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BIO-TECHNOLOGY AND ENERGY SAVING OF HIGH PERMONANCE OF
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DYED SILK FABRIC
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Heba F. Mansour1* and S.Shakra 2
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Wellington, NZ
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Helwan University, Egypt.
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E-mail: heba1fm@yahoo.co.uk
School of Chemical and Physical Science, Faculty of Science, Victoria University of
Textile Printing, Dyeing, and Finishing Department, Faculty of Applied Arts,
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2
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Research Centre, Cairo, Egypt
Dyeing, Printing and intermediates Department, Textile Research Division, National
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Abstract
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Owing to the interest of bio-textile processing and saving energy, the performance of
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silk fabric was cationized using serine and glycine amino acids. The dyeability was
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examined with acid and direct dyes using microwave irradiation (MW) in comparison
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with the conventional thermal method. Cationization with 10 % (v/v) serine, using a
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material to liquor ratio of M: L 20:1 for 60 min was suitable for better dyeing and
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washing fastness under the neutral conditions.
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SEM analysis and FTIR spectroscopy provided evidence that the amino acids were
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grafted onto silk through the formation of new covalent bonds which increase in the
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rate of adsorption and fixation of chemicals. (MW) assisted dyeing possesses potential
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production of new eco-friendly silk dyeing in reducing the technological time, and
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increasing the rate of dye molecules diffusion of into the fibers, avoiding the
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consumption of chemicals and energy in comparison with the conventional heating
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method.
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Key wards: Biotechnology, energy saving, amino acids, direct dyes, acid dyes,
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microwave
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1. Introduction
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There is an increasing interest in the textile industry to the environmental and energy
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saving processes. Biotechnological tools with the use of naturally occurring polymer
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materials for surface modification become very important and appear as an emerging
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technology to create a new range of high performance textile fabrics. (Van Hest, et al.,
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2001; Aberg, et al., 2004; Freddi, et al., 2004)
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Such polymers are attracted the attention of the researchers due to their availability of
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resources, cost, easy handling, having environmental biological degradability and
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being non-toxic adaptation to nature. On the other hand, their application enables the
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required level of beneficial effect with only the fiber surface, minimizing the whole
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fiber attack; as a result, the deterioration in fiber quality could be easily avoided.
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(Monti, et al., 2005)
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Silk has always been the symbol of royalty due to its lustrous appearance excellent
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drape, smooth surface, fineness, as peach like softness. The coloration of this royal
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fiber is also an art form. The process varies largely in the form of hanks and woven
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pieces, this mechanism of dyeing is dependent not only on free amino and carboxyl
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groups but also on the phenolic ones with accessible –OH group. Because of slightly
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cationic character of silk with isoelectric point at above pH 5.0, it can be dyed with
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anionic dye such as acid, metal complexes, reactive and selected direct dyes, putting
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in mind that its dyeing behavior resembles that of micro-fiber synthetic fibers where
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large amounts of dye are required to achieve moderate/deep shades, displaying
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typically low fastness to wet treatments. (Burkinshaw and Paraskevas, 2010) As a
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result, many surface modifications have been done to improve the fibers properties.
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(Strlic, et al., 2003; Zhu, et al., 2004; McPhail, et al., 2004; Salehi, et al., 2005;
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Sampaio, et al., 2005; Freddi, et al., 2006; Weibin, et al., 2007; Bai, et al., 2008;
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Burkinshaw and Paraskevas, 2010)
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Acid dyes (Broadbent,2011; Trotman,1991 ) are of many different chemical types, i)
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Sulphonated azo dyes constitute the major group and are mainly mono and bis-azo
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compounds ranging in color from yellow, through red to violet and brown, there are
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some navy blue bis-azo dyes that can build up to give blacks, the substantivity of azo
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dyes for polyamide and protein fibers is greater where the higher their molecular
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weight the lower the number of sulphonate groups per dye molecule. ii)
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Anthraquinone acid dyes complement the azo dyes, ranging in color from violet
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through blue to green and often have very good light fastness. iii) Acid dyes with
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triphenylmethane (blues and greens) and xanthenes (reds and violets) chromophores
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are less important types noted for their brilliant colors that often have only poor light
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fastness. These dyes are usually sodium salts of sulphonic acids, of less frequently of
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carboxylic acids and are therefore anionic in aqueous solution. They will dye fibres
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with cationic sites. These are usually substituted ammonium ion such as wool, Silk
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and nylon. They are commonly classified according to their dyeing behavior,
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especially in relation to the dyeing pH, their migration ability during dyeing and their
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washing fastness. The molecular weight and the degree of sulphonation of the dye
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molecule determine these dyeing characteristics.(Kan,
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classification of this type, based on their behavior in silk dyeing as; level dyeing or
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equalizing acid dyes, fast acid dyes, milling acid dyes and super-milling acid dyes.
