TECHNOLOGY OF TEXTILEPREPARATION AND FINISHING(TXL141; 3-0-0; 3 CREDITS)PREPARATION OF PROTEIN FIBRESPreparation of Wool Carbonization Scouring BleachingCARBONIZATIONObjective: To remove cellulosic impuritiesfrom wool by treatment with acid/acidproducing salts. Rawwool maybecontaminatedwithvegetablematterofcellulosicnature, consistingofseeds,burrs, grass etc. It needs to be removed in fibre stage itself fromwools with high content of vegetable matter Generally done by treatment with sulphuric acid Mineral acids turn cellulose into brittlecarbonaceous mass which can be removed bycrushing itSEQUENCESAcidification Drying/Baking Crushing Dusting NeutralizationProcessing Stages:Treatment with(5-7%w/v) sulphuric acidandacidstablewetting agent.Hydro extractionDrying at 60-70oC to low regainBakingat 110oCindryheat for 2min. (wool isrelativelystable to acidic conditions. The vegetable matter turnsbrown/black, becomes brittle)Crushingtobreakthedegradedvegetablematter tosmallfragments by passing through heavy fluted rollersDusted and Neutralized with sodium bicarbonate.Bleaching with acidic hydrogen peroxide to minimizeyellowing caused by carbonizationWOOL SCOURINGThe high amount of impurities may hinder the processing ofwool.The transfer of wool grease from fibres to metallic machineparts may lead to Dirt/oil accumulation on processing equipment Poor drafting performanceTherefore, wool is generally scoured at fibre stage.Presence of scales on wool fibre surface leads to a tendencyto felt/shrink.Scouring involves treatment with aqueous scouring liquorscontaining mainly surfactants.Efficacy of scouring can be increased by mechanicalagitation or stirring action. However this may also lead tofibre entanglement.WOOL SCOURING- SALIENT FEATURES Generally done at raw wool stage. Residual grease/wax is kept around 0.5-0.75%.Modern machines used Hopper bottomed bowls.Older machines Long bowls with flat bottoms.Older machines 4-5 long bowls (35-40 m.)Modern machines At least six bowls (16-28 m) Scouring may be carried out in a series of bowls Wool fibre mass is transported from one bowl to another with gentle stirring Non ionic surfactants are primarily used for contaminant removal Sodium carbonate may be used as builder sometimes to facilitate contaminant removal As wool gets cleaned progressively, the composition of treatment bowls keeps changing.AUXILIARIES USED The most important auxiliary for wool scouring isa detergent. Alkyl phenol ethoxylates have been used ashighly effective detergentsbut are being phased outdue to environmental concerns. Due to the Eco-friendly nature, fatty alcoholethoxylates arenowadays beingpreferredoverAlkyl phenol ethoxylates.TYPICAL COMPOSITION OF AUXILIARIES INA WOOL SCOURING MACHINE:Soap (%)Alkali (Na2CO3%)Temperature (oC)Time (Min)I BOWL 0.75 0.20 49-52 2.5-3II BOWL 0.5 0.1 46-49 2-2.5III BOWL 0.25 0.1 43-46 2IV BOWL Water only- 40-43 1.5 pH should never be above 10. Temp. 35 40oC but never above 60oC. WOOL SCOURING MACHINES There is a mechanism to continuously agitate wool ina rectangular bowl or shallow tank Wool is transported to the next bowl. Before being transported to the next stage, the woolmass is squeezed to minimize upstreamcontamination. Afeeding conveyor transfers the rawwool to thescouring trough. Thewool isagitatedandat thesametimemovedforward by the action of a unit situated just above thebowl. Anoutputconveyortransfersthewool totheotherbowl withanintermediate padunit squeezingthewool between the two bowls.SWING RAKE TYPE MACHINE The rakes move individually by a cam and crank arrangement. The rakes come down, press the wool, move it forward and rise vertically up in the process getting detached from the wool mass. They then move back, come down again and the cycle continues.HARROW TYPE MACHINEFor a gentler treatment. Here all the prongs movetogether. This is more suitable for finer wool,which can undergo damage and felting in a morevigorous swing rake machine.BOWL DESIGN In modern machines, the emphasis is on reducing the total length of bowls to reduce chances of fibre entanglement. This is achieved with