Glass fiber reinforced polyurethane composite and method of making

Abstract

This invention relates to the field of polymer composite materials technology, specifically providing a glass fiber reinforced polyurethane composite material and its preparation method. The composite material is composed of component A, component B, and reinforcing fibers in a mass ratio of (30-50):(41.1-78):(10-40), wherein: component A is isocyanate; component B includes: 35-55 parts by weight of a polyether / polyester polyol mixture, 3-8 parts by weight of a chain extender, 0.1-1 parts by weight of a catalyst, 0.5-2 parts by weight of a foam stabilizer, 0.5-2 parts by weight of an internal release agent, and 2-10 parts by weight of a functional filler, based on the total weight of component B; the functional filler is flake-shaped nano-kaolin; the reinforcing fibers are surface-modified chopped glass fibers that have undergone dual modification treatment with a silane coupling agent and a polyurethane prepolymer. The composite material of this invention exhibits excellent interfacial bonding strength, low coefficient of thermal expansion, high dimensional stability, and good processing flowability.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically providing a glass fiber reinforced polyurethane composite material and its preparation method. Background Technology

[0002] Polyurethane (PU) materials, due to their highly designable molecular structure and outstanding advantages such as excellent toughness, wear resistance, and chemical corrosion resistance, are widely used in coatings, elastomers, structural foams, and other fields. However, pure polyurethane resin systems have inherent defects such as low modulus, high coefficient of thermal expansion (CTE), and significant dimensional changes with temperature, making it difficult to directly meet the high requirements for dimensional stability and mechanical rigidity of precision components such as battery pack housings for new energy vehicles, structural components for drone fuselages, and brackets for high-end electrical equipment.

[0003] To overcome the above shortcomings, introducing glass fiber (hereinafter referred to as "glass fiber") as a reinforcing phase is a common technical approach to improve the strength and modulus of polyurethane composites. Glass fiber has the characteristics of high specific strength, relatively low cost, and good compatibility with polymer matrix processes, and has been widely used in the industrial production of various thermosetting and thermoplastic composites.

[0004] However, existing glass fiber reinforced polyurethane composites still face the following technical challenges in practical applications: (1) Poor interfacial bonding performance: Ordinary glass fiber has a smooth surface and is chemically inert, lacking effective functional groups that can chemically bond with polyurethane active groups (such as isocyanate groups and hydroxyl groups), resulting in weak interfacial adhesion between glass fiber and polyurethane matrix. Under external force, the interface is prone to debonding failure, which limits the effective transfer of stress from the matrix to the reinforcing phase and weakens the reinforcing efficiency of glass fiber; (2) Limited effect of reducing coefficient of thermal expansion: The key to reducing the coefficient of thermal expansion of composite materials lies in whether the glass fiber can form a highly oriented and uniformly dispersed load-bearing network in the matrix. Traditional blending or casting molding processes are difficult to effectively control the orientation and distribution of glass fiber. In some areas, the glass fiber agglomerates or is arranged in a disordered manner, resulting in an unsatisfactory reduction in the overall CTE of the composite material and a limited improvement effect on the size change with temperature. (3) Deterioration of processing fluidity under high glass fiber content: When the amount of glass fiber added is increased in pursuit of better mechanical and thermal properties, the viscosity of the system melt or reaction mixture increases significantly. In reaction injection molding (RIM) or casting molding processes, high viscosity materials are difficult to fill thin-walled or complex-cavity molds quickly and completely, which can easily lead to molding defects such as material shortage, bubbles or uneven local fiber distribution; (4) Significant anisotropy of the product: Under the influence of flow induction, glass fibers tend to align in the direction of flow, resulting in significant differences in shrinkage rate, thermal expansion behavior, and mechanical properties between the flow direction and the direction perpendicular to the flow direction. This anisotropy seriously affects the control of dimensional consistency of precision structural parts in different directions, reducing the dimensional stability and reliability of the final product.

[0005] In summary, how to build a strong interfacial bond between glass fiber and polyurethane while ensuring good processing fluidity, and at the same time achieve uniform dispersion and appropriate orientation control of glass fiber in the matrix to significantly reduce the coefficient of thermal expansion and suppress anisotropy of the product, remains a pressing technical problem to be solved in the field of glass fiber reinforced polyurethane composites.

[0006] Therefore, developing a glass fiber reinforced polyurethane composite material with excellent interfacial bonding, low thermal expansion, high dimensional stability, and good processing performance has significant industrial application value and practical significance. Summary of the Invention

[0007] The present invention aims to solve the technical problems of existing glass fiber reinforced polyurethane composites, such as poor interfacial bonding, unsatisfactory reduction of thermal expansion coefficient, difficult processing under high glass fiber content, and significant anisotropy of the products.

[0008] In a first aspect, the present invention provides a glass fiber reinforced polyurethane composite material, comprising component A, component B, and reinforcing fibers in a mass ratio of (30-50):(41.1-78):(10-40), wherein: Component A is an isocyanate; The B component comprises: 35-55 parts by weight of a polyether / polyester polyol mixture, 3-8 parts by weight of a chain extender, 0.1-1 parts by weight of a catalyst, 0.5-2 parts by weight of a foam stabilizer, 0.5-2 parts by weight of an internal release agent, and 2-10 parts by weight of a functional filler, wherein the parts by weight are based on the total weight of the B component, and the functional filler is flake-shaped nano-kaolin. The reinforcing fiber is a surface-modified short-cut glass fiber that has undergone dual modification treatment with silane coupling agent and polyurethane prepolymer.

[0009] In the preferred embodiment of the above-mentioned glass fiber reinforced polyurethane composite material, the ratio of the flexural modulus of the glass fiber reinforced polyurethane composite material in the flow direction to the vertical direction is ≤1.2.

[0010] In the preferred embodiment of the above-mentioned glass fiber reinforced polyurethane composite material, the aspect ratio of the sheet-like nano-kaolin is 50 to 100:1; and / or, the length of the surface-modified short-cut glass fiber is 1 to 6 mm.

[0011] In a second aspect, the present invention provides a method for preparing the glass fiber reinforced polyurethane composite material described in the first aspect, comprising the following steps: Fiberglass pretreatment: Short-cut glass fibers are modified sequentially with silane coupling agent and polyurethane prepolymer to obtain surface-modified short-cut glass fibers; Preparation of Component B: Dehydrate and mix all components of Component B except for the functional filler, then add the functional filler to obtain Component B; Turbulent mixing: Components A and B are metered and fed into a high-pressure mixing head, and the metered surface-modified chopped glass fiber is also fed into the same high-pressure mixing head; the high-pressure mixing head is equipped with a static mixing element, which causes the materials to be mixed in a turbulent manner under high pressure to obtain a mixture. Molding and curing: The mixture is injected into a preheated mold, and after being subjected to pressure reaction in the mold, it is demolded, removed and post-cured to obtain the glass fiber reinforced polyurethane composite material.

[0012] In the preferred embodiment of the above preparation method, in the glass fiber pretreatment step, after the surface-modified chopped glass fiber is treated with polyurethane prepolymer, the thickness of the polyurethane prepolymer layer on its surface is 50-200 nm, and the -NCO content in the polyurethane prepolymer layer is 5%-15%.

[0013] In the preferred embodiment of the above preparation method, in the turbulent mixing step, the pressure of the high pressure is 120-180 bar.

[0014] In the preferred embodiment of the above preparation method, in the turbulent mixing step, the surface-modified chopped glass fiber is fed in through a side feeder.

[0015] In the preferred embodiment of the above preparation method, during the turbulent mixing step, the residence time of the surface-modified chopped glass fiber in the high-pressure mixing head is no more than 0.5 seconds.

