A starch-based particleboard adhesive that cures rapidly at medium and low temperatures and its preparation method

Abstract

This invention discloses a starch-based particleboard adhesive that cures rapidly at medium and low temperatures and its preparation method, belonging to the field of adhesive preparation technology. The starch-based particleboard adhesive of this invention comprises component A and component B; component A includes: 150 parts starch, 200-300 parts water, 20-25 parts concentrated hydrochloric acid, 12-18 parts dilute nitric acid, 25-40 parts sodium hydroxide solution, 6-9 parts initiator, 27-35 parts grafted monomer, and 2-5 parts emulsifier; component B includes: 8-11 parts ethylenediamine, a post-crosslinking agent. This starch-based particleboard adhesive effectively solves the problems of high curing temperature and long curing time in existing starch adhesives. While maintaining a relatively fast curing speed, it can reduce the curing temperature to 105℃, reducing the energy consumption in particleboard production. It can be widely used in the hot-press bonding of particleboard, plywood, fiberboard, and wood blocks.

Description

Technical Field

[0001] This invention relates to a starch-based particleboard adhesive that cures rapidly at medium and low temperatures and its preparation method, belonging to the field of adhesive preparation technology. Background Technology

[0002] In recent years, with rapid economic development, domestic timber consumption has accelerated dramatically, leading to a surge in demand for timber resources. As a product that can fully utilize timber and improve timber resource utilization, engineered wood products have also seen increased demand. However, with the expansion of the adhesive industry, some problems with currently used wood adhesives have become increasingly prominent.

[0003] The traditional adhesives used in the vast majority of commercially available engineered wood products are primarily "three-aldehyde" resin adhesives, namely phenolic resin adhesives, urea-formaldehyde resin adhesives, and melamine-formaldehyde resin adhesives. While these are inexpensive and have relatively good performance, they cause significant pollution and health hazards. Formaldehyde is released during the production process and in the finished engineered wood products, leading to environmental pollution and endangering public health. Therefore, there is a need to develop an environmentally friendly, high-performance, safe, and non-toxic wood adhesive.

[0004] Starch is a natural, biodegradable, environmentally friendly, and renewable material. It is widely available, inexpensive, non-toxic, and pollution-free, making it widely used in processing industries. Compared to commonly available adhesives, using starch instead of synthetic organic products as a raw material for adhesive preparation reduces costs and avoids environmental pollution.

[0005] Currently, most common engineered wood products on the market are produced using a hot-pressing process. Particleboard, as one of the categories, has a relatively short hot-pressing process. It requires adhesives with high curing activity to cure quickly at a certain temperature, as well as low viscosity and certain water resistance. However, traditional starch adhesives have high viscosity, lack thermosetting properties, and have poor water resistance.

[0006] In response to the performance requirements of adhesives for particleboard, the applicant previously developed a thermosetting low-viscosity starch-based adhesive, which significantly improved water resistance and dry strength. However, it still suffers from long curing time, low curing efficiency, and high requirements for hot-pressing curing temperature. Under prolonged high-temperature hot pressing, particleboard is prone to becoming brittle and its mechanical properties decline, making it difficult to promote the wider and deeper application of starch-based adhesives. Summary of the Invention

[0007] [Technical Issues]

[0008] Starch-based adhesives suffer from problems such as long curing time, low curing efficiency, and high curing temperature during hot pressing. This results in long hot pressing times for particleboard, leading to reduced strength and high energy consumption in the production process, which cannot meet the needs of modern particleboard manufacturing.

[0009] [Technical Solution]

[0010] To address the aforementioned problems, this invention provides a starch-based particleboard adhesive that cures rapidly at medium and low temperatures, and its preparation method. This method involves grafting starch with a non-self-crosslinking monomer. No crosslinking curing occurs during the reaction, ensuring the adhesive's low viscosity. Graft modification improves the starch's resistance to retrogradation and introduces highly reactive crosslinkable functional groups into the starch, which enhances the reactivity of the crosslinking reaction and lowers the crosslinking temperature. Furthermore, to improve the effectiveness of the crosslinking reaction, the process is optimized by first subjecting the grafted monomer solution to a polymerization reaction at a lower temperature, generating an adhesive with certain properties. The oligomers with a high degree of polymerization facilitate the formation of high molecular weight grafted molecular chains on starch, making the cross-linking reaction easier, lowering the cross-linking temperature, and resulting in a more uniform distribution of the grafted molecular chains. This improves the dispersion of reaction sites and enhances the cross-linking effect. Subsequently, a post-cross-linking agent is used. When the resulting adhesive is added to the post-cross-linking agent and mixed evenly, it undergoes a rapid cross-linking reaction with the grafted starch at a lower temperature during hot pressing, forming a three-dimensional network structure that provides good thermosetting and water resistance. Furthermore, selecting a highly reactive cross-linking agent makes the cross-linking reaction easier and increases the curing speed.

[0011] Regarding the reactivity, this invention controls five key variables: initiator addition amount, monomer addition amount, reaction time, crosslinking agent addition amount, and crosslinking pH. It also uses a new grafting reaction preparation method, which enables the prepared adhesive to meet the low viscosity requirement. After adding the crosslinking agent, it can have a lower curing temperature and faster curing speed during hot pressing, shortening the hot pressing time and preventing the particleboard from becoming brittle at excessively high temperatures. While ensuring water resistance, thermosetting properties, and mechanical strength, it reduces the energy consumption and cost of particleboard production and improves production efficiency.

[0012] This invention provides precise control over the following key points:

[0013] ①Initiator addition amount

[0014] The amount of initiator added should not be less than 5% of the starch content: adding dilute nitric acid to the initiator solution can improve the initiation effect. Too little initiator will lead to a decrease in monomer grafting effect and a slowdown in curing speed; too much initiator will lead to a decrease in graft chain length, a decrease in crosslinking strength, and a decrease in particleboard strength; adding the initiator in batches will improve the effect.

