Preparation method of cassava starch-waste syrup-vinasse protein composite formaldehyde-free binder

Abstract

The invention discloses a preparation method of a cassava starch-waste syrup-vinasse protein composite formaldehyde-free binder. The environment-friendly formaldehyde-free binder is prepared by taking cassava starch, waste syrup and vinasse protein as main raw materials. The preparation method comprises the following steps: firstly, pretreating the vinasse protein extract, mixing with starch milk prepared in a certain proportion, gelatinizing, adding waste syrup, adjusting the pH value of a mixed solution, and then adding a cross-linking agent to realize a cross-linking reaction, thereby obtaining the binder. The binder prepared by the preparation method disclosed by the invention is free of formaldehyde emission in the production and use processes, and high-value utilization of various biomass resources such as waste syrup, vinasse and cassava starch is realized. The adhesive prepared by the invention has good adhesive property and water resistance, is green and environment-friendly, and can be widely applied to the field of artificial board manufacturing.

Description

Technical Field

[0001] This invention relates to the field of adhesives for engineered wood products, and more particularly to a method for preparing a formaldehyde-free adhesive composed of cassava starch, waste syrup, and distillers' grains protein. Background Technology

[0002] Formaldehyde-based adhesives such as urea-formaldehyde resin and phenolic resin have long dominated the engineered wood products industry due to their excellent bonding strength and water resistance. However, these adhesives continuously release formaldehyde during use, polluting indoor air and harming human health, and their raw materials are derived from non-renewable fossil resources. Therefore, developing adhesives that are renewable in origin and release no formaldehyde during production and use has become an urgent need for the industry.

[0003] Starch binders have advantages such as wide availability of raw materials, low price, and non-toxicity and environmental friendliness. However, traditional starch binders have defects such as poor water resistance and insufficient bonding strength, making it difficult to meet the performance requirements of industrialized board production. To improve the performance of starch binders, existing technologies often employ chemical modification or the addition of synthetic resins, but this often leads to increased costs or the introduction of harmful substances such as formaldehyde.

[0004] Sugar syrup, a byproduct of sugar refining, is rich in reducing sugars and can be used as a plasticizer and cross-linking promoter in starch binders, but its modification effect alone is limited. Distillers' grains, a major byproduct of the brewing industry with a huge annual output, are rich in protein and polysaccharides, but are currently mainly disposed of as low-value-added feed or fertilizer, failing to achieve high-value utilization of the resource. How to efficiently extract proteins from distillers' grains and apply them to the modification of starch-based binders, while maintaining a green and environmentally friendly process and controllable costs, is a pressing technical problem to be solved in this field. Summary of the Invention

[0005] Purpose of the invention: To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a formaldehyde-free adhesive composed of cassava starch, waste syrup, and distiller's grains protein. This method adds distiller's grains protein extracted by DES to the cassava starch-waste syrup adhesive system, which significantly improves the bonding strength and water resistance while achieving zero formaldehyde release during preparation and use. It also provides a new approach for the high-value utilization of waste syrup and distiller's grains.

[0006] Technical solution: The raw material composition of the cassava starch-waste syrup-distillers' grain protein composite formaldehyde-free binder of the present invention includes: cassava starch, waste syrup from sugar industry (filtered impurities), distillers' grain protein, crosslinking agent, water, and pH adjuster.

[0007] The preparation method of the cassava starch-waste syrup-distillers' grains protein composite formaldehyde-free binder of the present invention is as follows:

[0008] Step 1): Prepare choline chloride-urea DES green solvent. Mix the lees and DES solvent at a liquid-solid ratio of 1:5 and stir at 60 °C for 2 hours. After extraction, separate the solid and liquid by centrifugation or filtration to obtain the extract.

[0009] Step 2): Add ethanol as a back-extraction agent to the extract obtained in Step 1) to precipitate the wine lees protein and polysaccharides. Separate and dry the precipitate to obtain a mixture of wine lees protein and polysaccharides.

[0010] Step 3): Dissolve the distillers' grains protein obtained in Step 2) in water to form a 10%-20% distillers' grains protein solution, and stir to ensure uniform dissolution. Preliminarily adjust the pH of the distillers' grains protein solution to neutral or weakly alkaline using sodium hydroxide or hydrochloric acid.

