The most popular production method of starch adhes

2022-07-26
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Discussion on the production method of starch adhesive

preface

starch adhesive is a kind of adhesive used in corrugated box production in recent years. The main raw material is corn starch or cassava starch. Due to the wide source of raw materials, low price and good bonding performance, starch adhesive is used by most corrugated paper factories in the world. There are many methods to produce starch adhesive, and each has its own characteristics. The following introduces various methods to produce starch adhesive

1 production method of starch adhesive

1.1 alkali paste method

it is to mix water with starch and dilute alkali, heat up to 40 ℃, and stir continuously. This method is simple and uses few raw materials, but it is rarely used because the functional group of starch has not changed and the adhesion is not ideal

1.2 dextrin method

this method is made by directly roasting starch (190 ~ 230 ℃), or roasting at 110 ~ 140 ℃ in the presence of a small amount of hydrochloric acid and nitric acid, or by microbial fermentation. The adhesive made of it has good flowability, near neutral pH value and low corrosivity, but it can not change the functional base of starch, poor adhesion and anti-corrosion and anti mildew ability, can not be stored, the process is complex, the end point is difficult to control, the relative molecular weight fluctuates greatly, and the quality is unstable. Therefore, there are few applications at present

1.3 main body carrier method

it is to add a small amount of oxidized starch with sodium hydroxide, use the gelatinized thin paste as the carrier, and then mix the ungelatinized starch or oxidized starch as the main body. The raw starch or oxidized starch will burst and gelatinize by the sudden high temperature after gelatinization. The corrugated paper produced by this method has good quality, but it is only suitable for high-speed continuous machine production

1.4 oxidized starch method

it uses an oxidant to oxidize starch, so that the hydroxymethyl group on the 6 carbon of the glucose unit of the original starch is changed into aldehyde group and carboxyl group. The change of this functional group not only increases the adhesion between starch and paper fiber, but also improves its anti-corrosion and anti mildew ability. At the same time, oxidation can change the long molecular chain of starch into short molecular chain, so as to improve the fluidity of the prepared adhesive and facilitate the coating on the machine. According to the different process methods used in oxidation, it can be divided into hot method and cold method

141 hot method

the oxidants are usually hydrogen peroxide and sodium hypochlorite. The reaction is carried out at about 60 ℃ and the reaction time is 2H. The adhesive produced by this method has good adhesion and mould resistance. However, this method is hot-made at 60 ℃, so it must be hot-made and used. It cannot be stored and transported. It must be used as soon as it is made, which undoubtedly brings trouble to the production

1 42 cold method

that is, it is manufactured at room temperature and used at room temperature. The manufacturing temperature is consistent with the use temperature, and the viscosity is stable. In addition, this method is produced by cold method and the presence of aldehyde group. It is not easy to mold and rot, and can be stored and transported for a long time. Although the cold process has many advantages, the oxidation reaction at low temperature is an unfavorable factor. Therefore, in order to make the oxidation reaction proceed smoothly, it is necessary to select the appropriate catalyst. The production practice has proved that the most suitable catalyst for producing oxidized starch by cold method is nickel sulfate

2 new production methods of starch adhesives

the above introduces several production methods of starch adhesives. Although the adhesives produced by the above production methods are widely used in production, these adhesives also have some shortcomings. For example, the company also cooperates with Nippon to produce pure flavor polyurethane varnish and white paint suitable for children's products. It is difficult to control the oxidation degree with hydrogen peroxide and sodium hypochlorite as catalysts, 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, at present, researchers have developed many new methods to produce starch adhesive. The following are the introduction of the localization rate of equipment greater than 80%. 2.1 improved main body carrier method

the starch adhesive produced by the common main body carrier method is used to bond the paperboard and then immerse it in water. After about 20 minutes, the corrugated paper will separate from the ground paper, and the paperboard will be damaged. This kind of paperboard is not suitable for making cartons with special requirements, such as those used for packaging vegetables, fruits and foods, which are often in contact with water and stored in an ice warehouse or transported in a refrigerator truck. Therefore, In order to develop high purity rare earth separation technology and improve the service life of cartons, it is necessary to improve the water resistance of adhesives. The improved main carrier method is to add a certain amount of urea formaldehyde into starch adhesive, that is, urea formaldehyde starch adhesive is produced. Before urea formaldehyde is added, it must be neutralized with hydrochloric acid to make the pH value reach 91 ~ 92, and then 1% ~ 2% urea formaldehyde is added. The viscosity of the starch adhesive produced by this method is significantly increased, which has a certain effect on improving the water resistance of the paperboard. For example, the paperboard made of corrugated paper produced in Japan does not separate after soaking in water for more than 2h, which meets the production requirements

