Low-free-phenol modified furan resin for casting and preparation method thereof

Abstract

The invention discloses a low-free-phenol modified furan resin for casting and a preparation method thereof. The cellulose aldehyde compound is prepared by catalytic decomposition of the cellulose compound with the sulfuric acid and the aluminum-containing compound and then replaces part of formaldehyde and acetone for aldehyde-ketone reaction, free aldehyde in the resin is reduced, anacardol replaces part of phenol for reaction, and free phenol in the resin is effectively reduced; the polyhydric alcohol replaces part of furfuryl alcohol to react, and the prepared phenolic aldehyde modified furan resin introduces a straight chain structure on the basis of reducing the furfuryl alcohol content, so that the flexibility of the resin is improved; lignin is modified by six-membered ring lactone to increase reaction active sites and then reacts with furfuryl alcohol, the lignin modified furfuryl alcohol is prepared, the content of free aldehyde of furan resin is reduced, the curing speed of the resin is increased, raw materials do not contain nitrogen, the prepared resin generates less irritant gas in the casting process, and the nitrogen hole defect is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of modified furan resins, and particularly relates to a modified furan resin for casting with low free phenol and a preparation method thereof. Background Art

[0002] Furan resin is a kind of biomass resin synthesized based on biomass raw materials such as plant fibers, which is a rich renewable resource. After curing, furan resin has no active functional groups and is not easy to react, so it has advantages such as corrosion resistance, heat resistance, flame retardancy, and good mechanical properties, and is widely used in fields such as casting, chemical machinery, and adhesives. In order to avoid nitrogen pore defects and optimize the quality of castings, phenolic modified furan resin is usually used as a binder for casting. However, the existing technology has problems such as high contents of free formaldehyde and free phenol in furan resin, which often volatilize and decompose some harmful gases during the processes of molding, core making, and pouring, easily polluting the environment, high furfuryl alcohol content resulting in high viscosity and high production cost, and insufficient strength of the resin at room temperature.

[0003] The Chinese invention patent with publication number CN116622044B discloses a phenolic modified furan resin for casting with low free phenol and a preparation method thereof, including the following steps: performing a phenolic reaction on phenol and formaldehyde A at a reaction temperature of 50 - 70°C for a reaction time of 1.5 - 2 h; adding urea and formaldehyde B to the phenolic reaction product, and performing a urea - formaldehyde reaction at 80 - 100°C for a reaction time of 0.5 - 2 h; adding furfuryl alcohol A to the urea - formaldehyde reaction product, adjusting the pH value of the solution to 3 - 4, using formic acid as a catalyst, and reacting at 110 - 130°C for 0.5 - 1.5 h to make phenol - formaldehyde, urea - formaldehyde, and furfuryl alcohol polycondense into chains; after the polycondensation reaction is terminated, adding furfuryl alcohol B to the reaction system. The furan resin prepared by this preparation method can effectively reduce the free phenol content in the resin and endow the resin with excellent mechanical properties. However, the existing technology has the technical problem that the composition and process of furan resin have not been improved to improve the cost, strength, and environmental protection of furan resin. Summary of the Invention

[0004] The purpose of the present invention is to provide a modified furan resin for casting with low free phenol and a preparation method thereof, so as to solve the technical problem in the existing technology that the composition and process of furan resin have not been improved to improve the cost, strength, and environmental protection of furan resin.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A preparation method of a modified furan resin for casting with low free phenol, including the following steps:

[0007] S1. Ingredients: Weigh the cellulose aldehyde compounds, paraformaldehyde, acetone, alkali catalyst, phenol, cardanol, polyol, furfuryl alcohol, acid catalyst, lignin-modified furfuryl alcohol, ethanol, antioxidant, and moisture-proof agent required for each step and set them aside.

[0008] S2. Aldehyde-ketone reaction: Add the cellulose aldehyde compounds, paraformaldehyde, and acetone to the reaction kettle, add an alkali catalyst to adjust the pH to 9 - 10, heat up to 80 - 90 °C, react for 1 - 2 h, and dehydrate under reduced pressure to obtain mixture 1.

[0009] S3. Phenol-formaldehyde reaction: Add phenol, cardanol, paraformaldehyde, and furfuryl alcohol to the reaction kettle, add an alkali catalyst to adjust the pH to 8 - 9.5, heat up to 70 - 90 °C, react for 2 - 3 h, and dehydrate under reduced pressure to obtain mixture 2.

[0010] S4. Acidic reaction: Add mixture 1, mixture 2, polyol, and furfuryl alcohol to the reaction kettle, add an acid catalyst to adjust the pH to 2 - 3, heat up to 100 - 120 °C, react for 1 - 2 h, and dehydrate under reduced pressure to obtain mixture 3.

