Abstract
In the last two decades, the application of microwave heating to the processing of materials has to become increasingly widespread. Microwave-assisted foaming processes show promise for industrial commercialization due to the potential advantages that microwaves have shown compared to conventional methods. These include reducing process time, improved energy efficiency, solvent-free foaming, reduced processing steps, and improved product quality. However, the interaction of microwave energy with foaming materials, the effects of critical processing factors on microwave foaming behavior, and the foamed product’s final properties are still not well-explored. This article reviews the mechanism and principles of microwave foaming of different materials. The article critically evaluates the impact of influential foaming parameters such as blowing agent, viscosity, precursor properties, microwave conditions, additives, and filler on the interaction of microwave, foaming material, physical (expansion, cellular structure, and density), mechanical, and thermal properties of the resultant foamed product. Finally, the key challenges and opportunities for developing industrial microwave foaming processes are identified, and areas for potential future research works are highlighted.
Highlights
Foam materials exhibit a unique combination of properties that includes low density, low thermal conductivity, excellent insulation, and mechanical properties
Microwave processing has proved to be an attractive alternative heating method for materials processing. It has been effectively used for various applications from laboratory to industrial scales such as polymer processing [24], food processing [25], nanomaterial synthesis [26,27], foaming [28], pyrolysis [29], remediation of pollutants [30], and ore sorting [31]
Phenolic foams produced via microwave processing effectively overcome several environmental concerns linked to conventional foaming processes
Summary
Foam materials exhibit a unique combination of properties that includes low density, low thermal conductivity, excellent insulation, and mechanical properties. Bio-foams, another type of foam produced from bio-based materials, have received tremendous attention and show great industrial potential. Studies have revealed that extrusion is not the most effective process for producing a well-controlled cellular structure in foams. Microwave processing has proved to be an attractive alternative heating method for materials processing. It has been effectively used for various applications from laboratory to industrial scales such as polymer processing [24], food processing [25], nanomaterial synthesis [26,27], foaming [28], pyrolysis [29], remediation of pollutants [30], and ore sorting [31].
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