Flame-retardant glass fiber reinforced polypropylene plastic as well as preparation method and application thereof

Abstract

The invention relates to a flame-retardant glass fiber reinforced polypropylene plastic and a preparation method and application thereof.The preparation method comprises the following steps that S1, hydroxylated boron nitride nanosheets are added into N-methyl pyrrolidone, the pH is adjusted to 9.0-10.0, OH-BNNSs suspension liquid is obtained, chopped glass fiber suspension liquid subjected to surface treatment through a silane coupling agent is added, the pH is adjusted to 4.0-5.0, stirring is conducted for 30-60 min, and a flame-retardant glass fiber reinforced polypropylene plastic is obtained; the preparation method comprises the following steps: adding boron nitride nanosheets into glass fibers, continuously stirring to complete adsorption of the boron nitride nanosheets on the surfaces of the glass fibers, then quenching in liquid nitrogen, then removing a solvent through freeze drying, and carrying out electrostatic spinning treatment to obtain a boron nitride / glass fiber matrix; and S2, mixing a polypropylene matrix, the boron nitride / glass fiber matrix obtained in S1, maleic anhydride grafted polypropylene, alpha-zirconium phosphate, iron montmorillonite and an auxiliary agent at a high speed, and carrying out melt extrusion granulation to obtain the plastic. According to the invention, the boron nitride nanosheet subjected to lattice distortion and electric field orientation is constructed on the surface of the glass fiber to reconstruct a glass fiber reinforced polypropylene interface, so that the purpose of preparing the material of which the mechanical strength, flame retardance and weather resistance are synergistically improved is achieved.

Description

Technical Field

[0001] This invention relates to the technical field of polymer materials, and in particular to a flame-retardant glass fiber reinforced polypropylene plastic, its preparation method, and its application. Background Technology

[0002] Polypropylene (PP), with its advantages of low density, good chemical resistance, excellent processability, and relatively low cost, has become a widely used general-purpose plastic in the automotive, electronics, and other fields. However, pure PP has inherent drawbacks such as poor mechanical strength, poor heat resistance, and significant flammability (limiting oxygen index of only about 17%), which greatly limits its application in structural components with extremely high safety and reliability requirements, such as battery pack shells for new energy vehicles. To broaden its application scope, glass fiber (GF) is usually added for reinforcement, and flame retardants are added to improve fire safety, thus forming glass fiber reinforced flame-retardant polypropylene composites (FR-GFPP). Currently, technological development in this field mainly revolves around the following directions, but there are still significant technical bottlenecks.

[0003] The most common modification method is to melt-blend short or long glass fibers, flame retardants, compatibilizers, etc., with a polypropylene matrix. Among these, halogen-free flame retardant systems have become a key research focus due to their environmental compliance, such as those using intumescent flame retardants (IFR). Some studies have attempted to flame-retard glass fiber reinforced PP by combining a self-made nitrogen-phosphorus intumescent flame retardant with cage-type silsesquioxane (POSS), and investigated the effect of the compatibilizer maleic anhydride-grafted polypropylene (PP-g-MAH) on material properties. Another existing technology discloses a halogen-free flame-retardant long glass fiber reinforced polypropylene material, prepared using polypropylene, long glass fibers, compatibilizers, antioxidants, intumescent flame retardants, and synergists (such as acidified sepiolite) as raw materials through a specific impregnation and coating process. While these methods can improve the mechanical properties and flame retardancy rating of the material to some extent, their fundamental problem lies in the fact that the reinforcing phase (glass fiber), flame retardant phase, and polymer matrix only have simple physical blending and adsorption effects, resulting in relatively weak interfacial bonding. This weak interface is highly susceptible to becoming the starting point for crack initiation and propagation when subjected to complex stresses, resulting in insufficient toughness, especially impact toughness, in the material. More significantly, the "wick effect" of glass fiber severely reduces flame retardant properties. During combustion, glass fiber acts like a wick, adsorbing and transporting molten polymer, accelerating the combustion process, which poses a significant challenge to the preparation of high flame-retardant FR-GFPP.

[0004] To improve interfacial properties, researchers commonly treat glass fibers with silane coupling agents or add compatibilizers such as PP-g-MAH. For example, some technical solutions involve blending toughening and flame-retardant masterbatches with long glass fiber-reinforced PP composites, aiming to simultaneously improve the material's toughness and flame-retardant properties. Another recent patent designs multi-layer sheet structures, using polypropylene compositions with different melting points and flame-retardant contents for lamination and hot pressing to balance the material's tensile, impact, and flame-retardant properties. These methods are essentially macroscopic or molecular-scale interfacial modifications. While they can improve compatibility to some extent, they fail to actively and multi-scale structurally design and impart properties to the reinforcement itself at the microstructural level. The bonding between glass fiber and the matrix still mainly relies on limited chemical bonds and mechanical anchoring, resulting in a bottleneck in interfacial strengthening. Furthermore, their contribution to suppressing the "wick effect," actively guiding stress transfer, and simultaneously imparting special functions such as high thermal conductivity / high barrier properties to the interface is relatively limited.

