Mechanical Retention and Waterproof Properties of Bacterial Cellulose-Reinforced Thermoplastic Starch Biocomposites Modified with Sodium Hexametaphosphate

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 (sigma(f)) and impact strength (I-s) values of initial and conditioned BC-reinforced TPS, modified with varying amounts of SHMP(TPS100BC0.02SHMPx), and their blends with poly(lactic acid)((TPS100BC0.02SHMPx)(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 ((f)) was reduced to a minimal value as SHMP contents approached 10 phr. The sigma(f), I-s and (f) retention values of a (TPS100BC0.02SHMP10)(75)PLA(25) specimen conditioned for 56 days are 52%, 50% and 3 times its initial sigma(f), I-s and (f) values, respectively, which are 32.5 times, 8.9 times and 40% of those of a corresponding conditioned TPS100BC0.02 specimen, respectively. As evidenced by FTIR analyses of TPS100BC0.02SHMPx specimens, hydroxyl groups of TPS100BC0.02 resins were successfully reacted with the phosphate groups of SHMP molecules. New melting endotherms and diffraction peaks of V-H-type crystals were found on DSC thermograms and WAXD patterns of TPS or TPS100BC0.02 specimens conditioned for 7 days, while no new melting endotherm or diffraction peak was found for TPS100BC0.02SHMPx and/or (TPS100BC0.02SHMPx)(75)PLA(25) specimens conditioned for less than 14 and 28 days, respectively.