Lignocellulose modification method, adhesive and application thereof

Abstract

The invention provides a lignocellulose modification method, an adhesive and application thereof, and belongs to the technical field of functional modification of biomass materials. According to the method, lignocellulose and oxidation liquid are mixed and sheared, modification treatment is carried out, and the oxidation liquid comprises 2, 2, 6, 6-tetramethylpiperidine oxide, NaBr, NaClO, NaOH and water. According to the method, materials can be efficiently mixed through mixing and shearing, all the components make more sufficient contact, more reaction active groups are exposed through the physical shearing effect and mechanical decomposition of lignocellulose, the oxidation degree is enhanced, the oxidation liquid has the oxidation effect and the cellulose degradation effect, and the oxidation effect is improved. The bonding strength is improved by combining the limitation of the mass ratio of the components in the oxidation liquid and utilizing the synergistic effect of mixed shearing and the oxidation liquid.

Description

Technical Field

[0001] The present invention relates to the technical field of functional modification of biomass materials, and in particular to a lignocellulose modification method, an adhesive and applications thereof. Background Art

[0002] In the utilization of biomass materials, chemical modification of lignocellulosic biomass, a type of agricultural and forestry waste, not only improves its performance but also provides an effective solution for environmental protection. TEMPO (2,2,6,6-tetramethylpiperidinyl oxide) oxidation technology, as a highly effective cellulose modification method, can introduce carboxyl groups without destroying the cellulose backbone, thereby improving cellulose's reactivity. It has been widely used in the functionalization of cellulose. For example, in the papermaking industry, TEMPO-oxidized cellulose can enhance the tensile strength and burst resistance of paper.

[0003] However, the modified lignocellulose obtained by the TEMPO oxidation technology in the related art has the problem of low bonding strength. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a method for modifying lignocellulose, an adhesive and applications thereof. The adhesive obtained by the method for modifying lignocellulose of the present invention has the advantage of high bonding strength.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for modifying lignocellulose, comprising the following steps:

[0007] The lignocellulose is mixed with an oxidizing solution and sheared to perform a modification treatment. The oxidizing solution comprises 2,2,6,6-tetramethylpiperidinyl oxide, NaBr, NaClO, NaOH and water. The mass ratio of 2,2,6,6-tetramethylpiperidinyl oxide, NaBr, NaClO and NaOH in the oxidizing solution is 0.03:0.3:40-70:5.28.

[0008] Preferably, the mass ratio of 2,2,6,6-tetramethylpiperidinyl oxide, NaBr, NaClO and NaOH in the oxidation solution is 0.03:0.3:44.19-69.72:5.28.

[0009] Preferably, the mixing and shearing temperature is room temperature to 40° C., the solid-liquid feed mass ratio is 1:0.5 to 1.5, and the screw speed is 200 to 350 rpm.

[0010] Preferably, the pH value of the system obtained after the modification treatment is completed is less than 9.5.

[0011] Preferably, the lignocellulose comprises one or more of cotton stalks, soybean straw, pomace, bagasse and walnut shells.

[0012] Preferably, the particle size of the lignocellulose is 200-250 μm, and the solid content is 33 wt%.

[0013] The present invention also provides an adhesive prepared by the lignocellulose modification method described in the above technical solution.

[0014] Preferably, the carboxyl value of the adhesive is 1.2 to 1.6 mmol / g carboxylated lignocellulosic biomass.

[0015] The present invention also provides the application of the adhesive described in the above technical solution in the field of adhesion.

[0016] Preferably, the application comprises the following steps:

[0017] The adhesive and the curing agent are mixed and then bonded, and the mass ratio of the adhesive to the curing agent is 1:1.

[0018] The invention provides a lignocellulose modification method, comprising the following steps: mixing and shearing lignocellulose with an oxidizing liquid to perform a modification treatment, wherein the oxidizing liquid comprises 2,2,6,6-tetramethylpiperidinyl oxide, NaBr, NaClO, NaOH and water, and the mass ratio of 2,2,6,6-tetramethylpiperidinyl oxide, NaBr, NaClO and NaOH in the oxidizing liquid is 0.03:0.3:40-70:5.28.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] In the present invention, the mixed shearing can not only efficiently mix the materials and make the contact of the various components more complete, but also mechanically decompose the cellulose through physical shearing, so that more reactive groups are exposed and the degree of oxidation is enhanced. The oxidizing liquid not only has an oxidizing effect but also has the effect of degrading cellulose. Combined with the limitation of the mass ratio of 2,2,6,6-tetramethylpiperidinyl oxide, NaBr, NaClO and NaOH in the oxidizing liquid, the synergistic effect of mixed shearing and the oxidizing liquid is utilized to improve the bonding strength.