[0016] In the preferred embodiment of the above preparation method, in the step of preparing component B, after adding the functional filler, the mixture is uniformly mixed using a high-speed shear disperser with a shearing speed of 2000-5000 rpm and a shearing time of 0.5-2 hours.

[0017] In the preferred embodiment of the above preparation method, in the molding and curing steps, the preheating is preheating to 50-70°C; And / or, in the molding and curing steps, the pressure holding reaction time is 2 to 5 minutes, the post-curing temperature is 100 to 120°C, and the post-curing time is 2 to 4 hours.

[0018] By adopting the above technical solution, the present invention can achieve the following beneficial effects: (1) Excellent interfacial bonding strength: The surface of the short-cut glass fiber is modified by a dual process of silane coupling agent and polyurethane prepolymer, which realizes a multi-level bonding between the fiber and the matrix from chemical bonding to physical entanglement, significantly improving the interfacial adhesion and stress transfer efficiency. (2) Significantly reduced coefficient of thermal expansion (CTE): The synergistic effect of sheet-like nano-kaolin and chopped glass fibers. The sheet-like nano-kaolin can effectively restrict the thermal motion of the matrix resin, while the uniformly dispersed chopped glass fibers form a three-dimensional network structure. The combined effect of the two can reduce the CTE of the composite material to less than 30% of that of pure polyurethane (PU), which is close to the level of some engineering plastics; (3) Excellent dimensional stability and low warpage: The modified chopped glass fiber has a strong bond with the matrix, which reduces anisotropic shrinkage caused by interface defects and uneven fiber orientation; the addition of sheet-like nano-kaolin further inhibits uneven shrinkage, making the dimensional change rate of the product less than 0.1% under high temperature and high humidity conditions; (4) Good processing flowability: The flexible polyurethane prepolymer layer on the fiber surface can reduce friction and entanglement between glass fibers, and reduce the viscosity of the system under high fiber content; the flake-like nano-kaolin is pre-dispersed in component B to form a stable slurry, ensuring its uniform distribution in the final product and avoiding flow defects caused by agglomeration. The above characteristics make this composite material suitable for reaction injection molding (RIM) process, and can meet the molding requirements of thin-walled and complex cavity structures. Attached Figure Description

[0019] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which: Figure 1 This is a process flow diagram of the preparation method of the glass fiber reinforced polyurethane composite material of the present invention. Detailed Implementation

[0020] The following explains some of the terms used in this invention: In this invention, the term "MD" refers to the melt flow direction of the material in the mold cavity (Machine Direction / Flow Direction), and "TD" refers to the transverse direction perpendicular to the MD direction on the surface of the product (Transverse Direction). The MD / TD flexural modulus ratio is the ratio of the flexural modulus in the flow direction to the flexural modulus in the perpendicular direction.

[0021] Based on the technical problems of existing glass fiber reinforced polyurethane composites pointed out in the background art, such as poor interfacial bonding, unsatisfactory reduction of the coefficient of thermal expansion, processing difficulties at high glass fiber content, and significant anisotropy of the finished products, this invention provides a glass fiber reinforced polyurethane composite material and its preparation method. This glass fiber reinforced polyurethane composite material, through the synergistic effect of its components, exhibits excellent interfacial bonding strength, low coefficient of thermal expansion, high dimensional stability, and good processing flowability.

[0022] Specifically, in a first aspect, the present invention provides a glass fiber reinforced polyurethane composite material, comprising component A, component B, and reinforcing fibers in a mass ratio of (30-50):(41.1-78):(10-40), wherein: Component A is an isocyanate; The B component comprises: 35-55 parts by weight of a polyether / polyester polyol mixture, 3-8 parts by weight of a chain extender, 0.1-1 parts by weight of a catalyst, 0.5-2 parts by weight of a foam stabilizer, 0.5-2 parts by weight of an internal release agent, and 2-10 parts by weight of a functional filler, wherein the parts by weight are based on the total weight of the B component, and the functional filler is flake-shaped nano-kaolin. The reinforcing fiber is a surface-modified short-cut glass fiber that has undergone dual modification treatment with silane coupling agent and polyurethane prepolymer.

[0023] In the glass fiber reinforced polyurethane composite material provided by this invention, the surface of the chopped glass fiber is modified by a dual process of silane coupling agent and polyurethane prepolymer, achieving excellent interfacial bonding with the matrix and significantly improving interfacial adhesion and stress transfer efficiency. The synergistic effect of sheet-like nano-kaolin and the chopped glass fiber reduces the CTE of the composite material to less than 30% of that of pure PU. The strong bond between the modified glass fiber and the matrix, along with the addition of sheet-like nano-kaolin, endows the product with excellent dimensional stability and low warpage characteristics, with a dimensional change rate of less than 0.1% under high temperature and high humidity conditions. Simultaneously, the flexible polyurethane prepolymer layer on the glass fiber surface reduces frictional entanglement between fibers, and the pre-dispersion of sheet-like nano-kaolin ensures uniform distribution, giving the composite material good processing fluidity. It is suitable for RIM molding of complex thin-walled components, and is particularly suitable for precision structural parts with stringent requirements for dimensional stability, coefficient of thermal expansion, and mechanical properties, such as battery pack housings for new energy vehicles, fuselage structural parts for drones, and brackets for high-end electrical equipment.

[0024] In this invention, the reinforcing fiber is a surface-modified chopped glass fiber that has undergone dual modification treatment with a silane coupling agent and a polyurethane prepolymer. This results in the surface-modified chopped glass fiber being distributed in a non-completely oriented manner in the composite material. That is, the fibers are not all highly oriented along the flow direction, but rather exhibit a certain degree of random or weakly oriented distribution. This makes the ratio of the flexural modulus of the composite material in the flow direction to that in the vertical direction ≤1.2, thereby significantly reducing the anisotropy of the product, improving its dimensional stability, achieving excellent interfacial bonding with the matrix, and significantly improving interfacial adhesion and stress transfer efficiency.

[0025] In some specific embodiments, the silane coupling agent is at least one of aminopropyltriethoxysilane (KH550) or epoxysilane (KH560), and its main function is to improve the interfacial compatibility between chopped glass fiber and polyurethane matrix.

[0026] In some specific embodiments, the polyurethane prepolymer refers to an intermediate product with reactive end groups (i.e., isocyanate groups, -NCO) generated by the partial reaction of polyols (such as polyethers, polyesters) and excess diisocyanates (such as MDI, TDI). The coating layer formed on the fiber surface can chemically bond with component A or component B in subsequent reactions, thereby constructing a covalently bonded interfacial transition layer between the fiber and the matrix.

[0027] The components are commonly used in this field.

[0028] For example, the isocyanate is selected from one or more of diphenylmethane diisocyanate (MDI), polymeric MDI (PMDI), carbodiimide modified liquefied MDI, hydrogenated MDI (H12MDI), toluene diisocyanate (TDI), and isophorone diisocyanate (IPDI).

[0029] In some specific embodiments, the polymeric MDI (PMDI) is one or a combination of Wanhua Chemical Group Co., Ltd.'s PM200, Covestro AG's 44V20, or BASF AG's M20S.

[0030] In some specific embodiments, the carbodiimide-modified liquefied MDI is MM103 purchased from BASF.

[0031] The mass ratio of polyether polyol to polyester polyol in the polyether / polyester polyol mixture is (40-70):(30-60). The polyether polyol may be, for example, at least one of polypropylene glycol (PPG), polytetrahydrofuran ether glycol (PTMEG), and polyethylene oxide-propylene oxide co-ether glycol, with a number average molecular weight of 1000-3000 g / mol. The polyester polyol may be, for example, at least one of adipic acid-based polyester glycol, polycaprolactone glycol (PCL), and polycarbonate glycol (PCDL), with a number average molecular weight of 1000-3000 g / mol.

