Effect of fiber surface treatment on the fiber-matrix bond strength of natural fiber reinforced composites

The interfacial shear strength (IFSS) between natural fibers and a thermoplastic matrix has been improved by the morphological and silane chemical modification of the fiber surface. An alkaline treatment was used to enhance both the matrix fiber wetting and the chemical surface modification in order to improve the physicochemical interactions at the fiber-matrix interphase. For characterization of the mechanical properties of such interphase, a modification of the micromechanical techniques commonly used in the characterization of the IFSS for circular-cross-section smooth fibers is proposed. The relationships developed for circular fibers were modified to incorporate the natural fiber perimeter instead of an equivalent fiber diameter. From the micromechanical test's results it was found that both surface modifications, preimpregnation and chemical, improves the fiber-matrix IFSS. Finally, the results obtained from the single fiber fragmentation test seem to better agree with the effective mechanical properties measured for the laminated material than those obtained with the pull out test. (C) 1999 Elsevier Science Ltd. All rights reserved.