2008) The original
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Reactive dyes
(Broadbent,2011;
Trotman,1991)
were
initially introduced
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commercially for application to cellulosic fibers, and this is still their most important
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use. Reactive dyes have also been developed commercially for application on protein
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and polyamide fibers. Fiber reactive dyes are anionic water soluble colored organic
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compounds that are capable of forming a covalent bond between reactive groups of
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the dye molecule and neucleophilic groups on the polymer chain within the fiber,
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consequently, the dyes become chemically part of the fiber by producing dye-polymer
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linkages. (Meyer, et al., 1986; Gulrajani, 1993; Zuwang, 1998; Blackburn, et al.,
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1999; Rastogi , et al., 2001 )
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The four characteristic features of a typical reactive dye molecule are a reactive group
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(R) containing leaving group (X), a chromophoric group (C), a bridging group (B) and
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a solubilising group (S) as shown in following figure.
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Theoretically, all reactive dyes can be used for silk dyeing; however, to achieve the
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best quality of dyed silk fiber, reactive dyes have to satisfy the following special
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requirements; (Meyer, et al., 1986; Gulrajani, 1993; Zuwang, 1998; Blackburn, et al.,
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1999; Rastogi , et al., 2001 )
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a) Brilliancy of shade which is especially important for silk because many dyes on
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silk are much duller and the dyed silk shows lower degree of exhaustion.
b) Silk is damaged in an alkaline medium at high temperatures, so the reactive
dyeing should be carried out in an acidic or neutral dyeing bath
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c) The dyes should be highly stable in storage where the consumption of dyes in the
batch dyeing of silk is small.
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d) A high degree of covalent bonding should be achieved at the end of the dyeing
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process, minimizing the clearing treatment required to give maximum wet
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fastness.
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e) The rate of adsorption should be higher than the rate of reaction; otherwise the
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dyeing will be uneven, as a result; the reactivity should be moderate because the
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highly reactive dye will react even at low temperature reducing the possibility of
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leveling and migration, while a dye of low reactivity, on the other hand, requires
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extended time of dyeing at boil with consequent damage of material.
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Lanasol (CGY), Drimalan F (S) , and Hostalan (HOE) , Hostalan E(HOE) are at
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present commercially available that can be used on silk. Lanasol dyes (Ciba, 1966) are
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the most essentially bi-functional dyes that can be used on silk. These dyes are noted
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for their brightness and high reactivity. The level of fixation of these dyes is
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particularly high, leading to very high wet fastness properties; In fact these dyes
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maybe looked upon as tetra functional.
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α- bromoacrylamido [Lanasol (CGY)]
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5- chloro-2,4-difluoropyrimidyl [Drimalan F(S)]
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N-methltaurine-ethyl sulphone [Hostalan (HOE)]
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β –sulphatoethylsulphone [Hostalan E(HOE)]
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The heating process of textiles is more complex, as moisture migration in fibrous
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masses and web can take place in a number of ways, e.g. movement due to capillarity
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and gravity within the inter-fiber spaces, liquid diffusion along the fibers themselves
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due to moisture and temperature gradients, and vapor diffusion throughout the voids
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in the mass. (Bell, 2000; Robinson, et al., 2001)
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In most dyeing methods, heat technique is used to increase dyeing rates and to
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promote dye exhaustion, and fixation. This technique involves the application of heat
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to the surface of the material from another hot surface or medium by combination of
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radiation, convection, and conduction, which means that conventional heating
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technique, is a slow process, involving several stages in the transfer of energy before
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the material to be heated, thereby often cause dye migration problems.