[0032] The chain extender is selected from one or more of ethylene glycol (EG), 1,4-butanediol (BDO), 1,3-propanediol (PDO), diethylene glycol (DEG), 1,2-propanediol (PG), neopentyl glycol (NPG), hydroquinone dihydroxyethyl ether (HQEE), trimethylolpropane (TMP), and triethanolamine (TEOA), preferably 1,4-butanediol (BDO).

[0033] The catalyst is selected from at least one of bismuth neodecanoate, zinc isooctanoate, zinc-bismuth composite catalyst, triethylenediamine (TEDA), and dibutyltin dilaurate (DBTDL); more preferably, the catalyst is bismuth neodecanoate, zinc isooctanoate, or zinc-bismuth composite catalyst.

[0034] In some specific embodiments, the zinc-bismuth composite catalyst has a zinc-bismuth composite mass ratio of 3:1 to 5:1.

[0035] In one specific embodiment, the zinc-bismuth composite catalyst is Z8M (Jiaxing Runbo Chemical Technology Co., Ltd.), and the mass ratio of organic zinc to organic bismuth is 3:1, 4:1 or 5:1.

[0036] The foam stabilizer is selected from polyether-modified polysiloxane, and can be selected from one or more of Evonik B8409, Evonik B8462, Dow DC-193, Dow DC-2525, Momentive L-6900, and Momentive L-6910.

[0037] The internal release agent is selected from at least one of alkyl phosphate, zinc stearate, calcium stearate, montan wax, oxidized polyethylene wax, Loxiol G78S, and Acmos 1709.

[0038] In some specific embodiments, the alkyl phosphate ester used as an internal release agent refers to a class of compounds whose main components are alkyl phosphate monoesters, alkyl phosphate dieesters, or mixtures thereof, wherein the alkyl chain typically has 4 to 10 carbon atoms. 18 Preferably C8 to C 18 .

[0039] As an example, the alkyl phosphate is selected from hexadecyl phosphate and octadecyl phosphate.

[0040] In this invention, the ratio of the flexural modulus of the composite material in the flow direction to that in the vertical direction is ≤1.2.

[0041] For example, in one specific embodiment, the ratio of the flexural modulus of the composite material in the flow direction to that in the vertical direction is 1.15.

[0042] For example, in another specific embodiment, the ratio of the flexural modulus of the composite material in the flow direction to that in the vertical direction is 1.12.

[0043] In some specific embodiments, the aspect ratio of the sheet-like nano-kaolin is 50 to 100:1. For example, it can be 50:1, 60:1, 70:1, 80:1, or any value within the range.

[0044] Controlling the aspect ratio of the flake-shaped nano-kaolinite within the range of 50–100:1 facilitates its uniform dispersion in component B and enables it to form an effective lamellar barrier network in the composite material. Within this aspect ratio range, the kaolinite lamellars effectively restrict the thermal motion of the matrix resin, working synergistically with chopped glass fibers to significantly reduce the coefficient of thermal expansion of the composite material and improve the dimensional stability of the product.

[0045] In some specific embodiments, the length of the surface-modified chopped glass fiber is 1 to 6 mm. For example, it can be 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, or any value within the range.

[0046] Furthermore, the present invention provides a method for preparing the glass fiber reinforced polyurethane composite material described in the first aspect in a second aspect, such as... Figure 1 As shown, the preparation method includes the following steps: S1. Glass fiber pretreatment: Short glass fibers are modified sequentially with silane coupling agent and polyurethane prepolymer to obtain surface-modified short glass fibers. S2, Preparation of Component B: Dehydrate and mix all components of Component B except for the functional filler, then add the functional filler to obtain Component B; S3, Turbulent Mixing: Components A and B are metered according to their dosage and fed into a high-pressure mixing head. At the same time, the metered surface-modified chopped glass fiber is also fed into the same high-pressure mixing head. The high-pressure mixing head is equipped with a static mixing element, which causes the materials to be mixed in a turbulent manner under high pressure to obtain a mixture. S4. Molding and curing: The mixture is injected into a preheated mold, and after being subjected to pressure reaction in the mold, it is demolded, removed, and post-cured to obtain the glass fiber reinforced polyurethane composite material.

[0047] It is understandable that the order of the above steps S1 and S2 is not restricted. That is, glass fiber pretreatment can be performed first, component B preparation can be performed first, or both can be performed simultaneously, as long as surface-modified chopped glass fiber and component B can be obtained before the turbulent mixing in step S3.

[0048] The preparation method provided by this invention significantly enhances the interfacial bonding strength between glass fiber and polyurethane matrix through the dual modification of silane coupling agent and polyurethane prepolymer in the glass fiber pretreatment step. The introduction of functional fillers in the B-component preparation step further optimizes the system's processing performance and dimensional stability. In particular, the synergistic effect of static mixing elements and high-pressure conditions in the turbulent mixing step ensures thorough mixing of materials under turbulent conditions, effectively reducing the degree of unidirectional orientation of the glass fiber. This results in a composite material with incompletely oriented glass fiber distribution, significantly reducing anisotropy and improving dimensional stability. Furthermore, this method employs reaction injection molding, resulting in a short residence time of materials in the mixing head, low system viscosity, and good processing fluidity, meeting the molding requirements of thin-walled or complex cavity structures.

[0049] It should be noted that the static mixing element disposed within the high-pressure mixing head of the present invention can take various forms, such as mixing balls, mixing plates, etc. The high-pressure mixing head with static mixing elements can refer to the high-pressure static mixer structure disclosed in the prior art, such as the high-pressure static mixer disclosed in Chinese Utility Model Patent CN211963772U, which achieves uniform mixing by distributing multiple mixing balls within the mixing chamber, causing the material to split, turn, and merge when flowing through under high pressure. Furthermore, Chinese Utility Model Patent CN209901071U also discloses a high-pressure static mixer for ternary fluids, which has a mixing plate structure inside, enabling forced mixing of multiple fluid streams. The aforementioned arrangements of static mixing elements in the prior art can all be used in the high-pressure mixing head of the present invention to achieve turbulent mixing of components A and B and surface-modified chopped glass fibers.

[0050] In some specific embodiments, in step S1 of the glass fiber pretreatment, after the surface-modified chopped glass fiber is treated with polyurethane prepolymer, the thickness of the polyurethane prepolymer layer on its surface is 50-200 nm, and the -NCO content in the polyurethane prepolymer layer is 5%-15%. For example, the thickness of the polyurethane prepolymer layer can be 50 nm, 100 nm, 150 nm, 200 nm, or any value within the range; the -NCO content in the polyurethane prepolymer layer can be 5%, 8%, 10%, 12%, 15%, or any value within the range.

[0051] Controlling the thickness of the polyurethane prepolymer layer to 50–200 nm and the -NCO content to 5%–15% facilitates the formation of a continuous, stable, and appropriately reactive interfacial transition layer on the glass fiber surface. Within this range, the prepolymer layer can fully react with component A or component B, establishing a strong chemical bond between the fiber and the matrix while maintaining the integrity and cohesive strength of the interfacial layer itself. This results in excellent interfacial bonding and effectively improves the mechanical properties and dimensional stability of the composite material.

[0052] In step S3 of this invention, the material is turbulently mixed under high pressure by a high-pressure mixing head equipped with a static mixing element, which can reduce the degree of unidirectional orientation of the glass fibers. The reduction of the degree of unidirectional orientation of the glass fibers means that the surface-modified chopped glass fibers are not fully oriented in the resulting composite material, and the ratio of the flexural modulus of the composite material in the flow direction to that in the perpendicular direction is ≤1.2.

[0053] In some specific embodiments, in the turbulent mixing step S3, the high pressure is 120–180 bar. For example, it can be 120 bar, 150 bar, 180 bar, or any value within the range.

