Recycling and high-value utilization of polyethylene terephthalate wastes: A review.

Polyethelene terephthalate (PET) is a well-known thermoplastic, and recycling PET waste is important for the natural environment and human health. This study provides a comprehensive overview of the recycling and reuse of PET waste through energy recovery and physical, chemical, and biological recycling. This article summarizes the recycling methods and the high-value products derived from PET waste, specifically detailing the research progress on regenerated PET prepared by the mechanical recycling of fiber/yarn, fabric, and composite materials, and introduces the application of PET nanofibers recycled by physical dissolution and electrospinning in fields such as filtration, adsorption, electronics, and antibacterial materials. This article explains the energy recovery of PET through thermal decomposition and comprehensively discusses various chemical recycling methods, including the reaction mechanisms, catalysts, conversion efficiencies, and reaction products, with a brief introduction to PET biodegradation using hydrolytic enzymes provided. The analysis and comparison of various recycling methods indicated that the mechanical recycling method yielded PET products with a wide range of applications in composite materials. Electrospinning is a highly promising recycling strategy for fabricating recycled PET nanofibers. Compared to other methods, physical recycling has advantages such as low cost, low energy consumption, high value, simple processing, and environmental friendliness, making it the preferred choice for the recycling and high-value utilization of waste PET.

The Recyclability of Fire-Retarded Biobased Polyamide 11 (PA11) Composites Reinforced with Basalt Fibers (BFs): The Influence of Reprocessing on Structure, Properties, and Fire Behavior.

The growing requirements regarding the safety of using polymers and their composites are related to the emergence of more effective, sustainable, and hazardous-limited fire retardants (FRs). Significant amounts of FRs are usually required to effectively affect a polymer's burning behavior, while the knowledge of their recycling potential is still insufficient. At the same time, concerns are related not only to the reduced effectiveness of flame retardancy but also, above all, to the potential deterioration of mechanical properties caused by the degradation of temperature-affected additives under processing conditions. This study describes the impact of the four-time reprocessing of bio-based polyamide 11 (PA11) modified with an intumescent flame-retardant (IFR) system composed of ammonium polyphosphate (APP), melamine cyanurate (MC), and pentaerythritol (PER) and its composites containing additional short basalt fibers (BFs). Composites manufactured via twin-screw extrusion were subjected to four reprocessing cycles using injection molding. A comprehensive analysis of their structural, mechanical, and fire behavior changes in each cycle was conducted. The obtained results confirmed the safety of using the proposed fire-retarded polyamide and its composites while reprocessing under the recommended process parameters without the risk of significant changes in the structure. The partial increase in flammability of reprocessed PA-based materials caused mainly by polymer degradation has been described.

The development of recycling methods for bio-based materials - A challenge in the implementation of a circular economy: A review.

This review focuses on the characteristics of the most widely used biopolymers that contain starch, polylactic acid, cellulose and/or polybutylene succinate. Because worldwide production of bio-based materials has grown dynamically, their waste is increasingly found in the existing waste treatment plants. The development of recycling methods for bio-based materials remains a challenge in the implementation of a circular economy. This article summarizes the recycling methods for bio-based materials, which, in the hierarchy of waste management, is much more desirable than landfilling. Several methods of recycling are available for the end-of-life management of bio-based products, which include mechanical (reuse of waste as a valuable raw material for further processing), chemical (feedstock recycling) and organic (anaerobic digestion or composting) ones. The use of chemical or mechanical recycling is less favourable, more costly and requires the improvement of systems for separation of bio-based materials from the rest of the waste stream. Organic recycling can be a sustainable alternative to those two methods. In organic recycling, bio-based materials can be biologically treated under aerobic or anaerobic conditions, depending on the characteristics of the materials. The choice of the recycling method to be implemented depends on the economic situation and on the properties of the bio-based products and their susceptibility to degradation. Thus, it is necessary to label the products to indicate which method of recycling is most appropriate.

