Unmodified blends of two thermoplastic polyurethanes (TPU) and six polyolefines were used to study the influence of the component viscosities on the blend morphology and mechanical properties. Blends were produced by melt mixing using a twin screw extruder. Interactions between the blend components could not be detected by DSC, DMA, selective extraction, and SEM micrographs of cryofractures. The variation in tensile strength with blend composition produce a U-shaped curve with the minimum between 40 and 60 wt % of polyolefine. At similar viscosity ratios (h d /h m ), blends with polyether based TPU (TPU-eth) have a finer morphology than blends with polyester based TPU (TPU-est). This is due to the lower surface free energy of the polyether soft segments compared to the polyester soft segments. Different morphologies also lead to changes in mechanical behavior. Blends with TPU-eth show a lower decrease in tensile strength with blend composition than blends with TPU-est. The viscosity ratio between TPU and polyolefines can be directly correlated to the blend morphology obtained under similar blending conditions. TPU/PE blends show a lower dispersity than TPU/PP blends, due to the higher viscosity ratios of TPU/PE blends. This results in a greater reduction in tensile strength with the disperse phase content.

The coalescence behavior of immiscible blends was determined by annealing the melt without shear. The kinetics and the mechanism of coalescence were observed for blends of thermoplastic polyurethane (TPU) and polyolefins. Two different types of measurements were used to observe coalescence in quiescent melt at the processing temperature. On the one hand, the blend granules were annealed in bulk. The resulting particle sizes were determined by light microscopy and by SEM on particles separated from the blend. On the other hand, thin samples were annealed on a hot stage. Coalescence was observed in situ by light microscopy or static laser light scattering. It was found that the higher viscosity and elasticity ratios between polyethylene and TPU lead to a more pronounced coarsening of the morphology of 80/20 blends than in TPU/polypropylene. It has been shown that the process of reshaping coalescence is one mechanism of coalescence that occurs in quiescent melt. Another mechanism that was directly observed is a “domino effect” where one coalescence process causes the next one.

Thermoplastic polyurethane elastomers (TPU) and polyethylene (PE) form immiscible blends with an extremely low compatibility. In order to improve the dispersion, stability, and properties of these blends, polyethylene was grafted with maleic anhydride (PE‐g‐MA). Subsequently, it was blended with a commercial polyester ‐ type TPU in a twin‐screw extruder. With PE‐g‐MA as blend component, the particle size was dramatically reduced in comparison with PE. Coalescence was significantly reduced and the increase in particle size with composition was less pronounced than in blends with PE. In addition, the phase adhesion and the mechanical properties were improved by using PE‐g‐MA as minor component. Grafting of the MA onto the PE leads to a decrease of the molecular weight, the melt viscosity, and the mechanical properties of the pure PE. Hence, the reactive blend system exhibits a lower viscosity ratio. Comparison of these results with those from uncompatibilized blends with different viscosity ratios revealed that the reduction in viscosity ratio has a big influence on the blend morphology and because of that on the mechanical properties. In addition, there is a further effect on morphology and properties caused by the reduction in interfacial tension, which results from the compatibilizer formed at the interface.

ABSTRACT:The effect of the addition of ethylenic copolymers with different acrylic acid contents on the morphology and coalescence of blends of thermoplastic polyurethane and polypropylene has been investigated. The blends were prepared using a twin-screw extruder. Although the copolymers were immiscible with both blend components and no chemical reaction at the interface could be found, the blend properties were improved. Copolymers that form a stable interfacial layer between the blend components lead to a stabilization of the morphology. Addition of a copolymer containing 4% acrylic acid results in a markedly reduced particle size and improved mechanical properties in addition to the stabilization against coalescence. The copolymer concentration was varied over a wide range. One percent of copolymer was enough to reduce the particle size; about 3 wt % of added copolymer was sufficient to stabilize the morphology against coalescence in quiescent melt and to achieve an optimum in mechanical properties.

ABSTRACT:A study was performed with blends of thermoplastic polyurethanes and polyolefins to determine the structural requirements for a compatibilizer to be located at the interface. It was demonstrated that during the addition of an incompatible polymeric additive (i.e., incompatible with both blend constituents) to a polyurethanepolyolefin blend, the additive migrated to the interface. This interfacial phenomenon was proven to be virtually independent of compatibilizer viscosity or surface activity. Only when the compatibilizer was quite comparable to one of the phases did small differences in polarity govern whether the compatibilizer remained at the interface or formed micelles. This effect was demonstrated with a series of styrene-(ethylenebutylene)-styrene block copolymer compatibilizers.