Coagulating agent for magnesium inorganic adhesive, preparation method of coagulating agent, modified magnesium inorganic adhesive, preparation method of modified magnesium inorganic adhesive and application of modified magnesium inorganic adhesive in manufacturing of inorganic plywood

Abstract

The invention belongs to the technical field of inorganic adhesives for artificial boards, and particularly discloses a coagulant for a magnesium inorganic adhesive and a preparation method of the coagulant. According to the coagulation accelerator, a chitosan / polyphosphoric acid composite material is used as a coating layer for coating dibasic hydrogen phosphate serving as a coagulation accelerating component, so that slow release of the dibasic hydrogen phosphate is realized to play a coagulation accelerating role, and coagulation accelerating is further realized by virtue of water absorption of chitosan. The invention also discloses a modified magnesium inorganic adhesive and a preparation method thereof, the coagulant is added at a specific hydration stage of a magnesium inorganic adhesive basic system, and the modified adhesive with a proper coagulation accelerating effect is obtained by influencing a hydration process and a hydration product. The setting time is greatly shortened, so that the problem of low plate manufacturing efficiency in a low-temperature environment is solved, meanwhile, the requirement for reasonable operation time required by a plate manufacturing process is met, and the bonding strength reaches an equivalent or even higher level. The invention further discloses application of the modified magnesium inorganic adhesive in manufacturing of plywood.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic adhesives for artificial boards, and specifically relates to a coagulant for magnesium-based inorganic adhesives and a preparation method thereof, a modified magnesium-based inorganic adhesive containing the coagulant and a preparation method thereof, and the use of the modified magnesium-based inorganic adhesive in the production of inorganic plywood. Background Art

[0002] Inorganic adhesives, unlike organic adhesives, are used to bond wood-based panels, making them formaldehyde-free and flame-retardant. Among them, magnesium-based inorganic adhesives (magnesium oxychloride, magnesium oxysulfide, and magnesium phosphate) are gaining popularity in plywood due to their high compatibility with wood.

[0003] Research on the formulation of magnesium-based inorganic adhesives is becoming increasingly mature. For example, Chinese patent CN116574452A discloses a water-resistant magnesium oxychloride inorganic adhesive for plywood, which includes a mixture of magnesium oxide, anhydrous magnesium chloride, water, and a modifier, wherein the modifier is composed of phosphoric acid, nano-silicon dioxide, calcium chloride, isocyanate, and EVA emulsion in a mass ratio of 1:1 to 8:3 to 8:2 to 7.5:5 to 20. The raw materials are extensive, and as an adhesive for plywood, it does not contain organic volatiles such as formaldehyde. The prepared inorganic plywood has good bonding strength and water resistance, and can be widely used as furniture and building materials. For example, Chinese patent CN108237602A discloses an inorganic plywood and a production method thereof. The raw materials include poplar veneer and magnesium oxychloride cement, wherein the magnesium oxychloride cement is a mixture of 55-75 parts of magnesium oxide, 10-30 parts of magnesium chloride, and 5-25 parts of magnesium sulfate, with a water-cement ratio of 0.25-0.50. The production process comprises first dissolving magnesium chloride and magnesium sulfate in water, then adding magnesium oxide and stirring evenly, applying glue by brushing, and then assembling and hot-pressing to obtain the inorganic plywood. The inorganic plywood can achieve true zero formaldehyde emission and has excellent physical and mechanical properties, especially improved water absorption of the magnesium oxychloride cement. The production process is simple and easy to industrialize. The product can be used as furniture material, wall material, packaging material, etc. For example, Chinese patent CN115871067A discloses a moisture-resistant, formaldehyde-free, flame-retardant plywood and a preparation method thereof. The production steps include: veneer manufacturing, spraying of a phosphate system, spraying of a magnesium oxide system, curing and molding, and post-processing; the phosphate system includes phosphate, a setting agent, a waterproofing agent, and water, and the magnesium oxide system includes magnesium oxide, a modifier, and water; this technology uses a secondary slurry coating method to first avoid the two reactants from contacting and reacting prematurely, thereby forming hydration products and affecting the coating uniformity; and adopts a suitable sizing process, pressing and curing parameters, raw material ratio, etc. to improve the interfacial compatibility between the inorganic adhesive and the wood, thereby improving the bonding performance of the inorganic adhesive, ensuring that the adhesive can better penetrate into the veneer and closely contact with the veneer, thereby improving the density of the plywood.

[0004] However, in practical applications, such as when temperatures drop below 0°C in northern winter, the curing time of magnesium-based inorganic adhesives can be too long, affecting the production efficiency of inorganic plywood. Therefore, it is necessary to add appropriate substances to magnesium-based inorganic adhesives to promote their curing, thereby shortening the curing time and improving production efficiency. Summary of the Invention

[0005] To address the problem of long setting times for current magnesium-based inorganic adhesives at low temperatures, which results in low inorganic plywood production efficiency, the inventors of this invention, building on their extensive research into inorganic plywood, have proposed a novel coagulant for magnesium-based inorganic adhesives. This coagulant is particularly suitable for magnesium-based inorganic adhesives in the magnesium oxychloride and magnesium oxysulfide systems. By adding this coagulant to the magnesium-based inorganic adhesive at a specific reaction stage, it effectively promotes the crystallization process within the adhesive by influencing its hydration process, thereby accelerating its coagulant effect.

