A bio-based modified low-furfural alcohol furan resin and a preparation method thereof

Abstract

The application provides a bio-based modified low-furfuryl alcohol furan resin and a preparation method thereof, wherein the preparation method comprises the following steps: subjecting pentose to thermal activation treatment to obtain component A, subjecting cellulose to etherification modification to obtain component B, subjecting lignin to sulfonation modification to obtain component C, and then compounding the component A, the component B and the component C according to a preset proportion to obtain a bio-based compounded material; mixing furfuryl alcohol, the bio-based compounded material and formaldehyde, adding a composite catalyst to obtain a furan resin prepolymer; increasing the temperature to 105 DEG C to 115 DEG C and dehydrating under reduced pressure to form a resin network with a crosslinking structure; adding a crosslinking regulator and a formaldehyde capturing agent after temperature reduction to obtain the bio-based modified low-furfuryl alcohol furan resin. Through the compounding of the directional modification of the bio-based raw materials and the segmented regulation of the composite catalyst, the application realizes the accurate matching of the strength of the sand in 1h, 2h, 6h and 24h, and the content of free formaldehyde is less than or equal to 0.03%, and the application has good environmental protection performance.

Description

Technical Field

[0001] This invention relates to the field of furan resin technology, and more particularly to a bio-based modified low furfuryl alcohol furan resin and its preparation method. Background Technology

[0002] Furan resin, a widely used organic binder in the foundry industry, boasts advantages such as rapid curing speed, excellent collapsibility, high surface finish on castings, and stable bond strength. It is extensively applied in molding sand and core-shooting processes for cast iron, cast steel, and non-ferrous metal castings. Currently, the core raw material for industrial-grade furan resin is furfuryl alcohol, whose production primarily relies on biomass fermentation routes such as corn cobs and sugarcane bagasse, or chemical synthesis routes. Furfuryl alcohol raw material costs account for 60%–70% of the total resin cost, and its life-cycle carbon footprint is as high as approximately 8.2 kg CO2eq / kg. Developing low-cost, low-emission alternatives to furfuryl alcohol has become an urgent industry need.

[0003] Existing technologies attempt to modify furan resins using bio-based raw materials, with lignin, starch, cellulose, and other agricultural and forestry waste products being a research hotspot. However, this technology still suffers from the following core shortcomings: 1. The insufficient reactivity of single bio-based raw materials leads to significant strength decay; the steric hindrance of phenolic hydroxyl groups and the low density of active sites in the lignin molecular structure result in a cross-linking reaction efficiency of only 35%~40% with furan rings. The medium- and long-term strength (6h, 24h) of molding sand decreases by 5%~10% compared with traditional resins, making it difficult to meet the production requirements of high-strength castings.

[0004] 2. The bio-based raw materials have poor compatibility with the resin system, resulting in large strength fluctuations. Unmodified lignin and cellulose are unevenly dispersed in the resin, with agglomeration particle size reaching 50~80 μm. This leads to a molding sand strength fluctuation coefficient exceeding 8%, and the instantaneous strength can only be maintained at 0.35~0.40 MPa in 1 hour, which cannot meet the production requirements of immediate demolding in the core shooting process.

[0005] 3. The free formaldehyde content is too high and the environmental protection is insufficient. In the existing technology, the free formaldehyde content is usually ≥0.05%, which results in a strong pungent odor at the casting site, which has an adverse effect on the working environment and workers' health, and makes it difficult to meet the increasingly strict environmental emission standards.

[0006] Therefore, the existing technology needs further improvement. Summary of the Invention

[0007] In view of this, the present invention proposes a bio-based modified low furfuryl alcohol furan resin and its preparation method, which solves the technical problems of insufficient initial strength, medium and long-term strength decay and high free formaldehyde content caused by existing single bio-based modification.

[0008] The technical solution of this invention is implemented as follows: A method for preparing a bio-based modified low furfuryl alcohol furan resin includes the following steps: S1, pentose is heated in a water bath at 80℃-95℃ to obtain component A, cellulose and propylene oxide are reacted under alkaline conditions to obtain component B, lignin is sulfonated to obtain component C, and components A, B and C are compounded to obtain a bio-based compound. S2, mix furfuryl alcohol, the bio-based compound and formaldehyde, add a composite catalyst, and carry out a polycondensation reaction at 55℃-85℃ to obtain furan resin prepolymer; S3, heated to 105℃-115℃, and dehydrated under a vacuum of -0.085~-0.095MPa for 50-60min until the solid content of the furan resin prepolymer is 68%-72%, forming a resin network with a cross-linked structure; S4, after cooling, is mixed with a crosslinking regulator, formaldehyde scavenger and solvent to obtain a bio-based modified low furfuryl alcohol furan resin.

