Modelling of Curing Kinetics of Amine Cured Epoxy Resins for Vacuum Assisted Resin Infusion Molding Sudip Bhunia, Debdarsan Niyogi, Pramod Marru and Swati Neogi* Department of Chemical Engineering, Indian Institute of Technology, Kharagpur, 721302, India Epoxy resin, along with a suitable reinforcement such as glass, is used to manufacture windmill blades by vacuum assisted resin infusion molding (VARIM) process. For the simulation of VARIM process, the sub models are required to describe the rheological and thermochemical behaviour of the epoxy resin. In the present paper, the curing kinetics of amine cured epoxy resin, which is mostly used for wind blade manufacturing, are presented. The kinetic study is performed by measuring the exothermal heat generated during the curing of the amine cured epoxy resin system, using Differential Scanning Calorimeter (DSC), at different temperatures. The range of the temperature for the study is selected between the reaction onset temperature, which is about 70°C, and the peak reaction temperature, which is nearly 120°C. The reaction exotherm, as measured by DSC, is processed to obtain the reaction kinetic data such as the degree of reaction and the rate of reaction at different times and temperatures. A suitable model is proposed to describe the reaction kinetic data obtained experimentally. The unknown parameters of the models are determined by a nonlinear regression analysis on experimental data, while the kinetic rate constants are obtained based on Arrhenius Law. The proposed model is also compared with the models available in the literature. It is found that the proposed model is the simplest model, which accurately captures both the degree of cure and rate of cure qualitatively and quantitatively. Keywords: polymer chemistry, kinetics and mechanisms of reactions, mathematical modelling, composites, materials science and technology, polymers, rubber and plastics INTRODUCTION L arge and lightweight rotor blades boost up the power output of modern wind turbines. The stresses, strains and the forces on the blade tips exposed at approximately 90 m above ground are immense, which demands features such as toughness and weather resistance to survive an optimum life of 20 years. Such rotor blades are fabricated by vacuum assisted resin infusion molding (VARIM) process using amine cured epoxy resins. The choice of the resin used in VARTM depends on the wetting time and cure time of the manufacturing process. Also, the rate of resin cure depends on the process temperature and the exothermal heat generated during curing process, and it is nevertheless a function of pressure. Simulation of kinetics of amine cured epoxy resin formation based on trial and error has always been an expensive affair. Modern researchers employ computer simulation models for designing the process and one of the prerequisites for optimising the process parameters is the development of a suitable kinetic model. The chemical reaction that occurs during the curing of epoxy matrices plays a vital role in the process modelling of epoxy‐ based composites. The curing process is highly exothermic in nature, changing the liquid reactants to rigid cross‐linked structure that become insoluble and infusible. Several studies have shown that the curing of epoxy resins are typically governed by autocatalytic mechanism, which can be justified by the fact that epoxy group reacts with a primary amine and produces a secondary amine and then forms a tertiary amine. These curing reactions are also accelerated by the catalytic action of the hydroxyl group that is formed as a by‐product from the amine epoxy reaction. In general, cure kinetic models can be classified in two categories, namely, mechanistic kinetic models and the phenomenological or empirical kinetic models. An accurate mechanistic model to describe the curing kinetics is impossible because of the fact of the large variations in the resin formulations and most often, the exact formulation is not known. Therefore, efforts have been directed towards establishing phenomenological models for epoxy resins using differential scanning calorimetry (DSC). [1–3] The dynamic curing, [4] and the isothermal curing experiments are the two different approaches for cure kinetic study. Of these, the isothermal mode is often preferred because of its ability to produce the heat generation as a function of time without the occurrence of thermal gradients during the cure process, [5] as well as the data fitting to the cure kinetic model parameters is easier when isothermal data are available. LITERATURE REVIEW Some researchers started from the most fundamental empirical form, the simplest being an nth order two‐parameter cure kinetic rate equation [1,5,6] and given by: da dt ¼ kð1  aÞ n ð1Þ *Author to whom correspondence may be addressed. E‐mail address: swati@che.iitkgp.ernet.in Can. J. Chem. Eng. 92:703–711, 2014 © 2013 Canadian Society for Chemical Engineering DOI 10.1002/cjce.21862 Published online 5 June 2013 in Wiley Online Library (wileyonlinelibrary.com). VOLUME 92, APRIL 2014 THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING 703