Method for gluing and forming high-moisture bamboo

Abstract

This invention discloses a method for gluing and molding bamboo with high moisture content. Polyvinyl alcohol (PVA) is dissolved in deionized water, then a dispersant is added and stirred until dissolved. A plasticizer is then added and stirred until dissolved to obtain a modified PVA adhesive. Two pieces of bamboo with a moisture content of 40-70% are taken for gluing. The modified PVA adhesive is applied to the gluing surface of one piece of bamboo. The other piece of bamboo is immersed in a mixed solution of boric acid and sodium citrate. After immersion and drying, the two pieces of bamboo are joined together and pressed into shape using a press. Compared with existing methods, this method significantly improves the interfacial bonding performance between bamboo and the adhesive, enhances the adhesive strength, and significantly improves the gluing strength and water resistance of bamboo in humid environments. It also shortens the curing time, providing an efficient, environmentally friendly, and cost-effective solution for gluing bamboo with high moisture content.

Description

Technical Field

[0001] This invention relates to a method for gluing and molding bamboo with high moisture content, belonging to the field of bamboo processing technology. Background Technology

[0002] Thinly sliced ​​bamboo, as an important deep-processed bamboo product, has attracted increasing attention due to its unique physical and chemical properties and is widely used in furniture manufacturing, interior decoration, and construction. In the slicing process of bamboo engineered timber, controlling the moisture content of the bamboo is a crucial step. Traditional processing methods require reducing the moisture content of the bamboo to a certain level before bonding it with urea-formaldehyde resin adhesive. Although urea-formaldehyde resin adhesive has good bonding properties and a fast curing speed, making it suitable for industrial production, its water and heat resistance after curing is poor, and it is prone to cracking under high temperature and humidity conditions, resulting in insufficient bonding at the adhesive interface. Furthermore, the slicing process for thinly sliced ​​bamboo requires increasing the moisture content of the bamboo for slicing. Currently, adjusting the moisture content of bamboo in processing methods is not only time-consuming and energy-intensive but may also lead to bamboo waste and high labor costs.

[0003] To address the aforementioned issues, Chinese invention patent CN118081933A discloses a method for processing bamboo strips with high moisture content. This method involves finely planing the bamboo strips and then radially slicing them. The resulting thin sliced ​​bamboo skin is then toughened through atmospheric pressure impregnation and subsequently dried, resulting in a final bamboo skin with a moisture content of 12%. While this method simplifies the steps for controlling the moisture content of bamboo and improves the processing performance of the bamboo strips to some extent, it does not effectively address the need for gluing bamboo with high moisture content during the gluing process.

[0004] The abundant -OH groups in polyvinyl alcohol (PVA) endow it with excellent hydrophilicity, a property that makes it uniquely suitable for bamboo bonding applications with high moisture content. In applications where bamboo itself has a high moisture content, ordinary adhesives are difficult to spread and penetrate effectively on the moist bamboo surface. However, PVA, with its numerous -OH groups, can form hydrogen bonds with the hydroxyl groups on the bamboo surface, thereby enhancing the bonding force between the adhesive and the bamboo and achieving a better bonding effect.

[0005] Based on the aforementioned research background, the applicant selected polyvinyl alcohol (PVA) as an adhesive for bamboo bonding experiments. Experimental results showed that the bonding strength of bamboo using PVA adhesive reached 0.7 MPa, meeting the basic requirements for bonding. However, in practical applications, PVA adhesive still has shortcomings. During bamboo bonding, due to the strong intermolecular forces between PVA molecular chains, some -OH groups are encapsulated within the molecular chains and cannot fully react with the hydroxyl groups on the bamboo surface, resulting in only surface-layer -OH groups participating in the bonding reaction. This limitation of surface reaction leads to insufficiently strong and uniform bonding at the bonding interface, ultimately resulting in unsatisfactory strength and water resistance of the bonded material. This is mainly reflected in its low bonding strength, relatively poor water resistance, and long curing time, which to some extent limits its widespread application in bonding bamboo with high moisture content. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a bonding method for bamboo with high moisture content, which significantly improves the interfacial bonding performance between bamboo and adhesive, enhances the bonding strength of adhesive, and significantly improves the bonding strength and water resistance of bamboo in humid environments, while shortening the curing time. This provides an efficient, environmentally friendly and cost-effective solution for bonding bamboo with high moisture content.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for gluing and molding bamboo with high moisture content, comprising the following steps:

[0009] (1) Dissolve polyvinyl alcohol in deionized water, then add dispersant, stir to dissolve, then add plasticizer, stir to dissolve, and obtain modified PVA adhesive.

[0010] (2) Take two pieces of bamboo with a moisture content of 40-70% to be glued. Apply modified PVA adhesive to the gluing surface of one piece of bamboo. Soak the other piece of bamboo in a mixed solution of boric acid and sodium citrate. After the soaking, take it out and let it dry. Then, put the two pieces of bamboo together and press them into shape in a press.

