Sorbitan oleate modified castor oil-based waterborne polyurethane and preparation method thereof

Abstract

The invention discloses sorbitan oleate modified castor oil-based waterborne polyurethane and a preparation method, and belongs to the technical field of paints.Castor oil is used as a soft segment, isophorone diisocyanate is used as a hard segment, and the isocyanate index of polyurethane is fixed to be about 1.1; the preparation method comprises the following steps: introducing sorbitan oleate with rigid furan and an aliphatic hydrophobic side chain into a polyurethane molecular network by adopting a prepolymerization method, and preparing a series of sorbitan oleate modified castor oil based cationic waterborne polyurethane emulsions by adopting N-methyldiethanolamine as a cationic hydrophilic chain extender and 1-4 butanediol as a micromolecular chain extender. According to the sorbitan oleate modified castor oil-based waterborne polyurethane and the preparation method, sorbitan oleate is introduced into a polyurethane molecular network, so that the mechanical property of a castor oil-based waterborne polyurethane material is effectively improved, and the water resistance and corrosion resistance of the castor oil-based waterborne polyurethane material are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coatings, in particular to a sorbitan oleate modified castor oil-based waterborne polyurethane and a preparation method thereof. BACKGROUND

[0002] Bio-based monomer synthesis waterborne polyurethane emulsion has the advantages of environmental friendliness, renewability and low carbon emission, and is one of the important development directions of the coating industry. In recent years, the development of bio-based polyurethane emulsion with castor oil as a raw material instead of traditional petroleum-based polyols has become a hot and important research focus. The natural existence of hydroxyl in castor oil enables it to directly embed into the polyurethane structure as a soft segment, which is an advantage that other vegetable oils do not have. However, the waterborne polyurethane prepared by pure castor oil as a polyol has the problems of poor mechanical performance of the paint film, poor corrosion resistance and poor water resistance due to the high crosslinking degree, which limits its practical application. With the continuous widening of the application scenarios of waterborne polyurethane, higher requirements are put forward for the comprehensive performance of the paint film of waterborne polyurethane. SUMMARY

[0003] The purpose of the present application is to provide a sorbitan oleate modified castor oil-based waterborne polyurethane and a preparation method thereof. The introduction of sorbitan oleate (SP) into the polyurethane molecular network effectively improves the mechanical properties of the castor oil-based waterborne polyurethane material and improves the water resistance and corrosion resistance of the castor oil-based waterborne polyurethane material.

[0004] To achieve the above-mentioned purpose, the present application provides a sorbitan oleate modified castor oil-based waterborne polyurethane. The raw materials of the sorbitan oleate modified castor oil-based waterborne polyurethane include isophorone diisocyanate, N-methyldiethanolamine, castor oil and sorbitan oleate.

[0005] Preferably, the mass of isophorone diisocyanate is 9.0-9.5g, the mass of N-methyldiethanolamine is 1.0-1.5g, the mass of castor oil is 11.0-11.5g, and the molar ratio of the hydroxyl group of sorbitan oleate to the hydroxyl group of castor oil is (0-0.5):(1-0.5).

[0006] The present application also provides a preparation method of a sorbitan oleate modified castor oil-based waterborne polyurethane, which comprises the following steps:

[0007] S1, mixing the raw materials and stirring uniformly to obtain a mixed system;

[0008] S2, gradually warming the mixed system and adding dibutyltin dilaurate dropwise into the mixed system for reaction;

[0009] S3, after the reaction in S2 is completed, detecting the content of free -NCO in the mixed system after reaction, and adding 1,4-butanediol for continuous reaction after the detection is completed, and adding acetone during the reaction.

[0010] S4, the product obtained from S3 is subjected to infrared detection, the characteristic peak of -NCO disappears, cooling, acetic acid is added for neutralization reaction;

[0011] S5, after the neutralization reaction is completed, deionized water is added, and an emulsification reaction is carried out under high-speed rotation;

[0012] S6, after the emulsification reaction is completed, standing defoaming, rotary evaporation, the product SP modified waterborne polyurethane emulsion is obtained, and is recorded as WPU-SP.

