Liquid foaming of TPU with Methylal

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.

Effect of silica nanoparticles on the impregnation process, foaming dynamics and cell microstructure of styrene-methyl methacrylate copolymer/n-pentane foams

In the present study, two-step foaming procedure with a designed in-situ foaming observation apparatus was used to study the foaming dynamics of styrene-methyl methacrylate (St-MMA) copolymer/nanosilica composites. For this purpose, the St-MMA copolymer was synthesized using suspension copolymerization and its nanocomposites were prepared using solution method. The foaming dynamics was studied through temperature-induced (two-step batch foaming) method. Furthermore, the effects of content, size and surface chemistry of silica nanoparticles on the impregnation process, the foaming dynamics and the final morphology of prepared foams were investigated. The impregnation data showed that the presence of silica nanoparticles in matrix prolonged the impregnation and decreased diffusion coefficient. This effect would be clearer where nanoparticle contents are high and the temperature is quite above Tg. The foaming dynamics results illustrated that the nucleation and foaming rate were enhanced with the nanoparticle addition and its size reduction. At the St-MMA copolymer foaming system, the silica nanoparticles with hydrophilic surface chemistry are more efficient in comparison to hydrophobic nanoparticles where all foaming dynamics and the final microstructure parameters were improved.

The determination of n-pentane solubility and diffusivity in styrene–methyl methacrylate copolymers via designed apparatus

In this work, styrene–methyl methacrylate copolymer particles were synthesized by suspension polymerization process with different copolymer compositions. A system was designed to measure the solubility and diffusivity of n-pentane in the synthesized copolymers. The designed system consisted of the self-sealing cell equipped to the pressure and temperature controllers. The synthesized copolymer particles were impregnated by n-pentane and their expansion were recorded visually. Furthermore, the solubility and diffusivity of n-pentane in copolymer particles were measured by the same apparatus. The effect of different foaming conditions on the solubility and diffusivity of n-pentane in the samples were examined. It was concluded that the sorption pressure and temperature have contradictory effects on the solubility and diffusivity of n-pentane in styrene–methyl methacrylate copolymers at different sorption pressures. It was concluded that with methyl methacrylate content increment in copolymer, the diffusivity and dissolved n-pentane content in copolymer were reduced.