Recent Developments in the Microwave Processing of Polymers

Extract

As applications for polymeric materials continue to expand, cost-effective and environmentally responsible processing methods become vitally important. It is also becoming increasingly apparent that the success of some new materials is tightly coupled to their processing technologies because the development of their properties depends directly on the processing. In thermoplastic-toughened thermoset resins, for example, morphology development during processing is critical to the mechanical performance of the final material.

Microwave processing has enjoyed growing interest primarily because of the potential of uniformly heating relatively large volumes of materials very rapidly; this overcomes limitations due to the poor thermal conductivity of polymeric materials. Microwave radiation has a very large penetration depth in polymeric materials, and absorption follows a simple Beer-Lambert Law. Hence, depending on the material, very uniform heating profiles throughout the thickness of a material can be obtained up to 0.5 m. This bulk absorption of energy allows for substantially higher heating rates than can be obtained using conventional or infrared methods and for the retention of an acceptable heating profile. Other advantages of this technology include (1) more efficient heating and thus efficient use of energy (only the part is heated, not the walls and surrounding air); (2) shorter processing time for batch operations; (3) shorter process lines for continuous operations; (4) environmental superiority; (5) production of properties or morphologies not attainable using other processing techniques; and (6) the possibility of selective heating—the selective absorption of energy by one phase or part of a material—leading to a custom temperature profile within a part.