[0005] Currently, introducing nanofillers (such as montmorillonite and nano-oxides) is another way to improve the overall performance of composite materials. However, nanofillers are prone to agglomeration in polymer melts, making it difficult to achieve uniform dispersion and orderly arrangement. How to achieve precise and orderly loading of nanofillers at specific locations (such as stress-concentrated glass fiber interfaces) and simultaneously activate their multiple functions is a problem that has not yet been effectively solved by existing technologies.

[0006] In addition to meeting basic mechanical strength and flame retardancy requirements (typically requiring UL-94V-0 rating), the casing materials for new energy vehicle power batteries also face extremely stringent requirements regarding long-term weather resistance, electrolyte corrosion resistance, dimensional stability, and mechanical integrity at high temperatures. Existing conventional or slightly modified FR-GFPP materials typically offer limited and singular performance improvements, making it difficult to comprehensively meet all these stringent indicators. Especially under long-term thermo-oxidative aging or chemical corrosion, the fragile glass fiber-resin interface will be the first to degrade, leading to a sharp decline in material performance and potential safety risks. Therefore, there is an urgent need to develop a novel interface engineering strategy and composite material structural design to fundamentally strengthen the bond between glass fiber and the polypropylene matrix, simultaneously endowing the interface with excellent stress transfer, flame retardant synergy, and durable protection functions. This would allow for the preparation of flame-retardant reinforced polypropylene composite materials with comprehensive performance far exceeding current levels, suitable for next-generation power battery casings. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the first objective of this invention is to provide a method for preparing flame-retardant glass fiber reinforced polypropylene plastic. This method reconstructs the glass fiber reinforced polypropylene interface by constructing boron nitride nanosheets with lattice distortion and electric field orientation on the surface of glass fibers, thereby achieving the goal of simultaneously improving the material properties of mechanical strength, flame retardancy, and weather resistance.

[0008] The second objective of this invention is to provide a flame-retardant glass fiber reinforced polypropylene plastic that offers advantages in terms of mechanical strength, flame retardancy, and weather resistance.

[0009] The third objective of this invention is to provide an application of flame-retardant glass fiber reinforced polypropylene plastic, which has the advantages of ensuring high mechanical properties and high flame retardancy for battery casings, charging pile casings, power socket casings, or electrical appliance casings.

[0010] To achieve the first objective mentioned above, the present invention provides the following technical solution: A method for preparing flame-retardant glass fiber reinforced polypropylene plastic includes the following steps: S1 first adds hydroxylated boron nitride nanosheets to N-methylpyrrolidone, adjusts the pH to 9.0~10.0 to obtain an OH-BNNSs suspension, then adds a suspension of short-cut glass fibers surface-treated with silane coupling agent, adjusts the pH to 4.0~5.0, and continuously stirs to complete the adsorption of boron nitride nanosheets on the glass fiber surface. Then, it is quenched in liquid nitrogen, followed by freeze drying to remove the solvent, and then electrospinning to obtain a boron nitride / glass fiber matrix. S2 involves mixing polypropylene matrix, boron nitride / glass fiber matrix obtained in S1, maleic anhydride-grafted polypropylene, α-zirconium phosphate, iron montmorillonite, and additives at high speed, followed by melt extrusion granulation to obtain plastic.

[0011] Further, in S1, the concentration of the OH-BNNSs suspension is controlled to be 0.1~0.3wt%, the silane coupling agent is γ-aminopropyltriethoxysilane, the concentration of the chopped glass fiber suspension is 0.8~1.2wt%, and the length of the chopped glass fiber is 3~12mm.

[0012] Furthermore, in S1, the stirring time is controlled to be 30~120min and the stirring speed is 200~300rpm.

[0013] Furthermore, in S1, the quenching time is controlled to be 10~30s.

[0014] Furthermore, in S1, the freezing temperature is controlled at -5~5℃ and the drying time is controlled at 30~60min.

[0015] Furthermore, in S1, the electric field strength for electrospinning is controlled to be 5~20kV / cm, and the processing time is 5~15min.

[0016] Further, in S2, the ratio of polypropylene matrix, boron nitride / glass fiber matrix obtained in S1, maleic anhydride grafted polypropylene, α-zirconium phosphate, iron montmorillonite and additives is controlled to be 100: (15~35): (3~8): (10~15): (5~10): (2~5).

[0017] Furthermore, in S2, the additive is composed of raw materials comprising the following parts by weight: 0.5 to 1.5 parts antioxidant 1010, 0.5 to 1.5 parts ultraviolet absorber UV-531, 0.5 to 1.0 parts calcium stearate, and 0.5 to 1.0 parts silicone masterbatch.

[0018] Furthermore, in S2, the grafting degree of maleic anhydride-grafted polypropylene is 1.0 to 3.0%.

[0019] Furthermore, in S2, the temperatures of each section of the extruder from the feed inlet to the die head are controlled to be 160~170℃, 190~200℃, 200~210℃, and 200~205℃ respectively, the screw speed of the extruder is 250~350rpm, and the feeding speed is 15~20rpm.

[0020] To achieve the second objective mentioned above, the present invention provides the following technical solution: A flame-retardant glass fiber reinforced polypropylene plastic is prepared by the above-described method.

[0021] To achieve the third objective mentioned above, the present invention provides the following technical solution: Application of a flame-retardant glass fiber reinforced polypropylene plastic, wherein the plastic prepared by the above method is used in the manufacture of battery casings, charging pile casings, power socket casings or electrical appliance casings.

