Reinforcing And Toughening Modification Of Polylactide

Polylactide(PLA) has some disadvantages such as poor thermal stability,brittleness andhigh cost which blocks its wide application as general plastics. Aiming at these disadvantages ofpolylactide, in this paper, we studied the method to reinforce and toughen polylactide by meansof melting blend with the fillers, plasticizers and flexibilizer, which will widen the common useof the PLA. Meanwhile, it will accelerate the popularization of biodegradable materials.Theproperties of PLA composites were influenced by the kinds of fillers(inorganic fillers andorganic fillers),different treatment technics of fillers,the kinds of plasticizers and flexibilizer,processing technology, which were investigated by melting blend, hot-pressing, cutting samples,testing the mechanical properties and rheological behaviors respectively. Moreover, the interfaceconfiguration, the thermal stability and the crystallographic properties of composites wereanalyzed through studying the kinds of fillers, the contents of fillers, the kinds of plasticizers andflexibilizer by means of the scanning electron microscope (SEM), the thermogravimetry (TG)and the differential scanning calorimeter (DSC). The effects of the fillers and flexibilizer on thedegradation of PLA composites were investigated by uv-irradiation and alkaline solutionaccelerating ageing. The following conclusions can be summarized from the paper:1. The non-treated silicate fillers had some physical crosslinking with the polylactide(PLA),which reinforced and toughened the PLA composites. The difference of silicate fillerscharacteristic,dispersion and size of particles resulted in different physical crosslinking with thepolylactide(PLA) and different effect on reinforcing and toughening PLA.2. The silicate fillers treated with coupling agents had better disperseiveness and strongerinteraction with the matrix, which improved the mechanical properties of the composites. Theeffects of the silane coupling agents, KH560 and KH550, on the silicate fillers were better thanthe titanate coupling agent NDZ-101.Among them, the KH560 had the best effect.3. The fracture elongation of the PLA composites was greatly increased with the addition ofplasticizers PEG-2000 and TBC(tributyl citrate). Meantime, the tensile strength of the PLA composites was decreased. And, the plasticizers and inorganic fillers did not have better effecton PLA in the form of synergistic toughening.4. The polyester flexibilizer and inorganic fillers did have better synergistic toughening effecton PLA, in which polyester A had better toughening effect than polyester B.5. The effect of organic fillers (com starch and pea starch) on PLA was worse than inorganicfillers. But compared two kinds of organic fillers, the tensile strength of the compositescontaining the pea starch was higher than the composites containing the corn starch. The fractureelongation was opposite.6. The PLA composites with core-shell structure were prepared by twice melting blends. Inthis system, the talcum or the diatomite was the core and the polyester A was the shell.Compared with the once melting blend, the PLA/polyesterA/talcum composites prepared byonce melting blend had better mechanical tensile strength than the composites prepared by twicemelting blends. But the PLA/polyesterA/diatomite composites were opposite. ThePLA/polyesterA/diatomite composites prepared by twice melting blends had better mechanicaltensile strength than the composites prepared by once melting blends.7. The talcum had slight effect on the pseudoplastic rheological behavior of PLA, while thediatomite silica, white carbon black, plasticizers and fiexibilizer could reduce the viscosity ofPLA composites. Among them, the plasticizer decreased most.8. The data of TG experiment indicated that PLA was one-stage weightlessness and thethermal stability of PLA was slightly influenced by adding inorganic fillers. And compared tothat of neat PLA, the thermal degradable beginning temperature was moved forward with theaddition of plasticizer and flexibilizer.The results of the DSC experiment showed that inorganicfillers had the effect of inducing crystallinity and increasing the Tg and crystallinity of PLAcomposites while the plasticizer decreased the Tg and crystallinity and the flexibilizer had littleinfluence on the Tg and erystallinity.9. Under the uv-irradiation, the inorganic fillers could slower the degradation of PLAcomposites in different degrees. The tensile properties of the PLA composites by means of blendwith inorganic fillers and polyester A increased at first and then decreased with the increase oftime. Under the condition of alkalescence solution, PLA composites hydrolyzed fast. With thealkalescence solution concentration increasing, PLA composites hydrolyzed fastter. At the samesolution concentration, the PLA composites blent with fillers degraded at the fastest rate, thenwas the composites blent with fillers and elastomers, the last was the neat PLA.