Bio-based waterborne polyurethane and preparation method thereof

Abstract

The invention relates to the technical field of polyurethane, in particular to bio-based waterborne polyurethane and a preparation method thereof. The preparation method comprises the following steps: firstly, preparing dialdehyde cellulose by utilizing cellulose oxidation, then reacting the dialdehyde cellulose with hydroxylamine hydrochloride to prepare oximido modified cellulose, and finally introducing the oximido modified cellulose and dimethylglyoxime into a polyurethane system. Through the synergistic effect of the oximido modified cellulose and dimethylglyoxime, the bio-based waterborne polyurethane film has excellent self-repairing efficiency while keeping high tensile strength and elongation at break. The bio-based waterborne polyurethane is suitable for the fields of flexible electronic devices, coatings, biomedical materials and the like, and has wide application prospects and remarkable economic and social benefits.

Description

Technical Field

[0001] The invention relates to the technical field of polyurethane, and in particular to a bio-based waterborne polyurethane and a preparation method thereof. Background Art

[0002] Polyurethane materials have been widely used in coatings, flexible electronic devices, biomedical materials and other fields due to their excellent mechanical properties, wear resistance and chemical stability. However, the preparation of traditional polyurethane materials usually relies on petroleum-based raw materials, which are not only non-renewable, but also cause certain pollution to the environment, making it difficult to meet the current requirements of green and sustainable development. In addition, traditional polyurethane films are prone to microcracks or damage due to external forces or environmental factors during use, resulting in a decrease in mechanical properties, shortening the service life of the material, and increasing maintenance and replacement costs, thereby limiting its reliability in practical applications. Therefore, the development of a bio-based polyurethane material based on renewable resources can not only reduce dependence on petroleum resources, but also achieve excellent mechanical properties and self-healing capabilities, becoming an important research direction and hotspot in the current materials field.

[0003] In recent years, the introduction of dynamic covalent bonds has provided a new solution for the self-healing properties of polyurethane materials. A dynamic covalent bond is a chemical bond that can break and recombine under specific conditions. Its dynamic properties enable the material to self-repair by reorganizing the bonds after being damaged. Among them, the oxime-carbamate bond, as a typical dynamic covalent bond, can undergo a reversible reaction under environmental stimulation due to its unique chemical structure and dynamic properties, thereby giving the material excellent self-healing ability. However, a single dynamic bond design often fails to take into account both the mechanical properties and self-healing efficiency of the material, and is difficult to meet the needs of practical applications. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a bio-based waterborne polyurethane and a preparation method thereof, so as to provide a bio-based waterborne polyurethane having both excellent mechanical properties and high self-healing efficiency.

[0005] Based on the above purpose, the present invention provides a method for preparing a bio-based waterborne polyurethane, comprising the following steps:

[0006] (1) adding cellulose powder and sodium periodate to deionized water, then adjusting the pH to 4.5 with acetic acid-sodium acetate buffer, heating to 45-55° C. in a light-proof and nitrogen atmosphere, stirring and reacting for 3-5 hours, filtering with suction, washing with glycerol solution, filtering again after washing, washing, and vacuum drying to obtain dialdehyde cellulose;

[0007] (2) adding dialdehyde cellulose, hydroxylamine hydrochloride and sodium acetate into deionized water, heating to 55-65° C., stirring for 20-40 min, then heating to 75-85° C., stirring for 5-7 h, filtering, washing and vacuum drying to obtain oxime-modified cellulose;

[0008] (3) adding oxime-modified cellulose and diacetyl oxime to butanone and stirring for 20-40 minutes to obtain a modified solution;

[0009] (4) In a nitrogen atmosphere, bio-based polytetramethylene glycol and isophorone diisocyanate are mixed, the temperature is raised to 75-85°C, the mixture is stirred and reacted for 1.5-2.5 hours, the temperature is then lowered to 65-75°C, 2,2-dihydroxymethylpropionic acid and dibutyltin dilaurate are added, the mixture is stirred and reacted for 1.5-2.5 hours, the temperature is then lowered to 55-65°C, the modified liquid is added, the mixture is stirred and reacted for 2-4 hours, the temperature is then lowered to 45-55°C, triethylamine is added, the mixture is neutralized and reacted for 10-20 minutes, the mixture is cooled to room temperature, deionized water is added, the mixture is emulsified, butanone is removed by rotary evaporation, and a bio-based waterborne polyurethane is obtained.

