| Summary: | 博士 === 國立臺灣科技大學 === 高分子系 === 97 === In this study, the drawing behavior and physical properties of gel fiber specimens of UHMWPE ( U ) / LMWPE ( L ) and UHMWPE ( U ) / carbon nanotubes ( CNTs ) blends were investigated using compositions of gel solution and drawing processes. The influence of draw ratios ( DR ) of gel-spun ultrahigh molecular weight polyethylene ( UHMWPE ) fibers on resultant morphologies, tensile, degrees of orientation and crystal phase transition properties were investigated using wide angle X-ray diffraction ( WAXD ), differential scanning calorimetry ( DSC ) and scanning electron microscopy ( SEM ). The anisotropic crystalline structure with full concentric circular rings originally shown on the WAXD patterns of the as-prepared and drawn UHMWPE fibers gradually transform into oriented fibers with azimuthal spots on the equator as their DR values increase from 1 to 20, in which their orthorhombic crystals, percentage crystallinity, crystalline orientation and the birefringence values increase significantly. As evidenced by SEM and WAXD analysis, the chain-folded molecules originally present in kebab crystals of the as-prepared UHMWPE fiber specimens gradually transformed into shish-like crystals with relatively high orientation as their DR values increase from 1 to 20. In contrast, the crystallinity and crystal orientation values of the drawn UHMWPE specimens increase only slightly, as their DR values increase from 20 to 40, wherein both crystallinity values of orthorhombic and monoclinic crystals increase slightly. In fact, barely any oriented kebab but only shish crystals were observed on the surfaces of drawn UHMWPE fiber specimens with DR values higher than 20. The birefringence values increase only slightly with further increasing DR values, while crystallinity and crystal orientation values of the drawn UHMWPE fiber specimens remained relatively unchanged as their DR values increase from 40 to 150. In the meantime, the monoclinic crystals gradually grow at the expense of the orthorhombic form crystals as the DR values of drawn UHMWPE fiber specimens increase from 40 to 150. Possible reasons accounting for these interesting properties found for the drawn UHMWPE fibers with varying draw ratios are proposed in this study.
Moreover, a systematic study of the influence of the CNTs contents, UHMWPE concentrations and spinning temperatures on the ultradrawing properties and deformation mechanisms of a series of fiber specimens prepared from varying concentrations of gel solutions of ultrahigh molecular weight polyethylene and carbon nanotubes blends is carried out. The CNTs contents, UHMWPE concentrations and spinning temperatures of UHMWPE and CNTs added gel solutions exhibited significant influence on their rheological and spinning properties and the drawability of the corresponding UHMWPE/CNTs as-prepared fibers. Tremendously high shear viscosities ( �喒 ) of UHMWPE gel solutions were found as the temperatures reached 140 ℃, at which their�n�喒 values approached the maximum. After adding CNTs, the �喒 values of UHMWPE/CNTs gel solutions increase significantly and reach a maximum value as the CNTs contents increase up to a specific value. At each spinning temperature, the achievable draw ratios obtained for UHMWPE as-prepared fibers prepared near the optimum concentration are significantly higher than those of UHMWPE as-prepared fibers prepared at other concentrations. After addition of CNTs, the achievable draw ratios of UHMWPE/CNTs as-prepared fibers prepared near the optimum concentration improve consistently and reach a maximum value as their CNTs contents increase up to an optimum value. In fact, the achievable draw ratio of UHMWPE/CNTs as-prepared fibers prepared from the gel solution with the optimum CNTs, UHMWPE composition and spinning temperature are about 15 to 30% higher than those of the UHMWPE as-prepared fibers prepared at the optimum concentration. In order to understand these interesting drawing properties of the UHMWPE and UHMWPE/CNTs as-prepared fibers, the birefringence, thermal, morphological and tensile properties of the as-prepared and drawn fibers were investigated.
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