Method for manufacturing recyclable green fiberboard from agricultural straw and application

Abstract

The invention belongs to the technical field of artificial fiberboard production, and discloses a method for manufacturing a recyclable environment-friendly fiberboard from agricultural straws, and the method comprises the following steps: preparing materials, pretreating raw materials, dissociating the raw materials, adding chemicals, paving and forming, squeezing and dehydrating, and drying to obtain a finished product. According to the novel fiberboard, the agricultural straw is used as the raw material, self-adhesion can be generated among fibers by controlling the pretreatment and mechanical dissociation conditions, no trialdehyde adhesive needs to be added in the production process, and the prepared novel fiberboard is free of formaldehyde release and meets the requirement for green and sustainable development. The method is a green fiberboard manufacturing method which is wide in raw material source, simple, non-toxic and harmless.

Description

Technical Field

[0001] The invention belongs to the technical field of artificial fiberboard production, in particular to a method and application of manufacturing environmentally friendly fiberboard from agricultural straw. Background Art

[0002] The main raw material for the manufacture of man-made fiberboard is wood. In order to seek a larger supply of raw materials, agricultural straw has become one of the important options. Agricultural straw resources such as wheat straw, corn straw, cotton straw and rice straw are abundant. The output of agricultural straw is large, but there is a lack of simple and effective processing technology, resulting in low utilization rate of its high added value. Every year, a large amount of straw is directly returned to the fields or even burned. The burning of straw produces a large amount of carbon dioxide and PM. 2.5 Particles not only pollute the air, but also lead to the greenhouse effect, causing many environmental problems and waste of resources.

[0003] Fiberboard is widely used in furniture, building materials, automobile decoration and other fields. Due to the diversification of consumer groups and usage environments, higher requirements are placed on the performance of fiberboard, and the demand for green and environmentally friendly fiberboard has been rising year by year. In the production of traditional fiberboard, in order to improve the performance of fiberboard, adhesives are generally added. Most of the adhesives used are synthetic resin adhesives, among which "trialdehyde glue" (urea-formaldehyde resin, phenol-formaldehyde resin and melamine formaldehyde resin) is the most widely used. They will release free formaldehyde and other harmful substances during production and use, polluting the air and seriously affecting people's health. In addition, traditional fiberboard is difficult to recycle after being discarded, and the green upgrading and transformation of the artificial fiberboard industry is imperative.

[0004] Through searching, CN 110900778 A discloses a plant fiber artificial board and its preparation method and application. The physical properties of the board are enhanced by adding sawdust fibers, but the complete replacement of wood fiber with straw fiber is not achieved. Southeast University discloses a straw-based non-wood plant fiber artificial board and its preparation method in CN 1626747 A. Chemicals such as urea-formaldehyde resin binder are added during the preparation of the board, but zero use of "trialdehyde glue" is not achieved. CN103358381 A discloses a preparation method of an alkali steam-exploded straw glue-free artificial board. The straw raw material is soaked in an alkaline solution during the process, which increases the burden of wastewater treatment.

[0005] In view of the problem that the widespread use of "trialdehyde glue" in the current fiberboard production has adverse effects on people's health, the present invention provides a fiberboard manufacturing method that uses agricultural straw as raw material, adopts a green and pollution-free process, does not add adhesives, and has a simple production method. The method uses agricultural straw as raw material to prepare environmentally friendly fiberboard, which is not only beneficial to protecting forest resources and alleviating problems such as wood shortages, but also improves the use value of agricultural straw, and also has the effect of carbon fixation and carbon reduction, alleviates ecological environmental pressure, and meets the requirements of green and sustainable development. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method and application of manufacturing environmentally friendly fiberboard from agricultural straw.

[0007] The technical solution adopted by the present invention to solve its technical problem is:

[0008] A method for manufacturing recyclable and environmentally friendly fiberboard from agricultural straws, the method comprising the following steps: material preparation→raw material pretreatment→raw material separation→chemical addition→paving and forming→pressing and dehydration→drying→finished product.