[0010] Preferably, in step (2), the weight ratio of dialdehyde cellulose, hydroxylamine hydrochloride, sodium acetate and deionized water is 1:0.2-0.6:0.5-2:10-20.

[0011] Preferably, in step (3), the weight ratio of oxime-modified cellulose, diacetyl oxime and butanone is 0.05-0.2:0.3-1.5:4-10.

[0012] Preferably, in the step (4), the weight ratio of bio-based polytetramethylene ether diol, isophorone diisocyanate, 2,2-dihydroxymethylpropionic acid, dibutyltin dilaurate, modification liquid, triethylamine and deionized water is 15-42:8-24:1.21-3.63:0.05-0.2:4.35-11.7:0.91-2.73:75-220.

[0013] Preferably, the particle size of the cellulose powder in step (1) is 15-25 μm.

[0014] Preferably, in step (1), the weight ratio of cellulose powder, sodium periodate and deionized water is 1:0.5-1.5:8-12.

[0015] Preferably, the concentration of the glycerol solution in step (1) is 0.5wt%-1.5wt%.

[0016] Preferably, the weight average molecular weight of the bio-based polytetrahydrofuran ether diol in step (4) is 1000.

[0017] Preferably, the emulsification speed in step (4) is 1500-2500 rpm and the time is 0.5-1.5 h.

[0018] Furthermore, the present invention also provides a bio-based waterborne polyurethane obtained by the preparation method of the bio-based waterborne polyurethane.

[0019] Beneficial effects of the present invention:

[0020] The present invention provides a bio-based waterborne polyurethane and a preparation method thereof, and the prepared film has excellent mechanical properties and self-healing ability. By introducing oxime-modified cellulose and diacetyl oxime, the tensile strength, elongation at break and self-healing efficiency of the polyurethane film are significantly improved. The branched structure of oxime-modified cellulose provides more cross-linking sites, which react with isocyanate to form high-density dynamic oxime-carbamate bonds, enhance the strength and stability of the polyurethane network, optimize the microstructure of the film, and significantly improve the mechanical properties.

[0021] In addition, oxime-modified cellulose can fully stretch in the solvent to form a uniformly dispersed structure, further improving the performance of the film. The linear structure of diacetyl oxime plays a regulatory role in the system, appropriately reducing the crosslinking density, increasing the degree of freedom of the molecular chain, and promoting the reorganization and fracture repair process of the dynamic oxime-carbamate bond, thereby improving the flexibility and self-healing efficiency of the film. The synergistic effect of the two effectively regulates the crosslinking density and fluidity of the molecular chain inside the polyurethane, so that the film has excellent self-healing ability while maintaining high tensile strength and elongation at break.

[0022] The bio-based waterborne polyurethane provided by the present invention has broad application prospects in the fields of flexible electronic devices, coatings and biomedical materials, can meet the long-term use requirements in complex environments, and at the same time reduces the frequency of material replacement and maintenance costs, and has significant economic and social benefits. DETAILED DESCRIPTION

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0024] Embodiment 1:

[0025] (1) 1 g of cellulose powder and 0.5 g of sodium periodate were added to 8 g of deionized water, and then the pH was adjusted to 4.5 with acetic acid-sodium acetate buffer. The mixture was heated to 45° C. in a light-proof and nitrogen atmosphere, stirred for reaction for 3 h, filtered, and washed with a 0.5 wt% glycerol solution. After washing, the mixture was filtered again and washed with deionized water until neutral, and vacuum dried at 50° C. for 24 h to obtain dialdehyde cellulose;

[0026] (2) 1 g of dialdehyde cellulose, 0.2 g of hydroxylamine hydrochloride and 0.5 g of sodium acetate were added to 10 g of deionized water, heated to 55° C., stirred for 20 min, then heated to 75° C., stirred for 5 h, filtered, washed with deionized water three times, and vacuum dried at 50° C. for 24 h to obtain oxime-modified cellulose;

[0027] (3) adding 0.05 g of oxime-modified cellulose and 0.3 g of dimethylglyoxime to 4 g of butanone and stirring for 20 min to obtain a modified solution;

