Preparation And Properties Of Carbon Fiber/mullite Whiskers Synergistic Reinforced Resin-based Friction Materials

Carbon fibers and ceramic whiskers are often used as reinforcing fibers for resin-based friction materials because of their advantages of high specific strength,high specific modulus,high temperature resistance and fatigue resistance.However,the inherent smoothness and poor alignment of the carbon fiber and ceramic whiskers lead to the fiber/resin interface and the whisker/resin interface are prone to debonding and peeling,which limites the application in the harsh conditions.Increasing interface bonding strength between the reinforcing fiber and the resin can improve the structural stability,mechanical properties and thermal stability of the composites,which enhanced the wear resistance.Therefore,effective strategy to improve the interface bonding strength between reinforcing fibers and resin can expand the application fields.In this work,carbon fibers and mullite whiskers were used as reinforcing fibers in composite materials.The PDA and PAMAM coatings that on the surface of reinforcing fibers were prepared by liquid deposition and chemical grafting,which achieved the goal of non-destructive surface modification of reinforcing fibers.The composites were prepared by hot pressing methods,and further analyzed the influence of PDA and PAMAM coatings on the properties of carbon fiber/mullite whisker resin-based friction materials.The main conclusions were as follow:(1)Carbon fiber and mullite whiskers were used as reinforcing fibers to synthesize multiple phases in a phenolic resin matrix through a physical blending method,and a multi-scale collaborative reinforcement system to improve the friction and wear properties and mechanical properties of composites.The CP-20(20 wt%of carbon fibers and the 5 wt%of mullite whiskers)had the best performance in the prepared resin-based friction materials.By comparing the performance of composites prepared with different carbon fiber and mullite whisker addition ratios,it could be concluded that when the carbon fiber addition amount is 20 wt%The wear rate,average friction coefficient and fluctuation rate were 5.75×10-6 mm3(N·m),0.54 and 13%,respectively,showing the best comprehensive performance.(2)Dopamine can be deposited on the surface of carbon fibers and mullite whiskers to form nano-sized PDA coatings under aerobic and weak alkaline conditions.The-NH2 and-OH hydroxyl groups on the PDA coatings increased the surface activity of the reinforcing fibers.The surface was transformed by characterization testing of PDA modified composites with different concentrations.As the PDA concentration was 2 g/L,the composite had the best comprehensive performance,and the bending strength was 80.7 MPa,and it was improved by 34.1%than the unmodified composite.The wear rate of the composite was 2.4×10-6 mm3(N·m),which was 58.3%lower than that of the unmodified composite.(3)The surface functional groups of carbon fibers and mullite whiskers dendrimer secondary functionalized modified with PAMAM were analyzed by FITR,XPS and other methods.The result was confirmed that the polyamide-amine was successfully grafted onto the polydopamine coating through with-NH2 by Michael addition reaction.And through the analysis of the SEM images of the fiber surface,PAMAM macromolecules gradually formed an uniform,continuous functional coating on the fiber surface with the increase of the number of synthetic PAMAM generations.(4)The mechanical properties and tribological properties of composites which modified by PDA and PAMAM had been compared and analyzed.The results showed that chemically grafted of PAMAM could better improve the interfacial bonding strength between reinforcing fibers and resin.The bending strength was 104.6 MPa,and the wear rate was 0.91×10-6 mm3(N·m).Compared with 2.0PDA-CP.The bending strength was increased of 29.6%and the wear rate was 62.1%lower than 2.0PDA-CP.