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Interlaboratory comparison of melt flow rate testing of moisture sensitive plastics.

Rides, M; Allen, C R G; Omloo, H*; Nakayama, K*; Cancelli, G* (2009) Interlaboratory comparison of melt flow rate testing of moisture sensitive plastics. Polym. Test., 28 (6). pp. 572-591.

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The current melt flow rate method (ISO 1133) does not adequately cover the measurement of materials that degrade or further polymerise at the melt flow rate test conditions. Materials such as PET, PBT and PA containing absorbed water tend to degrade, sometimes rapidly, at melt temperatures. This will result in poor repeatability and reproducibility of melt flow rate results. The ISO Plastics Melt Rheology committee (TC61/SC5/WG 9) is currently developing a modified melt flow rate method for reliable measurement of moisture sensitive materials, e.g. PBT and PET, thereby providing an alternative to intrinsic viscosity measurements. The modified method controls more tightly the time-temperature history experienced by the material and thus the resultant variability in measured properties due to degradation.

The results of an intercomparison of testing of moisture sensitive polymers using the melt volume flow rate and melt mass flow rate methods is reported. A polypropylene, used as a benchmark material, and five moisture sensitive materials were tested by a number of laboratories measuring either melt volume flow rate (MVR) or melt mass flow rate (MFR), or both. For the PP material, the repeatability and reproducibility of measurements of MVR were up to 5% and 11% respectively, and for MFR were 7% and 21% respectively (95% confidence levels). For the moisture sensitive materials the repeatability and reproducibility of measurements varied significantly, with repeatability values up to 25% and reproducibility values up to 114% being obtained. By imposing moisture and temperature criteria in accordance with the proposed testing standard, the repeatability for MVR was significantly improved, reducing its value to 13%, but although the reproducibility reduced it remained high at 87%. The need to tightly control the sample preparation, in particular the drying and subsequent sample handing procedures, is considered critical to further improve the reliable measurement of such materials.

Item Type: Article
Keywords: melt flow rate, plastics, MVR, MFR, moisture sensitive
Subjects: Advanced Materials
Advanced Materials > Polymers
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/5135

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