Study On Copolymers Of Poly(L-lactic Acid) With Silk Fibroin Prepared Through Melt/solid Polymerization

Poly (lactic acid) (PLA) polymers are one of the most important environmental friendly polymers because of their biodegradability, renewable resources, and excellent properties. PLA polymers can be employed as a promising cost-effective alternative to commodity petrochemical-based plastics so as to lessen the dependence of plastics on oil and diminish the pollution caused by waste plastic products. The silk fibroin (SF) with the endophilicity to the human body cell can be used to modify PLA materials to enhance the biological compatibility of PLAs. Amino acids and the synthesis peptide chain have been used to modify poly(L-lactic acid) (PLLA) materials, but the research on PLLA modified by natural silk fibroin peptide chain has not been reported yet.In this paper, PLLA with low molecular weight was prepared through direct melt polycondensation of L-lactic acid. Viscometry, polarimetry, FT-IR, differential scanning calorimetry (DSC),X-ray diffraction(XRD), and nuclear magnetic resonance (NMR) were employed for the characterization of polymers obtained. The effects of reaction time, temperature, catalyst weight, molar ratio of two catalyst components were detected.The optical activity and molecular weight of PSFLA can change with the reaction conditions with Sn(Oct)2/p-toluene sulfonic acid as catalyst. The polymer color can deepen with the increase of temperature and reaction time,while the optical rotation becomes smaller with temperature and reaction time. PSFLA with higher viscosity can be prepared in following conditions: melt/solid reaction time 20 hours, temperatures 180℃, Sn(Oct)2 0.5wt%, the ratio of Sn(Oct)2/ p-toluene sulfonic acid 1/1.The optical activity and molecular weight of PSFLA can change with the reaction conditions with SnCl2/p-toluene sulfonic acid as catalyst. The polymer color can deepen with the increase of temperature and reaction time, while the optical rotation becomes smaller with temperature and reaction time. PSFLA with higher viscosity can be prepared in following conditions: melt/solid reaction time 20 hours, temperatures 170℃, SnCl2 0.5wt%, the ratio of SnCl2/ p-toluene sulfonic acid 1/1.