[0028] (4) Under a nitrogen atmosphere, 15 g of bio-based polytetrahydrofuran ether diol and 8 g of isophorone diisocyanate were mixed, the temperature was raised to 75 ° C, and the mixture was stirred for reaction for 1.5 h. The mixture was cooled to 65 ° C, 1.21 g of 2,2-dihydroxymethylpropionic acid and 0.05 g of dibutyltin dilaurate were added, and the mixture was stirred for reaction for 1.5 h. The mixture was cooled to 55 ° C, 4.35 g of modified liquid was added, and the mixture was stirred for reaction for 2 h. The mixture was cooled to 45 ° C, 0.91 g of triethylamine was added, and the mixture was neutralized for 10 min. The mixture was cooled to room temperature, 75 g of deionized water was added, and the mixture was emulsified at 1500 rpm for 0.5 h. The butanone was removed by rotary evaporation to obtain a bio-based waterborne polyurethane.

[0029] Embodiment 2:

[0030] (1) 1 g of cellulose powder and 1 g of sodium periodate were added to 10 g of deionized water, and then the pH was adjusted to 4.5 with acetic acid-sodium acetate buffer. The mixture was heated to 50° C. in a light-proof and nitrogen atmosphere, stirred for reaction for 4 h, filtered, and washed with a 1 wt% glycerol solution. After washing, the mixture was filtered again and washed with deionized water until neutral, and vacuum dried at 50° C. for 24 h to obtain dialdehyde cellulose;

[0031] (2) 1 g of dialdehyde cellulose, 0.4 g of hydroxylamine hydrochloride and 1 g of sodium acetate were added to 15 g of deionized water, heated to 60° C., stirred for 30 min, then heated to 80° C., stirred for 6 h, filtered, washed with deionized water for 3 times, and vacuum dried at 50° C. for 24 h to obtain oxime-modified cellulose;

[0032] (3) adding 0.1 g of oxime-modified cellulose and 0.5 g of dimethylglyoxime to 6 g of butanone and stirring for 30 min to obtain a modified solution;

[0033] (4) Under a nitrogen atmosphere, 30 g of bio-based polytetrahydrofuran ether diol and 16 g of isophorone diisocyanate were mixed, the temperature was raised to 80 ° C, and the mixture was stirred for reaction for 2 h. The mixture was then cooled to 70 ° C, 2.42 g of 2,2-dihydroxymethylpropionic acid and 0.1 g of dibutyltin dilaurate were added, the mixture was stirred for reaction for 2 h, the temperature was then cooled to 60 ° C, 6.6 g of modified liquid was added, the mixture was stirred for reaction for 3 h, the temperature was then cooled to 50 ° C, 1.82 g of triethylamine was added, the mixture was neutralized for 15 min, the mixture was cooled to room temperature, 150 g of deionized water was added, the mixture was emulsified at 2000 rpm for 1 h, butanone was removed by rotary evaporation, and a bio-based waterborne polyurethane was obtained.

[0034] Embodiment 3:

[0035] (1) 1 g of cellulose powder and 1.5 g of sodium periodate were added to 12 g of deionized water, and then the pH was adjusted to 4.5 with acetic acid-sodium acetate buffer. The mixture was heated to 55° C. in a light-proof and nitrogen atmosphere, stirred for reaction for 5 h, filtered, and washed with a 1.5 wt% glycerol solution. After washing, the mixture was filtered again and washed with deionized water until neutral. The mixture was vacuum dried at 50° C. for 24 h to obtain dialdehyde cellulose.

[0036] (2) 1 g of dialdehyde cellulose, 0.6 g of hydroxylamine hydrochloride and 2 g of sodium acetate were added to 20 g of deionized water, heated to 65° C., stirred for 40 min, then heated to 85° C., stirred for reaction for 7 h, filtered, washed with deionized water for 3 times, and vacuum dried at 50° C. for 24 h to obtain oxime-modified cellulose;

[0037] (3) adding 0.2 g of oxime-modified cellulose and 1.5 g of dimethylglyoxime to 10 g of butanone and stirring for 40 min to obtain a modified solution;

