Flame-retardant smoke-suppressing straw composite board and preparation method thereof

Abstract

The invention provides a flame-retardant smoke-suppressing straw composite board and a preparation method thereof. The preparation method comprises the following steps: step 1, dropwise adding phytic acid and a silane coupling agent to the surface of pretreated straw, and stirring until the phytic acid and the silane coupling agent are completely absorbed to obtain an initial compound; step 2, uniformly stirring and dispersing bio-based waterborne polyurethane, epoxy resin, ferric oxide and a bio-based nano flame retardant to obtain a prepolymer mixture; and 3, pouring the initial compound and the prepolymer mixture into a mold, and carrying out microwave-assisted cold pressing curing to obtain the flame-retardant and smoke-suppressing straw composite board. The silane coupling agent, the bio-based polyurethane and the epoxy resin are introduced while flame retardance and smoke suppression can be achieved, a formed three-dimensional network can anchor ferric oxide and the bio-based nano flame retardant, migration and hygroscopicity of the flame retardant are prevented, meanwhile, interface defects are reduced, the stress transmission efficiency is improved, and therefore the mechanical property is improved; and the durability and the long-term stability are improved.

Description

Technical Field

[0001] This invention relates to the field of flame-retardant and smoke-suppressing board technology, specifically to a flame-retardant and smoke-suppressing straw composite board and its preparation method. Background Technology

[0002] Green and low-carbon transformation has become the core direction for the development of various industries. Agricultural straw, as a massive biomass resource in my country with an annual output of up to 900 million tons, plays a crucial role in reducing environmental pollution and promoting a circular agricultural economy through its high-value utilization. However, currently, the resource utilization rate of straw in my country is less than 50%, and it is mainly used in low-value-added fields such as fuel and feed, with an extremely low proportion of high-value applications. Transforming straw into high-performance environmentally friendly materials, especially functional building materials that meet green building requirements, is an effective way to solve the problem of straw disposal.

[0003] Currently, using straw-filled polymer-based composites is one of the mainstream research directions, such as wood-plastic composites (WPC). Polyurethane is commonly used as the matrix due to its good adhesion and toughness. However, both polyurethane and straw are flammable materials with low limiting oxygen indexes, posing a high fire risk. Furthermore, combustion produces large amounts of smoke and toxic gases such as CO, posing a significant threat to life. Traditional solutions often rely on adding inorganic flame retardants, which often require large amounts to achieve flame-retardant effects. This severely damages the material's mechanical properties, increases its brittleness and density, and provides limited smoke suppression.

[0004] In recent years, domestic and international research has begun to explore bio-based flame retardants to improve environmental friendliness. Among them, phytic acid (PA) has attracted attention due to its high phosphorus content, renewability, and chelating ability. Existing technologies indicate that combining phytic acid with metal ions (Fe...) 3+ The combination of phytic acid and carbon during combustion can catalyze the formation of a protective layer, thereby simultaneously improving flame retardancy and smoke suppression properties. However, phytic acid has strong water absorption properties, which can easily cause the composite material to swell due to moisture absorption, leading to interface degradation, mechanical property degradation, and flame retardant failure, severely affecting its long-term service life in humid environments. Therefore, there is an urgent need for a straw composite material that simultaneously possesses high performance, high durability, and long-term stability. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] To address the shortcomings of existing technologies, this invention provides a flame-retardant and smoke-suppressing straw composite board and its preparation method. By selecting bio-based raw materials, employing multi-component synergistic flame retardancy and smoke suppression, and utilizing an efficient microwave-assisted curing process, the problems mentioned in the background technology are solved.

[0007] (II) Technical Solution

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] According to a first aspect of the present invention, a method for preparing a flame-retardant and smoke-suppressing straw composite board is provided, comprising the following steps:

[0010] Step 1: Add phytic acid and silane coupling agent to the surface of the pretreated straw, stir until completely absorbed, and obtain the initial complex;

[0011] Step 2: Stir and disperse the bio-based waterborne polyurethane, epoxy resin, iron oxide and bio-based nano flame retardant evenly to obtain a prepolymer mixture;

[0012] Step 3: Pour the mixture of the initial composite and the prepolymer into a mold and perform microwave-assisted cold pressing curing to obtain the flame-retardant and smoke-suppressing straw composite board.

