Transient elongational viscosity of LLDPE/LDPE blends and its relevance to bubble stability in the film blowing process

Abstract

Transient elongational viscosity of linear low density polyethylene (LLDPE) and its blends with 10% and 20% of low density polyethylene (LDPE) was measured at two temperatures by a constant strain rate elongational rheometer. In addition, the performance of the blends in the film blowing process was assessed in terms of bubble stability at two processing temperatures. An operating window for stable bubble production was determined. The elongational viscosity measurements on blends revealed stronger strain hardening characteristics at a higher temperature of testing. These results correlate favorably with findings from a bubble stability investigation where it was found that the size of the operating window for stable bubble production increased with increasing extrusion temperature. This work seems to indicate that increasing processing temperature during the film blowing of LLDPE‐rich blends could lead to a processability improvement of these blends as far as bubble stability is concerned.

Melt strength and film bubble instability of LLDPE/LDPE blends

“…The relevance of transient elongational viscosity measurements to the bubble instability of these blends has also been discussed. 19 In previous work, 20±23 we have discussed in detail the measurement of the melt strength and elongational viscosity of these LLDPE/LDPE blends, showing that the elongational properties of the blends were greatly enhanced compared with the LLDPE base polymers and synergism was observed for LDPE-rich blends.…”

Effect of biaxial drawing on morphology and properties of copolyamide nanocomposites produced by film blowing

“…As reported in a recent study, carried out by our research group on the extensional behavior of polyamide-based nanocomposites [11], the peculiar extensional thickening of nanocomposites can be reasonably related to the presence of silicate platelets, which build up three-dimensional arrangements, the so-called ''house of cards'' structures, hindering extensional flow similarly to branches of the macromolecular chains. Strain hardening of extensional viscosity has been generally observed for long chain-branched polyolefines, and a correlation between the increasing strain hardening characteristics and improved bubble stability for LLDPE-rich blends was recently found in literature [25].…”

Computer simulation of the film blowing process incorporating crystallization and viscoelasticity

“…The radius of the die exit is typically between 1 and 25 cm, while the gap thickness of the die exit is typically between 1 and 2 mm. The pressure difference inside the bubble is reportedly 50 Pa higher than the ambient pressure, and the initial velocity is between 1 and 5 cmls [Micic et al (1998)]. In the last fifty years or so, extensive studies were conducted on blown films.…”