Straw modified polyurethane material and preparation method thereof

Abstract

The invention discloses a straw modified polyurethane material and a preparation method thereof, and relates to the technical field of biomass comprehensive utilization, and the preparation method comprises the following specific steps: (1) straw liquefaction: adding a liquefying agent and a solid acid catalyst into crushed straw subjected to microwave treatment, uniformly mixing, and carrying out heat preservation under nitrogen protection; reacting at 120-180 DEG C for 2-3 hours, and filtering to obtain filtrate, namely a straw liquefied product; and (2) carrying out condensation polymerization on the straw liquefied product and an NCO group-terminated polyurethane prepolymer with an anionic branched chain, then adding triethylamine and deionized water into the obtained product, and dispersing to obtain the straw modified polyurethane aqueous dispersion. According to the method, waste rice straw resources are fully utilized to replace part of petroleum-based raw materials, consumption of petroleum resources is reduced, meanwhile, environmental pollution caused by straw incineration or waste is avoided, and resource recycling is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of comprehensive utilization of biomass, and particularly relates to a straw modified polyurethane material and a preparation method thereof. BACKGROUND

[0002] Polyurethane (PU) material has been widely used in many fields due to its excellent performance. Since the 1950s, the development of petroleum industry and chemical industry has enriched the raw material sources of polyurethane industry and improved the performance of many products, which once greatly promoted the prosperity of polyurethane industry. However, with the progress of society, the petroleum resources, which are important pillars of world economic development, will be exhausted day by day, and various polymer intermediates from petroleum will also be seriously troubled, which limits the source of raw materials of polyurethane industry and affects the development of polyurethane industry at all times. In addition, the petroleum-based chemical industry and the like are serious sources of environmental pollution, and with the improvement of people's material living standards and the increasing environmental awareness, it is more important to seek petroleum substitutes, develop new energy and new materials, and reduce and eliminate pollution from the source.

[0003] The synthesis reaction of PU is a step-by-step polymerization reaction of hydrogen transfer, which is generally obtained by the interaction of di- or multi-isocyanate and multi-alcohol compound, and -OH is the necessary reaction group.

[0004] The main component of straw is cellulose, which is the first largest natural organic matter and rich in hydroxyl natural cellulose. The active alcohol hydroxyl group has been used by human beings for thousands of years, and the straw has not been widely used so far. At present, the straw is discarded in large quantities, which not only wastes resources but also seriously pollutes the environment.

[0005] Therefore, it is a technical problem to be solved in the field of how to prepare polyurethane material by modifying straw. SUMMARY

[0006] In order to solve the problems of the existing polyurethane material depending on petroleum-based raw materials, wasting rice straw resources and polluting the environment, an environment-friendly and sustainable rice straw polyurethane new material and a preparation method thereof are provided, which simultaneously expand the application of the material in the field of interior wall coating and realize the unity of resource recycling and environmental protection benefits.

[0007] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: A preparation method of a straw modified polyurethane material, comprising the following specific steps: (1) straw liquefaction: adding liquefying agent and solid acid catalyst to the crushed straw treated by microwave, mixing uniformly, then filtering the filtrate obtained after reacting for 2-3h under the condition of 120-180℃ and nitrogen protection, which is the straw liquefaction product; it can destroy the compact crystal structure of cellulose in the straw due to hydrogen bond, soften the peripheral hemicellulose and lignin, and improve the activity of hydroxyl group participating in the reaction; (2) carrying out condensation reaction between the straw liquefaction product and NCO group terminated polyurethane prepolymer with anionic branched chain, then dispersing the obtained product in triethylamine and deionized water to obtain straw modified polyurethane aqueous dispersion.

[0008] Preferably, the microwave treatment condition in step (1) is treating for 3-5min under 400-500W, which can quickly destroy the cellulose crystal region; The particle size of the crushed straw is 80-100 mesh, which increases the contact area; The stirring speed of the reaction is 300-500r / min.

[0009] Preferably, the mass ratio of the crushed straw, liquefying agent and solid acid catalyst in step (1) is 100-120:250-300:4-5.

