DESC:TECHNICAL FIELD
[0001] The present disclosure relates to polymer recycling technology, in particular, the present disclosure relates to a method for valorization of multi-layered packaging waste through selective separation and upcycling of constituent polymers into high-performance vitrimer materials suitable for additive manufacturing applications.
BACKGROUND
[0002] Multi-layered packaging (MLP) waste represents one of the most challenging categories of plastic waste due to its complex structure comprising multiple polymer layers, including polyethylene terephthalate (PET), polypropylene (PP), and polyethylene (PE) bonded with adhesive layers. India generates approximately 4 million metric tonnes of MLP waste annually, constituting the 40-45% of all plastic waste in the country. The complex multi-layer structure makes separation extremely difficult through conventional recycling methods, resulting in most MLPs being directed to landfills or incineration facilities.
[0003] Current recycling approaches face several technical challenges including contamination from adhesive residues, property degradation due to mixed polymer processing, and incompatibility between different polymer types with varying thermal and chemical properties. Traditional mechanical recycling treats MLPs as homogeneous waste streams, producing low-quality, downcycled products with limited utilization. Additionally, chemical recycling methods require harsh conditions that degrade polymer chains, which results in significant material degradation. Further, even after successful separation, recovered materials have limited applications. Recovered polyolefins typically exhibit poor melt flow properties with excessively high melt flow index (MFI) values, making them unsuitable for high-value applications such as 3D printing feedstock where controlled flowability is essential for quality layer-by-layer addition. The recovered PET, when depolymerized to monomers, often remains underutilized as a simple chemical feedstock rather than being integrated into value-added polymer systems. Thus, there exists a technical problem of how to provide MLP waste valorization that provides an efficient polymer separation, maintains material quality, and produces high-value materials suitable for various applications with enhanced environmental sustainability.
SUMMARY
[0004] The present disclosure provides a method for valorization of multi-layered packaging waste. The present disclosure seeks to provide a solution to the existing technical problem of how to provide MLP waste valorization that provides an efficient polymer separation, maintains material quality, and produces high-value materials suitable for various applications with enhanced environmental sustainability. The present disclosure aims to provide a solution that overcomes, at least partially, the problems encountered in the prior art and provides an improved method for valorization of the multi-layered packaging waste.
[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 valorization of multi-layered packaging waste comprising treating multi-layered packaging waste comprising polyethylene terephthalate (PET), polypropylene (PP), and polyethylene (PE) layers with a treatment solution to simultaneously separate the PET layer from the PP and PE layers and convert the PET layer into bis(2-hydroxyethyl) terephthalate (BHET), functionalizing the recovered polyolefin components with maleic anhydride to form functionalized polyolefins, mixing the functionalized polyolefins with the BHET to form a polymer blend, processing the polymer blend under controlled temperature and pressure conditions to form vitrimers having dynamic covalent bonds, and converting the vitrimers into 3D printing feedstock suitable for various manufacturing applications.
[0007] Advantageously, the method is used to provide simultaneous separation and valorization of multi-layered packaging waste components through a bio-based treatment solution that effectively separates polyolefin lumps and produces BHET powder, thereby eliminating the need for sequential separation processes while maintaining polymer integrity and enabling the transformation of waste materials into high-performance vitrimers with enhanced mechanical properties suitable for 3D printing applications, ultimately establishing a circular economy framework that converts previously non-recyclable waste streams into valuable feedstock for additive manufacturing while utilizing environmentally sustainable processing conditions and reusable solution chemistry.
[0008] 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.
[0009] 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
[0010] 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.
[0011] 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 valorization of multi-layered packaging waste;
FIG. 2A is a graphical representation illustrating DSC thermal analysis of polyolefin lumps;
FIG. 2B is a graphical representation illustrating DSC thermal analysis of recovered powder;
FIG. 3 is a graphical representation illustrating FTIR spectroscopy analysis of recovered powder;
FIG. 4A is a schematic representation illustrating functionalization reaction mechanism;
FIG. 4B is a schematic representation illustrating vitrimer formation mechanism; and
FIG. 5 is a graphical representation illustrating mechanical properties comparison.
[0012] 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
[0013] Generally, multi-layered packaging waste remains difficult to valorize due to the complex adhesive bonding between dissimilar polymer layers and the lack of suitable methods to simultaneously separate and transform constituent materials into high-value products. The tightly bonded multi-layer structure prevents effective separation using conventional mechanical recycling methods, while chemical separation approaches often degrade polymer chains or require harsh processing conditions that compromise material quality. Furthermore, even when separation is achieved, the recovered polyolefins typically exhibit poor melt flow characteristics with excessively high melt flow index values, making them unsuitable for advanced manufacturing applications such as 3D printing where controlled flowability is essential. To address these fundamental limitations, the present disclosure provides a method involving a treatment solution treatment that simultaneously separates multi-layered packaging components and converts the PET fraction into bis(2-hydroxyethyl) terephthalate (BHET) while recovering intact polyolefin materials. The method is used to transform the recovered polyolefins through controlled functionalization and subsequent blending with the BHET to form vitrimer networks with dynamic covalent bonds, thereby creating high-performance materials suitable for additive manufacturing applications. The present disclosure enables the complete valorization of complex packaging waste streams by converting previously non-recyclable materials into valuable 3D printing feedstock with enhanced mechanical properties and controlled processing characteristics.
