A cellulose-based adhesive and a method for preparing the same

Abstract

The application provides a cellulose-based adhesive and a preparation method thereof, and the preparation method comprises the following steps: S1, pretreating plant fibers by using an alkali solution to obtain an intermediate with exposed fluff on the surface; the pretreatment comprises soaking the plant fibers at low temperature by using the alkali solution, taking out the soaked plant fibers, and filtering out the alkali solution after the plant fibers are restored to room temperature; S2, soaking the intermediate by using a divalent metal ion halide solution to obtain a cellulose-based adhesive with a water content of 13% to 18%. The cellulose-based adhesive is obtained by the preparation method. The cellulose-based adhesive prepared by the application has higher water retention capacity while ensuring appropriate bonding strength.

Description

Technical Field

[0001] This invention relates to the field of cellulose material application technology, specifically to a cellulose-based adhesive and its preparation method. Background Technology

[0002] Adhesives possess strong bonding power, bonding objects together through adhesion, and are widely used in daily life. However, most adhesives currently sold on the market are aldehyde-based and resin-based, which can cause certain harm to human health and the environment with long-term use. Therefore, providing a healthy and environmentally friendly cellulose-based adhesive is particularly important.

[0003] Currently, research has identified a highly efficient and rapid binding adhesive scheme using an aqueous solution of nanocellulose crystals. This scheme achieves directional and ordered arrangement of nanocellulose crystals through induced evaporation, leveraging intercrystalline interactions to achieve strong bonding and provide directional, robust adhesion. While this research innovatively uses nanocellulose as the main component of the binding adhesive, its high cost and complex preparation process limit its further application. Furthermore, cellulose-based materials have insufficient water retention, easily drying out in air, which reduces the adhesive strength and can even cause the binding adhesive to fail.

[0004] In summary, there is an urgent need for a low-cost, simple-to-prepare cellulose-based adhesive and its preparation method that can adjust water retention capacity. Summary of the Invention

[0005] The present invention aims to provide a cellulose-based adhesive and its preparation method, the specific technical solution of which is as follows:

[0006] In a first aspect, the present invention provides a method for preparing a cellulose-based adhesive, comprising the following steps:

[0007] Step S1: Pre-treat the plant fibers with an alkaline solution to obtain an intermediate with exposed fluffy surfaces; the pre-treatment includes soaking the plant fibers in an alkaline solution at low temperature, removing the soaked plant fibers, restoring them to room temperature, and filtering out the alkaline solution.

[0008] The alkaline solution has a molar concentration of 0.06 to 0.08 mol / L, the mass ratio of the alkaline solution to the plant fiber is 20:1 to 25:1, the soaking temperature is -30℃ to -18℃, and the soaking time is 2 to 4 hours.

[0009] Step S2: The intermediate is treated by soaking in a divalent metal ion halide solution to obtain a cellulose-based adhesive with a moisture content of 13% to 18%.

[0010] The molar concentration of the divalent metal ion halide solution is 0.05-0.15 mol / L, the soaking temperature is -30℃ to -18℃, and the soaking time is 2 to 6 hours.

[0011] Optionally, in step S2, the divalent metal ion halide solution includes at least one of a divalent calcium ion halide solution, a divalent magnesium ion halide solution, and a divalent zinc ion halide solution.

[0012] Optionally, the divalent calcium ion halide solution is a CaCl2 solution.

[0013] Optionally, the divalent magnesium ion halide solution is a MgCl2 solution.

[0014] Optionally, the divalent zinc ion halide solution is a ZnCl2 solution.

[0015] Optionally, in step S1, the preprocessing is performed at least twice.

[0016] Optionally, in step S1, the alkaline solution is a strong alkaline solution; the strong alkaline solution includes at least one of NaOH solution and KOH solution.

[0017] Optionally, the plant fiber comprises broken or unbroken plant cells.

[0018] Optionally, the preparation method of the cellulose-based adhesive further includes step S3, cleaning the cellulose-based adhesive with a cleaning agent; the cleaning agent includes at least one of deionized water and ethanol.

[0019] In a second aspect, the present invention provides a cellulose-based adhesive, which is prepared by the method for preparing the cellulose-based adhesive.

