Study On The Structure And Properties Of Fe₃O₄/PLLA Composites

The magnetic Fe3O4 nanoparticles had been synthesized by co-precipitation method and surface modified by oleic acid. The Fe3O4 and surface modified Fe3O4 nanoparticles were characterized by FTIR, TEM, XRD and magnetic property analyses. The poly(L-lactide) homopolymers (PLLA) and Poly(L-lactide)/Poly(ε-caprolactone) copolymers(PCLA) were polymerized by ring opening polymerization. The surface modified Fe3O4 nanoparticles were dispersed in polymer to fabricate a series of Fe3O4/PLLA and Fe3O4/PCLA composites with different compositions. The microstructure, mechanical properties, shape memory effects with different induced mechanism, degradable properties and biocompatibility were investigated systematically by DSC, XRD, SEM, tensile test, in vitro degradable test and biocompatibility test. The relationship between the microstructure and the properties were revealed.The experiment results show that the shape of oleic acid modified Fe3O4 nanoparticles with super-paramagnetic is spherical. The particle size distributes uniformly and their average grain size is about 9.1nm. Modified Fe3O4 nanoparticles can evenly dispersed in polymer matrix. There exist weak hydrogen bonds between surface modified Fe3O4 nanoparticles and PLLA polymer matrix.The tensile test results show that the elastic modulus, tensile strength and elongation at break of the composites first increase and then decrease with the increase of Fe3O4 nanoparticles content. When the content of Fe3O4 nanoparticles is 20wt%, the elastic modulus reaches a maximum value 21.2MPa. which is 112% higher than that of pure PLLA. When the content of Fe3O4 nanoparticles is 10wt%. the tensile strength and elongation at break get the maximum value for 93.1 MPa and 174.8%, which are 73% and 60% higher than those of pure PLLA, respectively.The shape memory properties are affected obviously by the addition of Fe3O4 nanoparticles. When the content of Fe3O4 nanoparticles is 10wt%. the composite possesses the best shape memory properties. The recovery stress of the composites reaches 7.82MPa when the deformation strain is 50%, which is 63.6% higher than that of pure PLLA.The shape memory effect induced by alternating magnetic field is investigated by bending test. The results show that the shape recovery rate of the (40wt%) Fe3O4/PCLA composite is 55.6% after the composite are put in the alternating magnetic field for 500 seconds. The frequency of the alternating magnetic field is 90kHz and magnetic field intensity is about 15kA/m. The low shape recovery rate is attributed to the low magnetic field frequency. The heat produed by the Fe3O4 nanoparticles is low under this alternating magnetic field conditions.The in vitro degradable test results show that the degradation rate of Fe3O4/PLLA composites is faster than that of pure PLLA. With the increase of the Fe3O4 nanoparticles content, the degradation rate of the composite increases. Hemolysis rate testing and dynamic clotting test results show that Fe3O4/PLLA composites have good biocompatibility.