[0009] Based on this technical solution, further step S1 includes: Corn stalks were hydrolyzed with dilute acid, filtered, and concentrated to obtain a pentose solution, which was then activated in a water bath at 85°C for 60 min and vacuum dried at 80°C for 2 h to obtain component A. Wheat straw cellulose was reacted with propylene oxide under alkaline conditions to prepare hydroxypropylated cellulose with a degree of substitution of 0.8-1.2, which is component B. Sulfonated lignin with a degree of sulfonation ≥1.5 mmol / g was prepared by sulfonation modification of sawdust lignin with concentrated sulfuric acid, which is component C. Components A, B and C were compounded in a weight ratio of (25-35):(35-45):(25-35) and stirred at 80℃ for 30 min to obtain a bio-based compound.

[0010] Based on this technical solution, further, the concentration of the dilute sulfuric acid is 6%, the hydrolysis temperature is 95℃, and the hydrolysis time is 2.5h; the volume ratio of the isopropanol aqueous solution is 6:4, and the molar ratio of propylene oxide to cellulose is 1.2:1; the concentration of the concentrated sulfuric acid is 98%, and the mass ratio of lignin to concentrated sulfuric acid is 1:2.

[0011] Based on this technical solution, further step S2 includes: S2.1, add furfuryl alcohol, bio-based compound, and formaldehyde aqueous solution in sequence, mix well, and heat to 55℃ and keep warm for 20 min to obtain mixed reaction solution; S2.2, add composite catalyst, heat to 85℃, and maintain the temperature for polycondensation until the viscosity of the mixed reaction liquid is 25mPa·s-30mPa·s, to obtain furan resin prepolymer.

[0012] Based on this technical solution, furfuryl alcohol, the bio-based compound and formaldehyde are further compounded in a weight ratio of (50-70):(30-50):(28-42), and the composite catalyst is a compound of oxalic acid, p-toluenesulfonic acid and phosphoric acid in a weight ratio of 2:1:0.5.

[0013] Based on this technical solution, further, the crosslinking regulator in step S4 is polyethylene glycol 400, the formaldehyde scavenger is a compound of urea and melamine in a mass ratio of 3:1, and the solvent is a compound of polyol acetate and 230# solvent oil in a weight ratio of 7:3.

[0014] On the other hand, a bio-based modified low furfuryl furan resin is prepared by the method for preparing the bio-based modified low furfuryl furan resin according to any one of the claims, comprising: a furfuryl alcohol matrix; and a bio-based compound dispersed in the matrix.

[0015] Based on this technical solution, furthermore, the bio-based content is ≥30%, and the tensile strength of the molding sand after the resin is cured meets the following requirements: 1h≥0.45MPa, 2h≥0.52MPa, 6h≥1.0MPa, 24h≥1.6MPa; and the free formaldehyde content is ≤0.03%.

[0016] The bio-based modified low furfuryl alcohol furan resin and its preparation method described in this invention have the following advantages over the prior art: This invention involves thermally activating pentose, etherifying cellulose, and sulfonating lignin, then blending these three components in a predetermined ratio to obtain a bio-based compound. This results in differentiated reactivity of the three raw materials during subsequent polycondensation reactions. Based on this, furfuryl alcohol, the bio-based compound, and formaldehyde are mixed, and a composite catalyst is added. The polycondensation reaction is then carried out at 55°C–85°C. The composite catalyst can control the reaction rate in stages, allowing activated pentose to preferentially and rapidly polycondense to support initial strength. Subsequently, hydroxypropyl cellulose promotes the densification of the intermediate cross-linked network through bridging, and finally, sulfonated lignin participates in copolymerization to form a long-term dense structure.

[0017] By heating to 105℃~115℃ and dehydrating under reduced pressure, a resin network with a cross-linked structure is formed, ensuring the full progress of the cross-linking reaction at each stage. After cooling, a cross-linking regulator and a formaldehyde scavenger are added to further optimize the cross-linking density and reduce the free formaldehyde content. Thus, this invention, with a furfuryl alcohol substitution rate of 30%~50%, still achieves molding sand tensile strength ≥0.45MPa at 1h, ≥0.52MPa at 2h, ≥1.0MPa at 6h, and ≥1.6MPa at 24h, with a strength fluctuation coefficient ≤2.7%, solving the problem of insufficient strength and large fluctuations at low furfuryl alcohol content in existing technologies. Simultaneously, since the bio-based raw materials are derived from agricultural and forestry waste, and the synergistic effect of the composite catalyst and formaldehyde scavenger reduces the free formaldehyde content to below 0.03%, the total life-cycle carbon footprint is reduced by 39%~47% compared to traditional resins, significantly improving the working environment of foundries and demonstrating excellent environmental performance and promising prospects for industrial application. Attached Figure Description

[0018] 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. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the preparation method of the bio-based modified low furfuryl alcohol furan resin according to an embodiment of the present invention. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention proposes a method for preparing a bio-based modified low furfuryl furan resin, such as... Figure 1 As shown, the steps include: S1. Component A is obtained by heating pentose in a water bath at 80℃~95℃. Component B is obtained by reacting cellulose with propylene oxide under alkaline conditions. Component C is obtained by sulfonating lignin. Components A, B, and C are then combined to obtain a bio-based compound.