[0020] The application of the technical solution of the present invention has at least the following beneficial effects:

[0021] (1) The preparation method of the cellulose-based adhesive described in this invention is low-cost, simple in preparation process, and can adjust water retention capacity. Specifically, this invention uses step S1 to pretreat plant fibers to obtain an intermediate with exposed villous surface, which facilitates increasing the contact area and exposing more cellulose hydroxyl groups; step S2 is used to soak the intermediate, so that divalent metal ions combine with cellulose hydroxyl groups to form a cellulose-based adhesive containing a cellulose hydroxyl-metal cation-cellulose hydroxyl structure, ensuring the retention rate of divalent metal ions in the cellulose-based adhesive, and the combined divalent metal ions can reversibly combine with water molecules, realizing real-time control of moisture in the cellulose-based adhesive, improving the water retention capacity of the cellulose-based adhesive, ensuring that the moisture content of the cellulose-based adhesive is 13% to 18%, preventing the cellulose-based adhesive from drying out due to water loss, reducing adhesion, or even failing; at the same time, when the moisture content of the cellulose-based adhesive is 13% to 18%, the corresponding adhesive strength is about 1.2 MPa, indicating that the cellulose-based adhesive has high adhesive strength.

[0022] Furthermore, due to steric hindrance, not all of the multiple coordination sites of divalent metal ions are occupied by cellulose hydroxyl groups, resulting in some coordination vacancies. These vacant sites are then occupied by lone pairs of electrons on oxygen atoms in water molecules, forming reversible coordination bonds between water molecules and divalent metal ions. When cellulose-based adhesives lose water, these coordination bonds dissociate to replenish the lost water. Simultaneously, the divalent metal ions can further absorb water molecules from the air, enhancing the water retention capacity of the cellulose-based adhesive and ensuring a moisture content of 13%–18%. This prevents the adhesive from drying out due to water loss, reducing its tackiness, or even becoming ineffective.

[0023] Furthermore, the principle behind the adhesive strength of the cellulose-based adhesive in this invention is as follows:

[0024] Plant fibers treated with alkali solution expose a fresh, fluffy surface. This surface has abundant hydroxyl structures, which bond together with each other via hydrogen bonds during the bonding process, providing adhesive force. At the same time, these fluffy fiber surface structures interlock and entwine with each other upon contact, forming a tooth-like structure that further enhances the bonding force.

[0025] (2) The CaCl2 solution, MgCl2 solution and ZnCl2 solution used in this invention have the following technical effects: on the one hand, the presence of chloride ions can avoid the hydrolysis of divalent metal ions and ensure the stability of divalent metal ions; on the other hand, stable divalent metal ions can provide multiple coordination sites to ensure the water retention capacity of cellulose-based adhesives; furthermore, CaCl2 solution, MgCl2 solution and ZnCl2 solution have good solubility and low price, and are highly practical.

[0026] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0028] Figure 1 This is a tensile SEM image of the cellulose-based adhesive structure prepared in Example 1 of the present invention. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art are within the scope of protection of the present invention.

[0030] Example 1:

[0031] A method for preparing a cellulose-based adhesive includes the following steps:

[0032] Step S1: The plant fiber (including cell-wall broken or non-cell-wall broken plant (derived from cotton) cells) is pretreated three times with an alkaline solution (specifically NaOH solution) to obtain an intermediate with exposed villi on the surface; the pretreatment includes soaking the plant fiber in the alkaline solution at low temperature, and taking out the soaked plant fiber, restoring it to room temperature, and filtering out the alkaline solution.

[0033] The alkaline solution has a molar concentration of 0.07 mol / L, the mass ratio of the alkaline solution to the plant fiber is 20:1, the soaking temperature is -18℃, and the soaking time (i.e., freezing time) is 4 hours.

[0034] Step S2: The intermediate is soaked in a divalent metal ion halide solution (specifically CaCl2 solution) to obtain a cellulose-based adhesive with a moisture content of 15%.

[0035] The molar concentration of the divalent metal ion halide solution is 0.1 mol / L, the immersion temperature is -18℃, and the immersion time (i.e., freezing time) is 4 hours.

