Functional Zein--Siloxane Bio-Hybrids

Bio-hybrid films have been prepared by a sol-gel method starting from thermoplasticized zein (TPZ) and 3-glycidoxypropyltrimethoxysilane (GOTMS). A two-step procedure was adopted including the silane functionalization of zein macromolecules by reactive melting and the subsequent hydrolysis and condensation step of anchored GOTMS units with in situ formation of silsesquioxane (SSQO) nanostructures. These nanostructures bond the zein macromolecules with each other through the reaction of the GOTMS epoxy moieties with zein amine groups. Small angle X-ray scattering, transmission electron microscopy, and FTIR spectroscopy confirmed the formation of the hybrid network consisting of 2 nm-sized SSQO nanostructures dispersed in the zein matrix along with the modification of the hierarchical structure of zein. The organic-inorganic network induces an enhancement of mechanical and functional performances. In fact, owing to the presence of 3 wt % of siloxane as SiO3/2, the maximum stress increases from 1.87 to 11.16 MPa, whereas the water uptake reduces from 100 to 20 wt % with respect to the neat TPZ. Furthermore, the bio-hybrids show an enhanced durability toward the biodegradation process.