28th Annual Green Chemistry & Engineering Conference

Characterizing permeability, flexibility, moisture uptake, and degradation in amorphous biopolymers and biopolymer blends using molecular simulations

Abstract:
Demand for biodegradable and renewable materials for packaging applications have increased to reduce environmental impact and petrochemical dependence. To address this problem, development of biodegradable polymers from renewable resources is of considerable interest. Amongst the materials directly obtained from biomass, starch is one of the most abundant and low-cost. However, starch films exhibit relatively low mechanical resistance properties and are particularly water sensitive, exhibiting relatively low mechanical resistance. Additionally, the high melting point and low thermal decomposition temperature of starch leads to poor thermal processability. Blends of starch with synthetic biopolymers, e.g. poly(lactic acid) (PLA), polycaprolactone (PCL), poly(hydroxyalkanoates) (PHA), poly(hydroxybutyrate) (PHB)) and common plasticizers, e.g. glycerol, and sorbitol are of significant interest. Molecular dynamics (MD) simulations of starch provide molecular-level detail in the morphology of pure and blended starch and their effect on key physical properties. For example, the plasticization effect of water on amorphous amylose starch can be calculated yielding Tg values that are in good agreement with experiment. Additionally, the elastic moduli of both polysaccharide materials and synthetic biopolymers are calculated in their pristine state as well as in blends. The values obtained from these studies are quantitatively in agreement with experimental values. Of particular interest is the effect of thermal and chemical, e.g. hydrolytic, degradation. We utilize these data to develop structure-property relationships to understand the morphology of complex amorphous and/or semi-crystalline starch formulations and how that morphology affects transport and thermomechanical properties.