Polyethylene terephthalate degradation under natural and accelerated weathering conditions

Solvent-induced crystallization of polyethylene terephthalate

The fabrication of poly(ethylene terephthalate), PET, into fibers, films, and containers usually involves molecular orientation caused by molecular strain, which may lead to stress- or strain-induced crystallization (SIC). The SIC of PET was studied by the methods of birefringence, density, thermal analysis, light scattering, and wide-angle X-ray. The development of crystallinity is discussed in relation to the rate of crystallization, the residual degree of orientation, and stress relaxation. The experimental procedure involves stretching samples at temperatures above the glass transition temperature, Tg, to a given extension ratio and at a specific strain rate of an Instron machine. At the end of stretching, the sample is annealed in the stretched state and at the stretching temperature for various periods of time, after which the sample is quickly quenched to room temperature for subsequent measurements. During stretching, the stress strain and the stress relaxation curves are recorded. The results indicate that the SIC of annealed, stretched PET can proceed in three different paths depending on the residual degree of orientation. At a low degree of residual orientation, as indicated by the birefringence value, annealing of stretched PET leads only to molecular relaxation, resulting in a decrease of birefringence. At intermediate orientation levels, annealing causes an initial decrease in birefringence followed by a gradual increase and finally a leveling off of birefringence after a fairly long period of time. At higher orientation levels, annealing causes a rapid increase in birefringence before leveling off. The interpretation of the above results is made using the measurements of light scattering, differential scanning calorimetry, and wide-angle X-ray. The rate of the SIC of PET is also discussed in terms of specific data analysis.

Strain-induced crystallization of poly(ethylene terephthalate)

The morphology and deformation behavior of uniaxially and biaxially oriented thin polyethylene terephthalate (PET) films was examined by bright field, diffraction and dark field electron microscopy. A large, 250-500 A, nodule structure was observed under a variety of conditions, in addition to the smaller 75–100 A nodules that have been reported previously. Dark field micrographs indicate that oriented PET, heat set at 180° to 240° C, is composed of small (140 A) isometric crystallites, with a tendency to orient the 100 plane in the plane of the film. It is suggested that the nodular structure and small isometric crystallites may contribute to PET ductility at low temperatures.

Deformation and annealing behavior. I. Polyethylene terephthalate films

This work aims to mainly use a recent resonance-enhanced atomic force microscopy coupled with infrared spectroscopy (AFM-IR) to follow the accelerated degradation process of a polyester (PET) membrane at the surface. By analyzing at the nanoscale of the chemical composition and the distribution of functional groups appearing on the aged sample surface, an understanding complementary on the mechanism of degradation under artificial weathering conditions is proposed, in which hydrolysis and photo-oxidation processes via perester and aromatic acid species are mainly observed. At the molecular level, our finding show a transfer from the trans conformer to the gauche conformer during the aging process, as shown by the increase of the characteristic IR bands of the gauche conformer at 1096 cm−1 and the decrease of the IR bands of the trans conformer at 1340 cm−1. It also appears that oxidation and chain scission reactions are mainly responsible of a reduction in degree of crystallinity, tensile properties and molecular weight of polyester membrane. The effect of thermal and physical degradation is negligible in this condition.

Nanoscale analysis of the photodegradation of polyester fibers by AFM-IR

Three recently published x-ray methods for determining the crystallinity of poly(ethylene terephthalate) are discussed and compared with density and infrared methods The effect of crystallite size is shown to account for most of the disagreement among the several methods A short method of estimating crystallinity from x-ray diffraction, suitable for counting techniques and requiring only two measurements, is presented and compared with the density method

X‐ray determination of crystallinity in poly(ethylene terephthalate)

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X‐ray determination of crystallinity in poly(ethylene terephthalate)