Preparation method and application of plant fiber flame-retardant thermal insulation foam material

Abstract

This invention discloses a method for preparing a plant fiber flame-retardant and heat-insulating foam material and its application, comprising the following steps: pre-treating pulp fiber raw materials to a freeness of 30-45°SR; mixing the pre-treated pulp fibers with bentonite and dopamine, and dispersing them at high speed to form a suspension; adding cellulose nanofibers and a foaming agent to the suspension for foaming, and injecting the wet foam into a mold for drainage and molding after the volume of the wet foam has stabilized; injecting the wet foam into the mold for drainage and molding, and drying to obtain a high-efficiency flame-retardant bio-foam material with a three-dimensional porous structure. This application achieves a synergistic breakthrough in flame retardancy, heat insulation, mechanical strength, and environmental friendliness throughout its entire life cycle through a biomimetic "brick-mud" structural design + polydopamine interface coupling + atmospheric pressure foaming and drying process, possessing both high performance and green sustainability, and has broad application prospects in building energy conservation, new energy fire prevention, and environmentally friendly packaging.

Description

Technical Field

[0001] This invention belongs to the field of new materials and green building materials technology, specifically relating to a method for preparing a plant fiber flame-retardant and heat-insulating foam material and its application. Background Technology

[0002] Against the backdrop of increasing global energy and environmental pressures, building energy conservation and fire safety have become crucial issues. While traditional petroleum-based insulation materials (such as EPS / XPS) possess good insulation properties, they suffer from problems such as flammability, release of toxic fumes, and non-degradability, hindering sustainable development. Cellulose, as a renewable and biodegradable biomass resource, has been used to prepare environmentally friendly foam materials, but it faces technical bottlenecks such as poor flame retardancy, insufficient structural stability, and susceptibility to collapse during drying. In recent years, biomimetic structural design has provided new insights for the development of high-performance foam materials. For example, polydopamine based on mussel adhesion proteins can enhance interfacial bonding, and bentonite can serve as an inorganic flame retardant. Although there has been considerable exploration in the preparation of cellulose-based foam materials through atmospheric pressure drying, achieving a highly efficient synergy between structural stability, flame retardancy, thermal insulation, and environmental friendliness throughout the entire life cycle remains a current research hotspot and key challenge.

[0003] Chinese patent CN118922514A discloses a flame-retardant and heat-insulating material, which is a laminate comprising a flame-retardant layer and an aerogel layer, with an overall thickness not exceeding 25.4 mm. This approach enhances heat insulation performance by introducing aerogel and achieves fire resistance by combining it with a flame-retardant layer, offering advantages in terms of thinness. However, this material is primarily prepared using synthetic polymers or inorganic substances, without employing renewable plant fibers as the main raw material. Therefore, it has limitations in terms of biodegradability and environmental friendliness. Furthermore, its preparation process relies on aerogel, a costly and complex component, hindering large-scale application.

[0004] Chinese patent CN114846062A discloses a flame-retardant and heat-insulating material formed from a resin composition. This composition includes a binder resin, low-melting-point inorganic substances, and high-melting-point inorganic substances, forming a porous structure within it to achieve both heat insulation and flame-retardant properties. This technical solution improves the structural integrity of the material at high temperatures by controlling the melting behavior of the inorganic fillers. However, this material system still uses petroleum-based resin as the continuous phase, lacking effective utilization of natural plant fibers and failing to consider both the material's renewability and low-carbon properties. Furthermore, its porous structure depends on specific heat treatment conditions and is difficult to maintain stably under normal pressure drying or conventional processing conditions, limiting its applicability in the field of green building materials.

[0005] In summary, while existing technologies offer various solutions for flame-retardant and heat-insulating materials, a significant technological gap remains in the preparation of foam materials using plant fibers as the main component, which possess structural stability, high-efficiency flame-retardant and heat-insulating properties, and environmental friendliness. This invention, "A Preparation Method and Application of Plant Fiber Flame-Retardant and Heat-Insulating Foam Material," aims to overcome these shortcomings through biomimetic interface design and a green foaming process, providing a novel foam material that can be dried under normal pressure, is fully bio-based, highly flame-retardant, and has low thermal conductivity. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing plant fiber flame-retardant and heat-insulating foam materials and their applications, thereby solving the aforementioned technical problems in the prior art.