[0006] The present invention specifically adopts the following technical solutions:

[0007] The first aspect of the present invention provides a coagulant for magnesium inorganic adhesives, which includes a coating layer and a coagulant-promoting component wrapped inside the coating layer; wherein the coating layer is made of a chitosan / polyphosphoric acid composite material, and the coagulant-promoting component is a dihydrogen phosphate.

[0008] Furthermore, the disalt of hydrogen phosphate is selected from any one of dipotassium hydrogen phosphate, disodium hydrogen phosphate, and diammonium hydrogen phosphate, or a mixture of at least two of them in any proportion.

[0009] Furthermore, the aqueous solution of polyphosphate in the chitosan / polyphosphoric acid composite material is alkaline, and may be any one of tripolyphosphate and pyrophosphate.

[0010] The coagulant provided by the present invention uses chitosan, which is structurally stable in the alkaline environment of the magnesium inorganic adhesive, as the main material of the coating layer. With the help of the cross-linking effect of polyphosphate, a composite coating layer material is formed, which provides a basis for coating the dihydrogen phosphate and further achieving sustained release. When it is applied to the magnesium inorganic adhesive, firstly, chitosan contains a large number of polar groups such as hydroxyl and amino groups, which has strong hygroscopicity and can reduce the moisture content in the magnesium inorganic adhesive and promote coagulation; secondly, the slowly released dihydrogen phosphate produces OH after hydrolysis. -, increasing the pH of the system can promote the curing reaction of the magnesium inorganic adhesive in the gel stage of the magnesium inorganic adhesive, thereby achieving a coagulant effect; thirdly, using dihydrogen phosphate as a coagulant component, the free phosphate reacts with magnesium ions and cations in the dihydrogen phosphate to form water-insoluble struvite crystals, which can also promote the coagulation of the adhesive system.

[0011] The second aspect of the present invention provides a method for preparing the above-mentioned coagulant for magnesium-based inorganic adhesive, comprising the steps of:

[0012] S1, dispersing chitosan in an acid solvent to prepare a chitosan solution;

[0013] S2, dissolving dihydrogen phosphate in water to prepare a dihydrogen phosphate aqueous solution;

[0014] S3, dissolving polyphosphate in water to prepare a polyphosphate aqueous solution;

[0015] S4, adding a dihydrogen phosphate aqueous solution to the chitosan solution until the pH of the obtained mixed system is 6 to 6.5, and stopping adding the dihydrogen phosphate aqueous solution;

[0016] S5. Mixing the mixed system with a pH of 6 to 6.5 with a polyphosphate aqueous solution to form a suspension, performing solid-liquid separation, and drying the obtained solid phase to obtain a coagulant for a magnesium inorganic adhesive.

[0017] Among them, the polyphosphate aqueous solution is alkaline.

[0018] It should be noted that steps S1 to S3 above do not specifically limit the order of the preparation process, but are merely used to list and distinguish different preparation processes. That is, there is no specific order requirement for preparing the chitosan solution, the dihydrogen phosphate aqueous solution, and the polyphosphate aqueous solution. Furthermore, steps S3 and S4 do not specifically limit the order of preparation. That is, the polyphosphate aqueous solution can be prepared after obtaining a mixed system with a pH of 6 to 6.5, or it can be prepared in advance.

[0019] In the above preparation process, the alkaline polysaccharide chitosan is first dissolved in an acid solvent to form a homogeneous solution. Subsequently, the acidic chitosan solution is mixed with an alkaline aqueous solution of dihydrogen phosphate. Part of the dihydrogen phosphate is acidified, converting to dihydrogen phosphate or phosphoric acid, and the pH of the chitosan solution increases, forming a gel-like system. Finally, the negatively charged polyphosphate ions in the polyphosphate undergo intramolecular and intermolecular crosslinking with the positively charged protonated amino groups in the chitosan. This crosslinking gelation process allows the two to form a membrane-forming composite membrane structure. Furthermore, the alkaline polyphosphate converts the acidified phosphoric acid and / or dihydrogen phosphate back to the alkaline dihydrogen phosphate, which then coats the dihydrogen phosphate in the composite membrane structure, forming a microcapsule structure containing the dihydrogen phosphate as the content and a chitosan / polyphosphoric acid composite as the coating layer. Furthermore, the alkaline nature of the polyphosphate solution also increases the pH of the chitosan formed in the system, promoting its precipitation and simultaneously performing a coating function.

[0020] Generally, in step S1 , the ratio of chitosan to acid solvent is controlled to be 1 kg to 5 kg:1 L to ensure good dissolution of chitosan.

[0021] Furthermore, the acid solvent is generally selected from dilute acid, such as hydrochloric acid or acetic acid, or a mixture of the two; the volume concentration of the acid solvent is generally controlled to be 1% to 2%.

