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Honest is one of the most modern corn wet millers in India having a diverse product portfolio of Maize Starches, Starches, Modified Starches, Liquid Glucose,
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Honest is one of the most modern corn wet millers in India having a diverse product portfolio of Maize Starches,
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Cationic starch


Cationic starches represent a unique class of high performance starch derivatives which have gained commercial acceptance because of their affinity towards negatively charged substrate such as cellulose, aqueous suspensions of minerals and slimes and biologically active macromolecules. They have already found extensive use in the paper manufacture in which they function as internal binders and retention aids for various fillers and emulsions and are added to the paper furnish before the sheet is formed. They are effective for improving such physical properties of paper as bursting and tensile strength, elongation, fold endurance, and pick resistance. Usually 0.5% to 1% addition of cooked cationic starch, gives the same improvement in the paper as does 1.5% to 2% addition of corn starch. Other benefits of the cationic starches are improved drainage on the wire, better sheet formation and enhancement of the sizing efficiency of an alum rosin size. Cationic starches also improve the retention of fillers such as titanium dioxide, clay, calcium carbonate which are frequently incorporated in the furnish to improve the opacity of high grade printing papers, fine writing papers, light weight papers such as bread wraps, glassine, etc. With increasing filler retention, the sheet loses strength because inert fillers reduce the number of sites for fiber to fiber bonding. Because cationic starch acts both to improve strength properties and filler retention. Its use gives high strength properties at higher level of filler retention.

A possible explanation for the improved strength obtain with cationic starch is that ionic attraction promotes a more intimate contact between the fibre surface and starch hydroxyls to increase hydrogen bond formation when the sheet is dried.

Chemical Composition :

Which possesses a cationic positive charge in water. The active group is a nitrogen compound, which is capable of forming salt. In aqueous solution these salts dissociate giving a positively charged starch radical.

Affinity for Cellulose :

The normal electro-kinetic potential of cellulosic fiber in water is negative. Thus, when Cationic starch is added to negative fiber system rapid absorption of Cationic starch occurs on the fiber surface. Cationic starch is more or less completely retained by the fiber system where as ordinary starch is far less retained. A beater starch will be efficient in the pulp alum system where as Cationic starch functions in the alum and alum free system.

The retention mechanism of the starch is explained by:

  • Filtration of the starch during sheet formation on the wire.
  • Absorption of a positively charged starch alum agglomerate
    by the negatively charged fiber.
  • Direct absorption of the starch on to the fibers by hydrogen
    bonds between the hydroxyl groups of the starch and hydroxyl
    groups of the cellulose

Under ordinary paper making conditions all the three mechanisms function to a degree resulting in increased strength properties in sheet.

In practice, starch retention lies in a range of 50% to 70% of that added. The excess is lost in white water. In case of Cationic starch, bonding occurs directly between the polymer and cellulose and does not require aluminium floc as intermediary. The opposite electrostatic charge between polymer and fiber increases the starch retention to almost 100% and this makes Cationic starch a superior wet-end additive.

Retention Aid for Filters :

Filler retention is expressed as a percentage of fillers found in the paper to the weight of fillers present in the breast-box stuff calculated on the same dry fiber basis.

When all the chemical additives are absent filler retention is around 20% to 50%.
Cationic starch is important in improving filler retention. China Clay, Calcium Carbonate etc. are covered with hydroxyl groups. These hydroxyl groups are attached from the aqueous medium and cause a negative electro-kinetic potential. The positively charged nitrogen group in Cationic starch radical is the reason for the combination between the polymer and negatively charged filler particles. Cationic starch combines therefore with Cellulose and China Clay.

Another successful application of Cationic starch is the improvement of titanium dioxide retention. The negative charges of titanium dioxide in water may be due to screening demand of the titanium ion, which causes it to attract positive hydroxyl ions.

From the above it may be concluded that Cationic starch is capable of bonding with negatively charged pigment particles and cellulose. In this way filler, fiber and fines are effectively bonded together. Because of these several bonds between Cationic starch polymer, fibers and fillers, a more effective flocculation occurs, resulting in an improved retention of fillers and fines on the machine wire.

Dosage :

Usual dosage of Cationic starch recommended is between 0.5% to 1.0% on the dry weight of cellulose and no solution of anionic substances such as anionic defoamers should be present in the system because they will affect efficiency of Cationic starch as a retention aid. After the addition of Cationic starch the furnish should not pass regions of high hydrodynamic shear. This can result in the irreversible breakdown of the filler agglomerate. Typical vigorous agitation in centricleaners and hydrocyclone is detrimental.

Preparation of Solution :

Cationic starch is used as a solution in water and 5% to 10% solution can be prepared in a tank by agitation and heating with steam for about half an hour.
The stock solution so prepared should be diluted while stirring to 0.5% to 1% concentration and passed through a fine mesh before adding it to the furnish. This reduces the viscosity and allows intimate contact.

Operating Procedure :

One method of addition is to meter 5% solution of Cationic starch in the machine circulating water so that the solution reaching the fan pump is 0.5% to 1% approximately. Sufficient time should be allowed for adequate mixing of back water and concentrated Cationic starch solution.

Another procedure is to dilute the concentrated solution by metering both the additional water and concentrated Cationic starch solution through a mixer, so, the material reaching the second stage dilution tank is premixed. From this the solution can be delivered to each machine through rotameter.

In case of completely closed stock supply system 0.5% to 1% Cationic starch solution should be added to the diluted stock with the aid of high pressure metering pump after centrifugal cleaners, but just before the pressure headbox.

The Cationic starch solution must be completely and thoroughly mixed at the point of addition. This is highly essential as incomplete mixing results in the formation of flocs and streaks on the wire. As a general rule, lower the pulp consistency, more uniform is the distribution of Cationic starch.

Therefore, the point of addition is very important and it should be added at a point where it will be adequately mixed by natural turbulence i.e.

  • Across the first compartment of the breastbox or headbox.
    For breastbox addition it is recommended to use a shower pipe
    which will distribute the solution of Cationic starch evenly across
    the complete width of the breastbox.
  • At the exit side of the secondary fan pump, to achieve good mixing in the laminar flow of the discharge pipe of the fan pump, the feed should end in multiple taps around the discharge pipe.

To evaluate the advantages or efficiency the stock is sampled in the breastbox for ash determination. The tray water should be analysed for fiber and filler solids and strength characteristics of the finished paper should be recorded.
The changes in the vacuum up to and including couch should be recorded. In short the use of Cationic starch has the following advantages:
1. Increase in filler and fiber retention
2. Increase in the strength property of the paper
3. Decrease of the suspended solids in the final effluent
4. Reduces BOD in the mill effluent.

Specification


% Moisture (Max)

 14.00
% Ash (Max)  0.5
% Nitrogen

 0.20    +/-    0.02

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