[0007] The objective of this invention can be achieved through the following technical solutions: A method for preparing a plant fiber flame-retardant and heat-insulating foam material includes the following steps: S1. The natural plant fiber pulp raw material is pre-treated by beating until the freeness is 30-45°SR to obtain the pre-treated pulp fiber. S2. Disperse the pretreated pulp fibers in Tris-HCl buffer, add dopamine, and stir at room temperature for 12-14 hours to allow dopamine to polymerize in situ on the fiber surface to form a polydopamine coating. Then add bentonite and shear disperse at 2000-5000 r / min to uniformly peel off and anchor the bentonite nanosheets to the polydopamine-modified fiber surface, forming a uniform suspension. S3. Add cellulose nanofibers and foaming agent to the suspension to foam. After the wet foam volume stabilizes, pour it into the mold to drain and form, thus completing the initial molding. S4. Inject the wet foam into the mold to drain and shape it, and dry it at 60-80℃ for 6-8 hours to obtain a high-efficiency flame-retardant bio-foam material. The resulting high-efficiency flame-retardant bio-foam material has the following performance parameters: Density is 17-28 mg / cm³ 3 ; Limiting oxygen index ≥44%; Vertical flammability rating: UL-94V-0; Thermal conductivity ≤49 mW / m·K; Carbon residue at 800℃ ≥54wt%.

[0008] Furthermore, the natural plant fiber pulp raw material is selected from one or a mixture of softwood pulp, hardwood pulp, bamboo pulp, hemp pulp, or waste paper pulp.

[0009] Furthermore, in S2, the added dopamine is 2-15 wt% of the oven-dry pulp fiber mass.

[0010] Furthermore, in S2, when dopamine is added, the pH is controlled to be 8.5-9.

[0011] Furthermore, in S2, the added bentonite is a layered silicate mineral with a nanoscale lamellar structure.

[0012] Furthermore, the mass ratio of bentonite to pulp fiber is 1:5 to 4:5.

[0013] Furthermore, in S3, the amount of cellulose nanofibers and foaming agent added is 0.1-0.5 wt% of the oven-dry weight of the pulp fiber.

[0014] Furthermore, in step S3, high-speed stirring is used during foaming, with a stirring speed of 2000-5000 r / min and a foaming time of 1-3 min.

[0015] Furthermore, its microstructure is as follows: the fiber network of pulp fibers serves as the framework, and layered silicate mineral nanosheets are uniformly and firmly attached to the surface of cellulose fibers and between pores through a polydopamine interface layer, forming a multi-level composite structure in the shape of a "brick-mud" imitation nacre layer.

[0016] An application of a plant fiber flame-retardant and heat-insulating foam material in building insulation, flame-retardant linings for transportation, fireproof encapsulation of electronic equipment, or environmentally friendly packaging materials.

[0017] The beneficial effects of this invention are: 1. The plant fiber flame-retardant and heat-insulating foam material obtained by the present invention has a structure in which cellulose fiber serves as a continuous phase to provide a biodegradable matrix, polydopamine serves as an interfacial coupling layer to enhance the compatibility of components and improve mechanical stability, and bentonite serves as an inorganic nanofiller to endow the material with efficient flame retardant and heat insulation properties; the three components work together through a biomimetic "brick-mud" structure to achieve a balance between high flame retardancy, low thermal conductivity and structural integrity at ultra-low density.

[0018] 2. The raw materials used in this invention are derived from renewable biomass and natural minerals. The process equipment requirements are low, energy consumption is significantly reduced, and it is compatible with continuous production. It does not require high pressure or low temperature conditions, thus overcoming the key bottleneck of large-scale preparation of biomass foam. After use, it can be physically recycled or naturally degraded. Its environmental impact throughout the entire life cycle is significantly lower than that of petroleum-based foam materials, providing a practical and feasible technical path for the industrialization of green materials.

[0019] 3. This invention enables polydopamine and bentonite to produce a multi-scale synergistic effect within the cellulose network. The resulting material not only possesses excellent thermal insulation properties but also outstanding fire safety performance: a limiting oxygen index as high as 44.8%, achieving the highest flame retardant rating of UL-94V-0, and a peak heat release rate that is 59.3% lower than that of pure cellulose foam. Simultaneously, the toughening effect of polydopamine and the reinforcing effect of bentonite allow the foam to maintain an ultra-low density of 17-28 mg / cm³. 3 At the same time, it achieves good structural stability and mechanical strength, realizing a comprehensive performance balance that is difficult to achieve with traditional materials.

