Crystallinity Of PET Research Articles

CRYSTALLIZATION OF POLY (ETHYLENE TEREPHTHALATE) IN ORGANIC SOLVENT

The amorphous and undrawn poly (ethylene terephthalate) (PET) was treated with several kinds of organic solvents and silicon oil at temperatures of -10°C to 200°C, and the fine structure was investigated by means of X-ray diffraction (wide-angle and small-angle) and density gradient tube. The degree of swelling of PET treated with benzyl alcohol, benzene, tetrachloroethylene, and chloroform increased with the rise of treatment temperature. On the other hand, the degree of swelling of PET treated with dimethyl formamide (DMF), dimethyl acetoamide, and nitrobenzene at -10°C_??_75°C increased with a lowering of temperature. This unusual swelling behavior of PET was discussed on the basis of the interaction between PET and organic solvent. The degree of crystallinity of PET treated with organic solvent increased with the rise of temperature in every case. The crystallization was almost completed up to about 10°C in DMF and benzene. Acceleration of the crystallization in organic solvent may be attributed to the fact that the glass transition temperature of PET is lowered in organic solvent. The dominant selective uniplanar orientation of (100) plane was found for the PET which was treated with DMF in lower temperature.

Structure and properties of polyethyleneterephthalate crystallized by annealing in the highly oriented state

The structure of polyethyleneterephthalate bristles drawn about five times in the amorphous state and subsequently crystallized at temperatures between 100 and 260‡ C has been studied by means of small-angle X-ray scattering. In addition density, heat of fusion and wide-angle scattering behaviour were measured. For comparison, similar experiments were carried out with undrawn samples. The results showed that the degree of crystallinity of PET cannot be calculated from density data on the basis of a simple two-phase model, since the effective densitiesρc* andρa* of the crystalline and amorphous regions depend strongly on crystallization and drawing conditions. With rising crystallization temperature the size of the mosaic blocks building up the crystalline layers and their longitudinal mutual order increase whereas the volume fraction of the crystalline region is only rather slightly effected by the annealing temperature. The difference between the effective densityρc* and the “X-ray density”ρc of the crystalline layers is supposed to be caused by lattice vacancies in the boundaries of the mosaic blocks.

Structure of terephthalate polymers I—Infra-red spectra and molecular structure of poly(ethylene terephthalate)

The ‘rigid’ crystalline model for poly(ethylene terephthalate) is not wholly consistent with the inra-red spectra of PET and model compounds, including polarized spectra in the far infra-red (600-20 cm−1). The results indicate that the extent of rotation of the glycol fragment about the terephthalate framework in the PET crystal appears to be greater than in the above model. The space group P1̄ is, however, conserved. There appears to be more rotational hindrance in the crystal than in the amorphous polymer about the CH2O and CO bonds and the existence of the discrete trans and gauche glycol configurations has been confirmed. The degree of crystallinity of PET is correlated with the trans glycol residue and a planar terephthalate framework. Conversely the amorphous content is correlated with the gauche form of the glycol residue and an accompanying distortion of the terephthalate framework from Vh to C2v symmetry. Assignments for the vibrational modes of the terephthalate framework have been made on the basis of Vh and C2v symmetries for the trans and gauche isomers in PET, respectively, using information from the related poly(cyclohexane-1,4-dimethylene terephthalate). The assignments of the vibrational modes for the ethylene glycol fragment on the basis of C2h symmetry (trans isomer) and C2 symmetry (gauche isomer) are also given together with assignments for the principal stretching, deformation and torsional modes of the backbone chain for each configuration. These are found to be in reasonable agreement with calculated values.