[0022] Generally, in step S2, the concentration of the dihydrogen phosphate aqueous solution is 0.15 mol / L to 0.45 mol / L.

[0023] Generally, in step S3, the concentration of the polyphosphate aqueous solution is 0.05 mol / L to 0.27 mol / L.

[0024] Furthermore, the volume ratio of the mixed system to the polyphosphate aqueous solution is 1 to 3:1.

[0025] Based on the solubility limitation of the above-mentioned chitosan solution (i.e. the solubility of chitosan in acid solvent), firstly, the role of the polyphosphate aqueous solution is not only to adapt chitosan to form a composite membrane structure, but also to exert an alkaline regulating effect on the acidified dihydrogen phosphate, so as to convert it from phosphoric acid and / or dihydrogen phosphate back to dihydrogen phosphate, so as to be coated. Therefore, the amount of polyphosphate aqueous solution used is more than that in the case of forming only a composite membrane structure. Secondly, the amount of dihydrogen phosphate aqueous solution added is also limited by the chitosan solution to control the appropriate pH of the mixed system of the two, to prevent excessive dihydrogen phosphate from causing the system to be alkaline and causing the direct precipitation of chitosan, thereby failing to form a cross-linked film with the polyphosphate in the polyphosphate in the subsequent process.

[0026] Furthermore, the polyphosphate used to prepare the polyphosphate aqueous solution is selected from any one of tripolyphosphate or pyrophosphate, preferably sodium tripolyphosphate.

[0027] The third aspect of the present invention provides a method for preparing a modified magnesium-based inorganic adhesive based on the above-mentioned coagulant, comprising the steps of: adding the above-mentioned coagulant to the magnesium-based inorganic adhesive base system when the pH of the system reaches 8.5 to 9 during the hydration reaction, and stirring evenly to obtain the modified magnesium-based inorganic adhesive.

[0028] It should be noted that the above pH measurement is not carried out after the magnesium inorganic adhesive base system has been hydrated and solidified to form a gel, but is a pH measurement carried out during the mixing and hydration process of the magnesium inorganic adhesive base system.

[0029] Specifically, the above-mentioned magnesium-based inorganic adhesive base system refers to a conventional magnesium-based inorganic adhesive of a magnesium-oxychloride system, a magnesium-based inorganic adhesive of a magnesium-oxysulfide system, or a mixed magnesium-based inorganic adhesive of the two.

[0030] Generally, the above basic system is obtained by uniformly mixing magnesium oxide, a soluble magnesium source, water and a modifier.

[0031] In the preparation of the above-mentioned magnesium-based inorganic adhesive basic system, the material selection, dosage ratio, etc. of each component are all conventional settings in magnesium-based inorganic adhesives, and the present invention does not impose too many restrictions.

[0032] The soluble magnesium source is specifically magnesium chloride and / or magnesium sulfate, so as to obtain a magnesium inorganic adhesive of a magnesium oxychloride system, a magnesium inorganic adhesive of a magnesium oxysulfide system, or a mixed magnesium inorganic adhesive of the two.

[0033] Generally, the molar ratio of active magnesium oxide, soluble magnesium source and water in magnesium oxide is 5-9:1:7-15.

[0034] Generally, the modifier can be selected from the conventional modifying components used for setting in the magnesium inorganic adhesive system, such as any one of citric acid, sodium citrate, malic acid, sodium malate, sodium silicate, and silica fume, or a mixture of at least two thereof; and the total amount of the modifier is generally controlled to be 0.5% to 2% of the mass of active magnesium oxide in magnesium oxide.

[0035] Specifically, the amount of the coagulant added (by mass) is 1% to 5% of the mass of the active magnesium oxide in the magnesium oxide.

[0036] For the magnesium inorganic adhesive base system, its hydration and condensation process generally includes three stages: sol, gel and crystallization. In the sol stage, magnesium oxide dissolves to form magnesium hydroxide, and magnesium hydroxide dissociates into Mg 2+ and OH -, hydrated magnesium chloride and / or hydrated magnesium sulfate dehydration, etc., so that the Mg in the solution 2+ and OH - As the plasma concentration increases, the pH value of the solution increases. When the gelation process begins, basic magnesium chloride and / or basic magnesium sulfate form colloidal particles. - and Mg 2+ The concentration of magnesium oxide decreases, the pH decreases, and part of the magnesium oxide is coated by the magnesium hydroxide formed by the reaction, which affects the further hydration reaction. At this time, the above-mentioned magnesium inorganic adhesive is added with a coagulant and slowly releases diammonium hydrogen phosphate, which produces OH. - It can effectively replenish the consumption in the system, and phosphate can complex Mg 2+ , promote the dissociation of magnesium hydroxide, and then promote the further formation of basic magnesium chloride and / or basic magnesium sulfate product phase, increase the concentration of gel particles, promote the transformation of gel particles into precipitated crystal phase, accelerate the arrival of the crystallization stage, and thus play a coagulation-promoting role.

[0037] The fourth aspect of the present invention provides a modified magnesium-based inorganic adhesive prepared by the above-mentioned preparation method, which includes a magnesium-based inorganic adhesive base system and the above-mentioned magnesium-based inorganic adhesive coagulant mixed into the base system when the base system is hydrated to a pH of 8.5 to 9.

