A method for preparing a green, formaldehyde-free, high-strength biocomposite material

Abstract

The present invention discloses a method for preparing a green, formaldehyde-free, high-strength biocomposite material, comprising the following steps: applying a layer of inner lining adhesive to the mold surface, then wrapping an inner lining fabric thereon, and performing preliminary drying and curing to obtain an inner lining layer; while preparing the inner lining layer, selecting bamboo strips with a thickness of 1 to 3 mm, applying a layer of adhesive to the surface of the bamboo strips, and then wrapping a bamboo staple fiber bundle around the surface of the bamboo strips to obtain a bamboo winding unit; and using a winding process to wrap the bamboo winding unit covered with a reinforcing layer adhesive around the outer surface of the inner lining layer. The present invention wraps bamboo staple fibers around the surface of the bamboo strips and further wraps them to prepare a reinforcing layer, forming multi-directionally raised fiber segments, thereby increasing the effective contact area between the bamboo strips and the resin matrix and improving the interfacial bonding strength. Compared with the prior art, the present invention significantly avoids problems such as interfacial delamination, bamboo strip slippage, and interlayer delamination of bamboo strips caused by insufficient interfacial bonding strength between the bamboo strips and the resin matrix.

Description

Technical Field

[0001] The present invention relates to the technical field of biocomposite materials, and in particular to a method for preparing a green, formaldehyde-free, high-strength biocomposite material. Background Art

[0002] Biocomposites are made from wood or non-wood fibers composed of natural fibers and polymer resins. Their use in various fields is increasing due to their environmentally friendly properties. Growing concern for reducing global warming, environmental damage, and pollution has led to significant scientific attention on developing environmentally friendly and biodegradable materials. Consequently, biocomposites have garnered significant attention due to their environmentally friendly and biodegradable properties.

[0003] Bamboo-wrapped composites are a new type of bio-based material made from bamboo, resin, and a winding process. Bamboo-wrapped composites are widely used in pipelines, pipe corridors, housing, containers, vehicles, military products, and other fields, playing a vital role in the development of the national economy.

[0004] At present, there are still some problems in the practical application of bamboo-wrapped composite materials: when subjected to large axial tension, the insufficient interfacial bonding strength between the bamboo strips and the resin matrix will lead to problems such as interface peeling, bamboo strip slippage and bamboo strip interlayer peeling; in addition, there is also the problem of insufficient axial tensile strength.

[0005] Therefore, it is necessary to provide a method for preparing a green, formaldehyde-free, high-strength biocomposite material to solve the above technical problems. Summary of the Invention

[0006] The present invention overcomes the deficiencies of the prior art and provides a method for preparing a green, formaldehyde-free, high-strength biocomposite material.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a green, formaldehyde-free, high-strength biocomposite material, comprising the following steps:

[0008] S1. Sprinkle a layer of lining adhesive on the surface of the mold, then wrap the lining fabric around it, and perform preliminary drying and curing to obtain the lining layer;

[0009] S2. While preparing the inner lining layer, select bamboo strips with a thickness of 1 to 3 mm, apply a layer of adhesive on the surface of the bamboo strips, and then wrap bamboo short fiber bundles on the surface of the bamboo strips to obtain a bamboo winding unit;

[0010] S3, evenly pouring the reinforcing layer adhesive on the bamboo winding unit, and then using a winding process to wrap the bamboo winding unit covered with the reinforcing layer adhesive on the outer surface of the lining layer to prepare a reinforcing layer;

[0011] S4, moving the reinforcement layer and the lining layer together with the mold into a curing oven for curing;

[0012] S5. Finish the surface of the solidified product and apply a protective layer on the outside of the reinforcement layer. After the protective layer is dry, demoulding is performed.

[0013] In a preferred embodiment of the present invention, before preparing the inner lining layer, a layer of release material is evenly wrapped around the surface of the mold.

[0014] In a preferred embodiment of the present invention, in said S1, the inner lining adhesive is in a preliminary solidified state, and the inner lining adhesive is one of polyester, polyurethane or polyurethane adhesive.

[0015] In a preferred embodiment of the present invention, the inner lining fabric is bamboo fiber non-woven fabric or mesh fabric.

[0016] In a preferred embodiment of the present invention, the bamboo staple fiber bundle comprises bamboo fibers of varying lengths, wherein the staple fibers having a length of 10 to 20 cm account for 50% to 60%.

[0017] In a preferred embodiment of the present invention, in S2, after the bamboo winding unit is prepared, preliminary curing is performed to put the adhesive into a preliminary curing state. During the preliminary curing process, the bamboo winding unit slowly rotates and sweeps air toward the bamboo short fibers on the surface of the bamboo winding unit.