[0013] Preferably, in S1, the stirring speed is 140-160 r / min, and the stirring is carried out under N2 protection.

[0014] Preferably, in S2, the temperature is gradually increased to 70-90 DEG C, the dropwise addition amount of dibutyltin dilaurate is 2-4 drops, and the reaction time is 2-4 h.

[0015] Preferably, in S3, the free -NCO content is detected by using di-n-butylamine titration method, the mass of 1,4-butanediol is 0.4-0.5 g, the reaction time is 0.5-1.5 h, and the mass of acetone is 1-25 g.

[0016] Preferably, in S4, the temperature is reduced to 20-40 DEG C, the mass of acetic acid is 0.2-10 g, the reaction time of the neutralization reaction is 20-40 min, and the reaction temperature of the neutralization reaction is room temperature.

[0017] Preferably, in S5, the speed of rotation is 1300-1800 r / min, the reaction time of the emulsification reaction is 20-40 min, and the reaction temperature of the emulsification reaction is room temperature.

[0018] Therefore, the sorbitan oleate modified castor oil-based waterborne polyurethane and the preparation method have the following beneficial effects:

[0019] 1, the present application uses castor oil as the soft segment, isophorone diisocyanate as the hard segment, fixes the isocyanate index of polyurethane at about 1.1, introduces sorbitan oleate with rigid furan and aliphatic hydrophobic side chain into the polyurethane molecular network by using the prepolymerization method, uses N-methyl diethanolamine as a cationic hydrophilic chain extender, and 1-4 butanediol as a small molecule chain extender, to prepare a SP modified castor oil-based cationic waterborne polyurethane emulsion.

[0020] 2, the present application solves the problem of too high flexibility and insufficient strength of the castor oil-based waterborne polyurethane material by introducing a rigid structure, at the same time, the nonpolar aliphatic hydrophobic side chain can improve the mechanical properties of the castor oil-based waterborne polyurethane coating while improving its water resistance and corrosion resistance, so that it has better comprehensive performance.

[0021] The technical solutions of the present application are described in further detail below with reference to the accompanying drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is an appearance diagram of the WPU-SP of the present application;

[0023] Figure 2 is a particle size distribution diagram of the WPU-SP of the present application;

[0024] Figure 3 is an infrared spectrum diagram of the WPU-SP paint film of the present application;

[0025] Figure 4 is a scanning electron microscope diagram of the WPU-SP paint film of the present application;

[0026] Figure 5 is a mechanical property diagram of the WPU-SP paint film of the present application;

[0027] Figure 6 is a gel content and waterproof performance diagram of the WPU-SP paint film of the present application;

[0028] Figure 7 is the abrasion resistance of the WPU-SP paint film of the present application;

[0029] Figure 8 is the thermogravimetric analysis and its derivative curve diagram of the WPU-SP paint film of the present application;

[0030] Figure 9 is the polarization curve diagram and Bode curve diagram of the WPU-SP paint film of the present application. DETAILED DESCRIPTION

[0031] The technical solutions of the present application are described in further detail below with reference to the accompanying drawings and examples.

[0032] Unless otherwise defined, the technical terms or scientific terms used in the present application shall have the usual meanings understood by those with ordinary skills in the art to which the present application belongs.

[0033] The raw materials used in the application are: isophorone diisocyanate (IPDI): 99%, Shanghai Maikelin Biochemical Technology Co., Ltd.; castor oil (CO): analytical pure (AR), Shanghai Yenn Chemical Technology Co., Ltd.; N-methyldiethanolamine (MDEA): 98%, Shanghai Maikelin Biochemical Technology Co., Ltd.; dibutyltin dilaurate (DBTDL, 95%), 1,4-butanediol (BDO, 99.7%), sorbitan oleate (SP, chemical pure): Shanghai Maikelin Biochemical Technology Co., Ltd.; acetic acid (HAc, 99.7%), N,N-dimethylformamide (DMF, 99.5%): Shanghai Yenn Chemical Technology Co., Ltd.; acetone (AC): AR, Luoyang Chemical Reagent Factory; deionized water: self-made.

