Date of Award

5-2004

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Biological Engineering

Advisor

Albert Co

Second Committee Member

Douglas W. Bousfield

Third Committee Member

David J. Neivandt

Abstract

Film casting process is an important process for the production of plastic films, but production ratese are often limited by an instability known as draw resonance. The effects of the Deborah number and the aspect ratio on the film casting process were investigated. The Deborah number is defined as the ratio of the characterisic time of the fluid to the characteristic time of the flow system while the aspect ratio is defined as the ratio fo the drawing length to the half width of the die. The operating variables of the film casting process are: extrusion velocity, take-up velocity and drawing length while the measurable variables are: velocity profile, temperature profile, width profile, thickness profile and the drawing force. The critical draw ratios of two Dowlex linear density polyethylene melts (LLDPE 2045A and LLDPE 2045G) were determined at different Deborah numbers and aspect ratio from: (I) thickness measurement and (ii) pressure measurements. The thickness measurement approach was adopted to determine the critical draw ratio for LLDPE 2045A while the pressure measurement approach was adopted to determine the critical draw ratio for LLDPE 2045G. For one case of LLDPE 2045G, both thickness and pressure measurements were carried out. The critical draw ratios obtained from the thickness measurements were found to be higher and more reliable than that from pressure measurements. No significant effect of the Deborah number on the critical number on the critical draw ratio for LLDPE 2045A were observed. Increase in temperature, reduction in neck-in, decrease in dimensionless force was observed as the Deborah number was increased. The critical draw ratio increased with aspect ratio at constant Deborah number. There was a significant change in the shape of the velocity profile as the Deborah number was increased while no significant effect on the shape of the velocity profile as the aspect ratio was increased. The aspect ratio had significant effect on the width profile; the neck-in for polymer B increased as the aspect ratio increased. The increase in the temperature with the aspect ratio was attributed to the changing extrusion velocity associated with the constant Deborah number.

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