[0011] S5. Neutralization and discharging: Add an alkali catalyst to mixture 3 to adjust the pH to 9 - 10, add lignin-modified furfuryl alcohol to the system, heat up to 70 - 90 °C, react for 1 - 2 h, cool the system to 40 - 50 °C, and discharge to obtain phenolic aldehyde-modified furan resin.

[0012] S6. Mixing and canning: Add phenolic aldehyde-modified furan resin to ethanol for dilution, and then add an antioxidant and a moisture-proof agent to obtain a modified furan resin product for casting with low free phenol.

[0013] Preferably, the reaction principle involved in S2 is as follows:

[0014]

[0015] Preferably, the reaction principle involved in S3 is as follows:

[0016]

[0017] Preferably, the antioxidant in S1 is any one or a combination of phenolic antioxidants, phosphite antioxidants, and thioester antioxidants.

[0018] Preferably, the phenolic antioxidant is any one or a combination of 525, 1010, 1076, and 3052.

[0019] Preferably, the phosphite antioxidant is any one or a combination of 168, 626, and 3019.

[0020] Preferably, the thioester antioxidant is any one or a combination of pentaerythritol tetra(3-laurylthiopropionate), dilauryl thiodipropionate, and dipalmitoyl thiodipropionate.

[0021] Preferably, the moisture-proof agent in S1 is any one or a combination of silane moisture-proof agents, dioctyl phthalate, 2,5-dihydroxymethylfuran, and ethyl silicate.

[0022] Preferably, the silane moisture-proof agent is any one or a combination of methyltrisiloxane, silanepropyl ether, and isobutylsilane.

[0023] Preferably, the mass fraction of paraformaldehyde in S2 is 92-96%.

[0024] Preferably, the mass ratio of the cellulose aldehyde compound, paraformaldehyde, and acetone in S2 is 60-100:20-30:100-120.

[0025] Preferably, the mass ratio of phenol, cardanol, paraformaldehyde, and furfuryl alcohol in S3 is 80-90:10-20:30-40:50-70.

[0026] Preferably, the base catalyst in S2, S3, and S5 is any one of sodium hydroxide, potassium hydroxide, and sodium carbonate.

[0027] Preferably, the polyol in S4 is any one or a combination of sorbitol, glycerol, and mannitol.

[0028] Preferably, the acid catalyst in S4 is any one or a combination of formic acid, phosphoric acid, and oxalic acid.

[0029] Preferably, the mass ratio of mixture 1, mixture 2, polyol, and furfuryl alcohol in S4 is 15-25:10-15:5-10:50-70.

[0030] Preferably, the mass ratio of mixture 3 and lignin-modified furfuryl alcohol in S5 is 5-8:2-3.

[0031] Preferably, the addition amount of ethanol in S6 is 10-20% of the mass of the phenolic aldehyde-modified furan resin.

[0032] Preferably, the mass ratio of the antioxidant and the moisture-proof agent in S6 is 1:1-3, and the total addition amount of the antioxidant and the moisture-proof agent is 1-5% of the mass of the phenolic aldehyde-modified furan resin.

[0033] Preferably, the preparation method of the cellulose aldehyde compound includes the following steps:

[0034] S11. Add the cellulose compound to 1 L of solvent, add 10 mL of 10 wt% sulfuric acid, 10 - 15 g of aluminum chloride, and 30 - 40 g of aluminum sulfate, and react at 170 - 190 °C for 1 - 1.5 h to obtain a reaction solution;

[0035] S12. After the reaction, add sodium bisulfite and continuously stir the reaction solution for 1 - 2 h, extract with 1 - 1.5 L of 5 - 10 wt% sodium chloride solution, collect the aqueous phase, add sodium hydroxide to control the pH to 10.5 - 11.5, then extract with 2 - 3 L of methyl isobutyl ketone, collect the organic phase, and rotary evaporate at 40 - 50 °C to obtain the cellulose aldehyde compound.

[0036] Preferably, in S11, the solvent is prepared by mixing deionized water and 4 - methylbutyrolactone in a volume ratio of 1:9.

[0037] Preferably, in S11, the cellulose compound is any one or a combination of cellulose, polyxylan hemicellulose, polyglucomannan hemicellulose, and polygalactoglucomannan hemicellulose.

[0038] Preferably, in S11, the concentration range of the cellulose compound in the solvent is 30 - 60 g / L.

[0039] Preferably, in S12, the addition amount of sodium bisulfite is 40 - 50% of the mass of the cellulose compound.

