PROCESS FOR PRODUCING BINDERLESS FORMALDEHYDE-FREE FIBERBOARD AND COPRODUCING FULVIC ACID FROM STRAW

Abstract

A process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw. All-element purification, activation, saccharification and separation are carried out on the non-wood fiber raw material through boiling and defibering to obtain primarily activated lignin, purified and activated fibers, monosaccharides of hemicellulose and non-wood fibers, and fulvic acid. Deep activation is carried out on activated lignin. The binderless formaldehyde-free fiberboard is produced by using sufficiently activated lignin and low-molecular-weight monosaccharides as a hardener and binder. By sufficiently activating the lignin, comprehensive utilization of straw fiber as resources is realized, and the special requirements of binderless formaldehyde-free fiberboard for high-quality fibrous raw material and high-activity lignin are met. The boiled dilute black liquor was subjected to extraction and concentrated to obtain fulvic acid, thereby avoiding pollution caused by pulping and board production. The distilled water obtained by carrying out evaporative concentration on the boiled dilute black liquor is reused.

Claims

1. A process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw, wherein non-wood fibers used as a raw material are subjected to purification, activation, saccharification and separation, and purified cellulose, sufficiently activated lignin, and monosaccharides of hemicellulose and non-wood fibers are used to produce the binderless formaldehyde-free fiberboard; fulvic acid is obtained during the purification, activation and saccharification; the process specifically comprises: a. carrying out purification and activation through boiling, defibering and pulp washing, and carrying out separation to obtain purified and activated cellulose and primary fulvic acid black liquor, wherein the primary fulvic acid black liquor is composed of primarily activated lignin and low-molecular-weight monosaccharides obtained after degradation; b. carrying out deep activation on the primarily activated lignin, wherein the deep activation specifically comprises: carrying out concentration, sulfonation and phenolation on the primary fulvic acid black liquor to obtain fulvic acid black liquor, wherein the fulvic acid black liquor is composed of deeply activated lignin and monosaccharides; and c. producing the binderless formaldehyde-free fiberboard from the purified and activated cellulose by using the deeply activated lignin and monosaccharides as a hardener and binder.

2. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 1, wherein the requirement of the fiberboard for the raw material and the requirement for the fulvic acid product are both met during the purification and activation by carrying out purification, activation and saccharification through boiling by an ammonium sulfite method: non-fibrous components such as pectin, wax, crude protein and crude fat and part of hemicellulose in the raw material are degraded into low-molecular-weight monosaccharides by boiling; and activated lignin is obtained by sulfonation and hydrolysis of lignin, thereby realizing primary separation of the cellulose and the lignin.

3. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 1, wherein the boiling process is carried out at 140-160° C. for 40-60 min, an amount of the ammonium sulfite is 8-15% by weight of the raw material, and the pH is 5-7.

4. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 1, wherein pulping black liquor is subjected to extraction through defibering and pulp washing to realize separation of the cellulose and the lignin, thereby obtaining the purified and activated cellulose and the black liquor of activated lignin and monosaccharides; the specific operations comprise: separating the cellulose from sulfonated lignin and part of native lignin by mechanical refining and defibering; and carrying out extraction on the black liquor by pulp washing to respectively obtain the cellulose and the primarily activated lignin black liquor; the purified and activated cellulose comprises part of native lignin and part of undegraded hemicellulose; and the primarily activated lignin black liquor, namely the primary fulvic acid black liquor, comprises sulfonated lignin, native lignin, low-molecular-weight monosaccharides generated by the degradation of the hemicellulose, and low-molecular-weight monosaccharides generated by the degradation of the non-wood fibers, and has a solid content of 8-10%; wherein the sulfonated lignin is the activated lignin.

5. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 4, wherein the carrying out deep activation on the primarily activated lignin is to carry out deep activation on the sulfonated lignin black liquor obtained after the extraction by pulp washing.

6. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 5, wherein the activation process comprises: carrying out concentration, sulfonation and phenolation on the primary fulvic acid black liquor.

7. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 1, wherein the concentration specifically comprises: carrying out multiple-effect evaporation to obtain fulvic acid thick black liquor having a solid content of 40-60%, wherein the distilled water obtained after the concentration is reused for the boiling and pulp washing.

8. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 1, wherein the sulfonation specifically comprises: carrying out deep sulfonation by utilizing waste heat of the evaporative concentration, wherein the process conditions are as follows: an amount of the ammonium sulfite added is 3-6% by weight of the black liquor, an amount of a catalyst added is 0.005-0.01% by weight of the thick black liquor, the catalyst is at least one of FeSO.sub.4, FeCl.sub.3 and CuSO.sub.4, the temperature is 80-95° C., the holding time is 90-180 min, and stirring is carried out every 1 min.

9. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 1, wherein the phenolation specifically comprises: carrying out phenolation on the thick black liquor obtained after the deep sulfonation, wherein the process conditions are as follows: an amount of a phenolation agent added is 0.01% by weight of the thick black liquor, the temperature is 70-80° C., and the holding time is 60-150 min.

10. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 9, wherein the phenolation agent is tannic acid, gallic acid, catechin, tea polyphenol or ferulic acid.

11. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 5, wherein the fulvic acid black liquor, that is, the deeply activated lignin, is used as the hardener and binder to produce the binderless formaldehyde-free fiberboard, and an amount of the fulvic acid black liquor added is 10-30% by weight of the purified fibrous raw material, based on dry fulvic acid.

12. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 1, wherein part of the activated fulvic acid thick black liquor is used as the binder to produce the binderless formaldehyde-free fiberboard, and the rest is sold directly as a commodity, or sold after being dried.

13. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 1, wherein the fulvic acid is mixed with the purified and activated fibrous raw material in the form of liquid, or the fulvic acid black liquor is dried and then mixed with the purified and activated fibrous raw material in the form of powder.

14. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 1, wherein the purified and activated cellulose and the activated lignin, that is, the fulvic acid, are used as the hardener and binder, a waterproofing agent is added, and post-treatment, comprising paving, pressing, drying, polishing and trimming, is carried out on the fiberboard.

15. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 1, wherein an input-output ratio of the raw material and the product is controlled: 2 tons of raw material produces 1 ton of fulvic acid dry powder and 1 ton of purified cellulose.

16. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 1, wherein the product performance is controlled: a beating degree of the purified fibers after the defibering is 20-30° SR, and the content of the dry fulvic acid effective component is greater than 40%.

17. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 1, wherein a treatment amount of the black liquor waste water is controlled: 1 ton of purified cellulose produces 8-10 tons of fulvic acid dilute black liquor, thereby producing 2 tons of fulvic acid thick black liquor, and the distilled water is reused.

18. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 1, wherein the color of the purified fibers is controlled: the pH is controlled to be less than 7, thereby ensuring the color of the fibers to be dark red.

19. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 1, wherein the non-wood fibers comprise wheat straw and mulberry shoot, crop straw raw materials, bamboo, reed, bagasse, palm oil husk, paper mulberry, wood scraps or branches.

20. The process for producing binderless formaldehyde-free fiberboard and coproducing fulvic acid from straw according to claim 19, wherein the crop straw raw materials comprise cotton straw.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and descriptions thereof are used to explain the present invention, and do not constitute an improper limitation of the present invention.

[0073] FIG. 1 is a top view of a cotton straw binderless formaldehyde-free fiberboard prepared in Embodiment 2 of the present invention, where the thickness of the board is 3 mm;

[0074] FIG. 2 is a side view of the cotton straw binderless formaldehyde-free fiberboard prepared in Embodiment 2 of the present invention;

[0075] FIG. 3 is fulvic acid black liquor prepared in Embodiment 2 of the present invention; and

[0076] FIG. 4 is fulvic acid dry powder prepared in Embodiment 2 of the present invention.

DETAILED DESCRIPTION

[0077] It should be noted that, the following detailed descriptions are all exemplary, and are intended to provide further descriptions of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those usually understood by a person of ordinary skill in the art to which the present invention belongs.

[0078] It should be noted that the terms used herein are merely used for describing specific implementations, and are not intended to limit exemplary implementations of the present invention. As used herein, the singular form is also intended to include the plural form unless the context clearly dictates otherwise. In addition, it should further be understood that, terms “comprise” and/or “include” used in this specification indicate that there are features, steps, operations, devices, components, and/or combinations thereof.