[0022] In summary, the beneficial technical effects of the present invention are as follows: 1. The preparation method of the present invention involves adjusting the OH-BNNSs suspension to alkalinity and adding a chopped glass fiber suspension to adjust it to acidity. This allows the positively charged aminated glass fiber surface to generate strong electrostatic adsorption with the negatively charged hydroxylated BN nanosheets, achieving high-density enrichment of BN nanosheets on the glass fiber surface. After quenching, lattice distortion of the BN nanosheets is induced. The lattice distortion rate of the BN nanosheets is approximately 10 ± 0.5%, and the crystal plane shift is approximately 0.8°. This introduces a large number of dislocations, vacancies, and other defects into the BN nanosheets and at the BN / glass fiber interface, and may cause partial amorphization of the BN nanosheets. These defects become active sites for subsequent diffusion and anchoring of PP polymer chains. Subsequently, after electrospinning, the BN nanosheets, due to their polarity after hydroxylation, will undergo directional rotation and alignment under the action of an electrostatic field, making their two-dimensional plane preferentially parallel to the direction of the electric field. When the material is under stress, the stress is efficiently transferred from the PP matrix → BN ordered layer → glass fiber, greatly reducing stress concentration and ensuring the mechanical properties of the material. 2. The preparation method of the present invention enables boron nitride / glass fiber matrix, α-zirconium phosphate, and iron montmorillonite to synergistically form a dense, continuous, and high-strength ceramic matrix during combustion. The high thermal conductivity of BN helps to uniformly dissipate heat energy and delay decomposition. α-ZrP decomposes at high temperature to generate phosphoric acid and cross-linked phosphorus oxides, catalyzing the dehydration of PP to form carbon. Iron ions in iron montmorillonite can undergo redox reactions with free radicals generated during combustion, effectively quenching the fire source and exerting a highly efficient gas-phase flame retardant effect. This greatly delays the diffusion of combustible gases and oxygen and inhibits molten droplets, thus achieving a flame retardant effect. 3. In the melt blending process of the polypropylene matrix and boron nitride / glass fiber matrix of the present invention, the anhydride groups of PP-g-MAH can undergo esterification reaction with the hydroxyl groups on the surface of BN nanosheets, and can also generate amide groups with the amino groups on the surface of aminated glass fiber. That is, PP-g-MAH improves the compatibility between polypropylene, hydroxylated BN nanosheets and aminated glass fiber, and significantly improves the interfacial bonding strength.

[0023] 4. The BN nanosheets in this invention have excellent shielding effect against ultraviolet light. When combined with additives, they can reduce the migration rate and enhance the long-term performance under the synergistic effect of BN and layered silicates, jointly resisting thermo-oxidative aging. Furthermore, the high thermal conductivity of BN and the enhanced interfacial bonding significantly reduce the thermal expansion coefficient of the composite material, making the size change of the battery shell minimal during thermal cycling and avoiding sealing failure due to stress cracking. 5. The flame-retardant glass fiber reinforced polypropylene plastic obtained by this invention has excellent comprehensive properties, with improved tensile strength, flexural strength, and impact strength. It also meets the high flame-retardant standard of UL-94 V-0. In long-term thermo-oxidative aging tests, the material exhibits excellent stability; after 500 hours of accelerated high-temperature aging, the mechanical property retention rate is still above 90%. Furthermore, the material has excellent corrosion resistance to chemical media such as electrolytes. In an electrolyte immersion test at 85℃ for 7 days, the mass change rate is less than 0.5%, and the dimensional change rate is controlled within 0.2%. Through special interface engineering design, the wicking effect of glass fibers is effectively suppressed, enabling the formation of a dense and continuous char layer during combustion, significantly preventing dripping. The material also exhibits excellent processing performance, with a moderate melt flow rate, suitable for injection molding of various complex structures. The resulting products have smooth surfaces without loose fibers, meeting the flame-retardant requirements of high-end battery casings. Attached Figure Description

[0024] Figure 1 This is a SEM image of the impact cross-section of the plastic sample obtained in Example 1 of this invention.

[0025] Figure 2 This is a SEM image of the combustion products of the plastic sample obtained in Example 1 of this invention. Detailed Implementation

[0026] To make the technical means, creative features, objectives and effects of this invention clearer and easier to understand, the invention will be further described below in conjunction with the accompanying drawings and specific embodiments. Example

