Processing of Thermoplastic Polyurethane Foam with Bi-Modal Structure Using Expandable Microspheres as Blowing Agent

This research investigated the processing of bi-modal thermoplastic polyurethane (TPU) foams
with a two-zone structure prepared from TPU compound and TPU solution to compare with single modal foams. The expandable microspheres (EM) were used as a blowing agent, which was added at 3, 5, and 7 phr into TPU compounds and then fabricated into a single-modal TPU foam at 175 °C. Then, the density, compressive absorption by hysteresis loss ratio measurements, and morphology of TPU foams were examined. The result suggested that the single-modal TPU foam with 7 phr of EM gave 0.536 g/cm3 of density and a 24.71% hysteresis loss ratio, which was higher than that with 3 and 5 phr of EM content and had a better cell foam distribution. Therefore, the EM content at 7 phr was appropriate for addition to single-modal TPU foam and was used for further preparation of the bi-modal TPU foam. The result suggested that the density and the hysteresis loss ratio of bi-modal TPU foam were higher than those of single-modal. This indicated that the bi-modal TPU foam was superior and suitable for compressive absorption TPU foam applications.