[0022] Step S1 includes: S1.1. The corn stalks were hydrolyzed with dilute acid, filtered, and concentrated to obtain a pentose solution. The solution was activated in a water bath at 85°C for 60 min and then vacuum dried at 80°C for 2 h to obtain component A.

[0023] During the dilute acid hydrolysis process, the concentration of dilute sulfuric acid was 6%, the hydrolysis temperature was 95℃, and the hydrolysis time was 2.5 h. Activation via water bath heating increased the hydroxyl reactivity of pentoses by more than 40%. This activation treatment makes the hydroxyl groups in the pentose molecules more readily participate in subsequent polycondensation reactions, providing support for initial strength. Water bath heating disrupts some of the hydrogen bonds between pentose molecules, increasing the exposure of hydroxyl groups and thus enhancing the rate of nucleophilic addition reactions with formaldehyde and furfuryl alcohol.

[0024] S1.2. Reaction of wheat straw cellulose with propylene oxide under alkaline conditions to prepare hydroxypropylated cellulose with a degree of substitution of 0.8~1.2, which is component B.

[0025] Specifically, wheat straw cellulose was added to an isopropanol aqueous solution with a volume ratio of 6:4, and sodium hydroxide was added at 5% of the dry weight of the cellulose. The mixture was heated to 70°C, and propylene oxide was added dropwise at a molar ratio of propylene oxide to cellulose of 1.2:1. The reaction was maintained at this temperature for 3 hours, and the pH was neutralized to 6-7 with acetic acid. The mixture was then filtered and vacuum dried at 60°C for 3 hours to obtain hydroxypropylated cellulose. The introduction of the hydroxypropyl group improved the compatibility of cellulose with the resin matrix, and its long-chain structure enhanced the toughness of the crosslinking network. Unmodified cellulose molecules have strong intermolecular hydrogen bonds and are prone to agglomeration in resins. The introduction of the hydroxypropyl group disrupts the hydrogen bond network and increases the dispersibility of cellulose in polar resin systems, providing uniform bridging sites for intermediate crosslinking.

[0026] S1.3. Sulfonate lignin from sawdust is modified by sulfonation with concentrated sulfuric acid to prepare sulfonated lignin with a degree of sulfonation ≥ 1.5 mmol / g, which is component C.

[0027] Specifically, sawdust lignin was mixed with 98% concentrated sulfuric acid at a mass ratio of 1:2, sulfonated at 60℃ for 2 hours, diluted with deionized water to a sulfuric acid concentration ≤5%, neutralized with calcium carbonate to a pH of 6-7, filtered, and spray-dried at an inlet air temperature of 180℃ and an outlet air temperature of 80℃ to obtain sulfonated lignin. The introduction of sulfonation groups improves the water solubility and reactivity of lignin. Unmodified lignin molecules have large steric hindrance of phenolic hydroxyl groups, resulting in a cross-linking efficiency of only 35%-40% with the furan ring. Sulfonation modification introduces highly polar sulfonic acid groups onto the aromatic rings of lignin, which not only increases water solubility but also activates the phenolic hydroxyl groups through electronic effects, making the electrophilic substitution reaction with the furan ring easier and thus enhancing the long-term cross-linking density.

[0028] S1.4. Mix components A, B, and C in a weight ratio of (25~35):(35~45):(25~35) and stir at 80℃ for 30 min to obtain a bio-based compound.

[0029] The three components are directionally modified to achieve staged crosslinking. Component A, the activated pentose, has a small molecular weight and high hydroxyl density, resulting in the fastest reaction rate. Component B, the hydroxypropylated cellulose, has a long molecular chain and moderate reactivity, enabling it to play a dual role in physical bridging and chemical crosslinking in the middle stage. Component C, the sulfonated lignin, has a stable aromatic ring structure and relatively slow reactivity, making it suitable for forming a rigid crosslinking network in the later stage. With the synergy of the composite catalyst, the staged crosslinking reaction can be carried out.

[0030] In one embodiment, if it is necessary to adjust the reactivity matching of the bio-based compound, this can be achieved by changing the ratio of the three components. For example, if it is desired to further improve the initial strength, the proportion of component A can be appropriately increased; if it is desired to enhance the long-term strength, the proportion of component C can be increased. By detecting the tensile strength of the molding sand at each stage, the ratio can be optimized in reverse until the target strength index is achieved.

[0031] S2. Mix furfuryl alcohol, the bio-based compound, and formaldehyde, add a composite catalyst, and carry out a polycondensation reaction at 55℃~85℃ to obtain furan resin prepolymer.

[0032] Step S2 includes: S2.1. By weight, add 50-70 parts furfuryl alcohol, 30-50 parts bio-based compound, and 28-42 parts 37% formaldehyde aqueous solution in sequence. After mixing evenly, heat to 55℃ and keep warm for 20 minutes to ensure that the components are fully mixed and obtain a mixed reaction solution.

[0033] The premixing stage allows the active hydroxyl groups in the bio-based compound to fully contact with formaldehyde and furfuryl alcohol, forming a homogeneous system. Holding at 55℃ for 20 minutes allows the reaction system to reach thermal equilibrium, while avoiding premature addition of the catalyst that could lead to localized overheating.

