The diameter and wall thickness of the bamboo from the root to the tip are gradually reduced. It is difficult to obtain the bamboo veneer by using the thin wood rotary cutting technology, but the bamboo curtain veneer can be obtained by using the bracts and the weaving technique. The bamboo curtain layer material developed in recent years is a new type of bamboo wood-based panel product which is obtained by a series of processes such as rubber coating, blanking and hot pressing. It not only eliminates the cumbersome manual knitting of bamboo plywood, but also avoids the complicated softening treatment and pressure equalization process of bamboo plywood, which simplifies the manufacturing process. The key to the production of bamboo curtain laminated timber is the bamboo curtain veneer, which is characterized by:
(1) The bamboo pieces in the bamboo veneer are arranged in parallel, and the braided line is perpendicular to the bamboo piece. The bamboo pieces in the veneer have no overlap and the surface is flat, so the amount of glue consumed during production is small, and the unit pressure required for hot pressing is also (2) The woven bamboo blind veneer can be kept in one piece, which realizes “single plate singulationâ€, which reduces the labor intensity of the core plate when the workers assemble the blank and improves the productivity; (3) The existence of the gap between the bamboo sheets in the bamboo curtain veneer makes the water vapor in the slab easy to be discharged during hot pressing, and there are almost no defects such as bubbling and delamination, and the production operation is easy, and the qualified product rate is high.
Since the end of the 1980s, the climax of research on structural wood-based panels has arisen at home and abroad. This process is in line with the inevitable trend of material science development. The mechanical properties of bamboo are better than wood. If the strength of the body can be fully reflected, the bamboo lumber can be widely used in structural products, and it is also a way to realize the value-added of its products.
2 Materials and methods
2.1 Experimental materials
The bamboo curtain veneer is longitudinally honed by bamboo (Phyllostachys pubescens) into a bamboo piece with a width of 10 mm and an average thickness of 2 mm. The bamboo pieces are arranged in parallel without overlapping, but there is a lateral gap between the pieces. Table 1 gives the thickness deviation and the bamboo gap, and measures the quality of the bamboo veneer. It can be seen from the table that the thickness of the veneer and the gap of the bamboo in the bamboo veneer board show a large coefficient of variation and the average deviation, indicating that the quality of the bamboo veneer is poor, which is mainly due to the structural characteristics of the bamboo veneer . Due to the one-way curved bending of the vascular bundle at the bamboo joint, not only the thickness of the bamboo joint is increased, but also the lateral gap of adjacent bamboo pieces in the bamboo curtain veneer is large.
The adhesive was urea-formaldehyde resin, pH 6.5, solid content 62%, viscosity 300 cp / 20 °C. There are also curing agents and reinforcing agents applied in an amount by weight of the solids content of the resin.
2.2 Manufacturing process
The bamboo curtain veneer is dried to a moisture content of 3% to 5%. It should be noted that the bamboo piece of bamboo yellow is not removed from the veneer, and after drying, a curvature with a large curvature appears on the bamboo yellow side, which destroys the flatness of the veneer. On the bamboo-yellow side, more transverse cracks were found, spaced about 4 cm apart, and even the cracks in the cracks occurred. This phenomenon is caused by the loose bamboo and yellow tissue on the inner side of the bamboo wall, the shrinkage rate is large, and the mechanical properties are poor. A quantitative reinforcing agent and a curing agent are added to the resin, and after being uniformly stirred, the single-plate is sizing on one side, and then vertically formed into slabs according to the principle of symmetry. After being closed for 50 to 60 minutes, it is sent to the press, and a layer of pressing process is used to press the bamboo curtain layer.
2.4 Performance Testing
The performance of the bamboo curtain layer is tested according to the relevant Japanese standards, and the indicators are mainly mechanical strength. The shear strength of the rubber layer is tested according to the Japanese common plywood standard for urea-formaldehyde resin, and the remaining mechanical indexes, including compressive strength (shun, horizontal and twill), static bending strength and elastic modulus (longitudinal and transverse) are in accordance with Japan. Structural plywood standard test. In addition, density and moisture content were also tested.
3.3 Influence of bamboo properties
3.3.1 The damaged piece of the test piece The bamboo piece gap is the constituent feature of the bamboo curtain layer. The bamboo curtain veneer composed of the dispersed phase of the bamboo piece in the test piece is different from the continuous continuous wooden veneer, which cannot continuously reduce the stress. Stress concentration occurs, and thus some of the test pieces have low detection strength, and the damage also has certain characteristics. The large thickness deviation of the bamboo piece makes the damaged surface have two forms when the shearing is applied, and the higher one is pulled off on one side of the core piece, and the lower part is partially pulled off on both sides of the core piece; It is a non-crushing "lantern" or "broken" shape, which is carried by a single core plate when bent, and the horizontal and lateral inspections are more prominent. Therefore, the quality of the bamboo veneer is an important factor affecting the mechanical properties of the bamboo curtain. The buckling should improve the parallelism and verticality of the sides of the bamboo. After the bamboo pieces are woven into a single board, the gap between the bamboo pieces is small, and the glued area is relatively increased.
