Chain-Extension And Amodification Of Poly (Lactic Acid)

This thesis primarily studied modification and chain extention ofpolylactic acid (PLA) with nano-modified attapulgite (Att)、2,2-(1,3-phenylene)-bis(2-oxazoline)(1,3-PBO)、 diisocyanate andterminated modifiers.Nano-modified attapulgite (Att) with good dispersion was obtainedby attapulgite pretreated with hydrochloric acid and silane couplingagent KH550. polylactic acid/nano-modified attapulgite (PLA/Att)composite was synthesized via directly melte polymerization using PLAas raw material and Att as modifier. The structure of the PLA/Attcomposite materials were characterized by spectroscopy (FT-IR) andthe properties were investigated by Ubbelohde viscosity-averagemolecular weight, differential scanning calorimetry (DSC), thermal-gravimetric analysis (TGA), scanning electron microscopy (SEM).Results show that when the content of Att was5wt%, Att nanoparticlesdispersed in PLA, and no obvious interface, measured the maximumviscosity-average molecular weight of the composite was20,110. Theoptimum reaction conditions are: reaction pressure0.098MPa, reactiontemperature150℃, reaction time10h. DSC and TG analysis show thatthe thermal properties of PLA/Att composites is improved and itsdecomposition consists one step.A new biodegradable poly(ester urethane)(PEU) was synthesizedvia directly melte polymerization with PLBO as raw material,PEG-NCO as chain extender and dibutyl tin dilaurate as catalyst. Thehydroxyl-terminated prepolymer (PLBO) was prepared with lacticacid(LA) and (1,3-PBO) by directly melt polycondensation and theisocyanate-terminated polyethylene glycol (PEG-NCO) was preparedwith hexamethylene diisocyanate (HDI) and PEG by polymerization.The research shows that the viscosity-average molecular weight can reach the maximum value—44,660in the optimum conditions:n(-OH)/n(-NCO)=1, reaction pressure0.096MPa, reaction temperature165℃, reaction time20min; The structure of the polymers werecharacterized by FT-IR and the properties were investigated by DSC,XRD, TG, SEM, and etc. The results indicate that the glass transitiontemperature(Tg) of PEU gets smaller than that of PLA and PLBO as aresult of the introduction of PEG, which results in the greatimprovement in flexibility; the thermal stability of PEU is improved,and the thermal decomposition of PEU consists of two steps: the firststep is the weight loss of PLA segment and the second step is thedegradation of PEG-NCO segment; XRD analysis show that thecrystallinity of PEU decreases, which also can indicate that theflexibility of PEU is enhanced after chain extension.The carboxyl-terminated modified PLA copolymers (P(LA/SA))was synthesized via directly melt polycondensation with LA as the rawmaterial and Sn(II)octoate as the catalyst at168℃and0.098MPa bythe method of a gradient increased temperature. Then, the LA basedpoly(ester-amide)(PEA) was synthesized with P(LA/SA) as prepolymerand1,3-PBO as extender. The highest molecular weights are achievedwith n(-oxazoline)/n(-COOH)=1.0/1.4at0.098MPa and150℃for15min. The structure were characterized by FT-IR and1H-NMR and theproperties were investigated by GPC, DSC, TGA, XRD, SEM. GPCanalysis indicate that the highest molecular weight is over360,000andas a result of the introduction of amide groups and benzene rings intoPLA/SA, the chain stiffness present a tendency upward detected in DSC.A distinct improvement compared with PLA in the thermal stability ofthe PEA with the chain extender is observed by TG, just as an one-stepthermal decomposition. The crystallinity of the PEA is higher than thatof P(LA/SA), but lower than that of PLA, which indicate that theflexibility of the PEA is superior to P(LA/SA).