Polyurethane adhesive enhanced by molecular pulley effect and preparation method and application thereof

Abstract

A polyurethane adhesive enhanced by molecular pulley effect and its preparation method and application, raw materials are proportioned as follows in mass fraction: isocyanate 24~26 parts, castor oil 12~14 parts, catalyst 0.2 parts, palygorskite end-capped polyrotaxan 1~4 parts. By introducing polyrotaxan into the polyurethane adhesive, the polyrotaxan can disperse the stress and dissipate the energy in the system through the molecular slip movement of the main molecular ring in the stretching process, and the compatibility between palygorskite and polyurethane is obviously improved through the synergistic effect of the interpenetrating network of multiple hydrogen bonds and the interface sliding structure, and the cohesive force and water-resistant bonding strength of the adhesive are significantly improved. The ester adhesive prepared by the present application has good bonding performance and toughness, is environment-friendly and sustainable, has low raw material cost, and has industrial application prospect. The problems of polymer chain internal rotation obstruction and chain slip difficulty caused by polyurethane filler aggregation in the prior art and low bonding strength of castor oil polyurethane adhesive are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of composite synthesis and wood-based panel technology, and particularly relates to a polyurethane adhesive enhanced by molecular pulley effect and a preparation method and application thereof. BACKGROUND

[0002] Polyurethane adhesive is prepared by the reaction of polyester or polyether polyol with isocyanate, and has excellent flexibility, low temperature resistance, wear resistance, good curing speed and other advantages, and has high adhesion to metals, wood, plastics and other substrates, and is widely used in furniture, packaging, construction, cargo, transportation and other industries. However, the polyols used to prepare polyurethane adhesives are usually derived from non-renewable petroleum resources, which has the disadvantages of pollution and high cost. With the vigorous promotion of green production by the country, some renewable biomass raw materials have been tapped and become substitutes for petroleum-based polyols. Vegetable oil is a typical renewable resource, and its availability and derivatization make it the most used renewable resource in industry and academia.

[0003] Castor oil is a castor oil acid triglyceride, which is abundant in reserves, low in price and non-toxic. Unlike other vegetable oils, its average hydroxyl function is 2.7, which is superior to other vegetable oils in preparing crosslinked macromolecules. Polyurethane adhesives prepared using castor oil as polyol have the advantages of high biodegradability and low ecological toxicity. In addition, the long-chain non-polar fatty acid segment of castor oil can improve the water resistance and moisture resistance of polyurethane adhesives. However, castor oil-based polyurethane adhesives have relatively low bonding strength, which significantly limits their application range. Therefore, it is necessary to further improve their performance.

[0004] At present, introducing natural clay as a filler into polyurethane adhesives has become one of the effective strategies to improve the mechanical strength of polyurethane. Palygorskite is a water-rich magnesium-aluminum silicate clay with a unique nanorod crystal structure, and has been widely studied due to its good mechanical strength and elasticity. However, palygorskite tends to agglomerate in the polymer matrix, and has poor compatibility with polyurethane adhesives, which greatly weakens the enhancement effect of palygorskite on the performance of polyurethane. Although various strategies have been used to modify palygorskite, such as mechanical modification, mercapto grafting modification, hydrothermal modification, etc., the interface between the modified palygorskite and the polyurethane adhesive still lacks effective stress transmission, resulting in low bonding strength and poor toughness of the polyurethane adhesive. Therefore, how to use innovative methods to achieve effective interface transmission and dissipation is a technical problem to be solved to realize the performance enhancement of polyurethane adhesives. SUMMARY

[0005] The technical problems solved by the present application are: in view of the problems of polymer chain internal rotation blocked and chain slip difficulty caused by the existing polyurethane filler aggregation and the low bonding strength of castor oil polyurethane adhesive in the prior art, the present application provides a polyurethane adhesive with enhanced molecular pulley effect, a preparation method and application thereof, and can realize the preparation of an environmentally friendly polyurethane adhesive with effective stress transfer, high strength and good water resistance.The castor oil polyurethane adhesive prepared by the present application has good bonding performance and toughness, and the raw materials of the polyurethane polyol castor oil are natural renewable materials, which are environmentally friendly and sustainable, and the raw material cost is low, and the synthesized polyurethane adhesive has industrial application prospect.

