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NPL aims to overcome failings in MFR testing.

Rides, M (2008) NPL aims to overcome failings in MFR testing. British Plastics & Rubber (Feb). p. 21.

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Measuring the melt flow rate properties of some commonly used plastics is not possible using the standard method as specified by ISO 1133. It is not suited to testing materials that are unstable at the testing conditions, such as materials that are sensitive to their absorbed water (e.g. polyethylene terephthalate, polybutylene terephthalate and nylons). These plastics can rapidly degrade at the test temperature due to their absorbed water causing considerable measurement difficulties. An alternative method for characterisation of such polymers, using solvents to measure intrinsic viscosity, is comparatively expensive, possesses environmental and health and safety problems, and generates fundamentally different properties data. As part of an ongoing international collaboration NPL are addressing this measurement problem by developing the melt flow rate method to improve its accuracy and precision for such difficult materials. It is anticipated that this standard will be published as an ISO standard in 2010.

A further issue that has been addressed by NPL is that melt flow rate testing predominantly characterises the shear flow behaviour of plastics. However, a significant proportion of plastics are converted in processes that are predominantly extensional stretching flow in nature, e.g. bottle blowing, film extrusion, vacuum forming. Thus for these processes it may be more appropriate to characterise the materials using an extensional flow technique. NPL have achieved this using only minor modification to the standard melt flow rate method by using a short length die instead of the standard 8 mm length die. It has been demonstrated that this can provide a better understanding of the processability of materials in extensional flows.

Item Type: Article
Keywords: melt, flow rate, moisture, extensional flow
Subjects: Advanced Materials
Advanced Materials > Polymer Rheology
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/4124

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