CN117047886B - A method for preparing adhesive-free bonded fiber board by microwave hot pressing - Google Patents

Abstract

The invention discloses a method for preparing adhesive-free adhesive fiber board by microwave hot pressing, which comprises adding acrylic acid, methylenebisacrylamide and initiator to water for mixed reaction, then adding isopropylacrylamide and chitosan for mixed reaction and vacuum drying to obtain dry gel; taking dry gel and adding it to water, and adding ammonia water to adjust pH, then adding laccase and stirring and mixing, then adding lignin and stirring and mixing evenly, and reacting and treating at 60-70°C to obtain adhesive; taking adhesive and adding citric acid solution to adjust pH, and soaking wood fiber in citric acid solution, then mixing wood fiber and adhesive, and then paving to obtain slab; placing the slab in microwave equipment for microwave heating, and then pressing and forming to obtain particleboard. The invention utilizes laccase to catalyze lignin to prepare aldehyde-free and environmentally friendly adhesive, and optimizes and adjusts the microwave hot pressing process in a targeted manner, so as to produce high-quality fiberboard with good mechanical properties.

Description

A method for preparing adhesive-free bonded fiber board by microwave hot pressing

Technical Field

The invention belongs to the technical field of fiber board production, and in particular relates to a method for preparing glue-free bonded fiber board by microwave hot pressing.

Background technique

Fiberboard, also known as density board, is a man-made board made of wood fiber or other plant fiber as raw materials, with urea-formaldehyde resin or other suitable adhesives applied. Adhesives and (or) additives can be applied during the manufacturing process. Fiberboard has the advantages of uniform material, small longitudinal and transverse strength difference, and not easy to crack, and is widely used. In the process of fiberboard manufacturing, there are many factors that affect product quality, mainly adhesive quality and glue application, hot pressing process, etc. The slab is heated as a whole, and the heat is transferred from the surface of the slab to the inside, so that the temperature inside and outside the slab reaches the curing temperature of the adhesive and is cured and formed. Due to the great differences in the composition ratio and curing conditions of different types of adhesives, their requirements for hot pressing process conditions are also different. In particular, when microwave hot pressing is used, the curing effects of different adhesives under microwave action are different. How to optimize the hot pressing process conditions for different adhesives to produce high-quality fiberboards is one of the current research focuses.

At the same time, as people's awareness of safety and environmental protection increases, trialdehyde resin glues such as urea-formaldehyde resin glue, phenol-formaldehyde resin glue, and melamine-modified urea-formaldehyde resin glue will release formaldehyde gas that is harmful to the environment and human health during production and use. Research and development of formaldehyde-free adhesives is also one of the hot spots in fiberboard production. Laccases (Lac) are polyphenol oxidases that can degrade lignin. They can catalyze lignin to produce phenoxy free radicals, and further cross-linking reactions between free radicals produce a complex carbohydrate complex. This complex can bond lignin, cellulose, and hemicellulose together to achieve gluing. Therefore, the use of laccase to catalyze the oxidation of lignin to prepare adhesives is a good alternative to trialdehyde resin glue. There is no need to add toxic chemical raw materials such as formaldehyde during its production process, and there is no problem of releasing toxic gases and harmful substances during use. It has great potential for development and application.

Summary of the invention

In view of the shortcomings in the current fiberboard production, the present invention discloses a method for preparing glue-free adhesive fiberboard by microwave hot pressing, using laccase to catalyze lignin to prepare formaldehyde-free and environmentally friendly adhesive, and optimizing and adjusting the microwave hot pressing process in a targeted manner, so as to produce high-quality fiberboard with good mechanical properties, thereby realizing the resource and high-value utilization of waste biomass such as lignin, straw, and wood powder.

The present invention is achieved by adopting the following technical solutions:

A method for preparing a non-adhesive fiber board by microwave hot pressing, comprising the following steps:

(1) Acrylic acid, methylenebisacrylamide, ammonium persulfate and sodium bisulfite are sequentially added to water and stirred to obtain a mixed solution A, and then the mixed solution A is placed in a water bath at a temperature of 30 to 40°C for reaction for 8 to 12 hours, and then isopropyl acrylamide and chitosan are sequentially added and stirred to obtain a mixed solution B, and then ammonium persulfate is added dropwise to the mixed solution B, and the mixture is stirred and reacted in a water bath at a temperature of 30 to 40°C for 12 to 24 hours, and then vacuum dried to obtain a dry gel; the mass ratio of the acrylic acid, methylenebisacrylamide, sodium bisulfite, isopropyl acrylamide, chitosan and water is (3 to 5): (0.2 to 0.5): (0.02 to 0.05): (2 to 5): (1 to 3): 100; the mass ratio of the total amount of the ammonium persulfate used to the acrylic acid is (0.05 to 0.08): (3 to 5);

