Development of expanded thermoplastic polyurethane (ETPU) bead foams: Dependency of the foam structure on TPU's hard segment content

In this thesis, we focus on bead foaming behavior of expanded thermoplastic polyurethane (ETPU) by using batch foaming process. Because TPU chemical composition and morphology directly affect the foam product features, different hard segments ratio and different polyols types of TPU were examined. Moreover, during the process, the effect of conditions which are saturation temperature, pressure and time on foam morphology were investigated. Cell nucleation phenomena were examined with pressure drop rate. Moreover, gas effect on crystalline segments under different conditions was investigated. Firstly, TPU samples were analyzed by thermal gravimetric analysis (TGA) to understand thermal decomposition behavior and the onset degradation temperature. Also, differential scanning calorimetry analysis (DSC) was used for understanding melting and crystallization behavior of TPU by non-isothermal analysis. According to results, process temperature range were investigated. For understanding the melt behavior and rheological properties of TPU, rheometer under oscilatory shear loads and melt flow indexer were used. To understand crystallization behavior of TPU under certain annealing temperature, isothermal analysis in DSC was used. By using thermal analysis, the temperature range was specified for foaming experiments. Under 2000psi for 30min different process temperatures were run until find reliable value for foaming processing. After finding the process temperature, all samples were foamed at 1000, 1500 and 2000psi for 30min in order to understand pressure effect on foaming. Later, samples were foamed at 15, 30 and 60min under 2000psi for investigating time effect on foam morphology. Furthermore, all foaming experiments were repeated again with very slow drop rate without obtaining foaming structure. Thus, gas effect on crystallization and cell nucleation phenomena were investigated. Finally, the foamed TPU samples were characterized. Firstly, the density of foamed samples and their expansion ratio were measured by Archimedes equation. Secondly, the morphology of cellular structure in foamed samples were observed using scanning electron microscope (SEM). After the analysis of cellular morphology; cell density and cell size were calculated for each samples. Hard segment effect on cell density and size were observed. To understand the effect of hard segment, gas under pressure and pressure drop rate on crystallization; thermal analysis was performed