High-strength environment-friendly recycled PET wood adhesive and preparation method thereof

Abstract

The invention relates to the technical field of adhesives, in particular to a high-strength environment-friendly recycled PET wood adhesive and a preparation method thereof.The high-strength environment-friendly recycled PET wood adhesive is prepared from 1 mol of recycled PET, 0.6-1.4 mol of polycarboxylic acid and 1.1-1.45 mol of distilled water; according to the adhesive, recycled PET is used as a main raw material, the situation that the recycled PET raw material is regarded as a polyhydric alcohol raw material for preparing a polyurethane product in the prior art is broken through, innovation is achieved in the aspect of the preparation theory, pollution of plastic waste to the environment can be effectively reduced, meanwhile, the application field of waste PET is expanded, all-component recycling of waste PET is achieved, and the adhesive has good application prospects. According to the present invention, the biomass citric acid is adopted as the reactant, such that the release of formaldehyde and other harmful substances in the traditional adhesive is avoided, the good environmental protection performance is provided, and the esterification reaction condition and the raw material ratio are optimized, such that the adhesive prepared at the normal pressure has excellent bonding strength and excellent water resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and in particular to a high-strength, environment-friendly recycled PET wood adhesive and a preparation method thereof. Background Art

[0002] At present, the adhesives used in the wood industry are still mainly "trialdehyde" adhesives, such as urea-formaldehyde, phenol-formaldehyde and melamine-formaldehyde resins, which account for more than 90% of the adhesive market for my country's wood industry. Although formaldehyde-based resin adhesives have mature technology, cost advantages and good dry-state bonding strength, they release formaldehyde (identified as a Class 1 carcinogen by the International Agency for Research on Cancer IARC) and are overly dependent on petroleum-based raw materials. At the same time, the bonding strength of adhesives under wet and hot conditions is generally low, which seriously restricts their application in humid environments and high-end architectural decoration fields. The development of high-performance wood adhesives that are resistant to wet and hot conditions and do not release formaldehyde has always been a research hotspot in the wood industry.

[0003] With the increasing awareness of environmental protection and the advancement of resource recycling, how to effectively utilize waste plastics has become an important issue. PET (polyethylene terephthalate) is a widely used plastic material, and its waste (such as used mineral water bottles) is huge. The development of highly water-resistant, environmentally friendly, formaldehyde-free wood adhesives using recycled PET as raw materials not only helps reduce the pollution of plastic waste to the environment, but also solves the typical defects of traditional wood adhesives, which has important environmental and economic significance.

[0004] Existing patents (patent number: 202110978418.X; patent number: 202210456673.2; patent number: 201010507669.1; patent number: 201110462073.9) propose adhesive products prepared with recycled PET as raw material, all of which are treated as a polyol and then reacted with isocyanate to prepare the resulting polyurethane adhesive. In addition, a variety of additives need to be added during the preparation process, and the preparation process is quite complicated.

[0005] The existing literature "Study on the Performance of Polyurethane Adhesives Prepared from Waste PET Resource Oligomer Polyols" reports a polyurethane adhesive product prepared with recycled PET as raw material, and the preparation process involves the purification of recycled PET, which is an extremely complicated process; the literature "Research on Single-Component Closed Polyurethane Adhesives Based on Waste PET Alcoholysis Products" reports a single-component closed polyurethane adhesive product prepared with recycled PET as raw material; the literature "Preparation and Performance Research of Flame-Retardant Water-Based Polyurethane Adhesives Based on Waste PET Alcoholysis Products" reports a water-based polyurethane adhesive product with flame retardant properties prepared with recycled PET as raw material.

[0006] Through the above technical summary, it can be found that the existing adhesive solutions prepared with recycled PET as raw materials all use the recycled degradation products of PET as a polyol in the synthesis of polyurethane products. The preparation conditions of the adhesives involved are harsh and require the participation of multiple additives. Most importantly, the more expensive isocyanate component is introduced, which is not in line with the development concept of green products in the wood industry.

[0007] In view of the above technical limitations, there is an urgent need to develop a simple, green, efficient and highly water-resistant innovative method for preparing wood adhesives using recycled PET as raw materials. While achieving efficient recycling of waste PET materials, the preparation of adhesive products can be achieved through a simple and replicable process, thus breaking through the bottleneck of traditional environmental protection, high strength and water resistance. Summary of the Invention

[0008] In order to overcome the problem that traditional adhesives use PET recycled degradation products as a polyol in the synthesis of polyurethane products, the preparation conditions of the adhesives are harsh and require the participation of multiple additives. The more expensive isocyanate component is introduced, resulting in the adhesive being unable to be prepared in a green and efficient manner.

