Infrared Dichroic and Viscoelastic Behaviors of Polyethylene-Polypropylene Systems Blended in Molten State

Abstract

In the previous papers report was presented of simultaneous measurement that was made of the films of low and high density polyethylene and polypropylene with respect to their change in infrared dichroism and the stress and strain during stress relaxation at constant length and stretching at constant rate of strain. This new rheo-optical method was found very effective in interpreting the stress-strain curves of these materials. Because this technique enables us to determine the molecular orientation of each component in a blend subjected to deformation from the dichroic ratio of some absorption bands characteristic to each component, it can be powerful means to study the true deformation mechanism of polymer blends which have been hitherto discussed only hypothetically. In the present paper report is made of measurement that has been made by this technique of the contribution of each component in polyethylene-polypropylene blends to the total deformation and its deformation mechanisms have been discussed. At the same time, the temperature dependences of the tensile storage modules E' and loss modulus E" have been measured for the same samples.The sample blends of high density polyethylene (PE) and isotactic polypropylene (PP) having different compositions were obtained by mixing the components in the molten state. The variation of the dichroism of 998, 730, and 720cm-1 bands with elongation has been observed during the stretching at a constant rate of strain, and the change in orientation functions for crystallographic c axis of each component has been determined. The result shows that when Φp>0.7 (Φp is the weight fraction of PP in the blend), PP becomes the continuous phase or matrix and PE becomes the dispersed phase, while when Φp<0.3, PE becomes the continuous phase and PP becomes the dispersed one. It has also been observed that the dispersed phase can not be elongated so much as the continuous phase. This is much more remarkable when the phase separation occurs. With the aid of such information, the results of temperature dependences of E' and E" for the blends have been interpreted consistently.