[0011] Step 4): Mix tapioca starch and cold water in a weight ratio of 1:2 to 1:3, and stir at low speed to form a uniform starch slurry.

[0012] Step 5): Add the pretreated distillers' grains protein solution from step 3) to the starch slurry obtained in step 4) according to the weight ratio of starch:distillers' grains protein (dry solids) = 100:10-100:50, while keeping the mixture stirred at a low speed.

[0013] Step 6): Heat the mixture obtained in step 5) to gelatinize it to 60-65℃ and stir continuously.

[0014] Step 7): Add the waste syrup to the gelatinized mixture from Step 6) at a weight ratio of starch to waste syrup (dry solids) of 100:20-100:40, and continue stirring until evenly mixed.

[0015] Step 8): Add dilute sodium hydroxide solution to the mixture obtained in step 7) to adjust the pH of the mixture to 8-9.

[0016] Step 9): Add the crosslinking agent to the mixture obtained in Step 8) according to the weight ratio of starch to crosslinking agent (on a dry solids basis) of 100:5-100:15, and continue stirring for 10-15 minutes.

[0017] Step 10): Heat the mixture obtained in step 9) to 85-95°C for crosslinking reaction, and keep it at this temperature for 30-60 minutes.

[0018] Step 11): Move the adhesive after the reaction in step 10) to room temperature, continue stirring and cooling to below 40°C to obtain a composite formaldehyde-free adhesive.

[0019] In step 9), the amount of crosslinking agent added is 5%-15% of the dry weight of starch.

[0020] In step 9), a silane coupling agent is added as an interfacial bonding improver.

[0021] The application method of the cassava starch-waste syrup-distillers' grains protein composite formaldehyde-free binder of the present invention includes the following steps:

[0022] 1) Apply adhesive: Apply or spray the composite formaldehyde-free adhesive onto the substrate to be bonded.

[0023] 2) Laying and pre-pressing: Lay the sizing material in the mold to form a slab, and pre-press it at room temperature to remove air;

[0024] 3) Cold pressing: Place the pre-pressed slab into a cold press, apply a pressure of 1-3 MPa at room temperature, and hold the pressure for 30-60 minutes;

[0025] 4) Post-curing and drying: Place the cold-pressed board into an oven or drying room and heat-treat it at 100-120°C for 2-4 hours to obtain the artificial board.

[0026] The amount of adhesive applied is 10%-20% of the oven-dry weight of the substrate.

[0027] The substrate is wood chips, straw powder, or cotton stalks.

[0028] In this invention, cassava starch provides the basic adhesive strength. Waste syrup acts as a plasticizer and reactant, improving toughness and water resistance, and participating in the Maillard reaction and caramelization. The protein molecules in distillers' grains contain various active groups (such as amino and carboxyl groups), which can generate stronger interactions with the hydroxyl groups of starch and fibrous materials, thereby improving initial adhesive strength. In addition, the polysaccharide components of distillers' grains have certain thickening and water-retaining effects, which can improve the uniformity and flexibility of the adhesive film and reduce the risk of cracking.

[0029] Preferably, the lees protein is selected from Gujing Winery, which has a relatively stable source of raw materials, and undergoes quality control.

[0030] In step 9), the crosslinking agent is selected from borax, citric acid, or ammonium zirconium carbonate. This crosslinking agent directly assists in the formation of a three-dimensional network structure, improving water resistance, bonding strength, and reducing viscosity. Furthermore, the crosslinking agent may help expose potential crosslinking sites, allowing amino and carboxyl groups in the distillers' grains protein to participate in the crosslinking reaction, further improving the overall strength and water resistance of the adhesive.

[0031] In step 3), the pH adjuster is sodium hydroxide or hydrochloric acid, adjusted to near neutral or weakly alkaline.

[0032] The method for preparing the cassava starch-waste syrup-distillers' grains protein composite formaldehyde-free adhesive of this invention produces a composite formaldehyde-free bio-based adhesive that is an amber-colored viscous liquid and does not contain formaldehyde.