[0010] Preferably, the liquefying agent in step (1) is polyethylene glycol 400 and glycerol with a mass ratio of 2-3:1, which takes into account the dissolution of hemicellulose and lignin; The solid acid catalyst is at least one of p-toluenesulfonic acid and potassium hydrogen sulfate, which catalyzes the directional hydrogen bond breaking.

[0011] Preferably, the preparation method of the NCO group terminated polyurethane prepolymer with anionic branched chain in step (2) is: reacting toluene diisocyanate and polyether polyol at 60-75℃ for 1.5-2.5h, then adding dimethylol propionic acid and continuing to react at 60-75℃ for 1.5-2.5h, sampling and detecting the NCO group content, stopping the reaction when the NCO mass fraction decreases to 8-10%, and obtaining the NCO group terminated polyurethane prepolymer with anionic branched chain.

[0012] Preferably, the mass ratio of toluene diisocyanate, polyether polyol and dimethylol propionic acid is 100-150:80-120:100-150.

[0013] Preferably, the mass ratio of the straw liquefaction product, NCO group terminated polyurethane prepolymer with anionic branched chain, triethylamine and deionized water in step (2) is 70-90:100:8-10:120-150.

[0014] Preferably, the crystallinity of the straw liquefaction product in step (2) is 28-30%, the hydroxyl value is 350-450 mgKOH / g, and the residue rate is ≤5%; The conditions of the polycondensation reaction are that the reaction temperature is 5-10°C higher than the conventional polyurethane polycondensation temperature, the reaction temperature is 70-80°C, the reaction time is 3-4h, the reaction time is 1-1.5h longer than the conventional reaction time, and the low-activity hydroxyl groups in the straw are fully reacted. The dispersion method is stirring at 1500-1800r / min for 45-60min at a pH value of 7.2-7.5.

[0015] Preferably, the solid content of the straw-modified polyurethane aqueous dispersion is 35-38%, the particle size is 100-300nm, the hydroxyl conversion rate is ≥90%, and the dispersion is not stratified after being stored at room temperature for 6-8 months, thereby solving the problems of conventional biomass-modified polyurethane, such as easy agglomeration and poor stability.

[0016] Preferably, the straw liquefaction product is uniformly added (1-2 drops / s) into the NCO group-capped polyurethane prepolymer with anionic branches in the polycondensation reaction, so as to avoid local -NCO excess and improve the hydroxyl conversion rate to more than 90%.

[0017] The straw-modified polyurethane material prepared by the preparation method in any one of the above.

[0018] The application of the straw-modified polyurethane material in the preparation of an interior wall coating.

[0019] Preferably, the straw polyurethane aqueous dispersion is used as a film-forming base, and then rutile titanium dioxide, calcium carbonate, talc and other pigments and fillers, as well as wetting dispersants, defoamers, leveling agents and other functional additives are added, and then the interior wall coating is prepared through processes such as mixing, dispersion and grinding.

[0020] Due to the porous structure of the straw segments, the air permeability of the coating film is improved by 20% (compared with conventional polyurethane coatings), the scrubbing resistance is ≥6000 times, and the formaldehyde emission is ≤0.02mg / m 3 .

[0021] Preferably, the polyurethane aqueous dispersion can be dried by demulsification to prepare a redispersible resin powder, and the straw segments enhance the redispersibility of the resin powder, and the dissolution speed is 30% faster than that of conventional polyurethane resin powder.

[0022] Compared with the prior art, the present application has the following beneficial effects: (1) The present application makes full use of the waste rice straw resources, replaces part of the petroleum-based raw materials, reduces the consumption of petroleum resources, avoids environmental pollution caused by straw burning or waste, and realizes resource recycling; (2) The hydroxyl groups in the straw liquefaction products of the present invention fully participate in the polymerization reaction, and the synthesized polyurethane new material has both the characteristics of natural biomass and the excellent properties of polyurethane. The interior wall coating prepared with it as the matrix has outstanding performance in terms of adhesion, scrub resistance, air permeability and weather resistance. (3) It has a wide range of applications. The rice straw polyurethane aqueous dispersion prepared by this invention can not only be used in interior wall coatings, but also be used to prepare redispersible resin powder through demulsification and drying, and can be extended to the fields of craft raw materials, with multiple application values. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings in this description are merely embodiments of the present invention.

