Cellulose nanocrystal modified polyurethane prepolymer and method of making the same

Abstract

The application provides a preparation method of cellulose nanocrystal modified polyurethane prepolymer, water in water suspension of cellulose nanocrystal is replaced by organic solvent; the obtained organic solvent suspension of cellulose nanocrystal is dispersed in polyol, heated, and distilled under reduced pressure to obtain polyol dispersion of cellulose nanocrystal; then isocyanate is added to carry out stirring reaction to obtain cellulose nanocrystal modified polyurethane prepolymer. The preparation method is simple to operate, does not need to introduce high-boiling-point solvent, and the aggregation phenomenon of cellulose nanocrystal is reduced, and the prepared cellulose nanocrystal modified polyurethane prepolymer has greater tensile strength. The application also provides a cellulose nanocrystal modified polyurethane prepolymer.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polyurethane preparation, in particular to a cellulose nanocrystal modified polyurethane prepolymer and a preparation method thereof. BACKGROUND

[0002] Polyurethane is a kind of soft and hard segment alternating multi-block copolymer containing repeating urethane structure in the molecular chain. Polyurethane material has the advantages of good elasticity, large toughness, wear resistance, solvent resistance, corrosion resistance, etc., and is widely used in civil, military and aviation fields. Most polyurethanes can be prepared by relatively low molecular weight polyurethane prepolymer, that is, polyurethane prepolymer is first prepared by reacting polyol or active hydrogen-containing raw material with isocyanate, and then the prepared polyurethane prepolymer is used as an intermediate for the next reaction to prepare polyurethane, thereby achieving the effect of optimizing formula, process and performance.

[0003] Cellulose nanocrystal has very large modulus and hardness. The use of cellulose nanocrystal in the preparation of cellulose nanocrystal modified polyurethane prepolymer can realize the modification of polyurethane prepolymer, so that the strength, toughness and other properties of polyurethane prepolymer are improved.

[0004] The cellulose nanocrystal raw material prepared by the existing technology by hydrolysis method, oxidation method and low eutectic solvent combined with mechanical treatment method is in water dispersion system. The cellulose nanocrystal raw material is usually directly used in the modification reaction of polyurethane prepolymer after being dried to remove water. This method has problems such as easy agglomeration of cellulose nanocrystal and weak interfacial bonding force of polyurethane prepolymer. Although the use of modified and dried cellulose nanocrystal in the modification reaction of polyurethane prepolymer can improve the interfacial bonding force of polyurethane prepolymer, this method still has problems such as easy agglomeration of cellulose nanocrystal, introduction of more high-boiling organic solvents, and complicated preparation process. Therefore, it is necessary to provide an efficient, simple, economical and environmentally friendly preparation method for preparing cellulose nanocrystal modified polyurethane prepolymer with better performance. SUMMARY

[0005] Therefore, the present application provides a preparation method of cellulose nanocrystal modified polyurethane prepolymer, which is efficient, simple, economical and environmentally friendly, and the prepared cellulose nanocrystal modified polyurethane prepolymer has strong interfacial bonding force and large tensile strength.

[0006] Specifically, the first aspect of the present application provides a preparation method of cellulose nanocrystal modified polyurethane prepolymer, comprising the following steps:

[0007] The water in the water suspension of cellulose nanocrystal is replaced by an organic solvent to obtain an organic solvent suspension of cellulose nanocrystal; the organic solvent includes one or more of alcohol solvents, ether solvents and alcohol-ether solvents;

[0008] The organic solvent suspension of cellulose nanocrystals is dispersed in a polyol, heated, and distilled under reduced pressure to obtain a polyol dispersion of cellulose nanocrystals;

[0009] An isocyanate is added to the polyol dispersion of cellulose nanocrystals, and the reaction is stirred to obtain the modified polyurethane prepolymer of cellulose nanocrystals.

[0010] The preparation method of the modified polyurethane prepolymer of cellulose nanocrystals in the present application uses an organic solvent to replace the water solvent in the water suspension of cellulose nanocrystals, and directly blends and disperses with a polyol in this state. The dehydration, mixing, dispersion, and modification reactions of cellulose nanocrystals are combined to obtain the modified polyurethane prepolymer of cellulose nanocrystals. This preparation method can prevent the aggregation of cellulose nanocrystals, and does not require the introduction of excessive high-boiling organic solvents. The process is efficient, simple, economical, and environmentally friendly. The prepared modified polyurethane prepolymer of cellulose nanocrystals has strong interfacial bonding force and high tensile strength.

[0011] In the present application, the boiling point of the organic solvent is less than or equal to 150℃, and the organic solvent is miscible with water and polyol.

[0012] Optionally, the organic solvent includes one or more of methanol, ethanol, propanol, isopropanol, and ethylene glycol monomethyl ether.

[0013] In the present application, the heating temperature is 80℃-130℃; the pressure of the distillation under reduced pressure is -0.1MPa to -0.05MPa, and the duration is 1h-4h.

