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Hypothesis Nonaqueous foams are found in a variety of applications, many of which contain volatile components that need to be removed during processing. Sparging air bubbles into the liquid can be used to aid in their removal, but the resulting foam can be stabilized or destabilized by several different mechanisms, the relative importance of which are not yet fully understood. Investigating the dynamics of thin film drainage, four competing mechanisms can be observed, such as solvent evaporation, film viscosification, and thermal and solutocapillary Marangoni flows. Experiments Experimental studies with isolated bubbles and/or bulk foams are needed to strengthen the fundamental knowledge of these systems. This paper presents interferometric measurements of the dynamic evolution of a film formed by a bubble rising to an air-liquid interface to shed light on this situation. Two different solvents with different degrees of volatility were investigated to reveal both qualitative and quantitative details on thin film drainage mechanisms in polymer-volatile mixtures. Findings Using interferometry, we found evidence that solvent evaporation and film viscosification both strongly influence the stability of interface. These findings were corroborated by comparison with bulk foam measurements, revealing a strong correlation between these two systems. [ABSTRACT FROM AUTHOR]

Insights into the effect of die swell on extrusion foam of thermoplastic polymers are presented. The die swell or Barus effect is the swelling of a viscoelastic material due to a fast elastic recovery after being subjected to stress. The elastic recovery is proportional to the energy stored in the material during the deformation that is released immediately when the material is free to expand. In extrusion foam, the elastic recovery happens at the die exit together with the foaming process (i.e., bubble nucleation and growth). Previous reports on extrusion have focused on modeling the die swell or foaming individually. We investigated the existence of a link between the die swell and foaming that is fundamental in designing the geometry of a die for extrusion foam. Simple and complex dies were used to measure the expansion ratio of a polyethylene blown with isobutane and CO2. It was found that the expansion ratio is anisotropic, the anisotropy in the expansion of the foam is due to the die swell strongly affecting the final shape of the product, and it cannot be neglected in standard application for extrusion foam. Surprisingly, it was found that the foam density changes at a high level of die swell because it is affected by the elastic recovery of the material. [ABSTRACT FROM AUTHOR]