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Blown films modeling

References to earlier literature may be found in all of the articles died above. There is a very good overview of blown film modeling in a French doctoral dissertation,... [Pg.173]

The blown film process is known to be difficult to operate, and a variety of instabilities have been observed on experimental and production film lines. We showed in the previous chapter (Figure 10.10) that even a simple viscoelastic model of film blowing can lead to multiple steady states that have very different bubble shapes for the same operating parameters. The dynamical response, both experimental and from blown film models, is even richer. The dynamics of solidification are undoubtedly an important factor in the transient response of the process, but the operating space exhibits a variety of response modes even with the conventional approach of fixing the location of solidification and requiring that the rate of change of the bubble radius vanish at that point. [Pg.192]

Model including flow-induced crystallization in the blown film... [Pg.465]

The blown film process has been studied analytically since the early 1970s (Table 24.1). The first analysis was proposed by Pearson and Petrie [3, 4], who followed a fluid mechanics approach. However, this model is restricted to Newtonian fluids under isothermal conditions. This first model has been modified several times to consider different aspects of the process, such as temperature variation and rheological behavior of the system. [Pg.465]

The physical and mathematical description of the ribbon extrusion process was first given by Pearson [24], who simplified the conservation equations by using a onedimensional, isothermal, Newtonian fluid approach, and neglected the effects of polymer solidification. As in the case of blown film processes, several modifications and models have been proposed for the ribbon extrusion process (Table 24.2). [Pg.466]

The preceding section has described a useful technique for characterizing blown film bubbles based on easfly calculated processing values. However, as indicated, the technique is generalized and only provides qualitative information about the degree of melt stretching imparted on the film. Many comprehensive studies have been performed to develop more sophisticated models that characterize bubble stresses and kinematics (shape and velocities). For more detailed reading on this subject, the reader is referred to additional resources [17—28]. [Pg.94]

Fig. 9. Comparison of model calculations of bubble radius and film velocity with blown film data for a low density polyethylene, 3.84-cm radius x 0.8-mm thickness die, 4.1-kg/hr throughput. Data of Tas. Experiment 12 inflation pressure = 118 Pa, take-up force = 7.6... Fig. 9. Comparison of model calculations of bubble radius and film velocity with blown film data for a low density polyethylene, 3.84-cm radius x 0.8-mm thickness die, 4.1-kg/hr throughput. Data of Tas. Experiment 12 inflation pressure = 118 Pa, take-up force = 7.6...
Modeling of the blown film process illustrates characteristics that are very different from those of fiber spinning, even with primitive representations of the heat transfer (37). These differences are a consequence of the hoop stress in the bubble. Multiple steady states are computed for fixed operating conditions, for example, and steady axisymmetric bubbles can vanish suddenly following small changes in operating parameters both phenomena are seen in practice. The... [Pg.6743]

Further indication of the importance of a proper dispersion of layered silicates in PNCs is provided by Ranade et al [21] in a study reporting a com-pai ison between the creep behavior of maleated and non-maleated polyethylene-montmorillonite layered silicate blown films. The authom claimed that maleated polyethylene (PE-g-MA) facilitated the dispersion of montmorillonite layered silicate in the polyethylene (PE) matrix. The creep experiments were perfonned at 25% and 50% of the yield stress and the resulting creep compliance was modeled with the Burgers model. The fitting parameters of the Burgei-s model for the creep behavior (evaluated at 50% of the yield stress) of neat PE matrix and relative PNCs are summarized in Table 9.2. [Pg.318]

The film-blowing process is used industrially to manufacture plastic films that are biaxially oriented. Many attempts have been made to predict and model this complex but important process, which continues to mystify rheologists and polymer processing engineers worldwide. A constitutive equation, able to predict well the polymer melt in all forms of deformation, is required to model the process, together with the standard conservation equations of continuity, momentum, and energy. Pearson and Petrie [125,126] were the first to predict the forces within the blown film by the use of the thin-shell approximation, force balances, and the Newtonian constitutive equation. The use of the thin-shell approximation and force balances is standard in any attempt to model the film-blowing process, and it has been used in the vast majority of subsequent studies. [Pg.173]

