PhD: "Low wax Australian-cotton reducing the scouring requirements of cotton fabric"
Cotton fibre is the most important natural textile fibre, but it requires intensive scouring to disrupt the hydrophobic cuticle to allow dye to penetrate. The standard fibre qualities and amount of waxy cuticle material on cotton fibre varies across genotype. Some research has been undertaken addressing the influence of environment and management on standard fibre qualities and wax content, however no clear effect of either has been shown on cotton fibre cuticular wax despite the influence these variables have been shown to have on other standard fibre qualities and the cuticular wax content of other aerial surfaces of cotton plants. Predicted changes in climate in future will influence the ambient temperature of growing regions, likely increasing the amount of heat stress on cotton plants and may also affect water availability leading to water deficit stress. The effects of heat and water stress during flowering and early to mid fibre development period was captured for two consecutive growing seasons in a field production scenario for five upland cotton genotypes that varied in their known tolerance to both heat and water stress. It was hypothesized that stress at this time would tend to influence fibre initiation phases that might affect fibre perimeter determination and fibre lengthening, as well as wax content which is known to be deposited typically before the secondary cell wall thickening phase of fibre development. For all genotypes, water deficit increased measured cross-sectional properties with an associated increase measured in micronaire for both experiments. Increases were also seen following heat stress for fineness and maturity ratio in the second season. For fibre length, either water deficit alone or a combination of water deficit and heat stress, reduced fibre length for all but two genotypes. The exceptions were the water stress tolerant genotype which did not respond to water stress alone, and the poor water stress tolerant genotype which did not respond to either stress. Heat stress alone appeared to play the dominant role in reducing
fibre length for the genotype included for its good water use efficiency. Either water deficit stress or a combination of both stress treatments, increased cotton fibre strength in one of the experiments, while only a combination of both stress types in the other experiment produced the same effect. Both heat and water deficit stress were shown to significantly influence fibre cuticular wax deposition, but the effect was genotype dependant with the greatest effect observed on the genotypes included for poor heat tolerance and poor water deficit tolerance. For these genotypes significant increases were measured in cuticular wax. In an attempt to replicate the effects of water stress seen the field experiment in a glasshouse setting, water deficit stress was applied to a white control genotype, a naturally coloured high wax green genotype, and the poor water stress tolerant genotype. The only effects of water stress on fibre properties were to increase fibre fineness and strength, and decrease length, for which a main effect of stress was measured. There were no significant effects on fibre cuticular wax content or other fibre cross-sectional properties. This was attributed to the possible differences in the severity of the stress between the two experiments. Following this, an investigation into the dyeability of fabrics made from three different naturally coloured upland cottons with varying wax content was undertaken. One common white cotton, and two un-common coloured cottons, one brown and one green, were used for experiments. It was hypothesised that following dyeing, fabrics that were not scoured would have inferior colour fastness following a standard fabric wash test. The effect was expected to be more prominent for fabric made from the higher wax content coloured cottons. Fabrics made from these cottons were subjected to either traditional NaOH caustic scouring or hot ETOH scouring which more specifically targets the waxes, before being dyed and washed. It was found that while NaOH scouring resulted in greater dye uptake on the brown fabric, the ethanol scouring resulted in greater dye uptake on the naturally high wax green fabric. The
NaOH scouring adequately disrupted the hydrophobic cuticle of all experimental fabrics resulting in a dye result that was colour fast following the application of a standard wash test. Further to this a novel assessment of cotton polysaccharide content by GC-MS of three fabrics was performed. Following scouring, dyeing and washing fabrics were analysed spectroscopically to assess the ability of traditional scouring to remove polysaccharides and to assess the influence these polysaccharides may have on fabric dyeability and colour fastness. It was shown that the non-cellulosic polysaccharide content was significantly greater in naturally coloured cotton, but it did not negatively affect dyeability, and could be adequately scoured using traditional NaOH scouring method. These results further highlight the importance of carefully managing cotton growing conditions and stress to reduce any impact on fibre quality and cuticular wax component that may negatively affect the dyeability of cotton fabrics.