Continuous Extrusion Foaming of Lignin Enhanced Thermoplastic Polyurethane (TPU)

In recent days, there has been growing concern about the potential negative impact of isocyanates part of TPU on environment and human health and their usages are being discouraged. Therefore, it is necessary to reduce/replace isocyanates and continuous foaming of lignin enhanced TPU will be an effective method, and also using renewable biomass as well as increasing the green material in TPU foam. For the extrusion of lignin enhanced foamed TPU with chemical foaming agent, the correlations between machine, chemical foaming agent and process parameters and the resulting foam quality are still unknown. Therefore the correlations between process parameters, chemical foaming agent contents and the resulting foam quality are examined in this paper. Due to the addition of various contents of lignin, the melt flow index, viscosity and density of TPU is influenced and their phase compatibility is found homogeneous. The thermal stability of TPU could be enhanced especially at high temperature due to the addition of lignin. It is also found that the chemical agent content has a significant influence on the TPU cellular structures and their content 1 wt% is optimum for finer cellular structures. The production of lignin enhanced TPU foam leads to density reduction for existing applications, but also opens new fields of application as the foaming reduces the material hardness without additional plasticizers.