Characterization of polymer foam evolution in unpressurized melt systems

The evolution of foam in unpressurized melt processing techniques, such as rotational molding, is different from high-pressure processes like injection foam molding, making comparisons difficult. This has driven the need for a dedicated technique for studying these systems. A unique test procedure was developed to capture and characterize foam evolution in test tubes under unpressurized conditions. A validation study found the procedure to be reliable, producing repeatable samples (height average (AVG) 39.69 ± 1.70 mm and density AVG 0.319 ± 0.012 g/cm³) and delivering comparable results to samples produced using the industrial rotational foam molding process. A study examined the effect of polymer particle size on the foam structures produced. Finer (>90 μm <106 μm) polymer powders produced more desirable structures, achieving 38.6% lower foam density and 43.8% taller peak foam height than coarser powders (>425 μm < 500 μm). Cycle times were much shorter (~15 min) in comparison with the industrial rotational molding process (>40 min) and required smaller amounts of materials, making it useful for rapid characterization. Future work is planned to apply the new procedure to investigate the effects of material and processing conditions on the foam structures produced under unpressurized conditions.