Small-angle x-ray scattering from amorphous polyethylene terephthalate

Small-angle x-ray scattering from amorphous polyethylene terephthelate (PET) has been detected. It is very weak, more than an order of magnitude less intense than is usually obtained from partially crystallized specimens. It is also of a continuous nature with the absence of any distinct interference peak. Based on the assumption of spherical particles, the diameters are in the range of 30–40 Å. This is somewhat smaller in size than is seen in electron microscopy, but reasonable since it is more a measure of the actual electron density fluctuation and not physical size. The scattering is sensitive to thermal treatment below the glass transition temperature and also depends on the source of the amorphous PET, e.g., films or fibers. When these data are combined with other analyses, parameters such as size, number density, and electron density of the particles can be segregated. The effects of the state of the amorphous material on subsequent crystallization is also presented and discussed.