[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 valorization of multi-layered packaging waste, in accordance with an embodiment of the present disclosure. With reference to FIG. 1, a method 100 includes steps 102 to 110.
[0016] At step 102, the method 100 includes treating multi-layered packaging (MLP) waste comprising polyethylene terephthalate (PET), polypropylene (PP), and polyethylene (PE) layers with a treatment solution to simultaneously separate the PET layer from the PP and PE layers and convert the PET layer into bis(2-hydroxyethyl) terephthalate (BHET). Multi-layered packaging waste refers to complex packaging materials containing multiple polymer films bonded together with adhesive layers, commonly found in food packaging, pharmaceutical blister packs, and the like. In an implementation, the treatment solution includes seawater as a sustainable solvent base, citric acid as a pH modifier and chelating agent, bio-derived organic acids selected from acetic acid, formic acid, levulinic acid, lactic acid, and oxalic acid functioning as swelling agents and bond disruptors, and metal salts including zinc acetate and aluminum chloride acting as catalysts for polymer chain scission and transesterification reactions. Moreover, the treatment of the MLP waste is performed at temperatures ranging from 220 to 250°C for 3 to 6 hours under controlled pH conditions of 1.0 to 2.5, enabling the organic acids to penetrate and swell the polymer matrix while metal ions polarize heteroatomic bonds within the adhesive layers. Additionally, the BHET represents the depolymerized monomer unit of PET, characterized by terminal hydroxyl groups and aromatic ester linkages. The simultaneous separation occurs through selective dissolution of adhesive interfaces combined with controlled depolymerization of PET chains, producing clean polyolefin lumps containing PP and PE components free from adhesive contamination alongside bis(2-hydroxyethyl) terephthalate (BHET) powder formed through glycolysis of PET chains. As a result, the treatment of the MLP waste with the treatment solution allows elimination of sequential processing steps, preservation of polymer molecular weight through controlled reaction conditions, complete removal of adhesive contamination, and generation of valuable chemical intermediates suitable for further processing into advanced materials.
[0017] In accordance with an embodiment, the treatment solution comprises seawater, citric acid, acetic acid, formic acid, zinc acetate, and aluminium chloride. In an implementation, the treatment solution comprises specific component ratios optimized for efficient MLP waste processing. The seawater is utilized in quantities ranging from 40 to 50 milliliters, providing the base solvent medium with naturally occurring metal ions including sodium and magnesium that enhance polymer swelling characteristics. Citric acid is incorporated at concentrations of 10 to 15 grams, functioning as both a pH modifier and chelating agent that facilitates metal ion coordination with polymer chains. The bio-derived organic acids, specifically acetic acid and formic acid, are each added in quantities of 8 to 12 milliliters at normality concentrations of 6 to 8 N, providing the acidic environment necessary for polymer swelling and adhesive bond disruption. Zinc acetate is included at concentrations of 3 to 7 grams, serving as a primary catalyst for transesterification reactions and polymer chain scission, while aluminum chloride is added at concentrations of 3 to 7 grams, acting as a Lewis acid catalyst that promotes selective depolymerization of PET components. The specific component ratios ensure optimal separation efficiency while maintaining solution reusability and environmental sustainability through controlled pH maintenance between 1.0 and 2.5.
[0018] In accordance with an embodiment, the treatment solution is reusable for one or more processing cycles while maintaining pH between 1.0 and 2.5. The reuse is enabled by the stability of the organic acids and catalytic salts under reaction conditions, which preserves their chemical activity and allows repeated application without significant loss of efficiency. The pH maintenance during solution reuse is achieved through periodic monitoring using standard pH measurement equipment. Initial solution pH of 1.0-1.5 typically increases to 1.8-2.5 during processing due to neutralization with packaging components. Between cycles, pH is re-adjusted to the operating range using additional citric acid. Maintaining the pH in the defined range ensures selective depolymerization of polyethylene terephthalate into bis(2-hydroxyethyl) terephthalate while preventing uncontrolled degradation of polypropylene and polyethylene layers, thereby achieving consistent separation and recovery across cycles with minimized environmental footprint due to fewer chemical discharges, and enhanced scalability of the valorization process for multi-layered packaging waste, supporting a more sustainable and economically viable circular economy model.
[0019] At step 104, the method 100 includes functionalizing the recovered polyolefin components with maleic anhydride to form functionalized polyolefins. In an implementation, the polyolefin refers to the separated polypropylene (PP) and polyethylene (PE) materials recovered from the treatment of the MLP waste as clean lumps free from adhesive contamination and PET residues. Further, functionalization of the recovered polyolefin refers to a chemical modification process where reactive functional groups are grafted onto the otherwise chemically inert polyolefin backbone to enable subsequent crosslinking reactions and vitrimer formation. The maleic anhydride serves as the functionalizing agent, providing reactive anhydride groups that can form covalent bonds with polymer chains and later participate in transesterification reactions with BHET. In an implementation, the functionalization process utilizes dicumyl peroxide as a free radical initiator at concentrations of 0.5 weight percent, styrene as a co-grafting agent at 10.62 weight percent to enhance grafting efficiency, and antioxidant stabilizers to prevent unwanted degradation reactions. The functionalization is performed through melt extrusion at temperatures of 180°C with screw speeds of 150 rpm for processing times of 2 minutes, enabling controlled radical grafting while minimizing polymer degradation. The maleic anhydride, typically added at 10 weight percent, undergoes radical-mediated grafting onto the polyolefin chains through hydrogen abstraction and subsequent coupling reactions, creating pendant anhydride groups distributed along the polymer backbone. These pendant anhydride groups provide reactive sites that can subsequently react with hydroxyl groups present in BHET through ring-opening reactions, forming ester linkages essential for vitrimer network formation. As a result, functionalization of the polyolefin components enables transformation of chemically inert polyolefin materials into reactive intermediates capable of forming dynamic covalent networks, provides controlled grafting density for optimal mechanical properties, eliminates compatibility issues between polyolefin and polyester components, and creates the chemical foundation necessary for vitrimer formation with enhanced mechanical performance and recyclability characteristics.
