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The design of flexible sensors which can be incorporated in textile structures is of decisive importance for the future development of wearables. In addition to their technical functionality, the materials chosen to construct the sensor should be nontoxic, affordable, and compatible with future recycling. Conductive fibres were produced by incorporation of carbon black into regenerated cellulose fibres. By incorporation of 23 wt.% and 27 wt.% carbon black, the surface resistance of the fibres reduced from 1.3 &times, 1010 &Omega, &middot, cm for standard viscose fibres to 2.7 &times, 103 and 475 &Omega, cm, respectively. Fibre tenacity reduced to 30&ndash, 50% of a standard viscose, however, it was sufficient to allow processing of the material in standard textile operations. A fibre blend of the conductive viscose fibres with polyester fibres was used to produce a needle-punched nonwoven material with piezo-electric properties, which was used as a pressure sensor in the very low pressure range of 400&ndash, 1000 Pa. The durability of the sensor was demonstrated in repetitive load/relaxation cycles. As a regenerated cellulose fibre, the carbon-black-incorporated cellulose fibre is compatible with standard textile processing operations and, thus, will be of high interest as a functional element in future wearables.

Production of concentrated natural dyes is a pre-requisite for a re-introduction of plant colorant based dyes into modern textile dyeing operations. Aluminium salts such as Al 2 (SO 4 ) 3 .14-15H 2 O or KAl(SO 4 ) 2 .12H 2 O can be used to precipitate extracted plant dyes from aqueous extracts at pH 5.0–5.5. Onion peel, Canadian Goldenrod and pomegranate peel were studied as representative sources for dye extraction. As an average 5% w/w of the extracted dry plant material could be collected as precipitate. After dissolving these residues in diluted oxalic acid, the quality of the dye lake was characterised by photometric analysis of the total phenol content in the dry using the Folin-Ciocalteau method, determination of the aluminium content and measurement of the absorbance at 400 nm. Representative values of TPH in the dry solid dyestuff range from 20 to 40% and representative values for the aluminium content were determined with 3–5% w/w. Colour strength of the dissolved lakes was determined in dyeing experiments using different substrates and mordants followed by measurement of CIELab coordinates and K/S value according Kubelka-Munk function. Compared to the direct use of plant extracts the colour strength of the lakes is lower, however chroma of the dyeings is higher, as the lake formation also represents a dye purification step.

The dyestuff content in plant sources is rather low, usually in the order of a few % of the mass of dry plant material. Introduction of plant dyes into technical scale textile dyeing operations thus requires handling, extraction and disposal of huge amounts of plant material. The precipitation of a solid, dyestuff-containing residue by addition of FeSO4·7H2O to the aqueous plant extract yields a highly concentrated plant dye. In this work Canadian Goldenrod (Solidago canadensis) was used as representative case to study production of a concentrated solid plant dye. An iron content of 5% w/w of the dry precipitate was analysed by photometry (1,10-Phenanthroliniumchloride). The content of total phenolics (TPH) calculated as gallic acid monohydrate equivalents according the Folin-Ciocalteau method, was determined with 45% w/w. The dyestuff precipitate was tested in standard dyeing experiments. Shade and colour depth were found comparable to dyeings obtained with direct use of plant extracts. Use of a concentrated natural dye product offers new approaches with regard to standardisation of dyestuff quality, handling and applicable dyeing techniques.

The aqueous extract of ash-tree bark (Fraxinus excelsior L.) was chosen as a model to study the shade reproducibility of dyeing on wool. A meta-mordanting process using FeSO4·7H2O mordant was chosen as a system with particular potential for industrial application. The exhaust dyeing process with immediate use of the extracts as a dyebath and direct addition of FeSO4·7H2O stock solution as a meta-mordant process showed good shade reproducibility and satisfying levelness of the dyed material. An increase of Fe(ii)-mordant above a dyebath concentration of 2–3 g l−1 did not result in further colour depth. Extraction of 1–2 g of bark was found sufficient to dye 1 g wool yarn to the darkest colour possible; use of higher amounts of bark did not yield substantially higher colour depth. The quality of bark and the extraction step were found to be of significant importance for the colour depth; thus, in an optimised process, conditions of extract formation have to be well controlled.

