Flame-retardant fiber-reinforced cork composite board and preparation method thereof

Abstract

The present application belongs to the technical field of composite materials, and particularly relates to a flame-retardant fiber-reinforced cork composite board and a preparation method thereof. The flame-retardant fiber-reinforced cork composite board comprises cork particles as a matrix, hemp fibers as a reinforcing phase, isocyanate as an adhesive, and ammonium polyphosphate as a flame retardant. The cork particles and the hemp fibers are mixed in a certain proportion. The ammonium polyphosphate and the isocyanate are mixed and then uniformly applied to the raw materials. After paving, three-stage stepped pressure reduction hot pressing is performed. The composite board has excellent synergistic flame-retardant effect without damaging the mechanical properties of the material, and has certain mechanical bearing capacity and fire safety, and is suitable for the fields of building decoration and thermal insulation.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to a flame-retardant fiber-reinforced cork composite board and its preparation method. Background Technology

[0002] In existing technologies, inorganic powder flame retardants such as ammonium polyphosphate (APP) typically achieve their flame-retardant effect by releasing non-combustible gases through thermal decomposition and promoting the dehydration and carbonization of the matrix. However, when these free flame-retardant particles are directly introduced into engineered wood products, significant differences in surface energy and interfacial compatibility between them and the biomass matrix lead to the formation of discontinuous distributions and "interfacial isolation layers" at the interface. This hinders the wetting and penetration of adhesives into the matrix, inducing interfacial defects and stress concentration, typically resulting in decreased static bending strength and significantly weakened internal bond strength. In severe cases, it can even cause delamination failure of the board. Traditional flame-retardant composite boards face a technical bottleneck: it is difficult to synergistically improve mechanical properties (especially internal bond strength) and flame-retardant performance. Summary of the Invention

[0003] This invention primarily provides a composite board that balances mechanical load-bearing capacity and fire safety, overcoming the problem in existing technologies where mechanical properties and flame-retardant properties cannot be simultaneously enhanced. The technical solution is as follows:

[0004] A flame-retardant fiber-reinforced cork composite board includes cork particles, plant fibers, and isocyanate and ammonium polyphosphate distributed between the interfaces of the cork particles and the plant fibers.

[0005] Furthermore, the internal bond strength is not less than 0.7 MPa.

[0006] Furthermore, the limiting oxygen index should be no less than 27%.

[0007] Furthermore, the softwood particles include one or more of pine particles, fir particles, spruce particles, fir particles, cork oak particles, cork oak particles, or regenerated softwood particles; the plant fibers include one or more of hemp fibers, bamboo fibers, cork oak bark fibers, coniferous fibers, or broadleaf fibers.

[0008] Furthermore, the isocyanate accounts for 8-12% of the mass of the mixture; the ammonium polyphosphate accounts for 3-8% of the mass of the isocyanate.

[0009] Furthermore, the cork particles have a particle size of 16-18 mesh.

[0010] Furthermore, the mass ratio of the cork particles to the fibers is 1:0.67~1.5.

[0011] A method for preparing the above-mentioned flame-retardant fiber-reinforced cork composite board includes the following steps: taking cork particles and mixing them evenly with plant fibers to obtain a mixture; taking isocyanate and ammonium polyphosphate to prepare a flame-retardant adhesive; then uniformly applying the flame-retardant adhesive to the mixture, stirring and mixing it thoroughly, then laying it into a mold for cold pressing and demolding; and hot pressing to obtain the composite board.

[0012] Furthermore, the hot pressing temperature is 150~170℃.

[0013] Furthermore, the hot pressing step includes: performing a three-stage stepped pressure reduction hot pressing, which involves holding at 2.6~3.5MPa for 250~350s, 1.6~2.5MPa for 150~250s, and 0.8~1.5MPa for 80~120s.