[0034] Example 1

[0035] The application provides a preparation method of sorbitan oleate modified castor oil based waterborne polyurethane, comprising the following steps:

[0036] S1, 9.23g isophorone diisocyanate, 1.35g N-methyldiethanolamine and 11.11g castor oil are placed in a 250mL four-necked flask with a stirrer, a condenser and a nitrogen gas conduit, and stirred uniformly under N2 protection, and the stirring speed is 150r / min, to obtain a mixed system;

[0037] S2, the mixed system is gradually heated to 80℃, 3 drops of dibutyltin dilaurate are added to the mixed system for reaction, and the reaction time is 3h;

[0038] S3, after the reaction in S2 is completed, the free -NCO content of the mixed system after reaction is detected by di-n-butylamine titration method, 0.45g of 1,4-butanediol is added after the free -NCO content is less than 0.1%, and the reaction time is 1.0h, and 15g of acetone is added during the reaction to adjust the viscosity of the mixed system;

[0039] S4, a small amount of the product obtained in S3 is taken for infrared detection, and when the characteristic peak of -NCO at 2270cm -1 disappears, the remaining product obtained in S3 is cooled to 30℃, 2g of acetic acid is added for neutralization reaction, the reaction time is 30min, and the reaction temperature is room temperature;

[0040] S5, after the neutralization reaction is completed, deionized water is added, and emulsification reaction is carried out under high speed rotation (1500r / min), the reaction time is 30min, and the reaction temperature is room temperature;

[0041] S6, after the emulsification reaction is completed, standing and defoaming are carried out, and the excess solvent is removed by rotary evaporation to obtain a product SP modified waterborne polyurethane emulsion, which is recorded as WPU-SP0.

[0042] Example 2

[0043] The operation of this example is the same as that of Example 1, except that in S1, in addition to 9.23 g of isophorone diisocyanate, 1.35 g of N-methyldiethanolamine and 11.11 g of castor oil, 0.125:0.875 of the molar ratio of the hydroxyl group of sorbitan oleate to the hydroxyl substance of castor oil is added, and S6 obtains the product SP modified waterborne polyurethane emulsion, which is recorded as WPU-SP12.5.

[0044] Example 3

[0045] The operation of this example is the same as that of Example 2, except that in S1, the molar ratio of the hydroxyl group of sorbitan oleate to the hydroxyl substance of castor oil is 0.250:0.750, and S6 obtains the product SP modified waterborne polyurethane emulsion, which is recorded as WPU-SP25.

[0046] Example 4

[0047] The operation of this example is the same as that of Example 2, except that in S1, the molar ratio of the hydroxyl group of sorbitan oleate to the hydroxyl substance of castor oil is 0.375:0.625, and S6 obtains the product SP modified waterborne polyurethane emulsion, which is recorded as WPU-SP37.5.

[0048] Example 5

[0049] The operation of this example is the same as that of Example 2, except that in S1, the molar ratio of the hydroxyl group of sorbitan oleate to the hydroxyl substance of castor oil is 0.5:0.5, and S6 obtains the product SP modified waterborne polyurethane emulsion, which is recorded as WPU-SP50.

[0050] The appearance of the products WPU-SP prepared in Examples 1-5 is shown in Figure 1 It can be seen from Figure 1 that with the increase of the content of sorbitan oleate, the product gradually changes from milky white to light yellow, and the transparency of the emulsion decreases, which is because sorbitan oleate exists in the form of yellow liquid in its original state after being added to the polyurethane segment.

[0051] The emulsion stability analysis of WPU-SP prepared in Examples 1-5 is carried out, the prepared WPU-SP is added into a 25 mL centrifuge tube, the centrifuge tube is placed in a centrifuge, the centrifugal speed is set to 3000 r / min, and after 30 min, it is taken out, and all samples do not appear precipitation and stratification phenomenon, proving that WPU-SP has good stability.

