Production method of low-formaldehyde high-strength eucalyptus bamboo mortise and tenon joint boards

Abstract

The invention discloses a production method of a low-formaldehyde and high-strength eucalyptus bamboo mortise and tenon splicing board. The splicing board is obtained by splicing and assembling a plurality of eucalyptus mortise and tenon strips and a plurality of bamboo mortise and tenon strips, and then pasting a surface layer on both sides. The left and right sides of the eucalyptus mortise and tenon strips are correspondingly provided with convex mortise and concave mortise strips. The bamboo mortise and tenon strips are composited by pasting a plurality of bamboo strips. The bamboo strips are then rotated 90 degrees to the side and cut into bamboo mortise and tenon strips with the same thickness as the diameter of the eucalyptus core. The left and right sides of the bamboo mortise and tenon strips are also correspondingly provided with convex mortise and concave mortise strips. One or more bamboo mortise and tenon strips are spliced ​​with mortise and tenon strips between two or more adjacent eucalyptus core mortise and tenon strips. The adhesive of the eucalyptus bamboo mortise and tenon splicing board adopts a modified urea-formaldehyde resin adhesive. The eucalyptus bamboo mortise and tenon splicing board of the invention has high bending strength, is not easy to twist and deform, and its volatile formaldehyde meets the national first-class wood board standard. It has good mildew resistance and antibacterial effect and is suitable for use as indoor office cabinets, furniture, floors and other boards.

Description

Technical Field

[0001] The invention belongs to the technical field of artificial boards, and particularly relates to a production method of a eucalyptus bamboo mortise and tenon joint board which is low in formaldehyde, high in strength, and mildew and corrosion resistant. Background Art

[0002] my country has numerous veneer and plywood manufacturers, with eucalyptus being the primary raw material. Strong market demand has led to its widespread use. Eucalyptus is typically processed by rotary-slicing logs into veneers, which are then dried and bonded together with adhesive to form multi-layer boards. These boards are commonly used in the production of furniture, office supplies, flooring, and other products. After rotary-slicing, only a round wood core, approximately 20-30 mm in diameter, remains. This core is often used as a mop handle, hoe handle, or firewood. Due to its limited usefulness, the remaining core after veneer processing has increased significantly, resulting in a significant waste of resources.

[0003] Due to environmental factors such as raw material shortages, the production of wood-based panels using eucalyptus core wood as raw material has only recently gained popularity in order to fully utilize resources. One production method involves processing and splicing wood cores into laminated lumber. Application research has found that eucalyptus core laminated lumber is often used as a base material for high-end furniture. However, due to the inherent tensile strength deficiency of the wood cores, the wood cores have poor bending strength. When inappropriate production methods are used, deformation and distortion can easily occur in environments with large temperature and humidity fluctuations, affecting the quality of the laminated lumber and failing to meet market demand. Therefore, there is a need for high-strength eucalyptus core laminated lumber.

[0004] At present, only literature has been found on the use of round wood cores for artistic photo frames or border decorative strips. The reason is that round wood cores are not easy to glue and splice into large boards (due to reasons such as easy peeling or separation), and factories are reluctant to splice them into large boards. There are also no public literature reports in China on the use of the wood pith of round wood cores combined with bamboo strips to make integrated panels for the production of furniture, office supplies, flooring, etc.

[0005] In addition, the adhesives currently used in multi-layer boards are mostly urea-formaldehyde resins. General urea-formaldehyde resins are obtained by reacting formaldehyde solution, urea, ammonia water, and melamine. Some are added with some additives to increase fire resistance and mildew resistance. The preparation of urea-formaldehyde resins requires special processes. If not controlled well, it is easy to cause high volatile formaldehyde, which cannot meet my country's formaldehyde emission standards for boards. Summary of the Invention

[0006] The purpose of the present invention is to provide a production method of high-strength bamboo eucalyptus mortise and tenon splicing boards. The high-strength bamboo eucalyptus mortise and tenon splicing boards are made by splicing mortise and tenon strips made from eucalyptus core and bamboo mortise and tenon strips. They have high bending strength and are not easy to twist and deform. The resulting wooden boards have mildew and anti-corrosion effects.