[0020] In accordance with an embodiment, the functionalizing comprises grafting styrene and maleic anhydride onto polyolefin chains using dicumyl peroxide initiator to form functionalized polyolefins. The dicumyl peroxide decomposes at elevated temperature to generate free radicals that abstract hydrogen atoms from the polyolefin backbone, thereby creating active sites for covalent bonding. Styrene acts as a co-grafting agent to stabilize the radical intermediates and enhance grafting efficiency, while maleic anhydride introduces pendant anhydride groups along the polyolefin chains that provide reactive functionalities for subsequent crosslinking with bis(2-hydroxyethyl) terephthalate. As a result, the functionalization is performed to transform the chemically inert polyolefins into reactive intermediates capable of dynamic covalent bond formation, improved compatibility between polyolefin and polyester fractions, enhanced interfacial adhesion in the final vitrimer network, and significant improvement in mechanical strength and recyclability of the upcycled materials.
[0021] In an implementation, the functionalization process employs specific compositional ratios to achieve optimal grafting efficiency and mechanical property enhancement. The recovered polyolefin components serve as the base material at 100 weight percent concentration when processing neat polyolefin, establishing the baseline composition for subsequent modification. For the preparation of functionalized polyolefins, maleic anhydride is incorporated at 10 weight percent concentration, providing sufficient reactive anhydride groups for grafting while avoiding excessive crosslinking that could compromise processability. Dicumyl peroxide initiator is added at 0.5 weight percent concentration, generating controlled radical concentrations necessary for efficient grafting without causing polymer degradation. Styrene co-grafting agent is included at a 10.62 weight percent concentration, stabilizing polymer radicals through aromatic resonance and enhancing overall grafting efficiency. Irganox antioxidant stabilizer is incorporated at a 0.5 weight percent concentration, preventing unwanted oxidative degradation during high-temperature processing while maintaining controlled functionalization reactions. The specific compositional ratios ensure reproducible grafting density and mechanical property enhancement while maintaining processing stability and preventing thermal degradation of the polyolefin backbone.
[0022] At step 106, the method 100 includes mixing the functionalized polyolefins with the BHET to form a polymer blend. The polymer blend refers to a homogeneous mixture of two or more distinct polymer components that are physically combined to achieve synergistic properties not attainable by individual components alone. The functionalized polyolefins comprise the maleic anhydride-grafted PP and PE materials from functionalizing the recovered polyolefin components with maleic anhydride to form functionalized polyolefins, containing reactive anhydride groups distributed along the polymer chains, while BHET represents the bis(2-hydroxyethyl) terephthalate powder obtained from PET depolymerization, containing terminal hydroxyl groups capable of chemical reaction. In an implementation, the mixing process incorporates BHET powder at concentrations ranging from 1 to 30 weight percent of the total blend composition, with zinc acetate catalyst added at 0.1 to 2.8 weight percent to facilitate subsequent transesterification reactions between anhydride and hydroxyl groups. In an implementation, the mixing of the functionalized polyolefins with the BHET to form the polymer blend is performed through melt blending techniques that ensure uniform distribution of BHET particles throughout the functionalized polyolefin matrix while maintaining controlled processing temperatures to prevent premature crosslinking reactions. The BHET acts as both a reactive crosslinking agent and a reinforcing filler, with its hydroxyl groups providing sites for covalent bond formation with the anhydride-functionalized polyolefin chains through ring-opening esterification reactions. Zinc acetate functions as a transesterification catalyst, promoting the formation and exchange of ester bonds at elevated temperatures, thereby enabling the dynamic covalent bond behavior characteristic of vitrimer materials. The polymer blend formation creates a precursor system wherein the functionalized polyolefin matrix provides mechanical integrity and processability while BHET supplies reactive sites for crosslink formation and dynamic bond exchange mechanisms. As a result, mixing the functionalized polyolefins with BHET enables creation of a reactive blend system capable of forming dynamic covalent networks, provides controlled crosslink density through BHET concentration adjustment, ensures uniform dispersion of reactive components for consistent material properties, and establishes the chemical foundation for vitrimer formation with enhanced mechanical performance and reprocessability characteristics.
