Rides, M; Kelly, A L*; Allen, C R G (2011) An investigation of high rate capillary extrusion rheometry of thermoplastics. Polym. Test., 30 (8). pp. 916-924.

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Abstract

A comparison of high rate extrusion rheometry was undertaken to assess the reproducibility of shear viscosity results obtained using standard laboratory extrusion rheometers and a Fanuc Roboshot injection moulding machine. Lower shear rate measurements were carried out using oscillatory and rotational rheometers to provide independent comparison of shear viscosity values in the regions of overlap between the methods. Shear viscosities were obtained at shear rates in the range 13 s-1 to 2.6 x 10^6 s-1 by capillary extrusion rheometry and up to 6 x 10^6 s-1 using a Fanuc Roboshot moulding machine. A significant source of error due to leakage of sample past the piston at the high pressures accounting for a factor of x10 error in measured shear viscosity was addressed through modification of the piston head to provide better sealing.

The high shear rate results generally demonstrated an overall good level of agreement for shear viscosities up to a shear rate of 2 x 10^5 s-1, with results varying typically by up to no more than approximately ± 20%. This level of reproducibility is considered to be favourable compared with the reproducibility value of ± 28% (95% confidence level) identified for capillary extrusion rheometry measurements at lower shear rates in ISO 11443 [1]. At higher shear rates, e.g. above a shear rate of 360,000 s-1 for polystyrene, deviations in the shear thinning behaviour were apparent, potentially linked to the pressure dependence of viscosity [2].

The effect of the Rabinowitsch correction on true shear viscosity - shear rate data has been highlighted with reference to the high density polyethylene that had a low value for its shear thinning coefficient n. This correction introduces a potentially large degree of uncertainty in the corrected shear viscosity values at high shear rates.

Item Type:	Article
Keywords:	rheometry, extrusion, high shear rate, shear viscosity, polymer, plastics
Subjects:	Advanced Materials Advanced Materials > Polymer Rheology Advanced Materials > Polymers
Identification number/DOI:	10.1016/j.polymertesting.2011.8.011
Last Modified:	02 Feb 2018 13:14
URI:	http://eprintspublications.npl.co.uk/id/eprint/5341

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