An alternative approach to study the evolution of foaming mechanisms in polymer foams based on an ex-situ analysis of the expansion kineticsThursday (08.10.2020) 14:00 - 14:20
The analysis of the cellular structure in polymer foams is the key to understand their final physical properties. This is usually done at the end of the process when the final foam has reached the targeted expansion. However, the modification or improvement of the final foam cellular structure requires a detailed understanding of how it evolves from the initial stages, that is, a study of the foaming mechanisms: nucleation, expansion, degeneration and stabilization. Several approaches have been used so far. Most of them are based on X-ray experiments that allow to in-situ registering and monitoring the evolution of the expansion and cellular structure during foam production. However, a very specific and expensive X-ray equipment is needed for this. There is a simpler approach which is based on producing foams at different times and ex-situ studying their cellular structures using image analysis of 2D micrographs. This approach has been used in this work to analyze the evolution of the foaming mechanisms in natural rubber foams cross-linked using high energy electrons. A wide range of irradiation dose (ID) were used, from 50 to 150 kGy, which led to very different cell sizes: from more than 100 µm when using the lowest ID to around 20 µm when using the highest ID. This is in fact one the lowest cell sizes ever reported in cross-linked natural rubber foams. The use of this approach allowed to detect that both a higher nucleation rate and lower degeneration rates at high ID were the main reasons behind such high reduction of the cell size in the natural rubber foams produced.