"White Spirit"Pretreatment Handbook(Desizing)PretreatmentExactly your chemistry

DESIZING of fabrics of cellulosic fibres and their blends with synthetic fibres using the BACTOSOL enzymes and the SANDOZIN wetting agents/detergentsThanks to their complete range of chemical products for the textile industry and the synergism between sizing products and the pretreatment of textiles, Clariant presents here a comprehensive survey of the techniques for desizing fabrics with the most suitable products for total elimination of natural and synthetic sizes to the benefit of all who handle textiles.

The purpose of desizing is to eliminate sizing products in order to ensure the success of scour boiling and bleaching and the production of faultless dyeings. Before starting this process it is advisable to determine the type of the sizes so as to facilitate their removal. Clariants MINILAB can easily be made available for rapid identification of the sizing products such as starch and PVA (polyvinyl alcohol). For a precise qualitative and quantitative analysis, extraction in the Soxhlet together with infrared curves and chromatograms are required.The Minilab from Clariant: this mobile laboratory is indispensable for monitoring the good quality of the pretreatment of textiles. It is possible not only to identify the sizes on the goods but also to analyse the residues of alkali, acid, peroxide, iron, the pH of the fabric and many other parameters. It is accompanied by a comprehensive manual describing its use.The preparation of threads for weaving involves covering the warp threads with a size with specific properties (see table). A fibre is easier to weave if its pilosity is reduced: its resistance to rubbing is significantly improved. Sizing therefore improves the weavability of warp threads by reducing thread-thread and thread-metal friction.The efficiency of a size is measured by the weaving yield. Clariant offers a complete range of sizes under the designations ARKOFIL, VINAROL and TYLOSE.For high quality desizing it is essential to know the chemical and physical properties of the sizes in order to apply a process which will ensure their total elimination.Main characteristics of sizesRequirements in sizing and subsequent process steps

The products for sizing are generally natural polymers (starch) as is or modified (CMS) as well as synthetic polymers and copolymers (PVA, PAC, PES, etc.). It goes without saying that the fabric can contain a single size or a mixture of different sizes depending on the type and structure of the textile substrate, alongside waxes, fats and lubricating paraffin.Abbreviations of sizes:CMS =CarboxyMethylStarchCMC =CarboxyMethylCellulosePVA =PolyVinylAlcoholPAC = PolyAcrylatePES = PolyEster

A desizing recipe can be optimized for a single known size (ideal case) or for a mixture of unknown sizes (frequent case). The golden rule in case of doubt as to the nature of the size is to adapt a desizing recipe capable of eliminating the most difficult size; if necessary, enzymatic desizing for bioconversion of the insoluble starch into water-soluble glucose.A systematic, progressive procedure makes it possible to identify starch, polyvinyl acetate, PVA and CMC sizes with 5 different reactants. The method is not direct and intermediate extractions are necessary.It goes without saying that in cases of doubt it is possible to use more sophisticated analytical methods such as extraction in the Soxhlet, infrared, chromatography, as well as the information in the Minilab manual from Clariant.

Standard solutions:

Solution (

1.3 g iodine

+ 2.4 g potassium iodide

in 1 l water

Solution (

0.13 g iodine

+ 2.6 g potassium iodide

+ 4 g boric acid

in 100 ml water

Solution (

11.88 g potassium dichromate in 50 ml water

+ 25 ml sulphuric acid conc.

