Objective: Starch-based biopolymer is hydrophilic in nature. Its commercial use has been limited by its high glass transition temperature. However, synergistic interactions among starch-based polymer haven’t been well documented due to the complex and inter-dependent interactions between water and plasticizers. This is an attempt to investigate the interactions in amylose/water (at different hydration) and amylose/water/glycerol (at different glycerol concentration) system via Molecular modeling.
Methodology: Simulation of amylose fragments was performed via the Materials Studio 4.4 software from Accelrys, San, Diego, on a Core2-based PC. Amorphous cell and Discover modules were used to build amylose cell and implemented the MD calculation by employing COMPASS (condensed-phased optimized molecular potentials for atomistic simulation studied) forcefield. Steepest descent approach followed by the conjugate gradient method with a convergence level of 0.01 kcal/mol/Å has been applied in the minimization step. Berendsen temperature fluctuations control method had been employed in all calculation stages, same as pressure control.
Results/Conclusions: Atomic model of amylose fragments had been successfully built in the present work with COMPASS forcefield. The density results from the 12 monomers amorphous cell subjecting for 5ns equilibrium simulation, 1.33 g/cm2, had exhibited excellence agreement with the theoretical density value for amylose starch (reference needed) as well as the Tg values. Anti-plasticization phenomenon was correlated to the overall high density value from low hydration system based on the fact that stronger amylose-plasticizer (antiplasticization) would result in a higher packing density (from the entangled amylose and plasticizers) within the simulation cell.