[0021] The cellulose modification method of the present invention combines the TEMPO oxidation method with physical mixing and shearing processing, which can effectively improve the chemical activity and physical properties of biomass, solve the problems of long processing cycle, high cost and difficult processing in the prior art, and can achieve large-scale production.

[0022] The present invention also provides an adhesive that regulates the degree of oxidation and degradation of wood cellulose. After being combined with a curing agent, it exhibits good bonding properties, and has broad application prospects, especially in the field of artificial board reinforcement materials. The carboxyl groups introduced by oxidation of the oxidizing liquid can produce cross-linking effects with various ions or groups to form a new type of environmentally friendly adhesive, reducing the use of formaldehyde adhesives. DETAILED DESCRIPTION

[0023] The present invention provides a method for modifying lignocellulose, comprising the following steps:

[0024] The lignocellulose is mixed with an oxidizing solution and sheared to perform a modification treatment. The oxidizing solution comprises 2,2,6,6-tetramethylpiperidinyl oxide, NaBr, NaClO, NaOH and water. The mass ratio of 2,2,6,6-tetramethylpiperidinyl oxide, NaBr, NaClO and NaOH in the oxidizing solution is 0.03:0.3:40-70:5.28.

[0025] In the present invention, 2,2,6,6-tetramethylpiperidinyl oxide and sodium bromide in the oxidizing solution are catalysts, which only affect the reaction rate but not the degree of oxidation. The role of sodium hydroxide is to maintain the pH of the system. Sodium hypochlorite is an oxidant. 2 mol of sodium hypochlorite can oxidize 1 mol of hydroxyl groups to carboxyl groups. Ideally, for every 180 g of lignocellulose (dry weight), at most 1 mol of hydroxyl groups can be oxidized to carboxyl groups, that is, 5.56 mmol carboxyl groups / g biomass. Assuming that the dry weight of the biomass is 180 g and the target oxidation degree is ammol / g biomass, the sodium hypochlorite feed is 26.80×ag.

[0026] In the present invention, the mass ratio of 2,2,6,6-tetramethylpiperidinyl oxide, NaBr, NaClO and NaOH in the oxidizing solution is preferably 0.03:0.3:44.19 to 69.72:5.28, specifically 0.03:0.3:44.19:5.28 or 0.03:0.3:69.72:5.28.

[0027] In the present invention, the mass ratio of 2,2,6,6-tetramethylpiperidinyl oxide to water in the oxidizing solution is preferably 0.03:500.

[0028] In the present invention, the mixing and shearing temperature is preferably room temperature to 40°C, specifically 20, 25, 30, 35 or 40°C, to ensure that the material does not excessively degrade or volatilize during efficient processing. The solid-liquid feed mass ratio is preferably 1:0.5 to 1.5, specifically 1:1, and the screw speed is preferably 200 to 350 rpm, specifically 200, 250 or 300 rpm.

[0029] In the present invention, the mixing and shearing is preferably carried out in a high-efficiency mixing and shearing machine.

[0030] In the present invention, the mixed shearing not only efficiently mixes the materials and allows for more complete contact between the components, but also mechanically decomposes the lignocellulose through physical shearing, exposing more reactive groups and enhancing the degree of oxidation. The oxidizing solution not only has an oxidizing effect but also has the effect of degrading cellulose. Combined with the limitation of the mass ratio of 2,2,6,6-tetramethylpiperidinyl oxide, NaBr, NaClO, and NaOH in the oxidizing solution, the synergistic effect of mixed shearing and the oxidizing solution is utilized to improve the bonding strength. The present invention can complete the oxidation treatment of biomass at a relatively low temperature (room temperature to 40°C) and improve its physical properties through physical mixed shearing processing, achieving an efficient combination of TEMPO oxidation and physical mixed shearing processing, providing a new solution for the industrial application of lignocellulosic biomass.

[0031] In the present invention, the lignocellulose preferably includes one or more of cotton stalks, soybean straws, pomace, bagasse and walnut shells.

[0032] In the present invention, the particle size of the lignocellulose is preferably 200-250 μm, and the solid content is preferably 33 wt %. The solid content refers to the content of pure solid lignocellulose measured after drying the moisture.

[0033] In the present invention, the pH value of the system obtained after the modification treatment is completed is preferably less than 9.5, indicating that the modification treatment is completed and the system can be used in combination with a curing agent to enhance the bonding strength of the artificial board.

