In this Review, we refer to these materials as ‘polymers’ when discussing their physicochemical properties and their synthesis before processing into their final shape, and use ‘plastics’ to describe the more commercially relevant forms of polymers processed into products. Most plastics are thermoplastics composed of linear polymer chains that allow thermal reshaping, such as those used in bottles and textiles, whereas some polymers are crosslinked during processing to form thermosets, which are tougher than thermoplastics and their shape is largely unaffected by temperature, such as those used in car tyres and epoxies. Once the polymeric material has been processed and formed into its final and commercially relevant shape, typically using heat, they are called plastics 1. These properties are determined by the structure of the repeating building blocks of the polymers: the monomers. Polymers exhibit diverse material properties - ranging, for example, from flexible to stiff, from permeable to impermeable and from hydrophilic to hydrophobic. Furthermore, clear regulation and financial incentives remain essential to scale from niche polymers to large-scale bioplastic market applications with truly sustainable impact. To guide converters and consumers in their purchasing choices, existing (bio)plastic identification standards and life cycle assessment guidelines need revision and homogenization.
Emerging chemical and biological methods can enable the ‘upcycling’ of increasing volumes of heterogeneous plastic and bioplastic waste into higher-quality materials. However, these benefits can have trade-offs, including negative agricultural impacts, competition with food production, unclear EOL management and higher costs. Compared with fossil-based plastics, bio-based plastics can have a lower carbon footprint and exhibit advantageous materials properties moreover, they can be compatible with existing recycling streams and some offer biodegradation as an EOL scenario if performed in controlled or predictable environments. In this Review, we assess the advantages and challenges of bioplastics in transitioning towards a circular economy. Carbon-neutral energy is used for production and products are reused or recycled at their end of life (EOL). Bioplastics - typically plastics manufactured from bio-based polymers - stand to contribute to more sustainable commercial plastic life cycles as part of a circular economy, in which virgin polymers are made from renewable or recycled raw materials.
0 kommentar(er)