[0033] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0034] (1) The present invention uses cassava starch, sugar syrup from sugar industry and wine lees protein to prepare a composite formaldehyde-free binder. In the preparation and use process, zero formaldehyde emission is achieved. Compared with the binders currently used, it meets the requirements of green environmental protection and sustainable development.

[0035] (2) This invention makes full use of agricultural by-products such as cassava starch, sugar syrup waste from the sugar industry and wine lees protein, and transforms them into high-value-added binder products. This not only broadens the resource utilization of waste, but also significantly reduces the cost of raw materials, resulting in good economic benefits.

[0036] (3) The present invention utilizes the active groups in the wine lees protein to enhance the bonding effect, uses waste syrup as a plasticizer to participate in the reaction, and constructs a stable three-dimensional network structure with a crosslinking agent. The adhesive prepared by the present invention exhibits excellent dry bonding strength and wet bonding strength, which meets the performance requirements of products such as artificial boards.

[0037] (4) The preparation method of the present invention is simple to operate and easy to scale up for industrial production; the prepared adhesive can be applied to the manufacture of various artificial boards and has good market application prospects. Detailed Implementation

[0038] The lees protein in this invention is prepared by the following method: a choline chloride-urea DES green solvent is prepared, and fresh lees from Gujing Distillery are mixed with DES solvent at a liquid-solid ratio of 1:5. The mixture is stirred and extracted at 60°C for 2 hours. After extraction, the extract is obtained by centrifugation. Ethanol is added to the extract to precipitate the protein and polysaccharides. The precipitate is separated and dried to obtain the lees protein.

[0039] Example 1:

[0040] First, prepare the distillers' grains protein as described above. Then, weigh 100 g of tapioca starch and add it to 250 g of cold water, stirring at low speed to form a starch slurry. Weigh 30 g of distillers' grains protein solid powder and dissolve it in 170 g of water to prepare a 15% solution, adjusting the pH to 8.0 with dilute sodium hydroxide solution. Add the protein solution to the starch slurry while stirring, and heat to 65°C to gelatinize. Add 50 g of waste syrup (60% dry matter content, equivalent to 30 g on a dry basis), stir evenly, adjust the pH to 8.5 with dilute sodium hydroxide, then add 10 g of citric acid, continue stirring for 15 minutes, raise the temperature to 90°C and maintain the temperature for 45 minutes. After the reaction is complete, continue stirring and cool to room temperature to obtain a composite formaldehyde-free binder.

[0041] Example 2:

[0042] First, prepare the distillers' grains protein as described above. Then, weigh 100 g of tapioca starch and add it to 250 g of cold water, stirring at low speed to form a uniform starch slurry. Weigh 30 g of distillers' grains protein solid powder and dissolve it in 170 g of water to prepare a 15% solution, adjusting the pH to 8.0 with dilute sodium hydroxide solution. Add the protein solution to the starch slurry while stirring, and heat to 65°C to gelatinize. Add 50 g of waste syrup (60% dry matter content, equivalent to 30 g on a dry basis), stir evenly, adjust the pH to 8.5 with dilute sodium hydroxide, then add 10 g of borax (pre-dissolved in a small amount of hot water), continue stirring for 15 minutes, raise the temperature to 90°C and maintain the temperature for 45 minutes. After the reaction is complete, continue stirring and cool to room temperature to obtain a composite formaldehyde-free binder.

[0043] Example 3:

[0044] First, prepare the distillers' grains protein as described above. Then, weigh 100 g of tapioca starch and add it to 250 g of cold water, stirring at low speed to form a uniform starch slurry. Weigh 50 g of distillers' grains protein solid powder and dissolve it in 283 g of water to prepare a 15% solution, adjusting the pH to 8.0 with dilute sodium hydroxide solution. Add the protein solution to the starch slurry while stirring, and heat to 65°C to gelatinize. Add 50 g of waste syrup (60% dry matter content, equivalent to 30 g on a dry basis), stir evenly, adjust the pH to 8.5 with dilute sodium hydroxide, then add 10 g of citric acid, continue stirring for 15 minutes, raise the temperature to 90°C and maintain the temperature for 45 minutes. After the reaction is complete, continue stirring and cool to room temperature to obtain a composite formaldehyde-free binder.