[0038] Among them, the magnesium inorganic adhesive basic system includes uniformly mixed magnesium oxide, soluble magnesium source, water and modifier.

[0039] A fifth aspect of the present invention provides a use of the modified magnesium-based inorganic adhesive in the production of inorganic plywood, wherein the modified magnesium-based inorganic adhesive is used as the adhesive.

[0040] The method for making inorganic plywood comprises the following steps:

[0041] Q1. Using the modified magnesium inorganic adhesive as an adhesive, apply glue to both sides of the veneer and assemble the veneer to obtain a slab;

[0042] Q2. The slab is at least subjected to cold pressing, curing, and veneering to produce inorganic plywood.

[0043] Specifically, in step Q1, the glue amount of the veneer is 170g / m 2 ~340g / m 2 .

[0044] Generally, in step Q2, the cold pressing pressure is controlled at 1MPa~2MPa, and the time is controlled at 18h~24h; the curing temperature is controlled at 25℃~40℃, and the time is controlled at 7d~15d; the veneer is veneered by hot pressing, and the moisture content is controlled at 8%~15%.

[0045] The above-mentioned processes of gluing, assembling, cold pressing, curing, veneering, etc. can all be operated by referring to existing general technologies.

[0046] The inorganic plywood formed based on the above-mentioned improved magnesium inorganic adhesive has a significantly shortened setting time at 0°C by at least 50% compared to the blank sample based on the general magnesium inorganic adhesive. At the same time, the sustained release property also ensures that the setting time is not too short to cause inconvenience in the board production operation; and the bonding strength remains at a comparable or even higher level. DETAILED DESCRIPTION

[0047] For a better understanding of the present invention, the following examples are further illustrative of the present invention and are only used to explain the content of the present invention, but not to limit the present invention. All similar embodiments listed based on the present invention should fall within the scope of protection.

[0048] Example 1

[0049] This embodiment provides a coagulant for a magnesium-based inorganic adhesive, which is prepared by the following method:

[0050] 1 kg of chitosan is weighed and dissolved in 100 L of 1% (volume concentration) hydrochloric acid solution to obtain a chitosan solution; 100 L of a 0.15 mol / L diammonium hydrogen phosphate aqueous solution is prepared; the diammonium hydrogen phosphate aqueous solution is gradually added to the chitosan solution until the pH of the mixed solution reaches 6; and an equal volume of a 0.05 mol / L sodium tripolyphosphate aqueous solution is added to the mixed solution with a pH of 6. The resulting suspension is stirred, centrifuged, and freeze-dried to obtain a diammonium hydrogen phosphate-chitosan / tripolyphosphate coating, which is a coagulant for a magnesium inorganic adhesive.

[0051] That is, the coagulant for magnesium inorganic adhesive comprises a coating layer made of chitosan / tripolyphosphate composite material and a coagulant component made of diammonium hydrogen phosphate and coated inside the coating layer.

[0052] Example 2

[0053] This embodiment provides a coagulant for a magnesium-based inorganic adhesive, which is prepared by the following method:

[0054] 5 kg of chitosan was weighed and dissolved in 100 L of 2% (volume concentration) acetic acid solution to obtain a chitosan solution; 100 L of a 0.45 mol / L diammonium hydrogen phosphate aqueous solution was prepared; the diammonium hydrogen phosphate aqueous solution was gradually added to the chitosan solution until the pH of the mixed solution reached 6.5; and half the volume of a 0.27 mol / L sodium tripolyphosphate aqueous solution was added to the mixed solution with a pH of 6.5 (i.e., the volume of the sodium tripolyphosphate aqueous solution was 1 / 2 of the volume of the mixed solution). The resulting suspension was stirred, centrifuged, and freeze-dried to obtain a diammonium hydrogen phosphate-chitosan / tripolyphosphate coating, which was a coagulant for a magnesium inorganic adhesive.

[0055] That is, the coagulant for magnesium inorganic adhesive comprises a coating layer made of chitosan / tripolyphosphate composite material and a coagulant component made of diammonium hydrogen phosphate and coated inside the coating layer.

[0056] Example 3

[0057] This embodiment provides a coagulant for a magnesium-based inorganic adhesive, which is prepared by the following method:

[0058] 3 kg of chitosan was weighed and dissolved in 100 L of 1.5% (volume concentration) acetic acid solution to obtain a chitosan solution; 100 L of a 0.3 mol / L diammonium hydrogen phosphate aqueous solution was prepared; the diammonium hydrogen phosphate aqueous solution was gradually added to the chitosan solution until the pH of the mixed solution reached 6.3; and 1 / 3 of the volume of a 0.16 mol / L sodium tripolyphosphate aqueous solution was added to the mixed solution with a pH of 6.3 (i.e., the volume of the sodium tripolyphosphate aqueous solution was 1 / 3 of the volume of the mixed solution). The resulting suspension was stirred, centrifuged, and freeze-dried to obtain a diammonium hydrogen phosphate-chitosan / tripolyphosphate coating, which was a coagulant for a magnesium inorganic adhesive.

