Xanthoproteic reaction for the evaluation of wool antifelting treatments

The substances responsible for the yellowing of wool treated with nitric acid are two amino acid constituents of the fibre: tryptophan and tyrosine. Nitric acid penetrates the fibres and carries out electrophilic aromatic substitution on the two above‐mentioned amino acid residues, producing different colour yields. The intensity of yellowing depends in various ways on the treatment conditions (time, temperature, nitric acid concentration, agitation, and liquor ratio). Yellowing evaluation shows abnormal yellowing depending on acid concentration in the range 5.6–5.9 m . Working in this region makes it possible to use the chromatic reaction in order to show the damage done to wool fibres by the oxidising agents utilised in normal antifelting treatments. Wool damage by the oxidants is usually evaluated by dyeing methods based on different affinity of damaged fibres. By contrast, the xanthoproteic reaction yields chromogens as a function of the accessibility of tryptophan and tyrosine residues for the action of nitric acid on damaged fibres, and can be used for assessing the degree of antifelting treatment and its possible unevenness through the development on the treated wool of a yellow coloration more intense than on untreated wool.     

Isolating the cuticle layer of wool: a comparison of methods

Various separation methods for cuticle isolation from whole wool have been studied. A method involving agitation of wool fibres in formic acid proved to be successful, producing a high yield of cuticle cells relatively free from contaminating cortical cells. The cuticle cells so isolated were characterised by amino acid analysis and scanning electron microscopy.     

A Method of Determining the Amount of Tryptophan in Wool by Hydrolysis with Sulphuric Acid for Short Periods

A method is described for determining the tryptophan content of proteins, particularly wool. The wool is hydrolysed in sulphuric acid for 2 h at 70°C and the tryptophan is determined colorimetrically. The method is quicker and more reproducible than previously used methods. The tryptophan contents of wool that had been modified by heating, treatment with chlorine, bleaching with hydrogen peroxide or exposure in a Fade-Ometer, determined using this method, are compared with those determined by other methods.     

Improving the dyeability of wool by treatment with chitosan

A study of pretreatment of wool fabrics with chitosan by a pad-dry method has been carried out. The pretreatment effectively eliminates differences in dyeing behaviour between damaged and undamaged wool fibres, with an increase in the rate of dye uptake and the exhaustion of acid and reactive dyes. Penetration of the fibre by dyes has been followed using fluorescence microscopy and the role of the chitosan coating in the dyeing process clarified. Similar colour fastness properties were obtained on both untreated and chitosan-treated wool fabrics. The chitosan coating on wool fabrics has been examined by scanning electron microscopy. Evidence for the presence of chitosan was sought using a colorimetric method. It is believed that an approximately uniform and adherent chitosan sheath is formed on individual wool fibres.     

Photodegradation of tryptophan in wool

The amino acid tryptophan is degraded upon light exposure or during acid and oxidative treatments. After irradiation of tryptophan solutions, the photodegradation products N′-formylkynurenine, kynurenine, tryptamine, and oxindolylalanine were identified by means of HPLC. These photoproducts of tryptophan contribute to the photoyellowing of wool. Oxygen plays a major role in tryptophan photodegradation. An attack of oxygen at the indole residue initiates the photodegradation reaction. The main photodegradation of tryptophan in proteins (e. g. in polytryptophan or in wool) is the cleavage of the indole ring and the formation of kynurenines. In irradiated wool, only N′-formylkynurenine was detected. N′-Formylkynurenine is known to be a photosensitiser.     

Synthesis of an amino coumarin‐based fluorescent reactive dye and its application to wool fibres