[0014] In the present application, the stirring reaction temperature is 60℃-100℃; and the stirring reaction time is 1h-3h.

[0015] In the present application, in the preparation raw materials of the modified polyurethane prepolymer of cellulose nanocrystals, the cellulose nanocrystals are 1-40 parts by mass, the polyol is 10-50 parts by mass, and the isocyanate is 5-20 parts by mass.

[0016] In the present application, the molecular weight of the polyol is 300g / mol-3000g / mol; the hydroxyl value of the polyol is 30mgKOH / g-300mgKOH / g; and the average functionality of the hydroxyl group of the polyol is greater than or equal to 2.

[0017] The preparation method provided in one aspect of the present application is efficient, simple, economical, and environmentally friendly, and is suitable for large-scale production. The modified polyurethane prepolymer of cellulose nanocrystals prepared by the method has strong interfacial bonding force and high tensile strength after curing.

[0018] The second aspect of the present application provides a cellulose nanocrystal modified polyurethane prepolymer, which is prepared by the preparation method provided in the first aspect of the present application.

[0019] In the present application, the mass ratio of the cellulose nanocrystal in the cellulose nanocrystal modified polyurethane prepolymer is 5%-40%.

[0020] In the present application, the tensile strength of the cellulose nanocrystal modified polyurethane prepolymer after curing is 13-17 MPa.

[0021] The cellulose nanocrystal modified polyurethane prepolymer provided in the second aspect of the present application exists in the form of slurry, which is fine, has good suspension stability, and has good dispersion state of cellulose nanocrystal, and the cellulose nanocrystal modified polyurethane prepolymer after curing has large tensile strength. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The process flow chart of the preparation method of the cellulose nanocrystal modified polyurethane prepolymer provided in the embodiments of the present application is shown. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only 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 skilled in the art without creative labor fall within the scope of protection of the present application.

[0024] Referring to Figure 1 The embodiments of the present application provide a preparation method of a cellulose nanocrystal modified polyurethane prepolymer, which comprises the following steps:

[0025] S10, replacing water in the water suspension of cellulose nanocrystal with an organic solvent to obtain an organic solvent suspension of cellulose nanocrystal; the organic solvent comprises one or more of an alcohol solvent, an ether solvent, and an alcohol-ether solvent;

[0026] S20, dispersing the organic solvent suspension of cellulose nanocrystal in a polyol, heating, and distilling under reduced pressure to obtain a polyol dispersion of cellulose nanocrystal;

[0027] S30, adding isocyanate to the polyol dispersion of cellulose nanocrystal and stirring to react to obtain a cellulose nanocrystal modified polyurethane prepolymer.

[0028] In the embodiments of the present application, the source of the cellulose nanocrystals can be a biomass raw material rich in cellulose components, such as cotton, hemp, straw, bagasse, paper, bacterial and tunicate extracts, etc. Among them, since the cellulose content of the cotton raw material is high, and the process of preparing cellulose nanocrystals from the cotton raw material is simple, it is easy to obtain cellulose nanocrystals, and in some embodiments of the present application, cotton raw material is selected as the raw material for preparing cellulose nanocrystals. Specifically, the cellulose nanocrystals can be prepared by one or more of the above-mentioned biomass raw materials by hydrolysis, oxidation and low eutectic solvent combined with mechanical treatment method, and the obtained cellulose nanocrystals are dispersed in water to form a water dispersion system. Among them, the hydrolysis method includes inorganic acid hydrolysis and cellulase catalytic hydrolysis. In some embodiments of the present application, after the inorganic acid hydrolysis method is used to prepare a crude cellulose nanocrystal mixture, the acid in the mixture is removed by centrifugation, and then the mixture is washed with deionized water for 5-10 times to obtain a water suspension of cellulose nanocrystals with a pH of 6.8-7.0. In specific embodiments, the pH of the final water suspension of cellulose nanocrystals can be 6.8, 6.9, 7.0, etc. In the embodiments of the present application, the cellulose nanocrystals have a rod-like or near-rod-like external structure, with a diameter of 1 nm-100 nm, specifically 1 nm, 5 nm, 10 nm, 25 nm, 50 nm, 75 nm, 100 nm, etc.; and a length of 20 nm-1 μm, specifically 20 nm, 50 nm, 100 nm, 250 nm, 500 nm, 750 nm, 1 μm, etc. In addition, the cellulose nanocrystals can also be prepared by using micron-sized cellulose crystals, which can be commercially available or self-prepared.

