Preparation method of environment-friendly flame-retardant waterborne polyurethane

Abstract

A preparation method of environment-friendly flame-retardant waterborne polyurethane relates to the technical field of polymer synthesis and comprises the following steps: drying polyol under high-temperature vacuum conditions; uniformly mixing the dried polyol and isocyanate, heating for reaction, adding a chain extender, a hydrophilic chain extender and acetone, uniformly mixing, heating for reaction, adding a catalyst, heating for reaction, and discharging to obtain a waterborne polyurethane prepolymer; adding an alkaline aqueous solution into the waterborne polyurethane prepolymer, uniformly stirring and emulsifying to obtain a waterborne polyurethane emulsion; adding a micromolecule chain extender into the waterborne polyurethane emulsion, adding a defoaming agent after complete reaction, reacting in a constant-temperature vacuum environment, cooling to room temperature after complete reaction, and filtering reaction liquid to obtain environment-friendly flame-retardant waterborne polyurethane; according to the invention, the bio-based polyol is introduced into a cross-linked network, the preparation process is environment-friendly and pollution-free, the preparation process is simple and does not contain halogen, and the prepared waterborne polyurethane coating film has the characteristic of excellent flame retardance.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer synthesis, and particularly to a preparation method of an environmentally friendly flame-retardant waterborne polyurethane. Background Art

[0002] In recent years, countries around the world have strengthened the concept of environmental protection. Solvent-based polyurethanes are restricted due to their large pollution, while waterborne polyurethanes, which contain no or a small amount of volatile organic solvents, have gradually become a research hotspot. Waterborne polyurethanes have excellent mechanical properties, easy processing, heat insulation, wear resistance and other advantages, and are widely used in many fields such as automobile manufacturing, transportation, footwear and medical treatment, clothing and footwear leather, etc. However, some raw materials of waterborne polyurethanes are harmful, such as a large number of organic solvents (such as acetone, methyl ethyl ketone, etc.), metal catalysts (such as tin compounds) and additives (formaldehyde may exist in the additives) used in the synthesis process, which cause pollution to the environment. It is necessary to develop a green synthesis process for waterborne polyurethanes. And the cured film of waterborne polyurethane is flammable, which restricts its application to a certain extent. Improving the flame-retardant performance of waterborne polyurethane also has forward-looking significance.

[0003] At present, there are two common methods for preparing flame-retardant waterborne polyurethanes. One is to add a flame retardant to the waterborne polyurethane emulsion by physical blending method, but the addition of an external flame retardant will reduce the stability and uniformity of the system, thereby reducing the performance of the material after application. The other is to introduce a flame-retardant monomer into the waterborne polyurethane chain through a chemical reaction. However, when a flame-retardant monomer is introduced into the waterborne polyurethane chain through a chemical reaction, its flame-retardant performance decreases with the extension of the use time. Summary of the Invention

[0004] The present invention aims to solve the disadvantages existing in the background art, and provides a preparation method of an environmentally friendly flame-retardant waterborne polyurethane, which solves at least some of the technical problems in the prior art.

[0005] To achieve the above object, the present invention provides the following technical solutions: A preparation method of an environmentally friendly flame-retardant waterborne polyurethane, comprising the following steps: Drying of polyol: The polyol is dried under vacuum at a temperature of 100 °C to 120 °C for 0.5 to 2 h until the water content in the polyol is lower than 0.05%; Preparation of prepolymer: The dried polyol is mixed evenly with an isocyanate and then heated for reaction. Then, a chain extender, a hydrophilic chain extender and acetone are added and mixed evenly, and then heated for reaction again. After adding a catalyst and heating for reaction, acetone is added for dilution before discharging to obtain a waterborne polyurethane prepolymer; Preparation of waterborne polyurethane emulsion: An alkaline aqueous solution is added to the waterborne polyurethane prepolymer, stirred evenly and emulsified to obtain a waterborne polyurethane emulsion; Post-chain-extended waterborne polyurethane: Add a small molecule chain extender to the waterborne polyurethane emulsion. After the reaction is complete, add an antifoaming agent and react in a constant temperature and vacuum environment. After the reaction is complete, cool to room temperature and filter the reaction solution to obtain an environmentally friendly flame-retardant waterborne polyurethane.

[0006] Further, the polyol is one or more of soybean oil, castor oil, polylactic acid, palm oil, cashew shell oil, isosorbide, lignin, non-halogenated flame retardant, modified soybean oil, modified castor oil, modified polylactic acid, modified palm oil, modified cashew shell oil, modified isosorbide, modified lignin, modified non-halogenated flame retardant; The number average molecular weight of the polyol is 500 - 4000.

