Preparation, Structure And Properties Of Poly(Lactic Acid)/Functionalized-graphene Nanocomposite Films

Recently, biodegradable and biocompatible poly(lactic acid)(PLA) has receivedmore and more attention, however, its wider application was limited by somedisadvantages such as relatively poor mechanical properties, thermal stability, gasbarrier property and crystallization. At the same time, graphene become one of themost ideal nanofillers to modify PLA since its high strength, high modulus, largesurface area as well as excellent electrical conductivity and thermal conductivity. Inorder to enhance the comprehensive properties of PLA, in this paper, we preparedpoly(lactic acid)/fuctionalized-graphene nanocomposite.Firstly, the graphite oxide was prepared by Hummers method，and transfer intographene oxide through ultrasonic exfoliate. Then the functionalized-graphene(GO-ODA) was prepared by functionalization with octadecylamine (ODA) toimprove its lipophilicity. GO sheets were fully exfoliated into monolayer and theinterlayer spacing of GO-ODA was increased to about1.8nm, which were verified bymeans of atomic force microscopy (AFM); the fourier transform infraredspectroscopy analysis (FT-IR) indicated that nucleophilic substitution occurredbetween the carboxylic groups at GO-edge and octadecylamine, GO-ODA developeda good lipophilicity and uniformly dispersed in chloroform solvent.Afterwards, we have prepared a series of PLA/GO-ODA nanocomposites bysolution-blending technique and investigated how GO-ODA contents influence theirmorphology, structures, thermal properties, crystallization propertis, mechanicalproperties and gas barrier property. We observed the morphological and structures ofGO-ODA nanosheets and nanocomposites by means of scanning electron microscope(SEM) and X-ray diffraction (XRD), the results suggested that GO-ODA weredispersed homogeneously in the PLA matrix without forming the aggregates, and theincorporation of GO-ODA had no impact on the crystalline of PLA. Thecrystallization behaviour, thermal stability, mechanical properties and gas barrierproperty of nanocomosites were characterized and evaluated by means of differentialscanning calorimetry (DSC), polar optical microscopy (POM), thermogravimetric analysis (TGA), mechanical properties test and oxygen permeability test. The DSCresults indicated that, with a very low loading of GO-ODA, the cold crystallizationtemperature of PLA all decreased, PLA-0.4and PLA-0.6were the lowest, itsuggested that GO-ODA could act as a heterogeneous nucleating agent and lead to anacceleration of crystal nucleus formation during the PLA nonisothermalcrystallization process; How the isothermal crystallization behaviour of PLAinfluenced by GO-ODA was investigated by POM, the result indicated that theincorporation of GO-ODA accelerate nucleation rate and the rate of crystal growth,meanwhile, spherulite size was decreased; The TGA results showed that the thermalstability of PLA was significantly improved, the thermal decomposition temperaturewas14℃higher than neat PLA at the5wt%mass loss; Mechanical properties testresults showed that the maximum tensile strength and modulus of PLA-0.2were~46.5%and85.7%greater than the neat PLA, respectively, the maximum elongationat break of PLA-0.6showed~200%increase over PLA; Oxygen permeability testresults indicated that the incorperation of GO-ODA promote gas barrier property ofPLA films.We prepared poly(lactic acid)/fuctionalized-graphene nanocomposite withexcellent performance. These superior reinforcing effects were attributed to the two-dimensional structure of GO-ODA uniformly dispersed in PLA matrix as well as theunique excellent properties of itself.