilomer formulation VIL-10, showing an endothermic melting peak at approximately 162 °C. The curve 506 demonstrates that ionic liquid crosslinking preserves the essential polypropylene crystalline domains and thermal processability. The comparison between curves 502, 504, and 506 depicts that all three formulations exhibit similar melting transitions within a narrow range of 162–163 °C, confirming that vitrilomer formation does not compromise crystalline stability or processing characteristics. As a result, the consistent melting behavior across all formulations validates that the upcycling process maintains thermal integrity, demonstrates compatibility with conventional polyolefin processing equipment, and confirms that vitrilomer materials remain recyclable at standard processing temperatures.
[0031] FIG. 5B is a graphical representation illustrating thermogravimetric analysis (TGA) of post-consumer recycled polyolefin and vitrilomer formulation, in accordance with an embodiment of the present disclosure. FIG. 5B is described in conjunction with elements from FIGs. 1 to 5A. With reference to FIG. 5B, there is shown a graphical representation 500B depicting the thermal degradation behavior of different polymer compositions as a function of temperature. The weight (%) is measured and represented on the ordinate axis, ranging from 0% to 100%. The temperature is measured in degrees Celsius (°C) on the abscissa axis, ranging from approximately 50 °C to 800 °C.
[0032] The graphical representation 500B includes a curve 508 representing the thermal degradation behavior of post-consumer recycled polyolefin (PCR PO), exhibiting thermal stability up to approximately 300 °C followed by rapid weight loss between 400–500 °C characteristic of polyolefin thermal decomposition. The curve 508 shows a single-stage degradation profile with decomposition occurring around 500°C, leaving minimal residual weight at elevated temperatures. The graphical representation 500B includes a curve 510 representing the thermal degradation behavior of vitrilomer formulation VIL-10, showing a comparable thermal stability profile with degradation at approximately 300 °C and major weight loss occurring within the same temperature range as the pristine material. The curve 510 demonstrates that ionic liquid crosslinking preserves the fundamental decomposition pathway of the base polyolefin without introducing any thermally labile components. The comparison between curves 508 and 510 depicts overlapping degradation profiles, confirming that the dual crosslinking system preserves the fundamental thermal decomposition characteristics of the base polyolefin material. The similar onset temperatures and degradation rates indicate that vitrilomer formation maintains compatibility with standard polyolefin processing equipment and recycling operations. As a result, the TGA analysis validates that vitrilomer materials retain the essential thermal stability required for multiple reprocessing cycles, demonstrates compatibility with standard polyolefin recycling process, and confirms the thermal integrity of the dual crosslinking system for sustainable upcycling applications.
[0033] FIG. 6A is a graphical representation illustrating rheological analysis of post-consumer recycled polyolefin and vitrilomer formulation, in accordance with an embodiment of the present disclosure. FIG. 6A is described in conjunction with elements from FIGs. 1 to 5B. With reference to FIG. 6A, there is shown a graphical representation 600A depicting the complex viscosity behavior of different polymer compositions as a function of angular frequency. The complex viscosity is measured in Pascal-seconds (Pa·s) and represented on the ordinate axis using a logarithmic scale ranging from 10² to 10⁴ Pa·s. The angular frequency is measured in radians per second (rad/s) and represented on the abscissa axis using a logarithmic scale ranging from approximately 10⁻¹ to 10² rad/s.
[0034] The graphical representation 600A includes a curve 602 representing the complex viscosity behavior of post-consumer recycled polyolefin (PCR PO), exhibiting moderate viscosity levels ranging from approximately 1.5 × 10³ Pa·s at low frequencies to 4 × 10² Pa·s at high frequencies. The curve 602 demonstrates typical thermoplastic polymer melt behavior with gradual viscosity reduction as angular frequency increases, indicating normal flow characteristics of the pristine recycled material without crosslinking modifications. The graphical representation 600A further includes a curve 604 representing the complex viscosity behavior of vitrilomer formulation VIL-10, showing elevated viscosity levels ranging from approximately 6 × 10³ Pa·s at low frequencies to 4 × 10² Pa·s at high frequencies. The curve 604 exhibits steeper viscosity reduction compared to the pristine material, confirming the presence of a crosslinked network structure formed through the dual crosslinking system comprising reversible ionic domains and covalent adaptive networks. The comparison between curves 602 and 604 demonstrates that VIL-10 exhibits approximately four fold higher viscosity at low frequencies while converging to similar values at high processing frequencies, indicating that the vitrilomer network provides enhanced melt strength while maintaining processability. The elevated low-frequency viscosity confirms successful network formation, while the convergence at high frequencies ensures compatibility with conventional polymer processing equipment. As a result, the rheological analysis validates the formation of a crosslinked vitrilomer network with enhanced melt strength, confirms the processability of the dual crosslinking system under standard processing conditions, and demonstrates the rheological characteristics required for sustainable recyclability across multiple reprocessing cycles.
