Glueless straw fiber board and preparation method thereof

Abstract

The application discloses a kind of no glue straw fiber board and preparation method thereof, belong to fiber board production field.The preparation method of the no glue straw fiber board includes: (1) by the component separation of straw raw material to small molecule auxiliary agent containing organic solvent, while component separation, small molecule auxiliary agent is activated to dissolved lignin and hemicellulose in situ;(2) the mixture after separation and activation is evaporated and concentrated, dried, and the activated product of lignin and hemicellulose in organic solvent gradually precipitates on the surface of cellulose fiber solid, and is reassembled with cellulose solid, to obtain activated product self-assembly coated cellulose fiber solid material;(3) the solid material after drying is formed by hot pressing.Compared with prior art, the production process of the no glue straw fiber board of the application adopts one-pot method, without adding any external adhesive, can obtain fiber board with high tensile strength, simple process, environment-friendly and pollution-free.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of straw fiber board production, and particularly provides a glue-free straw fiber board and a preparation method thereof. BACKGROUND

[0002] Straw is the general term for the stem and leaf (ear) parts of mature crops, usually refers to the remaining parts of crops such as wheat, rice, corn, potatoes, oilseeds, cotton, sugarcane and other crops after harvesting seeds, and is a low-cost, multi-purpose renewable biological resource. The main chemical composition content (cellulose, hemicellulose and lignin) of crop straw is similar to that of wood, and it can completely replace wood to manufacture artificial boards.

[0003] In the traditional wood processing method, synthetic resins such as phenolic resin and urea-formaldehyde resin are mostly used as adhesives to manufacture various artificial boards. However, the traditional synthetic resin adhesive contains a large amount of free formaldehyde, which not only causes air pollution, but also has great harm to human health. The glue-free plywood uses composite additives to replace traditional synthetic resin adhesives and other chemical products. During the hot pressing process, the cross-linking between the components of the composite filler raw material itself realizes the bonding effect, and does not contain harmful substances such as formaldehyde. It is a green product that does not pollute the environment and is harmless to the human body.

[0004] The patent document with publication number CN112025906A discloses a straw co-production of fulvic acid glue-free and formaldehyde-free fiber board production process. The invention uses non-wood fibers as raw materials to purify, activate and saccharify all elements through cooking and defibration, and separates to obtain preliminarily activated lignin and purified and activated fibers, as well as hemicellulose, non-wood fiber monosaccharide and fulvic acid. The activated lignin is subjected to deep activation treatment. The fully activated lignin and low molecular monosaccharide are used as curing agent and adhesive to produce glue-free and formaldehyde-free fiber board. Through the full activation of lignin, the comprehensive utilization of straw fiber resources is realized, and the special requirements of glue-free and formaldehyde-free fiber board for high-quality fiber raw materials and high-activity lignin are effectively met; the fulvic acid is obtained by directly extracting and concentrating the cooking dilute black liquor, and the distilled water obtained by evaporating and concentrating the cooking dilute black liquor is recycled.

[0005] The patent document with application number CN201410011629.6 discloses a manufacturing method of bamboo fiber glue-free board, which sequentially includes hot grinding and defibration, drying, laying, pre-pressing, sawing, hot-pressing forming, cooling and edge cutting processes. The hot-pressing temperature is 160℃-230℃, and the hot-pressing pressure is 30kg / cm 2 ~ 85kg / cm 2, hot pressing time 5min~30min, obtain bamboo fiber no glue plate, through the chemical composition of bamboo fiber in the degradation of low molecular weight under high temperature and high pressure, then under the action of temperature and pressure will not degrade the bamboo fiber together to form a high mechanical properties of no glue environmental protection plate. Because of the degradation of bamboo fiber to form a plate, the invention process does not need to provide adhesive, so as to effectively reduce the use of adhesive, reduce the production cost and pollution.

[0006] The above patent relates to the process of producing plate without adhesive, which eliminates the harm of formaldehyde release in the plate and is beneficial to promote the high value utilization of non-wood biomass raw materials. However, the above process involves a relatively complex production process, and the multiple activation and hot grinding process of lignin will produce a large amount of energy consumption, which will greatly increase the production cost.

