Dehydration of water-plasticized poly(vinyl alcohol) systems: particular behavior of isothermal mass transfer

BACKGROUND: Water-plasticized poly(vinyl alcohol) has been obtained by thermal processing. Dehydration is the key process for controlling the structure and performance of the water-soluble polymer, and mass transfer is an important part of dehydration. RESULTS: A simple new model of a hyperbolic-type function was developed to understand the mass transfer process of water-plasticized poly(vinyl alcohol) systems during isothermal dehydration. The model was verified by statistical tests. The physical parameters in the model were defined as the maximum weight loss fraction and characteristic time. The dehydration rate, the key physical parameter in mass transfer, was obtained from the differential equation of the model. By use of the model, the characteristics of dehydration of poly(vinyl alcohol) were determined: the complete mass transfer process can be divided into a fast mass transfer before a characteristic time (tau) and a slow mass transfer after tau, and dehydration temperatures can also be divided into two intervals by different activation energies. In addition, the dehydration rate is inversely proportional to the degree of crystallinity. CONCLUSION: The results of the new model agree reasonably well with experimental results obtained by thermogravimetry and weighing. Poly(vinyl alcohol), as a water-soluble semicrystalline polymer, exhibits a particular mass transfer behavior during dehydration. (C) 2008 Society of Chemical Industry