[0052] The WPU-SP prepared in Examples 1-5 was subjected to emulsion particle size analysis. 5 mL each of WPU-SP0, WPU-SP12.5, WPU-SP25, WPU-SP37.5, and WPU-SP50 were weighed and diluted to 1% of the total mass using water as a dispersant. The emulsion particle size was measured using a nanoparticle size analyzer and a Zeta potential analyzer. The results are as follows: Figure 2 As shown in Table 1. Figure 2 As can be seen from Table 1, with the increase of sorbitan oleate content, the particle size of WPU-SP increases slightly, but the stability is good. This is because the sorbitan oleate structure contains hydrophobic side chains. Compared with pure water-based polyurethane, the introduction of sorbitan oleate makes the emulsification of the prepolymer in the aqueous phase more difficult. At the same time, the hydrophobic side chains of sorbitan oleate enter the emulsion particles, forming an oil-in-water structure, which leads to an increase in the emulsion particle size.

[0053] Table 1 Effect of different SP dosages on the properties of WPU-SP emulsion

[0054] Sample Solids content / % Emulsion appearance Emulsion particle size / nm WPU-SP0 33.45 milky white 192.0 WPU-SP12.5 31.17 milky white 216.6 WPU-SP25 31.56 milky white 248.5 WPU-SP37.5 30.51 pale yellow 274.0 WPU-SP50 30.24 pale yellow 283.9

[0055] The SP modified waterborne polyurethane emulsions (WPU-SP) prepared in Examples 1-5 were dropped onto polytetrafluoroethylene plates respectively, and the paint films were formed after air-drying at room temperature for 48 hours. The paint films were placed in a 50° C. oven and dried for 24 hours to obtain five types of WPU-SP paint films.

[0056] The five WPU-SP paint films were analyzed by infrared spectroscopy. Figure 3 As shown. Figure 3 As can be seen, 2270cm -1 The absorption peak at 3328 cm-1 completely disappears, indicating that the -NCO group has been completely reacted; the absorption peak of -NH at 3328 cm-1 -1 The absorption peak at 1700 cm is attributed to the formation of urethane bonds; -1 and 1530cm -1 The absorption peaks at 2922 cm-1 are the stretching vibration peaks of -C=O and -C=C, indicating the successful synthesis of carbamate. -1 and 2842cm -1 The absorption peaks corresponding to -CH2 and -CH3 are at 2922 cm -1 The ratios of the absorption peak area to the -NH absorption peak area for WPU-SP0 to WPU-SP50 were 1.147, 1.216, 1.247, 1.266, and 1.305, respectively. The methylene absorption peak of the WPU-SP film was amplified. This is because sorbitan oleate contains a long aliphatic hydrophobic chain, which increases the methyl and methylene content in the waterborne polyurethane molecular structure. Therefore, sorbitan oleate has been successfully introduced into the polyurethane molecular chain segment.

[0057] The morphology of the five WPU-SP paint films was analyzed. The surface of the WPU-SP paint film was observed by scanning electron microscopy. The test mode was secondary electron and the scale was 20μm. The results are as follows: Figure 4 shown.

[0058] According to GB / T13452.2-2008, the paint film thickness (t p ) is calculated, t p From formula (1), we can get:

[0059]

[0060] Where: m a is the mass of the coating before curing, m b is the mass of the coating after curing, A is the coating area, and ρ is the coating density.

[0061] Table 2 Thickness of WPU-SP paint film

[0062]

[0063] from Figure 4 As can be seen in the figure, due to the high degree of crosslinking of the castor oil-based waterborne polyurethane, the paint film is smooth with only a few wrinkles. However, as the sorbitan oleate content gradually increases, more and more bumps and wrinkles appear on the paint film surface. This is because, on the one hand, the disturbance of the long aliphatic chains in sorbitan oleate causes the paint film to partially thicken, as shown in Table 2, with stacking between layers. On the other hand, the rigid furan rings in sorbitan oleate react with isocyanates to form a three-dimensional network structure, reducing the crosslink density of the paint film and keeping the crosslinking degree within a reasonable range. This results in the paint film having an excellent balance of strength and toughness, as well as good dielectric barrier properties.

