Preparation method of rosin-containing bio-based waterborne polyurethane leather coating material

Abstract

The invention provides a preparation method of a rosin-containing bio-based waterborne polyurethane leather coating material, and belongs to the field of bio-based surface coating materials. The method is characterized in that hydrogenated rosin ethylene glycol acrylate and mercapto propylene glycol are used as raw materials, and the rosin monomer containing double hydroxyl groups is synthesized in one step through a mercapto-alkene click reaction initiated by ultraviolet light. Then, the rosin monomer is used as a chain extender, and is subjected to gradual addition polymerization with polyhydric alcohols and diisocyanate to prepare the rosin-containing bio-based waterborne polyurethane leather coating material. The phenanthrene-like ring skeleton structure of rosin endows the polyurethane material with good mechanical strength and water resistance. Compared with other preparation methods, the method provided by the invention has the advantages that the process is relatively simple, synthesis steps are reduced, high-temperature operation is avoided, and a new way is provided for high-added-value utilization of rosin resources and development of bio-based polyurethane.

Description

Technical Field

[0001] The invention relates to the research field of bio-based surface coating materials, and in particular to a method for preparing a rosin-containing bio-based waterborne polyurethane leather coating material. Background Art

[0003] As a polymer material, polyurethane refers to a block copolymer with alternating soft and hard segments containing a large number of carbamate (-NH-COO-) structural units on the main chain. Its full name is polyurethane, which is the common PU in life. The soft segment is composed of oligomer polyols such as polyether and polyester, while the hard segment is composed of polyisocyanate and chain extender. The soft segment molecular chain accounts for a large proportion of the PU segment, which mainly affects the crystallinity, elasticity, low temperature performance and water resistance of the polymer. The hard segment usually affects the softening point, melting temperature and high temperature performance of the polymer. Therefore, the type, density and relative molecular mass of the soft and hard segments will directly affect the microphase morphology of the PU chain, and then affect the physical and chemical properties of the polymer. Utilizing the unique microphase structure and the designability of groups and segments, PU has been widely used in leather, shoemaking, construction, furniture, home appliances, automobiles and aerospace.

[0004] Polyurethane is mostly obtained by the reaction of polyisocyanate and polyol, but its synthetic raw materials, oligomer polyol and polyisocyanate, mostly come from non-renewable fossil resources. With the depletion of oil, people pay more and more attention to the use of renewable biomass resources as raw materials, and the development of environmentally friendly green and low-carbon new materials using biomass resources has received widespread attention. Researchers have begun to turn their attention to renewable biomass resources, trying to use molecules produced by plants and animals in nature, such as rosin, tannin, lignin, cellulose and other extracts, to synthesize new materials.

[0005] Among them, rosin is a forestry biomass resource with Chinese characteristics. China is a major producer and exporter of rosin, and its main component is a mixture of tricyclic diterpene resin acids. Rosin is a rich natural renewable plant resource with good biocompatibility, biodegradability and low cost. Rosin is modified mainly through two reactive groups - carboxyl and double bonds, which provides a basis for using rosin to replace petroleum products to synthesize new polymer materials. Through modification, it can be more fully utilized. Scientific and technological progress and economic development have put forward higher requirements on the production technology and quality of rosin modified products. As a renewable resource, deep processing, increasing product types, improving product quality and broadening its application range will have great development prospects and broad market space.

[0006] At present, there are also literature reports on the use of rosin as a raw material or monomer to prepare bio-based polyurethane. A Chinese patent document with publication number CN117510351A discloses a method for preparing a rosin polyurethane underwater adhesive, wherein the rosin glycol chain extender prepared is first subjected to chlorination reaction of rosin or its derivatives, then bromoethanol and an acid-binding agent are added to carry out a dehalogenation reaction, the product is purified to obtain 2-bromoethyl dehydrogenated rosin ester, then 2-bromoethyl dehydrogenated rosin ester and diethanolamine are reacted at 70-90°C for 18-30 hours, and purified to obtain the rosin glycol chain extender, and finally the rosin glycol chain extender is used to prepare an underwater high-strength polyurethane adhesive. The Chinese patent document with publication number CN114133517A discloses a rosin polyurethane and its synthesis method, and the invention content is to sequentially subject rosin anhydride to imidization reaction, chlorination reaction, and esterification reaction to obtain rosin polyol; then, the rosin polyol and diisocyanate are stirred evenly, and a catalyst is added to perform polyurethane reaction in a water bath; then, the reaction product is poured into a polytetrafluoroethylene mold, and the rosin polyurethane is obtained after drying. The Chinese patent document with publication number CN113603857A discloses a preparation method of rosin fluorescent polyurethane, and the invention content is to perform addition reaction of rosin and acrylic acid at a high temperature of 230°C for 2 hours to generate modified rosin containing double bonds, and then perform ring-opening reaction with glycidyl methacrylate in toluene at 120°C for 5 hours, introduce hydroxyl groups, and finally synthesize polyurethane. However, most of the above preparation methods involve multi-step reactions, which are cumbersome to operate, some also require high-temperature operation, high energy consumption, and may cause side reactions.

