In situ FTIR microscope study on crystallization of crystalline/crystalline polymer blends of bacterial copolyesters

Microscopic Fourier Transform Infrared Characterization on Two Types of Spherulite with Polymorphic Crystals in Poly(heptamethylene terephthalate)

FTIR microspectrometry with in situ temperature variation and IR-peak-mapping capability, and POM characterization were used to study the crystal distribution in dual spherulites in poly(heptamethylene terephthalate). By tracing the crystalline IR bands of the α-crystal and β-crystal to get the crystal distribution, the techniques resolve that the ringed and ringless spherulites comprise α- and β-crystals, respectively. In addition, temperature-dependent IR analyses on the spots related to the two crystals also reveal the α- and β-crystals melt at 98 and 104 °C, respectively. The ringed and ringless spherulites were proven to be correlated with the α- and β-crystal forms, respectively.

Crystallization of polylactide and its stereocomplex investigated by two-dimensional fourier transform infrared correlation spectroscopy employing carbonyl overtones

The band origins and transitions of weak vibrational modes developed in the 3500 cm(-1) region of polylactide (PLA) spectra during crystallization are investigated. The band assignment to the OH stretching mode of terminal hydroxyls is unlikely because the trace amount of chain-ends is negligible considering the long chain of high molecular weight polymer. The band intensity can be enhanced for quantitative study by increasing the sample film thickness. The results show that the transition patterns of these bands mimic those of C=O stretching modes. Therefore, these are assigned to C=O overtones. Two bands associated with crystalline and amorphous characteristics are revealed during cold crystallization. The crystalline C=O bands of PDLA and its stereocomplex counterpart are located at 3510 cm(-1) and 3482 cm(-1), respectively, indicating a weaker C=O bond in the latter crystal structure. Two-dimensional Fourier transform infrared (2D-FT-IR) correlation spectroscopy is then applied to study the correlation between C=O overtones and the crystalline characteristic band located near 900 cm(-1). The transitions of the two vibrational modes observed in crystallization of the stereocomplex are in-phase with each other. This reflects an involvement of short-range hydrogen bonding in the stereocomplex crystal structure. In contrast, crystallization of PDLA shows that the C=O overtone varies prior to that of the C-H character, indicating that dipole-dipole force is a crystal-induced interaction.

Uniaxial Drawing of Poly[(R)-3-hydroxybutyrate]/Cellulose Acetate Butyrate Blends and Their Orientation Behavior

Miscible blends of PHB and CAB were prepared by the solvent-casting method with various blend compositions, and their orientation behavior was investigated during uniaxial drawing. X-ray analysis revealed that the orientation of the crystallizable PHB component in the drawn PHB/CAB blends was changed from c-axis-orientation to a-axis-orientation with increasing CAB content. The a-axis-orientation was a result from the a-axis-oriented crystal growth caused by the intramolecular nucleation and the confined crystal growth. For quantitative assessment of the chain orientation, the Hermans orientation functions of the two respective components were obtained from the polarized FT-IR measurements. The orientation function of pure PHB stretched to 5 times of its initial length was approximately 0.8. However the value decreased rapidly with increasing CAB content, and it turned to a negative value from 30 wt.-% CAB content. This indicates that the PHB chains were aligned perpendicular to the drawing direction. On the contrary, the value of the CAB component remained almost unchanged at about 0.1 regardless of the blend composition and the annealing time, indicating that the CAB chains were constantly oriented parallel to the drawing direction without any chain relaxation. In addition, SAXS analysis suggested that the lamellar stacking direction also changed from parallel to perpendicular in the stretching direction with increasing CAB content.