[0064] The surface hardness and mechanical properties of the five WPU-SP paint films were analyzed. The surface hardness of the paint films was in accordance with GB / T6739-2006. The tensile test was conducted using an electronic universal testing machine in accordance with GB / T13022-1991. The sample size was 25mm×5mm and the tensile speed was 100mm / min. Each sample was tested three times and the average value was taken for statistical analysis. The mechanical property change curves of the WPU-SP paint films are shown in Figure 2. Figure 5The data are summarized in Table 3. Table 3 shows that the hardness of the WPU-SP film gradually increases from 2H to 4H. After the rigid furan ring is introduced into the polyurethane molecular network, the tensile strength of the WPU-SP film gradually increases from 4.02 MPa to 18.35 MPa. The elastic modulus of the WPU-SP film gradually increases from 57.41 MPa to 222.46 MPa, while the elongation at break gradually decreases from 435.11% to 178.95%. Generally speaking, although a low degree of crosslinking decreases the strength of the polyurethane film and increases its elongation at break, the rigid furan ring structure in sorbitan oleate also enhances its strength. Furthermore, as the proportion of sorbitan oleate increases, the castor oil content decreases, reducing the proportion of soft segments in the polyurethane, which also increases its strength. The synergistic effect of these factors increases the tensile strength of WPU-SP and decreases its elongation at break.

[0065] In addition, the synergistic effect of the hydrophobic side chains and intermolecular hydrogen bonds in sorbitan oleate also improves the toughness of the paint film. When external tension acts on the WPU-SP paint film, the plasticizing effect of the hydrophobic side chains suspended in the molecular chain segments is manifested, promoting the relative migration of the molecular network structure within the polymer, and to a certain extent consuming the external force acting on the film, thereby improving the toughness of the WPU-SP paint film material. Figure 5 As can be seen from the graph, when the -OH mole fraction of sorbitan oleate exceeds 37.5%, the mechanical properties of the paint film no longer change significantly, and the mechanical properties test results of WPU-SP37.5 and WPU-SP50 are better. Therefore, the addition of sorbitan oleate can significantly improve the mechanical properties of WPU paint films.

[0066] Table 3 Surface hardness and mechanical properties of WPU-SP paint film

[0067]

[0068] The crosslinking degree and waterproof performance of the five WPU-SP paint films were analyzed. The WPU-SP paint films dried to constant weight were placed in a Soxhlet extractor and refluxed for 72 h. The solvent was N,N-dimethylformamide. The mass of the WPU-SP paint film before and after immersion was recorded as m0 and m1, respectively. The crosslinking degree (ν e ):

[0069]

[0070] Cross-linked polymer networks swell but do not dissolve in solvents, whereas linear or branched polymers dissolve in solvents. Therefore, the degree of cross-linking can be calculated by measuring the content of insoluble gel components (i.e., gel content). The gel content test results of WPU-SP paint films are shown in Figure 2. Figure 6 As shown in (a) inFigure 6 As can be seen from (a) in the figure, the gel content of the WPU-SP0 paint film without the addition of sorbitan oleate is 78.12%. This is mainly because when castor oil is polymerized as a polyhydroxyl soft segment, the polyhydroxyl groups in its structure form internal crosslinks, which gives the paint film a certain degree of crosslinking. In addition, the crosslinking points formed by hydrogen bond interactions between polyurethane groups on the polyurethane molecular chain also give the polyurethane a certain degree of crosslinking. A higher crosslinking density will lead to problems of low strength and low toughness of the polyurethane paint film. Figure 6 As can be seen from (a), after the rigid furan ring of sorbitan oleate was introduced, the cross-linking degree of the WPU-SP film was reduced, and the film was strengthened and toughened.

[0071] The water contact angle of the WPU-SP paint film was measured using an optical contact angle meter using the sessile drop method. The water absorption rate of the WPU-SP paint film was measured using the immersion method: the WPU-SP paint film was cut into 5mm×5mm squares and the initial mass of the WPU-SP paint film was weighed, recorded as m1. The paint film was then immersed in water for 72 hours, removed, and the surface water stains were blotted with filter paper. The film was immediately weighed and recorded as m2. Three samples were collected for each group. The water absorption rate (W) was obtained by formula (3):

[0072]

[0073] The results of the water absorption and contact angle tests of the WPU-SP paint film are as follows: Figure 6 (b) and Table 4. Figure 6 As shown in Figure (b), the addition of sorbitan oleate significantly improves the hydrophobicity and water resistance of the WPU-SP film. With the addition of sorbitan oleate, the water absorption of the WPU-SP film decreases from 18.6% to 4.79%, and the water contact angle increases from 83.09° to 94.61°. This is because the hydrophobic side chains in the sorbitan oleate structure migrate to the WPU-SP film surface during film formation, enriching the film with hydrophobic alkane segments. This significantly reduces the wettability of water on the film surface, thereby increasing the water contact angle and enhancing the film's hydrophobicity and water resistance.