[0009] Furthermore, the specific steps are as follows:

[0010] (1) Material preparation: Process the agricultural straw raw materials into material segments of 5 mm to 50 mm, and screen out impurities such as mud and sand for later use;

[0011] (2) Raw material pretreatment: Add the prepared raw materials and water into a pressure vessel. The water added is tap water or recycled water from production. Keep the liquid-to-solid ratio between 2:1 and 8:1. Heat to a temperature of 140°C to 180°C and keep it at this temperature for 5 to 120 minutes before discharging the materials.

[0012] (3) Raw material dissociation: Mechanically dissociate the pretreated raw materials to obtain fiber-based materials;

[0013] (4) Chemical addition: In order to further improve the strength and water resistance of the product, the dissociated material is mechanically mixed with a reinforcing agent and a water repellent to obtain a uniformly mixed fiber material; wherein the amount of the reinforcing agent is 0.1% to 20% (relative to the mass of the absolutely dry fiber material), and the amount of the water repellent is 0.1% to 10% (relative to the mass of the absolutely dry fiber material);

[0014] (5) Laying and forming: pouring the mixed fiber material into the mold, laying it evenly, and then squeezing and dehydrating it. The squeezing pressure is 0.1Mpa to 15Mpa, and the squeezing time is 10s to 600s. Dehydration is performed until the mass concentration of the material is 20% to 50%. The water removed by squeezing is collected and centrally processed and recycled.

[0015] (6) Drying: Dry the product after squeezing and dehydration by heating drying and / or vacuum drying and / or natural drying. The heating drying temperature is 80°C to 180°C and the drying time is 0.1h to 6h. The vacuum drying conditions are 50°C to 100°C, the vacuum degree is -0.01Mpa to -0.10Mpa, and the time is 0.1h to 24h.

[0016] The moisture content of the product after drying is controlled to be no higher than 10%, that is, medium and high density fiberboards that meet the quality requirements of national standards are obtained.

[0017] Furthermore, the agricultural straw raw material in step (1) is wheat straw, corn straw, rice straw or cotton straw.

[0018] Furthermore, in the step (3), a disc refiner or a twin-screw refiner is used to dissociate the pretreated raw material.

[0019] Furthermore, in the step (5), the water extracted by squeezing is collected and then centrally treated by coagulation method, the clear liquid can be recycled to the raw material pretreatment stage, the concentrate can be mixed evenly with the dissociated material to press fiberboard, and can also be used as fertilizer or feed.

[0020] Furthermore, the reinforcing agent in step (4) includes one or more of polyamide epichlorohydrin resin, polyacrylamide, and styrene-butadiene latex; and the water repellent includes one or more of alkyl ketene dimer (AKD) emulsion, paraffin emulsion, rosin emulsion, and styrene-acrylic emulsion.

[0021] Furthermore, the national standards in step (6) are GB / T 11718-2021 "Medium Density Fiberboard" and GB / T31765-2015 "High Density Fiberboard".

[0022] Furthermore, the drying method in step (6) is natural drying, heat drying or vacuum drying, or a combination of these.

[0023] Application of the method as described above in the production of fiberboard.

[0024] The advantages and positive effects achieved by the present invention are:

[0025] 1. The present invention uses agricultural straw as raw material, and by controlling the pretreatment and mechanical dissociation conditions, the fibers are self-adhesive by hydrogen bonds. No "trialdehyde glue" is added during the production process, and the prepared fiberboard releases no formaldehyde, which is beneficial to the health of producers and consumers.

[0026] 2. The present invention uses agricultural straw as raw material to prepare environmentally friendly fiberboard. By controlling the production conditions, the product density can be adjusted to obtain medium-density fiberboard or high-density fiberboard to meet different application occasions. The obtained fiberboard has high strength and good moisture resistance. The static bending strength of medium-density fiberboard can reach 36Mpa, and the static bending strength of high-density fiberboard can reach 48Mpa, which exceeds the corresponding national standards.

[0027] 3. The present invention not only has a simple and easy preparation method, but also has no waste discharge in the production process. Water is recycled in the production process without external discharge, thus achieving "zero discharge" in the production process and improving resource utilization.

