Influence of compatibilizer addition on particle size and coalescence in TPU/PP blends

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.