[0038] (4) Under a nitrogen atmosphere, 42 g of bio-based polytetrahydrofuran ether diol and 24 g of isophorone diisocyanate were mixed, the temperature was raised to 85 ° C, and the mixture was stirred for reaction for 2.5 h. The mixture was cooled to 75 ° C, 3.63 g of 2,2-dihydroxymethylpropionic acid and 0.2 g of dibutyltin dilaurate were added, and the mixture was stirred for reaction for 2.5 h. The mixture was cooled to 65 ° C, 11.7 g of modified liquid was added, and the mixture was stirred for reaction for 4 h. The mixture was cooled to 55 ° C, 2.73 g of triethylamine was added, and the mixture was neutralized for 20 min. The mixture was cooled to room temperature, 220 g of deionized water was added, and the mixture was emulsified at 2500 rpm for 1.5 h. The butanone was removed by rotary evaporation to obtain a bio-based waterborne polyurethane.

[0039] Comparative Example 1:

[0040] The difference between Comparative Example 1 and Example 2 is that the oxime-modified cellulose in step (3) is replaced by dialdehyde cellulose;

[0041] The specific steps are as follows:

[0042] (1) 1 g of cellulose powder and 1 g of sodium periodate were added to 10 g of deionized water, and then the pH was adjusted to 4.5 with acetic acid-sodium acetate buffer. The mixture was heated to 50° C. in a light-proof and nitrogen atmosphere, stirred for reaction for 4 h, filtered, and washed with a 1 wt% glycerol solution. After washing, the mixture was filtered again and washed with deionized water until neutral, and vacuum dried at 50° C. for 24 h to obtain dialdehyde cellulose;

[0043] (2) adding 0.1 g of dialdehyde cellulose and 0.5 g of dimethylglyoxime to 6 g of butanone and stirring for 30 min to obtain a modified solution;

[0044] (3) Under a nitrogen atmosphere, 30 g of bio-based polytetrahydrofuran ether diol and 16 g of isophorone diisocyanate were mixed, the temperature was raised to 80 ° C, and the mixture was stirred for reaction for 2 h. The mixture was then cooled to 70 ° C, 2.42 g of 2,2-dihydroxymethylpropionic acid and 0.1 g of dibutyltin dilaurate were added, the mixture was stirred for reaction for 2 h, the temperature was then cooled to 60 ° C, 6.6 g of modified liquid was added, the mixture was stirred for reaction for 3 h, the temperature was then cooled to 50 ° C, 1.82 g of triethylamine was added, the mixture was neutralized for 15 min, the mixture was cooled to room temperature, 150 g of deionized water was added, the mixture was emulsified at 2000 rpm for 1 h, butanone was removed by rotary evaporation, and a bio-based waterborne polyurethane was obtained.

[0045] Comparative Example 2:

[0046] The difference between Comparative Example 2 and Example 2 is that the oxime-modified cellulose in step (3) is replaced by cellulose powder;

[0047] The specific steps are as follows:

[0048] (1) Add 0.1 g of cellulose powder and 0.5 g of dimethylglyoxime to 6 g of butanone and stir for 30 min to obtain a modified solution;

[0049] (2) Under a nitrogen atmosphere, 30 g of bio-based polytetrahydrofuran ether diol and 16 g of isophorone diisocyanate were mixed, the temperature was raised to 80 ° C, and the mixture was stirred for reaction for 2 h. The mixture was then cooled to 70 ° C, 2.42 g of 2,2-dihydroxymethylpropionic acid and 0.1 g of dibutyltin dilaurate were added, the mixture was stirred for reaction for 2 h, the temperature was then cooled to 60 ° C, 6.6 g of modified liquid was added, the mixture was stirred for reaction for 3 h, the temperature was then cooled to 50 ° C, 1.82 g of triethylamine was added, the mixture was neutralized for 15 min, the mixture was cooled to room temperature, 150 g of deionized water was added, the mixture was emulsified at 2000 rpm for 1 h, butanone was removed by rotary evaporation, and a bio-based waterborne polyurethane was obtained.