[0024] Figure 1 This is a schematic diagram of straw liquefaction according to an embodiment of the present invention; Figure 2 This is a flowchart illustrating the synthesis route of straw polyurethane according to an embodiment of the present invention. Detailed Implementation

[0025] Embodiments of the present invention are described below, examples of which are shown in the accompanying drawings. The embodiments described with reference to the drawings are exemplary and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0026] Figure 1 This diagram illustrates the liquefaction of rice straw. The upper left side shows the microstructure of the original rice straw, which is dominated by tightly interwoven fiber bundles (labeled as cellulose crystal regions). These bundles are cross-linked by strong hydrogen bonds. The internal hydroxyl groups (-OH) are encapsulated by polyhydroxyl groups within the crystal regions and hydrogen bonds, resulting in extremely low activity. The straw composition consists of cellulose (40-50%), hemicellulose (20-30%), and lignin (15-25%), exhibiting a complex and uneven structure. The lower left side shows the structure of a conventional petroleum-based polyol, where the hydroxyl groups (-OH) are fully exposed, exhibiting stable activity and requiring no pretreatment to participate in the reaction. The comparison clearly demonstrates that due to its complex crystal region and hydrogen bond structure, straw cannot directly replace petroleum-based polyols and must undergo a liquefaction process to break down the binding. This invention, through relevant processing, can replace petroleum-based polyols. The middle section shows the structure of the four-port reactor used in this embodiment, along with the relevant design for the process: 1-1) Input materials: crushed straw (80-100 mesh, to increase contact area) + mixed liquefaction agent (polyethylene glycol 400: glycerol = 2-3:1, to dissolve both hemicellulose and lignin) + solid acid catalyst (p-toluenesulfonic acid / potassium hydrogen sulfate, to directionally catalyze hydrogen bond breaking). 1-2) Reaction conditions: Microwave pretreatment (3-5 min, 400-500 W, to rapidly destroy cellulose crystal regions, unlike the slow heating of conventional heating) + nitrogen protection (to prevent oxidation) + 120-180℃ (suitable for the degradation of straw components, lower than the reaction temperature of petroleum-based polyols) + stirring (300-500 r / min, to ensure uniform contact of materials). 1-3) Process changes: fiber bundles loosen → hydrogen bonds break (dashed lines disappear) → hemicellulose / lignin dissolves → hydroxyl groups are gradually exposed, which visually demonstrates the targeted treatment of straw structure by the process; The right side shows the state diagram of the highly active product after liquefaction: a loose amorphous molecular fragment (cellulose degradation fragment + hemicellulose / lignin dissolved product, without obvious crystalline regions) is drawn, and the hydroxyl (-OH) symbol is large and densely distributed (the degree of freedom of OH is increased by 30-40%, and the activity is comparable to that of petroleum-based polyols). At the same time, key indicators are marked as crystallinity 28-30% (original 65%), hydroxyl value 350-450mgKOH / g, and residue rate ≤5%, which clearly shows that the liquefied product has the structural basis to efficiently replace petroleum-based polyols, laying the foundation for high conversion rate in subsequent polyurethane synthesis; Figure 2 This is a flowchart illustrating the synthesis route of straw polyurethane in an embodiment of the present invention. The purpose is to highlight the multi-hydroxyl structure characteristics of the straw liquefaction products. The reaction conditions designed in this invention differ from those of conventional polyurethane to achieve a high conversion rate. The flowchart uses arrows to connect "raw material differences - prepolymerization - polycondensation - water dispersion - application," with the following logic: 2-1) Raw material side: Due to the structural differences of polyhydroxy compounds, the initial raw materials were clearly defined in two separate branches, laying the groundwork for subsequent process design. Branch 1 (Straw Source): Liquefied straw products (natural polyhydroxy mixture, containing cellulose degradation fragments and hemicellulose derivatives, with heterogeneous hydroxyl positions / activities, unlike the single structure of petroleum-based products, related to...) Figure 1 Product on the right side; Branch 2 (basic polyurethane raw materials): petroleum-based raw materials (isocyanate TDI: single -NCO active site; polyether polyol N210: linear structure, stable hydroxyl activity; DMPA: carboxyl diol, providing hydrophilic group sites), conventional polyurethane raw materials: uniform structure, easy to control reaction conditions; 2-2) Step 1: Prepolymer synthesis (a routine basic step, preparing for subsequent adaptation) Raw materials: TDI+N210+DMPA, reaction conditions 60-75℃, 1.5-2.5h (conventional polyurethane prepolymerization conditions). Product: Anionic branched-chain capped polyurethane prepolymer containing highly active -NCO groups (molar ratio controllable), pH=4.5. Design purpose: To reserve active sites for precise reaction with the polyhydroxy fragments of straw liquefaction products in the subsequent process. 2-3) Second step: Polycondensation reaction (structural compatibility design), dedicated design: Raw materials: polyurethane prepolymer + liquefied straw products, the core of the reaction is the condensation of prepolymer-NCO and straw-OH; Targeted reaction conditions: 70-80℃ (5-10℃ higher than the conventional polyurethane polycondensation temperature to ensure sufficient reaction of low-activity hydroxyl groups in straw) + 3-4h (1-1.5h longer than the conventional reaction to solve the problem of reaction lag caused by uneven distribution of hydroxyl groups in straw) + uniform dripping (1-2 drops / second to avoid local excess of -NCO and increase hydroxyl conversion rate to over 90%). Structural change: Straw polyhydroxy fragments are incorporated into the polyurethane backbone to form a copolymer structure of petroleum-based segments and natural biomass fragments, which is different from the homopolymer structure of conventional all-petroleum-based polyurethane.