[0036] Step S3: Clean the surface of the cellulose-based adhesive of residual chemicals using a cleaning agent (specifically deionized water).

[0037] Example 2:

[0038] Unlike Example 1, in step S1, the plant fiber is derived from wood, the alkaline solution is KOH solution, and the soaking time is 3 hours; in step S2, the divalent metal ion halide solution is MgCl2 solution.

[0039] Example 3:

[0040] Unlike Example 1, in step S1, the plant fiber is derived from wheat straw, the alkaline solution is a 0.35 mol / L KOH solution and a 0.35 mol / L NaOH solution, the mass ratio of the alkaline solution to the plant fiber is 25:1, the soaking temperature is -25℃, and the soaking time is 2 hours; in step S2, the divalent metal ion halide solution is a ZnCl2 solution.

[0041] Comparative Example 1:

[0042] Unlike Example 1, a 0.1 mol / L calcium nitrate solution was used instead of the divalent metal ion halide solution in step S2.

[0043] Comparative Example 2:

[0044] Unlike Example 1, in step S2, the molar concentration of the divalent metal ion halide solution is 0.04 mol / L.

[0045] Comparative Example 3:

[0046] Unlike Example 1, in step S2, the molar concentration of the divalent metal ion halide solution is 0.16 mol / L.

[0047] Comparative Example 4:

[0048] Unlike Example 1, in step S2, the soaking temperature is -13°C.

[0049] Comparative Example 5:

[0050] Unlike Example 1, in step S2, the soaking temperature is -35°C.

[0051] Comparative Example 6:

[0052] Unlike Example 1, in step S2, the soaking time is 1 hour.

[0053] Comparative Example 7:

[0054] Unlike Example 1, in step S2, the soaking time is 7 hours.

[0055] Comparative Example 8:

[0056] Purchase commercially available hydroxypropyl methylcellulose-based adhesive, 100 mesh fineness, manufactured by Jinzhou Shunyue Building Materials Technology Co., Ltd.

[0057] Comparative Example 9:

[0058] Purchase commercially available acrylic adhesive, model XL-188, manufactured by Kunshan Haruo Hardware Manufacturing Co., Ltd.

[0059] Comparative Example 10:

[0060] Purchase commercially available white glue, model DCBRJ, manufactured by Hefei Bozhilai Trading Co., Ltd.

[0061] The cellulose-based adhesives prepared in Examples 1-3 and Comparative Examples 1-7, and the commercially available products in Comparative Examples 8-10, were tested for bond strength against rigid materials according to GB / T2790—1995 Adhesives 180° Peel Strength Test Method. The test results are shown in Table 1. Additionally, the moisture content of the cellulose-based adhesives prepared in Examples 1-3 and Comparative Examples 1-7 was tested. The test results are shown in Table 1. The moisture content test method was as follows: A test sample weighing M1 was placed in an oven at 105°C. For the first 4 hours, the weight of the test sample was measured every 30 minutes. After 4 hours, the weight was measured every 1 hour until the weight change of the test sample was less than 0.001g. The weight M2 of the test sample at this point was then measured. The moisture content of the test sample was calculated using (M1-M2) / M1.

[0062] Table 1. Test results of bond strength and moisture content

[0063]

[0064]

[0065] From the data in Table 1, we know that:

[0066] Compared to Comparative Example 1 which uses calcium nitrate, the cellulose-based adhesives prepared in Examples 1-3 of this invention have the advantage of low cost while ensuring suitable bonding strength and water retention capacity.

[0067] Compared to Comparative Examples 2-10, the cellulose-based adhesives prepared in Examples 1-3 of this invention not only ensure suitable bonding strength but also have high water retention capacity, maintaining a moisture content of 13% to 18%. This prevents the cellulose-based adhesives from drying out due to water loss, reducing their stickiness, or even failing.

[0068] Specifically, in Comparative Example 2, when the molar concentration of the divalent metal ion halide solution was reduced, the cellulose-based adhesive prepared had a lower water retention capacity, maintaining the moisture content at 6.5%.

