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A study of viscoelasticity and extrudate distortions of wood polymer composites

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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.

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Acknowledgement

The authors would like to thank Dr. D. Strutt for performing the FEM numerical calculations. Financial supports from McMaster Manufacturing Research Institute (MMRI) and the Extrusion Division of the Society of Plastics Engineers (Lew Erwin Memorial Scholarship to V. Hristov) are also gratefully acknowledged.

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  1. Department of Chemical Engineering, McMaster University, 1280 Main St. West, Hamilton, ON, L8S 4L7, Canada

    Velichko Hristov & John Vlachopoulos

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  1. Velichko Hristov
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  2. John Vlachopoulos
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Correspondence to John Vlachopoulos.

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Hristov, V., Vlachopoulos, J. A study of viscoelasticity and extrudate distortions of wood polymer composites. Rheol Acta 46, 773–783 (2007). https://doi.org/10.1007/s00397-007-0186-7

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  • DOI: https://doi.org/10.1007/s00397-007-0186-7

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