Effects of drying temperature, mercerizing, and coating on the properties of Colombian Coir fibers and their interfacial adhesion with polylactic acid

Abstract

In the present study, the influence of drying temperature, mercerization, and epoxy coating on the physicochemical and mechanical properties of Colombian CFs and their interfacial adhesion with a PLA matrix were studied. CFs were extracted from the mesocarp of Cocos nucifera husks by retting. The fibers were oven-dried at two drying temperatures, 40 °C and 90 °C. These samples were then mercerized and coated with epoxy resin. Pullout tests were performed to assess the bonding between the fibers and the PLA matrix. The results revealed that drying at 90 °C significantly enhanced fiber stiffness, yielding a Young’s modulus of 1.99 ± 0.48 GPa. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) revealed that the mercerization treatment partially removed lignin from the surface of the fibers, increasing their roughness and facilitating mechanical interlocking. The subsequent epoxy resin coating introduced functional groups that can enhance the wettability of PLA. Compared with the untreated fibers, the combination of the mercerized and polymeric coatings resulted in a 62% increase in the Young’s modulus (3.57 ± 0.95 GPa) and a 43% increase in the tensile strength (108.43 ± 35.72 MPa). Additionally, single-fiber pull-out tests revealed that mercerized and coated fibers (CM-PLA) had double the interfacial shear strength (0.916 MPa) of untreated fibers, demonstrating improved fiber‒matrix adhesion.