[0074] Table 4 Water absorption and water contact angle of WPU-SP paint film

[0075]

[0076] The wear resistance of the five WPU-SP paint films was tested: the WPU-SP paint films were cut into 40 mm × 40 mm sizes, and their mass was measured and recorded as m0. The paint films were polished 500 times with 800-grit sandpaper, and the load mass was set to 1000 g. The polished mass was then weighed and recorded as m1. The mass loss M was calculated according to formula (4):

[0077] M = (m0 - m1) (4);

[0078] The results are shown in Figure 7 From Figure 7 it can be seen that the mass loss of WPU-SP0 is 19.4 mg, and the wear resistance is weak; with the increase of the content of sorbitan oleate, the mass loss of the WPU-SP film is significantly reduced, which proves that the introduction of sorbitan oleate can indeed improve the wear resistance of the film, because the hydrophobic side chain of the structure extends to the surface of the film, effectively preventing further wear of the film by the friction medium. In addition, the hydrogen bonds formed between the structural molecular segments can significantly enhance the shear resistance of the film, thus playing a crucial role in the wear resistance of the film. The results show that the WPU-SP film has good wear resistance and mechanical properties.

[0079] The five kinds of WPU-SP films prepared were subjected to thermal gravimetric analysis: about 20 mg of WPU-SP film was heated in a nitrogen atmosphere at a heating rate of 10℃ / min from 10℃ to 600℃, and the results are shown in Figure 8 From Figure 8 (b) it can be seen that WPU-SP0-WPU-SP50 films all show three stages of thermal degradation temperature. The instability of the hard molecular chain segment or the rupture of the urethane bond is the first step leading to the thermal deterioration of the WPU-SP film. In the first stage of the initial thermal decomposition of the film (200-321℃), the main is the decomposition of urethane bond, and the thermal decomposition of WPU-SP film increases slightly in this stage; at 270℃, the mass retention rate of WPU-SP50 film decreases from 90% to 83% compared with WPU-SP0, because the urethane group connecting sorbitan oleate and isophorone diisocyanate is unstable due to the steric hindrance conflict between the two cyclic structures, leading to accelerated thermal decomposition process. The second stage of thermal decomposition of the film (321-395℃) is the thermal decomposition of C-O bond (358kJ / mol) and C-C bond (346kJ / mol) in the polyurethane soft chain, and the introduction of sorbitan oleate increases the number of furan ring and hydrophobic side chain in the molecular chain, so the mass retention rate of the film modified by sorbitan oleate is significantly improved in this stage, and the thermal stability of the film is improved. The third stage of thermal decomposition of the film (higher than 385℃) is mainly due to the further decomposition of small molecules, and the thermal decomposition of WPU-SP film also decreases with the increase of the content of sorbitan oleate in this stage.

[0080] The corrosion resistance of the five prepared WPU-SP paint films was tested: the Q235 steel plate coated with the WPU-SP paint film was used as the working electrode, the platinum electrode was used as the counter electrode, and the saturated calomel electrode was used as the reference electrode to construct a three-electrode system, and the polarization curve test was carried out in the mass fraction 3.5% NaCl solution, and the results are shown in Figure 9 and Table 5.

[0081] From Figure 9 (a), it can be seen that the bare Q235 steel plate has a larger corrosion current and a lower corrosion potential due to corrosion by the salt solution; in contrast, the WPU-SP paint film has a higher corrosion potential and a lower corrosion current, which indicates that the WPU-SP paint film has excellent corrosion resistance and water resistance. This is because during the film formation of the waterborne polyurethane emulsion, the long side chains in the WPU-SP migrate to the surface of the paint film, making the paint film surface rich in hydrophobic alkane chain segments, effectively blocking the intrusion of the salt solution, thereby protecting the metal substrate from corrosion. This is consistent with the results of the water resistance test.

