Lignin modified urea-formaldehyde resin adhesive and preparation method and application thereof

Abstract

The invention discloses a lignin modified urea-formaldehyde resin adhesive and a preparation method and application thereof. 1000 parts of formaldehyde, 45-140 parts of lignin, 8-28 parts of melamine,680-860 parts of urea, 10.5-51 parts of alkali and 10-20 parts of acid are used as raw materials, the lignin is added in two batches, the urea is added in three batches, and the lignin modified urea-formaldehyde resin adhesive is prepared by one-time addition reaction and three-time polycondensation reaction. The prepared adhesive has good initial adhesion, fast curing speed, high bonding strength, low content of free formaldehyde and good boiling water resistance. The adhesive can be used as a plywood adhesive, and the formaldehyde emission of the prepared plywood can reach the E0 standard,and the bonding strength meets the standard of a class II plywood. The lignin modified urea-formaldehyde resin adhesive has the advantages of simple preparation process, good stability, simple, fast and feasible quality control method, and low raw material cost, and is suitable for popularization and application.

Description

technical field [0001] The invention belongs to the technical field of urea-formaldehyde resin adhesives, and in particular relates to a lignin-modified urea-formaldehyde resin adhesive and its preparation method and application. Background technique [0002] my country's forest coverage rate is low and timber resources are scarce. Especially after the full launch of the natural forest protection project, the timber supply structure has undergone fundamental changes. The use of thinning timber, small-diameter timber, and low-quality timber to prepare wood-based panels through bonding composite technology is a An effective method to solve the problem of insufficient supply of wood materials. Adhesive is the key material in the preparation of wood-based panels. Urea-formaldehyde resin adhesives are widely used in the wood-based panel industry due to their easy-to-obtain raw materials, low cost, good heat resistance, and stable performance. According to incomplete statistics, in...

AI Technical Summary

Problems solved by technology

Adhesive is the key material in the preparation of wood-based panels. Urea-formaldehyde resin adhesives are widely used in the wood-based panel industry due to their easy-to-obtain raw materials, low cost, good heat resistance, and stable performance. According to incomplete statistics, in recent years, my country's urea-formaldehyde resin adhesives The dosage of the urea-formaldehyde resin adhesive is about 15 million tons (equivalent to 100% solid content), but the urea-formaldehyde resin has the disadvantages of releasing formaldehyde and poor boiling water resistance. Therefore, reducing the formaldehyde emission of the urea-formaldehyde resin adhesive and improving its water resistance have become the focus of attention. important question

[0003] In the process of synthesizing urea-formaldehyde resin adhesives, reducing the molar ratio of formaldehyde is an effective way to reduce the amount of formaldehyde released, but the reduction of the molar ratio of formaldehyde will lead to a decrease in the bonding strength of the urea-formaldehyde resin adhesive and poor water resistance

In order to obtain a urea-formaldehyde resin with low formaldehyde content, good water resistance and high strength, other substances are often added to modify the urea-formaldehyde resin during the synthesis process. The most common method is to add melamine and phenol, such as: the application number is CN201711292324.7 The patent application discloses "a production process of triamine urea-formaldehyde resin modified glue". This process is a typical "alkali-acid-alkali" method and the method of adding urea in batches. 1.10, the amount of melamine (relative to the mass fraction of urea) is 1.78-4.14%, which does not explain the boiling water resistance of the adhesive; and for example, the patent No. CN201310199740.8 discloses "a phenol-modified urea-formaldehyde resin Preparation method", the specific steps are as follows: react phenol and formaldehyde in the presence of a basic catalyst, add the first batch of urea for stirring, then raise the temperature of the mixed solution, then add alcohol compounds to it, and then add the second batch of urea For batches of urea, adjust the solution to be acidic with a weak acid compound, keep the temperature constant, and finally add the third batch of urea to the reaction vessel for sufficient reaction, then cool down to obtain a phenol-modified urea-formaldehyde resin, wherein the molar ratio of phenol, formaldehyde, and urea It is (0.15-0.8):(1.5-2.5):(0.5-1.5), the mass ratio of alcohol compound to urea is (0.2%-10.0%):1, which has no effect on the initial tack, curing speed, and bonding of the adhesive. In terms of strength, due to the high price of melamine and phenol, the production cost of urea-formaldehyde resin will increase, thus limiting its application

[0004] Lignin is the most abundant organic polymer next to cellulose in the plant kingdom. Its molecular structure contains different functional groups such as methoxyl, hydroxyl (alcohol and phenol), carbonyl, carboxyl, etc. With the advantages of degradation, no pollution, and wide range of sources, many researchers have successfully introduced lignin, a renewable resource, into wood adhesives, such as: Patent No. CN201310604628.8 discloses "a lignin with low formaldehyde release The preparation method of urea-formaldehyde resin adhesive", the specific preparation method is to add formaldehyde and lignin to the reaction container, adjust the solution to be alkaline with sodium hydroxide, heat to a certain degree, and after a period of heat preservation, add urea, corn starch, Propylene glycol, pentaerythritol, sodium borate, ferrous ammonium sulfate, glucoamylase and water are fully reacted for a period of time, then the solution is adjusted to be acidic with sulfuric acid, the temperature is raised for a period of time, and then the temperature is lowered, and the solution is adjusted to be alkaline with a weak base. Add titanium dioxide particles, stir evenly, and discharge to obtain an adhesive. Although the adhesive prepared by this method has good bonding strength and low formaldehyde emission, the cost of raw materials is high and the process is complicated.

[0005] The patent No. CN201310628813.0 discloses a "preparation method of lignin-modified phenolic resin adhesive", which adopts the method of adding alkali multiple times. The specific process is: add phenol, formaldehyde solution and water to the reactor, and stir Add lignin and tannin at low temperature, add the first batch of alkali to the reaction vessel, raise the temperature, and react at a constant temperature for a period of time, add the second batch of lye, continue to react for a period of time at the same temperature, raise the temperature again, and keep the temperature constant After a period of reaction, the lignin-modified phenolic resin adhesive can be obtained, wherein the molar ratio of formaldehyde to phenol is (1.8-3.0):1. Although this method improves the curing reaction speed of the adhesive, it does not explain its water resistance and adhesion Strength, and lignin and tannin are added in the process of synthesizing urea-formaldehyde resin, which is a compound modification, and the process is relatively complicated

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