[0007] The patent document with publication number CN101234504A discloses a flash fiberizing no glue light crop straw fiber composite material manufacturing method, which is to crush the straw raw material into units with a length of 20-30mm, and the moisture content is 50-60%, then put the straw units into a steam explosion processor, and then release the pressure and discharge the material by suddenly opening the valve, adopt two-stage steam explosion treatment process: pretreatment of straw units under lower steam pressure for 5-8min, then treatment under higher steam pressure for 2-5min, then suddenly open the valve to release the pressure and discharge the material, obtain dissociated fibers; plate forming; adopt closed steam hot pressing process, steam pressure 0.6-1.0MPa, steam time 10-30s, after steam, close the plate around, hot pressing temperature 180-190℃, hot pressing time 4-15min. Advantages: no environmental pollution in product production and use process; save the gluing process, reduce production cost; obtain light plate with different thickness.

[0008] The patent document with publication number CN110253708A discloses a high-strength straw no glue plate production process and plate, a straw no glue plate and its production process, including the following steps: 1) extracting fiber: extracting plant fiber from straw, steam explosion and mixing with alkali solution for activation; 2) short rod steam explosion: making straw into short rod, steam explosion and mixing with alkali solution for activation; 3) powder steam explosion: making straw into powder, steam explosion and mixing with alkali solution for activation; 4) pressing plate: mixing and pressing the materials obtained in steps 1) to 3) into plate.

[0009] The above patent adopts a steam explosion process for agricultural straw, which mainly physically decomposes the fiber raw material. It is difficult to achieve a large amount of lignin and hemicellulose dissolution from the raw material through degradation, so it is difficult for lignin and hemicellulose to have good adhesive properties, thereby affecting the mechanical properties of the formed board, resulting in low strength of the board.

[0010] The patent with application number CN202210039932.1 discloses a glue-free fiberboard raw material, its preparation method and glue-free fiberboard, belonging to the technical field of fiberboard. The invention uses carbonized wastewater treated wood chips: first, the carbonized wastewater is rotary evaporated to obtain a distillate and a residue. The distillate contains various acidic substances that can acid-hydrolyze the wood chips. During the high-temperature and high-pressure treatment process, lignin and hemicellulose in the wood chips are degraded into guaiacol and phenolic substances, which can act as adhesives during the preparation of the board. Then, the residue of the carbonized wastewater is added. The residue mainly contains lignin carbonization degradation products, which can further act as adhesives, thereby improving the mechanical properties of the board.

[0011] The patent with application number CN202110487853.2 proposes a glue-free wheat straw board preparation method. The wheat straw is processed into wheat straw particles using physical crushing methods. The active sites embedded in the interior of the particles are released through alkaline treatment. The straw is modified using chloroacetic acid and acryloyl chloride. Green and environmentally friendly hydrogen peroxide is used as a cross-linking polymerization initiator to prepare a board with super-strong mechanical properties.

[0012] The above process uses a chemical method to acid-hydrolyze or alkali-treat the biomass raw material. The above process promotes the adhesive properties of lignin and hemicellulose on the fibers through chemical reactions. However, a large amount of inorganic chemicals are used in this process, and the residual acid or alkali after the reaction remains in the board, making it difficult to recycle and reuse. Secondly, this process produces a large amount of wastewater during production, resulting in a large environmental load.

[0013] In summary, the preparation of glue-free fiberboard generally involves a complex production process. The existing process technology has problems such as high energy consumption, difficulty in recycling chemicals, and large environmental load, greatly increasing the production cost of fiberboard. SUMMARY

[0014] The present invention is aimed at overcoming the shortcomings of the prior art and provides a glue-free straw fiberboard preparation method that is simple and environmentally friendly.

