A series of azo disperse dyes was synthesised and the purified, synthesised dyes were characterised by proton nuclear magnetic resonance, thin-layer chromatography and melting point measurement. The spectroscopic properties of the dyes in solution were studied by dissolving the dyes in ethyl acetate and methyl benzoate. These were seen as mimicking the environment of the dye when inside dyed poly(lactic acid) and poly(ethylene terephthalate), respectively. Reflectance spectra of the dyes on both polyester substrates were also measured in order to correlate with the spectroscopic properties of the dyes in solution. The absorbance spectra of the dyes in solution exhibited a hypsochromic (lower wavelength of maximum exhaustion) shift when dissolved in ethyl acetate, compared with methyl benzoate. The occurrence of this yellow shift was attributed to the lower polarity of ethyl acetate compared with methyl benzoate. The colour of the dyes in ethyl acetate solution was also brighter and stronger (higher molar extinction coefficients) than that in methyl benzoate. Most of the synthesised dyes exhibited high levels of exhaustion onto the two polyester fabrics. However, the visual colour yields, for those dyes having approximately the same high level of exhaustion, were different, the dyed poly(lactic acid) being stronger (higher K ⁄ S value) as well as being yellower and a trace brighter than the dyed poly(ethylene terephthalate). This difference correlated well with the solvatochromic study of the dyes in ethyl acetate and methyl benzoate solution.

No abstract

This research aimed to study the dyeing properties on the PLA and silk yarns of the natural dyes obtained from various materials, viz. marigold petals (Tagetes erecta L.), rhubarb rhizomes (Radix et Rhizoma Rhei), garcinia barks (Garcinia Dulcis Kurz), turmeric rhizomes (Curcuma Longa Linn.), sappan barks (Caesalpinia sappan Linn.) and catechu barks (Acacia catechu Willd.). The color properties of the dyed yarns was determined and compared. The results observed the different color properties (L*, a* and b* values) and a shift of λmaxof the dyes on the PLA and silk yarns. This change in color properties of each natural dye was expected to be affected by the types of substrate (textile fiber) and also the chemical nature of the natural dyes. The study of the build-up properties indicated that the turmeric dye is the only natural dye which showed an outstanding performance on PLA and silk. A high degree of color yield of turmeric dye was obtained on both yarns, whereas a poor build-up was observed for the rest of the dyes.

This research studied the potential and efficiency of tamarind kernel powder as a thickener for pigment printing on cotton fabric in comparison with the commercial synthetic thickener. Two kinds of tamarind seed were studied. Both of tamarind seeds contained about 30% based on dry weight of outer seed coating and 70% of dry weight of tamarind kernel powder. The approximate composition of tamarind kernel powder were 2.39 – 3.19% fat, 16.43 – 17.07% protein, 1.20 – 1.68% crude fiber and 3.42-3.74% moisture based on weight of tamarind kernel powders. Two different extraction techniques were studied viz., boiling in water and using microwave. Tamarind kernel powder extracted by microwave method was suited for use as a thickener rather than those obtained by boiling in water method. As the tamarind kernel powder from microwave method was easier dissolved and the printing paste was smoother than those from boiling in water. The optimum concentration of tamarind kernel powder for pigment printing on cotton was 5% tamarind kernel powder obtained from the seed in relatively round shape and smooth surface because the color yield and rubbing fastness was similar to the commercial synthetic thickener.

This research aimed to study the use of curcumin as a natural dye for dyeing poly(lactic acid) and poly(ethylene terephthalate) fabrics. The study found that curcumin was dyeable on PLA and PET, providing a brilliant yellow color on the fabric. Curcumin could build up very well on PLA, while lower build up was on PET. At the same applied concentration, higher color yield was observed on the dyed PLA fabric. To achieve the same visual color yield, a significantly lower concentration of curcumin was required for PLA as compared with PET. The color shade of curcumin-dyed PLA differed from the PET analogue. A bathochromic shift of the K/S curve was found when the substrate was changed from PLA to PET. The influence of polymer media on the spectroscopic properties of curcumin could be elucidated by measuring absorbance properties of curcumin in ethyl acetate and methyl benzoate, being representatives of PLA and PET, respectively. At the same concentration, curcumin solution in ethyl acetate exhibited higher absorbance than that in methyl benzoate, corresponding to the deeper shade obtained when dyed on PLA as compared with PET. Bathochromic shift of absorbance curve was also observed when the solvent was changed from ethyl acetate to methyl benzoate.

Development of chitosan as a thickener for direct printing of natural dye on cotton fabric was investigated. Chitosan was applied as a thickener at various concentrations and its effect on the print properties was determined in comparison with the typical printing thickener, sodium alginate. The results exhibited that chitosan affected the fabric properties by increasing fabric yellowness and stiffness. However, with increasing chitosan concentrations, the yellowness reduced only marginally. Direct printing on cotton fabric with 3% Natural Chestnut at varying chitosan concentrations showed that the optimum chitosan concentration for the printing was at 3%w/v, being equivalent to the viscosity of 17,800 mPa. The 3%w/v chitosan imparted the ultimate color yield, print outline sharpness and a minimal dye bleeding on the unprinted area of the fabric. Use of chitosan concentration higher than 3%w/v led to poor print properties on the fabric. The efficiency as a thickener of chitosan was found to be superior to sodium alginate. A high color yield and good color fastness properties on cotton fabric were rendered in the case of chitosan thickener at the same applied concentration with sodium alginate.

Natural indigo dye, Indigofera tinctoria, was applied on poly (lactic acid) (PLA) fabrics by exhaust dyeing in the presence of 5 g/L sodium dithionite and 0.2 g/L NaOH. Three dyeing parameters e.g. dyeing temperature, dyeing time and dye concentration were studied. When 5%owf indigo dye was applied on PLA, the maximum color strength was obtained at 80°C and 60 minutes. The color strength also increased as the dye concentration increased in the range of 4–20%owf. Applying natural indigo dye to PLA fabrics is more attractive than the commercial one due to better energy savings and the process being environmentally friendly.

Abstract-The pretreatment processes prior to dyeing which were the scouring and bleaching, for the knitted fabric of PLA/cotton blend were studied comparing with the 100% cotton and PLA fabrics. These two pretreatment processes were studied in a sequence (scouring followed by H 2 O 2 bleaching) and altogether in the one-bath process. The scouring process of the blended fabric was compared when the different scouring agents were employed (NaOH, Na 2 CO 3 and pectinase enzyme). The two-bath and one-bath scouring/bleaching processes had a signified effect on the strength of the fabrics because the pretreatment processes typically used for cotton are in the alkaline condition which can deteriorate the PLA fiber. Therefore, the pretreatment conditions for the PLA/cotton blended fabric needed to be optimized to avoid fiber damage. From the research, it was observed that the pretreatments for the blended fabric, which was to enter the pale-shade dyeing, were scoured using 10%owf pectinase (60C, 60 min) as it enhanced a satisfactory water absorbency to the fabric without causing any adverse effect on the fabric strength. For deep-shade dyeing, the blended fabric should undergo the one-bath scouring/bleaching with 7%owf H 2 O 2 (100C, 60 min) which yielded a water absorbency and whiteness on the fabric to a standard level and the resulting fabric strength was highest and this one-bath pretreament was the time-saving process.