[0007] The present invention is achieved through the following technical solutions:

[0008] A method for producing a low-formaldehyde, high-strength eucalyptus bamboo mortise and tenon joint board, characterized in that: first, tenons and grooves are cut on both sides of the eucalyptus core remaining after processing the eucalyptus rotary-cut veneer; the bamboo slices are sliced ​​and glued together with a modified urea-formaldehyde resin adhesive; the bamboo slices are then rotated 90 degrees sideways and cut into bamboo mortise and tenon strips with the same thickness as the diameter of the eucalyptus core, and corresponding tenons and grooves are also cut on both sides; then, several eucalyptus mortise and tenon strips and several bamboo mortise and tenon strips are spliced ​​together, and a modified adhesive is also used between the tenons to obtain a spliced ​​composite board; then, a surface layer is adhered to the upper and lower sides of the spliced ​​board to obtain a mildew-proof, high-strength eucalyptus bamboo mortise and tenon joint spliced ​​board product.

[0009] When the eucalyptus wood mortise and tenon strips and the bamboo mortise and tenon strips are spliced ​​together, one or more bamboo mortise and tenon strips are spliced ​​between two or more adjacent eucalyptus wood core mortise and tenon strips with interval mortise and tenon strips.

[0010] When the above-mentioned eucalyptus mortise and tenon strips are spliced ​​and combined with several bamboo mortise and tenon strips, the bamboo slices are sliced ​​and processed, then overlapped with a modified adhesive, and then cut at a 90-degree angle to form bamboo mortise and tenon strips with the same thickness as the diameter of the eucalyptus core. The effect is to increase the stress of the bamboo slices and strengthen the toughness of the bamboo fibers. Compared with the addition of reinforcing bars between the eucalyptus cores (equivalent to the principle of adding steel bars to concrete), the composite board made has high bending strength and is not easy to twist and deform, which makes up for the disadvantage of insufficient stress when using only the eucalyptus core for splicing.

[0011] The eucalyptus bamboo mortise and tenon splicing panels described above can be made into single-layer or multi-layer composite panels. The mortise and tenon joints of the two adjacent layers of splicing panels need to be staggered and glued together; because some occasions require thickening of panels such as wall panels, furniture panels, desktop panels, and floors, more than two layers of panels can meet different needs.

[0012] The modified adhesive described above is a mildew-proof and antibacterial modified urea-formaldehyde resin, and its composition and weight percentage are as follows:

[0013] Formaldehyde solution 45-55%, (formaldehyde weight concentration is 35-40%);

[0014] Urea 18-25%;

[0015] Melamine 3-5%;

[0016] Ammonia water 8-10% (containing 20% ​​ammonia weight concentration);

[0017] Polyvinyl alcohol 3-5%;

[0018] Titanium dioxide 3-5%;

[0019] Copper powder 0.1-0.5%; (particle size of copper powder is less than 50 microns);

[0020] The rest are adjuvants;

[0021] The auxiliary agent includes bentonite and / or calcium carbonate, and the particle size is less than 50 microns.

[0022] The preparation method of the modified urea-formaldehyde resin is as follows:

[0023] (1) Adjust the pH value of 35-40% formaldehyde by mass to 8.0-8.5 with 20% sodium hydroxide solution under stirring;

[0024] (2) Add polyvinyl alcohol-urea and start heating. When the temperature reaches 85-90°C, add melamine and polyvinyl alcohol and time the reaction for 1-2 hours;

[0025] (3) After the reaction is completed, the pH value is adjusted to 4.6-4.7 with formic acid solution;

[0026] (4) Carrying out polycondensation reaction at 95-96°C until the viscosity reaches 0.25-0.40 / (Pa·s), i.e., when the product is cloudy when dropped into 35°C clean water, adding ammonia water, and then adjusting the pH value to 8.0-8.5 with 20% sodium hydroxide solution, to obtain polyurea-formaldehyde resin;

[0027] (5) Add titanium dioxide, copper powder and additives to the polycondensation urea-formaldehyde resin prepared above, stir and react for 0.5-1 hour to obtain a modified urea-formaldehyde adhesive.