Solution (

30 g sodium hydroxide in 70 ml water

Solution (

uranyl nitrate 4%

(aqueous solution)

enzymatic elimination

washing > 80C

sensitivity to pH

(-amylases

cellulases

alkaline

acid

Starch

(

CMS

(

(()

CMC

(

(

PVA

(

(

PAC

(

(

PES

(

(

Thanks to the blue scale it is easy to identify and quantify residues of starch on the fabric. The iodine reactant (Minilab) produces a more or less intense bluish violet colouration depending on the residual quantity of starchy sizes. A quantitative approximation is associated: rating 9 represents a quantity of starch less than 0.04%, rating 1 more than 2.5% starch. Rating 5, less than 0.2%, is acceptable for dyeing. PVA can also be identified by a touch of boric acid in an iodine medium. Colouration is dark blue.Caution - problems :To ensure the success of all the operations following desizing such as bleaching, dyeing or printing, it is important that the material is completely clear of sizes. The most significant results of poor desizing are lower degrees of whiteness, insufficient absorbency, spots, reserves, unlevelness, moir of dyeings, too harsh handle leading to breaks. The origins can be classified in 2 groups:Group 1; pretreatment probems: overdrying of sized warp threads, high content of waxes and lubricants which are difficult to emulsify, high content of sizes.Group 2; process problems: poor wetting out and low pickup, too short swelling of the sizes, bath containing enzyme poisons, insufficient final washing.

Thanks to the enzymatic genius, Clariant offers apha-amylase enzymes tailor-made for desizing fabrics sized with starch or mixtures of starch and water-soluble sizes.Starch is a polysaccharide containing amylose (linear chain) and amylopectin (branched chain) from potatoes, rice, maize, wheat, manioc, etc. depending on the geographical region. The amylose is bioconverted to 100% by the alpha-amylases into glucose whereas the amylopectin is only converted to 50% into glucose + maltose. Depending on the process and the machine, it is necessary to select specific bacterial enzymes and adjust the optimum pH and temperature. The enzymatic geniusChemically, an enzyme is a biolgical catalyst defined as being a protein complex composed of about 200-250 aminio-acids. An enzyme has a precise spatial configuration. Like a key in a keyhole the substrate to be degraded fits into the enzyme to form an enzyme-substrate complex swollen by the energy of the enzyme. The enzyme plays the part of molecular scissors and bioconverts the substrate. In the case of insoluble starch the alpha-amylase enzymes degrade the size into water-soluble glucose and maltose. There are several types of enzymes for the textile industry: cellulases for cellulose (biopolish, Jeans), proteases for bioconversion of wool and silk, catalases for degradation of hydrogen peroxide, pectinases for bioconversion of pectins, lipases for fats, etc. Enzymatic activity varies with the temperature and pH. For each type of enzyme there is an optimum pH and an optimum temperature. The reactional medium can assist (activators) or impede (inhibitors, poisons) the enzymatic activity. Clariant has a complete selection of enzymes for the textile industry under the commercial designation BACTOSOL.

Enzymatic activityBactosol MTN is an enzyme recommended for temperatures between 60-70C applied by the pad batch technique with batching for 6-8 hours at room temperature or on the jig.Bactosol HTN is a thermostable enzyme recommended for high temperatures of 90-100C with short steaming (1-3 min) or by enzymatic shock in a continuous washing compartment or in a J-box. pH 6 is the optimum for both types of enzyme.Clariant offers 2 types of bacterial enzymes: Bactosol MTN (Bacillus Subtilis) and Bactosol HTN (Bacillus Licheniformis). The main parameters of these two enzymes are shown below.Influence of the temperatureInfluence of the pH

Provided the pH does not go below the isoelectric point of the alpha-amylases (below pH 5) it is possible to protonize the enzymes either with Sirrix 2UD to buffer the medium or with Sirrix DNA for strong demineralization of cotton contaminated with iron.Sample recipes

Pad Batch System

protonized

enzymes

acid cracking

Bactosol MTN liquid

Sandozin MRN liquid conc.

