Study On Properties And Thermodynamic Constitutive Model Of TPI/HDPE Hybrid Shape Memory Polymers

In order to overcome the defects of poor mechanical properties of traditional shape memory polymer(SMP),this paper takes trans-1,4-polyisoprene(TPI)as the research object.The TPI matrix is toughened and modified by the thermoplastic elastomer preparation process,and the "TPI/HDPE" hybrid shape memory composite(SMPC)is developed.By changing the vulcanization system to control the vulcanization degree of the TPI component,the complementary advantages of the rubber-plastic blended thermoplastic elastomer can be realized.At the same time,the single and hybrid nano-fillers are introduced to give full play to the potential of high-performance fillers and further improve the mechanical properties of composite materials.Combined with the macroscopic thermal viscoelasticity theory and the microscopic phase transformation theory,a microscopic dynamic evolution model under the action of multi-factor coupling is established,and the optimization of the SMPC viscoelasticity theory is realized.First,from the perspective of the matrix,the HDPE components with low price and excellent thermodynamic properties are introduced to toughen and functionalize the TPI matrix.The thermodynamic and shape memory properties of TPI/HDPE hybrid SMPC with different blending ratios at different ambient temperatures are deeply discussed.Combined with the change of section microstructure,the influence law of component change of hybrid SMPC on the comprehensive properties of composites is revealed,and finally the optimal ratio scheme of hybrid matrix is given.Second,based on the concept of rubber plastic blend thermoplastic elastomer,the effect of dynamic vulcanization system on the crystallization and thermal properties of hybrid shape memory matrix is systematically studied by using mechanical melt blending process combined with dynamic vulcanization and hot-pressing technology,and the micro mechanism of the change of vulcanizing agent content on the mechanical and shape memory properties of TPI/HDPE hybrid SMPC is revealed.It can give full play to the excellent characteristics of plastics and rubber,and achieve the precise control of optimized vulcanization methods and efficient vulcanization systems.Third,the single reinforcing filler carbon nano tubes(CNTs)is introduced into the TPI/HDPE hybrid shape memory matrix,and a novel TPI/HDPE/CNTs ternary hybrid shape memory nanocomposite is prepared by mechanical melt blending process.Through a series of micro and macro thermodynamic tests,the influence of the content of single nano-filler on the thermodynamic properties of novel nanocomposites is revealed.Fourth,a novel preparation method of nano-fillers which can take into account the advantages of surface modification and physical blending is proposed,which fully exerts the synergistic effect between nanoparticles with different properties and effectively improves the interaction between nano-fillers and hybrid matrix.Firstly,the successful preparation of CNTs and silica(SiO2)hybrid nano-filler shell-core structure is achieved by surface modification.Then,combined with a series of macroscopic thermodynamics and shape memory performance characterization tests,the effect of different nano-filler composition on the comprehensive properties of composites is revealed.Finally,based on the wide application of macroscopic viscoelastic model in shape memory polymers,a novel thermodynamic viscoelastic constitutive model of hybrid SMPC is proposed.Combined with the concept of micro phenomenological model,the microstructure composed of reversible phase and fixed phase in parallel is constructed,and a three-dimensional parameter equation which can describe the cooperative change of various parameters in the process of phase transition is established.Through the dynamic evolution of multi-content and wide temperature domain in the static loading process,the consistency between the simulation results and the experimental conclusions is successfully proved,the micro-action mechanism of the macro-static mechanical behavior of hybrid SMPC is revealed,and then the effective prediction of the stress-strain response under the coupling action of matrix components and external environment is realized.