Environment-friendly, efficient process for mechanical recovery of waste lithium iron phosphate batteries.

Technology for recycling retired lithium batteries has become increasingly environment-friendly and efficient. In traditional recovery methods, pyrometallurgy or hydrometallurgy is often used as an auxiliary treatment method, which results in secondary pollution and increases the cost of harmless treatment. In this article, a new method for combined mechanical recycling of waste lithium iron phosphate (LFP) batteries is proposed to realize the classification and recycling of materials. Appearance inspections and performance tests were conducted on 1000 retired LFP batteries. After discharging and disassembling the defective batteries, the physical structure of the cathode binder was destroyed under ball-milling cycle stress, and the electrode material and metal foil were separated using ultrasonic cleaning technology. After treating the anode sheet with 100 W of ultrasonic power for 2 minutes, the anode material was completely stripped from the copper foil, and no cross-contamination between the copper foil and graphite was observed. After the cathode plate was ball-milled for 60 seconds with an abrasive particle size of 20 mm and then ultrasonically treated for 20 minutes with a power of 300 W, the stripping rate of the cathode material reached 99.0%, and the purities of the aluminium foil and LFP reached 100% and 98.1%, respectively.

Plastic waste recycling: existing Indian scenario and future opportunities.

This review article aims to suggest recycling technological options in India and illustrates plastic recycling clusters and reprocessing infrastructure for plastic waste (PW) recycling in India. The study shows that a majority of states in India are engaged in recycling, road construction, and co-processing in cement kilns while reprocessing capabilities among the reprocessors are highest for polypropylene (PP) and polyethylene (PE) polymer materials. This review suggests that there are key opportunities for mechanical recycling, chemical recycling, waste-to-energy approaches, and bio-based polymers as an alternative to deliver impact to India's PW problem. On the other hand, overall, polyurethane, nylon, and polyethylene terephthalate appear most competitive for chemical recycling. Compared to conventional fossil fuel energy sources, polyethylene (PE), polypropylene (PP), and polystyrene are the three main polymers with higher calorific values suitable for energy production. Also, multi-sensor-based artificial intelligence and blockchain technology and digitization for PW recycling can prove to be the future for India in the waste flow chain and its management. Overall, for a circular plastic economy in India, there is a necessity for a technology-enabled accountable quality-assured collaborative supply chain of virgin and recycled material. Supplementary Information: The online version contains supplementary material available at 10.1007/s13762-022-04079-x.

Chemical recycling: A critical assessment of potential process approaches.

Increased media coverage of plastic pollution in the environment and import bans on plastic waste in several countries have resulted in plastic waste becoming one of the most discussed waste streams in recent years. In the European Union (EU), only about one-third of the post-consumer plastic waste is recycled; the rest goes to energy recovery and landfilling in equal parts. In connection to the necessary increase in efforts to achieve the ambitious EU recycling targets, chemical recycling is currently receiving more and more attention. The assumption is that chemical recycling processes could open up new waste streams for recycling and generate valuable raw materials for the chemical industry. Although there exists no legal definition for chemical recycling, there is more or less agreement that it covers the conversion of plastic polymers into their monomers or chemical building blocks. Techniques such as gasification, pyrolysis and liquefaction as well as solvolysis can be used for chemical recycling. So far, only few large-scale plants for chemical recycling exist worldwide. This article presents the different processes by means of examples from (formerly) running installations and their suitability for plastics recycling is assessed. However, to date, only few chemical recycling plants are in continuous operation, and further scientific evidence for the ecological and economic benefits is still necessary for final evaluation.

A mini-review of the physical recycling methods for plastic parts in end-of-life vehicles.