The introduction of natural dyes into modern textile dyehouses requires the classification of products of standardised quality with regard to colour depth and shade of the dyeings. Canadian golden rod was chosen as a representative example to test the methods that are available to assess the quality of different crops of plant material which had been collected over a period of five years. Aqueous solutions containing the extracted flavonoid dyes were characterised by means of direct photometry, measurement of absorbance after addition of FeCl 2 , analysis of total phenolics (TPH) in the extract and dyeings on wool yarn. TPH calculated as gallic acid varied from 62 g/kg to 97 g/kg of plant material; only one sample exceeded this range with a value for TPH of 142 g/kg. Correlation among TPH, photometry in the presence of FeCl 2 and lightness of the dyeings can be used to characterise samples. However, correlation between the photometric results and colour depth of dyeings is not sufficient to permit characterisation of the plant material with regard to the final dyeing. At present, a combination of laboratory dyeings and CIELab coordinates was found to be suitable to establish an experimental basis for standardisation of plant material.

The food and beverage industry releases considerable amounts of wastes which contain natural dyes. Such wastes could serve as a sources for the extraction of natural dyes for textile-dyeing operations. The extraction of brilliant yellow and red colours from fruits and vegetables is of particular interest. Wastes, e.g. pressed berries, pressed grapes, distillation residues from strong liquor production, and wastes and peels from vegetable processing, have been extracted with boiling water and test dyeings on wool yarn were performed. Colour strength, shade and fastness properties of the dyeings have been tested. The extracts were applied as direct dyes and in the presence of iron(II) or alum mordants. The results prove the potential of such wastes as a source for natural dyestuff extraction. To obtain textile dyeings with acceptable fastness properties, however, rigorous selection of dyes and development of suited processes is required. A considerable number of red natural dyes need further research to optimise the low level of fastness to light. Copyright © 2005 Society of Chemical Industry

For many applications cellulose fibres are treated with concentrated solutions of swelling agents to increase reactivity and to achieve reorganisation of fibre structure. Representative examples are caustic soda, potassium hydroxide solution or liquid ammonia. These highly concentrated media bear considerable safety hazards during the technical handling thus alternative swelling agents are of interest. The thiocyanate-urea system investigated in this work offers high swelling potential for regenerated cellulose fibres. Experiments with different cations of M(+) in M(+) SCN(-) demonstrate the significant influence of the cation on the degree of fibre swelling. In concentrated NaSCN/urea solutions, at 80 °C, lyocell fibres expand the diameter from 12-14 to 100 μm. The treatment in the swelling agent also led to a significant increase in the water retention value which was accompanied by a strength loss of 20-40% of the initial value. FTIR analysis of treated fibres did not indicate substantial changes in structure of the cellulose polymer. Limited weight loss of up to 20% was observed despite the high expansion of the fibre.

BACKGROUND: Pomace from different grape varieties was studied with regard to the content of extractable anthocyanins. RESULTS: Total anthocyanin concentrations of 24.5–126 mg dm−3 were found in the extracts. The amount of extractable pigment was dependent on the variety of grape. The extracts were applied in textile dyeing operations using cotton fabric pre-mordanted with tannin as textile substrate. Red/violet shades were obtained that showed good water-fastness; however, limited light-fastness indicated need for improvement to fulfil requirements for textile application. CONCLUSION: Colour measurement by means of CIE-Lab coordinates and Kubelka–Munk value showed a direct correlation between extractable anthocyanin concentration and colour depth of the dyed material. Thus the analytically determined concentration of anthocyanins in the aqueous extract can serve as a measure of quality of grape pomace as raw material for textile dyeing application. Copyright © 2007 Society of Chemical Industry

Publisher Summary This chapter provides an overview of the potential for natural dyes to be used in textile dyeing, with special reference to plant-based materials found in food processing and food chain waste streams. It also discusses the requirements that have to be met for successful application of natural dyes in textile dyeing operations. Natural dyes present in plant wastes have to be extracted for use in the dyebath. The extraction step is discussed with regard to energy and chemicals, which forms a basis to compare different strategies to handle natural dyes in full technical scale. Results of a screening study to identify suitable wastes, released from the food and beverage industries, as potential sources for natural dyes are also illustrated in the chapter.

The production of natural dyes from plant sources available in the moderate climate of Austria (Europe) has been studied. Besides direct agricultural production, additional sources e.g., bark from timber industry and wastes from food industry have been investigated. Model calculations of energy consumption indicate that stabilised plant material e.g., dried plants, is favourable compared to dyestuff extracts. The low dyestuff content of the crops demands extraction of huge amounts of plant material, thus extraction should be performed in water only. Dyeing experiments indicate that based on a selection of dyestuffs and mordants an acceptable quality level can be reached.