Desizing effectiveness

As the Ca(OH)2 leaches from the particle and comes in contact with the unreacted AKD , it creates, with the moisture in the paper, a high pH environment, which can cause hydrolysis of the unreacted AKD and loss of the sizing effect on the PCC particle. This is then able to adsorb water, or ink, and create a desizing effect, although the fibre itself may still be sized. Obviously, the higher the entrapped lime level and the higher the filler content, the greater the effect. 

Desizing by chemical decomposition is applicable to starch-based sizes. Since starch and its hydrophilic derivatives are soluble in water, it might be assumed that a simple alkaline rinse with surfactant would be sufficient to effect removal from the fibre. As is also the case with some other size polymers, however, once the starch solution has dried to a film on the fibre surface it is much more difficult to effect rehydration and dissolution. Thus controlled chemical degradation is required to disintegrate and solubilise the size film without damaging the cellulosic fibre. Enzymatic, oxidative and hydrolytic degradation methods can be used. 

The poor adhesion of carboxymethylcellulose to synthetic fibres means that where such fibres are present, it can only be effective in combination with a synthetic size polymer (Table 10.6). This needs to be taken into account when considering suitable desizing procedures. If this cellulose derivative is to be used in conjunction with an electrolyte-sensitive acrylic acid copolymer, it is advisable to choose a salt-free carboxymethylcellulose. 

Many acrylic acid copolymers are water-soluble but unlike poly(vinyl alcohol) they are not degraded by alkali. In fact they need alkali for effective desizing as they are more soluble at alkaline pH than in neutral solutions. They are sensitive to acidic media, which should not be used. Solubilisation occurs by the formation of sodium carboxylate groups from the anionic polyacid. The polyelectrolyte formed in this way is readily soluble and shows a rapid rate of dissolution. However, the presence of electrolytes such as magnesium or calcium salts from hard water can inhibit removal [191]. 

The desizing of water-soluble size polymers can be summarised as follows. Batchwise or continuous methods can be used in both cases an adequate supply of hot water is needed during the washing-off. Hot water and detergent are needed to remove polyfvinyl alcohol) or carboxymethylcellulose. The addition of alkali may be beneficial with carboxymethylcellulose. Alkali is essential with modified starches and acrylic acid copolymers. Polyfvinyl alcohol) can be degraded effectively by alkaline oxidation. 

Table 10.22 Effect of desize and boil-off of cotton on AOX and whiteness values before and after chlorite bleaching [224]... 

A highly effective aqueous solution giving high weaving performance at low application levels on continuous filament viscose yarns. Readily removed in a neutral or mildly alkaline scour. Dyeing can be carried out without desizing. 

If LEONIL EB is used, a separate enzymatic desizing process can usually be omitted, thus effecting considerable savings in time, energy and water. 

CNC PAL 100 may be run in conjunction with enzymes to promote even wetting with no adverse effect on the desizing agent. 

SCOUR DR is designed to aid in the removal of oil spots and stains from fabrics during preparation. It may be used effectively in the desize bath if one is used or in any wet processing step prior to bleaching or dyeing. The use of 1-3% on the weight of the fabric is recommended for heavily stained goods. 

Desizing agent all purpose biodegradable scouring agent for continuous and batch pre-/after scouring. Effective at wide pH range. 

Anionic/solvent detergent for use in alkaline scouring and bleaching of cotton for removal of oils and waxes. Effective in enzyme desizing. 

T-C 9100 is effective when applied to soiled fabric which is to be heat-set prior to desizing or scouring. 

The complete line of NEODOL surfactants consists of some 15 individual products based on alcohols in the C9 to Cl 5 range with distinctive performance characteristics which make them exceptionally effective in various textile applications. NEODOL surfactants can therefore be selected for specific high performance qualities in traditional textile applications such as lubrication, desizing, scouring, mercer-ization, printing and dyeing—as well as for the newer applications such as foam finishing and foam mercerization. 

The pH of the desizing bath is maintained by adding acid or alkali. The effects of pH and temperature on enzyme activity are shown in Figs. 3-3 and 3-4 respectively. However storing the enzyme at a fixed temperature shows that the activity steadily decreases with time (Fig. 3-5). In general, changes in pH, tem-... 

Sometimes sodium or potassium chloride (0.18-1.0%) is added to the desizing bath for pancreative enzymes to get its full activity. For malt a-amylase calcium ion is effective and sequestering agent must be avoided in the desize bath. These salts are particularly used for desize mixture by affording heat protection to enzyme, increased stability of the enzyme and efficiency. On the other hand, heavy metal ions such as copper, iron etc. may combine with enzyme and inhibit its activity [8]. Sometimes hydrocarbon solvents such as xylene (50 ml/1) along with suitable emulsifier (4 g/1) are also added to facilitate removal of waxy components of the size. 

Recently a cold desizing process using sodium sulphide in a weakly alkaline solution is reported [23]. The rate of desizing is increased 5-fold compared with alkali alone. A mechanism involving a catalytic effect of the sodium sulphide in the hydrolysis of glucoside bonds in the polysaccharide is proposed. 

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