Flame-retardant conveying belt and preparation method thereof

Abstract

The invention discloses a bio-based flame-retardant conveyor belt and a preparation method thereof. The bio-based flame-retardant conveyor belt is prepared from the following raw materials: 18-22% of sisal fibers, 12-15% of nano cellulose whiskers (with the diameter of 20-50nm), 35-40% of a PLA / PBAT blend, 4-6% of acetyl tributyl citrate, 3-5% of phytic acid ionic liquid and 12.5-16% of a functional additive. Through the synergistic enhancement of the sisal fibers and the nanocellulose whiskers, the efficient flame retardance of the phytic acid ionic liquid and the compounding effect of the functional aids, the product has excellent flame retardance, mechanical strength and ultraviolet aging resistance, and is particularly suitable for severe working condition environments such as mines and metallurgy.

Description

Technical Field

[0001] The present invention relates to the technical field of conveyor belt manufacturing, and in particular to a flame-retardant conveyor belt and a preparation method thereof. Background Art

[0002] Flame-retardant conveyor belts, key components in industrial transportation systems, are widely used in mining, metallurgy, chemical engineering, and other fields. While traditional rubber-based conveyor belts offer excellent mechanical properties, they suffer from significant deficiencies in flame retardancy, environmental friendliness, and weather resistance. Particularly under harsh operating conditions such as high temperature, high humidity, and UV radiation, conventional conveyor belts are prone to aging, cracking, and a loss of flame retardancy, severely impacting their service life and safety. With increasingly stringent environmental regulations, the development of environmentally friendly conveyor belts that combine excellent flame retardancy with mechanical strength has become an urgent industry need.

[0003] Conveyor belts using halogenated flame retardants, while effective, produce toxic fumes and corrosive gases during combustion. Inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide, while environmentally friendly, require high dosages to achieve optimal flame retardancy, often leading to a significant decrease in the material's mechanical properties. Furthermore, while conventional reinforcement materials such as glass fiber or carbon fiber can improve strength, they lack compatibility with the matrix and hinder recycling. Balancing flame retardancy, mechanical strength, and environmental performance has become a major technical bottleneck in the development of flame-retardant conveyor belts.

[0004] Bio-based composite materials provide a new approach to solving the above problems. Sisal fiber and nanocellulose, as natural reinforcing materials, are biodegradable and have high specific strength, but their flame retardant properties are insufficient when used alone. Although bio-based polymers such as polylactic acid (PLA) are environmentally friendly, they have disadvantages such as high brittleness and poor heat resistance. In recent years, ionic liquid flame retardants have attracted attention due to their high efficiency, low smoke and non-toxic properties, but their compatibility with bio-based materials and synergistic flame retardant mechanism still need in-depth research. Developing new composite flame retardant systems to achieve the synergistic effect of flame retardants and reinforcing materials is an effective way to improve the comprehensive performance of conveyor belts. Summary of the Invention

[0005] The purpose of the present invention is to provide a flame-retardant conveyor belt and a preparation method thereof, which solves the problems of poor biodegradability, low flame retardant efficiency and insufficient UV resistance of existing flame-retardant conveyor belts.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions: A flame retardant conveyor belt, the raw materials of which include, by mass percentage: Sisal fiber: 18-22%; Nanocellulose whiskers: 12-15%; PLA / PBAT blend: 35-40%; Plasticizer: 4-6%; Phytic acid ionic liquid: 3-5%; Functional additives: 12.5-16%.

