Preparation Of MC Nylon 6/Carbon Fiber Composites By In-situ Polymerization

Carbon fiber-reinforced thermoplastic has attracted more and more attentions due to its advantages such as shorter shaping time,higher impact strength and good recyclability over carbon fiber-reinforced thermoset composite.However,the melt viscosity of the thermoplastic matrix is usually 100 to 1000 times higher than the uncured thermosets and the melt flowability is much lower than that of the prepolymer of thermoset.As the result,it is difficult to impregnate the thermoplastic into the continuous carbon fiber bundles,which has become one of the major technical obstacles for the development of continuous carbon fiber reinforced thermoplastic resin composites.Under this background,this dissertation tries to prepare MC nylon 6/carbon fiber composites by vacuum assistant resin infusion process(VARI)with in-situ anionic polymerization ofε-caprolactam,where the problem in impregnation of carbon fibers with high viscosity nylon 6 is avoided.The anionic polymerization process of MC nylon 6 resin is firstly investigated.With sodium hydroxide(NaOH)as the initiator and toluene diisocyanate(TDI)as the activator,anionic polymerization ofε-caprolactam was carried out under different temperature for different time.A series of MC nylon 6 resins have been obtained and the effect of polymerization condition has been investigated.The structures and properties of MC nylon 6 were evaluated by means of FTIR,DSC,TGA and WAXD.The relative viscosity measurement results revealed that the relative viscosity and viscosity average molecular weight of MC nylon 6 obtained at a polymerization temperature of160°C and a polymerization time of 40 min were as high as 4.84 and 3.3×10~4 g/mol,respectively.FTIR analysis showed that the infrared characteristic of MC nylon 6 was the same as the commercial nylon 6.DSC,TGA results demonstrated that the polymerization temperature and polymerization time have little effect on the thermal properties of the polymer while WAXD results confirmed that the crystal form of the resulting MC nylon 6 is alpha crystal form.A series of MC nylon 6/carbon fiber composites were then prepared employing the VARI process with the in-situ anionic polymerizationε-caprolactam.The mechanical properties,structure,thermal properties and morphology of the composites were evaluated with universal testing machine,FTIR,DSC,TGA,WAXD,metallographic microscope,scanning electron microscope.The relative viscosity and the viscosity average molecular weight of the matrix of the composite prepared at160°C for 40 min were 3.82 and 2.08×10~4 g/mol,respectively.The tensile strength of this composite was 197 MPa,the elongation at break was 5.9%,the bending strength was 310 MPa and the flexural modulus was 26.6 GPa.The DSC test revealed that the crystallization temperature of the matrix in the composite was similar to that of pure MC nylon 6 while lower than that of commercial nylon 6.On the other hand,the crystallization enthalpy and melting enthalpy of the matrix resin in the composites were significantly higher than those of the pure MC nylon 6 and commercial nylon 6,indicating that the carbon fiber has a significant promoting effect on the crystallization of the matrix resin.TGA results revealed that the decomposition temperature of the composites was higher than pure MC nylon 6,indicating that the addition of carbon fiber improves the thermal stability of the composite.WAXD results showed that carbon fiber has no effect on the crystal form of the matrix nylon resin.The metallographic microscope and scanning electron microscope pictures of the composite demonstrated that the carbon fibers were fully impregnated and evenly distributed in MC nylon 6 matrix.All the results suggest that it is basically practicable to prepare nylon 6/carbon fiber composite with VARI process.