The objective of the current study was to introduce the coumarin structure into a conventional reactive dye system. A fluorescent reactive dye was synthesised based upon 7‐amino‐4‐methylcoumarin. The dye was obtained by a multi‐step sequence initiated by displacement of a chlorine group from 2,4,6‐trichloro‐1,3,5‐triazine using H‐acid. Diazo coupling of 3‐aminobenzenesulphato‐ethylsulphone to this adduct, followed by a second chlorine displacement using aminomethylcoumarin completed the sequence. The fluorescent dye and the non‐fluorescent precursor were characterised by mass spectrometry, infrared spectroscopy and capillary electrophoresis. The newly synthesised dye was applied to wool fibres using an exhaust dyeing method. The exhaustion, fixation and total efficiency values were calculated by ultraviolet–visible spectrophotometric analysis of the dyebath. The synthesised red dye presented high values for exhaustion, fixation and total efficiency on the wool fibres. The novel dye, after its application to the wool fibres, exhibited fluorescence under an ultraviolet light. This feature confirmed that the novel dye retained the inherent characteristic feature of fluorescence on the wool fibres. The dyed wool fibres exhibited level 4–5 of light fastness when compared with international wool light fastness standards.     

Eco-friendly approach on wool pretreatment and effect on the wool structure and dyeability

This research investigated the effect of various proteolytic enzymatic pretreatment on morphological and chemical features and the dyeability properties of wool fibres. Scoured merino wool fibres are treated with protease, papain, trypsin, and pepsin in specified conditions. Each enzyme activity measurement was provided by appropriate methods such as Bradford, BAPNA (N-benzoyl-1-arginine-p-nitroanilide), and BSA (Bovine Serum Albumin). Enzymatic processes were carried out for 24 h in the incubator set at 40°C, 100 rpm, and specified pH with 1 mg/ml enzyme concentration. Whiteness index (Stensby) and yellowness index (ASTM D 1925) were examined after enzymatic pretreatment. Pepsin and trypsin-treated wool fibres showed the highest whiteness index as 61.3 and 61.1, respectively whilst untreated wool fibres had 52.2. Fourier-transform infrared (FTIR) analysis revealed the increase in the intensity of amide-related bands and hydroxyl bands after enzymatic treatment. Scanning electron microscopy (SEM) photomicrographs manifested the cuticle layer is partially removed in enzyme-treated fibres. Elemental identification was provided by SEM–energy-dispersive X-ray spectroscopy (EDX). It appears that the sulphur bonds decreased after the treatment and the pepsin-treated fibres have fewer bonds of all. To examine the damage to the structure, photomicrographs were taken using fluorescence and light microscopes. The alkali solubility test (ASTM D1283) was also conducted to compare different enzyme types. Wool fibres were dyed in 2.0% concentration with reactive dyestuff. Dyeability and colorimetric features of fibres were measured by a spectrophotometer. The washing fastness test showed that all the samples have good results and the colour change after washing was better in enzyme-treated samples (grade 5) compared to untreated wool fibres (grade 4–5).     

Dyeing of Blends of Wool and Man-made Fibres

The blending of wool with man-made fibres is described generally. It is shown how the results of dyeing wool-man-made-fibre blends are controlled by physical properties such as wet tensile modulus; it is also indicated how a wide range of coloured effects can be obtained with different man-made fibres. The dyeing of blends containing wool is considered first from the point of view of the circulation of dye liquor through a mass of fibre and then of the relative dye absorption by the blend components. The relationship between tensile modulus and behaviour in wet processing is illustrated by laboratory work on the measurement of rate of flow through a mass of loose fibre. It is concluded that the dyeing of loose fibres in blend form could be a practical proposition and in some cases could result in over-all economies in processing. The relative dye absorption by fibres in blends is discussed in detail and fibres are classified according to their substantivity for acid or for direct dyes. One group consists of regenerated-protein, polyamide, and elastomeric fibres, a second group of viscose rayon fibres, and a third, larger, group of hydrophobic fibres, e.g. acetate, polyester, and acrylic fibres. The cross-staining of wool by dyes intended for the man-made fibre is considered, with particular reference to blends of acetate and wool; the effect of dyebath conditions, e.g. pH and temperature, is referred to and methods are outlined for minimising staining. Some three-fibre blends are then briefly considered. Finally, possible future developments, with particular reference to blends, are discussed.     

Increase in dye pick-up of wool caused by the Maillard reaction

Glucose molecules may enter into a Maillard reaction with reactive amino groups present in wool, transforming these groups to their N-glycoside derivatives. No changes to the physical or mechanical properties of wool fibres following glucose treatment have been observed. However, an increase in the pick-up of reactive and acid dyes was recorded after wool was pretreated with an aqueous glucose solution.     

