A method for preparing polyvinyl alcohol flame-retardant films using carbon dots from coffee shells and its application

Abstract

This invention proposes a method and application for preparing polyvinyl alcohol (PVA) flame-retardant films using coffee shell carbon dots, belonging to the field of composite material technology. The method includes the following steps: mixing a coffee shell carbon dot solution with PVA, heating in an oil bath and then cooling to room temperature; casting the cooled coffee shell carbon dot-PVA solution into a film; and drying to obtain a coffee shell carbon dot-based PVA flame-retardant film. This invention utilizes coffee shells as a raw material to prepare carbon dots, mainly utilizing the caffeic acid and chlorogenic acid in the coffee shells, achieving resource utilization of waste materials, reducing the production cost of the flame-retardant film, and producing a lightweight flame-retardant film with certain mechanical strength. It is suitable for various fields requiring lightweight flame-retardant materials, and exhibits excellent flame-retardant properties, effectively delaying or preventing flame spread and improving material safety. The preparation method is simple and more suitable for widespread application.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, and in particular relates to a method and application for preparing polyvinyl alcohol flame-retardant films using carbon dots from coffee shells. Background Technology

[0002] Flame-retardant films are functional film materials that can effectively inhibit or delay the spread of flames. They are lightweight, flexible, and easy to process, and have wide applications in electronics, building decoration, and transportation. For example, in electronics, flame-retardant films can be used as insulating layers on printed circuit boards to prevent fires caused by short circuits; in building decoration, they can be used as surface coatings for wallpaper, flooring, and other materials to improve the fire safety rating of buildings; and in transportation, they can be used as interior materials for aircraft, high-speed trains, and other vehicles to reduce fire risk. With increasing awareness of safety and environmental protection, the demand for flame-retardant films is growing, and higher performance requirements are being placed on them.

[0003] However, traditional flame-retardant films still have many shortcomings in practical applications. First, traditional flame retardants such as aluminum hydroxide and magnesium hydroxide often require large amounts to achieve the desired flame-retardant effect, which significantly reduces the mechanical properties and transparency of the film, limiting its application range. Second, some flame retardants, such as halogenated flame retardants, produce toxic and harmful gases during combustion, posing a threat to the environment and human health, which contradicts the current green and environmentally friendly development concept. Furthermore, some novel flame retardants, such as nano-flame retardants and organophosphorus flame retardants, although possessing high flame-retardant efficiency, have complex preparation processes and high costs, making large-scale industrial production difficult. These problems severely restrict the further development and application of flame-retardant films.

[0004] Therefore, this invention proposes a method for preparing PVA flame-retardant films using carbon dots from coffee shells. Summary of the Invention

[0005] The mechanical and flame-retardant properties of composite materials are typically improved by adding expensive nanoparticles (such as MXene, graphene oxide, boron nitride, etc.) or complex chemical modifications. However, these methods are not only costly but also involve complex preparation processes, limiting their large-scale application. To address these technical problems, this invention proposes a method and application for preparing PVA flame-retardant films using coffee shell carbon dots. The polyvinyl alcohol flame-retardant film obtained by this invention can achieve similar effects to the aforementioned expensive nanoparticle or complex chemically modified films, while avoiding the use of expensive materials and simplifying the preparation process. This invention utilizes the interfacial interaction between coffee shell carbon dots (CS-CDs) and the polyvinyl alcohol (PVA) matrix, which not only improves the mechanical strength of the film but also significantly enhances its flame-retardant properties, providing a new approach for developing high-performance, low-cost flame-retardant materials.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention:

[0008] A method for preparing a polyvinyl alcohol flame-retardant film using coffee shell carbon dots, comprising the following steps:

[0009] Mix the coffee shell carbon dots (CS-CDs) solution with polyvinyl alcohol (PVA), heat it in an oil bath and then cool it to room temperature. Cast the cooled coffee shell carbon dot-polyvinyl alcohol solution into a film, and obtain a coffee shell carbon dot-based polyvinyl alcohol flame-retardant film after drying.