[0027] Example 1: A method for preparing flame-retardant glass fiber reinforced polypropylene plastic disclosed in this invention includes the following steps: S1 First, hydroxylated boron nitride nanosheets were added to N-methylpyrrolidone, and the pH was adjusted to 9.5±0.1 to obtain a 0.2wt% OH-BNNSs suspension. Then, a 1.0wt% chopped glass fiber suspension with a silane coupling agent (γ-aminopropyltriethoxysilane) surface treatment was added. The length of the chopped glass fiber ranged from 3 to 12 mm. The pH was adjusted to 4.5±0.1, and the mixture was stirred continuously at 250 rpm for 60 min to complete the adsorption of boron nitride nanosheets on the glass fiber surface. Then, the mixture was quenched in liquid nitrogen for 15 s. Subsequently, the solvent was removed by freeze drying at 0℃ for 40 min. Finally, the mixture was electrospun at an electric field strength of 15 kV / cm for 10 min to obtain a boron nitride / glass fiber matrix. In S2, 100 parts of polypropylene matrix, 25 parts of boron nitride / glass fiber matrix obtained in S1, 6 parts of maleic anhydride-grafted polypropylene, 12 parts of α-zirconium phosphate, 8 parts of iron montmorillonite, 1.2 parts of antioxidant 1010, 1.3 parts of UV absorber UV-531, 0.8 parts of calcium stearate, and 0.6 parts of silicone masterbatch are added to a high-speed mixer. The grafting degree of maleic anhydride-grafted polypropylene is controlled to be 2.0%. After high-speed mixing at 1000 rpm for 10 minutes, the mixture is melt-extruded and granulated. The temperatures of each section of the extruder from the feed inlet to the die head are controlled to be 165℃, 195℃, 205℃, and 205℃ respectively. The screw speed of the extruder is 300 rpm, and the feed speed is 18 rpm, to obtain plastic.

[0028] The present invention also discloses a flame-retardant glass fiber reinforced polypropylene plastic, which is prepared by the above-described method.

[0029] This invention also discloses the application of a flame-retardant glass fiber reinforced polypropylene plastic, wherein the plastic prepared by the above method is used in the preparation of battery casings, charging pile casings, power socket casings or electrical appliance casings.

[0030] Example 2: This is a method for preparing flame-retardant glass fiber reinforced polypropylene plastic disclosed in this invention. The difference from Example 1 is that it includes the following steps: S1 First, hydroxylated boron nitride nanosheets were added to N-methylpyrrolidone, and the pH was adjusted to 9.5±0.1 to obtain a 0.1wt% OH-BNNSs suspension. Then, a 0.8wt% chopped glass fiber suspension with a silane coupling agent (γ-aminopropyltriethoxysilane) surface treatment was added. The length of the chopped glass fiber ranged from 3 to 12 mm. The pH was adjusted to 4.5±0.1, and the mixture was stirred continuously at 250 rpm for 60 min to complete the adsorption of boron nitride nanosheets on the glass fiber surface. Then, the mixture was quenched in liquid nitrogen for 15 s. Subsequently, the solvent was removed by freeze drying at 0℃ for 40 min. Finally, the mixture was electrospun at an electric field strength of 15 kV / cm for 10 min to obtain the boron nitride / glass fiber matrix. In S2, 100 parts of polypropylene matrix, 25 parts of boron nitride / glass fiber matrix obtained in S1, 6 parts of maleic anhydride-grafted polypropylene, 12 parts of α-zirconium phosphate, 8 parts of iron montmorillonite, 1.2 parts of antioxidant 1010, 1.3 parts of UV absorber UV-531, 0.8 parts of calcium stearate, and 0.6 parts of silicone masterbatch are added to a high-speed mixer. The grafting degree of maleic anhydride-grafted polypropylene is controlled to be 2.0%. After high-speed mixing at 1000 rpm for 10 minutes, the mixture is melt-extruded and granulated. The temperatures of each section of the extruder from the feed inlet to the die head are controlled to be 165℃, 195℃, 205℃, and 205℃ respectively. The screw speed of the extruder is 300 rpm, and the feed speed is 18 rpm, to obtain plastic.

[0031] Example 3: This is a method for preparing flame-retardant glass fiber reinforced polypropylene plastic disclosed in this invention. The difference from Example 1 is that it includes the following steps: S1 First, hydroxylated boron nitride nanosheets were added to N-methylpyrrolidone, and the pH was adjusted to 9.5±0.1 to obtain a 0.3wt% OH-BNNSs suspension. Then, a 1.2wt% chopped glass fiber suspension with a silane coupling agent (γ-aminopropyltriethoxysilane) surface treatment was added. The length of the chopped glass fiber ranged from 3 to 12 mm. The pH was adjusted to 4.5±0.1, and the mixture was stirred continuously at 250 rpm for 60 min to complete the adsorption of boron nitride nanosheets on the glass fiber surface. Then, the mixture was quenched in liquid nitrogen for 15 s. Subsequently, the solvent was removed by freeze drying at 0℃ for 40 min. Finally, the mixture was electrospun at an electric field strength of 15 kV / cm for 10 min to obtain the boron nitride / glass fiber matrix. In S2, 100 parts of polypropylene matrix, 25 parts of boron nitride / glass fiber matrix obtained in S1, 6 parts of maleic anhydride-grafted polypropylene, 12 parts of α-zirconium phosphate, 8 parts of iron montmorillonite, 1.2 parts of antioxidant 1010, 1.3 parts of UV absorber UV-531, 0.8 parts of calcium stearate, and 0.6 parts of silicone masterbatch are added to a high-speed mixer. The grafting degree of maleic anhydride-grafted polypropylene is controlled to be 2.0%. After high-speed mixing at 1000 rpm for 10 minutes, the mixture is melt-extruded and granulated. The temperatures of each section of the extruder from the feed inlet to the die head are controlled to be 165℃, 195℃, 205℃, and 205℃ respectively. The screw speed of the extruder is 300 rpm, and the feed speed is 18 rpm, to obtain plastic.