[0009] The technical solution of the present invention is: a high-strength environmentally friendly recycled PET wood adhesive, comprising the following components: 1 mol of recycled PET, 0.6-1.4 mol of polycarboxylic acid and 1.1-1.45 mol of distilled water.

[0010] Preferably, an acid catalyst is also included, and the amount of the acid catalyst added is 1-3.5% of the total mass of the reaction system. The acid catalyst is specifically any one or more of concentrated sulfuric acid, phosphoric acid and p-toluenesulfonic acid.

[0011] As a preference, the solid content of the adhesive is 55%-65%, and the adhesive coating amount on one side of the board is 140-160g / m 2 .

[0012] Preferably, the raw material for recycling PET comes from discarded mineral water bottles.

[0013] Preferably, the polycarboxylic acid is any one or more of maleic acid, oxalic acid and citric acid.

[0014] A method for preparing a high-strength, environmentally friendly recycled PET wood adhesive comprises preparing the high-strength, environmentally friendly recycled PET wood adhesive as described above, and the steps are as follows:

[0015] S1: Preparation of degradation liquid

[0016] 20g of ethylene glycol and 0.25g of a deep eutectic solvent were added to a flask and stirred mechanically at 300-400 rpm for 10-15 minutes to fully mix the two and prepare a highly efficient degradation liquid. The introduction of the deep eutectic solvent can significantly reduce the degradation temperature of PET, saving more than 30% energy compared to traditional degradation methods. The solvent can also be recovered and reused through simple distillation, making it environmentally friendly.

[0017] S2: PET pretreatment and degradation

[0018] S21: 5g of discarded mineral water bottles were selected and shredded into small pieces. The pieces were then soaked in 5% sodium hydroxide solution for 10-15 minutes to remove the bottle labels and surface stains. The pieces were then rinsed repeatedly with clean water until neutral, and finally dried in a 60°C oven to constant weight.

[0019] S22: adding the dried crushed material to the prepared degradation solution, placing the reaction system in a beaker equipped with a magnetic stirring device and a temperature control system, performing magnetic stirring at 200° C., controlling the stirring speed at 200-300 rpm, and reacting for 1.5 hours. During this process, ethylene glycol acts as an alcoholysis agent, and under the synergistic effect of the deep eutectic solvent, promotes the cleavage of PET molecular chains, causing degradation reaction, and ultimately obtaining a brick-red mixed liquid;

[0020] S3: Recycled PET separation

[0021] S31: slowly adding the mixed liquid to 1000 mL of distilled water, and vigorously stirring at 300-400 rpm for 1 hour, so as to fully precipitate the undissolved solid impurities by dilution and stirring;

[0022] S32: Filter through a Buchner funnel with filter paper to remove undissolved solids, and place the resulting filtrate in a freezer at -5°C for 24 hours to allow the degraded PET to crystallize from the solution;

[0023] S33: Filtering again to obtain the degraded recycled PET solid, and drying it in a 45°C oven for 24 hours to remove residual moisture and obtain pure recycled PET;

[0024] S4: Preparation of prepolymer by esterification reaction

[0025] Recycled PET and polycarboxylic acid are added to a reaction vessel equipped with a stirrer, a thermometer, a condenser, and a nitrogen protection device in a set molar ratio. An acid catalyst is added at 1-3.5% of the total mass of the reaction system. The reaction system is first heated to 130° C. and stirred at 150-250 rpm for 10 minutes to fully mix the materials. The temperature is then gradually raised to 150° C. and stirred at this temperature for 25-55 minutes. During the esterification reaction, the carboxyl groups of the polycarboxylic acid react with the hydroxyl groups of the recycled PET to produce an adhesive prepolymer with a specific degree of polymerization and viscosity. By controlling the reaction temperature and time, the molecular structure and properties of the prepolymer can be precisely controlled.

[0026] S5: Mixing adhesive

[0027] Take a certain amount of adhesive prepolymer, add a calculated amount of water according to a solid content ratio of 55%-65%, and continue stirring for 10-15 minutes at a stirring speed of 100-150 rpm to fully dissolve and disperse the prepolymer in the water to form a uniform and stable wood adhesive with good fluidity and bonding properties.

