Preparation And Property Of Polyurethane Composites Strengthened By Aramid Fibers

Composite material is made from two or more than two kinds of single material by artificial compounding using the physics or chemistry methods. Polyurethane has high tensile strength, high elasticity and elongation at break., and aramid fibers have high tensile strength and tensile modulus, high thermal resistance and low density. A kind of composite material with perfect mechanical property could be made by integrating the high elasticity of PU and the high rigidity of aramid fiber. In this paper, Preparation of polyurethane composites strengthened by Aramid fibers are investigated.Firstly, the polyurethane is synthesized using isocyanate and polypolyols by prepolymerization method. The influences of n(NCO/OH) in prepolymer and polymer on polyurethane are analyzed. An excellent technics to synthesize polyurethane is found as follows: polydiethylene glycoladipate is used as the polypolyols, n(NCO/OH) in prepolymer is 5:1, the time of prepolymerization is 150 min, after prepolymerization 1,4-butanediol is added, the n(NCO/OH) in polymer is 1.08, the time of curing action is 2-3 hr, the temperature of curing action is 80℃.Secondly, short aramid fiber is interfused into prepolymer in the middle step of preparation of polyurethane. Polyurethane resin composite reinforced by short aramid fiber is made by advance shaping and moulding process. The influences of advance shaping time, moulding time, the temperature and pressure of moulding, n(NCO/OH) in polymer and the fiber's concentration on property of composite are refocused. The proper molding process is obtained as following: advance shaping at 80℃for 4hr,then molding at 170℃for 30min keeping pressure at 4MPa ,cooling naturally down to room temperature. The proper n(NCO/OH) in polymer is 1.13.Thirdly, the surface of aramid fiber is modified by H₂ and air plasma treatment, the influences of air plasma treatment and H₂ plasma treatment on aramid fiber are investigated by the surface tensile force components testing, the fiber's surface morphology examination, the experiment of fiber methylene blue adsorption and the fiber's breaking tensile strength testing. The results show that: Plasma treatment can activate the aramid fiber, increase the polar groups of the fiber surface, increase the fiber surface tensile force and surface free energy. The total fiber surface tensile force was increased 37% to 63.2 MN·m^-1, and the percent of polarity P increased from 58.0% to 69.9% after H₂ plasma treatment for 3 min. The total fiber surface tensile force was increased 37.8% to 63.4 MN·m^-1, and the percent of polarity P increased from 58.0% to 66.7% after air plasma treatment for 3 min. After plasma treatment, the single fiber tensile strength did not have obvious change, and the tuber on the fiber surface increased, the fiber surface area became larger after plasma treatment. It has been suggested that air plasma treatment and H₂ plasma treatment are effective processes for aramid fiber while its excellent tensile mechanical strength can be retained.