[0040] Preferably, the preparation method of the lignin - modified furfuryl alcohol includes the following steps:

[0041] S21. Add 20 - 30 g of lignin to 100 g of N, N - dimethylformamide under a nitrogen atmosphere, add 1 - 3 g of an organic base catalyst, stir for 1 - 2 h, dissolve 10 - 15 g of a six - membered ring lactone in 10 g of N, N - dimethylformamide and then drop it into the system. During the dropping process, keep the system temperature at 10 - 25 °C. After the dropping is completed, maintain the temperature at 10 - 25 °C and stir for 2 - 3 h, then raise the temperature to 100 - 120 °C and react for 4 - 6 h. Precipitate with 1 wt% hydrochloric acid, collect the precipitate, wash it with deionized water, and dry it to obtain the modified lignin;

[0042] S22. Add the modified lignin and furfuryl alcohol to a reaction kettle, add sodium hydroxide to control the pH to 9 - 10, the reaction temperature is 100 - 120 °C, the reaction time is 1 - 2 h, and dehydrate under reduced pressure to obtain the lignin - modified furfuryl alcohol.

[0043] Preferably, in S21, the organic base catalyst is any one or a combination of 1,8 - diazabicyclo - bicyclo(5.4.0) - 7 - undecene, 1,5 - diazabicyclo[4.3.0]non - 5 - ene, and 4 - dimethylaminopyridine.

[0044] Preferably, the six-membered lactone in S21 is any one or a combination of dihydroxycoumarin, δ-octalactone, and δ-tetradecalactone.

[0045] Preferably, the addition amount of the modified lignin in S22 is 5-15% of the mass of furfuryl alcohol added in S22.

[0046] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows:

[0047] 1. Based on the prior art, the modified furan resin for casting with low free phenol prepared by the present invention uses a cellulose aldehyde compound to replace part of formaldehyde and acetone for the aldol reaction, reducing the free aldehyde in the resin. Cardanol replaces part of phenol for the reaction. The hydroxyl unsaturated double bond of cardanol has a greater addition reaction with formaldehyde than its steric hindrance effect, and the reaction is relatively sufficient, effectively reducing the free phenol in the resin. Polyol replaces part of furfuryl alcohol for the reaction. The prepared phenolic modified furan resin introduces a linear structure on the basis of reducing the furfuryl alcohol content, increasing the flexibility of the resin. The raw materials do not contain nitrogen, so the resin produced during casting generates less irritating gas, avoiding nitrogen pore defects and causing little environmental pollution.

[0048] 2. The present invention catalytically decomposes a cellulose compound with sulfuric acid and an aluminum-containing compound to prepare a cellulose aldehyde compound, which has the characteristics of short reaction time, low cost, and easy large-scale industrial production. Using the cellulose aldehyde compound to replace part of formaldehyde and acetone for the aldol reaction reduces the production cost and improves the strength of the resin.

[0049] 3. The present invention modifies lignin with a six-membered lactone to increase the reactive sites, and then reacts with furfuryl alcohol to obtain modified lignin furfuryl alcohol, reducing the content of free aldehyde in the furan resin. Moreover, the bridging effect of the modified lignin during crosslinking with the curing agent is enhanced, improving the curing speed of the resin. Detailed Embodiments

[0050] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0051] Paraformaldehyde, acetone, and phenol involved in the embodiments of the present invention are purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; cardanol is purchased from Hubei Chengfeng Chemical Co., Ltd.; polyol and furfuryl alcohol are purchased from Nantong Runfeng Petrochemical Co., Ltd.; the antioxidant and the moisture-proof agent are both purchased from Merck Chemical.

[0052] Example 1. The preparation method of the modified furan resin for casting with low free phenol includes the following steps:

[0053] S1. Weigh the cellulose aldehyde compound, paraformaldehyde, acetone, alkali catalyst, phenol, cardanol, polyol, furfuryl alcohol, acid catalyst, lignin-modified furfuryl alcohol, ethanol, antioxidant, and moisture-proof agent required for each step. The alkali catalyst is sodium hydroxide, the polyol is sorbitol, the acid catalyst is formic acid, the antioxidant is prepared by mixing 1010 and 168 in a mass ratio of 1:2, and the moisture-proof agent is prepared by mixing methyltrisiloxane and 2,5-dihydroxymethylfuran in a mass ratio of 1:1. Set aside.

[0054] S2. Aldehyde-ketone reaction: Add 60 g of cellulose aldehyde compound, 20 g of paraformaldehyde, and 100 g of acetone to the reaction kettle, add an alkali catalyst to adjust the pH to 9, raise the temperature to 80 °C, react for 2 h, and dehydrate under reduced pressure to obtain mixture 1.

