| As the fourth intelligent material,shape memory polymer is a polymer material that has received widespread attention in recent years.Because of its shape memory effect,it can quickly respond to external stimuli,which makes shape memory polymer become a research hotspot.Compared with other memory materials,shape memory polymer has many advantages,such as light weight,low price,designable driver mode,adjustable glass transition temperature,large recoverable deformation,etc.Meanwhile,it also has the disadvantages of low shape restorative force,low strength,low modulus,so it is very necessary to explore the modification of shape memory polymer.4D printing technology is an important molding method of shape memory polymer,which can meet the flexibility and complexity of intelligent structure design and manufacturing.The key of this paper is to form the intelligent structure based on modified shape memory polymer by 4D printing.In this paper,it emphatically introduces the methods and properties of preparing polylactic acid(PLA)composites to enhance shape memory by mixing elastomer,carbon nanotube,polyurethane respectively,analyzes its potential applications in actuators,sensors and robots,it is of great significance to promote the development of modified shape memory polymer materials and the design and manufacture of 4D printing intelligent structure.The principle of elastomer enhancing shape memory of poly was studied.The effect of printing parameters on the interlayer binding force of PLA/elastomer hybrid composite sample is analyzed,selected the best printing parameters,and proposed a new enhancement method of lateral printing and interlayer overlap to further improve the binding performance of PLA and elastomer.The influence of the proportion and distribution of elastomer on the impact strength of PLA/elastomer hybrid composite sample was investigated.The effects of the addition of elastomer on the shape memory recovery rate,recovery force,recovery time and cycling performance of PLA samples were analyzed.Researches show that the maximum interlayer binding force is 165.11N under the optimal printing parameters.The maximum impact strength of PLA/elastomer hybrid composite sample can reach 36.71 k J/m2,which is 9.87 times higher than that of pure PLA sample.The recovery rate of shape memory is close to 100%,and the fastest recovery time is 116.67s,which is 40.68%shorter than the pure PLA sample,and shows good shape memory cycling performance.The peak value of shape restoring force is 2.885N,which is 6.92 times higher than that of pure PLA sample.The principle of elastomer enhancing shape memory of poly/carbon nanotubes was studied.The effect of the filling ratio of carbon nanotubes on the conductivity of PLA/carbon nanotubes composites was analyzed.The effect of the filling ratio of carbon nanotubes on the shape memory performance of PLA/carbon nanotubes composite samples was investigated under the condition of thermal stimulation response.The influence of the filling ratio of carbon nanotubes and the presence of elastomer enhancement on the shape memory performance of the sample was investigated under the condition of electrical stimulation response.The influence of carbon nanotube filling on the shape restoring force of the sample was analyzed.Researches show that the PLA/carbon nanotube composite sample has excellent electrical conductivity and good electrically driven shape memory effect,and the fastest recovery time is 60s.Meanwhile,the addition of elastomer increases the shape memory recovery rate to more than 94%.The peak value of shape restoring force is 0.878N,which is 4.22 times higher than that of pure PLA sample.The principle of shape memory enhancement of poly by polyurethane was studied.The effects of polyurethane filling ratio on the tensile properties,bending properties and impact properties of PLA/polyurethane composite 3D printed samples were studied.In view of the good toughening effect of PLA/polyurethane composites,a special shape memory behavior characterization was proposed under the condition of cold programming and hot stimulation response.According to this,the shape memory performance,cyclic shape memory performance and cyclic mechanical properties of the sample were analyzed.A negative Poisson's ratio reversible energy absorber was designed and manufactured for its high energy absorption capacity in cold programming process.Researches show that The tensile strength and flexural strength of the PLA/polyurethane composite sample can be maintained at a high level,and its impact strength reaches 11.482 k J/m~2,which is 5.243 times higher than that of the pure PLA original.The shape memory recovery rate of the samples is close to 100%under cold-programming and hot stimulus response.Compared with the typical shape memory behavior programming stage,the storage modulus of PLA/polyurethane composite sample in the cold-programming stage is nearly 600 times higher.The energy absorber designed according to this principle has energy absorption up to 2.517J and good reversible cycle performance. |
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