[0015] ②Graft monomer addition amount

[0016] The amount of graft monomer added should not be less than 18% of the starch content: insufficient graft monomer addition will lead to a decrease in the storage stability, bonding strength and water resistance of starch adhesives;

[0017] ③Reaction time

[0018] The reaction time should not be less than 4 hours: too short or too long a reaction time will affect the grafting effect of monomers on starch, resulting in a decrease in the bonding strength of the adhesive and a decrease in water resistance.

[0019] ④ Crosslinking agent addition amount

[0020] The amount of crosslinking agent added should not be less than 40% of the amount of monomer: too little crosslinking agent will lead to a decrease in the curing activity of the adhesive and a decrease in the final strength.

[0021] ⑤ Crosslinking pH

[0022] The pH of the system during curing and crosslinking should not be lower than 5.5: If the pH is too low during crosslinking, the adhesive will cure slowly, the curing effect will be poor, and it will be impossible to achieve the effect of rapid curing at a lower temperature.

[0023] The first objective of this invention is to provide a starch-based particleboard adhesive that cures rapidly at medium and low temperatures. The starch-based particleboard adhesive comprises component A and component B. Component A, by weight, comprises: 150 parts starch, 200-300 parts water, 20-25 parts concentrated hydrochloric acid, 12-18 parts dilute nitric acid, 25-40 parts sodium hydroxide solution, 6-9 parts cerium ammonium nitrate initiator, 27-35 parts graft monomer, and 2-5 parts emulsifier. Component B, by weight, comprises: 8-11 parts ethylenediamine, a post-crosslinking agent.

[0024] In one embodiment, the starch is any one or a combination of several of the following: corn starch, waxy corn starch, tapioca starch, wheat starch, potato starch, rice starch, and mung bean starch.

[0025] In one embodiment, the medium-low temperature is 90°C to 120°C.

[0026] In one embodiment, the concentrated hydrochloric acid is 12-15 mol / L concentrated hydrochloric acid.

[0027] In one embodiment, the sodium hydroxide solution is a sodium hydroxide solution with a concentration of 10-15 mol / L.

[0028] In one embodiment, the dilute nitric acid is a nitric acid solution of 0.5 to 1 mol / L.

[0029] In one embodiment, the emulsifier is hexadecyltrimethylammonium bromide.

[0030] In one embodiment, the grafting monomer is allyl glycidyl ether.

[0031] A second objective of this invention is to provide a method for preparing the starch-based particleboard adhesive described above, the method comprising the following steps:

[0032] (1) In a reaction vessel, starch and water are mixed to form a starch milk with a concentration of 30-50% by mass based on dry starch. After stirring evenly, the temperature is raised to 50-60℃, and hydrochloric acid diluted to 4-8 mol / L is added for acid hydrolysis. After acid hydrolysis, sodium hydroxide solution is added to adjust the pH to 3-5 and gelatinize to obtain a gelatinized starch milk solution.

[0033] (2) Add the initiator to dilute nitric acid to prepare an initiator solution. Take 10-20% of the initiator solution by volume and add it to the grafted monomer. After mixing evenly, add it to the reactor for prepolymerization. Then, lower the system temperature to room temperature to obtain the prepolymerization solution.

[0034] (3) Cool the gelatinized starch milk solution obtained in step (1) to 50-70°C, add an initiator solution with a volume ratio of 50-80%, and then add sodium hydroxide solution to adjust the pH to 3-5.

[0035] (4) The prepolymer solution obtained in step (2) is added dropwise at a uniform rate to the starch emulsion solution after the initiator is added in (3) to carry out the graft polymerization reaction. After the dropwise addition is completed, the remaining initiator solution is added, sodium hydroxide solution is added, the pH is adjusted to 3-5, and the temperature is kept for 30-45 minutes to obtain the polymerized modified starch-based emulsion.

[0036] (5) Dissolve the emulsifier in water to prepare a 4% to 7% emulsifier solution, add it to the starch-based emulsion obtained in step (4), heat it to 75 to 85°C, and keep it warm for 90 to 120 minutes to obtain the polymerized modified adhesive.

[0037] (6) Cool the polymerized modified adhesive obtained in step (5) to 30-50°C and adjust the pH of the adhesive to 6-8 to obtain starch-based particleboard adhesive.

[0038] (7) Before preparing the particleboard, the starch-based adhesive prepared in step (6) is stirred and mixed evenly with the post-crosslinking agent, and then the particleboard is hot-pressed.

[0039] In one embodiment, the acid hydrolysis time in step (1) is 2 to 4 hours.

[0040] In one embodiment, the gelatinization in step (1) is carried out at a temperature of 60–90°C for 30–60 min.

[0041] In one embodiment, the prepolymerization temperature in step (2) is 50-60°C and the time is 30-45 min.

[0042] In one embodiment, the dripping time in step (4) is controlled to be between 90 and 120 minutes.

[0043] In one embodiment, the temperature of the hot pressing in step (7) is 90°C to 120°C, and the pressure is 6 to 10 MPa.

[0044] A third object of the present invention is the application of the starch-based particleboard adhesive described above in the hot-press bonding of particleboard, plywood, fiberboard, and wood blocks.

[0045] In one embodiment, the hot-press bonding method of the particleboard involves uniformly mixing starch-based particleboard adhesive with particleboard chips, laying them out, and then pressing them into shape under hot-pressing conditions of 90℃~120℃ and 6~10MPa.

[0046] A fourth objective of this invention is to provide a method for reducing the hot-pressing temperature of particleboard, wherein the method uses the starch-based particleboard adhesive described above for hot-pressing bonding of particleboard.

[0047] [Beneficial Effects]

[0048] (1) This invention disrupts the crystalline structure of starch by gelatinizing it, allowing monomer molecules to better enter the spaces between starch molecules, resulting in more monomers reacting with starch and improving reaction efficiency and grafting effect. Prepolymerization of the grafted monomers increases the chain length of the grafted molecules, enhances the degree of polymerization, promotes crosslinking, and improves the activity and strength of the crosslinking reaction. The grafting efficiency is improved by adding initiators in batches. The selected grafted monomers do not undergo self-crosslinking during the reaction or at room temperature after storage, improving storability. After adding the crosslinking agent, hot pressing allows for a crosslinking reaction, forming a three-dimensional network structure, ensuring strong water resistance and bonding strength.