[0055] S3. Phenol-formaldehyde reaction: Add 80 g of phenol, 10 g of cardanol, 30 g of paraformaldehyde, and 50 g of furfuryl alcohol to the reaction kettle, add an alkali catalyst to adjust the pH to 8, raise the temperature to 70 °C, react for 3 h, and dehydrate under reduced pressure to obtain mixture 2.

[0056] S4. Acidic reaction: Add 250 g of mixture 1, 150 g of mixture 2, 100 g of polyol, and 500 g of furfuryl alcohol to the reaction kettle, add an acid catalyst to adjust the pH to 2, raise the temperature to 100 °C, react for 1 h, and dehydrate under reduced pressure to obtain mixture 3.

[0057] S5. Neutralization and discharging: Add an alkali catalyst to 500 g of mixture 3 to adjust the pH to 9, add 200 g of lignin-modified furfuryl alcohol to the system, raise the temperature to 70 °C, react for 1 h, cool the system to 40 °C, and discharge to obtain phenolic aldehyde-modified furan resin.

[0058] S6. Mixing and canning: Add 500 g of phenolic aldehyde-modified furan resin to 100 g of ethanol for dilution, and then add 5 g of antioxidant and 15 g of moisture-proof agent to obtain the modified furan resin product for casting with low free phenol.

[0059] The preparation method of the cellulose aldehyde compound in this example includes the following steps:

[0060] S11. Mix 100 mL of deionized water and 900 mL of 4-methylbutyrolactone to prepare a solvent. Add 50 g of cellulose to 1 L of the solvent, add 10 mL of 10 wt% sulfuric acid, 10 g of aluminum chloride, and 30 g of aluminum sulfate, and react at 170 °C for 1.5 h to obtain a reaction solution.

[0061] S12. After the reaction is completed, 25 g of sodium bisulfite is added and the reaction solution is continuously stirred for 2 h. Then, 1 L of 5 wt% sodium chloride solution is added for extraction. The aqueous phase is collected, and sodium hydroxide solution is added to control the pH to 10.5. Then, 2 L of methyl isobutyl ketone is added for extraction. The organic phase is collected and rotary evaporated at 40 °C to obtain the cellulose aldehyde compound.

[0062] The preparation method of the lignin-modified furfuryl alcohol in this example includes the following steps:

[0063] S21. 20 g of lignin is added to 100 g of N,N-dimethylformamide under a nitrogen atmosphere, 1 g of 1,8-diazabicyclo-bicyclo(5.4.0)-7-undecene is added, and the mixture is stirred for 1 h. 10 g of coumarin-3,4-diol is dissolved in 10 g of N,N-dimethylformamide and then added dropwise to the system. During the dropping process, the temperature of the system is maintained at 10 °C. After the dropping is completed, the mixture is stirred at 10 °C for 2 h, then heated to 100 °C and reacted for 6 h. It is precipitated with 1 wt% hydrochloric acid, the precipitate is collected, washed with deionized water, and dried to obtain the modified lignin.

[0064] S22. 20 g of the modified lignin and 300 g of furfuryl alcohol are added to the reaction kettle, sodium hydroxide is added to control the pH to 9, the reaction temperature is 100 °C, and the reaction time is 2 h. Then, dehydration under reduced pressure is carried out to obtain the lignin-modified furfuryl alcohol.

[0065] Example 2. The preparation method of the modified furan resin for casting with low free phenol in this example includes the following steps:

[0066] S1. Weighing: Weigh the cellulose aldehyde compound, paraformaldehyde, acetone, alkali catalyst, phenol, cashew phenol, polyol, furfuryl alcohol, acid catalyst, lignin-modified furfuryl alcohol, ethanol, antioxidant, and moisture-proof agent required for each step. The alkali catalyst is potassium hydroxide, the polyol is mannitol, the acid catalyst is phosphoric acid, the antioxidant is prepared by mixing 1076 and 626 in a mass ratio of 1:3, and the moisture-proof agent is prepared by mixing 3-(trimethoxysilyl)-1-propanethiol and tetraethyl orthosilicate in a mass ratio of 1:1. Set aside.

[0067] S2. Aldehyde-ketone reaction: 70 g of the cellulose aldehyde compound, 25 g of paraformaldehyde, and 115 g of acetone are added to the reaction kettle, and the alkali catalyst is added to adjust the pH to 9. Then, the temperature is raised to 85 °C and the reaction is carried out for 1 h. Dehydration under reduced pressure is carried out to obtain mixture 1.

[0068] S3. Phenol-formaldehyde reaction: 85 g of phenol, 15 g of cashew phenol, 30 g of paraformaldehyde, and 55 g of furfuryl alcohol are added to the reaction kettle, and the alkali catalyst is added to adjust the pH to 8.5. Then, the temperature is raised to 75 °C and the reaction is carried out for 2 h. Dehydration under reduced pressure is carried out to obtain mixture 2.