Although the use of plastic components is increasing in the automotive industry, yet the recovery rates of these materials in end-of-life vehicle (ELV) is lower compared to metals. One of the main problems of ELV plastic waste is poor separation and sorting. Large car plastic parts consist of fibre-reinforced plastics, whereas other components end up in the automotive shredder residue (ASR), featuring a very heterogeneous mix of light materials that contains mostly non-metallic materials such as textiles, plastics, cartridges and wood. Generally, ASR was disposed in landfill or diverted to thermal treatments, such as pyrolysis or gasification, for energy recovery. Currently, the recovery of raw materials from various waste streams plays a key role in new European strategy for plastics in a circular economy. The approach of physical recycling methods described in this mini-review helps to maintain the value of polymer materials in the value chain allowing the reuse in the original or similar application.

Mechanical Recycling of Packaging Plastics: A Review.

The current global plastics economy is highly linear, with the exceptional performance and low carbon footprint of polymeric materials at odds with dramatic increases in plastic waste. Transitioning to a circular economy that retains plastic in its highest value condition is essential to reduce environmental impacts, promoting reduction, reuse, and recycling. Mechanical recycling is an essential tool in an environmentally and economically sustainable economy of plastics, but current mechanical recycling processes are limited by cost, degradation of mechanical properties, and inconsistent quality products. This review covers the current methods and challenges for the mechanical recycling of the five main packaging plastics: poly(ethylene terephthalate), polyethylene, polypropylene, polystyrene, and poly(vinyl chloride) through the lens of a circular economy. Their reprocessing induced degradation mechanisms are introduced and strategies to improve their recycling are discussed. Additionally, this review briefly examines approaches to improve polymer blending in mixed plastic waste streams and applications of lower quality recyclate.

Development of recycled blends based on cables and wires with plastic cabinets: An effective solution for value addition of hazardous waste plastics.

The recycling of polyvinyl chloride (PVC) recovered from the plastic insulations in wires and cables is a rising concern in the current situation due to its hazardous behaviour during recycling. Similarly, high-impact polystyrene (HIPS) and acrylonitrile butadiene styrene (ABS) used in the structural components of electrical and electronic equipment are also generated in large quantities. In the current work, three agendas were fixed: (a) to determine the effect of recycled polymeric material (HIPS and ABS) recovered from different sources on the mechanical property of the polymeric blends; (b) to formulate a high-impact strength blend; and (c) to deduce a mechanism for improved impact strength. The mechanical characterizations were conducted on the entire blends formulated. Among them, the recycled blend composed of recycled PVC (r-PVC) and recycled ABS (r-ABS) (segregated from uninterrupted power supply housing) and recycled HIPS (r-HIPS; collected from television housing) was confined for further physio-mechanical and thermal analysis. Besides, the r-PVC/r-ABS systems had shown better mechanical properties than r-PVC/r-HIPS systems in similar composition. The impact strength of blend r-PVC/r-ABS (70:30) was found to be 250 J/m, which was 200% more than the blend r-PVC/r-ABS (0:100). The compatibility and non-compatibility in PVC/ABS and PVC/HIPS blends respectively were explained with thermal, mechanical and morphological characterizations. Furthermore, a plausible cross-linking mechanism is developed between ABS and PVC, which controls the release of chlorine atoms into the environment.

Mechano-microbial systems: An ecofriendly approach for copper bioleaching from waste printed circuit board.

Waste printed circuit board (PCB) is attracting serious concerns because the recycling of its valuable metallic portion is made difficult by the existence of hazardous substances. The objective of the present study was to develop a simplified approach for copper bioleaching from waste PCB. In this context, we intended mechano-microbial systems symbolized as SET-I (spore suspension + potato dextrose broth medium + waste PCB powder), SET-II (pre-cultured until the logarithmic phase, without waste PCB powder), and SET-III (fungal metabolites produced at stationary phase). The results of bioleaching studies showed that the developed method achieved the highest copper leaching of 85% by the SET-III approach. This study provides an insight for bioleaching copper from waste PCB. Furthermore, this approach can be established as an ecofriendly method for copper bioleaching by using an integrated system.

Cost analysis of plastic solid waste recycling in an urban district in Turkey.

