Synthesis, Characterization And Performance Study Of Ethyl Cellulose Graft Poly (L-lactic Acid) Copolymer

Cellulose and starch are abundant in nature resources which is bio-renewable, bio-degradable, environmentally friendly and other advantages that petroleum based polymer materials do not have, but both materials can be used as polymer materials after modification. Ethyl cellulose (EC) and poly (L-lactic acid) (PLLA) derived from cellulose and starch respectively, but the performance of each have shortage, Modifications of ethyl cellulose by grafting of poly lactic acid segments give new material both advantages, It will have a wide potential applications.In this dissertation, a novel graft copolymer (EC-g-PLLA) was prepared via grafting Poly (L-lactic acid) onto ethyl cellulose backbone in bulk by ring open polymerization using Sn(Oct)2 as an initiator. We systematically studied the reaction conditions, structure and performance of graft copolymers with different graft ratio. The main results are as follows:(1) The graft copolymers were characterized by means of GPC, FTIR and NMR. GPC chromatograms showed that the molecular weight of EC-g-PLLA had a substantial increase compared with EC; IR spectra found that the strong peak at 1760cm-1 was the absorption band of the C = O group in PLLA; 1H NMR spectrum found PLLA segments in copolymers clearly. The above characterization confirmed that EC-g-PLLAs were successfully synthesized.(2) The effects of the purity of L-lactide, feed weight ratio, initiator content ration, reaction time and reaction temperature on the graft ratio were investigated systematically. The results showed that we can obtain high graft rate EC-g-PLLA using lower purity L-lactide; With the feed weight ratio increased, the graft ratio increased and the conversion ratio decreased; In the experimental conditions, with the increase of reaction time, reaction temperature and initiator content ration, the graft ratio increased, but the trend slowing down.(3) DSC tests showed that with the increase of the graft ratio, the glass transition temperature (Tg) of EC-g-PLLA decreased and finally approaching to PLLA; TG tests found that the initial decomposition temperature of EC-g-PLLA were lower than PLLA and EC, but generally rose with graft ratio; XRD dates showed that when G%≤200%, the copolymers were amorpHous, when G%≥252%, the graft copolymer appeared sharp crystallization peak at 2θ= 16.63°and 19.0°in x-ray diagrams and the crystalline peak intensity rose with the graft ratio.(4) Film study of EC-g-PLLA found when the graft ratio between 165% and 262%, the Poly (L-lactic acid) segments have suitable length which can play a better internal sticization role, EC-g-PLLA have a good film-forming Properties; using 10% weight of different graft ratio copolymers to compatibilized the EC / PLLA (4:5) blends system, we found that the blends system had been improved significantly by EC-g-PLLA, in the experimental five selected graft copolymers, G% = 92% had the best compatibilization effect, with the graft ratio increased, the compatibilization effect became worse, when G% = 354%, the system appeared pHase separation.(5) Degradation of EC-g-PLLA films of different graft ratio in assigned time and environment at 37℃were studied , The results showed degradation in NaOH was larger than in HCl and PBS, EC-g-PLLA had similar weight loss in HCl and PBS, but in PBS is slightly larger. In NaOH, weight loss increased with the rise of graft ratio, in HCl and PBS G% = 262% had the maximum weight loss.