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The saving of time and energy are obviously of interest in textile industries. The
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introduction of new techniques which will allow less energy to be user is a highly
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important area of activity to consider. Alternative energy sources such as microwave
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have been used. The investigation of the 900 MHz (Mc/second) frequency band and
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the development of a magnetron valve operating at this frequency are capable of
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producing 25 kW of output power which have placed microwaves on the industrial
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map as well as made microwave units suitable for modern material processing
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techniques. These irradiations have the ability to produce rapid and uniform heating
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throughout the material exposed to them via the dielectric heating which can be
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explained as the conversion of energy from wave into thermal form in the dielectric
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materials. (Haggag, et al., 1995; Burbage, 2002; Hakeim, et al., 2003; Kim, et al.,
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2003; Haghi, 2003 )
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From the ecological point of view, this study was focused on treating silk fabric with
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the amino acids polymers; serine and glycine to detect the physical modification in its
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structure which might be reflected on its dyeability and fastness properties. A
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comparative silk dyeing with acid and direct dyes were carried out by conventional
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heating method in comparison with microwave (MW) irradiation assisted dyeing.
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Scanning electron microscope (SEM) analysis and FTIR spectroscopy was applied to
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detect silk surface modification, in addition the color strength and fastness to washing
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was carried out to determine the efficiency of dyeing after modification.
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2. Experimental
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2.1.Materials
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Degummed and bleached plain Habotain silk fabric (30 g/m2) purchased from
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Sherazad Com. NZ was further treated at a liquor ratio of 50:1 with 2 g/ Nonidet®
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P 40 Substitute (Sigma-Aldrich NZ. Ltd.), for 15 min at 80°C then thoroughly
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rinsed and dried at ambient temperature. (Mansour and Heffernan, 2010)
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Serine (Sigma–Aldrich, Steinheim, France), glycine (Ajax Finechem, Auckland,
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New Zealand) were prepared at the concentrations as follows: 10% (w/v) (0.95M)
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of serine, 20% (w/v) (2.66M) of glycine. These chemicals was each added into
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deionizedwater and mixed by a magnetic stirrer at 60 oC until a clear solution was
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obtained.
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Acid dye “Nylason Red N- 2RBL” was purchased from Clariant and reactive dye
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“Lanasol Red B” was purchased from Swiss color, in addition to acetic acid and
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sodium carbonate which are all of laboratory grade chemicals.
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2.2. Amino acids treatment
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Silk samples were immersed in concentrations between (2.5-25) % (v/v) aqueous
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solutions of serine and glycine. Samples were treated at L: R ratios of (20:1, 30:1 and
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40:1) (prepared from the stock solution) at room temperature for time intervals varied
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between (10-90) min. After which, the sample was padded with the pre-treating
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solutions at 100% pick up, using a padding machine (Tsuji Dyeing Machine Mfg
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Osaka, Japan), steamed at 80 oC for for 5 min to dry the pre-treating solution, then
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finally fixed at 110 oC for 2min in the laboratory oven. After pretreatment, silk
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samples were characterized by Fourier transform infrared-attenuated total reflectance
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(FTIR-ATR, Spectrum One, PerkinElmer,U.K.), to confirm the existence of amino
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acids onto silk.
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2.3. Dyeing
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Dyeing was carried out by exhaustion method with two different heating systems. i) in
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the conventional heating system, silk samples were added to the dye bath with a
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material to liquor ratio of 1:60 at 40 oC, then the temperature was increased gradually
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to 80 oC in 30.min., the dyeing process was continued at this temperature for further
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30 min. The pH of dyeing solution was maintained with acetic acid and sodium
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carbonate at 3, 5, 7, and 9. The dyed fabrics were then washed, rinsed, and dried. ii) In
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the MW system, dyeing was carried out with LG microwave MC-200 TRS of 900
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watt power and 2450 MHz-frequency at time intervals of (5, 10, 15, 2, 25, and 30)
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min. at various MW powers of (180, 360, 540, 720, and 900) watt. The effect of dye
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concentration, pH value, was studied at the optimum determined power of 720 watt
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and 15 min. Dyeing samples were rinsed in hot water and washed-off at L: R 50:1,
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using 2 g/L non ionic detergent [Nonidet ® P 40 Substitute, Sigma- Aldrich NZ Ltd,
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at 80 oC, for 15 min.