[0034] S2.2 Add 0.4~1.2 parts of composite catalyst, heat to 85℃ at a rate of 0.8℃ / min, and maintain the temperature for polycondensation until the viscosity of the mixed reaction liquid reaches 25~30mPa·s to obtain furan resin prepolymer.

[0035] The composite catalyst is a mixture of oxalic acid, p-toluenesulfonic acid, and phosphoric acid in a weight ratio of 2:1:0.5. Oxalic acid (pKa=1.25) is a strong acid, rapidly catalyzing the Mannich condensation reaction of furfuryl alcohol and formaldehyde in the initial stage of the reaction to form a linear prepolymer framework. P-toluenesulfonic acid (pKa=0.70) is a moderate acid, promoting the crosslinking of pentose and hydroxypropylated cellulose with the prepolymer in the middle stage to form a preliminary network. Phosphoric acid (pKa1=2.12) is the weakest acid, slowly catalyzing the copolymerization of sulfonated lignin and furan rings in the later stage, avoiding excessively rapid crosslinking that could lead to increased brittleness.

[0036] In one embodiment, if the viscosity reaches the target value too early during the polycondensation process, for example, if the viscosity exceeds 30 mPa·s when the temperature is raised to 70°C, it indicates that the initial reaction is too fast, and the amount of composite catalyst or the heating rate can be appropriately reduced. If the viscosity remains below 25 mPa·s for a long time after holding at 85°C, it indicates that the reaction activity is insufficient, and the amount of catalyst can be appropriately increased or the holding time can be extended. By monitoring the refractive index or viscosity online, the reaction progress can be judged in real time.

[0037] To determine if the viscosity of the mixed reaction solution meets the requirements, a rotational viscometer is used. Take a small amount of the reaction solution, cool it to 25°C, and use an NDJ-8S rotational viscometer with a suitable rotor. Record the reading after it stabilizes. If the viscosity is within the range of 25 mPa·s to 30 mPa·s, proceed to the next step; if the viscosity is too low, continue the reaction at this temperature, checking every 10 minutes; if the viscosity is too high, exceeding 30 mPa·s, it indicates over-reaction, and the deviation should be recorded, adjusting the catalyst dosage or reaction time for subsequent batches.

[0038] S3. Heat to 105℃~115℃ and dehydrate under reduced pressure. Dehydrate under vacuum of -0.085MPa~-0.095MPa for 50min~60min until the solid content of the system is 68%~72%, forming a resin network with a cross-linked structure.

[0039] The reactor temperature was increased to 115℃ at a rate of 2℃ / 10min. The vacuum system was activated, and the vacuum level was controlled between -0.085MPa and -0.095MPa. Dehydration was carried out at 105~115℃. During the dehydration process, water and low-boiling-point impurities in the system were evaporated, while simultaneously promoting the continued progress of various cross-linking reactions. This step serves two purposes: firstly, it physically removes water and unreacted free formaldehyde generated by the polycondensation reaction, increasing the resin solid content; secondly, chemically, it utilizes high temperature and vacuum conditions to further promote the condensation reaction between residual hydroxymethyl groups on the prepolymer and active hydrogen on the bio-based components, transforming the cross-linking network from a linear to a three-dimensional structure.

[0040] To determine whether the solid content of the system meets the requirements, the drying method is used: take 10g of sample, dry it in an oven at 120℃ for 2 hours, weigh it, and calculate the solid content. If the solid content is less than 68%, continue dehydration for 10-15 minutes and test again; if the solid content is greater than 72%, it indicates excessive dehydration, which may affect the storage stability of the resin. The dehydration time for subsequent batches needs to be recorded and adjusted.

[0041] S4. After cooling, a crosslinking regulator and a formaldehyde scavenger are added to obtain a bio-based modified low furfuryl alcohol furan resin.

[0042] Cool to below 80℃, add 12-25 parts by weight of solvent, which is a mixture of polyol acetate and 230# solvent oil in a weight ratio of 7:3, and stir for 30 minutes to ensure the solvent and resin are fully mixed. Continue cooling to below 60℃, then add 0.3-0.9 parts by weight of crosslinking regulator polyethylene glycol 400 and 0.2-0.6 parts by weight of formaldehyde scavenger, which is a mixture of urea and melamine in a weight ratio of 3:1. Adjust the stirring speed to 110-130 r / min, mix thoroughly, and keep warm for 25 minutes. Filter through a 100-mesh filter to remove impurities, and discharge to obtain the bio-based modified low furfuryl alcohol furan resin product. Store in a sealed container in a cool, dry place.