Photoreactivity of Wool Dyed with Reactive Dyes

Presented at the 13th Congress of the International Federation of Associations of Textile Chemists and Colourists in London on 20 September 1984. Processes induced by two kinds of illumination (ultra-violet and Xenotest) in wool dyed with reactive dyes ha ve been investigated as a function of time. The fading of dyed fibres has been determined in terms of the conditions of illumination. The degradation of wool was followed on the basis of changes in alkali solubility and tensile characteristics. Moreo ver the colour change of the dyed fibres was also determined. Correlation was found between the chemical structure of the dye, the extent of fading and the photodegradation undergone by the wool. On the basis of amino acid analysis conclusions were drawn on the photodegradation mechanism of wool, both uncoloured and dyed with reactive dyes. Reactive dyes protect wool against photodegradation, and at the same time the light fastness of reactive dyes on wool is 1–1.5 units higher than on cotton, both under ultra-violet (u.v.) and Xenotest irradiation.     

Bioavailability of amino acids in beans (Phaseolus vulgaris)]

Biological availability of amino acids of three common bean (Phaseolus vulgaris) varieties was evaluated in four, healthy adult subjects, consuming bean-based diets by the amino acid absorption technique and the short-term nitrogen balance method. The amino acid composition was determined according to the ionic interchange method, and tryptophan was estimated by a colorimetric procedure. The essential amino acid (EAA) and non-essential amino acid (NEAA) pattern suggests that no significant differences in content exists in the three bean varieties. When the EAA patterns were compared with those of FAO/WHO, the limiting AA in decreasing order were found to be: tryptophan, valine and threonine (sulfur AA are not considered because the hydrolysis used in this study destroys them); and the AA surpassing the reference pattern were the aromatic AA and isoleucine. Apparent (AD) and true (TD) digestibilities of the EAA fluctuated between 33 and 59% and 60 and 85%, respectively, for black beans. With red beans, these results diminished: 29 and 55% AD and 64 and 81% TD, while for white beans the limits extended: 18 and 57% AD and 36 and 86% TD. Valine proved to be the EAA of lower biological availability, and lysine and phenylalanine the most available. It is suggested that the low digestibility of valine could be due to the amino acid imbalance existing in the bean protein, since this contains an excess of isoleucine and leucine in relation to valine. The AD and TD of the AAE with respect to the NEAA were of 0.89 and 0.98 for black bean, 0.89 and 0.96 for the red and 0.77 and 0.90 for the white, which indicates that biological availability of the NEAA is higher than that of the EAA. Findings thus confirm that biological determination of the TD of protein permits prediction of the TD of the AA, since a positive correlation (r = 0.93) statistically significant was found (p less than 0.05) among them. Utilization of the TD parameter instead of that of AD to estimate the protein quality is therefore recommended.     

New Amino Acids in Alkali-treated Wool

Examination of alkali-treated wool has indicated the presence of one amino acid, β-aminoalanine, not previously reported. 2,4-Diaminobutyric acid was also formed during fractionation of the wool. The possibility of the former occurring as a crosslink in alkali-treated wool and the feasibility of detecting crosslinks by keratose fractionation are discussed. A method for estimation of β-aminoalanine in protein hydrolysates is reported.     

The effect of glucose oxidase enzyme on wool fibres

Glucose oxidase is a type of enzyme that converts glucose into hydrogen peroxide and gluconic acid by enzymatic reaction. Glucose oxidase is widely used in industry; however, in the textile industry, glucose oxidase has only received academic interest. Previously, wool was bleached by some reducing agents; however, currently in industry, hydrogen peroxide dominates the bleaching of wool fibres. In this study, the effect of glucose oxidase enzyme treatment on wool merino fibres and dyeability properties was investigated. Wool fibres were treated with glucose oxidase enzyme, after which the whiteness index (Stensby) and yellowness index (ASTM D 1925 and ASTM E 313) were investigated. Scanning electron microscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy were used to identify the morphological structure of wool fibres and their atomic content. The chemical damage caused by enzyme was investigated using a fluorescence and a light microscope, and the alkali solubility (ASTM D 1283) was determined. After enzymatic treatment, the wool fibres were dyed at a 2.0% concentration with reactive dyes. Dyeability (K/S) and CIELab values were assessed with a Minolta CM 3600 D spectrophotometer (D65, 10°). The washing fastness of wool fibres was investigated according to TS EN ISO 105-C06 (A1S).     

