Preparation And Mechanical Properties Of Sodium Hexametaphosphate Modified Thermoplastic Starch Based Biocomposites

Water proof and strength retention properties of thermoplastic starch?TPS?resins were successfully improved by reacting with sodium hexametaphosphate?SHMP?during their reaction processes.The tensile strengths??f?and impact strengths?I_s?values of initial and aged TPS₁₀₀BC_0.02SHMP_x and(TPS₁₀₀BC_0.02SHMP_x)₇₅PLA₂₅ specimens improved significantly and reached a maximal value as SHMP contents approached an optimal value at 10 part per hundred parts of TPS resin?PHR?.However,their moisture content and elongation at break??f?values reduced to a minimal value,respectively,as SHMP contents approached the optimal value at 10 PHR.After aging at 20?/50%relative humidity?RH?for168 days,the ?f,I_s and sf retention values of aged(TPS₁₀₀BC_0.02SHMP10)₇₅PLA₂₅ specimen remained at 12.7 MPa,0.5 KJ/m2 and 14.3%,respectively,which were equivalent to 34%,31%and 3.1 times of their initial ?f,I_s and ?f values,respectively;and more than 64 and 10 times higher but 25%lower than those of corresponding aged TPS and TPS₁₀₀BC_0.02 specimens,respectively.As evidenced by the newly developed P-O-C-stretching bands and nearly disappeared P-O-P stretching,P-O bending,P-O and P=O stretching bands on FT-IR spectra of TPS₁₀₀BC_0.02SHMP_x series specimens,hydroxyl groups of TPS₁₀₀BC_0.02 resins were successfully reacted with the phosphate groups of SHMP molecules during their modification processes.Clearly separated PLA droplets were found on the fracture surface of(TPS₁₀₀BC_0.02)₇₅PLA₂₅ specimen.In contrast,significantly less and smaller separated PLA droplets were found on fracture surfaces of(TPS₁₀₀BC_0.02SHMP_x)₇₅PLA₂₅ specimens.New melting endotherms and diffraction peaks of VH-type crystals were found on DSC thermograms and WAXD patterns of aged TPS or TPS₁₀₀BC_0.02 specimens,respectively,while no new melting endotherm or diffraction peak was found for TPS₁₀₀BC_0.02SHMP_x and/or(TPS₁₀₀BC_0.02SHMP_x)₇₅PLA₂₅ specimens aged at 20?/50/%RH for 28 days.Possible reasons accounting for the above improved water proof and strength retention properties of TPS₁₀₀BC_0.02SHMP_x and(TPS₁₀₀BC_0.02SHMP_x)₇₅PLA₂₅ specimens were discussed in this study.