[0028] The modified urea-formaldehyde adhesive of the present invention differs from commercially available urea-formaldehyde resins or those described in literature. The present invention also incorporates melamine, polyvinyl alcohol, titanium dioxide, copper powder, and additives such as micron-sized bentonite or calcium carbonate. The following describes the effects of adding melamine, polyvinyl alcohol, titanium dioxide, copper powder, and additives such as micron-sized bentonite or calcium carbonate:

[0029] 1. Adding melamine and polyvinyl alcohol can reduce the brittleness of the adhesive and increase its toughness. It can also improve the initial adhesion and aging resistance of the adhesive.

[0030] 2. Adding titanium dioxide and micron-grade bentonite and / or calcium carbonate can improve the water resistance of the adhesive and increase the bonding strength. The storage stability of the resulting wood board is also improved, and the tensile strength and compressive strength can also be increased.

[0031] 3. The addition of copper powder and titanium dioxide is to improve the antibacterial and mildew-proof effects of the wooden board. It can also reduce volatile formaldehyde, improve the gluing stability, heat resistance and surface smoothness of the wooden board, and extend the service life of the wooden board.

[0032] 4. The role of adding micron-grade bentonite or calcium carbonate as an auxiliary agent: Since the molecular structure of urea-formaldehyde resin contains polar oxygen atoms, bentonite or calcium carbonate has ions combined with polar oxygen atoms. Adding micron-grade bentonite or calcium carbonate can reduce the release of formaldehyde, improve the bonding strength, improve the bonding force between adhesives, and seal the water-absorbing groups of the resin. Urea-formaldehyde resin is hard, scratch-resistant, resistant to weak acids, weak bases, grease and other media, and has good flexibility. The produced wood boards are suitable for the preparation of environmentally friendly indoor plywood. The storage stability formaldehyde release reaches the national standard E0 level standard. It not only improves the initial viscosity, reduces shrinkage, and has the effect of preventing sedimentation

[0033] Micron-grade bentonite or calcium carbonate, when used in adhesives, have excellent compatibility with the adhesive, accelerating the crosslinking reaction, significantly improving the system's thixotropy, enhancing dimensional stability, and improving the adhesive's mechanical properties. In appropriate amounts, these additives can achieve both filling and reinforcement. Furthermore, they can impart a glossy and smooth surface finish. Furthermore, the addition of micron-grade bentonite or calcium carbonate to urea-formaldehyde resin adhesives can further impart mildew and antibacterial properties to wood panels.

[0034] Advantages of the present invention:

[0035] 1. It can improve the strength of the wood board

[0036] After slicing, the bamboo strips are glued together with a modified urea-formaldehyde resin adhesive. The strips are then cut sideways at a 90-degree angle to form bamboo mortise and tenon strips of the same thickness as the eucalyptus core diameter. Corresponding mortise and tenon grooves are also cut on both sides. Several eucalyptus and bamboo mortise and tenon strips are then spliced ​​together. The eucalyptus and bamboo mortise and tenon spliced ​​boards of the present invention have high bending strength and are not easily deformed. Their volatile formaldehyde content meets the national standard for first-class wood boards (E0), and they are mildew-resistant and have excellent antibacterial properties. They are suitable for indoor use in office cabinets, furniture, flooring, and other applications.