[0029] In the embodiments of the present application, the above-mentioned cellulose nanocrystals, polyols and isocyanate are blended and reacted to prepare cellulose nanocrystal-modified polyurethane prepolymer. The polyurethane prepolymer is a reactive intermediate containing urethane groups in the backbone, which is obtained by the reaction of polyols and isocyanate. The polyols and isocyanate provide soft segments and hard segments of the polyurethane prepolymer, respectively. The polyurethane prepolymer can undergo chain extension reaction with low molecular weight compounds containing active hydrogen to obtain linear polyurethane or cross-linked polyurethane, which can be used to produce various polyurethane elastic products. The cellulose nanocrystals in the cellulose nanocrystal-modified polyurethane prepolymer can modify the polyurethane prepolymer, so that the strength and toughness of the polyurethane prepolymer are improved.

[0030] In the preparation process of the cellulose nanocrystal modified polyurethane prepolymer, due to the difficulty of water in the water suspension of cellulose nanocrystals to be miscible with polyols, and the existence of water will have a greater impact on the process of polyols and isocyanate to generate polyurethane prepolymer, usually need to first to the water suspension of cellulose nanocrystals dehydration treatment, but directly to the water suspension of cellulose nanocrystals drying dehydration is easy to cause the aggregation of cellulose nanocrystals, and then it is difficult to play its nanometer size role, so that the interface binding force of the cellulose nanocrystal modified polyurethane prepolymer prepared is poor. The organic solvent is used to wash the water suspension of cellulose nanocrystals by centrifugation or filtration several times in the embodiment of the application, so that the water in the water suspension of cellulose nanocrystals is replaced by the organic solvent to form an organic solvent suspension of cellulose nanocrystals. This process can better remove the water in the water suspension of cellulose nanocrystals without drying treatment, thereby avoiding the occurrence of the aggregation phenomenon of cellulose nanocrystals caused by drying dehydration. That is, by replacing the water in the water suspension of cellulose nanocrystals with an organic solvent, the cellulose nanocrystals can be dispersed in the organic solvent instead of water, so that the cellulose nanocrystals remain dispersed during the dehydration process of the water suspension of cellulose nanocrystals without aggregation, which is conducive to the better play of the nanometer size of cellulose nanocrystals, thereby improving the interface binding force of the cellulose nanocrystal modified polyurethane prepolymer. In addition, the organic solvent used to wash the water suspension of cellulose nanocrystals can be recycled several times, which is conducive to improving the utilization rate of reagents and reducing waste.

[0031] In the embodiment of the application, the organic solvent used to replace the water in the water suspension of cellulose nanocrystals serves as a carrier for the dispersion of cellulose nanocrystals, which has the characteristics of lower boiling point, easy miscibility with water, easy dispersion of cellulose nanocrystals, and easy solubility in polyols. Among them, the organic solvent with lower boiling point is conducive to reducing the heating temperature for removing the organic solvent in S20 by heating, saving energy, and also conducive to the more complete removal of the organic solvent, reducing the residual of the organic solvent in the system, and improving the purity of the final product. In the embodiment of the application, the boiling point of the organic solvent can be less than or equal to 150℃, specifically 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, etc. Easy miscibility with water helps to more completely wash away the water in the water suspension of cellulose nanocrystals during the washing process of the water suspension of cellulose nanocrystals. Easy dispersion of cellulose nanocrystals in the organic solvent helps to reduce the aggregation of cellulose nanocrystals in the organic solvent. Solubility in polyols helps to maintain a good dispersion state during the transfer of cellulose nanocrystals from the organic solvent to polyols. Based on the above characteristics, the organic solvent in the embodiment of the application can be one or more of methanol, ethanol, propanol, isopropanol, and ethylene glycol monomethyl ether, but is not limited thereto.

[0032] In the embodiments of the present application, the cellulose nanocrystals dispersed in the organic solvent can be dispersed in the polyol at the same time by directly mixing the organic solvent suspension of the cellulose nanocrystals obtained by replacing the organic solvent with the polyol in liquid state. Since the preparation process of the polyurethane prepolymer is relatively strict to water, the aqueous reaction environment can adversely affect the preparation of the polyurethane prepolymer, and water is easy to remain in the polyol. Therefore, by heating and reducing the pressure of the system after uniformly mixing, the residual water in the system and the organic solvent brought by the organic solvent suspension of the cellulose nanocrystals prepared in S10 can be removed, and the polyol dispersion of the cellulose nanocrystals is obtained. The system without water and the above-mentioned organic solvent can provide a suitable reaction environment for the preparation of the cellulose nanocrystal modified polyurethane prepolymer. The heating temperature is greater than or equal to the temperature at which water and organic solvent can be evaporated. In the embodiments of the present application, the heating temperature can be 80-130°C, and specifically can be 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, etc. In order to further remove the residual water and organic solvent, the pressure can be reduced to-0.05 to-0.1 MPa in the embodiments of the present application, and specifically can be-0.05 MPa, -0.06 MPa, -0.07 MPa, -0.08 MPa, -0.09 MPa, -0.1 MPa, etc.