(2) The dry gel obtained in step (1) is added to water, and ammonia water is added to adjust the pH to 7.0-8.0, and then laccase is added and stirred for 20-30 minutes, and then lignin is added and stirred and mixed evenly, and the mixture is reacted at 60-70° C. for 8-16 hours to obtain an adhesive; the mass ratio of the dry gel, laccase, lignin and water is (5-10):(1-3):(20-30):100;

(3) Adding citric acid solution to the adhesive in step (2) to adjust the pH to 4.0-5.0, soaking wood fiber in the citric acid solution for 3-5 minutes, then mixing the wood fiber with the adhesive, wherein the mass ratio of the wood fiber to the adhesive is 10:(1-3), drying the mixed wood fiber to a moisture content of 8-10%, and then paving to obtain a slab;

(4) Preheating the slab obtained in step (3) at 50-60°C for 3-5 minutes, then placing the slab in a microwave device for microwave heating, with a heating power density of 2-5 W/g·m ³ and a heating time of 30-60 seconds, and pressing the microwave-heated slab into a fiber board.

Furthermore, in step (2), the lignin is one or more of alkali lignin, acetic acid lignin, sulfate lignin, fermentation residue lignin and papermaking black liquor lignin.

Furthermore, in step (3), the wood fiber is obtained by chipping, crushing, steaming, softening, hot grinding and drying one or both of eucalyptus and pine.

Furthermore, in step (1), acrylic acid, methylenebisacrylamide, ammonium persulfate and sodium bisulfite are sequentially added to water and stirred at a speed of 300 to 500 r/min to obtain a mixed solution A; ammonium persulfate is added dropwise to the mixed solution B and stirred for 12 to 24 hours in a water bath at a temperature of 30 to 40°C and a speed of 50 to 80 r/min. When preparing the mixed solution A, controlling a higher stirring speed is conducive to uniformly mixing the components such as acrylic acid, methylenebisacrylamide, ammonium persulfate and sodium bisulfite; when the mixed solution B is heated for reaction, controlling a lower stirring speed is conducive to the cross-linking reaction of polyacrylic acid with isopropylacrylamide and chitosan to prepare a gel.

Furthermore, in step (3), the mass fraction of the citric acid solution is 8-10%.

Furthermore, in step (3), the wood fiber mixed with the glue is dried at 60-80° C. to a moisture content of 8-10%.

Furthermore, in step (4), the frequency of the microwave is 800 to 3000 MHz.

Compared with the prior art, this technical solution has the following beneficial effects:

1. The present invention uses acrylic acid to react under the action of methylenebisacrylamide, ammonium persulfate and sodium bisulfite to obtain polyacrylic acid, and cross-links it with isopropylacrylamide and chitosan to obtain a hydrogel with pH corresponding properties. The swelling rate of the hydrogel under alkaline conditions is significantly higher than the swelling rate under acidic conditions. Therefore, the present invention mixes the obtained hydrogel with laccase, and adds ammonia water to adjust the pH to 7.0-8.0. In this way, the hydrogel has a large swelling rate, can effectively adsorb and fix laccase, and improve the stability and heat resistance of laccase. Then, lignin is added to react under the conditions of laccase and 60-70°C to produce phenoxy free radicals. The free radicals further cross-link to produce a complex carbohydrate complex. This complex can be used as an adhesive to bond lignin, cellulose and hemicellulose together to achieve bonding. In addition, compared with the water phase, the hydrogel can better promote the dispersion of lignin and improve its contact with laccase, thereby improving the reaction efficiency and obtaining an adhesive with good bonding performance.

2. Before mixing the obtained adhesive with wood fiber, the present invention first uses a citric acid solution to adjust the pH of the adhesive to 4.0-5.0. Under acidic conditions, the swelling rate of the hydrogel is greatly reduced and a cross-linked network structure is formed, which is beneficial to the bonding of the adhesive and the wood fiber. At the same time, the present invention also uses a citric acid solution to soak the wood fiber and treat the surface of the wood fiber, which is beneficial to the interaction between the wood fiber and the carbohydrate complex in the adhesive, increases the internal stress of the combination of the wood fiber and the adhesive, and prevents the fiberboard from cracking. In addition, the hydrogel and a small amount of unreacted lignin are evenly dispersed in the fiberboard, which can also improve the mechanical properties of the fiberboard.

