Development of the hottest low toxicity urea forma

2022-10-19
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Development of low toxic urea formaldehyde resin adhesive

1 preface

urea formaldehyde resin adhesive is widely used in wood processing industry because of its low cost, easy availability of raw materials, convenient use, colorless and high bonding strength. However, the main defects of urea formaldehyde adhesive are high content of free formaldehyde and high toxicity. Especially in some domestic small and medium-sized enterprises, the free formaldehyde content of urea formaldehyde adhesive produced and used is as high as 3 ~ 7%, which not only pollutes the environment and damages the physical and mental health of producers, but also affects the health of consumers due to the continuous release of formaldehyde during the use of products. In order to reduce the content of free formaldehyde, the synthesis process of urea formaldehyde adhesive was studied in this paper, and some results were obtained

2 experimental part

2.1 instrument

electric mixer, water bath pot, electric stove, balance, tensile testing machine, three mouth bottle, thermometer, etc

2.2 reagent

formaldehyde: analytically pure (37%), Shijiazhuang organic chemical plant; Urea: industrial grade, Shijiazhuang Yuanshi fertilizer plant; Ammonium chloride: analytically pure, Beijing chemical plant; Sodium hydroxide: analytical pure, Xinji chemical experimental plant

2.3 resin synthesis process

the molar ratio of formaldehyde to urea is 160:1,140:1 and 120:1. Urea is added in three times, 70% of the total urea is added in the first time, 25% of the total urea is added in the second time, and 5% of the total urea is added in the third time. The specific process is as follows: add formaldehyde into a three mouth bottle, start the agitator, and adjust the pH value to 7 with NaOH solution (15%) However, modified materials such as Geon bio are their core business 8 ~ 8.2. Add the first urea, react at a certain temperature for a period of time, add the second urea, raise the temperature, and keep it warm for a period of time, and adjust the pH value to 5 ~ 6 with NH4Cl solution (20%). Continue the heat preservation reaction. When the reaction solution appears white turbidity, test the end point. After reaching the end point, immediately cool it with cold water, add the third urea, when the temperature drops below 40 ℃, adjust the pH value to about 80 with NaOH solution (15%), and discharge

3 test results and conclusions

3 1 product performance index

3 2 conclusion

(1) it can be seen from Figure 1 that with the increase of molar ratio, the bonding strength gradually increases, when the molar ratio reaches 1 At 4 ∶ 1, the bonding strength increases very slowly. It can be seen from Figure 2 that with the increase of molar ratio, the content of free aldehyde gradually increases. When the molar ratio reaches 1.4:1, the content of free aldehyde increases very quickly. It can be seen from the above two figures that the molar ratio of formaldehyde and urea of 1.4:1 is more appropriate. At this time, the content of free aldehyde is low, the bonding strength is high, and the bonding strength meets the standard specified in GB

(2) this experiment uses three times of feeding. The first stage of the reaction between urea and formaldehyde is the addition reaction. The high molar number of formaldehyde is conducive to the formation of Dihydroxymethyl urea, which plays an important role in the bonding strength and adhesive stability. In the second stage, the molar number of formaldehyde is low, and the free aldehyde naturally decreases in the reaction. The addition of the third batch is conducive to capturing unreacted formaldehyde, so three times of feeding is conducive to reducing the content of free formaldehyde

(3) the key to synthesis lies in the control of temperature and pH value. If the control is not good, the viscosity of the glue solution will be too large, the water solubility of the resin will be poor, the storage period will be shortened, and the gel phenomenon will appear in the heavy case

(4) in the production process, the non dehydration process is adopted, with simple equipment, short production cycle, time saving, energy saving and low cost

(5) the molar ratio of formaldehyde to urea can be reduced again, but when the molar ratio has decreased to 1 05:1 in the past half century, the prepared adhesive has short service life, poor initial viscosity, extended curing time, and the physical and chemical properties of the plate have also decreased. Therefore, significantly reducing the molar ratio is not the only way

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