[0018] In a preferred embodiment of the present invention, the adhesive for the reinforcement layer is a mixture of resin, bamboo powder and walnut powder, wherein the mass ratio of the resin to the adhesive for the reinforcement layer is 0.7-0.8:1.

[0019] In a preferred embodiment of the present invention, in said S3, a plurality of layers of bamboo winding units are wound around the surface of the inner lining layer, and a dislocation of half the width of the bamboo strips is provided between each winding layer.

[0020] In a preferred embodiment of the present invention, in said S3, the winding process is that the mold rotates and a pressure roller is used to apply pressure on the surface of each winding layer, and the pressure is 500-1500N.

[0021] In a preferred embodiment of the present invention, the pressure in the curing furnace is maintained at 210-510 kPa.

[0022] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0023] (1) The present invention discloses a method for preparing a green, formaldehyde-free, high-strength biocomposite material, in which short bamboo fibers are wrapped around the surface of bamboo strips and further wrapped to prepare a reinforcement layer, forming multi-directionally raised fiber segments, thereby increasing the effective contact area between the bamboo strips and the resin matrix and improving the interface bonding strength. Compared with the prior art, the method significantly avoids the problems of interface peeling, bamboo strip slippage, and interlayer peeling of bamboo strips caused by insufficient interface bonding strength between the bamboo strips and the resin matrix.

[0024] (2) The present invention wraps bamboo fibers of different lengths on the surface of the bamboo strips, and short fibers with a length of 10 to 20 cm account for more than half of the total. During the wrapping process, one end of several short fibers will curl up, forming fluffy fiber segments on the surface of the bamboo strips. These disordered bamboo short fibers will change the fiber orientation of the bamboo strips, making the bamboo strips present a more multidirectional distribution in the composite material, further improving the strength of the material under axial loading.

[0025] (3) The adhesive of the bamboo winding unit of the present invention is in a preliminary curing state, which can maintain the connection between the bamboo short fibers and the bamboo strips, and can also ensure that its surface still has a certain adhesive property. In the process of preliminary curing, the bamboo winding unit is slowly rotated and air is swept to the bamboo short fibers on its surface to achieve uniformity of the curing state and reduce the occurrence of bamboo short fiber agglomeration.

[0026] (4) The winding process of the present invention is to rotate the mold and use a pressure roller to apply a certain pressure to the surface of each winding layer, so that the winding layers are tightly bonded and excess adhesive is squeezed out, and finally the mass fraction of the resin is maintained at 45% to 55%, so that the prepared biocomposite material has higher density and structural strength.

[0027] (5) During the curing process of the reinforcement layer, the present invention maintains the pressure in the curing furnace at 210 to 510 kPa. When pressure is applied to the resin in the product, the pressure can help the resin better penetrate into the fiber material and fill the gaps between the fibers, thereby reducing the generation of bubbles. The bubbles will gradually shrink under the action of external pressure, and the resin molecules will also be arranged more closely under pressure, which is beneficial to the dissolution and discharge of the bubbles, so that it has higher structural strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments described in the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive efforts.

[0029] Figure 1The present invention is a flow chart of a method for preparing a green, formaldehyde-free, high-strength biocomposite material according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0032] Example

[0033] like Figure 1 As shown, the present invention provides a method for preparing a green, formaldehyde-free, high-strength biocomposite material, comprising the following steps:

[0034] Before preparing the inner lining layer, a layer of release material is evenly wrapped around the surface of the mold.

[0035] A layer of demoulding material is evenly wound from one end of the mold toward the other end. The demoulding material is preferably a polyester film. Check that the demoulding material has no gaps and wrinkles. This is the demoulding layer, which is used to demould the product from the mold after preparation is completed.

[0036] S1. Pour a layer of lining adhesive onto the mold surface, then wrap the lining fabric around it and perform preliminary drying and curing to obtain the lining layer. The adhesive is evenly poured onto the release layer. Multiple layers of lining fabric can be wrapped around the mold according to the designed material strength requirements, and adhesive is applied once for each layer of lining fabric wrapped. The lining fabric is a bamboo fiber non-woven fabric or a mesh fabric.

[0037] S2. While preparing the inner lining layer, select bamboo strips with a thickness of 1 to 3 mm, sprinkle a layer of adhesive on the surface of the bamboo strips, and then wrap the bamboo staple fiber bundles on the surface of the bamboo strips to obtain a bamboo winding unit; the adhesive is preferably consistent with the adhesive of the inner lining layer, and the wrapping method of the bamboo staple fiber bundles is preferably a cross spiral from one end of the bamboo strips to the other end, and the wrapping rate is 70% to 80%.

