Preparation method of biomass leather tanning agent based on corncob extract

Abstract

The present invention discloses a method for preparing a biomass leather tanning agent based on corncob extract, which comprises the following steps: washing corncobs with distilled water, drying, crushing, and sieving; mixing corncob powder with a NaOH solution, heating and reacting; cooling to room temperature; adjusting the pH of the reaction solution to 6-7; precipitating with alcohol; filtering to obtain a filtrate; decompressing and distilling the filtrate to obtain a concentrated solution; adjusting the pH of the concentrated solution to 2-4; freeze-drying to obtain a polysaccharide; dissolving the polysaccharide in anhydrous ethanol; adding boron trifluoride etherate; mixing uniformly; dropping glycidyl ether; heating and reacting; and dialyzing with ultrapure water. The biomass tanning agent prepared by the present invention is soluble in water, has a simple preparation process, and has a wide molecular weight distribution. It can cross-link with leather fibers at different levels, effectively improving the shrinkage temperature, filling properties, and softness of leather, and overcoming the defects of brittle and hard leather after tanning with small molecule epoxy tanning agents.

Description

Technical Field

[0001] The invention belongs to the technical field of chrome-free tanning agent preparation, and particularly relates to a method for preparing a biomass leather tanning agent based on corncob extract. Background Art

[0002] Tanning is a crucial step in leather processing. Chrome tanning agents are highly regarded in the leather industry for their ability to impart strong aging resistance and excellent sensory properties. However, traditional chrome tanning agents suffer from low utilization rates and significant environmental pollution. To address these challenges and promote the development of clean leathermaking technologies, researchers are committed to developing more environmentally friendly and sustainable biomass-based chrome-free tanning agents. Corncob is a promising biomass resource, and its extracts have widespread applications in various fields. It is also a cheap, readily available, and environmentally sustainable resource. However, there is currently a lack of biomass-based chrome-free tanning agents based on corncob extracts on the market, and existing reports have also encountered some problems. For example, Jiang et al. catalytically converted hemicellulose using AlCl₃·6H₂O in a microwave reactor at 140°C, and further degraded the hemicellulose with the help of H₂O₂. Finally, by combining the tanning agent with a Zr compound, the shrinkage temperature of the tanned leather reached 83.5°C. However, the resulting corncob extract had a narrow molecular weight distribution (1960–3894 g / mol), and the catalytic conversion process was demanding. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing a biomass leather tanning agent based on corn cob extract. The tanning agent has a wide molecular weight distribution, can be cross-linked with leather fibers at different levels, and effectively improves the shrinkage temperature and softness of leather.

[0004] The technical solution adopted by the present invention is a method for preparing a biomass leather tanning agent based on corn cob extract, which is specifically implemented according to the following steps:

[0005] Step 1, washing corn cobs with distilled water, drying, crushing, and sieving to obtain corn cob powder;

[0006] Step 2: mixing corn cob powder and NaOH solution, heating to react, cooling to room temperature, adjusting the pH of the reaction solution to 6-7 with hydrochloric acid, adding anhydrous ethanol for alcohol precipitation, and filtering to obtain a filtrate;

[0007] Step 3, distilling the filtrate in step 2 under reduced pressure to obtain a concentrate, then adjusting the pH of the concentrate to 2-4 with hydrochloric acid, and freeze-drying to obtain a polysaccharide;

[0008] Step 4: dissolve the polysaccharide in anhydrous ethanol, add boron trifluoride ether, mix well, then slowly drop glycidyl ether, heat to react, quench with water after the reaction is completed, cool to room temperature, and dialyze with ultrapure water to obtain a biomass leather tanning agent.

[0009] The present invention is also characterized in that:

[0010] In step 1, the drying temperature is 100-115° C.; when sieving, a sieve with a mesh size of 60-100 is used.

