The determination of the melt flow rate (MFR) and the melt volume rate (MVR) is described in various international standards. The most common are ISO 1133 and ASTM D1238. Both standards describe similar tests which differ slightly. This article is intended to give a short overview and to show the differences.

ISO 1133-1 and ISO 1133-2

The old ISO 1133:2005 was split and replaced by ISO 1133-1:2011, which describes the general test method. In addition, ISO 1133-2:2011 has been published for materials sensitive to a time- temperature history and/or moisture. Depending on the test material, the appropriate standard must be used.

ISO 1133-1 basically describes two different procedures. In procedure A, the extruded strand is cut off in defined time steps during the measurement. The MFR is determined from the weight of the strand sections. In procedure B, the piston speed is measured and the MVR is calculated from it. The melt density can be used to convert between MVR and MFR.

The measurements are always carried out in a measurement range 50-20 mm in front of the capillary with a melting time of 5 min. For low-viscosity materials, a capillary half the size (half diameter, half length) may also be used. The Determination of the flow rate ratio (FRR) is also described in the standard.

ISO 1133-2 is, in simple terms, a tightening of ISO 1133-1. The main differences are: In the case of hygroscopic materials, pre-drying and determination of the residual moisture are prescribed. The time sequence for filling and measuring is more strictly regulated. A more precise temperature control is required.

ASTM D1238

The American standard ASTM D1238 also describes two procedures A and B which correspond to the basic measuring procedure of ISO 1133-1 procedures A and B. The biggest differences to ISO 1133-1 are: The melting time is 7 min instead of 5 min. The standard measuring distance is between 46-20.6 mm (1 inch length) in front of the capillary and there is a shortened measuring distance for highly viscous materials of 46-39.65 mm (1/4 inch length). In addition, slightly different requirements are placed on the temperature distribution in the test channel. There is no equivalent to the more stringent ISO 1133-2. However, the standard directly mentions, that appropriate pre-conditioning of sample is necessary.

The measurements with the “half-die” (capillary with half diameter and length; same dimensions as in ISO 1133) are described as procedure C. With the exception of the capillary, the procedure corresponds to Procedure B. Procedure D describes an multi-weight measurement for determining the FRR with only one filling of the barrel.

Plastometer for ISO 1133 and ASTM D1238, certified according to ISO 17025

All GÖTTFERT plastometers are designed to meet ISO 1133-1 and ISO 1133-2 as well as ASTM D1238. In each case the most stringent requirements are met. Optionally, the final inspection and maintenance of our machines can also be carried out according to the strict laboratory management standard ISO 17025.