hopper bottomed (deeper) bowls which ensure better dirt removal. Machine type Old NewBowl design Shallow and flatDeep (hopper bottomed)Width Long ShortNo. of bowls 4-5 6Cumulative length of bowls (m)35-50 16-28Temperature (oC) ~40- 50 ~30WOOL BLEACHING Wool is bleached with hydrogen peroxide. Thechlorine based oxidative bleaching agents are notsuitable for wool. Generalbleachingsequenceis: pH-8.5-9at50-60Cfor two hours. The activator should be mild alkali. The stabilizers used are phosphates, tetra sodiumpyrophosphate or sodium tri polyphosphate. Since wool can be damaged under alkaline condition,an alternative is to bleach in acidic conditions using aper acid activator (pH 5-6). This is a BASF promoted process, bleaching is done atpH 5 with activator Prestogen W at 80C for an hour.CONTD H2O2and peroxy compounds can causeprogressive oxidation of disulphide bonds in wool Resulting in fibre damage which can beaccentuated in subsequent dyeing. Hence prebleached wool should be dyedpreferably below 80C. Another variant of acidic bleaching wasdeveloped by IWS and BASF. In this process, wool is padded with 350 gpl H2O2solution acidified by 2 gpl formic acid. By batching (cold-pad-batch) overnight, excellentbleaching is obtained.REDUCTIVE BLEACHINGReductive bleaching of wool is carried out with followingagents. Thiourea dioxide Sodium dithionite Zinc formaldehyde sulphoxylate Sodium formaldehyde sulphoxylate Sodiumdithionite is the preferredreducingagent.Bleaching is carried out at 45-65C at pH- 5.5-6 for 1hour. Bleaching can also be carried out with thioureadioxide. Toprevent heavymetal catalyzeddecompositionofbleachbath, inclusionof asequesteringagent isamust. The bleaching is carried out at pH 7 at 80C foran hour.COMBINED OXIDATIVE REDUCTIVEBLEACHING Peroxide bleached wool has a reddish tone Whereasreductivelybleachedwool oftenhasagreenishtingebutanatural whiteisgenerallythe demand of the industry. Asequential oxidativeandreductivebleachingprocessissupposedtoperoxideaneutralwhitecolour. Bleaching with thio urea oxide is 3 times cheaperin cost and also has the advantage of low COD &BOD. In this approach wool is first bleached withalkaline H2O2 at 60C for 1 hour. To the bath thiourea is added and pH adjusted to4.5-5.5. Thioureais convertedto thiourea dioxide andbleachingiscarriedoutat60Cforanother25min, followed by washing and rinsing. Thus in the first stage oxidative bleachingoccurs with H2O2and reductive bleachingtakes place in the 2nd stage with thiourea dioxide.SILK DEGUMMINGObjective: To impart softhandleandlustreto silkby removing sericin, anyimpuritiespickedupduringreeling throwing etc. Somenatural wax, coloring matterand minerals may also beremoved during degumming. Sericin is a protein which forms bulk of the gumor the outer protective coat in a silk filament Hence the process consists of cleavage of peptidebonds of sericin, either by hydrolytic or othermethods, and its subsequent removal fromfibroin by solubilization or dispersion in water.FOLLOWING ARE THE MAIN DEGUMMINGPROCESSES: Extraction with water. Boil-off in soap. Degumming with alkalies. Degumming with acids. Degumming with enzymes. Degumming with organic amines. Although both fibroin and sericin are proteins,they differ significantly in their constitution.GIVEN BELOW IS THE TYPICAL AMINO ACID COMPOSITIONOF FIBROIN AND SERICIN: The main constituents of fibroin are glycine, alanine and serine whereas In sericin it is serine, aspartic acid and glycine. Hence any degumming method should target the peptide bonds between the amino acids found in majority in sericin. However, in practice, methods have been developed on empirical basis.EXTRACTION WITH WATER Sericin removal can be achieved in water at high temperatures. It is not a commercial process. Upto 96% sericin can be removed by extracting it with water at 115oC for 3 hours. Although there is still a doubt if the removal occurs through hydrolysis or dissolution.BOIL-OFF IN SOAP It is an old process and seems to be still favored commercially. Olive oil soap (Marseille soap) is the most widely used soap. Following is a typical