A fast-curing bio-based hot melt adhesive and its preparation method

Abstract

The present invention belongs to the technical field of hot melt adhesive preparation, and particularly relates to a fast-curing bio-based hot melt adhesive and a preparation method thereof. Using cyclic siloxane, mercapto acid and polyetheramine as raw materials, a silicone-modified polyetheramine is obtained through ring-opening polymerization, thiol-ene click reaction and amidation reaction, and then it is mixed with dimer acid, sebacic acid, antioxidant, catalyst, organoborosiloxane and stearic acid, and ethylenediamine is added to obtain the fast-curing bio-based hot melt adhesive. The prepared hot melt adhesive has good low-temperature resistance, adhesiveness and self-healing property, and uses dimer acid as the main bio-based raw material, having good biodegradability and being environmentally friendly and sustainable.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot melt adhesive preparation, and particularly relates to a fast-curing bio-based hot melt adhesive and a preparation method thereof. Background Art

[0002] Hot melt adhesive is a solvent-free adhesive prepared by melt blending a thermoplastic polymer as a base material, adding tackifying resins, waxes, antioxidants and other components. Compared with traditional solvent-based adhesives and inorganic adhesives, it has the advantages of no volatile organic compounds, water resistance without delamination, fast curing speed and repeatable adhesion, and is easy to process, recyclable, with a higher degree of automation and lower cost. Hot melt adhesives can generally be divided into ethylene-based, polyamide-based, polyester-based, polyurethane-based, and thermoplastic rubber-based, etc. Polyamide resin hot melt adhesives are widely used in industrial production and are obtained by polycondensation of dibasic acids and diamines or polyamines. Dimer acid-based polyamide resin is a kind of polyamide resin, which is a product obtained by polycondensation reaction of dimer acid with diamines or polyamines. Dimer acid is generally a polymer synthesized by heating and catalyzing two identical or different unsaturated fatty acids with 18 carbon atoms, and the raw materials can also be obtained from renewable resources. With the continuous enhancement of people's environmental protection awareness, low-pollution or pollution-free environmentally friendly hot melt adhesives have attracted the attention of the industry. Therefore, developing more environmentally friendly adhesives with a wider range of applications is of great significance for the development of the adhesive industry.

[0003] Chinese Patent with Publication No. CN115725259B discloses a reactive polyurethane hot melt adhesive and a preparation method thereof, which is prepared by mixing polyether polyol, polyester polyol, tackifying resin, thermoplastic resin, polyisocyanate, adhesion promoter and catalyst. By modifying the polyether polyol with polysiloxane and introducing the polysiloxane molecular chain, the mutual slip ability of the molecular chains of the PUR adhesive is improved, and the initial adhesion performance of the product is effectively enhanced. The characteristic that the polysiloxane molecular chain is in a curled and helical conformation is that the prepared hot melt adhesive has excellent fatigue resistance. Chinese Patent with Publication No. CN115851213B discloses a reactive polyurethane hot melt adhesive for bonding nitrile rubber and a preparation method thereof, which is prepared by mixing crystalline polyester polyol, liquid polyester polyol, dimer acid-modified polyol, isocyanate, adhesion promoter, hydroxyl-terminated nitrile rubber, catalyst, carbon black and antioxidant. By adding an appropriate amount of dimer acid-modified polyol, it has good wettability with NBR, so that PUR has good adhesion to NBR. The prepared reactive polyurethane hot melt adhesive for bonding nitrile rubber can obtain excellent bonding strength without surface treatment of NBR materials in the bonding application of NBR materials, which can greatly improve the bonding efficiency of NBR materials and reduce costs.

[0004] However, with the continuous development of hot melt adhesives, their application environments are becoming increasingly complex. Therefore, higher requirements are put forward for the preparation of weather-resistant hot melt adhesives, especially low-temperature resistant hot melt adhesives. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention provides a fast-curing bio-based hot melt adhesive and its preparation method. Using cyclic siloxane, mercapto acid and polyetheramine as raw materials, through ring-opening polymerization, thiol-ene click reaction and amidation reaction, a silicone-modified polyetheramine is obtained. Then, it is mixed with dimer acid, sebacic acid, antioxidant, catalyst, organoborosiloxane and stearic acid, and ethylenediamine is added to obtain the fast-curing bio-based hot melt adhesive. The prepared hot melt adhesive has good low-temperature resistance, adhesiveness and self-healing properties.

[0006] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0007] A preparation method of a fast-curing bio-based hot melt adhesive, comprising the following steps:

[0008] S1. Obtain a polysiloxane with a branched vinyl structure by ring-opening polymerization of cyclic siloxane;

[0009] S2. Obtain a polysiloxane containing an alkyl side chain by thiol-ene click reaction of the polysiloxane with a branched vinyl structure and mercapto acid;

[0010] S3. Obtain a silicone-modified polyetheramine by amidation reaction of the polysiloxane containing an alkyl side chain and polyetheramine;

[0011] S4. Add dimer acid, sebacic acid, silicone-modified polyetheramine, antioxidant and catalyst to a reaction kettle, stir and heat to 110-130 °C, with a stirring rate of 200-300 rpm. When adding ethylenediamine, turn off the heating and let it heat up naturally. Ethylenediamine is added dropwise, with a dropping control time of 50-70 min and a temperature control of 130-150 °C. After the addition is completed, control the temperature at 130-150 °C and keep it warm for 1-2 h, then raise the temperature to 230-250 °C and keep it warm for 20-40 min;