[0037] After the bamboo slices are stacked and glued together, the left and right sides of the side-turned bamboo mortise and tenon strips are correspondingly provided with protruding and recessed tenons. One or more bamboo mortise and tenon strips are spliced ​​between two or more adjacent eucalyptus core mortise and tenon strips. Finally, after trimming the edges and attaching the veneer layer, the adhesive surface is evenly coated with modified urea-formaldehyde resin glue during the splicing process. When a bamboo mortise and tenon strip is spliced ​​between two adjacent eucalyptus core mortise and tenon strips, the eucalyptus core mortise and tenon strips and the bamboo mortise and tenon strips are spliced ​​in an alternating mortise and tenon arrangement. The protruding tenon of the first bamboo mortise and tenon strip is connected to the recessed tenon and tenon of the first eucalyptus core mortise and tenon strip, the protruding tenon of the second eucalyptus core mortise and tenon strip is connected to the recessed tenon and tenon of the first bamboo mortise and tenon strip, the protruding tenon of the second bamboo mortise and tenon strip is connected to the recessed tenon and tenon of the second eucalyptus core mortise and tenon strip, and so on. The mortise and tenon joints are spliced ​​to the required width. When a bamboo mortise and tenon strip is spliced ​​with mortise and tenon strips at intervals between adjacent eucalyptus core mortise and tenon strips, the multiple eucalyptus core mortise and tenon strips are first mortise and tenon spliced ​​to a eucalyptus core mortise and tenon board of designed width, and then the eucalyptus core mortise and tenon board and the bamboo mortise and tenon strips are alternately mortise and tenon spliced, the mortise and tenon protrusion of the first bamboo mortise and tenon strip is connected to the mortise and tenon concave on one side of the first eucalyptus core mortise and tenon board, the mortise and tenon protrusion of one side of the second eucalyptus core mortise and tenon board is connected to the mortise and tenon concave on one side of the second eucalyptus core mortise and tenon board, and so on, the mortise and tenon strips are spliced ​​to the required width, and finally the veneer layer is pasted after trimming. It is also possible that the eucalyptus core mortise and tenon strips do not need to be pre-assembled into a eucalyptus core mortise and tenon board, and the eucalyptus core mortise and tenon strips and the bamboo mortise and tenon strips can be directly spliced ​​in sequence according to the required number of strips and positions. When multiple adjacent eucalyptus core mortise and tenon strips are spliced ​​with multiple bamboo mortise and tenon strips at intervals, first mortise and tenon the multiple eucalyptus core mortise and tenon strips to a eucalyptus core mortise and tenon board of designed width, and then mortise and tenon the multiple bamboo mortise and tenon strips to a bamboo mortise and tenon board of designed width, and then the eucalyptus core mortise and tenon board and the bamboo mortise and tenon board are alternately mortise and tenoned, the convex tenon of the first bamboo mortise and tenon board is connected with the concave tenon of one side of the first eucalyptus core mortise and tenon board, and the second eucalyptus core mortise and tenon board is connected with the concave tenon of the second eucalyptus core mortise and tenon board. The mortise and tenon joints on one side connect to the mortise and tenon joints on the first bamboo mortise and tenon board. The mortise and tenon joints on the second bamboo mortise and tenon board connect to the mortise and tenon joints on one side of the second eucalyptus core mortise and tenon board. This process continues in this order until the desired width is achieved. Finally, trim the edges and apply the veneer layer. Alternatively, the eucalyptus core and bamboo mortise and tenon strips do not need to be pre-assembled into eucalyptus core and bamboo mortise and tenon boards. The eucalyptus core and bamboo mortise and tenon strips can be directly spliced ​​together in the desired number of positions. This results in higher strength than not only simple eucalyptus core spliced ​​boards, but also than ordinary multi-layer boards (see Table 1).

[0038] When the required thickness of the high-strength bamboo eucalyptus mortise and tenon splicing board is large, it is made by pasting and compounding multiple pieces of the above-mentioned splicing boards, and then pasting a veneer layer on both sides. When the multiple splicing boards are pasted and compounded, the mortise and tenon joints of the two adjacent splicing boards above and below need to be staggered and pasted.

[0039] The use of multi-component composite additives such as melamine, polyvinyl alcohol, titanium dioxide, bentonite, and / or calcium carbonate can significantly improve performance, for example, reducing the brittleness of eucalyptus cores and enhancing water resistance, bond strength, and aging resistance. The adhesive is then applied using a neutral-weak acid-weak base composite process, reacting at moderate temperatures. The resulting urea-formaldehyde resin has a shear strength over 10 times that of the original urea-formaldehyde adhesive, significantly enhancing the water resistance and boiling resistance of the spliced ​​board.

[0040] 2. Improve water resistance

[0041] Adding a small amount of melamine, polyvinyl alcohol, and titanium dioxide as crosslinking agents during the synthesis of urea-formaldehyde resin can also significantly improve water resistance. Adding fillers such as bentonite and / or calcium carbonate during the glue preparation can also improve water resistance.

[0042] 3. Improve bonding strength. Adding bentonite or calcium carbonate can reduce the rapid volatilization of water during the production process.