[0007] Further, the steps for preparing the prepolymer are specifically as follows: Mix the dried polyol and isocyanate evenly, and react at 80°C to 100°C for 1 - 2 h; After the reaction is complete, add a chain extender, a hydrophilic chain extender and acetone, mix evenly, and react at 70°C to 100°C for 2 - 3 h; Finally, add a catalyst and react at 60 - 80°C for 2 - 4 h. Before discharging, add acetone for dilution to obtain a waterborne polyurethane prepolymer.

[0008] Further, the chain extender, hydrophilic chain extender, acetone and catalyst are all dried before use, and their moisture content is lower than 0.05%.

[0009] Further, the isocyanate is any one or more of isophorone diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, toluene diisocyanate.

[0010] Further, the chain extender is any one or more of ethylene glycol, 1,4-butanediol, methylpropanediol, trimethylolpropane, glycerol; The hydrophilic chain extender is any one or more of dimethylolpropionic acid, dimethylolbutyric acid; The catalyst is any one or more of dibutyltin dilaurate, stannous octoate, organobismuth.

[0011] Further, the alkaline aqueous solution is any one or more of triethylamine aqueous solution, diethanolamine aqueous solution, triethanolamine aqueous solution, sodium hydroxide aqueous solution, sodium bicarbonate aqueous solution, sodium acetate aqueous solution, ammonia water; During the preparation of the waterborne polyurethane emulsion, the solid content of the system is 20% - 50%, and the reaction temperature is 20°C - 40°C.

[0012] Further, the small molecule chain extender is any one or more of ethylenediamine, piperazine, isophorone diamine, hydrazine hydrate, diethylenetriamine, and silane coupling agent.

[0013] Further, the polyol, chain extender, and hydrophilic chain extender are dried by a vacuum method, the drying temperature is 100°C to 130°C, and the air pressure ≥ -0.08 MPa; The catalyst is dried in a blast drying oven at 100°C.

[0014] Further, the dosage of the catalyst accounts for 0.1% to 0.5% of the total mass of the polyol and isocyanate.

[0015] Advantages of the present invention: (1) Compared with the prior art, the present invention introduces bio-based polyol into its cross-linking network, is environmentally friendly and pollution-free during the preparation process, has a simple preparation process, and does not contain halogens; (2) The waterborne polyurethane coating film prepared by the present invention has excellent flame retardancy characteristics, and the waterborne polyurethane coating film prepared by the present invention has higher breaking strength and shorter elongation at break. Specific embodiments

[0016] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts belong to the protection scope of the present invention.

[0017] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are only examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numerals and / or reference letters in different examples. This repetition is for the purpose of simplification and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides examples of various specific processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0018] The preparation method of the environment-friendly flame-retardant waterborne polyurethane is as follows: Step 1: Drying of polyol Weigh 100 - 500 g of polyol into a four-necked flask equipped with a stirrer, a thermometer, a constant-pressure funnel, and a vacuum pump. Turn on the stirrer and the vacuum pump, heat up to 100°C - 120°C, adjust the pressure to ≤ -0.08 MPa, and keep drying under constant temperature and pressure for 0.5 - 2 hours until the water content of the polyol < 0.05% (the percentage of the mass of water in the polyol to the total mass of the polyol).

[0019] It should be noted that: the polyol is one or several of soybean oil, castor oil, polylactic acid, palm oil, cashew shell oil, isosorbide, lignin, Exolit OP 550, polyester BY3009T polyol monomer, etc. or modified substances of the above biomass organic polyols, and the number-average molecular weight range of the polyol as a whole is 500 - 4000.

[0020] Step 2: Preparation of aqueous polyurethane prepolymer Lower the temperature of the polyol obtained in Step 1 below 80°C, then add 30 - 130 g of diisocyanate to the polyol using a constant-pressure funnel, stir evenly, gradually raise the temperature to 70°C - 100°C, and carry out a constant-temperature reaction for 1 - 3 h until the -NCO content in the mixture reaches 2.00% - 5.00%.

[0021] Then cool down to below 80°C, add 1 - 5 g of dried chain extender, 5 - 20 g of dried hydrophilic chain extender, and 10 - 50 g of acetone, and carry out a constant-temperature reaction for 2 - 5 h.

[0022] Finally, add 0.5 - 5 g of catalyst and 10 - 100 g of acetone, stir evenly, gradually raise the temperature to 60°C - 100°C, and carry out a chain extension reaction under constant temperature conditions for 2 - 5 h until the -NCO content in the mixture reaches the designed value again, i.e., 2.00% - 5.00%. Finally, add 50 - 110 g of acetone to obtain the aqueous polyurethane prepolymer.