[0012] Using dimer acid as the main bio-based raw material provides a good foundation for flexibility and adhesion. The addition of sebacic acid helps to regulate the structure and properties of the molecular chain. The antioxidant can effectively prevent the oxidative degradation of the material during processing and use, and the catalyst can promote the efficient progress of the reaction. Ethylenediamine is added dropwise slowly, which is different from the traditional one-time mixing or rapid dropwise addition, and can avoid problems such as increased side reactions, unstable product properties, and gelation caused by too fast local reactions. By precisely controlling the dropping speed and temperature, the molecular weight distribution of the polymer can be effectively regulated, thereby significantly improving the mechanical properties of the hot melt adhesive. After the dropping is completed, the temperature is controlled and kept warm to provide sufficient time for the reaction, enabling the reactants to react more fully, promoting the growth and cross-linking of the molecular chain, improving the uniformity and stability of the product, and ensuring the consistency of the properties of the prepared hot melt adhesive. Further raising the temperature and keeping it warm for a period of time, the reaction proceeds at a higher temperature, which is conducive to forming a more perfect polymer network structure and enhancing the intermolecular force, thereby endowing the hot melt adhesive with high mechanical strength.

[0013] S5. After the heat preservation is completed, vacuum polymerization is carried out. After the polymerization is completed, nitrogen is used to break the vacuum, and the temperature is lowered and the material is discharged to obtain the polymer. The vacuum operation can effectively remove small molecule substances such as water and unreacted monomers in the reaction system, can effectively improve the purity of the product, reduce the adverse effects of impurities on the product performance, help to form a denser polymer structure, and further improve the performance of the hot melt adhesive product.

[0014] S6. Add the polymer and organoborosiloxane into the reaction kettle, heat to 110 - 130 °C, stir and react for 1 - 3 h, add stearic acid and control the vacuum degree, vacuum stir for 20 - 40 min, lower the temperature and discharge the material to obtain the fast-curing bio-based hot melt adhesive.

[0015] Hot melt adhesive is a solid adhesive composed of thermoplastic polymers, antioxidants, etc. According to the use temperature, hot melt adhesives can be divided into high-temperature, medium-temperature and low-temperature hot melt adhesives. Hot melt adhesives are widely used in people's daily lives. However, with the increasingly complex and diverse use environments, traditional hot melt adhesives face problems such as a sharp decline in flexibility and easy brittleness in low-temperature environments, which seriously affect the use range of hot melt adhesives. At the same time, with the continuous enhancement of environmental awareness, the industry has an urgent need for the research and development of bio-based hot melt adhesives. Therefore, in this invention, dimer acid is used as a bio-based raw material and mixed with sebacic acid, polyamide, ethylenediamine, etc. to prepare hot melt adhesives. However, bio-based hot melt adhesives are difficult to meet the high-standard requirements in terms of bonding strength and low-temperature resistance. Therefore, during the preparation process, siloxane is used to modify polyetheramine to improve the flexibility, low-temperature resistance and adhesiveness of the prepared product, and at the same time, organoborosiloxane is introduced to enhance the self-healing performance of the product.

[0016] Further, the specific preparation process of step S1 is as follows: Under an inert atmosphere, preferably a nitrogen atmosphere, octamethylcyclotetrasiloxane, tetramethyltetravinylcyclotetrasiloxane, an initiator, and a hexamethyldisiloxane terminator are added to a reactor. The temperature is raised to 110 - 130 °C and reacted for 3 - 5 h, and then the temperature is raised to 140 - 150 °C and reacted for 1 - 2 h. After the reaction is completed, the reaction product is dissolved and precipitated with dichloromethane and methanol 3 - 5 times and then dried to obtain the polysiloxane with a branched vinyl structure; wherein, the molar ratio of octamethylcyclotetrasiloxane, tetramethyltetravinylcyclotetrasiloxane, the initiator, and the hexamethyldisiloxane terminator is 120 - 130:6.8 - 8.5:0.1:0.11 - 0.15; the drying conditions are: in a vacuum drying oven, vacuum drying at 50 - 60 °C for 14 - 20 h.

[0017] Further, the preparation process of the initiator is as follows: Tetramethylammonium hydroxide solution and octamethylcyclotetrasiloxane monomer are added to a reactor, heated to 40 - 50 °C, and dehydrated under vacuum conditions for 1 - 2 h, with a vacuum degree of -0.1 MPa. After dehydration, the reaction system is purged with nitrogen 3 - 5 times, and then the temperature is raised to 85 - 95 °C for polymerization. After reacting for 12 - 16 h, heating is stopped and the temperature is lowered to room temperature. Then, anhydrous toluene is added to the reactor to obtain the initiator; wherein the mass ratio of the tetramethylammonium hydroxide solution, the octamethylcyclotetrasiloxane monomer, and the anhydrous toluene is 0.42 - 0.52:10:22 - 32; the mass fraction of the tetramethylammonium hydroxide solution is 25 wt%.