[0028] Preferably, in the process of preparing recycled PET, the degradation liquid consists of ethylene glycol and a low eutectic solvent, and the low eutectic solvent consists of urea and zinc chloride in a molar ratio of 1:1, wherein every 5g of discarded mineral water bottles corresponds to 20g of ethylene glycol and 0.25g of low eutectic solvent.

[0029] Preferably, in step S33, the hydroxyl value of the recovered PET reaches 230-240 mgKOH / g after treatment.

[0030] As a preference, in step S5, assuming the mass of the adhesive prepolymer is m 预聚体 , the mass of water added is m 水 , the total mass of the adhesive after preparation is m 总 , the solid content ratio is p, where p ranges from 55% to 65%. According to the definition of solid content, And m 总 =m 预聚体 +m 水 , from which we can infer:

[0031] The beneficial effects of the present invention are as follows: the adhesive utilizes recycled PET as the main raw material, which breaks through the existing technology that regards recycled PET raw materials as polyol raw materials for preparing polyurethane products. It is innovative from the perspective of preparation theory, can effectively reduce the pollution of plastic waste to the environment, and at the same time expands the application field of waste PET, realizes the recycling of all its components, and does not require additional purification processes and generates no waste products.

[0032] By using biomass polycarboxylic acid as a reactant, the release of harmful substances such as formaldehyde in traditional adhesives is avoided, and it has good environmental performance.

[0033] By optimizing the esterification reaction conditions and raw material ratio, the adhesive prepared under normal pressure has excellent bonding strength and water resistance.

[0034] This adhesive product exhibits excellent bonding strength and water resistance. After immersion in 63°C water for three hours, its strength retention reaches over 95%, significantly outperforming existing technologies. It also meets the application requirements for Class I plywood as specified in the national standard GB / T9846-2015, passes the boiling test, and provides weather-resistant plywood suitable for outdoor use without formaldehyde emissions. This enables efficient and green recycling of waste PET materials, expanding their application areas.

[0035] Recycled PET is widely available and low in cost, has a simple preparation process, does not require high temperature and high pressure conditions, and has good economic feasibility.

[0036] The present invention not only uses citric acid as a reactant, but also allows the use of other polycarboxylic acids such as maleic acid and oxalic acid as substitutes, thereby increasing the diversity of raw materials and further improving the performance and application range of the adhesive. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to the embodiments.

[0038] The present invention provides an embodiment: a high-strength environmentally friendly recycled PET wood adhesive, comprising the following components: 1 mol of recycled PET, 0.6-1.4 mol of polycarboxylic acid, and 1.1-1.45 mol of distilled water;

[0039] An acid catalyst is also included, the amount of the acid catalyst added is 1-3.5% of the total mass of the reaction system, and the acid catalyst is specifically selected from any one or more of concentrated sulfuric acid, phosphoric acid and p-toluenesulfonic acid;

[0040] The solid content of the adhesive is 55%-65%, and the adhesive coating amount on one side of the board is 140-160g / m 2 .

[0041] The raw materials for recycled PET come from discarded mineral water bottles.

[0042] The polycarboxylic acid is specifically any one or more of maleic acid, oxalic acid and citric acid.

[0043] A method for preparing a high-strength, environmentally friendly recycled PET wood adhesive comprises preparing the high-strength, environmentally friendly recycled PET wood adhesive described above, and the steps are as follows:

[0044] S1: Preparation of degradation liquid

[0045] 20g of ethylene glycol and 0.25g of a low eutectic solvent are added to a flask, and mechanical stirring is used at a speed of 300-400 rpm for 10-15 minutes to fully mix the two and prepare a high-efficiency degradation liquid; the degradation liquid is composed of ethylene glycol and a low eutectic solvent, and the low eutectic solvent is composed of urea and zinc chloride in a molar ratio of 1:1, wherein every 5g of discarded mineral water bottles corresponds to 20g of ethylene glycol and 0.25g of a low eutectic solvent. The introduction of the low eutectic solvent can significantly reduce the degradation temperature of PET, which can save more than 30% energy compared to traditional degradation methods. The solvent can also be recovered and reused by simple distillation, which is environmentally friendly.

[0046] S2: PET pretreatment and degradation

[0047] S21: 5g of discarded mineral water bottles were selected and shredded into small pieces. The pieces were then soaked in 5% sodium hydroxide solution for 10-15 minutes to remove the bottle labels and surface stains. The pieces were then rinsed repeatedly with clean water until neutral, and finally dried in a 60°C oven to constant weight.