[0054] In some specific embodiments, in step S3 of the turbulent mixing, the surface-modified chopped glass fibers are fed in via a side feeder. Using a side feeder to directly deliver the chopped glass fibers into the high-pressure mixing head for mixing with components A and B avoids premature contact between the glass fibers and the liquid components, preventing agglomeration or pre-wetting. This ensures the glass fibers enter the turbulent mixing zone in a dry, loose state, achieving uniform dispersion in the high-pressure turbulent field. Simultaneously, it helps maintain the integrity of the prepolymer coating layer on the glass fiber surface, fully leveraging its interfacial reinforcement effect.

[0055] In some specific embodiments, during the turbulent mixing step S3, the residence time of the surface-modified chopped glass fiber in the high-pressure mixing head is no more than 0.5 seconds. For example, it can be 0.4 seconds, 0.3 seconds, 0.2 seconds, or any value within the range.

[0056] By controlling the residence time of surface-modified chopped glass fibers in the high-pressure mixing head to ≤0.5 seconds, it is possible to ensure thorough mixing of the materials while effectively preventing reorientation of the glass fibers due to excessive shearing time. This ensures that the glass fibers in the composite material are not fully oriented, achieving a flexural modulus ratio of ≤1.2 between the flow direction and the vertical direction. Furthermore, this residence time also helps to prevent pre-gelling of the polyurethane system within the mixing head, ensuring process stability and continuous production.

[0057] In some specific embodiments, in step S2 of the preparation of component B, after adding the functional filler, the mixture is homogenized using a high-speed shear disperser at a shearing speed of 2000–5000 rpm for 0.5–2 hours. For example, the shearing speed can be 2000 rpm, 3000 rpm, 4000 rpm, 5000 rpm, or any value within the range described. Through high-speed shear dispersion, flake-like nano-kaolin can be pre-formed into a stable and uniform slurry in component B. This pre-dispersion process facilitates the alignment of kaolin flakes perpendicular to the thickness direction during subsequent molding, thereby further reducing the coefficient of thermal expansion of the composite material. Simultaneously, this pre-dispersion process also ensures the uniform distribution of kaolin in the final product, avoiding flow defects caused by agglomeration.

[0058] In this invention, the dehydration described in step S2 can be carried out under conventional conditions in the art, such as heating, vacuuming, or a combination thereof, and this invention is not limited thereto. The purpose of dehydration is to remove adsorbed moisture from the raw materials (especially polyether / polyester polyols) in component B. Because polyol raw materials have strong hydrophilicity, they easily adsorb moisture from the air. If moisture remains, it will react with component A (isocyanate) to generate carbon dioxide, leading to bubbles and cracks in the product. Simultaneously, it consumes isocyanate and may deactivate the catalyst, severely affecting the product's performance. Therefore, dehydration before the preparation of component B ensures the quality of the composite material.

[0059] In some preferred embodiments, the dehydration is carried out under vacuum.

[0060] In some specific embodiments, in the molding and curing step S4, the preheating is preheating to 50-70°C; for example, it can be preheating to 50°C, 55°C, 60°C, 65°C, 70°C or any value within the range.

[0061] In some specific embodiments, in step S4 of the molding and curing process, the pressure holding reaction time is 2–5 minutes, the post-curing temperature is 100–120°C, and the post-curing time is 2–4 hours. For example, the pressure holding reaction time can be 2 minutes, 3 minutes, 4 minutes, 5 minutes, or any value within the range; the post-curing temperature can be 100°C, 105°C, 110°C, 115°C, 120°C, or any value within the range; and the post-curing time can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or any value within the range.

[0062] The glass fiber reinforced polyurethane composite material and its preparation method of the present invention will be described in detail below through several specific embodiments.

[0063] The polyurethane prepolymer solutions used in the following examples and comparative examples were prepared using the following method: Add PPG or PTMEG with a number average molecular weight of 1000-2000 to a reactor and dehydrate under vacuum at 100-110℃ and -0.095MPa for 2-3 hours. After removing the water, cool to 40-50℃. Purge with nitrogen and slowly add carbodiimide-modified liquefied MDI or PMDI at an NCO / OH molar ratio R = 2.0-3.0, stirring until homogeneous. Heat to 70-80℃ and maintain the temperature for 2-3 hours. Monitor the -NCO content in the system using di-n-butylamine titration. Stop the reaction when the target range is reached. The product obtained is a polyurethane prepolymer. Cool the system to below 40℃ and dilute with anhydrous ethyl acetate or anhydrous methyl ethyl ketone to a polyurethane prepolymer solid content of 30%-50%. Add 0.05% benzoyl chloride by weight of the total solid mass of the polyurethane prepolymer as a stabilizer and stir until homogeneous to obtain the polyurethane prepolymer solution.

[0064] The polyurethane prepolymer solutions in Examples 1-4 were prepared using PPG and carbodiimide-modified liquefied MDI (MM103); the polyurethane prepolymer solutions in Examples 5-8 were prepared using PTMEG and PMDI (PM200).

[0065] The viscosity of the obtained polyurethane prepolymer solution at 25°C was controlled to be 50–200 mPa·s. The viscosity was adjusted by the following methods: fixing the molecular weight of the polyol to 1000–2000; controlling the NCO / OH molar ratio R to 2.0–3.0, with a higher R value resulting in lower viscosity; and adjusting the amount of solvent to achieve a solid content of 30%–50%, with a lower solid content resulting in lower viscosity.

[0066] The -NCO content in the obtained polyurethane prepolymer solution is controlled to be 5% to 15% by mass. The -NCO content is precisely controlled by the following methods: the feed is precisely metered according to the NCO / OH molar ratio R = 2.0 to 3.0; the reaction process is monitored in real time by di-n-butylamine titration, and the reaction is terminated immediately when the target value is reached; solvent dilution only changes the viscosity and does not change the percentage of -NCO in the system.

[0067] Example 1 This embodiment provides a glass fiber reinforced polyurethane composite material and its preparation method. The glass fiber reinforced polyurethane composite material is composed of the following components, and the amount of each component is by weight: Preparation method: S1. Fiberglass pretreatment: Short-cut fiberglass is placed in a fluidized bed and sprayed with an ethanol solution of 2% silane coupling agent (KH550) until the cumulative amount of the sprayed solution reaches 100 mL. After drying, a polyurethane prepolymer solution with a viscosity of 100 mPa·s at 25°C is sprayed to make the polyurethane prepolymer layer on the surface of the fiberglass reach a thickness of 100 nm. The -NCO content in the polyurethane prepolymer layer is 10%. After curing at a low temperature of 60°C, modified short-cut fiberglass with a polyurethane prepolymer layer on the surface is obtained.

[0068] Preparation of Components S2 and B: Polyether / polyester polyol, chain extender, catalyst, foam stabilizer, and internal release agent were added to a reactor and dehydrated for 2 hours at 105℃ and a vacuum of -0.095 MPa, and then mixed evenly. Then, flake-shaped nano-kaolin was added, and the mixture was treated with a high-speed shear disperser at a shear rate of 3000 rpm for 1 hour to form a uniform dispersion system, thus obtaining Component B.

[0069] S3. Turbulent Mixing: Components A and B are precisely metered and fed into a high-pressure mixing head. Simultaneously, metered surface-modified chopped glass fibers are continuously and uniformly fed into the same high-pressure mixing head via a side feeder. The high-pressure mixing head is equipped with a static mixing element, causing the materials to mix in a turbulent state under a pressure of 160 bar, thereby reducing the degree of unidirectional orientation of the glass fibers and obtaining a uniformly mixed material. The feeding rate of the side feeder is proportionally linked to the output rates of components A and B, ensuring that the weight ratio of surface-modified chopped glass fibers to the total output of components A and B remains constant. The residence time of the surface-modified chopped glass fibers in the mixing head is 0.3 seconds.

