Natural Polymers from Biomass Resources as Feedstocks for Thermoplastic Materials

With the objective of a more sustainable circular economy, one long-term goal is the utilization of renewable resources as feedstock for the production of polymer-based materials. In order to successfully process such materials using existing industrial-scale technologies or even recycling processes, the natural polymers must have thermoplastic properties. With only a few exceptions, natural polymers are not thermoplastic. However, chemical and physical modification techniques are able to induce thermoplasticity in natural polymers from biomass resources such as cellulose, lignin, and chitin. Modification techniques focus on masking the hydroxyl groups to disrupt dense hydrogen bonding and so enable polymer chain mobility upon heating. The introduction of long alkyl chains into the polymer backbone effectively improves the thermoplastic processing of natural polymers. With regard to polymer blending, chemical grafting and graft copolymerization are powerful tools for enhancing compatibility. For both chemical and physical modification, solvents such as ionic liquids and deep eutectic solvents are currently being explored for biomass and fiber processing and show promise for the future development of thermoplastic biopolymers. This review describes possible modifications, potential processing difficulties, and gives a summary of relevant studies described in the scientific literature.