Morphology control and ionic crosslinking of pectin domains to enhance the toughness of solvent cast PVA/pectin blends

Abstract

AbstractBlending water soluble synthetic polymers, such as polyvinyl alcohol (PVA), with natural polymers, such as pectin, has many advantages. However, due to the brittle nature of pectin, the mechanical properties become inferior in the blends. In this work, two strategies to enhance the toughness and tensile strength of solvent cast PVA/pectin blends are presented. This study shows that the tensile strength and toughness of PVA/pectin 80/20 blends can be enhanced by decreasing the solvent evaporation rate. The phase separation proceeds through 'nucleation and growth' and spinodal decomposition, respectively, at lower and higher rates of solvent evaporation. The equilibrium phase morphology has spherical domains of pectin dispersed in the PVA matrix. The size of the pectin domains and the separation between them are controlled by the solvent evaporation rate. At higher rates of solvent evaporation, pectin domains are larger and farther apart from each other and vice versa. Ionically crosslinking the pectin domains with calcium, further enhances the tensile strength and toughness of the blends compared to that of pure PVA. When the pectin domains are small, the failure happens at larger strains through 'cavitation' and 'shear yielding' and when pectin domains are large, the failure happens at smaller strains and the failure mechanism shifts to 'multiple crazing'.