[0049] (2) The grafted monomer and crosslinking agent used in this invention solves the problems of easy curing during the reaction of starch adhesive and the need for curing at high temperature and slow curing speed during use. It further reduces the curing time of starch adhesive to less than 90s and reduces the hot pressing temperature to 105℃, thereby improving the production efficiency of particleboard and reducing energy consumption in the production process.

[0050] (3) The particleboard prepared by starch adhesive in this invention meets the performance requirements of P2 type particleboard in GB / T 4897-2015. It can be soaked in water at 20℃ for 2 hours without damage, and the water absorption thickness expansion rate is 7%, which shows good water resistance. This further improves the application of starch-based adhesive. Detailed Implementation

[0051] The present invention will be further described below with reference to the embodiments. It should be understood that these embodiments are for illustrative purposes only and do not limit the scope of protection of the present invention.

[0052] Determination of adhesive curing time:

[0053] Add 30g of adhesive and 3g of post-crosslinking agent to beakers and mix thoroughly. Transfer 2.0g of the mixture to a test tube, insert a stirring rod into the test tube, place it in a beaker containing boiling water, and start timing. The sample will solidify under stirring. When the stirring rod can no longer stir, stop timing. The measured time is the curing time. Perform three parallel experiments for each sample and take the average value.

[0054] Example 1

[0055] A starch-based particleboard adhesive that cures rapidly at medium and low temperatures, wherein the formulation of the starch-based particleboard adhesive is as follows:

[0056]

[0057] The preparation method of the starch-based particleboard adhesive includes:

[0058] (1) Mix starch and water to make a starch milk with a starch mass fraction of 50%, stir and mix evenly, and then heat to 60°C;

[0059] (2) Prepare a 6.5 mol / L dilute hydrochloric acid solution by dissolving 18 ml of 12 mol / L concentrated hydrochloric acid in it. Add the solution to the starch milk in step (1) and hydrolyze for 2 hours. Then add 10 mol / L sodium hydroxide solution to adjust the pH of the starch milk to 4. Keep it at 80℃ for 30 minutes to gelatinize it.

[0060] (3) Add 7.5g of initiator (cerium ammonium nitrate) to 15ml of dilute nitric acid to prepare an initiator solution. Take 2.5ml of the initiator solution and add it to the grafted monomer (allyl glycidyl ether). After mixing evenly, add it to the reactor, heat it to 55℃, prepolymerize for 30min, and then lower the system temperature to room temperature.

[0061] (4) Cool the gelatinized starch milk obtained in step (2) to 60°C, add 12 ml of the initiator solution prepared in step (3), and then add sodium hydroxide solution to adjust the pH to 4.

[0062] (5) The prepolymerized solution obtained in step (3) is added dropwise at a uniform rate to the starch emulsion solution after the initiator is added in step (4) to carry out the graft polymerization reaction. The dropwise addition time is controlled at 100 min and the reaction temperature is maintained at 60℃. After the dropwise addition is completed, the remaining initiator solution is added, sodium hydroxide solution is added, the pH is adjusted to 4, and the temperature is maintained for 30 min. The polymerized modified starch-based emulsion is obtained.

[0063] (6) Dissolve the emulsifier (hexadecyltrimethylammonium bromide) in water to prepare a 5% emulsifier solution, add it to the starch-based emulsion obtained in step (5), heat it to 82.5°C, and keep it at that temperature for 90 minutes to obtain the polymer-modified adhesive.

[0064] (7) Cool the polymerized modified adhesive obtained in step (6) to 45°C and adjust the pH of the adhesive to 6 to obtain the starch-based adhesive.

[0065] (8) Before preparing the particleboard, add 8.5g of post-crosslinking agent (ethylenediamine) to the adhesive prepared in step (7) above, mix evenly by stirring, and then hot press the particleboard.

[0066] The adhesive product obtained in this embodiment is milky white in appearance, with low viscosity and strong fluidity, meeting the requirements for particleboard. The curing time of the adhesive was measured, and the results showed that the curing time of this starch-based particleboard adhesive was 90 seconds. After hot pressing at 105℃ and 10MPa for 5 minutes, the resulting particleboard exhibited a water absorption thickness expansion rate of 7%, meeting the requirements of the national standard P2 type particleboard.

[0067] Example 2

[0068] A starch-based particleboard adhesive that cures rapidly at medium and low temperatures, wherein the formulation of the starch-based particleboard adhesive is as follows:

[0069]

[0070] The preparation method of the starch-based particleboard adhesive includes:

[0071] (1) Mix starch and water to make a starch milk with a starch mass fraction of 50%, stir and mix evenly, and then heat to 60°C;

[0072] (2) Prepare a 6.5 mol / L dilute hydrochloric acid solution by dissolving 18 ml of 12 mol / L concentrated hydrochloric acid in it. Add the solution to the starch milk in step (1) and hydrolyze for 2 hours. Then add 10 mol / L sodium hydroxide solution to adjust the pH of the starch milk to 4. Keep it at 80℃ for 30 minutes to gelatinize it.

[0073] (3) Add 4g of initiator (cerium ammonium nitrate) to 15ml of dilute nitric acid to prepare an initiator solution. Take 2.5ml of the initiator solution and add it to the grafted monomer (allyl glycidyl ether). After mixing evenly, add it to the reactor, heat it to 55℃, prepolymerize for 30min, and then lower the system temperature to room temperature.

[0074] (4) Cool the gelatinized starch milk obtained in step (2) to 60°C, add 12 ml of the initiator solution prepared in step (3), and then add sodium hydroxide solution to adjust the pH to 4.

[0075] (5) The prepolymerized solution obtained in step (3) is added dropwise at a uniform rate to the starch emulsion solution after the initiator is added in step (4) to carry out the graft polymerization reaction. The dropwise addition time is controlled at 100 min and the reaction temperature is maintained at 60℃. After the dropwise addition is completed, the remaining initiator solution is added, sodium hydroxide solution is added, the pH is adjusted to 4, and the temperature is maintained for 30 min. The polymerized modified starch-based emulsion is obtained.

