CN117047886A - Method for preparing non-adhesive fiber board through microwave hot pressing - Google Patents

Abstract

The invention discloses a method for preparing glue-free bonded fiber sheets by microwave hot pressing. The method includes adding acrylic acid, methylene bisacrylamide, initiator, etc. into water for a mixing reaction, and then adding isopropylacrylamide and chitopolymer. After the sugar mixing reaction, vacuum drying is performed to obtain a xerogel; add the xerogel to water, and add ammonia to adjust the pH, then add laccase and stir to mix, then add lignin, stir and mix evenly, and react at 60 to 70°C Process to obtain an adhesive; add the adhesive to a citric acid solution to adjust the pH, soak the wood fiber in the citric acid solution, then mix the wood fiber and the adhesive to mix the glue, and then pave it to obtain a slab; The blank is placed in a microwave equipment for microwave heating, and then pressed into a plate to form a particleboard. The present invention uses laccase to catalyze lignin to prepare aldehyde-free and environmentally friendly adhesive, and performs targeted optimization and adjustment of the microwave hot pressing process to produce high-quality fiberboards with good mechanical properties.

Description

A method for preparing glueless bonded fiber sheets by microwave hot pressing

Technical field

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

Background technique

Fiberboard, also known as density board, is an artificial board made of wood fiber or other plant fiber as raw material and applied with urea-formaldehyde resin or other suitable adhesives. Adhesives and/or additives may be applied during the manufacturing process. Fiber board has the advantages of uniform material, small vertical and horizontal strength difference, not easy to crack, etc., and is widely used. In the fiberboard manufacturing process, there are many factors that affect product quality, including adhesive quality and sizing amount, hot pressing process, etc. The entire slab is heated, 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 the slab is solidified and formed. Since there are great differences in the composition ratio and curing conditions of different types of adhesives, they also have different requirements for hot pressing process conditions. Especially when microwave hot pressing is used, the curing effects of different adhesives under the action of microwaves are different. How to optimize the hot pressing process conditions for different adhesives to produce high-quality fiberboards is one of the focuses of current research.

At the same time, as people's awareness of safety and environmental protection increases, the production and use of trialdehyde resin glues such as urea-formaldehyde resin glue, phenolic resin glue, and melamine-modified urea-formaldehyde resin glue will release formaldehyde that is harmful to the environment and human health. Gas, research and development of formaldehyde-free adhesives are also one of the hot spots in fiberboard production. Laccase (Laccases, Lac) is a polyphenol oxidase that can degrade lignin. It can catalyze lignin to produce phenoxy free radicals, and further cross-linking reactions between free radicals produce a complex sugar complex. This complex can bind lignin, cellulose and hemicellulose together to achieve gluing. Therefore, the use of laccase-catalyzed 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 when used. , has huge potential for development and application.

Contents of the invention

In view of the shortcomings in the current production of fiberboards, the present invention discloses a method for preparing glue-free bonded fiber boards by microwave hot pressing, using laccase to catalyze lignin to prepare aldehyde-free and environmentally friendly adhesives, and targeting the microwave hot pressing process. Through the optimization and adjustment of properties, high-quality fiberboards with good mechanical properties can be produced, and waste biomass such as lignin, straw, and wood powder can be recycled and used in high value.

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

A method for preparing glueless bonded fiber sheets by microwave hot pressing, which includes the following steps:

(1) Add acrylic acid, methylene bisacrylamide, ammonium persulfate and sodium bisulfite to the water in sequence, stir and mix to obtain a mixed liquid A, and then place the mixed liquid A in a water bath with a temperature of 30 to 40°C for reaction. 8 to 12 hours, and then add isopropylacrylamide and chitosan in sequence, stir and mix to obtain mixed liquid B, then add ammonium persulfate dropwise to mixed liquid B and stir in a water bath with a temperature of 30 to 40°C for reaction 12 ~24h, followed by vacuum drying to obtain a xerogel; the mass ratio of acrylic acid, methylene bisacrylamide, sodium bisulfite, isopropylacrylamide, chitosan and water is (3~5): (0.2 ~0.5): (0.02~0.05): (2~5): (1~3):100; the mass ratio of the total amount of ammonium persulfate to the acrylic acid is (0.05~0.08): (3~5 );