[0018] Further, the specific preparation process of step S2 is as follows: Under an inert atmosphere, preferably a nitrogen atmosphere, the polysiloxane with a branched vinyl structure, toluene, and the photoinitiator benzoin dimethyl ether are added to a reactor and mixed evenly, and then mercapto acid is added thereto. After the addition is completed, it is irradiated with an ultraviolet lamp. After the reaction is completed, it is dissolved and precipitated with tetrahydrofuran and methanol 3 - 5 times and then dried to obtain the polysiloxane containing an alkyl side chain; wherein, the mass ratio of the polysiloxane with a branched vinyl structure, toluene, the photoinitiator, and the mercapto acid is 1 - 1.5:4 - 6:0.01:1.2 - 2.4; the drying conditions are vacuum drying in a vacuum drying oven at 75 - 95 °C for 14 - 20 h; the ultraviolet lamp irradiation conditions: 365 nm, 120 W, irradiation for 20 - 40 min; the mercapto acid is any one or a mixture of several of 4-mercaptobutyric acid, 5-mercaptopentanoic acid, 6-mercaptohexanoic acid, 8-mercaptooctanoic acid, 11-mercaptoundecanoic acid, 14-mercaptotetradecanoic acid, 16-mercaptohexadecanoic acid.

[0019] Further, the specific preparation process of step S3 is as follows: Add dichloromethane, alkyl-branched polysiloxane and polyetheramine into a reactor, control the temperature at 0 - 4 °C, after mixing evenly, add 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and stir for 6 - 10 min, then stir at room temperature for 18 - 25 h, then add the same volume of dichloromethane thereto, and then wash successively with dilute hydrochloric acid, water and sodium bicarbonate aqueous solution, and dry the organic phase with magnesium sulfate to obtain the polysiloxane-modified polyetheramine; wherein the mass ratio of dichloromethane (total amount of dichloromethane added twice), alkyl-branched polysiloxane, polyetheramine and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide is 80 - 120:7 - 15:4 - 12:2 - 5, the concentration of dilute hydrochloric acid is 0.5 M, the concentration of sodium bicarbonate solution is 4%, and the volume ratio of dichloromethane (total volume of dichloromethane added twice), dilute hydrochloric acid, water and sodium bicarbonate aqueous solution is 6:4:2:3.

[0020] Polysiloxane has a silicon-oxygen main chain structure with inorganic characteristics and a combination of organic groups connected to silicon atoms - having special semi-inorganic and semi-organic molecular structure characteristics. The siloxane group part in its molecule is easy to chemically react with the hydroxyl groups on the surface of inorganic materials to form stable silicon-oxygen bonds, thereby achieving a firm bond with inorganic materials. At the same time, the organic functional groups in the molecule can interact with organic materials to further enhance the adhesion strength with organic materials. Therefore, polysiloxane is used to modify polyamide and used in the preparation of hot melt adhesives to improve the adhesiveness of hot melt adhesives. However, although polysiloxane has extremely high molecular chain flexibility and structural regularity, having a low glass transition temperature also makes polysiloxane prone to low-temperature crystallization before the glass transition temperature, making it difficult to meet the application requirements in special low-temperature environments. Since the better the flexibility of the polymer molecular chain, the stronger its activity ability at low temperatures and the better its low-temperature resistance, and at the same time, by adjusting the structure of the molecular chain, the regularity of the molecular chain can be destroyed to inhibit low-temperature crystallization. The alkyl molecular chain is composed of carbon atoms and hydrogen atoms, and the carbon atoms are connected by single bonds. The internal rotation barrier of this single bond is small, making the entire chain have good flexibility. In addition, the bond length and bond angle between carbon atoms in the alkyl chain also enable the molecular chain to bend and twist more easily, thus showing good flexibility. Therefore, in this application, polysiloxane with a branched ethylene structure is synthesized, and then through an efficient thiol-ene click reaction with mercapto acid containing a flexible alkyl molecular chain, flexible alkyl branches are introduced into the side chain of polysiloxane to make it have certain low-temperature resistance.

[0021] Further, the preparation method of the organoborosiloxane is as follows: Place the hydroxyl silicone oil in an aluminum beaker and place it on a constant temperature magnetic stirrer. Heat it to 100 - 105 °C, and add the pretreated boric acid to it in small amounts and multiple times. After the addition is completed, raise the temperature to 120 - 125 °C, and then raise it to 150 - 155 °C under sufficient stirring, and keep the temperature for 15 - 25 minutes to obtain the organoborosiloxane.

[0022] The organosilicon boroxane is synthesized by dehydration condensation between the silicon hydroxyl groups at the ends of the molecular chains of the hydroxyl-terminated polydimethylsiloxane and the boron hydroxyl groups of boric acid. Since its molecular chain contains more Si - O - Si structures, the bond length of the Si - O bond is longer, and the steric hindrance and rotational barrier are lower. Therefore, its molecular chain shows good flexibility. The boron atoms with vacancies can act as acceptors for the lone pair electrons of oxygen atoms in adjacent molecular chains to form non-bonded complexes between molecules. The interaction between boron and oxygen atoms can cause dynamic physical cross-linking between molecular chains. This bonding effect is in a dynamic process of continuous dissociation and reformation, making it have excellent self-healing performance. When damaged, the molecular chains can entangle with each other, and the dynamic reversible boron-oxygen bonds and dynamic hydrogen bonds can re-bond at room temperature without any external stimulus, thus achieving rapid self-repair of the damaged part. In addition, during the mixing process with the polymer, the Si - O - Si structure contained in the polymer can cross-link with the Si - O - Si structure contained in the organosilicon boroxane, thereby forming a three-dimensional silicon oxide network structure, further increasing the mechanical properties of the prepared hot melt adhesive.