[0013] This invention involves dripping phytic acid onto the surface of straw while simultaneously adding a silane coupling agent. The silane coupling agent reacts with phytic acid molecules to generate a hydrophobic phytic acid derivative, which is then mixed with a prepolymer mixture. The silane coupling agent undergoes hydrolysis, forming a strong chemical bond with the straw fibers and polyurethane matrix. This anchors iron oxide and bio-based nano-flame retardants within the matrix, addressing flame retardant migration and hygroscopicity. Furthermore, the bio-based waterborne polyurethane and epoxy resin can form an interpenetrating network, improving toughness and rigidity while resolving flame retardant migration.

[0014] Preferably, in step 1, the pretreatment method for the straw is low-temperature plasma treatment, and the parameters of the low-temperature plasma treatment are: oxygen flow rate of 20-100 sccm, pressure of 20-100 Pa, discharge power of 50-300 W, electrode distance of 2-5 cm, and treatment time of 1-10 min.

[0015] The pretreatment method of straw in this invention adopts low-temperature plasma treatment, which can avoid excessive degradation of cellulose by chemical reagents, retain the strength of the straw itself. At the same time, the low-temperature plasma treatment not only improves the surface roughness of the straw, but also introduces a large number of oxygen-containing groups on the surface of the straw. These groups can then form stronger chemical bonds with the functional groups of bio-based waterborne polyurethane and epoxy resin, greatly enhancing interfacial compatibility and bonding strength, and improving the durability of the composite board.

[0016] Preferably, in step 1, the mass ratio of straw, phytic acid, and silane coupling agent is 100:5 to 15:1 to 5.

[0017] More preferably, in step 1, the mass ratio of straw, phytic acid and silane coupling agent is 100:8-12:2-3.

[0018] Preferably, in step 2, the mass ratio of bio-based waterborne polyurethane, epoxy resin, iron oxide and bio-based nano flame retardant in the prepolymer mixture is 50-70:20-40:3-8:5-15.

[0019] More preferably, the mass ratio of bio-based waterborne polyurethane, epoxy resin, iron oxide and bio-based nano flame retardant in the prepolymer mixture is 60:30:5:10.

[0020] Preferably, in step 2, the bio-based nano flame retardant is selected from lignin nanocellulose and / or chitosan nanoparticles.

[0021] Preferably, in step 3, the mass ratio of the initial complex to the prepolymer mixture is 1:0.7 to 1.1.

[0022] Preferably, in step 3, the conditions for microwave-assisted cold pressing curing are: pressure of 1-5 MPa, microwave power of 500-1500 W, and microwave time of 3-10 min.

[0023] According to a second aspect of the present invention, a flame-retardant and smoke-suppressing straw composite board obtained according to the above preparation method is provided.

[0024] Beneficial effects

[0025] This invention provides a flame-retardant and smoke-suppressing straw composite board and its preparation method. It has the following beneficial effects:

[0026] (1) The present solution provides a method for preparing a flame-retardant and smoke-suppressing straw composite board. Through the synergistic effect of phytic acid and bio-based nano flame retardant, and the oxidation of soot particles during the combustion process catalyzed by iron oxide, the generation of dense smoke is reduced. The dense carbon layer promoted by phytic acid effectively inhibits the overflow of precursor substances of volatile smoke particles, thereby achieving the flame-retardant and smoke-suppressing effect. One end of the silane coupling agent reacts with the hydroxyl groups on the surface of straw, and the other end reacts with the functional groups of bio-based polyurethane and epoxy resin, forming a strong chemical bond at the inorganic / organic interface. The three-dimensional network formed can not only anchor iron oxide and bio-based nano flame retardant to prevent the migration and hygroscopicity of flame retardant, but also reduce interface defects and improve stress transmission efficiency, thereby improving the bending strength, tensile strength and impact resistance of the composite board.

