Small-angle X-ray scattering (SAXS) studies were undertaken to explore possible morphological explanations for poor mechanical strength in the petaloid bases of poly(ethylene terephthalate) (PET) bottles. The bottles were manufactured using a two-stage injection stretch blow molding process. Splitting of PET bottle bases under load is both inconvenient and expensive. In this study, SAXS data were collected with a 100 mu m square X-ray beam to establish the molecular morphology as a function of position across the base topology. An amorphous region was identified in the base center (i.e., close to the injection gate of the preform) with biaxially orientated, semicrystalline regions in the feet and valleys of the bottle bases. For bottles that had split under load, the transition between these two regions displayed uniaxial orientation that would lead to reduced mechanical strength in the circumferential direction. Reasons for this effect are explored. (c) 2006 Wiley Periodicals, Inc.

Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) were used to probe the final morphology of linear and novel branched poly(ethylene terephthalate) (PET) samples having undergone shear-induced crystallization. The branched PET samples were produced via a reactive extrusion process designed to increase the melt strength of PET and to broaden the processing options available to include extrusion blow molding and thermoforming. The highest molar mass, and, therefore, the most branched samples exhibited highly anisotropic final SAXS morphologies indicating that the semicrystalline lamellas were preferentially oriented perpendicular to the flow direction. The lower molar mass samples all displayed isotropic final SAXS morphologies indicating that chain relaxation had occurred prior to crystallization. For the high molar mass samples, chain entanglements slow the relaxation time after exposure to shear and the chain orientation induced by the shear produced an enhanced nucleation effect for the subsequent crystallization leading to faster crystallization kinetics.Ruthenium tetroxide (RuO2 ) was employed successfully to provide a lamellar scale contrast for analyzing PET crystals by TEM. Long string-like crystals were observed for all of the samples regardless of their orientation with respect to the flow direction. These crystals often displayed a significant degree of orientation over the short range. Analysis using Fourier transforms on filtered TEM images produced d-spacings generally comparable to those obtained from the SAXS analysis, in the 100-200 angstrom range.

Reaction-induced, phase separation has been studied in polymer blends., A model crystalline-amorphous system consisted of semicrystalline polyoxyethylene (POE) dissolved in the monomer styrene, which was used as a reactive solvent to ease processing. When the styrene was polymerized to polystyrene (PS) in the mold, phase separation and phase inversion are induced, and a polymer blend was formed. Polyoxyethylene was selected with a molar mass, M-n = 8578 g mol(-1) and a polydispersity of 1.19, as determined by using gel permeation chromatography. The polymerization of styrene was initiated by using 1 wt% benzoin methyl ether and 0.2 wt% 2,2'-azobisisobutyronitrile under ultraviolet light. The polymerization kinetics were determined by monitoring the reduction in the intensity of the C=C stretching vibration band at 1631 cm(-1) in the Raman spectrum of styrene. The onset times for the liquid-solid (L-S) phase separation and crystallization of POE from styrene/PS were observed by using simultaneous small-angle x-ray scattering (SAXS) and wide-angle x-ray scattering. Onset times for L-S phase separation determined from the SAXS data were combined with the styrene polymerization kinetics to plot the L-S phase separation data onto a ternary phase diagram for the reactive system POE/styrene/PS at 45degreesC and 50degreesC.

The first ever time-resolved small-angle X-ray scattering (SAXS) data from the undulator 15-ID-D beamline (ChemMatCARS) are presented. A 1.3 A (9.54 keV) X-ray beam was selected to study the structure development in a polypropylene sample during shear-induced crystallization. A Linkam CSS450 shear cell provided the temperature and shear control. The polypropylene was first melted and then quenched to the crystallization temperature, where a step shear was applied. The SAXS data were collected using a Bruker 6000 CCD detector, which provided images of excellent resolution. The SAXS images (with 180 degrees rotational symmetry) indicated that the polypropylene crystallizes with a high degree of anisotropy, and the lamellae are oriented perpendicular to the flow direction.

The morphology development in model polymer blends was investigated in relation to the processing pathway. Reaction-induced phase separation was used to make polyoxyethylene (POE) and polystyrene (PS) blends from a solution of POE/styrene. As the styrene underwent polymerization by photo-initiation with ultraviolet light, phase separation, and phase inversion were induced, whereby the POE became the matrix phase. Optical microscopy showed that liquid-liquid (L-L) phase separation occurred soon after the styrene polymerization Was initiated. Nucleation and growth was identified as the mechanism of L-L phase separation. Polystyrene/styrene-rich domains formed in a POE/styrene-rich matrix. The domain size developed until arrested by the POE liquid-solid phase separating and crystallizing, since the experiments were conducted below the melt temperature of POE. The POE crystal growth process also followed a nucleation and growth mechanism. The time to the onset of crystallization was observed to decrease as the POE content increased, until the POE formed a saturated solution in styrene. As the crystallization onset time decreased, the PS-rich domain size also decreased. The phase diagram previously established can now be used to describe (and predict) the number density and size of the PS-rich domains in the POE matrix of the blends.

Structure-property relations were studied in reaction-induced, phase-separated polymer blends. An amorphous-amorphous system consisted of polystyrene (PS) dissolved in the monomer 2-phenoxyethyl acrylate (POA). When the POA was polymerized to poly(2-phenoxyethyl acrylate) (PPOA), phase separation and phase inversion were induced, and a polymer blend was formed. The reaction kinetics were measured by monitoring the reduction in the intensity of the C╤C stretching vibration band in the Raman spectrum of POA. The phase separation kinetics were determined using light transmission experiments and were combined with the reaction kinetics so that a ternary phase diagram could be defined for the reactive system. Structure development was monitored using small-angle laser light scattering (SALLS) and optical microscopy, which showed that spinodal decomposition was the mechanism of liquid-liquid phase separation. Plots of the relative invariant with time showed an increase in the degree of phase separation. The Fourier transforms of the microscopy images had peaks in the radial intensity distributions, again implying that spinodal decomposition was the phase separation mechanism. Tensile testing showed that PPOA was soft and rubbery at 20°C. Both PS and PPOA had comparable toughness when tested to failure; however, the blend containing 17 wt% PS had a toughness more than 10 times that of either PS or PPOA in isolation. Both modulus and tensile strength increased with PS content, while the ultimate strain decreased. The Nielsen model best described the tensile modulus data, providing further evidence for co-continuous phase structure.