[0007] The components of the present invention achieve excellent performance of the flame retardant conveyor belt through synergistic action: sisal fiber is used as a natural reinforcing material, and the hydroxyl groups on its cellulose molecular chain form hydrogen bonds with the ester groups in the PLA / PBAT matrix, while the rough structure of the fiber surface enhances the mechanical interlocking effect; nanocellulose whiskers form a three-dimensional network in the matrix through high specific surface area and rigid rod-like structure, and their surface is modified by silane coupling agent to form covalent bonds with the polymer matrix, significantly improving the tensile strength and modulus of the composite material; PLA provides rigidity and PBAT provides toughness in the PLA / PBAT blend, and the two are melt-blended to form a microphase separation structure to achieve a balance between rigidity and toughness; acetyl tributyl citrate plasticizer weakens the interaction between polymer chains by inserting between PLA molecular chains, reduces the glass transition temperature, and improves processing fluidity; the phosphate groups in the phytic acid ionic liquid decompose at high temperature to generate phosphoric acid and polyphosphate. Phosphoric acid promotes the formation of a dense carbon layer on the substrate surface, while the nitrogen in the ionic liquid synergistically acts as a vapor-phase flame retardant with the water vapor produced by the decomposition of magnesium hydroxide. Magnesium hydroxide absorbs heat and releases water vapor upon thermal decomposition, diluting the concentration of combustible gases. The decomposition product, magnesium oxide, forms a carbon layer with the phytic acid ionic liquid, which together form a thermal insulation barrier. Hindered amine anti-UV agents effectively inhibit UV-induced polymer chain breakage by capturing free radicals and decomposing peroxides. High-molecular-weight polymeric hindered amines achieve long-term stability through molecular chain entanglement, while bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate provides surface protection through molecular migration. Electron beam irradiation creates a cross-linked network in the polymer chains, enhancing the material's thermal and dimensional stability. Surface embossing increases surface roughness, improving the friction coefficient between the conveyor belt and the drive pulley, while edge chamfering effectively prevents edge cracking during use. Through the synergistic physical and chemical interactions described above, these components impart the conveyor belt with excellent flame retardancy, mechanical strength, and weather resistance.

[0008] According to a preferred embodiment of the present invention, the diameter of the nanocellulose whiskers is 20-50 nm.

[0009] According to a preferred embodiment of the present invention, the plasticizer is acetyl tributyl citrate.

[0010] According to a preferred embodiment of the present invention, the functional auxiliary agent consists of magnesium hydroxide and an anti-ultraviolet agent.

[0011] According to a preferred embodiment of the present invention, the mass percentage of the magnesium hydroxide and the anti-ultraviolet agent is 10:1.

[0012] According to a preferred embodiment of the present invention, the anti-ultraviolet agent is a hindered amine anti-ultraviolet agent.

[0013] According to a preferred embodiment of the present invention, the hindered amine anti-ultraviolet agent is selected from at least one of high molecular weight polymeric hindered amines, neutral non-polymeric hindered amines and bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate.

[0014] The present invention also provides a method for preparing the flame-retardant conveyor belt, comprising the following steps: S1, sisal fibers were cut into 5-10 mm lengths and dried in an 80°C oven for 4 hours to remove moisture; nanocellulose whiskers were surface treated with a 0.5% silane coupling agent ethanol solution, stirred at 60°C for 2 hours, and then vacuum dried; the PLA / PBAT blend was vacuum dried at 60°C for 12 hours to remove moisture; magnesium hydroxide and anti-ultraviolet agents in the functional additives were pre-mixed in a high-speed mixer at 500 rpm for 15 minutes; S2, the dried PLA / PBAT blend is added to the main feed port of a twin-screw extruder at a barrel temperature of 160-180°C; sisal fiber, nanocellulose whiskers, and functional additives are added sequentially through the side feed port; acetyl tributyl citrate and phytic acid ionic liquid are injected into the melting section via a liquid injection pump; the screw speed is controlled at 80-100 rpm and the mixing time is 8-10 minutes; S3: The uniformly mixed material is extruded through a T-die at a die temperature of 175°C; a three-roll calender is used for calendering; the roller temperatures are: upper roller 90°C / middle roller 100°C / lower roller 80°C; the conveyor belt thickness is controlled within the range of 8-12mm by a tension control system; the surface is embossed with a pattern depth of 0.5-1.0mm.

[0015] According to a preferred embodiment of the present invention, the preparation method further includes: heat treating the formed conveyor belt at 80°C for 2 hours to eliminate internal stress; cross-linking treatment using electron beam irradiation; cutting into specified sizes after natural cooling to room temperature; and edge chamfering treatment using a drum grinder.

