Online measurements of crystallinity using Raman spectroscopy during blown film extrusion of a linear low-density polyethylene

Real‐time, Raman spectroscopic measurements of crystallinity during the blown film extrusion of a linear low‐density polyethylene (LLDPE) are reported. The take‐up ratio (TUR), inflation air pressure, and cooling conditions were varied, and their effect on the development of crystallinity was studied. The results indicate that the crystallization process starts at the freeze line, increases along the film line, and finally plateaus. It was observed that with changing processing conditions, the differences in the profiles for crystallinity were evident when plotted as a function of time rather than distance along the machine direction. The influence of take‐up ratio and bubble inflation air pressure on the development of crystallinity clearly established the role of flow‐induced crystallization during film extrusion. Polym. Eng. Sci. 44:1484–1490, 2004. © 2004 Society of Plastics Engineers.