[0006] The technical scheme is: a polyurethane adhesive with enhanced molecular pulley effect, raw materials are as follows in mass fraction: isocyanate 24-26 parts, castor oil 12-14 parts, catalyst 0.2 parts, and palygorskite end-capped polyrotaxane 1-4 parts.

[0007] As preferred, the preparation method of the palygorskite end-capped polyrotaxane is as follows: the functional pretreated palygorskite and the quasi-polyrotaxane are stirred and reacted in anhydrous acetone, and after filtration, washing and vacuum drying, the palygorskite end-capped polyrotaxane is obtained, and the mass ratio of the functional pretreated palygorskite and the quasi-polyrotaxane is (0.05-0.11):1.

[0008] As preferred, the preparation method of the functional pretreated palygorskite is as follows: the purified palygorskite is reacted with silane coupling agent γ-aminopropyltrimethoxysilane to obtain aminated palygorskite, and then the modified palygorskite is obtained through N-hydroxysuccinimide, wherein the mass ratio of the palygorskite, the γ-aminopropyltrimethoxysilane and the N-hydroxysuccinimide is 1:0.2-0.4:0.5-1.

[0009] As preferred, the purified palygorskite is palygorskite activated by hydrochloric acid with a pH of 6-7.

[0010] As preferred, the preparation method of the quasi-polyrotaxane is as follows: the aminopropyl end-capped polydimethylsiloxane is ultrasonically treated with an aqueous solution of cyclodextrin, and then stirred at room temperature, and then the reacted solution is filtered and vacuum dried to obtain the quasi-polyrotaxane, wherein the weight ratio of the aminopropyl end-capped polydimethylsiloxane and the cyclodextrin is 1:(5.5-7).

[0011] As preferred, the catalyst is dibutyltin dilaurate or triethylamine.

[0012] Based on the above preparation method of the polyurethane adhesive with enhanced molecular pulley effect, the steps are as follows:

[0013] (1) Castor oil and isocyanate are added into a reaction kettle, stirred uniformly, and reacted at 35-60 DEG C for 20-40 min to prepare an isocyanate-terminated prepolymer, which is vacuum degassed for standby (vacuum degassing is used to remove bubbles or gas in the system, which helps to improve the stability of the reaction system);

[0014] (2) Then, palygorskite-terminated polyrotaxan and a catalyst are added for crosslinking modification to obtain a polyurethane adhesive enhanced by molecular pulley effect.

[0015] The polyurethane adhesive enhanced by molecular pulley effect is applied to the preparation of wood-based panels.

[0016] Preferably, the polyurethane adhesive is used for the gluing of poplar veneers, and the gluing is performed by using a hot-pressing process with a hot-pressing temperature of 120-135 DEG C, a hot-pressing pressure of 1.0-1.5 MPa, and a hot-pressing time of 5-8 min.

[0017] Preferably, the polyurethane adhesive is used for the gluing of particle boards with a glue application amount of 5-6 wt%, a pressure of 1.6-3.0 MPa, a temperature of 135-150 DEG C, and a time of 4-5 min.

[0018] The polyurethane adhesive is improved by introducing polyrotaxan into the polyurethane adhesive, the polyrotaxan can disperse stress and dissipate energy in the system through molecular slip movement of the host molecule ring during stretching, and the compatibility between palygorskite and polyurethane is obviously improved through the synergistic effect of the interpenetrating network of multiple hydrogen bonds and the interface sliding structure, so that the cohesive force and water-resistant bonding strength of the adhesive are significantly improved.

[0019] Advantages: (1) The polyurethane adhesive of the present application overcomes the problem of difficulty in internal rotation and chain slip of the polymer chain caused by the aggregation of the existing polyurethane filler by using the molecular slip effect of the host molecule ring of the polyrotaxan during stretching. When the polyurethane adhesive is subjected to external force, the guest molecule chains of the polyrotaxan can effectively form crystals between them, hinder the expansion of cracks, and significantly improve the adhesive layer toughness, cohesive force and bonding strength of the adhesive.