[0045] Example 4:

[0046] First, prepare the distillers' grains protein as described above. Then, weigh 100 g of tapioca starch and add it to 250 g of cold water, stirring at low speed to form a uniform starch slurry. Weigh 30 g of distillers' grains protein solid powder and dissolve it in 170 g of water to prepare a 15% solution, adjusting the pH to 8.0 with dilute sodium hydroxide solution. Add the protein solution to the starch slurry while stirring, and heat to 65°C to gelatinize. Add 50 g of waste syrup (60% dry matter content, equivalent to 30 g on a dry basis), stir evenly, adjust the pH to 8.5 with dilute sodium hydroxide, then add 10 g of citric acid, continue stirring for 15 minutes, raise the temperature to 95°C and maintain the temperature for 45 minutes. After the reaction is complete, continue stirring and cool to room temperature to obtain a composite formaldehyde-free binder.

[0047] Compare with Example 1:

[0048] Weigh 100 g of tapioca starch and add it to 250 g of cold water. Stir at low speed to form a starch slurry and heat to 65°C to gelatinize. Add 50 g of waste syrup (60% dry matter content, equivalent to 30 g on a dry basis), stir well, adjust the pH to 8.5 with dilute sodium hydroxide, then add 10 g of citric acid and continue stirring for 15 minutes. Heat to 90°C and keep the temperature for 45 minutes. After the reaction is complete, continue stirring and cool to room temperature to obtain the binder.

[0049] Compare with Example 2:

[0050] Prepare distillers' grains protein as described above. Weigh 100 g of tapioca starch and add it to 250 g of cold water, stirring at low speed to form a starch slurry. Weigh 30 g of distillers' grains protein solid powder and dissolve it in 170 g of water to prepare a 15% solution, adjusting the pH to 8.0 with dilute sodium hydroxide solution. Slowly add the protein solution to the starch slurry while stirring, and heat to 65°C to gelatinize. Add 50 g of waste syrup (60% dry matter content, equivalent to 30 g on a dry basis), stir evenly, adjust the pH to 8.5 with dilute sodium hydroxide, raise the temperature to 90°C and maintain the temperature for 45 minutes. After the reaction is complete, continue stirring and cool to room temperature to obtain the binder.

[0051] Compare with Example 3:

[0052] Weigh 100 g of tapioca starch and add it to 250 g of cold water. Stir at low speed to form a uniform starch slurry and heat to 65°C to gelatinize. Add 50 g of waste syrup (60% dry matter content, equivalent to 30 g on a dry basis), stir well, adjust the pH to 8.5 with dilute sodium hydroxide, heat to 90°C and keep the temperature for 45 minutes. After the reaction is complete, continue stirring and cool to room temperature to obtain the binder.

[0053] Performance testing:

[0054] Three-layer plywood was prepared using poplar veneer as the substrate, following the method specified in national standard GB / T 17657-2013. The adhesive application rate was 180 g / m² (double-sided). The pressing process was as follows: pre-pressing at room temperature for 30 minutes, cold pressing at 1.0 MPa for 30 minutes, and then hot-pressing and curing at 120℃ for 2 hours. The dry and wet bond strengths of the adhesives prepared in different examples and control examples were tested (measured after immersion in hot water at 63℃ for 3 hours). Each group of samples was tested 5 times and the average value was taken. The results are shown in Table 1.

[0055] Table 1 Comparison of adhesive strength tests in different embodiments and control examples

[0056] sample Dry bond strength (MPa) Wet bond strength (MPa) Example 1 1.88 1.15 Example 2 1.75 1.02 Example 3 1.94 1.21 Example 4 1.91 1.18 Compare with Example 1 1.05 0.42 Compare with Example 2 0.85 0.21 Compare with Example 3 0.62 /

[0057] Note: The wet bond strength of control example 3 was extremely low, and the sample completely delaminated during the test, making it impossible to obtain valid data.