[0043] In the post-treatment steps, the solvent's role is to reduce resin viscosity and improve its wettability on the molding sand. Polyol acetate is highly polar and has good compatibility with bio-based components; 230# solvent oil is a non-polar component that can adjust the overall solubility parameters, allowing the resin to spread evenly on the molding sand surface. The crosslinking regulator, polyethylene glycol 400, contains ether bonds and terminal hydroxyl groups in its molecular chain, enabling it to form hydrogen bonds with the resin network. It acts as a flexible spacer between crosslinking points, preventing brittleness caused by excessive crosslinking, and simultaneously controlling the crosslinking density to ensure stable strength development. Among the formaldehyde scavengers, urea has a fast reaction rate, quickly capturing free formaldehyde to form hydroxymethylurea; melamine has a slightly slower reaction rate, but the resulting triazine ring structure is more stable, providing long-term fixation of residual formaldehyde. Together, they reduce the free formaldehyde content to below 0.03%. A 25-minute heat treatment ensures the capture reaction proceeds fully, and filtration removes any small amounts of insoluble matter that may form.

[0044] In one embodiment, to ensure that the free formaldehyde content is below 0.03%, the heat preservation time can be extended to 30-40 minutes after adding the formaldehyde scavenger, or the amount of formaldehyde scavenger can be appropriately increased. The free formaldehyde content is detected using the acetylacetone spectrophotometric method in GB / T 27708-2011. If the detection result is higher than 0.03%, a small amount of formaldehyde scavenger, 10%-20% of the original amount, is added, and stirring is continued for 15 minutes before retesting until the standard is met.

[0045] In one embodiment, the resin formation process involves multiple chemical reactions, the specific reaction equations of which are as follows: 1. Mannich polycondensation reaction of furfuryl alcohol and formaldehyde Furfuryl alcohol (furfuryl alcohol) and formaldehyde undergo a Mannich condensation reaction under the action of a composite catalyst to form a linear resin prepolymer containing furan rings, providing a basic framework for subsequent crosslinking. The complete reaction equation is as follows: 2. Crosslinking reaction between pentose and resin prepolymer Pentoses activated by water bath heating (taking D-xylose as an example, molecular formula C5H) 10 O5) undergoes a condensation reaction with the hydroxyl groups of the resin prepolymer via hydroxyl groups, rapidly forming a preliminary cross-linked network. The complete reaction equation (structural formula) is as follows: 3. The "bridging" crosslinking reaction of hydroxypropyl cellulose The hydroxypropyl group (-O-CH2-CH(OH)-CH3) of hydroxypropyl cellulose (HPC) undergoes a condensation reaction with the hydroxymethyl group of the resin molecular chain, achieving "bridging" between molecular chains through the long-chain structure and promoting the densification of the cross-linked network. The complete reaction equation (structural formula) is as follows: 4. Copolymerization reaction of sulfonated lignin with furan ring Sulfonated lignin (taking the phenolic hydroxyl structure as an example) undergoes a copolymerization reaction with the furan ring in the resin molecular chain to form a stable aromatic cross-linked structure, which enhances long-term strength. The complete reaction equation (structural formula) is as follows: 5. Formaldehyde capture reaction The addition reaction of urea with formaldehyde: The amino group in the urea molecule undergoes nucleophilic addition with the aldehyde group in formaldehyde to generate hydroxymethylurea, which rapidly captures free formaldehyde in the system. Complete reaction equation (structural formula): The addition reaction of melamine with formaldehyde: The amino group in the melamine molecule reacts with formaldehyde to form a stable triazine ring structure, achieving long-term fixation of free formaldehyde. Complete reaction equation (structural formula): The two reactions proceed in synergy: urea rapidly captures free formaldehyde (reaction rate constant k1 = 0.8 × 10⁻³ L / (mol·s)), while melamine forms a stable triazine ring structure (reaction rate constant k2 = 1.2 × 10⁻³ L / (mol·s)), ensuring that the free formaldehyde content is reduced to below 0.03%. Example 1

[0046] Corn stalks were hydrolyzed with 6% dilute sulfuric acid at 95℃ for 2.5 h, filtered and concentrated to obtain a pentose solution. This solution was activated in a water bath at 85℃ for 60 min, and then vacuum dried at 80℃ for 2 h to obtain component A. Wheat straw cellulose was added to an isopropanol aqueous solution with a volume ratio of 6:4, and sodium hydroxide was added at 5% of the dry weight of cellulose. The temperature was raised to 70℃, and propylene oxide was added dropwise at a molar ratio of propylene oxide to cellulose of 1.2:1. The reaction was maintained at this temperature for 3 h, neutralized with acetic acid to pH=6.5, filtered, and vacuum dried at 60℃ for 3 h to obtain hydroxypropylated cellulose with a degree of hydroxypropyl substitution of 1.0, which is component B. Wood chip lignin was mixed with 98% concentrated sulfuric acid at a mass ratio of 1:2 and sulfonated at 60℃ for 2 hours. The mixture was then diluted with deionized water to a sulfuric acid concentration of 5%, neutralized with calcium carbonate to pH 6.5, filtered, and spray-dried at an inlet air temperature of 180℃ and an outlet air temperature of 80℃ to obtain sulfonated lignin with a sulfonation degree of 1.6 mmol / g, which is component C. Components A, B, and C were mixed at a weight ratio of 30:40:30 and stirred at 80℃ for 30 minutes to obtain a bio-based compound.