[0043] 4. After adding copper powder to urea-formaldehyde resin, the inventors have found that the role of copper is that a trace amount of copper plays an antibacterial and sterilizing function, and can kill more than 99.9% of bacteria on its surface within two hours, including Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa ( Pseudomonas aeruginosa ) and many other bacteria. The principle is that copper, upon contact with bacteria, ruptures their outer membranes. The copper then acts on the punctures, destroying the bacteria's active enzymes. As a result, the bacteria are unable to breathe, eat, digest, or produce energy, depriving the cells of essential nutrients (protein) and water, ultimately withering. Therefore, trace amounts of copper can have both antibacterial and sterilizing properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is the production process flow chart of the high-strength bamboo eucalyptus mortise and tenon joint board;

[0045] Figure 2 This is a structural diagram of a high-strength bamboo eucalyptus mortise and tenon joint board (single layer);

[0046] Figure 3 This is a diagram of the mortise and tenon structure cut out on either side of the eucalyptus wood core;

[0047] Figure 4 This is a diagram of the mortise and tenon structure on both sides of the bamboo piece after it is rotated sideways;

[0048] Figure 5 This is a schematic diagram of the structure of a multi-layer bamboo eucalyptus mortise and tenon joint composite board (three layers)

[0049] Figure 6 This is a diagram of another type of eucalyptus wood core with bud-shaped mortise and tenon joints on both sides;

[0050] Figure 7 This is a comparison of the mildew resistance of ordinary urea-formaldehyde resin and modified urea-formaldehyde resin after being left outdoors (with a canopy). The storage time was 90 days, the air humidity was 80-90 degrees, and the temperature was 20-32 degrees Celsius. The board on the left shows mildew, while the one on the right is not.

[0051] Figure 2-Figure 5 The names corresponding to the serial numbers are:

[0052] 1. Veneer layer; 2. Eucalyptus core mortise and tenon strips; 3. Bamboo mortise and tenon strips; 4. Convex tenon; 5. Concave tenon. DETAILED DESCRIPTION

[0053] In order to describe the present technology more clearly, the present technology is further described in detail below with reference to embodiments.

[0054] Example 1

[0055] A low-formaldehyde, high-strength bamboo eucalyptus mortise and tenon joint board is obtained by gluing the eucalyptus core remaining after processing eucalyptus rotary-cut veneer to bamboo strips; the left and right sides of the eucalyptus core are correspondingly provided with tenon protrusions 4 and tenon recesses 5; the bamboo strips are sliced ​​and glued together with a modified urea-formaldehyde resin adhesive, then the bamboo strips are rotated 90 degrees sideways and cut into bamboo strips with the same thickness as the diameter of the eucalyptus core, with the tenon protrusions 4 and tenon recesses 5 correspondingly opened; a plurality of eucalyptus core tenon strips 2 and a plurality of bamboo strip tenon strips 3 are glued with a modified urea-formaldehyde resin adhesive, and the tenons are sequentially spliced ​​into the required width of the board, and finally the board is obtained by trimming the edges and gluing a veneer layer 1.

[0056] The modified adhesive is a mildew-proof and antibacterial modified urea-formaldehyde resin, and its composition and weight percentage are as follows:

[0057] 45 kg of formaldehyde solution with a formaldehyde concentration of 37% by weight; 20 kg of urea; 4 kg of melamine; 8 kg of ammonia water (containing 20% ​​ammonia); 3 kg of polyvinyl alcohol; 3 kg of titanium dioxide; 0.2 kg of copper powder; and 16.8 kg of bentonite (fine powder with a diameter of less than 50 microns) to make a total weight of 100 kg (100%).

[0058] The preparation method of the modified urea-formaldehyde resin is as follows:

[0059] (2) adjusting the pH value of 37% formaldehyde by weight to 8.0-8.5 with 20% sodium hydroxide solution under stirring;

[0060] (2) Add polyvinyl alcohol-urea and start heating. When the temperature reaches 85-90°C, add melamine and polyvinyl alcohol and time the reaction for 1-2 hours;

[0061] (3) After the reaction is completed, the pH value is adjusted to 4.6-4.7 with formic acid solution;

[0062] (4) Carry out polycondensation reaction at 95-96°C, measure viscosity at regular intervals, and when the viscosity reaches 0.25-0.40 / (Pa·s), add ammonia water when it becomes cloudy after being dropped into 35°C clean water, and then adjust the pH value to 8.0-8.5 with 20% sodium hydroxide solution to obtain polyurea-formaldehyde resin;

[0063] (5) Add titanium dioxide, copper powder and bentonite to the polycondensation urea-formaldehyde resin prepared above, stir and react for 0.5-1 hour to obtain a modified urea-formaldehyde adhesive.

