A numerical model of the viscosity of an epoxy prepreg resin system

Abstract

The development of the viscosity.of a thermoset material during processing is complicated because of the dependence of the initial material state and the kinetic rate of conversion from a liquid to a solid material. Uncured thermoset materials typically have a low enough viscosity such that the consumption of energy to generate flow is relatively low. However, as the curing process advances, the flow mechanisms become hindered by the development of a network gel during crosslinking. Once the resin has reached the appropriate degree of cure for gelation, the resin system is incapable of large fluid-like deformations. In this research, the rheological properties of an epoxy resin system used in laminate processing were measured and numerically fit with a modification to the dual Arrhenius model to predict the progression of the viscosity during cure. The numerical results were compared with the experimental measurements, and it was found that the model predicts the experimental observations quite well. It was found that the initial degree of cure of the prepreg is not as significant a factor as the temperature rate dependence on the processing time between the point of flow onset and gelation. However, the minimum viscosity during processing is strongly influenced by the initial degree of cure of the prepreg system. IlPTRODUCTIONoper characterization of the progression in the P viscosity of thermoset resins is important in the methodology of defining appropriate processing conditions for various processing methods. For example, the minimum viscosity and the point of gelation are important parameters in the determination of the applied pressure and temperature profiles during processing of glass-fiber reinforced, copper-clad laminates. If the minimum viscosity is too high or the gel-point is reached too soon during processing, the consequence may include improper fiber wetting and diminished adhesion characteristics between the prepreg and copper-foil. The determination of the time and the degree of cure at gelation have also been found to play an important role in the prediction of the mechanical property development as well as the residual stress developed during the cure of thermoset resins [1][2][3][4][5].This study investigates the advancement of the viscosity and the point of gelation as a function of the initial degree of cure of a DICY cured epoxy system prepreg. With a modification to the dual Arrhenius model, it is shown that the viscosity and the point of gelation of the epoxy prepreg system can be predicted. MATERIALSThe epoxy resin used in this investigation is a DICY cured epoxy resin formulation used in the manufacturing of copper-clad laminates. After the epoxy resin system is applied to the glass fiber mat, the dimethylformamide and acetone solvents are evaporated

Determination of optimum cure parameters of 977‐2A carbon/epoxy composites for quickstep processing

“…Apart from the viscosity execution, another important factor determined from rheological analysis is the gel point (GP). It has been known that if the minimum viscosity is extremely high or the GP is attained rapidly during processing, the consequences may include improper fiber wetting and poor adhesion between fiber and matrix 28. The determination of GP is, therefore, very important as it plays a vital role in the prediction of mechanical property increase during the cure of thermosets resin.…”

Effect of chemical structure on the crosslinking behavior of bismaleimides: Rheological study

“…The most frequently used model to describe the viscosity change during the resin curing is dual Arrhenius viscosity model [60][61][62][63][64]:…”

An ex-situ state-based approach using rheological properties to measure and model cure in polymer composites

“…In the liquid stage, the focus of the models is on the viscosity as a function of conversion. [8][9][10][11] On the other hand in the second category, the reacting cross-linked polymer is assumed to be mechanically a solid (e.g., a thermoset past the gel point) but is undergoing a simultaneous chemical transformation. 5,[12][13][14][15] In these models, the effects of the viscous behavior of the material in the solid stage are usually limited to the calculation of relaxation modulus of an epoxy resin or prepreg.…”