[0082] Figure 9 (b) is the test result of different WPU-SP paint films after being immersed in the mass fraction 3.5% NaCl solution for 24h. In the Bode modulus diagram, the higher the impedance modulus value in the low frequency region, the better the corrosion resistance, and the results are consistent with the polarization curve test results.

[0083] Table 5 Polarization curve parameters of different paint films

[0084]

[0085]

[0086] In combination with the mechanical properties, thermal stability, corrosion resistance and water resistance test of the WPU-SP paint film, it is found that when the molar fraction of -OH in the sorbitan oleate is 37.5%, the comprehensive performance of the paint film is relatively good.

[0087] Therefore, the preparation method of the sorbitan oleate modified castor oil based waterborne polyurethane described above is adopted, which effectively improves the mechanical properties of the castor oil based waterborne polyurethane material, and improves the water resistance and corrosion resistance of the castor oil based waterborne polyurethane material.

[0088] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application but not to limit them, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A sorbitan oleate-modified castor oil-based waterborne polyurethane, characterized in that: The sorbitan oleate-modified castor oil-based waterborne polyurethane comprises the following raw materials: isophorone diisocyanate, N-methyldiethanolamine, castor oil and sorbitan oleate.

2. The sorbitan oleate-modified castor oil-based waterborne polyurethane according to claim 1, characterized in that: The mass of isophorone diisocyanate is 9.0-9.5 g, the mass of N-methyldiethanolamine is 1.0-1.5 g, the mass of castor oil is 11.0-11.5 g, and the ratio of the amount of hydroxyl groups of sorbitan oleate to the amount of hydroxyl groups of castor oil is (0-0.5):(1-0.5).

3. The method for preparing a sorbitan oleate-modified castor oil-based waterborne polyurethane according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1. Mix the raw materials and stir them evenly to obtain a mixed system; S2, gradually heating the mixed system, and dropwise adding dibutyltin dilaurate into the mixed system to react; After the reaction in S3 and S2 is completed, the free -NCO content in the mixed system after the reaction is detected. After the detection is completed, 1,4-butanediol is added to continue the reaction, and acetone is added during the reaction; S4. Take the product obtained in S3 and perform infrared detection. After the characteristic peak of -NCO disappears, cool it down and add acetic acid to carry out neutralization reaction; S5. After the neutralization reaction is completed, deionized water is added and an emulsification reaction is carried out under high-speed rotation; S6. After the emulsification reaction is completed, the mixture is allowed to stand for defoaming and subjected to rotary evaporation to obtain the product SP modified aqueous polyurethane emulsion, which is recorded as WPU-SP.

4. The method for preparing a sorbitan oleate modified castor oil-based waterborne polyurethane according to claim 3, wherein: In S1, the stirring speed is 140-160 r / min, and the stirring is carried out under N2 protection.

5. The method for preparing a sorbitan oleate modified castor oil-based waterborne polyurethane according to claim 3, wherein: In S2, the temperature is gradually raised to 70-90°C, 2-4 drops of dibutyltin dilaurate are added, and the reaction time is 2-4 hours.

6. The method for preparing a sorbitan oleate modified castor oil-based waterborne polyurethane according to claim 3, wherein: In S3, the free -NCO content is determined by di-n-butylamine titration, the mass of 1,4-butanediol is 0.4-0.5 g, the reaction time is 0.5-1.5 h, and the mass of acetone is 1-25 g.

7. The method for preparing a sorbitan oleate modified castor oil-based waterborne polyurethane according to claim 3, wherein: In S4, the temperature is lowered to 20-40° C., the mass of acetic acid is 0.2-10 g, the reaction time of the neutralization reaction is 20-40 min, and the reaction temperature of the neutralization reaction is room temperature.

8. The method for preparing a sorbitan oleate modified castor oil-based waterborne polyurethane according to claim 3, wherein: In S5, the rotation speed is 1300-1800 r / min, the reaction time of the emulsification reaction is 20-40 min, and the reaction temperature of the emulsification reaction is room temperature.

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