[0027] 2-4) Step 3: Water Dispersion (Optimization of Dispersion for Adapted Straw Fragments) Raw materials: Condensation product + triethylamine (to neutralize DMPA carboxyl groups) + deionized water; Targeted conditions: pH=7.2-7.5 (adjusted to the pH range for stable dispersion of straw fragments; the pH of conventional polyurethane can be relaxed to 6-8) + high-speed stirring 1500-1800r / min (300-500r / min higher than conventional stirring rate to overcome the possible agglomeration tendency of straw fragments). Product: RSPU aqueous dispersion, solid content 35-38%, particle size 100-300nm, hydroxyl conversion rate ≥90%, no stratification after 6-8 months of storage at room temperature, solving the problems of easy agglomeration and poor stability of conventional biomass modified polyurethane.

[0028] 2-5) Applications: Performance advantages resulting from structural characteristics extend from RSPU aqueous dispersions to two other applications, demonstrating the structure-performance relationship: Adding pigments / fillers / auxiliaries → Interior wall coatings. Due to the porous structure of straw fragments, the breathability of the coating film is increased by 20% (compared to conventional polyurethane coatings), with a scrub resistance of ≥6000 cycles and formaldehyde emission ≤0.02mg / m³. 3 ; Demulsification and drying → redispersible resin powder; straw fragments enhance the redispersibility of the resin powder, and the dissolution rate is 30% faster than that of conventional polyurethane resin powder. Example 1 This invention provides a method for preparing straw-modified polyurethane material, specifically including the following steps: (1) Liquefaction of rice straw: Take dry rice straw (moisture content ≤10%), crush it to 80 mesh using a pulverizer, weigh 100g and place it in a 500mL four-necked reactor. Microwave pretreatment is performed for 4min with a microwave power of 400W. Then, add 250g of mixed liquefaction agent (polyethylene glycol 400: glycerol = 2:1, mass ratio) to the reactor and add 4g of solid acid catalyst (p-toluenesulfonic acid). Purge the reactor with nitrogen gas (flow rate 50mL / min) to replace the air in the reactor 3 times. After sealing, heat to 150℃, stir at 400r / min, and react at a constant temperature for 3h. After the reaction is completed, cool to room temperature, filter with a 100-mesh filter, and collect the filtrate as the rice straw liquefaction product. Performance test data: The hydroxyl value of the liquefied product is 420 mg KOH / g, the acid value is 3.2 mg KOH / g, the residue rate is 3.5%, and the moisture content is 1.8%. X-ray diffraction (XRD) analysis showed that the crystallinity of straw cellulose decreased from the initial 65% to 28%, indicating that the hydrogen bonds were fully broken and the hydroxyl activity was significantly improved. Environmental data: This embodiment consumes 100g of rice straw, which is equivalent to reducing CO2 emissions from burning 0.08kg of straw (referencing the "Emission Coefficient of Agricultural Waste Incineration," the CO2 emission coefficient for rice straw incineration is 0.8kg / kg). Simultaneously, it replaces 15% of the petroleum-based polyol in subsequent synthesis steps, reducing petroleum resource consumption by approximately 0.06kg (based on a petroleum-based polyol density of 1.05g / cm³). 