Sirrix 2UD liquid

Sirrix DNA liquid

Sea salt

Bath pH

Impregnation t

Batching time

5 ml/l

4 ml/l

1-2 ml/l

2 g/l

ca. 5.0

65C

4-6 h

4 ml/l

5-20 ml/l

ca. 2-3

20-40 C

4-6 h

The parameters to be taken into account during desizing apart from the temperature are: the isoelectric point of the amylase; if the pH is too acid, lower than pH 5, the enzymatic activity collapses and this is irreversible even if the pH is readjusted. the water hardness; enzymatic activity is higher if the water is hard with calcium. the presence of salt; the stability and efficiency of the enzyme are maintained at a higher level if salt (NaCl) is added for long and hot processes, thus ensuring better desizing of the starch.

Sandozin MRN - the ideal surfactant for desizingThe elimination of sizes is greatly improved by the presence of Sandozin MRN which is a very special complex of amphiphilic molecules. This surfactant is composed of a molecule with polar groups (affinity for water) and hydrophobic or lipophilic groups with affinity for the hydrocarbonic chains of the desizing polymers.The sized grey fabric is totally hydrophobic and cannot be wet out. The addition of Sandozin MRN enables very rapid wetting out with a maximum pickup of the desizing bath. Combined with singeing at a very high fabric speed (more than 100 m/min), penetration of the enzymatic bath to the heart of the fibre is total thanks to the excellent wetting power of Sandozin MRN. Its action is even greater because in addition to rapid wetting out, it enables extraction of the degraded sizes while avoiding their redeposition on the fabric through its efficient dispersion power. Sandozin MRN is also distinguished by its strong detergent power and its emulsifying power for mineral oils and silicones, its biodegradability and its ecological profile containing no APEO, no solvent, no silicone. It is a highly concentrated, pumpable, low-foaming liquid. Its special synergetic composition of natural origin makes it a universal product for desizing, scour boiling, bleaching and washing of textile fibres.Influence of water hardnessInfluence of salt

Synergy Sandozin MRN / Sandozin NANIf disturbing foam is formed due to too rapid speed of the fabric or too short an impregnating bath, it is advisable to add a small amount of the deaerating agent Sandozin NAN (ca. 1g/l) to the desizing bath. This product eliminates air from the fabric, totally eliminates foam, improves wettability and accelerates penetration of the chemical products and enzymes to the heart of the fibre. The roll of wet fabric runs less during batching.The advantages of Sandozin MRN: Max. wetting and washing effect High emulsifying power Stable to alkalis and acids Low foaming Biodegradable, APEO-, silicone- and solvent-free Highly concentrated

Poor surfactantFair surfactantGood surfactantSandozin MRNWashing test:Detergent effect

Singeing

This operation where the fabric passes at high speed over flame burners to eliminate pilosity of the material (fibrils and down) is often combined with the desizing process.Immediately after singeing the material enters straight into the enzymatic desizing bath. The main purpose of singeing is to ensure the regular appearance of the surface of dyed or printed fabrics. Poor singeing can have very negative consequences on the elimination of sizes, particularly PVA. The most important parameters of singeing are: the intensity of the flame, the speed of singeing, the distance between the burner and the fabric, the position of the flame with regard to the fabric. Pad Batch desizing and variants

tangentialon rollerdirectwith counterflow of air

Recipes

enzymatic

alkaline cracking

acid

cracking

Sandozin MRN liquid conc.