[0048] S22: adding the dried crushed material to the prepared degradation solution, placing the reaction system in a beaker equipped with a magnetic stirring device and a temperature control system, performing magnetic stirring at 200° C., controlling the stirring speed at 200-300 rpm, and reacting for 1.5 hours. During this process, ethylene glycol acts as an alcoholysis agent, and under the synergistic effect of the deep eutectic solvent, promotes the cleavage of PET molecular chains, causing degradation reaction, and ultimately obtaining a brick-red mixed liquid;

[0049] S3: Recycled PET separation

[0050] S31: slowly adding the mixed liquid to 1000 mL of distilled water, and vigorously stirring at 300-400 rpm for 1 hour, so as to fully precipitate the undissolved solid impurities by dilution and stirring;

[0051] S32: Filter through a Buchner funnel with filter paper to remove undissolved solids, and place the resulting filtrate in a freezer at -5°C for 24 hours to allow the degraded PET to crystallize from the solution;

[0052] S33: Filtering again to obtain degraded recycled PET solid, and drying it in a 45°C oven for 24 hours to remove residual moisture, thereby obtaining pure recycled PET. The hydroxyl value of the recycled PET after treatment reaches 230-240 mgKOH / g;

[0053] S4: Preparation of prepolymer by esterification reaction

[0054] Recycled PET and polycarboxylic acid are added to a reaction vessel equipped with a stirrer, a thermometer, a condenser, and a nitrogen protection device in a set molar ratio. An acid catalyst is added at 1-3.5% of the total mass of the reaction system. The reaction system is first heated to 130° C. and stirred at 150-250 rpm for 10 minutes to fully mix the materials. The temperature is then gradually raised to 150° C. and stirred at this temperature for 25-55 minutes. During the esterification reaction, the carboxyl groups of the polycarboxylic acid react with the hydroxyl groups of the recycled PET to produce an adhesive prepolymer with a specific degree of polymerization and viscosity. By controlling the reaction temperature and time, the molecular structure and properties of the prepolymer can be precisely controlled.

[0055] S5: Mixing adhesive

[0056] Take a certain amount of adhesive prepolymer, add a calculated mass of water according to a solid content ratio of 55%-65%, and continue stirring for 10-15 minutes at a stirring speed of 100-150 rpm to fully dissolve and disperse the prepolymer in water to form a uniform and stable wood adhesive with good fluidity and bonding properties. Assume that the mass of the adhesive prepolymer is m 预聚体 , the mass of water added is m 水 , the total mass of the adhesive after preparation is m 总 , the solid content ratio is p, where p ranges from 55% to 65%. According to the definition of solid content, And m 总 =m 预聚体 +m 水 , from which we can infer:

[0057] Example 1

[0058] Basic experiments:

[0059] Objective: To verify the performance of the basic solution, i.e., the adhesive with a molar ratio of recycled PET to citric acid of 1:1.2.

[0060] S1: Preparation of degradation liquid

[0061] 20g of ethylene glycol and 0.25g of a low eutectic solvent are added to a flask, and mechanical stirring is used at a speed of 300-400 rpm for 10δ15 minutes to fully mix the two and prepare a high-efficiency degradation liquid. The degradation liquid is composed of ethylene glycol and the low eutectic solvent, and the low eutectic solvent is composed of urea and zinc chloride in a molar ratio of 1:1. Among them, 20g of ethylene glycol and 0.25g of the low eutectic solvent are corresponding to every 5g of discarded mineral water bottles. The introduction of the low eutectic solvent can significantly reduce the degradation temperature of PET, and compared with traditional degradation methods, it can save more than 30% energy. In addition, the solvent can be recovered and reused through simple distillation, which is green and environmentally friendly.

[0062] S2: PET pretreatment and degradation

[0063] S21: 5g of discarded mineral water bottles were selected and shredded into small pieces. The pieces were then soaked in 5% sodium hydroxide solution for 10-15 minutes to remove the bottle labels and surface stains. The pieces were then rinsed repeatedly with clean water until neutral, and finally dried in a 60°C oven to constant weight.