(2) Add the dry gel obtained in step (1) to water, and add ammonia to adjust the pH to 7.0-8.0, then add laccase and stir for 20-30 minutes, then add lignin, stir and mix evenly, and The adhesive is obtained by reaction treatment at 60-70°C for 8-16 hours; the mass ratio of the xerogel, laccase, lignin and water is (5-10): (1-3): (20-30): 100;

(3) Take the adhesive in step (2) and add citric acid solution to adjust the pH to 4.0~5.0, and soak the wood fiber in the citric acid solution for 3~5 minutes, then mix the wood fiber and adhesive to mix the glue. The mass ratio of wood fiber and adhesive is 10: (1-3), the wood fiber mixed with glue is dried to a moisture content of 8-10%, and then paved to obtain a slab;

(4) Preheat the slab obtained in step (3) at 50-60°C for 3-5 minutes, and then place the slab in a microwave equipment for microwave heating with a heating power density of 2-5W/g·m ³ , the heating time is 30 to 60 seconds, and the microwave-heated slab is pressed and formed to obtain particle board.

Further, in step (1), the lignin is one or more of alkali lignin, acetate lignin, sulfate lignin, fermentation residue lignin and papermaking black liquor lignin.

Further, in step (1), the wood fiber is obtained by shaving one or both of eucalyptus and pine wood, cooking and softening, heat grinding, and drying.

Further, in step (1), acrylic acid, methylene bisacrylamide, ammonium persulfate and sodium bisulfite are sequentially added to the water and stirred at a speed of 300 to 500 r/min to obtain mixed liquid A; Add ammonium persulfate dropwise to mixed liquid B, then stir and react for 12 to 24 hours in a water bath with a temperature of 30 to 40°C and a speed of 50 to 80 r/min. When preparing Mixed Liquid A, controlling a higher stirring speed is beneficial to evenly mixing acrylic acid, methylene bisacrylamide, ammonium persulfate, sodium bisulfite and other components; when Mixed Liquid B is heated for reaction, controlling a lower stirring speed The stirring speed is conducive to the cross-linking reaction of polyacrylic acid with isopropylacrylamide and chitosan to prepare gel.

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

Further, in step (3), the glue-mixed wood fiber is dried at 60-80°C until the moisture content is 8-10%.

Further, in step (4), the frequency of the microwave is 800-3000MHz.

Compared with the existing technology, this technical solution has the following beneficial effects:

1. The present invention uses acrylic acid to react under the action of methylene bisacrylamide, ammonium persulfate, sodium bisulfite, etc. to obtain polyacrylic acid, and cross-links it with isopropylacrylamide and chitosan to obtain polyacrylic acid with pH Hydrogel with corresponding properties, the swelling rate of the hydrogel under alkaline conditions is significantly higher than that under acidic conditions, so the present invention mixes the obtained hydrogel with laccase, and adds ammonia water to adjust The pH is adjusted to 7.0~8.0, so that the hydrogel has a large swelling rate, which can effectively absorb and fix laccase, improve the stability and heat resistance of laccase, and then add lignin to the laccase and 60~70°C. The reaction under the conditions produces phenoxy free radicals, and further cross-linking reactions between free radicals produce a complex sugar complex. This complex can be used as an adhesive to bind lignin, cellulose and hemicellulose together. Achieve gluing. Moreover, compared with water, 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 gluing performance.

2. Before mixing the obtained adhesive with wood fiber, the present invention first uses 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 is formed. -like structure, which is beneficial to the gluing of the adhesive and the wood fiber. At the same time, the present invention also uses 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 sugar complex in the adhesive. It increases the internal stress of the combination of wood fiber and adhesive and prevents cracking of the fiberboard. Moreover, the even dispersion of hydrogel and a small amount of unreacted lignin in the fiberboard can also improve the mechanical properties of the fiberboard.

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

Detailed ways

The following examples further illustrate the present invention, but are not intended to limit the present invention. For specific experimental conditions and methods not specified in the following examples, the technical means used are usually conventional means well known to those skilled in the art.