[0011] Furthermore, in step (1), the degree of polymerization of the polyvinyl alcohol is 1700-2400, and the degree of hydrolysis is 87%-99%. This polyvinyl alcohol has good water solubility and film-forming properties, which can provide excellent matrix properties for adhesives, ensuring good adhesion and film-forming effect on a variety of substrates.

[0012] Furthermore, in step (1), the modified PVA adhesive has a polyvinyl alcohol mass concentration of 8-12%, a dispersant mass concentration of 0.5-3%, and a plasticizer mass concentration of 10-15%.

[0013] Furthermore, in step (1), the dispersant is polyvinylpyrrolidone (PVP). PVP is a synthetic polymeric surfactant with good surface activity and dispersing properties. It can effectively reduce the surface tension of the system, promote uniform dispersion among the components, and thus improve the stability and adhesive properties of the adhesive.

[0014] Further, in step (1), the plasticizer is either glycerol or ethylene glycol. Glycerol is more preferred, as it is a naturally sourced polyol with good compatibility and plasticizing efficiency, significantly improving the flexibility of the adhesive and enhancing its adaptability to different substrates. The addition of glycerol can lower the glass transition temperature of PVA, improving its flexibility and ductility at low temperatures while maintaining good adhesive properties.

[0015] Furthermore, in step (2), the concentration of boric acid in the mixed solution of boric acid and sodium citrate is 0.25-0.5 mol / L, and the concentration of sodium citrate is 0.25-0.5 mol / L.

[0016] The addition of sodium citrate alters the arrangement of PVA molecular chains, disrupting the PVA's own hydrogen bond network and reducing the intermolecular forces. Hydroxyl groups that might have been encapsulated or strongly interacted form a loose aggregated structure due to the rearrangement of the molecular chains. Boric acid can undergo a cross-linking reaction with the hydroxyl groups on the PVA molecular chains, forming a stable boron-oxygen bond network structure, thereby significantly enhancing the mechanical strength and water resistance of PVA.

[0017] Furthermore, in step (2), the coating amount is 200-400 g / m². 2 .

[0018] Furthermore, in step (2), the pressing pressure is 0.5-1.5 MPa and the time is 40-60 min.

[0019] The beneficial effects of this invention are:

[0020] 1) This invention provides a bonding method for bamboo with high moisture content. The bamboo is pretreated with a mixed solution of boric acid and sodium citrate, and then bonded to a bamboo surface coated with a modified PVA adhesive. An in-situ reaction occurs on the bonded surface. During this process, sodium citrate disrupts the hydrogen bond network of PVA, reducing the intermolecular forces and causing the hydroxyl groups on the surface to form a loose aggregated structure due to the rearrangement of the molecular chains. Simultaneously, boric acid reacts with the hydroxyl groups on the PVA molecular chains to form a stable boron-oxygen bond network structure. This dual-action mechanism significantly improves the interfacial bonding performance between bamboo and the adhesive, enhances the adhesive strength, and significantly improves the bonding strength and water resistance of bamboo in humid environments, while shortening the curing time. This provides an efficient, environmentally friendly, and cost-effective solution for bonding bamboo with high moisture content.

[0021] 2) The method of the present invention can achieve effective bonding of materials, thereby avoiding the strict control of the moisture content of bamboo in the traditional processing process, optimizing the process to improve the production efficiency of slicing thin bamboo, and reducing energy consumption and cost. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments.

[0023] In the following examples and comparative examples, the degree of polymerization of polyvinyl alcohol used was 1700-2400 and the degree of alcoholysis was 87%-99%; the bamboo used was all bamboo strips (2000mm in length, 10mm in width, and 5mm in thickness) cut from newly felled round bamboo with a moisture content of 60%, but not limited to these.

[0024] Comparative Example 1

[0025] A method for gluing and molding bamboo with high moisture content, comprising the following steps:

[0026] (1) Dissolve polyvinyl alcohol in deionized water, stir thoroughly to dissolve, and prepare a PVA solution with a mass concentration of 10% as a PVA adhesive;

[0027] (2) Take two bamboo strips to be glued, and apply PVA adhesive to the gluing surfaces of the two bamboo strips respectively, with an adhesive application amount of 300g / m². 2 Two bamboo strips are spliced ​​together and placed in a press. They are pressed for 45 minutes at a pressure of 1.0 MPa and room temperature to obtain side-pressed bamboo boards.

[0028] This comparative example uses pure polyvinyl alcohol solution as adhesive, which can meet the bonding requirements. The adhesive has strong fluidity during the application process and a curing time of 16 hours.

