Application Of Caster Oil On The Modification Of Polylactide

Poly(L-lactic acid) (PLLA)is an environmental friendly material due to its biodegradability, biocompatibility and nontoxicity, and it is producible from the renewable sources. Although PLLA and its copolymers have been intensively studied, it is difficult to broaden its practical application range of PLA,due to its inherent brittleness and high price.In this thesis, the influence of castor oil as an initiator on the ring-opening polymerization of lactide and the effect of the castor oil as a plasticizer on the PLA blend were studied. The chemical structure and thermal properties of the polymers were characterized by DSC, TGA, FT-IR and NMR. Castor oil was used to control the molecular weight of PLA and to increase the polymerization speed. The high molecular weight PLA was obtained when the amount of castor oil amount was lower than 1%. The results of FT-IR and NMR showed that the chemical bonds were formed between castor oil and lactic acid molecules.Castor oil as a plasticizer could increase the plasticity of PLA, but the mechanical strength of PLA decrease at the same time. When the content of castor oil in the blends was 20wt%,the elongation at breakreached over 240%.The castor oil-lactic acid copolymers had the high toughening effect on PLA, and the effect was more obvious with the increase of its content. The incorporation of isophorone diisocyanate (IPDI) could further increase the mechanical properties of PLA. When the IPDI content was 0.5%, the tensile strength and elastic modulus reached 62.5MPa and 2108MPa, respectively. The elongation at break and notched impact strength than the samples without adding IPDI were11.3% and 9.5kJ/m2 respectively.With the combination of the nucleation agent (talc) and IPDI,the heat resistance of PLA was effectively improveed.Based on this. The strengthen PLA composite further increased after the addition of glass fiber, and the notched impact strength was 2 to 3 times higher than that the pure PLA.