Flame-retardant PC composite material based on high-temperature interfacial cross-linking and in-situ reinforcing process thereof

Abstract

This invention discloses a flame-retardant PC composite material based on high-temperature interfacial crosslinking and its in-situ reinforcement process. The composite material comprises polycarbonate resin, reinforcing fibers with a thermally responsive interface, a flame-retardant synergist, and processing aids. The core of this invention lies in the sequential formation of a thermally responsive interface layer and a sacrificial protective layer on the surface of the reinforcing fibers. The thermally responsive interface layer is formed by covalent grafting of a silane coupling agent containing peroxy bonds, while the sacrificial protective layer is a low-melting-point coating material. This design endows the material with temperature-triggered intelligent response characteristics: during routine processing and use, the protective layer ensures interface stability and slowly repairs the bonding force; under high-temperature fire conditions, the interface layer rapidly triggers crosslinking to form char, significantly improving flame-retardant efficiency and effectively suppressing melt dripping and the "wick effect." This invention simultaneously achieves high mechanical strength, long-term durability, and inherent flame-retardant safety in the material, making it suitable for high-requirement fields such as electronics, electrical appliances, and new energy vehicles.

Description

Technical Field

[0001] This invention relates to the field of flame-retardant PC composite material preparation technology, specifically to a flame-retardant PC composite material based on high-temperature interfacial crosslinking and its in-situ reinforcement process. Background Technology

[0002] Polycarbonate (PC) resin, due to its excellent impact strength, heat resistance, dimensional stability, and light transmittance, has become a key basic material for high-end equipment such as electronics, new energy vehicles, and rail transportation. In these application scenarios, components not only need to bear structural loads and possess high mechanical properties, but also must meet stringent flame-retardant safety standards to prevent fire risks caused by electrical faults, localized overheating, etc.

[0003] Introducing glass fiber (GF) reinforcement is a commonly used and effective method in the industry to improve the rigidity, strength, and heat resistance of polycarbonate. However, the addition of glass fiber also significantly increases the difficulty of flame-retardant design of the material, mainly in the following aspects:

[0004] The "wick effect" significantly reduces flame retardant safety. Under combustion conditions, molten polycarbonate wets the surface of glass fibers, and the high thermal conductivity of the fibers accelerates heat transfer, guiding the polymer melt towards the ignition source, thereby intensifying flame propagation and promoting combustion. This effect easily leads to molten dripping, triggering secondary ignition, greatly weakening the effectiveness of existing flame retardant systems and threatening overall fire safety.

[0005] There is a significant contradiction between high flame retardancy requirements and maintaining mechanical properties. To suppress the wick effect and meet relevant flame retardancy standards, it is often necessary to significantly increase the amount of flame retardant added. Especially when using inorganic filler-type flame retardants, high filler content can disrupt the continuity of the matrix, introduce stress concentration points, and severely impair the toughness and impact strength of the material. In addition, the poor interfacial compatibility between the flame retardant and the matrix and fibers further induces interfacial delamination, becoming a contributing factor to early material failure.

[0006] Traditional flame retardant technologies are still mainly based on "passive protection," relying heavily on the simple blending of flame retardants to achieve flame retardancy through physical isolation during combustion or the capture of gaseous free radicals. These methods cannot fundamentally solve the wick effect problem exacerbated by interfacial failure, nor can they simultaneously improve flame retardant efficiency while maintaining the overall mechanical properties of the material.

[0007] In view of this, this paper proposes a flame-retardant polycarbonate composite material based on high-temperature interfacial crosslinking and its in-situ reinforcement process. The aim is to achieve a synergistic improvement in flame-retardant performance and mechanical properties through rational design at the interfacial level, providing a new path for the application of high-performance engineering plastics in safety-sensitive fields. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a flame-retardant PC composite material based on high-temperature interfacial crosslinking and its in-situ reinforcement process. In this invention, a flame-retardant PC composite material based on high-temperature interfacial crosslinking comprises the following components in parts by weight:

[0009] 70-85 parts of polycarbonate resin;

[0010] 15-25 parts of reinforcing fiber with a thermally responsive interface;

[0011] 3-6 parts of flame retardant synergist;

[0012] Processing aids: 0.5–1.1 parts;

[0013] Among them, the reinforcing fiber with a thermally responsive interface is a glass fiber surface with a thermally responsive interface layer and a sacrificial protective layer sequentially constructed.

[0014] The thermally responsive interface layer is formed by reacting a pretreated glass fiber surface with a silane coupling agent containing peroxy bonds;

[0015] The sacrificial protective layer is a low-melting-point coating material that covers the outside of the thermally responsive interface layer;

[0016] The melting point of the sacrificial protective layer is lower than the processing temperature of the polycarbonate composite material, and its thermal decomposition temperature is higher than the triggering decomposition temperature of the peroxy bonds in the thermally responsive interface layer.