[0064] Example 2

[0065] A low-formaldehyde, high-strength bamboo eucalyptus mortise and tenon joint board is obtained by gluing the eucalyptus core remaining after processing eucalyptus rotary-cut veneer to bamboo strips; the left and right sides of the eucalyptus core are correspondingly provided with tenon protrusions 4 and tenon recesses 5; the bamboo strips are sliced ​​and glued together with a modified urea-formaldehyde resin adhesive, then the bamboo strips are rotated 90 degrees sideways and cut into bamboo strips with the same thickness as the diameter of the eucalyptus core, with the tenon protrusions 4 and tenon recesses 5 correspondingly opened; a plurality of eucalyptus core tenon strips 2 and a plurality of bamboo strip tenon strips 3 are glued with a modified urea-formaldehyde resin adhesive, and the tenons are sequentially spliced ​​into the required width of the board, and finally the board is obtained by trimming the edges and gluing a veneer layer 1.

[0066] The modified adhesive is a mildew-proof and antibacterial modified urea-formaldehyde resin, and its components and weight percentages are as follows: 50 kg of formaldehyde solution with a formaldehyde concentration of 35-40% by weight; 23 kg of urea; 4 kg of melamine; 9 kg of ammonia water (containing 20% ​​ammonia); 5 kg of polyvinyl alcohol; 4 kg of titanium dioxide; 0.1 kg of copper powder with a particle size of less than 50 microns; and 4.9 kg of calcium carbonate with a particle size of less than 50 microns.

[0067] The preparation method of the modified urea-formaldehyde resin is as follows:

[0068] (1) 35-40% by mass of formaldehyde was stirred with 20% sodium hydroxide solution to adjust the pH to 8.0-8.5;

[0069] (2) Add polyvinyl alcohol-urea and start heating. When the temperature reaches 85-90°C, add melamine and polyvinyl alcohol and time the reaction for 1-2 hours;

[0070] (3) After the reaction is completed, the pH value is adjusted to 4.6-4.7 with formic acid solution;

[0071] (4) Carry out polycondensation reaction at 95-96°C, measure viscosity at regular intervals, and when the viscosity reaches 0.25-0.40 / (Pa·s), add ammonia water when it becomes cloudy after being dropped into 35°C clean water, and then adjust the pH value to 8.0-8.5 with 20% sodium hydroxide solution to obtain polyurea-formaldehyde resin;

[0072] (5) Add titanium dioxide, copper powder and calcium carbonate to the polycondensation urea-formaldehyde resin prepared above, stir and react for 0.5-1 hour to obtain a modified urea-formaldehyde adhesive.

[0073] Example 3

[0074] A low-formaldehyde, high-strength bamboo eucalyptus mortise and tenon joint board is obtained by gluing the eucalyptus core remaining after processing eucalyptus rotary-cut veneer to bamboo strips; the left and right sides of the eucalyptus core are correspondingly provided with tenon protrusions 4 and tenon recesses 5; the bamboo strips are sliced ​​and glued together with a modified urea-formaldehyde resin adhesive, then the bamboo strips are rotated 90 degrees sideways and cut into bamboo strips with the same thickness as the diameter of the eucalyptus core, with the tenon protrusions 4 and tenon recesses 5 correspondingly opened; a plurality of eucalyptus core tenon strips 2 and a plurality of bamboo strip tenon strips 3 are glued with a modified urea-formaldehyde resin adhesive, and the tenons are sequentially spliced ​​into the required width of the board, and finally the board is obtained by trimming the edges and gluing a veneer layer 1.

[0075] The modified adhesive is a mildew-proof and antibacterial modified urea-formaldehyde resin, and its composition and weight percentage are as follows:

[0076] 55 kg of formaldehyde solution with a formaldehyde concentration of 35% by weight; 22 kg of urea; 3 kg of melamine; 8 kg of ammonia water (containing 20% ​​ammonia); 2 kg of polyvinyl alcohol; 3 kg of titanium dioxide; 0.3 kg of copper powder; 4 kg of bentonite with a particle size of less than 50 microns and 2.7 kg of calcium carbonate.

