The Study On Interfacial Modification Of Carbon Fiber Reinforced Nylon 66 Composites

Nowadays,carbon fiber(CF)reinforced nylon 66(PA66)composite materials are widely used in various fields of industrial production.However,the surface of pure CF is chemically inert because there are no active groups.Thus the interfacial bonding strength with PA66 is weak and the reinforcement of CF cannot be effective.In general,the CF reinforced thermoplastic resin is processed by melt blending and injection molding.Therefore,it is necessary to consider whether the modified CF has strong thermal stability,the modified surface structure is maintained during processing and the interfacial compatibility of the composite is improved.In this paper,in terms of two different chemical grafting methods,polyethyleneimine(PEI)with a large amount of active amino groups and high resistance were used as bridge to graft multi-walled carbon nanotube(MWCNT)onto the surface of CF.The main contents and results are as follows:(1)A double grafted layer structure(CNT@PEI)was formed on the surface of the CF by an amidation reaction of the acid-oxidized CF.The XPS results confirmed CNT@PEI-CF was covered with a double grafted layer.Interface stability investigated showed thermal stability(under injection molding temperature,about 270 ?)and structural stability of CNT@PEI-CF/PA66 interface were both improved,but PA66 crystallization behavior affected by CNT@PEI-CF was identical with that of pure PA66.The contact angle tests exhibited that its compatibility with PA66 was also enhanced.Its interfacial shear strength(IFSS),composite tensile strength and elastic modulus increased by 64.74%,27.58%and 22.68%compared with that of untreated-CF and composite,respectively.The appearance of the"fish scale-like "fracture morphology resulted from the double grafed layer modification is the strong evidence for the interface enhancement of the composite materials.This CF surface modification method can also be extended to most other thermoplastic resin composites.(2)In order to avoid the damage of carbon fiber and the environmental pollution of toxic chemical agents for strong acid oxidation treatment,dopamine(DA)is used to self-polymerize on the surface of carbon fiber as polydopamine(PDA),the PEI and CNT@PDA were grafted onto the surface of the CF by Schiff base reaction between carbonyl and amino groups,respectively.The results of SEM observation showed that a large number of MWCNT were uniformly distributed in three-dimensional network on the surface of CF.XPS analysis showed that the MWCNT was grafted on the surface of CF by Schiff base reaction.The TGA showed that the thermal decomposition temperature of PDA was much higher than processing temprature of PA66,and CNT@PDA-CF showed good thermal stability.CNT@PDA-CF/PA66 composites also exhibited excellent interfacial structural stability,crystallization stability and good interfacial compatibility.The IFSS and tensile strength of its composites of CNT@PDA-CF/PA66 increased by 52.43%and 19.24%compared with that of untreated-CF/PA66,respectively.The "fish scale-like" fracture morphology on the surface of the fiber in the tensile fracture resulted from double grafted layer modification is the clear evidence for the interface enhancement.