Commercial PPTA fibers ( Kevlar 49® and Twaron 1055®) and copolyaramid fibers (Trevar®) are subjected to various hydrolytic and chemical treatments. Tensile modulus, tensile strength, and elongation at break are measured, and mechanical property deterioration is compared. Copolyaramid fibers show improved hydrolytic stability and chemical resistance compared to PPTA fibers. The time dependence of degradation processes can be described by two decreasing exponential functions. WAXS measurements detect only slight differences in the crystalline structure and superstructure of the treated fibers. Thus, the main origin of mechanical degradation is the destruction of intercrystalline links such as tie molecules or tie crystallites. ' Technora® and Trevar® are registered trademarks of Teijin Limited and Hoechst, respectively.
PVC-and PC-films doped with various fluorescent molecules were uniaxially drawn below and just above the glass transition temperature. The orientation of fluorescent probes and polymer segments is discussed, comparing Hermans' orientation factors evaluated from birefringence for the segments and from dichroism and fluorescence polarization for the probes. Moreover, the orientation of the fluorescent probes is related to that of hypothetical units, orientated according to the pseudoaffine deformation mechanism.
Atactic polystyrene (PS) is doped in solution with various fluorescent molecules and cast to fdms. Rectangular samples, cut from these films, are uniaxially drawn at 100 ~ and 110 ~ The orientation of the'fluorescent probes is characterized by UVdichroism and fluorescence polarization, that of the polymer segments by IR-dichroism and birefringence. It is observed that the fluorescent molecules depending on their structure tend to orientate more or less perpendicular to the drawing direction. This can be understood by assuming that the benzene rings of the fluorescent probes try to associate to those of the polymer. As consistent values of the angle between the 2850 cm -~ transition moment and the chain axis and of the intrinsic birefringence result 70 ~ and -0.10 respectively.
Samples cut from it-polypropylene films of three different thicknesses are drawn at room temperature varying draw velocity. As characteristic variables of drawing process under neck formation yield stress, draw stress, neck propagation velocity and temperature of neck surface are measured. The characteristic variables are found to differ depending on thickness. The temperature rise of neck surface increases with growing thickness, whereas draw stress decreases. The variation of characteristic variables can partially be interpreted by thickness differences; for a complete understanding small morphological differences, depending on sample thickness, have to be taken into consideration,
SynopsisWide-angle x-ray diffraction experiments on Kevlar 49 fibers, irradiated with y-rays from a Corn source, indicated that radiation-induced cross-linking in the form of H-bonding occurred within the microparacrystals (mPC) in the lateral direction b of the unit cell and had led to an increase in the mPC size in this direction. On the other hand, the mPC size Zzoo along the axis and normal to the [200] netplanes did not change by radiation. In effect, the mPC size normal to the [110] netplanes increased from 4.23 nm to a maximum value of 6.04 nm at the 600 MRad dose level, after which it decreased. The mPC size in the direction of the fiber axis was 102 nm and did not change significantly by radiation (102-109 nm). Thus, essentially, the mPCs grew solely in the b direction. The paracrystalline distortion parameter (g) in the direction of the fiber axis was 2.8% and was not changed significantly by radiation (g = 2.9 f 0.2%). The equatorial "crystallinity" maintained a value of 76% until a dose of 50 MRad and then became 73% at 100 MRad and 70% after this dose level The netplane distances were not affected by radiation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.