[0010] The coffee shell carbon dots (CS-CDs) of the present invention are different from other carbon dots in that their excellent flame-retardant properties mainly depend on the caffeic acid and chlorogenic acid rich in coffee shells:

[0011] (1) Specificity of functional groups

[0012] Caffeic acid (4-hydroxycinnamic acid) and chlorogenic acid (ester of caffeic acid and quinic acid) are both polyphenolic compounds, rich in catechol hydroxyl (-OH), carboxylic acid groups (-COOH) and unsaturated double bonds (C=C). These groups are retained and anchored on the surface of the carbon dots during the preparation process of the carbon dots (hydrothermal carbonization), forming a unique surface functional group array. Among them, the formed catechol structure can provide Lewis basic sites, which can form hydrogen bonds with the polar groups (-NH-, -OH) of the polymer, enhance the interfacial compatibility, and avoid the aggregation of carbon dots. The formed carboxylic acid groups undergo decarboxylation reactions (-COOH→CO2↑) at high temperatures (>200°C), absorb heat (about 150 kJ / mol) and release non-combustible gases, diluting the concentration of combustible gases. The formed π-π conjugate system can improve the thermal stability of the carbon dots (decomposition temperature >500°C), and at the same time promote the graphitization degree of the carbon layer. In contrast, the surface of traditional carbon dots (such as glucose-based carbon dots) is mainly composed of alcohol hydroxyl (-OH), lacking carboxylic acid and conjugated double bonds, resulting in less gas release (CO2 release amount <40% of CS-CDs) and low charring efficiency during thermal decomposition.

[0013] (2) Thermal decomposition behavior - multiple flame-retardant synergistic effect

[0014] The flame retardant properties of CS-CDs mainly rely on the thermal decomposition process. First, there is the dehydration stage (100-200℃), where surface hydroxyl groups condense, releasing H2O and lowering the surface temperature of the material. In the decarboxylation / esterification stage (200-350℃), caffeic acid is decarboxylated to generate styrene, which further cyclizes to form an aromatic carbon precursor. Chlorogenic ester bonds break, releasing caffeic acid and quinic acid. Quinic acid dehydrates to form a cyclic ether structure, enhancing the cross-linking of the carbon layer. During this stage, CO2 and CO are released, forming a physical barrier. Then, in the carbonization stage (>350℃), the remaining polyphenol skeleton carbonizes, forming a nitrogen / oxygen-containing graphitized carbon layer, which rapidly dissipates heat.

[0015] (3) Acid-base synergistic carbonization mechanism

[0016] The carboxylic acid groups (acidic) on the surface of CS-CDs react with polyvinyl alcohol (PVA) to form a cross-linked network, which improves the mechanical strength of the carbon layer.

[0017] (4) Free radical capture-phenolic structure chemical flame retardancy

[0018] The phenolic hydroxyl groups (-OH) of caffeic acid and chlorogenic acid release H₂ during combustion. + It captures free radicals in the flame to terminate the chain combustion reaction.

[0019] Furthermore, the mass ratio of the coffee shell carbon dot solution to polyvinyl alcohol is 6:1.

[0020] Furthermore, the preparation method of the coffee shell carbon dot solution includes the following steps:

[0021] Coffee shells were added to deionized water for a hydrothermal reaction. After the hydrothermal reaction was completed, the mixture was cooled to room temperature, centrifuged, and the supernatant was collected. After drying, a coffee shell carbon dot solution with a mass concentration of 1% was obtained.

[0022] In the method for preparing coffee shell carbon dot solution, the ratio of coffee shell to deionized water is 1g:100mL.

[0023] In the preparation method of coffee shell carbon dot solution, the hydrothermal reaction temperature is 180℃ and the time is 10h.

[0024] In the method for preparing coffee shell carbon dot solution, the drying temperature is 80℃ and the time is 12h.

[0025] Furthermore, the oil bath heating temperature is 95°C, and the time is 5 hours.

[0026] Furthermore, the drying temperature is 30°C and the drying time is 6 hours.

[0027] In this invention, the strong interfacial bonding between coffee shell carbon dots and the PVA matrix, formed through non-covalent bonds such as π-π interactions, hydrogen bonds, and van der Waals forces, effectively optimizes the energy dissipation mechanism. The unique caffeic acid and chlorogenic acid in the coffee shell, used to calcify the carbon dots, is the most distinctive feature that differentiates this carbon dot from others, significantly enhancing the fracture resistance and overall ductility of the film material. Furthermore, the uniform dispersion and unique micro-carbonization structure of the coffee shell carbon dots further improve the toughness and strength of the film, enabling it to maintain high strength while possessing excellent ductility and mechanical properties. In addition, the unique graphitized conjugated structure and micro-carbonization characteristics of the coffee shell carbon dots effectively promote the formation of a char layer during combustion, inhibiting heat and oxygen transfer, thereby significantly improving the flame-retardant properties of the material.