[0059] That is, the coagulant for magnesium inorganic adhesive comprises a coating layer made of chitosan / tripolyphosphate composite material and a coagulant component made of diammonium hydrogen phosphate and coated inside the coating layer.

[0060] Example 4

[0061] This embodiment provides a coagulant for a magnesium-based inorganic adhesive, which is prepared by the following method:

[0062] 3 kg of chitosan was weighed and dissolved in 100 L of 1.5% (volume concentration) acetic acid solution to obtain a chitosan solution; 100 L of a 0.25 mol / L disodium hydrogen phosphate aqueous solution was prepared; the disodium hydrogen phosphate aqueous solution was gradually added to the chitosan solution until the pH of the mixed solution reached 6.5; and 1 / 3 of the volume of a 0.16 mol / L sodium pyrophosphate aqueous solution was added to the mixed solution with a pH of 6.5 (i.e., the volume of the sodium pyrophosphate aqueous solution was 1 / 3 of the volume of the mixed solution). The resulting suspension was stirred, centrifuged, and freeze-dried to obtain a disodium hydrogen phosphate-chitosan / pyrophosphate coating, which was a coagulant for a magnesium inorganic adhesive.

[0063] That is, the coagulant for magnesium inorganic adhesive comprises a coating layer made of chitosan / pyrophosphate composite material and a coagulant component coated inside the coating layer and made of disodium hydrogen phosphate.

[0064] In the above-mentioned Examples 1 to 4, when preparing the coating layer with chitosan as the main material, the more mature technology of sodium tripolyphosphate was mainly used, but the present invention is not limited to this. Obviously, other alkaline substances that can provide polyphosphates, such as pyrophosphates or tripolyphosphates containing other cations, can also be used.

[0065] Example 5

[0066] This embodiment provides a modified magnesium-based inorganic adhesive, which is obtained by modifying the magnesium-based inorganic adhesive in Example 1 with a coagulant.

[0067] It is prepared by the following method:

[0068] First, magnesium oxide, magnesium chloride, water, citric acid and sodium silicate are mixed as a magnesium-based inorganic adhesive base system.

[0069] The molar ratio of active magnesium oxide, magnesium chloride, and water in the magnesium oxide is 5:1:7. The amount of citric acid added is 0.5% of the mass of the active magnesium oxide in the magnesium oxide, and the amount of sodium silicate added is 0.5% of the mass of the active magnesium oxide in the magnesium oxide.

[0070] Secondly, after the pH of the above-mentioned magnesium inorganic adhesive base system is 9 during mixing and hydration, the magnesium inorganic adhesive coagulant prepared in Example 1 is added (the addition amount is 5% of the mass of active magnesium oxide in magnesium oxide), and the mixture is quickly stirred to obtain a modified magnesium inorganic adhesive.

[0071] Example 6

[0072] This embodiment provides a modified magnesium-based inorganic adhesive, which is obtained by modifying the magnesium-based inorganic adhesive in Example 2 with a coagulant.

[0073] It is prepared by the following method:

[0074] First, magnesium oxide, magnesium sulfate, water and malic acid are mixed as a magnesium-based inorganic adhesive base system.

[0075] The molar ratio of active magnesium oxide, magnesium sulfate, and water in the magnesium oxide is 9:1:15. The amount of malic acid added is 1% of the mass of the active magnesium oxide in the magnesium oxide.

[0076] Secondly, after the pH of the above-mentioned magnesium inorganic adhesive base system is 8.8 during mixing and hydration, the magnesium inorganic adhesive coagulant prepared in Example 2 is added (the addition amount is 1% of the mass of active magnesium oxide in magnesium oxide), and the mixture is quickly stirred to obtain a modified magnesium inorganic adhesive.

[0077] Example 7

[0078] This embodiment provides a modified magnesium-based inorganic adhesive, which is obtained by modifying the magnesium-based inorganic adhesive in Example 3 with a coagulant.

[0079] It is prepared by the following method:

[0080] First, magnesium oxide, magnesium chloride, water, malic acid and sodium silicate are mixed as a magnesium-based inorganic adhesive base system.

[0081] The molar ratio of active magnesium oxide, magnesium chloride, and water in the magnesium oxide is 7:1:10. The amount of malic acid added is 0.5% of the mass of the active magnesium oxide in the magnesium oxide, and the amount of sodium silicate added is 1.5% of the mass of the active magnesium oxide in the magnesium oxide.

[0082] Secondly, after the pH of the above-mentioned magnesium inorganic adhesive base system is 8.9 during mixing and hydration, the magnesium inorganic adhesive coagulant prepared in Example 3 is added (the addition amount is 3% of the mass of active magnesium oxide in magnesium oxide), and the mixture is quickly stirred to obtain a modified magnesium inorganic adhesive.

[0083] Example 8

[0084] This embodiment provides a modified magnesium-based inorganic adhesive, which is obtained by modifying the magnesium-based inorganic adhesive in Example 4 with a coagulant.

[0085] It is prepared by the following method:

[0086] First, magnesium oxide, magnesium chloride, water, citric acid and sodium silicate are mixed as a magnesium-based inorganic adhesive base system.

