A straw veneer and preparation method thereof

Abstract

The embodiment of the present application discloses a straw veneer and a preparation method thereof, wherein the straw veneer is formed by self-bonding of straw fibers, and the veneer is subjected to high temperature heat treatment. The straw veneer in the present application is formed by self-bonding of straw fibers, and the veneer only includes straw fibers, so that large-scale and industrialized application of straw can be achieved; at the same time, the value of multi-layer plywood is relatively high, so high value-added utilization of straw can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of plywood, and more specifically, to a straw veneer. The invention also relates to a method suitable for preparing the straw veneer. Background Art

[0002] The technology of replacing wood with straw refers to the technology of using straw materials instead of wood to prepare solid wood boards or composite boards, which can not only achieve high added value and industrial utilization of straw, but also reduce the use of wood. This technology has generally gone through three stages. In the first stage, traditional adhesives were used to glue crop straw fragments or fibers, but they could not be well promoted due to their poor waterproof performance. For example, the technical solution recorded in the publication number CN1473691A in the Chinese Patent Library, entitled "Straw Medium and High Density Artificial Boards and Production Process Methods and Uses".

[0003] In the second stage, isocyanate adhesive is used to bond the straw fragments. However, due to the strong bonding property of isocyanate to metal and the relatively expensive raw material price, many practical production problems such as demoulding and loose slabs need to be solved, as well as the problem of how to reduce the manufacturing cost. For example, the technical solution recorded in the Chinese patent library with publication number CN108189192A and the name "a straw-based artificial board"; another example is the adhesive and its use method recorded in the publication number CN104293274A and the name "a special adhesive for straw-based artificial board and the preparation of straw-based artificial board".

[0004] In the third stage, straw is made into powder by wood-plastic composite technology and then co-extruded with plastic to make waterproof material, but the role of straw is to replace wood powder, and the added value is still relatively low. For example, the product and preparation method recorded in the Chinese patent library with publication number CN102153801A and the name "A straw plastic and its production method"

[0005] In summary, there is currently a lack of a high value-added, industrializable approach to straw utilization. Summary of the invention

[0006] The present application provides a straw single board and a preparation method thereof.

[0007] In a first aspect of the present application, a straw veneer is provided. The straw veneer is formed by self-bonding straw fibers and has a wood texture.

[0008] In some embodiments, the straw fiber is treated to remove hemicellulose.

[0009] In some embodiments, the hemicellulose content of the straw fiber is quantitatively measured by liquid chromatography and is no higher than 20%.

[0010] In some embodiments, the straw single board has a thickness of 0.2 to 3.0 mm.

[0011] In some embodiments, the straw single board has a thickness of 0.2 to 1.0 mm.

[0012] In a second aspect of the present application, a method for preparing the straw veneer as described above is provided, wherein a layer of the straw fiber is paved on a lower pressing plate at room temperature to form a paving layer, the paving layer is restricted on all sides, an upper pressing plate with a temperature of 250 to 290°C contacts the surface of the paving layer without pressure, and the upper pressing plate is withdrawn after a period of time; the above-mentioned actions are repeated to obtain a square material blank formed by stacking a plurality of the paving layers; finally, the upper pressing plate presses the surface of the square material blank at a temperature of 250 to 290°C and a certain pressure, and the upper pressing plate is withdrawn after a period of time to obtain the square material; and the square material is cut to obtain the straw veneer.

[0013] In some embodiments, the lower pressing plate is heated up starting from when the upper pressing plate contacts the surface of the second pavement layer; with each additional pavement layer, the temperature of the lower pressing plate increases by a fixed value until the upper pressing plate contacts the surface of the last pavement layer, at which time the lower pressing plate is isothermal with the upper pressing plate.

[0014] In some embodiments, the contact time between the upper pressing plate and the pavement layer satisfies the following formula:

[0015] t = 30 + a × (b - 5);

[0016] Wherein, t is the contact time, unit is s; a is any constant between 5 and 7, unit is s / mm; b is the thickness of the pavement layer, unit is mm.

