Accessible Requires Authentication Published by De Gruyter March 1, 2013

Sparse Long-chain Branching's Effect on the Film-casting Behavior of PE

C. W. Seay and D. G. Baird


The degree of film-width reduction or necking during film-casting is analyzed for three metallocene-catalyzed linear low density polyethylenes, LLDPE, with varying degrees of sparse long-chain branching, LCB. The resins included three sparsely LCB polyethylene, PE, materials with varying LCB content ranging from linear to 0.57 LCB/10000 CH2 along with a Ziegler-Natta polymerized LLDPE and a tubular free-radical polymerized low density polyethylene, LDPE. The last two resins are used as reference materials. The primary objective of this analysis is to evaluate whether uniaxial extensional rheological characteristics, in particular strain-hardening, that are a result of LCB influence the film-necking properties. At the lowest drawdown ratio, necking is observed to be reduced with increasing LCB, and thus strain-hardening characteristics. At the higher drawdown ratios it is observed that LCB no longer reduces necking and the curves merge to the results found for linear PE, except in the case of LDPE, which shows reduced necking at all drawdown ratios. Furthermore, comparisons of film necking are also made to separate the effects of molecular weight distribution, MWD, and LCB. The results indicate that both broadening the MWD and the addition of sparse LCB reduce the degree of necking, but to a lesser degree in the case of broadening the MWD. Analysis of the uniaxial extensional and dynamic shear rheology with the pom-pom constitutive model reveals that a distribution of branches along shorter relaxation time modes is important in reducing necking at higher drawdown ratios. Factors such as shear viscosity effects, extrudate swell, and non-isothermal behavior were eliminated as contributing factors.

2 Mail address: Donald G. Baird, Department of Chemical Engineering, Virginia Tech., 128 Randolph Hall, Blacksburg, VA 24061-0211, USA E-mail:


Axelson, D., et al., A Quantitative Analysis of Low-density (Branched) Polyethylenes by Carbon-13 Fourier Transform Nuclear Magnetic Resonance at 67.9 MHz, Macromolecules, 12, 4252(1979).10.1021/ma60067a010 Search in Google Scholar

Bird, R., et al.: Dynamics of Polymer Liquids: Fluid Mechanics, 2, Wiley Interscience, New York(1987). Search in Google Scholar

Blackwell, R., et al., Molecular Drag-strain Coupling in Branched Polymer Melts, J. Rheol., 44, 121136(2000).10.1122/1.551081 Search in Google Scholar

Canning, K., Co, A., Edge Effects in Film Casting of Molten Polymers, J. Plast. Film Sheeting, 16, 188203(2000).10.1177/875608700772677553 Search in Google Scholar

Dobroth, T., Erwin, L., Causes of Edge beads in Cast Films, Polym. Eng. Sci., 26, 462467(1986).10.1002/pen.760260704 Search in Google Scholar

Doerpinghaus, P., Baird, D., Assessing the Branching Architecture of Sparsely Branched Metallocene-Catalyzed Polyethylenes Using the Pompom Constitutive Model, Macromolecules, 35, 1008710095(2002).10.1021/ma021332m Search in Google Scholar

Doerpinghaus, P., Baird, D., Separating the Effects of Sparse Long-chain Branching on Rheology from those due to Molecular Weight in Polyethylenes, J. Rheol., 47, 717736(2003).10.1122/1.1567751 Search in Google Scholar

Flory, P.: Principles of Polymer Chemistry, Cornell University Press, Ithaca, NY(1953). Search in Google Scholar

Inkson, N., et al., Predicting Low Density Polyethylene Melt Rheology in Elongational and Shear Flows with ‘Pom-Pom’ Constitutive Equations, J. Rheol., 43, 873896(1999).10.1122/1.551036 Search in Google Scholar

Ito, H., et al., A Model of Neck-in Phenomenon in Film Casting Process, Journal of the Society of Rheology, Japan, 31, 157163(2003). Search in Google Scholar

Iyengar, V., Co, A., Film Casting of a Modified Giesekus Fluid: Stability Analysis, Chem. Eng. Sci., 51, 14171430(1996).10.1016/0009-2509(95)00316-9 Search in Google Scholar