[0070] S4. Molding and Curing: Quickly inject the uniformly mixed material into a mold that has been preheated to 60°C, hold the pressure for 3 minutes, open the mold and remove the product, and then cure it at 110°C for 3 hours to obtain the final composite material product.

[0071] Example 2 This embodiment provides a glass fiber reinforced polyurethane composite material and its preparation method. The glass fiber reinforced polyurethane composite material is composed of the following components, and the amount of each component is by weight: Preparation method: S1. Fiberglass pretreatment: Short-cut fiberglass is placed in a fluidized bed and sprayed with an ethanol solution of 2% silane coupling agent (KH550) until the cumulative amount of the sprayed solution reaches 120 mL. After drying, a polyurethane prepolymer solution with a viscosity of 120 mPa·s at 25°C is sprayed to make the polyurethane prepolymer layer on the surface of the fiberglass reach a thickness of 120 nm. The -NCO content in the polyurethane prepolymer layer is 11%. After curing at a low temperature of 60°C, modified short-cut fiberglass with a polyurethane prepolymer layer on the surface is obtained.

[0072] Preparation of Components S2 and B: Polyether / polyester polyol, chain extender, catalyst, foam stabilizer, and internal release agent were added to a reactor and dehydrated for 2 hours at 105℃ and a vacuum of -0.095 MPa, and then mixed evenly. Then, flake-shaped nano-kaolin was added, and the mixture was treated with a high-speed shear disperser at a shear rate of 3500 rpm for 1 hour to form a uniform dispersion system, thus obtaining Component B.

[0073] S3. Turbulent Mixing: Components A and B are precisely metered and fed into a high-pressure mixing head. Simultaneously, metered surface-modified chopped glass fibers are continuously and uniformly fed into the same high-pressure mixing head via a side feeder. The high-pressure mixing head is equipped with a static mixing element, which creates a turbulent mixing state under a pressure of 150 bar to reduce the degree of unidirectional orientation of the glass fibers, thereby obtaining a uniformly mixed material. The feeding rate of the side feeder is proportionally linked to the output rates of components A and B, ensuring that the weight ratio of surface-modified chopped glass fibers to the total output of components A and B remains constant. The residence time of the surface-modified chopped glass fibers in the mixing head is 0.2 seconds.

[0074] S4. Molding and Curing: Quickly inject the uniformly mixed material into a mold that has been preheated to 60°C, hold the pressure for 3.5 minutes, open the mold and remove the product, and then cure it at 110°C for 3 hours to obtain the final composite material product.

[0075] Example 3 This embodiment provides a glass fiber reinforced polyurethane composite material and its preparation method. The glass fiber reinforced polyurethane composite material is composed of the following components, and the amount of each component is by weight: Preparation method: S1. Fiberglass pretreatment: Short-cut fiberglass is placed in a fluidized bed and sprayed with an ethanol solution of 1.5% silane coupling agent (KH560) until the cumulative amount of the sprayed solution reaches 80 mL. After drying, a polyurethane prepolymer solution with a viscosity of 50 mPa·s at 25°C is sprayed to make the polyurethane prepolymer layer on the surface of the fiberglass reach a thickness of 50 nm. The -NCO content in the polyurethane prepolymer layer is 5%. After low-temperature curing at 60°C, modified short-cut fiberglass with a polyurethane prepolymer layer on the surface is obtained.

[0076] Preparation of Components S2 and B: Polyether / polyester polyol, chain extender, catalyst, foam stabilizer, and internal release agent were added to a reactor and dehydrated for 2 hours at 110℃ and a vacuum of -0.095 MPa, and then mixed evenly. Then, flake-shaped nano-kaolin was added, and the mixture was treated with a high-speed shear disperser at a shear rate of 2000 rpm for 2 hours to form a uniform dispersion system, thus obtaining Component B.

[0077] S3. Turbulent Mixing: Components A and B are precisely metered and fed into a high-pressure mixing head. Simultaneously, metered surface-modified chopped glass fibers are continuously and uniformly fed into the same high-pressure mixing head via a side feeder. The high-pressure mixing head is equipped with a static mixing element, causing the materials to mix in a turbulent state under a pressure of 120 bar, thereby reducing the degree of unidirectional orientation of the glass fibers and obtaining a uniformly mixed material. The feeding rate of the side feeder is proportionally linked to the output rates of components A and B, ensuring that the weight ratio of surface-modified chopped glass fibers to the total output of components A and B remains constant. The residence time of the surface-modified chopped glass fibers in the mixing head is 0.5 seconds.

[0078] S4. Molding and Curing: Quickly inject the uniformly mixed material into a mold that has been preheated to 50°C, hold the pressure for 2 minutes, open the mold and remove the product, and then cure it at 100°C for 4 hours to obtain the final composite material product.

[0079] Example 4 This embodiment provides a glass fiber reinforced polyurethane composite material and its preparation method. The glass fiber reinforced polyurethane composite material is composed of the following components, and the amount of each component is by weight: Preparation method: S1. Fiberglass pretreatment: Short-cut fiberglass is placed in a fluidized bed and sprayed with an ethanol solution of 2.5% silane coupling agent (KH550) until the cumulative amount of the sprayed solution reaches 150 mL. After drying, a polyurethane prepolymer solution with a viscosity of 200 mPa·s at 25°C is sprayed to make the polyurethane prepolymer layer on the surface of the fiberglass reach a thickness of 200 nm. The -NCO content in the polyurethane prepolymer layer is 15%. After curing at a low temperature of 70°C, modified short-cut fiberglass with a polyurethane prepolymer layer on the surface is obtained.

[0080] Preparation of Components S2 and B: Polyether / polyester polyol, chain extender, catalyst, foam stabilizer, and internal release agent were added to a reactor and dehydrated for 3 hours at 100℃ and a vacuum of -0.09 MPa, and then mixed evenly. Then, flake-shaped nano-kaolin was added, and the mixture was treated with a high-speed shear disperser at a shear rate of 5000 rpm for 0.5 hours to form a uniform dispersion system, thus obtaining Component B.

[0081] S3. Turbulent Mixing: Components A and B are precisely metered and fed into a high-pressure mixing head. Simultaneously, metered surface-modified chopped glass fibers are continuously and uniformly fed into the same high-pressure mixing head via a side feeder. The high-pressure mixing head is equipped with a static mixing element, causing the materials to mix in a turbulent state under a pressure of 180 bar, thereby reducing the degree of unidirectional orientation of the glass fibers and obtaining a uniformly mixed material. The feeding rate of the side feeder is proportionally linked to the output rates of components A and B, ensuring that the weight ratio of surface-modified chopped glass fibers to the total output of components A and B remains constant. The residence time of the surface-modified chopped glass fibers in the mixing head is 0.2 seconds.

[0082] S4. Molding and Curing: Quickly inject the uniformly mixed material into a mold that has been preheated to 70°C, hold the pressure for 5 minutes, open the mold and remove the product, and then cure it at 120°C for 2 hours to obtain the final composite material product.

[0083] Example 5 This embodiment provides a glass fiber reinforced polyurethane composite material and its preparation method. The glass fiber reinforced polyurethane composite material is composed of the following components, and the amount of each component is by weight: Preparation method: S1. Fiberglass pretreatment: Short-cut fiberglass is placed in a fluidized bed and sprayed with an ethanol solution of 2% silane coupling agent (KH550) until the cumulative amount of the sprayed solution reaches 110 mL. After drying, a polyurethane prepolymer solution with a viscosity of 120 mPa·s at 25°C is sprayed to make the polyurethane prepolymer layer on the surface of the fiberglass reach a thickness of 120 nm. The -NCO content in the polyurethane prepolymer layer is 9%. After curing at a low temperature of 65°C, modified short-cut fiberglass with a polyurethane prepolymer layer on the surface is obtained.

