Microwave energy polymer processing

Microwave processing has been used to process thermoset polymers and polymer composites, including polyesters, polyurethanes polyimides and epoxies, and in most studies it has been concluded that the curing speed is faster using microwave energy (Clark and Sutton, 1996). The effects of continuous and pulsed microwave irradiation on the polymerization rate and final properties also have been studied, and it was demonstrated that, for certain epoxies, a pulsed microwave cure resulted in improvements in mechanical properties, better temperature uniformity and a faster polymerization mte (Thuillier and Jullien, 1989). 

Technical — Greater output due to increased level of transmissible energy — Reduced wear due to lower proportion of mechanical energy — Greater process flexibility due to third, independently controlled, energy source — More rapid process control with no- delay control of microwave energy supply - Narrowed selection of processable basic polymers. Nonpolar plastics cannot be heated with microwaves - Not yet known how much energy can be transmitted by microwaves - Microwave-transparent inserts required in extruder... 

Microwave radiations are the powerful tool for the elimination reaction of the poly(phenylene vinylene)-polyelectrolyte precursor polymer (PPV precursor) into the fully conjugated polymer. The extent of the elimination process was determined from the amount of residual sulfur in the film after the irradiation process. The microwave induced elimination process was also attempted using PPV precursor films that have been impregnated with anionic compounds containing iron. The molecular mechanisms for the observations are discussed and comparison with the elimination reaction induced by other energy sources has been made (Torres-Filho et al., 1994). 

The effect of microwave power on the polymerization process under microwave irradiation (domestic microwave oven) was studied by Zhang et al. (2004). They found that molecular weight of the polymer was increased and reached a maximum, when 90% conversion was reached up to 255 W. When a higher microwave energy (510 W) was applied, the molecular weight first increased and subsequently decreased in time due to transesterification reactions. 

D. A. Lewis The challenges and opportunities of processing polymers using micro-wave energy. Proceedings from the International Conference on Microwave Chemistry,Prague, Czech Republic 1998. 

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