by E.N. Step, M. Delvaux, H. Zhang, D. Strassler and A. Sanchez, Cabot; and A. Sendijarevic, I. Sendijarevic and V. Sendijarevic, Troy Polymers
Common inorganic fillers like chopped glass or carbon fibers are often added to TPUs to increase their hardness. Hardness improvement in TPU, as in other types of plastics, is typically accompanied by a loss of elongation at break and a decrease in dynamic performance.
Fumed silica is widely used as a reinforcement additive in silicone elastomers with significant mechanical property benefits, namely increased tensile strength, elongation and tear strength, among others. However, the use of fumed silica in thermoplastics is limited because of the difficulty to effectively add them via melt compounding by an extruder. Fumed silicas are extremely light; they have a bulk density of about 50 to 100 g/l. Thus, feeding this low density powder into the extruder, as well as conveying and mixing it with a viscous polymer melt, presents a challenge in typical plastics compounding operations.