Effect of atmospheric plasma treatment on pad-dyeing of natural dyes on wool

Plasma treatment is an emerging surface modification technique that alters dye uptake of wool without using chemicals or water for pre-treatment. Padding is an established continuous dyeing technique known for its efficient use of water, time and energy. This study combined these two techniques for colouration of wool fabric using two natural dyes derived from the Acacia plant family. The investigation focused on the effects of plasma treatment and obtaining unique patterning effects. Helium (100%) and a mixture of helium and nitrogen (95%/5%) were used as the plasma gases under atmospheric conditions. Plasma treated wool fabric was padded with the above natural dyes. Copper sulphate and ferrous sulphate were applied on the dyed fabric as mordant yielding neutral shades of beige and grey respectively. Up to a 30% enhancement of dye adsorption on plasma treated wool substrate was observed as compared to untreated sample for both gases used. This higher adsorption indicates the hydrophilic character of the natural dyes used. Key performance parameters such as fastness to washing, rubbing and light were tested and found to be satisfactory. A single process tone-on-tone pattern was achieved by controlling the plasma exposure of treated area. This study concluded that a merger of natural dyes with modern plasma treatment and padding techniques for wool colouration was feasible

Application of natural dyes by padding technique on textiles

This thesis presents the findings from investigations into adapting the padding process for dyeing cotton and wool using natural dyes. The aim was to apply traditional dyes employing current and emerging technologies of textile colouration. This synergistic amalgamation led to a cleaner production process with low environmental impact. Mordant dyes (derived from Acacia catechu and Acacia nilotica) and vat dyes (Indigofera tinctoria) were evaluated. The work on mordant dyes focused on determining optimal process parameters (padding sequence, mordanting method and mordant concentration). Post-mordanting with copper (II) sulfate or iron (II) sulphate yielded the darkest shades for both dyes. Ideal process sequence for copper (II) sulfate was pad (dye) → dry → steam followed by pad (mordant) → steam → dry while for iron (II) sulfate it was pad (dye) → steam → dry followed by pad (mordant) → steam → dry for both dyes. Similarly, use of the first mordant yielded a beige shade while a yellow-grey shade was obtained with the second. Optimum mordant concentration for 10 g/l dye was 15 g/l copper (II) sulfate or 5 g/l iron (II) sulphate for both dyes. These were lower than those recommended for exhaust dyeing (5% OWM) and padding (60 g/l) reported in the literature. Atomic absorption spectroscopy revealed higher amount of metal in the dyed fabric compared to identically mordanted fabric, confirming the formation of a dye-metal-textile complex. FTIR spectra were distinctly different for the two dyes investigated. However, the spectra for dyed samples, coloured using the above dyes in combination with the same mordant, exhibited minimal differences. This indicated that metal plays a major role in defining the bonds created during dye-metal-textile complex formation causing a similarity in shade. Darker shades were obtained by atmospheric pressure plasma pretreatment of the textile, or including chitosan in the pad liquor. Pure helium and a 95/5 helium/nitrogen mixture were evaluated as the plasma gas. Exposure to either plasma improved the wettability of wool. Wool treated in pure helium plasma for 14 seconds exhibited a 30% increase in the depth of shade. A tone-on-tone pattern was created in a single padding operation by selective plasma pretreatment. Incorporation of 0.05% chitosan in the pad liquor resulted in a 20% darker shade while imparting antimicrobial properties to the dyed fabric. Indigo was applied on cotton by the vat dyeing process of pad (dye) → dry → pad (reducing chemicals) → steam. In this process, sodium dithionite and sodium hydroxide, the common reducing agent and alkali in exhaust dyeing of indigo, were replaced by thiourea dioxide and sodium carbonate respectively. Although equivalent shades were obtained, the use of sodium carbonate required comparatively longer steaming time. Natural indigo produced a darker shade when reduced using the alternative chemicals perhaps due to its higher reactivity resulting from its lower crystallinity as compared to synthetic indigo. However, printing with synthetic indigo resulted in darker shades. The discrepancy between printing and dyeing may be attributed to interference by the print paste thickener on diffusion of reduced indigo into the fabric

Extraction and Optimization of Natural Dye from Hambo Hambo (Cassia singueana)

This investigation was aimed at introducing natural dye extracted from the bark of Cassia Singueana plant for dyeing chrome tanned sheep skin crust leather. The colorant was extracted by aqueous extraction and its strength evaluated using UV-Visible spectroscopy. The extraction with the highest strength (3.9 at λmax of 400 nm) was obtained at temperature of 95°C, concentration of 60 g/l, and time of 60 minutes. The possibility of using aloe vera juice and mango bark extract as natural mordants for leather coloration was investigated. Dyeing was conducted with and without mordant using different combinations of temperature, time, pH, and concentration of mordants. All three mordanting techniques were evaluated. The color strength (K/S), CIE L⁎a⁎b⁎ values, and fastness properties (light, rubbing, and perspiration) of dyed leather samples were evaluated using appropriate instruments and according to international standards. Majority of samples exhibited that fastness result was in the range of good-excellent. Significantly better color fastness was obtained in case of leather samples premordanted with aloe vera. This study leads to the conclusion that dye extracted from bark of Cassia singueana can be used as colorant for tanned leather with the selected natural mordants

Assessment of Changes in Corn Husk Fibres after Acid Treatment

Sustainability is desirable in any activity, including farming. Adding value to agricultural wastes such as stover (waste from corn cultivation) would provide financial benefits to farmers while reducing the environmental load of disposal. The literature identifies stover as being a raw material for bio-ethanol and a reinforcement for composites. Fibre from corn husks is generally extracted using an alkali digestion method followed optionally by enzymatic degradation. In this study, acid treatment was investigated for its feasibility to improve the desirable characteristics of alkali extracted corn husk fibres. The results revealed that increasing the acid concentration decreased fibre properties such as average fibre length, linear density and elongation at break. However, breaking tenacity achieved a maximum value, on treatment with 7.5 g/l sulfuric acid, before decreasing. These properties indicate the treatment’s adequacy for use in textile products. Acid treatment did not significantly alter thermo-gravimetric analysis values, indicating that the fibre could withstand wet processing conditions

Plasma treatment in textile industry

Plasma technology applied to textiles is a dry, environmentally- and worker-friendly method to achieve surface alteration without modifying the bulk properties of different materials. In particular, atmospheric non-thermal plasmas are suited because most textile materials are heat sensitive polymers and applicable in a continuous processes. In the last years plasma technology has become a very active, high growth research field, assuming a great importance among all available material surface modifications in textile industry. The main objective of this review is to provide a critical update on the current state of art relating plasma technologies applied to textile industryFernando Oliveira (SFRH/BD/65254/2009) acknowledges Fundacao para a Cioncia e Tecnologia, Portugal, for its doctoral grant financial support. Andrea Zille (C2011-UMINHO-2C2T-01) acknowledges funding from Programa Compromisso para a Cioncia 2008, Portugal