recipe:Marseille soap20-30% owf Time90-120 min. Temperature90-100oC M:L1:40 Amount of sericin removal also depends on the type of soap used in the degumming process. Degumming depends on the alkali formed on hydrolysis of soap and the soaps hydrolyzing the most have the highest degumming power.MELTING TEMPERATURES OF FATTY ACIDSAcid Name Structure Melting PointLauric (C12) CH3(CH2)10COOH +44Palmitic (C16) CH3(CH2)14COOH +63Stearic (C18) CH3(CH2)16COOH +70Oleic (C18) CH3(CH2)7CH=CH(CH2)7COOH +16Linoleic (C18) CH3(CH2)4(CH=CHCH2)2(CH2)6COOH -5Linolenic (C18) CH3CH2(CH=CHCH2)3(CH2)6COOH -11Arachidonic (C20) CH3(CH2)4(CH=CHCH2)4(CH2)2COOH -50Fatty acid PercentageOleic acid 55 to 83%Linoleic acid 3.5 to 21%Palmitic acid 7.5 to 20%Stearic acid 0.5 to 5%-Linolenic acid 0 to 1.5%COMPOSITION OF OLIVE OILc) Degumming with Alkali Buffer Withalkalis, thepHof theboilingbathshouldbemaintainedbetween 9.5-10.5. Below pH 9.5, the rate of degumming is too slow and above 10.5,the risk of chemical damage is high. Hence many times, alkaline buffers likeSodium carbonate/sodium bicarbonate,Sodium hydrogen phosphate/trisodium phosphate,Potassium tetraborate/boric acid etc. have been used. Typical recipe is given below:Sod. Carbonate (0.5M) 5.3 gplSod. Bicarbonate (0.05M) 4.2 gplNon-ionic Surfactant 3gplTemperature 95oCTime 20 min.d) Degumming with Organic Acids Mineral acids may cause significant damage to silk, hence generally only organic acids are used. A typical recipe is given below: The mechanism of acid attack on silk peptide bonds is shown below:Tartaric acid (0.05 M) pH- 2.3 8 gplNon-ionic Surfactant 3 gplTemperature 110oCTime 60 minTREATMENT CONDITIONS AND OBSERVED RESPONSES FOR YARNSDEGUMMED WITH ORGANIC ACIDSe) Degumming with Enzymes Considered to be a safer method which results in minimal damage to silk. Carried out at milder temperature and pH The natural hydrophobic impurities are not removed effectively. One of the advantages lies in the fact that enzymes specifically targeting peptides bonds occurring in majority in sericin can be selected. Since the constitution of sericin and fibroin is different, such enzymes will have minimum action on fibroin. The main enzymes used are trypsin, papain and bacterial enzymes. Trypsin Trypsin is a serine protease with the highest activity at pH range 7-9 and 37C. Ammonium bicarbonate (0.1 M/l) can be used as buffer. It is applied at 1-2% owf for 1-4 h. Better degumming results when alkalis are combined with proteolyticenzymes. Pretreatment with alkaline solution swells sericin and results not only in better degumming but also in better scouring (wax, fat removal).o Papain Obtained from papyrus latex. Most effective at 70-90oC temperature and at pH-5. It is a sulphydryl enzyme and hence requires a sulphydryl (-SH) compound as an activator. Has a wider specificity towards polypeptides as compared to trypsin. Bacterial enzymesAlkalase, developed by Novo nordisk is claimed to be more effective than trypsin or papain.Specificity of proteasesf) Degumming with Aliphatic Amines Methyl, dimethyl, ethyl and trimethyl amines can be used. Amines show good degumming (upto 90 % sericin removal) with little loss in tensile strength. Typical recipe:Trimethyl Amine 0.25 MN.I.D. 3 gplTemperature 80oCTime 45 min.M:L ratio 1:25COMPARATIVE ASSESSMENT OF DIFFERENTDEGUMMING METHODS Different methods have been evaluated on the basis of weight and strength loss after degumming.Agent Weight LossStrength Loss Marseille Soap100100 Carbonate + Bicarbonate buffer 10082.2 Tartaric Acid10081.3 Methyl Amine97.7119 Alkalase 85.5112.9 BLEACHING OF SILK Bulk of the naturally occurring colour in the silk is actually contained in sericin. Since the degumming process is not able to remove the sericin completely, retains some of its natural tint after boiling off. Widely bleached with hydrogen peroxide with a typical recipe: Alkali used is either ammonia or tetra sodium pyrophosphate.Parameter Mulberry silk Wild silk H2O2(35% w/v) 15-20 ml/l 20-30 ml/lStabilizer 2 gpl 4 gplM:L ratio 1 : 20 1 : 30Temperature 75-80 80-90Time (hr) 1-2 3-4pH 8.5-9 8.5-9