[0023] The present invention also provides a fast-curing bio-based hot melt adhesive, and the fast-curing bio-based hot melt adhesive is obtained by using the preparation method of any one of the above technical solutions.

[0024] The present invention has the following excellent effects:

[0025] Using dimer acid as the main bio-based raw material, it has good biodegradability, environmental protection and sustainability; and a polysiloxane with a branched ethylene structure is synthesized and a mercapto acid containing a flexible alkyl molecular chain is used to introduce flexible alkyl branches into the side chain of the polysiloxane through an efficient thiol-ene click reaction to further improve the low-temperature resistance of the prepared hot melt adhesive. At the same time, an organoborosiloxane with self-healing performance is added during the preparation of the hot melt adhesive. When damaged, the molecular chains can entangle with each other, and the dynamic reversible boron-oxygen bonds and dynamic hydrogen bonds can re-bond at room temperature without any external stimulus, thus achieving rapid self-repair of the damaged part. And during the mixing process with the polymer, the Si - O - Si structures contained on different molecular chains cross-link with each other to form a three-dimensional silicon oxide network structure, further increasing the mechanical properties of the prepared hot melt adhesive. Detailed embodiments

[0026] Next, in combination with the embodiments of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present application.

[0027] The dimer acid (industrial product, monoacid content 3%, dimer content 85%, trimer 12%, relative molecular mass 560) used in the present invention was purchased from Jinan Zhuobang Economic and Trade Co., Ltd., octamethylcyclotetrasiloxane (purity 98%), tetramethyltetravinylcyclotetrasiloxane (purity 96.5%), tetramethylammonium hydroxide (purity 25 wt%), benzoin dimethyl ether (purity 98%) were purchased from Aladdin Chemistry & 3A, hexamethyldisiloxane (purity 99%) was purchased from Macklin, dichloromethane (analytical pure AR), toluene (purity 99%) were purchased from Xilong Scientific, 8-mercaptooctanoic acid (purity ≥95%), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (purity ≥95%), polyetheramine (D-400), sebacic acid (analytical pure), stearic acid (purity ≥98.5%) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., hydroxy silicone oil (analytical pure, 2.4%) was purchased from Changzhou Polyyou New Material Technology Co., Ltd., boric acid (analytical pure) was purchased from Tianjin Hengxing Chemical Reagent Manufacturing Co., Ltd. All reagents are commercially available.

[0028] Example 1

[0029] A preparation method of a fast-curing bio-based hot melt adhesive, comprising the following steps:

[0030] S1. Under a nitrogen atmosphere, octamethylcyclotetrasiloxane, tetramethyltetravinylcyclotetrasiloxane, an initiator and a hexamethyldisiloxane terminator are added to a reactor, the temperature is raised to 120 °C and reacted for 4 h, and then the temperature is raised to 145 °C and reacted for 2 h. After the reaction is completed, the reaction product is dissolved and precipitated 4 times with dichloromethane and methanol and then dried to obtain a polysiloxane with a branched vinyl structure; wherein, the molar ratio of octamethylcyclotetrasiloxane, tetramethyltetravinylcyclotetrasiloxane, the initiator and the hexamethyldisiloxane terminator is 120:7.2:0.1:0.12; the drying conditions are: in a vacuum drying oven, vacuum drying at 55 °C for 16 h;

[0031] Among them, the preparation process of the initiator is as follows: Add tetramethylammonium hydroxide solution and octamethylcyclotetrasiloxane monomer into the reactor, heat to 45°C, remove water under vacuum conditions for 2 h, with a vacuum degree of -0.1 MPa. After water removal, displace the reaction system with nitrogen 4 times, then raise the temperature to 90°C for polymerization. After reacting for 14 h, stop heating and lower the temperature to room temperature, keep the reactor sealed, and then add anhydrous toluene into the reactor to obtain the initiator; among them, the mass ratio of tetramethylammonium hydroxide solution, octamethylcyclotetrasiloxane monomer and anhydrous toluene is 0.48:10:25; the mass fraction of the tetramethylammonium hydroxide solution is 25 wt%.

[0032] S2. Under a nitrogen atmosphere, add polysiloxane with a branched ethylene structure, toluene and photoinitiator benzoin dimethyl ether into the reactor, mix them evenly, then add mercapto acid thereto. After the addition is completed, irradiate with an ultraviolet lamp. After the reaction ends, dissolve and precipitate 4 times with tetrahydrofuran and methanol and then dry to obtain polysiloxane containing an alkyl side chain; among them, the mass ratio of polysiloxane with a branched ethylene structure, toluene, photoinitiator and mercapto acid is 1.2:5:0.01:1.6; the drying conditions are vacuum drying at 85°C for 18 h in a vacuum drying oven; the ultraviolet lamp irradiation conditions: 365 nm, 120 W, irradiate for 30 min; the mercapto acid is 8-mercaptooctanoic acid.