It also produces partial bonding of the bamboo pieces, which has good integrity and improved strength properties.
3.3.2 Variability Bamboo variability is large, but the variability of the performance of bamboo curtains is not obvious. The laminated material reconstituted by bamboo curtain veneers weakens the variability of bamboo. Comparing the coefficient of variation of each index, the shear strength is the largest, the density and water content are the smallest, the other indicators are moderate, and the coefficient of variation of the grain (longitudinal) is smaller than that of the horizontal (lateral) and twill, because the thickness of the bamboo veneer is The deviation and the gap between the bamboo pieces caused the specimen to have different forms of damage. In addition, the number of rotation design selection factors is large, and if the factor variation interval Δj is small, errors may occur and variability may be increased.
3.3.3 moldy bamboo curtain layer exposed to the air for 4 months, the surface found more dark green mold spots, which is caused by the bamboo itself is rich in sugar, starch, nitrogen compounds and other nutrients, is a bamboo The common defects of quality products have yet to be further deepened into the mildew resistance from the characteristics of bamboo.
4 Conclusions and recommendations
(1) Bamboo curtain layer is a new way to utilize the abundant bamboo resources in China and develop the bamboo industry. Its production can alleviate the tension of China's timber resources, and is also an important way to achieve greater value-added of bamboo products.
(2) The bamboo curtain layer has high mechanical properties, and some indicators fully reflect the strength advantage of the bamboo itself. The shear strength meets the standard requirements of Japanese ordinary plywood. The compressive strength, static bending strength and elastic modulus exceed the standard requirements of Japanese structural plywood. The product can be used for structural plates.
(3) The bamboo curtain veneer is a constituent unit of the bamboo curtain laminated material, which has a large thickness deviation and a bamboo interstitial gap, resulting in different damage forms during the detection. Improving the quality of bamboo blind veneers will help improve the mechanical properties and variability of bamboo curtain laminates.
(4) It is feasible to study the nonlinear relationship between the performance index of bamboo curtain layer and the process parameters by rotating design. Reducing the number of variable factors or increasing the spacing of the changes is beneficial to the significance of the experimental results.
(5) The mildew resistance of bamboo products needs further study.
(1) The bamboo pieces in the bamboo veneer are arranged in parallel, and the braided line is perpendicular to the bamboo piece. The bamboo pieces in the veneer have no overlap and the surface is flat, so the amount of glue consumed during production is small, and the unit pressure required for hot pressing is also (2) The woven bamboo blind veneer can be kept in one piece, which realizes “single plate singulationâ€, which reduces the labor intensity of the core plate when the workers assemble the blank and improves the productivity; (3) The existence of the gap between the bamboo sheets in the bamboo curtain veneer makes the water vapor in the slab easy to be discharged during hot pressing, and there are almost no defects such as bubbling and delamination, and the production operation is easy, and the qualified product rate is high.
Since the end of the 1980s, the climax of research on structural wood-based panels has arisen at home and abroad. This process is in line with the inevitable trend of material science development. The mechanical properties of bamboo are better than wood. If the strength of the body can be fully reflected, the bamboo lumber can be widely used in structural products, and it is also a way to realize the value-added of its products.
2 Materials and methods
2.1 Experimental materials
The bamboo curtain veneer is longitudinally honed by bamboo (Phyllostachys pubescens) into a bamboo piece with a width of 10 mm and an average thickness of 2 mm. The bamboo pieces are arranged in parallel without overlapping, but there is a lateral gap between the pieces. Table 1 gives the thickness deviation and the bamboo gap, and measures the quality of the bamboo veneer. It can be seen from the table that the thickness of the veneer and the gap of the bamboo in the bamboo veneer board show a large coefficient of variation and the average deviation, indicating that the quality of the bamboo veneer is poor, which is mainly due to the structural characteristics of the bamboo veneer . Due to the one-way curved bending of the vascular bundle at the bamboo joint, not only the thickness of the bamboo joint is increased, but also the lateral gap of adjacent bamboo pieces in the bamboo curtain veneer is large.
The adhesive was urea-formaldehyde resin, pH 6.5, solid content 62%, viscosity 300 cp / 20 °C. There are also curing agents and reinforcing agents applied in an amount by weight of the solids content of the resin.
