Starch adhesive production method

Foreword

Starch adhesives are used in recent years as a kind of adhesive for the production of corrugated boxes. The main raw material is corn starch or tapioca starch. Due to the wide source of raw materials for the production of starch adhesives, low price, and good bonding properties, most corrugated paper mills in the world use it for making adhesives. There are many methods for producing starch adhesives, and each has its own characteristics. The following describes various methods for producing starch adhesives.

1 Starch adhesive production method

1.1 The alkaline paste method

It mixes water with starch and dilute alkali, warms up to 40°C, and continuously stirs and serves. This method is simple in technology and uses less raw materials, but is rarely used because the functional groups of starch have not changed and the adhesion is not satisfactory.

1.2 Dextrin method

In this method, the starch is directly calcined (190-230 DEG C), or calcined in the presence of a small amount of hydrochloric acid and nitric acid at 110-140 DEG C, or by microbial fermentation. The adhesive made of it has good flow property, near-neutral pH value and low corrosion, but it can not change the functional groups of starch, and has poor adhesive force, anti-corrosion and anti-mildew properties, can not be stored, the process is more complicated, and the end point is difficult to control. , Relative molecular mass fluctuations, quality instability. Therefore, the current application is also relatively small.

1.3 Subject-Bearer Method

It is a small amount of oxidized starch plus sodium hydroxide, paste after the diluted paste as a carrier, and then the un-gelatinized starch or oxidized starch as the main mix together, relying on the sudden high temperature after the glue will raw starch or oxidized starch Burst and gelatinized. The corrugated paper produced by this method is of good quality, but is only suitable for high speed continuous machine production.

1.4 Oxidized starch method

It oxidizes the starch with an oxidizing agent to change the hydroxymethyl group at the 6-position carbon of the original starch to an aldehyde group and a carboxyl group. This change of the functional group not only increases the binding force between starch and paper fiber, but also improves the It's antiseptic and mold proof ability. At the same time, the oxidation can make the long molecular chain of starch into a short molecular chain, so that the obtained adhesive has improved fluidity and is easy to be coated on the machine. According to the different process methods used for oxidation, it can be divided into hot and cold methods. Two kinds of law.

1 4 1 Thermal Method

The oxidizing agent is usually hydrogen peroxide and sodium hypochlorite. The reaction proceeds at about 60° C. and the reaction time is 2 h. The adhesive produced by this method has better adhesion and mildew resistance, but the method is made at 60°C and must be hot for heating. It can not be stored and transported, and it can be used with the system. This undoubtedly brings about production. trouble.

1 4 2 Cold Method

That is, at room temperature, it is manufactured at normal temperature. The production temperature is consistent with the use temperature, and the viscosity is stable. This method is based on the cold process and the presence of aldehyde groups. It is not prone to mildew and rot and can be stored and transported for a long period of time. Although the advantages of the cold process for producing an adhesive are many, it is a disadvantage to realize the oxidation reaction at a low temperature. Therefore, in order to make the oxidation reaction proceed smoothly, a suitable catalyst must be selected. Production practice has proved that the most suitable catalyst for the production of oxidized starch by the cold process is nickel sulfate.

2 New method of starch adhesive production

The above describes the production methods of several kinds of starch adhesives. Although adhesives produced by the above production methods are widely used in production, these adhesives also have certain deficiencies. If hydrogen peroxide and sodium hypochlorite are used as catalysts, the oxidation degree is not easy to control, the quality of the finished product is not stable enough, the drying speed is slow, and the water resistance is poor. With the continuous development of science and technology, researchers have now developed a number of new methods for the production of starch adhesives, which are described below. 2.1 Improve the main body - the carrier method

The starch-based adhesive produced by the conventional bulk-carrier method is used to bond cardboard and then dipped in water. Corrugated paper is separated from the ground paper for about 20 minutes and the cardboard is destroyed. This kind of paperboard is not suitable for making special requirements for cartons, such as packaging vegetables and fruits. Cartons used in foods are often in contact with water and stored in ice storage or in refrigerated trucks. Therefore, in order to increase the useful life of cartons, it is necessary to increase the water resistance of adhesives. The improved bulk-carrier method involves adding a certain amount of urea formaldehyde to the starch adhesive, ie, a urea-formaldehyde-starch adhesive is produced. Before the addition of urea formaldehyde, it must be neutralized with hydrochloric acid to achieve a pH of 9 to 9 and then 1% to 2% of urea formaldehyde. The viscosity of the starch adhesive produced by this method is obviously increased, and the resistance to cardboard is increased. Water-based has a certain effect, such as the use of corrugated paper made in Japan is still not separated after more than 2h of water immersion, in line with production requirements.

