Effect of a Second Crystalline Modification in Polyethylene on X-Ray Crystallinity Measurements

Abstract

FROM several investigations it is known that in solid polyethylene which has undergone severe mechanical treatment a second crystalline modification may occur besides the normal rhombic one¹. In the X-ray diagram the strongest reflexion of this second modification coincides with the maximum in the so-called amorphous band (the broad halo of diffraction emanating from the amorphous regions). In view of the fact that the amorphous band in unbranched polyethylenes appears to be abnormally narrow, Slichter² suggests that the second modification also occurs in undeformed polyethylene. In this communication I want to point out that this suggestion may explain certain anomalies in the results of the density and crystallinity measurements described below.