Comparative study of chemical and physical foaming methods for injection-molded thermoplastic polyurethane

Abstract

Thermoplastic polyurethane is one of the most versatile thermoplastic materials being used in a myriad of industrial and commercial applications. Thermoplastic polyurethane foams are finding new applications in various industries including the furniture, automotive, sportswear, and packaging industries because of their easy processability and desirable customizable properties. In this study, three methods of manufacturing injection molded low density foams were investigated and compared: (1) using chemical blowing agents, (2) using microcellular injection molding with N2 as the blowing agent, and (3) using a combination of supercritical gas-laden pellets injection molding foaming technology and microcellular injection molding processes using co-blowing agents CO2 and N2. Thermal, rheological, microscopic imaging, and mechanical testing were carried out on the molded samples with increasing amounts of blowing agents. The results showed that the use of physical blowing agents yielded softer foams, while the use of CO2 and N2 as co-blowing agents helped to manufacture foams with lower bulk densities, better microstructures, and lower hysteresis loss ratios. Chemical blowing agent-foamed thermoplastic polyurethane showed an earlier onset of degradation. The average cell size decreased and the cell density increased with the use of co-blowing agents. A further increase in gas saturation levels showed a degradation of microstructure by cell coalescence.

Advances in microcellular injection moulding

“…22 CBAs used are ammonium, sodium bicarbonate or complex inert gas-releasing materials 21,23 and typically produce final parts with lower cell densities and larger average cell size. 24 This article provides a review of the research activities conducted in the field of MIM. The principle of the technology is presented together with applications.…”

Preparation of microcellular thermoplastic polyurethane (TPU) foam and its tensile property

“…For the formation of TPU foam, many blowing agents have been used such as butane , azodicarbonamide , and NaHCO 3 [19]. It should be noted that most of them are toxic, which furtherly lead the polymer matrix to additional degradation . Carbon dioxide (CO 2 ) as the blowing agent has many advantages including environment‐friend, adjustive solvent power, plasticization, enhanced diffusion rate, and complete separation from polymer .…”

Effect of Cell Morphology on Flexural Behavior of Injection-Molded Microcellular Polycarbonate

“…For instance, the use of a chemical blowing agent causes diminished thermal stability, whereas a physical blowing agent results in a smaller cell size and higher cell density. It was also found to be more suitable for achieving low-density foams [ 3 , 12 , 13 , 14 , 15 , 16 ].…”