[0069] S4, Acidic reaction: Add 150 g of mixture 1, 100 g of mixture 2, 50 g of polyol, and 700 g of furfuryl alcohol into a reaction kettle. Add an acid catalyst to adjust the pH to 3, heat up to 110 °C, react for 1 h, and dehydrate under reduced pressure to obtain mixture 3;

[0070] S5, Neutralization and discharging: Add an alkali catalyst to 600 g of mixture 3 to adjust the pH to 9. Add 200 g of lignin-modified furfuryl alcohol into the system, heat up to 75 °C, react for 1 h, cool the system to 50 °C, and discharge to obtain phenolic aldehyde-modified furan resin.

[0071] S6, Mixing and canning: Add 500 g of phenolic aldehyde-modified furan resin, dilute it with 250 g of ethanol, then add 2 g of antioxidant and 4 g of moisture-proof agent to obtain a modified furan resin product for casting with low free phenol.

[0072] The preparation method of the cellulose aldehyde compound in this example is the same as that in Example 1.

[0073] The preparation method of the lignin-modified furfuryl alcohol in this example is the same as that in Example 1.

[0074] Example 3. The preparation method of the modified furan resin for casting with low free phenol in this example includes the following steps:

[0075] S1, Batching: Weigh the cellulose aldehyde compound, paraformaldehyde, acetone, alkali catalyst, phenol, cashew phenol, polyol, furfuryl alcohol, acid catalyst, lignin-modified furfuryl alcohol, ethanol, antioxidant, and moisture-proof agent required for each step. The alkali catalyst is sodium carbonate, the polyol is glycerol, the acid catalyst is oxalic acid, the antioxidant is prepared by mixing 3019 and pentaerythritol tetrakis(3-laurylthiopropionate) in a mass ratio of 1:1, and the moisture-proof agent is prepared by mixing dioctyl phthalate, 2,5-dihydroxymethylfuran, and ethyl silicate in a mass ratio of 2:2:1. Set aside;

[0076] S2, Aldehyde-ketone reaction: Add 80 g of cellulose aldehyde compound, 30 g of paraformaldehyde, and 110 g of acetone into a reaction kettle. Add an alkali catalyst to adjust the pH to 9.5, heat up to 90 °C, react for 2 h, and dehydrate under reduced pressure to obtain mixture 1;

[0077] S3, Phenolic aldehyde reaction: Add 90 g of phenol, 10 g of cashew phenol, 30 g of paraformaldehyde, and 70 g of furfuryl alcohol into a reaction kettle. Add an alkali catalyst to adjust the pH to 8.5, heat up to 80 °C, react for 2 h, and dehydrate under reduced pressure to obtain mixture 2;

[0078] S4. Acidic reaction: Add 170 g of mixture 1, 120 g of mixture 2, 90 g of polyol, and 600 g of furfuryl alcohol into a reaction kettle. Add an acid catalyst to adjust the pH to 2.5, heat up to 120 °C, react for 1 h, and dehydrate under reduced pressure to obtain mixture 3;

[0079] S5. Neutralization and discharging: Add an alkali catalyst to 600 g of mixture 3 to adjust the pH to 10. Add 300 g of lignin-modified furfuryl alcohol into the system, heat up to 90 °C, react for 1.5 h, cool the system to 50 °C, and discharge to obtain phenolic aldehyde-modified furan resin.

[0080] S6. Mixing and canning: Add 500 g of phenolic aldehyde-modified furan resin, dilute it with 50 g of ethanol, then add 3 g of antioxidant and 7 g of moisture-proof agent to obtain a modified furan resin product for casting with low free phenol.

[0081] The difference in the preparation method of the cellulose aldehyde compound in this example from that in Example 1 lies in that the cellulose compound is replaced by polyxylan hemicellulose, polyglucomannan hemicellulose, and polygalactoglucomannan hemicellulose.

[0082] The preparation method of the lignin-modified furfuryl alcohol in this example is the same as that in Example 1.