[0064] S22: The dried crushed material is added to the prepared degradation liquid, and the reaction system is placed in a beaker equipped with a magnetic stirring device and a temperature control system. The system is magnetically stirred at 200°C, and the stirring speed is controlled at 200-300 rpm. The reaction is carried out for 1.5 hours. During this process, ethylene glycol acts as an alcoholysis agent. Under the synergistic effect of the low eutectic solvent, the PET molecular chain is broken, and a degradation reaction occurs, eventually obtaining a brick-red mixed liquid.

[0065] S3: Recycled PET separation

[0066] S31: slowly adding the mixed liquid to 1000 mL of distilled water, and vigorously stirring at 300-400 rpm for 1 hour, so as to fully precipitate the undissolved solid impurities by dilution and stirring;

[0067] S32: Filter through a Buchner funnel with filter paper to remove undissolved solids, and place the resulting filtrate in a freezer at -5°C for 24 hours to allow the degraded PET to crystallize from the solution;

[0068] S33: The degraded recycled PET solid is filtered again and dried in a 45°C oven for 24 hours to remove residual moisture and obtain pure recycled PET. The hydroxyl value of the recycled PET after treatment reaches 230-240 mgKOH / g.

[0069] S4: Preparation of prepolymer by esterification reaction

[0070] Recycled PET and citric acid were added to a reaction vessel equipped with a stirrer, a thermometer, a condenser and a nitrogen protection device in a molar ratio of 1:1.2, and 2% by mass of p-toluenesulfonic acid was added as a catalyst. The mixture was stirred at 150°C for 30 minutes to obtain an adhesive prepolymer.

[0071] S5: Mixing adhesive

[0072] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0073] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0074] Example 2

[0075] The optimized citric acid ratio is 1:0.6

[0076] Objective: To explore the performance of adhesives at lower citric acid ratios.

[0077] S1-S3 were all carried out according to the steps of Example 1.

[0078] S4: Preparation of prepolymer by esterification reaction

[0079] Recycled PET and citric acid were added in a molar ratio of 1:0.6 into a reaction vessel equipped with a stirrer, a thermometer, a condenser and a nitrogen protection device, 2% by mass of p-toluenesulfonic acid was added as a catalyst, and the mixture was stirred at 150° C. for 30 minutes to obtain an adhesive prepolymer.

[0080] S5: Mixing adhesive

[0081] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0082] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0083] Example 3

[0084] The optimized citric acid ratio is 1:1.4

[0085] Objective: To explore the performance of adhesives with higher citric acid ratios.

[0086] S1-S3 were all carried out according to the steps of Example 1.

[0087] S4: Preparation of prepolymer by esterification reaction

[0088] Recycled PET and citric acid were added in a molar ratio of 1:1.4 into a reaction vessel equipped with a stirrer, a thermometer, a condenser and a nitrogen protection device, 2% by mass of p-toluenesulfonic acid was added as a catalyst, and the mixture was stirred at 150°C for 30 minutes to obtain an adhesive prepolymer.

[0089] S5: Mixing adhesive

[0090] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0091] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0092] Example 4

[0093] The optimized reaction time is 55 minutes

[0094] Objective: To explore the effect of prolonged reaction time on adhesive properties.

[0095] S1-S3 were all carried out according to the steps of Example 1.

[0096] S4: Preparation of prepolymer by esterification reaction

[0097] Recycled PET and citric acid were added in a molar ratio of 1:1.2 into a reaction vessel equipped with a stirrer, a thermometer, a condenser and a nitrogen protection device, 2% by mass of p-toluenesulfonic acid was added as a catalyst, and the mixture was stirred at 150°C for 55 minutes to obtain an adhesive prepolymer.

[0098] S5: Mixing adhesive

[0099] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0100] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0101] Example 5

[0102] The optimized reaction time is 25 minutes

[0103] Objective: To explore the effect of shortening reaction time on adhesive properties.

[0104] S1-S3 were all carried out according to the steps of Example 1.

[0105] S4: Preparation of prepolymer by esterification reaction

[0106] Recycled PET and citric acid were added in a molar ratio of 1:1.2 into a reaction vessel equipped with a stirrer, a thermometer, a condenser and a nitrogen protection device, 2% by mass of p-toluenesulfonic acid was added as a catalyst, and stirred at 150°C for 25 minutes to obtain an adhesive prepolymer.

[0107] S5: Mixing adhesive

[0108] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0109] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0110] Example 6

[0111] The optimized reaction temperature is 130℃

[0112] Objective: To explore the effect of lowering reaction temperature on adhesive properties.

[0113] S1-S3 were all carried out according to the steps of Example 1.

