lesteric liquid crystals whose pitch decreases with increasing solvent concentration and whose optical properties suggest a left-handed helicoidal arrangement. (U.

We have developed a new procedure by which one may measure diffusion constants and spinodal curves in polymer blends. Exponential growth in the concentration gradient (c -c0) was observed during the early stages of phase separation, after which time the Cahn-Hilliard expression becomes clearly inadequate. From the growth of the scattering intensity and the angular dependence of that scattering, it was possible to give a complete quantitative description of the early stages of polymer blend phase separation in the PS/PVME system. References and Notes(1) van Aartsen,

SYNOPSISClassical morphological analysis has been performed on novel PET fibers of high modulus and low shrinkage (HMLS). As expected, amorphous orientation controls the degree of shrinkage and tenacity. The uniqueness of these materials is derived from a hign "effective" crosslink density which results in a high retractive force during elevated temperature shrinkage and significant stress-amplification during room temperature extension. Although the morphological origin of the high effective crosslink density is unknown, it is speculated that the interfibrillar regions contribute to the observed behavior by suppressing yielding.

Improvements in Young's modulus and strength (tenacity) of poly(ethylene terephthalate) (PET) fibers were obtained by drawing unoriented nanocomposite filaments containing low concentrations (<3 wt%) of various organically modified montmorillonites (MMTs) in a second step at temperatures above the glass transition. Prior to melt spinning, solid‐state polymerization was used to rebuild lost molecular weight, due to MMT‐induced degradation, to a level suitable for producing high strength fibers. Greater improvements in mechanical properties occurred when the MMT stacks were intercalated with PET. A nominal 1 wt% loading of dimethyl‐dehydrogenated tallow quaternary ammonium surface modified MMT in drawn PET fiber showed a 28% and 63% increase in Young's modulus and strength, respectively. Relative to an unfilled PET fiber, these results surpassed the upper bound of the rule of mixtures estimate and suggested that both the type of surface modification and concentration of MMT affect the degree of PET orientation and crystallinity. Furthermore, drawability above Tg and elongation at break increased upon the addition of organically modified MMT to unoriented PET fibers, which was a key distinction of this work from others examining similar systems. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers

ABSTRACT:The orientation of the noncrystalline (amorphous) phase in poly (ethylene terephthalate) fibers is analyzed by separating the amorphous scattering in the wideangle x-ray diffraction patterns into isotropic and anisotropic components. Two parameters are used to characterize the amorphous orientation-the fraction of the anisotropic component and its degree of orientation. The x-ray amorphous orientation parameters are compared with the sonic modulus and the birefringence values. Our results illustrate that the intrinsic birefringence of the amorphous phase is not ''intrinsic'' but depends on its density. The role of the oriented amorphous phase in determining the strength (tenacity) and the dimensional stability (shrinkage) of the fibers is discussed. We conclude that although amorphous orientation determines the shrinkage, other factors such as the connectivity between the amorphous phase and the crystalline regions play an important role in determining the tenacity of the fibers.