[0077] The preparation method of the modified urea-formaldehyde resin is as follows:

[0078] (1) 35-40% by mass of formaldehyde was stirred with 20% sodium hydroxide solution to adjust the pH to 8.0-8.5;

[0079] (2) Add polyvinyl alcohol-urea and start heating. When the temperature reaches 85-90°C, add melamine and polyvinyl alcohol and time the reaction for 1-2 hours;

[0080] (3) After the reaction is completed, the pH value is adjusted to 4.6-4.7 with formic acid solution;

[0081] (4) Carry out polycondensation reaction at 95-96°C, measure viscosity at regular intervals, and when the viscosity reaches 0.25-0.40 / (Pa·s), add ammonia water when it becomes cloudy after being dropped into 35°C clean water, and then adjust the pH value to 8.0-8.5 with 20% sodium hydroxide solution to obtain polyurea-formaldehyde resin;

[0082] (5) Add titanium dioxide, copper powder and calcium carbonate to the polycondensation urea-formaldehyde resin prepared above, stir and react for 0.5-1 hour to obtain a modified urea-formaldehyde adhesive.

[0083] Comparative Example 1

[0084] (For specific samples, see Figure 7 , and conduct a wood board mold test with and without copper powder added).

[0085] A high-strength bamboo and eucalyptus mortise and tenon joint board is prepared by laminating and pasting the joint boards prepared in Example 1, 2 or 3, and then pasting a veneer layer 1 on both sides. When the joint boards are laminated and pasted, the bamboo strips are cut at a 90-degree angle to form bamboo mortise and tenon strips with the same thickness as the diameter of the eucalyptus core, and the strips are pasted using a modified adhesive.

[0086] The raw materials used to prepare the modified urea-formaldehyde resin were largely the same as those in Examples 1-3, except that copper powder was omitted. The composition and weight percentages were as follows: 50 kg of formaldehyde solution, with a formaldehyde concentration of 35-40% by weight; 20 kg of urea; 4 kg of melamine; 8 kg of aqueous ammonia (containing 20% ​​ammonia); 4 kg of polyvinyl alcohol; 3 kg of titanium dioxide; and 11 kg of bentonite with a particle size of less than 50 μm. The production method was the same as in Example 1.

[0087] Comparative Example 2

[0088] (No polyvinyl alcohol added; titanium dioxide is compared with Examples 1-3)

[0089] A high-strength bamboo and eucalyptus mortise and tenon joint board is prepared by laminating and pasting the joint boards prepared in Example 1, 2 or 3, and then pasting a veneer layer 1 on both sides. When the joint boards are laminated and pasted, the bamboo strips are cut at a 90-degree angle to form bamboo mortise and tenon strips with the same thickness as the diameter of the eucalyptus core, and the strips are pasted using a modified adhesive.

[0090] The preparation of the modified urea-formaldehyde resin is the same as in Example 1-3, but without adding polyvinyl alcohol and titanium dioxide. The composition and weight percentage of the modified urea-formaldehyde resin are as follows:

[0091] The urea-formaldehyde resin is a mildew-proof and modified urea-formaldehyde resin, and its composition and weight percentage are as follows:

[0092] 50 kg of formaldehyde solution (35-40% formaldehyde by weight concentration); 18 kg of urea; 5 kg of melamine; 8 kg of ammonia water (20% ammonia content); 0.2 kg of copper powder (no polyvinyl alcohol or titanium dioxide added); and the remainder being bentonite or calcium carbonate. The production method is the same as in Example 1.

[0093] Comparative Example 3

[0094] A high-strength bamboo and eucalyptus mortise and tenon joint board is prepared by laminating and pasting the joint boards prepared in Example 1, 2 or 3, and then pasting a veneer layer 1 on both sides. When the joint boards are laminated and pasted, the bamboo strips are cut at a 90-degree angle to form bamboo mortise and tenon strips with the same thickness as the diameter of the eucalyptus core and adhered using an adhesive.

[0095] The preparation of the modified urea-formaldehyde resin was the same as in Example 1-3, except that bentonite and calcium carbonate were not added at the end. The composition and weight percentages thereof were as follows:

[0096] The modified adhesive composition and weight percentage are as follows:

[0097] 55 kg of formaldehyde solution, with a formaldehyde concentration of 35-40% by weight; 23 kg of urea; 5 kg of melamine; 10 kg of ammonia water (containing 20% ​​ammonia); 4 kg of polyvinyl alcohol; 2.8 kg of titanium dioxide; and 0.2 kg of copper powder. The production method is the same as in Example 1.