[0016] The beneficial effects of the present invention are: This invention significantly improves the mechanical properties and durability of conveyor belts through the synergistic reinforcement of sisal fibers and nanocellulose whiskers. The natural fiber structure of sisal fibers provides excellent tensile strength and impact resistance, while the nanocellulose whiskers, with a diameter of 20-50 nm, form a three-dimensional network reinforcement system within the PLA / PBAT matrix through their high specific surface area and rigid structure. This combination enables the conveyor belt to achieve a tensile strength of over 35 MPa while maintaining excellent flexibility, an increase of approximately 40% compared to traditional rubber conveyor belts, and abrasion resistance increased by over 30%, making it particularly suitable for heavy-load transportation conditions.

[0017] The flame retardant system of the present invention achieves a highly efficient and environmentally friendly flame retardant effect through the synergistic effect of phytic acid ionic liquid and magnesium hydroxide. Phytic acid ionic liquid decomposes at high temperatures to form a dense carbon layer, and its phosphate groups and magnesium oxide produced by the decomposition of magnesium hydroxide jointly construct a heat insulation barrier, allowing the conveyor belt to meet the FV-0 flame retardant standard. Compared with traditional halogen-based flame retardants, the smoke density of this system is reduced by more than 60% during combustion, and no toxic gases are released. The addition of hindered amine anti-ultraviolet agents in the functional additives ensures that the mechanical properties of the product are still retained at a rate of more than 90% after 1000 hours of outdoor use, solving the problem of conventional conveyor belts being prone to aging and cracking.

[0018] The preparation process of the present invention ensures optimal dispersion and interface bonding of the components by optimizing mixing, calendering and subsequent processing parameters. The twin-screw extrusion process allows for uniform dispersion of the nanomaterials, the three-roll calendering molding ensures product dimensional stability, and electron beam irradiation cross-linking further enhances the thermal stability of the material. Surface embossing treatment increases the friction coefficient by 25%, and edge chamfering effectively prevents edge cracking during use. The entire process enables continuous production, with a 20% increase in production efficiency compared to traditional processes, and fully complies with environmental protection requirements, providing a reliable solution for the industrial production of flame-retardant conveyor belts. DETAILED DESCRIPTION

[0019] The following specific implementation methods are only used to further illustrate the present application and should not be understood as limiting the scope of protection of the present application. Technicians in this field may make some non-essential improvements and adjustments to the present application based on the above application content.

[0020] 1. Implementation Example 1 This embodiment provides a flame-retardant conveyor belt with a total mass of 1000 g. The specific formula and preparation method are as follows: the formula consists of: 200 g of sisal fiber (length 5-10 mm, dried at 80°C for 4 h), 150 g of nanocellulose whiskers (diameter 20-50 nm, treated with 0.5% silane coupling agent), 380 g of PLA / PBAT blend (PLA to PBAT mass ratio 6:4, vacuum dried at 60°C for 12 h), 50 g of acetyl tributyl citrate, 40 g of phytic acid ionic liquid, and 142.5 g of a functional additive (130 g of magnesium hydroxide and 12.5 g of bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate mixed at a ratio of 10:1). Preparation method: Pretreatment: The sisal fiber was cut and dried, the nanocellulose whiskers were treated with a silane coupling agent ethanol solution and vacuum dried, and the PLA / PBAT blend was dried and set aside; Mixing: PLA / PBAT was added to a twin-screw extruder (barrel temperature 160°C), sisal fiber, nanocellulose whiskers and functional additives were added through the side feed port, plasticizer and phytic acid ionic liquid were injected by a liquid injection pump, the screw speed was 90 rpm, and mixing was carried out for 9 minutes; Molding: The melt was extruded through a T-die (175°C), calendered on a three-roll calender (roller temperature 90 / 100 / 80°C), the thickness was controlled to 10 mm, and the surface was embossed (depth 0.8 mm); Post-treatment: Heat treatment at 80°C for 2 h to eliminate internal stress, electron beam irradiation (dose 18 kGy), naturally cooled and then cut, and the edge chamfering was performed (radius 2.5 mm).