[0032] Example 4: This is a method for preparing flame-retardant glass fiber reinforced polypropylene plastic disclosed in this invention. The difference from Example 1 is that it includes the following steps: S1 First, hydroxylated boron nitride nanosheets were added to N-methylpyrrolidone, and the pH was adjusted to 9.5±0.1 to obtain a 0.2wt% OH-BNNSs suspension. Then, a 1.0wt% chopped glass fiber suspension with a silane coupling agent (γ-aminopropyltriethoxysilane) surface treatment was added. The length of the chopped glass fiber ranged from 3 to 12 mm. The pH was adjusted to 4.5±0.1, and the mixture was stirred continuously at 250 rpm for 60 min to complete the adsorption of boron nitride nanosheets on the glass fiber surface. Then, the mixture was quenched in liquid nitrogen for 15 s. Subsequently, the solvent was removed by freeze drying at 0 °C for 40 min. Finally, the mixture was electrospun at an electric field strength of 5 kV / cm for 10 min to obtain a boron nitride / glass fiber matrix. In S2, 100 parts of polypropylene matrix, 25 parts of boron nitride / glass fiber matrix obtained in S1, 6 parts of maleic anhydride-grafted polypropylene, 12 parts of α-zirconium phosphate, 8 parts of iron montmorillonite, 1.2 parts of antioxidant 1010, 1.3 parts of UV absorber UV-531, 0.8 parts of calcium stearate, and 0.6 parts of silicone masterbatch are added to a high-speed mixer. The grafting degree of maleic anhydride-grafted polypropylene is controlled to be 2.0%. After high-speed mixing at 1000 rpm for 10 minutes, the mixture is melt-extruded and granulated. The temperatures of each section of the extruder from the feed inlet to the die head are controlled to be 165℃, 195℃, 205℃, and 205℃ respectively. The screw speed of the extruder is 300 rpm, and the feed speed is 18 rpm, to obtain plastic.

[0033] Example 5: This is a method for preparing flame-retardant glass fiber reinforced polypropylene plastic disclosed in this invention. The difference from Example 1 is that it includes the following steps: S1 First, hydroxylated boron nitride nanosheets were added to N-methylpyrrolidone, and the pH was adjusted to 9.5±0.1 to obtain a 0.2wt% OH-BNNSs suspension. Then, a 1.0wt% chopped glass fiber suspension with a silane coupling agent (γ-aminopropyltriethoxysilane) surface treatment was added. The length of the chopped glass fiber ranged from 3 to 12 mm. The pH was adjusted to 4.5±0.1, and the mixture was stirred continuously at 250 rpm for 60 min to complete the adsorption of boron nitride nanosheets on the glass fiber surface. Then, the mixture was quenched in liquid nitrogen for 15 s. Subsequently, the solvent was removed by freeze drying at 0℃ for 40 min. Finally, the mixture was electrospun at an electric field strength of 20 kV / cm for 10 min to obtain the boron nitride / glass fiber matrix. In S2, 100 parts of polypropylene matrix, 25 parts of boron nitride / glass fiber matrix obtained in S1, 6 parts of maleic anhydride-grafted polypropylene, 12 parts of α-zirconium phosphate, 8 parts of iron montmorillonite, 1.2 parts of antioxidant 1010, 1.3 parts of UV absorber UV-531, 0.8 parts of calcium stearate, and 0.6 parts of silicone masterbatch are added to a high-speed mixer. The grafting degree of maleic anhydride-grafted polypropylene is controlled to be 2.0%. After high-speed mixing at 1000 rpm for 10 minutes, the mixture is melt-extruded and granulated. The temperatures of each section of the extruder from the feed inlet to the die head are controlled to be 165℃, 195℃, 205℃, and 205℃ respectively. The screw speed of the extruder is 300 rpm, and the feed speed is 18 rpm, to obtain plastic.

[0034] Example 6: This is a method for preparing flame-retardant glass fiber reinforced polypropylene plastic disclosed in this invention. The difference from Example 1 is that it includes the following steps: S1 First, hydroxylated boron nitride nanosheets were added to N-methylpyrrolidone, and the pH was adjusted to 9.5±0.1 to obtain a 0.2wt% OH-BNNSs suspension. Then, a 1.0wt% chopped glass fiber suspension with a silane coupling agent (γ-aminopropyltriethoxysilane) surface treatment was added. The length of the chopped glass fiber ranged from 3 to 12 mm. The pH was adjusted to 4.5±0.1, and the mixture was stirred continuously at 250 rpm for 60 min to complete the adsorption of boron nitride nanosheets on the glass fiber surface. Then, the mixture was quenched in liquid nitrogen for 15 s. Subsequently, the solvent was removed by freeze drying at 0℃ for 40 min. Finally, the mixture was electrospun at an electric field strength of 15 kV / cm for 10 min to obtain a boron nitride / glass fiber matrix. In S2, 100 parts of polypropylene matrix, 15 parts of boron nitride / glass fiber matrix obtained in S1, 3 parts of maleic anhydride-grafted polypropylene, 10 parts of α-zirconium phosphate, 5 parts of iron montmorillonite, 0.5 parts of antioxidant 1010, 0.5 parts of UV absorber UV-531, 0.5 parts of calcium stearate, and 0.5 parts of silicone masterbatch are added to a high-speed mixer. The grafting degree of maleic anhydride-grafted polypropylene is controlled at 2.0%. After high-speed mixing at 1000 pm for 10 min, the mixture is melt-extruded and granulated. The temperatures of each section of the extruder from the feed inlet to the die head are controlled at 165℃, 195℃, 205℃, and 205℃ respectively. The screw speed of the extruder is 300 rpm, and the feed speed is 18 rpm, to obtain plastic.