[0028] 4. The present invention is not only a green fiberboard manufacturing method with a wide source of raw materials, simple method, and non-toxic and harmless, but also the obtained product can be recycled after being discarded and reused in the manufacture of fiberboard, or used as a raw material for the papermaking industry to make paper and paperboard like waste paper, which meets the requirements of green, low-carbon and sustainable development. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the embodiments. The following embodiments are descriptive rather than restrictive, and the protection scope of the present invention cannot be limited by the following embodiments.

[0030] The various experimental operations involved in the specific embodiments are all routine techniques in the art. For parts not specially annotated in this document, ordinary technicians in the art can implement them by referring to various commonly used reference books, scientific and technological literature or related instructions, manuals, etc. before the filing date of this invention.

[0031] A method for manufacturing recyclable and environmentally friendly fiberboard from agricultural straws, the method comprising the following steps: material preparation→raw material pretreatment→raw material separation→chemical addition→paving and forming→pressing and dehydration→drying→finished product.

[0032] Preferably, the specific steps are as follows:

[0033] (1) Material preparation: Process the agricultural straw raw materials into material segments of 5 mm to 50 mm, and screen out impurities such as mud and sand for later use;

[0034] (2) Raw material pretreatment: Add the prepared raw materials and water into a pressure vessel. The water added is tap water or recycled water from production. Keep the liquid-to-solid ratio between 2:1 and 8:1. Heat to a temperature of 140°C to 180°C and keep it at this temperature for 5 to 120 minutes before discharging the materials.

[0035] (3) Raw material dissociation: Mechanically dissociate the pretreated raw materials to obtain fiber-based materials;

[0036] (4) Chemical addition: In order to further improve the strength and water resistance of the product, the dissociated material is mechanically mixed with a reinforcing agent and a water repellent to obtain a uniformly mixed fiber material; wherein the amount of the reinforcing agent is 0.1% to 20% (relative to the mass of the absolutely dry fiber material), and the amount of the water repellent is 0.1% to 10% (relative to the mass of the absolutely dry fiber material);

[0037] (5) Laying and forming: pouring the mixed fiber material into the mold, laying it evenly, and then squeezing and dehydrating it. The squeezing pressure is 0.1Mpa to 15Mpa, and the squeezing time is 10s to 600s. Dehydration is performed until the mass concentration of the material is 20% to 50%. The water removed by squeezing is collected and centrally processed and recycled.

[0038] (6) Drying: Dry the product after squeezing and dehydration by heating drying and / or vacuum drying and / or natural drying. The heating drying temperature is 80°C to 180°C and the drying time is 0.1h to 6h. The vacuum drying conditions are 50°C to 100°C, the vacuum degree is -0.01Mpa to -0.10Mpa, and the time is 0.1h to 24h.

[0039] The moisture content of the product after drying is controlled to be no higher than 10%, that is, a medium- and high-density fiberboard that meets the quality requirements of national standards is obtained.

[0040] Preferably, the agricultural straw raw material in step (1) is wheat straw, corn straw, rice straw or cotton straw.

[0041] Preferably, in step (3), a disc refiner or a twin-screw refiner is used to dissociate the pretreated raw material.

[0042] Preferably, the water extracted by squeezing in step (5) is collected and centrally treated by coagulation, the clear liquid can be recycled to the raw material pretreatment stage, the concentrate can be mixed evenly with the dissociated material to press fiberboard, and can also be used as fertilizer or feed.

[0043] Preferably, the reinforcing agent in step (4) includes one or more of polyamide epichlorohydrin resin, polyacrylamide, and styrene-butadiene latex; and the water repellent includes one or more of alkyl ketene dimer (AKD) emulsion, paraffin emulsion, rosin emulsion, and styrene-acrylic emulsion.

[0044] Preferably, the national standards in step (6) are GB / T 11718-2021 "Medium Density Fiberboard" and GB / T31765-2015 "High Density Fiberboard".

[0045] Preferably, the drying method in step (6) is natural drying, heat drying or vacuum drying, or a combination of these.

[0046] Application of the method as described above in the production of fiberboard.