[0020] (2) The castor oil-based polyurethane adhesive prepared by the present application is environmentally friendly and sustainable, has low raw material cost, and is easy to be applied in actual scale. DETAILED DESCRIPTION

[0021] The present application is described by specific examples, which can easily enable the skilled person in the art to understand other advantages and effects of the present application. In addition, the present application can also be applied according to different specific embodiments, and the details in the specification can also be appropriately adjusted according to different views and applications to ensure that the original meaning of the present application is not deviated. It should be noted that the following examples and their features can be combined with each other without contradiction.

[0022] In the embodiments of the present specification, each raw material is obtained from a general commercially available product unless otherwise specified.

[0023] The preparation method of the palygorskite-capped polyrotaxane used in the following examples includes:

[0024] (1) 50 mL of 37% hydrochloric acid was added to 15 g of 9 wt% palygorskite aqueous solution and stirred overnight, and then washed by centrifugation until the pH was 6-7 to obtain acid-treated palygorskite. 0.2-0.4 g of γ-aminopropyl triethoxysilane was added to 10 mL of toluene solution and stirred to completely dissolve, and then 1 g of acid-treated palygorskite was added, and stirred in a water bath at 80°C for 3 hours, and then filtered, washed and dried.

[0025] (2) 3.5 parts of palygorskite in step (1) was dissolved in 0.9 parts of succinic anhydride solution, and stirred at 60°C for 2 hours under nitrogen atmosphere. Then 1.8 parts of N-hydroxysuccinimide and 5 mL of dichloromethane as solvent were added, and stirred at 40°C for 24 hours. After filtration, rotary evaporation and washing, the pretreated palygorskite was obtained.

[0026] (3) 2 parts of aminopropyl-capped polydimethylsiloxane was added to 25 parts of a γ-cyclodextrin aqueous solution (including 11-14 parts of γ-cyclodextrin), and the mixture was ultrasonically treated in a water bath for 1 hour, and then stirred at 35°C overnight. Then the above reaction solution was filtered and vacuum dried to obtain a quasi-polyrotaxane. The palygorskite of step (2) was dissolved in 10 mL of anhydrous acetone, and the quasi-polyrotaxane was stirred at 50°C for 6 hours, and then filtered, centrifuged and dried to obtain the palygorskite-capped polyrotaxane.

[0027] Example 1

[0028] The present embodiment provides a preparation method of a high-performance castor oil polyurethane adhesive.

[0029] (1) 12 parts of dehydrated castor oil and 24 parts of diphenyl methane diisocyanate were stirred and mixed, and reacted at 60°C for 40 minutes, and vacuum degassed three times for standby use.

[0030] (2) 1 part of palygorskite-capped polyrotaxane was dissolved in 1.5 parts of anhydrous acetone, and added to step (1), and 0.2 parts of dibutyltin dilaurate was added as a catalyst, and stirred uniformly at room temperature to obtain a high-performance palygorskite-capped polyrotaxane reinforced castor oil-based polyurethane adhesive.

[0031] Example 2

[0032] (1) 12 parts of dehydrated castor oil and 24 parts of diphenyl methane diisocyanate were stirred and mixed, and reacted at 60°C for 40 minutes, and vacuum degassed three times for standby use.

[0033] (2) 2 parts of palygorskite end-capped polyrotaxan was dissolved in 1.5 parts of anhydrous acetone, added to step (1), and 0.2 parts of dibutyltin dilaurate was added as a catalyst, and stirred uniformly at room temperature to obtain a high-performance palygorskite end-capped polyrotaxan reinforced castor oil-based polyurethane adhesive.

[0034] Example 3

[0035] (1) 12 parts of dehydrated castor oil and 24 parts of diphenyl methane diisocyanate were stirred and mixed, reacted at 60°C for 40 minutes, and vacuum degassed three times for standby use.