[0084] Preparation of Components S2 and B: Polyether / polyester polyol, chain extender, catalyst, foam stabilizer, and internal release agent were added to a reactor and dehydrated for 2.5 hours at 105℃ and a vacuum of -0.095 MPa, and then mixed evenly. Then, flake-shaped nano-kaolin was added, and the mixture was treated with a high-speed shear disperser at a shear rate of 4000 rpm for 1.2 hours to form a uniform dispersion system, thus obtaining Component B.

[0085] S3. Turbulent Mixing: Components A and B are precisely metered and fed into a high-pressure mixing head. Simultaneously, metered surface-modified chopped glass fibers are continuously and uniformly fed into the same high-pressure mixing head via a side feeder. The high-pressure mixing head is equipped with a static mixing element, which creates a turbulent mixing state under a pressure of 150 bar to reduce the degree of unidirectional orientation of the glass fibers, thereby obtaining a uniformly mixed material. The feeding rate of the side feeder is proportionally linked to the output rates of components A and B, ensuring that the weight ratio of surface-modified chopped glass fibers to the total output of components A and B remains constant. The residence time of the surface-modified chopped glass fibers in the mixing head is 0.35 seconds.

[0086] S4. Molding and Curing: Quickly inject the uniformly mixed material into a mold that has been preheated to 65°C, hold the pressure for 3.5 minutes, open the mold and remove the product, and then cure it at 115°C for 2.5 hours to obtain the final composite material product.

[0087] Example 6 This embodiment provides a glass fiber reinforced polyurethane composite material and its preparation method. The glass fiber reinforced polyurethane composite material is composed of the following components, and the amount of each component is by weight: Preparation method: S1. Fiberglass pretreatment: Short-cut fiberglass is placed in a fluidized bed and sprayed with an ethanol solution of 2.2% silane coupling agent (KH560) until the cumulative amount of the sprayed solution reaches 90 mL. After drying, a polyurethane prepolymer solution with a viscosity of 80 mPa·s at 25°C is sprayed to make the polyurethane prepolymer layer on the surface of the fiberglass reach a thickness of 80 nm. The -NCO content in the polyurethane prepolymer layer is 12%. After low-temperature curing at 60°C, modified short-cut fiberglass with a polyurethane prepolymer layer on the surface is obtained.

[0088] Preparation of Components S2 and B: Polyether / polyester polyol, chain extender, catalyst, foam stabilizer, and internal release agent were added to a reactor and dehydrated for 2.2 hours at 108℃ and a vacuum of -0.098 MPa until homogeneous. Then, flake-shaped nano-kaolin was added, and the mixture was treated with a high-speed shear disperser at a shear rate of 2500 rpm for 1.8 hours to form a homogeneous dispersion system, thus obtaining Component B.

[0089] S3. Turbulent Mixing: Components A and B are precisely metered and fed into a high-pressure mixing head. Simultaneously, metered surface-modified chopped glass fibers are continuously and uniformly fed into the same high-pressure mixing head via a side feeder. The high-pressure mixing head is equipped with a static mixing element, causing the materials to mix in a turbulent state under a pressure of 140 bar, thereby reducing the degree of unidirectional orientation of the glass fibers and obtaining a uniformly mixed material. The feeding rate of the side feeder is proportionally linked to the output rates of components A and B, ensuring that the weight ratio of surface-modified chopped glass fibers to the total output of components A and B remains constant. The residence time of the surface-modified chopped glass fibers in the mixing head is 0.4 seconds.

[0090] S4. Molding and Curing: The uniformly mixed material is quickly injected into a mold that has been preheated to 55°C. After holding the pressure for 4 minutes, the mold is opened and the product is removed. It is then cured at 105°C for 3.5 hours to obtain the final composite material product.

[0091] Example 7 This embodiment provides a glass fiber reinforced polyurethane composite material and its preparation method. The glass fiber reinforced polyurethane composite material is composed of the following components, and the amount of each component is by weight: Preparation method: S1. Fiberglass pretreatment: Short-cut fiberglass is placed in a fluidized bed and sprayed with an ethanol solution of 1.8% silane coupling agent (KH550) until the cumulative amount of the sprayed solution reaches 90 mL. After drying, a polyurethane prepolymer solution with a viscosity of 80 mPa·s at 25°C is sprayed to make the polyurethane prepolymer layer on the surface of the fiberglass reach a thickness of 80 nm. The -NCO content in the polyurethane prepolymer layer is 8%. After low-temperature curing at 60°C, modified short-cut fiberglass with a polyurethane prepolymer layer on the surface is obtained.

[0092] Preparation of Components S2 and B: Polyether / polyester polyol, chain extender, catalyst, foam stabilizer, and internal release agent were added to a reactor and dehydrated for 2 hours at 105℃ and a vacuum of -0.095 MPa, and then mixed evenly. Then, flake-shaped nano-kaolin was added, and the mixture was treated with a high-speed shear disperser at a shear rate of 2500 rpm for 1.5 hours to form a uniform dispersion system, thus obtaining Component B.

[0093] S3. Turbulent Mixing: Components A and B are precisely metered and fed into a high-pressure mixing head. Simultaneously, metered surface-modified chopped glass fibers are continuously and uniformly fed into the same high-pressure mixing head via a side feeder. The high-pressure mixing head is equipped with a static mixing element, causing the materials to mix in a turbulent state under a pressure of 140 bar, thereby reducing the degree of unidirectional orientation of the glass fibers and obtaining a uniformly mixed material. The feeding rate of the side feeder is proportionally linked to the output rates of components A and B, ensuring that the weight ratio of surface-modified chopped glass fibers to the total output of components A and B remains constant. The residence time of the surface-modified chopped glass fibers in the mixing head is 0.3 seconds.

[0094] S4. Molding and Curing: Quickly inject the uniformly mixed material into a mold that has been preheated to 60°C, hold the pressure for 3 minutes, open the mold and remove the product, and then cure it at 110°C for 3 hours to obtain the final composite material product.

[0095] Example 8 This embodiment provides a glass fiber reinforced polyurethane composite material and its preparation method. The glass fiber reinforced polyurethane composite material is composed of the following components, and the amount of each component is by weight: Preparation method: S1. Fiberglass pretreatment: Short-cut fiberglass is placed in a fluidized bed and sprayed with an ethanol solution of 2.2% silane coupling agent (KH550) until the cumulative amount of the sprayed solution reaches 130 mL. After drying, a polyurethane prepolymer solution with a viscosity of 150 mPa·s at 25°C is sprayed to make the polyurethane prepolymer layer on the surface of the fiberglass reach a thickness of 150 nm. The -NCO content in the polyurethane prepolymer layer is 12%. After low-temperature curing at 65°C, modified short-cut fiberglass with a polyurethane prepolymer layer on the surface is obtained.

[0096] Preparation of Components S2 and B: Polyether / polyester polyol, chain extender, catalyst, foam stabilizer, and internal release agent were added to a reactor and dehydrated for 2.5 hours at 105℃ and a vacuum of -0.095 MPa, and then mixed evenly. Then, flake-shaped nano-kaolin was added, and the mixture was treated with a high-speed shear disperser at a shear rate of 4500 rpm for 0.8 hours to form a uniform dispersion system, thus obtaining Component B.

[0097] S3. Turbulent Mixing: Components A and B are precisely metered and fed into a high-pressure mixing head. Simultaneously, metered surface-modified chopped glass fibers are continuously and uniformly fed into the same high-pressure mixing head via a side feeder. The high-pressure mixing head is equipped with a static mixing element, causing the materials to mix in a turbulent state under a pressure of 170 bar, thereby reducing the degree of unidirectional orientation of the glass fibers and obtaining a uniformly mixed material. The feeding rate of the side feeder is proportionally linked to the output rates of components A and B, ensuring that the weight ratio of surface-modified chopped glass fibers to the total output of components A and B remains constant. The residence time of the surface-modified chopped glass fibers in the mixing head is 0.25 seconds.