[0047] Specifically, the relevant preparation and detection are as follows:

[0048] Example 1

[0049] An environmentally friendly fiberboard made from agricultural straw, the preparation method of which comprises the following steps:

[0050] Corn stalks were cut into sections of about 30 mm, and impurities such as mud and sand were screened out. They were added to a pressure vessel with tap water at a liquid-solid ratio of 5:1, heated to 160°C, and kept at this temperature for 30 minutes before discharging. The mass concentration of the material was adjusted to 15wt%, and a disc refiner was used to perform two-stage mechanical treatment. The first stage controlled the disc grinding gap to be 0.40mm; the second stage controlled the disc grinding gap to be 0.20mm. 3% (relative to the mass of the absolute dry material) of polyamide epichlorohydrin resin and 2% (relative to the mass of the absolute dry material) of alkyl ketene dimer (AKD) emulsion were added to the material treated above under stirring, and the fully mixed material was poured into a mold. After paving evenly, it was squeezed and dehydrated at a pressure of 5.0Mpa and a pressurizing time of 180s. The mass concentration of the material after squeezing was 40wt%. After demoulding by pressing, the product was dried at a vacuum degree of -0.10 MPa and a temperature of 90°C for 12 hours. After drying, the moisture content was controlled within the range of 6% to 10%, and a medium-density environmentally friendly artificial fiberboard of corn straw was obtained. The indicators are shown in Table 1.

[0051] Example 2

[0052] An environmentally friendly fiberboard made from agricultural straw, the preparation method of which comprises the following steps:

[0053] Wheat straw is cut into sections of about 45 mm, and after impurities such as mud and sand are screened out, it is added to a pressure vessel with tap water, with a liquid-solid ratio of 3:1, heated to a temperature of 150°C, and kept at this temperature for 60 minutes before discharging. The mass concentration of the material is adjusted to about 20wt%, and a twin-screw refiner is used to perform mechanical dissociation. 10% (relative to the mass of the absolute dry material) of polyamide epichlorohydrin resin, 5% (relative to the mass of the absolute dry material) of styrene-butadiene latex and 10% (relative to the mass of the absolute dry material) of alkyl ketene dimer (AKD) emulsion are added to the material treated above under stirring. The fully mixed material is poured into a mold, and after evenly paving, two squeeze dehydration processes are performed. The first squeeze pressure is 0.6Mpa, the press time is 120s, and the second squeeze is 10.0Mpa, the press time is 240s, and the mass concentration of the squeezed material is 48wt%. After heating and drying at a temperature of 150°C for 0.5 h, the drying was continued for 3 h at a vacuum degree of -0.08 MPa and a temperature of 70°C. After drying, the moisture content was controlled within the range of 6% to 10%, and a medium-density environmentally friendly wheat straw artificial fiberboard was obtained. The indicators are shown in Table 1.

[0054] Example 3

[0055] An environmentally friendly fiberboard made from agricultural straw, the preparation method of which comprises the following steps:

[0056] The cotton straw is cut into sections of about 20 mm, and impurities such as mud and sand are screened out. It is added to a pressure vessel with tap water at a liquid-solid ratio of 5:1, heated to a temperature of 165°C, and kept at this temperature for 30 minutes before discharging. The mass concentration of the material is adjusted to about 12wt%, and a disc refiner is used to mechanically dissociate it, and the disc grinding gap is controlled to be 0.20mm. To the material treated above, 5% (relative to the mass of the absolute dry material) of polyamide epichlorohydrin resin, 3% (relative to the mass of the absolute dry material) of alkyl ketene dimer emulsion (AKD) and 3% (relative to the mass of the absolute dry material) of styrene-acrylic emulsion are added respectively under stirring. The fully mixed material is poured into a mold, and after paving evenly, it is squeezed and dehydrated at a pressure of 12.0Mpa and a pressurizing time of 240s. The mass concentration of the material after squeezing is 50wt%. After the sample was dried to a moisture content of about 30% under natural conditions, it was vacuum dried for 4 hours at a vacuum degree of -0.06 MPa and a temperature of 80°C. After drying, the moisture content was controlled within the range of 6% to 10%, and a medium-density environmentally friendly artificial fiberboard made of cotton stalks was obtained. The indicators are shown in Table 1.