[0011] In step 2, the concentration of the NaOH solution is 1 to 3 mol / L; the solid-liquid ratio of the corn cob powder to the NaOH solution is 1:10 to 25; and the volume ratio of anhydrous ethanol to the reaction solution is 2 to 4:1.

[0012] In step 2, the heating reaction is at 50-80° C. and the heating reaction time is 3-5 h.

[0013] Step 3, specifically: distilling the filtrate in step 2 under reduced pressure at 70° C. to concentrate the solution to 1 / 10 of the original volume, then adjusting the pH of the concentrate to 2-4 using 1-3 mol / L hydrochloric acid, and freeze-drying at -60° C. for 48 hours to obtain a polysaccharide;

[0014] In step 4, the amount of boron trifluoride ether added is 1 wt% to 5 wt% of the total mass of the polysaccharide and the glycidyl ether; and the molar ratio of the polysaccharide to the glycidyl ether is 1:1 to 3.

[0015] In step 4, the heating reaction temperature is 50-80° C., the heating reaction time is 3-6 h, and the dialysis time is 12-36 h.

[0016] The present invention has the following beneficial effects: the biomass tanning agent prepared by the present invention is soluble in water, has a simple preparation process, and has a wide molecular weight distribution. It can cross-link with leather fibers at different levels, effectively improving the shrinkage temperature (84°C) of leather, the filling properties, and the softness of leather, overcoming the defects of brittle and hard leather after tanning with small molecule epoxy tanning agents. In addition, the biomass tanning agent prepared by the present invention is derived from the biological world, is inexpensive, and has a simple preparation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a synthetic route of the biomass leather tanning agent prepared by the method of the present invention;

[0018] Figure 2 This is a particle size distribution diagram of the biomass leather tanning agent prepared by the method of the present invention;

[0019] Figure 3 This is a molecular weight distribution diagram of the biomass leather tanning agent prepared by the method of the present invention;

[0020] Figure 4 This is an infrared spectrum of the biomass leather tanning agent prepared by the method of the present invention;

[0021] Figure 5This is a scanning electron microscope image of the longitudinal section of leather tanned with a low molecular weight epoxy tanning agent;

[0022] Figure 6 This is a scanning electron microscope image of the longitudinal section of leather tanned with the biomass tanning agent prepared by the method of the present invention. DETAILED DESCRIPTION

[0023] The present invention will be described in detail below with reference to specific embodiments and the accompanying drawings.

[0024] The present invention provides a method for preparing a biomass leather tanning agent based on corncob extract. The method utilizes a one-step addition reaction to prepare an epoxy-modified corncob polysaccharide tanning agent. First, heteropolysaccharides from the corncob are extracted using an alkaline method. The pH of the solution is adjusted with dilute hydrochloric acid to further hydrolyze the cellulose into soluble oligosaccharides. The extracted corncob polysaccharide is dissolved in anhydrous ethanol and reacted with glycidyl ether under the catalysis of boron trifluoride ether to obtain an epoxy-modified polysaccharide tanning agent.

[0025] Please follow the steps below to implement:

[0026] Step 1, repeatedly washing the corn cob with distilled water to remove impurities, drying, crushing, and sieving after washing to obtain corn cob powder;

[0027] The drying temperature is 100-115°C; when sieving, use a sieve with a mesh size of 60-100;

[0028] Step 2: mixing corn cob powder and NaOH solution, heating to react, cooling to room temperature, adjusting the pH of the reaction solution to 6-7 with 1-3 mol / L hydrochloric acid, adding anhydrous ethanol for alcohol precipitation, and filtering to obtain a filtrate;

[0029] The concentration of NaOH solution is 1-3 mol / L; the solid-liquid ratio of corn cob powder to NaOH solution is 1:10-25; the heating reaction is at 50-80°C and the heating reaction time is 3-5 hours;

[0030] The volume ratio of anhydrous ethanol to the reaction solution is 2 to 4:1;

