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Optimisation of Acid Digestion Conditions for Volume Fraction Measurements of Hard to Digest Fibre-Reinforced Polymer Composites

Pemberton, R; Edser, D; Gower, M (2020) Optimisation of Acid Digestion Conditions for Volume Fraction Measurements of Hard to Digest Fibre-Reinforced Polymer Composites. NPL Report. MN 12

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Abstract

Acid digestion is a widely used method for determining matrix, fibre and void content of fibre-reinforced polymer composites. Current test standards governing the use of these methods prescribe, for some polymer systems, particularly hazardous chemicals including sulphuric acid and hydrogen peroxide. To reduce the health and safety risks associated with the measurement, it would be beneficial for users of these standards to conduct digestion using nitric acid only, being a far safer chemical to use. In order to develop and validate methods however, there is a requirement to assess if digestion conditions are only digesting the required material, e.g. polymer matrix and not the reinforcing fibre. This Measurement Note reports on methods developed to perform digestion measurements on composite systems incorporating phenolic, cyanate ester and polyfurfuryl alcohol polymer matrices using nitric acid only. These materials were chosen as systems known to be particularly difficult to digest without attacking the fibres. The methods have been validated by characterising the appearance of residual fibres from the digestion process using scanning electron microscopy (SEM). For all polymer systems investigated in this work it was found that digestion in a mixture of 5 ml nitric acid and 5 ml deionised water for 60 mins at 160°C successfully digested the material without leaving undigested polymer or attacking the fibres. These digestion conditions include acid profiles, times and temperatures currently outside the recommendations of ISO and ASTM test standards.

Item Type: Report/Guide (NPL Report)
NPL Report No.: MN 12
Subjects: Advanced Materials > Composites
Divisions: Engineering
Identification number/DOI: 10.47120/npl.MN12
Last Modified: 07 Sep 2020 09:29
URI: http://eprintspublications.npl.co.uk/id/eprint/8837

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