[0017] Furthermore, in the technical solution of the present invention, the silane coupling agent containing peroxy bonds is 3-(tert-butylperoxy)-1-propyltriethoxysilane.

[0018] Furthermore, in the technical solution of the present invention, the low-melting-point coating material is any one of polyethylene wax, polyethylene glycol, or zinc stearate.

[0019] Furthermore, in the technical solution of the present invention, the flame retardant synergist is aluminum diethylphosphinate.

[0020] Furthermore, in the technical solution of the present invention, the processing aids include a lubricant and an antioxidant. The lubricant is pentaerythritol stearate, and the antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1-1.3:2.

[0021] Furthermore, in the technical solution of the present invention, the preparation steps of the reinforcing fiber having a thermally responsive interface include:

[0022] ① Pre-treat the glass fiber to activate its surface. Immerse the activated glass fiber in a 1-3 wt% peroxysilane coupling agent solution and react at 40-60℃ for 2-4 hours. After grafting, remove the glass fiber and dry and cure it.

[0023] The pretreatment involves heat-treating the glass fiber at 500-600℃ for 3-5 minutes, followed by oxygen plasma treatment for 100-200 seconds, with an oxygen concentration of 30%-50%.

[0024] ② The cured fiber is immersed in a solution of low-melting-point coating material, pulled up and cooled to form a sacrificial protective layer on its surface, thus obtaining a reinforced fiber with a thermally responsive interface.

[0025] A process for preparing flame-retardant PC composite materials based on high-temperature interfacial crosslinking includes the following steps:

[0026] ①Dry the polycarbonate resin until the moisture content is less than 0.02%, and mix the dried polycarbonate resin, flame retardant synergist, processing aid and reinforcing fiber with thermal response interface in a uniform manner according to the formula to obtain a mixture;

[0027] ② The mixture is melt-blended using a twin-screw extruder, and then extruded, cooled, and pelletized. The melt-blending temperature is controlled at 230-250℃.

[0028] The twin-screw extruder has a screw speed of 300-350 rpm, and the reinforcing fibers with a thermally responsive interface are added via side feeding.

[0029] Furthermore, the technical solution of the present invention also includes a product molding step: the composite material granules obtained after pelletizing are molded into products by an injection molding machine, the injection temperature is controlled at 240-260℃, and the mold temperature is controlled at 80-100℃.

[0030] Effective gain:

[0031] In the technical solution of this invention, reinforcing fibers with a thermally responsive interface layer and a sacrificial protective layer sequentially constructed on their surface are designed. During the melt blending and granulation process, the sacrificial protective layer melts at the processing temperature, forming a viscous liquid film that coats the fibers. This liquid film acts as a physical barrier, effectively isolating the high temperature and shear stress within the twin-screw extruder, protecting the peroxide bonds in the thermally responsive interface layer, and reducing the breakage and decomposition of peroxide bonds. This mechanism ensures that the highly active components of the material can be stably processed under standard industrial equipment, laying the technological foundation for the realization of intelligent functions.

[0032] At normal operating temperatures, the sacrificial protective layer re-cures, but its microporous structure allows trace amounts of water molecules from the environment to pass through. These water molecules induce an extremely slow hydrolysis reaction of the peroxide bonds in the thermally responsive interface layer, continuously generating polar functional groups such as carboxyl groups. These groups undergo dynamic exchange reactions with the end groups of the polycarbonate matrix, maintaining a strong interfacial bond between the glass fiber and the PC matrix. This ensures that the composite material maintains superior tensile, flexural, and impact strength during long-term service, significantly enhancing its resistance to thermo-oxidative and damp-heat aging, and extending its service life.

[0033] Under high-temperature conditions such as fire, the sacrificial protective layer rapidly decomposes and fails. The peroxy bonds in the thermal response interface layer absorb a large amount of heat and undergo explosive breakage, generating a high concentration of free radicals. These free radicals efficiently catalyze cross-linking reactions in adjacent PC molecular chains, instantly forming a dense and robust char layer on the material surface. This char layer effectively isolates heat and oxygen, enabling the material to meet the extremely high flame retardant standard of UL94 V-0. Simultaneously, the rapid charring and cross-linking behavior in the interface region firmly anchors the molten PC to the glass fiber skeleton, fundamentally suppressing the fatal "molten dripping" and "wick effect" during polymer combustion, greatly improving fire safety and achieving intrinsic flame retardancy.