[0017] In some embodiments, the thickness of the pavement layer is b=5-10 mm.

[0018] In some embodiments, the upper pressing plate maintains a temperature of 280-290°C until all the paving layers are laid, and then the temperature of the upper pressing plate drops to 250-260°C and contacts the surface of the square blank until the pressing of the square blank is completed.

[0019] In some embodiments, when the upper pressing plate completes laying of all the paving layers and starts to cool down, the lower pressing plate starts to cool down at the same time. After the upper pressing plate and the lower pressing plate both cool down to 250-260°C, the upper pressing plate contacts the surface of the square material blank and starts to press the square material.

[0020] In some embodiments, the pressure applied by the upper pressing plate to the square blank is 5-7 MPa.

[0021] In some embodiments, the step of filling adhesive is further included. In the step of filling adhesive, the back side of the straw veneer is fixed and kept flat by a vacuum adsorption plate, and the front side of the straw veneer is passed through a pair of rollers of adhesive facing upward.

[0022] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The straw veneer in the present application is formed by self-bonding of straw fibers, and the straw veneer only includes straw fibers, so large-scale and industrialized application of straw can be achieved; on the other hand, the straw veneer can be used for veneer and production of multi-layer composite panels, and has relatively high application and sales value, so high value-added utilization of straw can be achieved.

[0024] 2. Furthermore, after the straw fibers are treated to remove hemicellulose, the lignin in the straw fibers can play a bonding role, and a relatively tight bond can be formed between the straw fibers, so that the prepared straw veneer has a higher density than the veneer of the prior art.

[0025] 3. In the preparation method of the straw veneer of the present application, firstly, by laying the paving layer layer by layer and applying high temperature without pressure to the paving layer, it can be ensured that each paving layer is heated evenly. At the same time, the high temperature can remove the hemicellulose from the straw fiber (1) in the paving layer, so that the lignin therein can replace the adhesive to play a bonding role, at least in the process of cutting, so that the square material can maintain its shape; (2) in the pressing process, a square material with a relatively higher average density can be obtained, and then a straw veneer with a higher density can be obtained; (3) it is colored and has a dark brown color similar to wood, and each paving layer and the upper and lower thickness of the paving layer are heated for different times, which can form a color difference, and after cutting at a suitable angle and method, a straw veneer with simulated wood grain can be obtained.

[0026] 4. Furthermore, the lower pressure plate gradually heats up as the pavement layers are laid one by one, which is conducive to forming color differences between the various pavement layers and forming color differences in different thicknesses of the same pavement layer.

[0027] 5. Furthermore, in the step of applying glue, a vacuum adsorption plate is used to fix the back of the straw veneer and keep it flat, and the adhesive is applied to the surface of the straw veneer by roller coating, so that the adhesive can penetrate into the straw fibers of the veneer under the driving force of vacuum adsorption, promote the stability of the structure and shape of the straw veneer, and avoid the problem of straw fiber falling off due to the possible instability of the self-adhesive effect of the straw fibers. In addition, since the adhesive is evenly rolled on the surface of the straw veneer and penetrates inward under the action of uniform vacuum adsorption, this method is more uniform in gluing than the prior art process of first mixing the straw fibers with glue and then pressing them, and has higher production efficiency and less glue application than the prior art process of first pressing and then dipping them.

[0028] On the other hand, since the straw fibers in the straw veneer are treated to remove hemicellulose during assembly and heat contact, the lignin therein is exposed to the outside, allowing the lignin in adjacent straw fibers to form a connection relationship, so even a relatively small amount of glue can achieve good bonding performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative labor.

[0030] Figure 1 This is a surface picture of the straw multi-layer simulated plywood of Example 1 of the present application.

[0031] Figure 2 This is a surface picture of a straw density board prepared by mixing straw fibers with isocyanate adhesive using existing technology.

[0032] Figure 3 This is a process flow chart of the process of preparing the single board of Examples 1 to 11 of the present application.