3. The method of the present invention adopts the method of microwave hot pressing, and according to the characteristics of the adhesive, the slab is first preheated and then microwave hot pressing is performed, which is beneficial to uniform and rapid heating of the slab, the temperature difference between different parts of the slab is small, the adhesive is heated evenly, the curing effect is good, and the produced fiberboard has better mechanical properties.

Detailed ways

The present invention is further described by the following examples, but is not intended to be limiting of the present invention. Specific experimental conditions and methods not specified in the following examples are conventional methods known to those skilled in the art.

Embodiment 1: A method for preparing a non-adhesive fiber board by microwave hot pressing, comprising the following steps:

(1) Acrylic acid, methylenebisacrylamide, ammonium persulfate and sodium bisulfite are sequentially added to water and stirred at a speed of 400 r/min to obtain a mixed solution A, and then the mixed solution A is placed in a water bath at a temperature of 35°C for reaction for 10 hours, and then isopropyl acrylamide and chitosan are sequentially added and stirred to obtain a mixed solution B, and then ammonium persulfate is added dropwise to the mixed solution B, and the mixture is stirred in a water bath at a temperature of 35°C and a speed of 60 r/min for reaction for 16 hours, and then vacuum dried to obtain a dry gel; the acrylic acid, methylenebisacrylamide, sodium bisulfite , isopropyl acrylamide, chitosan and water in a mass ratio of 4:0.3:0.04:3:2:100; the mass ratio of the total amount of ammonium persulfate to the acrylic acid is 0.06:4; (2) taking the dry gel obtained in step (1) and adding it to water, and adding ammonia water to adjust the pH to 7.5, then adding laccase and stirring and mixing for 25 minutes, and then adding lignin and stirring and mixing evenly, and reacting at 65°C for 10 hours to obtain an adhesive; the mass ratio of the dry gel, laccase, lignin and water is 6.5:2:25:100; the lignin is alkaline lignin;

(3) The adhesive in step (2) is added with a citric acid solution to adjust the pH to 4.3, and the wood fiber is soaked in the citric acid solution for 4 minutes, and then the wood fiber and the adhesive are mixed and glued, wherein the mass ratio of the wood fiber to the adhesive is 10:2, and the mixed wood fiber is dried at 70° C. to a moisture content of 9%, and then paved to obtain a slab; the mass fraction of the citric acid solution is 9%; the wood fiber is obtained by chipping, crushing, steaming, softening, hot grinding, and drying eucalyptus wood;

(4) The slab obtained in step (3) was preheated at 55°C for 4 minutes, and then placed in a microwave device for microwave heating. The heating power density was 3 W/g· ^m3 , the heating time was 45 seconds, and the frequency of the microwave was 2450 MHz. The microwave-heated slab was pressed into a fiber board.

Example 2: A method for preparing a non-adhesive fiber board by microwave hot pressing, comprising the following steps:

(1) Acrylic acid, methylenebisacrylamide, ammonium persulfate and sodium bisulfite are sequentially added to water and stirred at a speed of 300 r/min to obtain a mixed solution A, then the mixed solution A is placed in a water bath at a temperature of 30°C for reaction for 8 hours, and then isopropyl acrylamide and chitosan are sequentially added and stirred to obtain a mixed solution B, and then ammonium persulfate is added dropwise to the mixed solution B, and the mixture is stirred in a water bath at a temperature of 30°C and a speed of 50 r/min for reaction for 12 hours, and then vacuum dried to obtain a dry gel; the mass ratio of the acrylic acid, methylenebisacrylamide, sodium bisulfite, isopropyl acrylamide, chitosan and water is 3:0.2:0.02:2:1:100; the mass ratio of the total amount of the ammonium persulfate to the acrylic acid is 0.05:3;

(2) The dry gel obtained in step (1) is added to water, and ammonia water is added to adjust the pH to 7.0, and then laccase is added and stirred for 20 minutes, and then lignin is added and stirred and mixed evenly, and the mixture is reacted at 60° C. for 8 hours to obtain an adhesive; the mass ratio of the dry gel, laccase, lignin and water is 5:1:20:100; and the lignin is sulfate lignin;

(3) The adhesive in step (2) is added with a citric acid solution to adjust the pH to 4.0, and wood fibers are soaked in the citric acid solution for 3 minutes, and then the wood fibers are mixed with the adhesive, wherein the mass ratio of the wood fibers to the adhesive is 10:1, and the mixed wood fibers are dried at 60° C. to a moisture content of 8%, and then paved to obtain a slab; the mass fraction of the citric acid solution is 8%; the wood fibers are obtained by chipping, crushing, steaming, softening, hot grinding, and drying eucalyptus and pine;

(4) The slab obtained in step (3) is preheated at 50°C for 3 minutes, and then placed in a microwave device for microwave heating, with a heating power density of 2 W/g· ^m3 , a heating time of 30 seconds, and a microwave frequency of 800 MHz. The microwave-heated slab is pressed into a fiber board.

