Production and application of the hottest oxidized

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Production and use of oxidized starch adhesive in corrugated box

the quality of corrugated box under the condition of the same paper and processing technology, the appearance of opal is a dense glass block, which mainly depends on the adhesive used. Therefore, adhesives play a key role in the production of corrugated boxes

at present, most carton factories in China are small enterprises without drying equipment. Therefore, although the use of sodium silicate as the corrugated box adhesive has the disadvantages of high alkalinity, easy moisture absorption and efflorescence, high corrosivity, and the use of sodium silicate is strictly restricted by the state, most enterprises still use sodium silicate as the adhesive because of its low price and rapid drying, rather than using the starch adhesive with relatively slow drying speed. Therefore, how to develop starch adhesives with the same drying speed and low price as sodium silicate as soon as possible is an urgent problem to be solved. After more than 10 years of research and exploration, we have developed a quick drying starch adhesive, which has been used by Hunan packaging enterprises for many years. It has been proved that its production process is simple, its quality is stable, its storage period is long, it is not easy to gel, and its drying speed is equivalent to that of sodium silicate. The cost of adhesive per ton is about 350 yuan, and the production cost is 25-30% lower than that of sodium silicate. The cartons made of this adhesive have been tested by Hunan entry exit inspection and Quarantine Bureau, and all indicators have exceeded the standard of export packaging cartons

I. oxidation reaction mechanism of adhesive

oxidized starch paste has high stability, greatly weakened retrogradation, little tendency to condense into gel, high fluidity, good transparency and strong adhesion. The adhesive we developed is made of oxidized starch paste with nickel sulfate as catalyst and sodium hypochlorite as oxidant at room temperature. When the starch oxidation reaches a certain depth, other auxiliary materials are added. Sodium hypooxate decomposes under the action of heating or catalyst in the aqueous solution, releasing the primary ecology [o] with strong oxidation ability. Under the action of primary ecology [o], starch undergoes an oxidation reaction, which breaks the glycoside bond between the glucose based rings of starch and degrades, resulting in lower polymerization degree, reduced molecular weight, increased water solubility and affinity, so as to produce adhesives with higher solid content and improve the drying ability. At the same time, due to oxidation, the hydroxymethyl group in starch becomes aldehyde group. Further oxidation can also turn part into hydroxyl, which increases the hydroxyl base with strong binding force in paper fiber, so as to greatly improve the adhesion of oxidized starch. In addition, due to the aldehyde group produced after oxidation, the fermentation and biodegradation of starch by microorganisms are prevented, and the adhesive made has improved the anti-corrosion and mildew resistance

the rate of oxidation reaction increases with the increase of temperature and oxidation dose. At room temperature, in order to improve the speed of oxidation reaction, nickel sulfate is added as a catalyst, so that the oxidation reaction can be carried out even below 10 ℃. For self-made and self-use small and medium-sized enterprises, due to the small amount of adhesive used every day, in order to reduce production costs, the amount of oxidant can be appropriately reduced to extend the oxidation time to reach the oxidation depth. Generally, it can be oxidized for about 12 hours at night

II. Production of adhesives

1. Raw materials and formula starch: corn starch or cassava starch can be used, with white color, more than 100 mesh, water content less than 14%, protein content less than 0.5%, no mildew, no caking

liquid alkali: industrial products with a content of 30% ± 0.02 (solid alkali is also acceptable)

oxidant: industrial grade sodium hypochlorite with effective chlorine content of 10%

oxidation catalyst: industrial grade nickel sulfate, prepared into 0.5% aqueous solution when used

crosslinking agent: industrial grade borax, which is prepared into 2% aqueous solution with cold water when used

additives: sulfur, nitrogen, phosphorus, organic matter and other substances, all of which are industrial grade

the basic formula is shown in Table 1

2. main equipment and process flow

the main equipment is reactor and electric mixer. Because the reaction process is carried out at room temperature and weak alkaline, it is not corrosive. It can be welded with steel sheet or covered with brick cement. The motor power can be 3-5 kW depending on the output, and the mixing speed is 60-70 rpm. The whole production process is carried out in the reactor

the production process of adhesive is shown in Figure 1

3. Production method

oxidation: first add 100 kg of water in the reactor, add 14 kg of sodium hypochlorite under continuous stirring, then add 100 kg of cassava starch, mix well, and finally add 25 g of 0.5% nickel sulfate solution, stir for about 5 minutes, and let it be static and oxidized overnight

gelatinization: first add 100 kg of water, mix well, add 30 kg of 10% solution pre prepared with 30% liquid alkali for gelatinization, stir for about 20 minutes to make it a uniform and transparent pale yellow colloid, and then add 3 kg of 5% concentration of desiccant and 3 kg of stabilizer

crosslinking: add 3.5kg borax under stirring to prepare a 2% solution and an appropriate amount of water in advance. Measure its viscosity with No. 4 cup to 40-50s. Finally, add about 20g of defoamer tributyl phosphate according to the amount of foam

third, the main factors affecting the quality of adhesive

the quality of cold catalytic oxidation starch adhesive is related to many factors. The appearance of the adhesive with good quality must be clear and transparent, slightly light yellow, non foaming, with appropriate viscosity, high stability, long storage period, fast drying speed and strong adhesion. Only several factors affecting quality are discussed below

