The effect of hydration and chemical treatments on natural fibres

Abstract

This Thesis reports on an investigation of the interaction of keratin fibres with different actives both in liquid and vapour phases. The extent and rate of small molecule uptake with the virgin human and chemically treated hair fibres via experimental sorption was studied with molecules designed to modify keratin chemistry, ammonia and mono-ethanol amine, as well as water vapour and selected organic molecules. Thermal, mechanical characterisation, protein loss and SEM were also performed. The diffusion kinetics of MEA into keratin fibres for 0.1-5% v/v MEA in water at 30 and 50oC exhibited two clear regimes of sorption behaviour. Single fibre tensile tests showed that the Young’s modulus and the tensile failure stress for 5% MEA treated fibres were 50% lower after 9 hours of treatment. SEM images and protein content analysis evidenced significant surface damage as well as high levels of protein loss, confirming for the first time this important damage process. The additives salicylic acid and isosteryl isosterate were shown to reverse the moisture losses associated with significant fibre damage e.g. 5% MEA. A range of hydrophobic and hydrophilic sorbates confirmed the hydrophilic sorption behaviour of hair. Gravimetric water sorption experiments confirmed that chemically induced damage affected levels of water and organic vapour sorption by hair. Non-polar sorbates exhibited low uptake for both damaged and virgin hair. The presence of hysteresis in all samples may be related to the swelling upon sorption. Ramped sorption experiments confirmed a potential transition event at 64% RH, which maybe the relative humidity glass transition of the fibres. A novel inverse gas chromatographic method for determining the surface area of virgin hair to be 0.22 m2/g and for damaged fibres 0.12 m2/g. The effect of humidity on the surface area of hair for the first time is also reported, showing clear humidity induced swelling of the fibres.