[0007] The applicant noted that hydrogenated rosin is the main type of modified rosin. It is a conjugated double bond of abietic resin acid that reacts with hydrogen under certain conditions. When part of the double bonds are saturated with hydrogen, it is called dihydrorosin (hydrogenated rosin); when all are saturated with hydrogen, it is called tetrahydrorosin (perhydrorosin). The double bond structure of hydrogenated rosin is changed, the ring structure is more stable, and the negative effects of double bonds are eliminated. Due to its large volume and high rigidity of the alicyclic structure, its toxicity is lower than that of rosin. It has excellent antioxidant properties, low brittleness, strong adhesion, and light color. It can be used in coatings, adhesives, thickeners, flux, rubber and other fields. Hydrogenated rosin ethylene glycol acrylate (EGHRA) is prepared by esterification of hydrogenated rosin with acrylic acid and ethylene glycol. Its molecular structure contains the alicyclic structure of hydrogenated rosin and the double bonds of acrylic acid, which makes it have good reactivity and chemical stability.

[0008] Based on this, the present invention discloses a method for preparing a bio-based waterborne polyurethane leather coating material containing rosin. A rosin monomer containing dihydroxyl is prepared under the action of light through a mercapto-ene click reaction, and then introduced into polyurethane in the form of a chain extender. The present invention does not require multi-step reactions, cumbersome operations, and high-temperature reactions, greatly reducing energy consumption and the generation of by-products.

[0009] The dihydroxy-containing rosin monomer retains the phenanthrene ring skeleton structure of rosin, has good rigidity and stability, and can give polyurethane higher cohesive energy, thereby improving the heat resistance and mechanical strength of the material. The dihydroxy rosin monomer is used as a chain extender and then introduced into the polyurethane matrix through addition polymerization to replace part of the petrochemical raw materials, which helps to reduce dependence on non-renewable resources. This method has not been reported in literature or patents. Summary of the invention

[0010] The present invention provides a method for preparing a bio-based waterborne polyurethane leather coating material containing rosin. The method is characterized in that the preparation method firstly obtains a polyurethane prepolymer by reacting a polyol with a diisocyanate, then adds a rosin monomer containing a dihydroxyl group as a molecular chain extender to perform a stepwise addition polymerization reaction, then adds a hydrophilic chain extender to perform a hydrophilic chain extension reaction, and finally obtains the material by neutralization reaction and water-based emulsification operation. The specific steps are as follows:

[0011] (1) adding diisocyanate and hydroxyl group of polyol into a reactor in a molar ratio of (4-10):1, adding an appropriate amount of solvent to ensure that the solid content of the reaction system is 30%, the temperature is 70-90° C., the stirring speed is 600-3000 rpm, and the stirring reaction is carried out for 0.5-2 hours to obtain a polyurethane prepolymer;

[0012] (2) adding a dihydroxy-containing rosin monomer as a molecular chain extender into a reactor, wherein the molar ratio of the dihydroxy-containing rosin monomer to diisocyanate is (0.05-0.5):1, the temperature is 50-90° C., the stirring speed is 200-2000 rpm, and the reaction is carried out under a catalyst condition for 1-4 hours;

[0013] (3) adding the hydrophilic chain extender dimethylol propionic acid and diisocyanate in a molar ratio of (0.08-0.7):1 into the reactor at a temperature of 60-90° C. and a stirring speed of 200-2000 rpm, and reacting for 1-4 hours under catalyst conditions;

[0014] (4) adding a neutralizing agent, triethylamine or triethanolamine, to the reactor, and carrying out a neutralization reaction for 0.5 to 4 hours at a temperature of 20 to 50° C. and a stirring speed of 500 to 3000 rpm, and adjusting the pH to 8 to 10;

[0015] (5) adding the reaction product to a certain amount of deionized water, stirring at high speed for 10 to 30 minutes at a stirring speed of 4000 to 9000 rpm, stirring at low speed for 1 to 2 hours at a stirring speed of 2000 to 3000 rpm, and concentrating the product to a solid content of 15% to 35% to obtain a water-based polyurethane material containing rosin;