[0036] (2) 3 parts of palygorskite end-capped polyrotaxan was dissolved in 1.5 parts of anhydrous acetone, added to step (1), and 0.2 parts of dibutyltin dilaurate was added as a catalyst, and stirred uniformly at room temperature to obtain a high-performance palygorskite end-capped polyrotaxan reinforced castor oil-based polyurethane adhesive.

[0037] Example 4

[0038] (1) 12 parts of dehydrated castor oil and 24 parts of diphenyl methane diisocyanate were stirred and mixed, reacted at 60°C for 40 minutes, and vacuum degassed three times for standby use.

[0039] (2) 4 parts of palygorskite end-capped polyrotaxan was dissolved in 1.5 parts of anhydrous acetone, added to step (1), and 0.2 parts of dibutyltin dilaurate was added as a catalyst, and stirred uniformly at room temperature to obtain a high-performance palygorskite end-capped polyrotaxan reinforced castor oil-based polyurethane adhesive.

[0040] Example 5

[0041] (1) 14 parts of dehydrated castor oil and 24 parts of diphenyl methane diisocyanate were stirred and mixed, reacted at 60°C for 40 minutes, and vacuum degassed three times for standby use.

[0042] (2) 3 parts of palygorskite end-capped polyrotaxan was dissolved in 1.5 parts of anhydrous acetone, added to step (1), and 0.2 parts of dibutyltin dilaurate was added as a catalyst, and stirred uniformly at room temperature to obtain a high-performance palygorskite end-capped polyrotaxan reinforced castor oil-based polyurethane adhesive.

[0043] Example 6

[0044] (1) 12 parts of dehydrated castor oil and 26 parts of diphenyl methane diisocyanate were stirred and mixed, reacted at 60°C for 40 minutes, and vacuum degassed three times for standby use.

[0045] (2) 3 parts of palygorskite end-capped polyrotaxan was dissolved in 1.5 parts of anhydrous acetone, added to step (1), and 0.2 parts of dibutyltin dilaurate was added as a catalyst, and stirred uniformly at room temperature to obtain a high-performance palygorskite end-capped polyrotaxan reinforced castor oil-based polyurethane adhesive.

[0046] Comparative Example 1

[0047] Mix 12 parts of dehydrated castor oil with 24 parts of diphenylmethane diisocyanate, add 0.2 parts of dibutyltin dilaurate as catalyst, react at 60°C for 40 minutes to obtain castor oil polyurethane adhesive.

[0048] Comparative Example 2

[0049] Mix 12 parts of dehydrated castor oil with 24 parts of diphenylmethane diisocyanate, add 3 parts of palygorskite, 0.2 parts of dibutyltin dilaurate as catalyst, react at 60°C for 40 minutes to obtain palygorskite reinforced castor oil based polyurethane adhesive.

[0050] Comparative Example 3

[0051] Mix 12 parts of dehydrated castor oil with 24 parts of diphenylmethane diisocyanate, add 0.2 parts of dibutyltin dilaurate as catalyst, react at 60°C for 40 minutes. Dissolve 3 parts of palygorskite end-capped polyrotaxane in 1.5 parts of anhydrous acetone, add to the above reaction, stir uniformly at room temperature to obtain modified castor oil polyurethane adhesive.

[0052] Comparative Example 4

[0053] React 1 part of acid treated palygorskite with 0.5 parts of chitosan in 50 mL of deionized water for 6 hours (80°C), then vacuum dry at 60°C overnight to obtain chitosan modified palygorskite. Add 3 parts of chitosan modified palygorskite to a mixture of 12 parts of dehydrated castor oil and 24 parts of diphenylmethane diisocyanate, add 0.2 parts of dibutyltin dilaurate as catalyst, react at 60°C for 40 minutes to obtain modified castor oil polyurethane adhesive.