[0034] The present invention also provides an adhesive prepared by the lignocellulose modification method described in the above technical solution.

[0035] In the present invention, the carboxyl value of the adhesive is preferably 1.2 to 1.6 mmol / g carboxylated lignocellulosic biomass.

[0036] The present invention also provides the application of the adhesive described in the above technical solution in the field of adhesion.

[0037] In the present invention, the application preferably comprises the following steps:

[0038] The adhesive and the curing agent are mixed and then bonded, and the mass ratio of the adhesive to the curing agent is 1:1.

[0039] In the present invention, the curing agent preferably includes one or more of 1,4-succinic anhydride, styrene maleic anhydride copolymer and polyvinylamine.

[0040] In the present invention, the application is preferably for bonding wood-based panels.

[0041] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0042] The wood cellulose used in the examples and comparative examples of the present invention was prepared from cotton stalks after crushing and screening, with a particle size of 200-250 μm and a solid content of 33 wt %.

[0043] Example 1

[0044] Take 500g of lignocellulose as the solid material, dissolve 0.03g of TEMPO, 0.3g of NaBr, 44.19g of NaClO, and 5.28g of NaOH in water to prepare a 500g aqueous solution as the liquid material. Set the high-efficiency mixing and shearing equipment temperature to 30°C, the solid-liquid feed mass ratio to 1:1, and the screw speed to 300rpm. Measure the product pH. When the pH is less than 9.5, the adhesive is obtained, with a carboxyl value of 1.2mmol / g of biomass.

[0045] Example 2

[0046] Take 500g of lignocellulose as the solid material, dissolve 0.03g of TEMPO, 0.3g of NaBr, 69.72g of NaClO, and 5.28g of NaOH in water to prepare a 500g aqueous solution as the liquid material. Set the high-efficiency mixing and shearing equipment temperature to 30°C, the solid-liquid feed mass ratio to 1:1, and the screw speed to 300rpm. Measure the product pH. When the pH is less than 9.5, the adhesive is obtained, with a carboxyl value of 1.6mmol / g of biomass.

[0047] Comparative Example 1

[0048] Take 500g of lignocellulose as the solid material, dissolve 0.03g of TEMPO, 0.3g of NaBr, 14.73g of NaClO, and 5.28g of NaOH in water to prepare a 500g aqueous solution as the liquid material. Set the high-efficiency mixing and shearing equipment temperature to 30°C, the solid-liquid feed mass ratio to 1:1, and the screw speed to 300rpm. Measure the product pH. When the pH is less than 9.5, the adhesive is obtained, with a carboxyl value of 0.4mmol / g of biomass.

[0049] Comparative Example 2

[0050] Take 500g of lignocellulose as the solid material, dissolve 0.03g of TEMPO, 0.3g of NaBr, 24.46g of NaClO, and 5.28g of NaOH in water to prepare a 500g aqueous solution as the liquid material. Set the high-efficiency mixing and shearing equipment temperature to 30°C, the solid-liquid feed mass ratio to 1:1, and the screw speed to 300rpm. Measure the product pH. When the pH is less than 9.5, the adhesive is obtained, with a carboxyl value of 0.8mmol / g of biomass.

[0051] Comparative Example 3

[0052] Take 500g of lignocellulose as the solid material, dissolve 0.03g of TEMPO, 0.3g of NaBr, 73.65g of NaClO, and 5.28g of NaOH in water to prepare a 500g aqueous solution as the liquid material. Set the high-efficiency mixing and shearing equipment temperature to 30°C, the solid-liquid feed mass ratio to 1:1, and the screw speed to 300rpm. Measure the product pH. When the pH is less than 9.5, the adhesive is obtained, with a carboxyl value of 2.0mmol / g of biomass.

[0053] Comparative Example 4

[0054] Take 500g of lignocellulose as the solid material, dissolve 0.03g of TEMPO, 0.3g of NaBr, 139.44g of NaClO, and 5.28g of NaOH in water to prepare a 500g aqueous solution as the liquid material. Set the high-efficiency mixing and shearing equipment temperature to 30°C, the solid-liquid feed mass ratio to 1:1, and the screw speed to 300rpm. Measure the product pH. When the pH is less than 9.5, the adhesive is obtained, with a carboxyl value of 3.02mmol / g of biomass.

[0055] Comparative Example 5

[0056] The same as Example 1, the only difference is that the high-efficiency mixing and shearing equipment is replaced by a stirring device, and the carboxyl value of the obtained adhesive is 0.2 mmol / g biomass.

