Research On The Influencing Factors And Functionalization Of Thermally Induced Shape Memory Composite System

Shape Memory Polymer(SMP)is a polymeric material whose initial shape can be restored in response to external conditions(e.g.heat,electricity,light,chemical induction,etc.)after the initial shape of the product has been changed and fixed under certain conditions.There has been much research on SMP by researchers,but little research has been done on the internal factors of blended polymers that affect shape memory performance.In this paper,we investigated the influence of thermodynamic properties,interfaces and thermodynamic parameters on shape memory properties,and we prepared a high-temperature shape memory composite with flame retardancy and environmental protection through the modification of PLLA-based shape memory composites.The main research contents are as follows:Firstly:Three different block polymers,such as PCL-PEG-PCL,PLLA-PEG-PLLA and P(CL-LA)-PEG-P(CL-LA),were synthesized as switch phases to construct shape memory biodegradable blends with PLLA.The effect of the relationship between the two phases on the shape memory behaviour was investigated by scanning electron microscopy,interfacial tension,differential scanning calorimetry and dynamic mechanical analysis.The results showed that the blends with higher enthalpy entropy and lower surface tension had the best shape memory performance,with shape fixation rate(R_f)and recovery rate(R_r)reaching 96.1%and 97.6%,respectively.With the thermodynamic properties playing a major role and the interface playing a secondary role,a proper fit will contribute to the shape memory effect of biodegradable polymers.Secondly:shape memory P(CL-LA)-PEG-P(CL-LA)/PLLA blends were investigated by adding a third filler,such as hexagonal boron nitride,prepared synthetic reduced graphene oxide(RGO)and crystals of home-made inorganic substances,to study the effects of changes in thermal parameters such as thermal conductivity,specific heat capacity and thermal diffusion coefficient on the shape memory blends.The results showed that the blends with high thermal conductivity,low specific heat capacity and high thermal diffusion coefficient achieved the best shape memory performance,with shape fixation rate(R_f)and recovery rate(R_r)reaching over 95.5%.The thermodynamic parameters of the blended film improved the ability and speed of the blended system to conduct heat,prompting the thermal movement of the molecular chains and significantly improving the shape memory performance of the system.Thirdly:A high temperature shape memory composite with flame retardancy was constructed using soluble thermoplastic polyimide(PI)as the stationary phase,PLLA as the switching phase and modified hexagonal boron nitride(PEG-BN)as the flame retardant.The PI/PLLA/PEG-BN composite showed good shape memory effect at high temperature,with shape fixation rate(R_f)and recovery rate(R_r)reached 92.5%and 94.4%.In addition,thermal weight loss,ultimate oxygen index and vertical combustion method studies showed that the composite exhibits good flame retardancy with an ultimate oxygen index of 26.8%and a vertical combustion rating of V-1.The composite can be used in special applications such as fires and other harsh environments where it can act as a"self-protector".