[0050] Comparative Example 3:

[0051] The difference between Comparative Example 3 and Example 2 is that the oxime-modified cellulose in step (3) is replaced by diacetyl oxime;

[0052] The specific steps are as follows:

[0053] (1) 1 g of cellulose powder and 1 g of sodium periodate were added to 10 g of deionized water, and then the pH was adjusted to 4.5 with acetic acid-sodium acetate buffer. The mixture was heated to 50° C. in a light-proof and nitrogen atmosphere, stirred for reaction for 4 h, filtered, and washed with a 1 wt% glycerol solution. After washing, the mixture was filtered again and washed with deionized water until neutral, and vacuum dried at 50° C. for 24 h to obtain dialdehyde cellulose;

[0054] (2) 1 g of dialdehyde cellulose, 0.4 g of hydroxylamine hydrochloride and 1 g of sodium acetate were added to 15 g of deionized water, heated to 60° C., stirred for 30 min, then heated to 80° C., stirred for 6 h, filtered, washed with deionized water for 3 times, and vacuum dried at 50° C. for 24 h to obtain oxime-modified cellulose;

[0055] (3) Add 0.6 g of dimethylglyoxime to 6 g of butanone and stir for 30 min to obtain a modified solution;

[0056] (4) Under a nitrogen atmosphere, 30 g of bio-based polytetrahydrofuran ether diol and 16 g of isophorone diisocyanate were mixed, the temperature was raised to 80 ° C, and the mixture was stirred for reaction for 2 h. The mixture was then cooled to 70 ° C, 2.42 g of 2,2-dihydroxymethylpropionic acid and 0.1 g of dibutyltin dilaurate were added, the mixture was stirred for reaction for 2 h, the temperature was then cooled to 60 ° C, 6.6 g of modified liquid was added, the mixture was stirred for reaction for 3 h, the temperature was then cooled to 50 ° C, 1.82 g of triethylamine was added, the mixture was neutralized for 15 min, the mixture was cooled to room temperature, 150 g of deionized water was added, the mixture was emulsified at 2000 rpm for 1 h, butanone was removed by rotary evaporation, and a bio-based waterborne polyurethane was obtained.

[0057] Comparative Example 4:

[0058] The difference between Comparative Example 4 and Example 2 is that the diacetyl oxime in step (3) is replaced by oxime-modified cellulose;

[0059] The specific steps are as follows:

[0060] (1) 1 g of cellulose powder and 1 g of sodium periodate were added to 10 g of deionized water, and then the pH was adjusted to 4.5 with acetic acid-sodium acetate buffer. The mixture was heated to 50° C. in a light-proof and nitrogen atmosphere, stirred for reaction for 4 h, filtered, and washed with a 1 wt% glycerol solution. After washing, the mixture was filtered again and washed with deionized water until neutral, and vacuum dried at 50° C. for 24 h to obtain dialdehyde cellulose;

[0061] (2) 1 g of dialdehyde cellulose, 0.4 g of hydroxylamine hydrochloride and 1 g of sodium acetate were added to 15 g of deionized water, heated to 60° C., stirred for 30 min, then heated to 80° C., stirred for 6 h, filtered, washed with deionized water for 3 times, and vacuum dried at 50° C. for 24 h to obtain oxime-modified cellulose;

[0062] (3) adding 0.6 g of oxime-modified cellulose to 6 g of butanone and stirring for 30 min to obtain a modified solution;

[0063] (4) Under a nitrogen atmosphere, 30 g of bio-based polytetrahydrofuran ether diol and 16 g of isophorone diisocyanate were mixed, the temperature was raised to 80 ° C, and the mixture was stirred for reaction for 2 h. The mixture was then cooled to 70 ° C, 2.42 g of 2,2-dihydroxymethylpropionic acid and 0.1 g of dibutyltin dilaurate were added, the mixture was stirred for reaction for 2 h, the temperature was then cooled to 60 ° C, 6.6 g of modified liquid was added, the mixture was stirred for reaction for 3 h, the temperature was then cooled to 50 ° C, 1.82 g of triethylamine was added, the mixture was neutralized for 15 min, the mixture was cooled to room temperature, 150 g of deionized water was added, the mixture was emulsified at 2000 rpm for 1 h, butanone was removed by rotary evaporation, and a bio-based waterborne polyurethane was obtained.