[0033] S3. Add dichloromethane, polysiloxane containing an alkyl side chain and polyetheramine into the reactor, control the temperature at 0°C, mix them evenly, then add 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and stir for 8 min, then stir at room temperature for 22 h, and then add the same volume of dichloromethane thereto. Then wash with dilute hydrochloric acid, water and sodium bicarbonate aqueous solution in sequence. Dry the organic phase with magnesium sulfate to obtain siloxane-modified polyetheramine; among them, the mass ratio of dichloromethane (total amount of dichloromethane added twice), polysiloxane containing an alkyl side chain, polyetheramine and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide is 110:12:8:3, the concentration of the dilute hydrochloric acid is 0.5 M, the concentration of the sodium bicarbonate solution is 4%, and the volume ratio of dichloromethane (total volume of dichloromethane added twice), dilute hydrochloric acid, water and sodium bicarbonate aqueous solution is 6:4:2:3.

[0034] S4. Add 350 parts by weight of dimer acid, 25 parts by weight of sebacic acid, 65 parts by weight of siloxane-modified polyetheramine, 8 parts by weight of antioxidant 2,6-di-tert-butyl-4-methylphenol and 1.2 parts by weight of catalyst bismuth isooctanoate into the reaction kettle, stir and heat to 120°C, with a stirring rate of 250 rpm. When adding 38 parts by weight of ethylenediamine, turn off the heating and let it rise in temperature naturally. The ethylenediamine is added dropwise, and the dropping time is controlled for 60 min, and the temperature is controlled at 140°C. After the addition is completed, control the temperature at 140°C and keep it warm for 2 h, then raise the temperature to 240°C and keep it warm for 30 min.

[0035] S5. After the heat preservation is completed, carry out vacuum polymerization, control the vacuum degree below -0.092 MPa, the vacuum pumping time is 30 min. After the polymerization is completed, break the vacuum with nitrogen, cool down and discharge the material, and the cooling rate is 5 °C / min to obtain the polymer;

[0036] S6. Add 450 parts by weight of the polymer and 18 parts by weight of organoborosiloxane into the reaction kettle, heat to 120 °C, stir and react for 2 h, add 4 parts by weight of stearic acid and control the vacuum degree to -0.095 MPa, carry out vacuum pumping and stirring for 30 min, cool down and discharge the material to obtain the fast-curing bio-based hot melt adhesive.

[0037] Among them, the preparation method of the organoborosiloxane is as follows: Place 65 parts by weight of hydroxy silicone oil in an aluminum beaker, and place it on a constant temperature magnetic stirrer, heat up to 105 °C, add 1.8 parts by weight of pretreated boric acid to it in small amounts and multiple times, add it in 6 times, with an interval of 10 min each time. After the addition is completed, raise the temperature to 125 °C, and raise the temperature to 155 °C under sufficient stirring, and keep warm for 20 min to obtain the organoborosiloxane; the pretreatment process of the boric acid is: grind the boric acid in a mortar for 35 min.

[0038] Example Two

[0039] This example is different from Example One as follows:

[0040] In step S1, after adding octamethylcyclotetrasiloxane, tetramethyltetravinylcyclotetrasiloxane, initiator and hexamethyldisiloxane endblocking agent into the reactor, raise the temperature to 110 °C and react for 3 h, then raise the temperature to 140 °C and react for 1 h. After the reaction is completed, dissolve and precipitate the reaction product with dichloromethane and methanol 3 times and then dry it; the molar ratio of octamethylcyclotetrasiloxane, tetramethyltetravinylcyclotetrasiloxane, initiator and hexamethyldisiloxane endblocking agent is 120:6.8:0.1:0.11; the drying conditions are: in a vacuum drying oven, vacuum dry at 50 °C for 14 h.

[0041] In the preparation process of the initiator, add tetramethylammonium hydroxide solution and octamethylcyclotetrasiloxane monomer into the reactor, heat to 40 °C, remove water under vacuum conditions for 1 h. After removing water, displace the reaction system with nitrogen 3 times, and then raise the temperature to 85 °C for polymerization. Stop heating after reacting for 12 h; the mass ratio of tetramethylammonium hydroxide solution, octamethylcyclotetrasiloxane monomer and anhydrous toluene is 0.42:10:22.

[0042] In step S2, after the reaction is completed, it is dissolved and precipitated 3 times with tetrahydrofuran and methanol and then dried. The mass ratio of the polysiloxane with branched vinyl structure, toluene, photoinitiator and mercapto acid is 1:4:0.01:1.2; the drying conditions are vacuum drying at 75 °C for 14 h in a vacuum drying oven; the ultraviolet lamp irradiation conditions are: 365 nm, 120 W, irradiation for 20 min.

[0043] In step S3, dichloromethane, polysiloxane with alkyl branches and polyetheramine are added to the reactor, the temperature is controlled at 2 °C, and after mixing evenly, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide is added and stirred for 6 min, and then stirred at room temperature for 18 h. The mass ratio of dichloromethane (the total amount of dichloromethane added twice), polysiloxane with alkyl branches, polyetheramine and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide is 80:7:4:2.