[0083] Example 4. The preparation method of the modified furan resin for casting with low free phenol in this example includes the following steps:

[0084] S1. Batching: Weigh the cellulose aldehyde compound, paraformaldehyde, acetone, alkali catalyst, phenol, cashew phenol, polyol, furfuryl alcohol, acid catalyst, lignin-modified furfuryl alcohol, ethanol, antioxidant, and moisture-proof agent required for each step. The alkali catalyst is sodium hydroxide, the polyol is mannitol, the acid catalyst is formic acid, the antioxidant is prepared by mixing 525, dilauryl thiodipropionate, and distearyl thiodipropionate in a mass ratio of 3:1:1, and the moisture-proof agent is prepared by mixing isobutylsilane and 2,5-dihydroxymethylfuran in a mass ratio of 1:2, and set aside;

[0085] S2. Aldehyde-ketone reaction: Add 100 g of cellulose aldehyde compound, 30 g of paraformaldehyde, and 120 g of acetone into a reaction kettle. Add an alkali catalyst to adjust the pH to 10, heat up to 90 °C, react for 1 h, and dehydrate under reduced pressure to obtain mixture 1;

[0086] S3. Phenolic aldehyde reaction: Add 90 g of phenol, 20 g of cashew phenol, 40 g of paraformaldehyde, and 50 g of furfuryl alcohol into a reaction kettle. Add an alkali catalyst to adjust the pH to 9.5, heat up to 90 °C, react for 3 h, and dehydrate under reduced pressure to obtain mixture 2;

[0087] S4, Acidic reaction: Add 250 g of mixture 1, 150 g of mixture 2, 100 g of polyol, and 500 g of furfuryl alcohol into a reaction kettle. Add an acid catalyst to adjust the pH to 3, heat up to 120 °C, react for 2 h, and dehydrate under reduced pressure to obtain mixture 3;

[0088] S5, Neutralization and discharging: Add an alkali catalyst to 800 g of mixture 3 to adjust the pH to 10. Add 200 g of lignin-modified furfuryl alcohol into the system, heat up to 80 °C, react for 2 h, cool the system to 50 °C, and discharge to obtain phenolic aldehyde-modified furan resin.

[0089] S6, Mixing and canning: Add 500 g of phenolic aldehyde-modified furan resin, dilute it with 100 g of ethanol, and then add 10 g of antioxidant and 10 g of moisture-proof agent to obtain a modified furan resin product for casting with low free phenol.

[0090] The preparation method of the cellulose aldehyde compound in this example is the same as that in Example 1.

[0091] The difference between the preparation method of the lignin-modified furfuryl alcohol in this example and that in Example 1 is that the six-membered ring lactone is replaced by δ-tetradecalactone.

[0092] Comparative Example 1. The difference between this comparative example and Example 1 is that the aldehyde-ketone reaction in S2 is replaced by preparing mixture 1 by urea-formaldehyde reaction of urea and paraformaldehyde.

[0093] Comparative Example 2. The difference between this comparative example and Example 1 is that no lignin-modified furfuryl alcohol is added during the preparation of phenolic aldehyde-modified furan resin.

[0094] Comparative Example 3. The difference between this comparative example and Example 1 is that the phenolic aldehyde-modified furan resin is not diluted with ethanol and the antioxidant and moisture-proof agent are directly added.

[0095] Performance test

[0096] Send the furan resins prepared in each example and comparative example to a relevant institution for testing, and measure the viscosity, the content of free formaldehyde, and the content of free phenol according to JB / T7526-2008 "Self-hardening furan resin for casting".

[0097] The test results are shown in Table 1 below:

[0098] Table 1 Performance determination of furan resin

[0099]

[0100]

[0101] Resin sand strength test: Weigh 1 kg of standard sand and put it into a sand mixer. While stirring, add 5 g of p-toluenesulfonic acid curing agent, and then add 10 g of furan resin prepared in each example and comparative example. After mixing for 1 minute, pour it into a mold and compact it. Measure the tensile strength of the resin sand after curing at room temperature for 1 h and 24 h.

[0102] Resin sand moisture resistance test: Weigh 1 kg of standard sand and put it into a sand mixer. While stirring, add 5 g of p-toluenesulfonic acid curing agent, and then add 10 g of furan resin prepared in each example and comparative example. After mixing for 1 minute, pour it into a mold and compact it. Cure at room temperature, and measure the tensile strength of the resin sand after curing for 24 h under the relative humidity condition of 10% and after curing for 24 h under the relative humidity condition of 90% respectively.

[0103] The test results are shown in Table 2 below:

[0104] Table 2 Performance test of resin sand

[0105]

[0106] Gas evolution test: According to the gas evolution measurement method specified in JB / T 9226—2008 "Coatings for sand casting", dry the resin sand prepared in each example and comparative example at 150 °C for 2 h, grind it into powder, heat the gas evolution instrument to 1000 °C, put the powder into a quartz tube, and record the gas evolution of the powder.

