Mechanical and chemical recycling of solid plastic waste.

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.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/marc.202000415

Mechanical Recycling of Packaging Plastics: A Review.

Recycling of waste from polymer materials: An overview of the recent works

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Advances and approaches for chemical recycling of plastic waste

Polymeric waste materials should be considered resources for the manufacture of new products through recycling processes, with a similar status as virgin fossil-based plastics and biopolymers from renewable resources. Several efforts can be done to achieve this qualitative quantum leap and introduce recycled products in the market with competitive performance. Detailed scientific knowledge about the degradation processes to which polymeric materials are subjected under their life cycle is important when discussing their further waste recovery possibilities and the performance of recycled plastic. The development of fast and reliable analytical methods for the quality assessment of recycled plastics is fundamental to guarantee their performance in new applications. Three key quality properties have been previously defined for this quality analysis: degree of mixing (composition), degree of degradation, and presence of low molecular weight compounds (degradation products, contaminants, additives).A dual experimental approach employing multiple processing and thermooxidation is proposed to model the life cycle of recycled high-impact polystyrene (HIPS) used in packaging applications, and in electrical and electronic equipment (EE these effects ultimately influence the long-term stability, and the rheological and mechanical behaviour of HIPS. The PB phase has proved to be the initiation point of HIPS degradation throughout the life cycle. Thermo-oxidation seems to have more severe effects on HIPS properties; therefore, it can be concluded that previous service life may be the part of the life cycle with the greatest influence on the recycling possibilities and performance of HIPS recyclates in second-market applications.Different strategies are presented for the quality analysis of recycled styrenic polymers from packaging waste and electrical and electronic equipment. The results from the life cycle degradation simulation were compared with those obtained from real samples from a large-scale mechanical recycling plant. The presence and emission of low molecular weight compounds from recycled HIPS from packaging waste has been critically discussed using solvent and headspace extraction procedures. Special attention has been devoted to the determination of brominated flame retardants in recycled HIPS from electrical and electronic equipment using advanced extraction and chromatographic techniques, due to the legislative and environmental implications of these additives.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/mame.200700393

Quality Concepts for the Improved Use of Recycled Polymeric Materials: A Review

Polypropylene (PP) was injection moulded several times to mimic the effect of recycling procedures. The influence of the recycling was studied by following changes in chemical structure, melt viscosity, crystallisation behaviour, and tensile and fracture properties. The main effect of recycling is the lowering of the melt viscosity, which is attributed to molecular weight decrease. Recycled PP exhibits greater crystallisation rate, higher crystallinity and equilibrium melting temperature than those measured for virgin PP. Elastic modulus and yield stress increase with the number of recycling steps. However, elongation at break and fracture toughness decrease.

Effects of recycling on the microstructure and the mechanical properties of isotactic polypropylene

Effect of dissolution-based recycling on the degradation and the mechanical properties of acrylonitrile-butadiene-styrene copolymer

Characterisation of the impact behaviour of polymer thermoplastics

Effects of injection moulding induced morphology on the fracture behaviour of virgin and recycled polypropylene

Fracture behaviour of virgin and six times recycled isotactic polypropylene (PP) has been studied. Instrumented Charpy impact tests have been carried out to characterise the fracture parameters and scanning electron microscopy was used to study the fracture surfaces. Recycled PP presents slightly smaller spherulites and lower fracture toughness than virgin one. Fractography analysis reveals that crazing is the dominant fracture micromechanism for both materials, and that the difference in fracture toughness is a consequence of the smaller plastically deformed volume at the notch tip of the recycled polypropylene.

I. Urrutibeascoa

Papers

Effects of recycling on the microstructure and the mechanical properties of isotactic polypropylene

Effect of dissolution-based recycling on the degradation and the mechanical properties of acrylonitrile-butadiene-styrene copolymer

Characterisation of the impact behaviour of polymer thermoplastics

Effects of injection moulding induced morphology on the fracture behaviour of virgin and recycled polypropylene

Fracture behaviour of virgin and recycled isotactic polypropylene