Study On The Microstructure And Properties Of TiO₂/PLA System Nanocomposites

The TiO₂ nanoparticles were surface-grafted modified by different kinds of modification methods.The surface-grafted modified TiO₂ nanoparticles were characterized by FTIR,TG and TEM analyses.1-TiO₂ nanoparticles (surface-grafted modified by the solution polymerization of L-lactic acid) and r-TiO₂ nanoparticles(surface-grafted modified by the ring-opening polymerization ofε-caprolactone) were dispersed in PLLA and PCLA to fabricate the composite,respectively.The microstructure,mechanical properties, shape memory properties and biodegradable properties were investigated systematically by DSC,XRD,SEM,tensile test and in vitro degradable test.The relationship between the microstructure and the properties were illuminated.The experimental results show that the PLLA and PCL were grafted onto the surface of TiO₂ nanopartictes through the ring-opening polymerization of L-lactide,solution polymerization of L-lactic acid and ring-opening polymerization ofε-caprolactone.The maximum grafting rate was 6%,8.5%and 19.9%,respectively.There existed chemical bond between the surface-grafted modified TiO₂ nanoparticles and polymer matrix.The results of SEM and TEM show that grafted modified TiO₂ nanoparticles can be dispersed homogeneously in chloroform and polymer matrix.The tensile strength of the composites can be enhanced obviously by the addition 1-TiO₂ nanoparticles.When the content of 1-TiO₂ nanoparticles was 5wt%,the tensile strength reached a maximum value 72MPa,which was 23.1% higher than that of pure PLLA.However,the elongation break of composites decreases with the addition of 1-TiO₂ nanoparticles.Comparing with the pure PLLA,the shape recovery rate of 1-TiO₂/PLLA composite were slightly improved and recovery stress were enhanced evidently.The(5wt%)1-TiO₂/PLLA composite exhibits the maximum shape recovery rate and recovery stress.The in vitro degradable test results show that the degradation rate of 1-TiO₂/PLLA composite is faster than that of PLLA.With the increase of the 1-TiO₂ nanoparticles content,the degradation rate of the composite increases.The tensile test results show that the mechanical properties of r-TiO₂/PCLA composite are superior to those of pure PCLA.When the content of r-TiO₂ nanoparticles is 5wt%,the tensile strength and theelongation at break of r-TiO₂/PCLA composite are 113.8%and 19.8%higher than those of pure PCLA, respectively.In the mean time,this composite possesses the best shape memory properties.The shape recovery rate of the composite is 99.5%and the recovery stress reaches 6.3MPa.The degradation rate of r-TiO₂/PCLA composite is evidently faster than that of pure PCLA.