Hydrazide-hydrazone-modified polyamide as reinforcement and dispersion aid for poly(lactic acid)/hydroxyapatite nanocomposites

Abstract

Hydrazide-hydrazone based polyamide (HHPA) was synthesized from an aromatic diamine containing hydrazide-hydrazone group and dodecanedioic acid via direct polycondensation. The surface modified hydroxyapatite (SMHA) was prepared using a modification process of hydroxyapatite nanoparticles (HAN) with imine functionalized polyethyleneimine (FPEI). The new pol(ylactic acid) (PLA)/HAN/HHPA nanocomposites with increased heat and combustion resistance, and improved mechanical and gas barrier properties were fabricated using solution casting method. The structure and morphology of the prepared PLA nanocomposites were evaluated using FTIR, FE-SEM, and XRD techniques. The synergistic effect of SMHA and HHPA was studied on the heat and combustion resistance, gas barrier properties, and mechanical strength of PLA. The findings exhibited that HAN was homogeneously dispersed in the PLA polymeric network, due to the excellent interfacial interactions. The TGA results of nanocomposites revealed that PLA containing 3 mass% of each SMHA and HHPA additives, named PHP6, offers more heat resistance, in both N2 and air environment, compared to the neat PLA. According to the MCC results, the heat release rate peaks reduced from 555 W/g to 357 W/g for PLA containing 6 mass% of each SMHA and HHPA additives, named PHP12. From mechanical test, the tensile strength of PHP6 was obtained 88.27 MPa, which was 48 MPa higher than the neat PLA. Furthermore, the gas barrier studies for CO2 and N2 indicated that the incorporation of both HHPA and SMHA results in reduced permeability and solubility coefficients compared to the neat PLA, where PHP2 and PHP6 samples outperform other samples.