Preparation And Characterization Of Poly(D, L-lactide)/ Multi-walled Carbon Nanotubes Composite Materials

Polylactide is one member of aliphatic polyester with excellent properties, suchas biodegradability, biocompatibility, bioabsorbablity and processability, which iswidely used as biomedical material and general purpose plastic. Polylactide hasseveral optical isomers, among which poly(D,L-lactide) (PDLLA) is mostcommonlyusedduetoitsexcellentmedicalvalues.However,PDLLAalso hassomeshortages, such as poor thermal stability, low mechanical property, insulation and soon. Fortunately, carbon nanotubes show excellent properties in these aspects.Therefore, in this thesis we chose carboxyl functionalized-multiwalled carbonnanotubes (MWNT-COOH) as the modified material for PDLLA, and observed theproperties of the PDLLA/MWNT-COOH composites at the same time. The maincontentsandresultsofthisthesisaresummarizedasfollows:(1) The basic performance of PDLLA and MWNT-COOH had beencharacterized. The results showed that PDLLA was an amorphous polymer withmethyl, methine and ester in its molecular structure. MWNT-COOH had a largeaspect ratio and its X-ray diffraction peaks was similar to the peaks of graphite,meanwhile,carboxylwasfoundinitsmolecularstructuretoo.(2) PDLLA with different components MWNT-COOH composites wereprepared by solution co-blending method, and their related properties were studied.Differential scanning calorimeter (DSC), Thermo gravimetric analyzer (TGA),Scanning electron microscopy (SEM) were used to characterize the performance ofthe composites, the mechanical and electrical properties of the composites weremeasured using a Nanoindentation system and High Resistance Meter, respectively.The shape memory properties of the composites were also observed via a simpledemonstration experiment. The results indicated that the glass temperatures of purePDLLA and the PDLLA/MWNT-COOH composites were all about 53°C. Thethermal stabilities of the composites increased continuouslywith increasingcontentsof MWNT-COOH, and the degradation temperature of PDLLA/7 wt%MWNT-COOH composite increased by 25.6°C compared with that of the purePDLLA. The agglomeration of MWNT-COOH was slight when its weight fractionwas not more than 5 wt%,whereas the dispersion ability of the MWNT-COOHdecreased and a lot of agglomerates formed when its content increased to 7 wt%. Meanwhile, both the elastic modulus and hardness of the composites reached amaximum value at 5 wt%, and the corresponding value are 5.958 GPa and 248.81MPa, respectively. The volume electrical conductivities of the composites increasedcontinuously with the increasing of MWNT-COOH, and it was almost 8 orders ofmagnitude improvement for composite with 7 wt% MWNT-COOH compared withthat of the pure PDLLA. The shape memory effects of samples made of tenalphasbetsr corresponding to the shortened form of composites were obvious, andthe final shape of the deformed samples after recovering was very similar to theirinitialshape.(3) PDLLA and PDLLA/5 wt% MWNT-COOH fibers were preparedsuccessfully by electrospinning, and scanning electron microscopy (SEM) was usedto characterize their morphology. The results indicated that the diameters of PDLLAfibers wereuniform,andtheirsurfaces weresmoothtoo.Thediameters ofPDLLA/5wt% MWNT-COOH composite fibers were uniform too, however, their surfaceswererough.