[0023] In an implementation, the vitrimer formation process utilizes specific compositional ratios optimized for mechanical property enhancement and dynamic covalent bond formation. The functionalized polyolefin components, comprising the maleic anhydride-grafted PP and PE materials, constitute 84 weight percent of the total vitrimer composition, providing the primary structural matrix and mechanical integrity of the final material. BHET powder is incorporated at 15 weight percent concentration, serving as both a reactive crosslinking agent and reinforcing component that enhances yield strength through dynamic covalent bond formation. Zinc acetate catalyst is added at 1 weight percent concentration, facilitating transesterification reactions between anhydride groups of functionalized polyolefins and hydroxyl groups of BHET molecules while enabling dynamic bond exchange mechanisms at elevated temperatures. The specific compositional ratios create an optimal balance between crosslink density and processability, ensuring enhanced mechanical properties while maintaining the reprocessability characteristics essential for vitrimer behaviour. The 84:15:1 ratio of functionalized polyolefin to BHET to zinc acetate catalyst represents the optimized formulation that provides a yield strength from 14 MPa to 21 MPa while reducing melt flow index to the controlled range of 4 to 5 grams per 10 minutes suitable for 3D printing applications.
[0024] In accordance with an embodiment, the method 100 further comprises utilizing the BHET as a separate feedstock for producing polyester materials. The BHET powder recovered from the treatment of multi-layered packaging waste serves as a valuable monomeric feedstock for polyester synthesis, representing bis(2-hydroxyethyl) terephthalate molecules containing both terminal hydroxyl groups and aromatic ester linkages essential for polymerization reactions. Polyester materials refer to a class of synthetic polymers formed through condensation polymerization of diol and diacid components, commonly used in textile fibres, packaging films, and engineering plastics applications. In an implementation, the BHET functions as a bifunctional monomer that can undergo polycondensation reactions with other diol or diacid components to form new polyester chains through ester bond formation. The terminal hydroxyl groups of BHET molecules provide reactive sites for chain extension reactions, while the aromatic ester backbone contributes to thermal stability and mechanical properties of the resulting polyester materials. The utilization of BHET as a separate feedstock enables the production of virgin-quality polyester materials without the quality degradation typically associated with mechanical recycling of PET waste. The BHET feedstock maintains high purity and chemical integrity due to the controlled depolymerization conditions employed in the treatment solution methodology, ensuring consistent polymerization behaviour and final product properties. The separate utilization pathway allows for diversified waste valorization strategies wherein BHET can be directed toward polyester production while polyolefin components are processed into vitrimer materials, maximizing the value recovery from multi-layered packaging waste streams. As a result, utilizing BHET as a separate feedstock enables production of high-quality polyester materials from waste-derived monomers, provides an alternative valorization pathway that maximizes economic value recovery, creates opportunities for closed-loop recycling in polyester applications, and establishes multiple end-use options for complete utilization of all multi-layered packaging waste components.
[0025] At step 108, the method 100 includes processing the polymer blend under controlled temperature and pressure conditions to form vitrimers having dynamic covalent bonds. Vitrimers represent a class of crosslinked polymer networks that combine the mechanical properties and chemical resistance of thermosets with the processability and recyclability of thermoplastics through dynamic covalent bond exchange mechanisms. Dynamic covalent bonds refer to reversible chemical linkages that can break and reform under specific conditions, typically elevated temperatures, allowing the crosslinked network to flow and be reprocessed while maintaining structural integrity at operating temperatures. In an implementation, the processing involves melt extrusion at temperatures ranging from 170 to 220°C with screw speeds of 150 to 200 rpm for processing durations of 1 to 3 minutes, providing sufficient thermal energy and mechanical mixing to promote transesterification reactions between the anhydride-functionalized polyolefin chains and hydroxyl groups of BHET. The controlled temperature conditions activate the zinc acetate catalyst, facilitating ester bond formation and subsequent bond exchange reactions that create a three-dimensional crosslinked network with dynamic characteristics. Pressure conditions during processing ensure intimate contact between reactive components while preventing volatile loss and maintaining uniform heat transfer throughout the polymer blend. The transesterification reactions occur through nucleophilic attack of BHET hydroxyl groups on anhydride carbonyls, forming ester linkages that can subsequently undergo exchange reactions with other ester bonds in the presence of the zinc catalyst at elevated temperatures. The resulting vitrimer network exhibits permanent crosslinking at ambient conditions but demonstrates thermoplastic-like behavior above the topology freezing temperature, where bond exchange becomes kinetically favorable. As a result, processing the polymer blend under controlled conditions enables formation of dynamic crosslinked networks with enhanced mechanical properties, provides reprocessability through controlled bond exchange mechanisms, creates materials with improved thermal stability and chemical resistance compared to linear polymers, and generates vitrimer networks suitable for advanced manufacturing applications requiring both high performance and recyclability characteristics.
[0026] At step 110, the method 100 includes converting the vitrimers into 3D printing feedstock suitable for various manufacturing applications. In an implementation, the 3D printing feedstock refers to processed polymer materials with controlled rheological properties and consistent quality characteristics specifically designed for additive manufacturing processes, typically in the form of filaments, pellets, or powders depending on the printing technology employed. The conversion process involves controlling the melt flow characteristics of the vitrimer materials to achieve optimal printability parameters, particularly targeting melt flow index (MFI) values in the range of 4 to 5 grams per 10 minutes which provides the controlled flowability essential for successful layer-by-layer deposition. In an implementation, the conversion utilizes pelletizing or granulation techniques following the vitrimer formation process, creating uniform particle sizes that facilitate consistent feeding and melting behavior during 3D printing operations. The vitrimer feedstock exhibits superior processing characteristics compared to conventional recycled polyolefins due to the controlled crosslink density and dynamic bond exchange mechanisms that prevent excessive flow while maintaining adequate melt processability. Manufacturing applications encompass a wide range of products including furniture components, containers, automotive parts, consumer goods, and structural elements that benefit from the enhanced mechanical properties and recyclability of vitrimer materials. The controlled flowability prevents common 3D printing defects such as layer delamination, warpage, and dimensional instability that typically occur with high MFI recycled materials, while the dynamic covalent bonds enable inter-layer bonding during the printing process. The vitrimer feedstock maintains consistent material properties across multiple processing cycles due to the reversible nature of the crosslink network, allowing printed objects to be recycled back into feedstock without significant property degradation. As a result, converting vitrimers into 3D printing feedstock enables transformation of waste materials into high-value manufacturing inputs, provides controlled processing characteristics superior to conventional recycled polymers, creates materials suitable for producing durable and recyclable 3D printed products, and establishes a circular economy framework where end-of-life products can be reprocessed into new feedstock materials without compromising performance characteristics.
