Study of instabilities in film blowing

Abstract

Bubble instabilities observed in film blowing using four different polyolefins are discussed: high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and polypropylene (PP). Special attention is given to the effect of the frost line height on the bubble stability, an effect mostly ignored in the literature. A video-camera system was used to record the bubble shape and oscillations. In general, three forms of instabilities and combinations were observed: (1) axisymmetric periodic variations in the bubble diameter; (2) helical motions of the bubble; and (3) variations in the position of the solidifcation line. The four resins show different stability behaviors. The LDPE has the most stable operating space and the PP is the most unstable one. No correlation was observed between bubble stability and oscillato y shear rheological properties of the resins. Instability is enhanced by increasing take-up ratio, increasing blow-up ratio, and decreasing frost line height. Furthermore, for the LDPE, some operating points were not attainable and multiple steady states were, observed. Our results are in a poor agreement with the predictions Cain and Denn's 1988 analysis.

Numerical modelling and experimental verification of blown film processing

“…The bubble is stable in this space for 2.2 < BUR < 3. This was in agreement with Ghaneh-Fard et al [9] who found that at low constant MDD ratio the bubble was stable at low frost line heights for a range of BURs. This particular FLH showed the smallest window of stable conditions.…”

“…The analysis of bubble stability in film blowing has largely focused on PEs (HDPE, LLDPE and LDPE), mainly due to their superior melt strength in comparison to other polymers such as PP. Only recently have results been reported on the bubble stability of PP [9]. Ghaneh-Fard et al [9] studied the bubble stability of PP and found PP to have a much smaller stable operating window in comparison to PEs.…”

“…Only recently have results been reported on the bubble stability of PP [9]. Ghaneh-Fard et al [9] studied the bubble stability of PP and found PP to have a much smaller stable operating window in comparison to PEs.…”

“…BI and HI have been reported by a number of investigators [5][6][7][8][9], however, FLHI was only recently reported by Ghaneh-Fard et al [5,9], after previous authors were using the term "meta stable" [2] which was misleading for time-dependent oscillations in FLH. Results on bubble stability have generally been qualitative until recently when Sweeney et al [10] utilised a video analysis system as an effective non-contact, real time device for quantifying instabilities during film blowing.…”

Application of continuation method for tracking steady-state contours in viscoelastic film blowing

“…There have been many theoretical attempts and experimental observations on this process over last four decades due to its academic and industrial importance (Han and Park, 1975;Kanai and White, 1984;Cain and Denn, 1988;Ghaneh-Fard et al, 1996;Yoon and Park, 2000;Doufas and McHugh, 2001;Fang et al, 2005;Zhang and Lafleur, 2008;Pirkle and Braatz, 2010). Especially, various theoretical issues including stability and sensitivity as well as multiple base flows have been explored for elucidating intricate phenomena occurring in film blowing systems (Hyun et al, 2004;Shin et al, 2007;Pirkle and Braatz, 2010).…”