[0033] Figure 4 This is a process flow chart of the sizing steps of Examples 12 to 15 of the present application.

[0034] In the figure: 100, straw single board, 201, 202, 220 paving layer, 200, square material blank, 300, square material, 410, lower pressing plate, 420, side plate, 430, upper pressing plate, 500, vacuum adsorption plate, 600, roller pair. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this application.

[0036] Examples 1 to 7

[0037] Reference Figure 1 The straw veneer 100 shown is formed by self-bonding of straw fibers that have been treated with hemicellulose removal. The straw fibers are subjected to high-temperature heat treatment to deepen their color, so that the straw veneer 100 has a color and texture similar to wood. Typically, the length of the straw fibers is 2 to 5 mm, and the hemicellulose content quantitatively measured from the straw fibers constituting the straw veneer 100 by liquid chromatography is no more than 20%. The average moisture content of the prepared straw veneer 100 is 5 to 6%.

[0038] The product structures of the straw single board 100 of Examples 1 to 7 are shown in Table 1.

[0039] Table 1. Product structure comparison table of straw veneer 100 in Examples 1 to 7

[0040]

[0041] Reference Figure 3 As shown, the present application also provides a method for preparing the aforementioned straw veneer 100. The equipment used in the process includes at least a mold with an opening on the top surface, and an upper pressing plate 430 with the same width as the opening on the top surface of the mold, the bottom plate of the mold can be used as a heat source and can be regarded as a lower pressing plate 410, and the four side plates 420 of the mold can provide restrictions on the surroundings of the pavement layer.

[0042] During preparation, the lower pressing plate 410 is at room temperature (room temperature, T b0 =25°C), a layer of straw fiber is laid on the lower pressing plate 410 to form the first laying layer 201, and the average moisture content of the straw fiber is 3%. The upper pressing plate 430 has a T a The upper pressing plate 430 is lowered to contact the surface of the first pavement layer 201 without pressure, and the upper pressing plate 430 is withdrawn after a period of time t. The contact time between the upper pressing plate 430 and the pavement layer satisfies the following formula:

[0043] t = 30 + a × (b - 5);

[0044] Wherein, t is the contact time, unit is s; a is a constant, unit is s / mm; b is the thickness of the pavement layer, unit is mm.

[0045] A second layer of straw fiber is laid on the first paving layer 201 to form a second paving layer 202. At the same time, the temperature of the lower pressing plate 410 is raised by ΔT. b , the upper pressing plate 430 contacts the surface of the second paving layer 202 without pressure after the original temperature drops, and after a period of time t, the upper pressing plate 430 is withdrawn. In this embodiment, the thickness of each paving layer is the same, so the time t is equal. Repeat the above steps, and when each layer of straw fiber is paved, the temperature of the lower pressing plate 410 is increased by △T b , until 20 paving layers 201, 202, 220 are paved to obtain the square material blank 200, at which time, the temperature of the lower pressing plate 410 is substantially the same as the temperature of the upper pressing plate 430. In practice, it may be difficult to point out a clear boundary between two adjacent paving layers, but their paving sequences are different, and due to different heating times and different heating times in the same layer, macroscopically visible color differences can be formed. The dividing line formed by the color difference can be understood as the boundary of each paving layer. At the same time, those skilled in the art can understand that at this boundary, the straw fibers of adjacent paving layers may penetrate and blend with each other. At the same time, after a thermal contact period of time t, the hemicellulose content quantitatively measured by liquid chromatography on the straw fibers in any paving layer is not higher than 20%, so as to improve the bonding performance between the straw fibers.

[0046] After obtaining the square material blank 200, the upper pressing plate 430 presses the surface of the square material blank 200 at the original temperature and a certain pressure P for 30 minutes to obtain the square material 300. Finally, the square material 300 is sliced ​​at an angle perpendicular to the surface to obtain the straw veneer 100. Of course, those skilled in the art can know how to obtain straw veneers 100 of different colors and textures by changing the cutting angle.