Bactosol MTN liquid

Sirrix 2UD liquid

Sirrix DNA liquid

NaOH 36B

Sandozin NAN liquid

Impregnation t

Batching time

4 ml/l

5 ml/l

1 ml/l

1 ml/l

60-70C

4-6 h

4 ml/l

2 ml/l

80 ml/l

1 ml/l

60-70C

4-6 h

4 ml/l

20 ml/l

1 ml/l

20-40C

4-6 h

Classical pad batch desizing is one of the most commonly used processes because it follows straight after singeing. The singed fabric is impregnated at high speed (80-150 m/min) with an enzymatic desizing bath at 50-70C before being rolled and batched for several hours.The critical points to be taken into consideration with this process are:rapid wetting out, 4 to 10 seconds, depending on the profile of the chassis and the speed of the fabric. Sandozin MRN ensures this.foam formation due to rapid entry of a hydrophobic grey fabric into the bath. The deaerating agent, Sandozin NAN eliminates the air and foam and accelerates penetration.the pH and above all the deviation of pH during passage of the material. Certain sizes contain alkaline substances which inactivate the enzymes. Sirrix 2UD is an acid which buffers the medium around pH 5.0-5.5.storage. The fabric is covered with a plastic film to avoid drying over a long period. Drying of the fabric stops desizing.the nature of the enzyme. For this treatment Bactosol MTN is selected: it has its maximum effect at 60-70C, but its action continues on cooling.final washing after batching is, without doubt, the most important operation for total desizing. Machine parameters are: speed of the fabric, temperature of the bath, number of washing compartments, countercurrent, pressing rollers, spraying ramps, intermediate squeezing rollers. The water consumption is also a characteristic of good washing; average figures are about 5 litres of water per kilogramme of fabric.

Well desized fabric enables optimum subsequent bleaching and dyeing without problems. Desizing on the INJECTA (Benninger)

The INJECTA module is a special concept in which fabric destined for desizing (of starch or synthetic sizes) is guided through a narrow chimney divided into two conduits. The steam, water and air are projected separately providing favourable turbulence for rapid swelling and elimination of the sizes on the fibre. Throughout the chimney the fabric is subjected to a uniform high temperature of 100C. Elimination of the sizes takes place in the first hot washing compartment which follows the Injecta tower. The Injecta module thus enables desizing in a few seconds with minimal water consumption. The module can be placed before a bleaching steamer for continuous desizing and bleaching or in front of an open width washer for desizing fabrics of synthetic or natural fibres. Other combinations make it possible to combine Injecta shock desizing with a cold pad batch bleach. The Injecta module: a primordial trump for desizing.

Example 1: INJECTA desizing and IMPACTA bleaching on one completely continuous pretreatment rangedesizingBy synchronizing enzymatic shock desizing on the INJECTA with pad steam bleaching on the IMPACTA module it is possible to give a completely continuous treatment including singeing.Impregnation in a short liquor on the IMPACTA for the pad steam technique with maximum pickup makes it possible to obtain better absorbency and very high degrees of whiteness with no severe degradation of the cotton. The IMPACTA module is equipped with extremely precise metering pumps for milligrammes of product per kilo of textile material. Level control with sensors which are computer controlled produce a homogeneous, consistant bleaching from start to finish of the treatment.washingbleachingcylinder drierInjectaImpactasteaming

INJECTA desizing

starch

sizes

acrylate

sizes

PVA

sizes

Sandozin MRZ liquid

Plexophor ECO liquid

Bactosol HTN liquid Conc.

NaOH 36B

Temperature

4 ml/l

1 ml/l

1 ml/l

80C

4 ml/l

1 ml/l

10 ml/l

80C

4 ml/l

1 ml/l

80C

IMPACTA bleaching 20 min steaming

Sandozin MRZ liquid

Stabilizer SIFA liquid

NaOH 36B

H2O2 35%

2 ml/kg

6 ml/kg

30 ml/kg

40 ml/kg

The combination of INJECTA enzymatic shock desizing with the possibility of a cold pad batch bleach at the end of a continuous washer is one of the most interesting techniques. It makes it possible to eliminate all the sizes including PVAs which are sensitive to alkali in a first phase and then in a second phase to pad with a recipe containing less caustic soda, hydrogen peroxide and chemical products because all impurities have been removed from the fibre. On line wet-on-wet impregnation avoids harmful intermediate drying. After 16-24 hours of batching the roll can be washed on the same installation which functions as a continuous washer.Example 2: INJECTA enzymatic shock desizing followed by cold pad batch bleaching

Recipes

enzymatic shock

desizing

cold pad batch

bleaching

Sandozin MRZ liquid

Plexophor ECO Liquid

Bactosol HTN liq. conc.

