Research Work for the Improvement of the Durability of Glass Fiber-Reinforced Nylon 66 by Modifying the Glass Fiber Diameter

As for the polyamide (nylon) resins, i.e., nylon 6, nylon 66, nylon 46 and so on, when they are reinforced by glass fibers (GF), their static mechanical strength and heat distortion temperature increase considerably, and many faults of them are improved. However, when repeating stress is applied to a GF-reinforced nylon, the interface stress concentration between nylon and GF is easily to happen and so, depending upon working condition, the damage phenomenon similar to fatigue flaking is often observed for the GF-reinforced nylon by the reason of the insufficiency of interface strength between nylon and GF. In this study, thus, it mainly focused on the improvement of the fatigue property of GF-reinforced nylon. Actually, we compounded of nylon 66 and GF the fiber diameter of which was smaller than conventional GF, and investigated the mechanical and physical properties of the nylon 66 / GF composite we prepared. As a result, it was recognized that the fatigue property of the nylon 66 reinforced by GF the fiber diameter of which was 6μm was improved compared to nylon 66 reinforced by ordinary GF whose diameter was 13μm. In addition, it was revealed that the values of static mechanical strength and impact strength of the composite consisting of nylon 66 and GF having the diameter of 6μm also increased in comparison with a conventional GF-reinforced nylon 66. Moreover, a good result with respect to the evaluation of high temperature oxidation stability was obtained for the nylon 66 reinforced by GF having the diameter of 6 μm. Our developed material based on nylon 66 / the modified GF composite has the properties that permit applying our new nylon / GF composite to the material used for the reduction gear of the Electric Power Steering (EPS) system used under severe condition.