Studies in the Chemistry of Proteins and Polypeptides Mechanism of Dye Sorption and Photodegradation on Wool and Nylon

Simple mono-azo dyes derived from m- and p-substituted aniline derivatives and beta-naphthol-3:6-disulphonic acid were applied to wool, silk and nylon and their fading rates studied under mercury arc or carbon arc illumination. In the latter case the samples were exposed in different conditions of acidity along with the B.S.I. standards, which were used as an actionometer in assessing the fading rates, averaged over a large number of experiments. In exposures to the mercury vapour lamp the time required to produce a just perceptible change was also noted. In both cases the values obtained were compared with those given by the unsubstituted dye and plotted against the '6' value (Hammett) in order to study the effect of the substituents on fading. For comparison the same set of dyes were then applied to different cellulosic materials and their fading rates again measured. Parallel thermal oxidation studies of the same dyes by hydrogen peroxide in aqueous solution were also made. On the basis of the results obtained it is tentatively suggested that dyes are reduced when irradiated on protein substrates, the substrate playing a specific part in the reaction, whereas they are photo chemically oxidised on cellulosic materials which act only as inert substrates, on which the dye is dispersed in different physical states, the nature of which affects the fading rates. Nylon in the above experiments behaved like cellulose, and in an opposite sense to wool or gelatin, in spite of its similarity of molecular structure in many respects. The next section of the thesis describes work,designed to elucidate the nature of the reactions taking place in dyeing nylon and wool, which took the form of the application to these fibres of a number of organic compounds containing one or more simple groups, e.g., azo, hydroxy, amino groups, normally present in dye molecules, on dry wool or nylon from dry organic solvents. The results have revealed a number of interesting facts regarding the structure and bonding properties of these fibres, which are discussed in detail. It is found that only compounds capable of forming hydrogen bonds of OH...O type are sorbed readily on these fibres and then only provided that their molecular size is such that they are capable of negotiating the pores of the fibre in the dry state. Compounds having an uninterrupted conjugated system of double bonds, e.g. benzene, azobenzene, were found to be sorbed apparently by van der Waals attraction. Nylon showed some differences compared with wool, which may be related to pore-size differences. This work was followed by vapour phase sorption experiments of dry methanol on wool. The results are consistent with the view that hydrogen bonds are formed during sorption. In further experiments, dyed and deaminated wool and wool dried by various solvent methods showed effects apparently due to blocking of the pores either by submicroscopic dye crystallites or by firmly held benzene