[0035] Example 7: This is a method for preparing flame-retardant glass fiber reinforced polypropylene plastic disclosed in this invention. The difference from Example 1 is that it includes the following steps: S1 First, hydroxylated boron nitride nanosheets were added to N-methylpyrrolidone, and the pH was adjusted to 9.5±0.1 to obtain a 0.2wt% OH-BNNSs suspension. Then, a 1.0wt% chopped glass fiber suspension with a silane coupling agent (γ-aminopropyltriethoxysilane) surface treatment was added. The length of the chopped glass fiber ranged from 3 to 12 mm. The pH was adjusted to 4.5±0.1, and the mixture was stirred continuously at 250 rpm for 60 min to complete the adsorption of boron nitride nanosheets on the glass fiber surface. Then, the mixture was quenched in liquid nitrogen for 15 s. Subsequently, the solvent was removed by freeze drying at 0℃ for 40 min. Finally, the mixture was electrospun at an electric field strength of 15 kV / cm for 10 min to obtain a boron nitride / glass fiber matrix. In S2, 100 parts of polypropylene matrix, 20 parts of boron nitride / glass fiber matrix obtained in S1, 5 parts of maleic anhydride-grafted polypropylene, 14 parts of α-zirconium phosphate, 6 parts of iron montmorillonite, 1.0 part of antioxidant 1010, 1.0 part of UV absorber UV-531, 0.6 parts of calcium stearate, and 0.8 parts of silicone masterbatch are added to a high-speed mixer. The grafting degree of maleic anhydride-grafted polypropylene is controlled to be 2.0%. After high-speed mixing at 1000 rpm for 10 minutes, the mixture is melt-extruded and granulated. The temperatures of each section of the extruder from the feed inlet to the die head are controlled to be 165℃, 195℃, 205℃, and 205℃ respectively. The screw speed of the extruder is 300 rpm, and the feed speed is 18 rpm, to obtain plastic.

[0036] Example 8: This is a method for preparing flame-retardant glass fiber reinforced polypropylene plastic disclosed in this invention. The difference from Example 1 is that it includes the following steps: S1 First, hydroxylated boron nitride nanosheets were added to N-methylpyrrolidone, and the pH was adjusted to 9.5±0.1 to obtain a 0.2wt% OH-BNNSs suspension. Then, a 1.0wt% chopped glass fiber suspension with a silane coupling agent (γ-aminopropyltriethoxysilane) surface treatment was added. The length of the chopped glass fiber ranged from 3 to 12 mm. The pH was adjusted to 4.5±0.1, and the mixture was stirred continuously at 250 rpm for 60 min to complete the adsorption of boron nitride nanosheets on the glass fiber surface. Then, the mixture was quenched in liquid nitrogen for 15 s. Subsequently, the solvent was removed by freeze drying at 0℃ for 40 min. Finally, the mixture was electrospun at an electric field strength of 15 kV / cm for 10 min to obtain a boron nitride / glass fiber matrix. In S2, 100 parts of polypropylene matrix, 35 parts of boron nitride / glass fiber matrix obtained in S1, 8 parts of maleic anhydride-grafted polypropylene, 15 parts of α-zirconium phosphate, 10 parts of iron montmorillonite, 1.5 parts of antioxidant 1010, 1.5 parts of UV absorber UV-531, 1.0 part of calcium stearate, and 1.0 part of silicone masterbatch are added to a high-speed mixer. The grafting degree of maleic anhydride-grafted polypropylene is controlled at 2.0%. After high-speed mixing at 1000 rpm for 10 minutes, the mixture is melt-extruded and granulated. The temperatures of each section of the extruder from the feed inlet to the die head are controlled to be 165℃, 195℃, 205℃, and 205℃ respectively. The screw speed of the extruder is 300 rpm, and the feed speed is 18 rpm, to obtain plastic.

[0037] Example 9: This is a method for preparing flame-retardant glass fiber reinforced polypropylene plastic disclosed in this invention. The difference from Example 1 is that it includes the following steps: S1 First, hydroxylated boron nitride nanosheets were added to N-methylpyrrolidone, and the pH was adjusted to 9.5±0.1 to obtain a 0.2wt% OH-BNNSs suspension. Then, a 1.0wt% chopped glass fiber suspension with a silane coupling agent (γ-aminopropyltriethoxysilane) surface treatment was added. The length of the chopped glass fiber ranged from 3 to 12 mm. The pH was adjusted to 4.5±0.1, and the mixture was stirred continuously at 200 rpm for 30 min to complete the adsorption of boron nitride nanosheets on the glass fiber surface. Then, the mixture was quenched in liquid nitrogen for 10 s. Subsequently, the solvent was removed by freeze drying at -5℃ for 30 min. Finally, the mixture was electrospun at an electric field strength of 15 kV / cm for 5 min to obtain the boron nitride / glass fiber matrix. In S2, 100 parts of polypropylene matrix, 25 parts of boron nitride / glass fiber matrix obtained in S1, 6 parts of maleic anhydride-grafted polypropylene, 12 parts of α-zirconium phosphate, 8 parts of iron montmorillonite, 1.2 parts of antioxidant 1010, 1.3 parts of UV absorber UV-531, 0.8 parts of calcium stearate, and 0.6 parts of silicone masterbatch are added to a high-speed mixer. The grafting degree of maleic anhydride-grafted polypropylene is controlled to be 2.0%. After high-speed mixing at 1000 pm for 10 min, the mixture is melt-extruded and granulated. The temperatures of each section of the extruder from the feed inlet to the die head are controlled to be 160℃, 180℃, 200℃, and 200℃ respectively. The screw speed of the extruder is 250 rpm, and the feed speed is 15 rpm, to obtain plastic.

