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Sodium Perborate for Starch Industry

It is well known that borax compound is used widely for adhensive industry, people often know sodium tetraborate instead of sodium perborate, but people also know to add sodium hydroxide(caustic soda) and hydrogen peroxide during production process of adhensive from starch. However they seldom know sodium perborate is compound resulting after reacting with sodium tetraborate with sodium hyroxide(to come sodium metaborate firstly), then reacting with hydrogen peroxide to come sodium perborate. The new technologies declose the know-how about using sodium perborate tetrahydrate typically like production process of corrugated paperboard starch (Glue Powder). Cardboard Laminator

Starch is a carbohydrate synthesised in corn, tapioca, potato and most other plants out of dextrose units. The polymer exists in two forms: a linear structure of about 500 units, amylose and a branched structure of several thousand units, amylopectin. The relative amounts of amylose and amylopectin differ between different types of plants. The linear amylose constitutes 27% of normal corn starch, the branched amylopectin makes up the remaining 73%. Some corn species have been selected for their high amylose content they contain up to 70 % amylose.

Starch, starch derivatives and modified starches have found a large number of applications in such diverse fields as food, feed, detergents, pharmacy and the paper and corrugating industry. In the field of corrugated paperboard adhesives, liquid mixtures of starch and sodium perborate are known.

JP 56129278 (Derwent Abstract) describes adhesives containing starch, sodium perborate, water and sodium hydroxide. These adhesives have low viscosity and high speed adhesion.

EP 0049 009 describes a process for preparing starch glue from starch, in particular native starch whereof part of starch is gelatinised in water in an alkaline medium optionally followed by the addition of additives such as boron-chemicals. The dry material content of starch is 20-45% by weight and additives such as sodium perborate are added. Highly preferred is sodium perborate together with a copper sulfate catalyst.

The basic purpose for the use of starch in the paper coating industry is to bind the pigment particles to each other and to the paper substrate. In order to achieve this adhesive effect of starch, the starch has to be gelatinised. The usual method to gelatinise the starch is to heat the slurried starch above the temperature required for gelatinisation. Under these conditions the granules swell and fragments are formed resulting in a colloidal dispersion which then acts as an adhesive.

When native starch is simply cooked in this manner the resulting adhesive is much too viscous to meet the water balance requirements needed for high solids coating formulations. The so prepared starch is too viscous for applications and shows a very high set back behaviour.

The final viscosity of the starch can be influenced by chemically or thermally treating the starch prior to use. Depending on the properties desired, a number of chemical methods may be used by the starch supplier to modify the dry starch product. Alternatively, the user can employ a suitable conversion process (e.g. enzyme, thermal, thermal/chemical) when preparing the sizing solution. The starch cooking process may be either batch or continuous.

In general, for enzymatic conversion of native starch, alpha-amylase is used as the preferred hydrolytic enzyme. By varying the amount of enzyme, the reaction time or the temperature, different end viscosities can be obtained.

When the desired viscosity has been reached the reaction should be stopped. This can be done by increasing the temperature to a value at which the enzyme is inactivated. This is generally at temperatures higher than 95°C for the alpha-amylases employed in starch conversion. Since at somewhat elevated altitude this temperature cannot be reached in vessels at ambient pressure it may be desirable to use the other way of inactivating enzymes i.e. by addition of chemicals.

Chemicals, which may be used for this application are copper sulphate, sodium phosphate, and zinc containing compounds. In order not to influence the reaction these and similar compounds are added at the end of the enzymatic conversion that is in the slurry. The inactivation of the enzyme by the metal ions is generally performed with a concurrent increase in temperature.

The compounds containing heavy metals are not longer considered applicable for this purpose due to environmental constraints. Moreover, the paper manufacturers are faced with the problem of adding the chemicals in a controlled and dosed manner. This requires additional investment, manpower and maintenance.

A further alternative would be to change the pH in order to inactivate the enzymes. However, this would require a further addition of neutralising or buffering compounds as otherwise the quality of the starch paste would cause problems when used in the paper production process.

We have now found that a desired and stable starch end viscosity can be obtained which works under all ambient pressure conditions and does not require the addition of inactivation chemicals by the paper manufacturer.

The process for preparing viscosity stable starch comprises the following steps:
◦a) preparing a slurry with a concentration from 25 to 38% solids preferably 35% solids, containing native starch and from 0.1% w/w to 0.5% w/w sodium perborate based on native starch,
1) adding an effective amount of hydrolytic enzyme to the slurry,
2) heating the slurry to a temperature of between 65° and 80 °C,
3) keeping the slurry at the temperature of between 65° and 80 °C until a desired end viscosity is reached,
4) further increasing the temperature to a value of which leads to enzyme inactivation,
5) allowing the starch slurry to cool.

Surprisingly the use of sodium perborate under the present conditions does not negatively influence the conversion reaction. During the whole enzymatic process, the sodium perborate does not influence the enzymatic conversion and by increasing the temperature at the end of the conversion, the perborate starts deactivating the enzyme.

a process for inactivating hydrolytic enzymes, preferably alpha-amylase, in a starch slurry by sodium perborate characterised in that sodium perborate is added to native starch and the temperature is increased to a value of which leads to enzyme inactivation. The inactivation of hydrolytic enzymes such as alpha-amylase can be obtained by adding prior to the enzymatic conversion sodium perborate to the slurry of native starch. After the enzymatic conversion the temperature is increased and the sodium perborate starts deactivating the enzyme.

Furthermore, the current invention relates to a process for inactivating hydrolytic enzymes wherein the temperature is increased to 85°C, preferably to 90°C, more preferably to 95°C.

Finally, the use of the viscosity stable starch obtained according to the new process for the surface application and/or coating of paper.

The benefits to use sodium perborate for glue powder manufacturing:

The dry composition of native starch and sodium perborate is stable

The presence of sodium perborate does not influence negatively the enzymatic conversion

Tthe paper manufacturer does not need a separate dosing facility and does not have to bother with the controlled dosing of sodium perborate

The dry composition can be applied for inactivation of hydrolytic enzymes

A slight temperature increase is sufficient for starting the deactivation of the enzyme by the sodium perborate already present in the mixture.

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