Kelvin-Voigt model was applied to blown-film process of pure LDPE and LDPE filled with Calcium Carbonate particles, and orientation and mechanical properties of blown-film were analyzed in order to explain rheological phenomena. Isopropyl triisostearoyltitanate was used to observe the effect of coupling agent.
The addition of particles decreased die swelling but increased shear modulus and viscosity. The increment of viscosity was accentuated by higher loading level and lower shear stress.
The characteristic retardation time, which was defined as the ratio of viscosity to apparent modulus and obtained from shear viscosity and post extrusion swelling, was nearly independent of the loading level of filler and increased as shear rate decreased.
Coupling agent, filler loading level and shear rate gave no influence on the activation energy of the viscous flow of $CaCO_3$-filled-LDPE, the value of which was $10^3$ J/mole.
Bubble diameter decreased with increment of draw ratio and decrement of hoop stress, and became smaller when coupling agent was not used.
Blown bubble shape measured in blown-film process could be predicted more suitably by Kelvin-Voigt model using Finger's strain tensor than by purely viscous or elastic model.
Orientation and mechanical properties were affected by the experimental conditions.
As stress in a specified direction increased, birefringence and tensile strength of that direction increased but elongation at break point decreased.
As birefringence increased, tensile strength increased but elongation at break point decreased.