[0098] S4. Molding and Curing: Quickly inject the uniformly mixed material into a mold that has been preheated to 65°C, hold the pressure for 4 minutes, open the mold and remove the product, and then cure it at 115°C for 2.5 hours to obtain the final composite material product.

[0099] Comparative Example 1 This comparative example provides a glass fiber polyurethane composite material and its preparation method. Unlike Example 1, the components do not contain sheet-like nano-kaolin.

[0100] Preparation method: S1. Glass fiber pretreatment: Same as in Example 1. Short-cut glass fibers are placed in a fluidized bed and sprayed with an ethanol solution of 2% silane coupling agent (KH550) at a concentration of 100 mL. After drying, a polyurethane prepolymer solution (viscosity 25℃ 100 mPa·s) is sprayed to make the surface prepolymer layer thickness reach 100 nm with -NCO content of 10%. It is cured at 60℃ to obtain surface-modified short-cut glass fibers.

[0101] Preparation of S2 and B components: A mixture of polyether / polyester polyols (30 parts by weight of PPG-2000 and 20 parts by weight of PBA-1000), chain extender (5 parts by weight of BDO), catalyst (0.5 parts by weight of zinc-bismuth composite catalyst), foam stabilizer (1 part by weight of Evonik B8409), and internal release agent (1 part by weight of Loxiol G78S) were added to a reactor and dehydrated at 105°C and a vacuum of -0.095 MPa for 2 hours and mixed evenly (unlike Example 1, no functional filler flake nano-kaolin was added, and no high-speed shear dispersion treatment was performed) to obtain component B.

[0102] S3, Turbulent Mixing: Same as Example 1. Component A (40 parts by weight), component B (62.5 parts by weight), and surface-modified chopped glass fiber (25 parts by weight) are turbulently mixed in a 160 bar high-pressure mixing head with a residence time of 0.3 seconds.

[0103] S4. Molding and Curing: Same as in Example 1. Preheat the mold to 60°C, hold the pressure for 3 minutes, and then cure at 110°C for 3 hours.

[0104] Comparative Example 2 This comparative example provides a glass fiber polyurethane composite material and its preparation method. The composition is the same as in Example 1. The difference is that the short-cut glass fiber in the preparation method is not double-modified, but only modified with an ethanol solution of silane coupling agent (KH550).

[0105] Preparation method: S1. Fiberglass pretreatment: Short-cut fiberglass is placed in a fluidized bed and sprayed with an ethanol solution of 2% silane coupling agent (KH550) at a concentration of 100 mL. After drying (unlike in Example 1, polyurethane prepolymer solution is not sprayed after drying), short-cut fiberglass treated only with silane coupling agent is obtained.

[0106] Preparation of components S2 and B: Same as in Example 1 (containing 5 parts by weight of sheet-like nano-kaolin, high-speed shearing at 3000 rpm for 1 hour).

[0107] S3, Turbulent mixing: Same as Example 1 (40 parts by weight of component A, 62.5 parts by weight of component B, 25 parts by weight of surface-modified chopped glass fiber, turbulent mixing in a 160 bar high-pressure mixing head, residence time 0.3 seconds).

[0108] S4. Molding and curing: Same as in Example 1 (preheat the mold to 60°C, hold pressure for 3 minutes, and cure at 110°C for 3 hours).

[0109] Comparative Example 3 This comparative example provides a glass fiber polyurethane composite material and its preparation method. The difference from Example 1 is that the flake-like nano-kaolinite in the components is replaced with lightweight calcium carbonate, and the chopped glass fibers are not surface-modified. The preparation method employs a conventional blending process, as detailed below: S1. Fiberglass drying: The chopped fiberglass is dried at 80°C for 4 hours to obtain dried chopped fiberglass (without surface modification treatment). Preparation of S2 and B components: Polyether / polyester polyol, chain extender, catalyst, foam stabilizer, and internal release agent were added to a reactor and dehydrated at 105℃ and a vacuum of -0.095MPa for 2 hours, and then mixed evenly. Light calcium carbonate was then added, and the mixture was treated with a high-speed shear disperser at a shear rate of 3000rpm for 1 hour to form a uniform dispersion system, thus obtaining component B. S3. Blending: Add the dried chopped glass fibers to component B and stir at 2000 rpm for 20 minutes using a high-speed disperser to initially disperse them; then add component A and stir rapidly for 2 minutes to mix evenly. S4. Molding and Curing: Quickly inject the uniformly mixed material into a mold that has been preheated to 60°C, hold the pressure in the mold for 3 minutes, open the mold and take out the product, and then cure it at 110°C for 3 hours to obtain the final composite material product.

[0110] Experimental Example 1 This test case investigated the performance of the composite materials in each embodiment and comparative example.

[0111] The testing method is as follows: (1) Tensile strength The test was conducted according to ISO 527-2:2025, "Plastics – Determination of tensile properties – Part 2: Test conditions for molded and extruded plastics". A1 type (injection molded) standard specimens were used, with specimen dimensions conforming to ISO 20753:2023. Under conditions of 23±2℃ and 50±10% relative humidity, the test was performed using a universal testing machine at a constant tensile rate of 5 mm / min. The maximum tensile stress at specimen fracture was recorded, which is the tensile strength of the composite material, expressed in MPa.

[0112] (2) Flexural modulus The test was conducted according to ISO 178:2019, "Determination of flexural properties of plastics". A three-point bending loading method was used, with a specimen size of 80mm × 10mm × 4mm, a span of 64mm, and a test speed of 2mm / min. The load-deflection curve was tested and recorded at a temperature of 23±2℃, and the flexural modulus was calculated using the standard formula, in MPa.

[0113] (3) Coefficient of thermal expansion (CTE) The test was conducted according to ISO 11359-2:2021, "Plastics – Determination of thermomechanical analysis (TMA) – Part 2: Determination of linear thermal expansion coefficient and glass transition temperature". The sample size was 20 mm × 5 mm × 4 mm, the test temperature range was -30 °C to 100 °C, the heating rate was 5 °C / min, and a nitrogen atmosphere was used. The dimensional changes of the sample with temperature were recorded, and the linear thermal expansion coefficient was calculated using the standard formula, with units of ppm / K.

[0114] (4) Anisotropy index The modulus ratio method was used to calculate the anisotropy index, with the ratio of the longitudinal (MD direction) flexural modulus to the transverse (TD direction) flexural modulus of the composite material as the anisotropy index. The flexural moduli in the MD direction and the TD direction were obtained by testing according to the method described in item (2) of this test example.

[0115] (5) Warpage Testing was conducted using a coordinate measuring machine or a high-precision flatness measuring instrument. A composite material sample measuring 100mm × 100mm × 2mm was placed on a standard flat platform, and the maximum vertical distance between the bottom surface of the sample and the standard plane was measured and recorded as the warpage, in mm. Three parallel samples were tested for each sample, and the maximum value was taken. The smaller the warpage value, the better the flatness and resistance to warping deformation of the composite material.

[0116] (6) Dimensional change rate after damp heat aging A standard sample measuring 100mm × 10mm × 4mm was placed in a constant temperature and humidity aging chamber and aged continuously for 168 hours at 85℃ and 85% relative humidity. The length of the sample in the flow direction (MD) was measured before and after aging, and the dimensional change rate was calculated using the following formula: Dimensional change rate (%) = (L1 - L0) / L0 × 100%, where L0 is the length before aging and L1 is the length after aging. Five parallel samples were tested for each sample, and the arithmetic mean was taken.