[0016] The amount of the dihydroxy-containing rosin monomer is 5-30wt% of the total mass of the polyurethane. The preparation of the dihydroxy-containing rosin monomer is characterized by using hydrogenated rosin ethylene glycol acrylate (EGHRA) and mercaptopropylene glycol (TPG) as raw materials, and under ultraviolet light conditions, a photoinitiator is used to induce an addition reaction between vinyl and mercapto to generate the dihydroxy-containing rosin monomer. The specific steps are as follows:

[0017] (a) adding mercaptopropylene glycol, hydrogenated rosin ethylene glycol acrylate monomer, photoinitiator benzoin dimethyl ether and solvent ethyl acetate into a reactor, and after being completely dissolved, introducing nitrogen for 10 minutes to remove oxygen in the bottle, and sealing; reacting under ultraviolet light for 0.5 to 1 hour, the light intensity is 50% to 100%; wherein the molar ratio of hydrogenated rosin ethylene glycol acrylate to mercaptopropylene glycol is (0.5 to 5):1, the mass ratio of photoinitiator benzoin dimethyl ether to the total reactants is (0.5% to 1%):1, and the amount of solvent ethyl acetate added is such that the solid content of the reaction system is 10wt%;

[0018] (b) After the reaction is completed, the product is taken out and most of the solvent is removed by a rotary evaporator; the concentrated product is precipitated in n-hexane for 2 to 3 times, and finally vacuum dried at 40° C. for 18 to 24 hours to obtain a rosin monomer containing dihydroxyl groups.

[0019] The method for preparing a rosin-containing bio-based waterborne polyurethane leather coating material is characterized in that the click reaction of thiol and vinyl is utilized to retain the dihydroxyl and phenanthrene-like ring skeleton structure of rosin.

[0020] The method for preparing a rosin-containing bio-based waterborne polyurethane leather coating material is characterized in that the polyol is one or a mixture of polyethylene glycol, polytetramethylene glycol, polycaprolactone diol, terminal hydroxyl polysiloxane, terminal hydroxyl polylactic acid, and polycarbonate diol.

[0021] The method for preparing a rosin-containing bio-based waterborne polyurethane leather coating material is characterized in that the diisocyanate is one or a mixture of isophorone diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, lysine diisocyanate, 1,6-hexamethylene diisocyanate, and cyclohexane dimethylene diisocyanate.

[0022] The invention discloses a method for preparing a water-based polyurethane coating material containing rosin. The preparation method comprises the following steps: firstly synthesizing a rosin monomer chain extender containing dihydroxyl groups, and then introducing the rosin monomer chain extender into a polyurethane matrix by using an addition polymerization reaction. The rosin monomer chain extender containing dihydroxyl groups has excellent rosin group performance, and the dihydroxyl groups in the structure can undergo a condensation reaction with diisocyanate, thereby being introduced into the polyurethane matrix at a molecular level, and while maintaining the high transparency and film-forming performance of the coating material, the mechanical properties of the polyurethane can be increased. Moreover, rosin is a renewable natural resource, and using the rosin monomer as a chain extender helps to reduce dependence on non-renewable petroleum resources, which is in line with the development concept of green chemistry. The byproducts of the click reaction are usually harmless, which is in line with the principle of green chemistry.

[0023] Specific implementation cases

[0024] Three embodiments of the present invention are given below to specifically illustrate a method for preparing a rosin-containing waterborne polyurethane coating material.

[0025] Example 1

[0026] The preparation of rosin monomer containing dihydroxyl groups is as follows: weigh 4.04g of hydrogenated rosin ethylene glycol acrylate into a weighing bottle, add 1.08g of mercaptopropylene glycol and 0.05g of initiator benzoin dimethyl ether, and add 52mL of solvent (ethyl acetate). Stir magnetically for 1h. After the solid reagent is completely dissolved, pass nitrogen for 15min to remove the oxygen inside the reaction container. After sealing, react under ultraviolet irradiation for 1h, and the light intensity is 50%. After the reaction is completed, take out the product, evaporate most of the solvent with a rotary evaporator, wash the concentrated product with tetrahydrofuran 3 times, and finally dry it in a vacuum drying oven at 40°C for 24h. The reaction product, rosin monomer containing dihydroxyl groups, is obtained.