3 (conversion) (2) Preparation of polyurethane prepolymer with anionic branches: In a dry 500mL four-necked flask, 120g of toluene diisocyanate (TDI, purity 99.5%) and 90g of polyether polyol (N210, hydroxyl value 56mgKOH / g) were added, the temperature was raised to 65℃, and the reaction was stirred for 1.5h; then 12g of dimethylolpropionic acid (DMPA, purity 99%) was added, the temperature was raised to 75℃, and the reaction was continued for 2.5h; the NCO group content was measured by sampling, and the reaction was stopped when the NCO mass fraction dropped to 8-10%, and anionic branched polyurethane prepolymer was obtained; Performance test data: The prepolymer appears as a pale yellow transparent liquid with a viscosity (25℃) of 3500 mPa. The prepolymer contained 9.2% NCO and had a pH of 4.5. Gel permeation chromatography (GPC) analysis showed a number-average molecular weight (Mn) of 8500 and a molecular weight distribution index (PDI) of 1.8, indicating that the prepolymer had good molecular structure uniformity. Environmental data: When reacting with liquefied straw, the amount of TDI used can be reduced by 30% (compared to pure petroleum-based polyurethane synthesis). The CO2 emission per unit product during TDI production is about 5 kg / kg. Therefore, every 100g of prepolymer prepared can reduce CO2 emissions by 0.138kg (calculated based on a 30% reduction in TDI). (3) Synthesis of rice straw polyurethane (RSPU) aqueous dispersion (low straw substitution rate): Take 70g of the liquefied straw product prepared in step (1) and slowly drop it into 100g of the prepolymer prepared in step (2) (dropping rate 1 drop / second), keep the temperature at 75℃, stir and react for 3.5h, then add 8g of triethylamine (purity 99%) to neutralize to pH=7.5, and then slowly add 120g of deionized water under high speed stirring (1500r / min) and disperse for 45min to obtain RSPU aqueous dispersion; Performance test data: The aqueous dispersion is a milky white semi-transparent liquid with a solid content of 35%, a particle size (dynamic light scattering method) of 220 nm, and a zeta potential of -38 mV (good stability, no delamination after 6 months of storage at room temperature); the coating film (50 μm thickness after drying) has a tensile strength of 2.8 MPa, an elongation at break of 180%, and an adhesion (cross-cut test) grade of 1. Environmental data: In this embodiment, 70g of liquefied straw is used to replace 70g of petroleum-based polyol (calculated based on equal hydroxyl activity). The energy consumption for the production of petroleum-based polyol is approximately 8MJ / kg, thus saving 560MJ of energy consumption (equivalent to reducing the consumption of 13.4g of standard coal, with reference to 1MJ≈0.024kg of standard coal). At the same time, it reduces SO2 emissions by 0.04kg during the production of petroleum-based raw materials (emission coefficient 0.6kg / kg petroleum-based polyol).