The usage of plastics has exponentially increased in our daily lives over the past 50 years because of its durability, low costs and potential for diverse applications, such as widespread use as disposable items. In this study, first, the recycling cost of plastic wastes has been estimated by using actual data taken from a recycling centre, where plastic solid wastes were collected separately. The total amount of plastic wastes recycled at the centre was approximately 695 tonnes. The operating cost of plastics separation at the recycling centre, the transport of plastic wastes, labouring, maintenance, electricity, insurance and chemical costs were taken into consideration in the cost evaluation. Accordingly, the unit cost of recycling was calculated as US$0.40 kg-1 of plastic waste. This cost was compared with the predicted plastic recycling cost in the same region using statistical values. The predicted recycling cost was estimated based on assuming segregated collection by the municipalities of all PSW in municipal solid waste. Then the resulting unit cost of recycling was found to be US$0.25 kg-1 of plastic waste. In addition, the recycling costs were also evaluated including the revenue from the sales of recycled plastic granular. According to the evaluated total cost of plastic recycling, it can be concluded that mechanical recycling of plastics can only be an economical option if the recovery of plastics is improved.

Valorization of poly(lactic acid) wastes via mechanical recycling: Improvement of the properties of the recycled polymer.

Poly(lactic acid) (PLA) is a biobased polymer that represents one of the most interesting alternatives to fossil-fuel based polymers in food packaging applications. Most of the PLA used in food packaging is used only once and then discarded, even though the PLA types used in packaging have good properties and stability. Therefore, it seems reasonable to consider the possibility of recycling the used polymer through a mechanical recycling process. The main aims of this work are to study the effect of the mechanical recycling on the properties of PLA and the usefulness of different upgrading methods to obtain recycled PLA with improved properties. A commercial type of PLA was subjected to accelerated thermal, photochemical and hydrolytic aging and then reprocessed. During reprocessing, aged PLA was blended with virgin PLA and a commercial chain extender was added. Results point out that recycling causes the degradation of PLA, and negatively affects the thermal stability and mechanical properties. However, addition of virgin PLA, and the chain extender, led to an increase of up to 9% in the intrinsic viscosity and 8% in the Vickers hardness of the recycled material. These results suggest that mechanically recycled PLA with improved performance can be obtained, a fact which might improve the recyclability of PLA and thus the environmental impact of this material.

Influence of non-metallic parts of waste printed circuit boards on the properties of plasticised polyvinyl chloride recycled from the waste wire.

Extreme complexity in the range of metallic and non-metallic parts present in waste printed circuit boards leads to incineration for collecting valuable metals. The non-metallic parts of the printed circuit board can be used effectively without affecting the environment. In this study, the non-metallic parts of the printed circuit board, which is made up by cross-linked resin and fibre, was used as a filler in recycled plasticised polyvinyl chloride collected from waste wires and cables. The properties of the plasticised polyvinyl chloride matrix and plasticised polyvinyl chloride-non-metallic parts of printed circuit board composite were compared with each other by means of mechanical properties and thermal properties. Both mechanical and thermal properties results indicated that incorporation of non-metallic parts of printed circuit board significantly improved the hardness, stiffness, abrasion resistance and thermal stability of plasticised polyvinyl chloride-non-metallic parts of printed circuit board composite; however, the tensile strength of the composite material is not improved because of poor adhesion between the plasticised polyvinyl chloride matrix and non-metallic parts of printed circuit board filler. The poor chemical interaction is also observed from Fourier transform infrared spectroscopy results. This plasticised polyvinyl chloride-non-metallic parts of printed circuit board composite can reduce the leaching of a hazardous element from the printed circuit board with effective utilisation of plastics fraction from waste wires and cables.

Combined mechanical process recycling technology for recovering copper and aluminium components of spent lithium-iron phosphate batteries.