[0035] FIG. 6B is a graphical representation illustrating rheological analysis of post-consumer recycled polyolefin and vitrilomer formulation, in accordance with an embodiment of the present disclosure. FIG. 6B is described in conjunction with elements from FIGs 1 to 6A. With reference to FIG. 6B, there is shown a graphical representation 600B depicting the storage modulus behavior of different polymer compositions as a function of angular frequency. The storage modulus is measured in megapascals (MPa) and represented on the ordinate axis using a logarithmic scale ranging from 10¹ to 10⁴ MPa. The angular frequency is measured in radians per second (rad/s) and represented on the abscissa axis using a logarithmic scale ranging from approximately 10⁻¹ to 10² rad/s.
[0036] The graphical representation 600B includes a curve 606 representing the storage modulus behavior of post-consumer recycled polyolefin (PCR PO), exhibiting moderate elastic modulus ranging from approximately 2 × 10¹ MPa at low frequencies to 2 × 10⁴ MPa at high frequencies. The curve 606 demonstrates viscoelastic polymer behavior with gradual modulus increase as angular frequency increases, indicating normal elastic response characteristics of the pristine recycled material without crosslinking modifications. The graphical representation 600B further includes a curve 608 representing the storage modulus behavior of vitrilomer formulation VIL-10, showing elevated elastic modulus ranging from approximately 4 × 10² MPa at low frequencies to 4 × 10⁴ MPa at high frequencies. The curve 608 exhibits consistently higher storage modulus compared to the pristine material across all frequencies, confirming the presence of a crosslinked network structure formed through the dual crosslinking system comprising reversible ionic domains and covalent adaptive networks. The comparison between curves 606 and 608 demonstrates that VIL-10 exhibits higher storage modulus at low frequencies, indicating that the vitrilomer network provides enhanced elastic properties and dimensional stability. As a result, the storage modulus analysis validates the formation of a crosslinked vitrilomer network with enhanced elastic properties, confirms the mechanical stability provided by the dual crosslinking system, and demonstrates the enhanced dimensional stability required for sustainable recyclability across multiple reprocessing cycles.
[0037] FIG. 7 is a graphical representation illustrating reprocessability comparison between post-consumer recycled polyolefin and vitrilomer formulation across multiple recycling cycles, in accordance with an embodiment of the present disclosure. FIG. 7 is described in conjunction with elements from FIGs. 1 to 6B. With reference to FIG. 7, there is shown a graphical representation 700 depicting the mechanical performance characteristics of different polymer compositions before and after multiple reprocessing cycles. The yield strength is measured in megapascals (MPa) and represented on the left ordinate axis. The elongation at break is measured in percentage and represented on the right ordinate axis. Four sample conditions are represented on the abscissa axis, including PCR PO (pristine post-consumer recycled polyolefin), PCR PO R3 (post-consumer recycled polyolefin after three reprocessing cycles), VIL-10 (vitrilomer formulation with 10 wt% ionic liquid crosslinker), and VIL-10 R3 (vitrilomer formulation after three reprocessing cycles).