[0029] Tests were conducted according to the methods in the national standard GB / T17657-2022, and the bond strength was measured to be 0.7 MPa, with a second-class impregnation peel thickness of 10 mm. The surface was sprayed with water before the planing process, allowing for subsequent planing operations, but cracking occurred.

[0030] Comparative Example 2

[0031] A method for gluing and molding bamboo with high moisture content, comprising the following steps:

[0032] (1) Dissolve polyvinyl alcohol in deionized water, then add dispersant polyvinylpyrrolidone, stir to dissolve, then add plasticizer glycerin, stir to dissolve, and obtain modified PVA adhesive. In the modified PVA adhesive, the mass concentration of polyvinyl alcohol is 10%, the mass concentration of dispersant is 1%, and the mass concentration of plasticizer is 12%.

[0033] (2) Take two bamboo strips to be glued, and apply modified PVA adhesive to the gluing surface of one of the bamboo strips. The amount of adhesive applied is 300g / m². 2 Another bamboo strip is immersed in a 0.5 mol / L sodium citrate solution for 10 minutes. After that, it is taken out and dried. The two bamboo strips are spliced ​​together and placed in a press. They are pressed at a pressure of 1.0 MPa and room temperature for 45 minutes to obtain a side-pressed bamboo board.

[0034] In this comparative example, a combination of sodium citrate impregnation and modified PVA adhesive was used to achieve bonding, with a curing time of 12 hours.

[0035] Tests were conducted according to the methods in the national standard GB / T17657-2022, and the bond strength was measured to be 1.52 MPa. No peeling occurred in the Class II immersion peel test. The surface was sprayed with water before the planing process, but slight cracking occurred during subsequent planing.

[0036] Comparative Example 3

[0037] A method for gluing and molding bamboo with high moisture content, comprising the following steps:

[0038] (1) Dissolve polyvinyl alcohol in deionized water, then add dispersant polyvinylpyrrolidone, stir to dissolve, then add plasticizer glycerin, stir to dissolve, and obtain modified PVA adhesive. In the modified PVA adhesive, the mass concentration of polyvinyl alcohol is 10%, the mass concentration of dispersant is 1%, and the mass concentration of plasticizer is 12%.

[0039] (2) Take two bamboo strips to be glued, and apply modified PVA adhesive to the gluing surface of one of the bamboo strips. The amount of adhesive applied is 300g / m². 2Another bamboo strip is immersed in a 0.5 mol / L boric acid solution for 10 minutes. After that, it is taken out and dried. The two bamboo strips are spliced ​​together and placed in a press. They are pressed at a pressure of 1.0 MPa and room temperature for 45 minutes to obtain a side-pressed bamboo board.

[0040] In this comparative example, a combination of boric acid impregnation and modified PVA adhesive was used to achieve bonding, with a curing time of 12 hours.

[0041] Tests were conducted according to the methods in the national standard GB / T17657-2022, and the bond strength was measured to be 1.02 MPa, with a second-class impregnation peel length of 4.3 mm. The surface was sprayed with water before the planing process, but cracking occurred during subsequent planing.

[0042] Example 1

[0043] A method for gluing and molding bamboo with high moisture content, comprising the following steps:

[0044] (1) Dissolve polyvinyl alcohol in deionized water, then add dispersant polyvinylpyrrolidone, stir to dissolve, then add plasticizer glycerin, stir to dissolve, and obtain modified PVA adhesive. In the modified PVA adhesive, the mass concentration of polyvinyl alcohol is 10%, the mass concentration of dispersant is 1%, and the mass concentration of plasticizer is 12%.

[0045] (2) Take two bamboo strips to be glued, and apply modified PVA adhesive to the gluing surface of one of the bamboo strips. The amount of adhesive applied is 300g / m². 2 Another bamboo strip is immersed in a mixed solution of boric acid and sodium citrate (the concentration of boric acid in the mixed solution is 0.5 mol / L and the concentration of sodium citrate is 0.5 mol / L) for 10 minutes. After that, it is taken out and dried. The two bamboo strips are spliced ​​together and placed in a press. They are pressed at a pressure of 1.0 MPa and room temperature for 45 minutes to obtain side-pressed bamboo board.

[0046] Using the method of this embodiment, bonding can be achieved, and the curing time can reach 5 hours.

[0047] Tests were conducted according to the methods in the national standard GB / T17657-2022. The bond strength was measured to be 3.97 MPa, with a wood breakage rate exceeding 60% (wood breakage rate refers to the percentage of the total area of ​​wood remaining on the fractured surface of the specimen to the shear area of ​​the specimen during bond strength testing. It is an important indicator for evaluating the bonding quality of wood-bonded products; a higher wood breakage rate indicates a larger proportion of failure occurring in the wood area, and in this case, the bond strength is higher than the strength of the wood itself, indicating better bonding quality). No peeling occurred in the Class II immersion peeling test. The surface was sprayed with water before planing, allowing subsequent planing operations to proceed without cracking.