[0047] By weight, 65 parts furfuryl alcohol, 35 parts bio-based compound, and 32 parts 37% formaldehyde aqueous solution were added to the reactor. After mixing evenly, the mixture was heated to 55℃ and held for 20 min. 0.6 parts of a composite catalyst were added. The composite catalyst consisted of oxalic acid, p-toluenesulfonic acid, and phosphoric acid in a weight ratio of 2:1:0.5. The temperature was increased to 85℃ at 0.8℃ / min, and polycondensation was carried out until the system viscosity reached 28 mPa·s, thus obtaining the furan resin prepolymer.

[0048] The temperature was increased to 115°C at a rate of 2°C / 10 min, the vacuum system was turned on, and the vacuum degree was controlled at -0.09 MPa. The system was dehydrated at 110°C for 50 min until the solid content of the system reached 68%, forming a resin network with a cross-linked structure.

[0049] The vacuum was closed, and the temperature was lowered to 80°C. 15 parts of solvent (a mixture of polyol acetate and 230# solvent oil at a weight ratio of 7:3) were added, and the mixture was stirred for 30 minutes. The temperature was further lowered to 60°C, and 0.5 parts of crosslinking regulator polyethylene glycol 400 and 0.3 parts of formaldehyde scavenger (a mixture of urea and melamine at a weight ratio of 3:1) were added sequentially. The mixture was stirred for 25 minutes. The mixture was filtered through a 100-mesh filter, and the product was discharged to obtain bio-based modified low-furfuryl alcohol furan resin. Example 2

[0050] Components A, B, and C were prepared according to the method in Example 1. Components A, B, and C were mixed in a weight ratio of 28:42:30 and stirred at 80°C for 30 min to obtain a bio-based compound.

[0051] By weight, 60 parts furfuryl alcohol, 40 parts bio-based compound, and 35 parts 37% formaldehyde aqueous solution were added to the reactor. After mixing evenly, the mixture was heated to 55℃ and held for 20 min. Then, 0.75 parts of composite catalyst were added, and the temperature was increased to 85℃ at a rate of 0.8℃ / min. The mixture was held for polycondensation until the viscosity of the system reached 28 mPa·s, thus obtaining the furan resin prepolymer.

[0052] After the polycondensation reaction is completed and before the dehydration process is heated, the system temperature is lowered to 70°C, 0.1 parts of formaldehyde scavenging agent are added, and the mixture is stirred for 15 minutes to capture some of the free formaldehyde in advance, thereby reducing the volatilization loss of formaldehyde during the subsequent dehydration process.

[0053] The temperature was increased to 115°C at a rate of 2°C / 10 min, the vacuum system was turned on, and the vacuum degree was controlled at -0.09 MPa. The system was dehydrated at 110°C for 55 min until the solid content of the system reached 70%, forming a resin network with a cross-linked structure.

[0054] The vacuum was turned off, and the temperature was lowered to 80°C. 18 parts of solvent were added, and the mixture was stirred for 30 minutes. The temperature was further lowered to 60°C, and 0.6 parts of crosslinking regulator polyethylene glycol 400 and 0.4 parts of formaldehyde scavenger were added sequentially, and the mixture was stirred for 25 minutes. The mixture was filtered through a 100-mesh filter, and the product was discharged to obtain bio-based modified low-furfuryl alcohol furan resin. Example 3

[0055] Components A, B, and C were prepared according to the method in Example 1. Components A, B, and C were mixed in a weight ratio of 32:38:30 and stirred at 80°C for 30 min to obtain a bio-based compound.

[0056] By weight, 55 parts furfuryl alcohol, 45 parts bio-based compound, and 38 parts 37% formaldehyde aqueous solution were added to the reactor. After mixing evenly, the mixture was heated to 55℃ and held for 20 min. Then, 0.9 parts of composite catalyst were added, and the temperature was increased to 85℃ at a rate of 0.8℃ / min. The mixture was held at this temperature for polycondensation until the viscosity of the system reached 28 mPa·s, thus obtaining the furan resin prepolymer.

[0057] The temperature was increased to 115°C at a rate of 2°C / 10 min, the vacuum system was turned on, and the vacuum degree was controlled at -0.09 MPa. The system was dehydrated at 110°C for 60 min until the solid content of the system reached 72%, forming a resin network with a cross-linked structure.

[0058] Turn off the vacuum, cool to 80°C, add 20 parts of solvent, and stir for 30 minutes. Continue cooling to 60°C, then add 0.7 parts of crosslinking regulator polyethylene glycol 400 and 0.5 parts of formaldehyde scavenger, and stir for 25 minutes. Filter through a 100-mesh filter and discharge to obtain bio-based modified low furfuryl alcohol furan resin.

[0059] Comparative Example 1 The difference from Example 2 is that: no bio-based compound was used, the amount of furfuryl alcohol was 100 parts, no composite catalyst was used, instead oxalic acid monoacid catalysis was used, no solvent was used, instead a mixed diester was used, the formaldehyde scavenger was urea alone without melamine compound, and there was no bio-based substitute.