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2.4. Measurements
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
The color yields (K/S) of the dyeings were determined by Cary 100 UV-Vis
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Spectrophotometer. The dye absorbance was measured in the visible spectrum
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region from 400 nm to 700 nm and the reflectance at the wavelength of maximum
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absorption (λmax) was used to calculate the color yield of dyed fabrics by the
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Kubelka-Munk Equation (Kubelka, 1948; Garland, 1993) as follows: (Kubelka,
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1948; Garland,1993)
F/R= (1-R) 2 / 2R = K/S
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Where K is the absorption coefficient of the substrate, S is the scattering
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coefficient of the substrate and R is the reflectance of the dyed fabric at λmax.
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
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Scanning electron microscopy (SEM) micrographs of the samples were prepared
with a Leo 1455VP scanning electron microscope (Cambridge, England).
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
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3. Results and Discussion
FTIR spectra were recorded on a Nicolet Nexus670 instrument.
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3.1. Amino acids cationization treatment
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Figure 1 shows that the weight gain of silk fibers increased rapidly with 10 and 20 %
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of serine and glycine respectively, and then proceeded at a lower rate, tending to a
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plateau. Water is a valuable material in the textile industry, when large volume of
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effluent is produced, it causes serious environmental problems. In this respect,
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optimizing the liquor ratio; L: R is an important factor for silk treatment process to
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save considerable amounts of energy and chemicals. To study the effect of L: R ratio,
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samples were treated at different ratios (20:1, 30:1 and 40:1) for 60 oC until a clear
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solution was obtained. As shown in Figure 2, the results showed that the weight gain
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did not change significantly with an increase in L: R ratios. Thus the best L: R was
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20:1. The negligible difference in weight gain yield at different L: R ratios might be
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the result of saturation of the silk with amino acids.
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The effect of time on silk treatment with 10% serine and 20% glycine was studied
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from (10-90) min and represented in Figure 3. It was denoted that the silk weight gain
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increases more rapidly during the first 60 min, and then proceeds at a lower rate. The
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extent of weight gain attained by the fibers may depend on morphological, chemical,
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and structural properties of the fibrous substrate. Silk is a fibrous secretion consisting
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of few protein components, the surface and internal morphologies are drastically
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different, as a result, these features might significantly affect the adsorption and
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diffusion of chemicals. Additionally, the different amino acid compositions that entail
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different numbers of functional groups potentially reactive toward anhydrides are
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available within the fiber matrix. At the optimum concentration of amino acids due to
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the availability of the more active cites on treated silk samples, the rate of grafting is
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very fast. In contrast; by increasing the amino acids amounts above the optimum
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concentration, the active cites on the samples are occupied and relatively limited cites
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are available for reaction of serine and glycine with samples which can be seen by
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smooth weight gain of the samples represented by the SEM microscope.
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Surface morphology of silk was elucidated by SEM technique to highlight the
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modification and influence of amino acids on the silk samples was represented in
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Figure 4. The surface smoothness of untreated silk (a), fibers treated with serine and
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glycine (b & c) showed the presence of variable amounts of foreign material deposited
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onto silk. The morphological features of amino acids treated silk fibers were slightly
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different. Based on the SEM results, it is reasonable to assume that the presence of
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these deposits may be considered responsible for the weight gain by treated fibers.
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This phenomenon was much more pronounced for serine treated silk, which showed
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the formation of a continuous coating layer. The SEM micrographs in show that the
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untreated fibers in the yarn are distributed loosely, and the amino acids also provided
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a similar fiber arrangement. Serine treated surface appeared to be as smooth as the
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untreated surface while glycine, increased roughness of the silk fibers. These
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pretreatments contain many functional groups and may give higher color strength.