2.2 Manufacturing process
The bamboo curtain veneer is dried to a moisture content of 3% to 5%. It should be noted that the bamboo piece of bamboo yellow is not removed from the veneer, and after drying, a curvature with a large curvature appears on the bamboo yellow side, which destroys the flatness of the veneer. On the bamboo-yellow side, more transverse cracks were found, spaced about 4 cm apart, and even the cracks in the cracks occurred. This phenomenon is caused by the loose bamboo and yellow tissue on the inner side of the bamboo wall, the shrinkage rate is large, and the mechanical properties are poor. A quantitative reinforcing agent and a curing agent are added to the resin, and after being uniformly stirred, the single-plate is sizing on one side, and then vertically formed into slabs according to the principle of symmetry. After being closed for 50 to 60 minutes, it is sent to the press, and a layer of pressing process is used to press the bamboo curtain layer.
2.4 Performance Testing
The performance of the bamboo curtain layer is tested according to the relevant Japanese standards, and the indicators are mainly mechanical strength. The shear strength of the rubber layer is tested according to the Japanese common plywood standard for urea-formaldehyde resin, and the remaining mechanical indexes, including compressive strength (shun, horizontal and twill), static bending strength and elastic modulus (longitudinal and transverse) are in accordance with Japan. Structural plywood standard test. In addition, density and moisture content were also tested.
3.3 Influence of bamboo properties
3.3.1 The damaged piece of the test piece The bamboo piece gap is the constituent feature of the bamboo curtain layer. The bamboo curtain veneer composed of the dispersed phase of the bamboo piece in the test piece is different from the continuous continuous wooden veneer, which cannot continuously reduce the stress. Stress concentration occurs, and thus some of the test pieces have low detection strength, and the damage also has certain characteristics. The large thickness deviation of the bamboo piece makes the damaged surface have two forms when the shearing is applied, and the higher one is pulled off on one side of the core piece, and the lower part is partially pulled off on both sides of the core piece; It is a non-crushing "lantern" or "broken" shape, which is carried by a single core plate when bent, and the horizontal and lateral inspections are more prominent. Therefore, the quality of the bamboo veneer is an important factor affecting the mechanical properties of the bamboo curtain. The buckling should improve the parallelism and verticality of the sides of the bamboo. After the bamboo pieces are woven into a single board, the gap between the bamboo pieces is small, and the glued area is relatively increased.
It also produces partial bonding of the bamboo pieces, which has good integrity and improved strength properties.
3.3.2 Variability Bamboo variability is large, but the variability of the performance of bamboo curtains is not obvious. The laminated material reconstituted by bamboo curtain veneers weakens the variability of bamboo. Comparing the coefficient of variation of each index, the shear strength is the largest, the density and water content are the smallest, the other indicators are moderate, and the coefficient of variation of the grain (longitudinal) is smaller than that of the horizontal (lateral) and twill, because the thickness of the bamboo veneer is The deviation and the gap between the bamboo pieces caused the specimen to have different forms of damage. In addition, the number of rotation design selection factors is large, and if the factor variation interval Δj is small, errors may occur and variability may be increased.
3.3.3 moldy bamboo curtain layer exposed to the air for 4 months, the surface found more dark green mold spots, which is caused by the bamboo itself is rich in sugar, starch, nitrogen compounds and other nutrients, is a bamboo The common defects of quality products have yet to be further deepened into the mildew resistance from the characteristics of bamboo.
4 Conclusions and recommendations
(1) Bamboo curtain layer is a new way to utilize the abundant bamboo resources in China and develop the bamboo industry. Its production can alleviate the tension of China's timber resources, and is also an important way to achieve greater value-added of bamboo products.
(2) The bamboo curtain layer has high mechanical properties, and some indicators fully reflect the strength advantage of the bamboo itself. The shear strength meets the standard requirements of Japanese ordinary plywood. The compressive strength, static bending strength and elastic modulus exceed the standard requirements of Japanese structural plywood. The product can be used for structural plates.
(3) The bamboo curtain veneer is a constituent unit of the bamboo curtain laminated material, which has a large thickness deviation and a bamboo interstitial gap, resulting in different damage forms during the detection. Improving the quality of bamboo blind veneers will help improve the mechanical properties and variability of bamboo curtain laminates.
(4) It is feasible to study the nonlinear relationship between the performance index of bamboo curtain layer and the process parameters by rotating design. Reducing the number of variable factors or increasing the spacing of the changes is beneficial to the significance of the experimental results.
(5) The mildew resistance of bamboo products needs further study.
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