[0057] Example 4

[0058] An environmentally friendly fiberboard made from agricultural straw, the preparation method of which comprises the following steps:

[0059] Cut corn stalks into sections of about 25 mm, sieve out impurities such as mud and sand, add them to a pressure vessel, add process water extracted by coagulation treatment, and the liquid-solid ratio is 4:1. Insufficient water can be supplemented with tap water, heat to 175 ° C, and keep warm at this temperature for 20 minutes before discharging. Adjust the mass concentration of the material to about 15wt%, use a disc refiner to mechanically dissociate it, and control the disc grinding gap to 0.20mm. Add 8% (relative to the mass of the absolute dry material) of polyamide epichlorohydrin resin, 2% (relative to the mass of the absolute dry material) of polyacrylamide, 3% (relative to the mass of the absolute dry material) of alkyl ketene dimer (AKD) emulsion and 2% of rosin emulsion to the material treated above under stirring. The fully mixed material is poured into the mold, and after being evenly spread, it is squeezed and dehydrated. The first squeezing pressure is 0.8Mpa, and the pressing time is 120s; the second squeezing is 15.0Mpa, and the pressing time is 180s. The mass concentration of the material after squeezing is 48wt%. The water removed by squeezing is collected and coagulated, and the obtained supernatant is recycled. The squeezed sample is vacuum dried for 8h under the conditions of vacuum degree of -0.10Mpa and temperature of 90℃. After drying, the moisture content of the sample is controlled in the range of 6% to 10%, and a high-density environmentally friendly artificial fiberboard made of corn straw is obtained, and the indicators are shown in Table 1.

[0060] Example 5

[0061] An environmentally friendly fiberboard made from agricultural straw, the preparation method of which comprises the following steps:

[0062] Process the wheat straw into 30mm segments, remove impurities such as mud and sand, and add it to a pressure vessel with tap water at a liquid-solid ratio of 5:1. Heat it to 170°C and keep it at this temperature for 30 minutes before discharging. Adjust the mass concentration of the material to about 12wt%, use a disc refiner to mechanically dissociate it, and control the disc refiner gap to 0.20mm. Add 10% (relative to the mass of the absolute dry material) of polyamide epichlorohydrin resin, 3% (relative to the mass of the absolute dry material) of alkyl ketene dimer emulsion and 2% (relative to the mass of the absolute dry material) of paraffin emulsion to the material treated above under stirring. Pour the fully mixed material into the mold, spread it evenly, and then squeeze and dehydrate it. The first squeezing pressure is 0.6Mpa, and the pressing time is 120s; the second squeezing is 12.0Mpa, and the pressing time is 180s. The mass concentration of the material after squeezing is 45wt%. The pressed samples were vacuum dried for 12 h at a vacuum degree of -0.10 MPa and a temperature of 80°C. The moisture content of the samples was controlled within the range of 6% to 10% after drying to obtain a wheat straw high-density environmentally friendly artificial fiberboard, the indicators of which are shown in Table 1.

[0063] Table 1 Properties of the obtained environmentally friendly fiberboard

[0064] Example 1 Example 2 Example 3 Example 4 Example 5 <![CDATA[Density (g / cm 3 )]]> 0.74 0.76 0.77 0.84 0.90 Thickness(mm) 2.5 2.4 2.5 2.2 1.9 Water absorption thickness expansion rate (%) 16 12 17 13 12 Static bending strength (MPa) 31.3 33.0 32.0 40.4 48.0 Flexural modulus (MPa) 3320 3190 2830 4290 5140 <![CDATA[Formaldehyde emission (mg / m 3 )]]> 0 0 0 0 0 Dimensional stability(mm) 0.2 0.1 0.3 0.4 0.3