[0064] Comparative Example 5:

[0065] The difference between Comparative Example 5 and Example 2 is that: no modifying liquid is added in step (4);

[0066] The specific steps are as follows:

[0067] Under a nitrogen atmosphere, 30 g of bio-based polytetramethylene ether diol and 16 g of isophorone diisocyanate were mixed, heated to 80 ° C, stirred for reaction for 2 h, then cooled to 70 ° C, 2.42 g of 2,2-dihydroxymethylpropionic acid and 0.1 g of dibutyltin dilaurate were added, and the stirring reaction continued for 2 h. The temperature was then cooled to 60 ° C, and the stirring reaction continued for 3 h. The temperature was then cooled to 50 ° C, 1.82 g of triethylamine was added, and the neutralization reaction was carried out for 15 min. The mixture was cooled to room temperature, 150 g of deionized water was added, and the mixture was emulsified at 2000 rpm for 1 h. The butanone was removed by rotary evaporation to obtain a bio-based waterborne polyurethane.

[0068] Performance Test:

[0069] Preparation of polyurethane film: Bio-based waterborne polyurethane was poured into a polytetrafluoroethylene template, dried at room temperature for 5 days, and then placed in a vacuum drying oven at 50°C for 1 day to obtain a bio-based waterborne polyurethane film.

[0070] Mechanical properties test: The tensile test was carried out with an electronic tensile testing machine at a rate of 100 mm / min to obtain the tensile strength and elongation at break. The results are shown in Table 1.

[0071] Self-healing performance test: Use an electronic tensile testing machine to perform a tensile test at a rate of 100 mm / min, record the original tensile strength, use a blade to cut a new piece of film in half from the middle, and quickly fit the broken surface tightly. After drying in a 60°C oven for 2 hours, use an electronic tensile testing machine to record the tensile strength of the healed film. The self-healing efficiency of the film is calculated by the original tensile strength and the tensile strength of the healed film. The results are shown in Table 1.

[0072] Table 1 Performance test results

[0073]

[0074]

[0075] Data Analysis:

[0076] From the data of Examples 1-3 in Table 1, it can be seen that the film prepared from the bio-based waterborne polyurethane provided by the present invention has high tensile strength and elongation at break, and most importantly, the self-repair efficiency can reach more than 90%, which helps to significantly extend the service life of the film and improve its reliability and durability in practical applications. High self-repair efficiency can effectively repair microcracks or damage caused by external forces or environmental factors during the use of the film, thereby maintaining the mechanical properties and functionality of the material, reducing the frequency of material replacement, and reducing maintenance costs, and has broad application prospects in the fields of flexible electronic devices, coatings, and biomedical materials.

[0077] It can be seen from the data of Example 2 and Comparative Examples 1-2 in Table 1 that when the oxime-modified cellulose is replaced by dialdehyde cellulose or cellulose powder, the mechanical properties of the polyurethane film are significantly reduced, and the self-healing ability is almost lost. This is mainly due to the dynamic oxime-carbamate that can be formed by the oxime-modified cellulose and isocyanate, thereby achieving self-healing ability, and the oxime-modified cellulose effectively increases the cross-linking sites on the cellulose, thereby improving the mechanical properties of the polyurethane film, and the oxime-modified cellulose can stretch in butanone to form a uniformly dispersed structure, further optimizing the microstructure and performance of the polyurethane film.

[0078] From the data of Example 2 and Comparative Example 3 in Table 1, it can be seen that the film formed by the waterborne polyurethane modified with only oxime-modified cellulose has a lower elongation at break and self-repairing ability. This is mainly because the branched structure of oxime-modified cellulose provides more cross-linking sites, resulting in an excessively high cross-linking density of the polyurethane, and limits the mobility of the molecular chains inside the polyurethane, thereby reducing the flexibility of the material and significantly reducing the elongation at break. At the same time, the limited mobility of the molecular chains will also weaken the reorganization ability of the dynamic oxime-carbamate bond, thereby reducing the self-repairing efficiency of the film.

[0079] From the data of Example 2 and Comparative Example 4 in Table 1, it can be seen that the film formed by using only dimethylglyoxime-modified waterborne polyurethane has low tensile strength and self-healing ability. This is mainly because the oxime-modified cellulose has a branched structure, which can provide more cross-linking sites and form a higher density of dynamic oxime-carbamate bonds with isocyanate, thereby significantly enhancing the mechanical properties and self-healing ability of the film. However, dimethylglyoxime only has a linear structure and fewer cross-linking sites, resulting in a loose network structure of the formed polyurethane.

