Preparation And Properties Of Polylactide With Shape Memory Performance

The polymer based on nanocomposites has attracted extensive attention due to its flexible design and low production cost.The shape memory properties for the composite of rigid nanoparticles and polymers can be obtained by adjusting the rigid network structure or the composition of polymers,which will expand the application range of polymers significantly.Polylactide（PLA）is a biodegradable biomedical polymer material with good bio-compatibility.The practical application of polylactide is limited for its brittleness and insufficient mechanical properties.The research goal of this paper is adopted to design polylactide materials with excellent properties and shape memory properties.The polylactide based on graphene nanocomposites with uniform distribution has been prepared by compounding polylactide copolymer with the functionalized graphene.The structure and properties of the obtained composites have also been studied in detail.Homopolymers of polylactide,L-polylactide（PLLA）and D,L-polylactide（PDLLA）,as well as copolymers of lactide（LA）and caprolactone（?-CL）,PLCL and PDLCL,were synthesized by melting ring opening polymerization of ring ester with stannous octanoate as catalyst.PLLA is a crystalline polymer with melting temperature T_mabove 160 ^oC.PDLLA owns an amorphous structure,and the glass transition temperature T_gis above 50 ^oC.Polycaprolactone PCL is a crystalline polymer with melting temperature T_mabout 60 ^oC.The microstructure of PLCL will change according to the composition of copolymerization.When the content of comonomer lactide L-LA is less than 50 mol%,the crystallization of copolymer PLCL is mainly determined by PCL polymer chain,and the melting point of copolymer is low.When the content of comonomer lactide is more than 50 mol%,the crystallization of PLCL copolymer is mainly caused by PLLA.With the increase of lactide content,the melting temperature of the copolymer significantly increased more than 150 ^oC.Due to the amorphous structure of PDLLA,there is no melting transition of PDLCL copolymer.The results show that the microstructure of PLCL can be adjusted by controlling the proportion of L-LA and?-CL comonomer.The polylactide based graphene composites was prepared by compounding polylactide copolymer with graphene.The compatibility between rigid nano graphite sheet and polymer is poor,and direct composite cannot be used to make graphite dispersed uniformly.In this paper,the functionalized graphene oxide（FGO）was prepared by oxidation-reduction of graphite sheets.The reaction of active group on FGO with polytrimethylene carbonate（PTMC）to obtain FGO grafted PTMC,i.e.FGO-g-PTMC.With its good compatibility between PTMC and PLA,the graphene is uniformly dispersed in the polymer matrix to form a homogeneous composite structure.Compared with PLCL/PTMC blends,the tensile strength and elongation at break of the composites with FGO 3%increased by 9.92 Mpa and 19.66%,respectively.The dynamic mechanical behavior of PLCL/PTMC blends and PLCL/FGO-g-PTMC composites were studied.The storage modulus of PLCL/PTMC is lower than that of the composite,and the loss tangent is greater than that of the composite,which indicates that a stable cross-linked structure is formed in the composite,and the recovery performance of elastic deformation has been improved.The deformation fixation ratio and recovery ratio of the composite are higher than those of the blend,especially the deformation fixation rate and deformation recovery rate of PLCL/FGO-g-PTMC with FGO 3%are more than 95%,which indicates that the composites have good thermally induced shape memory properties.The addition of FGO forms a conductive network in the polymer matrix,and the material obtains the properties of electrically induced shape memory properties.The composite can complete the recovery of deformation within15 s only under the voltage of 30 V.The results show that polylactide composites with shape memory performance under different conditions can be prepared through the selection of comonomers and the design of rigid composite network.The prepared intelligent polylactide nanocomposite with excellent mechanical properties is expected to be applied in intelligent medical devices,tissue engineering,electronic devices and other fields.