Structure And Properties Of The Biodegradable Shape Memory Poly(L-lactide)-based Blends

The poly(L-lactide)(PLLA) homopolymer, the poly(L-lactide-co-glycolide)(PLGA) andthe poly(L-lactide-co-ε-caprolactone)(PLCL) copolymer were synthesized by the ringopenning polymerization. A series of PLLA/PLGA and PLLA/PLCL blends with differentcompositions were prepared by solution blending method. The microstructure, mechanicalproperties, triple-shape memory effect and degradation properties were investigatedsystematically by FTIR, DSC, XRD, tensile test and in vitro degradable test. The relationshipamong the composition, microstructure and the properties were illuminated. On this basis, themodified MgO nanoparticles were introduced into the polymer blends, and the effects of theMgO content on the microstructure, mechanical properties, triple-shape memory effect anddegradation properties were studied and the mechanism was also revealed.The experimental results show that PLLA/PLGA blends have good compatibility. Theaddition of PLGA obstructs the crystal of PLLA, which decrease the crystallinity of PLLA.When the PLGA content is high, the blends have the small PLGA crystal. The PLGA contenthas apparently influence on the mechanical properties of polymer blends. The elastic modulusand tensile strength of the blends are between those of PLLA and PLGA. However, theelongation at break of the blends have the maximum value when the PLGA content is40wt%.PLLA has good compatibility with PLCL. The contents of PLCL have significant effecton the Tg, Tm and crystallinity of PLLA/PLCL blends. The crystal of PLCL cannot be foundin the polymer blends. With the increase of the PLCL content, the elastic modulus, tensilestrength and elongation at break of the PLLA/PLCL blends increase initially and thendecrease.The DMA results show that the PLLA/PLGA and PLLA/PLCL blends have broad glasstransition. Two different temperature interval can be defined in this broad transition, eachcorresponding to individual shape memory process, which make the PLLA/PLGA andPLLA/PLCL blends present triple-shape memory effect. The experiment results show that theshape retention rates of blends are high in40℃and in70℃. Howerver, the shape recoveryrates of blend increase initially and then decrease with the increase of PLGA or PLCL content.When the PLGA or PLCL content is40wt%, the blends have the best triple-shape memoryeffect. Surface-modified MgO nanoparticles by stearic acid can evenly dispersed in polymerblend matrix. There exist weak hydrogen bonds between surface-modified MgO nanoparticlesand polymer blend matrix. With the increase of MgO content, the crystallinity of compositesdecreases. The elastic modulus and tensile strength of composites increase with particlecontent and show a maximum at1wt%particle loading. Further increasing the particle contentleads to reduction in elastic modulus and tensile strength. However, the elongation at break ofcomposites decreases with the increase of MgO content. MgO/PLLA/PLGA andMgO/PLLA/PLCL composites have triple-shape memory effect. MgO nanoparticles acting asphysical crosslinks play a fixed phase role. When the MgO content is1wt%, the compositeshave the best triple-shape memory effect.The in vitro degradable test results show that the degradation rates of PLLA/PLGA orPLLA/PLCL blends are faster than that of pure PLLA. With the increase of PLGA or PLCLcontent, the degradation rates of the blends increase. The addition of MgO nanoparticleaccelerates the degration. With the increase of MgO content, the degradation rates of thecomposites increase. The in vitro pH value determination results indicate that the MgOnanoparticles can neutralize effectively the acidoid resulting from the degradation of polymerblends matrix.