Janzen, J., Colby, R., Diagnosing long-chain branching in polyethylenes, J. Mol. Struc., 485, 569584(1999).10.1016/S0022-2860(99)00097-6 Search in Google Scholar

Kajiwara, T., et al., Relationship between Neck-in Phenomena and Rheological Properties in Film Casting, Nihon Reoroji Gakkaishi, 34, 97103(2006).10.1678/rheology.34.97 Search in Google Scholar

Kim, J., et al., Transient Solutions of the Dynamics of Film Casting Process Using 2-D Viscoelastic Model, J. Non-Newtonian Fluid Mech., 132, 5360(2005).10.1016/j.jnnfm.2005.10.002 Search in Google Scholar

Lee, J., et al., Kinematic Waves and Draw Resonance in Film Casting Process, J. Non-Newtonian Fluid Mech., 101, 4354(2001).10.1016/S0377-0257(01)00155-0 Search in Google Scholar

McLeish, T., Larson, R., Molecular Constitutive Equations for a Class of Branched Polymers: The Pom-Pom Polymer, J. Rheol., 42, 81110(1998).10.1122/1.550933 Search in Google Scholar

Minoshima, W., White, J., Instability Phenomena in Tubular Film, and Melt Spinning of Rheologically Characterized High Density, Low Density and Linear Low Density Polyethylenes, J. Non-Newtonian Fluid Mech., 19, 275302(1986).10.1016/0377-0257(86)80053-2 Search in Google Scholar

Pis-Lopez, M., Co, A., Multilayer Film Casting of Modified Giesekus Fluids Part 1. Steady-State Analysis, J. Non-Newtonian Fluid Mech., 66, 7193(1996a).10.1016/0377-0257(96)01468-1 Search in Google Scholar

Pis-Lopez, M., Co, A., Multilayer Film Casting of Modified Giesekus Fluids Part 2. Linear Stability Analysis, J. Non-Newtonian Fluid Mech., 66, 95114(1996b).10.1016/0377-0257(96)01469-3 Search in Google Scholar

Sakaki, K., et al., Three-Dimensional Flow Simulation of a Film-Casting Process, Polym. Eng. Sci., 36, 18211831(1996).10.1002/pen.10577 Search in Google Scholar

Satoh, N., et al., Viscoelastic Simulation of Film Casting Process for a Polymer Melt, Polym. Eng. Sci., 41, 15641579(2001).10.1002/pen.10855 Search in Google Scholar

Silagy, D., et al., Study of the Stability of the Film Casting Process, Polym. Eng. Sci., 36, 26142625(1996).10.1002/pen.10661 Search in Google Scholar

Silagy, D., et al., Stationary and Stability Analysis of the Film Casting Process, J. Non-Newtonian Fluid Mech., 79, 563583(1998).10.1016/S0377-0257(98)00119-0 Search in Google Scholar

Smith, S., Stolle, D., Numerical Simulation of Film Casting Using an Updated Lagrangian Finite Element Algorithm, Polym. Eng. Sci., 43, 11051122(2003).10.1002/pen.10094 Search in Google Scholar

Sollogoub, C., et al., Non-isothermal Viscoelastic Numerical Model of the Cast-film Process, J. Non-Newtonian Fluid Mech., 138, 7686(2006).10.1016/j.jnnfm.2005.11.011 Search in Google Scholar

Tanner, R., Theory of Die Swell, J. Polym. Sci., Part A: Polym. Chem., 8, 20672070(1970). Search in Google Scholar

Zheng, H., et al., Three-Dimensional Simulation of the Non-Isothermal Cast Film Process of Polymer Melts, J. Polym. Res., 13, 433440(2006).10.1007/s10965-006-9064-8 Search in Google Scholar

Zimm, B., Stockmayer, W., The Dimensions of Chain Molecules Containing Branches and Rings, J. Am. Chem. Soc., 17, 13011314(1949). Search in Google Scholar

Received: 2008-05-06
Accepted: 2008-11-11
Published Online: 2013-03-01
Published in Print: 2009-03-01

© 2009, Carl Hanser Verlag, Munich