Characterizing the foaming process of polymers: Review of experimental methods

Polymer foams have become increasingly significant in both scientific research and commercial applications due to their wide range of uses. Traditionally, the optimization of polymer foaming processes has relied on time-consuming trial-and-error methods, which has delayed scientific progress in this area. Recent studies suggest that achieving the desired foam properties requires the simultaneous optimization of both formulation and process. This approach moves beyond basic "before" and "after" investigations, advocating for a more thorough exploration of the entire foam expansion process, from the initial mixture to the final polymer foam. In this review article, we provide a detailed overview of the existing experimental techniques for in-situcharacterization of the foaming process across various types of polymer foams, with a natural emphasis on polyurethane systems due to their prominent representation in the academic literature. We examine the strengths and weaknesses of these methods and provide recommendations for future advancements in this field. By carefully adopting these more advanced approaches, it is possible to better understand and optimize the foaming process, leading to improved control over final properties of polymer foams. This review aims to contribute to enhancing the academic and practical knowledge of polymer foaming, ensuring more efficient and innovative developments in the industry.