Embodiment 1: A method for preparing glueless bonded fiber sheets by microwave hot pressing, which includes the following steps:

(1) Add acrylic acid, methylene bisacrylamide, ammonium persulfate and sodium bisulfite to water in sequence, stir and mix at a speed of 400r/min to obtain mixed liquid A, and then place mixed liquid A at a temperature of React for 10 hours in a water bath at 35°C, then add isopropylacrylamide and chitosan in sequence, stir and mix to obtain a mixed liquid B, then add ammonium persulfate dropwise to the mixed liquid B, and then place in a water bath at a temperature of 35°C and increase the speed. The reaction was stirred for 16 hours at 60 r/min, and then dried under vacuum to obtain a xerogel; the mass ratio of acrylic acid, methylene bisacrylamide, sodium bisulfite, isopropylacrylamide, chitosan and water was 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; the lignin is alkali lignin; the wood fiber is obtained from eucalyptus wood. Obtained by shavings, crushing, cooking, softening, hot grinding and drying;

(2) Add the dry gel obtained in step (1) to water, and add ammonia to adjust the pH to 7.5, then add laccase and stir and mix for 25 minutes, then add lignin, stir and mix evenly, and react at 65°C Treat for 10 hours to obtain an adhesive; the mass ratio of the xerogel, laccase, lignin and water is 6.5:2:25:100;

(3) Take the adhesive in step (2) and add citric acid solution to adjust the pH to 4.3, and soak the wood fiber in the citric acid solution for 4 minutes, and then mix the wood fiber and the adhesive to mix the glue. The mass ratio of the adhesive is 10:2. The glue-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% ;

(4) Preheat the slab obtained in step (3) at 55°C for 4 minutes, and then place the slab in a microwave equipment for microwave heating. The heating power density is 3W/g·m ³ and the heating time is 45s. The frequency of the microwave is 2450 MHz, and the slab heated by the microwave is pressed and formed to obtain a particleboard.

Embodiment 2: A method for preparing glueless bonded fiber sheets by microwave hot pressing, which includes the following steps:

(1) Add acrylic acid, methylene bisacrylamide, ammonium persulfate and sodium bisulfite to water in sequence, stir and mix at a speed of 300r/min to obtain mixed liquid A, and then place mixed liquid A at a temperature of React for 8 hours in a water bath at 30°C, then add isopropylacrylamide and chitosan in sequence, stir and mix to obtain a mixed liquid B, then add ammonium persulfate dropwise to the mixed liquid B, and then place in a water bath at a temperature of 30°C and increase the speed. The reaction was stirred for 12 hours at 50 r/min, and then dried under vacuum to obtain a xerogel; the mass ratio of acrylic acid, methylene bisacrylamide, sodium bisulfite, isopropylacrylamide, chitosan and water was 3:0.2:0.02:2:1:100; the mass ratio of the total amount of ammonium persulfate to the acrylic acid is 0.05:3; the lignin is sulfate lignin; the wood fiber is eucalyptus wood And pine wood is obtained by chipping, cooking, softening, hot grinding and drying;

(2) Add the dry gel obtained in step (1) to water, and add ammonia to adjust the pH to 7.0, then add laccase and stir and mix for 20 minutes, then add lignin, stir and mix evenly, and react at 60°C Treat for 8 hours to obtain an adhesive; the mass ratio of the xerogel, laccase, lignin and water is 5:1:20:100;

(3) Take the adhesive in step (2) and add citric acid solution to adjust the pH to 4.0, and soak the wood fiber in the citric acid solution for 3 minutes, and then mix the wood fiber and the adhesive to mix the glue. The mass ratio of the adhesive is 10:1. The glue-mixed wood fiber is 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% ;

(4) Preheat the slab obtained in step (3) at 50°C for 3 minutes, and then place the slab in a microwave equipment for microwave heating. The heating power density is 2W/g·m ³ and the heating time is 30s. The frequency of the microwave is 800 MHz, and the slab heated by the microwave is pressed and formed to obtain a particleboard.