[0023] It should be noted that: in the above synthesis method, the chain extender and the aqueous chain extender used need to be dried to a water content < 0.05%; the chain extender and the aqueous chain extender used can synthesize the polyurethane prepolymer, and at the same time, evenly introduce hydrophilic functional groups into the molecular chain to improve the emulsification of the polyurethane prepolymer in water later; The determination of the -NCO content in the mixture is carried out by acid titration.

[0024] Step 3: Neutralization and emulsification of the prepolymer Transfer the prepolymer to an emulsifying kettle, turn on the stirring device, add 5 - 15 g of neutralizing agent (the neutralizing agent is an alkali), stir for 3 - 10 min for neutralization, then adjust the rotation speed to high-speed stirring, quickly add 400 - 1500 g of deionized water, and stir at high speed for 5 - 20 min until it is completely and evenly dispersed to obtain an aqueous polyurethane emulsion.

[0025] Step 4: Post - chain extension of aqueous polyurethane The polyurethane prepolymer further undergoes a chain - growth reaction with the post - chain extender in the aqueous solution to further increase the molecular weight of the polyurethane. The specific steps are to slowly add 5 - 60 g of a hydrazine hydrate solution of the post - chain extender with a mass fraction of 10% - 20% to the aqueous polyurethane emulsion and react for 10 - 20 min.

[0026] Then slowly add 3 - 8 drops of defoamer, stir evenly, then slowly heat up to 50 - 80 °C, adjust the vacuum pressure to ≤ - 0.08 MPa, hold the reaction for 1 - 2 h and then terminate the reaction, and then cool down to room temperature. After filtration, an environmentally friendly flame - retardant aqueous polyurethane can be obtained.

[0027] It should be noted that: The method for measuring the - NCO content in the prepolymer is as follows: When the reaction proceeds to a certain extent, accurately weigh about 1 g of the sample, and the weighing should be accurate to 0.001 g.

[0028] Place the sample in a clean 250 - ml conical flask.

[0029] Then accurately transfer 40 ml of a dibutylamine - toluene solution with a concentration of 0.1 mol / L to the sample using a pipette, shake it to mix evenly, and let it stand at room temperature for 20 - 40 min.

[0030] After the reaction is complete, add 40 - 50 ml of isopropanol, and at the same time wash the bottle mouth to terminate the reaction.

[0031] Drop in 2 - 3 drops of bromocresol green ethanol solution (mass fraction is about 0.1%) indicator. At this time, the system is blue.

[0032] Then titrate with a 0.1 mol / L hydrochloric acid standard solution until the blue color disappears, gradually changes from green to cyan and finally to yellow and remains unchanged for 1 min. At this time, it is the titration end point; Record the volume of the consumed hydrochloric acid standard solution as V2; According to the above steps, without weighing the sample for a blank control test, the volume of the consumed hydrochloric acid standard solution is V1; Then substitute it into the following formula for calculation to obtain the mass fraction of - NCO in the mixture at this time.

[0033] NCO% = (V1 - V2) × C × 0.042 / M × 100% Wherein, V1 is the volume (mL) of the standard hydrochloric acid solution used in the blank test; V2 is the volume (mL) of the standard hydrochloric acid solution used in the titration test; C is the molar concentration of the standard hydrochloric acid solution, mol / L; M is the mass (g) of the sample.

[0034] Example 1 Step 1: Drying of polyol First, add 300 g of castor oil and 105 g of polyester polyol BY3009T into a 1000 mL four-necked flask equipped with an electric stirrer, a thermometer, a constant pressure funnel, and a vacuum pump. Turn on the electric stirrer to stir, heat up the oil bath to 100 - 105 °C, turn on the vacuum pump to evacuate the four-necked flask. Start timing when the vacuum pressure ≤ -0.08 MPa, and perform vacuum dehydration for 0.5 - 1 h.

[0035] Step 2: Preparation of aqueous polyurethane prepolymer When the water content in the polyol < 0.05%, turn off the vacuum pump and lower the temperature of the oil bath. When the thermometer temperature drops to 70 °C, slowly add 83 g of isophorone diisocyanate through the constant pressure funnel. After adding, stir evenly. When the temperature reaches 95 °C, start timing and carry out a constant temperature reaction for 2 h.

[0036] Determine the -NCO content in the mixture by titration to reach the designed value.

[0037] Then cool down to 75 °C and add 3 g of dried trimethylolpropane, 19 g of dried dimethylolpropionic acid, and 20 g of acetone, stir evenly, gradually heat up to 80 °C, and carry out a constant temperature chain extension reaction for 2 h.

