The rheological properties of molten mixtures of polyoxymethylene and copolyamide: Their fibrillation and microstructure

Abstract

Abstract The rheological properties of molten mixtures of polyoxymethylene and copolyamide have been investigated by the methods of capillary viscometry over a wide range of shear stresses. It has been found that at relatively close values of the melt viscosity polyoxymethylene (POM) and copolyamide (CPA) form mixtures which differ markedly in viscosity and elastic properties from the original polymers. Depending on the magnitude of the shear stress, the viscosity of mixtures of definite composition may be either higher or lower than the viscosity of the components. Three‐ to tenfold swelling of the stream emerging from the capillary is observed for such mixtures, whereas at the same temperatures and stresses no swelling of the POM and CPA extrudates is practically observed. The data obtained are accounted for by the fact that the flow of mixtures through the capillary involves the formation of hundreds of thousands of ultrathin fibres of POM in the matrix of CPA, which are oriented along the flow axis.