Preparation And Properties Of Modified Chitin Whisker/ PLLA Nanocomposites

Poly(L-lactic acid) has been widely used in biomedical materials field due to the biocompatibility, biodegradability, good mechanical properties and processability. However, the mechanical properties of PLLA are not ideal as the hard tissue repair materials such as bone screw and bone plate. At the same time, PLLA will release the acidic degradation products, which may lead to noninfectious inflammatory responses in the body. Whats more, the degradation rate of PLLA is difficulty to control. Therefore, it is necessary for such material is properly modified to improve the mechanical properties, decline noninfectious inflammatory responses and control the degradation rate.As a natural alkaline polysaccharide, chitin owns good biocompatibility, hydrophilicity and excellent osteogenic activity. Chitin whisker(CHW) is a kind of single crystal prepared by acid hydrolysis of chitin. Due to the excellent mechanical strength and modulus, CHW has be an ideal polymer nano-filler. The aim of this paper is to improve both the strength and toughness of PLLA with CHW. Moreover, in order to resolve the dispersion of whiskers and interfacial adhesion between whiskers and PLLA matrix, grafted CHW were synthesized. Meanwhile, as one of alkaline polysaccharide, CHW and grafted CHW can neutralize acidic degradation product of PLLA matrix and control the degradation rate.CHW was firstly prepared by acid hydrolysis of chitin. Then, a series of CHW-g-PLLA with different grafting efficiency were obtained by the solution ring-opening polymerization of L-lactide using CHW as a macroinitiator with different nCHW:nL-lactide. The morphology and size, chemical composition, crystalline property and thermostability of CHW before and after surface modification were characterized by FESEM、TEM、AFM、POM、IR、XRD and TG. Results revealed that needle-like CHW with nano-size was achieved, and surface modification has little effect on the morphology and crystalline property of CHW. However, the dispersion of whisker in water and ethanol was improved, and the whisker size became smaller after surface modification. The grafting efficiency of PLLA segments on the surface of CHW can be controlled to some extent by changing the molar ratio of CHW to L-lactide.Then, the pure PLLA and different mass ratio of CHW / PLLA, CHW-g-PLLA / PLLA nanocomposite films were prepared by the way of solution casting,whose crystallization behavior, thermal properties, fracture surface, tensile properties, the swelling performance, pro / hydrophobicity and compatibility of in vitro were investigated. The results showed that, the addition of the heterogeneous nucleation agents, CHW and CHW-g-PLLA, significantly improved the crystallization rate of PLLA matrix resulting in a smaller size crystal ball. The addition of CHW and CHW-g-PLLA into PLLA were able to increase the tensile strength and modulus of PLLA, and when the content of whiskers increase to 5%, the value of the tensile strength and modulus were maximum. While the mechanical properties of CHW-g-PLLA / PLLA composite films were significantly better than the corresponding CHW / PLLA. CHW and CHW-g-PLLA were added into PLLA, improved the hydrophilic properties and swelling of the matrix PLLA, at the same time, the cell compatibility of PLLA was improved.Finally, the pure PLLA, CHW / PLLA, CHW-g-PLLA / PLLA nanocomposite Spline were prepared by the method of melt blending/injection molding. The mechanical properties, interface compatibility, crystallization behavior and in vitro degradation of the splines were studied. The results showed that: when the content of the whiskers were the same, the interfacial compatibility of CHW-g-PLLA/PLLA was better than CHW/PLLA. When the content of the whiskers increased to 5%, the strength, modulus and toughness of CHW / PLLA and CHW-g-PLLA / PLLA splines were both optimalizing. Observily, the strength and modulus of CHW-g-PLLA / PLLA were better than CHW / PLLA. DSC results show that, the isothermal crystallization temperature and the melting temperature of the material are reduced with the content of CHW and CHW-g-PLLA increasing. The crystallization temperature and the melting temperature of the material are significantly reduced with the increase of cooling rate. The degradation experiments in vitro showed that: in the early stage of degradation, the join of CHW slowed the degradation of PLLA, while the degradation of CHW-g-PLLA PLLA is promoted. In the meantime, CHW and CHW-g-PLLA joined slowed the decrease of the p H values of their degradation liquid.