[0021] Example 2 The specific implementation method is the same as that of Example 1, except that the total mass is 1000g, and the formula is adjusted to: 180g sisal fiber, 120g nanocellulose whiskers, 350g PLA / PBAT blend, 40g acetyl tributyl citrate, 30g phytic acid ionic liquid, and 125g functional additives (113.6g magnesium hydroxide + 11.4g anti-ultraviolet agent). The preparation process is the same as that of Example 1, and the mixing time is 8 minutes.

[0022] Example 3 The specific implementation method is the same as that of Example 1, except that the total mass is 1000g, and the formula is adjusted to: 220g sisal fiber, 150g nanocellulose whiskers, 400g PLA / PBAT blend, 60g acetyl tributyl citrate, 50g phytic acid ionic liquid, and 160g functional additives (145.5g magnesium hydroxide + 14.5g anti-ultraviolet agent). The preparation process is the same as that of Example 1, and the mixing time is 10 minutes.

[0023] Comparative Example 1 The specific implementation method is the same as Example 1, except that the total mass is 1000g, and the formula does not contain phytic acid ionic liquid and nanocellulose whiskers: 200g sisal fiber, 530g PLA / PBAT blend, 50g acetyl tributyl citrate, 142.5g functional additives (130g magnesium hydroxide + 12.5g anti-UV agent), and deionized water is added to 1000g. The nanocellulose treatment step is omitted from the preparation process, and mixing is performed directly.

[0024] Comparative Example 2 The specific implementation method is the same as that of Example 1, except that the total mass is 1000 g, a common plasticizer (50 g of dioctyl phthalate) is used instead of acetyl tributyl citrate, and the rest of the formula is the same as that of Example 1. In the preparation process, the plasticizer injection temperature is adjusted to 170°C.

[0025] Comparative Example 3 The specific implementation method is the same as that of Example 1, except that the total mass is 1000 g, and a traditional flame retardant system is used: 200 g of sisal fiber, 380 g of PLA / PBAT blend, 50 g of decabromodiphenylethane (instead of phytic acid ionic liquid), and 100 g of aluminum hydroxide (instead of functional additive). The preparation process omits the electron beam irradiation step, and the rest is the same as that of Example 1.

[0026] 2. Performance Testing The flame-retardant conveyor belts prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to the following method: Testing methods: Tensile strength and elongation at break were tested in accordance with GB / T 3685-2009; the flame retardancy rating (UL-94) was determined using the vertical combustion method according to GB / T 2408-2021; mechanical retention was measured after UV aging (500h QUV, 60°C) according to GB / T 16422.3-2014; the 5% weight loss temperature was measured using a thermogravimetric analyzer (TGA) (N2 atmosphere, 10°C / min); phthalate content was determined according to GB / T 2917.1-2002; and abrasion resistance was tested in accordance with GB / T 9867-2008 (CS-10 wheels, 1kg load).

[0027] Performance test results: Table 1: Performance test results of various embodiments and comparative examples