[0038] S3. Evenly pour the reinforcing layer adhesive on the bamboo winding unit, and then use a winding process to wind the bamboo winding unit covered with the reinforcing layer adhesive on the outer surface of the lining layer to prepare a reinforcing layer; this can be achieved by passing the bamboo winding unit through a pool filled with the reinforcing layer adhesive.

[0039] S4. Move the reinforcement layer and the lining layer together with the mold to a curing oven for curing. The curing parameters are set according to the type of adhesive used. During the curing process, the mold is controlled to rotate at a constant speed so that the lining layer and the reinforcement layer are evenly heated in the curing oven.

[0040] S5. Finish the surface of the solidified product and apply a protective layer on the outside of the reinforcement layer. After the protective layer is dry, demoulding is performed.

[0041] The present invention discloses a method for preparing a green, formaldehyde-free, high-strength biocomposite material. Bamboo short fibers are wrapped around the surface of bamboo strips, and further wrapped to prepare a reinforcement layer, forming multi-directionally raised fiber segments, thereby increasing the effective contact area between the bamboo strips and the resin matrix and improving the bonding strength of the interface. Compared with the existing technology, the method significantly avoids problems such as interface peeling, bamboo strip slippage, and peeling between bamboo strip layers caused by insufficient interface bonding strength between the bamboo strips and the resin matrix, and the prepared biocomposite material has higher axial tensile strength.

[0042] The mold is a cylindrical mold customized according to the size and shape of the product. Hangers are used at both ends to keep the mold in a suspended state, and the mold can be driven to rotate by a rotation setting to facilitate the winding work of each layer. This is existing technology and will not be described in detail here.

[0043] In step S1 , the inner lining adhesive is in a preliminary solidified state, and the inner lining adhesive is one of polyester, polyurethane or polyurethane adhesive.

[0044] The inner lining adhesive is preferably a polyurethane adhesive. During the curing process, the inner lining layer only needs to be left in the mold in a rotating state for 3 to 6 hours. During the initial curing of the inner lining layer, the inner lining layer adhesive is kept in a preliminary curing state. In this state, the inner lining layer adhesive is not viscous, which can maintain the shape of the inner lining fabric stable, preventing deformation or displacement in subsequent processes. It also maintains a certain degree of adhesion, ensuring a good bond between the reinforcement layer and the inner lining layer, and improving the structural strength of the biocomposite material.

[0045] During the preparation of the inner lining layer, a pressing roller is used to press the surface of the inner lining layer fabric to eliminate bubbles in the inner lining layer adhesive.

[0046] In this embodiment, the bamboo short fiber bundle includes bamboo fibers of different lengths, of which short fibers with a length of 10 to 20 cm account for 50% to 60%; a small amount of long bamboo fibers serve as the main body of the fiber bundle, connecting the short fibers thereto.

[0047] The present invention wraps bamboo fibers of varying lengths on the surface of bamboo strips, with short fibers of 10 to 20 cm in length accounting for more than half. During the wrapping process, one end of several short fibers will curl up, forming fluffy fiber segments on the surface of the bamboo strips. These disordered bamboo short fibers will change the fiber orientation of the bamboo strips, making the bamboo strips present a more multidirectional distribution in the composite material, further improving the strength of the material under axial loading.

[0048] In step S2, after the bamboo winding unit is prepared, preliminary curing is performed to put the adhesive into a preliminary curing state. During the preliminary curing process, the bamboo winding unit rotates slowly and sweeps air toward the bamboo short fibers on the surface of the bamboo winding unit.

[0049] The adhesive of the bamboo winding unit is in a preliminary curing state, which can maintain the connection between the bamboo short fibers and the bamboo strips, and can also ensure that its surface still has certain bonding properties. During the preliminary curing process, the bamboo winding unit is slowly rotated and air is swept to the bamboo short fibers on its surface to achieve uniformity of the curing state and reduce the occurrence of bamboo short fiber agglomeration.

[0050] In this embodiment, the reinforcing layer adhesive is a mixture of resin, bamboo powder, and walnut powder, with a mass ratio of resin to reinforcing layer adhesive of 0.7 to 0.8:1. The resin, bamboo powder, and walnut powder mixture is used as the reinforcing layer adhesive, and the bamboo powder and walnut powder can serve as fillers to increase the material's toughness and wear resistance.

[0051] In step S3, a plurality of layers of bamboo winding units are wound around the surface of the inner lining layer, and a dislocation of half the width of the bamboo strips is set between each winding layer.