Embodiment 3: A method for preparing a non-adhesive fiber board by microwave hot pressing, comprising the following steps:

(1) Acrylic acid, methylenebisacrylamide, ammonium persulfate and sodium bisulfite are sequentially added to water and stirred at a speed of 350 r/min to obtain a mixed solution A, then the mixed solution A is placed in a water bath at a temperature of 38°C for reaction for 10 hours, and then isopropyl acrylamide and chitosan are sequentially added and stirred to obtain a mixed solution B, and then ammonium persulfate is added dropwise to the mixed solution B, and the mixture is stirred in a water bath at a temperature of 32°C and a speed of 70 r/min for reaction for 18 hours, and then vacuum dried to obtain a dry gel; the mass ratio of the acrylic acid, methylenebisacrylamide, sodium bisulfite, isopropyl acrylamide, chitosan and water is 4:0.4:0.04:4.5:2.5:100; the mass ratio of the total amount of the ammonium persulfate to the acrylic acid is 0.07:3.5;

(2) The dry gel obtained in step (1) is added to water, and ammonia water is added to adjust the pH to 7.5, and then laccase is added and stirred for 25 minutes, and then lignin is added and stirred and mixed evenly, and the mixture is reacted at 68° C. for 10 hours to obtain an adhesive; the mass ratio of the dry gel, laccase, lignin and water is 8:2:25:100; and the lignin is alkaline lignin;

(3) The adhesive in step (2) is added with a citric acid solution to adjust the pH to 4.5, and wood fibers are soaked in the citric acid solution for 4 minutes, and then the wood fibers are mixed with the adhesive, wherein the mass ratio of the wood fibers to the adhesive is 10:2.5, and the mixed wood fibers are dried at 75° C. to a moisture content of 9%, and then paved to obtain a slab; the mass fraction of the citric acid solution is 8.5%; the wood fibers are obtained by chipping, crushing, steaming, softening, hot grinding, and drying pine wood;

(4) The slab obtained in step (3) was preheated at 56°C for 4 minutes, and then placed in a microwave device for microwave heating. The heating power density was 4 W/g·m ³ , the heating time was 50 seconds, and the microwave frequency was 915 MHz. The microwave-heated slab was pressed into a fiberboard.

Example 4: A method for preparing a non-adhesive fiber board by microwave hot pressing, comprising the following steps:

(1) Acrylic acid, methylenebisacrylamide, ammonium persulfate and sodium bisulfite are sequentially added to water and stirred at a speed of 500 r/min to obtain a mixed solution A, then the mixed solution A is placed in a water bath at a temperature of 40°C for reaction for 12 hours, and then isopropyl acrylamide and chitosan are sequentially added and stirred to obtain a mixed solution B, and then ammonium persulfate is added dropwise to the mixed solution B, and the mixture is stirred in a water bath at a temperature of 40°C and a speed of 80 r/min for reaction for 24 hours, and then vacuum dried to obtain a dry gel; the mass ratio of the acrylic acid, methylenebisacrylamide, sodium bisulfite, isopropyl acrylamide, chitosan and water is 5:0.5:0.05:5:3:100; the mass ratio of the total amount of the ammonium persulfate to the acrylic acid is 0.08:5;

(2) The dry gel obtained in step (1) is added to water, and ammonia water is added to adjust the pH to 8.0, and then laccase is added and stirred for 30 minutes, and then lignin is added and stirred and mixed evenly, and the mixture is reacted at 70° C. for 16 hours to obtain an adhesive; the mass ratio of the dry gel, laccase, lignin and water is 10:3:30:100; the lignin is alkali lignin and papermaking black liquor lignin;

(3) The adhesive in step (2) is added with a citric acid solution to adjust the pH to 5.0, and the wood fiber is soaked in the citric acid solution for 5 minutes, and then the wood fiber and the adhesive are mixed and glued, wherein the mass ratio of the wood fiber to the adhesive is 10:3, and the mixed wood fiber is dried at 80° C. to a moisture content of 10%, and then paved to obtain a slab; the mass fraction of the citric acid solution is 10%; the wood fiber is obtained by chipping, crushing, steaming, softening, hot grinding, and drying eucalyptus wood;

(4) The slab obtained in step (3) was preheated at 60°C for 5 minutes, and then placed in a microwave device for microwave heating. The heating power density was 5 W/g·m ³ , the heating time was 60 seconds, and the microwave frequency was 3000 MHz. The microwave-heated slab was pressed into a fiber board.

