Evaluation of Thermal Behavior and Cure Kinetics of a Curauá Fiber Prepreg by the Non-Isothermal Method

Abstract

Curauá fibers have low-cost, low density, biodegradability and offer a relative high tensile strength level when applied in composites materials. The prepreg is a composite material constituted by fibers impregnated with a measured amount of resin matrix. Learning more about how the thermal properties of the matrix can be affected by curauá fibers, this work evaluated the thermal behavior and cure kinetics of a curauá fibers/ epoxy prepreg through Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). The in natura or alkali treated (KOH or NaOH) curauá fibers blankets impregnated with epoxy resin were prepared using a manual rolling process. The prepreg samples containing 20 wt.% of fibers were analyzed when the matrix in the composite presented a semisolid tacky (B-stage). The prepreg cure kinetics was investigated by a non-isothermal isoconversional method, and the Tg was evaluate using the DSC data. The variables related to the curing kinetics were obtained on dynamic conditions with heating rates of 2.5, 5.0 and 10 °C/min. The prepreg activation energy was calculated at a given function of the extent of conversion. According to the dynamic runs, the prepreg Tg was higher for treated fibers than in natura. The 2.5 °C/min rate provided a curing cycle with a lower and controlled temperature when compared to the others heating rates and the humidity weight loss of prepreg amounted was ~2.8%. The KOH prepreg presents the highest activation energy and the in natura prepreg the lowest one. The kinetic conditions established will be used in further experiments to obtain natural fibers composites from prepregs.