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FTIR spectra were investigated to manifest the existence and formation of the newly
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formed bonds over silk due to the treatment of the samples with serine and glycine
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amino acids. As shown in Figure. 5a; FTIR spectrum of silk as shown in is
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characterized by the absorption peaks of the unmodified silk fabric found at 3273,
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1617, and 1514cm−1, are assigned to the –NH stretching and –NH bending of the
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amino groups, respectively, which are typical of polypeptides and proteins and allow
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their conformational characterization. (Arai, et al., 2001) The IR spectra of the amino
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acid (spectra b, c) pretreatments are found at around 3300 cm−1 and 1600, 1500
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cm−1, attributing to the N–H stretching of –NH3+ and N–H bending, respectively.
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Moreover, the band of amino acid at around 1400cm−1 is due to the carboxylate
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anion. From the IR spectra, it is found that each amino acid is possibly dissociated to
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the –COO− and –NH3+ groups. The result suggests that the cationic charge of the
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amino group on the silk surface can attract ionically with the negative charges e.g: the
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sulfonate group (–SO3−) presented in the dye molecule increasing the dye uptake. On
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the other hand, on treating silk with amino acids solutions, the hydrophilicity of the
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fabric is improved. These pretreatments can improve the dye uptake because of the
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aqueous dye medium, whereas the number of hydrophilic groups (–NH2) increase and
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cause the formation of hydrogen bond by water molecules. (Arai, et al., 2001) The
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pre-treating materials with low MW yield more hydrophilicity occurred because they
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can easily dissolve and can diffuse faster than those of high MW materials, that’s why
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glycine (Mw =75gmol−1) provided a higher hydrophilicity value in compared with
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serine (Mw = 105gmol−1) because it is of low molecular weight.
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3.1. Dyeing process
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Although silk contains notably fewer acidic and basic side chains than its
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proteinaceous relative, wool which results in silk displaying much lower acid
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absorption than wool (silk: 150 mmol kg_1; wool: 840 mmol kg_1, the acidic and,
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especially the basic amino groups in silk, are considered to be of prime importance in
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the uptake of anionic dyes onto the substrate. In this context, the adsorption of anionic
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(commonly sulfonated) dyes, such as acid dyes or direct dyes, onto silk under acidic
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conditions is generally considered to arise through the operation of, principally
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electrostatic forces, including ion-ion forces and H-bonding, with van der Waals’
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forces, hydrophobic interactions as well as pep interactions also contributing to dye
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fiber substantivity. (Sashina, et al., 2006; Kan, 2008)
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Consequently, as proposed for the exhaustion trends obtained for acid and reactive
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dyes on silk can be attributed to mostly electrostatic attraction operating between each
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of the sulfonated dye molecules and protonated amino groups in the substrate,
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although van der Waals’ forces, hydrophobic interactions as well as pep interactions
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are also likely to contribute. The acid protonates the fibre’s amino groups, so they
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become cationic. Dyeing involves exchange of the anion associated with an
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ammonium ion in the fiber with a dye in the bath as follows:
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Silk –NH2(S) + H+ (aq) + HSO4-(aq)
Silk –NH3+HSO4-(S)
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Silk –NH3+HSO4-(S) + Dye – SO3-(aq)
Silk –NH3+ Dye- SO3-(S) +
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HSO4-(aq)
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In case of reactive dyes, covalent dye polymer bonds are formed, as follows:
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+ Silk-NH2
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Dye [Lanasol (CGY)]
+ HBr
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Amino acid cationization increases the active sites on the silk fabric surface. It is
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known that the binding of amino acids to silk is due to the ionic interactions, such as
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carboxyl groups in silk forming salts with the free amino groups in serine and glycine,
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and hydrogen bonding interactions between hydroxyl and amide groups of the silk
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with the hydroxyl groups of the amino acids. The following aspects may be of great
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importance in dyestuff substantively: first, the number and position of the negatively
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charged sulphonic acid groups (dye-SO3) and the attraction to positively charged
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cationised protein based silk substrates. Secondly, the amino groups of the untreated
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silk or the unblocked portion in the cationised ones which is capable of entering into
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hydrogen bond formation with groups such as -OH, - CO, -N-N- and Br in the
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dyestuff molecule. Thirdly, reactive dyestuffs that posses high planarity have
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abundant opportunities for hydrogen bonding and van der Waals forces to take place
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between silk and dyestuff.