[0057] Comparative Example 6

[0058] The same as Example 2, except that the high-efficiency mixing and shearing equipment was replaced by a stirring device, and the carboxyl value of the obtained adhesive was 0.2 mmol / g biomass.

[0059] Determination of the adhesive effect of the adhesive: The adhesives obtained in the examples and comparative examples were respectively mixed with a curing agent (1,4-succinic anhydride) in a mass ratio of 1:1, and the pH value was adjusted to 7. 2Three-layer plywood was prepared and tested according to the bonding strength test method described in GB / T 17657-2013. The test results are shown in Table 1. It can be seen that the performance of the adhesives obtained in Examples 1 and 2 meets the strength requirements of Class I and Class II plywood described in GB / T 9846-2015. Theoretically, the higher the degree of oxidation of the adhesive product (the higher the carboxyl content), the more reactive sites there are for reacting with the curing agent, and the stronger the bonding strength. However, the bonding strength is also related to the molecular weight of the adhesive. The oxidizing liquid not only has an oxidizing effect, but also has the effect of degrading cellulose. Although the adhesives of Comparative Examples 3 and 4 have a high degree of oxidation, the degree of degradation of the cellulose is too great, resulting in a decrease in the final bonding strength. The adhesives prepared in the examples of the present invention exhibit good bonding performance when combined with the curing agent within a certain degree of oxidation and degradation. Comparative Examples 5 and 6 show that compared with high-efficiency mixing and shearing equipment, the degree of physical degradation of cellulose by the stirring device is limited. The lignocellulosic biomass still exists in the form of macromolecules, with fewer reactive sites, and the amount of carboxylated cellulose cannot reach the expected amount. Even if the feed is the same as in Example 1 or 2, the bonding strength will deteriorate.

[0060] Table 1 Bonding strength test results of adhesives obtained in Examples and Comparative Examples

[0061] Hot water immersion (MPa) Boil-dry-boil (MPa) Comparative Example 1 0.65±0.09 0.57±0.06 Comparative Example 2 0.76±0.10 0.65±0.8 Example 1 1.26±0.09 1.11±0.24 Example 2 1.27±0.09 0.93±0.05 Comparative Example 3 1.20±0.16 0.71±0.24 Comparative Example 4 0.91±0.20 0.89±0.06 Comparative Example 5 0.62±0.12 0.35±0.08 Comparative Example 6 0.72±0.20 0.41±0.09

[0062] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation thereto. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications shall also be considered within the scope of protection of the present invention.

Claims

1. A method for modifying lignocellulose, characterized in that: The following steps are involved: The lignocellulose is mixed with an oxidizing solution and sheared to perform a modification treatment. The oxidizing solution comprises 2,2,6,6-tetramethylpiperidinyl oxide, NaBr, NaClO, NaOH and water. The mass ratio of 2,2,6,6-tetramethylpiperidinyl oxide, NaBr, NaClO and NaOH in the oxidizing solution is 0.03:0.3:40-70:5.

28.

2. The method for modifying lignocellulose according to claim 1, wherein: The mass ratio of 2,2,6,6-tetramethylpiperidinyl oxide, NaBr, NaClO and NaOH in the oxidation solution is 0.03:0.3:44.19-69.72:5.

28.

3. The method for modifying lignocellulose according to claim 1 or 2, characterized in that: The mixing and shearing temperature is room temperature to 40° C., the solid-liquid feed mass ratio is 1:0.5 to 1.5, and the screw speed is 250 to 300 rpm.

4. The method for modifying lignocellulose according to claim 1 or 2, characterized in that: The pH value of the system obtained after the modification treatment is completed is less than 9.

5.

5. The method for modifying lignocellulose according to claim 1, wherein: The lignocellulose includes one or more of cotton stalks, soybean straws, pomace, bagasse and walnut shells.

6. The method for modifying lignocellulose according to claim 1 or 5, characterized in that: The particle size of the wood cellulose is 200-250 μm, and the solid content is 33 wt %.

7. An adhesive, characterized in that: The cellulose fiber is prepared by the lignocellulose modification method according to any one of claims 1 to 6.

8. The adhesive according to claim 7, characterized in that The carboxyl value of the adhesive is 1.2 to 1.6 mmol / g of carboxylated lignocellulosic biomass.

9. Use of the adhesive according to claim 7 in the field of adhesion.

10. The use according to claim 9, characterized in that The following steps are involved: The adhesive and the curing agent are mixed and then bonded, and the mass ratio of the adhesive to the curing agent is 1:1.