[0033] In the embodiments of the present application, the polyol, as one of the raw materials for the synthesis of the polyurethane prepolymer, has a molecular weight, a hydroxyl value, and an average functionality of hydroxyl groups, etc., all of which can have a great influence on the performance of the polyurethane prepolymer. Among them, the polyol with a suitable molecular weight can obtain a more moderate viscosity, thereby not only being conducive to obtaining a polyurethane prepolymer with stronger interfacial bonding force and greater tensile strength, but also being conducive to reducing the agglomeration of the cellulose nanocrystals, making the cellulose nanocrystals better dispersed in the polyol, and thereby better exerting the nanometer size effect of the nanocrystals. In order to make the polyol exert a better effect, in the embodiments of the present application, the molecular weight of the polyol can be 300 g / mol-3000 g / mol, and specifically can be 300 g / mol, 500 g / mol, 1000 g / mol, 1500 g / mol, 2000 g / mol, 2500 g / mol, 3000 g / mol, etc. The hydroxyl value of the polyol refers to the milligrams of potassium hydroxide corresponding to the hydroxyl groups in one gram of the sample, expressed in mgKOH / g. In the embodiments of the present application, the hydroxyl value of the polyol can be 30 mgKOH / g-300 mgKOH / g, and specifically can be 30 mgKOH / g, 50 mgKOH / g, 100 mgKOH / g, 150 mgKOH / g, 200 mgKOH / g, 250 mgKOH / g, 300 mgKOH / g, etc. The average functionality of the hydroxyl value refers to the linear condensation stage before reaching the gel point in the mixed condensation or co-condensation reaction of two or more monomers, and can reflect the ratio of the actual number of hydroxyl groups that can participate in the reaction to the total amount of substance of the monomers. In the embodiments of the present application, the average functionality of the hydroxyl groups of the polyol can be greater than or equal to 2, for example, can be 2, 2.5, 3, etc. In order to meet the above requirements, in the embodiments of the present application, the polyol can be one or more of polyoxyethylene polyol, polyoxypropylene polyol, polyoxybutylene polyol, and physical or chemical modified products of each of the above polyols.

[0034] In the embodiments of the present application, the isocyanate, as another raw material for the synthesis of the polyurethane prepolymer, is added to the polyol dispersion of the cellulose nanocrystals for stirring reaction, so that the hydroxyl groups on the cellulose nanocrystals react with the isocyanate groups on the isocyanate, and chemical combination occurs, i.e. the cellulose nanocrystal-modified polyurethane prepolymer is obtained. In this process, the cellulose nanocrystals can remain in a well-dispersed state and less agglomeration occurs, and the addition of isocyanate can realize the in-situ dispersion and modification of the cellulose nanocrystals, which is conducive to simplifying the preparation process of the cellulose nanocrystal-modified polyurethane prepolymer, and at the same time, is conducive to greatly promoting the cellulose nanocrystals to exert their nanometer size effect, so that the cellulose nanocrystal-modified polyurethane prepolymer prepared has better interfacial bonding force.

[0035] Controlling the temperature of the stirring reaction within a suitable range can make the isocyanate have better reactivity, thereby improving the yield of the cellulose nanocrystal-modified polyurethane prepolymer. Specifically, the reaction system with a suitable temperature is conducive to obtaining a more suitable reaction speed, thereby improving the preparation efficiency of the product to some extent; on the other hand, it is conducive to keeping the isocyanate at a suitable activity, reducing the occurrence of side reactions, and thereby improving the product purity. In the embodiments of the present application, the temperature of the stirring reaction can be controlled within the range of 60-100°C, so as to improve the preparation efficiency and obtain a cellulose nanocrystal-modified polyurethane prepolymer with higher purity. In specific embodiments, the temperature of the stirring reaction can be 60°C, 70°C, 80°C, 90°C, 100°C, etc. In addition, the present application can make the raw materials more uniform by stirring during the reaction, which can also help to improve the reaction efficiency. In the embodiments of the present application, ultrasonic-assisted stirring can also be used to obtain better mixing effect of the reaction raw materials. In order to make the reaction more sufficient, the reaction time can be controlled to be 1-3h in the embodiments of the present application, and can be 1h, 1.5h, 2h, 2.5h, 3h, etc.

[0036] The isocyanate includes one or more of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), 1,5-naphthalene diisocyanate (NDI), hexamethylene diisocyanate (HDI), methylcyclohexyl diisocyanate (hydrogenated TDI), 4,4'-dicyclohexylmethane diisocyanate (HMDI), isophorone diisocyanate (IPDI), p-phenylene diisocyanate (PPDI), p-xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), 1,4-cyclohexane diisocyanate (CHDI), cyclohexane dimethylene diisocyanate (HXDI), trimethyl-1,6-hexamethylene diisocyanate (TMHDI), norbornane diisocyanate (NBDI), dimethyl diphenyl diisocyanate (TODI), and methylcyclohexyl diisocyanate (HTDI), but is not limited thereto.

