Study of alkali and acetylation treatments on sisal fibers compatibility with low-amine/epoxy stoichiometric ratio

Abstract

Sisal fibers are one of the most commercially utilized as reinforcing agents in composite materials. However, sisal fibers are very hydrophilic because they contain many hydroxyl groups, so their interfacial bonding is low when mixed with a non-polar polymer matrix. One method to improve the fiber-matrix interfacial bond is to modify the sisal fiber surface with chemical treatment. This study evaluated the influence of various chemical treatments on the tensile properties and interfacial adhesion of sisal fibers reinforced with low-amine/epoxy stoichiometric ratio resin. The sisal fibers were subjected to a series of treatments, including 2 wt% alkali for 4 h, acetylation for 1 h, and a combined alkali and acetylation treatment. The FT-IR analysis confirmed the success of the acetylation process by the presence of the carbonyl signal (1728 cm−1). The XRD analysis indicated that the crystallinity index of the sisal fiber (65 %) was increased after alkali (75 %) and acetylation (66 %) treatments. The alkali-treated sisal fibers showed the highest tensile strength (728 MPa) but the lowest interfacial shear strength (17.7 MPa). The acetylated-treated sisal fibers exhibited the highest tensile modulus (44.5 GPa) and interfacial shear strength (25 MPa). However, the combination of alkali and acetylation treatments reduced the tensile strength of the fiber from 659 to 619 MPa. The TGA results revealed that the maximum degradation temperature of sisal fibers (344 °C) was increased after alkali (349 °C), acetylation (348 °C), and a combination of alkali and acetylation (350 °C) treatments. The results suggest that acetylation treatment is highly beneficial for advanced composite applications.