Saleh A. Jabarin

Gel Permeation Chromatography of Polyethylene Terephalate

Abstract This paper describes the development of the gel permeation chromatography (GPC) technique for the measurements of cyclic trimer content, molecular weights, and molecular weight distribution of polyethylene terephthalate (PET), utilizing a solvent system of o-chlorophenol-chloroform. Mark-Houwink constants for this solvent system are also described. The GPC technique was applied to the study of the cyclic trimer content, molecular weights and molecular weight distribution of a variety of commercial PET resins. The results indicate that the cyclic trimer content in PET is dependent on molecular weight, polycondensation process and catalyst system. Solidstate polymerized PET contains less cyclic trimer than PET made by the melt-phase process of the same molecular weight. The cyclic trimer content in solid-stated PET appears to be dependent on the conditions of solid-state polymerization. The polydispersity index determine for a variety of PET samples is higher than the theoretically predicted value ...

Transport Properties of Oriented Poly(Vinyl Chloride)

In commercial thermoplastic forming operations, poly(vinyl chloride), or PVC, is stretched to several times its original dimensions at fixed rates and temperatures. The stretching operation is usually followed by rapid quenching which freezes in the strain-orientation imparted to the polymer during forming. Since orientation is known to strongly influence physical properties, it was of interest to correlate several critical end-use properties with the range of processing conditions which PVC might experience during a typical forming operation. In addition to mechanical strength, gas and vapor transport are perhaps the most critical properties from the packager’s point of view. This report describes the influence of 1) degree of biaxial orientation, 2) stretching rate, and 3) stretching temperature on the oxygen and water vapor transport parameters of non-impact modified PVC. The diffusion and solubility coefficients, as well as permeability, were determined for oxygen transport, while only equilibrium permeability was measured for water vapor. Structural changes were monitored by measuring both birefringence and density as a function of orientation. Since processing temperature was found to have a pronounced effect on properties, separate annealing studies were carried out, where variations in the transport properties were correlated with structural changes as measured by both x-ray diffraction and differential scanning calorimetry, DSC.