Pole figures obtained by wide-angle X-ray diffraction have been used to quantify and characterize the molecular orientations induced in low-density poly(ethylene) films prepared by the tubular film process. Small-angle X-ray scattering was employed to determine the type and orientation of the morphology within the films. All films were found to possess a combination of two morphologies: a surface transcrystalline layer and a row-nucleated morphology caused by crystallization in low-stress conditions. For the first series of blown films, in which the draw-down ratio was increased from 1.9 to 7.9 for a constant blow-up ratio of 1.68, the a axis was observed to increase its orientation along the extrusion direction, signifying that the row-nucleated structures intensify their orientation along this same direction. The amount of transcrystalline material decreases upon increasing the draw-down ratio. Unexpectedly, the amorphous regions tend to become biaxially oriented in the higher drawn samples. In the second series of films, the blow-up ratio was increased from 1.60 to 2.74 for a constant draw-down ratio of 4.2. In this case, the row-nucleated morphology became progressively oriented in the film plane upon bubble enlargement, thus creating an uniplanar orientation of the molecular chains in the film plane. The amorphous regions, weakly oriented on the onset along the extrusion direction, gradually become biaxially oriented in the film plane upon increasing the blow-up ratio. Finally, it was shown that molecular orientation measurements can be used to verify the consistency of the processing conditions in blown film production.

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A preliminary crystal structure of syndiotactic poly(β-hydroxybutyrate), syn PHB, was derived by using X-ray fiber and powder diffraction data in conjunction with computational modeling. The X-ray fiber diagram of highly stretched 69% syn PHB gave 23 reflections and a fiber repeat of 7.69 Å. The diffraction trace of a powder syn PHB octamer provided well-resolved d spacing measurements from which an orthorhombic unit cell of dimensions a = 7.84 Å, b = 14.90 Å, c = 7.69 Å is proposed. Conformational analysis with a syndiotactic diad repeat unit gave six low-energy chains with a fiber repeat of 7.69 Å. The most favorable chain conformation had dihedral angles similar to isotactic PHB but with a more extended integral helix. There is no energy preference for a right-handed or left-handed helix. The P212121 space group was selected based on observed systematic absences, the tentative orthorhombic unit cell, and favorable packing energies. The 21 symmetry in the chain direction is between neighboring sets of anticline packed helices of syn PHB. The structural model of syn PHB put forth is based on favorable packing energies and a reasonable fit of simulated X-ray diffraction data with the experimental results, which were further evaluated by a Rietveld analysis.

The level of thermo-oxidative degradation in a series of unstabilized and unfilled nitrile rubbers (NBR) varying in acrylonitrile (ACN) content (18–43.5 wt%) was investigated on heat-aged samples (40–120 °C) by Attenuated Total Reflectance–Fourier Transform Infrared (ATR-FTIR) spectroscopy. A similar degradation profile evolution was observed regardless of ACN content with the generation of hydroxyl-, carbonyl-, and ester-based products with a concomitant loss of the 1,4-trans, 1,4-cis, and 1,2-vinyl butadienes. The magnitude of IR active group absorption loss is greatest in the lowest ACN NBR concentration and steadily lessens toward higher ACN levels (1,4-cis > 1,2-vinyl > 1,4-trans >> butadiene methylenes). The 18% ACN NBR possesses two distinct kinetically different degradation regimes (80–120 and 40–80 °C). Activation energies by carbonyl growth and 1,4-trans loss increase from 71 to 87 kJ mol−1 and from 71 to 79 kJ mol−1 respectively, for decreasing ACN (43.5–18%) content. The rate of consumption of the 1,4-trans butadiene group is mainly affected by thermo-oxidative carbonyl-based and addition-cross-linking reactions, the latter being lower in activation energy for low to mid ACN NBRs. The high oxidation rate behavior of the lowest acrylonitrile rubber is attributed to its higher oxygen permeability rates. Cross-linking due to addition-type reactions is favored for higher 1,4 unsaturation levels.

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