[0014] By adopting the above scheme, the method of the present invention has the following advantages:

[0015] 1. Using the isocyanate (MDI) and APP system of the present invention, and under the three-stage gradient pressure reduction hot pressing process at 160°C, not only is the interface performance not degraded due to the introduction of APP, but the static bending strength and internal bond strength are simultaneously improved, while maintaining excellent flame retardant performance, showing significant unexpected technical effects.

[0016] 2. In the hot-pressing curing process of this invention, the highly reactive isocyanate groups (–NCO) in MDI react with the hydroxyl groups on the surface of cork particles and hemp fibers to generate stable urethane covalent bonds, thereby constructing a basic interfacial cross-linking structure. More importantly, in the initial stage of hot pressing at 160℃, APP undergoes slight thermal decomposition and releases phosphoric acid substances with weak acid properties in the interfacial region, thus forming a transient slightly acidic local environment. This slightly acidic environment can promote the interfacial reaction between –NCO and hydroxyl groups, increasing the curing rate of isocyanate and the degree of interfacial reaction, thereby improving the density of interfacial covalent bonds and the degree of cross-linking. At the same time, the nitrogen-containing active components generated by the decomposition of APP in this system can further react with unreacted or partially activated –NCO groups to form a dimer or polyurea structure (–NH–CO–NH–) cross-linking network, which, together with hydrogen bonding, constructs a multi-scale synergistically reinforced interfacial structure system, thereby significantly improving the structural integrity and overall mechanical properties of the adhesive layer and achieving a significant increase in internal bond strength. Attached Figure Description

[0017] Figure 1 The following is a comparison chart of the performance of composite panels in the examples and comparative examples, where (a) internal bond strength, (b) static bending strength, and (c) limiting oxygen index.

[0018] Figure 2The following are surface and cross-sectional views of the composite panels in the examples and comparative examples, where (a) is the control group and (b) is the flame-retardant group. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example: (1) First, weigh 17-mesh pine wood particles and hemp fibers according to a predetermined ratio and mix them thoroughly to obtain a mixture; then, weigh 10% isocyanate according to the mass of the mixture and mix 5% ammonium polyphosphate according to the mass of the adhesive to prepare a flame retardant adhesive liquid; then, apply the flame retardant adhesive liquid evenly to the mixture, stir and mix thoroughly, then lay it into a 250mm×250mm mold for cold pressing and demolding to obtain a board blank; finally, place the board blank in a 160℃ flat vulcanizing machine and hot press it according to a three-stage stepped pressure reduction process of 3MPa for 300s, 2MPa for 200s, and 1MPa for 100s. After hot pressing, take it out and cool it to obtain a composite board.

[0021] Comparative Example 1: The difference from the embodiment is as follows:

[0022] It does not contain ammonium polyphosphate.

[0023] Comparative Example 2: The difference from the embodiment is as follows:

[0024] The mass of isocyanate accounts for 5% of the mass of the mixture.

[0025] Comparative Example 3: The difference from the embodiment is as follows:

[0026] The isocyanate accounts for 5% of the mass of the mixture and does not contain ammonium polyphosphate.

[0027] Comparative Example 4: The difference from the embodiment is as follows:

[0028] The mass of isocyanate accounts for 2% of the mass of the mixture.

[0029] Comparative Example 5: The difference from the embodiment is as follows:

[0030] The isocyanate accounts for 2% of the mass of the mixture and does not contain ammonium polyphosphate.

[0031] Sample testing of examples and comparative examples

[0032] Examples containing ammonium polyphosphate, Comparative Examples 2 and 4 were designated as the flame retardant group, while Comparative Examples 1, 3, and 5 without ammonium polyphosphate were designated as the control group. The internal bond strength, static bending strength, and limiting oxygen index of the examples and each comparative example were tested, and the results are shown in the table below. Figure 1 As shown.