Embodiment 3: A method for preparing glueless bonded fiber sheets by microwave hot pressing, which includes the following steps:

(1) Add acrylic acid, methylene bisacrylamide, ammonium persulfate and sodium bisulfite to water in sequence, stir and mix at a speed of 350r/min to obtain mixed liquid A, and then place mixed liquid A at a temperature of React for 10 hours in a water bath at 38°C, then add isopropylacrylamide and chitosan in sequence, stir and mix to obtain a mixed liquid B, then add ammonium persulfate dropwise to the mixed liquid B, and then place in a water bath at a temperature of 32°C and speed The reaction was stirred for 18 hours at 70 r/min, and then dried under vacuum to obtain a xerogel; the mass ratio of acrylic acid, methylene bisacrylamide, sodium bisulfite, isopropylacrylamide, chitosan and water was 4:0.4:0.04:4.5:2.5:100; the mass ratio of the total amount of ammonium persulfate to the acrylic acid is 0.07:3.5; the lignin is alkali lignin; the wood fiber is obtained by cutting pine wood Obtained by crushing slices, cooking to soften, hot grinding and drying;

(2) Add the dry gel obtained in step (1) to water, and add ammonia to adjust the pH to 7.5, then add laccase and stir and mix for 25 minutes, then add lignin, stir and mix evenly, and react at 68°C Treat for 10 hours to obtain an adhesive; the mass ratio of the xerogel, laccase, lignin and water is 8:2:25:100;

(3) Take the adhesive in step (2) and add citric acid solution to adjust the pH to 4.5, and soak the wood fiber in the citric acid solution for 4 minutes, and then mix the wood fiber and the adhesive to mix the glue. The mass ratio of the adhesive is 10:2.5. The glue-mixed wood fiber is 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% ;

(4) Preheat the slab obtained in step (3) at 56°C for 4 minutes, and then place the slab in a microwave equipment for microwave heating. The heating power density is 4W/g·m ³ and the heating time is 50s. The frequency of the microwave is 915 MHz, and the slab heated by the microwave is pressed and formed to obtain a particleboard.

Embodiment 4: A method for preparing glueless bonded fiber sheets by microwave hot pressing, which includes the following steps:

(1) Add acrylic acid, methylene bisacrylamide, ammonium persulfate and sodium bisulfite to water in sequence, stir and mix at a speed of 500r/min to obtain mixed liquid A, and then place mixed liquid A at a temperature of React for 12 hours in a water bath at 40°C, then add isopropylacrylamide and chitosan in sequence, stir and mix to obtain a mixed liquid B, then add ammonium persulfate dropwise to the mixed liquid B, and then place in a water bath at a temperature of 40°C and speed The reaction was stirred for 24 hours at 80 r/min, and then dried under vacuum to obtain a xerogel; the mass ratio of acrylic acid, methylene bisacrylamide, sodium bisulfite, isopropylacrylamide, chitosan and water was 5:0.5:0.05:5:3:100; the mass ratio of the total amount of ammonium persulfate to the acrylic acid is 0.08:5; the lignin is alkali lignin and papermaking black liquor lignin; the wood Fiber is obtained from eucalyptus wood by shaving, crushing, cooking to soften, hot grinding, and drying;

(2) Add the dry gel obtained in step (1) to water, and add ammonia to adjust the pH to 8.0, then add laccase and stir and mix for 30 minutes, then add lignin, stir and mix evenly, and react at 70°C Treat for 16 hours to obtain an adhesive; the mass ratio of the xerogel, laccase, lignin and water is 10:3:30:100;

(3) Take the adhesive in step (2) and add citric acid solution to adjust the pH to 5.0, and soak the wood fiber in the citric acid solution for 5 minutes, and then mix the wood fiber and the adhesive to mix the glue. The mass ratio of the adhesive is 10:3. The glue-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% ;

(4) Preheat the slab obtained in step (3) at 60°C for 5 minutes, and then place the slab in a microwave equipment for microwave heating. The heating power density is 5W/g·m ³ and the heating time is 60s. The frequency of the microwave is 3000MHz, and the slab heated by the microwave is pressed and formed to obtain a particleboard.

Comparative Example 1: The only difference between the method for preparing glueless fiber sheets by microwave hot pressing and the method described in Example 1 is that step (1) is omitted and dry coagulation is not used in step (2). Glue, instead, directly add laccase to water to adjust the pH value, then add lignin and stir to mix evenly.

Comparative Example 2: The only difference between the microwave hot pressing method for preparing glueless fiber sheets and the method described in Example 1 is that in step (3), the wood fibers are not soaked in the citric acid solution. Instead of soaking, mix the wood fiber and adhesive directly.