[0076] (6) Dissolve the emulsifier (hexadecyltrimethylammonium bromide) in water to prepare a 5% emulsifier solution, add it to the starch-based emulsion obtained in step (5), heat it to 82.5°C, and keep it warm for 90 minutes to obtain the polymer-modified adhesive.

[0077] (7) Cool the polymerized modified adhesive obtained in step (6) to 45°C and adjust the pH of the adhesive to 6 to obtain the starch-based adhesive.

[0078] (8) Before preparing the particleboard, add 8.5g of post-crosslinking agent (ethylenediamine) to the adhesive, mix evenly by stirring, and then hot press the particleboard.

[0079] The adhesive product obtained in this embodiment is milky white in appearance, with low viscosity and strong fluidity, meeting the requirements for particleboard. The curing time of the adhesive was measured, and the results showed that the curing time of this starch-based particleboard adhesive was 210 s. After hot pressing at 105℃ and 10 MPa for 5 minutes, the resulting particleboard had a water absorption thickness expansion rate of 17%, which does not meet the requirements of the national standard P2 type particleboard.

[0080] Examples 1 and 2 demonstrate the effect of initiator addition on adhesive viscosity. The results show that insufficient initiator leads to poor initiation effect, resulting in poor grafting effect, affecting the curing performance of the adhesive, and ultimately impacting the strength and water resistance of the particleboard.

[0081] Example 3

[0082] A starch-based particleboard adhesive that cures rapidly at medium and low temperatures, wherein the formulation of the starch-based particleboard adhesive is as follows:

[0083]

[0084] The preparation method of the starch-based particleboard adhesive includes:

[0085] (1) Mix starch and water to make a starch milk with a starch mass fraction of 50%, stir and mix evenly, and then heat to 60°C;

[0086] (2) Prepare a 6.5 mol / L dilute hydrochloric acid solution by dissolving 18 ml of 12 mol / L concentrated hydrochloric acid in it. Add the solution to the starch milk in step (1) and hydrolyze for 2 hours. Then add 10 mol / L sodium hydroxide solution to adjust the pH of the starch milk to 4. Keep it at 80℃ for 30 minutes to gelatinize it.

[0087] (3) Add 7.5g of initiator (ammonium persulfate) to 15ml of dilute nitric acid to prepare an initiator solution. Take 2.5ml of the initiator solution and add it to the grafted monomer (allyl glycidyl ether). After mixing evenly, add it to the reactor, heat it to 55℃, prepolymerize for 30min, and then lower the system temperature to room temperature.

[0088] (4) Cool the gelatinized starch milk obtained in step (2) to 60°C, add 12 ml of the initiator solution prepared in step (3), and then add sodium hydroxide solution to adjust the pH to 4.

[0089] (5) The prepolymerized solution obtained in step (3) is added dropwise at a uniform rate to the starch emulsion solution after the initiator is added in step (4) to carry out the graft polymerization reaction. The dropwise addition time is controlled at 100 min and the reaction temperature is maintained at 60℃. After the dropwise addition is completed, the remaining initiator solution is added, sodium hydroxide solution is added, the pH is adjusted to 4, and the temperature is maintained for 30 min. The polymerized modified starch-based emulsion is obtained.

[0090] (6) Dissolve the emulsifier (hexadecyltrimethylammonium bromide) in water to prepare a 5% emulsifier solution, add it to the starch-based emulsion obtained in step (5), heat it to 82.5°C, and keep it at that temperature for 90 minutes to obtain the polymer-modified adhesive.

[0091] (7) Cool the polymerized modified adhesive obtained in step (6) to 45°C and adjust the pH of the adhesive to 6 to obtain the starch-based adhesive.

[0092] (8) Before preparing the particleboard, add 8.5g of post-crosslinking agent (ethylenediamine) to the adhesive, mix evenly by stirring, and then hot press the particleboard.

[0093] The adhesive product obtained in this embodiment is milky white in appearance, has low viscosity, and strong fluidity, meeting the requirements for particleboard. The curing time of the adhesive was measured, and the results showed that the curing time of this starch-based particleboard adhesive was 220 seconds. After hot pressing at 105℃ and 10MPa for 5 minutes, the resulting particleboard disintegrated when soaked in water, failing to meet the requirements of the national standard P2 type particleboard.

[0094] Examples 1 and 3 demonstrate the effect of initiator type on adhesive curing time. The results show that using cerium ammonium nitrate initiator at a reaction temperature of 60°C results in better grafting of monomer and starch, and the prepared adhesive has good curing performance, meeting the requirements for rapid curing of particleboard adhesive. However, starch adhesive prepared by using ammonium persulfate initiator for monomer grafting has poor grafting effect, resulting in poor curing performance, longer curing time under hot pressing at 105°C, low curing efficiency, and poor water resistance, which cannot meet the requirements for particleboard adhesive.

[0095] Example 4

[0096] A starch-based particleboard adhesive that cures rapidly at medium and low temperatures, wherein the formulation of the starch-based particleboard adhesive is as follows:

[0097]

[0098]

[0099] The preparation method of the starch-based particleboard adhesive includes:

[0100] (1) Mix starch and water to make a starch milk with a starch mass fraction of 50%, stir and mix evenly, and then heat to 60°C;

[0101] (2) Prepare a 6.5 mol / L dilute hydrochloric acid solution by dissolving 18 ml of 12 mol / L concentrated hydrochloric acid in it. Add the solution to the starch milk in step (1) and hydrolyze for 2 hours. Then add 10 mol / L sodium hydroxide solution to adjust the pH of the starch milk to 4. Keep it at 80℃ for 30 minutes to gelatinize it.