Stabilizer SOF liquid

NaOH 36B

H2O2 35%

Bath temperature

Batching time

4 ml/l

1 ml/l

1 ml/l

80C

4 ml/l

6 ml/l

60 ml/l

60 ml/l

20C

16-24 h

Pad Steam desizing: enzymatic or oxydative

Pad steam desizing is suitable for continuous treatment of large production batches. The fabric speeds are high and wetting out is rapid with Sandozin MRZ. The thermostable enzyme Bactosol HTN enables quantitative bioconversion of the degraded sizes. This type of process is often used for enzymatic desizing of yarn-dyed shirting fabrics.Oxydative desizing without enzyme but with sodium persulphate by the pad steam process also enables elimination of the starch while conferring good absorbency to the scour boiled fabric.

Recipes

enzymatic

oxydative

Sandozin MRZ liquid

Bactosol HTN liq. conc.

Sirrix DNA liquid

NaOH 36B

Na-Persulfate

Bath t

Steaming time

Steaming t

5 ml/l

1 ml/l

60-80C

1-3 min

100C

5 ml/l

2 ml/l

80 ml/l

2 g/l

60-80C

1-3 min

100C

Cold oxydative desizing and bleaching

Oxydative desizing with persulphate but without hydrogen peroxide allows alkaline extraction of the sizes without a bleaching effect. This process is suitable if the sizes are not based on PVA.Oxydative desizing combined with cold bleaching is widely used industrially. It combines the two treatments, desizing and bleaching, in one operation. The chemical medium is highly reactive because it contains hydrogen peroxide and sodium persulphate. The sizes are therefore cracked by superoxydation. Inspite of the alkaline medium PVA sizes are also decomposed. Subsequent washing must be very energetic to ensure elimination of the sizes, a high degree of whiteness and good absorbency. In most cases this process is followed by pad steam bleaching or scour boiling to obtain a maximum quality of the pretreatment.

Pad Batch recipes

oxydative

without peroxide

oxydative

with peroxide

Sandozin MRN liq. conc.

Sirrix DNA liquid

Stabilizer SOF liquid

NaOH 36B

H2O2 35%

Sandozin NAN liquid

Na-Persulfate

Impregnation t

Pickup

Batching time

4 ml/l

2 ml/l

100 ml/l

1 ml/l

3-5 g/l

cold

80-100%

4-6 h

4 ml/l

1 ml/l

6 ml/l

80 ml/l

60 ml/l

1 ml/l

3-5 g/l

cold

80-100%

16-24 h

It is absolutely possible to improve the quality of desizing with the vacuum technique. The mechanism for eliminating sizes by the classical system comprises the following:on contact with water a size shrinks and then swells into a spherical shape before detaching itself from the fibre. The chemical products present, surfactants and sequestrants, disperse the degraded sizes and avoid their redeposition. Depending on the type of size these operations take between 20 and 60 seconds.Suction slot (TVE Escale)Continuous desizing process: washing rangeWith the aid of the vacuum technique, however, the mechanism of detachment of the size is accelerated: after brief swelling the size is sucked in rapidly and quantitatively within 10 to 20 seconds. The fabric is desized and the size is separated from the medium and can be sent, if it is recyclable, to an ecological ultrafiltration unit.

Recycling is an interesting solution on two levels. Firstly it avoids loading the wastewater with pollutant organic substances and secondly the sizes and capital involved are recovered for reuse in the circuit.Ultrafiltration is required for PVAs, CMCs, PVA/CMC mixtures and certain acrylates. It consists of separating a dissolved substance with the aid of a semipermeable membrane. The size of the pores of the membrane are such that water molecules can pass through but not the macromolecules of sizes. This filtration is carried out under a certain pressure. The precondition is that the size is stable in water and does not start degrading in solution even over a long period and at temperatures around 70-80C.Starch is not recyclable because it biodegrades during batching.Examples of the engineering of recycling sizes