Preparation And Characterization Of PLLA/HA Composites Basing On PLLA/PDLA Stereocomplex

Polylactic acid(PLA)/hydroxyapatite(HA)composites are excellent bone repairing biomaterials due to their excellent biological properties.However,the interfacial incompatibility of organic-inorganic composites and the poor dispersion of inorganic fillers in organic substrates have limited the applications of PLA/HA composites.Poly(L-lactic acid)(PLLA)and poly(D-lactic acid)(PDLA)can form stereocomplexes due to their different configurations,which lead to strong interaction between the two molecular chains.This characteristic can be used to improve the interfacial bonding between PLA and n-HA,and thus improve the dispersion of nano-scaled HA in PLA matrix.In this thesis,PDLA chains with different molecular weights(i.e.,5000,10000 and 20000)were grafted onto the surface of HA nanorods(n-HA)via transesterification(n-HA-PDLA),and then n-HA-PDLAs were blended with PLLA with high molecular weight(100,000).For comparison,n-HA-PLLA was prepared and blended with PLLA similarily.A variety of characterizations(FTIR、SEM、TEM、DLS、TGA、AFM、DSC、DMTA and mechanical property measurements,etc.)were used to study the prepared PLA/HA composites.(1)The dispersibility of unmodified n-HA,n-HA-PLLA and n-HA-PDLA in PLLA and the mechanical properties of corresponding composites were investigated and compared.It was found that the unmodified n-HA aggregated seriously in PLLA,while n-HA-PLLA and n-HA-PDLA could be well dispersed in the PLLA matrix.At the same addition amount of n-HA-PLLA or n-HA-PDLA,both the PLLA/n-HA-PLLA and PLLA/n-HA-PDLA composites showed higher tensile strengthes and elongations at break than the PLLA/n-HA composite.(2)The reinforcing effects of n-HA-PLLA and n-HA-PDLA on PLLA were studied.When the molecular weights of grafted PLLA and PDLA were similar,it was found that the tensile strength and the elongation at break of PLLA/n-HA-PDLA composite films were higher than those of the PLLA/n-HA-PLLA composite films.(3)The formation of stereocomplex at the interface between PLLA and n-HA-PDLA was confirmed by DSC,DMTA and AFM analysis.When the molecular weights of grafted PLLA and PDLA were similar,it was found that the PLLA/n-HA-PDLA composite had higher melting point and melting enthalpy than those of PLLA/n-HA-PLLA composite.Compared with n-HA-PLLA,the effect of n-HA-PDLA on the formation of PLLA spherulites was more significant.(4)The effects of the chain lengths of the PDLA oligomers grafted onto n-HA on both mechanical and thermal properties of PLLA/n-HA-PDLA composites were investigated.It was found that the interfacial interaction and the thickness of interface layer between n-HA and PLLA increased as the length of grafted PDLA chains increasing,showing moderate toughening effect.The results of this thesis reveal that the stereocomplex between PLLA and PDLA can be used to improve the interfacial compatibility between PLA and inorganic fillers,which help to improve the dispersibility of nano-sized inorganic fillers in PLA matrix.This strategy is envisioned a feasible way in developing PLA-based organic-inorganic composites with improved performances,which will find wide applications in bone repairing.