[0027] The method 100 demonstrates mechanical property enhancement through the vitrimer formation process, as quantified through comparative analysis of neat polyolefin and polyolefin vitrimer materials. Neat polyolefin recovered from multi-layered packaging waste treatment exhibits a yield strength of 14 MPa with an elongation at yield of 80 percent, representing the baseline mechanical performance of the separated polyolefin components before vitrimer formation. The high elongation at yield characteristic reflects the presence of polyethylene components that contribute to ductility but limit strength properties. Following vitrimer formation through processing the polymer blend of functionalized polyolefins with BHET powder, the resulting polyolefin vitrimer demonstrates enhanced mechanical performance with yield strength increased to 21 MPa and elongation at yield reduced to 33 percent. The yield strength improvement of approximately 50 percent validates the effectiveness of the dynamic covalent bond formation in enhancing material performance, while the controlled reduction in elongation indicates successful crosslink network formation that restricts polymer chain mobility at ambient conditions. The mechanical property enhancement confirms that the valorization process not only enables waste recycling but creates materials with superior performance characteristics compared to conventional recycled polyolefins, establishing the commercial viability of the waste-derived vitrimer materials for advanced manufacturing applications.
[0028] In accordance with an embodiment, the controlled temperature conditions comprise separation temperatures of 220-250°C and vitrimer formation temperatures of 170-220°C. The controlled temperature conditions include maintaining separation temperatures between 220°C and 250°C for efficient depolymerization of polyethylene terephthalate into bis(2-hydroxyethyl) terephthalate and recovery of intact polyolefin lumps, followed by vitrimer formation temperatures between 170°C and 220°C to promote transesterification reactions without causing thermal degradation. The selected ranges ensure sufficient energy for bond cleavage and polymer activation while preventing unwanted side reactions in order to provide a precise thermal control that achieves selective polymer separation, preserves molecular integrity of the recovered polyolefins, and enables reliable vitrimer formation suitable for advanced applications.
[0029] In accordance with an embodiment, the dynamic covalent bonds comprise transesterification bonds that enable reversible cross-linking and recyclability of the vitrimers. The dynamic covalent bonds are transesterification linkages formed between hydroxyl groups of bis(2-hydroxyethyl) terephthalate and anhydride groups of functionalized polyolefins, which allow reversible cross-linking under elevated temperatures. The reversibility enables the vitrimer network to maintain thermoset-like strength at ambient conditions while behaving like a thermoplastic during reprocessing.
[0030] In accordance with an embodiment, the 3D printing feedstock is produced in the form of pellets, powder, or filament suitable for different additive manufacturing processes. The controlled conversion ensures consistent particle size distribution and rheological characteristics required for stable feeding and deposition. The technical advantage is compatibility with diverse 3D printing technologies, improved flowability for defect-free printing, and expanded applicability of waste-derived vitrimers in multiple industrial sectors.
[0031] In accordance with an embodiment, the polymer blend comprises 75-90 wt% functionalized polyolefins, 10-20 wt% BHET, and 0.5-1.5 wt% zinc acetate catalyst. The composition ensures an optimal balance of matrix strength from functionalized polyolefins, crosslinking reactivity from bis(2-hydroxyethyl) terephthalate, and catalytic activity from zinc acetate to facilitate efficient transesterification and provides a uniform crosslinked network density, improved mechanical strength, and controlled melt flow properties tailored for additive manufacturing.
[0032] In accordance with an embodiment, the vitrimers exhibit yield strength of 18-24 MPa and melt flow index of 4-5 g/10min. The performance metrics result from dynamic crosslink density that restricts polymer chain mobility at service conditions while maintaining reprocessability at elevated temperatures in order to provide a durable, recyclable, and high-value products from previously non-recyclable packaging waste.
[0033] Advantageously, the method 100 is used to provide simultaneous separation and valorization of multi-layered packaging waste components through a bio-based treatment solution that effectively separates polyolefin lumps and produces BHET powder, thereby eliminating the need for sequential separation processes while maintaining polymer integrity and enabling the transformation of waste materials into high-performance vitrimers with enhanced mechanical properties suitable for 3D printing applications, ultimately establishing a circular economy framework that converts previously non-recyclable waste streams into valuable feedstock for additive manufacturing while utilizing environmentally sustainable processing conditions and reusable solution chemistry.