[0102] (3) Add 7.5g of initiator (cerium ammonium nitrate) to 15ml of dilute nitric acid to prepare an initiator solution. Take 2.5ml of the initiator solution and add it to the grafted monomer (allyl glycidyl ether). After mixing evenly, add it to the reactor, heat it to 55℃, prepolymerize for 30min, and then lower the system temperature to room temperature.

[0103] (4) Cool the gelatinized starch milk obtained in step (2) to 60°C, add 12 ml of the initiator solution prepared in step (3), and then add sodium hydroxide solution to adjust the pH to 4.

[0104] (5) The prepolymerized solution obtained in step (3) is added dropwise at a uniform rate to the starch emulsion solution after the initiator is added in step (4) to carry out the graft polymerization reaction. The dropwise addition time is controlled at 100 min and the reaction temperature is maintained at 60℃. After the dropwise addition is completed, the remaining initiator solution is added, sodium hydroxide solution is added, the pH is adjusted to 4, and the temperature is maintained for 30 min. The polymerized modified starch-based emulsion is obtained.

[0105] (6) Dissolve the emulsifier (hexadecyltrimethylammonium bromide) in water to prepare a 5% emulsifier solution, add it to the starch-based emulsion obtained in step (5), heat it to 82.5°C, and keep it at that temperature for 90 minutes to obtain the polymer-modified adhesive.

[0106] (7) Cool the polymerized modified adhesive obtained in step (6) to 45°C and adjust the pH of the adhesive to 6 to obtain the starch-based adhesive.

[0107] (8) Before preparing the particleboard, add 8.5g of post-crosslinking agent (ethylenediamine) to the adhesive prepared in step (7) above, mix evenly by stirring, and then hot press the particleboard.

[0108] The adhesive product obtained in this embodiment is milky white in appearance, has low viscosity, and strong fluidity, meeting the requirements for particleboard. The curing time of the adhesive was measured, and the results showed that the curing time of this starch-based particleboard adhesive was 190 seconds. After hot pressing at 105℃ and 10MPa for 5 minutes, the resulting particleboard had a water absorption thickness expansion rate of 13%, which does not meet the requirements of the national standard P2 type particleboard.

[0109] Examples 1 and 4 demonstrate the effect of graft monomer addition on the curing performance of the adhesive. The data results show that if the amount of graft monomer added is too small, the amount of monomer grafted onto the starch is small, resulting in too few crosslinkable groups on the starch adhesive, which affects the curing performance of the adhesive and ultimately reduces the strength and water resistance of the particleboard.

[0110] Example 5

[0111] A starch-based particleboard adhesive that cures rapidly at medium and low temperatures, wherein the formulation of the starch-based particleboard adhesive is as follows:

[0112]

[0113] The preparation method of the starch-based particleboard adhesive includes:

[0114] (1) Mix starch and water to make a starch milk with a starch mass fraction of 50%, stir and mix evenly, and then heat to 60°C;

[0115] (2) Prepare a 6.5 mol / L dilute hydrochloric acid solution by dissolving 18 ml of 12 mol / L concentrated hydrochloric acid in it. Add the solution to the starch milk in step (1) and hydrolyze for 2 hours. Then add 10 mol / L sodium hydroxide solution to adjust the pH of the starch milk to 4. Keep it at 80℃ for 30 minutes to gelatinize it.

[0116] (3) Add 7.5g of initiator (cerium ammonium nitrate) to 15ml of dilute nitric acid to prepare an initiator solution. Take 2.5ml of the initiator solution and add it to the grafted monomer (ethylene glycol dimethacrylate). After mixing evenly, add it to the reactor, heat it to 55℃, prepolymerize for 30min, and then lower the system temperature to room temperature.

[0117] (4) Cool the gelatinized starch milk obtained in step (2) to 60°C, add 12 ml of the initiator solution prepared in step (3), and then add sodium hydroxide solution to adjust the pH to 4.

[0118] (5) The prepolymerized solution obtained in step (3) is added dropwise at a uniform rate to the starch emulsion solution after the initiator is added in step (4) to carry out the graft polymerization reaction. The dropwise addition time is controlled at 100 min and the reaction temperature is maintained at 60℃. After the dropwise addition is completed, the remaining initiator solution is added, sodium hydroxide solution is added, the pH is adjusted to 4, and the temperature is maintained for 30 min. The polymerized modified starch-based emulsion is obtained.

[0119] (6) Dissolve the emulsifier (hexadecyltrimethylammonium bromide) in water to prepare a 5% emulsifier solution, add it to the starch-based emulsion obtained in step (5), heat it to 82.5°C, and keep it at that temperature for 90 minutes to obtain the polymer-modified adhesive.

[0120] (7) Cool the polymerized modified adhesive obtained in step (6) to 45°C and adjust the pH of the adhesive to 6 to obtain the starch-based adhesive.

[0121] (8) Before preparing the particleboard, add 8.5g of post-crosslinking agent (ethylenediamine) to the adhesive prepared in step (7) above, mix evenly by stirring, and then hot press the particleboard.

[0122] The adhesive product obtained in this embodiment is milky white in appearance, has low viscosity, and strong fluidity, meeting the requirements for particleboard. The curing time of the adhesive was measured, and the results showed that the curing time of this starch-based particleboard adhesive was 180 seconds. After hot pressing at 105℃ and 10MPa for 5 minutes, the resulting particleboard had a water absorption thickness expansion rate of 16%, which does not meet the requirements of the national standard P2 type particleboard.

[0123] Examples 1 and 5 demonstrate the effect of grafted monomers on the curing time of adhesives. Adhesives prepared using allyl glycidyl ether in combination with ethylenediamine at a hot-pressing temperature of 105°C have a shorter curing time, meeting the requirements for rapid curing of particleboard adhesives. In contrast, adhesives prepared using ethylene glycol dimethacrylate in combination with ethylenediamine have a longer curing time at 105°C, resulting in lower curing efficiency and poor water resistance, failing to meet the requirements for particleboard adhesives.

