The Flow Rate Ratio (FRR) is based on two Melt Flow Rate (MFR) values instead of only one MFR as generally measured at present. MFR is a determination of the amount of melted material which, in ten minutes, is pressed through a die by a piston using a constant load.
The material used consists of polyethylene grades. This method can of course be used for other thermoplastics which could be tested under the same conditions as the ones listed in the Annex, Table 1.
Through FRR, the previous MFR is now extended to two measurements at different loads. This gives a higher accuracy in quality control for plastics. An improvement of accuracy is achieved since the ratio between two MFRvalues (FRR) indicates shear-thinning properties. The MFRvalue obtained by the lowest weight indicates the zero shear viscosity which correlates with the weight average molecular weight (Mw). By quoting MFR (for the lowest weight) and FRR more information is supplied about the material.
Note: The low rates of shear obtained during a MFR test are not comparable to the shear rates under normal processing conditions.