[0060] Comparative Example 2 The difference from Example 2 is that the bio-based compound uses only 30 parts of unmodified industrial lignin, does not contain component A and component B, does not use a composite catalyst, and instead uses p-toluenesulfonic acid monoacid catalysis.

[0061] Comparative Example 3 The difference from Example 2 is that components A, B, and C in the bio-based compound were not directionally modified and were directly compounded in the same proportion. The remaining steps and parameters are the same as in Example 2.

[0062] Tensile strength test of molding sand Using standard Φ50mm figure-eight block specimens, tensile strength was tested at 1h, 2h, 6h, and 24h using an electronic universal testing machine (accuracy ±0.5%). Molding sand mix: Resin was added at 2.0% of the total molding sand mass, and the curing agent was a 40% p-toluenesulfonic acid aqueous solution, added at 28% of the resin weight. Mixing process: The molding sand was preheated to 20~25℃, resin was added and stirred for 2 minutes, followed by the curing agent and stirring for 3 minutes to ensure uniform mixing. After molding, the mixture was cured at room temperature and 55% humidity.

[0063] The test results are shown in Table 1.

[0064] Table 1. Tensile strength test results of molding sand Group 1h intensity 2h intensity 6h intensity 24h intensity Intensity fluctuation coefficient (24h) Example 1 0.46 0.53 1.02 1.63 2.7% Example 2 0.48 0.55 1.05 1.68 2.5% Example 3 0.47 0.54 1.03 1.65 2.6% Comparative Example 1 0.38 0.45 0.82 1.35 3.1% Comparative Example 2 0.36 0.42 0.78 1.28 4.8% Comparative Example 3 0.41 0.48 0.90 1.42 3.9% As can be seen from Table 1, the tensile strength of Examples 1-3 at 1h, 2h, 6h, and 24h is significantly better than that of Comparative Examples 1-3, and the strength fluctuation coefficient is ≤2.7%, indicating that the furan resin prepared by the method of the present invention has a balanced and stable strength development at each curing stage, which fully meets the differentiated strength requirements of immediate demolding and subsequent casting in the core shooting process.

[0065] The bio-based content was determined using radiocarbon dating according to ASTM D6866-2022 standard; the free formaldehyde content was determined using acetylacetone spectrophotometry according to GB / T 27708-2011 standard; the carbon footprint was calculated using the Life Cycle Assessment (LCA) method according to ISO 14040 / 14044 standard; the dispersed particle size was determined using a laser particle size analyzer; and the wetting angle was determined using a contact angle meter. The test results are shown in Table 2. Table 2 Test Results of Environmental Protection Related Indicators Group Bio-based content (%) Free formaldehyde (%) <![CDATA[Carbon footprint (kg CO2eq / kg)]]> Dispersed particle size (μm) Wetting angle (°) Example 1 31 0.024 4.9 15-25 28 Example 2 34 0.022 4.6 12-20 26 Example 3 37 0.026 4.3 10-18 25 Comparative Example 1 0 0.088 8.2 - 35 Comparative Example 2 19 0.065 6.8 40-60 32 Comparative Example 3 33 0.052 4.7 30-45 30 As shown in Table 2, the free formaldehyde content in the embodiments of the present invention is as low as 0.022%~0.026%, which is much lower than that in Comparative Example 1 and Comparative Example 2, and significantly lower than that of traditional resins. The bio-based content is ≥30%, the furfuryl alcohol replacement rate is 30%~50%, and the carbon footprint is reduced by 39%~47% compared with traditional resins. The dispersed particle size is controlled at 10~25μm, and the wetting angle is reduced to 25~28°, indicating that the bio-based raw materials have good compatibility with the resin, and the resin has excellent wettability on molding sand.

[0066] Fourier transform infrared spectroscopy (FT-IR) was used to detect the resin samples of Example 2 and Comparative Examples 1-3, and the hydroxyl groups (3400 cm⁻¹) were analyzed. -1 ), ether bond (1100cm) -1 ), furan ring (1600cm) -1 ) and methylene bridge (2920cm) -1 The characteristic peak intensities (expressed as relative absorption intensities) are shown in Table 3.

[0067] Table 3 Results of reaction efficiency test Group 1h intensity 2h intensity 6h intensity 24h intensity Group <![CDATA[Hydroxyl (3400 cm -1 ).]]> <![CDATA[Ether bond (1100 cm -1 )]]> <![CDATA[Furan ring (1600 cm -1 )]]> <![CDATA[Methylene bridge (2920 cm -1 ).]]> Example 2 0.32 0.85 0.78 0.65 Comparative Example 1 0.45 0.62 0.82 0.48 Comparative Example 2 0.38 0.58 0.75 0.42 Comparative Example 3 0.36 0.68 0.76 0.51 As can be seen from Table 3, the intensity of the characteristic peaks of the ether bond and methylene bridge in Example 2 is significantly higher than that in Comparative Examples 1-3, proving that its crosslinking reaction is more complete and a denser resin network is formed, which is consistent with the strength test results.

