Film blowing stability

Despite the big effect on shear sensitivity at low shear rates, low levels of metallocene LCB do not necessarily yield any improvement at high shear rates [95, 128] In extensional flows, metallocene-LCB may improve melt strength and melt stability due to a strain hardening effect, giving improved film blowing stability and more even film thickness [119]. 

Effect of Newtonian viscosity on the film blowing stability... 

The predicted effect of the Newtonian viscosity on the film blowing stability is depicted in Figure 6a. It is clearly shown that an increase in the Newtonian viscosity leads to the increase in the film blowing processing window. In particular, the model predicts that an increase in the Newtonian viscosity (i.e. Mw) of the melt increases the capability to achieve much higher final film thickness for certain BUR a condition which is very desirable for heavy-duty bags production. On the other hand the model predicts that an increase in the Newtonian viscosity enhances the ability of the melt to stretch i.e. one can produce lower final film thickness compared to the case where the material has lower Newtonian viscosity. 

The predicted effect of the die radius and freeze line height on the film blowing stability is depicted in Figures 6c-6d. It is again clear from these Figures that an increase... 

The effect of the freeze line height on the film blowing stability depicted in Figure 6d shows that the model predicts that an increase in the freeze line height decrease the processing window which is in very good agreement with the experimental data reported in the open literature [12]. 

Products A wide range of bimodal and unimodal products, with a full control of comonomer distribution, can be produced, with densities ranging from 918 to 970 kg/m3 and melt flowrate from less than 0.1 to over 100. The molecular weight distribution can be controlled from narrow to broad. Advanced properties are tailor-made applications such as pipe strength, film bubble stability as well as high ESCR and stiffness in blow molding. Other special applications include extrusion coating and wire cable. 

The SH plays a positive role in film blowing (15, 44) or in wire coating ( ). LPX-30 does not show this effect and Its processability Index Is low. On the other hand, SH of LDPE Is quite high and so Is the processability Index. The accepted mechanism for Improvement of fllm bubble stability Is self healing of a potentially weak spot by a local Increase of extenslonal viscosity caused by SH. It Is Important to note that adding to LPX-30 either 10 wtZ LDPE, 202 LLDPE-10 or lOZ LPX-24 was sufficient for generation of SH. The subsequent trial on a production line confirmed these results Increased bubble stability allowed for higher production rates of the blends. 

The residual antioxidant content (Table 3) was determined and compared to the stability of each material. In the material stabilized with a-tocopherol (PE-toc), 60% of the original amount of a-tocopherol was lost during the preparation of the films and during the film-blowing. In contrast, only 34% of the synthetic antioxidant Irganox 1076 (PE-Irgl076) was lost. 

Micic, R, S. N. Bhattacharya, and G. Field. 1998. Transient elongational viscosity of LLDPE/LDPE blends and its relevance to bubble stability in the film blowing process. Polymer Engineering and Science 38 1685-1693. 

The percolation threshold near 0p 0.2 is evident in several plots of t/o versus (j), of LDPE/branched PE (Pcot et al. 2003), LDPE/HDPE (Sarkhel et al. 2006), or melt strength of LDPE/LLDPE (Field et al. 1999 Ho et al. 2002). The latter authors noted that for film-blowing bubble stability, miscibility and melt strength in elongatimi are important For good process ability of LLDPE, >20 wt% of LDPE was required. 

Ghijsels, A., Ente, J. and Raadsen, J. (1990) Melt strength behavior of polyethylene and its relation to bubble stability in film blowing, Int. Polymer Processing 5, 284-286. 

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