Recent Developments in Synthesis, Properties, Applications and Recycling of Bio-Based Elastomers

Abstract

In 2021, global plastics production was 390.7 Mt; in 2022, it was 400.3 Mt, showing an increase of 2.4%, and this rising tendency will increase yearly. Of this data, less than 2% correspond to bio-based plastics. Currently, polymers, including elastomers, are non-recyclable and come from non-renewable sources. Additionally, most elastomers are thermosets, making them complex to recycle and reuse. It takes hundreds to thousands of years to decompose or biodegrade, contributing to plastic waste accumulation, nano and microplastic formation, and environmental pollution. Due to this, the synthesis of elastomers from natural and renewable resources has attracted the attention of researchers and industries. In this review paper, new methods and strategies are proposed for the preparation of bio-based elastomers. The main goals are the advances and improvements in the synthesis, properties, and applications of bio-based elastomers from natural and industrial rubbers, polyurethanes, polyesters, and polyethers, and an approach to their circular economy and sustainability. Olefin metathesis is proposed as a novel and sustainable method for the synthesis of bio-based elastomers, which allows for the depolymerization or degradation of rubbers with the use of essential oils, terpenes, fatty acids, and fatty alcohols from natural resources such as chain transfer agents (CTA) or donors of the terminal groups in the main chain, which allow for control of the molecular weights and functional groups, obtaining new compounds, oligomers, and bio-based elastomers with an added value for the application of new polymers and materials. This tendency contributes to the development of bio-based elastomers that can reduce carbon emissions, avoid cross-contamination from fossil fuels, and obtain a greener material with biodegradable and/or compostable behavior.

Keywords: bio-based elastomer; circular economy; elastomeric properties; olefin metathesis; polyester; polyether; polyurethane; rubbers; sustainability.

Figure 1

Crosslinked epoxidized natural rubber (ENR) with dicarboxylic acid.

Figure 2

Essential oils in the citrus peels and cuticle of the citrus fruit.

Figure 3

Synthesis of bio-based NR with d-limonene via cross-metathesis.

Figure 4

Synthesis of bio-based diols and polyols from natural and renewable resources used to synthesize polyurethanes.

Figure 5

Synthesis of bio-based polyurethane elastomer from polyols obtained by industrial or natural rubbers degradation (providing the elastomeric part) and essential oils or fatty alcohols derived from natural resources. R is for rubber repetitive unit (R = H for PB, BR; R = CH₃ for PI, IR, NR). R₁ is for vegetable oil, unsatured diol, fatty alcohol, or terpene (e.g., 9-decen-1-ol, 10-undecen-1-ol, castor oil (Ricinus communis), citronellol, geraniol, myrcenol, eugenol). R₂ is for aromatic or aliphatic structures for diisocyanates (e.g., MDI, TDI, IPDI, HDI). R₃ is for C₂–C₆ chain extender length (e.g., ethanediol, propanediol, butanediol, hexanediol).

Figure 6

Some applications of polyester and polyether elastomers are used as copolymers. R and R1: alkylene; Ar: aromatic ring.

Figure 7

Future of bio-based elastomers applications for (a) biomedical (reprinted/adapted with permission from Ref. [84], 2023, Elsevier), (b) sensors (reprinted/adapted with permission from Ref. [97], 2023, OAE), (c) bone reconstruction (reprinted/adapted with the permission from Ref. [98], 2023, ACS publications), (d) advanced materials (reprinted with permission from Ref. [99], 2023, Elsevier), and (e) drug delivery (reprinted/adapted from Ref. [100], 2023, Elsevier).