[0028] The second technical solution of the present invention:

[0029] A coffee shell carbon dot-based polyvinyl alcohol flame retardant film, prepared according to the method described above, wherein the thickness of the coffee shell carbon dot-based polyvinyl alcohol flame retardant film is 0.25 mm.

[0030] The third technical solution of the present invention:

[0031] The application of the coffee shell carbon dot-based polyvinyl alcohol flame-retardant film in the preparation of flame-retardant film materials.

[0032] Compared with the prior art, the present invention has the following advantages and technical effects:

[0033] (1) Carbon dots (CDs), as a novel carbon-based nanomaterial, have attracted widespread attention due to their unique structure and properties. Carbon dots possess characteristics such as small size, large specific surface area, and abundant surface functional groups, demonstrating great application potential in fields such as bioimaging, photocatalysis, and sensors. This invention uses CS-CDs as raw materials and mixes them with PVA to prepare flame-retardant films. This is because coffee shell carbon dots have excellent flame-retardant properties; their carbon core structure can form a dense carbon layer at high temperatures, effectively isolating heat and oxygen transfer, thereby inhibiting combustion. Compared with traditional flame retardants, the coffee shell carbon dots obtained in this invention not only have high flame-retardant efficiency but are also environmentally friendly and non-toxic, and do not release harmful gases during combustion. Therefore, this invention introduces coffee shell carbon dots into the preparation of flame-retardant films, which is expected to overcome the shortcomings of traditional flame-retardant films and promote the development of flame-retardant films towards high efficiency, environmental protection, and multifunctionality.

[0034] (2) The carbon dots used in this invention are prepared using coffee shells as raw materials, which realizes the resource utilization of waste, reduces environmental pollution, and conforms to the concept of sustainable development. Coffee shells are agricultural waste, which are widely available and inexpensive, thus reducing the production cost of flame retardant films.

[0035] (3) The flame-retardant film prepared by the present invention is lightweight and has certain mechanical strength, and is suitable for a variety of fields that require lightweight flame-retardant materials. It also has excellent flame-retardant properties, which can effectively delay or prevent the spread of flames and improve the safety of materials.

[0036] (4) The method for preparing the flame-retardant film of the present invention is simple and more suitable for widespread application. Attached Figure Description

[0037] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0038] Figure 1 The stress-strain curves of the thin films in Example 1 and Comparative Examples 1-2 are shown.

[0039] Figure 2 The stress (fracture strength) test results are for the films of Example 1 and Comparative Examples 1-2;

[0040] Figure 3 The fracture strain test results are for the thin films of Example 1 and Comparative Examples 1-2;

[0041] Figure 4 The toughness test results are for the films of Example 1 and Comparative Examples 1-2;

[0042] Figure 5 The limiting oxygen index (LOI) test results are for the films of Example 1 and Comparative Examples 1-3. Detailed Implementation

[0043] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0044] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0045] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0046] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0047] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0048] This invention provides a method for preparing polyvinyl alcohol flame-retardant films using carbon dots from coffee shells, comprising the following steps:

[0049] A coffee shell carbon dot (CS-CDs) solution was mixed with polyvinyl alcohol (PVA), heated in an oil bath, and then cooled to room temperature. The cooled coffee shell carbon dot-PVA solution was then cast into a film and dried to obtain a coffee shell carbon dot-based polyvinyl alcohol flame-retardant film.

[0050] In a preferred embodiment of the present invention, the mass ratio of coffee shell carbon dot solution to polyvinyl alcohol is 6:1.

[0051] In a preferred embodiment of the present invention, the method for preparing the coffee shell carbon dot solution includes the following steps:

[0052] Coffee shells were added to deionized water for a hydrothermal reaction. After the hydrothermal reaction was completed, the mixture was cooled to room temperature, centrifuged, and the supernatant was collected and dried to obtain a coffee shell carbon dot solution.

[0053] In the preparation method of coffee shell carbon dot solution, the ratio of coffee shell to deionized water is 1g:100mL, the hydrothermal reaction temperature is 180℃ and the time is 10h, and the drying temperature is 80℃ and the time is 12h.

[0054] In a preferred embodiment of the present invention, the oil bath heating temperature is 95°C and the time is 5 hours.

[0055] In a preferred embodiment of the present invention, the drying temperature is 30°C and the drying time is 6 hours.

