Extrusion of polypropylene foams with hydrocerol and isopentane

Abstract

An experimental investigation was conducted to research the cell nucleation behavior in the extrusion foam processing of polypropylene (PP) using hydrocerol and isopentane. While the hydrocerol and isopentane are considered to function a s the nucleating agent which determines the cell-population density and a s the blowing agent to control the volume expansion ratio respectively, both agents affected the cell-population density. In addition, synergistic effects of these agents on the cell density were observed. In foam processing with hydrocerol, a higher cell-population density was noted at lower processing pressures and at higher polymer flow rates. This phenomenon is of interest since the cell density, in general, increases a s the processing pressure increases when only a physical blowing agent is used in the foam processing. The experimental results indicate that the nucleation in the foam processing with hydrocerol is governed by a heterogeneous nucleation mechanism; also, the quality of the mixing of the polymer and the agents, as well a s the amount of gas lost during the plastication of the pellets in the barrel, exerts a strong influence on the resulting cell density.

Rotational foam molding of polypropylene with control of melt strength

“…As fine-celled foams are always preferred because of their better mechanical and thermal properties, the deteriorating effect of cell coalescence on the cell population density is an undesired outcome of the cell growth step in polymer foaming and therefore remedial measures have to be undertaken. 4,[11][12][13] On the other hand, thermodynamically, the cell tendency to coalesce can be explained by the tendency of the overall system to lower the total free energy. In polymer foaming, such a tendency is accomplished by reducing the total surface area of two smaller cells into one smaller surface area of one bigger cell by their coalescing.…”

“…It is, therefore, considered an undesired outcome of the cell-growth stage in polymer foaming, suppression of which requires remedial action. 4,[11][12][13] Two principal strategies are commonly used for successful cellcoarsening suppression. The first is based on nucleation of the cells almost simultaneously in order to induce cell growth uniformity, while the second is based on reduction of the processing time as much as possible.…”

Effect of chain extender and water-quenching on the properties of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) foams for its production by extrusion foaming

“…With this technique, blowing agents can be physical (PBAs) or chemical (CBAs). PHAs have already been foamed with super critical CO 2 gas as PBA [6], with exothermic CBAs such as azodicarbonamide (ADA) [5,7], or with more eco-friendly endothermic CBAs mainly based on sodium bicarbonate (SB) and citric acid [5,8,9]. The use of PBAs requires extruders with PBA-pumping systems and, in some cases, screws with special profiles, thus meaning that special processing machinery is necessary.…”

The simultaneous effect of nucleating and blowing agents on the cellular structure of polypropylene foamed via the extrusion process

“…The cell nucleation, bubble growth and the final cell morphology of extruded PP foams have been studied extensively (2)(3)(4)(5)(6). Earlier studies attempted to enhance the melt strength by partial crosslinking of PP (7).…”