[0038] Finally, cool down to 60 °C and add 0.5 g of organic bismuth and 25 g of acetone, heat up to 65 °C and react for 3 h until the -NCO content in the mixture reaches the designed value again.

[0039] Add 100 g of acetone before discharging to obtain the aqueous polyurethane prepolymer.

[0040] Step 3: Neutralization and emulsification of the prepolymer Immediately transfer the obtained prepolymer to an emulsification kettle to obtain 707 g of the prepolymer. Then add 14 g of triethylamine to the prepolymer and stir for 2 min. After the prepolymer is completely neutralized, increase the stirring speed to 2500 r / min and quickly add 1255 g of deionized water, and stir at high speed for 8 min.

[0041] Step 4: Post-chain extension of aqueous polyurethane Slowly add 25 g of ethylenediamine diluted with water to 10% to the emulsion obtained in Step 3, continue to stir at high speed for 3 min, then add 0.2 g of defoamer, reduce the stirring speed to 800 r / min, and stir to defoam for 5 min.

[0042] Then transfer it to a 2000 mL four-necked flask equipped with a thermometer and a stirring device, heat it while stirring, adjust the vacuum pump pressure to ≤ -0.08 MPa. When the temperature rises to 60 °C, maintain this temperature for a constant reaction for 2 h. When it cools to room temperature, filter the emulsion to obtain environmentally friendly flame-retardant waterborne polyurethane.

[0043] Example 2 Step 1: Drying of polyol First, add 100 g of modified cashew shell oil and 78 g of Exolit OP 550 to a 500 mL four-necked flask equipped with an electric stirrer, a thermometer, a constant pressure funnel, and a vacuum pump. Turn on the electric stirrer to stir, heat the oil bath to 100 - 105 °C, turn on the vacuum pump to evacuate the four-necked flask. Start timing when the vacuum pressure ≤ -0.08 MPa, and perform vacuum dehydration for 0.5 - 1 h.

[0044] Step 2: Preparation of waterborne polyurethane prepolymer When the water content in the polyol < 0.05%, turn off the vacuum pump, reduce the temperature of the oil bath. When the thermometer temperature drops to 70 °C, slowly add 36 g of toluene diisocyanate through the constant pressure funnel. After adding, stir evenly. When the temperature reaches 85 °C, start timing and perform a constant temperature reaction for 2 h. Use titration to determine that the -NCO content in the mixture reaches the designed value.

[0045] Then cool down to 75 °C and add 1 g of dried trimethylolpropane, 8 g of dried dimethylolpropionic acid, and 10 g of acetone, stir evenly, gradually heat up to 80 °C, and perform a constant temperature chain extension reaction for 2 h.

[0046] Finally, cool down to 60 °C and add 0.5 g of organic bismuth and 10 g of acetone, heat up to 65 °C and react for 3 h until the -NCO content in the mixture reaches the designed value again.

[0047] Add 62 g of acetone before discharging to obtain the waterborne polyurethane prepolymer.

[0048] Step 3: Neutralization and emulsification of prepolymer Immediately transfer the obtained prepolymer to an emulsification kettle to obtain 295 g of prepolymer. Then add 6 g of triethylamine to the prepolymer, stir for 2 min. After the prepolymer is completely neutralized, increase the stirring speed to 2500 r / min, quickly add 526 g of deionized water, and stir at high speed for 8 min.

[0049] Step 4: Post-chain extension of waterborne polyurethane Slowly add 20 g of piperazine diluted to 10% with water dropwise to the emulsion obtained in Step 3. After continuing to stir at high speed for 3 min, add 0.2 g of defoamer, reduce the stirring speed to 800 r / min, and stir to defoam for 5 min.

[0050] Then transfer it to a 1000 mL four-necked flask equipped with a thermometer and a stirring device. Heat it up while stirring, and adjust the vacuum pump pressure to ≤ -0.08 MPa. When the temperature rises to 60 °C, maintain this temperature for constant temperature reaction for 2 h. When it cools down to room temperature, filter the emulsion to obtain environmentally friendly flame-retardant waterborne polyurethane.

[0051] The mechanical properties of Example 1, Example 2 and the common waterborne polyurethane as the comparative example were tested respectively by GB / 1040-2006, and the flame retardancy was tested by measuring the limiting oxygen index of the polyurethane film. The results are shown in Table 1 below.

[0052] Table 1

[0053] It can be seen from the above table that the flame retardancy of the waterborne polyurethane synthesized in Example 1 and Example 2 is greatly improved compared with that of the comparative example, and the elongation at break is lower.