[0033] Group Example Internal bond strength (MPa) Static bending strength (MPa) Limiting oxygen index (%) Flame retardant group Example 0.905±0.1332 24.89±0.1565 32.8±1.64 control group Comparative Example 1 0.502±0.0312 22.88±3.63 30.3±1.52 Flame retardant group Comparative Example 2 0.502±0.0125 13.39±0.7332 27.3±1.36 control group Comparative Example 3 0.484±0.0069 12.82±3.72 26.8±1.34 Flame retardant group Comparative Example 4 0.461±0.0025 12.27±0.2509 26.8±1.34 control group Comparative Example 5 0.430±0.0054 11.19±1.82 25.8±1.29

[0034] From Table 1 and Figure 1 It can be seen that, under the condition that the isocyanate addition amount is 10%, compared with Comparative Example 1 without the addition of ammonium polyphosphate, the internal bond strength of the board in Example 1 increased from 0.502 MPa to 0.905 MPa. This indicates that while ammonium polyphosphate imparts flame retardant properties to the composite board, it can also improve the interfacial bonding performance of the board and increase its internal bond strength.

[0035] In Examples 1, 2, and 4, the amounts of ammonium polyphosphate added were 0.5%, 0.25%, and 0.1% of the dry mass of the mixture, respectively. Under the experimental conditions, the example with an addition of 0.5% ammonium polyphosphate exhibited higher internal bond strength, indicating that an appropriate amount of ammonium polyphosphate is beneficial to improving the bonding performance of the composite board.

[0036] Depend on Figure 2 The surface and cross-sectional morphology of the composite board shown indicate that when the isocyanate content is 10%, the board surface is relatively smooth, the cross-sectional structure is relatively dense and uniform, and the bonding between particles and fibers is tighter. These results suggest that an appropriate amount of isocyanate addition is beneficial for improving the internal structural uniformity and interfacial bonding of the composite board, thereby enhancing its mechanical properties.

[0037] For those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of this invention.

Claims

1. A flame-retardant fiber-reinforced cork composite board, characterized in that, It includes softwood particles, plant fibers, and isocyanates and ammonium polyphosphates distributed between the interfaces of the softwood particles and plant fibers.

2. The flame-retardant fiber-reinforced cork composite board according to claim 1, characterized in that, The internal bond strength is not less than 0.7 MPa.

3. The flame-retardant fiber-reinforced cork composite board according to claim 1, characterized in that, The limiting oxygen index is not less than 27%.

4. The flame-retardant fiber-reinforced cork composite board according to claim 1, characterized in that, The softwood particles include one or more of pine particles, fir particles, spruce particles, fir particles, cork oak particles, cork oak particles, or regenerated softwood particles; the plant fibers include one or more of hemp fibers, bamboo fibers, cork oak bark fibers, coniferous fibers, or broadleaf fibers.

5. The flame-retardant fiber-reinforced cork composite board according to claim 1, characterized in that, The isocyanate accounts for 8-12% of the mass of the mixture; the ammonium polyphosphate accounts for 3-8% of the mass of the isocyanate.

6. The flame-retardant fiber-reinforced cork composite board according to claim 1, characterized in that, The cork particles have a particle size of 16-18 mesh.

7. The flame-retardant fiber-reinforced cork composite board according to claim 1, characterized in that, The mass ratio of cork particles to fibers is 1:0.67~1.

5.

8. A method for preparing a flame-retardant fiber-reinforced cork composite board according to any one of claims 1 to 7, characterized in that, The process includes the following steps: mixing softwood particles and plant fibers evenly to obtain a mixture; mixing isocyanate and ammonium polyphosphate to prepare a flame-retardant adhesive; then evenly applying the flame-retardant adhesive to the mixture, stirring thoroughly, and then laying it into a mold for cold pressing and demolding; and finally hot pressing to obtain a composite board.

9. The method for preparing the flame-retardant fiber-reinforced cork composite board according to claim 8, characterized in that, The hot pressing temperature is 150~170℃.

10. The method for preparing the flame-retardant fiber-reinforced cork composite board according to claim 8, characterized in that, The hot pressing process includes: performing a three-stage stepped pressure reduction hot pressing process, which involves holding the pressure at 2.6~3.5MPa for 250~350s, at 1.6~2.5MPa for 150~250s, and at 0.8~1.5MPa for 80~120s.

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