The recycling processes of spent lithium iron phosphate batteries comprise thermal, wet, and biological and mechanical treatments. Limited research has been conducted on the combined mechanical process recycling technology and such works are limited to the separation of metal and non-metal materials, which belongs to mechanical recovery. In this article the combined mechanical process recycling technology of spent lithium iron phosphate batteries and the separation of metals has been investigated. The spent lithium iron phosphate batteries monomer with the completely discharged electrolyte was subjected to perforation discharge. The shell was directly recycled and the inner core was directly separated into a positive electrode piece, dissepiment, and negative electrode piece. The dissociation rate of the positive and negative materials reached 100.0% after crushing when the temperature and time reached 300 °C and 120 min. The crushed products were collected and sequentially sieved after the low-temperature thermal treatment. Then, nonferrous metals (copper and aluminium) were separated from the crushed spent lithium iron phosphate batteries by eddy current separation with particle size -4 + 0.4. The optimised operation parameters of eddy current separation were fed at speeds of 40 r min-1, and the rotation speed of the magnetic field was 800 r min-1. The nonferrous metals of copper and aluminium were separated by the method of pneumatic separation. The optimal air speed was 0.34 m s-1 for the particle-size -1.6 + 0.4 mm and 12.85-14.23 m s-1 for the particle-size -4 + 1.6 mm. The present recycling process is eco-friendly and highly efficient and produces little waste.

Effect of simulated mechanical recycling processes on the structure and properties of poly(lactic acid).

The aim of this work is to study the effects of different simulated mechanical recycling processes on the structure and properties of PLA. A commercial grade of PLA was melt compounded and compression molded, then subjected to two different recycling processes. The first recycling process consisted of an accelerated ageing and a second melt processing step, while the other recycling process included an accelerated ageing, a demanding washing process and a second melt processing step. The intrinsic viscosity measurements indicate that both recycling processes produce a degradation in PLA, which is more pronounced in the sample subjected to the washing process. DSC results suggest an increase in the mobility of the polymer chains in the recycled materials; however the degree of crystallinity of PLA seems unchanged. The optical, mechanical and gas barrier properties of PLA do not seem to be largely affected by the degradation suffered during the different recycling processes. These results suggest that, despite the degradation of PLA, the impact of the different simulated mechanical recycling processes on the final properties is limited. Thus, the potential use of recycled PLA in packaging applications is not jeopardized.

Influence of acrylonitrile butadiene rubber on recyclability of blends prepared from poly(vinyl chloride) and poly(methyl methacrylate).

The current investigation deals with the recycling possibilities of poly(vinyl chloride) and poly(methyl methacrylate) in the presence of acrylonitrile butadiene rubber. Recycled blends of poly(vinyl chloride)/poly(methyl methacrylate) are successfully formed from the plastic constituents, those are recovered from waste computer products. However, lower impact performance of the blend and lower stability of the poly(vinyl chloride) phase in the recycled blend restricts its further usage in industrial purposes. Therefore, effective utilisation acrylonitrile butadiene rubber in a recycled blend was considered for improving mechanical and thermal performance. Incorporation of acrylonitrile butadiene rubber resulted in the improvement in impact performance as well as elongation-at-break of the recycled blend. The optimum impact performance was found in the blend with 9 wt% acrylonitrile butadiene rubber, which shows 363% of enhancement as compared with its parent blend. Moreover, incorporated acrylonitrile butadiene rubber also stabilises the poly(vinyl chloride) phase present in the recycled blend, similarly Fourier transform infrared spectroscopy studies indicate the interactions of various functionalities present in the recycled blend and acrylonitrile butadiene rubber. In addition to this, thermogravimetric analysis indicates the improvement in the thermal stability of the recycled blend after the addition of acrylonitrile butadiene rubber into it. The existence of partial miscibility in the recycled blend was identified using differential scanning calorimetry and scanning electron microscopy.

Material recycling of post-consumer polyolefin bulk plastics: Influences on waste sorting and treatment processes in consideration of product qualities achievable.