[0020] 4. The raw materials used in this invention—fiber pulp, dopamine, and bentonite—are all derived from renewable or mineral resources, reducing dependence on fossil fuels at the source. Life cycle assessments show that compared to petroleum-based foams such as polystyrene and polyurethane, the material of this invention has significant advantages in 14 environmental indicators, including global warming potential and ecotoxicity. Furthermore, the material can be recycled through simple physical crushing and re-foaming after use. Its cellulose component exhibits a natural degradation rate of over 85% in soil within approximately 50 days, ultimately decomposing into harmless substances, truly embodying the "cradle-to-cradle" green design concept and demonstrating outstanding environmental benefits. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0022] Figure 1 This is a preparation route diagram of a plant fiber flame-retardant and heat-insulating foam material according to an embodiment of the present invention; Figure 2 This is a comparison diagram of the foam material of this invention and ordinary materials; Figure 3 This is a scanning electron microscope image of the interior of the foam material according to an embodiment of the present invention; Figure 4 This is a DES diagram of elemental silicon in the foam material of this invention embodiment; Figure 5 This is an infrared spectrum of the foam material according to an embodiment of the present invention; Figure 6 This is a comparison diagram of horizontal (left) and vertical (right) combustion samples of foam material according to an embodiment of the present invention; Figure 7 This is a comparison chart of the limiting oxygen index (LOI) of embodiments of the present invention; Figure 8 This is a comparison diagram of the biodegradation of the composite foam material (left) and polystyrene foam (right) in the embodiments of the invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0024] like Figure 1 As shown, this invention provides a method for preparing multi-scale biomimetic structural foam materials, including the following steps: S1. Unbleached softwood pulp fiber raw materials are subjected to pulping pretreatment. Natural plant fiber pulp can be used alone or mixed in any proportion. The pulping process is carried out using a PFI refiner, and the degree of freeness is measured by a Schubert freeness meter to a freeness of 30-50°SR, which improves fiber dispersion and ensures that the fibers are fully fibrillated but not over-cut, thereby forming a continuous network skeleton in the subsequent foaming process.

[0025] In the raw materials, cellulose fibers are derived from sustainably managed softwood pulp, providing a biodegradable matrix; polydopamine precursor: dopamine hydrochloride, which self-polymerizes under alkaline conditions to form an adhesive interface; bentonite: sodium montmorillonite, with a lamellar thickness of 1 nm, is used to enhance flame retardancy and thermal stability.

[0026] S2. The pretreated pulp fibers were dispersed in a Tris-HCl buffer solution with a pH of 8.5. The Tris-HCl buffer solution was prepared by tris(hydroxymethyl)aminomethane and hydrochloric acid, with a concentration of 10 mmol / L. The pH was precisely adjusted to 8.5 using 1 mol / L hydrochloric acid or sodium hydroxide solution. Dopamine was added at an amount of 2-20 wt% of the oven-dry fiber mass, along with bentonite (the mass ratio of bentonite to pulp fiber was 5:1 to 5:4, i.e., the mass ratio of pulp fiber to bentonite was controlled to be 5:1, 5:2, 5:3, or 5:4, respectively, as Example 1, Example 2, Example 3, and Example 4). The mixture was stirred at room temperature for 12 hours to allow dopamine to polymerize in situ on the fiber surface to form a polydopamine coating. Subsequently, the mixture was sheared at a high speed of 2000-5000 r / min to uniformly exfoliate and anchor the bentonite nanosheets onto the polydopamine-modified fiber surface, forming a stable composite suspension.

[0027] S3. Add cellulose nanofibers and foaming agent sodium dodecyl sulfate (addition amount is 0.1-0.5 wt% of the total mass of the suspension) to the suspension. Mechanically foam for 1-3 minutes under high speed stirring. After the wet foam volume stabilizes, quickly inject it into a custom mold coated with polytetrafluoroethylene. Drainage is assisted by gravity and negative pressure to initially form the foam.

[0028] S4. Place the drained wet foam, along with the mold, in a 60℃ oven and dry under normal pressure for 5-8 hours. The moisture evaporates slowly through the pore channels. The presence of the polydopamine layer slows down the pore wall shrinkage caused by capillary force, preventing structural collapse. After drying, allow it to cool naturally to room temperature. After demolding, you will obtain a multi-scale biomimetic flame-retardant and heat-insulating foam material with a three-dimensional porous network structure. The resulting composite foam material includes the following performance parameters: Density is 17-28 mg / cm³ 3 ; Limiting oxygen index ≥44%; Vertical flammability rating: UL-94V-0; Thermal conductivity ≤49mW / m·K; Carbon residue at 800℃ ≥54wt%.

