Continuous foam extrusion of polyvinylidene fluoride (PVDF): Chemical microfoam formation

This paper focuses on the development of polyvinylidene fluoride microfoam by implementing a chemical blowing agent through a continuous process. The objective was to investigate the effects caused by varying concentrations of chemical blowing agent, the use of a master batch as formulation variables, and variation of die temperature on the properties of polyvinylidene fluoride foam produced continuously. By using a 10% master batch formulation (contains 2% chemical blowing agent in final product), the cell density was increased while the cell size and foam density were decreased; the average cell size, cell density, and void fraction were found to be 50 μm, 7.7 × 106 cells/cm3, and 33%, respectively. This is due to the increased cell density primarily due to the increased nucleation sites. At a lower chemical blowing agent, concentration of 1%, the die temperature was varied over a range of 125–145 °C, as this is approximately the melting point of the polyvinylidene fluoride. Decreasing the die temperature from 135 °C to 130 °C caused the cell density to increase and cell size to decrease, while void fraction decreased from 58% to 39%. This is due to the loss of melt strength upon increasing the temperature of the melt PVDF as it exits the die.