2.2 potassium permanganate method

generally, oxidized starch is made by using hydrogen peroxide and sodium hypochlorite as oxidants to react with starch, but it has the disadvantages of difficult to control the oxidation degree and unstable quality of finished products. Using potassium permanganate and hydrogen peroxide as oxidants can control the reaction degree through the self color development of potassium permanganate, and the product quality is better than the former. Acidic potassium permanganate oxidizes some reduced alcohol groups in starch to carboxyl, aldehyde and ketone groups. The depth of oxidative degradation can be controlled by the addition of oxidant, so as to prepare oxidized starch with a certain depth. Then sodium hydroxide is added to make it bond with the non oxidized alcohol groups in starch, resulting in swelling and gelatinization with adhesive viscosity. Finally, borax, a complexing agent, is added to make the finished product have cross-linking and tackifying effect, which is conducive to accelerating the bonding, The interaction of manganese ion and sodium hydroxide can produce a colloidal curing film, which can improve the water resistance of the adhesive

2.3 solid adhesive

production method this kind of adhesive is mixed with modified starch (oxidized starch 16% ~ 21%), sodium hydroxide (13%) and borax (0.4%). The oxidized starch can be prepared by using sodium hypochlorite and hydrogen peroxide as oxidants. For specific use, various components can be weighed according to the formula according to different purposes, and different water quantities (generally 76% ~ 81%) can be taken. Sodium hydroxide and borax are mixed into a solution of certain concentration, and oxidized starch is mixed into a slurry. Slowly add sodium hydroxide solution, stir for 2min, and then stand. After the slurry is completely gelatinized, add borax solution, dilute it with the remaining water to the appropriate consistency, and stir evenly, The required adhesive can be obtained after a little standing. The biggest advantage of this adhesive is that the transportation cost is very low, and it is easy to pack. The weight reduction of 100kg can increase the endurance distance of storage by about 10%, which is more progressiveness than liquid adhesive

2.4 α— Application of amylase

generally, the solid content of starch adhesive is low, which prolongs the drying time of paperboard during use, resulting in lower production efficiency and poor control of production conditions. Sometimes, it will not cause the failure of starch adhesive during storage. In order to increase the solid content of starch adhesive, the simplest method is to use α— Amylase hydrolyzes long chain molecules of starch into short chain molecules to control the viscosity of starch within a certain range to meet the needs of carton industry. The results showed that α— The optimum temperature for starch hydrolysis by amylase is 90 ℃, and the pH value of the reaction is 60 ~ 62. After the reaction, EDTA is the most effective to end the reaction above 100 ℃, which can minimize the residual enzyme activity and inhibit the viscosity reduction of the adhesive during storage

2.5 production method of highly dispersive starch adhesive

this kind of starch adhesive is a new type of starch adhesive prepared by enzymatic hydrolysis and composite modification method. It can be used for the preparation of color waterborne coatings on the outer surface of cartons, wood and metal packaging. It is an ideal substitute for Arabic gum and peach gum. The general production process is as follows: first, the starch is mixed with water to form a slurry of about 25%, the pH value of the slurry is adjusted to be 60 ~ 65, the liquefied amylase is added, and the liquid is heated and liquefied at 90 ~ 92 ℃ for 15 ~ 60min. After cooling, the obtained liquid is denatured, then decolorized, filtered, removed, concentrated, and then added with dispersant, lubricant, defoamer, bactericide, etc. the light brown opaque viscous liquid is obtained by blending evenly. The coating contrast test shows that this starch adhesive has good effect on various pigments and can be used as a substitute for Arabic gum and peach gum

in addition, the liquid starch adhesive can be dried and crushed to form a solid fine powder, which is convenient for storage and transportation, and is conducive to overcoming the disadvantages of the gradual increase of the viscosity of liquid products, so it has a broad application prospect

3 conclusion

the above mainly introduces the general methods and new methods for the production of starch adhesive. It can be seen that the new methods for the production of starch adhesive have obvious advantages compared with the general methods, and are the development direction of starch adhesive in the future. Its application and promotion are of great significance to the development of China's packaging industry

information source: fine chemicals in the 21st century

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