Abstract Quenched amorphous films of poly(ethylene terephthalate) (PET) are stretched at temperatures less than T g ; changes in density, wide‐angle x‐ray diffraction, and small‐angle light scattering are observed. The density increase upon stretching is attributed to an increase in crystallinity accompanied by an increase in the intensity of somewhat diffuse wide‐angle x‐ray diffraction and of both V V and H V small‐angle light scattering patterns. The formation of oriented rodlike superstructure may be discerned from small‐angle light scattering. Annealing of these samples increases the crystallinity as measured from density and leads to an increase in the perfection of crystalline and supercrystalline structure as measured by wide‐angle x‐ray diffraction and small‐angle light scattering. The rodlike morphology changes to form spherulitelike aggregates as observed by small‐angle light scattering and light micrographs. A model is proposed to explain the observations. Studies are extended to stretching films of PET above their T g and observing changes in birefringence, density, wide‐angle x‐ray diffraction and small‐angle light scattering as a function of elongation and stretching temperature. The formation of defomed spherulitelike superstructure may be discèrned from light micrographs. Results are compared with those obtained upon stretching films below T g .
Abstract Poly(ethylene terephthalate) (PET) and bisphenol‐a‐polycarbonate (PC) are known to form a miscible blend whereas ternary blends of PET, PC, and polypropylene (PP) form two phases. This is based on the considerations of various chemical events which may occur in these systems. The role of ester‐carbonate interchange reactions during melt mixing and fabricating is found to be unimportant. Differential scanning calorimetric analysis of the ternary blends shows that there appears to occur an exothermic transition in the heating mode of the instrument. This exothermic event was found to be suppressed considerably by incorporating suitable additives into the system. Degradation reactions studied by thermogravimetric analysis and a dilute solution viscometric technique reveal that there exists some kind of interaction among the components even with the immiscible PP component.
Abstract Morphology of blends of Liquid Crystalline (LC) co-polyesters and polyethylene terephthalate (PET) with a varying percentage of the liquid crystalline component were studied primarily by small angle light scattering (SALS), polarising microscopy and wide angle X-ray diffraction. The crystallization behaviour of these blends was studied with the help of density measurements and differential scanning calorimetry (DSC). It was observed that a small amount of LC component in PET changes the morphological and crystallization behaviour of PET. It also affects the mechanical properties of PET significantly.
Isotope-assisted metabolic flux analysis (MFA) is a powerful methodology to quantify intracellular fluxes via isotope labeling experiments (ILEs). In batch cultures, which are often convenient, inexpensive or inevitable especially for eukaryotic systems, MFA is complicated by the presence of the initially present biomass. This unlabeled biomass may either mix with the newly synthesized labeled biomass or reflux into the metabolic network, thus masking the true labeling patterns in the newly synthesized biomass. Here, we report a detailed investigation of such metabolite reflux in cell suspensions of the tree poplar. In ILEs supplying 28% or 98% U-(13)C glucose as the sole organic carbon source, biomass components exhibited lower (13)C enrichments than the supplied glucose as well as anomalous isotopomers not explainable by simple mixing of the initial and newly synthesized biomass. These anomalous labeling patterns were most prominent in a 98% U-(13)C glucose ILE. By comparing the performance of light- and dark-grown cells as well as by analyzing the isotope labeling patterns in aspartic and glutamic acids, we eliminated photosynthetic or anaplerotic fixation of extracellular (12)CO2 as explanations for the anomalous labeling patterns. We further investigated four different metabolic models for interpreting the labeling patterns and evaluating fluxes: (i) a carbon source (glucose) dilution model, (ii) an isotopomer correction model with uniform dilution for all amino acids, (iii) an isotopomer correction model with variable dilution for different amino acids, and (iv) a comprehensive metabolite reflux model. Of these, the metabolite reflux model provided a substantially better fit for the observed labeling patterns (sum of squared residues: 538) than the other three models whose sum of squared residues were (i) 4626, (ii) 4983, and (iii) 1748, respectively. We compared fluxes determined using the metabolite reflux model to those determined using an independent methodology involving an excessively long ILE to wash out initial biomass and a minimal reflux model. This comparison showed identical or similar distributions for a majority of fluxes, thus validating our comprehensive reflux model. In summary, we have demonstrated the need for quantifying interactions between initially present biomass and newly synthesized biomass in batch ILEs, especially through the use of ≈100% U-(13)C carbon sources. Our ILEs reveal a high amount of metabolite reflux in poplar cell suspensions, which is well explained by a comprehensive metabolite reflux model.
Abstract A 70:30 blend of polyamide 6 (PA 6) and acrylonitrile butadiene styrene terpolymer (ABS), with and without a compatibilizer, was used as the matrix for reinforcement with short glass fibers. The compatibilizer used was a copolymer of styrene maleic anhydride (SMA) and its level was kept at 5 wt.-% in the blend. The glass fiber content was varied from 10 to 30 wt.-%. The blends and corresponding composites were compounded using a single screw extruder and test samples were prepared by injection molding. Tensile, flexural and impact properties were determined using the injection molded test samples according to ASTM standards. Morphological studies were carried out on fractured tensile test specimens using scanning electron microscopy (SEM). In general, the mechanical properties improved by the addition of glass fibers to the blend matrices and increased with increasing glass fiber content. The compatibilizer (SMA) has no favorable effect on the mechanical properties of the composites although it has a significant effect on the blends of PA 6 and ABS. SMA increases the melt viscosity of the blend and its addition to the blend results in greater damage to the fibers in the composite during processing. The fiber-matrix adhesion appears to be better in the absence of SMA. The morphological observations have been correlated with mechanical properties.
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