[0117] (7) Heat distortion temperature (HDT) The test was conducted according to ISO 75-1:2020 and ISO 75-2:2020, "Determination of heat distortion temperature of plastics". A flat loading method was used, with a specimen size of 80mm × 10mm × 4mm. A normal stress of 1.80MPa was applied, and the heating rate was 120℃ / h. The temperature at which the deflection at the midpoint of the specimen reached 0.34mm was recorded as the heat distortion temperature, expressed in °C.

[0118] (8) Apparent melt viscosity The tests were conducted using a capillary rheometer with a capillary die diameter of 1.0 mm and an aspect ratio (L / D) of 30:1. Before testing, the samples were dried at 120°C for 2 hours. The test temperature was set to 120°C, and the shear rate to 1000 s⁻¹.-1 Record the melt viscosity value at steady state, in Pa·s.

[0119] (9) Interface integration evaluation The composite material sample was subjected to low-temperature brittle fracture treatment with liquid nitrogen, and the fracture surface was treated with gold sputtering (sputtering time 100 seconds). The microstructure of the fracture surface was observed by scanning electron microscopy (SEM) under an accelerating voltage of 10kV to evaluate the interfacial bonding state between the matrix and the filler / fiber.

[0120] The test results are shown in Table 1: Table 1. Performance test results of composite materials in each embodiment and comparative example. The results in Table 1 show that: All embodiments outperform all comparative examples in all performance metrics, specifically as follows: Comprehensive mechanical properties: The tensile strength of Examples 1-8 is 132-158 MPa, the flexural modulus is 7.5-9.2 GPa, and the HDT is 178-198℃, all of which are superior to those of Comparative Examples 1-3 (tensile strength 95-128 MPa, flexural modulus 4.5-6.5 GPa, HDT 125-155℃). This indicates that the present invention significantly improves the rigidity and heat resistance of the composite material while maintaining the good toughness of polyurethane.

[0121] CTE and Anisotropy: Comparative Example 1 and Comparative Example 1: After adding sheet-like nano-kaolin, the CTE decreased from 48ppm / K to 28ppm / K (a reduction of 42%), and the anisotropy index decreased from 1.85 to 1.15, indicating that the sheet-like filler effectively suppressed the anisotropic shrinkage caused by glass fiber orientation.

[0122] Comparative Example 1 and Comparative Example 2: When glass fiber is not double modified, even with kaolin, the CTE is still high (52ppm / K) and the anisotropy index is also high (2.10), indicating that poor interfacial bonding will lead to a decrease in reinforcement efficiency and an increase in anisotropy.

[0123] Comparing Example 1 and Comparative Example 3: The anisotropy index of Comparative Example 3 (conventional process) is as high as 2.50, meaning that the product exhibits significant differences in performance between the flow direction and the vertical direction, making it extremely prone to warping. In contrast, the ratio of Example 1 is only 1.15, approaching isotropy. This fully demonstrates the synergistic effect of the dual-modified glass fiber, sheet kaolin, and turbulent mixing process.

[0124] Warpage: The warpage of Examples 1-8 is 0.16-0.25 mm / 100 mm, which is much lower than that of Comparative Examples 1-3 (0.65-1.20 mm / 100 mm), further verifying the excellent dimensional stability of the composite material of the present invention.

[0125] Processability: The apparent melt viscosity of Examples 1-8 was 290-380 Pa·s, which was lower than that of Comparative Examples 1-3 (580-780 Pa·s). This indicates that the surface flexible polyurethane layer effectively reduced the friction between glass fibers, allowing the high glass fiber content system to still have good flowability, making it suitable for RIM molding of complex thin-walled parts.

[0126] Dimensional stability during damp heat aging: The dimensional change rates of Examples 1-8 were 0.02-0.05%, which were significantly better than the 0.18-0.42% of Comparative Examples 1-3. This is due to the excellent interfacial bonding, which prevented expansion caused by moisture penetration along the interface.

[0127] Interface and evaluation: The interface bonding evaluation for all embodiments was "minimal / very little glass fiber pull-out, complete / relatively complete matrix encapsulation," while Comparative Examples 1-3 showed "partial glass fiber pull-out," "numerous glass fiber pull-out, smooth surface," or "significant glass fiber agglomeration, partial debonding." This indicates that the present invention significantly improves the interfacial bonding quality between glass fiber and resin matrix through the synergistic effect of dual-modified glass fiber, sheet-like nano-kaolin, and turbulent mixing process.

[0128] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A glass fiber reinforced polyurethane composite material, characterized in that, The mixture consists of component A, component B, and reinforcing fibers in a mass ratio of (30–50): (41.1–78): (10–40). Composition, in which: Component A is an isocyanate; The B component comprises: 35-55 parts by weight of a polyether / polyester polyol mixture, 3-8 parts by weight of a chain extender, 0.1-1 parts by weight of a catalyst, 0.5-2 parts by weight of a foam stabilizer, 0.5-2 parts by weight of an internal release agent, and 2-10 parts by weight of a functional filler, wherein the parts by weight are based on the total weight of the B component, and the functional filler is flake-shaped nano-kaolin. The reinforcing fiber is a surface-modified short-cut glass fiber that has undergone dual modification treatment with silane coupling agent and polyurethane prepolymer.

2. The glass fiber reinforced polyurethane composite material according to claim 1, characterized in that, The glass fiber reinforced polyurethane composite material has a flexural modulus ratio of ≤1.2 in the flow direction to the vertical direction.

3. The glass fiber reinforced polyurethane composite material according to claim 1 or 2, characterized in that, The aspect ratio of the sheet-like nano-kaolin is 50 to 100:1; And / or, the length of the surface-modified chopped glass fiber is 1 to 6 mm.

4. A method for preparing the glass fiber reinforced polyurethane composite material according to any one of claims 1-3, characterized in that, The preparation method includes the following steps: Fiberglass pretreatment: Short-cut glass fibers are modified sequentially with silane coupling agent and polyurethane prepolymer to obtain surface-modified short-cut glass fibers; Preparation of Component B: Dehydrate and mix all components of Component B except for the functional filler, then add the functional filler to obtain Component B; Turbulent mixing: Components A and B are metered and fed into a high-pressure mixing head, and the metered surface-modified chopped glass fiber is also fed into the same high-pressure mixing head; the high-pressure mixing head is equipped with a static mixing element, which causes the materials to be mixed in a turbulent manner under high pressure to obtain a mixture. Molding and curing: The mixture is injected into a preheated mold, and after being subjected to pressure reaction in the mold, it is demolded, removed and post-cured to obtain the glass fiber reinforced polyurethane composite material.

5. The preparation method according to claim 4, characterized in that, In the glass fiber pretreatment step, after the surface-modified chopped glass fiber is treated with polyurethane prepolymer, the thickness of the polyurethane prepolymer layer on its surface is 50-200 nm, and the -NCO content in the polyurethane prepolymer layer is 5%-15%.

6. The preparation method according to claim 4, characterized in that, In the turbulent mixing step, the pressure of the high pressure is 120–180 bar.

7. The preparation method according to claim 4, characterized in that, In the turbulent mixing step, the surface-modified chopped glass fibers are fed in via a side feeder.

8. The preparation method according to claim 4, characterized in that, The residence time of the surface-modified chopped glass fiber in the high-pressure mixing head is no more than 0.5 seconds.

9. The preparation method according to claim 4, characterized in that, In the preparation step of component B, after adding the functional filler, the mixture is uniformly mixed using a high-speed shear disperser with a shearing speed of 2000-5000 rpm and a shearing time of 0.5-2 hours.

10. The preparation method according to claim 4, characterized in that, In the molding and curing steps, the preheating is to preheat to 50-70°C; And / or, in the molding and curing steps, the pressure holding reaction time is 2 to 5 minutes, the post-curing temperature is 100 to 120°C, and the curing time is 2 to 4 hours.

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