[0029] When the mass ratio of bentonite to pulp fiber is 5:4, the density of the resulting foam material is 26-28 mg / cm³. 3 Thermal conductivity ≤49 mW / (m·K), limiting oxygen index can reach 44.8%.

[0030] Table 1

[0031] Peak heat release rate (PHRR) ≤ 60.3 kW / m 2 (35kW / m) 2 (under heat flow) The microstructure of the composite foam material consists of bentonite nanosheets firmly and uniformly anchored to the surface of cellulose fibers through a polydopamine layer.

[0032] Application of a composite foam material in building insulation, flame-retardant lining for transportation, fireproof encapsulation of electronic equipment, or environmentally friendly packaging materials.

[0033] The specific experimental method involved first weighing 20 g of oven-dried unbleached softwood pulp and adding it to a fiber decomposer. Water was added to adjust the suspension concentration to 2 wt%, and the pulp was dispersed under high-speed stirring. Subsequently, the pulp was dispersed in Tris-HCl buffer at pH 8.5, and dopamine hydrochloride (added at 2-20 wt% of the oven-dried fiber mass) and bentonite were added. The mixture was stirred continuously at room temperature for 12 h.

[0034] After thorough mixing, cellulose nanofibers and sodium dodecyl sulfate (0.1-0.5 wt% of the suspension) were added to the system along with 0.8 g of the mixture, and the mixture was stirred at high speed to foam. When the wet foam reached its maximum and stabilized volume, it was quickly poured into a polytetrafluoroethylene mold with a drainage bottom to remove excess water. Subsequently, it was placed in a 60 ℃ oven and dried under normal pressure for 5-8 h. The mixture was divided into groups according to the mass ratio of bentonite to oven-dried fiber (0:5, 1:5, 2:5, 3:5, 4:5), with pure cellulose foam without added dopamine and bentonite serving as a blank control group.

[0035] Cellulose and bentonite were composited with polydopamine to prepare a foam material. Bentonite nanosheets were firmly attached to the fiber surface through a polydopamine coating, and the three components synergistically constructed a lightweight, high-strength porous material. The foam sample was cut into regular shapes and weighed; its density was calculated to be approximately 28 mg / cm³. 3 This indicates that the addition of functional components achieves high performance while maintaining the material's ultra-low density characteristics. By comparing the appearance of the sample with the blank control group (…), Figure 2 As shown in the figure, it can be observed that the foam with added bentonite and polydopamine has a regular shape and uniform structure after molding. In contrast, the cellulose foam in the blank control group showed obvious shrinkage and structural collapse after drying.

[0036] The microstructure of the materials was observed using SEM, and the samples in each group were examined using scanning electron microscopy. Figure 3 As shown, it can be clearly seen that the bentonite sheets are uniformly coated with polydopamine and anchored on the surface and pores of the cellulose fiber network. With the decrease in the proportion of bentonite added, its coverage and uniformity of distribution on the fiber surface also decrease accordingly. EDS scanning analysis ( Figure 4 This further confirms the uniform distribution of silicon (from bentonite) throughout the material, which helps to achieve consistent and efficient flame-retardant and heat-insulating performance.

[0037] Infrared spectrum of materials ( Figure 5 The image shows the typical characteristic peak of cellulose: 3320 cm⁻¹. -1 (OH / NH stretching vibration), 1631 cm -1 (OH bending). Simultaneously, characteristic peaks related to the vibration of the benzene ring skeleton in polydopamine and peaks related to the vibration of the bentonite silica skeleton also appeared in the spectrum, confirming the successful recombination of the components.

[0038] The flame retardant properties of the materials were evaluated using vertical and horizontal burning (UL-94) and limiting oxygen index (LOI) tests, such as... Figure 6 and Figure 7As shown, the blank sample ignited rapidly upon contact with fire, with a fast flame spread, while the HEFBF-4 sample self-extinguished rapidly after the fire source was removed within 10 seconds of ignition, without any molten droplets. Its limiting oxygen index reached 44.8%, achieving the UL-94 V-0 rating. Cone calorimetry testing showed that the peak heat release rate (PHRR) of HEFBF-4 was only 60.3 kW / m³. 2 Compared to pure cellulose foam (148.9 kW / m³), 2 The CO2 yield was reduced by 59.3%; the total heat release (THR) was also reduced by 44.7%. In addition, the peak CO2 yield and effective heat of combustion both decreased significantly, indicating that the combustion intensity was effectively suppressed.