[0027] The invention discloses a preparation method of a water-based polyurethane coating material containing rosin, wherein the specific operation steps are as follows: 20.00 g of polytetrahydrofuran ether (Mn=2000) is weighed and added into a three-necked flask, and vacuum dried and dehydrated at 110° C. for 2 h, cooled to 85° C. and protected by nitrogen, and 15.56 g of isophorone diisocyanate and 139 mL of ethyl acetate solvent are added, and stirred for reaction for 1 h. The mixture is cooled to 70° C., and 13.37 g of a rosin monomer chain extender containing dihydroxy (accounting for 25 wt% of the total mass of the polyurethane) and a catalyst are added, and the reaction is carried out for 1 h. After the reaction is completed, 4.56 g of dimethylol propionic acid is added, and the reaction is stirred for 2 h. Triethylamine is added, and the reaction is carried out for 30 min, and the pH is adjusted to 6-10. Finally, deionized water was added, and the mixture was emulsified at a high speed of 5000 rpm for 40 minutes, and then at a low speed of 2000 rpm for 1 hour. The reaction product was concentrated to a solid content of 20% to obtain a rosin-containing water-based polyurethane emulsion.

[0028] Example 2

[0029] The preparation of dihydroxy rosin-containing monomers is as follows: weigh 4.85g of hydrogenated rosin ethylene glycol acrylate in a weighing bottle, add 1.29g of mercaptopropylene glycol and 0.05g of initiator benzoin dimethyl ether, and add 62mL of solvent (ethyl acetate). Stir magnetically for 1h. After the solid reagent is completely dissolved, pass nitrogen for 15min to remove the oxygen inside the reaction container. After sealing, react under ultraviolet irradiation for 1h, and the light intensity is 50%. After the reaction is completed, take out the product, evaporate most of the solvent with a rotary evaporator, wash the concentrated product 3 times with tetrahydrofuran, and finally dry it in a vacuum drying oven at 40°C for 24h. The reaction product is a rosin monomer containing dihydroxy.

[0030] The preparation of a water-based polyurethane coating material containing rosin is as follows: 20.00g of polycarbonate diol (Mn=2000) is weighed and added to a three-necked flask, vacuum dried and dehydrated at 110°C for 2h, cooled to 85°C and protected by nitrogen, 11.77g of 1,6-hexamethylene diisocyanate and 133mL of ethyl acetate solvent are added, and stirred for reaction for 1h. After cooling to 70°C, 15.34g of a rosin monomer chain extender containing dihydroxy (accounting for 30wt% of the total mass of the polyurethane) and a catalyst are added to react for 1h. After the reaction is completed, 4.02g of dimethylol propionic acid is added and stirred for reaction for 2h. Triethylamine is added to react for 30min, and the pH is adjusted to 6-10. Finally, deionized water was added, and the mixture was emulsified at a high speed of 5000 rpm for 40 minutes, and then at a low speed of 2000 rpm for 1 hour. The reaction product was concentrated to a solid content of 20% to obtain a rosin-containing water-based polyurethane emulsion.

[0031] Example 3

[0032] The preparation of dihydroxy rosin-containing monomers is as follows: weigh 8.09g of hydrogenated rosin ethylene glycol acrylate in a weighing bottle, add 2.16g of mercaptopropylene glycol and 0.05g of initiator benzoin dimethyl ether, and add 103mL of solvent (ethyl acetate). Stir magnetically for 1h. After the solid reagent is completely dissolved, pass nitrogen for 15min to remove the oxygen inside the reaction container. After sealing, react under ultraviolet irradiation for 1h, and the light intensity is 50%. After the reaction is completed, take out the product, evaporate most of the solvent with a rotary evaporator, wash the concentrated product with tetrahydrofuran 3 times, and finally dry it in a vacuum drying oven at 40°C for 24h. The reaction product is a rosin monomer containing dihydroxy.

[0033] The invention discloses a preparation method of a water-based polyurethane coating material containing rosin. The specific operation steps are as follows: 20.00g of polyethylene glycol (Mn=2000) is weighed and added to a three-necked flask, and the mixture is vacuum dried and dehydrated at 110°C for 2h, cooled to 85°C and protected by nitrogen, and 17.50g of diphenylmethane diisocyanate and 138mL of ethyl acetate solvent are added, and the mixture is stirred and reacted for 1h. The mixture is cooled to 70°C, and 10.69g of a rosin monomer chain extender containing dihydroxy (accounting for 20wt% of the total mass of the polyurethane) and a catalyst are added and reacted for 1h. After the reaction is completed, 5.23g of dimethylol propionic acid is added and stirred and reacted for 2h. Triethylamine is added and reacted for 30min, and the pH is adjusted to 6-10. Finally, deionized water is added, and an emulsifier is used to emulsify the mixture at a high speed for 40min at a stirring speed of 5000rpm, and then the mixture is emulsified at a low speed for 1h at a stirring speed of 2000rpm, and the reaction product is concentrated to a solid content of 20%, thereby obtaining a water-based polyurethane emulsion containing rosin.