[0028] As shown in Table 1, the present invention, through a comparison of the data from Examples 1-3 and Comparative Examples 1-3, focuses on resolving the following technical issues: Traditional flame retardants (such as decabromodiphenylethane and aluminum hydroxide in Comparative Example 3) contain halogens or are inefficient, resulting in poor thermal stability (a 5% weight loss temperature of only 303°C) and weak mechanical properties (tensile strength of 29.4 MPa). Furthermore, traditional plasticizers (dioctyl phthalate in Comparative Example 2) pose toxicity risks (phthalate detection level of 5800 ppm). In contrast, the present invention utilizes phytic acid ionic liquid and acetyl tributyl citrate, respectively, to achieve halogen-free flame retardancy (UL-94 V-0 / V-1 ratings for Examples 1-3) and environmentally friendly plasticization (phthalate was not detected). After removing the nanocellulose whiskers and phytic acid ionic liquid from Comparative Example 1, the tensile strength (24.6 MPa) and flame retardancy (not rated) significantly deteriorate, demonstrating that the two synergistically enhance the material's mechanical properties (reaching 38.5 MPa in Example 1) and build a flame-retardant network. In addition, the traditional formula (Comparative Examples 1-3) has lower UV aging resistance (mechanical retention rate 68.4-80.2%) and wear resistance (wear loss 18.9-25.6 mg) than Examples 1-3 (mechanical retention rate 89.5-94.1%, wear loss 11.3-14.2 mg), indicating that the nanocellulose whiskers and electron beam irradiation process optimize the material's anti-aging ability and surface structure, while the synergistic effect of the PLA / PBAT blend and functional additives (magnesium hydroxide + anti-UV agent) balances flexibility (elongation at break 250-310%) and wear resistance, breaking through the technical bottleneck of traditional conveyor belts that are difficult to strike a balance between environmental protection, flame retardancy, mechanical properties and durability.

[0029] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A flame retardant conveyor belt, characterized in that: In terms of mass percentage, the raw materials include: Sisal fiber: 18-22%; Nanocellulose whiskers: 12-15%; PLA / PBAT blend: 35-40%; Plasticizer: 4-6%; Phytic acid ionic liquid: 3-5%; Functional additives: 12.5-16%.

2. The flame-retardant conveyor belt according to claim 1, characterized in that: The diameter of the nanocellulose whiskers is 20-50 nm.

3. The flame retardant conveyor belt according to claim 1, characterized in that: The plasticizer is acetyl tributyl citrate.

4. The flame retardant conveyor belt according to claim 1, characterized in that: The functional auxiliary agent consists of magnesium hydroxide and an anti-ultraviolet agent.

5. The flame retardant conveyor belt according to claim 4, characterized in that: The mass percentage of the magnesium hydroxide and the anti-ultraviolet agent is 10:

1.

6. The flame retardant conveyor belt according to claim 4, characterized in that: The anti-ultraviolet agent is a hindered amine anti-ultraviolet agent.

7. The flame retardant conveyor belt according to claim 1, characterized in that: The hindered amine anti-ultraviolet agent is selected from at least one of high molecular weight polymeric hindered amines, neutral non-polymeric hindered amines and bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate.

8. A method for preparing a flame-retardant conveyor belt according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1, sisal fibers were cut into 5-10 mm lengths and dried in an 80°C oven for 4 hours to remove moisture; nanocellulose whiskers were surface treated with a 0.5% silane coupling agent ethanol solution, stirred at 60°C for 2 hours, and then vacuum dried; the PLA / PBAT blend was vacuum dried at 60°C for 12 hours to remove moisture; magnesium hydroxide and anti-UV agents in the functional additives were pre-mixed in a high-speed mixer at 500 rpm for 15 minutes; S2, the dried PLA / PBAT blend is added to the main feed port of a twin-screw extruder at a barrel temperature of 160-180°C; sisal fiber, nanocellulose whiskers, and functional additives are added sequentially through the side feed port; acetyl tributyl citrate and phytic acid ionic liquid are injected into the melting section via a liquid injection pump; the screw speed is controlled at 80-100 rpm and the mixing time is 8-10 minutes; S3: The uniformly mixed material is extruded through a T-die at a die temperature of 175°C; a three-roll calender is used for calendering; the roller temperatures are: upper roller 90°C / middle roller 100°C / lower roller 80°C; the conveyor belt thickness is controlled within the range of 8-12mm by a tension control system; the surface is embossed with a pattern depth of 0.5-1.0mm.

9. The method for preparing a flame-retardant conveyor belt according to claim 8, characterized in that: The preparation method further includes: heat treating the formed conveyor belt at 80° C. for 2 hours to eliminate internal stress; cross-linking treatment by electron beam irradiation; naturally cooling to room temperature and cutting into specified sizes; and performing edge chamfering treatment by a drum grinder.

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