[0027] (2) The flame-retardant and smoke-suppressing straw composite board provided by this solution covers the phytic acid and straw surface with a hydrophobic molecular film by a silane coupling agent. At the same time, the amino group in the silane coupling agent also interacts with the phosphate group in the phytic acid molecule, which can firmly anchor the phytic acid to the straw surface and reduce the possibility of its free migration due to moisture absorption. In addition, the three-dimensional network structure formed by epoxy resin and bio-based polyurethane completely wraps the straw fibers after hydrophobic treatment and chelation reaction, thereby improving the durability and long-term stability of the composite board. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with embodiments. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0030] To better illustrate the content of this invention, the following description is provided in conjunction with specific embodiments.

[0031] Example 1

[0032] A flame-retardant and flammable straw composite board is prepared by the following steps:

[0033] Step 1: Introduce oxygen at a flow rate of 50 sccm, set the pressure to 30 Pa, the discharge power to 100 W, and the electrode distance to 3 cm, and perform low-temperature plasma treatment on the straw for 5 min.

[0034] Step 2: Add 100 parts of straw treated with low temperature plasma to an aqueous solution containing 10 parts of phytic acid and 4 parts of silane coupling agent, and stir until completely absorbed to obtain the initial complex.

[0035] Step 3: Mix 60 parts of bio-based waterborne polyurethane, 30 parts of epoxy resin, 5 parts of iron oxide and 10 parts of lignin nanocellulose evenly to obtain a prepolymer mixture.

[0036] Step 4: Mix the initial composite and prepolymer mixture at a mass ratio of 1:1 and pour it into a mold. Set the pressure to 3MPa, the microwave power to 1000W, and microwave-assisted cold pressing curing treatment for 5 minutes to obtain flame-retardant and smoke-suppressing straw composite board.

[0037] Example 2

[0038] The preparation method of this embodiment is the same as that of Example 1, except that in step 4, the mass ratio of the initial complex to the prepolymer mixture is 1:0.7.

[0039] Example 3

[0040] The preparation method of this embodiment is the same as that of Example 1, except that in step 4, the mass ratio of the initial complex to the prepolymer mixture is 1:0.9.

[0041] Example 4

[0042] The preparation method of this embodiment is the same as that of Example 1, except that in step 4, the mass ratio of the initial complex to the prepolymer mixture is 1:1.1.

[0043] Example 5

[0044] The preparation method of this embodiment is the same as that of Example 1. The difference is that in step 2, the mass ratio of straw after low-temperature plasma treatment to phytic acid and silane coupling agent is 100:5:1.

[0045] Example 6

[0046] The preparation method of this embodiment is the same as that of Example 1. The difference is that in step 2, the mass ratio of straw after low-temperature plasma treatment to phytic acid and silane coupling agent is 100:15:5.

[0047] Example 7

[0048] The preparation method of this embodiment is the same as that of Example 1, except that in step 3, the mass ratio of bio-based waterborne polyurethane, epoxy resin, iron oxide and lignin nanofibers in the prepolymer mixture is 50:35:8:7.

[0049] Example 8

[0050] The preparation method of this embodiment is the same as that of Example 1, except that in step 3, the mass ratio of bio-based waterborne polyurethane, epoxy resin, iron oxide and lignin nanofibers in the prepolymer mixture is 70:20:5:5.

[0051] Comparative Example 1

[0052] The preparation method of this comparative example is the same as that of Example 1, except that no silane coupling agent was added in step 2.

[0053] Comparative Example 2

[0054] The preparation method of this comparative example is the same as that of Example 1, except that epoxy resin was not added in step 3.

[0055] Comparative Example 3

[0056] The preparation method of this embodiment is the same as that of Example 1, except that the pretreatment method of straw in step 1 is: soaking the straw in a mixed solution of 2.5M sodium hydroxide and 4M sodium sulfite at 85℃ for 6 hours.

[0057] Performance testing

[0058] The flame-retardant and smoke-suppressing straw composite boards prepared in the above embodiments and comparative examples were subjected to performance tests.