[0098] Table 1 below shows experimental data of several examples and comparisons of the present invention. Comparative Example 2 is a case where no copper powder is added, and Comparative Example 3 is a case where no modified bentonite is added.

[0099] The test standard adopted is GB / T 9846-2015 (ordinary plywood).

[0100] GB 18580-2017 (Limits of formaldehyde emissions from wood-based panels and their products for interior decoration and renovation).

[0101]

[0102] Note: 1. The moisture content, bonding strength, static bending strength and elastic modulus of Examples 1-3 and Comparative Examples were tested within 5 days after processing.

[0103] 2. Comparative Example 1 was placed outdoors for 3 months (under a canopy) without moisture content testing.

[0104] 3. Comparative Example 2 does not add polyvinyl alcohol and titanium dioxide, and the strength value is lower.

[0105] 4. The processing of Comparative Example 3 was the same as that of Examples 1-3. Since bentonite and / or calcium carbonate were not added, the bonding strength was slightly poor, and other parameters (static bending strength, elastic modulus) were not tested.

[0106] The above description is not a limitation of the present application, and the present application is not limited to the above examples. Any changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present application should fall within the scope of protection of the present application.

Claims

1. A method for producing low-formaldehyde, high-strength eucalyptus bamboo mortise and tenon joint boards, characterized by: First, tenon protrusions (4) and tenon grooves (5) are cut on both sides of the eucalyptus core remaining after processing the eucalyptus rotary cut veneer; bamboo slices are sliced ​​and glued together with modified urea-formaldehyde resin adhesive, and then the bamboo slices are rotated 90 degrees to the side and cut into bamboo tenon strips with the same thickness as the diameter of the eucalyptus core, and corresponding tenon protrusions (4) and tenon grooves (5) are also cut on both sides, and then a number of eucalyptus core tenon strips (2) and a number of bamboo tenon strips (3) are spliced ​​together, and the modified adhesive is also used between the tenons to obtain a spliced ​​composite board, and then the surface layer (1) is pasted on the upper and lower sides of the spliced ​​board to obtain a high-strength eucalyptus bamboo tenon spliced ​​board product that is insect-proof and mildew-proof; When the eucalyptus core mortise and tenon strips (2) and the bamboo mortise and tenon strips (3) are spliced ​​together, one or more bamboo mortise and tenon strips are spliced ​​between adjacent eucalyptus core mortise and tenon strips; The modified adhesive is a modified urea-formaldehyde resin that is mildew-proof, bacteriostatic and fire-resistant, and its composition and weight percentage are as follows: Formaldehyde solution 45-55%, its formaldehyde weight concentration is 35-40%; Urea 18-25%; Melamine 3-5%; Ammonia water 8-10%, ammonia concentration of 20% by weight; Polyvinyl alcohol 3-5%; Titanium dioxide 3-5%; Copper powder 0.1-0.5%, the particle size of the copper powder is less than 50 microns; The rest are additives; the additives include bentonite and / or calcium carbonate, with a particle size of less than 50 microns; The preparation method of the modified urea-formaldehyde resin is as follows: (1) 35-40% by mass of formaldehyde was adjusted to pH 8.0-8.5 with 20% sodium hydroxide solution under stirring; (2) Add polyvinyl alcohol-urea and start heating. When the temperature reaches 85-90°C, add melamine and polyvinyl alcohol and time the reaction for 1-2 hours; (3) After the reaction is completed, the pH value is adjusted to 4.6-4.7 with formic acid solution; (4) Carrying out polycondensation reaction at 95-96°C until the viscosity reaches 0.25-0.40 / (Pa·s), i.e., when the product is cloudy when dropped into 35°C clean water, adding ammonia water, and then adjusting the pH value to 8.0-8.5 with 20% sodium hydroxide solution, to obtain polyurea-formaldehyde resin; (5) Add titanium dioxide, copper powder and additives to the polycondensation urea-formaldehyde resin prepared above, stir and react for 0.5-1 hour to obtain a modified urea-formaldehyde adhesive.

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