[0087] The molar ratio of active magnesium oxide, magnesium chloride, and water in the magnesium oxide is 7:1:10. The amount of malic acid added is 0.5% of the mass of the active magnesium oxide in the magnesium oxide, and the amount of sodium silicate added is 1.5% of the mass of the active magnesium oxide in the magnesium oxide.

[0088] Secondly, after the pH of the above-mentioned magnesium inorganic adhesive base system is 8.7 during mixing and hydration, the magnesium inorganic adhesive coagulant prepared in Example 4 is added (the addition amount is 3% of the mass of active magnesium oxide in magnesium oxide), and the mixture is quickly stirred to obtain a modified magnesium inorganic adhesive.

[0089] Example 9

[0090] This embodiment provides an application of a modified magnesium-based inorganic adhesive in inorganic plywood, that is, the modified magnesium-based inorganic adhesive in Example 5 is used to process and manufacture inorganic plywood.

[0091] It is produced by the following method:

[0092] First, according to 170g / m 2 The modified magnesium-based inorganic adhesive in Example 5 is applied layer by layer to the single board, and the slabs are assembled to obtain slabs.

[0093] Then, the slab was cold pressed at a pressure of 2MPa for 24 hours, cured at 40°C for 15 days, cored, repaired, sanded, and hot pressed to control the veneer moisture content to 8% to produce inorganic plywood.

[0094] Example 10

[0095] This embodiment provides an application of a modified magnesium-based inorganic adhesive in inorganic plywood, that is, the modified magnesium-based inorganic adhesive in Example 6 is used to process and manufacture inorganic plywood.

[0096] It is produced by the following method:

[0097] First, according to 340g / m 2 The modified magnesium-based inorganic adhesive in Example 6 is applied layer by layer to the single board, and the slabs are assembled to obtain slabs.

[0098] Then, the slab was cold pressed at a pressure of 1 MPa for 18 hours, cured at 25°C for 7 days, cored, repaired, sanded, and hot pressed to control the veneer moisture content at 15% to produce inorganic plywood.

[0099] Example 11

[0100] This embodiment provides an application of a modified magnesium-based inorganic adhesive in inorganic plywood, that is, the modified magnesium-based inorganic adhesive in Example 7 is used to process and manufacture inorganic plywood.

[0101] It is produced by the following method:

[0102] First, according to 255g / m 2 The modified magnesium-based inorganic adhesive in Example 7 is applied layer by layer to the single board, and the slabs are assembled to obtain slabs.

[0103] Then, the slab was cold pressed at a pressure of 1.5 MPa for 20 hours, cured at 30°C for 12 days, cored, repaired, sanded, and hot pressed to control the veneer moisture content at 12% to produce inorganic plywood.

[0104] Example 12

[0105] This embodiment provides an application of a modified magnesium-based inorganic adhesive in inorganic plywood, that is, the modified magnesium-based inorganic adhesive in Example 8 is used to process and manufacture inorganic plywood.

[0106] It is produced by the following method:

[0107] First, according to 255g / m 2 The modified magnesium-based inorganic adhesive in Example 8 is applied layer by layer onto the single plate, and the plates are assembled to obtain plate blanks.

[0108] Then, the slab was cold pressed at a pressure of 1.5 MPa for 20 hours, cured at 30°C for 12 days, cored, repaired, sanded, and hot pressed to control the veneer moisture content at 12% to produce inorganic plywood.

[0109] For the coagulant used in the magnesium-based inorganic adhesive described above, the use of polyphosphate and chitosan components during its preparation, as well as their combination, all play a key role in its ability to accelerate coagulability in the magnesium-based inorganic adhesive. Furthermore, the timing of adding the coagulant-modified magnesium-based inorganic adhesive also plays a key role in its ultimate ability to accelerate coagulability. To this end, the following comparative experiments were conducted.

[0110] Comparative Example 1

[0111] This comparative example is intended to illustrate the necessity of using polyphosphate in the preparation process of a coagulant for a magnesium inorganic adhesive.

[0112] The similarities between this comparative example and Example 3 are not described here, and only the differences from Example 3 are described. This comparative example differs from Example 3 in that sodium tripolyphosphate is not added, but an aqueous solution of diammonium hydrogen phosphate is gradually added to the chitosan solution until the pH of the mixed solution reaches 6.3. After the reaction is sufficient, centrifugation and drying are performed to obtain a comparative composite coagulant.

[0113] Comparative Example 2

[0114] This comparative example is intended to illustrate the necessity of chitosan as the main material of the coating layer in the coagulant for magnesium inorganic adhesive.

[0115] The similarities between this comparative example and Example 3 are not described here, and only the differences from Example 3 are described. This comparative example differs from Example 3 in that chitosan is not added, but instead an aqueous solution of diammonium hydrogen phosphate and an aqueous solution of sodium tripolyphosphate are mixed in a volume ratio of 3:1, and after the reaction is sufficient, centrifugation and drying are performed to obtain a comparative composite coagulant.