[0031] Step 3, distilling the filtrate in step 2 under reduced pressure at 70° C. to concentrate the solution to 1 / 10 of the original volume, then adjusting the pH of the concentrate to 2-4 using 1-3 mol / L hydrochloric acid, and freeze-drying at -60° C. for 48 hours to obtain a polysaccharide;

[0032] Step 4: dissolving the polysaccharide in anhydrous ethanol, adding a catalyst of boron trifluoride etherate, mixing evenly, then slowly dropping glycidyl ether, heating to react, quenching with a very small amount of water after the reaction is completed, cooling to room temperature, and dialyzing with ultrapure water to obtain a biomass leather tanning agent;

[0033] The amount of boron trifluoride ether added is 1 wt% to 5 wt% of the total mass of the polysaccharide and the glycidyl ether; the molar ratio of the polysaccharide to the glycidyl ether is 1:1 to 3;

[0034] The heating reaction temperature is 50-80°C, the heating reaction time is 3-6 hours, and the dialysis time is 12-36 hours.

[0035] The synthetic route of the biomass leather tanning agent prepared by the method of the present invention is as follows: Figure 1 As shown, the polysaccharide extracted from corncobs is primarily xylan. Catalyzed by boron trifluoride etherate, the hydroxyl groups on the corncob polysaccharide react with the epoxy groups on the glycidyl ether molecules. Compared to the monomolecular glycidyl ether, the resulting tanning agent exhibits a different molecular weight distribution, with the smaller molecular weight fractions cross-linking with the leather collagen fibers, while the larger molecular weight fractions act as fillers.

[0036] The particle size of the corn polysaccharide samples prepared in the present invention before and after modification was tested. Figure 2 As shown in Figure 2, the particle size distribution of the extracted polysaccharide is relatively wide. After grafting with epoxy tanning agent with a single molecular weight, the particle size is slightly reduced, but still shows the characteristics of wide particle size distribution. In addition, the molecular weight distribution of the modified corn cob polysaccharide was also tested, and the results are shown in Figure 2. Figure 3 Tanning agents of different sizes can penetrate different layers of leather fibers and cross-link, effectively solving the problems of insufficient filling and poor hand feel of tanned leather.

[0037] Example 1

[0038] The preparation of the biomass leather tanning agent based on corncob extract of the present invention is specifically carried out according to the following steps:

[0039] Step 1: remove impurities from 20 g corn cobs, dry them at 100° C., grind them, and pass them through a 60-mesh sieve;

[0040] Step 2: Place the corn cob powder prepared in step 1 in a three-necked flask, mix 10 g of corn cob powder with 100 ml of 1 mol / l NaOH solution, heat to 50° C., react for 5 h, cool to room temperature after the reaction is complete, collect the extract, adjust the pH of the extract to 6 with 1 mol / L hydrochloric acid solution, precipitate with 3 volumes of alcohol, and collect the filtrate;

[0041] Step 3: Concentrate the filtrate in step 2, adjust the pH value of the solution to 2 with 1 mol / L hydrochloric acid solution, and freeze-dry.

[0042] Step 4: Dissolve 3 g of the polysaccharide extracted in step 3 in anhydrous ethanol, add 0.0672 g of boron trifluoride etherate, mix thoroughly, and slowly dropwise add 3.5 g of glycidyl ether to the flask. Heat at 50°C for 3 hours, then quench with a small amount of water, cool to room temperature, dialyze against ultrapure water for 12 hours, and freeze-dry. The molecular weight of the tanning agent is approximately 1169 Mw, and the shrinkage temperature of the tanned leather is 81.6°C.

[0043] Example 2

[0044] The preparation of the biomass leather tanning agent based on corncob extract of the present invention is specifically carried out according to the following steps:

[0045] Step 1: After removing impurities from 20 g of corn cobs, drying at 110° C., crushing, and passing through an 80-mesh sieve;

[0046] Step 2: Place the corn cob powder in step 1 in a three-necked flask, mix 10 g of corn cob powder with 150 ml of 2 mol / L NaOH solution, heat to 60° C., react for 4 hours, cool to room temperature after the reaction, collect the extract, adjust the pH of the extract to 6.5 with 2 mol / L hydrochloric acid solution, precipitate with 3 volumes of alcohol, and collect the filtrate;

[0047] Step 3: Concentrate the filtrate in step 2, adjust the pH value of the solution to 2 with 2 mol / L hydrochloric acid solution, and freeze-dry.