[0047] As a preferred embodiment, during the thermal contact process of the pavement layer, the upper pressing plate 430 has a relatively high temperature T a , and before the square material 300 starts to be pressed, it drops to a relatively low temperature T a ’ That is, the difference between Example 7 and Example 6 is that during the thermal contact process of the pavement layer, the temperature T of the upper pressing plate 430 is a = 285 ± 2 ° C; after all the paving layers are laid, the temperature of the upper pressing plate 430 drops to T a ’ =255±2℃, and always keep T during the pressing process of the square material 300 a ’ temperature.

[0048] The process parameters for preparing the single boards of Examples 1 to 7 are shown in Table 2.

[0049] Table 2. Comparison of process parameters for preparing single boards in Examples 1 to 7

[0050]

[0051] Embodiments 8 to 11

[0052] The embodiment provides a straw veneer 100 formed by self-bonding of straw fibers that have been treated with hemicellulose removal, and an adhesive is filled between the straw fibers to form a state where the straw fibers and the adhesive are mixed. The straw veneer 100 has a color and texture similar to wood because the straw fibers are subjected to high-temperature heat treatment and the color of the material deepens. Typically, the length of the straw fibers is 2 to 5 mm, and the hemicellulose content that can be quantitatively measured from the straw fibers constituting the straw veneer 100 by liquid chromatography is no more than 20%.

[0053] The process parameters for preparing the single board of Examples 8 to 11 are the same as those of Example 7, except that before the straw fibers are laid to form a paving layer, a step of filling adhesive is also included. Specifically, the adhesive is applied to the surface of the straw fibers by mixing glue, the amount of glue applied is 4 to 6%, and the moisture content of the straw fibers after glue application is 3 to 5%.

[0054] The product structures of the straw single board 100 of Examples 8 to 11 are shown in Table 3.

[0055] Table 3. Product structure comparison table of straw single board 100 in Examples 8 to 11

[0056]

[0057] Embodiments 12 to 15

[0058] The embodiment provides a straw veneer 100 formed by self-bonding of hemicellulose-removed straw fibers, and adhesive is filled between the straw fibers in at least a portion of the thickness layer, forming a mixed state of the straw fibers and the adhesive in at least a portion of the thickness layer. The straw veneer has the color and texture of wood.

[0059] The process parameters for preparing the veneers of Examples 12 to 15 are the same as those of Example 7, except that after the square material 300 is cut to obtain the straw veneer 100, the straw veneer 100 is filled with adhesive, which is to fix the back of the straw veneer 100 through a vacuum adsorption plate 500 and keep it flat, and the front of the straw veneer 100 is facing upward through the adhesive roller pair 600. Specifically, referring to Figure 4As shown, the vacuum adsorption plate 500 is a part of the vacuum adsorption mechanism of the prior art, and the format of the vacuum adsorption plate 500 is slightly larger than the format of the straw veneer 100. The roller pair 600 of the adhesive is a part of the roller coater of the prior art, and the roller pair 600 is connected to the glue pool pipeline through a hydraulic pump, and the roller pair 600 is located above the vacuum adsorption plate 500. The back of the straw veneer 100 is fixed and kept flat under the action of the vacuum adsorption force provided by the vacuum adsorption plate 500, and the front side is coated with the adhesive by the roller pair 600 to form an adhesive coating. This process can be completed by moving the vacuum adsorption plate 500 (using a mechanical arm or a screw servo mechanism) to carry the straw veneer 100 through the roller pair 600 to complete the coating of the entire format, and can also be completed by moving the roller pair 600 (using a screw servo mechanism).

[0060] By means of the vacuum adsorption force provided by the vacuum adsorption plate 500, the adhesive coating is completely adsorbed and penetrates into the interior of the straw veneer 100, and the surface of the straw veneer 100 is non-sticky. At the same time, since the adhesive filling of this method is after the straw veneer 100 is pressed and formed, the adhesive only adheres to the surface of the straw fiber and no longer penetrates into the interior of the fiber, so combined with the process of removing hemicellulose, a lower amount of glue can be used under the premise of achieving the same bonding strength (characterized by internal bonding strength).