Radiation induced graft copolymerization of methyl methacrylate on natural and modified wool III. Thermal behaviour

The thermal behaviour of natural wool and chemically modified wool fibres (oxidized, reduced, methylated and crosslinked) and their graft-copolymers with methyl methacrylate were investigated by dynamic thermogravimetry in air and differential thermal analysis in nitrogen atmosphere. The relative thermal stability depended on the chemical modification and oxidized wool was found to be thermally more stable than natural wool. Grafting reduced the overall thermal stability of the fibres.     

Pretreatment of wool/polyester blended fabrics to enhance titanium dioxide nanoparticle adsorption and self‐cleaning properties

This research aims to enhance the self‐cleaning properties of fibre‐blended fabric using surface pretreatment prior to the application of titanium dioxide nanoparticles. To this end, the polyester/wool fabric was modified, in that the wool fibres were oxidised with potassium permanganate and the polyester fibres were hydrolysed with lipase before nano processing. Butane tetracarboxylic acid was also used to enhance the adsorption of the nanoparticles and also to stabilise them on the fabric surface. The self‐cleaning properties of the fabric were examined through staining of the fabric with CI Basic Blue 9 and then discolouring by exposing to ultraviolet and daylight irradiation. Some other properties of the treated fabrics, such as water drop absorption, crease recovery angle and bending were investigated and are discussed in detail. The colour changes of different samples indicated an appropriate discoloration on the titanium dioxide‐treated fabrics after ultraviolet and daylight irradiation. Overall, the surface pretreatment of the wool and polyester fibres improved the self‐cleaning properties of the fabric significantly.     

A Protein Chemical Investigation of the Chlorine-Hercosett Process

The cause of the weight loss that occurs during continuous chlorination and Hercosett treatment of wool tops has been investigated. Wool top samples were collected and their amino acid composition determined. Samples from the treatment baths were collected after 20 h use and the amino acid contents and the protein fractions of the residues after evaporation were estimated. The results showed that proteins released in an industrial acid-chlorination procedure originated from the exocuticle of the wool (including the a-layer). The major part of the solubilised wool proteins was found in the sulphite bath. This can be explained by the fact that the degraded wool proteins are negatively charged and are released from the wool after raising the pH and the salt concentration of the treatment bath.     

Grafting onto wool: 8. Amino-acid compositions of various fractions of wool graft copolymers synthesised by methanol-benzoyl peroxide system

The amino-acid composition of the mother protein in the graft copolymer synthesised by the methanol—benzoyl peroxide initiating system was investigated. True graft copolymers were successfully separated from the grafted fibres by applying a fractional precipitation method. Analyses showed that the mother protein contains less cystine, threonine, serine, proline but more lysine, aspartic acid, glutamic acid, alanine and leucine than wool. The amino-acid compositions of any of the fractions obtained were almost identical to that of the low-sulphur S-carboxymethylkerateine protein which is considered to originate in crystalline microfibrils. On the formation of grafting centres in the protein chains in the complex structure of wool, such a selectivity has also been observed for the case of lithium bromide and peroxydisulphate redox initiating system. It was suggested, however, that there are two different types of molecule in the low sulphur protein components involved in these two graft copolymers.     