[0048] Step 4: Dissolve 3g of the polysaccharide extracted in step 3 in anhydrous ethanol, add 0.1g of boron trifluoride etherate, and mix thoroughly. Slowly add 7g of glycidyl ether dropwise to the flask, heat at 60°C, react for 3 hours, quench with a small amount of water, cool to room temperature, dialyze against ultrapure water for 12 hours, and freeze-dry. The molecular weight of the tanning agent is approximately 598MW, and the shrinkage temperature of the tanned leather is 82.4°C.

[0049] Example 3

[0050] The preparation of the biomass leather tanning agent based on corncob extract of the present invention is specifically carried out according to the following steps:

[0051] Step 1: After removing impurities from 20 g of corn cobs, drying at 110° C., crushing, and passing through an 80-mesh sieve;

[0052] Step 2: Place the corn cob powder in step 1 in a three-necked flask, mix 10 g of corn cob powder with 200 ml of 3 mol / L NaOH solution, heat to 70° C., react for 3 hours, cool to room temperature after the reaction, collect the extract, adjust the pH of the extract to 6 with 3 mol / L hydrochloric acid solution, precipitate with 4 times the volume of alcohol, and collect the filtrate;

[0053] Step 3: Concentrate the filtrate in step 2, adjust the pH value of the solution to 4 with 3 mol / L hydrochloric acid solution, and freeze-dry.

[0054] Step 4: Dissolve 3g of the polysaccharide extracted in step 3 in anhydrous ethanol, add 0.0672g of boron trifluoride etherate, and mix thoroughly. Slowly add 10.5g of glycidyl ether dropwise to the flask, heat at 70°C, react for 5 hours, quench with a small amount of water, cool to room temperature, dialyze against ultrapure water for 24 hours, and freeze-dry. The molecular weight of the tanning agent is approximately 164,705Mw, and the shrinkage temperature of the tanned leather is 80.9°C.

[0055] Example 4

[0056] The preparation of the biomass leather tanning agent based on corncob extract of the present invention is specifically carried out according to the following steps:

[0057] Step 1: remove impurities from 20 g corn cobs, dry them at 115° C., grind them, and pass them through a 100-mesh sieve;

[0058] Step 2: Place the corn cob powder prepared in step 1 in a three-necked flask, mix 10 g of corn cob powder with 250 ml of 2 mol / L NaOH solution, heat to 80° C., react for 3 h, cool to room temperature after the reaction is completed, collect the extract, adjust the pH of the extract to 6 with 2 mol / L hydrochloric acid solution, precipitate with 3 volumes of alcohol, and collect the filtrate;

[0059] Step 3: Concentrate the filtrate in step 2, adjust the pH value of the solution to 3 with 2 mol / L hydrochloric acid solution, and freeze-dry.

[0060] Step 4: Dissolve 3g of the polysaccharide extracted in step 3 in anhydrous ethanol, add 0.1175g of boron trifluoride etherate, and mix thoroughly. Slowly add 8.75g of glycidyl ether dropwise to the flask, heat at 80°C, react for 3 hours, quench with a small amount of water, cool to room temperature, dialyze against ultrapure water for 24 hours, and freeze-dry. The molecular weight of the tanning agent is approximately 16,470 Mw, and the shrinkage temperature of the tanned leather is 83.5°C.

