Curing kinetics study of chemically modified pineapple leaf fiber/epoxy composite

Abstract

Agricultural by-products have long hinder farmers, and subsequently, the food supply chain. Making use of their natural by-products will both reduce waste and increase industrial production. In particular, pineapple leaf fibers (PALF) can be extensively studied. Here, the curing kinetics of chemically modified PALF/epoxy resin crosslinked by an anhydride hardener was investigated by non-isothermal and isothermal methods with the differential scanning calorimetry technique. In this study, the Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa methods, as well as Kamal's model, were employed to analyze the curing behavior of epoxy in non-isothermal and isothermal processes, respectively. The highest activation energies for pure epoxy and PALF/epoxy composite calculated differ when using the methods. Additionally, a decreasing trend in the activation energy values during the late stages of epoxy curing was observed. The results from Kamal's model indicate that the k 1 values of the PALF/epoxy composite are only greater than those of pure epoxy at 100°C and 110°C. However, all the k 2 values of PALF/epoxy are greater than those of pure epoxy. Additionally, the m value of the PALF/epoxy composite is lower than that of pure epoxy only at 100°C, while the n and m+n values of the PALF/epoxy composite are all greater than those of pure epoxy. Moreover, the results reveal that the Cure Index of the PALF/epoxy composite was larger than ΔH* and smaller than ΔT*. With PALF, it was found that the epoxy resin’s curing rate was increased and the activation energy was reduced. Meanwhile, the degree of crosslinks was less than that of the virgin resin. It is speculated that the hydroxyl groups on the plant fibers and the amine groups on the coupling agent-modified fibers can promote the cross-linking reaction. However, the curing reaction of the composite is affected by steric obstacles and high viscosity resulting from the addition of PALFs.