Copolymerization Modification Of Poly (D, L-lactic Acid) And Its Application On The Mulching Films

As environmentally friendly biomass-based materials, the development and use of poly(lactic acid)(PLA) materials have a great significance for energy and environment crisis of theworld. PLA materials are mostly obtained by the ring-opening polymerization of lactide, whichlead to high production costs. And the nature brittleness has been limited its promotion andapplication.In this paper, condensation polymerization, copolymerization and composite modification ofPLA were investigated. Degradation performance of PLA/PEG copolymer mulching films wasobserved in cotton fields. Structure and properties of all samples were examined by FT-IR、DSC、GPC、TG、XRD、1H NMR and mechanical testing. The outcomes are as followings:(1) Direct condensation polymerization of Poly (D, L-lactic acid)PDLLA was obtained via poly-condensation of D, L-lactic acid. Polymer was synthesizedwith a molecular weight about11000under the optimal conditions of temperature at170~180oC,with pressure no more than6kPa and catalyst dosage0.5wt.%(stannous octoate, mass fractionof DLLA) for10~12h. There were four broad and weak peaks at14.9o、16.8o、19.2oand22.4oonthe XRD patterns of the polymers, which indicated that PDLLA has a poor crystallizationbehavior.(2) PEG/PDLLAcopolymers obtained by polymerizing lactic acid and Poly (ethylene glycol)In order to improve the concentration of carboxyl, dicarboxylic PDLLA was prepared firstlywith the reaction of DLLA and1,4-succinic acid. And then PEG was added so as to get thecopolymer. Compared with the homo-polymer, the glass transition temperature (Tg) of copolymersdecreased from49.4oC to42.6oC and the maximum decomposition temperature decreased from289oC to282oC, respectively. The degradation test indicated that the addition of PEG can promotewater absorption of PLA.(3) Preparation and Properties of PLA/OMMT nanocompositesThrough the study of the reaction conditions and the effect of different molecular weight PEG,PEG4000was selected as a modifier of Na-MMT. The optimal conditions were as follows: themass ratio of ethanol/Na-MMT and was50:1and then processed in an ultrasonic for1h. Thetemperature was increased to80oC, keeping the condition for1h with a stirring rate of1000rpm.Then PEG was added into the mixture (mass ratio of PEG/Na-MMT was0.2) and the stirring ratewas increased for3h. XRD showed the d001was increased to1.87nm for the OMMT20from0.98nm for Na-MMT. TG results indicated that the coating amount and the effective utilization of PEGwere13.27wt.%and79.60%respectively. Tensile properties of the PLA/OMMT20compositematerials demonstrated that OMMT20could simultaneously improve the strength and toughnessof PLA. When the mass ratio of OMMT20/PLA was1.0wt.%PLA, the tensile strength andelongation at break reached the best as55.07MPa and3.40%. Compared with PLA, they improved by9.8%and27.3%, respectively(4) Degradation of novel completely Biodegradable Mulching Film in fieldThe mechanical properties and molecular weight decreased with the extending of time.Tensile strength and the molecular weight of PLA/PEG copolymer mulching films decreased by17~41%and55%of the original state after about60days, respectively. After120days, the brittleand fracture obviously increased and mechanical strength almost complete loss.