[0015] The technical solution adopted by the present invention to solve its technical problems is: a glue-free straw fiberboard preparation method, comprising:

[0016] (1) The straw raw material is subjected to component separation by an organic solvent containing a small molecule additive, and the small molecule additive activates lignin and hemicellulose in situ during the component separation;

[0017] (2) The mixture after separation and activation is subjected to evaporation concentration and drying to recover the organic solvent, and the activation products of lignin and hemicellulose in the organic solvent gradually precipitate on the surface of the cellulose fiber solid during the evaporation concentration and drying, and reassemble with the cellulose solid to obtain a cellulose fiber solid material coated with the activation products self-assembled;

[0018] (3) The dried solid material is subjected to hot pressing to obtain a glue-free straw fiber board.

[0019] As a preferred embodiment, the straw raw material is a segmental straw with a length of 2-3 cm, and the straw can be rice straw, corn straw, wheat straw, giant reed, bamboo cane, bamboo, and furniture board waste.

[0020] As a preferred embodiment, the mass ratio of the small molecule additive to the organic solvent is 1:(5-15), and particularly preferably 1:(8-12).

[0021] As a preferred embodiment, the small molecule additive is one or a mixture of two or more of ethylene glycol, 1,3-propanediol, 2,3-butanediol, phenol, o-dihydroxybenzene, m-trihydroxybenzene, and m-dihydroxybenzene.

[0022] As a preferred embodiment, the organic solvent is one or a mixture of two or more of formic acid, acetic acid, lactic acid, oxalic acid, methanol, and ethanol.

[0023] As a preferred embodiment, the mass ratio of the straw raw material to the organic solvent is 1:(5-15), and particularly preferably 1:(8-12).

[0024] As a preferred embodiment, the separation and activation temperature in step (1) is 50-180°C, particularly preferably 90-150°C, and most preferably 120-140°C; and the separation and activation time is 0.5-5h, particularly preferably 2-4h, and most preferably 2-3h.

[0025] As a preferred embodiment, step (2) is performed at 70-90°C and 0.01-0.05 MPa for vacuum evaporation concentration and drying. The drying temperature is particularly preferably 80-90°C, and the pressure is particularly preferably 0.01-0.02 MPa.

[0026] As a preferred embodiment, the solid content of the material after drying in step (2) is 50-90%, and particularly preferably 60-70%.

[0027] Preferably, in step (3), the hot-pressing temperature is 120-220℃, particularly preferably 130-180℃; the hot-pressing pressure is 5-40 MPa, particularly preferably 10-20 MPa; and the hot-pressing time is 5-15 min, particularly preferably 5-10 min.

[0028] The straw fiber board prepared by the preparation method has smooth appearance, and the tensile strength can reach 7-10 MPa, and different specifications of fiber boards can be obtained through simple mechanical cutting, which can meet the performance requirements of building materials and furniture boards.

[0029] The present application separates components of straw raw materials by using organic solvents containing small molecule additives, and modifies lignin in situ during the separation process, thereby improving the chemical reaction activity of lignin, and the extracted lignin and hemicellulose degradation products are reassembled with cellulose fibers to form a solid of hemicellulose and lignin degradation modified products coated cellulose fibers, and further hot-pressed to obtain a glue-free straw fiber board, which has the following outstanding advantages compared with the prior art:

[0030] (1) The whole process adopts one-pot method, which plays the bonding role of hemicellulose and lignin and the rigid support role of cellulose fibers, and can obtain a fiber board with high tensile strength without adding any external adhesive;

[0031] (2) After the reaction is completed, no further separation and purification is needed, the operation process is simple, the energy consumption is low, the chemicals are easy to recycle and reuse, and it is green and environmentally friendly;

[0032] (3) The activation of lignin is realized synchronously during the separation process, and the process flow is shortened;

[0033] (4) No wet hot-pressing is needed, and there is no water flow;

[0034] (5) All components are utilized, which provides a new feasible technical scheme for the full utilization of straw. DETAILED DESCRIPTION

[0035] The present application will be further described below in conjunction with specific examples, but not as a limitation to the present application.

[0036] Unless otherwise specified, the content of each component used below is the mass percentage content.