[0038] The graphical representation 700 includes a bar 702 depicting the yield strength of post-consumer recycled polyolefin (PCR PO), showing approximately 28 MPa as the baseline mechanical performance of untreated recycled material. The graphical representation 700 further includes a bar 704 depicting the elongation at break of PCR PO, showing approximately 100%, representing the initial ductility characteristics of the pristine recycled polyolefin before any processing modifications. The graphical representation 700 includes a bar 706 depicting the yield strength of post-consumer recycled polyolefin after three reprocessing cycles (PCR PO R3), showing reduced performance at approximately 24 MPa, demonstrating significant strength degradation due to repeated thermal processing. A bar 708 depicts the elongation at break of PCR PO R3, showing reduced ductility at approximately 68%, indicating substantial brittleness development through conventional recycling cycles. The graphical representation 700 further includes a bar 710 depicting the yield strength of the VIL-10 formulation with 10 wt% ionic liquid crosslinker, showing approximately 28 MPa, maintaining equivalent strength to the pristine material while a bar 712 depicts elongation at break of approximately 383%, demonstrating flexibility enhancement through dual crosslinking system formation. A bar 714 depicts the yield strength of the VIL-10 formulation after three reprocessing cycles (VIL-10 R3), showing maintained performance at approximately 28 MPa, while a bar 716 depicts elongation at break of approximately 372%, indicating minimal property loss during repeated recycling. The comparison between bars 706 and 714 demonstrates that VIL-10 maintains yield strength while PCR PO shows 14% degradation, and the comparison between bars 708 and 716 depicts that VIL-10 retains 97% elongation compared to 68% retention in conventional recycling. As a result, the recyclability analysis confirms that vitrilomer formation with dual crosslinking prevents mechanical property degradation across multiple reprocessing cycles, validates the enhanced recyclability performance of the crosslinked network system, and establishes the sustainable reprocessing capability required in thermoplastic waste management.
[0039] 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 and claim 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 upcycling thermoplastic polyolefin wastes, comprising:
functionalizing post-consumer recycled polyolefins with maleic anhydride and styrene in the presence of a radical initiator to obtain grafted polyolefins;
crosslinking the grafted polyolefins with a vitrimeric ionic liquid crosslinker at elevated temperature to form a crosslinked polymer network; and
obtaining a crosslinked material with a dual crosslinking system comprising reversible ionic domains and covalent adaptive networks.
2. The method (100) as claimed in claim 1, wherein the post-consumer recycled polyolefins are selected from polypropylene, polyethylene, or blends thereof.
3. The method (100) as claimed in claim 1, wherein the vitrimeric ionic liquid crosslinker is present in an amount ranging from 1 to 30 wt% based on the total weight of the composition, and the grafted polyolefins comprise 70 to 99 wt% of the total composition.
4. The method (100) as claimed in claim 1, wherein the post-consumer recycled polyolefins are functionalized with maleic anhydride in an amount ranging from 5-20 wt%, styrene in an amount ranging from 5-20 wt%, and dicumyl peroxide as radical initiator in an amount ranging from 0.1 to 2 wt%.
5. The method (100) as claimed in claim 1, wherein the vitrimeric ionic liquid crosslinker is selected from bis(2-hydroxyethyl) dimethylammonium chloride, benzyl dimethyl(2-(2-(octyloxy)ethoxy)ethyl) ammonium chloride, or 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.
6. The method (100) as claimed in claim 1, wherein the crosslinked polymer network exhibits a gel content of at least 25% as measured by extraction in boiling xylene and maintains mechanical properties after multiple reprocessing cycles with yield strength recovery of at least 95% and elongation at break recovery of at least 95% of their respective first-cycle values.
7. The method (100) as claimed in claim 1, wherein crosslinking the grafted polyolefins with a vitrimeric ionic liquid crosslinker is carried out at a range of 180°C to 220°C for 1-2 minutes at a range of 100 to 150 rpm, and the resulting crosslinked polymer network exhibits a melt flow index of 6-7 g/10 min.
8. The method (100) as claimed in claim 1, wherein the crosslinked polymer network exhibits improved elongation at break of 350-400% while maintaining yield strength of 25-30 MPa.
9. The method (100) as claimed in claim 1, wherein the crosslinked polymer network exhibits thermal stability with a melting temperature of 162°C and crystallization temperature of 130°C.
10. The method (100) as claimed in claim 1, wherein functionalizing post-consumer recycled polyolefins with maleic anhydride and styrene is performed at a range of 180°C to 220°C for 1 to 3 minutes at a range of 100 to 150 rpm screw speed using reactive extrusion.