[0044] In step S4, 250 parts by weight of dimer acid, 12 parts by weight of sebacic acid, 25 parts by weight of silicone-modified polyetheramine, 3 parts by weight of antioxidant 2,6-di-tert-butyl-4-methylphenol and 0.6 parts by weight of catalyst bismuth isooctanoate are added to the reaction kettle, stirred and heated to 110 °C, the stirring rate is 200 rpm, heating is turned off when 28 parts by weight of ethylenediamine is added. When adding ethylenediamine, the dropping is controlled for 50 min and the temperature is controlled at 130 °C. After the addition is completed, the temperature is controlled at 130 °C for heat preservation for 1 h, and then the temperature is raised to 230 °C for heat preservation for 20 min.

[0045] In step S5, the time for vacuum pumping is 20 min, and the cooling rate during cooling and discharging is 5 °C / min.

[0046] In step S6, 260 parts by weight of the polymer and 8 parts by weight of organoborosiloxane are added to the reaction kettle, heated to 110 °C, stirred and reacted for 1 h, 1.2 parts by weight of stearic acid is added and the vacuum degree is controlled at -0.095 MPa, and vacuum pumping and stirring are carried out for 20 min.

[0047] The rest all refer to Example 1.

[0048] Example 3

[0049] Compared with Example 1, this example has the following differences:

[0050] In step S1, octamethylcyclotetrasiloxane, tetramethyltetravinylcyclotetrasiloxane, an initiator, and a hexamethyldisiloxane capping agent are added to the reactor, and then the temperature is raised to 130 °C and reacted for 5 h. After that, the temperature is raised to 150 °C and reacted for 2 h. After the reaction is completed, the reaction product is dissolved and precipitated 5 times with dichloromethane and methanol and then dried; the molar ratio of octamethylcyclotetrasiloxane, tetramethyltetravinylcyclotetrasiloxane, the initiator, and the hexamethyldisiloxane capping agent is 130:8.5:0.1:0.15; the drying conditions are: in a vacuum drying oven, vacuum drying at 60 °C for 20 h.

[0051] In the preparation process of the initiator, a tetramethylammonium hydroxide solution and octamethylcyclotetrasiloxane monomer are added to the reactor, heated to 50 °C, and dehydrated under vacuum conditions for 2 h. After dehydration, the reaction system is purged with nitrogen 5 times, and then the temperature is raised to 95 °C for polymerization, and the heating is stopped after reacting for 16 h; the mass ratio of the tetramethylammonium hydroxide solution, octamethylcyclotetrasiloxane monomer, and anhydrous toluene is 0.52:10:32.

[0052] In step S2, after the reaction is completed, it is dissolved and precipitated 5 times with tetrahydrofuran and methanol and then dried. The mass ratio of the polysiloxane with branched-chain vinyl structure, toluene, a photoinitiator, and mercapto acid is 1.5:6:0.01:2.4; the drying conditions are vacuum drying at 95 °C for 20 h in a vacuum drying oven; the ultraviolet lamp irradiation conditions are: 365 nm, 120 W, irradiated for 40 min.

[0053] In step S3, dichloromethane, polysiloxane with alkyl branches, and polyetheramine are added to the reactor, the temperature is controlled at 4 °C, and after mixing evenly, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide is added and stirred for 10 min, and then stirred at room temperature for 25 h. The mass ratio of dichloromethane (total amount of dichloromethane added twice), polysiloxane with alkyl branches, polyetheramine, and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide is 120:15:12:5.

[0054] In step S4, 400 parts by weight of dimer acid, 28 parts by weight of sebacic acid, 72 parts by weight of silicone-modified polyetheramine, 12 parts by weight of antioxidant 2,6-di-tert-butyl-4-methylphenol, and 1.8 parts by weight of catalyst bismuth isooctanoate are added to the reaction kettle, stirred and heated to 130 °C, the stirring rate is 300 rpm, and heating is turned off when 42 parts by weight of ethylenediamine is added. When adding ethylenediamine, the dropping is controlled for 70 min, the temperature is controlled at 150 °C, and after the addition is completed, the temperature is controlled at 150 °C for heat preservation for 2 h, and then the temperature is raised to 250 °C for heat preservation for 40 min.

[0055] In step S5, the time for vacuum pumping is 40 min, and the cooling rate during cooling and discharging is 10 °C / min.

[0056] In step S6, 520 parts by weight of the polymer and 25 parts by weight of the organoborosiloxane are added to the reaction kettle, heated to 130 °C, stirred and reacted for 3 h, 6 parts by weight of stearic acid is added, and the vacuum degree is controlled to be -0.095 MPa, and vacuum pumping and stirring are carried out for 40 min.

[0057] The rest are all referred to Example 1.

[0058] Comparative Example 1

[0059] Compared with Example 1, in the preparation process of step S2, the mercapto acid is replaced with 4-mercaptobutyric acid, and the rest are all referred to Example 1.

[0060] Comparative Example 2

[0061] Compared with Example 1, in the preparation process of step S2, the mercapto acid is replaced with 5-mercaptopentanoic acid, and the rest are all referred to Example 1.

