| Smart material is a new type of functional material that can sense external stimuli and generate response to drive,and has the functions of sensing,driving and controlling.Among them,shape memory polymers have shown great applications in aerospace,biomedicine,biomimetic engineering,electronic components,intelligent robots and other fields due to their own advantages of low density,large deformation,rich driving methods,and easy modification and processing.Value makes it stand out among a wide variety of smart materials,and has become the most widely studied smart deformable material.However,most shape memory polymers have a single deformation mode,which is difficult to meet the complex needs of various fields.In addition,with the wide application of shape memory polymers,both mechanical properties and shape memory properties,and at the same time adjusting the deformation mode according to actual working conditions,as well as having the characteristics of remote control and selective recovery,are also technical problems to be solved urgently.After hundreds of millions of years of evolution and development,animals and plants in nature have evolved nearly perfect structures to better adapt to the external environment,providing important inspiration for the structural design,multiple responses,and deformation modes of shape memory polymers.Therefore,in this paper,in order to solve the problems of single deformation mode and remote driving mode of shape memory polymer,the multi-layer and filament winding arrangement structure of the main awn of the yellowback grass seed is used as a bionic model for structural design,based on its microstructure characteristics,design the preparation of bionic materials,know that shapes with different deformation modes have the preparation of composite materials.In this paper,polylactic acid(PLA)is used as the main material,combined with the high modulus semi-crystalline thermoplastic polymer polyether ether ketone(PEEK)and acrylonitrile-butadiene-styrene copolymer(ABS)to improve mold molding and 3D printing manufacturing technology to prepare shape memory polymer materials with high mechanical strength and controllable deformation,selfdeformable materials with multiple stimulus responses,and composite materials with multiple shape memory effects and two-way shape memory.The main research contents and conclusions of this paper are as follows:(1)PLA/PEEK shape memory composites are physical blends with good chemical stability and good molding effect.When the content of PEEK is 0-40%,with the increase of PEEK content,the shape memory characteristics first improve and then decrease with the increase of PEEK content.Among them,when the content of PEEK is 5%-20%,the shape memory characteristics are better.When the content of PEEK is 15% the shape memory characteristics are the best,the shape fixation rate is 99.2%,the shape recovery rate is 99.1%,and the response time is the shortest,which can recover rapidly within 2 s;When the PEEK content is more than 20%,the shape fixation rate and shape recovery rate gradually decrease,the response speed slows down,and the shape memory characteristics decrease.With the increase of PEEK content,the tensile properties increased first and then decreased.When PEEK content was 10%,the tensile strength was the highest,which was 20.6 MPa.At the same time,with the increase of PEEK content,the restoring force during deformation first increases and then decreases.When peek content is 15%,the restoring force is the largest,594 m N,which is 11.9 times of pure PLA.(2)Based on the main awn part of the yellow backgrass seeds arrangement of the fibers,a bionic double-layer network structure model of 3D printing is established.Through the 3D printing technology of fused deposition,the extruded filaments were pre-stretched during the printing process,and the temporary shape is fixed through the restriction of the bottom plate and the printing layer.The self-deformable functional material without pre-shaping is successfully prepared,which solves the problem of low shaping accuracy of the shape memory polymer and realizes a multi-modal self deformation process.At the same time,carbon black ink is used as the light-to-heat conversion agent.By coating the carbon black ink on the whole or part of the selfdeformable sample,it can realize the remote driving deformation under the stimulation of the near-infrared light laser,and realize the global and local light-driven self-folding deformation and deformation,and the deformation time is about 5 s.(3)The thickness,filling rate,number of peripheral turns and printing height of the sample are important factors affecting the deformation amplitude and response speed of the self deformable material.Among them,the thickness of the sample has the most significant influence.In the thickness range of 0.5 mm to 1.7 mm,the larger the thickness of the sample,the smaller the deformation amplitude and the longer the self deformation time,and the deformation amplitude of the sample with the thickness of0.5 mm is the largest,the deformation angle is about 312°,and the deformation time is the shortest,about 1.2 s.(4)Nine kinds of thermal actuators such as self deformable flowers,DNA imitation double helix structure,bionic octopus,self suture,self expansion support and programmable sequential self deformable Mimosa,and four kinds of optical drive devices such as self folding hinge,flowers,box and bionic hand were prepared,which realized diversified,high-precision and multimodal self deformable design under temperature and optical drive.(5)The prepared composite with multiple shape memory effect adopts four shaping methods,namely,high temperature step-by-step reduction shaping,high temperature one-time shaping,3D printing pre stretching shaping and high temperature overall stretching shaping.Among them,high temperature step-by-step reduction shaping needs two steps,and there are three shapes in the deformation process;Once forming at high temperature requires one step,and there are three shapes in the deformation process;3D printing pre-stretch shaping does not need manual shaping,and there are three shapes in the deformation process;High temperature overall tensile forming needs one step,and there are four shapes in the deformation process.The different processes of temporary shape assignment of the four molding methods will directly affect the multiple shape memory process of composites.The shape recovery rate in the recovery process of high-temperature primary molding is the highest,and the recovery rate is about 96.8%.The shape memory process of 3D printing pre molding has the least steps and simple operation;At the same time,the filling path of 3D printing is consistent with the deformation direction,which can promote the multiple shape memory effect and improve the shape fixation rate,shape recovery rate,response speed and deformation force of composites.(6)In the preparation of multiple shape memory composites,the composite mode of the two polymers directly affects the contact area of the two materials.The interlayer composite mode has the largest contact area,and its deformation force is the largest compared with other layout modes.For interlayer composite,the sample with an interlayer intersection angle of 90° is better than the sample with an interlayer intersection angle of 0°,the maximum deformation forces in the two stages are 43 m N and 56 m N.(7)Using PLA and ABS materials,shape memory polymer materials with twoway deformation were successfully prepared by using 3D printing PLA and ABS integrated molding,self deformation PLA and self deformation ABS back-to-back composite molding,and self deformation PLA and self deformation ABS face-to-face composite molding.Among them,the bidirectional deformation materials prepared by3 D printing PLA and ABS integrated molding have the best combination,but the deformation range is relatively low,about 0.8% of the length of the material itself,while the deformation amplitude of the two-way deformation material composed of self deformation PLA and self deformation ABS is the largest,which is about 21% of the length of the material itself.(8)In the preparation of shape memory composites with two-way deformation,when the mass ratio of ABS to PLA is 7:10,the deformation force of PLA can drive the non softened ABS to biaxially deform.The three-point fixed composite method is better than the flexible film coated composite method,which is more conducive to force transmission.The deformation amplitude of the three-point fixed two-way deformation material is about 10% of the length of the material itself.The three-point fixed method significantly improves the deformation amplitude of the two-way deformation material. |
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