Comparative Example 1: The method for preparing glue-free bonded fiber board by microwave hot pressing described in this comparative example is different from the method described in Example 1 only in that step (1) is omitted and in step (2), dry gel is not used. Instead, laccase is directly added to water to adjust the pH value, and then lignin is added and stirred to mix evenly.

Comparative Example 2: The method for preparing glue-free bonded fiber board by microwave hot pressing described in this comparative example is different from the method described in Example 1 only in that in step (3), the wood fibers are not immersed in citric acid solution, but are directly mixed with adhesive.

Experimental example: Fiberboard was prepared according to the method described in Examples 1 to 4 and Comparative Examples 1 to 2, and then the obtained fiberboard was tested for performance according to the national standard GB/T11718-2021 medium density fiberboard. The specific results are shown in Table 1.

Table 1 Performance test results of fiberboard

In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims (4)

1. A method for preparing a non-adhesive fiber board by microwave hot pressing is characterized in that: the method comprises the following steps:

(1) Sequentially adding acrylic acid, methylene bisacrylamide, ammonium persulfate and sodium bisulfate into water, stirring and mixing at the speed of 300-500 r/min to obtain a mixed solution A, then placing the mixed solution A into a water bath at the temperature of 30-40 ℃ for reaction for 8-12 h, sequentially adding isopropylacrylamide and chitosan, stirring and mixing to obtain a mixed solution B, dropwise adding ammonium persulfate into the mixed solution B, stirring and reacting for 12-24 h at the speed of 50-80 r/min in a water bath at the temperature of 30-40 ℃, and then vacuum drying to obtain xerogel; the mass ratio of the acrylic acid to the methylene bisacrylamide to the sodium bisulphite to the isopropyl acrylamide to the chitosan to the water is (3-5): 0.2-0.5): 0.02-0.05): 2-5): 1-3): 100; the mass ratio of the total dosage of the ammonium persulfate to the acrylic acid is (0.05-0.08) to (3-5);

(2) Adding the xerogel obtained in the step (1) into water, adding ammonia water to adjust the pH to 7.0-8.0, adding laccase, stirring and mixing for 20-30 min, adding lignin, stirring and mixing uniformly, and reacting at 60-70 ℃ for 8-16 h to obtain the adhesive; the mass ratio of the xerogel to the laccase to the lignin to the water is (5-10): 1-3): 20-30): 100;

(3) Adding citric acid solution into the adhesive in the step (2) to adjust the pH value to 4.0-5.0, soaking wood fibers in the citric acid solution for 3-5 min, mixing the wood fibers with the adhesive, stirring the mixture, wherein the mass ratio of the wood fibers to the adhesive is 10 (1-3), drying the mixed wood fibers at 60-80 ℃ until the water content is 8-10%, and paving to obtain a plate blank; the mass fraction of the citric acid solution is 8-10%;

(4) Preheating the plate blank obtained in the step (3) at 50-60 ℃ for 3-5min, then placing the plate blank in microwave equipment for microwave heating, wherein the heating power density is 2-5W/g.m ³, the heating time is 30-60 s, and performing pressing plate molding on the plate blank subjected to microwave heating to obtain the fiber plate.

2. The method for preparing the non-adhesive fiber board by microwave hot pressing according to claim 1, wherein the method comprises the following steps: in the step (2), the lignin is one or more of alkali lignin, acetic acid lignin, kraft lignin, fermentation residue lignin and papermaking black liquor lignin.

3. The method for preparing the non-adhesive fiber board by microwave hot pressing according to claim 1, wherein the method comprises the following steps: in the step (3), the wood fiber is obtained by taking one or two of eucalyptus and pine, chipping, crushing, steaming, softening, hot grinding and drying.

4. The method for preparing the non-adhesive fiber board by microwave hot pressing according to claim 1, wherein the method comprises the following steps: in the step (4), the frequency of the microwaves is 800-3000 MHz.