[0054] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications within the scope of the technical solution of the present invention to obtain equivalent embodiments with equivalent changes, but as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A preparation method of an environmentally friendly flame-retardant waterborne polyurethane, characterized in that, It includes the following steps: Drying of polyol: The polyol is dried under vacuum conditions at a temperature of 100°C to 120°C for 0.5 to 2 hours until the water content in the polyol is lower than 0.05%; Preparation of prepolymer: The dried polyol is mixed evenly with isocyanate and then heated for reaction. Then chain extender, hydrophilic chain extender and acetone are added and mixed evenly, and then heated for reaction again. After adding catalyst and heating for reaction, acetone is added for dilution before discharging to obtain aqueous polyurethane prepolymer; Preparation of aqueous polyurethane emulsion: An alkaline aqueous solution is added to the aqueous polyurethane prepolymer and stirred evenly for emulsification to obtain an aqueous polyurethane emulsion; Post-chain extension of aqueous polyurethane: A small molecule chain extender is added to the aqueous polyurethane emulsion. After the reaction is complete, an antifoaming agent is added and the reaction is carried out in a constant temperature and vacuum environment. After the reaction is complete, it is cooled to room temperature, and the reaction solution is filtered to obtain environmentally friendly flame-retardant aqueous polyurethane.

2. The preparation method of the environment-friendly flame-retardant aqueous polyurethane according to claim 1, wherein, The polyol is one or more of soybean oil, castor oil, polylactic acid, palm oil, cashew shell oil, isosorbide, lignin, non-halogenated flame retardant, modified soybean oil, modified castor oil, modified polylactic acid, modified palm oil, modified cashew shell oil, modified isosorbide, modified lignin, modified non-halogenated flame retardant; The number average molecular weight of the polyol is 500 - 4000.

3. The preparation method of the environment-friendly flame-retardant waterborne polyurethane according to claim 1, characterized in that, The specific steps for preparing the prepolymer are as follows: The dried polyol is mixed evenly with isocyanate and heated to react under the condition of 80°C to 100°C for 1 to 2 hours; After the reaction is complete, chain extender, hydrophilic chain extender and acetone are added, mixed evenly, and reacted under the condition of 70°C to 100°C for 2 to 3 hours; Finally, catalyst is added and reacted under the condition of 60 - 80°C for 2 to 4 hours. After the reaction is complete, acetone is added for dilution before discharging to obtain aqueous polyurethane prepolymer.

4. The preparation method of the environment-friendly flame-retardant aqueous polyurethane according to claim 1 or 3, characterized in that, The chain extender, hydrophilic chain extender, acetone and catalyst are all dried before use, and their water content is lower than 0.05%.

5. The preparation method of the environment-friendly flame-retardant waterborne polyurethane according to claim 1, wherein, The isocyanate is any one or more of isophorone diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, toluene diisocyanate; 6. The preparation method of the environment-friendly flame-retardant waterborne polyurethane according to claim 1, characterized in that, The chain extender is any one or more of ethylene glycol, 1,4-butanediol, methylpropanediol, trimethylolpropane, glycerol; The hydrophilic chain extender is any one or more of dimethylolpropionic acid, dimethylolbutyric acid; The catalyst is any one or more of dibutyltin dilaurate, stannous octoate, organic bismuth; 7. The preparation method of the environment-friendly flame-retardant aqueous polyurethane according to claim 1, characterized in that, The alkaline aqueous solution is any one or more of triethylamine aqueous solution, diethanolamine aqueous solution, triethanolamine aqueous solution, sodium hydroxide aqueous solution, sodium bicarbonate aqueous solution, sodium acetate aqueous solution, ammonia water; During the preparation of the aqueous polyurethane emulsion, the solid content of the system is 20% - 50%, and the reaction temperature is 20°C - 40°C.

8. The preparation method of the environment-friendly flame-retardant waterborne polyurethane according to claim 1, characterized in that, The small molecule chain extender is any one or more of ethylenediamine, piperazine, isophorone diamine, hydrazine hydrate, diethylenetriamine, silane coupling agent; 9. The preparation method of the environment-friendly flame-retardant aqueous polyurethane according to claim 4, wherein The polyol, chain extender, and hydrophilic chain extender are dried by vacuum pumping, the drying temperature is 100°C - 130°C, and the air pressure ≥ -0.08 MPa; The catalyst is dried in a blast drying oven at 100°C.

10. The preparation method of the environment-friendly flame-retardant waterborne polyurethane according to claim 4, wherein, The dosage of the catalyst accounts for 0.1% to 0.5% of the total mass of the polyol and the isocyanate.

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