[0061] The product structures of the straw single board 100 of Examples 12 to 15 are shown in Table 4.

[0062] Table 4. Product structure comparison table of straw single board 100 of Examples 12 to 15

[0063]

[0064]

[0065] The product performance of the straw veneer 100 of each embodiment is shown in Table 5. Among them, the control groups 1 and 2 are straw density boards with a thickness of 3 mm prepared by using straw fiber mixed with phenolic resin adhesive and urea-formaldehyde resin adhesive by means of the prior art. Figure 2 As shown, the glue application amounts of control groups 1 and 2 were both 10-12%.

[0066] Table 5. Product performance comparison table of straw single board 100 in various embodiments

[0067]

[0068] The above description is intended to be illustrative and not limiting. Upon reading the above description, many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art. Therefore, the scope of the present teachings should not be determined with reference to the above description, but should be determined with reference to the appended claims and the full scope of equivalents to which such claims are entitled. For the purpose of comprehensiveness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the preceding claims is not intended to be a waiver of the subject matter, nor should it be considered that the applicant has not considered the subject matter to be part of the disclosed application subject matter.

Claims

1. A straw veneer, characterized in that: The straw veneer is formed by self-bonding of straw fibers and has a wood texture, and the straw veneer is subjected to high-temperature heat treatment; The preparation method of the straw veneer comprises the following steps: laying a layer of the straw fiber on a lower pressing plate at room temperature to form a paving layer, the paving layer is restricted on all sides, an upper pressing plate with a temperature of 250 to 290° C. contacts the surface of the paving layer without pressure, and the upper pressing plate is withdrawn after a period of time; repeating the above-mentioned actions of laying a layer of the straw fiber, the upper pressing plate contacting the surface of the paving layer without pressure, and the upper pressing plate withdrawing to obtain a square material blank formed by stacking a plurality of the paving layers; finally, the upper pressing plate presses the surface of the square material blank at a temperature of 250 to 290° C. and a certain pressure, and the upper pressing plate is withdrawn after a period of time to obtain the square material; Cutting the square material to obtain the straw veneer; The lower press plate is heated from the moment the upper press plate contacts the surface of the second pavement layer; the temperature of the lower press plate increases by a fixed value each time a pavement layer is added, until the upper press plate contacts the surface of the last pavement layer, at which point the lower press plate becomes isothermal as the upper press plate.

2. The straw veneer according to claim 1, characterized in that: The straw fibers are treated by removing hemicellulose.

3. The straw veneer according to claim 1 or 2, characterized in that: The thickness of the straw single board is 0.2-3.0 mm.

4. The straw veneer according to claim 1, characterized in that: The contact time between the upper pressing plate and the pavement layer satisfies the following formula: t = 30 + a × (b - 5); Wherein, t is the contact time, unit is s; a is any constant between 5 and 7, unit is s / mm; b is the thickness of the pavement layer, unit is mm.

5. The straw veneer according to claim 1, characterized in that: The upper pressing plate is maintained at 280-290° C. until all the paving layers are laid, and then the temperature of the upper pressing plate is reduced to 250-260° C. and then contacts the surface of the square material blank until the pressing of the square material is completed.

6. The straw veneer according to claim 5, characterized in that: When the upper pressing plate completes laying of all the paving layers and starts to cool down, the lower pressing plate also starts to cool down until the upper pressing plate and the lower pressing plate both drop to 250-260°C. Then, the upper pressing plate contacts the surface of the square material blank and starts to press the square material.

7. The straw veneer according to claim 1, characterized in that: The pressure applied by the upper pressing plate to the square blank is 5-7 MPa.

8. The straw veneer according to claim 1, characterized in that: The method further comprises a step of filling adhesive, in which the back side of the straw veneer is fixed and kept flat by a vacuum adsorption plate, and the front side of the straw veneer is passed through a pair of rollers of adhesive facing upward.

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