Supercritical CO₂ Extrusion Foaming and Steam-Chest Molding of Polypropylene/Thermoplastic Polyurethane Bead Foams

Abstract

An efficient and green preparation strategy is critical in promoting the marketization of expanded polypropylene (EPP) products. In this work, supercritical CO2 extrusion foaming in cooperating with wind-cooling granulator technology was creatively used to prepare polypropylene (PP)/thermoplastic polyurethane (TPU) composite bead foams with controllable cellular structures and geometric shapes like capsule, sphericity, and pie shaped. It is found that the addition of TPU can help to promote uniform cellular structures. More importantly, the procedure of polymer melting, gas dispersion, foaming, and pelletizing can be completed in a one-step continuous process, with the advantages of high efficiency, low cost, controllable microstructures of the bead foams, and so on. Besides, the effect of processing parameters on the cellular structures, expansion ratio, and open-cell content of the bead foams was studied. Specifically, the cell growth progress and morphology evolution of the composite foam beads were recorded by a high-definition camera and microtechniques. In addition, the extruded bead foams were shaped into the foam board via steam-chest molding, and its interbead bonding mechanism and thermal insulation properties were studied. The as-prepared foam board exhibits low density (0.08 g/cm3) and thermal conductivity (46 mW/(m K)), which are expected to be used in the field of thermal insulation. This project contributes to the establishment of large-scale preparation and theory of bead foams and is expected to be applied to other polymeric foams.

Extruded polylactide bead foams using anhydrous supercritical CO2 extrusion foaming

“…Compared with autoclave foaming, extrusion foaming is more cost-efficient, time-saving, and has no wastewater generation. 12,13 Because the gas solubilization, compounding, foaming, and pelletizing can happen in a one-step process. However, it is far more difficult to endow the materials with proper cellular structures and low density in the molten state (like extrusion foaming) than in the solid state (like autoclave foaming).…”

“…In this work, based on our previous research, an anhydrous supercritical CO 2 extrusion foaming combined with wind-cooling pelletizing technology was used to prepare PLA bead foams. 12,13 The foaming ability of the PLA matrix was improved by the addition of the chain extender. Four types of PLA bead foams with different morphologies, cellular structures, and opencell content were designed and prepared by different technologies.…”

“…Nowadays, bead foams can be produced with two different techniques: autoclave foaming and extrusion foaming. Compared with autoclave foaming, extrusion foaming is more cost‐efficient, time‐saving, and has no wastewater generation 12,13 . Because the gas solubilization, compounding, foaming, and pelletizing can happen in a one‐step process.…”

“…In this work, based on our previous research, an anhydrous supercritical CO 2 extrusion foaming combined with wind‐cooling pelletizing technology was used to prepare PLA bead foams 12,13 . The foaming ability of the PLA matrix was improved by the addition of the chain extender.…”

Mechanically Robust Foamed Polypropylene/Bamboo Powder Composite Basketworks by CO2 Extrusion Foaming

“…In addition, the foaming process can introduce cellular structures inside the materials and has the potential to develop sandwich structures. , Typically, foam injection molding can regulate skin–cellular–skin sandwich structures for the polymer foams, but the solid structure on both sides limits its softness and the fixed mold also limits the difficulty of preparing large-size samples. In comparison, supercritical CO 2 continuous extrusion foaming with the advantages of economical and energy-saving can be used to prepare polymer foams with various morphologies, such as foam beads, foam strips, foam boards, and foam sheets . However, it is still relatively rare to prepare sandwich structures by extrusion foaming, mostly by co-extrusion, which is very demanding for the extruder die and equipment.…”