[0068] This invention involves the directional modification of pentose, cellulose, and lignin, enabling these three raw materials to exhibit differentiated reactivity during the polycondensation reaction. Under the segmented regulation of the composite catalysts oxalic acid, p-toluenesulfonic acid, and phosphoric acid, they sequentially participate in the initial, middle, and late stages of cross-linking reactions. Activated pentose rapidly cross-links within 1-2 hours, meeting the requirement for immediate demolding; hydroxypropylated cellulose promotes the densification of the cross-linked network through bridging within 6 hours; and sulfonated lignin forms a stable aromatic cross-linked structure within 24 hours, enhancing long-term strength. The synergistic effect of these three components allows for strength exceeding that of traditional resins at all stages, even with a furfuryl alcohol substitution rate as high as 30%-50%, exhibiting minimal strength fluctuations and extremely low free formaldehyde content.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a bio-based modified low-furfuryl alcohol furan resin, characterized in that, Includes the following steps: S1, pentose is heated in a water bath at 80℃-95℃ to obtain component A, cellulose and propylene oxide are reacted under alkaline conditions to obtain component B, lignin is sulfonated to obtain component C, and components A, B and C are compounded to obtain a bio-based compound. S2, mix furfuryl alcohol, the bio-based compound and formaldehyde, add a composite catalyst, and carry out a polycondensation reaction at 55℃-85℃ to obtain furan resin prepolymer; S3, heated to 105℃-115℃, and dehydrated under a vacuum of -0.085~-0.095MPa for 50-60min until the solid content of the furan resin prepolymer is 68%-72%, forming a resin network with a cross-linked structure; S4, after cooling, is mixed with a crosslinking regulator, formaldehyde scavenger and solvent to obtain a bio-based modified low furfuryl alcohol furan resin.

2. The method for preparing the bio-based modified low-furfuryl alcohol furan resin as described in claim 1, characterized in that, Step S1 includes: Corn stalks were hydrolyzed with dilute acid, filtered, and concentrated to obtain a pentose solution, which was then activated in a water bath at 85°C for 60 min and vacuum dried at 80°C for 2 h to obtain component A. Wheat straw cellulose was reacted with propylene oxide under alkaline conditions to prepare hydroxypropylated cellulose with a degree of substitution of 0.8-1.2, which is component B. Sulfonated lignin with a degree of sulfonation ≥1.5 mmol / g was prepared by sulfonation modification of sawdust lignin with concentrated sulfuric acid, which is component C. Components A, B and C were compounded in a weight ratio of (25-35):(35-45):(25-35) and stirred at 80℃ for 30 min to obtain a bio-based compound.

3. The method for preparing the bio-based modified low-furfuryl alcohol furan resin as described in claim 2, characterized in that, The dilute sulfuric acid concentration is 6%, the hydrolysis temperature is 95℃, and the hydrolysis time is 2.5h; the volume ratio of the isopropanol aqueous solution is 6:4, and the molar ratio of propylene oxide to cellulose is 1.2:1; the concentration of the concentrated sulfuric acid is 98%, and the mass ratio of lignin to concentrated sulfuric acid is 1:

2.

4. The method for preparing the bio-based modified low-furfuryl alcohol furan resin as described in claim 1, characterized in that, Step S2 includes: S2.1, add furfuryl alcohol, bio-based compound, and formaldehyde aqueous solution in sequence, mix well, and heat to 55℃ and keep warm for 20 min to obtain mixed reaction solution; S2.2, add composite catalyst, heat to 85℃, and maintain the temperature for polycondensation until the viscosity of the mixed reaction liquid is 25mPa·s-30mPa·s, to obtain furan resin prepolymer.

5. The method for preparing the bio-based modified low-furfuryl alcohol furan resin as described in claim 4, characterized in that, The furfuryl alcohol, the bio-based compound, and formaldehyde are compounded in a weight ratio of (50-70):(30-50):(28-42), and the composite catalyst is a compound of oxalic acid, p-toluenesulfonic acid, and phosphoric acid in a weight ratio of 2:1:0.

5.

6. The method for preparing the bio-based modified low-furfuryl alcohol furan resin as described in claim 1, characterized in that, The crosslinking regulator in step S4 is polyethylene glycol 400, the formaldehyde scavenger is a mixture of urea and melamine in a mass ratio of 3:1, and the solvent is a mixture of polyol acetate and 230# solvent oil in a weight ratio of 7:

3.

7. A bio-based modified low furfuryl furan resin, prepared by the method for preparing the bio-based modified low furfuryl furan resin according to any one of claims 1-6, characterized in that, include: furfuryl alcohol base; And bio-based complexes dispersed in the matrix.

8. The bio-based modified low furfuryl alcohol furan resin as described in claim 7, characterized in that, The bio-based content is ≥30%, and the tensile strength of the molding sand after the resin is cured meets the following requirements: 1h≥0.45MPa, 2h≥0.52MPa, 6h≥1.0MPa, 24h≥1.6MPa; free formaldehyde content ≤0.03%.

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