[0059] (1) Hygroscopicity test: The test was conducted according to the ASTM D570 standard. The straw composite board was placed in an oven and dried to constant weight. Then the straw composite board was completely immersed in distilled water and kept at 23°C for 24 hours. After taking it out, all water droplets on the surface were wiped off with absorbent paper, and the hygroscopicity was tested.

[0060] (2) Bending strength: According to the ASTM D790 standard, a universal testing machine is used to apply a load to the center of the plate at a speed of 2 mm / min until the plate breaks, and the bending strength is tested.

[0061] (3) Tensile strength: According to ASTM D638, the specimen is stretched at a constant speed of 5 mm / min using a universal testing machine until it breaks, and the tensile strength is tested.

[0062] (4) Impact resistance: The impact strength of the plate was tested using a pendulum impact tester according to ASTM D6110 standard;

[0063] The test results are shown in Table 1.

[0064] Table 1

[0065]

[0066] According to the test results in Table 1, the present invention introduces a silane coupling agent to react with the functional groups of bio-based polyurethane and epoxy resin, forming a strong chemical bond at the inorganic / organic interface. The resulting three-dimensional network can anchor iron oxide and bio-based flame retardant, preventing the migration and moisture absorption of the flame retardant. The moisture absorption rate can be controlled to below 13%, thereby improving the bending strength, tensile strength and impact toughness of the composite board.

[0067] A comparison of Comparative Examples 1-2 with Example 1 shows that omitting the silane coupling agent or epoxy resin leads to interface deterioration, a significant increase in moisture absorption, and a substantial decrease in mechanical properties. Comparative Example 3, which uses chemical reagents to treat straw, not only damages the straw surface but also reduces its strength, resulting in increased water absorption and decreased mechanical properties. This invention, through the selection of the aforementioned raw materials and combined with the processing technology, achieves flame retardancy and smoke suppression while improving the durability and long-term stability of the board material.

[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a flame-retardant and smoke-suppressing straw composite board, characterized in that: Includes the following steps: Step 1: Add phytic acid and silane coupling agent to the surface of the pretreated straw, stir until completely absorbed, and obtain the initial complex; Step 2: Stir and disperse the bio-based waterborne polyurethane, epoxy resin, iron oxide and bio-based nano flame retardant evenly to obtain a prepolymer mixture; Step 3: Pour the mixture of the initial composite and the prepolymer into a mold and perform microwave-assisted cold pressing curing to obtain the flame-retardant and smoke-suppressing straw composite board.

2. The method for preparing a flame-retardant and smoke-suppressing straw composite board according to claim 1, characterized in that: In step 1, the pretreatment method for the straw is low-temperature plasma treatment. The parameters of the low-temperature plasma treatment are: oxygen flow rate of 20-100 sccm, pressure of 20-100 Pa, discharge power of 50-300 W, electrode distance of 2-5 cm, and treatment time of 1-10 min.

3. The method for preparing a flame-retardant and smoke-suppressing straw composite board according to claim 1, characterized in that: In step 1, the mass ratio of straw, phytic acid and silane coupling agent is 100:5 to 15:1 to 5.

4. The method for preparing a flame-retardant and smoke-suppressing straw composite board according to claim 1, characterized in that: In step 2, the mass ratio of bio-based waterborne polyurethane, epoxy resin, iron oxide and bio-based nano flame retardant in the prepolymer mixture is 50-70:20-40:3-8:5-15.

5. The method for preparing a flame-retardant and smoke-suppressing straw composite board according to claim 1, characterized in that: In step 2, the bio-based nano flame retardant is selected from lignin nanocellulose and / or chitosan nanoparticles.

6. The method for preparing a flame-retardant and smoke-suppressing straw composite board according to claim 1, characterized in that: In step 3, the mass ratio of the initial composite to the prepolymer mixture is 1:0.7 to 1.

1.

7. The method for preparing a flame-retardant and smoke-suppressing straw composite board according to claim 1, characterized in that: In step 3, the conditions for microwave-assisted cold pressing curing are: pressure of 1-5 MPa, microwave power of 500-1500 W, and microwave time of 3-10 min.

8. A flame-retardant and smoke-suppressing straw composite board obtained by the preparation method according to any one of claims 1 to 7.

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