Performance, rheological behavior and enzymatic degradation of poly(lactic acid)/modified fulvic acid composites

Fulvic acid (FA) was modified with p-phenylenediamine via iodine and triphenylphosphine as catalyst. The microstructure characterization for modified fulvic acid (MFA) were investigated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, respectively, which demonstrated that MFA was characteristic of amide derivative. Moreover, poly(lactic acid) (PLA)/MFA composites was prepared with MFA as filler by melt blending. The mechanical tests showed that the impact strength of PLA/(0.5wt%) MFA composites were increased by 97.2%. Scanning electron microscopy demonstrated that the impact fracture of PLA/(0.5wt%) MFA composites were characteristic ductile fracture. The rheological behavior analysis showed that PLA had good interfacial compatibility with MFA. The crystallinity of PLA was increased from 4.9% to 36.9% with the introduction of MFA. The polarized optical microscopy presented that the crystallization nucleation rate of PLA were rapidly increased, which resulted in the increased comprehensive performance of PLA. The results of enzymatic degradation mechanism showed that MFA increased the K_m of proteinase K, and had some inhibition to the degradation of PLA, but PLA still remained degraded evidently.