[0116] Comparative Example 3

[0117] This comparative example is intended to illustrate the effect of the combination mode of chitosan and dihydrogen phosphate on their coagulant-promoting effect.

[0118] The similarities between this comparative example and Example 6 are not described here, and only the differences from Example 6 are described. This comparative example differs from Example 6 in that equal amounts of chitosan and diammonium hydrogen phosphate solids from Example 3 are added to the same magnesium-based inorganic adhesive base system in Example 6 after the pH of the system reaches 8.9 during mixing and hydration to prepare a comparative modified adhesive.

[0119] Comparative Example 4

[0120] This comparative example is intended to illustrate the necessity of the timing of adding a coagulant when modifying a magnesium inorganic adhesive with a coagulant.

[0121] The similarities between this comparative example and Example 6 are not described here, and only the differences from Example 6 are described. The difference between this comparative example and Example 6 is that the coagulant for magnesium-based inorganic adhesive prepared in Example 3 is added and mixed together when preparing the magnesium-based inorganic adhesive base system (that is, added simultaneously with magnesium oxide, magnesium sulfate, water and malic acid), rather than adding it after the pH of the base system changes to 8.9 during mixing and hydration; the rest is as described in Example 6 to prepare a comparative modified adhesive.

[0122] Based on the comparative composite coagulants prepared in the above comparative examples 1 to 2, comparative modified adhesives were prepared respectively by adopting the same preparation method of the modified magnesium inorganic adhesive as in Example 6; and based on the obtained comparative modified adhesives, comparative plywood was prepared respectively by adopting the same inorganic plywood preparation method as in Example 9.

[0123] The bonding strength of the inorganic plywood produced in Examples 7-9, as well as the comparative plywood produced using the comparative composite coagulant in Comparative Examples 1-2 and the comparative modified adhesive in Comparative Examples 3-4, was tested according to Class II bonding strength in GB / T 9846, "Ordinary Plywood." The setting time was calculated as the curing time required for the adhesive to dry naturally after being applied to the veneer surface (at 0°C).

[0124] At the same time, an inorganic plywood was provided as a blank group using the magnesium inorganic adhesive base system in Example 6 as the adhesive and the same manufacturing process as in Example 9.

[0125] The bonding strength of each inorganic plywood and the setting time of the adhesive therein are shown in Table 1 below.

[0126] Table 1 Bonding strength of various plywoods and setting time of adhesives

[0127]

[0128] As can be seen from Table 1, the coagulant for magnesium-based inorganic adhesive provided by the present invention, when used to modify the magnesium-based inorganic adhesive and produce inorganic plywood, maintains at least comparable bond strength, or even significantly improves, compared to inorganic plywood without the coagulant. This is because the addition of the coagulant during the gel phase of hydration of the magnesium-based inorganic adhesive base system, where the slowly released diammonium hydrogen phosphate further promotes the production of more basic magnesium chloride, ultimately forming the strength phase of the adhesive and exhibiting superior bond strength. Furthermore, the setting time of the adhesive is significantly shortened, by at least 50%.

[0129] In comparison, the magnesium inorganic adhesive modified based on the comparative composite coagulant in Comparative Example 1 does not add sodium tripolyphosphate during the preparation process. The added chitosan-diammonium hydrogen phosphate mixture makes the system acidic due to the presence of acetic acid, while the corresponding comparative composite coagulant obtained essentially does not contain alkaline diammonium hydrogen phosphate. Therefore, it has no accelerating effect on the magnesium inorganic gelling agent, resulting in a longer coagulation time of the corresponding adhesive on the surface of the veneer, which is not conducive to the curing and molding of the magnesium inorganic adhesive in winter.

[0130] The magnesium inorganic adhesive modified based on the comparative composite coagulant in Comparative Example 2 has no chitosan added to the system, and the mixed system of sodium tripolyphosphate-diammonium hydrogen phosphate is alkaline. However, the phosphate and ammonium groups are in direct contact with the basic system of the magnesium inorganic adhesive, and a large amount of insoluble particulate matter (struvite crystals) will be quickly formed during stirring, thereby hindering the formation of the main strength phase crystals (518 phase) of the magnesium inorganic adhesive, which ultimately manifests as a decrease in the bonding strength of the board and a poor bonding effect. In addition, due to the above-mentioned excessively rapid crystallization and condensation process, it is not convenient for the construction operation of the board production.

[0131] Based on the comparative modified adhesive in Comparative Example 3, it can be seen that the simple mixture of chitosan and diammonium hydrogen phosphate cannot exert a coagulant effect. This is because chitosan cannot dissolve under alkaline conditions and will exist as solid particles in the adhesive, which has an adverse effect on the bonding strength. Secondly, diammonium hydrogen phosphate loses the slow-release effect of chitosan and dissolves directly in the adhesive, releasing a large amount of OH - It is not conducive to the dissolution of early magnesium oxide in magnesium inorganic adhesives, and shows a slow setting effect. Although these OH - Then, in the gel forming stage, it can promote the formation of basic magnesium sulfate and show a coagulant effect, but for the overall hydration and coagulation process of the magnesium inorganic adhesive, the coagulant effect is limited.