Cao, B. and Campbell, G.A. (1990) Viscoplastic-elastic modeling of tubular blown film processing. AIChE J., 36, 420 30. [Pg.193]

Macosko CW (1994) Rheology principles, measuremaits and applications. Wiley, New York Maier D, Eckstein A, Friedrich C, Honerkamp JL (1998) Evaluation of models combining rheological data with molecular weight distribution. J Rheol 42 1153-1173 Majumder KK, Hobbs G, Bhattacharya SN (2007) Molecular, ifaeological, and crystalline properties of low-density polyethylene in blown film extrusion. Polym Eng Sci 47 1983-1991 Marrucci G (1991) Liquid crystallinity in polymers principles and fundamental properties. VCH, New York... [Pg.100]

Campbell, G. A. and B. Cao. 1987. The Interaction of Crystallinity, Elasticoplasticity, and a Two-Phase Model on Blown Film Bubble Shape. J. Plast. Eilm Sheet.. 3, 158-170. [Pg.308]

Key Word Blown film, bubble instabilities, modeling. [Pg.1267]

Polyolefin foams are easier to model than polyurethane (PU) foams, since the polymer mechanical properties does not change with foam density. An increase in water content decreases the density of PU foams, but increases the hard block content of the PU, hence increasing its Young s modulus. However, the microstructure of semi-crystalline PE and PP in foams is not spherulitic, as in bulk mouldings. Rodriguez-Perez and co-workers (20) showed that the cell faces in PE foams contain oriented crystals. Consequently, their properties are anisotropic. Mechanical data for PE or PP injection mouldings should not be used for modelling foam properties. Ideally the mechanical properties of the PE/PP in the cell faces should be measured. However, as such data is not available, it is possible to use data for blown PE film, since this is also biaxially stretched, and the texture of the crystalline orientation is known to be similar to that in foam faces. [Pg.12]

Although qualitatively similar to the experimental SME results, our previous simulation results had difficulties with particle evaporation [160]. Figure 1.34 illustrates particle evaporation. To overcome evaporation, the model parameters have been adjusted. 3D visualization techniques were also used to monitor the issue, and the full-blown 3D capabilities [157] allow for a detailed, nanostmctural analysis of the PFPE lubricant films. [Pg.39]

Artificial lipid bilayer membranes can be made [22,23] either by coating an orifice separating two compartments with a thin layer of dissolved lipid (which afterwards drains to form a bilayered structure—the so-called black film ) or by merely shaking a suspension of phospholipid in water until an emulsion of submicroscopic particles is obtained—the so-called liposome . Treatment of such an emulsion by sonication can convert it from a collection of concentric multilayers to single-walled bilayers. Bilayers may also be blown at the end of a capillary tube. Such bilayer preparations have been very heavily studied as models for cell membranes. They have the advantage that their composition can be controlled and the effect of various phospholipid components and of cholesterol on membrane properties can be examined. Such preparations focus attention on the lipid components of the membrane for investigation, without the complication of protein carriers or pore-forming molecules. Finally, the solutions at the two membrane interfaces can readily be manipulated. Many, but not all, of the studies on artificial membranes support the view developed in the previous sections of this chapter that membranes behave in terms of their permeability properties as fairly structured and by no means extremely non-polar sheets of barrier molecules. [Pg.22]

Model studies have helped considerably in understanding blown PE films. The x-ray diffraction patterns from these films could not be interpreted unambiguously and their microstructure was unclear until Keller and Machin [76] produced the same structures in model drawn films. They described the structure and showed how it was formed during crystallization from an oriented melt. This helped in many ways as, for example, the effect of molecular weight distribution on film properties could be understood by its effect on the structure formation. The orienta-... [Pg.197]

The vibrational changes that occur on orientation and crystallization have been used to research the origin of the residual orientation frequently found in blown or extruded film. These materials frequently show quite well developed orientation, and hence are useful as shrink wrapping. As the flowing melts from which they are formed are optically dichroic, it seems reasonable to propose a model involving flow-orientation-crystallization and solidfication in an oriented manner. It has been shown, however, that the orientation of a flowing polyethylene melt (as measured by infrared, Raman diffraction and X-ray diffraction) is very small [38]. [Pg.198]


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