Enhanced foaming ability of thermoplastic polyurethane by crystallization during mold-opening foam injection molding with supercritical N2 as blowing agents

This study provides an insight into the foaming of thermoplastic polyurethane (TPU), which was improved by the crystallization of hard segment domains. This study investigated the effects of packing time in the mold-opening foam injection molding (MOFIM) technology on the crystallization behavior of hard segments in TPU and the cell morphology of TPU foams. It was observed that the prolongation of the packing time, corresponding to a longer crystallization time before foaming, induced an increased crystallinity in the injection-molded TPU solids and foams due to the crystals becoming more close-packed. The enhancement of the foamability of TPU was attributed not only to the increased crystallinity of hard segments, but also to the broader distribution of crystals at the same crystallinity. Furthermore, TPU foams with greater hardness have smaller cell size, higher cell density, and narrower distribution in cell size owing to their higher viscosity and storage modulus than those with lower hardness prepared under the same conditions.(c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study investigates the improvement in the foaming of thermoplastic polyurethane (TPU) by enhancing the crystallization of hard segments. The effects of packing time in MOFIM technology on the crystallization behavior of hard segments and the cell morphology of TPU foams are studied. It is found that prolonging the packing time increases the crystallinity of TPU solids and foams due to closer-packed crystals. The enhanced foamability of TPU is attributed to both increased crystallinity of hard segments and broader distribution of crystals at the same crystallinity. Moreover, TPU foams with higher hardness have smaller cell size, higher cell density, and narrower distribution in cell size due to their higher viscosity and storage modulus.