Since the advent of honeycomb paperboard, people have paid great attention to it because of its wide applicability and good performance, and the adhesive used for bonding core paper and facial paper can be said to have a certain decisive effect on the performance of honeycomb paperboard, so research Adhesives with excellent performance are of great value. At present, the corn starch adhesive, which is widely concerned, is more and more used in the paper packaging industry as a natural adhesive with good performance, no toxicity, and low price. Has become a development trend. However, in actual production, the problems of low solid content, slow drying speed, and low initial tack of starch adhesives have brought obstacles to the further promotion of starch adhesives, and also brought many problems to the production of honeycomb paperboard. In response to this problem, I conducted a lot of experimental research, and the solid content of the starch binder developed at the end could reach 35%, which obviously improved the drying speed and improved the initial viscosity, and reduced the cost.
1. Process flow and steps
(1) Oxidation stage
Weigh a certain amount of starch, add a certain amount of water (starch: water is 1: 3), the temperature is room temperature. Stir with a mixer, then add a certain amount of NaOH solution, adjust the PH value to about 10, and finally add CuSO4 solution, H2O2 solution and an appropriate amount of defoamer, stirring for 1h.
(2) Gelatinization stage
Add an appropriate amount of filler to the above solution, and then add NaOH solution to cause gelatinization reaction and fully react. The reaction time is controlled at about 20 min.
(3) Suspension stage
Stabilizer was added to stop the reaction, stirring for about 5min.
(4) Network and stage
Add the solution made of borax, slowly add to the liquid, and stir for 5 min.
2. Experimental analysis
(1) Oxidation stage
1. Oxidizer
In order to increase the solubility and fluidity of starch and prevent the glue from settling, etc., the method of oxidative degradation is often used in the preparation of corn starch adhesive. Considering factors such as the ease of controlling the oxidation conditions, raw material cost, and color requirements of the product, this experiment used the starch binder prepared by the H2O2 oxidation method, and in order to shorten the oxidation time, the catalytic oxidation method was used. The catalyst used in this study was CuSO4.
When corn starch is oxidized with 30% H2O2, there are carboxyl, carbonyl and aldehyde functional groups in the starch. The formation ratio of the three functional groups is related to the pH value of the reaction system. When the pH is in the range of 9 to 10, the amount of carboxyl groups generated is relatively large. When the pH is around 7, the amount of carbonyl and aldehyde groups formed is relatively large, because the carboxyl group has a strong adhesion to fiber materials. The carboxyl group is anionic under alkaline conditions, which can reduce the association between starch molecules and improve the storage stability of the starch binder. Therefore, the pH value of the reaction system should be controlled at about 10 to facilitate the generation of more carboxyl groups. This is why the appropriate NaOH solution was added at the beginning. In this experiment, the dosage of oxidant was controlled at about 4%.
2. Catalyst
Copper ion has obvious catalytic effect on hydrogen peroxide oxidized starch. When no catalyst is used, the carboxyl content of the oxidized starch is quite low. Once the catalyst is added, the carboxyl group content increases rapidly, and as the amount of catalyst increases, the carboxyl group content increases. This is mainly due to the fact that the addition of the catalyst disrupts the starch granule structure, increases the chance of contact between the oxidant and the starch molecules, improves the oxidation effect, and increases the carboxyl group content.
3. Defoamer
In the process of production and use, due to the large amount of bubbles generated in the oxidation stage of starch, which affects the normal sizing of the adhesive, especially using hydrogen peroxide as the oxidant, it is easier to produce foam. Silicone oil, tributyl phosphate, n-octanol, etc. were used. In this study, tributyl phosphate was selected. It should be noted that the amount of defoamer should not be too much. Excessive amount will reduce the surface tension of the adhesive and lose the viscosity, and the adhesive strength will not meet the requirements. The optimal amount is 0.3-0.5% of the amount of starch.
(2) Gelatinization stage
1. Packing
Domestic honeycomb carton is mainly produced with straw pulp paper, which has rough surface and large water absorption rate. For example, when the moisture of the adhesive itself is large, most of the moisture is absorbed by the straw paper after sizing, and the natural drying speed will be significantly slowed down. Add a certain amount of bentonite as a filler to the corn starch binder to increase the solid content and reduce the moisture. It can also effectively block the pores on the surface of the corrugated fiber and prevent moisture from penetrating into the paper to achieve the purpose of rapid drying.
2. Gelatinizer
NaOH acts as a gelatinizer, it combines with the unoxidized hydroxyl groups in oxidized starch, breaks the hydrogen bond, weakens the force between the starch molecules, makes it dissolve and gelatinize, and reacts with the functional group of oxidized starch to form sodium salt and increase It improves the hydrophilicity and solubility of starch, increases the viscosity and hardness of the adhesive, at the same time it improves the antifreeze properties of starch glue, increases the fluidity of starch glue, and makes it easy to store. If the amount is too much, although the adhesive has good transparency and good fluidity, the viscosity of the glue will decrease and affect the viscosity, and it is easy to produce foam, causing degumming phenomenon, and the alkali is too strong, which has a certain corrosive effect on paper fibers Paper surface is easy to yellow. If the amount is too small, it will cause insufficient starch gelatinization, small cohesion and poor fluidity. Experiments show that the amount of alkali should be controlled at 8% ~ 10% of starch dosage.
3. Suspension stage
Add stabilizer to neutralize the unreacted excess NaOH solution to prevent the gelatinization reaction from continuing, otherwise the viscosity of the adhesive will decrease, which will affect the stability of the product.
4. Complexation stage
In order to improve the crosslinking degree and initial viscosity of the adhesive, borax was added as a crosslinking agent. The cross-linking agent is used to cross-link the linear structure macromolecule or the branched linear structure small molecule starch, and the linear structure is transformed into the network structure. Therefore, the selected cross-linking agent is borax binder. Adding borax after gelatinization can make short-chain oxidized starch to form a complex with its hydroxyl group or hydroxyl group and boron atoms. Through these irregular cross-links, a network structure is formed, which has a cross-linking thickening effect and is beneficial to improve Initial adhesion and accelerated drying speed, in addition to anti-corrosion, anti-seepage and termination reaction. But the amount is not as much as possible, too much will make the adhesive fluidity worse, jelly-like, difficult to glue, the gum is brittle. Too little complexing is not enough, poor adhesion. The experiment determined that the amount of borax should be controlled at about 0.5% of the amount of starch.
Conclusion
The solid content of starch binder produced by this method can reach 35%, which effectively solves the problems of slow drying speed and low initial viscosity, and can be stored under high temperature and high humidity (temperature 30 ℃, humidity 90%) About 25 days, the production process is simple and the quality is high, which greatly guarantees the production of high-quality honeycomb paperboard and has greater market value.
Pla Forks,Plastic Fork,Disposable Cutlery Fork,Compostable Fork
Anhui Jianfeng Environmental Protection Technology Co., Ltd , https://www.ahbiocutleries.com