The Curing Kinetics And Process Optimization Of CMC/Epoxy Resin Composites

Sodium carboxymethyl cellulose(CMC),a kind of surfactant,have good dispersibility for CNTs and have potential applications to make the CNTs/epoxy composites.CMC is also a biocompatible polymer materials and can be used to prepare polymer matrix composites by blending or hybrid with other polymers.In this paper,the CMC/E44 and CMC/E51 composites were first prepared and the curing kinetics of E44 and E51 epoxy resin with and without CMC and cured with 4,4'-diamino diphenylmethane(DDM)hardener was studied by non-isothermal differential scanning calorimetry(DSC).The curing kinetic equations of studied systems were obtained.On this basis,considering the heat transfer and exothermic effects of curing process,the temperature and curing degree fields were simulated by finite element method and the macrokinetics(thermo-chemical kinetics)models were established.Based on macrokinetics and extrapolation,the optimization and analysis method of curing process was established.In the end,dynamic mechanical properties and thermal stability of compostites were studied by using DMA and TGA.The changes of activation energy(E)versus curing degree(a)were estimated by using Friedman,Kissinger-Akahira-Sunose and Starink isoconversional methods,respectively.The E resulted from different isoconversional methods are different,but the variations of E versus a obtained with different methods have the same trend even.For the E44 epoxy system,the E is significant decrease from 43.5 to 14.5 kJ/mol when the a increases from 0.05 to 0.95.For the CMC/E44,E51 and CMC/E51 systems,there are no obvious difference in E when the curing degree increases from 0.05 to 0.95.The approximative range of E obtained is 40?50 kJ/mol for CMC/E44 and 45?55 kJ/mol for E51 and CMC/E51.The isoconversional analysis showed that adding CMC maybe generate more polyether structure.nth-order model was used to describe the curing kinetics of CMC/E44/DDM and CMC/E51/DDM and the model parameters were calculated by Kissinger and Crane mothed.The model data simulation results indicated that the nth-order model had a great distinction with the experimental data.Sestak-Berggren(SB)model can be used to describe the curing reaction process of CMC/E44/DDM and CMC/E51/DDM.However,for the systems which E have a larger changes with a,the SB model is not good enough to describe their curing processes.For these systems,Sun-Gang E variable model was used,but the results indicated that the calculated value of the Sun-Gang model is inconsistent with the experimental value.In this case,we proposed a modified Sun-Gang E variable model based on the assumption of variable E to describe the curing kinetics of these systems.Compared with the SB model,this modified Sun-Gang E variable model showed a better agreement with the experimental data and also reflected the variations of E versus a.The modified Sun-Gang E variable model is not only applicable to the systems of this study,but also to other systems which the E have obvious changes.The curing kinetic equations of CMC/E44/DDM and CMC/E51/DDM were obtained through curing kinetic studies.And then,the macrokinetics of curing process were investigated and the temperature and curing degree fields were simulated by finite element method.The variation of temperature and curing degree fields versus time were obtained.The macrokinetic studies showed that the thermal shock can be formed within the matrix during the curing process.The effects of processing temperature,heating rate and substrate geometry of matrix on the thermal shock were discussed.The higher processing temperature,the faster heating rate,the thicker matrix,is the more significant thermal shock and the earlier peak of thermal shock occurs.The thermal stress of curing process was investigated by using macrokinetics.The stages and positions of thermal stress in curing process were pointed out.This is the theoretical evidence for explaining the surface cracking of the matrix in curing process.The research result showed that thermal stress is mainly appears at the curing and the post-curing heat-up stage.During the curing stage,the temperature gradient and curing degree gradient are major factors that caused thermal stress.For the post-curing heat-up stage,the temperature gradient is a major factor that causes thermal stress.In the whole curing process,the maximal thermal stress occurs at the surface of matrix.Through post-curing stage,the thermal stress could be eliminated.Combines the traditional extrapolation and macrokinetics,the evaluation and optimization method of curing process was established.Using this method,the calculation method and optimization step of curing processing time can be given theoretically.Because of the universality of the model derivation process for the thermosetting resin,the optimum method of curing process not only applicable to the systems of this study,but also to other thermosetting resin.The obtained conclusions have significance for the curing process optimization of thermosetting resin.The dynamic mechanical properties and thermal stability of CMC/E44 and CMC/E51 composites were investigated by using DMA and TGA.The effects of curing process on the properties were analyzed.Studies have shown that the influence of the curing process on the performance is very notable,which can be comparable to physical blending or chemical modification to some extent.By curing process optimization,the glass transition temperature(Tg)of cured epoxy E51 resin is comparable to the highest Tg which was reported by the literature,the decomposition temperature(T5)is significantly higher than that reported in the literature for this system.