Embodiment 1

[0079] Wheat straw was used as the raw material and pulverized to 2-5 cm for later use. The process included:

[0080] Step one: The raw material was washed.

[0081] Step two: Primary purification, activation and saccharification were carried out through boiling. Add materials according to the following proportions: 2 tons of absolute dry raw material and 200 kg of ammonium sulfite were prepared, water is added according to a solid-to-liquid ratio of 1:5, the mixture was added to a spherical boiler and heated to 120° C., and steam was released. The mixture was heated to 160° C., held for 60 min and discharged. The primary purification, activation and saccharification were completed through the boiling, so that the non-wood fiber components, such as pectin, wax and the like were degraded into low-molecular-weight monosaccharides which were dissolved in the boiling liquor, and part of the hemicellulose was degraded and saccharified and were dissolved in the boiling liquor. Meanwhile, part of the lignin was sulfonated and hydrolyzed, and thus was activated, so that the whole lignin was split and primarily separated from cellulose.

[0082] Step three: The cellulose and the lignin were separated through refining and defibering. The pulp concentration was 30%. The high consistency refiner adopted two-stage grinding. The first grinding gap was 0.3 mm, and the second grinding gap was 0.15 mm. The beating degree was 25° SR. Through the refining and defibering, the whole split lignin was separated from the cellulose. The lignin included not only all the activated sulfonated lignin, but also the unactivated native lignin. Thus, the lignin and the cellulose were no longer bound with each other, but released and separated from each other.

[0083] Step four: Pulp washing was carried out to extract fulvic acid, thereby obtaining fiber pulp and fulvic acid. Counter flow washing was used to extract the fulvic acid dilution. Double-roller squeezers were used, and the counter flow washing was carried out according to 1st, 2nd, 3rd and 4th procedures. That is, in sequence, distilled water was added from the inlet of the 4th squeezer, and the fulvic acid was extracted from the outlet of the 4th squeezer; the distilled water was added from the inlet of the 3rd squeezer, and the fulvic acid was extracted from the outlet of the 3rd squeezer; the distilled water was added from the inlet of the 2nd squeezer, and the fulvic acid was extracted from the outlet of the 2nd squeezer; and the distilled water was added from the inlet of the 1st squeezer, and the fulvic acid was extracted from the outlet of the 1st squeezer. 8 tons of fulvic acid dilute black liquor per ton of pulp was obtained.

[0084] The fulvic acid was extracted through the pulp washing, thereby obtaining the fiber pulp and the fulvic acid black liquor. The fiber pulp contained purified fibers with their original activity, and part of unsulfonated and unhydrolyzed lignin and part of undegraded hemicellulose were taken away. Except the purified cellulose, part of hemicellulose and part of lignin that had been taken away, the other components in the fibrous raw material were all retained in the fulvic acid black liquor. Thus, the fulvic acid black liquor included: activated lignin (ammonium lignosulfonate), native lignin, and monosaccharides obtained after saccharification and degradation of hemicellulose and non-wood fibers. The obtained fibers were light brown in color.

[0085] Step five: Evaporative concentration was carried out. Multiple-effect evaporative concentration was carried out to obtain 2 tons of fulvic acid thick black liquor and 6 tons of distilled water per ton of pulp. The fulvic acid thick black liquor was obtained, and the distilled water was reused.

[0086] Step six: Deep activation was carried out on the fulvic acid.

[0087] First, sulfonation: deep sulfonation was carried out by utilizing waste heat of the evaporative concentration. The process conditions were as follows: an amount of ammonium sulfite added was 4% by weight of the black liquor, an amount of a catalyst FeSO.sub.4 added was 0.01% by weight of the thick black liquor, the temperature was 85° C., the holding time was 120 min, and stirring was carried out every 1 min.

[0088] Second, phenolation: phenolation was carried out on the thick black liquor obtained after the deep sulfonation. The process conditions were as follows: an amount of a phenolation agent added was 0.01% by weight of the thick black liquor, the temperature was 80° C., the holding time was 90 min, and stirring was carried out every minute. The phenolation agent included tannic acid, gallic acid, catechin and tea polyphenol in a ratio of 1:1:1:1.