[0056] This invention also proposes a coffee shell carbon dot-based polyvinyl alcohol flame retardant film, which is prepared according to the above method and has a thickness of 0.25 mm.

[0057] In a preferred embodiment of the present invention, room temperature refers to 20-30°C.

[0058] All raw materials used in this invention were purchased from the market, with polyvinyl alcohol purchased from Chengdu Jiacai Technology Co., Ltd.

[0059] The technical solution of the present invention will be further illustrated by the following embodiments.

[0060] Example 1

[0061] A method for preparing polyvinyl alcohol flame-retardant films using carbon dots from coffee shells includes the following steps:

[0062] (1) 1g of coffee shells were ground to 100μm using a grinder, added to 100mL of deionized water, placed in a reaction vessel, heated at 180℃ for 10h, and allowed to cool naturally to room temperature to obtain the initial solution of coffee shell carbon dots.

[0063] (2) The prepared coffee shell carbon dot initial solution was centrifuged and the supernatant was extracted. The extracted supernatant was placed in an oven and dried at 80°C for 12 hours to remove excess water, resulting in a coffee shell carbon dot solution with a mass concentration of 1%.

[0064] (3) Take 12g of coffee shell carbon dot solution cooled to room temperature, add 2g of polyvinyl alcohol, pour into a round bottom flask, and heat at 95°C for 5h using an oil bath to obtain coffee shell carbon dot-polyvinyl alcohol solution.

[0065] (4) Pour the coffee shell carbon dot-polyvinyl alcohol solution cooled to room temperature into a mold to cast a film, and place it in an oven to dry at 30°C for 6 hours to obtain a coffee shell carbon dot-based polyvinyl alcohol flame retardant film.

[0066] Comparative Example 1

[0067] A method for preparing a polyvinyl alcohol film includes the following steps:

[0068] Add 1g of polyvinyl alcohol to 100mL of deionized water, pour the solution into a round-bottom flask, and heat it at 95℃ for 4 hours using an oil bath to obtain a polyvinyl alcohol solution. After cooling, pour the solution into a mold to cast a film and place it in an oven to dry at 30℃ for 6 hours to obtain a polyvinyl alcohol film.

[0069] Comparative Example 2

[0070] A method for preparing a polyvinyl alcohol flame-retardant film using coffee shells includes the following steps:

[0071] 1g of coffee shells were ground to 100μm using a grinder, added to 100mL of deionized water, and then 1.96g of polyvinyl alcohol was added. The mixture was poured into a round-bottom flask and heated in an oil bath at 95℃ for 4 hours to obtain a coffee shell polyvinyl alcohol solution. After cooling, the solution was placed in an oven and dried at 30℃ for 6 hours to obtain a coffee shell polyvinyl alcohol film.

[0072] Comparative Example 3

[0073] A method for preparing polyvinyl alcohol flame-retardant films using carbon dots from coffee shells includes the following steps:

[0074] (1) 1g of coffee shells were ground to 500μm using a grinder, added to 100mL of deionized water, placed in a reaction vessel, heated at 160℃ for 8h, and allowed to cool naturally to room temperature to obtain the initial solution of coffee shell carbon dots.

[0075] (2) The prepared coffee shell carbon dot initial solution was centrifuged and the supernatant was extracted. The extracted supernatant was placed in an oven and dried at 90°C for 12 hours to remove excess water, resulting in a coffee shell carbon dot solution with a mass concentration of 1%.

[0076] (3) Take 6g of coffee shell carbon dot solution cooled to room temperature, add 2g of polyvinyl alcohol, pour into a round bottom flask, and heat at 95°C for 5h using an oil bath to obtain coffee shell carbon dot-polyvinyl alcohol solution.

[0077] (4) Pour the coffee shell carbon dot-polyvinyl alcohol solution cooled to room temperature into a mold to cast a film, and place it in an oven to dry at 30°C for 6 hours to obtain a coffee shell carbon dot-based polyvinyl alcohol flame retardant film.

[0078] Performance testing

[0079] The films prepared in Example 1 and Comparative Examples 1-2 were cut into rectangular samples (5cm×1cm×0.25mm) and their tensile properties were tested at room temperature. The results are shown in Table 1.

[0080] Uniaxial tensile testing was performed using an electronic universal testing machine (Shenzhen Sun Technology Co., Ltd., China), with an elongation speed of 5 mm / min.