[0037] In the embodiment of the present application, after the isocyanate is added into the polyol dispersion of cellulose nanocrystals and stirred for a period of time, a catalyst and a chain extender can also be added to continue the stirring reaction, thereby facilitating the catalytic reaction and making the obtained polyurethane prepolymer have longer chain segments. The stirring reaction time can be 1 h-2 h, and specifically can be 1 h, 1.5 h, 2 h, etc. In addition, after the catalyst and the chain extender are added and stirred for a period of time, an antioxidant and a stabilizer can also be further added to continue the stirring reaction, thereby facilitating the inhibition of oxidation reaction and maintaining the stability of the reaction system. The stirring reaction time can be 0.5 h-1 h, and specifically can be 0.5 h, 0.6 h, 0.8 h, 1 h, etc. The catalyst includes one or more of stannous octoate, dibutyltin dilaurate, 2,2-dimorpholinyl diethyl ether, triethylenediamine, and triethanolamine, but is not limited thereto. The chain extender includes one or more of ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, hexanediol, and diethylene glycol, but is not limited thereto. The antioxidant includes one or more of 2,6-di-tert-butyl-p-cresol (BHT), CHINOX1010, CHINOX1076, CHINOX1098, CHINOX1024, CHINOX245, CHINOX1035, and CHINOX1135, but is not limited thereto. The stabilizer includes one or more of phosphoric acid, benzoyl chloride, dimethyl sulfate, p-toluenesulfonic acid methyl ester, acetyl chloride, and toluenesulfonate, but is not limited thereto.

[0038] In the embodiment of the present application, there is a certain mass ratio relationship between the raw materials for preparing the cellulose nanocrystal-modified polyurethane prepolymer. Specifically, the cellulose nanocrystals can be 1-40 parts by mass, the polyol can be 10-50 parts by mass, the isocyanate can be 5-20 parts by mass, the catalyst can be 0-1 parts by mass, the stabilizer can be 0.01-0.1 parts by mass, the antioxidant can be 0.1-1 parts by mass, and the chain extender can be 0-10 parts by mass. In addition, the mass fraction of the organic solvent as the cellulose nanocrystal dispersion carrier can be 10-100 parts. The appropriate mass ratio of each component can make the reaction proceed more smoothly and fully, and at the same time, the cellulose nanocrystal-modified polyurethane prepolymer prepared can have stronger interfacial bonding force and greater tensile strength.

[0039] Specifically, the cellulose nanocrystals can be 1 part, 2 parts, 5 parts, 10 parts, 20 parts, 30 parts, 40 parts, etc.; the polyol can be 10 parts, 20 parts, 30 parts, 40 parts, 50 parts, etc.; the isocyanate can be 5 parts, 10 parts, 15 parts, 20 parts, etc.; the catalyst can be 0 parts, 0.5 parts, 1 part, etc.; the stabilizer can be 0.01 parts, 0.02 parts, 0.05 parts, 0.08 parts, 0.1 parts, etc.; the antioxidant can be 0.1 parts, 0.2 parts, 0.5 parts, 0.8 parts, 1 part, etc.; the chain extender can be 0 parts, 1 part, 2 parts, 5 parts, 6 parts, 8 parts, 10 parts, etc. The organic solvent can be 10 parts, 20 parts, 30 parts, 40 parts, 50 parts, 60 parts, 70 parts, 80 parts, 90 parts, 100 parts, etc.

[0040] In the embodiments of the present application, cellulose nanocrystal-modified polyurethane prepolymer with different interfacial bonding forces can be obtained by controlling the mass ratio of cellulose nanocrystals in the raw materials for preparing cellulose nanocrystal-modified polyurethane prepolymer. Controlling the mass ratio of cellulose nanocrystals in the raw materials for preparing cellulose nanocrystal-modified polyurethane prepolymer within a suitable range is beneficial to effectively exert the bonding effect of cellulose nanocrystals, while reducing unnecessary waste caused by excessive use of cellulose nanocrystals. In the embodiments of the present application, the mass ratio of cellulose nanocrystals in the raw materials for preparing cellulose nanocrystal-modified polyurethane prepolymer can be 5%-40%, specifically 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc.

[0041] In the embodiments of the present application, after the cellulose nanocrystal-modified polyurethane prepolymer prepared by the above preparation method is degassed under reduced pressure, a cellulose nanocrystal-modified polyurethane prepolymer slurry is obtained, which can be packaged after sealing to obtain a finished product.

[0042] The above preparation method is simple, economical and environmentally friendly, and is suitable for large-scale production.

[0043] The embodiments of the present application also provide a cellulose nanocrystal-modified polyurethane prepolymer prepared by the above preparation method.

