Synthesis of polybutylene succinate via Lipase-Catalyzed Transesterification: Enzyme Stability, reuse and PBS properties in bulk polycondensations

Abstract

Environmental problems involving the inappropriate disposal of non-biodegradable polymers and the production of petrochemical monomers have stimulated the interest in the development of renewable and biodegradable polymers. Among those, polybutylene succinate (PBS) has been highlighted, as it is a biodegradable polyester, synthesized from monomers that can be originated from fermentation processes. Moreover, regarding the application of biocompatible and non-toxic polymers in pharmaceutical and biomedical areas, enzymes can be considered an interesting alternative when compared to metallic catalysts. Therefore, this work aimed to investigate the lipase-catalyzed bulk polycondensation of diethyl succinate and 1,4-butanediol and to evaluate the molar mass distribution of the PBS produced. The recovery of the biocatalyst for application in reuse cycles was also performed. Preliminary tests indicated an enzyme concentration of 10% by mass (regarding the monomers) and a synthesis temperature of 90 °C as the best-operating conditions, in terms of weight of collected by-product (related to the conversion of the functional groups) and the molar masses (Mw: 4,000 g.mol−1), in reactions that lasted 90 min. These conditions were used in the subsequent recycling tests of the biocatalyst. The reuse of Novozym 435 allowed for 6 cycles, with good catalytic activity in the first 4 cycles. Moreover, the loss of enzyme activity in the last cycles was recovered through enzyme partial replacement (addition of 25% of fresh enzyme to 75% of used one). The promising results of enzymatic polycondensations performed in bulk aim to contribute to the development of not only more environmentally friendly polymers but also the use of greener reaction conditions.