[0058] As shown in Table 1, the cassava starch-waste syrup-fermented grain protein composite formaldehyde-free binder (Examples 1-4) prepared according to the method of the present invention exhibits superior bonding performance in both dry and wet conditions compared to the control examples. Comparing Example 1 with Control Example 1, the addition of fermented grain protein increased the dry strength from 1.05 MPa to 1.88 MPa and the wet strength from 0.42 MPa to 1.15 MPa, indicating that fermented grain protein significantly enhances the adhesive's bonding performance and water resistance. Comparing Example 1 with Control Example 2, the addition of the crosslinking agent citric acid increased the dry strength from 0.85 MPa to 1.88 MPa and the wet strength from 0.21 MPa to 1.15 MPa, indicating that the three-dimensional network structure formed by the crosslinking agent is crucial for strength and water resistance. Control Example 3 had a dry strength of only 0.62 MPa and almost no water resistance. Example 1, by combining the two, showed a significant improvement in performance, demonstrating the significant synergistic effect of fermented grain protein and the crosslinking agent.

[0059] A comparison of Examples 1 and 2 shows that citric acid is slightly better than borax as a crosslinking agent in this system; a comparison of Examples 1 and 3 shows that the dry strength and wet strength are further improved after the amount of protein added is increased; a comparison of Examples 1 and 4 shows that increasing the reaction temperature has limited effect on performance improvement.

Claims

1. A method for preparing a formaldehyde-free cassava starch-waste syrup-distillers' grains protein composite binder, characterized in that, The binder is a mixture of cassava starch, waste syrup, distiller's grains protein, crosslinking agent, water, and pH adjuster. The method includes the following steps: Step 1): Prepare choline chloride-urea DES green solvent, mix the lees and DES solvent at a liquid-solid ratio of 1:5, stir and extract at 60℃, and then separate the solid and liquid to obtain the extract. Step 2): Add ethanol as a back-extraction agent to the extract to precipitate the lees protein and polysaccharide, separate and dry the precipitate to obtain lees protein and polysaccharide; Step 3): Dissolve the distillers' grains protein obtained in Step 2) in water to form a distillers' grains protein solution with a concentration of 10% to 20%, and stir until dissolved; adjust the pH of the distillers' grains protein solution to neutral or weakly alkaline using a pH adjuster. Step 4): Mix tapioca starch and water in a weight ratio of 1:2 to 1:3 to form a starch slurry; Step 5): Add the distillers' grains protein solution from step 3) to the starch slurry from step 4) at a weight ratio of 100:10-100:50 to obtain a mixture, while stirring. Step 6): Heat the mixture obtained in Step 5) to gelatinize it to 60-65℃ and stir. Step 7): Add the waste syrup to the gelatinized mixture from Step 6) with a weight ratio of starch to waste syrup dry solids of 100:20-100:40, and stir to mix. Step 8): Add dilute sodium hydroxide solution to the mixture obtained in step 7) to adjust the pH of the mixture to 8-9; Step 9): Add the crosslinking agent to the mixture obtained in Step 8) with a weight ratio of starch:crosslinking agent dry solids of 100:5-100:15 and stir for 10-15 minutes. Step 10): Heat the mixture obtained in step 9) to 85-95°C for crosslinking reaction and keep it at that temperature for 30-60 minutes. Step 11): Move the adhesive after the reaction in step 10) to room temperature, continue stirring and cooling to below 40°C to obtain a composite formaldehyde-free adhesive.

2. A method for preparing a cassava starch-waste syrup-distillers' grains protein composite formaldehyde-free binder, characterized in that: Includes the following steps: 1) Prepare a green solvent of choline chloride-urea DES. Mix the lees and DES solvent at a liquid-solid ratio of 1:

5. Stir and extract at 60°C for 2 hours. Centrifuge to obtain the extract. Add ethanol to the extract to precipitate the protein and polysaccharide. Separate and dry the precipitate to obtain lees protein. 2) Add 100 g of tapioca starch to 250 g of water and stir to form a starch milk; weigh 30 g of distillers' grains protein solid powder and dissolve it in 170 g of water to prepare a 15% solution, and adjust the pH to 8.0 with dilute sodium hydroxide solution. The protein solution was added to the starch milk under stirring and heated to 65°C for gelatinization. 50 g of waste syrup was added, and after stirring, the pH was adjusted to 8.5 with dilute sodium hydroxide. Then, 10 g of citric acid was added and stirred for 15 minutes. The temperature was raised to 90°C and kept at that temperature for 45 minutes. After the reaction was completed, the mixture was stirred and cooled to room temperature to obtain the composite formaldehyde-free adhesive.

