Study On Flame Retardant Properties Of RTM Molding Fiber Reinforced In Situ Polymerized Nylon 6

The melt impregnation process of continuous fiber reinforced thermoplastic composites has the advantages of relatively simple process and easy implementation.However,due to the high viscosity of the thermoplastic resin,the impregnation difficulty of the fibers is increased,which reduces the degree of fiber dispersion and the quality of resin coverage on the fibers,thereby affecting the mechanical properties of the product and not conducive to the molding of complex samples.In addition,due to the inherent flammability of resin-based composite materials,their application is highly restricted in places with high fire safety requirements such as high-speed trains and airplanes.This project utilizes the low viscosity characteristics of monomer resin molecules to design and build an in-situ polymerization fiber reinforced PA6RTM molding experimental platform.Multiple flame retardants suitable for this molding process were selected,and the effects of different addition methods of flame retardants and monomer resin injection and mixing temperature on the uniformity of composite material products and the degree of flame retardant precipitation were explored;The effects of different kinds and contents of flame retardants on the flame retardant properties of composites were investigated,and the flame retardant mechanism was revealed.The flame retardant model of RTM fiber reinforced in-situ polymerized nylon 6 composites was initially established.The mechanical properties and thermophysical properties of composite products with different types and contents of flame retardants were further compared and analyzed,and their influence laws were discussed.The main research results are as follows:1.According to the principle of monomer polymerization,an experimental platform of flame-retardant fiber-reinforced in-situ polymerization PA6 RTM was designed and built,which included three units:resin providing device,reaction molding device and air pressure adjusting device.The flame-retardant fiber-reinforced nylon 6 composite board was successfully prepared,and taking C as an example,the best addition mode and mixed injection temperature of flame retardant were determined.The best mixed injection method is to place the flame retardant in equal parts in the A and B material tanks for melting,stirring,vacuuming,and then mixed and injected into the preset fiber mold;The optimal injection temperature is 95℃.2.Flame-retardant fiber-reinforced composite products were prepared by RTM molding,and the flame retardant effects of three kinds of flame-retardant fiber-reinforced composite materials were proved by various evaluation methods such as limiting oxygen index,vertical combustion grade and cone calorimetry test.The results show that the composite with flame retardant C has the best flame retardant effect,and when the content is 15wt%,the total amount and rate of heat release of the composite are significantly reduced.The flame retardant mechanism of the optimal flame retardant on fiber reinforced composites was analyzed by means of thermogravimetry and thermogravimetry-mass spectrometry.It was concluded that the optimal flame retardant C had synergistic effect of nitrogen and phosphorus,and had both gas phase and condensed phase flame retardant characteristics.At the same time,combined with the influence of fiber on the"wick effect"of composites,a flame retardant model of RTM fiber reinforced in-situ polymerized nylon 6composites was established.3.Based on the above research,the crystallinity,melting point,thermal deformation temperature,density,porosity and mechanical properties of composite products with different kinds and contents of flame retardants were investigated,and the effect of fiber content on the mechanical properties of composite products was studied.The results show that with the increase of flame retardant content,the mechanical properties of the three flame retardant composites and the crystallinity of the matrix resin show a trend of increasing first and then decreasing,and the thermal deformation temperature and the melting point of the matrix resin of the three flame retardant composites basically show a downward trend.The mechanical properties of composites increase linearly with the increase of fiber content.Except for the flame retardant B,the addition of C and A will not reduce the conversion rate of monomer resin.Comprehensive analysis shows that when the addition amount of flame retardant C is 15wt%,the limiting oxygen index is 28.5%,the vertical combustion grade reaches UL94V-2,and the flame retardancy is the best.At this time,the tensile strength,notch impact strength,flexural strength,flexural modulus,and interlaminar shear strength of the composite sample are197.55MPa,66.84kJ/m~2,218.4MPa,5.64GPa,and 26.95MPa,respectively,except for the impact strength,The other mechanical performance indicators are higher than those of composite materials without flame retardants added.