[0081] Toughness is calculated based on the area under the stress-strain curve using the formula shown below:

[0082] ΔU=∫σds

[0083] In the formula, σ and ε are the stress and strain of the thin film, respectively, and ΔU is the toughness.

[0084] Table 1. Results of tensile strength and toughness measurements of films in Example 1 and Comparative Examples 1-2

[0085] Specimen Tensile strength (MPa) <![CDATA[Toughness (MJ / m 3 )]]> Example 1 185 227 Comparative Example 1 32 5.38 Comparative Example 2 23 2.89

[0086] As can be seen from the data in Table 1, the film prepared in Example 1 has the highest tensile strength and toughness, reaching 185 MPa and 227 MJ / m, respectively. 3 Furthermore, by comparing the data changes in Comparative Examples 1-2 with those in Example 1, it can be seen that the mechanical properties of the film incorporating coffee shell carbon dots are much higher than those of the film without coffee shell carbon dots, indicating that the embodiments of the present invention can prepare films with excellent mechanical properties.

[0087] Figure 1 The stress-strain curves of the thin films in Example 1 and Comparative Examples 1-2 are shown below. Figure 1 As can be seen, both the pure polyvinyl alcohol (PVA) film (Comparative Example 1) and the ordinary coffee shell PVA film (Comparative Example 2) exhibit low mechanical properties, with limited elongation at break and tensile strength, failing to meet the requirements for high-performance materials. Specifically, the stress-strain curves of the pure PVA film (Comparative Example 1) and the ordinary coffee shell PVA film (Comparative Example 2) show low elongation at break, indicating poor ductility and failing to reach the ideal level. In contrast, the coffee shell carbon dot-based PVA film prepared in Example 1 exhibits significantly improved mechanical properties, with its stress-strain curve showing an elongation at break of 224%, while the tensile strength is also significantly improved. This superior mechanical property is attributed to the strong bonding interface formed between the coffee shell carbon dots and the PVA matrix through non-covalent bonds such as π-π interactions, hydrogen bonds, and van der Waals forces, effectively improving stress transfer efficiency and the overall ductility of the material. Furthermore, the uniform dispersion and micro-carbonization structure of the coffee shell carbon dots further enhance the toughness and strength of the film, enabling it to maintain high ductility while possessing excellent mechanical properties. This result indicates that coffee shell carbon dot-based polyvinyl alcohol films have broad application potential in the fields of high-performance flame-retardant materials and flexible films.

[0088] Figure 2 The stress (fracture strength) test results for the films of Example 1 and Comparative Examples 1-2 are provided by [the relevant authority / organization]. Figure 2 It can be seen that the pure polyvinyl alcohol (PVA) film (Comparative Example 1) and the ordinary coffee shell polyvinyl alcohol film (Comparative Example 2) exhibited lower stress. In contrast, the coffee shell carbon dot-based polyvinyl alcohol film prepared in Example 1 had better stress, which was significantly improved compared to Comparative Examples 1 and 2.

[0089] Figure 3 The fracture strain test results of the thin films in Example 1 and Comparative Examples 1-2 are provided by... Figure 3It can be seen that the pure polyvinyl alcohol (PVA) film (Comparative Example 1) and the ordinary coffee shell polyvinyl alcohol film (Comparative Example 2) exhibited lower strain. In contrast, the coffee shell carbon dot-based polyvinyl alcohol film prepared in Example 1 had better strain, which was significantly improved compared to Comparative Examples 1 and 2.

[0090] Figure 4 The toughness test results for the films of Example 1 and Comparative Examples 1-2 are shown below. The results indicate that the pure polyvinyl alcohol (PVA) film (Comparative Example 1) and the ordinary coffee shell PVA film (Comparative Example 2) exhibit low toughness, failing to meet the toughness requirements for high-performance materials. Specifically, the pure PVA film (Comparative Example 1) and the ordinary coffee shell PVA film (Comparative Example 2) have low toughness values, demonstrating poor fracture resistance. In contrast, the coffee shell carbon dot-based PVA film prepared in Example 1 exhibits superior toughness, with a significantly improved toughness value reaching 227 MJ / m. 3 The performance significantly surpasses that of the films in Comparative Examples 1 and 2. This remarkable performance improvement is primarily attributed to the strong interfacial bonding between the coffee shell carbon dots and the PVA matrix, achieved through non-covalent bonds such as π-π interactions, hydrogen bonds, and van der Waals forces. This effectively optimizes the energy dissipation mechanism and significantly enhances the material's fracture resistance. Furthermore, the uniform dispersion of the coffee shell carbon dots and their unique micro-carbonization structure further enhance the film's toughness, enabling it to maintain high strength while possessing excellent ductility. This result demonstrates that the coffee shell carbon dot-based polyvinyl alcohol film of this invention has significant application potential in the fields of high-performance flame-retardant materials and toughness-enhancing films.