3. A method for preparing a cassava starch-waste syrup-distillers' grains protein composite formaldehyde-free binder, characterized in that: Includes the following steps: 1) Prepare a green solvent of choline chloride-urea DES. Mix the lees and DES solvent at a liquid-solid ratio of 1:

5. Stir and extract at 60°C for 2 hours. Centrifuge to obtain the extract. Add ethanol to the extract to precipitate the protein and polysaccharide. Separate and dry the precipitate to obtain lees protein. 2) Add 100 g of tapioca starch to 250 g of water and stir to form a starch milk; dissolve 30 g of distillers' grains protein solid powder in 170 g of water to prepare a 15% solution, and adjust the pH to 8.0 with dilute sodium hydroxide solution; The protein solution was added to the starch milk under stirring and heated to 65°C for gelatinization. 50 g of waste syrup was added and stirred. The pH was adjusted to 8.5 with dilute sodium hydroxide. Then 10 g of borax was added and stirred for 15 minutes. The temperature was raised to 90°C and kept at that temperature for 45 minutes. After the reaction was completed, the mixture was stirred and cooled to room temperature to obtain the composite formaldehyde-free binder.

4. A method for preparing a formaldehyde-free cassava starch-waste syrup-distillers' grains protein composite binder, characterized in that: Includes the following steps: 1) Prepare a green solvent of choline chloride-urea DES. Mix the lees and DES solvent at a liquid-solid ratio of 1:

5. Stir and extract at 60°C for 2 hours. Centrifuge to obtain the extract. Add ethanol to the extract to precipitate the protein and polysaccharide. Separate and dry the precipitate to obtain lees protein. 2) Add 100 g of tapioca starch to 250 g of cold water and stir to form a starch milk; weigh 50 g of distillers' grains protein solid powder and dissolve it in 283 g of water to prepare a 15% solution, and adjust the pH to 8.0 with dilute sodium hydroxide solution. The protein solution was added to the starch milk under stirring and heated to 65°C for gelatinization. 50 g of waste syrup was added, and after stirring, the pH was adjusted to 8.5 with dilute sodium hydroxide. Then, 10 g of citric acid was added and stirred for 15 minutes. The temperature was raised to 90°C and kept at that temperature for 45 minutes. After the reaction was completed, the mixture was stirred and cooled to room temperature to obtain the composite formaldehyde-free adhesive.

5. The preparation method of the cassava starch-waste syrup-distillers' grains protein composite formaldehyde-free binder according to claim 1, characterized in that: In step 9), the amount of crosslinking agent added is 5%-15% of the dry weight of starch.

6. The preparation method of the cassava starch-waste syrup-distillers' grains protein composite formaldehyde-free binder according to claim 1, characterized in that: In step 9), the crosslinking agent is selected from borax, citric acid, or ammonium zirconium carbonate.

7. The preparation method of the cassava starch-waste syrup-distillers' grains protein composite formaldehyde-free binder according to claim 1, characterized in that: In step 9), a silane coupling agent is added as an interfacial bonding improver.

8. A method for applying a formaldehyde-free cassava starch-waste syrup-distillers' grains protein composite binder, characterized in that: The composite formaldehyde-free adhesive is prepared by the preparation method of claim 1, and the application method includes the following steps: 1) Applying adhesive: Apply or spray the composite formaldehyde-free adhesive onto the substrate to be bonded. 2) Laying and pre-pressing: Lay the sizing material in the mold to form a slab, and pre-press it at room temperature to remove air; 3) Cold pressing: Place the pre-pressed slab into a cold press, apply a pressure of 1-3 MPa at room temperature, and hold the pressure for 30-60 minutes; 4) Post-curing and drying: Place the cold-pressed boards into an oven or drying room and heat-treat at 100-120°C for 2-4 hours.

9. The application method of the cassava starch-waste syrup-distillers' grains protein composite formaldehyde-free binder according to claim 8, characterized in that: The amount of adhesive applied is 10%-20% of the oven-dry weight of the substrate.

10. The application method of the cassava starch-waste syrup-distillers' grains protein composite formaldehyde-free binder according to claim 8, characterized in that: The substrate is wood chips, straw powder, or cotton stalks.