[0044] In the embodiment of the present application, the cellulose nanocrystal content in the cellulose nanocrystal modified polyurethane prepolymer can have a greater impact on the tensile strength of the cellulose nanocrystal modified polyurethane prepolymer after curing. Controlling the cellulose nanocrystal content in the cellulose nanocrystal modified polyurethane prepolymer within a suitable range is beneficial on the one hand to fully modify the cellulose nanocrystal to the polyurethane prepolymer, so that the cellulose nanocrystal modified polyurethane prepolymer is reinforced and toughened, and after curing, a higher tensile strength can be obtained; on the other hand, it is beneficial to reduce unnecessary waste caused by excessive use of cellulose nanocrystals. In the embodiment of the present application, the mass fraction of cellulose nanocrystals in the cellulose nanocrystal modified polyurethane prepolymer can be 5%-40%, specifically 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc.

[0045] The cellulose nanocrystal modified polyurethane prepolymer described above exists in the form of slurry, and the slurry is fine, has good suspension stability, and the dispersion state of the cellulose nanocrystals is good, and the cellulose nanocrystal modified polyurethane prepolymer after curing has a large tensile strength. In the embodiment of the present application, the tensile strength of the cellulose nanocrystal modified polyurethane prepolymer after curing is 13-17 MPa, specifically 13 MPa, 14 MPa, 15 MPa, 16 MPa, 17 MPa, etc.

[0046] The cellulose nanocrystal modified polyurethane prepolymer provided in the embodiment of the present application can be applied in the fields of civilian, military and aviation, etc., for example, it can be applied in the preparation of battery folding adhesive.

[0047] The embodiments of the present application will be further described in the following multiple examples.

[0048] Example 1

[0049] A preparation method of a cellulose nanocrystal modified polyurethane prepolymer, comprising the following steps:

[0050] (1) Take pure cotton raw materials, prepare a crude cellulose nanocrystal mixture by acid hydrolysis method, then remove the acid in the mixture by centrifugation, and then centrifugally wash the cellulose nanocrystals with deionized water for 5 times to obtain a cellulose nanocrystal water suspension with pH=6.8;

[0051] (2) Further centrifugally wash the cellulose nanocrystal water suspension with ethanol for 3 times, and after washing, ultrasonic treatment for 20 min to obtain an organic solvent suspension of dispersed cellulose nanocrystals; the boiling point of ethanol is 78℃;

[0052] (3) 30 parts of polypropylene glycol were weighed into a reaction kettle, and ultrasonic stirring was started, and 5 parts of cellulose nanocrystal organic solvent suspension containing cellulose nanocrystals was slowly added, and heating was started at the same time, and when the temperature rose to 120 DEG C, the pressure in the reaction kettle was reduced to -0.01 MPa, and a small amount of residual water and low molecular organic solvent was distilled off, and the vacuum distillation process lasted for 1 h;

[0053] (4) After the temperature of the reaction kettle was reduced to 80 DEG C, 8 parts of toluene diisocyanate (TDI) were added for ultrasonic stirring reaction for 3 h;

[0054] (5) 0.05 parts of stannous octoate catalyst and 2 parts of butanediol chain extender were added for continuous reaction for 1 h;

[0055] (6) 0.2 parts of CHINOX1010 antioxidant and 0.05 parts of phosphoric acid stabilizer were added for continuous reaction for 0.5 h;

[0056] (7) The prepared cellulose nanocrystal modified polyurethane prepolymer was subjected to vacuum degassing bubble treatment to obtain a cellulose nanocrystal modified polyurethane prepolymer; the cellulose nanocrystal modified polyurethane prepolymer exists in the form of slurry.

[0057] Example 2

[0058] A method for preparing a cellulose nanocrystal modified polyurethane prepolymer, which is only different from example 1 in that in step (3), 10 parts of cellulose nanocrystal organic solvent suspension containing cellulose nanocrystals is added.

[0059] Example 3

[0060] A method for preparing a cellulose nanocrystal modified polyurethane prepolymer, which is only different from example 1 in that in step (3), 20 parts of cellulose nanocrystal organic solvent suspension containing cellulose nanocrystals is added.

[0061] Example 4

[0062] A method for preparing a cellulose nanocrystal modified polyurethane prepolymer, which is only different from example 1 in that in step (3), 1 part of cellulose nanocrystal organic solvent suspension containing cellulose nanocrystals is added.

[0063] Example 5

[0064] A method for preparing a cellulose nanocrystal modified polyurethane prepolymer, which is only different from example 1 in that in step (3), 40 parts of cellulose nanocrystal organic solvent suspension containing cellulose nanocrystals is added.

[0065] Example 6

[0066] A method for preparing a cellulose nanocrystal-modified polyurethane prepolymer, which is only different from example 1 in that in step (2), the cellulose nanocrystal aqueous suspension is further centrifugally washed with ethylene glycol monomethyl ether, and the boiling point of ethylene glycol monomethyl ether is 124.5°C.

[0067] Example 7

[0068] A method for preparing a cellulose nanocrystal-modified polyurethane prepolymer, which is only different from example 1 in that in step (3), an organic solvent suspension of cellulose nanocrystals containing 0.5 parts of the above cellulose nanocrystals is added.