2.2 Potassium permanganate method

The conventional oxidized starch is prepared by the action of hydrogen peroxide and sodium hypochlorite as the oxidizing agent and starch, but it has the disadvantages that the degree of oxidation is not easy to control and the quality of the finished product is unstable, and potassium permanganate and hydrogen peroxide are used as oxidants. The degree of reaction can be controlled by the self-coloring of potassium permanganate, and the quality of the produced product is superior to the former. The acidic potassium permanganate oxidizes partially reductive alcohol groups in starch to carboxyl, aldehyde and ketone groups. This oxidative degradation depth can be controlled by the addition of an oxidizing agent to obtain a certain depth of oxidized starch, and then sodium hydroxide is added. It is combined with the unoxidized alcohol groups in the starch, resulting in swelling and gelatinization with adhesiveness. Finally, the complexing agent borax is added, so that the finished product has cross-linked thickening effect, which facilitates the acceleration of adhesion, and the effect of manganese ion and sodium hydroxide can be achieved. Produces a colloidal cured film that improves the water resistance of the adhesive.

2.3 Solid adhesive

Production method This adhesive is made by mixing starch (oxidized starch 16% to 21%), sodium hydroxide (1 3%) and borax (0 4%) as the main raw materials. The preparation of oxidized starch can be performed by using sodium hypochlorite and hydrogen peroxide as oxidants. In the specific use, according to different uses, according to the formula, the various components can be weighed, and the different amounts of water (usually in the range of 76% to 81%) can be divided. The sodium hydroxide and borax are respectively formulated into a certain concentration of solution. And oxidized starch into a slurry, slowly adding sodium hydroxide solution, stirring for 2min after standing, until the slurry is completely gelatinized, add borax solution, and use the remaining water to dilute to the appropriate consistency, stirring evenly, slightly more static Make the necessary adhesive. The biggest advantage of this type of adhesive is its very low shipping costs and its ease of packaging and storage. It has many advancements over liquid adhesives.

2.4 The application of alpha-amylase

The general starch adhesive has a low solids content, and it prolongs the drying time of the paperboard during use, which leads to a decrease in the production efficiency, a poor control of the production conditions, and sometimes does not cause the starch adhesive to be invalid in the storage period. In order to increase the solid content of the starch adhesive, the simplest method is to use alpha-amylase to hydrolyze starch long-chain molecules to short-chain molecules, so that the viscosity of the starch is controlled within a certain range to meet the needs of the carton industry. The results showed that the optimal temperature for the hydrolysis of starch with α-amylase obtained from Bacillus subtilis was 90° C. The pH of the reaction was 60-62. After the reaction was over, the reaction was terminated with EDTA at 100° C. or more. Effectively, it can minimize the residual enzyme activity, thereby inhibiting the viscosity of the adhesive during storage.

2.5 Highly Dispersible Starch Adhesive Production Method

The starch adhesive is a new type of starch adhesive prepared by enzymolysis-compounding denaturation method and can be used for preparing color water-based paints on the outer surface of cartons, woods, and metal packagings, and is an ideal substitute for gum arabic and peach gum. The approximate process of production is to first adjust the starch to about 25% slurry with water, adjust the pH of the slurry to 60-65, add liquefied amylase, heat and liquefy at 90-92°C for 15 to 60 minutes after heating. The obtained liquefied liquid is cooled and then subjected to a denaturation treatment, and then subjected to decoloration, filtration, impurity removal, and concentration, followed by addition of a dispersant, a lubricant, an antifoaming agent, a bactericide, etc., to obtain a pale tan opaque viscous liquid by blending evenly. The coating contrast test proves that this starch glue adhesive has good effects for various pigments and can be used as a substitute for gum arabic and peach gum.

In addition, the liquid starch adhesive can be dried and crushed to become a solid fine powder, which is convenient for storage and transportation, and is beneficial to overcome the disadvantages that the viscosity of the liquid product gradually increases, and has broad application prospects.

3 Conclusion

The above describes mainly the general methods and new methods of starch adhesive production. It can be seen that the new method of producing starch adhesives has obvious advantages compared with the general methods. It is the development direction of future starch adhesives, and it will be applied and promoted to China. The development of the packaging industry is of great significance.

Source: 21st Century Fine Chemicals Network