Repair of Protein Radicals by Antioxidants

In vivo, proteins are the main targets for radicals and other reactive species. Their reactions result in formation of amino acid radicals on the protein surface that often yield tryptophan and tyrosyl radicals or, in the presence of O₂, protein peroxyl radicals and hydroperoxides. All these species may propagate damage to biomolecules. Low molecular weight antioxidants, such as ascorbate, urate, and glutathione, are part of the defense system and function by repairing damaged proteins. We briefly review the existing knowledge about protein and amino acid radicals and their repair by antioxidants, including results of our investigations. The main question addressed is whether the antioxidants ascorbate, urate, and glutathione are able to repair amino acid radicals in model compounds and in proteins in vitro by pulse radiolysis. We show that ascorbate and urate repair tryptophan and tyrosyl radicals efficiently and inhibit proton-coupled electron transfer from tyrosine residues to tryptophan radicals in a number of proteins. In contrast, repair by glutathione is much slower. Ascorbate also rapidly reduces the peroxyl radicals of the N-acetylamide derivatives of glycine, alanine, and proline, whereas glutathione reduces peroxyl radicals in lysozyme. In vivo urate, ascorbate, and glutathione may prevent biological damage or, at least, reduce its rate, because they: (a) repair tryptophan and tyrosyl radicals in proteins and (b) reduce protein peroxyl radicals to the corresponding protein hydroperoxides. Most likely, in vivo, ascorbate and glutathione do not inhibit the reaction of C-centered amino acid radicals with O₂. Glutathione is less efficient that urate and ascorbate in repairing protein radicals; furthermore, the resulting glutathiyl radical is harmful. Ascorbate may be the more important repair agent in cells and tissues characterized by high ascorbate concentrations, such as the lens and brain; urate may be mainly responsible for repair in tissue compartments with higher urate concentrations, such as in plasma and saliva.     

Synthese von anionischen N-acylierten L-Aminosäuren,Oligopeptiden und Proteinhydrolysaten als Eiweißtenside und deren Anwendung in der Wollveredlung

Synthesis of anionic N-acylated L-amino acids, oligopeptides and protein hydrolysates as protein-based surfactants and their application in wool finishing. As model compounds for protein-fatty acid condensation products, ten L-amino acids were N-acylated with fatty acid chlorides by Schotten-Baumann reaction. Structural variation in the non-polar part of the molecule was achieved by using saturated fatty acids of different chain length (C₈–C₁₈). The terminal carboxyl group was modified by reaction with different amino acids. Furthermore, N-octanoyl-, N-dodecanoyl-di, -tripeptides and protein-fatty acid condensation products were synthesized by Schotten-Baumann reaction. A dependence of the surface activity on both molecular weight and amino acid composition of the peptide moiety was found after determination of the surface tension-concentration isotherms: critical micelle concentration (CMC) of the surfactant solutions increase with increasing molecular weight and higher polarity of the peptide part. This coincides with a reduction of surface activity. With increasing alkyl chain length, however, the surface activity increases as can be seen from the decrease in CMC. For the synthesized anionic protein-based surfactants good biodegradabilities (68–78% BOD₅/COD) were determined. The sorption characteristics of protein derivatives on wool were studied in wool finishing processes. An increased bath exhaustion and a more intense coloration of wool were obtained during dyeing of wool by addition of N-acyl-L-amino acids or commercially available protein-fatty acid condensates.     

The Yellowing and Bleaching of Wool

The yellowing of wool is a complex phenomenon which is induced by a variety of agencies such as light, heat and aqueous chemical reactions. Yellowing of wool by light depends critically on the wavelength distribution of the light (u. v. region), humidity and the type of prebleach given to the wool; if fluorescent whitening agents (FWAs) are employed in the bleaching process then the sensitivity to photo-yellowing is drastically increased. The copious amount of work carried out to overcome this complex situation will be summarised and the important role of the aromatic indole amino acid, tryptophan, will be detailed. In contrast to photoyellowing, exposure of wool to visible blue light (maximal effect 420–450 nm) promotes photobleaching of the yellow pigments, giving rise to complaints of colour change, especially in wool products dyed to pastel colours. To remove natural yellowness, chemical bleaching of wool is usually carried out by using hydrogen peroxide, the usage of which should be carefully controlled because of its fibre damaging characteristics. Optimisation of wool peroxide bleaching procedures has therefore been the subject of much work and these studies will be reviewed. Bleaching of wool with reducing agents is often practised either as an alternative to peroxide bleaching or more usually as an aftertreatment of peroxide-bleached wool to improve the whiteness and stability to light. Trade practice in the field of wool bleaching has recently been critically reviewed; the results and recommendations of this assessment will be given. More recently, significant progress has been made in the field of selective dark fibre bleaching and in the bleaching of heavily pigmented wools (e.g. karakul) using methods based on ferrous ion mordanting.