[0048] Example 2

[0049] A method for gluing and molding bamboo with high moisture content, comprising the following steps:

[0050] (1) Polyvinyl alcohol is dissolved in deionized water, then dispersant polyvinylpyrrolidone is added, and after stirring and dissolving, plasticizer glycerin is added and stirred and dissolved to obtain modified PVA adhesive. In the modified PVA adhesive, the mass concentration of polyvinyl alcohol is 10%, the mass concentration of dispersant is 1%, and the mass concentration of plasticizer is 12%.

[0051] (2) Take two bamboo strips to be glued, and apply modified PVA adhesive to the gluing surface of one of the bamboo strips. The amount of adhesive applied is 300g / m². 2 Another bamboo strip is immersed in a mixed solution of boric acid and sodium citrate (the concentration of boric acid in the mixed solution is 0.5 mol / L and the concentration of sodium citrate is 0.25 mol / L) for 10 minutes. After that, it is taken out and dried. The two bamboo strips are spliced ​​together and placed in a press. They are pressed at a pressure of 1.0 MPa and room temperature for 45 minutes to obtain side-pressed bamboo board.

[0052] Using the method of this embodiment, bonding can be achieved, and the curing time can reach 8 hours.

[0053] Tests were conducted according to the methods in the national standard GB / T17657-2022. The bond strength was measured to be 2.697 MPa, and the wood breakage rate reached 40%. No peeling occurred in the Class II impregnation peeling test. The surface was sprayed with water before the planing process, allowing subsequent planing operations to proceed without any cracking.

[0054] Example 3

[0055] A method for gluing and molding bamboo with high moisture content, comprising the following steps:

[0056] (1) Dissolve polyvinyl alcohol in deionized water, then add dispersant polyvinylpyrrolidone, stir to dissolve, then add plasticizer glycerin, stir to dissolve, and obtain modified PVA adhesive. In the modified PVA adhesive, the mass concentration of polyvinyl alcohol is 10%, the mass concentration of dispersant is 1%, and the mass concentration of plasticizer is 12%.

[0057] (2) Take two bamboo strips to be glued, and apply modified PVA adhesive to the gluing surface of one of the bamboo strips. The amount of adhesive applied is 300g / m². 2 Another bamboo strip is immersed in a mixed solution of boric acid and sodium citrate (the concentration of boric acid in the mixed solution is 0.25 mol / L and the concentration of sodium citrate is 0.5 mol / L) for 10 minutes. After that, it is taken out and dried. The two bamboo strips are spliced ​​together and placed in a press. They are pressed at a pressure of 1.0 MPa and room temperature for 45 minutes to obtain a side-pressed bamboo board.

[0058] Using the method of this embodiment, bonding can be achieved, and the curing time can reach 7 hours.

[0059] Tests were conducted according to the methods in the national standard GB / T17657-2022. The bond strength was measured to be 3.13 MPa, and the wood breakage rate exceeded 60%. No peeling occurred in the Class II impregnation peeling test. The surface was sprayed with water before the planing process, allowing subsequent planing operations to proceed without any cracking.

Claims

1. A method for gluing and molding high moisture content bamboo, characterized in that, Includes the following steps: (1) Dissolve polyvinyl alcohol in deionized water, then add dispersant, stir to dissolve, then add plasticizer, stir to dissolve, and obtain modified PVA adhesive; (2) Take two pieces of bamboo with a moisture content of 40-70% to be glued. Apply modified PVA adhesive to the glued surface of one piece of bamboo. Soak the other piece of bamboo in a mixed solution of boric acid and sodium citrate. After the soaking, take it out and dry it. Then put the two pieces of bamboo together and press them into shape in a press. In step (1), the dispersant is polyvinylpyrrolidone, and the plasticizer is either glycerol or ethylene glycol; in the modified PVA adhesive, the mass concentration of polyvinyl alcohol is 8-12%, the mass concentration of the dispersant is 0.5-3%, and the mass concentration of the plasticizer is 10-15%. In step (2), the concentration of boric acid in the mixed solution of boric acid and sodium citrate is 0.25-0.5 mol / L, and the concentration of sodium citrate is 0.25-0.5 mol / L.

2. The gluing and molding method for high moisture content bamboo as described in claim 1, characterized in that, In step (1), the degree of polymerization of the polyvinyl alcohol is 1700-2400 and the degree of hydrolysis is 87%-99%.

3. The gluing and molding method for high moisture content bamboo as described in claim 1, characterized in that, In step (2), the coating amount of modified PVA adhesive is 200-400 g / m².

4. The gluing and molding method for high moisture content bamboo as described in claim 1, characterized in that, In step (2), the pressing pressure is 0.5-1.5 MPa and the time is 40-60 min.