[0054] Test Example

[0055] The castor oil polyurethane adhesives prepared in the examples and comparative examples were used for the bonding of poplar single boards (coating amount 180 g / m 2 , hot pressing at 120°C, 1.2 MPa for 5 minutes). The bonding strength test was carried out by the method of national standard GB / T 17657-2013, the tensile speed was 20 mm / min. The bonding strength results of the castor oil polyurethane adhesives prepared in examples 1-6 and comparative examples 1-4 to wood are shown in the following table 1.

[0056] Table 1

[0057]

[0058] As can be seen from the above table, the dry / wet bonding strength of the examples is significantly improved compared to Comparative Example 1 and Comparative Example 2. Mainly due to the limitation of the properties of the unmodified castor oil polyurethane, the cohesive strength of the adhesive is not enough to provide sufficient bonding force, and the bonding strength is low. The introduction of palygorskite can improve the bonding performance to a certain extent, but palygorskite is easy to agglomerate, and the compatibility with polyurethane adhesive is weak, which greatly weakens the reinforcing effect of palygorskite. In the examples, the palygorskite is modified to prepare palygorskite-terminated polyrotaxan, which has good plasticizing and reinforcing effect, and can improve the viscosity of the polyurethane adhesive, making it easier to coat and form a uniform adhesive layer, which is beneficial to significantly improve the bonding strength. Under the condition of the same amount of dehydrated castor oil and isocyanate, the dry / wet bonding strength of Example 3 is the highest. Adding the same amount of palygorskite-terminated polyrotaxan, increasing castor oil (Example 5) or isocyanate (Example 6) will cause the bonding strength to increase or decrease. Because the increase of castor oil may cause the crosslinking density in the adhesive to decrease, the looseness of the molecular structure of the adhesive is increased, thereby reducing the bonding strength. While increasing the isocyanate content within a proper range helps to form a more compact network structure, enhancing the bonding strength of the adhesive. Compared with Example 3, changing the addition order of the catalyst (Comparative Example 3) will reduce the bonding strength of the adhesive, mainly because the catalyst added first in Comparative Example 3 makes the isocyanate and castor oil react rapidly at a certain ratio, affecting the crosslinking reaction of the palygorskite-terminated polyrotaxan in the polyurethane adhesive. Compared with Comparative Example 4, the bonding strength of Example 3 is significantly better under the condition of the same amount of modifier, mainly because the introduction of polyrotaxan makes the interface between palygorskite and polyurethane adhesive have effective stress transfer, enhancing the bonding strength of the polyurethane adhesive.

[0059] The castor oil polyurethane adhesive films prepared in the examples and comparative examples were subjected to tensile testing at a tensile speed of 50 mm / min. The toughness of the adhesive was evaluated. The toughness results of the castor oil polyurethane adhesives prepared in Examples 1-6 and Comparative Examples 1-4 after curing are shown in Table 2 below.

[0060] Table 2

[0061]

[0062] As shown in Table 2, the toughness of the adhesive of the examples is significantly higher than that of the comparative examples, indicating that the toughness of the polyurethane adhesive with palygorskite-terminated polyrotaxan is significantly enhanced, mainly because the palygorskite-terminated polyrotaxan has a molecular pulley effect. When the adhesive is subjected to external force impact, the internal polymer chain can effectively realize stress transfer through rotation and chain slippage, reduce stress concentration, and promote the significant enhancement of the toughness of the polyurethane adhesive.

[0063] The castor oil polyurethane adhesives prepared in the examples and comparative examples were applied in the preparation of flakeboard (adhesion amount 6%, pressure, temperature, time: 1.6 MPa, 135 °C, 5 minutes), and the internal bonding strength of the flakeboard was tested (vertical tensile speed 2 mm / min). The internal bonding strength of the flakeboard bonded by the castor oil polyurethane adhesives prepared in examples 1-6 and comparative examples 1-4 was shown in Table 3.