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Figure 6 shows the effect of 10% serine cationization on the the average percentage
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color strength of silk samples dyed with acid and reactive dyes in comparison with the
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color strength of the un-modified sample. It was denoted that the color strength (K/S)
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values of the cationized silk samples increased relative to the untreated ones. This
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follows the expected trend because the cationic treatment leads to an increase in the
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dye uptake, which results in an increase in the depth of shade. Pretreatment with
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cationic reagents would introduce cationic groups into silk samples, thus improving
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both substantivity and reactivity. (Haroun and Mansour, 2007) At the same time, the
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dyed cationic samples appeared much darker than the untreated ones when compared
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visually.
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The influence of the overall dye molecule structure is quite important. This effect is
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illustrated by the significant differences in color yield which increases among the
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studied dyes.
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As shown in Figure 7a, b; the dye uptake increased progressively as colorant
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concentration increased. With increasing concentration, more dye transferred to fabric
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and the depth of color became stronger. Finally, the reactive dyes show higher dye
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uptake than acid dyes at higher dye concentrations. The curves illustrated that the
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maximum color strength value of the untreated silk was achieved at dye concentration
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9% for both of acid and reactive dyes, while in case of cationized silk, the maximum
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color strength was achieved at dye concentration (7 and 5) % owf in case of acid and
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reactive dyes respectively. It can be concluded that for the cationized silk low dye
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concentration was recommended relative to the untreated ones. This may be due to the
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increase in the cationized samples’ reactivity, consequently, the dye concentration
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needed decreased due to the greater affinity of the cationized silk towards acid and
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reactive dyes in comparison with the untreated one. (Haroun and Mansour, 2007)
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Figure 8 shows the effect of dyeing bath pH on the color strength of cationized silk
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samples dyed with acid and reactive dyes. It was recorded that the maximum color
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strength was achieved in the neutral medium due to the cationization that provided
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additional sites to the fabric, as a result; the isoelectric point was changed and the dye
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ability of the cationised silk was increased in the neutral medium. (Haroun and
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Mansour, 2007)
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The main features which distinguish microwave heating from convective heating
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process is that because liquids absorb the bulk of the electromagnetic energy at
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microwave frequencies, the energy is transmitted directly to the wet material. The
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process does not rely on conduction of heat from the surface of the product and thus
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increased heat transfer occurs, speeding up the heating process. This has the
2
advantage of eliminating case hardening of the products which is usually associated
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with convective hot air heating operations. Another feature is the large increase in the
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dielectric loss factor with moisture content. This can be used with great effect to
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produce a moisture leveling phenomenon during the drying process since the
6
electromagnetic energy will selectively or preferentially dry the wettest regions. (Wu,
7
et al., 1998)
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Results of the effect of dyeing time at different microwave irradiation powers on the
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color strength values of the applied acid and reactive dyes were illustrated in Figure 9.
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It was denoted that the increasing of dyeing time to 20 min at (180-900) watt lead to
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an increase in the color strength values in comparison with the conventional heating
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system. In contrast, prolong dyeing than 20 min (25-30) at powers of (540-900) watt
13
lead to a decrease in color strength values. However, the results indicated that an
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increase of dyeing time causes an increase of the color strength values at microwave
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irradiation powers of (180-360) watt. Prolong exposure to microwave irradiation (25-
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30) at powers of (540-900), the dyes molecules can be separated from the fabric and
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migrated again to the dye bath causing a decrease in the color strength values. While
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at
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color strength values.
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Microwave irradiation assisted dyeing allows the silk samples to be heated
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simultaneously without needing the transfer of heat from the surface into samples. As
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a result, the dye bath reaches its specific temp of dyeing process possessing the
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maximum color strength values after only 20 min via microwave irradiation.
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In fact, with increasing of microwave power, the absorption increases by loss material
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(loose material; absorptive electromagnetic such as water….etc.) exist in the aqueous
(180) power, the energy was low requiring an increase in time to increase the
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1
media. In microwave heating, the most important variable in determining the power
2
absorption is the loss factor, which is fixed by the electrical properties of the material.
