Preparation And Properties Of Polylactic Acid Composite Material Research

Biocompatible and biodegradable poly (lactide acid)(PLA) is an aliphatic thermoplastic polyester with excellent performances such as nontoxicity, nonirritant, high strength, high transparency, processibility and so on. It can biodegrade and be absorbed, and may eventually decompose into carbon dioxide and water in the environment, which makes it wide interests in the degradable materials. However, the applications of PLA have been limited in taking the place of the petroleum based plastic because of its high prices, slow degradation and poor thermal stability. Moreover, PLA has been limited in the field of tissue engineering scaffold as a single-component material due to its short of hydrophilicity. Modification of PLA is hence an effective strategy to improve its performances and further extend its applications. In this work, the Starch/PLA, Jute fiber/PLA and Hydroxyapatite/PLA composites were prepared via melt mixing. The mechanism of synergism in Starch/PLA blended with maleic anhydride grafted polylactic acid, a polymer compatibilizer, and epoxidized soybean oil (ESO), a reactive plasticizer, and the degradation of materials, the influences of the fibers treated with different methods on the mechanical properties and thermal stability of JF/PLA composites, the dispersion of the surface modified HA in the matrix and the effects of physicochemical properties of HA/PLA nanocomposites on the cytocompatibility were investigated.(1) The PLA-g-MAH synthesized by using dicumyl peroxide (DCP) as the initiator and ESO were used as polymer compatibilizer and reactive plasticizer respectively to increase the compatibility in Starch/PLA composites through synergistic compatibilization. In the presence of PLA-g-MAH and ESO, the dispersibility of Starch in PLA and compatibility between Starch and PLA dramatically increased as confirmed by Field Emission Scanning Electron Microscopy (FESEM). The break elongation and impact strength of the composites containing10wt%starch can reach24.47%and6.6 KJ/m2, which is213.71%and51.72%increased comparing with that of PLA. The rheological behavior of the composites showed that with addition of starch, the dynamic modulus of the blend increased significantly, showing evident solid-like response in the low-frequency region due to the formation of the network, and the zero shear viscosity also increased with increasing the starch filling content. The biodegradability of the composites was investigated by the cover soil method. The composites with50wt%starch which has lower price by45.8%and has faster degradation rate as compared to that of pure PLA.(2) The flexural modulus and impact strength of PLA were enhanced because of the addition of JF. After the fibers were treated with alkali and coupling agent, the flexural strength and vicat softening temperature of PLA composite were improved accordingly. The tensile strength, flexural strength and modulus, impact strength and softening temperature of PLA/JF composite filled with20wt%fiber and treated by alkali were increased by13.5%,38.5%,50.7%,30.1%and29℃, respectively. While fibers were treated with coupling agent, those properties were increased by16.0%,41.3%,78.9%,26.2%and34℃, respectively. The storage modulus increased substantially and the loss factor decreased with the addition of JF. The addition of JF fiber favored the crystallization of PLA, as confirmed by DSC measurement. SEM micrographs of the fracture surface of the specimen indicated that the adhesion between fiber and matrix could be improved by the Jute fibers treated with alkali and coupling agent.(3) To improve the interfacial interactions between PLA and HA and the dispersibility of HA nanoparticles in PLA matrix, HA nanoparticles were surface modified with dodecyl alcohol through esterification reaction. Modified HA (mHA) nanoparticles filled in PLA can effectively improve the hydrophilic property of PLA. The surface modification of HA results in1) good dispersibility of HA nanoparticles in PLA matrix as revealed by Field Emission Scanning Electron Microscopy (FESEM) and rheology method;2) good interfacial interactions between PLA and HA as revealed by mechanical properties measurement and Dynamic Mechanical Thermal Analysis (DMTA). mHA/PLA nanocomposite film demonstrates better cartilage cell attachment, spreading and proliferation than that of PLA and HA/PLA film. The reasons for the good cytocompatability were believed to be1) good dispersibility of the osteoinductive mHA nanoparticles in the PLA matrix;2) good interfacial interactions between the PLA and mHA nanoparticles;3) balanced hydrophobic/hydrophilic property. This newly developed mHA/PLA nanocomposites prepared by melt blending showed great potential in bone tissue engineering applications.