| Ultra-high molecular weight polyethylene fibres, with outstanding mechanical properties, e.g. light weight, high specific strength and high specific modulus, have been used in different applications such as ropes, cut resistant textiles and bullet resistant composite materials. However, the poor creep resistance of UHMWPE fibres, which is determined by their simple molecular structure and the poor inter-molecular interaction of van der waals force, causes shortening of lifetime and is limiting for permanent loading of the fibres used in ropes. Therefore, the research on the route for improving the creep resistance of UHMWPE fibres and then realizing its continuous treatment is of great theoretical and practical significances.An intermittent irradiation equipment with high pressure mercury lamp was used as the UV light source and the influence of crosslinker and photosensitizer on the photocrosslinking and properties of UHMWPE fibres were evaluated to optimize the composition of the crosslinking liquid. A homemade intermittent irradiation equipment with low pressure lamps was made, and the UHMWPE fibres treated by photosensitizer were exposed to a variety of UV light sources respectively to detect whether it is possible to use the low pressure mercury lamps as the UV light source for photocrosslinking instead of the high pressure mercury lamp. An continuous UV irradiation equipment was made, and the effect of impregnation time of crosslinking liquid and UV irradiation time on the properties of UHMWPE fibres photocrosslinked by this equipment was investigated. The surface morphology of the fibres was observed by SEM, and the crystal structure of the fibres was investigated by DSC and XRD. The conventional mechanical properties of the fibres were determined using an Instron5966Materials Testing Machine. And the creep of the fibres was examined by loading a dead weight on a fibre.The results show that the crystallinity of the irradiated fibres decreases slightly. Horizontal cracks appear on the surface of the modified fibres and the number of the cracks increases with increasing concentration of the crosslinker. The creep resistance is improved significantly, and the structure and conventional mechanical properties are almost the same as the original fibre. The properties of the fibre treated with both of crosslinker and photosensitizer are inferior to the former and the mechanical properties decrease with increasing concentration of crosslinker. The intensity of UV irradiation of the low pressure mercury lamps is a quarter of the intensity of the high pressure mercury lamp, and this leads to a lower gel content of the fibres exposed to the low pressure lamps than the one to the high pressure lamp under a same irradiation time. Improvement of the creep resistance of UHMWPE fibres is significant and the plateau creep rate of the photocrosslinked fibres is67percentage of the original fibre. However, the tensile strength of the fibres irradiated by the low pressure mercury lamps are superior to the one treated by the high pressure mercury lamp in that the low pressure mercury lamps do not induce damage to macromolecules in amorphous region as the high pressure mercury lamp does. In the experiments of continuous UV irradiation, the influence of the impregnation time in the crosslinking liquid on the improvement of creep resistance of modified fibres is more important than the one of UV irradiation time. And the creep property can be improved significantly after impregnation with crosslinking liquid for6hours and then photocrosslinking with the continuous UV irradiation equipment for45minutes. |
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