Investigating the characterisation and stability of polyamide 6,6 in heritage artefacts

Abstract

Near?infrared reflectance spectroscopy (NIR) is investigated as a method of non?invasive, in situ analysis of contemporary textile material. Besides providing spectral signatures, the advantages of NIR include the non?contact nature of the reflectance technique and the use of a remote, flexible probe. A spectral database of well?defined reference material has been collected. This was recorded using a standardised protocol taking into account the need to interrogate objects within a collection. The differentiation of silk and synthetic polyamide can pose particular problems for curators of historic textiles due to the similarities in their visual appearance. NIR spectroscopy coupled with multivariate analysis is investigated for the differentiation of the polyamide sub?classes, found extensively within textile collections. Two multivariate methods of classification have been applied and it is shown that, with the appropriate spectral processing and calibration, both of these techniques are appropriate for sub?class discrimination.

Synthetic polyamides are frequently found in conjunction with natural organic materials, and are often exposed to the same pest treatments as natural polymers. In the event of an infestation there are a number of eradication measures possible, including the application of raised and lowered temperatures. However, these treatments take unaged aliphatic polyamides above, and well below, their glass transition temperature, respectively. For this reason the stability of new and aged polyamide textile material has been investigated.

Polyamide 6,6 test material was tested ‘as received’ and in an artificially aged condition. Samples were subsequently subject to ?30°C, room temperature or 58°C. In addition, samples were treated with and without the application of a load, enabling an assessment of risk if treated whilst hanging and supporting their own weight. Structural alterations were monitored using polarized and non?polarized mid infrared spectroscopy, tensile testing and differential scanning calorimetry. In addition, dynamic mechanical thermal analysis creep experiments were carried out to supplement the information provided by the in situ creep tests. It is evident from the results that the thermal treatments have a significant effect on the behaviour and structure of the aged polyamide. The implication for in situ treatment of this material in collections is clear, and must therefore be approached with caution. Analysis of the experimental data suggest that the changes observed can be related to the degree of crystallinity produced by the changes in temperature and by the presence of stress during treatment.

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