[0089] Comparison before and after activation of fulvic acid:

TABLE-US-00001 Test item Unit After activation Before activation Fulvic acid (FA) d % 42.67 39.01 Total acidic group d, mmol/g 4.02 1.16 Carboxyl d, mmol/g 3.08 0.52 Phenolic hydroxyl d, mmol/g 0.94 0.64 Water content Mad % 5.6 5.27

[0090] The distilled water was reused for boiling and fulvic acid dilute black liquor extraction. Step seven: 20% of the fulvic acid thick black liquor was directly used for production of binderless formaldehyde-free fiberboard, and the rest (80%) of the fulvic acid thick black liquor was sold as a commodity, or spray-dried to obtain the commodity fulvic acid dry powder.

[0091] Step eight: The board was produced, and indexes were tested.

[0092] Experimental conditions: SYD1 test hot press, produced by Shanghai Liangjun Hydraulic Equipment Co., Ltd., and a flat pressing method were adopted for testing. The wheat straw purified fiber pulp with an absolute dry weight of 1 kg prepared in step four, 200 g of fulvic acid dry powder and 20 g of paraffin were taken and dried until the water content reached 15%, and the mixture was stirred uniformly in a glue stirrer for later use. The high-density fiberboard having a size of 300 mm*300 mm and a thickness of 3 mm was produced. The hot pressing pressure was 3.5 MPa, the hot pressing temperature was 190° C., and the hot pressing time was 9 min.

[0093] Test index:

TABLE-US-00002 Density (g/cm.sup.3) 0.97 Static bending strength (MPa) 38 Elastic modulus (MPa) 3910 Internal bond strength (MPa) 0.96 Thickness expansion rate of 16 water absorbing (%):

[0094] The main indexes meet or exceed the standard for Common Type in GB/T 31765-2015 “High Density Fiberboard”.

Embodiment 2

[0095] Cotton straw was used as the raw material and pulverized to 2-5 cm for later use. The process included:

[0096] Step one: The raw material was washed.

[0097] Step two: Primary purification, activation and saccharification were carried out through boiling. Add materials according to the following proportions: 1 kg of absolute dry raw material and 200 g of ammonium sulfite were prepared, water is added according to a solid-to-liquid ratio of 1:5, the mixture was added to a 15 L electric heating rotary boiler and heated to 120° C., and steam was released. The mixture was heated to 160° C., held for 60 min and discharged. The primary purification and activation were completed through the boiling, so that the non-wood fiber components, such as pectin, wax were degraded into low-molecular-weight monosaccharides which were dissolved in the boiling liquor, and part of the hemicellulose was degraded and saccharified and were dissolved in the boiling liquor. Meanwhile, part of the lignin was sulfonated and hydrolyzed, and thus was activated, so that the whole lignin was split and primarily separated from cellulose.

[0098] Step three: The cellulose and the lignin were separated through refining and defibering. The pulp concentration was 20%, and the refining was carried out in a KRK300 test refiner. The first grinding gap was 0.5 mm, the second grinding gap was 0.25 mm, and the third grinding gap was 0.15 mm. The beating degree was 28° SR. Through the refining and defibering, the whole split lignin was separated from the cellulose. The lignin included not only all the activated sulfonated lignin, but also the unactivated native lignin. Thus, the lignin and the cellulose were no longer bound with each other, but released and separated from each other.

[0099] Step four: Pulp washing was carried out to extract fulvic acid, thereby obtaining fiber pulp and fulvic acid black liquor. The fibers were dark brown.

[0100] The total water consumption during the three stages of refining was controlled within 5 kg, and plus clear water for pulp washing, the total water consumption was controlled within 10 kg.

[0101] The fulvic acid was extracted through the pulp washing, thereby obtaining the fiber pulp and the fulvic acid black liquor. The fiber pulp contained purified fibers with their original activity, and part of lignin and part of undegraded hemicellulose were taken away. Except the purified fibers, part of hemicellulose and part of lignin that had been taken away, the other components in the fibrous raw material were all retained in the fulvic acid black liquor. Thus, the fulvic acid included: activated lignin (ammonium lignosulfonate), native lignin, and monosaccharides obtained after saccharification and degradation of hemicellulose and non-wood fibers.

[0102] Step five: Evaporative concentration was carried out. Evaporation was carried out in an open port at 98° C. until the black liquor was concentrated to 2 L.