[0029] Example 2 This invention provides a method for preparing straw-modified polyurethane material, specifically including the following steps: (1) Liquefaction of rice straw: Take dried rice straw and crush it to 100 mesh. Weigh 120g and place it in a 500mL reactor. Microwave pretreatment for 5min (power 500W). Then add 300g of mixed liquefaction agent (polyethylene glycol 400: glycerol = 3:1) and 5g of catalyst (potassium hydrogen sulfate). After nitrogen replacement, heat to 160℃, stir at 500r / min, react for 2.5h, cool and filter. Collect the filtrate as rice straw liquefaction product. Performance test data: liquefied product hydroxyl value 450 mg KOH / g, acid value 2.8 mg KOH / g, residue rate 2.8%, water content 1.5%; Fourier transform infrared spectroscopy (FTIR) shows that at 3400 cm⁻¹... -1 The intensity of the characteristic peak of hydroxyl groups increased by 40% compared with the original straw, proving that the hydroxyl exposure was increased and the reactivity was enhanced; Environmental data: Utilizing 120g of rice straw can reduce CO2 emissions from burning by 0.096kg. In subsequent synthesis, it can replace 20% of petroleum-based polyols, reducing petroleum consumption by approximately 0.08kg, while simultaneously avoiding 0.002kg of particulate matter (PM2.5) generated from straw burning. 2.5 Emissions (emission coefficients refer to the "Integrated Emission Standard for Air Pollutants"); (2) The preparation of polyurethane prepolymer with anionic side chains is the same as in Example 1; (3) Synthesis of rice straw polyurethane (RSPU) aqueous dispersion (high straw substitution rate): Take 90g of the liquefied straw product prepared in step (1) and drop it into 100g of the prepolymer prepared in step (2) (dropping rate 2 drops / second), temperature 80℃, stir and react for 4h; then add 10g of triethylamine to neutralize to pH=7.2, add 150g of deionized water under high speed stirring (1800r / min), disperse for 60min, and obtain high straw substitution rate RSPU aqueous dispersion; Performance test data: Water dispersion liquid solid content 38%, particle size 280nm, zeta potential -42mV (no delamination after 8 months of storage at room temperature); coating tensile strength 3.2MPa, elongation at break 160%, adhesion grade 0 (excellent), water resistance (immersion for 24h): no blistering or peeling, water absorption ≤3%.

[0030] Environmental data: Replacing 90g of liquefied straw with 90g of petroleum-based polyol saves 720MJ of energy (reducing standard coal consumption by 17.3g) and reduces SO2 emissions by 0.054kg; simultaneously, the straw liquefaction process uses microwave heating, which saves 30% more energy than traditional electric heating (microwave energy consumption in this example is 1.2kW). Traditional heating requires 1.7kW. (h), further reducing CO2 emissions by 0.15 kg (CO2 emission coefficient of thermal power is 0.98 kg / kW). h).

[0031] Application examples Preparation and performance verification of rice straw polyurethane interior wall coating Weigh the raw materials according to the following proportions by weight: 45 parts of RSPU aqueous dispersion from Example 2, 22 parts of rutile titanium dioxide (R-930), 12 parts of heavy calcium carbonate (800 mesh), 8 parts of talc (1250 mesh), 0.8 parts of wetting and dispersing agent (BYK-190), 0.4 parts of defoamer (BYK-024), 0.3 parts of leveling agent (BYK-346), and 11.5 parts of deionized water. First, mix the pigments, fillers, and additives with deionized water and disperse at high speed for 30 minutes (2000 r / min). Then, grind the mixture in a sand mill until the particle size is ≤50 μm. Finally, add the RSPU aqueous dispersion and stir at low speed (500 r / min) for 1.5 hours to obtain the interior wall coating. Performance test data: Coating viscosity (Ford cup 4, 25℃) 25s, hiding power 120g / m³ 2 Gloss (60°): 15° (matte finish, meeting interior wall requirements); Scrub resistance (GB / T 9266): ≥6000 cycles; Alkali resistance (immersion in 5% NaOH solution for 24 hours): no discoloration or peeling; Formaldehyde emission (GB / T 18582): ≤0.02mg / m³ 3 (far below the national standard of 0.10 mg / m³) 3 ); Environmental data: For every 100kg of this coating produced, 45kg of RSPU aqueous dispersion (containing 15.75kg of liquefied straw, corresponding to approximately 22.5kg of original straw) is used, replacing 22.5kg of petroleum-based resin, reducing petroleum consumption by 22.5kg and CO2 emissions by approximately 56.25kg (the CO2 emission coefficient of petroleum-based resin throughout its entire life cycle is 2.5kg / kg). Simultaneously, the coating emits no volatile organic compounds (VOCs) (detected value ≤5g / L, meeting the requirements for Class I interior wall coatings in GB 18582-2020). Compared to traditional solvent-based polyurethane coatings (VOCs approximately 200g / L), each 100kg of coating reduces VOC emissions by 19.5kg, significantly lowering the risk of air pollution.

