Synthesis of fully bio-based copolymers with tailor-made properties for sustainable food packaging applications

Abstract

The use of biopolymers as packaging materials to replace petrochemical polymers is becoming an emerging trend due to their natural and renewable origin and biodegradability. However, most biopolymers still show low flexibility, high melting temperature, and poor barrier properties in terms of water and aroma vapors and oxygen gas, which habitually reduce their application in food packaging. Therefore, the use of biopolymers in the form of monolayers is currently restricted to low-performance applications, such as plastic bags, lid films, or food-contact disposables. One potential strategy to increase the use of biopolymers in food packaging is currently focused on the development of copolymers with controlled molar ratios of different monomers. In the case of condensation biopolymers, such as biopolyesters and biopolyamides, the presence of ester and amide groups separated by alkane segments of different length, in combination with the chain symmetry, determines the final properties of the biopolymers. Whereas the polar ester and amide groups contribute to the mechanical strength, thermal resistance, and chemical stability, the long-chain aliphatic methylene groups provide mechanical flexibility and water resistance. Therefore playing with the methylene-to-ester (CH2/COOH) and amide (CH2/CONH) ratios biopolyesters and biopolyamides with specific properties can be successfully designed. In the present study, different fully bio-based polyesters and polyamides with varying CH2/COOH and CH2/CONH ratios were synthetized by polycondenstion from biomass derived monomers reactions and analyzed. To this end, the biopolymers were thermocompressed into films and fully characterized to ascertain the effect of the comonomer content on their crystallinity, optical, thermal, mechanical, and barrier properties. Finally, the application of the newly developed bio-based copolyesters and copolyamides films was validated by packaging meat in thermo-sealed bags and the food shelf life was assessed for a period of up to 14 days of cold storage. The resultant copolymers represent a Circular Bioeconomy solution, where their monomers derived from biomass and their packaging can be organically recycled in a compost or subjected to mechanical and chemical processes of recycling.

Postprint (published version)