Surface tension, interfacial tension, and morphology in blends of thermoplastic polyurethanes and polyolefins. Part I. Surface tension of melts of TPU model substances and polyolefins

The pendant drop analysis was used to determine surface tensions γ of polymer melts. For thermoplastic polyurethane (TPU) elastomers, which are block copolymers of crystallisable hard segments (HS) and amorphous soft segments (SS), the surface tensions of the different segments in the melt were measured for the first time. As model compounds for the SS polyetherdiols (PEt-diols) and a polyesterdiol (PEs-diol) were used. To suppress the influence of the hydroxyl end groups on the surface properties the diols were either acetylated or chain extended with a diisocyanate. The influence of the molecular weight and the endcapping method was investigated. All TPU segments exhibit higher surface tensions than that measured for polyolefins due to their polar character except the acetylated PEt-diols with γ-values between those of polypropylene and polyethylene. With 48–45 mN/m at 120–165 °C, the highest surface tension was determined for an amorphous HS model. The surface tensions of both PEs-diols are higher than that of the PEt-diol model compounds. While the surface tensions of the acetylated and MDI extended PEs-diols exhibit the same temperature dependence, differences were found between the surface tension of the acetylated and MDI extended PEt-diols, which diminish with increasing molecular weight of the model substances.