[0114] S4: Preparation of prepolymer by esterification reaction

[0115] Recycled PET and citric acid were added in a molar ratio of 1:1.2 into a reaction vessel equipped with a stirrer, a thermometer, a condenser and a nitrogen protection device, 2% by mass of p-toluenesulfonic acid was added as a catalyst, and the mixture was stirred at 130°C for 30 minutes to obtain an adhesive prepolymer.

[0116] S5: Mixing adhesive

[0117] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0118] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0119] Example 7

[0120] The optimized reaction temperature is 160℃

[0121] Objective: To explore the effect of increasing reaction temperature on adhesive properties.

[0122] S1-S3 were all carried out according to the steps of Example 1.

[0123] S4: Preparation of prepolymer by esterification reaction

[0124] Recycled PET and citric acid were added in a molar ratio of 1:1.2 into a reaction vessel equipped with a stirrer, a thermometer, a condenser and a nitrogen protection device, 2% by mass of p-toluenesulfonic acid was added as a catalyst, and the mixture was stirred at 160°C for 30 minutes to obtain an adhesive prepolymer.

[0125] S5: Mixing adhesive

[0126] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0127] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0128] Comparative Example 1

[0129] High citric acid ratio: 1:1.6

[0130] Purpose: To demonstrate the problems caused by excessively high citric acid content.

[0131] S1-S3 were all carried out according to the steps of Example 1.

[0132] S4: Preparation of prepolymer by esterification reaction

[0133] Recycled PET and citric acid were added to a reaction vessel in a molar ratio of 1:1.6, 2% by mass of p-toluenesulfonic acid was added as a catalyst, and the mixture was stirred at 150° C. for 30 minutes to obtain an adhesive prepolymer.

[0134] S5: Mixing adhesive

[0135] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0136] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0137] Comparative Example 2

[0138] Low citric acid ratio: 1:0.4

[0139] Purpose: To demonstrate the problems caused by insufficient citric acid.

[0140] S1-S3 were all carried out according to the steps of Example 1.

[0141] S4: Preparation of prepolymer by esterification reaction

[0142] Recycled PET and citric acid were added to a reaction vessel in a molar ratio of 1:0.4, 2% by mass of p-toluenesulfonic acid was added as a catalyst, and the mixture was stirred at 150° C. for 30 minutes to obtain an adhesive prepolymer.

[0143] S5: Mixing adhesive

[0144] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0145] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0146] Comparative Example 3

[0147] No recycled PET, only citric acid

[0148] Purpose: To demonstrate the problems associated with a lack of recycled PET.

[0149] S1-S3 were all carried out according to the steps of Example 1.

[0150] S4: Preparation of prepolymer by esterification reaction

[0151] According to the hydroxyl value of the recycled PET, only 1 mol of citric acid was used as the calculation standard for the amount of citric acid added. 2% by mass of p-toluenesulfonic acid was added as a catalyst, and the mixture was stirred at 150° C. for 30 minutes to obtain an adhesive prepolymer.

[0152] S5: Mixing adhesive

[0153] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0154] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0155] Comparative Example 4

[0156] The reaction temperature is too low, 125°C

[0157] Purpose: To demonstrate the problems that arise when the reaction temperature exceeds the minimum temperature limit.

[0158] S1-S3 were all carried out according to the steps of Example 1.

[0159] S4: Preparation of prepolymer by esterification reaction

[0160] Recycled PET and citric acid were added in a molar ratio of 1:1.2 into a reaction vessel equipped with a stirrer, a thermometer, a condenser and a nitrogen protection device, 2% by mass of p-toluenesulfonic acid was added as a catalyst, and the mixture was stirred at 125°C for 30 minutes to obtain an adhesive prepolymer.

[0161] S5: Mixing adhesive

[0162] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0163] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0164] Comparative Example 5

[0165] The reaction temperature is too high, 165°C

[0166] Purpose: To demonstrate the problems that arise when the reaction temperature exceeds the maximum temperature limit.

[0167] S1-S3 were all carried out according to the steps of Example 1.

[0168] S4: Preparation of prepolymer by esterification reaction

[0169] Recycled PET and citric acid were added to a reaction vessel in a molar ratio of 1:1.2, 2% by mass of p-toluenesulfonic acid was added as a catalyst, and the mixture was stirred at 165° C. for 30 minutes to obtain an adhesive prepolymer.