[0124] Example 6

[0125] A starch-based particleboard adhesive that cures rapidly at medium and low temperatures, wherein the formulation of the starch-based particleboard adhesive is as follows:

[0126]

[0127] The preparation method of the starch-based particleboard adhesive includes:

[0128] (1) Mix starch and water to make a starch milk with a starch mass fraction of 50%, stir and mix evenly, and then heat to 60°C;

[0129] (2) Prepare a 6.5 mol / L dilute hydrochloric acid solution by dissolving 18 ml of 12 mol / L concentrated hydrochloric acid in it. Add the solution to the starch milk in step (1) and hydrolyze for 2 hours. Then add 10 mol / L sodium hydroxide solution to adjust the pH of the starch milk to 4. Keep it at 80℃ for 30 minutes to gelatinize it.

[0130] (3) Add 7.5g of initiator (cerium ammonium nitrate) to 15ml of dilute nitric acid to prepare an initiator solution. Take 2.5ml of the initiator solution and add it to the grafted monomer (allyl glycidyl ether). After mixing evenly, add it to the reactor, heat it to 55℃, prepolymerize for 30min, and then lower the system temperature to room temperature.

[0131] (4) Cool the gelatinized starch milk obtained in step (2) to 60°C, add 12 ml of the initiator solution prepared in step (3), and then add sodium hydroxide solution to adjust the pH to 4.

[0132] (5) The prepolymerized solution obtained in step (3) is added dropwise at a uniform rate to the starch emulsion solution after the initiator is added in step (4) to carry out the graft polymerization reaction. The dropwise addition time is controlled at 60 min and the reaction temperature is maintained at 60℃. After the dropwise addition is completed, the remaining initiator solution is added, sodium hydroxide solution is added, the pH is adjusted to 4, and the temperature is maintained for 20 min. The polymerized modified starch-based emulsion is obtained.

[0133] (6) Dissolve the emulsifier (hexadecyltrimethylammonium bromide) in water to prepare a 5% emulsifier solution, add it to the starch-based emulsion obtained in step (5), heat it to 82.5°C, and keep it at that temperature for 90 minutes to obtain the polymer-modified adhesive.

[0134] (7) Cool the polymerized modified adhesive obtained in step (6) to 45°C and adjust the pH of the adhesive to 6 to obtain the starch-based adhesive.

[0135] (8) Before preparing the particleboard, add 8.5g of post-crosslinking agent (ethylenediamine) to the adhesive prepared in step (7) above, mix evenly by stirring, and then hot press the particleboard.

[0136] The adhesive product obtained in this embodiment is milky white in appearance, has low viscosity, and strong fluidity, meeting the requirements for particleboard. The curing time of the adhesive was measured, and the results showed that the curing time of this starch-based particleboard adhesive was 260 seconds. After hot pressing at 105℃ and 10MPa for 5 minutes, the resulting particleboard had a water absorption thickness expansion rate of 19%, which does not meet the requirements of the national standard P2 type particleboard.

[0137] Examples 1 and 6 demonstrate the effect of reaction time on the curing time of the adhesive. The results show that reducing the polymerization reaction time of monomer grafting leads to a decrease in the grafting rate of monomers on starch, thereby affecting the effect and rate of crosslinking reaction and resulting in a longer curing time.

[0138] Example 7

[0139] Formulation (mass / g): A starch-based particleboard adhesive that cures rapidly at medium and low temperatures, wherein the formulation of the starch-based particleboard adhesive is as follows:

[0140]

[0141]

[0142] The preparation method of the starch-based particleboard adhesive includes:

[0143] (1) Mix starch and water to make a starch milk with a starch mass fraction of 50%, stir and mix evenly, and then heat to 60°C;

[0144] (2) Prepare a 6.5 mol / L dilute hydrochloric acid solution by dissolving 18 ml of 12 mol / L concentrated hydrochloric acid in it. Add the solution to the starch milk in step (1) and hydrolyze for 2 hours. Then add 10 mol / L sodium hydroxide solution to adjust the pH of the starch milk to 4. Keep it at 80℃ for 30 minutes to gelatinize it.

[0145] (3) Add 7.5g of initiator (cerium ammonium nitrate) to 15ml of dilute nitric acid to prepare an initiator solution. Take 2.5ml of the initiator solution and add it to the grafted monomer (allyl glycidyl ether). After mixing evenly, add it to the reactor, heat it to 55℃, prepolymerize for 30min, and then lower the system temperature to room temperature.

[0146] (4) Cool the gelatinized starch milk obtained in step (2) to 60°C, add 12 ml of the initiator solution prepared in step (3), and then add sodium hydroxide solution to adjust the pH to 4.

[0147] (5) The prepolymerized solution obtained in step (3) is added dropwise at a uniform rate to the starch emulsion solution after the initiator is added in step (4) to carry out the graft polymerization reaction. The dropwise addition time is controlled at 100 min and the reaction temperature is maintained at 60℃. After the dropwise addition is completed, the remaining initiator solution is added, sodium hydroxide solution is added, the pH is adjusted to 4, and the temperature is maintained for 30 min. The polymerized modified starch-based emulsion is obtained.

[0148] (6) Dissolve the emulsifier (hexadecyltrimethylammonium bromide) in water to prepare a 5% emulsifier solution, add it to the starch-based emulsion obtained in step (5), heat it to 82.5°C, and keep it at that temperature for 90 minutes to obtain the polymer-modified adhesive.

[0149] (7) Cool the polymerized modified adhesive obtained in step (6) to 45°C and adjust the pH of the adhesive to 6 to obtain the starch-based adhesive.

[0150] (8) No post-crosslinking agent is added before the particleboard is prepared, and the particleboard is directly hot-pressed.

[0151] The adhesive product obtained in this embodiment is milky white in appearance, has low viscosity, and strong fluidity, meeting the requirements for particleboard. The determination of the adhesive's curing time showed that this starch-based particleboard adhesive could not cure and did not meet the requirements for particleboard use.