[0038] Example 10: This is a method for preparing flame-retardant glass fiber reinforced polypropylene plastic disclosed in this invention. The difference from Example 1 is that it includes the following steps: S1 First, hydroxylated boron nitride nanosheets were added to N-methylpyrrolidone, and the pH was adjusted to 9.5±0.1 to obtain a 0.2wt% OH-BNNSs suspension. Then, a 1.0wt% chopped glass fiber suspension with a silane coupling agent (γ-aminopropyltriethoxysilane) surface treatment was added. The length of the chopped glass fiber ranged from 3 to 12 mm. The pH was adjusted to 4.5±0.1, and the mixture was stirred continuously at 300 rpm for 120 min to complete the adsorption of boron nitride nanosheets on the glass fiber surface. Then, the mixture was quenched in liquid nitrogen for 30 s. Subsequently, the solvent was removed by freeze drying at 5 °C for 60 min. Finally, the mixture was electrospun at an electric field strength of 15 kV / cm for 15 min to obtain the boron nitride / glass fiber matrix. In S2, 100 parts of polypropylene matrix, 25 parts of boron nitride / glass fiber matrix obtained in S1, 6 parts of maleic anhydride-grafted polypropylene, 12 parts of α-zirconium phosphate, 8 parts of iron montmorillonite, 1.2 parts of antioxidant 1010, 1.3 parts of UV absorber UV-531, 0.8 parts of calcium stearate, and 0.6 parts of silicone masterbatch are added to a high-speed mixer. The grafting degree of maleic anhydride-grafted polypropylene is controlled to be 2.0%. After high-speed mixing at 1000 pm for 10 min, the mixture is melt-extruded and granulated. The temperatures of each section of the extruder from the feed inlet to the die head are controlled to be 170℃, 200℃, 210℃, and 205℃ respectively. The screw speed of the extruder is 350 rpm, and the feed speed is 20 rpm, to obtain plastic. Comparative Example

[0039] Comparative Example 1: This is a method for preparing flame-retardant glass fiber reinforced polypropylene plastic disclosed in this invention. The difference from Example 1 is that in S1, short-cut glass fiber suspension is used to replace OH-BNNSs suspension in an equal amount to obtain glass fiber matrix.

[0040] Comparative Example 2: This is a method for preparing flame-retardant glass fiber reinforced polypropylene plastic disclosed in this invention. The difference from Example 1 is that in S1, electrospinning is not performed.

[0041] Comparative Example 3: This is a method for preparing flame-retardant glass fiber reinforced polypropylene plastic disclosed in this invention. The difference from Example 1 is that α-zirconium phosphate and iron montmorillonite are not used in S2.

[0042] Comparative Example 4: This is a method for preparing flame-retardant glass fiber reinforced polypropylene plastic disclosed in this invention. The difference from Example 1 is that no additives are used in S2. Performance testing

[0043] The plastics obtained in Example 1 and the plastics obtained in Comparative Examples 1-4 were made into test strips, and their flame retardant properties, mechanical properties, thermal properties, weather resistance, and chemical properties were tested. The results are shown in Table 1 below. The plastics obtained in Example 1 were also made into test strips, and SEM analysis of the impact fracture surface and combustion products was performed. The results are shown in Table 1 below. Figure 1 and 2 As shown.