[0037] Example 1:

[0038] 100 g of corn stalks were weighed and thoroughly mixed with 1000 g of 85% formic acid (mass fraction) and 100 g of ethylene glycol. The mixture was reacted at 120 °C for 2 hours. After the reaction, the mixture of all products and the cooking solution was vacuum evaporated and concentrated at 80 °C and 0.01 MPa. The recovered cooking reagent was reused. The dried solid (65% solid content) was hot-pressed to obtain a glue-free fiberboard. The hot-pressing pressure was 15 MPa, the hot-pressing temperature was 140 °C, and the hot-pressing time was 10 min. According to GB / T 17657—2022, the glue-free fiberboard was cut into standard specimens, and its tensile strength was determined to be 8.8 MPa.

[0039] Example 2:

[0040] 100 g of corn stalks were weighed and thoroughly mixed with 1000 g of 85% ethanol (mass fraction) and 100 g of ethylene glycol. The mixture was reacted at 170 °C for 2 hours. After the reaction, the mixture of all products and the cooking solution was vacuum evaporated and concentrated at 80 °C and 0.01 MPa. The recovered cooking reagent was reused. The dried solid (65% solid content) was hot-pressed to obtain glue-free fiberboard. The hot-pressing pressure was 15 MPa, the hot-pressing temperature was 140 °C, and the hot-pressing time was 10 min. According to the requirements of GB / T17657—2022, the glue-free fiberboard was cut into standard specimens, and its tensile strength was determined to be 7.4 MPa.

[0041] Example 3:

[0042] 100 g of *Arundo donax* was weighed and thoroughly mixed with 1000 g of 85% formic acid (mass fraction) and 100 g of ethylene glycol. The mixture was reacted at 140℃ for 2 hours. After the reaction, the mixture of all products and the cooking liquid was vacuum evaporated and concentrated at 80℃ and 0.01 MPa. The recovered cooking reagent was reused. The dried solid (65% solid content) was hot-pressed to obtain a glue-free fiberboard. The hot-pressing pressure was 15 MPa, the hot-pressing temperature was 140℃, and the hot-pressing time was 10 min. According to GB / T 17657—2022, the glue-free fiberboard was cut into standard specimens, and its tensile strength was determined to be 9.2 MPa.

[0043] Example 4:

[0044] 100 g of furniture scraps were weighed and thoroughly mixed with 1000 g of 85% formic acid (mass fraction) and 100 g of ethylene glycol. The mixture was reacted at 140 °C for 2 hours. After the reaction, the mixture of all products and the cooking solution was vacuum evaporated and concentrated at 80 °C and 0.01 MPa. The recovered cooking reagent was reused. The dried solid (65% solid content) was hot-pressed to obtain glue-free fiberboard. The hot-pressing pressure was 15 MPa, the hot-pressing temperature was 140 °C, and the hot-pressing time was 10 min. According to GB / T 17657—2022, the glue-free fiberboard was cut into standard specimens, and its tensile strength was determined to be 9.1 MPa.

[0045] Example 5:

[0046] 100 g of corn stalks were weighed and thoroughly mixed with 1000 g of 85% formic acid (mass fraction) and 100 g of phenol. The mixture was reacted at 120 °C for 2 hours. After the reaction, the mixture of all products and the cooking solution was vacuum evaporated and concentrated at 80 °C and 0.01 MPa. The recovered cooking reagent was reused. The dried solid (65% solid content) was hot-pressed to obtain glue-free fiberboard. The hot-pressing pressure was 15 MPa, the hot-pressing temperature was 150 °C, and the hot-pressing time was 8 minutes. According to the requirements of GB / T17657—2022, the glue-free fiberboard was cut into standard specimens, and its tensile strength was determined to be 9.0 MPa.

[0047] Example 6:

[0048] 100 g of wheat was weighed and thoroughly mixed with 1000 g of 85% formic acid (mass fraction) and 100 g of ethylene glycol. The mixture was reacted at 120 °C for 2 hours. After the reaction, the mixture of all products and the cooking liquid was vacuum evaporated and concentrated at 80 °C and 0.01 MPa. The recovered cooking reagent was reused. The dried solid (65% solid content) was hot-pressed to obtain a glue-free fiberboard. The hot-pressing pressure was 15 MPa, the hot-pressing temperature was 160 °C, and the hot-pressing time was 5 min. According to the requirements of GB / T 17657—2022, the glue-free fiberboard was cut into standard specimens, and its tensile strength was determined to be 8.4 MPa.