[0034] FIG. 2A is a graphical representation illustrating differential scanning calorimetry (DSC) thermal analysis of polyolefin lumps recovered from multi-layered packaging waste treatment, in accordance with an embodiment of the present disclosure. FIG. 2A is described in conjunction with elements from FIG. 1. With reference to FIG. 2A, there is shown a graphical representation 200A depicting the heat flow behaviour of separated polyolefin components 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 shown as downward peaks and exothermic transitions shown as upward peaks. The temperature is measured in degrees Celsius (°C) on the abscissa axis, ranging from approximately 50°C to 250°C.
[0035] The graphical representation 200A includes a curve 202 representing the thermal behaviour of polyolefin lumps obtained from treating multi-layered packaging waste with the treatment solution. The curve 202 exhibits multiple distinct thermal transitions confirming the successful separation and recovery of individual polyolefin components from the complex multi-layered structure. The curve 202 shows an exothermic crystallization peak 204 at approximately 113°C corresponding to the crystallization temperature of polyethylene (PE) during cooling. The curve 202 displays an exothermic crystallization peak 206 at approximately 118°C corresponding to the crystallization temperature of polypropylene (PP) during cooling. Additionally, the curve 202 shows an endothermic melting peak 208 at approximately 123°C corresponding to the melting temperature of polyethylene (PE) components, and an endothermic melting peak 210 at approximately 160°C corresponding to the melting temperature of polypropylene (PP) components present in the recovered polyolefin lumps. The presence of distinct crystallization and melting transitions for both PE and PP confirms that the treatment solution effectively separated the polyolefin layers while preserving the individual polymer characteristics and molecular integrity. As a result, the sharp thermal peaks indicate that the recovered polyolefin components maintain their crystalline structure and thermal properties, demonstrating that the separation process does not cause significant polymer degradation or crosslinking.
[0036] FIG. 2B is a graphical representation illustrating differential scanning calorimetry (DSC) thermal analysis of recovered powder obtained from multi-layered packaging waste treatment, in accordance with an embodiment of the present disclosure. FIG. 2B is described in conjunction with elements from FIGs. 1 and 2A. With reference to FIG. 2B, there is shown a graphical representation 200B depicting the heat flow behaviour of recovered powder 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 shown as downward peaks and exothermic transitions shown as upward peaks. The temperature is measured in degrees Celsius (°C) on the abscissa axis, ranging from approximately 50°C to 300°C.
[0037] The graphical representation 200B includes a curve 212 representing the thermal behaviour of recovered powder obtained from treating multi-layered packaging waste with the treatment solution. The curve 212 exhibits a relatively flat thermal profile with minimal distinct thermal transitions, confirming the amorphous nature of the bis(2-hydroxyethyl) terephthalate (BHET) powder formed through controlled depolymerization of PET layers. The curve 212 shows a gradual thermal transition region 214 at approximately 150-200°C representing the glass transition and thermal stability range of the BHET powder. The absence of sharp melting peaks characteristic of crystalline polymers confirms that the recovered powder consists primarily of amorphous BHET monomer units rather than intact PET polymer chains. The smooth, continuous thermal profile without distinct crystallization or melting events validates the complete depolymerization of PET into its monomeric constituents through the treatment solution methodology. The thermal stability of the recovered powder up to approximately 250-300°C demonstrates the chemical integrity of the BHET molecules and their suitability for subsequent processing steps. The lack of additional thermal transitions confirms the absence of polyolefin contamination or residual adhesive materials in the recovered powder, demonstrating the selective separation capability of the treatment solution. As a result, the thermal analysis of the recovered powder validates the successful depolymerization of PET layers into pure BHET monomer units, confirms the absence of cross-contamination from other polymer components, and establishes the thermal processing window for subsequent vitrimer formation reactions.
[0038] FIG. 3 is a graphical representation illustrating Fourier transform infrared (FTIR) spectroscopy analysis of recovered powder obtained from multi-layered packaging waste treatment, in accordance with an embodiment of the present disclosure. FIG. 3 is described in conjunction with elements from FIGs. 1, 2A, and 2B. With reference to FIG. 3, there is shown a graphical representation 300 depicting the infrared absorption characteristics of recovered powder across different wavenumbers. The transmittance percentage is represented on the ordinate axis, quantifying the amount of infrared light that passes through the sample as a percentage of the original light intensity. The wavenumber is measured in centimetres inverse (cm?¹) on the abscissa axis, ranging from approximately 1000 to 4000 cm?¹, representing the number of wavelengths per unit distance.
[0039] The graphical representation 300 includes a curve 302 representing the FTIR spectral behaviour of recovered powder obtained from treating multi-layered packaging waste with the treatment solution. The curve 302 exhibits characteristic absorption peaks confirming the chemical identity of the recovered powder as bis(2-hydroxyethyl) terephthalate (BHET) formed through controlled depolymerization of PET layers. The curve 302 shows a distinct absorption peak 304 at approximately 1721 cm?¹ corresponding to ester carbonyl (C=O) stretching vibrations, which represents the signature functional group of BHET molecules. The curve 302 displays an absorption peak 306 at approximately 2969 cm?¹ corresponding to aromatic C-H stretching vibrations from the terephthalic acid aromatic ring structure preserved in the BHET monomer. Additionally, the curve 302 exhibits an absorption peak 308 at approximately 3420 cm?¹ corresponding to O-H stretching vibrations from the terminal hydroxyl groups present in BHET molecules. The presence of these three characteristic absorption peaks provides definitive spectroscopic confirmation that the recovered powder consists of BHET monomer units containing both the aromatic ester backbone and terminal hydroxyl functionalities essential for subsequent vitrimer formation. The sharp, well-defined absorption peaks indicate high purity of the recovered BHET powder without significant contamination from other polymer components or degradation products. The spectroscopic analysis validates the selective depolymerization of PET layers while confirming the chemical integrity and reactive functionality of the recovered BHET suitable for crosslinking reactions with functionalized polyolefins. As a result, the FTIR analysis of the recovered powder confirms the successful conversion of PET layers into pure BHET monomer units, validates the absence of polyolefin or adhesive contamination, establishes the presence of reactive hydroxyl groups necessary for vitrimer formation, and demonstrates the chemical selectivity and effectiveness of the treatment solution methodology.
