Confined batch foaming of semi‐crystalline rubbery elastomers with carbon dioxide using a mold

Abstract

Confined foaming of poly(ethylene-co-vinyl acetate-co-carbon monoxide) using carbon dioxide as a physical blowing agent in a mold with either permeable or impermeable boundaries has been explored as a strategy to control final foam dimensions and morphology. The results are discussed in terms of comparisons to free-foaming experiments conducted at the same pressure and temperature conditions following the same pressurization and depressurization paths. Foaming experiments were carried out at 30 and 40 C and 100, 200, and 300 bar followed by rapid depressurization of the foaming cell. Confined foaming led to smaller pores with more uniform distributions across the polymer cross-section. However, bulk foam densities of the foams generated under confinement were higher than those generated under the free-foaming mode. Surface characteristics and skin layer formation were altered by expansion against both the permeable and impermeable boundaries. Confined foaming promotes uniform pore distribution and overall dimensional uniformity and may impart surface texture but the trade-off is in the degree to which the bulk foam density can be lowered.

Impacts of cellulose nanofibers on the morphological behavior and dynamic mechanical thermal properties of extruded polylactic acid/cellulose nanofibril nanocomposite foam

“…Many activities have been done to improve the mechanical properties of PLA, but these actions do not meet the requirements of industrialization due to the type of process. [58][59][60] The incorporation of CNF into the PLA foam matrix has been reported in some studies. In these studies, the effect of CNF on the strain and viscosity of PLA foams has been investigated and it has been concluded that CNF reduces cell size and also increases cell density and foam density.…”

Developing Insulating Polymeric Foams: Strategies and Research Needs from a Circular Economy Perspective

“…There is currently increased interest in the use of CO 2 as a blowing agent due to the mentioned safety and environmental reasons, as well as cost considerations [36,43,73,74]. The main drawback of its use is its higher diffusivity than that of long-chain hydrocarbons such as pentane, which affects the maximum expansion ratio achievable [32], the thermal aging of the foam [75], and can cause post-foaming shrinkage [72,76,77]. Strategies to overcome this will be discussed in Section 4.2.2.…”

“…CO 2 is a suitable blowing agent given its high solubility and produced plasticization, which allows to foam at lower temperatures and supports the stabilization step when the plasticization is lost upon desorption [45]. However, the shrinkage and collapse of the cellular structure of the resulting foams due to its high diffusivity in the hot polymer matrix are problematic, in particular with low rigidity [71,72] and elastomeric [76,77] polymers. A long-established strategy to overcome this has been the use of long chain hydrocarbons as blowing agents [57,136].…”

“…A study on the effect of confined foaming of rubbery elastomers in a mold vs. free foaming with CO 2 has recently been published [76]. It concluded that, through confined foaming with permeable molds, dimensionally stable foams could be obtained with a higher cell uniformity but also density than in the case of free foaming.…”

Foaming of PCL-Based Composites Using scCO2: Structure and Physical Properties

“…There are also many scientific reports in the literature on the adaptation of the manufacturing process to obtain porous structures with the appropriate properties. An ideal summary of the considerations concerning the influence of the mold shape on the foam properties was made in [ 45 ].…”