Molecular weight is an important factor in the processing of polymer materials, and it should be well controlled to obtain desired physical properties in final products for end-use applications. Degradation processes of all kinds, including hydrolytic, thermal, and oxidative degradations, cause chain scission in macromolecules and a reduction in molecular weight. The main purpose of this research is to illustrate the importance of degradation in the drying of poly(ethylene terephthalate) (PET) before processing and the loss of weight and mechanical properties in textile materials during washing. Several techniques were used to investigate the hydrolytic degradation of PET and its effect on changes in molecular weight. Hydrolytic conditions were used to expose fiber-grade PET chips in water at 85°C for different periods of time. Solution viscometry and end-group analysis were used as the main methods for determining the extent of degradation. The experimental results show that PET is susceptible to hydrolysis. Also, we that as the time of retention in hydrolytic condition increased, the molecular weight decreases, but the rate of chain cleavage decreased to some extent, at which point there was no more sensible degradation. The obtained moisture content data confirmed the end-group analysis and viscometry results. Predictive analytical relationships for the estimation of the extent of degradation based on solution viscosity and end-group analysis are presented.

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The presence of polymer–particle interactions in composite materials leads to the formation of interfacial layers with physical properties significantly different from those of the polymer matrix and fillers. Mathematical modeling of the interfacial morphology in mixed matrix membranes (MMMs) not only considerably depends on the assumed interface thickness, but also is related to the applied modeling algorithm. In the current study, a new algorithm is developed to estimate the interface thickness based on findings of molecular dynamics and Monte Carlo simulations in the literature as well as the size and the loading of the particles. Moreover, effective permeability of the MMMs is predicted with no need to evaluate the permeability of the particles and the type of interfacial morphology by only adjusting the reduced permeability factor in the range of −0.5 to 1. On the basis of the proposed modeling approach, characteristic parameters of encapsulated particles by interfacial layer, β and γ, can be simply determined from the corresponding contour line of γ and β for the description of permeability through it. Initially, the effective permeability of composites comprising encapsulated particles by the interfacial layer is assessed by adjusting only one parameter after determining effective interface thickness. The comparison between the predictions and the reported experimental permeability data of 17 series of the MMMs confirmed that the accuracy of the modified Maxwell model based on the proposed modeling approach is more than 95% for more than 90% of the predictions, while the maximum average absolute relative error (AARE) is 8.3%.

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