[0069] In Comparative Example 3, when the molar concentration of the divalent metal ion halide solution was increased, the prepared cellulose-based adhesive exhibited high water retention capacity, maintaining a moisture content of 17.8%; however, the corresponding bond strength did not increase significantly. Therefore, from a cost perspective, increasing the molar concentration of the divalent metal ion halide solution is not recommended.

[0070] In Comparative Example 4, when the soaking temperature in step S2 was increased, the cellulose-based adhesive prepared thereby had a lower water retention capacity, resulting in a moisture content of 10.0%.

[0071] In Comparative Example 5, when the soaking temperature in step S2 was reduced, the cellulose-based adhesive prepared thereby had a lower water retention capacity, resulting in a moisture content of 5.8%.

[0072] This indicates that raising or lowering the soaking temperature in step S2 will reduce the water retention capacity of the cellulose-based adhesive. The reason may be that using too high or too low a soaking temperature in step S2 is not conducive to the combination of divalent metal ions and cellulose hydroxyl groups, thereby reducing the water retention capacity of the cellulose-based adhesive.

[0073] In Comparative Example 6, when the soaking time in step S2 was reduced, the cellulose-based adhesive prepared had a lower water retention capacity, resulting in a moisture content of 7.6%.

[0074] In Comparative Example 7, when the soaking time in step S2 was increased, the cellulose-based adhesive prepared had a higher water retention capacity, maintaining the moisture content at 23.5%; however, excessive moisture content would reduce the bonding strength.

[0075] Depend on Figure 1 As can be seen in the tensile SEM image of the cellulose-based adhesive structure prepared in Example 1, the fibers at the non-fractured parts exhibit a dense structure of twisted entanglement; while at the fractured parts, the fibers are pulled out and broken, which is also proof of the interlocking and entanglement of fibers. A fluffy structure can also be observed on the surface of the fractured fibers.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a cellulose-based adhesive, characterized in that, Includes the following steps: Step S1: Pre-treat the plant fibers with an alkaline solution to obtain an intermediate with exposed fluffy surfaces; the pre-treatment includes soaking the plant fibers in an alkaline solution at low temperature, removing the soaked plant fibers, restoring them to room temperature, and filtering out the alkaline solution. The alkaline solution has a molar concentration of 0.06 to 0.08 mol / L, the mass ratio of the alkaline solution to the plant fiber is 20:1 to 25:1, the soaking temperature is -30℃ to -18℃, and the soaking time is 2 to 4 hours. Step S2: The intermediate is treated by soaking in a divalent metal ion halide solution to obtain a cellulose-based adhesive with a moisture content of 13% to 18%. The molar concentration of the divalent metal ion halide solution is 0.05-0.15 mol / L, the soaking temperature is -30℃ to -18℃, and the soaking time is 2 to 6 hours.

2. The method for preparing the cellulose-based adhesive according to claim 1, characterized in that, In step S2, the divalent metal ion halide solution includes at least one of divalent calcium ion halide solution, divalent magnesium ion halide solution, and divalent zinc ion halide solution.

3. The method for preparing the cellulose-based adhesive according to claim 2, characterized in that, The divalent calcium ion halide solution is a CaCl2 solution.

4. The method for preparing the cellulose-based adhesive according to claim 2, characterized in that, The divalent magnesium ion halide solution is a MgCl2 solution.

5. The method for preparing the cellulose-based adhesive according to claim 2, characterized in that, The divalent zinc ion halide solution is a ZnCl2 solution.

6. The method for preparing the cellulose-based adhesive according to claim 1, characterized in that, In step S1, the preprocessing is performed at least twice.

7. The method for preparing the cellulose-based adhesive according to claim 1, characterized in that, In step S1, the alkaline solution is a strong alkaline solution; the strong alkaline solution includes at least one of NaOH solution and KOH solution.

8. The method for preparing the cellulose-based adhesive according to claim 1, characterized in that, The plant fibers comprise plant cells, either with or without broken cell walls.

9. The method for preparing the cellulose-based adhesive according to any one of claims 1-8, characterized in that, The method also includes step S3, which involves cleaning the cellulose-based adhesive with a cleaning agent, wherein the cleaning agent includes at least one of deionized water and ethanol.

10. A cellulose-based adhesive, characterized in that, It was prepared using the method for preparing cellulose-based adhesives as described in claim 9.

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