[0152] Example 8

[0153] A starch-based particleboard adhesive that cures rapidly at medium and low temperatures, wherein the formulation of the starch-based particleboard adhesive is as follows:

[0154]

[0155]

[0156] The preparation method of the starch-based particleboard adhesive includes:

[0157] (1) Mix starch and water to make a starch milk with a starch mass fraction of 50%, stir and mix evenly, and then heat to 60°C;

[0158] (2) Prepare a 6.5 mol / L dilute hydrochloric acid solution by dissolving 18 ml of 12 mol / L concentrated hydrochloric acid in it. Add the solution to the starch milk in step (1) and hydrolyze for 2 hours. Then add 10 mol / L sodium hydroxide solution to adjust the pH of the starch milk to 4. Keep it at 80℃ for 30 minutes to gelatinize it.

[0159] (3) Add 7.5g of initiator (cerium ammonium nitrate) to 15ml of dilute nitric acid to prepare an initiator solution. Take 2.5ml of the initiator solution and add it to the grafted monomer (allyl glycidyl ether). After mixing evenly, add it to the reactor, heat it to 55℃, prepolymerize for 30min, and then lower the system temperature to room temperature.

[0160] (4) Cool the gelatinized starch milk obtained in step (2) to 60°C, add 12 ml of the initiator solution prepared in step (3), and then add sodium hydroxide solution to adjust the pH to 4.

[0161] (5) The prepolymerized solution obtained in step (3) is added dropwise at a uniform rate to the starch emulsion solution after the initiator is added in step (4) to carry out the graft polymerization reaction. The dropwise addition time is controlled at 100 min and the reaction temperature is maintained at 60℃. After the dropwise addition is completed, the remaining initiator solution is added, sodium hydroxide solution is added, the pH is adjusted to 4, and the temperature is maintained for 30 min. The polymerized modified starch-based emulsion is obtained.

[0162] (6) Dissolve the emulsifier (hexadecyltrimethylammonium bromide) in water to prepare a 5% emulsifier solution, add it to the starch-based emulsion obtained in step (5), heat it to 82.5°C, and keep it at that temperature for 90 minutes to obtain the polymer-modified adhesive.

[0163] (7) Cool the polymerized modified adhesive obtained in step (6) to 45°C and adjust the pH of the adhesive to 6 to obtain the starch-based adhesive.

[0164] (8) Before preparing the particleboard, add 8.5g of post-crosslinking agent (m-phenylenediamine) to the adhesive prepared in step (7) above, mix evenly by stirring, and then hot press the particleboard.

[0165] The adhesive product obtained in this embodiment is milky white in appearance, has low viscosity, and strong fluidity, meeting the requirements for particleboard. The curing time of the adhesive was measured, and the results showed that the curing time of this starch-based particleboard adhesive was 320 seconds. After hot pressing at 105℃ and 10MPa for 5 minutes, the resulting particleboard had a water absorption thickness expansion rate of 35%, which does not meet the requirements of the national standard P2 type particleboard.

[0166] Examples 1, 7, and 8 demonstrate the effect of post-crosslinking agents on the curing time of adhesives. The results show that adding the post-crosslinking agent ethylenediamine enables rapid curing at lower temperatures, while adhesives without post-crosslinking agents cannot cure. Adding other post-crosslinking agents, such as m-phenylenediamine, reduces the curing performance of the adhesive, slows down the curing speed, and affects the performance of the adhesive.

[0167] Example 9

[0168] A starch-based particleboard adhesive that cures rapidly at medium and low temperatures, wherein the formulation of the starch-based particleboard adhesive is as follows:

[0169]

[0170] The preparation method of the starch-based particleboard adhesive includes:

[0171] (1) Mix starch and water to make a starch milk with a starch mass fraction of 50%, stir and mix evenly, and then heat to 60°C;

[0172] (2) Prepare a 6.5 mol / L dilute hydrochloric acid solution by dissolving 18 ml of 12 mol / L concentrated hydrochloric acid in it. Add the solution to the starch milk in step (1) and hydrolyze for 2 hours. Then add 10 mol / L sodium hydroxide solution to adjust the pH of the starch milk to 4. Keep it at 80℃ for 30 minutes to gelatinize it.

[0173] (3) Add 7.5g of initiator (cerium ammonium nitrate) to 15ml of dilute nitric acid to prepare an initiator solution. Take 2.5ml of the initiator solution and add it to the grafted monomer (allyl glycidyl ether). After mixing evenly, add it to the reactor, heat it to 55℃, prepolymerize for 30min, and then lower the system temperature to room temperature.

[0174] (4) Cool the gelatinized starch milk obtained in step (2) to 60°C, add 12 ml of the initiator solution prepared in step (3), and then add sodium hydroxide solution to adjust the pH to 4.

[0175] (5) The prepolymerized solution obtained in step (3) is added dropwise at a uniform rate to the starch emulsion solution after the initiator is added in step (4) to carry out the graft polymerization reaction. The dropwise addition time is controlled at 100 min and the reaction temperature is maintained at 60℃. After the dropwise addition is completed, the remaining initiator solution is added, sodium hydroxide solution is added, the pH is adjusted to 4, and the temperature is maintained for 30 min. The polymerized modified starch-based emulsion is obtained.

[0176] (6) Dissolve the emulsifier (hexadecyltrimethylammonium bromide) in water to prepare a 5% emulsifier solution, add it to the starch-based emulsion obtained in step (5), heat it to 82.5°C, and keep it at that temperature for 90 minutes to obtain the polymer-modified adhesive.

[0177] (7) Cool the polymerized modified adhesive obtained in step (6) to 45°C and adjust the pH of the adhesive to 4 to obtain the starch-based adhesive.

[0178] (8) Before preparing the particleboard, add 8.5g of post-crosslinking agent (ethylenediamine) to the adhesive, mix evenly by stirring, and then hot press the particleboard.

[0179] The adhesive product obtained in this embodiment is milky white in appearance, has low viscosity, and strong fluidity, which meets the requirements for particleboard. The curing time of the adhesive was measured, and the results showed that the curing time of this starch-based particleboard adhesive was 150 seconds. After hot pressing at 105℃ and 10MPa for 5 minutes, the resulting particleboard had a water absorption thickness expansion rate of 11%, which does not meet the requirements of the national standard P2 type particleboard.