[0040] FIG. 4A is a schematic representation illustrating the reaction mechanism for functionalization of recovered polyolefin components with maleic anhydride to form functionalized polyolefins, in accordance with an embodiment of the present disclosure. FIG. 4A is described in conjunction with elements from FIGs. 1 to 3. With reference to FIG. 4A, there is shown a schematic representation 400A that depicts the chemical transformation pathway for converting recovered polyolefin components into reactive intermediates suitable for vitrimer formation.
[0041] The schematic representation 400A includes an operation 402 showing the starting materials required for the functionalization process. The operation 402 comprises post-consumer recycled polyolefin (PCR-PO) having a backbone structure where R represents hydrogen for polyethylene (PE) or methyl groups for polypropylene (PP). The operation 402 further includes styrene present at 10.62 weight percent functioning as a co-grafting agent, maleic anhydride (MA) present at 10 weight percent serving as the functionalizing agent, dicumyl peroxide (DCP) present at 0.5 weight percent acting as a free radical initiator, and Irganox antioxidant stabilizer present at 0.5 weight percent. The schematic representation 400A includes an operation 404 showing the functionalized polyolefin (m'-PCR PO) formed through the grafting reaction performed at 150 rpm for 2 minutes at 180°C.
[0042] The transformation from operation 402 to operation 404 demonstrates the formation of functionalized polyolefin through radical-mediated grafting mechanisms. The dicumyl peroxide initiator decomposes at elevated temperatures to generate free radicals that abstract hydrogen atoms from the polyolefin chains in operation 402, creating reactive macroradical sites along the polymer backbone. The styrene co-grafting agent stabilizes the polymer radicals and enhances grafting efficiency by providing aromatic stabilization to the radical intermediates. The maleic anhydride undergoes grafting onto the activated polyolefin chains through radical addition mechanisms, creating pendant anhydride groups distributed along the polymer backbone as shown in operation 404. The resulting functionalized polyolefin in operation 404 contains reactive anhydride functionalities that can subsequently participate in ring-opening reactions with hydroxyl groups present in BHET to form ester linkages essential for vitrimer network formation. The Irganox antioxidant prevents unwanted oxidative degradation during the high-temperature processing, ensuring controlled functionalization without polymer chain scission. As a result, the transformation from operation 402 to operation 404 converts chemically inert polyolefin components into reactive intermediates capable of forming dynamic covalent networks, provides controlled grafting density for optimal crosslinking behaviour, enables compatibility between polyolefin and polyester components, and creates the chemical foundation necessary for subsequent vitrimer formation with enhanced mechanical properties and recyclability characteristics.
[0043] FIG. 4B is a schematic representation illustrating the reaction mechanism for vitrimer formation through crosslinking of functionalized polyolefins with BHET, in accordance with an embodiment of the present disclosure. FIG. 4B is described in conjunction with elements from FIGs. 1 to 4A. With reference to FIG. 4B, there is shown a schematic representation 400B that depicts the chemical crosslinking pathway for converting functionalized polyolefins and BHET into vitrimer networks having dynamic covalent bonds.
[0044] The schematic representation 400B includes an operation 406 showing the reactants required for vitrimer formation. The operation 406 comprises functionalized polyolefin (m'-PO) obtained from the functionalization process, containing pendant anhydride groups distributed along the polymer backbone where R represents hydrogen for polyethylene (PE) or methyl groups for polypropylene (PP). The operation 406 further includes bis(2-hydroxyethyl) terephthalate (BHET) molecules containing terminal hydroxyl groups and aromatic ester linkages, and zinc acetate catalyst present to facilitate transesterification reactions. The crosslinking reaction is performed at 150 rpm for 2 minutes at 180°C under melt processing conditions. The schematic representation 400B includes an operation 408 showing the resulting polyolefin vitrimer (PO-V) formed through the crosslinking reaction between functionalized polyolefins and BHET.
[0045] The transformation from operation 406 to operation 408 demonstrates the formation of vitrimer networks through transesterification mechanisms. The zinc acetate catalyst activates the crosslinking reaction by promoting nucleophilic attack of BHET hydroxyl groups on the anhydride carbonyls of the functionalized polyolefin chains in operation 406, forming ester linkages that create three-dimensional crosslinked networks. The transesterification reactions create dynamic covalent ester bonds that can break and reform under elevated temperatures, enabling the vitrimer characteristics of processability combined with crosslinked network properties. The BHET molecules act as crosslinking agents, connecting multiple functionalized polyolefin chains through ester bond formation to create the network structure shown in operation 408. The resulting polyolefin vitrimer in operation 408 exhibits enhanced mechanical properties due to the crosslinked network structure while maintaining reprocessability through dynamic bond exchange mechanisms facilitated by the zinc acetate catalyst at elevated temperatures. The vitrimer network demonstrates permanent crosslinking at ambient conditions but exhibits thermoplastic-like behaviour above the topology freezing temperature where bond exchange becomes kinetically favourable. As a result, the transformation from operation 406 to operation 408 creates dynamic crosslinked networks with enhanced mechanical properties, provides materials with controlled flowability suitable for 3D printing applications, enables reprocessability through bond exchange mechanisms, and establishes vitrimer networks that combine the advantages of thermosets and thermoplastics for advanced manufacturing applications.