[0061] Example 5

[0062] The preparation of the biomass leather tanning agent based on corncob extract of the present invention is specifically carried out according to the following steps:

[0063] Step 1: After removing impurities from 20 g of corn cobs, drying at 105° C., crushing, and passing through an 80-mesh sieve;

[0064] Step 2: Place the corn cob powder prepared in step 1 in a three-necked flask, mix 10 g of corn cob powder with 250 ml of 2 mol / L NaOH solution, heat to 80° C., react for 3 hours, cool to room temperature after the reaction is completed, collect the extract, adjust the pH of the extract to 6.5 with 2 mol / L hydrochloric acid solution, precipitate with 3 times the volume of alcohol, and collect the filtrate;

[0065] Step 3: Concentrate the filtrate in step 2, adjust the pH value of the solution to 4 with 2 mol / L hydrochloric acid solution, and freeze-dry.

[0066] Step 4: Dissolve 3g of the polysaccharide extracted in step 3 in anhydrous ethanol, add 0.235g of boron trifluoride etherate, and mix thoroughly. Slowly add 8.75g of glycidyl ether dropwise to the flask, heat at 80°C, react for 3 hours, quench with a small amount of water, cool to room temperature, dialyze against ultrapure water for 24 hours, and freeze-dry. The molecular weight of the tanning agent is approximately 377,629Mw, and the shrinkage temperature of the tanned leather is 80.5°C.

[0067] The structure of the tanning agent was characterized by infrared spectroscopy ( Figure 4 ), compared with CP, CP-GTE has a -1 and 910-752cm -1 Nearby, an absorption peak similar to that of GTE appeared. These results fully demonstrated the successful modification of corncob polysaccharide.

[0068] The epoxy modified corncob polysaccharide tanning agent with a wide molecular weight distribution prepared by the method of the present invention is compared with the leather tanned with a small molecular weight epoxy tanning agent, which shows that the epoxy modified corncob polysaccharide tanning agent with a wide molecular weight distribution prepared by the method ( Figure 6 ) The degree of dispersion of leather fibers after tanning is greater than that of small molecule epoxy reagents ( Figure 5 ).

Claims

1. A method for preparing a biomass leather tanning agent based on corncob extract, characterized in that: Please follow the steps below to implement: Step 1, washing corn cobs with distilled water, drying, crushing, and sieving to obtain corn cob powder; Step 2: mixing corn cob powder and NaOH solution, heating to react, cooling to room temperature, adjusting the pH of the reaction solution to 6-7 with hydrochloric acid, adding anhydrous ethanol for alcohol precipitation, and filtering to obtain a filtrate; The concentration of NaOH solution is 1-3 mol / L; the solid-liquid ratio of corn cob powder to NaOH solution is 1:10-25; the volume ratio of anhydrous ethanol to reaction solution is 2-4:1; Step 3, distilling the filtrate in step 2 under reduced pressure to obtain a concentrate, then adjusting the pH of the concentrate to 2-4 with hydrochloric acid, and freeze-drying to obtain a polysaccharide; Step 4: dissolving the polysaccharide in anhydrous ethanol, adding boron trifluoride etherate, mixing evenly, then slowly dropping glycidyl ether, heating to react, quenching with water after the reaction is completed, cooling to room temperature, and dialyzing with ultrapure water to obtain a biomass leather tanning agent; The amount of boron trifluoride ether added is 1wt-5wt% of the total mass of the polysaccharide and the glycidyl ether; the molar ratio of the polysaccharide to the glycidyl ether is 1:1-3.

2. The method for preparing a biomass leather tanning agent based on corncob extract according to claim 1, characterized in that: In the step 1, the drying temperature is 100-115° C.; when sieving, a sieve with a mesh size of 60-100 is used.

3. The method for preparing a biomass leather tanning agent based on corncob extract according to claim 1, characterized in that: In the step 2, the heating reaction is performed at 50-80° C. for 3-5 hours.

4. The method for preparing a biomass leather tanning agent based on corncob extract according to claim 1, characterized in that: In step 4, the heating reaction temperature is 50-80° C., the heating reaction time is 3-6 hours, and the dialysis time is 12-36 hours.

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