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The effective loss factor of a wet material is derived from the solid matrix, the bound
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water and the free water. The latter is dominant at the higher moisture content and is
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derived from the ionic conductivity of dissolved salts and the loss due to the rotation
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of dipolar molecules in the applied electrical field. In the absence of dissolved salts,
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the loss factor is a maximum in the microwave region. (Robinson, 2001).
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Dielectric heating by microwave can be explained as the conversion of energy from
9
wave into thermal form in the dielectric materials. Materials with high dielectric
10
constants, such as water, salt, and alcohol, can be self-heated by the rotation and
11
relaxation of dipole during the radiation of microwave. Therefore, microwave heat as
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a heat source can be used in dyeing. (Kim, 2003) Therefore, increasing of kinetic
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energy of the dyes molecules lead to a decline in the required time needed for
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transferring of dyes molecules into the fibers samples. In addition, at this condition,
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the swelling rate of silk was increased and the dyeing process was reached its
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optimum condition rapidly.
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The maximum heating rate is established immediately at the beginning of the process
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because the initial moisture content was below the critical sample moisture content
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and there was sufficient microwave power in the cavity. The microwave heating of
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samples showed the higher heating rates and consequently faster heat-up times, higher
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temperature and pressure gradients within the material. At this stage a “pumping”
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effect within the material becomes apparent. This pumping effect is primarily caused
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by an internal pressure buildup which forces the free liquid in the pores of the
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samples. Although this pumping action does increase heating rate, the increased
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temperature and pressure that occur can cause damage to the material. In heating with
17
1
microwave irradiation under fixed conditions, water is evaporated from the exposed
2
silk surfaces and replaced by water migrating from within the fabric structure. During
3
this process, a steady state is established and the fabric temperature and evaporation
4
rate remain almost constant. (Lin and Liu, 1994)
5
By the way, in case of conventional heating system, heat transfer was carried out by
6
conduction, this means that the surface of silk samples was first heated, then heat
7
transfers through the samples, needing much more time (60 min) for transferring the
8
heat from the dye bath into silk samples to reach the same color strength value as
9
microwave irradiation system.
10
3.2. Fastness to washing
11
Wash fastness properties were improved by cationization due to the formation of ionic
12
bonds between the cationized silk and the used dyestuffs. However, when the cationic
13
reagent concentration was increased the degree of staining decreased because less dye
14
was transported to the washing bath. These results show that the staining problem can
15
be solved for industrial applications when avoiding excess dye usage and by
16
optimizing the washing off process. The solubility of any high molecular weight
17
hydrolysed dye molecules that remain after dyeing to cationic silk is expected to be
18
low, therefore, less dye desorption is expected during washing, consequently, the
19
fastness ratings are improved.
20
On the other hand, it was anticipated that the covalent attachment of the reactive dye
21
molecules to the fiber would produce very high wash fastness because covalent bonds
22
were the strongest known binding forces between molecules. The energy required to
23
break this bond would be of the same order as that required breaking covalent bonds
24
in the fiber itself as a result, reactive dyeings possess much higher wash fastness in
25
comparison with acid dyeings. Finally, samples dyed with microwave irradiation
18
1
showed a little improvement on wash fastness and reduction of staining on cotton and
2
wool samples.
3
Conclusion
4
It is recommended to decrease the pollution resultants for both the economical and
5
environmental points of view. In this regard this research was dealing on the pollution
6
prevention of silk dyeing with acid and reactive dyes using biological treatment, and
7
modern energy save equipments. The performance of silk fabrics, especially their was
8
improved via grafting with natural biodegradable, environmentally friendly natural
9
amino acids (serine and glycine). FTIR spectra of samples confirmed the formation of
10
amide functional groups and SEM images were in good agreement with the FTIR
11
spectra.
12
Higher color strength values and better good washing fastness were achieved after
13
cationization of silk with 10% serine, using a material to liquor ratio of 1:20 for 60
14
min., in comparison with 20 % glycine under the same conditions. Cationiztion
15
enhances dyeing of silk under neutral conditions instead of the acidic one. Microwave
16
assisted dyeing was undertaken to improve the color yield as an economical modern
17
technique that can effectively lower energy and cost of dyeing because of short
18
heating time.