[0049] Example 7:

[0050] 100 g of corn stalks were weighed and thoroughly mixed with 1000 g of 85% formic acid (mass fraction) and 80 g of ethylene glycol. The mixture was reacted at 120℃ for 2 hours. After the reaction, the mixture of all products and the cooking solution was vacuum evaporated and concentrated at 80℃ and 0.01 MPa. The recovered cooking reagent was reused. The dried solid (65% solid content) was hot-pressed to obtain glue-free fiberboard. The hot-pressing pressure was 15 MPa, the hot-pressing temperature was 140℃, and the hot-pressing time was 10 min. According to GB / T 17657—2022, the glue-free fiberboard was cut into standard specimens, and its tensile strength was determined to be 7.8 MPa.

[0051] Example 8:

[0052] 100 g of corn stalks were weighed and thoroughly mixed with 1000 g of 85% formic acid (mass fraction) and 100 g of resorcinol. The mixture was reacted at 120℃ for 2 hours. After the reaction, the mixture of all products and the cooking solution was vacuum evaporated and concentrated at 80℃ and 0.01 MPa. The recovered cooking reagent was reused. The dried solid (65% solid content) was hot-pressed to obtain glue-free fiberboard. The hot-pressing pressure was 15 MPa, the hot-pressing temperature was 140℃, and the hot-pressing time was 10 min. According to GB / T 17657—2022, the glue-free fiberboard was cut into standard specimens, and its tensile strength was determined to be 9.0 MPa.

[0053] Example 9:

[0054] 100 g of corn stalks were weighed and thoroughly mixed with 1000 g of 85% formic acid (mass fraction) and 100 g of pyrogallol. The mixture was reacted at 120℃ for 2 hours. After the reaction, the mixture of all products and the cooking solution was vacuum evaporated and concentrated at 80℃ and 0.01 MPa. The recovered cooking reagent was reused. The dried solid (65% solid content) was hot-pressed to obtain glue-free fiberboard. The hot-pressing pressure was 15 MPa, the hot-pressing temperature was 140℃, and the hot-pressing time was 10 min. According to the requirements of GB / T 17657—2022, the glue-free fiberboard was cut into standard specimens, and its tensile strength was determined to be 9.1 MPa.

[0055] Example 10:

[0056] 100 g of corn stalks were weighed and added to 1000 g of 85% formic acid (mass fraction) and 100 g of 1,3-propanediol. The mixture was thoroughly mixed and reacted at 120℃ for 2 hours. After the reaction, the mixture of all products and the cooking liquid was vacuum evaporated and concentrated at 80℃ and 0.01 MPa. The recovered cooking reagent was reused. The dried solid (65% solid content) was hot-pressed to obtain glue-free fiberboard. The hot-pressing pressure was 15 MPa, the hot-pressing temperature was 140℃, and the hot-pressing time was 10 min. According to GB / T 17657—2022, the glue-free fiberboard was cut into standard specimens, and its tensile strength was determined to be 8.3 MPa.

[0057] Example 11:

[0058] 100 g of corn stalks were weighed and added to 1000 g of 85% formic acid (mass fraction) and 100 g of 2,3-butanediol. The mixture was thoroughly mixed and reacted at 120℃ for 2 hours. After the reaction, the mixture of all products and the cooking liquid was vacuum evaporated and concentrated at 80℃ and 0.01 MPa. The recovered cooking reagent was reused. The dried solid (65% solid content) was hot-pressed to obtain a glue-free fiberboard. The hot-pressing pressure was 15 MPa, the hot-pressing temperature was 140℃, and the hot-pressing time was 10 min. According to GB / T 17657—2022, the glue-free fiberboard was cut into standard specimens, and its tensile strength was determined to be 8.1 MPa.