[0062] Comparative Example 3

[0063] Compared with Example 1, in the preparation process of step S2, the mercapto acid is replaced with 6-mercaptohexanoic acid, and the rest are all referred to Example 1.

[0064] Comparative Example 4

[0065] Compared with Example 1, in the preparation process of step S2, the mercapto acid is replaced with 11-mercaptoundecanoic acid, and the rest are all referred to Example 1.

[0066] Comparative Example 5

[0067] Compared with Example 1, in the preparation process of step S2, the mercapto acid is replaced with 14-mercaptotetradecanoic acid, and the rest are all referred to Example 1.

[0068] Comparative Example 6

[0069] Compared with Example 1, in the preparation process of step S2, the mercapto acid is replaced with 16-mercaptohexadecanoic acid, and the rest are all referred to Example 1.

[0070] Comparative Example 7

[0071] Compared with Example 1, in this comparative example, the polyetheramine is modified by blending vinyl-terminated dimethyl polysiloxane and polyetheramine, and the rest are referred to Example 1, specifically as follows:

[0072] A preparation method of a bio-based hot melt adhesive, comprising the following steps:

[0073] A1. Add vinyl-terminated dimethyl polysiloxane and polyetheramine into the reactor, heat to 65 °C, and stir and mix for 20 min to obtain polyetheramine modified with vinyl-terminated dimethyl polysiloxane;

[0074] A2. Refer to step S4 in Example 1, where the silicone-modified polyetheramine is replaced with polyetheramine modified with vinyl-terminated dimethyl polysiloxane;

[0075] A3. Refer to step S5 in Example 1;

[0076] A4. Refer to step S6 in Example 1.

[0077] Comparative Example 8

[0078] Compared with Example 1, in this comparative example, the polyetheramine is not modified, and the rest refers to Example 1, specifically as follows:

[0079] A preparation method of a bio-based hot melt adhesive, comprising the following steps:

[0080] B1. Refer to step S4 in Example 1, where the silicone-modified polyetheramine is replaced with polyetheramine;

[0081] B2. Refer to step S5 in Example 1;

[0082] B3. Refer to step S6 in Example 1.

[0083] Comparative Example 9

[0084] Compared with Example 1, in this comparative example, the polyetheramine is not modified, and organoborosiloxane is not added during the preparation process. The rest refers to Example 1, specifically as follows:

[0085] A preparation method of a bio-based hot melt adhesive, comprising the following steps:

[0086] B1. Refer to step S4 in Example 1, where the silicone-modified polyetheramine is replaced with polyetheramine;

[0087] B2. Refer to step S5 in Example 1;

[0088] B3. Refer to step S6 in Example 1, where organoborosiloxane is not added.

[0089] Related tests:

[0090] Tensile strength and elongation at break test: The samples prepared in each example and comparative example were made into dumbbell shapes according to the standard ASTM-D638-2003. After measuring the thickness, the tensile properties and low-temperature flexibility were tested. Among them, the low-temperature flexibility is the limit temperature value at which fracture occurs in a non-tensile state, and the low-temperature elongation at break is the tensile elongation at a temperature of -50°C. The test results are shown in Table 1.

[0091] Table 1 Test results of low-temperature flexibility, tensile strength and elongation at break

[0092]

[0093] Open time test method: Referring to HG / T 3716-2003 Determination of open time of hot-melt adhesives, the samples prepared in each example and comparative example were tested. The test was carried out in an environment with a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The melting temperature of the hot-melt adhesive was 150°C ± 2°C, and the test interval was 5 s. The test results are shown in Table 2. Among them, the shorter the open time, the better the quick-drying property of the hot-melt adhesive.

[0094] Table 2 Test results of open time

[0095]

[0096] Tensile shear strength test: The samples prepared in each example and comparative example were used for bonding between wood boards and between PE boards and PET boards. After preparing two groups of specimens, referring to GB / T 7124-2008 Determination of Tensile Shear Strength of Adhesives (Rigid Material to Rigid Material), the tensile shear strength between the samples and different substrates in the two groups of specimens was tested. The tensile rate was 10 mm / min. Among them, the low-temperature (-40°C) tensile shear strength refers to cooling to low temperature (-40°C) after lamination and then testing at low temperature (-40°C). The test results are shown in Table 3. Among them, the higher the tensile shear strength, the higher the bonding strength of the hot-melt adhesive to the substrate and the better the bonding performance.

[0097] Table 3 Test results of tensile shear strength

[0098]

[0099] It can be found from the test results in Table 3 that among the test results of Example 1 and Comparative Examples 1 to 6, the tensile shear strength increases with the increase of the flexible chain of mercapto acid, but its performance decreases instead with the continuous increase of the flexible chain. This is because with the increase of the length of the flexible alkyl chain, the too long flexible alkyl chain is prone to cause intramolecular crosslinking, resulting in a decrease in performance.

