Design,Preparation And Mechanism Study Of Reversible Shape Memory Polymer With Amorphous Region As Switching Phase

Smart material is a new kind of material that can sense external stimuli and produce specific response in time.Compared with other smart materials,reversible shape memory polymer(SMP)is one of the most widely used smart materials.Reversible SMP can be converted reversibly between original shape and temporary shape under external stimulation.However,the switching phases of all reversible SMP can be divided into two categories:crystalline region and liquid crystal.Reversible SMP excitation results in rapid softening and significant decrease of mechanical properties due to crystallization melting or orientation destruction of liquid crystal,which makes it difficult to do work.This defect has become a bottleneck problem restricting the development and application of reversible SMP.Therefore,in order to solve the above problems,this study developed a new reversible SMP switching phase,which has important significance for expanding the development prospect and application field of reversible SMP.In this study,reversible shape memory ultra-high molecular weight polyethylene(UHMWPE),reversible shape memory UHMWPE/ multi-walled carbon nanotubes(MWCNTs)composites and reversible shape memory UHMWPE fibers were successfully prepared using amorphous region as switching phase.The results of IR and Raman spectroscopy experiments show that the material successfully introduces internal stress into the polymer matrix by simple training,so as to realize the reversible shape memory effect without external force.In this study,UHMWPE was used as the polymer matrix,the amorphous region in UHMWPE was used as the switching phase,the chain entanglement was used as the internal stress provider,and the crystal region was used as the strengthening phase.No melting/crystallization occurred in the crystal region during the reversible deformation process of the material,so as to ensure that the material would not have obvious softening and mechanical property degradation during the excitation process like common reversible SMP.The working mechanism of reversible shape memory UHMWPE matrix is as follows: During the heating process,the orientation of the amorphous region of UHMWPE with highly oriented molecular structure after training gradually decreases under the drive of entropy increase,resulting in the molecular chain in the amorphous region gradually changing from the highly oriented state to the isotropic state.Due to the large shrinkage of the molecular chain in the training direction,the material shrinks macroscopically.In the cooling process,the molecular chain shrinkage force caused by the increase of entropy gradually decreases,so the molecular chain in the amorphous region of UHMWPE will gradually return to the highly oriented state under the internal stress,resulting in macroscopic elongation of the material.It is due to the synergistic effect of molecular chain of amorphous region,the shrinkage force caused by entropy increase and the internal stress(tensile stress)introduced by training that the reversible deformation of the material in the cyclic rising and cooling process is successfully realized.The DMA results showed that the reversible strains of reversible shape memory UHMWPE,reversible shape memory UHMWPE/MWCNTs composites and reversible shape memory UHMWPE fibers were 13.97%,21.87% and 9.28%,respectively.The reversible strain of UHMWPE/MWCNTs composites increased by 7.9% with the addition of MWCNTs.The tensile strength of reversible shape memory UHMWPE,reversible shape memory UHMWPE/MWCNTs composite and reversible shape memory UHMWPE fiber were 151.56 MPa,178.70 MPa and 1384.60 MPa,respectively,and the elongation at break were 39.33%,32.88% and 8.57%.The tensile strength of reversible shape memory UHMWPE/MWCNTs composites increased by 17.91% compared with reversible shape memory UHMWPE,indicating that the introduction of MWCNTs played a role in strengthening the filler for UHMWPE matrix.In this study,the reversible shape memory UHMWPE was used as the driver,and the temperature-responsive lifting platform,temperature-responsive flexible zoom lens and lens group were further developed.Reversible shape memory UHMWPE(0.086 g)can drive the lifting platform(19.107 g)which is 222 times its own mass to rise and fall reversibly,and the reversible change rate of lifting platform height is 29.48%.When 22.835 g of weight is further loaded on the lifting platform,the reversible shape memory UHMWPE can still achieve the reversible change rate of 25.86% of the lifting platform height under the condition of 488 times of the switching mass.The image change rate of the temperature-responsive flexible zoom lens is 101.85%,which is 61.65% higher than that of the temperature-responsive flexible zoom lens.In this study,reversible shape memory UHMWPE/MWCNTs composites were used as resistance components to further develop sliding rheostat.