Crystallization Studies of LLDPE during Tubular Blown Film Processing

Abstract

The final physical properties of semi-crystalline blown films are highly dependent on the crystalline morphology and orientation of polymer chains within the film. Simultaneous on-line SALS (Small Angle Light Scattering) and IR (Infrared) temperature measurements were successfully used to study crystallization during tubular blown film extrusion of LLDPE. SALS patterns were recorded at various vertical positions along the bubble. For LLDPE, an undeformed spherelulitic structure is formed if the stress level during processing is not too high. The change in average scattered intensity with axial position can be described using multiple step Avrami kinetic processes in parallel. The first step accounts for crystal growth and corresponds to the well-known temperature plateau. The later processes start with the impingement of the growing spherulites and may reflect secondary crystallization and orientation processes. Because the magnitude of the average intensity is responsive to changes in process conditions, the on-line SALS system is potentially a useful tool for monitoring process-property interactions.

Polymer crystallization studies under processing-relevant conditions at the SAXS/WAXS DUBBLE beamline at the ESRF

“…Recently, efforts to monitor the structure evolution during film blowing in real time have been made, using techniques such as small-angle light scattering (Bullwinkel et al, 2001), Raman spectroscopy (Gururajan & Ogale, 2009) or X-ray diffraction using sealed tubes (Gururajan et al, 2008). While the advantages of using commercial X-ray sources for structural analysis are evident, they still lack the collimation which is so beneficial when using synchrotron radiation.…”

Transient solutions of the dynamics in low-speed fiber spinning process accompanied by flow-induced crystallization

“…According to the experimental results reported in the literature [18,20,29], the flow-induced crystallization occurs for iPP resins even at low speeds in fiber spinning and film casting. The spinline profiles of many state variables then exhibit very different shapes as compared with the no-crystallization cases as shown in Fig.…”

“…Resolving the problem is equally warranted in other important polymer processing operations such as film casting [19] and film blowing [20,21] where the same flow-induced crystallization plays a crucial role in shaping their dynamics of extensional deformation.…”

Structure Development of Low-Density Polyethylenes During Film Blowing: A Real-Time Wide-Angle X-ray Diffraction Study

“…In film blowing lines in industry, online measurements of the film quality are established by means of optical quality check in order to locate surface defects such as shark‐skin or to detect the occurrence of melt fracture. On a smaller scale, several researchers report on real‐time measurements combined with different methods such as SALS, Raman spectroscopy or birefringence . Among various characterization methods, X‐ray diffraction techniques such as Small Angle X‐ray Scattering (SAXS) or Wide Angle X‐ray Diffraction (WAXD), provides for a direct measurement technique to obtain the crystallinity and molecular orientation within a sample.…”