[0100] Self-healing performance test: The sample prepared in Example 1 was made into dumbbell shape according to the standard ASTM-D638-2003. A double-layer blade was prepared using a craft knife (100×18×0.5 mm). A 100 g weight was placed above the double blades to control the applied force, and a cut mark was generated under the action of gravity. The repair situation of the scratch on the sample surface was observed using a LEXTOLS4000 type laser confocal microscope produced by OLYMPUS Corporation of Japan. The test results are shown in Table 4, where the average value of the absolute value of the height difference at each point was used to characterize the surface roughness of the sample, and it was represented by S α It can be seen from the test results that as time goes by, the roughness of the cut mark generated on the sample prepared in Example 1 gradually decreases, indicating that the prepared sample has certain healing performance without external force.

[0101] Table 4 Self-healing performance test results

[0102]

[0103] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0104] Although the embodiments of the present application have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present application. The scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a fast-curing bio-based hot melt adhesive, characterized in that: The following steps are involved: S1, obtaining a polysiloxane with a branched vinyl structure by a ring-opening polymerization reaction of cyclosiloxane; S2, polysiloxane with branched vinyl structure and mercapto acid are reacted by mercapto-ene click reaction to obtain polysiloxane containing alkyl branches; S3, obtaining siloxane-modified polyetheramine by amidation reaction of alkyl branched polysiloxane and polyetheramine; S4, adding dimer acid, sebacic acid, siloxane-modified polyetheramine, antioxidant and catalyst into the reaction kettle, stirring and heating to 110-130°C, adding ethylenediamine and turning off the heating, after the addition is completed, controlling the temperature at 130-150°C for 1-2h, and then raising the temperature to 230-250°C for 20-40min; S5, after the heat preservation is completed, vacuum polymerization is carried out, and after the polymerization is completed, nitrogen is used to break the air, and the temperature is lowered to discharge the material to obtain a polymer; S6, adding the polymer and the organoborosiloxane into a reaction kettle, heating to 110-130° C., stirring for 1-3 hours, adding stearic acid and controlling the vacuum degree, vacuuming and stirring for 20-40 minutes, cooling and discharging, and obtaining the fast-curing bio-based hot melt adhesive; The specific preparation process of step S3 is as follows: adding dichloromethane, alkyl branched polysiloxane and polyetheramine to a reactor, controlling the temperature at 0-4°C, adding 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide after mixing evenly, stirring for 6-10 minutes, and then stirring at room temperature for 18-25 hours, adding dichloromethane thereto, and then washing with dilute hydrochloric acid, water and sodium bicarbonate aqueous solution in sequence, and drying the organic phase with magnesium sulfate to obtain the siloxane-modified polyetheramine; wherein the mass ratio of dichloromethane, alkyl branched polysiloxane, polyetheramine and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide is 80-120:7-15:4-12:2-5.

2. The method for preparing the fast-curing bio-based hot melt adhesive according to claim 1, characterized in that: The specific preparation process of step S1 is as follows: under an inert atmosphere, octamethylcyclotetrasiloxane, tetramethyltetravinylcyclotetrasiloxane, an initiator and a hexamethyldisiloxane end-capping agent are added to a reactor, the temperature is increased to 110-130° C. for reaction for 3-5 hours, and then the temperature is increased to 140-150° C. for reaction for 1-2 hours. After the reaction is completed, the polysiloxane with a branched vinyl structure is obtained by dissolving and precipitating with dichloromethane and methanol for 3-5 times and then drying.

3. The method for preparing the fast-curing bio-based hot melt adhesive according to claim 2, characterized in that: The preparation process of the initiator is as follows: adding tetramethylammonium hydroxide solution and octamethylcyclotetrasiloxane monomer into a reactor, heating to 40-50°C, removing water under vacuum conditions for 1-2 hours, replacing the reaction system with nitrogen after removing water, and then raising the temperature to 85-95°C for polymerization, stopping heating after reacting for 12-16 hours, and lowering the temperature to room temperature, and then adding anhydrous toluene into the reactor to obtain the initiator.

4. The method for preparing the fast-curing bio-based hot melt adhesive according to claim 1, characterized in that: The specific preparation process of step S2 is as follows: under an inert atmosphere, polysiloxane with a branched ethylene structure, toluene and a photoinitiator are added to a reactor, mixed evenly, and then mercapto acid is added thereto. After the addition is completed, it is irradiated with an ultraviolet lamp. After the reaction is completed, tetrahydrofuran and methanol are used for dissolution-precipitation 3-5 times and then dried to obtain the polysiloxane containing alkyl branches.

5. The method for preparing the fast-curing bio-based hot melt adhesive according to claim 4, characterized in that: The drying conditions after dissolution and precipitation with tetrahydrofuran and methanol for 3-5 times are 75-95° C. in a vacuum drying oven for 14-20 hours.

6. The method for preparing the fast-curing bio-based hot melt adhesive according to claim 1, characterized in that: The preparation method of the organic borosiloxane is as follows: hydroxy silicone oil is placed in an aluminum beaker, and the beaker is placed on a constant temperature magnetic stirrer, and the temperature is raised to 100-105° C., and pretreated boric acid is added thereto in small amounts and multiple times. After the addition is completed, the temperature is raised to 120-125° C., and then raised to 150-155° C. with sufficient stirring, and kept warm for 15-25 minutes to obtain the organic borosiloxane.

7. A fast-curing bio-based hot melt adhesive, characterized in that: The fast-curing bio-based hot melt adhesive is obtained by the preparation method according to any one of claims 1 to 6.

Images