APPLICATION OF BIREFRINGENCE To FILM BLOWING

Abstract

This paper presents a brief review of the flow birefringence technique and the analysis of the transmission of light through the blown film at an oblique angle. The rheological application of the technique is based on the stress-optical law whose validity and restrictions are discussed. The technique is able to fully determine the stress tensor in the bubble by using different light paths. Preliminary birefringence measurements are reported. The birefringence value is very low in the melt zone. However, it increases drastically in the vicinity of the frost line height where crystallization begins. The birefringence continues to increase above the frost line. It appears that the birefringence is highly affected by crystallization. The orientation of the crystalline phase is considerably higher than that of the molten polymer chains.

Keywords

film blowing birefringence technique molecular orientation polyethylene.

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