[0080] From the data of Example 2 and Comparative Example 5 in Table 1, it can be seen that oxime-modified cellulose and dimethylglyoxime effectively regulate the crosslinking density, fluidity and number of dynamic oxime-carbamate bonds of the internal molecular chain of polyurethane through synergistic action, thereby giving the material a higher self-repairing efficiency while achieving excellent mechanical properties. The branched structure of oxime-modified cellulose provides more crosslinking sites, enhances the strength and stability of the polyurethane network, but too high a crosslinking density may limit the fluidity of the molecular chain, affecting the flexibility and self-repairing ability of the material. The linear structure of dimethylglyoxime plays a regulatory role in the system, appropriately reduces the crosslinking density, increases the degree of freedom of the molecular chain, thereby promoting the reorganization and fracture repair process of the dynamic oxime-carbamate bond. The synergistic effect of the two enables the polyurethane film to have excellent self-repairing efficiency while maintaining high tensile strength and elongation at break, meeting the use requirements in complex environments.

[0081] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

Claims

1. A method for preparing a bio-based waterborne polyurethane, characterized in that: The following steps are involved: (1) adding cellulose powder and sodium periodate to deionized water, then adjusting the pH to 4.5 with acetic acid-sodium acetate buffer, heating to 45-55° C. in a light-proof and nitrogen atmosphere, stirring and reacting for 3-5 hours, filtering with suction, washing with glycerol solution, filtering again after washing, washing, and vacuum drying to obtain dialdehyde cellulose; (2) adding dialdehyde cellulose, hydroxylamine hydrochloride and sodium acetate into deionized water, heating to 55-65° C., stirring for 20-40 min, then heating to 75-85° C., stirring for 5-7 h, filtering, washing and vacuum drying to obtain oxime-modified cellulose; (3) adding oxime-modified cellulose and diacetyl oxime to butanone and stirring for 20-40 minutes to obtain a modified solution; (4) In a nitrogen atmosphere, bio-based polytetramethylene glycol and isophorone diisocyanate are mixed, the temperature is raised to 75-85°C, the mixture is stirred and reacted for 1.5-2.5 hours, the temperature is then lowered to 65-75°C, 2,2-dihydroxymethylpropionic acid and dibutyltin dilaurate are added, the mixture is stirred and reacted for 1.5-2.5 hours, the temperature is then lowered to 55-65°C, the modified liquid is added, the mixture is stirred and reacted for 2-4 hours, the temperature is then lowered to 45-55°C, triethylamine is added, the mixture is neutralized and reacted for 10-20 minutes, the mixture is cooled to room temperature, deionized water is added, the mixture is emulsified, butanone is removed by rotary evaporation, and a bio-based waterborne polyurethane is obtained. In the step (2), the weight ratio of dialdehyde cellulose, hydroxylamine hydrochloride, sodium acetate and deionized water is 1:0.2-0.6:0.5-2:10-20; In the step (3), the weight ratio of oxime-modified cellulose, diacetyl oxime and butanone is 0.05-0.2:0.3-1.5:4-10; In the step (4), the weight ratio of bio-based polytetramethylene ether diol, isophorone diisocyanate, 2,2-dihydroxymethyl propionic acid, dibutyltin dilaurate, modification liquid, triethylamine and deionized water is 15-42:8-24:1.21-3.63:0.05-0.2:4.35-11.7:0.91-2.73:75-220.

2. The method for preparing the bio-based waterborne polyurethane according to claim 1, characterized in that: The particle size of the cellulose powder in step (1) is 15-25 μm.

3. The method for preparing the bio-based waterborne polyurethane according to claim 1, characterized in that: In the step (1), the weight ratio of cellulose powder, sodium periodate and deionized water is 1:0.5-1.5:8-12.

4. The method for preparing the bio-based waterborne polyurethane according to claim 1, characterized in that: The concentration of the glycerol solution in step (1) is 0.5wt%-1.5wt%.

5. The method for preparing the bio-based waterborne polyurethane according to claim 1, characterized in that: The weight average molecular weight of the bio-based polytetrahydrofuran ether diol in the step (4) is 1000.

6. The method for preparing the bio-based waterborne polyurethane according to claim 1, characterized in that: The emulsification speed in step (4) is 1500-2500 rpm and the emulsification time is 0.5-1.5 h.

7. A bio-based waterborne polyurethane, characterized in that: The bio-based waterborne polyurethane is obtained by the preparation method of any one of claims 1 to 6.

Images