[0064] Table 3

[0065]

[0066] The results in Table 3 showed that the internal bonding strength of the flakeboard bonded by the palygorskite-capped polyrotaxane modified castor oil polyurethane adhesive was significantly higher than that of the comparative examples. With the same amount of dehydrated castor oil and isocyanate, the internal bonding strength of examples 2 and 3 was relatively high, and more addition of palygorskite-capped polyrotaxane led to the decrease of the internal bonding strength of the adhesive (example 4). Mainly due to the excessive addition of palygorskite-capped polyrotaxane may weaken the adhesion of the adhesive, thereby affecting the bonding strength of the adhesive and the flakeboard. Therefore, it is important to balance the appropriate amount of palygorskite-capped polyrotaxane to maintain the performance of the adhesive and effectively improve the internal bonding strength of the flakeboard. With the same amount of palygorskite-capped polyrotaxane, the increase of the isocyanate content led to the slight increase of the internal bonding strength of the flakeboard (example 6), because the high reactivity of the isocyanate group would promote the bonding of the polyurethane adhesive and the flakeboard to some extent.

[0067] Although the general concept, specific embodiments and tests of the present application have been described in detail above, it is obvious for those skilled in the art to make some modifications or improvements on the basis of the present application. Therefore, these modifications or improvements made without changing the original meaning of the present application are considered to be within the scope of protection of the present application.

Claims

1. A polyurethane adhesive enhanced by molecular pulley effect, characterized in that, The raw materials are proportioned by mass fraction as follows: isocyanate 24-26 parts, castor oil 12-14 parts, catalyst 0.2 parts, and palygorskite end-capped polyrotaxan 1-4 parts; The preparation method of the palygorskite end-capped polyrotaxan is as follows: functionalized pretreated palygorskite and quasi-polyrotaxan are stirred and reacted in anhydrous acetone, and after filtration, washing, and vacuum drying, the palygorskite end-capped polyrotaxan is obtained, and the mass ratio of the functionalized pretreated palygorskite to the quasi-polyrotaxan is (0.05-0.11):1; The preparation method of the functionalized pretreated palygorskite is as follows: purified palygorskite is reacted with silane coupling agent γ-aminopropyltrimethoxysilane to obtain aminated palygorskite, and then the modified palygorskite is obtained through N-hydroxysuccinimide, wherein the mass ratio of the palygorskite, the γ-aminopropyltrimethoxysilane, and the N-hydroxysuccinimide is 1:0.2-0.4:0.5-1; The preparation method of the quasi-polyrotaxan is as follows: aminopropyl end-capped polydimethylsiloxane is ultrasonically treated with an aqueous solution of cyclodextrin, and then stirred at room temperature, and then the reacted solution is filtered and vacuum dried to obtain the quasi-polyrotaxan, wherein the weight ratio of the aminopropyl end-capped polydimethylsiloxane to the cyclodextrin is 1:(5.5-7); The preparation method of the polyurethane adhesive enhanced by the molecular pulley effect is as follows: (1) castor oil and isocyanate are added to a reaction kettle, stirred uniformly, and reacted at 35-60°C for 20-40 min to prepare an isocyanate end-capped prepolymer, which is vacuum degassed for standby; (2) then palygorskite end-capped polyrotaxan and a catalyst are added for crosslinking modification to obtain the polyurethane adhesive enhanced by the molecular pulley effect.

2. The polyurethane adhesive enhanced by molecular pulley effect according to claim 1, characterized in that, The purified palygorskite is palygorskite activated by hydrochloric acid with a pH of 6-7.

3. The polyurethane adhesive enhanced by molecular pulley effect according to claim 1, characterized in that, The catalyst is dibutyltin dilaurate or triethylamine.

4. Use of the polyurethane adhesive enhanced by the molecular pulley effect according to claim 1 in the preparation of wood-based panels.

5. Use according to claim 4, characterized in that, The polyurethane adhesive is used for gluing poplar veneers, and hot pressing technology is adopted for gluing, with a hot pressing temperature of 120-135°C, a hot pressing pressure of 1.0-1.5 MPa, and a hot pressing time of 5-8 min.

6. Use according to claim 4, characterized in that, The polyurethane adhesive is used for gluing particle boards, with a glue application amount of 5-6 wt%, and a pressure, temperature, and time of 1.6-3.0 MPa, 135-150°C, and 4-5 min, respectively.

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