[0132] Based on the comparative modified adhesive in Comparative Example 4, since the coagulant was added too early, the slowly released diammonium hydrogen phosphate would complex Mg in the sol stage of the hydration process of the magnesium inorganic adhesive base system. 2+ , release OH - etc., playing a role in slowing down the setting; but since diammonium hydrogen phosphate plays a role similar to a buffer, it releases OH in the subsequent gel stage. - , which can promote the dissolution of magnesium hydroxide, thereby shortening the gel stage time. However, for magnesium-based inorganic adhesive systems, the gel stage lasts longer than the sol stage, so the final effect is extremely limited and cannot fundamentally solve the problem of low production efficiency caused by the long coagulation time of the board at low temperatures.

[0133] The above-mentioned coagulant for magnesium inorganic adhesive provided by the present invention, through specific material selection and structural design, is mixed and added at a specific hydration stage of the magnesium inorganic adhesive, thereby affecting the hydration process of the magnesium inorganic adhesive, achieving accelerated hydration and coagulation of the magnesium inorganic adhesive at extremely low temperatures, and providing sufficient guarantee for its production efficiency when used as an adhesive for plywood.

[0134] The embodiments used above are only for illustrating and explaining the contents of the present invention and do not constitute any special limitation to the present invention. Any form of modification made without departing from the basic concept of the present invention, as well as obvious modifications derived therefrom, fall within the scope of protection of the present invention.

Claims

1. A coagulant for magnesium inorganic adhesive, characterized in that: It comprises a coating layer and a coagulant-promoting component wrapped inside the coating layer; wherein the coating layer is made of a chitosan / polyphosphoric acid composite material, the aqueous solution of polyphosphate in the chitosan / polyphosphoric acid composite material is alkaline, and the coagulant-promoting component is dihydrogen phosphate.

2. The coagulant for magnesium inorganic adhesive according to claim 1, characterized in that: The disalt of hydrogen phosphate is selected from any one of dipotassium hydrogen phosphate, disodium hydrogen phosphate, and diammonium hydrogen phosphate, or a mixture of at least two of them in any proportion.

3. The coagulant for magnesium-based inorganic adhesive according to claim 1 or 2, characterized in that: The polyphosphate in the chitosan / polyphosphoric acid composite material is selected from any one of tripolyphosphate and pyrophosphate.

4. The method for preparing a coagulant for magnesium-based inorganic adhesive according to any one of claims 1 to 3, wherein: Including steps: Preparation of chitosan solution: dispersing chitosan in an acid solvent to prepare a chitosan solution; Preparation of dihydrogen phosphate aqueous solution; Preparation of polyphosphate aqueous solution; adding the dihydrogen phosphate aqueous solution to the chitosan solution until the pH of the obtained mixed system is 6 to 6.5; A mixed system with a pH of 6 to 6.5 is mixed with the polyphosphate aqueous solution to form a suspension, and the suspension is separated into a solid and liquid phase, and the obtained solid phase is dried to obtain the coagulant for the magnesium inorganic adhesive.

5. The preparation method according to claim 4, characterized in that In the step of preparing the chitosan solution, the ratio of the chitosan to the acid solvent is 1kg to 5kg:1L; The concentration of the dihydrogen phosphate aqueous solution is 0.15 mol / L to 0.45 mol / L; The concentration of the polyphosphate aqueous solution is 0.05 mol / L to 0.27 mol / L; The volume ratio of the mixed system with a pH of 6 to 6.5 to the polyphosphate aqueous solution is 1 to 3:

1.

6. The preparation method according to claim 4 or 5, characterized in that The polyphosphate used to prepare the polyphosphate aqueous solution is selected from any one of tripolyphosphate or pyrophosphate.

7. A modified magnesium inorganic adhesive, characterized in that: It comprises a magnesium inorganic adhesive base system and a coagulant added when the magnesium inorganic adhesive base system is hydrated to a system pH of 8.5 to 9; wherein the coagulant is the coagulant for magnesium inorganic adhesive according to any one of claims 1 to 3.

8. The modified magnesium-based inorganic adhesive according to claim 7, characterized in that: The magnesium-based inorganic adhesive base system includes uniformly mixed magnesium oxide, a soluble magnesium source, water and a modifier; preferably, the soluble magnesium source is selected from any one of magnesium chloride and magnesium sulfate, or a mixture of magnesium chloride and magnesium sulfate in any proportion.

9. The modified magnesium-based inorganic adhesive according to claim 8, characterized in that: The mass of the coagulant is 1% to 5% of the mass of the active magnesium oxide in the magnesium oxide.

10. The method for preparing the modified magnesium-based inorganic adhesive according to any one of claims 7 to 9, characterized in that: The method comprises the following steps: when the magnesium inorganic adhesive base system undergoes hydration reaction and the pH value of the system is 8.5-9, adding the coagulant and mixing them evenly.

11. Use of the modified magnesium-based inorganic adhesive according to any one of claims 7 to 9 in the production of inorganic plywood.

12. The use according to claim 11, characterized in that The sizing amount of the modified magnesium inorganic adhesive on the single board is 170g / m 2 ~340g / m 2 .

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