Synthesis Of Poly (_L-lactide-co-castor Oil) Copolymer And Toughening Poly (Lactic Acid)

In this thesis, Poly(L-lactide-co-castor oil) copolymer (PLACO) was prepared by meltcondensation polymerization ofL-lactide (L-LA) with castor oil (CO.). Stannous octoate(Sn(Oct)2) was used as a catalyst. The reaction kinetics of different synthesis conditionswere studied, and then, the structure and properties were characterized and measurement.Later, we adopted CO. and low molecular weight PLACO as tougheners to toughenpoly(lactic acid)4032D (PLA). The influence of the kinds and content of tougheners on thedynamic mechanical properties and mechanical properties of PLA were studied.Firstly, The research on the reaction kinetics of polymerization showed the optimalreaction conditions were temperature:160℃, time:2h, catalyzer Sn(Oct)2:0.5(wt)‰.Under the optimal conditions, there were the fastest polymerization rate, the highestconversion, and the narrowest polydispersity index. Low doses of CO., the conversion waslinear with polymerization time. The process ofL-LA polymerization accorded with the firstgrade reaction kinetics. The kinetic indicated that Sn(Oct)2controlled ring-openingpolymerization ofL-LA exhibited living and controlling features. But, when the reactantratio m(L-LA): m(CO.) were100:50and100:100, the polymerization forL-LA were outof accord with the first grade reaction kinetics. Furthermore, the presence of air led todecrease the polymerization rate and conversion, broaden the polydispersity index, increasethe degradation rate, and the color turning into yellow.Secondly, the molar mass, structure and properties of PLACO were investigated bymeans of GPC, FTIR, TGA, DMA, XRD and contact angle measurement. The GPC resultsrevealed that CO. ratio could control the molar mass of PLACO. The FTIR showed that thecopolymers included both ester groups of PLLA segments and carbon-carbon double bondsof CO. segments. The TGA analysis indicated that the lager molar mass could improve thethermostability of the copolymers, and the addition of CO. could improve thermostability ofcopolymers. The DMA analysis confirmed that the tensile modulus, toughness andglass-transition temperature of copolymers increased with increasing CO. content. The XRDdates suggested that the crystallization of PLACO was mainly caused by PLLA segments,and the crystal unit cell of PLACO contained α crystal form only. The test of contact anglesshowed that CO. could improve the hydrophily of copolymers. Finally, we adopted CO., PLACO-19(m(L-LA):m(CO.)=100:50) and PLACO-20(m(L-LA):m(CO.)=100:100) as tougheners to toughen PLA. There was a certaincompatibility between CO. and PLA. The compatibility of PLA with PLACO was better.CO. and PLACO-20respectively made the elongation at break of PLA increase to69.3%and24.2%. When CO. modified PLA, the tensile strength and tensile modulus of PLAdecreased to24.7MPa and1309.1MPa. Compared with CO., the tensile strength andtensile modulus of PLACO-20toughened PLA still were40.7MPa and1604.3MPa. Inaddition, PLACO-19had less effect on the elongation at break, tensile strength and tensilemodulus of PLA.