Enhanced mechanical, thermal, and degradation properties of zein composite films by citrate ester composite elastomer based on hydrothermal carbon microspheres

Improving the toughness and strength of zein films simultaneously by a sustainable way is an urgent need. In this study, it is proposed to use hydrothermal carbon microspheres (HCM) and citrate ester (CE) to prepare hydrothermal carbon microspheres/citrate ester (HCE) to meet the inherent mechanical challenges of zein films. The results showed that the HCE with excellent structure and properties was obtained by ester bond and hydrogen bond, which also achieved the simultaneous improvement of zein film strength and toughness. Introducing HCM to HCE accelerated the degradation of zein whether for in water, orthophosphate solution, or soil environment. Additionally, the HCE increased the thermal decomposition residue, delayed the maximum decomposition peak temperature, and thus improved the thermal stability of zein. As a comparison, 3% HCM added CE exhibited the best performance improvement effects to zein film with the tensile strength of 2.37 MPa, tensile modulus of 0.81 GPa, elongation at break of 45.81%, hydrolysis rate of 44.12%, PBS degradation rate of 47.35%, buried degradation rate of 87.58%, and maximum decomposition peak temperatures of 270°C and 385°C. Having excellent properties and sustainability of the HCE provides a promising strategy for developing sustainable and high-performance zein composites.