Liquid foaming of TPU with Methylal

• Published in: Heliyon Vol. 10; no. 12; p. e32420
• Main Authors: Miele, Lorenzo, Di Lorenzo, Emilia, Guissart, Céline, Di Maio, Ernesto
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 30.06.2024; Elsevier
• Subjects: Blowing agents; Dimethoxymethane; Liquid foaming; Methylal; TPU; TPU; Liquid foaming; Blowing agents; Dimethoxymethane; Methylal
• ISSN: 2405-8440; 2405-8440
• DOI: 10.1016/j.heliyon.2024.e32420

This work investigates the peculiarities of using a liquid blowing agent, namely dimethoxymethane (Methylal) to foam a thermoplastic polyurethane (TPU) in the laboratory practice of batch foaming equipment. We preliminarily measured thermodynamic properties of the polymer/gas system relevant to foaming, namely the vapor-liquid pressures at the TPU foaming temperatures. Three different paths were then explored for foaming. First, we used Methylal under its liquid-vapor equilibrium condition, in which both liquid and vapor are present. Secondly, we used Methylal in the liquid state to experiment with liquid foaming strategies. We have observed specific aspects, details, and issues related to the use of liquid blowing agents and devised strategies to deal with them. Finally, we used Methylal as a co-blowing agent together with CO2. In all cases, we examined the impact of pressure, pressure drop rate, and temperature on foam density and morphology. Overall, liquid foaming has proven to be a viable technique and Methylal an effective blowing agent, especially in cooperation with other gaseous blowing agents, where it significantly improves the expansion ratio of the final product. •Batch foaming attempts by using a liquid blowing agent with thermoplastic polyurethane are reported.•Use of a liquid blowing agent requires adapting and re-designing the laboratory equipment.•The very high solubility of liquid Methylal in TPU (75%w/w at 5.5bar and 116°C) determines foam collapse.•Such large solubilities were used in combination with CO2 to achieve low-density (100kg/m3 ca.) and fine-morphology foams.