[0059] Example 12:

[0060] 100 g of corn stalks were weighed and thoroughly mixed with 1000 g of 85% formic acid (mass fraction) and 100 g of ethylene glycol. The mixture was reacted at 120℃ for 2 hours. After the reaction, the mixture of all products and the cooking liquid was vacuum evaporated and concentrated at 80℃ and 0.01 MPa. The recovered cooking reagent was reused. The dried solid (60% solid content) was hot-pressed to obtain glue-free fiberboard. The hot-pressing pressure was 15 MPa, the hot-pressing temperature was 140℃, and the hot-pressing time was 10 min. According to GB / T 17657—2022, the glue-free fiberboard was cut into standard specimens, and its tensile strength was determined to be 8.2 MPa.

[0061] Example 13:

[0062] 100 g of corn stalks were weighed and thoroughly mixed with 1000 g of 85% formic acid (mass fraction) and 100 g of ethylene glycol. The mixture was reacted at 120℃ for 2 hours. After the reaction, the mixture of all products and the cooking solution was vacuum evaporated and concentrated at 80℃ and 0.01 MPa. The recovered cooking reagent was reused. The dried solid (70% solid content) was hot-pressed to obtain glue-free fiberboard. The hot-pressing pressure was 15 MPa, the hot-pressing temperature was 140℃, and the hot-pressing time was 10 min. According to GB / T 17657—2022, the glue-free fiberboard was cut into standard specimens, and its tensile strength was determined to be 8.3 MPa.

[0063] Example 14:

[0064] 100 g of corn stalks were weighed and thoroughly mixed with 1000 g of 85% formic acid (mass fraction) and 100 g of ethylene glycol. The mixture was reacted at 120℃ for 2 hours. After the reaction, the mixture of all products and the cooking solution was vacuum evaporated and concentrated at 90℃ and 0.02 MPa. The recovered cooking reagent was reused. The dried solid (65% solid content) was hot-pressed to obtain glue-free fiberboard. The hot-pressing pressure was 15 MPa, the hot-pressing temperature was 140℃, and the hot-pressing time was 10 min. According to GB / T 17657—2022, the glue-free fiberboard was cut into standard specimens, and its tensile strength was determined to be 7.4 MPa.

Claims

1. A method for preparing a glue-free straw fiberboard, characterized in that... The preparation steps are as follows: (1) The straw raw material is separated into components by an organic solvent containing small molecule adjuvants. At the same time as the components are separated, the small molecule adjuvants activate the dissolved lignin and hemicellulose in situ. The small molecule adjuvants are one or a mixture of two or more substances, such as ethylene glycol, 1,3-propanediol, 2,3-butanediol, phenol, catechol, phloroglucinol and resorcinol. The organic solvent is one or a mixture of two or more substances, such as formic acid, acetic acid, lactic acid, oxalic acid, methanol and ethanol. The mass ratio of small molecule adjuvants to organic solvent is 1:(5-15). The separation and activation temperature is 50-180℃ and the separation and activation time is 0.5-5h. (2) The activated mixture is evaporated, concentrated, dried and the organic solvent is recovered. The lignin and hemicellulose activation products in the organic solvent gradually precipitate on the surface of the cellulose fiber solid during the evaporation, concentration and drying process, and reassemble with the cellulose solid to obtain the cellulose fiber solid material with self-assembled activation products. (3) The solid content of the dried solid material is 50-90%. After hot pressing, glue-free straw fiberboard is obtained.

2. The method for preparing glue-free straw fiberboard according to claim 1, characterized in that: The ratio of straw raw material to organic solvent is 1:(5-15).

3. The method for preparing glue-free straw fiberboard according to claim 1 or 2, characterized in that: Step (2) The mixture is concentrated and dried by vacuum evaporation at 70-90℃ and 0.01-0.05Mpa.

4. The method for preparing glue-free straw fiberboard according to claim 3, characterized in that: In step (3), the hot pressing temperature is 120-220℃ and the hot pressing pressure is 5-40MPa.

5. A glue-free straw fiberboard, obtained by the preparation method described in any one of claims 1-4.