[0180] Examples 1 and 9 demonstrate the effect of crosslinking pH on the curing time of the adhesive. The results show that at pH = 6, the addition of the post-crosslinking agent ethylenediamine allows for rapid curing at a lower temperature, while at pH = 4, the curing speed is slower, and the cured adhesive exhibits poor water resistance, thus affecting its performance.

Claims

1. A starch-based particleboard adhesive that cures rapidly at medium and low temperatures, characterized in that, The starch-based particleboard adhesive comprises component A and component B; Component A, by mass parts, comprises: 150 parts starch, 200-300 parts water, 20-25 parts concentrated hydrochloric acid, 12-18 parts dilute nitric acid, 25-40 parts sodium hydroxide solution, 6-9 parts cerium ammonium nitrate initiator, 27-35 parts graft monomer, and 2-5 parts emulsifier; Component B, by mass parts, comprises: 8-11 parts ethylenediamine, a post-crosslinking agent; the graft monomer is allyl glycidyl ether. The preparation of the starch-based particleboard adhesive includes the following steps: (1) In a reaction vessel, starch and water are mixed to form a starch milk with a concentration of 30-50% by mass based on dry starch. After stirring evenly, the temperature is raised to 50-60℃, and hydrochloric acid diluted to 4-8 mol / L is added for acid hydrolysis. After acid hydrolysis, sodium hydroxide solution is added to adjust the pH to 3-5 and gelatinize to obtain a gelatinized starch milk solution. (2) Add the initiator to dilute nitric acid to prepare an initiator solution. Take an initiator solution with a volume ratio of 10~20% and add it to the grafted monomer. After mixing evenly, add it to the reactor for prepolymerization. Then lower the system temperature to room temperature to obtain a prepolymerization solution. (3) Cool the gelatinized starch emulsion solution obtained in step (1) to 50~70℃, add an initiator solution with a volume ratio of 50~80%, and then add sodium hydroxide solution to adjust the pH to 3~5; (4) The prepolymer solution obtained in step (2) is added dropwise at a uniform rate to the starch emulsion solution after the initiator is added in (3) to carry out the graft polymerization reaction. After the dropwise addition is completed, the remaining initiator solution is added, sodium hydroxide solution is added, the pH is adjusted to 3~5, and the temperature is kept for 30~45 min to obtain the polymerized modified starch-based emulsion. The dripping time is controlled between 90 and 120 minutes. (5) Dissolve the emulsifier in water to prepare a 4%~7% emulsifier solution, add it to the starch-based emulsion obtained in step (4), heat it to 75~85℃, and keep it warm for 90~120 min to obtain the polymerized modified adhesive. (6) Cool the polymerized modified adhesive obtained in step (5) to 30~50℃ and adjust the pH of the adhesive to 6~8 to obtain the starch-based adhesive. (7) Before preparing the particleboard, the starch-based adhesive prepared in step (6) is stirred and mixed evenly with the post-crosslinking agent, and then the particleboard is hot-pressed.

2. The starch-based particleboard adhesive according to claim 1, characterized in that, The starch is any one or a combination of several of the following: corn starch, tapioca starch, wheat starch, potato starch, rice starch, and mung bean starch.

3. The starch-based particleboard adhesive according to claim 1, characterized in that, The starch is waxy corn starch.

4. The starch-based particleboard adhesive according to claim 1, characterized in that, The concentrated hydrochloric acid is 12~15 mol / L.

5. The starch-based particleboard adhesive according to claim 1, characterized in that, The emulsifier is hexadecyltrimethylammonium bromide.

6. The application of the starch-based particleboard adhesive according to any one of claims 1 to 5 in the hot-press bonding of particleboard.

7. The method for preparing the starch-based particleboard adhesive according to any one of claims 1 to 5, characterized in that, The preparation method includes the following: (1) In a reaction vessel, starch and water are mixed to form a starch milk with a concentration of 30-50% by mass based on dry starch. After stirring evenly, the temperature is raised to 50-60℃, and hydrochloric acid diluted to 4-8 mol / L is added for acid hydrolysis. After acid hydrolysis, sodium hydroxide solution is added to adjust the pH to 3-5 and gelatinize to obtain a gelatinized starch milk solution. (2) Add the initiator to dilute nitric acid to prepare an initiator solution. Take an initiator solution with a volume ratio of 10~20% and add it to the grafted monomer. After mixing evenly, add it to the reactor for prepolymerization. Then lower the system temperature to room temperature to obtain a prepolymerization solution. (3) Cool the gelatinized starch emulsion solution obtained in step (1) to 50~70℃, add an initiator solution with a volume ratio of 50~80%, and then add sodium hydroxide solution to adjust the pH to 3~5; (4) The prepolymer solution obtained in step (2) is added dropwise at a uniform rate to the starch emulsion solution after the initiator is added in (3) to carry out the graft polymerization reaction. After the dropwise addition is completed, the remaining initiator solution is added, sodium hydroxide solution is added, the pH is adjusted to 3~5, and the temperature is kept for 30~45 min to obtain the polymerized modified starch-based emulsion; the dropwise addition time is controlled at 90~120 min. (5) Dissolve the emulsifier in water to prepare a 4%~7% emulsifier solution, add it to the starch-based emulsion obtained in step (4), heat it to 75~85℃, and keep it warm for 90~120 min to obtain the polymerized modified adhesive. (6) Cool the polymerized modified adhesive obtained in step (5) to 30~50℃ and adjust the pH of the adhesive to 6~8 to obtain the starch-based adhesive. (7) Before preparing the particleboard, the starch-based adhesive prepared in step (6) is stirred and mixed evenly with the post-crosslinking agent, and then the particleboard is hot-pressed.

8. The preparation method according to claim 7, characterized in that, The temperature of the hot pressing in step (7) is 90℃~120℃ and the pressure is 6~10MPa.

9. A method for reducing the hot-pressing temperature of particleboard, characterized in that, The method uses the starch-based particleboard adhesive according to any one of claims 1 to 5 for hot-press bonding of particleboard.

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