Effect of plasticiser on the morphology, mechanical properties and permeability of albumen-based nanobiocomposites

Abstract

This paper delves into the role plasticisers play in the formulation and processing of bioplastics and nanobiocomposites, trying to understand their effect on nanoclays dispersion and, consequently, on mechanical and gas barrier properties of protein-based nanobiocomposites. Egg white protein/montmorillonite clay nanobiocomposites were obtained by thermomechanical processing plasticised with varying molar concentration of different components (water, glycerol, polyethylene glycol). The extent of dispersion of the filler was evaluated by X-ray diffraction and transmission electron microscopy. Tensile tests and solid-state rheological measurements were conducted to evaluate glass transition temperature and thermomechanical behaviour of plasticised protein-clay nanobiocomposites, whereas gas permeability tests were used to study their gas barrier properties. The results showed that the samples plasticised by a blend of 1:1 glycerol/water presented the most exfoliated structures, resulting in an improvement in gas barrier and mechanical properties. Morphological analyses combined with tensile and permeability tests have shown a lesser effect of polyethylene glycol of 300 molecular weight (PEG 300) on the exfoliation extent into such nanobiocomposites. Moreover, the larger size of PEG 300 does not allow the formation of a structure as compact as in the case of water and glycerol, as a consequence of an apparent phase separation, leaving more spaces that facilitate the diffusion of gases through the material.