[0039] To investigate the degradation behavior and recycling potential of the material of this invention in the natural environment, soil burial biodegradation experiments and material recycling and reprocessing experiments were conducted. For example... Figure 8 As shown, the sample and polystyrene foam were buried together in natural soil, and morphological changes were observed periodically. The results showed that the polystyrene foam remained almost unchanged during burial, while the cellulose matrix of the sample underwent significant decomposition after about 50 days, the foam structure gradually disintegrated, and it eventually returned to the natural environment.

[0040] This invention achieves a synergistic breakthrough in flame retardancy, heat insulation, mechanical strength, and environmental friendliness throughout the entire life cycle through a biomimetic "brick-mud" structural design, polydopamine interface coupling, and atmospheric pressure foaming and drying process. It combines high performance with green sustainability and has broad application prospects in fields such as building energy conservation, new energy fire prevention, and environmentally friendly packaging.

[0041] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for preparing a plant fiber flame-retardant and heat-insulating foam material, characterized in that, Includes the following steps: S1. The natural plant fiber pulp raw material is pre-treated by beating until the freeness is 30-45°SR to obtain the pre-treated pulp fiber. S2. Disperse the pretreated pulp fibers in Tris-HCl buffer, add dopamine, and stir at room temperature for 12-14 hours to allow dopamine to polymerize in situ on the fiber surface to form a polydopamine coating. Then add bentonite and shear disperse at 2000-5000 r / min to uniformly peel off and anchor the bentonite nanosheets to the polydopamine-modified fiber surface, forming a uniform suspension. S3. Add cellulose nanofibers and foaming agent to the suspension to foam. After the wet foam volume stabilizes, pour it into the mold to drain and form, thus completing the initial molding. S4. Inject the wet foam into the mold to drain and shape it, and dry it at 60-80℃ for 6-8 hours to obtain a high-efficiency flame-retardant bio-foam material. The resulting high-efficiency flame-retardant bio-foam material has the following performance parameters: Density is 17-28 mg / cm³ 3 ; Limiting oxygen index ≥44%; Vertical flammability rating: UL-94V-0; Thermal conductivity ≤49 mW / m·K; Carbon residue at 800℃ ≥54wt%.

2. The method for preparing plant fiber flame-retardant and heat-insulating foam material according to claim 1, characterized in that, The natural plant fiber pulp raw material is selected from one or a mixture of softwood pulp, hardwood pulp, bamboo pulp, hemp pulp or waste paper pulp.

3. The method for preparing plant fiber flame-retardant and heat-insulating foam material according to claim 1, characterized in that, In S2, the added dopamine is 2-15 wt% of the oven-dry pulp fiber mass.

4. The method for preparing plant fiber flame-retardant and heat-insulating foam material according to claim 3, characterized in that, In S2, when dopamine is added, the pH is controlled to be 8.5-9.

5. The method for preparing plant fiber flame-retardant and heat-insulating foam material according to claim 1, characterized in that, In S2, the added bentonite is a layered silicate mineral with a nanoscale lamellar structure.

6. The method for preparing plant fiber flame-retardant and heat-insulating foam material according to claim 5, characterized in that, The mass ratio of bentonite to pulp fiber is 1:5 to 4:

5.

7. The method for preparing plant fiber flame-retardant and heat-insulating foam material according to claim 1, characterized in that, In S3, the amount of cellulose nanofibers and foaming agent added is 0.1-0.5 wt% of the oven-dry weight of pulp fibers.

8. The method for preparing plant fiber flame-retardant and heat-insulating foam material according to claim 1, characterized in that, In step S3, during foaming, high-speed stirring is used, with a stirring speed of 2000-5000 r / min and a foaming time of 1-3 min.

9. A plant fiber flame-retardant and heat-insulating foam material prepared by the method according to any one of claims 1-8, characterized in that, Its microstructure is as follows: the fiber network of pulp fiber serves as the skeleton, and layered silicate mineral nanosheets are uniformly and firmly attached to the surface of cellulose fiber and between pores through polydopamine interface layer, forming a multi-level composite structure with a "brick-mud" shape that resembles nacre.

10. A plant fiber flame-retardant and heat-insulating foam material, characterized in that, Applications in building insulation, flame-retardant linings for transportation, fireproof encapsulation of electronic equipment, or environmentally friendly packaging materials.

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