Hydrolysis effects on the molecular weight degradation of condensation polymers as estimated from their prior drying condition

A simple model has been developed to evaluate the potential random degradation of hydrolyzable polymers as a function of water remaining after drying but prior to processing. Molecular weight retention was found to be dependent on the initial molecular weight of the polymer as well as the hydrolysis efficiency, but independent of polymer crystallinity. At the same water content and hydrolysis efficiency, the model indicated that higher molecular weight polymers would be expected to yield a more significant molecular weight reduction. The potential degradation of hydrolyzable condensation polymers was also estimated from drying conditions recommended by producer companies. The results calculated from the hydrolysis model were in most instances consistent with producer company recommended drying conditions. A review of the literature also found that while the sensitivity of nylons to hydrolysis decreases with moisture content, nylon 6/6 specifically can sometimes increase in brittleness and viscosity to an unacceptable level after drying below a critical moisture content. Thus nylon 6/6 was found to have a preferred range of moisture content for optimum processing. The need for a test method to evaluate hydrolysis efficiency for hydrolyzable polymers was also discussed. Such a standard could be important in the practical evaluation of new materials developed to minimize hydrolysis susceptibility.