Zein composite film with excellent toughness: Effects of pyrolysis biochar and hydrochar microspheres

The novelty of this study is providing a new toughening strategy in terms of the challenge of improving the poor toughness of zein film. Two types of biochar, pyrolysis biochar (PB) and hydrochar microspheres (HM), were blended into the zein system through solution casting to develop zein composite films with excellent toughness. The effects of biochar types and contents on the mechanical properties of the resulting composite films were investigated. The results indicated that better compatibility of zein composite films was achieved due to the hydrogen bond formed by biochar and hydrophilic amino acid in zein. A better surface structure of HM composite films was obtained than PB composite films by the uniform size and regular shape of HM. Better thermal stability shown in PB contributed to better thermal properties in the zein system than HM. Mechanical properties showed that tensile strength and modulus were increased with increasing PB or HM contents. Although increasing PB or HM contents decreased the elongation at break, the elongation at break reached a maximum of 475.47% at 0.1 g HM added composite film showing excellent toughness due to the strong interface binding and micro-nano size effect. The composite films prepared in this study have broad application prospects in packaging and agricultural films.