[0107] The test results are shown in Table 3 below:

[0108] Table 3 Gas evolution test

[0109] Serial number Gas generation amount (mL / g) Example 1 7.1 Example 2 7.0 Example 3 7.3 Example 4 7.4 Comparative example 1 15.2 Comparative example 2 10.6 Comparative example 3 7.6

[0110] As can be seen from the data in the table, the viscosity of the furan resins prepared in Examples 1 to 4 was between 31.3 and 36.8 mPa·s, the content of free formaldehyde was 0.14 to 0.17%, and the content of free phenol was 0.14 to 0.18%. This shows that the furan resin prepared by the present invention meets the requirements of industrial production, and can reduce the content of free formaldehyde and free phenol, being environmentally friendly; in Comparative Example 2, no lignin-modified furfuryl alcohol was added, resulting in the failure to effectively fix the free formaldehyde and free phenol in the furan resin. Therefore, the contents of its free formaldehyde and free phenol are higher than those of the examples; the tensile strength of the furan resins prepared in Examples 1 to 4 after curing at room temperature for 1 h was between 1.61 and 1.65 MPa, and the tensile strength after curing at room temperature for 2 h was between 1.71 and 1.81 MPa, indicating that the furan resin prepared by the present invention has a good curing rate; the tensile strength of the furan resins prepared in Examples 1 to 4 after curing for 24 h under a relative humidity condition of 10% was between 1.70 and 1.81 MPa, and the tensile strength after curing for 24 h under a relative humidity condition of 10% was between 1.52 and 1.57 MPa, indicating that the furan resin prepared by the present invention has excellent moisture resistance; the gas evolution of the furan resins prepared in Examples 1 to 4 was 7.0 to 7.4 mL / g. In Comparative Example 1, the raw material of the furan resin contained urea, resulting in a relatively high nitrogen content and an increase in the gas decomposed under high-temperature conditions, so its gas evolution was 15.2 mL / g, indicating that the furan resin prepared by the present invention has a lower gas evolution.

[0111] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

[0112] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the present invention to only the specific embodiments. Obviously, according to the content of this specification, many modifications and changes can be made. This specification selects and specifically describes these embodiments in order to better explain the principle and practical application of the present invention, so that those skilled in the technical field can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. Preparation method of modified furan resin for casting with low free phenol, characterized in that, It includes the following steps: S1. Batching: Weigh the cellulose aldehyde compounds, paraformaldehyde, acetone, alkali catalyst, phenol, cardanol, polyol, furfuryl alcohol, acid catalyst, lignin-modified furfuryl alcohol, ethanol, antioxidant and moisture-proof agent required for each step and set aside; S2. Aldehyde-ketone reaction: Add the cellulose aldehyde compounds, paraformaldehyde and acetone into a reaction kettle, add an alkali catalyst to adjust the pH to 9-10, heat up to 80-90 °C, react for 1-2 h, and dehydrate under reduced pressure to obtain mixture 1; S3. Phenol-formaldehyde reaction: Add phenol, cardanol, paraformaldehyde and furfuryl alcohol into a reaction kettle, add an alkali catalyst to adjust the pH to 8-9.5, heat up to 70-90 °C, react for 2-3 h, and dehydrate under reduced pressure to obtain mixture 2; S4. Acidic reaction: Add mixture 1, mixture 2, polyol and furfuryl alcohol into a reaction kettle, add an acid catalyst to adjust the pH to 2-3, heat up to 100-120 °C, react for 1-2 h, and dehydrate under reduced pressure to obtain mixture 3; S5. Neutralization and discharging: Add an alkali catalyst to mixture 3 to adjust the pH to 9-10, add lignin-modified furfuryl alcohol into the system, heat up to 70-90 °C, react for 1-2 h, cool the system to 40-50 °C, and discharge to obtain phenolic aldehyde-modified furan resin. S6. Mixing and canning: Add ethanol to dilute the phenolic aldehyde-modified furan resin, and then add an antioxidant and a moisture-proof agent to obtain a modified furan resin product for casting with low free phenol.

2. The preparation method of the modified furan resin for casting with low free phenol according to claim 1, characterized in that, The preparation method of the cellulose aldehyde compound includes the following steps: S11. Add the cellulose compound into 1 L of solvent, add 10 mL of 10 wt% sulfuric acid, 10-15 g of aluminum chloride and 30-40 g of aluminum sulfate, react at 170-190 °C for 1-1.5 h to obtain a reaction solution; S12. After the reaction is completed, add sodium bisulfite and continuously stir the reaction solution for 1-2 h, add 1-1.5 L of 5-10 wt% sodium chloride solution for extraction, collect the aqueous phase, add sodium hydroxide to control the pH to 10.5-11.5, then add 2-3 L of methyl isobutyl ketone for extraction, collect the organic phase, and rotary evaporate at 40-50 °C to obtain the cellulose aldehyde compound.

