Mechanical retention and waterproof properties of bacterial cellulose-reinforced thermoplastic starch biocomposites modified with sodium hexametaphosphate

Abstract

The waterproof and strength retention properties of bacterial cellulose (BC)-reinforced thermoplastic starch (TPS) resins were successfully improved by reacting with sodium hexametaphosphate (SHMP). After modification with SHMP, the tensile strength (σf) and impact strength (I s) values of initial and conditioned BC-reinforced TPS, modified with varying amounts of SHMP(TPS 100 BC 0.02 SHMP x), and their blends with poly(lactic acid)((TPS 100 BC 0.02 SHMP x) 75 PLA 25) specimens improved significantly and reached a maximal value as SHMP content approached 10 parts per hundred parts of TPS resin (phr), while their moisture content and elongation at break (εf) was reduced to a minimal value as SHMP contents approached 10 phr. The σf, Is and σf retention values of a (TPS 100 BC 0.02 SHMP 10) 75 PLA 25 specimen conditioned for 56 days are 52%, 50% and 3 times its initial σf, Is and εf values, respectively, which are 32.5 times, 8.9 times and 40% of those of a corresponding conditioned TPS 100 BC 0.02 specimen, respectively. As evidenced by FTIR analyses of TPS 100 BC 0.02 SHMP x specimens, hydroxyl groups of TPS 100 BC 0.02 resins were successfully reacted with the phosphate groups of SHMP molecules. New melting endotherms and diffraction peaks of VH-type crystals were found on DSC thermograms and WAXD patterns of TPS or TPS 100 BC 0.02 specimens conditioned for 7 days, while no new melting endotherm or diffraction peak was found for TPS 100 BC 0.02 SHMP x and/or (TPS 100 BC 0.02 SHMP x) 75 PLA 25 specimens conditioned for less than 14 and 28 days, respectively.