[0065] The detection methods of the physical indicators in Table 1 refer to the national standard GB / T17657-2013 "Test methods for physical and chemical properties of artificial boards and veneer artificial boards", and the fiberboard prepared in the example is tested for static bending strength, water absorption expansion rate, dimensional stability, formaldehyde release, etc. Referring to the relevant indicators in GB / T 11718-2021 "Medium Density Fiberboard", the artificial fiber boards obtained in Examples 1 to 3 are medium density fiberboards, and their static bending strength and elastic modulus are greater than 27.0 MPa and 2700 MPa of ordinary medium density fiberboards, and can be increased by up to 30%; referring to the relevant indicators in GB / T 31765-2015 "High Density Fiberboard", the artificial fiber boards obtained in Examples 4 and 5 are high-density fiberboards, and their static bending strength and elastic modulus are also greater than 38.0 MPa and 3900 MPa of ordinary high-density fiberboards, and can be increased by up to 35%; the water absorption thickness expansion rate of the obtained medium density fiberboard is much better than the national standard of 45%, and the water absorption thickness expansion rate of the high-density fiberboard is better than the national standard of 16%, which reflects the excellent moisture resistance of the board.

[0066] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments.

Claims

1. A method for manufacturing recyclable environmentally friendly fiberboard from agricultural straw, characterized in that: The method comprises the following steps: material preparation→raw material pretreatment→raw material dissociation→chemical addition→paving and forming→pressing and dehydration→drying→finished product.

2. The method according to claim 1, characterized in that: The specific steps are as follows: (1) Material preparation: Process the agricultural straw raw materials into material segments of 5 mm to 50 mm, and screen out impurities before use; (2) Raw material pretreatment: Add the prepared raw materials and water into a pressure vessel. The water added is tap water or recycled water from production. Keep the liquid-to-solid ratio between 2:1 and 8:

1. Heat to a temperature of 140°C to 180°C and keep it at this temperature for 5 to 120 minutes before discharging the materials. (3) Raw material dissociation: Mechanically dissociate the pretreated raw materials to obtain fiber-based materials; (4) Chemical addition: mechanically mixing the dissociated material with a reinforcing agent and a water repellent to obtain a uniformly mixed fiber material; wherein the reinforcing agent is used in an amount of 0.1% to 20% (relative to the mass of the absolutely dry fiber material), and the water repellent is used in an amount of 0.1% to 10% (relative to the mass of the absolutely dry fiber material); (5) Laying and forming: pouring the mixed fiber material into the mold, laying it evenly, and then squeezing and dehydrating it. The squeezing pressure is 0.1Mpa to 15Mpa, and the squeezing time is 10s to 600s. Dehydration is performed until the mass concentration of the material is 20% to 50%. The water removed by squeezing is collected and centrally processed and recycled. (6) Drying: Dry the product after squeezing and dehydration by heating drying and / or vacuum drying and / or natural drying. The heating drying temperature is 80°C to 180°C and the drying time is 0.1h to 6h. The vacuum drying conditions are 50°C to 100°C, the vacuum degree is -0.01Mpa to -0.10Mpa, and the time is 0.1h to 24h. The moisture content of the product after drying is controlled to be no higher than 10%, that is, medium and high density fiberboards that meet the quality requirements of national standards are obtained.

3. The method according to claim 2, characterized in that: The agricultural straw raw material in step (1) is wheat straw, corn straw, rice straw or cotton straw.

4. The method according to claim 2, characterized in that: In the step (3), a disc refiner or a twin-screw refiner is used to dissociate the pretreated raw materials.

5. The method according to claim 2, characterized in that: In the step (5), the water extracted by squeezing is collected and then centrally treated by coagulation method. The clear liquid can be recycled to the raw material pretreatment stage, and the concentrate can be mixed evenly with the dissociated material to press fiberboard, and can also be used as fertilizer and feed.

6. The method according to claim 2, characterized in that: The reinforcing agent in step (4) includes one or more of polyamide epichlorohydrin resin, polyacrylamide, and styrene-butadiene latex; the water repellent includes one or more of alkyl ketene dimer (AKD) emulsion, paraffin emulsion, rosin emulsion, and styrene-acrylic emulsion.

7. The method according to claim 2, characterized in that: The national standards in step (6) are GB / T11718-2021 "Medium Density Fiberboard" and GB / T 31765-2015 "High Density Fiberboard".

8. The method according to any one of claims 1 to 7, characterized in that: The drying method in step (6) is natural drying, heat drying or vacuum drying, or a combination of these.

9. Use of the method according to any one of claims 1 to 8 in the production of fiberboard.