[0069] Example 8

[0070] A method for preparing a cellulose nanocrystal-modified polyurethane prepolymer, which is only different from example 1 in that in step (3), an organic solvent suspension of cellulose nanocrystals containing 45 parts of the above cellulose nanocrystals is added.

[0071] In order to highlight the beneficial effects of the present application, the following comparative examples are set:

[0072] Comparative Example 1

[0073] A method for preparing a cellulose nanocrystal-modified polyurethane prepolymer, comprising the following steps:

[0074] (1) Take pure cotton raw materials, prepare a crude cellulose nanocrystal mixture by acid hydrolysis method, then remove the acid in the mixture by centrifugation, then centrifugally wash the cellulose nanocrystals with deionized water for 5 times to obtain a cellulose nanocrystal aqueous suspension with pH = 6.8, and then dry the obtained cellulose nanocrystal aqueous suspension in a vacuum drying oven to obtain a cellulose nanocrystal powder;

[0075] (2) Weigh 30 parts of polypropylene glycol into a reaction kettle, slowly add 5 parts of the above cellulose nanocrystal powder, and then increase the temperature of the reaction kettle to 80°C, and then add 8 parts of toluene diisocyanate (TDI) for stirring reaction for 3h;

[0076] (3) Add 0.05 parts of stannous octoate catalyst and 2 parts of butanediol chain extender for continuous reaction for 1h;

[0077] (4) Add 0.2 parts of CHINOX1010 antioxidant and 0.05 parts of phosphoric acid stabilizer for continuous reaction for 0.5h;

[0078] (5) The prepared cellulose nanocrystal-modified polyurethane prepolymer is subjected to vacuum degassing bubble treatment to obtain a cellulose nanocrystal-modified polyurethane prepolymer; the cellulose nanocrystal-modified polyurethane prepolymer exists in the form of slurry.

[0079] Comparative Example 2

[0080] A method for preparing cellulose nanocrystal modified polyurethane prepolymer, comprising the following steps:

[0081] (1) Take pure cotton raw materials, use acid hydrolysis method to obtain a crude cellulose nanocrystal mixture, then use centrifugal method to remove the acid in the mixture, then use deionized water to centrifugal wash the cellulose nanocrystal 5 times to obtain a cellulose nanocrystal water suspension with pH = 6.8, place the obtained cellulose nanocrystal water suspension in a vacuum drying oven for drying to obtain a cellulose nanocrystal powder;

[0082] (2) Disperse the obtained cellulose nanocrystal powder in N,N-dimethylformamide (DMF), add toluene diisocyanate (TDI) for modification, heat to 80 degrees, and stir for 3 hours, filter the modified cellulose nanocrystal dispersion and vacuum dry to obtain a modified cellulose nanocrystal powder;

[0083] (3) Take 30 parts of polypropylene glycol in a reaction kettle, slowly add 5 parts of the above modified cellulose nanocrystal powder, heat the reaction kettle to 80℃, then add 8 parts of toluene diisocyanate (TDI) for stirring reaction for 3 hours;

[0084] (4) Add 0.05 parts of stannous octoate catalyst and 2 parts of butanediol chain extender and continue to react for 1 hour;

[0085] (5) Add 0.2 parts of CHINOX1010 antioxidant and 0.05 parts of phosphoric acid stabilizer and continue to react for 0.5 hours;

[0086] (6) The prepared cellulose nanocrystal modified polyurethane prepolymer is subjected to vacuum degassing bubble treatment to obtain a cellulose nanocrystal modified polyurethane prepolymer; the cellulose nanocrystal modified polyurethane prepolymer exists in the form of slurry.

[0087] In order to effectively support the beneficial effects brought by the technical solutions of the embodiments of the present application, the cellulose nanocrystal modified polyurethane prepolymers prepared in Examples 1-8 and Comparative Examples 1-2 are subjected to the following tests:

[0088] Appearance test: using naked eye observation method, place the cellulose nanocrystal modified polyurethane prepolymer slurry in front of bright light, and judge the fineness of the slurry surface according to the reflection of the slurry surface.

[0089] Suspension stability test: the prepared cellulose nanocrystal modified polyurethane prepolymer slurry was loaded into a transparent bottle, the liquid level of each slurry in the bottle was kept consistent, then the transparent bottle containing the slurry was placed in a glove box, vacuumized and filled with nitrogen, sealed and placed in a water-free nitrogen atmosphere for 120 h, and whether the slurry was stratified was observed. The slurry without stratification indicated good suspension stability, the stratified slurry indicated poor suspension stability, and the more obvious the stratification, the poorer the suspension stability.

[0090] Cellulose nanocrystal dispersion state test: the prepared cellulose nanocrystal modified polyurethane prepolymer slurry was coated on a substrate to a thickness of 0.2 mm, then placed in a constant temperature and humidity chamber with a temperature of 25°C and a humidity of 50% RH, and after 48 h, a coating layer was formed, and the dispersion state of the cellulose nanocrystals in the coating layer was observed by electron scanning electron microscopy.

