Microwave Drying of Polymers

The technical feasibility of using microwaves to dry various types of commercial polymers was investigated in batch-mode experiments with a 1-k W microwave generator/cavity. The polymers tested were polypropylene, low-density polyethylene, hydroxyelhyl cellulose, polyisoprene rubber, and vinyl chloride/vinyl acetate copolymer. A variety of microwave-drying conditions was employed, including input power levels between 100 and 1000 W. and sample amounts from 5 to 100 g. A series of drying curves (moisture content versus time) was generated, and changes in the physical properties of the dried materials were determined. The results show that the polyolefin resins, polypropylene and polyethylene, are very good candidates for drying with microwave energy. Hydroxyethyl cellulose and vinyl chloride/vinyl acetate copolymer, on the other hand, demonstrated good potential only under some drying conditions, while for others, severe degradation (burning) of these materials occurred. Finally, polyisoprene rubber displayed completely undesired microwave-drying characteristics, thus showing little promise in the application of the technique.