19
20
21
22
23
24
25
19
1
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1
2
3
4
5
6
7
8
9
10
11
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13
14
15
16
Figure 1: effect of amino acids concentration on the weight gain of silk samples
24
10
9
8
weight gain %
7
6
5
serine
4
glycine
3
2
1
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
5
10
15
conc. %
20
25
30
25
1
Figure 2: Effect of liquor ratio of amino acids cationization bath on the weight
2
gain of silk samples; 10% v/v serine, and 20% v/v glycine at 60oC until a clear
3
solution was obtained
serine
glycine
10
weight gain %
9
8
7
6
5
4
3
2
1
0
L:R 1:20
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
L:R 1:20
L:R 1:20
26
1
Figure 3: Effect of amino acids cationization reaction time on the weight gain of
2
silk samples; 10% v/v serine, and 20% v/v glycine at 60oC, L:R 1: 20
10
9
8
weight gain [%]
7
6
5
4
serine
3
glycine
2
1
0
0
3
4
5
6
7
8
9
10
11
12
13
14
15
16
20
40
60
Reaction time [min]
80
100
27
1
Figure 4: SEM micrographs of a:untreated silk , b: serine treated silk, and c:
2
glycine treated silk
3
4
5
6
7
8
9
10
11
12
13
14
15
16
a
b
C
28
1
Figure 5: FTIR spectroscopy of a: un treated silk, b: serine treated silk, c:
2
glycine treated silk
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
29
1
Figure 6: Effect of 10% serine cationization on the color strength of silk samples
2
dyed with 1% owf acid and reactive dyes by conventional heating method using
3
liquor ratio of 1:60, at 80oC, for 60 min.
4
samples dyed with acid dye
acid
Reactive
6
64%
cationized
36%
control
5
K/S
4
a
3
Samples dyed with reactive dyes
2
35%
Control
1
0
control
5
6
7
8
9
10
11
12
13
14
15
16
17
18
cationized
65%
Cationized
30
1
Figure 7: Effect of dye concentration a) acid dyes and b) reactive dyes on the
2
color strength of control and cationized silk samples with 10% serine, dyeing was
3
carried out by conventional heating system using liquor ratio of 1:60, at 80oC, for
4
60 min.
control sample
cationized sample
16
14
12
K/S
10
8
a
6
4
2
0
0%
2%
4%
6%
8%
10%
acid dye concentration % owf
5
control sample
cationized sample
18
16
14
K/S
12
10
b
8
6
4
2
0
0%
6
7
2%
4%
6%
8%
reactive dye concentration % owf
10%
31
1
Figure 8: Effect of pH values on the color strength of cationized silk samples with
2
10% serine, dyeing was carried out by conventional heating system using liquor
3
ratio of 1:60, at 80oC, for 60 min.
acid dye
reactive dye
18
16
14
K/S
12
10
8
6
4
2
0
pH 3
4
5
6
7
8
9
10
11
12
13
14
15
16
pH 5
pH values
pH 7
32
1
Figure 9: Effect of different microwave powers assisted a) acid dye, b) reactive
2
dye- dyeing time on the color strength of of cationized silk samples with 10%
3
serine, dyeing was carried out by conventional heating system using liquor ratio
4
of 1:60, at 80oC, for 60 min.
18 watt
36 watt
54 watt
72 watt
9 watt
conventional heating system
16
14
12
K/S
10
8
6
a
4
2
0
0
10
20
30
40
50
60
70
Time min
5
18 watt
36 watt
54 watt
72 watt
9 watt
conventional heating system
18
16
14
K/S
12
10
8
6
b
4
2
0
0
6
7
10
20
30
40
Time min
50
60
70
33
1
Table 1: Wash fastness properties of silk samples dyed with acid and reactive
2
dyes
Wash Fastness
Conventional heating
MW assisted dyeing
system
system
Samples
wf
Control acid
St. cotton
St. wool
wf
St. cotton
St. wool
4
3-4
3-4
4-5
4
4
4-5
4
4
5
4-5
4-5
5
4-5
4-5
5
4-5
4-5
5
5
5
5
5
5
dyed sample
Control reactive
dyed sample
Cationized acid
dyed sample
Cationized reactive
dyed sample
3
4
5
6
7
8