Chemical modification of apricot kernel shell waste and its effect on phenolic novolac epoxy composites

Abstract

Apricot kernel is one of the most abundant types of agro-waste in the eastern Anatolia regions of Turkey. In this study, apricot kernel shells (AKShs) were chemically modified using levulinic acid (LA) for the first time, and their potential for developing biobased composites was evaluated. Phenol novolac epoxy resin was used as matrix owing to its high thermal and superior adhesion properties. Shell treatments to improve interfacial bonding were carried out using alkali, acetic acid, and LA. These treatments were aimed at improving the mechanical properties, wettability, and bonding of the composites. Moreover, these treatments could prevent the deterioration of the fiber/matrix interface (hydrophilic and hydrophobic effect) and mitigate damage to the fiber during production, which is one of the main reasons for the reduced strength of the composites. The thermal characteristics, crystallinity index, chemical composition, and surface morphology of the untreated and chemically modified AKShs and composites were studied by thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy, respectively. In addition, the composites were analyzed in detail using mechanical tests and contact angle measurements. The chemical treatment using LA resulted in composites with superior mechanical behavior.