Material recycling of post-consumer bulk plastics made up of polyolefins is well developed. In this article, it is examined which effects on waste sorting and treatment processes influence the qualities of polyolefin-recyclats. It is shown that the properties and their changes during the product life-cycle of a polyolefin are defined by its way of polymerisation, its nature as a thermoplast, additives, other compound and composite materials, but also by the mechanical treatments during the production, its use where contact to foreign materials is possible and the waste sorting and treatment processes. Because of the sum of the effects influencing the quality of polyolefin-recyclats, conclusions are drawn for the material recycling of polyolefins to reach high qualities of their recyclats. Also, legal requirements like the EU regulation 1907/2006 concerning the registration, evaluation, authorisation and restrictions on chemicals are considered.

Characterisation of recycled acrylonitrile-butadiene-styrene and high-impact polystyrene from waste computer equipment in Brazil.

Polymeric materials constitute a considerable fraction of waste computer equipment and polymers acrylonitrile-butadiene-styrene and high-impact polystyrene are the main thermoplastic polymeric components found in waste computer equipment. Identification, separation and characterisation of additives present in acrylonitrile-butadiene-styrene and high-impact polystyrene are fundamental procedures to mechanical recycling of these polymers. The aim of this study was to evaluate the methods for identification of acrylonitrile-butadiene-styrene and high-impact polystyrene from waste computer equipment in Brazil, as well as their potential for mechanical recycling. The imprecise utilisation of symbols for identification of the polymers and the presence of additives containing toxic elements in determinate computer devices are some of the difficulties found for recycling of acrylonitrile-butadiene-styrene and high-impact polystyrene from waste computer equipment. However, the considerable performance of mechanical properties of the recycled acrylonitrile-butadiene-styrene and high-impact polystyrene when compared with the virgin materials confirms the potential for mechanical recycling of these polymers.

Recycled PET/PA6 Fibers from Waste Textile with Improved Hydrophilicity by In-Situ Reaction-Induced Capacity Enhancement.

Due to the increasing amounts of textile waste, textile to textile recycling is of prime concern. Polyethylene terephthalate (PET) represents the most extensively used type of chemical fiber. Its spinnability suffers from impurities and degradation in the processing, which limits its recycling to new fibers. Here, recycled polyester is blended with a small amount of recycled nylon, and the regenerated fibers, which demonstrated good mechanical properties, were obtained via a melt spinning machine. The mechanical properties, thermal properties, rheological properties, and chemical structure of the modified recycled fibers were investigated. It was found that when compared with rPET-T fibers, the elongation at break of rPET-Ax fibers increased to 17.48%, and the strength at break decreased to 3.79 cN/dtex. The compatibility of PET and PA6 copolymer were enhanced by copolymers produced by in-situ reaction in the processing. Meanwhile, the existence of PA6 increases the crystallization temperature and improves the hydrophilicity of the fibers. This study realized the high-value recycling of waste PET fabric to new fibers, which opens a door for the large utilization of waste textiles.

Global discharge of microplastics from mechanical recycling of plastic waste.

The increasing production of plastic products and generation of plastic waste have had increasingly negative environmental impacts. Although recycling could reduce plastic pollution, microplastics can be generated during the process of crushing plastic products during mechanical recycling. We conducted crushing tests with 13 different plastics and documented the size distribution of particles generated. We then estimated the discharge of microplastics associated with recycling and their removal in wastewater treatment plants. We estimated that the global discharge of microplastics would increase from 0.017 Mt in 2000 to 0.749 Mt in 2060. Although mechanical recycling was estimated to account for 3.1% of the total emissions of microplastics for 2017, discharges of microplastics from plastic recycling may increase, even if plastic pollution from well-known sources decreases. Non-OECD (Organization for Economic Cooperation and Development) Asia could be a major discharging region and would play a vital role in reducing discharges of microplastics. Reduction of the discharge of microplastics will require less use of plastic products and upgrading wastewater treatment in many countries.