Influence mechanism of the hottest urea formaldehy

2022-08-15
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The influence mechanism of urea formaldehyde resin on the properties of oxidized starch agent

corrugated box is the most widely used packaging box. In addition to the corrugated board itself, the quality of the adhesive used is also an important factor affecting the quality of corrugated box. In recent years, oxidized starch adhesives are often used in the production of corrugated boxes. Oxidized starch adhesive has the characteristics of high strength, light weight, no corrosion, no pollution and so on, but at the same time, because its water content is as high as 60% - 70%, it has the disadvantages of short storage period, poor water resistance, slow drying speed of paperboard, poor initial adhesion and so on, which further affects the overall quality of cartons. By adding urea formaldehyde resin into the oxidized starch adhesive, the oxidized starch adhesive is modified, which can greatly improve its adhesion, fluidity and water resistance

(I) influence mechanism of urea formaldehyde resin on the properties of oxidized starch adhesive

the modified oxidized starch contains hydrophilic aldehyde, carboxyl and hydroxyl groups. The good process layout in urea formaldehyde resin makes the amplifier extremely stable, containing a large amount of Dihydroxymethyl urea, which has active hydroxymethyl. When urea formaldehyde resin is added to oxidized starch adhesive, dimethylol urea and oligomer in the resin will react with hydroxyl group in starch molecule to form semi acetal and acetal structure, which is a cross-linking structure with starch chain. It is precisely because the urea formaldehyde resin reacts with the modified starch to form a hydrophobic structure. Once the processing affects the coating on the corrugated board, a layer of adhesive film will be formed, which effectively prevents the penetration of water into the board, improves the initial adhesion and water resistance of the starch adhesive, and shortens the drying time

(II) effect of urea formaldehyde resin on the properties of oxidized starch adhesive

l, experiment

add the specified amount of water and starch into the reactor, mix evenly, raise the temperature to 50 ℃ ~ 60 ℃, add a certain amount of oxidant hydrogen peroxide at constant temperature, and react for a period of time; Add sodium thiosulfate solution to stop the oxidation reaction: after stirring, add the prepared sodium hydroxide solution for gelatinization, add borax and polyvinyl alcohol solution, and then continue stirring, cool to below 40 ℃ and discharge the material to make oxidized starch adhesive. The self-made urea formaldehyde resin was mixed with oxidized starch adhesive at 40 ℃ according to different percentages to make composite starch adhesive. Through experiments, the drying speed, water resistance and initial adhesion of the composite starch adhesive were tested, and the effect of the amount of urea formaldehyde resin on the properties of oxidized starch adhesive was studied

2. Results and discussion

(1) the influence of the amount of urea formaldehyde resin added on the drying speed. The drying speed was tested by weighing method. The drying rate of adhesive is evaluated by the water loss rate per gram of adhesive. See Table 1 and figure 1 for the influence of different urea formaldehyde additions on the drying speed

it can be seen from Figure 1 that the addition of urea formaldehyde resin directly affects the drying speed of the adhesive. When the amount of urea formaldehyde resin is 10%, the drying speed is the fastest, especially in the first 10 minutes. When the addition amount is 5% and 2%, the drying speed is faster than that of a single oxidized starch adhesive, but there is little change between them. When the addition amount of urea formaldehyde resin is 15%, the drying speed decreases, which is due to excessive addition and too thick adhesive film, which affects the drying speed. Therefore, when urea formaldehyde resin is used to improve the drying speed of adhesive, its addition amount is between 5% and 10%

(2) the influence of the amount of urea formaldehyde resin added on the water resistance. Stick the composite starch adhesive until the end of 2013. The connected paperboard is completely immersed in water. Time it until the adhesive layer is naturally separated. Evaluate the water resistance of the adhesive with the immersion time

it can be seen from Figure 2 that the water resistance of the adhesive increases with the increase of the addition proportion of urea formaldehyde resin. When the addition amount is greater than 10%, the effect on improving the water resistance of the adhesive film is not obvious, and the production cost of the adhesive will be increased. In addition, when the addition of urea formaldehyde resin exceeds 15%, the film thickness will be increased and the drying time of the adhesive will be reduced. Considering the drying speed and water resistance, the addition amount of urea formaldehyde resin can be selected at 5% - 10%, which can meet the ideal moisture-proof requirements

(3) the effect of the amount of urea formaldehyde resin added on the initial adhesion of the adhesive

the area is taken as 5 × A piece of 10mm2 corrugated board is evenly coated with adhesive, bonded with another piece of paper of the same size and variety, and a certain pressure is applied. After 10 minutes, the adhesive layer is peeled off, the paper surface fuzzing area is checked, and the initial bonding force is evaluated by its percentage in the total bonding area

Table 3 shows the comparison of initial adhesion force of different types of adhesives. The results show that the oxidized starch adhesive added with urea formaldehyde resin is superior to the other two adhesives in terms of initial bonding force and bonding area in one minute. The bonding area of corrugated board can reach 42.7% in one minute, which greatly shortens the initial bonding time of corrugated board, and can enter the next production process in a short time, thus improving the production efficiency

to sum up, as a modifier of starch adhesive, urea formaldehyde resin can improve the drying speed, water resistance, initial bonding force and other properties of the electronic universal testing machine, and the influence on the performance varies with the amount of addition. Through experimental research, comprehensively considering the drying speed, water resistance, initial adhesion and production cost of the adhesive, it is concluded that the best proportion scheme of urea formaldehyde resin and oxidized starch is: urea formaldehyde resin is 5% - 10% of the total mass. (text: Wan Lili, Han Yongsheng)

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