Experimental example: Prepare fiberboards according to the methods described in Examples 1 to 4 and Comparative Examples 1 to 2, and then perform performance testing on the obtained fiberboards in accordance with the national standard for medium density fiberboards GB/T11718-2021. The specific results are shown in Table 1.

Table 1 Performance test results of fiberboard

In addition, it should be understood that although this specification is described in terms of implementations, not each implementation only contains an independent technical solution. This description of the specification is only for the sake of clarity, and those skilled in the art should take the specification as a whole. , the technical solutions in each embodiment can also be appropriately combined to form other implementations that can be understood by those skilled in the art.

Claims (7)

1. A method for preparing glueless bonded fiber sheets by microwave hot pressing, which is characterized in that: it includes the following steps: (1) Add acrylic acid, methylene bisacrylamide, ammonium persulfate and sodium bisulfite to the water in sequence, stir and mix to obtain a mixed liquid A, and then place the mixed liquid A in a water bath with a temperature of 30 to 40°C for reaction. 8 to 12 hours, and then add isopropylacrylamide and chitosan in sequence, stir and mix to obtain mixed liquid B, then add ammonium persulfate dropwise to mixed liquid B and stir in a water bath with a temperature of 30 to 40°C for reaction 12 ~24h, followed by vacuum drying to obtain a xerogel; the mass ratio of acrylic acid, methylene bisacrylamide, sodium bisulfite, isopropylacrylamide, chitosan and water is (3~5): (0.2 ~0.5): (0.02~0.05): (2~5): (1~3):100; the mass ratio of the total amount of ammonium persulfate to the acrylic acid is (0.05~0.08): (3~5 ); (2) Add the dry gel obtained in step (1) to water, and add ammonia to adjust the pH to 7.0-8.0, then add laccase and stir for 20-30 minutes, then add lignin, stir and mix evenly, and The adhesive is obtained by reaction treatment at 60-70°C for 8-16 hours; the mass ratio of the xerogel, laccase, lignin and water is (5-10): (1-3): (20-30): 100; (3) Take the adhesive in step (2) and add citric acid solution to adjust the pH to 4.0~5.0, and soak the wood fiber in the citric acid solution for 3~5 minutes, then mix the wood fiber and adhesive to mix the glue. The mass ratio of wood fiber and adhesive is 10: (1-3), the wood fiber mixed with glue is dried to a moisture content of 8-10%, and then paved to obtain a slab; (4) Preheat the slab obtained in step (3) at 50-60°C for 3-5 minutes, and then place the slab in a microwave equipment for microwave heating with a heating power density of 2-5W/g·m ³ , the heating time is 30 to 60 seconds, and the microwave-heated slab is pressed and formed to obtain particle board. 2. The method for preparing glue-free fiber sheets by microwave hot pressing according to claim 1, characterized in that: in step (1), the lignin is alkali lignin, acetate lignin, sulfate lignin, One or more of fermentation residue lignin and papermaking black liquor lignin. 3. The method for preparing glueless fiber sheets by microwave hot pressing according to claim 1, characterized in that: in step (1), the wood fiber is made from one or both of eucalyptus and pine. It is obtained by chipping, crushing, cooking, softening, hot grinding and drying. 4. The method for preparing glueless fiber sheets by microwave hot pressing according to claim 1, characterized in that: in step (1), acrylic acid, methylene bisacrylamide, ammonium persulfate and sodium bisulfite are Add to the water in turn and stir and mix at a speed of 300-500r/min to obtain a mixed liquid A; add ammonium persulfate dropwise to the mixed liquid B and then place it in a water bath with a temperature of 30-40°C and a speed of 50-80r/min. The reaction was stirred for 12 to 24 hours. 5. The method for preparing glueless fiber sheets by microwave hot pressing according to claim 1, characterized in that in step (3), the mass fraction of the citric acid solution is 8 to 10%. 6. The method for preparing glue-free bonded fiber sheets by microwave hot pressing according to claim 1, characterized in that: in step (3), the glue-mixed wood fibers are dried at 60 to 80°C until the moisture content is 8~10%. 7. The method for preparing glueless fiber sheets by microwave hot pressing according to claim 1, characterized in that in step (4), the frequency of the microwave is 800-3000 MHz.