[0103] Step six: Deep activation was carried out on the fulvic acid.

[0104] First, sulfonation: deep sulfonation was carried out by utilizing waste heat of the evaporative concentration. The process conditions were as follows: an amount of ammonium sulfite added was 4% by weight of the black liquor, an amount of a catalyst FeSO.sub.4 added was 0.01% by weight of the thick black liquor, the temperature was 85° C., the holding time was 120 min, and stirring was carried out every 1 min.

[0105] Second, phenolation: phenolation was carried out on the thick black liquor obtained after the deep sulfonation. The process conditions were as follows: an amount of a phenolation agent added was 0.01% by weight of the thick black liquor, the temperature was 80° C., the holding time was 90 min, and stirring was carried out every minute. The phenolation agent included tannic acid, gallic acid, catechin and tea polyphenol in a ratio of 1:1:1:1.

[0106] Step seven: The fulvic acid thick black liquor obtained after the deep activation was directly used for production of binderless formaldehyde-free fiberboard.

[0107] Step eight: The board was produced, and indexes were tested.

[0108] Experimental conditions: SYD1 test hot press, produced by Shanghai Liangjun Hydraulic Equipment Co., Ltd., and a flat pressing method were adopted for testing. The cotton straw purified fiber pulp with an absolute dry weight of 1 kg prepared in step four, 400 g of fulvic acid thick black liquor and 20 g of paraffin were taken and dried until the water content reached 15%, and the mixture was stirred uniformly in a glue stirrer for later use. The high-density fiberboard having a size of 300 mm*300 mm and a thickness of 3 mm was produced. The hot pressing pressure was 3.5 MPa, the hot pressing temperature was 190° C., and the hot pressing time was 9 min.

[0109] Test index:

TABLE-US-00003 Density (g/cm.sup.3) 0.98 Static bending strength (MPa) 39 Elastic modulus (MPa) 3976 Internal bond strength (MPa) 0.98 Thickness expansion rate of 16 water absorbing (%):

[0110] The main indexes meet or exceed the standard for Common Type in GB/T 31765-2015 “High Density Fiberboard”.

Embodiment 3

[0111] Cotton straw was used as the raw material.

[0112] Step one to step seven were the same as in Embodiment 2.

[0113] Step eight: The board was produced, and indexes were tested.

[0114] Experimental conditions: SYD1 test hot press, produced by Shanghai Liangjun Hydraulic Equipment Co., Ltd., and a flat pressing method were adopted for testing. The cotton straw purified fiber pulp with an absolute dry weight of 1 kg, 400 g of fulvic acid black liquor and 20 g of paraffin were taken and dried until the water content reached 15%, and the mixture was stirred uniformly in a glue stirrer for later use. The high-density fiberboard having a size of 300 mm*300 mm and a thickness of 3 mm was produced. The hot pressing pressure was 4 MPa, the hot pressing temperature was 200° C., and the hot pressing time was 10 min.

[0115] Test index:

TABLE-US-00004 Density (g/cm.sup.3) 1.03 Static bending strength (MPa) 44 Elastic modulus (MPa) 4120 Internal bond strength (MPa) 1.15 Thickness expansion rate of 14 water absorbing (%):

[0116] The main indexes meet or exceed the standard for Common Type in GB/T 31765-2015 “High Density Fiberboard”.

Embodiment 4

[0117] Cotton straw was used as the raw material.

[0118] Step one to step seven were the same as in Embodiment 2.

[0119] Step eight: The board was produced, and indexes were tested.

[0120] Experimental conditions: SYD1 test hot press, produced by Shanghai Liangjun Hydraulic Equipment Co., Ltd., and a flat pressing method were adopted for testing. The cotton straw purified fiber pulp with an absolute dry weight of 1 kg, 200 g of fulvic acid black liquor and 20 g of paraffin were taken and dried until the water content reached 15%, and the mixture was stirred uniformly in a glue stirrer for later use. The high-density fiberboard having a size of 300 mm*300 mm and a thickness of 3 mm was produced. The hot pressing pressure was 3.5 MPa, the hot pressing temperature was 190° C., and the hot pressing time was 12 min.

