Dynamics and criteria for bubble instabilities in a single layer film blowing extrusion

Abstract

In this paper, the performance of a new in‐line scanning camera system for the study of various bubble instabilities in film blowing extrusion is critically evaluated. Three commercial film‐grade polyethylenes, LmPE, LLDPE and LDPE, were used to generate the bubble instabilities. Reliable and objective criteria for differentiating various bubble instabilities such as draw resonance, helicoidal instability, and frost line height instability are proposed by using the new device. Detailed dynamics of each bubble instability was carefully investigated as a function of time in a broad range of the take‐up ratio (TUR), blow‐up ratio (BUR) and frost line height (FLH). In addition, effects of melt temperature and mass flow rates on dynamics of the bubble instabilities are discussed. It was found that the new system could capture the main characteristics of all bubble instabilities quantitatively. It was also found that magnitude and periodicity of radius variation during draw resonance of LmPE decreased as TUR increased at constant FLH and BUR. This implies that the origin of draw resonance in film blowing seems to be different from that observed in fiber spinning. In the case of helicoidal instability, eccentricity, which defines the deviation of the bubble center from the die center, decreased as TUR increased. However, the bubble could not be stabilized as expected. A graphical quantification approach to determine the stable zone in the bubble stability map is also discussed.

Variational Principle Based Stability Analysis of Non-isothermal Film Blowing Process for Non-Newtonian Fluids

“…As can be seen, increase of the mass flow rate leads to reduction of the film blowing stability window, which is in agreement with the open literature [16]. The theoretical results depicted in Figure 10 suggest that the effect of the mass flow rate on film blowing stability window width has almost linear character.…”

“…As can be seen, increase in the melt/die temperature leads to narrowing of the film blowing stability window, which is in agreement with the open literature [16]. Interestingly, the calculated results depicted in Figure 12 suggest that the relationship between the melt/die temperature and minimum achievable film thickness during the film blowing process has no monotonic character.…”

“…As can be seen, increase in the flow activation energy leads to widening of the film blowing stability window which is in good agreement with the experimental reality [16] where it has been clearly demonstrated that the film blowing process is more stable for high flow activation energy LDPE in comparison with low activation energy LLDPE polymer. Interestingly, the calculated results depicted in Figure 5 suggest that the relationship between the flow activation energy and minimum achievable film thickness during the film blowing process has no monotonic character.…”

“…It is clearly visible that the increased bubble cooling intensity (i.e. with the increased heat transfer coefficient) leads to processing window widening and vice versa, which is in good correspondence with the open literature [16]. Moreover, the theoretical results indicate that the high thickness polymer films (which are usually used for the heavy-duty bags production) can only be produced by utilizing highly effective film blowing cooling system.…”

Modeling of Non-Isothermal Film Blowing Process for Polyolefines by Using Variational Principles

“…The final film created in this way, can be applied in a food processing, as well as, in a health service or waste industry. Although, the film blowing process has been continuously developing from latest 1930´s, even now the process is not fully understood yet because there are some problems, which bring significant processing limitations [1][2][3][4][5][6][7][8][9][10][11][12], such as bubble instabilities . The most popular way to optimize the film blowing process is modeling.…”