Interfacial Design And Structural Properties Of Kevlar Fiber Reinforced Nylon 6 Composites

The structure of every arrangement of material confirms its existent forms, and then ensures its properties. The whole properties of composites relate to not only reinforcement phase and matrix phase, but also the interface between these two phases. Interface is a very important micro-structure of composites. As the bridge between reinforcement fiber and matrix, the interface has an important effect on the physical, chemical and mechanical properties of composites. However, the interface between fiber and matrix is the weak area in composites which are reinforced by fiber, therefore the improvement of interfacial adhesion, the hotspot in composites research, is of great significance.Chemical disposal were used to treat the surface of Kevlar fiber (KF), and interface of KF with different chemical properties was designed. The KF which treated and untreated were used to reinforce nylon6/Kevlar fiber (PA6/KF) composites, then PA6/KF composites with different interfacial properties were designed. X-ray Photoelectron Spectroscopy, Fourier Transform Infrared Spectroscopy, Differential Scanning Calorimetry, Environmental Scanning Electron Microscopy, Polarized Light Microscopy and the like were carried out to study the appearance and chemical components of KF, at the same time, particular attention was paid to the effect of surface treatment on the crystalline behaviour, melting behaviour, interfacial crystalline effect, mechanical properties and fracture morphologies of PA6/KF composites.The thesis chose two routes to treat KF: firstly, -COOH and -NH2 were induced onto the surface of KF by hydrolyzation; secondly, treated by adipyl choloride and toluene-2,4-diisocyanate individually; Thirdly, stabilized by carprolactam; Finally, The anionic grafting of nylon 6 onto the the surface of KF could be available.The results showed that the grafted polymer of the surface of Kevlar fiber is greatly similar to matrix, -COOH and -NH2 could catalyze the anionic grafting of carprolactam after they were treated by adipyl choloride, toluene-2,4-diisocyanate individually and then stabilized by carprolactam. The grafting degree of KF which was treated by adipyl choloride was higher than that of KF treated by toluene-2,4-diisocyanate.The isothermal crystallization of PA6 was dominated by nucleation while the KF played an role of heterogeneous nucleation agent in the process of crystallization ofPA6 and increased its crystalline rate, the effect of untreated KF was the most obvious, the KF treated by toluene-2,4-diisocyanate took second place; KF has improved the initial crystalline temperature (Tonset) of PA6 while reduced its total crystalline time (ttotal) during the nonisothermal crystalline process; the induction of KF also could influence the melting behavior of PA6; KF could do crystalline nucleation to matrix, and form interfacial transcrystallization, the nucleation of KF increased with crystalline temperature; under the same situation, treated KF could form compacter and more integrated transcrystallization than that of untreated KF.The composites which were reinforced by untreated KF would destroy from the interface, while the composites which were reinforced by treated KF would destroy from other places partly, which contributed to improving the tensile strength, flexural strength and flexural modulus, however, the impact strength declined. All these work provided important information for the interfacial optimal design of composites.