[0091] Figure 5The limiting oxygen index (LOI) test results for the films of Example 1 and Comparative Examples 1-3 are shown. The LOI results indicate that the pure polyvinyl alcohol (PVA) film (Comparative Example 1) has an LOI value of 19.6%, exhibiting poor flame retardant performance and failing to meet the requirements for high-performance flame retardant materials. The LOI value of the ordinary coffee shell PVA film (Comparative Example 2) is slightly improved to 21.6%, indicating that the addition of coffee shells improves flame retardant performance to some extent, but the improvement is limited and still cannot meet higher standards of flame retardancy. In contrast, the coffee shell carbon dot-based PVA film prepared in Example 1 shows a significant improvement in flame retardant performance, with an LOI value as high as 28.9%, far exceeding that of the films in Comparative Examples 1 and 2. This significant performance improvement is mainly attributed to the introduction of coffee shell carbon dots. Their unique graphitized conjugated structure and micro-carbonization characteristics effectively promote the formation of a char layer during combustion, inhibiting heat and oxygen transfer, thereby significantly improving the flame retardant performance of the material. Furthermore, the strong interfacial bonding between the coffee shell carbon dots and the PVA matrix, formed through non-covalent bonds such as π-π interactions, hydrogen bonds, and van der Waals forces, further enhances the material's stability and flame-retardant efficiency. Compared to Example 1, the LOI value in Comparative Example 3 decreased due to the reduced amount of carbon dot solution added. This result indicates that the coffee shell carbon dot-based polyvinyl alcohol film of the present invention has significant application potential in the field of high-performance flame-retardant materials, providing a new approach for developing efficient and environmentally friendly flame-retardant materials.

[0092] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing polyvinyl alcohol flame-retardant films using carbon dots from coffee shells, characterized in that, Includes the following steps: Coffee shell carbon dot solution was mixed with polyvinyl alcohol, heated in an oil bath and then cooled to room temperature. The cooled coffee shell carbon dot-polyvinyl alcohol solution was cast into a film and dried to obtain a coffee shell carbon dot-based polyvinyl alcohol flame retardant film. The mass ratio of the coffee shell carbon dot solution to polyvinyl alcohol is 6:1; The preparation method of the coffee shell carbon dot solution includes the following steps: Coffee shells were added to water for a hydrothermal reaction. After the hydrothermal reaction was completed, the mixture was cooled to room temperature, centrifuged, and the supernatant was collected. After drying, a coffee shell carbon dot solution with a mass concentration of 1% was obtained. The hydrothermal reaction was carried out at a temperature of 180°C for 10 hours. The coffee shell carbon dot solution contains caffeic acid and chlorogenic acid.

2. The method for preparing polyvinyl alcohol flame-retardant film using coffee shell carbon dots according to claim 1, characterized in that, The ratio of coffee shells to water is 1g:100mL.

3. The method for preparing polyvinyl alcohol flame-retardant film using carbon dots from coffee shells according to claim 1, characterized in that, In the method for preparing coffee shell carbon dot solution, the drying temperature is 80℃ and the time is 12h.

4. The method for preparing polyvinyl alcohol flame-retardant film using carbon dots from coffee shells according to claim 1, characterized in that, The oil bath heating temperature is 95℃, and the time is 5 hours.

5. The method for preparing polyvinyl alcohol flame-retardant film using coffee shell carbon dots according to claim 1, characterized in that, In the method for preparing polyvinyl alcohol flame-retardant film using carbon dots from coffee shells, the drying temperature is 30°C and the drying time is 6 hours.

6. A coffee shell carbon dot-based polyvinyl alcohol flame-retardant film, characterized in that, The coffee shell carbon dot-based polyvinyl alcohol flame retardant film prepared according to any one of claims 1-5 has a thickness of 0.25 mm.

7. The application of the coffee shell carbon dot-based polyvinyl alcohol flame-retardant film as described in claim 6 in the preparation of flame-retardant film materials.

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