[0170] S5: Mixing adhesive

[0171] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0172] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0173] Comparative Example 6

[0174] The reaction time is too short, 20 minutes

[0175] Purpose: To demonstrate the problem of reaction time exceeding the minimum temperature limit.

[0176] S1-S3 were all carried out according to the steps of Example 1.

[0177] S4: Preparation of prepolymer by esterification reaction

[0178] Recycled PET and citric acid were added into a reaction vessel equipped with a stirrer, a thermometer, a condenser and a nitrogen protection device in a molar ratio of 1:1.2, 2% by mass of p-toluenesulfonic acid was added as a catalyst, and the mixture was stirred at 150° C. for 20 minutes to obtain an adhesive prepolymer.

[0179] S5: Mixing adhesive

[0180] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0181] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0182] Comparative Example 7

[0183] The reaction time is too short, 60 minutes

[0184] Purpose: To demonstrate the problem of reaction time exceeding the maximum temperature limit.

[0185] S1-S3 were all carried out according to the steps of Example 1.

[0186] S4: Preparation of prepolymer by esterification reaction

[0187] Recycled PET and citric acid were added to a reaction vessel in a molar ratio of 1:1.2, 2% by mass of p-toluenesulfonic acid was added as a catalyst, and the mixture was stirred at 150° C. for 60 minutes to obtain an adhesive prepolymer.

[0188] S5: Mixing adhesive

[0189] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0190] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0191] Comparative Example 8

[0192] The catalyst dosage is low, 0.5%

[0193] Purpose: To demonstrate the problems that arise when catalyst usage exceeds the minimum limit.

[0194] S1-S3 were all carried out according to the steps of Example 1.

[0195] S4: Preparation of prepolymer by esterification reaction

[0196] Recycled PET and citric acid were added into a reaction vessel at a molar ratio of 1:1.2, 0.5% by mass of p-toluenesulfonic acid was added as a catalyst, and the mixture was stirred at 150° C. for 30 minutes to obtain an adhesive prepolymer.

[0197] S5: Mixing adhesive

[0198] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0199] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0200] Comparative Example 9

[0201] The catalyst dosage is low, 4%.

[0202] Purpose: To demonstrate the problem of exceeding the maximum catalyst dosage.

[0203] S1-S3 were all carried out according to the steps of Example 1.

[0204] S4: Preparation of prepolymer by esterification reaction

[0205] Recycled PET and citric acid were added to a reaction vessel in a molar ratio of 1:1.2, 4% by mass of p-toluenesulfonic acid was added as a catalyst, and the mixture was stirred at 150° C. for 30 minutes to obtain an adhesive prepolymer.

[0206] S5: Mixing adhesive

[0207] Take a certain amount of adhesive prepolymer and prepare it into an aqueous solution with a solid content of 60%.

[0208] The mixture was stirred for 15 minutes to obtain the high-performance wood adhesive made from recycled PET.

[0209] The adhesive prepared by the above process is used for the preparation of three-layer amine wood plywood, and the glue coating amount on both sides of the core board is 140-160g / m 2 The hot pressing process is: pressure: 1.2MPa, time: 1min / mm, temperature: 200℃. The pressed plywood is placed for 1 week before the bonding strength test. The test conditions are in accordance with the requirements of the national standard GB / T 17657-2022.

[0210] The specific test results are shown in Table 1:

[0211]

[0212]

[0213] Table 1

[0214] Note: “---” means no data.

[0215] As shown in Table 1, the environmentally friendly recycled PET wood adhesive prepared by the method of the present invention has excellent water resistance and bonding strength, and has obvious advantages over all comparative examples.

[0216] It should be understood by those skilled in the art that the above embodiments are merely exemplary embodiments and that various changes, substitutions, and alterations may be made without departing from the spirit and scope of the present application.

Claims

1. A high-strength environmentally friendly recycled PET wood adhesive, characterized in that: The method comprises the following components: 1 mol of recovered PET, 0.6-1.4 mol of polycarboxylic acid and 1.1-1.45 mol of distilled water.

2. The high-strength, environmentally friendly recycled PET wood adhesive according to claim 1, characterized in that: The method further comprises an acid catalyst, the amount of which is 1-3.5% of the total mass of the reaction system. The acid catalyst is specifically selected from any one or more of concentrated sulfuric acid, phosphoric acid and p-toluenesulfonic acid.

