Investigation On Shape Memory Properties Of Epoxy Modified By SiO₂/HTBN

Shape memory epoxy resin has attracted great interest in aerospace application or others attributed to its different advantages of low shrinkage rate and high strength,whereas obvious brittleness restricts the application of epoxy. In this paper, this research is aim to improve the toughness of the resin and expand its application in various fields through the modification of epoxy resin.The performance of epoxy resin can be adjusted by reaction conditions and reactants or modified by different toughening agents. The thermosetting epoxy-based shape memory polymer was obtained by the co-reacting of E-51 epoxy resin, Methyl ethyl Imidazole as an accelerator and Tetrahydromethylphthalic anhydride(an anhydride curing agent) in two curing process. And three kinds of composite materials were prepared,namely SiO2/Epoxy, HTBN/Epoxy and SiO2/HTBN/Epoxy. Their structure and shape memory behavior were characterized by experimental apparatus such as FTIR, DSC,expansion device indicator, SEM and so on.The study showed that, epoxy resin obtained by the curing system 1(post-curing) has excellent mechanical properties, low degree of curing, good toughness and lower Tg. And its shape memory effect is better than curing system 2, presenting better reproducibility.The shape fixity ratioes of all obtained epoxy resins were up to 99.4% and the shape recovery ratio approached 100%. We studied the recovery relaxation time of pure epoxy and three kinds of composite materials obtained by the curing system 1. It was found that effects of deformation temperature and recovery temperature give evidence for relaxation time variation. To investigate the relaxation time in the recovering process, two different deformation conditions are applied. In the first condition, the specimen were folded at low temperature and recovered at high temperature, and in the second one, they were folded at high temperature and recovered at low temperature. The relation of relaxation time and recovery temperature corresponding to the positive temperature difference follows Eyring equatio, and the relation corresponding to the negative temperature difference follows WLF semi-empirical equation. However, the relation merely meets with WLF equation inthe second condition of folding at high temperature and recovery at low temperature. In this work, the results reveal the obvious temperature dependence of relaxation process of this epoxy resin, and demonstrate the feasibility of Boltzmann equation in research of shape recovery behavior. Bending strength of epoxy decreased with the increment of bending numbers, whereas recovery time was effected by storage time of the sample deformed or not, the former increased but the latter decreased. What’s more, the toughening system of the composites with three phases, 2%SiO2/15%HTBN/Epoxy,exhibited well overall performance, including low glass transition temperature(76 ℃),large impact strength(10.94 KJ ? m-2), more repeat numbers and corresponding high recovery ratio, which integrate the merits of SiO2 and HTBN.