[0044] Table 1

[0045] As can be seen from Table 1, Figure 1, and Figure 2, 1) Example 1 exhibits the best performance across all indicators; it achieves a UL-94 rating of V-0 with no dripping, a limiting oxygen index (LOI) as high as 32.5%, and a 55% reduction in peak heat release rate, demonstrating excellent flame retardant properties; its tensile strength of 95.5 MPa, flexural modulus of 7600 MPa, and notched impact strength of 9.8 kJ / m² demonstrate excellent mechanical properties; its heat distortion temperature of 158℃, thermal conductivity of 0.46 W / (m·K), and linear thermal expansion coefficient of 2.4 K show good thermal properties; and its 93% heat aging retention rate at 150℃ and 96% electrolyte immersion retention rate at 85℃ prove its excellent durability. Figure 1 Scanning electron microscopy of the impact fracture surface showed that the glass fibers modified with hydroxylated boron nitride nanosheets were uniformly dispersed in the polypropylene matrix. No obvious agglomeration of the fibers was observed; individual fibers were independent and randomly oriented, with no significant regional differences in distribution density. Figure 2 Scanning electron microscopy of the combustion products showed that they formed a continuous, dense char layer structure without obvious pores or cracks. The surface of this char layer was smooth and showed no signs of peeling, effectively blocking heat transfer and oxygen diffusion, and preventing the flame from spreading further to the substrate material. 2) The mechanical properties, thermal conductivity and dimensional stability of Comparative Example 1 (without BN nanosheets) decreased significantly, while the flame retardant properties and thermal aging properties also decreased to some extent, which fully demonstrates the key role of BN nanosheets in providing mechanical reinforcement, constructing thermal conductive pathways and constraining dimensions. 3) The mechanical properties and thermal conductivity of Comparative Example 2 (without electrostatic field alignment) were somewhat reduced compared to Example 1, and the pHRR was also slightly less reduced. This indicates that the random orientation of the BN nanosheets reduced the stress transfer efficiency and the integrity of the thermal network, verifying the importance of electric field orientation for performance optimization. 4) Comparative Example 3 (without added α-zirconium phosphate / iron montmorillonite) completely lost its flame retardant properties, exhibiting violent combustion, an LOI of only 21.0% (close to pure PP), and a pHRR reduction of only 10%, while other properties such as mechanical, thermal and durability remained basically unchanged. This directly confirms that the "catalytic char formation-free radical capture" synergistic flame retardant system constructed by α-zirconium phosphate and iron montmorillonite is the core to achieving a high flame retardant rating. 5) Comparative Example 4 (without additives) showed a sharp deterioration in long-term thermal stability while other properties remained basically maintained, highlighting the indispensability of the additive system in ensuring the long-term durability of the material.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing flame-retardant glass fiber reinforced polypropylene plastic, characterized in that: Includes the following steps, S1 first adds hydroxylated boron nitride nanosheets to N-methylpyrrolidone, adjusts the pH to 9.0~10.0 to obtain an OH-BNNSs suspension, then adds a suspension of short-cut glass fibers surface-treated with silane coupling agent, adjusts the pH to 4.0~5.0, and continuously stirs to complete the adsorption of boron nitride nanosheets on the glass fiber surface. Then, it is quenched in liquid nitrogen, followed by freeze drying to remove the solvent, and then electrospinning to obtain a boron nitride / glass fiber matrix. S2 involves mixing polypropylene matrix, boron nitride / glass fiber matrix obtained in S1, maleic anhydride-grafted polypropylene, α-zirconium phosphate, iron montmorillonite, and additives at high speed, followed by melt extrusion granulation to obtain plastic.

2. The method for preparing a flame-retardant glass fiber reinforced polypropylene plastic according to claim 1, characterized in that: In S1, the concentration of the OH-BNNSs suspension is controlled to be 0.1~0.3wt%, the silane coupling agent is γ-aminopropyltriethoxysilane, the concentration of the chopped glass fiber suspension is 0.8~1.2wt%, and the length of the chopped glass fiber is 3~12mm.

3. The method for preparing a flame-retardant glass fiber reinforced polypropylene plastic according to claim 2, characterized in that: In S1, the stirring time is controlled to be 30~120min and the stirring speed is 200~300rpm.

4. The method for preparing a flame-retardant glass fiber reinforced polypropylene plastic according to claim 2, characterized in that: In S1, the quenching time is controlled to be 10~30s, the freezing temperature is -5~5℃, the drying time is 30~60min, the electric field strength of the electrospinning treatment is 5~20kV / cm, and the treatment time is 5~15min.

5. The method for preparing a flame-retardant glass fiber reinforced polypropylene plastic according to claim 1, characterized in that: In S2, the ratio of polypropylene matrix, boron nitride / glass fiber matrix obtained in S1, maleic anhydride grafted polypropylene, α-zirconium phosphate, iron montmorillonite and additives is controlled to be 100: (15~35): (3~8): (10~15): (5~10): (2~5).

6. The method for preparing a flame-retardant glass fiber reinforced polypropylene plastic according to claim 5, characterized in that: In S2, the additive is composed of the following raw materials in parts by weight: 0.5 to 1.5 parts antioxidant 1010, 0.5 to 1.5 parts ultraviolet absorber UV-531, 0.5 to 1.0 parts calcium stearate, and 0.5 to 1.0 parts silicone masterbatch.

7. The method for preparing a flame-retardant glass fiber reinforced polypropylene plastic according to claim 5, characterized in that: In S2, the grafting degree of maleic anhydride-grafted polypropylene is 1.0~3.0%.

8. The method for preparing a flame-retardant glass fiber reinforced polypropylene plastic according to claim 5, characterized in that: In S2, the temperatures of each section of the extruder from the feed inlet to the die head are controlled to be 160~170℃, 190~200℃, 200~210℃, and 200~205℃ respectively, the screw speed of the extruder is 250~350rpm, and the feeding speed is 15~20rpm.

9. A flame-retardant glass fiber reinforced polypropylene plastic, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 8.

10. An application of a flame-retardant glass fiber reinforced polypropylene plastic, characterized in that: Application of plastics prepared by any of the preparation methods according to claims 1 to 8 in the preparation of battery casings, charging pile casings, power socket casings or electrical appliance casings.

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