[0046] FIG. 5 is a graphical representation illustrating mechanical properties comparison between neat polyolefin and polyolefin vitrimer obtained from multi-layered packaging waste valorization, in accordance with an embodiment of the present disclosure. With reference to FIG. 5, there is shown a graphical representation 500 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 yield is measured in percentage and represented on the right ordinate axis. Two polymer formulations, PO (neat polyolefin) and PO-V (polyolefin vitrimer), are represented on the abscissa axis.
[0047] The graphical representation 500 includes a bar 502 depicting the yield strength of neat polyolefin (PO) obtained from multi-layered packaging waste separation. The bar 502 shows a yield strength of approximately 14 MPa, representing the baseline mechanical performance of the recovered polyolefin components before vitrimer formation. The graphical representation 500 includes a bar 504 depicting the elongation at yield of neat polyolefin (PO), showing approximately 80% elongation at yield, indicating the high ductility characteristic of polyethylene-containing polyolefin blends. Additionally, the graphical representation 500 includes a bar 506 depicting the yield strength of polyolefin vitrimer (PO-V) formed through processing the polymer blend of functionalized polyolefins with BHET. The bar 506 shows a yield strength of approximately 21 MPa, representing a substantial improvement in mechanical performance compared to neat polyolefin. The graphical representation 500 includes a bar 508 depicting the elongation at yield of polyolefin vitrimer (PO-V), showing approximately 33% elongation at yield, indicating controlled ductility resulting from dynamic covalent bond formation. The comparison between bars 502 and 506 demonstrates that vitrimer formation increases yield strength by approximately 50%, from 14 MPa to 21 MPa, confirming the mechanical enhancement achieved through dynamic covalent bond networks. The reduction in elongation at yield from bar 504 to bar 508, decreasing from 80% to 33%, indicates the formation of crosslinked network structure that restricts polymer chain mobility at room temperature while maintaining processability at elevated temperatures. The mechanical property enhancement validates the effectiveness of functionalizing recovered polyolefin components with maleic anhydride and subsequent crosslinking with BHET powder to form vitrimer networks. The yield strength improvement demonstrates that the treatment solution methodology not only enables waste valorization but also creates materials with superior mechanical performance compared to the original waste-derived components. As a result, the mechanical analysis confirms that vitrimer formation significantly enhances material performance, validates the technical effectiveness of the valorization process, establishes the commercial viability of waste-derived products, and demonstrates the successful transformation of low-value waste materials into high-performance polymer networks suitable for advanced manufacturing applications.
[0048] 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 valorization of multi-layered packaging waste comprising:
treating multi-layered packaging waste comprising polyethylene terephthalate (PET), polypropylene (PP), and polyethylene (PE) layers with a treatment solution to simultaneously separate the PET layer from the PP and PE layers and convert the PET layer into bis(2-hydroxyethyl) terephthalate (BHET);
functionalizing the recovered polyolefin components with maleic anhydride to form functionalized polyolefins;
mixing the functionalized polyolefins with the BHET to form a polymer blend;
processing the polymer blend under controlled temperature conditions to form vitrimers having dynamic covalent bonds; and
converting the vitrimers into 3D printing feedstock suitable for various manufacturing applications.
2. The method (100) as claimed in claim 1, further comprises utilizing the BHET as a separate feedstock for producing polyester materials.
3. The method (100) as claimed in claim 1, wherein the treatment solution comprises seawater, citric acid, acetic acid, formic acid, zinc acetate, and aluminium chloride.
4. The method (100) as claimed in claim 1, wherein functionalizing comprises grafting styrene and maleic anhydride onto polyolefin chains using dicumyl peroxide initiator to form functionalized polyolefins.
5. The method (100) as claimed in claim 1, wherein the controlled temperature conditions comprise separation temperatures of 220-250°C and vitrimer formation temperatures of 170-220°C.
6. The method (100) as claimed in claim 1, wherein the dynamic covalent bonds comprise transesterification bonds that enable reversible cross-linking and recyclability of the vitrimers.
7. The method (100) as claimed in claim 1, wherein the 3D printing feedstock is produced in the form of pellets, powder, or filament suitable for different additive manufacturing processes.
8. The method (100) as claimed in claim 1, wherein the polymer blend comprises 75-90 wt% functionalized polyolefins, 10-20 wt% BHET, and 0.5-1.5 wt% zinc acetate catalyst.
9. The method (100) as claimed in claim 1, wherein the vitrimers exhibit yield strength of 18-24 MPa and melt flow index of 4-5 g/10min.
10. The method (100) as claimed in claim 3, wherein the treatment solution is reusable for one or more processing cycles while maintaining pH between 1.0 and 2.5.