Study On The Reinforcing Effect Of Glass Fiber And Carbon Nanotubes On Polymer Composite

The interface between the reinforcements and resin has a significant influence on the mechanical properties of the composites since the interface plays an important role on transferring the load or other information from the resin to reinforcements. Inside the interface, the composition, the arrangement of molecule, thermal property, and mechanical properties vary with position in gradual or sudden manner. To improve the properties of the composites, improving the wetting behavior between the reinforcement and resin is critical. Surface modification of reinforcements can increase the wetting property between the resin and reinforcement and can consequently improve the properties of the composites.The reinforcing effect of the glass fiber and the carbon nanotube on polymer composites as well as their surface modification has been investigated in this study. The present work includes five parts as following.(1) On the basis of Young's equation, Fowkes-van Oss-Chaudhury-Good surface energy method (FOCG Method) and Owens method, the changes of surface energy and the interfacial energy between the glass fiber and the epoxy after the modification of glass fiber using various silane coupling agents have been studied. For the most of the traditional methods, interfacial energy should be calculated by measuring contact angles of several kinds of liquid on the surface and the data are influenced by many factors such as humidity and temperature, so the procedure is complicated and the repeatability of the data is not very good. What is most important, contact angle of the liquid on some materials such as glass microparticle and nanotube composites can not be measured because of the precision of the contact angle measurement instrument. To address this issue, we developed a new method to determine the surface energy and interfacial energy. Using AFM method we can calculate the surface energy of the functional glass fiber and interfacial energy by measuring the micro-contact-angle between the glass and resin. This method can overcome the disadvantages listed above and take the reaction between the resin and modified glass fiber inside the interface which could influence the surface and interfacial energy into account. In order to prove the veracity of the traditional methods (FOCG method and Owens method) and AFM method, the mechanical properties of the composites were also tested.(2) Many researches have proved that only using silane coupling agents to modify the glass fiber, no significant improvement of wetting behavior between the resin and the glass fiber was found. We combined the silane coupling agent and glycidyl methacrylate (GMA) to modify the glass substrate, and AFM was used to study the wetting behavior between this kind of functionalized glass substrate and epoxy. When y-Methacryloxypropyl trimethoxysilane (KH-570) was grafted to the glass substrate, the GMA molecule could attach to the glass substrate through the reaction of unsaturated double bond belonged to KH-570 and GMA molecules. The AFM results indicated that the epoxy resin could wet PMGA-functionalized glass substrate well.(3) A practical use of chemical modifications of MWNTs for improving the reinforcing effect of nanotubes on water-soluble epoxy was demonstrated. With the aid of ultrasonication, the resulting MWNT-PAA reinforced epoxy composites efficiently due to existence of strong covalent linkage with epoxy. The high degree dispersion of MWNT-PAA in matrix provides strong interaction between carbon nanotubes and the epoxy and thus increasing the mechanical properties of the epoxy composites. Mechanical test confirmed the reinforcing effect of MWNT-PAA for composites. The SEM analyses revealed that a fine dispersion of MWNTs was achieved throughout the epoxy matrix due to high solubility of MWNT-PAA and strong interaction between the nanotubes and epoxy.(4) The carboxylic groups of the MWNT-PAA were converted to acyl chloride-functionalized MWNT by using SOCI2, then the nanotubes were reacted with octadecylamine (ODA) to yielded MWNT-ODA. After the segment of octadecylamine replaced the carboxylic groups on the MWNT-PAA, the solubility of MWNT-ODA changed a lot compared to MWNT-PAA. The MWNT-ODA becomes soluble in many organic solvents but insoluble in water. The preparation of organic solvents soluble carbon nanotubes from water soluble carbon nanotube has never been reported. The mechanical properties of SBS were enhanced by adding MWNT-ODA. According to the SEM results of the fracture surface of the composites, the interfacial interaction between the SBS and MWNTs were increased by this modification.(5) In order to further reveal the dispersion of MWNT-ODA in SBS, MWNT-ODA/SBS thin films were prepared by spin-coating the MWNT-ODA/SBS chloroform solution on Si substrate. The AFM results indicated that when MWNT-ODA at low concentration, the MWNT-ODA had a uniform dispersion in SBS, but when the concentration of MWNT-ODA exceeded 1 wt%, the nanotubes self-assembled forming sphere structure. The diameter of the sphere is related to the concentration of MWNT-ODA added, the thickness of the composites thin film and the concentration of MWNT-ODA/SBS solution. According to the AFM and SEM results, the sphere was composed of MWNT-ODA and SBS. The phase separation of MWNT-ODA and SBS indicated the interaction between the MWNT-ODA and SBS was not strong enough to overcome the cohesive force between the MWNT-ODA, thus at high MWNT-ODA concentration the MWNT-ODA and SBS become phase separation.