Study On The Preparation Of Para-Aramid Fiber Reinforced Comosite Tape And Its Performance

Para-aramid fiber had excellent performance such as high tensile strength, high modulus, low heat shrinkage and low breakage elongation, therefore it became an ideal reinforcing fiber material and has been widely used in many fields. In this thesis, water-borne polyurethane (WPU) and high density polyethylene (HDPE) were used as matrix, para-aramid fiber reinforced composite tapes were made by using a home-made device with different processing conditions. In order to find optimal processing parameters, a statistical analyzing method was taken to evaluate the mechanical performance of the resultant tapes. Meanwhile, the moist aging properties of the resultant tapes were also investigated.The mechanical results of the composite tapes were analyzed by using Weibull statistics, the statistical stress and size parameter were used to characterize the tensile strength and its deviation, therefore the optimal processing parameters could be obtained. The result shows that for the WPU matrixed composite tapes, the optimal heating temperature was 180℃, the optimal speed of fiber passing through the heating box was 0.36m/min and the optimal stress for the tape formation was 19.6MPa. While for the HDPE matrixed composite tapes, optimal tapes could be got when the heating temperature was 260℃, the speed of fiber passing through the heating box was 0.36m/min, and the stress for the tape formation was 16.3MPa. When the WPU was used as matrix, the volume fraction of para-aramid fibers in the composite tapes was about 80%, the fibers were adhered together, then the tension disproportion of single filaments in para-aramid fiber bundle was effectively avoided and the actual tensile strengths of the prepared composite tapes were greatly higher than their theoretical values. For HDPE matrixed composite tape, the volume fraction of para-aramid fibers in the composite tapes was about 7%, the actual tensile strengths of the composite tapes were a little bit higher than their theoretical values.The results of moisture content measurement showed that the absorption characteristics of the para-aramid fiber reinforced composite tape, the moisture absorption of WPU matrixed and HDPE matrixed composite tape both increased rapidly at the early hygrothermal aging, and then the increase in the moisture absorption changed slowly until an equilibrium moisture content was reached. The tensile strengths of the prepared composite tape decreased with the increase of the moisture content, the final tensile strength of WPU matixed composite tape was about 75% of their original tensile strength, and the final tensile strength of HDPE matixed composite tape was about 65% of their original tensile strength.The effects of the moisture environments on the dynamic mechanical thermal properties of the para-aramid fiber reinforced composite tape were investigated by dynamic mechanical thermal analysis (DMTA).The results showed that the storage modulus (E') of the WPU matixed composite tape and the HDPE matixed composite tape decreased with hygrothermal aging time, while the loss factor(tanδ)increased, and the decrease in glass transition temperature (Tg) of the composite tape was relative to the increase in the moisture absorption of the composite tapes.The results of scanning electron microscope (SEM) showed that decrease in the tensile properties of the composite tapes in moisture environments was caused by the swell and plasticization of matrix, the interfacial debonding and resultant microstructure changes of matrix and interface.