[0091] Tensile strength test: the cellulose nanocrystal modified polyurethane prepolymer slurry was injected into a mold, and after curing for 48 h in an environment with a temperature of 25°C and a humidity of 50% RH, the tensile strength test was performed according to GB / T 1701-2001.

[0092] The test results are shown in Table 1 below:

[0093] Table 1

[0094]

[0095] As shown in Table 1, the cellulose nanocrystal modified polyurethane prepolymer slurry prepared in Examples 1-8 has a finer surface, better suspension stability, less aggregation of cellulose nanocrystals, better dispersion state, and greater tensile strength of the cured cellulose nanocrystal modified polyurethane prepolymer, and has better strength and toughness.

[0096] Compared with Examples 1-6, the cellulose nanocrystal content in the organic solvent suspension of cellulose nanocrystals added in Example 7 is smaller, the modification of the polyurethane prepolymer by the cellulose nanocrystals is less sufficient, the reinforcing and toughening effect of the polyurethane prepolymer by the cellulose nanocrystals is weaker, and the tensile strength of the cured cellulose nanocrystal modified polyurethane prepolymer is lower.

[0097] Compared with Examples 1-6, the cellulose nanocrystal content in the organic solvent suspension of cellulose nanocrystals added in Example 8 is larger, the cellulose nanocrystals are slightly aggregated, the cellulose nanocrystal modified polyurethane prepolymer slurry prepared has a finer surface and medium suspension stability, and the tensile strength of the cured cellulose nanocrystal modified polyurethane prepolymer is lower.

[0098] Comparative Example 1 dried the aqueous suspension of cellulose nanocrystals into cellulose nanocrystal powder before following the subsequent steps, leading to a large amount of agglomeration of cellulose nanocrystals, the surface of the prepared cellulose nanocrystal-modified polyurethane prepolymer slurry was rough, the suspension stability was poor, and the tensile strength of the cured cellulose nanocrystal-modified polyurethane prepolymer was also low.

[0099] Comparative Example 2 further modified the cellulose nanocrystal powder before drying again to obtain modified cellulose nanocrystal powder, and then prepared according to the subsequent steps, leading to a large amount of agglomeration of cellulose nanocrystals, the surface of the prepared cellulose nanocrystal-modified polyurethane prepolymer slurry was not fine enough, the suspension stability was not good enough, and the tensile strength of the cured cellulose nanocrystal-modified polyurethane prepolymer was also low.

Claims

1. A method for preparing a cellulose nanocrystal-modified polyurethane prepolymer, characterized by, The method comprises the following steps: water in a water suspension of cellulose nanocrystals is replaced by an organic solvent to obtain an organic solvent suspension of cellulose nanocrystals; the organic solvent comprises one or more of an alcohol solvent, an ether solvent, and an alcohol-ether solvent; the organic solvent suspension of cellulose nanocrystals is dispersed in a polyol, heated, and distilled under reduced pressure to obtain a polyol dispersion of cellulose nanocrystals; an isocyanate is added to the polyol dispersion of cellulose nanocrystals, and the mixture is stirred and reacted to obtain a cellulose nanocrystal-modified polyurethane prepolymer; in the preparation of the cellulose nanocrystal-modified polyurethane prepolymer, the cellulose nanocrystals are 1-40 parts by mass, the polyol is 10-50 parts by mass, and the isocyanate is 5-20 parts by mass.

2. The production method according to claim 1, wherein The boiling point of the organic solvent is less than or equal to 150°C, and the organic solvent is miscible with water and polyol.

3. The production method according to claim 1 or 2, characterized by, The organic solvent comprises one or more of methanol, ethanol, propanol, isopropanol, and ethylene glycol monomethyl ether.

4. The production method according to claim 1, wherein The heating temperature is 80-130°C; the pressure for the distillation under reduced pressure is -0.1 MPa to -0.05 MPa, and the duration is 1-4 hours.

5. The production method according to claim 1, wherein The stirring and reaction temperature is 60-100°C; the stirring and reaction time is 1-3 hours.

6. The production method according to claim 1, wherein The molecular weight of the polyol is 300-3000 g / mol; the hydroxyl value of the polyol is 30-300 mgKOH / g; and the average functionality of the hydroxyl group of the polyol is greater than or equal to 2.

7. A cellulose nanocrystal-modified polyurethane prepolymer, characterized in that, The cellulose nanocrystal-modified polyurethane prepolymer is prepared by the method of any one of claims 1-6.

8. The cellulose nanocrystal-modified polyurethane prepolymer according to claim 7, wherein, The mass fraction of cellulose nanocrystals in the cellulose nanocrystal-modified polyurethane prepolymer is 5%-40%.

9. The cellulose nanocrystal-modified polyurethane prepolymer according to claim 7 or 8, wherein, The tensile strength of the cellulose nanocrystal-modified polyurethane prepolymer after curing is 13-17 MPa.

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