1. The relationship between oxidant dosage, oxidation time and oxidation temperature sodium hypochlorite is a strong oxidant. For a certain amount of starch, under the same other conditions, the oxidation speed will increase with the increase of oxidant dosage. In other words, the viscosity of the adhesive will decrease. Therefore, the appropriate dosage of oxidant should be determined according to the actual production situation. If the oxidation time needs to be shortened, the dosage of oxidant can be appropriately increased. When the oxidation depth is reached, sodium thiosulfate, a terminator, can be added to terminate the reaction. Small and medium-sized enterprises can make use of the night time to oxidize for their own use, so as to prolong the oxidation time, so as to reduce the consumption of oxidants, reduce the consumption of raw materials, and achieve the purpose of reducing costs

the temperature of the oxidation reaction also affects the speed of the oxidation reaction. The higher the temperature is, the faster the oxidation reaction speed is. Under the same other conditions, the viscosity of the adhesive is smaller when the experimental machine can be operated before passing the examination. Therefore, the dosage and oxidation time of different oxidants should be controlled according to different temperature conditions

2. Influence of sodium hydroxide dosage

in cold starch, sodium hydroxide, as a gelatinizer, can make oxidized starch insoluble in water and water form a uniform, transparent and sticky starch paste. This is because after adding sodium hydroxide, its hydroxyl combines with the hydroxyl group in the starch molecule, breaking the hydrogen bond between the starch macromolecules and the original hydroxyl group in the molecules, making the macromolecules swell and gelatinize. In addition, sodium hydroxide turns the carboxyl group in oxygen molecules into sodium carboxylate group, which increases the solubility with water. At the same time, sodium hydroxide can stabilize amylose solution in the absence of oxygen, making the adhesive difficult to gel. However, the more sodium hydroxide is added, the better. Its dosage and temperature should be strictly controlled. When the dosage is too large, the paper fiber will be damaged due to too high alkalinity, and when the air humidity is high, it is easy to absorb moisture and turn yellow. On the other hand, when adding sodium hydroxide, the concentration should not be too high. Due to the high concentration, the gelatinization reaction is intense, which is very easy to saccharify, so that the glue is thrown by the glue dispenser, and the flower glue phenomenon appears on the corrugated peak mounted, which causes the paperboard to open and difficult to dry. Generally, the addition amount (solid) of sodium hydroxide is 9-10% of the amount of starch, and the concentration when adding is 10%

3. The influence of the amount of hydroxyborax

borax as a crosslinking agent, when hydrolyzed in aqueous solution, it takes boron and oxygen as the central ions, and can combine with hydroxyl and carboxyl groups in the adhesive as ligands to form a polynuclear complex with like structure, so as to increase the viscosity. It can be better fixed on the paper surface with carboxyl group, increase the initial adhesion of the adhesive, and make the generated thin haze a measure of the turbid appearance of the film. The film is firm, and improves the water resistance and natural drying ability. However, borax should not be added too much, otherwise it will make the adhesive layer brittle and cause degumming

4. the role of additives

in the adhesive, additives are added to achieve the purpose of quick drying, stability and anti gelling, so as to extend the storage period. We add an inorganic double salt and water-soluble nitrogen-containing organic matter to the formula as a drying agent. Although the dosage is small, it does play a role in drying. We cut the raw material paper for corrugated board into uniform size of 120 × 80mm paper pieces shall be painted according to the amount of 100 grams of adhesive per square meter. Each cardboard is glued by five layers of paper. The total amount of adhesive applied shall be controlled within the range of 0.02 grams. Otherwise, change the paper and stick it again. Put the glued cardboard under the condition of 20 ℃ temperature and 80% humidity for drying. In the early stage, weigh every 30 minutes, and when it is nearly completely dry, weigh every 6 minutes, so as to measure the drying data of pure oxidized starch adhesive, oxidized starch adhesive with desiccant and sodium silicate. See Table 2 for details

the data in Table 2 shows that the initial drying performance of the adhesive with drier is better than that of pure oxidized starch and sodium silicate, and the total drying performance is equivalent to that of sodium silicate. Add stabilizer to the adhesive, so that the fluidity, viscosity and color of the adhesive remain basically unchanged after being stored for 1.5 months

v. actual use

the adhesive produced with this formula has been used in packaging enterprises in Hunan Province for more than 10 years, especially in the middle age of long-term action, and the effect is good: tear the adhesive surface after 7 minutes, and it can be completely hairy, without runningness, and it can be moved arbitrarily after 15 minutes of pressure; The production process is simple and the cost is low, which saves more than 30% of the cost compared with water glass. Tested by Hunan entry exit inspection and Quarantine Bureau, the average bonding strength reached 80N/10cm, exceeding the national standard (58.8n/10cm). (text/Huang Yawen)

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