Study On Curing Kinetics And Properties Of Shape Memory Epoxy Resin With Two-stage Curing Characteristic

With more application of thermoset epoxy resin shape memory composites in space structure technology, the challenge of using smaller launch volume to reduce cost is geting more attention. Application of space deployable structure provides an effective way to solve this problem. Shape memory materials for space deployable structure have some disadvantages, including two-way shape memory reversibility, poor thermal stability, low heat resistant and mechanical strength. Hence, we design a new two stage curing method to improve the properties of composites. The feasibility of two stage curing method, the material preparation conditions, isothermal and non-isothermal curing kinetics, shape memory property, dynamic mechanical properties, tensile strength, microstructure, heat resistant, the storage life and stability of thermoset epoxy resin composites have been studied. At the same time, the kinetic equations of various systems have been established.Firstly, the appropriate room temperature and latent curing agents have been selected among a wide variety of curing agents. The non-isothermal differential scanning calorimetry (DSC) and gel time tests are used to investigate the feasibility of two stage curing method, the results prove that the two different curing stages can implement successfully. The optimal curing processes have been confirmed by non-isothermal DSC method with different heating rates, and various theory curing degree systems have been prepared. The characteristics groups and theory curing degree are studied by fourier transform infrared spectroscopy (FTIR) tests.Secondly, the n-order and autocatalytic reaction models under non-isothermal condition are used to fit the experimental results of two different curing stages, and the kinetic equations are established. On the other hand, the reaction mechanisms of two different reaction processes are discussed by three FR，FWO and KAS non-model fitting methods. The results show that the addition of latent curing agent hardly influence the first curing stage, and during this curing period, the latent curing agent is not triggered by carefully controlling the curing conditions. For the second curing stage, plenty of hydroxyl (-OH) are generated during the first curing stage, and these–OH promote the second curing stage effectively. Then, the model fitting method under isothermal condition is used to study thereaction processes, reaction mechanisms and the interplay between two different curing stages. The kinetic equations are established. The relationships between reaction time and conversion in various systems are successfully predicted by the FWO method. Lastly, the dynamic mechanical analysis (DMA) tests are utilized to determine the glass transition temperature (Tg) and storage modulus (Er). The fold-deploy shape memory tests are used to evaluate the shape-memory performance of thermoset epoxy resin composites, including shape memory response rate, response time, fixed rate and fold-deploy cycles times. The results show that the composites, after first stage curing, possess good shape memory property. The empirical equations between Tg and conversion are established by combining dynamic equations and predicted curves, showing the credible kinetic equation can guide the desired of the practical reactive process. The tensile tests and scanning electron microscope (SEM) characterization are used to evaluate tensile strength and fracture morphology respectively. Moreover, the storage life and stability of thermoset epoxy resin materials after first curing stage are evaluated by the fold-deploy cycles and standing storage tests. The results show that these composites can store for at least12months at room temperature. Moreover, the shape memory fixed rate can be kept above98%, and the second curing stage is not triggered.