Improving adhesion between kevlar®129 fibers and natural rubber matrix using morphological treatments and coupling agents

Kevlar fibers are known for their exceptionally high tensile strength, and hence used in a wide variety of high performance applications ranging from military to aerospace and civil applications. However, the expected strength of composites fabricated using Kevlar fibers has not been reached due to poor interfacial adhesion between the fiber and matrix of the composite. This poor interfacial adhesion has been attributed to the highly crystalline and oriented molecular structure of the fiber. Herein, we present new methods to improve the adhesion between Kevlar fibers and natural rubber matrix. Pre-Treatments were used to create new surface morphologies on the fiber. The pre-Treated fibers were then subject to treatments with coupling agents. The coupling agents were soaked also in the presence of supercritical carbon dioxide (scCO²). Treated fibers were embedded in rubber matrix and adhesion was measured by fiber bundle pull-out adhesion test. Adhesion was found to improve by around a 100%. Comparative results are reported for both untreated fibers and a range of pre-Treatments. Failure analysis of fiber surface revealed a suppression of interfacial failure. The effect of pre-Treatments on fiber properties are also characterized, and the optimization between fiber properties, fiber-matrix interface properties, and overall composite properties are discussed.