A study of viscoelasticity and extrudate distortions of wood polymer composites |
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Authors: | Velichko Hristov John Vlachopoulos |
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Institution: | (1) Department of Chemical Engineering, McMaster University, 1280 Main St. West, Hamilton, ON, L8S 4L7, Canada |
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Abstract: | Natural fiber composites exhibit a characteristic surface tearing and extrudate distortions upon exiting from extrusion dies.
This type of defect is characterized by highly rough, cracked, and distorted extrudate surface. In this study, the extrudate
distortions and viscoelastic nature of metallocene-catalyzed polyethylene (mPE)/wood flour composites have been investigated.
As the wood flour loading increases the region of linear viscoelasticity shortens. The first normal stress difference decreases,
while the storage modulus increases. It was observed that increasing the wood flour loading up to 50 wt% aggravated the surface
tearing; however, 60 wt% wood flour in mPE completely eliminated the surface defect. It was also found that increasing the
shear rate improved the surface appearance of the filled compounds. This is due to the increased wall slip velocity of the
composites at high shear rates and wood filler loadings. Increasing the diameter of the die at the same aspect ratio generally
provides more severe surface tearing.
This paper was presented at the 3rd Annual Rheology Conference, AERC 2006, April 27–29, 2006, Crete, Greece. |
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Keywords: | Wood polymer composites Viscoelasticity Sharkskin Surface tearing |
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