Interaction of water with polymers at low relative humidities

Abstract

The purpose of this thesis was to study the interaction of water with very large molecules (e.g. polymers). The first part of the thesis deals with orlon which is: It was hoped to use this material to study the interaction of water with the -C≡N group. This study was unsuccessful because: 1. The difficulty of obtaining pure polyacrylonitrile (most samples of orlon are copolymerised with other polymers) 2. It was found that the hydrogen on the carbon to which the nitrile group is attached did not exchange. Although this was interesting in itself, it makes orlon a much less suitable material for studying polymer properties in general. The main part of this thesis is devoted to the study of adsorption of water onto wool. Wool was not only of interest because of its great commercial importance but also because it takes up such large quantities of water (c.a. 35 gm H2O per 100 gm wool at 100% relative humidity). An answer to the following questions was sought: (i) Which groups in wool adsorb water? (ii) Why do the water adsorbing properties of wool appear to differ from those of nylon? It was shown that all the polar groups in wool can take up water. Thus adsorption occurs not only on the -NH and -CO groups of the peptide links but also on the hydrophilic groups of the amino acids in the side chains. The reason wool takes up so much more water than nylon (c.a. 50% to 90% depending on the relative humidity) is because wool has many polar groups in its side chains, and also nylon is much more crystalline than wool which means only a smaller fraction of the nylon is accessible to adsorb water. The final section of the thesis deals with the adsorption of water onto wool at relative humidities of less than one per Cent. Although the results were only qualitative in nature, due to the many technical difficulties of working at very low relative humidities, they clearly suggest that at very low relative humidities the amorphous regions in the wool fibre go into a glassy state.