[0121] Test index:

TABLE-US-00005 Density (g/cm.sub.3) 0.96 Static bending strength (MPa) 39 Elastic modulus (MPa) 3936 Internal bond strength (MPa) 0.97 Thickness expansion rate of 16 water absorbing (%):

[0122] The main indexes meet or exceed the standard for Common Type in GB/T 31765-2015 “High Density Fiberboard”.

Embodiment 5

[0123] Cotton straw was used as the raw material.

[0124] Step one: The raw material was washed.

[0125] Step two: Primary purification and activation were carried out through boiling. Add materials according to the following proportions: 1 kg of absolute dry raw material and 200 g of ammonium sulfite were prepared, water is added according to a solid-to-liquid ratio of 1:5, the mixture was added to a 15 L boiler and heated to 120° C., and steam was released. The mixture was heated to 160° C., held for 120 min and discharged.

[0126] The measured yield of fulvic acid (on dry basis) was 34%.

[0127] The boiling time was extended from 60 min to 120 min, and the yield of fulvic acid was 34%, which did not reach the target expected value of 40% and did not increase but decrease. Practice had proved that the yield of fiber pulp was decreased from 50% to 45%. This indicated that too long boiling time reduced the yield of fulvic acid and the yield of fiber pulp. In production, the boiling scheme needs to be optimized according to the raw material conditions and product requirements.

Embodiment 6

[0128] Cotton straw was used as the raw material.

[0129] Step one: The raw material was washed.

[0130] Step two: Primary purification and activation were carried out through boiling. Add materials according to the following proportions: 1 kg of absolute dry raw material and 100 g of ammonium sulfite were prepared, water is added according to a solid-to-liquid ratio of 1:5, the mixture was added to a 15 L boiler and heated to 120° C., and steam was released. The mixture was heated to 140° C., held for 60 min and discharged.

[0131] The measured yield of fulvic acid (on dry basis) was 26%.

[0132] This indicated that the boiling intensity was insufficient, and the content of fulvic acid was 26% on dry basis, which was not ideal.

Embodiment 7

[0133] Cotton straw was used as the raw material.

[0134] Step one to step seven were the same as in Embodiment 2.

[0135] Step eight: The board was produced, and indexes were tested.

[0136] Experimental conditions: SYD1 test hot press, produced by Shanghai Liangjun Hydraulic Equipment Co., Ltd., and a flat pressing method were adopted for testing. The cotton straw purified fiber pulp with an absolute dry weight of 1 kg, 0 g of fulvic acid black liquor and 20 g of paraffin were taken and dried until the water content reached 15%, and the mixture was stirred uniformly in a glue stirrer for later use. The high-density fiberboard having a size of 300 mm*300 mm and a thickness of 3 mm was produced. The hot pressing pressure was 3.5 MPa, the hot pressing temperature was 190° C., and the hot pressing time was 9 min.

[0137] Test index:

TABLE-US-00006 Density (g/cm.sup.3) 0.78 Static bending strength (MPa) 26 Elastic modulus (MPa) 2420 Internal bond strength (MPa 0.55 Thickness expansion rate of 26 water absorbing (%):

[0138] The main indexes do not meet the standard for Common Type in GB/T 31765-2015 “High Density Fiberboard”.

Embodiment 8

[0139] The difference from Embodiment 2 is that: in step six, the process conditions for the phenolation were as follows: an amount of a phenolation agent added was 0.01% by weight of the thick black liquor, the temperature was 70° C., the holding time was 150 min, and stirring was carried out every minute.

Embodiment 9

[0140] The difference from Embodiment 2 is that: in step six, the process conditions for the phenolation were as follows: an amount of a phenolation agent added was 0.01% by weight of the thick black liquor, the phenolation agent included tannic acid, gallic acid, catechin, tea polyphenol and ferulic acid in a ratio of 1:1:1:1:1, the temperature was 75° C., the holding time was 100 min, and stirring was carried out every minute.

[0141] It should be finally noted that the foregoing descriptions are merely preferred embodiments of the present invention, but are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for a person of ordinary skill in the art, modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent replacements can be made to some technical features in the technical solutions. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention. The specific implementations of the present invention are described above, but are not intended to limit the protection scope of the present invention. A person skilled in the art should understand that various modifications or deformations may be made without creative efforts based on the technical solutions of the present invention, and such modifications or deformations shall fall within the protection scope of the present invention.