3. The preparation method of the modified furan resin for casting with low free phenol according to claim 2, characterized in that, In S11, the solvent is prepared by mixing deionized water and 4-methylbutyrolactone according to a volume ratio of 1:

9. The cellulose compound is any one or a combination of cellulose, polyxylan hemicellulose, polyglucan mannan hemicellulose, and polygalactan glucan mannan hemicellulose. The concentration range of the cellulose compound in the solvent is 30-60 g / L; the addition amount of sodium bisulfite in S12 is 40-50% of the mass of the cellulose compound.

4. The preparation method of the modified furan resin for casting with low free phenol according to claim 1, characterized in that, The preparation method of the lignin-modified furfuryl alcohol includes the following steps: S21. Add 20 - 30 g of lignin into 100 g of N,N - dimethylformamide under a nitrogen atmosphere. Add 1 - 3 g of an organic base catalyst and stir for 1 - 2 h. Dissolve 10 - 15 g of six - membered ring lactone in 10 g of N,N - dimethylformamide and then drop it into the system. Keep the system temperature at 10 - 25 °C during the dropping process. After the dropping is completed, maintain the temperature at 10 - 25 °C and stir for 2 - 3 h. Then raise the temperature to 100 - 120 °C and react for 4 - 6 h. Precipitate with 1 wt% hydrochloric acid, collect the precipitate, wash it with deionized water, and dry it to obtain modified lignin; S22. Add the modified lignin and furfuryl alcohol into a reaction kettle, add sodium hydroxide to control the pH to 9 - 10, the reaction temperature is 100 - 120 °C, and the reaction time is 1 - 2 h. Dehydrate under reduced pressure to obtain lignin - modified furfuryl alcohol.

5. The preparation method of the modified furan resin for casting with low free phenol according to claim 4, characterized in that, In S21, the organic base catalyst is any one or a combination of 1,8 - diazabicyclo - bicyclo(5.4.0) - 7 - undecene, 1,5 - diazabicyclo[4.3.0]non - 5 - ene, 4 - dimethylaminopyridine; the six - membered ring lactone is any one or a combination of coumarin - 3,4 - diol, δ - octalactone, δ - tetradecalactone; in S22, the addition amount of the modified lignin is 5 - 15% of the mass of the furfuryl alcohol added in S22.

6. The preparation method of the modified furan resin for casting with low free phenol according to claim 1, characterized in that, In S1, the antioxidant is any one or a combination of hindered phenol antioxidants, phosphite antioxidants, thioester antioxidants; the hindered phenol antioxidants are any one or a combination of 525, 1010, 1076, 3052; the phosphite antioxidants are any one or a combination of 168, 626, 3019; the thioester antioxidants are any one or a combination of pentaerythritol tetrakis(3 - laurylthiopropionate), dilauryl thiodipropionate, dipalmitoyl thiodipropionate; the moisture - resistant agent is any one or a combination of silane moisture - resistant agents, dioctyl phthalate, 2,5 - bis(hydroxymethyl)furan, ethyl silicate; the silane moisture - resistant agents are any one or a combination of methyltrisiloxane, silanepropyl ether, isobutylsilane; in S2, the mass fraction of paraformaldehyde is 92 - 96%, and the mass ratio of the cellulose aldehyde compound, paraformaldehyde and acetone is 60 - 100:20 - 30:100 - 120; in S3, the mass ratio of phenol, cardanol, paraformaldehyde and furfuryl alcohol is 80 - 90:10 - 20:30 - 40:50 - 70; in S2, S3 and S5, the base catalyst is any one of sodium hydroxide, potassium hydroxide, sodium carbonate.

7. The preparation method of the modified furan resin for casting with low free phenol according to claim 1, characterized in that, In S4, the polyol is any one or a combination of sorbitol, glycerol, mannitol; the acid catalyst is any one of formic acid, phosphoric acid, oxalic acid, and the mass ratio of mixture 1, mixture 2, polyol and furfuryl alcohol is 15 - 25:10 - 15:5 - 10:50 - 70.

8. The preparation method of the modified furan resin for casting with low free phenol according to claim 1, characterized in that, In S5, the mass ratio of mixture 3 to lignin-modified furfuryl alcohol is 5-8:2-3; in S6, the addition amount of ethanol is 10-20% of the mass of phenolic-modified furan resin, the mass ratio of antioxidant to moisture-proof agent is 1:1-3, and the total addition amount of antioxidant and moisture-proof agent is 1-5% of the mass of phenolic-modified furan resin.

9. A modified furan resin for casting with low free phenol prepared by the preparation method of the modified furan resin for casting with low free phenol according to any one of claims 1-8.

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