3. The high-strength, environmentally friendly recycled PET wood adhesive according to claim 1, characterized in that: The solid content of the adhesive is 55%-65%, and the adhesive coating amount on one side of the board is 140-160g / m 2 .

4. The high-strength, environmentally friendly recycled PET wood adhesive according to claim 1, characterized in that: The raw materials for recycled PET come from discarded mineral water bottles.

5. The high-strength, environmentally friendly recycled PET wood adhesive according to claim 1, characterized in that: The polycarboxylic acid is specifically any one or more of maleic acid, oxalic acid and citric acid.

6. A method for preparing a high-strength environmentally friendly recycled PET wood adhesive, characterized in that The method comprises the following steps: S1: Preparation of degradation liquid 20 g of ethylene glycol and 0.25 g of a deep eutectic solvent were added to a flask and stirred mechanically at 300-400 rpm for 10-15 minutes to fully mix the two to prepare a highly efficient degradation liquid; S2: PET pretreatment and degradation S2 1: Select 5g of discarded mineral water bottles, cut them into small pieces, and then soak them in 5% sodium hydroxide solution for 10-15 minutes to remove the bottle labels and surface stains. Rinse them repeatedly with clean water until neutral, and finally dry them in a 60℃ oven to constant weight. S22: adding the dried crushed material to the prepared degradation solution, placing the reaction system in a beaker equipped with a magnetic stirring device and a temperature control system, performing magnetic stirring at 200° C., controlling the stirring speed at 200-300 rpm, and reacting for 1.5 hours. During this process, ethylene glycol acts as an alcoholysis agent, and under the synergistic effect of the deep eutectic solvent, promotes the cleavage of PET molecular chains, causing degradation reaction, and ultimately obtaining a brick-red mixed liquid; S3: Recycled PET separation S31: slowly adding the mixed liquid to 1000 mL of distilled water, and vigorously stirring at 300-400 rpm for 1 hour, so as to fully precipitate the undissolved solid impurities by dilution and stirring; S32: Filter through a Buchner funnel with filter paper to remove undissolved solids, and place the resulting filtrate in a freezer at 5°C for 24 hours to allow the degraded PET to crystallize from the solution; S33: Filtering again to obtain the degraded recycled PET solid, and drying it in a 45°C oven for 24 hours to remove residual moisture and obtain pure recycled PET; S4: Preparation of prepolymer by esterification reaction Recycled PET and polycarboxylic acid are added to a reaction vessel equipped with a stirrer, a thermometer, a condenser, and a nitrogen protection device in a set molar ratio. An acid catalyst is added at 1-3.5% of the total mass of the reaction system. The reaction system is first heated to 130° C. and stirred at 150-250 rpm for 10 minutes to fully mix the materials. The temperature is then gradually raised to 150° C. and stirred at this temperature for 25-55 minutes. During the esterification reaction, the carboxyl groups of the polycarboxylic acid react with the hydroxyl groups of the recycled PET to produce an adhesive prepolymer with a specific degree of polymerization and viscosity. By controlling the reaction temperature and time, the molecular structure and properties of the prepolymer can be precisely controlled. S5: Mixing adhesive Take a certain amount of adhesive prepolymer, add a calculated amount of water according to a solid content ratio of 55%-65%, and continue stirring for 10-15 minutes at a stirring speed of 100-150 rpm to fully dissolve and disperse the prepolymer in the water to form a uniform and stable wood adhesive with good fluidity and bonding properties.

7. The method for preparing the high-strength, environmentally friendly recycled PET wood adhesive according to claim 6, wherein: In the process of preparing recycled PET, the degradation liquid is composed of ethylene glycol and a low eutectic solvent, and the low eutectic solvent is composed of urea and zinc chloride in a molar ratio of 1:1, where every 5g of discarded mineral water bottles corresponds to 20g of ethylene glycol and 0.25g of low eutectic solvent.

8. The method for preparing the high-strength, environmentally friendly recycled PET wood adhesive according to claim 6, wherein: In step S33, the hydroxyl value of the recovered PET reaches 230-240 mgKOH / g after treatment.

9. The method for preparing the high-strength, environmentally friendly recycled PET wood adhesive according to claim 6, wherein: In step S5, let the mass of the adhesive prepolymer be m 预聚体 , the mass of water added is m 水 , the total mass of the adhesive after preparation is m 总 , the solid content ratio is p, where p ranges from 55% to 65%. According to the definition of solid content, And m 总 =m 预聚体 +m 水 , from which we can infer:

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