[0052] The dislocation of half the width of the bamboo strips is set between each winding layer of the present invention, which can enable the bamboo short fibers on the surface of the bamboo strips in different winding layers to have more different forms of contact, increase the contact area between each winding layer, and thus improve the bonding strength and adhesion between each winding layer, and make the stress between different winding layers more evenly distributed, which helps to reduce stress concentration and improve the material's resistance to bending and stretching.

[0053] In step S3 , the winding process is that the mold rotates and a pressure roller is used to apply pressure to the surface of each winding layer, with the pressure being 500 to 1500N.

[0054] The winding process of the present invention is to rotate the mold and use a pressure roller to apply a certain pressure to the surface of each winding layer, so that the winding layers are tightly bonded and excess adhesive is squeezed out, and finally the mass fraction of the resin is maintained at 45% to 55%, so that the prepared biocomposite material has higher density and structural strength.

[0055] In this embodiment, the pressure in the curing furnace is maintained at 210-510 kPa.

[0056] During the curing process of the reinforcement layer, the present invention maintains the pressure in the curing furnace at 210-510 kPa. When pressure is applied to the resin in the product, the pressure can help the resin better penetrate into the fiber material and fill the gaps between the fibers, thereby reducing the generation of bubbles. The bubbles will gradually shrink under the action of external pressure, and the resin molecules will also be under pressure and arranged more closely, which is beneficial to the dissolution and discharge of the bubbles, making it have higher structural strength.

[0057] It is worth noting that during the initial curing or final curing process, the mold is rotated continuously and slowly to ensure that the mold is evenly heated in the curing oven.

[0058] In step S5, the surface of the product is corrected by using a grinding device to make the surface smooth, and threads or buckling structures for connection or installation can be processed on the product as needed.

[0059] In step S5, the protective layer is preferably applied using a spraying device, and the anti-corrosion and waterproof material is sprayed on the outer side of the reinforcement layer.

[0060] In step S5, the demoulding process: one end of the product to be demoulded is pressed against the demoulding device, and the mold is pulled out axially by the traction device. The product to be demoulded is held in place, and the demoulding work is completed when the mold is completely pulled out of the demoulded product.

[0061] The preparation method of the green, formaldehyde-free, high-strength biocomposite material is applied to the preparation of bamboo-wound composite pressure pipes and bamboo-wound pipe corridors.

[0062] Example 1

[0063] A bamboo-wound composite pressure pipe sample with a diameter of 1000 mm was prepared using the above preparation method:

[0064] Preparation of the inner lining layer: A release layer is wrapped around the mold, and then a layer of bamboo fiber non-woven fabric is used and polyurethane adhesive is applied to prepare an inner lining layer with a thickness of 1.5 mm. The inner lining layer is rotated with the mold and aired for 4 hours.

[0065] Preparation of bamboo winding unit: Use bamboo strips with a width of 10 mm and a thickness of 2 mm after end-to-end connection treatment, pass the bamboo strips through a pool filled with polyurethane adhesive, and then wrap bamboo short fiber bundles on their surface with a wrapping rate of 75%. Rotate and dry for 3 hours, and sweep air on their surface.

[0066] Preparation of the reinforcement layer: A layer of reinforcement layer adhesive was poured on the surface of the bamboo winding unit, where the mass ratio of resin to reinforcement layer adhesive was 0.8:1. Then, 8 layers of bamboo winding units were wound on the surface of the lining layer, and a dislocation of half the width of the bamboo strips was set between each winding layer. During the winding process, a pressure roller was used to apply 1200N of pressure to the surface of the winding layer.

[0067] The reinforcement layer and the lining layer are moved together with the mold to a curing oven for curing. The pressure in the curing oven is controlled at 450 kPa.

[0068] The surface of the cured product is trimmed, and a protective layer is applied on the outside of the reinforcement layer. After the protective layer is dried, the product is demoulded to obtain a bamboo-wrapped composite pressure pipe sample.

[0069] Example 2

[0070] Based on Example 1, a bamboo-wound composite pressure pipe sample with a diameter of 600 mm was prepared. In the preparation of the reinforcement layer, 5 layers of bamboo-wound units were wound on the surface of the inner lining layer to prepare the bamboo-wound composite pressure pipe sample.

[0071] Comparative Example 1

[0072] Based on Example 1, a bamboo-wound composite pressure pipe sample with a diameter of 1000 mm was prepared. The bamboo strips with a width of 10 mm and a thickness of 2 mm after the end-to-end connection treatment were also used, but no wrapping treatment was performed to prepare the bamboo-wound composite pressure pipe sample.