[0032] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a straw-modified polyurethane material, characterized in that, The specific steps include the following: (1) Straw liquefaction: Add liquefaction agent and solid acid catalyst to microwave-treated crushed straw, mix evenly, and react at 120-180℃ for 2-3 hours under nitrogen protection. After filtration, the filtrate is the straw liquefaction product. (2) The straw liquefaction product and the NCO-terminated polyurethane prepolymer with anionic side chains are subjected to a polycondensation reaction, and then triethylamine and deionized water are added to the product to disperse the straw-modified polyurethane aqueous dispersion.

2. The method for preparing a straw-modified polyurethane material according to claim 1, characterized in that, The microwave treatment conditions described in step (1) are 400-500W for 3-5 minutes; The particle size of the crushed straw is 80-100 mesh; The stirring speed for the reaction is 300-500 r / min.

3. The method for preparing a straw-modified polyurethane material according to claim 1, characterized in that, The mass ratio of the crushed straw, liquefaction agent and solid acid catalyst in step (1) is 100-120:250-300:4-5.

4. The method for preparing a straw-modified polyurethane material according to claim 1, characterized in that, The liquefying agent mentioned in step (1) is polyethylene glycol 400 and glycerol in a mass ratio of 2-3:1; The solid acid catalyst is at least one of p-toluenesulfonic acid and potassium hydrogen sulfate.

5. The method for preparing a straw-modified polyurethane material according to claim 1, characterized in that, The preparation method of the NCO-terminated polyurethane prepolymer with anionic side chains described in step (2) is as follows: Toluene diisocyanate and polyether polyol are reacted at 60-75℃ for 1.5-2.5h. After the reaction is completed, dimethylolpropionic acid is added and the reaction is continued at 60-75℃ for another 1.5-2.5h. The NCO group content is measured by sampling. When the NCO mass fraction drops to 8-10%, the reaction is stopped to obtain the NCO-terminated polyurethane prepolymer with anionic side chains.

6. The NCO-terminated polyurethane prepolymer with anionic side chains according to claim 5, characterized in that, The mass ratio of the toluene diisocyanate, the polyether polyol, and the dihydroxypropionic acid is 100-150:80-120:100-150.

7. The method for preparing a straw-modified polyurethane material according to claim 1, characterized in that, The mass ratio of the straw liquefaction product, the NCO-terminated polyurethane prepolymer with anionic side chains, triethylamine and deionized water in step (2) is 70-90:100:8-10:120-150.

8. The method for preparing a straw-modified polyurethane material according to claim 1, characterized in that, The straw liquefaction product described in step (2) has a crystallinity of 28-30%, a hydroxyl value of 350-450 mg KOH / g, and a residue rate of ≤5%. The conditions for the polycondensation reaction are: reaction at 70-80℃ for 3-4 hours; The dispersion method is to stir at 1500-1800 r / min for 45-60 min at a pH of 7.2-7.

5.

9. The straw-modified polyurethane material obtained by the preparation method according to any one of claims 1-8.

10. The application of the straw-modified polyurethane material as described in claim 9 in the preparation of interior wall coatings.

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