Preparation And Properties Of Self-Healing Shape Memory Composites

In recent years,shape memory polymers（SMPs）and self-healing polymers（SHPs）,as two major branches of smart materials,have achieved rapid development in functional devices preparation and practical applications.However,integrating shape memory and self-healing properties into one polymer system remains a great challenge.Ionomers have become one of the most studied polymer materials in the field of supramolecular self-healing due to their unique structures,however,their shape recovery properties are poor.Based on the shape memory effect（SME）mechanism,this study controls the content of reversible phase and stationary phase,so as to improve the shape recovery performance of EMNa ionomer,and endow the material with multiple SME,reconfigurable and self-healing properties at the same time.The specific research contents are as follows:1.Ethylene-methyl acrylate copolymer（EMA）is introduced into sodium ion neutralized ethylene-methacrylate random copolymer（EMNa）.The effects of EMA content on the thermal,mechanical,shape memory and self-healing properties of EMNa/EMA blends are studied.The results show that the introduction of EMA not only increases the content of reversible phase in the system,but also has good compatibility between EMNa and EMA,which can efficiently transfer the driving force required for shape recovery through the two-phase interface.When the content of EMA is 30 wt%,EMNa/EMA-30 can revert from temporary shape to permanent shape in 8 s.At the same time,EMNa is used as the matrix to maintain the self-healing property of the material.The tensile strength of EMNa/EMA-30 is 15.9 MPa after three times of through-cutting at the same position,and the shape memory property of the sample is completely recovered after repair.In addition,the permanent shape of EMNa/EMA-30 can be reconstructed by thermo-induced solid plastic behavior.2.Polycaprolactone（PCL）with good biocompatibility and low melting point is introduced into EMNa ionomer.PCL can reduce the shape memory transition temperature(T_sw)of EMNa/PCL blends and endow material with triple shape memory properties.Shape memory test shows that EMNa/PCL-50 exhibites excellent dual shape memory behavior at 75℃,with a shape recovery rate of 93.8%and a shape recovery time of 12 s.In addition,EMNa/PCL-50 can remember two different temporary shapes at 75℃and 25℃,respectively.The self-repair test shows that the tensile strength and elongation at break repair efficiencies of EMNa/PCL-50 are 84.3%and 87.1%after 2 h healing.The reconstructed EMNa/PCL-50 returns to its permanent shape within 14 s.（3）With the preferred EMNa/PCL-50 system as the matrix,halloysite nanotubes（HNTs）are selected as the reinforcing phase to further improve the shape memory and self-healing properties of the composites.On the one hand,HNTs play a heterogeneous nucleation role in the system,which improves the crystallization capacity of the material,and thus increases the content of reversible phase.On the other hand,HNTs can form a“second network”and increase the content of the stationary phase.The shape memory tests show that when the content of HNTs is 3 wt%,the shape fixation rate and shape recovery rate of EMNa/PCL/HNTS-3.0 composite are up to 97.9%and 98.5%,and the sample still shows excellent shape recovery behavior under 300%large deformation.The self-repair tests show that the repair efficiencies of tensile strength and elongation at break of EMNa/PCL/HNTS-3.0 are91.2%and 93.5%,respectively.In addition,the sample still shows excellent shape memory behavior after 15 shape memory cycles.