Advanced polymer fibers/films based on synthetic nanocomposites and regenerated cellulose

This dissertation deals with several fundamental studies on structure, property and processing relationships of two new types of advanced polymer fibers and films based on: (1) polymer nanocomposites containing modified carbon nanotubes (CNTs) or nanofibers (CNF), (2) regenerated cellulose wet spun from environmentally friendly solvents. Structural changes during deformation, including those of crystal structures and of overall morphology of nanocomposite fibers and films, were investigated by in situ synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). Structures of polymer nanocomposites and of cellulose solution were also characterized by using rheology and laser light scattering, respectively.; The small dimensions and unique physical properties of CNT and CNF can be useful over a wide range of polymer applications, such as nanocomposites. An in-depth understanding of interactions between CNT/CNF and polymer chains as well as structures of resulting nanocomposites is essential for further development of CNT/CNF polymer nanocomposite fibers.; Surface modifications of CNT/CNF are an effect pathway to affect the filler/polymer interactions and the morphology of nanocomposite, such as CNT/CNF dispersion, structure and orientation of both CNT/CNF and polymer chains in nanocomposite. In this study, surfaces of CNT/CNF were modified using several types of functional groups and the resulting structure-property relationship of polymer nanocompoistes was investigated. CNF modified with short hydrocarbon chains (octadecylamide groups) was used to toughen a stiff ultra-high molecular weight polyethylene (UHMWPE) matrix. The modified CNF served as a solvent carrier in UHMWPE to soften the stiff polymer matrix. It was proposed that an interfacial solubilization of the long-chain polymers could significantly enhance the elongation-to-break ratio during deformation, resulting in a super-tough UHMWPE film/fiber. In UHMWPE/low molecular weight PE blend system, the octadecylamide modified multi-walled nanotube (MWNT) could form a network and increase the relaxation time of the system, thus favoring the formation of highly oriented shish structures and inducing the crystallization during flow. This finding could be very important for processing and developing of MWNT/UHMWPE fibers and films.; A dense layer of alkyl fluoride chains on MWNT (FMWNT) greatly improved the compatibility of FMWNT with fluoro-ethylene-propylene (FEP) polymers, whereby good dispersion of FMWNT in the matrix could be achieved, thereby improving the yield strength and modulus of FMWNT/FEP nanocomposite fibers; When stretching at 140°C, the acidic groups on oxidized MWNT (OMWNT) induced strong polar-polar interactions between OMWNT and polyvinylidene fluoride (PVDF) chain and facilitated the alpha phase to beta phase transformation of PVDF as well as the load transfer process; while the weak interaction between FMWNT and PVDF chain resisted the alpha phase to beta phase transformation of PVDF, resulting in FMWNT/PVDF films having a higher stress but lower elongation when compared with those of OMWNT/PVDF films. The dis-continous hydrophobic and hydrophilic regions on the surface of OMWNT and OCNF could induce nano-channel formation in the poly(vinylalcohol) (PVA) matrix, initially observed in OCNF/PVA gel fibers as well as hot-drawn fibers and finally was used as composite membranes for water filtration.; The structure and processing relationship of regenerated cellulose fibers from environmental friendly solvents (NaOH/urea or thiourea aqueous solution) at different wet spinning processes was also studied. The crystallinity, crystal size and orientation for the regenerated cellulose fibers changed under different spinning conditions. At high flow rate and high draw ratio (e.g. in the multi-roller drawing process), the crystal orientation of the regenerated cellulose fibers was significantly enhanced. Several methods including flow...