[0073] Comparative Example 2

[0074] Based on Example 1, a bamboo-wound composite pressure pipe sample with a diameter of 600 mm was prepared. Bamboo strips with a width of 10 mm and a thickness of 2 mm after end-to-end connection were also used, but no wrapping treatment was performed. In the preparation of the reinforcement layer, 5 layers of bamboo wrapping units were wrapped on the surface of the inner lining layer to prepare a bamboo-wound composite pressure pipe sample.

[0075] Example 1 Example 2 Comparative Example 1 Comparative Example 2 <![CDATA[Initial ring stiffness / (N / m 2 )]]> 7518 6833 7169 6498 Axial tensile strength / MPa 21.17 20.45 19.89 19.28 Flexural modulus / GPa 2.61 2.52 2.48 2.41

[0076] Table 1. Physical and mechanical properties

[0077] As shown in Table 1, the physical and mechanical properties of the samples prepared above were tested in accordance with GR / T 37805-2019. The prepared samples were all qualified products. However, the samples after wrapping the bamboo strips with bamboo staple fibers had higher ring stiffness and axial tensile strength than the samples without bamboo strips. Therefore, it can be concluded that wrapping bamboo staple fibers on the surface of bamboo strips and further winding them to prepare a reinforcement layer to form multi-directionally raised fiber segments, thereby increasing the effective contact area between the bamboo strips and the resin matrix, improving the bonding strength of the interface, and can improve the structural strength of the material.

[0078] The above description is based on the ideal embodiment of the present invention. Based on the above description, relevant personnel can make various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the content of the specification and must be determined according to the scope of the claims.

Claims

1. A method for preparing a green, formaldehyde-free, high-strength biocomposite material, characterized in that: The following steps are involved: S1. Sprinkle a layer of lining adhesive on the surface of the mold, then wrap the lining fabric around it, and perform preliminary drying and curing to obtain the lining layer; S2. While preparing the inner lining layer, select bamboo strips with a thickness of 1 to 3 mm, apply a layer of adhesive on the surface of the bamboo strips, and then wrap a bamboo short fiber bundle around the surface of the bamboo strips to obtain a bamboo winding unit; the bamboo short fiber bundle includes bamboo fibers of varying lengths, of which short fibers with a length of 10 to 20 cm account for 50% to 60%; S3, evenly pouring the reinforcing layer adhesive on the bamboo winding unit, and then using a winding process to wrap the bamboo winding unit covered with the reinforcing layer adhesive on the outer surface of the lining layer to prepare a reinforcing layer; S4, moving the reinforcement layer and the lining layer together with the mold into a curing oven for curing; S5. Finish the surface of the solidified product and apply a protective layer on the outside of the reinforcement layer. After the protective layer is dry, demoulding is performed.

2. The method for preparing a green, formaldehyde-free, high-strength biocomposite material according to claim 1, characterized in that: Before preparing the inner lining layer, a layer of release material is evenly wrapped around the surface of the mold.

3. The method for preparing a green, formaldehyde-free, high-strength biocomposite material according to claim 1, characterized in that: In the above S1, the inner lining adhesive is in a preliminary solidified state, and the inner lining adhesive is one of polyester adhesive and polyurethane adhesive.

4. The method for preparing a green, formaldehyde-free, high-strength biocomposite material according to claim 1, characterized in that: The inner lining fabric is bamboo fiber non-woven fabric or mesh fabric.

5. The method for preparing a green, formaldehyde-free, high-strength biocomposite material according to claim 1, characterized in that: In S2, after the bamboo winding unit is prepared, preliminary curing is performed to put the adhesive into a preliminary curing state. During the preliminary curing process, the bamboo winding unit rotates slowly and sweeps air toward the bamboo short fibers on the surface of the bamboo winding unit.

6. The method for preparing a green, formaldehyde-free, high-strength biocomposite material according to claim 1, characterized in that: The reinforcing layer adhesive is a mixture of resin, bamboo powder and walnut powder, wherein the mass ratio of the resin to the reinforcing layer adhesive is 0.7-0.8:

1.

7. The method for preparing a green, formaldehyde-free, high-strength biocomposite material according to claim 1, characterized in that: In the step S3, a plurality of layers of bamboo winding units are wound on the surface of the inner lining layer, and a dislocation of half the width of the bamboo strips is provided between each winding layer.

8. The method for preparing a green, formaldehyde-free, high-strength biocomposite material according to claim 1, characterized in that: In the S3 , the winding process is that the mold rotates and a pressure roller is used to apply pressure on the surface of each winding layer, with the pressure being 500 to 1500N.

9. The method for preparing a green, formaldehyde-free, high-strength biocomposite material according to claim 1, characterized in that: The pressure in the curing oven is maintained at 210-510 kPa.

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