Claims

1. A method for preparing a rosin-containing bio-based waterborne polyurethane leather coating material, characterized in that The preparation method is to first obtain a polyurethane prepolymer by reacting a polyol with a diisocyanate, then add a rosin monomer containing a dihydroxyl group as a molecular chain extender to conduct a stepwise addition polymerization reaction, then add a hydrophilic chain extender to conduct a hydrophilic chain extension reaction, and finally obtain the polyurethane prepolymer by neutralization reaction and aqueous emulsification operation. The specific steps are as follows: (1) adding diisocyanate and hydroxyl group of polyol into a reactor in a molar ratio of (4-10):1, adding an appropriate amount of solvent to ensure that the solid content of the reaction system is 30%, the temperature is 70-90° C., the stirring speed is 600-3000 rpm, and the stirring reaction is carried out for 0.5-2 hours to obtain a polyurethane prepolymer; (2) adding a dihydroxy-containing rosin monomer as a molecular chain extender into a reactor, wherein the molar ratio of the dihydroxy-containing rosin monomer to diisocyanate is (0.05-0.5):1, the temperature is 50-90° C., the stirring speed is 200-2000 rpm, and the reaction is carried out under a catalyst condition for 1-4 hours; (3) adding the hydrophilic chain extender dimethylol propionic acid and diisocyanate in a molar ratio of (0.08-0.7):1 into the reactor at a temperature of 60-90° C. and a stirring speed of 200-2000 rpm, and reacting for 1-4 hours under catalyst conditions; (4) adding a neutralizing agent, triethylamine or triethanolamine, to the reactor, and carrying out a neutralization reaction for 0.5 to 4 hours at a temperature of 20 to 50° C. and a stirring speed of 500 to 3000 rpm, and adjusting the pH to 8 to 10; (5) adding the reaction product to a certain amount of deionized water, stirring at high speed for 10 to 30 minutes at a stirring speed of 4000 to 9000 rpm, stirring at low speed for 1 to 2 hours at a stirring speed of 2000 to 3000 rpm, and concentrating the product to a solid content of 15% to 35% to obtain a water-based polyurethane material containing rosin; The amount of the dihydroxy-containing rosin monomer is 5-30wt% of the total mass of the polyurethane. The preparation of the dihydroxy-containing rosin monomer is characterized by using hydrogenated rosin ethylene glycol acrylate (EGHRA) and mercaptopropylene glycol (TPG) as raw materials, and under ultraviolet light conditions, a photoinitiator is used to induce an addition reaction between vinyl and mercapto to generate the dihydroxy-containing rosin monomer. The specific steps are as follows: (a) adding mercaptopropylene glycol, hydrogenated rosin ethylene glycol acrylate monomer, photoinitiator benzoin dimethyl ether and solvent ethyl acetate into a reactor, and after being completely dissolved, introducing nitrogen for 10 minutes to remove oxygen in the bottle, and sealing; reacting under ultraviolet light for 0.5 to 1 hour, the light intensity is 50% to 100%; wherein the molar ratio of hydrogenated rosin ethylene glycol acrylate to mercaptopropylene glycol is (0.5 to 5):1, the mass ratio of photoinitiator benzoin dimethyl ether to the total reactants is (0.5% to 1%):1, and the amount of solvent ethyl acetate added is such that the solid content of the reaction system is 10wt%; (b) After the reaction is completed, the product is taken out and most of the solvent is removed by a rotary evaporator; the concentrated product is precipitated in n-hexane for 2 to 3 times, and finally vacuum dried at 40° C. for 18 to 24 hours to obtain a rosin monomer containing dihydroxyl groups.

2. The method for preparing a rosin-containing bio-based waterborne polyurethane leather coating material according to claim 1, characterized in that The phenanthrene-like skeleton structure of rosin was retained by utilizing the click reaction between thiol and vinyl.

3. The method for preparing a rosin-containing bio-based waterborne polyurethane leather coating material according to claim 1, characterized in that The polyol is one or a mixture of several of polyethylene glycol, polytetramethylene glycol, polycaprolactone glycol, hydroxyl-terminated polysiloxane, hydroxyl-terminated polylactic acid and polycarbonate diol.

4. The method for preparing a rosin-containing bio-based waterborne polyurethane leather coating material according to claim 1, characterized in that The diisocyanate is one or a mixture of isophorone diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, lysine diisocyanate, 1,6-hexamethylene diisocyanate and cyclohexane dimethylene diisocyanate.