[0034] Other features and advantages of the present invention will be set forth in the following description. Attached Figure Description

[0035] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a process flow diagram of a flame-retardant PC composite material preparation process based on high-temperature interfacial crosslinking according to the present invention. Detailed Implementation

[0037] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0038] This invention proposes a flame-retardant PC composite material based on high-temperature interfacial crosslinking, comprising the following components in parts by weight:

[0039] 70-85 parts of polycarbonate resin;

[0040] 15-25 parts of reinforcing fiber with a thermally responsive interface;

[0041] 3-6 parts of flame retardant synergist;

[0042] Processing aids: 0.5–1.1 parts;

[0043] The reinforcing fiber with a thermally responsive interface consists of a thermally responsive interface layer and a sacrificial protective layer sequentially constructed on the surface of the glass fiber. The thermally responsive interface layer is formed by reacting a pretreated glass fiber surface with a silane coupling agent containing peroxy bonds. The sacrificial protective layer is a low-melting-point coating material that covers the outside of the thermally responsive interface layer. The melting point of the sacrificial protective layer is lower than the processing temperature of the polycarbonate composite material, and its thermal decomposition temperature is higher than the triggering decomposition temperature of the peroxy bonds in the thermally responsive interface layer.

[0044] Specifically, the polycarbonate resin constitutes the continuous phase of the material, providing basic mechanical strength, toughness, heat resistance and transparency, with a melt index of 10-10.5 g / 10min. In this embodiment, the polycarbonate resin is selected from Covestro, model Makrolon 2605 or from Mitsubishi Engineering Plastics, model Iupilon S-3000VR.

[0045] Specifically, the reinforcing fibers with thermally responsive interfaces serve as a rigid skeleton, improving the strength, stiffness, and heat resistance of the composite material. Simultaneously, the thermally responsive interface layer on its surface triggers interfacial cross-linking and catalytic char formation at high temperatures, achieving intrinsic flame retardancy.

[0046] In this embodiment, the silane coupling agent containing a peroxide bond is 3-(tert-butylperoxy)-1-propyltriethoxysilane. Selected from Hubei Xinlantian New Materials Co., Ltd., it is produced by a hydrosilylation reaction between triethoxysilane and allyl chloride to generate 3-chloropropyltriethoxysilane. Then, under alkaline conditions, 3-chloropropyltriethoxysilane undergoes a nucleophilic substitution reaction with tert-butylhydrogen peroxide, where the chlorine atom is replaced by the tert-butylperoxy group, to generate 3-(tert-butylperoxy)-1-propyltriethoxysilane, with the specific molecular formula (CH3)3C-OO-(CH2)3-Si(OC2H5)3.

[0047] Specifically, the low-melting-point coating material is any one of polyethylene wax, polyethylene glycol, or zinc stearate. In this embodiment, the polyethylene wax is selected from Honeywell, model AC. ® 6A; Polyethylene glycol is selected from Dow Chemical, model PEG 6000, and zinc stearate is selected from Dow Chemical, model industrial grade.

[0048] Specifically, the flame retardant synergist is aluminum diethylphosphonate. In this embodiment, aluminum diethylphosphonate is selected from Changzhou Aidi'er New Materials, model ADP-100.

[0049] Specifically, the processing aids include a lubricant and an antioxidant. The lubricant is pentaerythritol stearate, and the antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1-1.3:2. In this embodiment, pentaerythritol stearate is selected from Qingdao Bangli Chemical Co., Ltd., model PETS; antioxidant 1010 is selected from Beijing Jiyi Chemical Co., Ltd., model AN 1010; and antioxidant 168 is selected from Beijing Jiyi Chemical Co., Ltd., model AN 168.

[0050] Furthermore, antioxidant 1010 and antioxidant 168 are dry-mixed in proportion using a high-speed mixer at a speed of 800-1200 rpm for 5-8 minutes. Intermittent mixing is used, mixing for 2 minutes, pausing for 1 minute to allow the material to fall back, and then mixing again to ensure no dead zones.

[0051] Another aspect of this invention proposes an in-situ reinforcement process for PC composite materials, comprising the following steps:

[0052] ① Heat-treat the glass fiber at 500-600℃ for 3-5 minutes, then perform oxygen plasma treatment for 100-200 seconds under an oxygen concentration of 30%-50% to complete the pretreatment of the glass fiber and activate its surface. Immerse the activated glass fiber in a 1-3 wt% peroxysilane coupling agent solution and react at 40-60℃ for 2-4 hours. After grafting, remove the glass fiber and dry and cure it.

[0053] Specifically, under normal use, the peroxide bonds in the thermal response interface layer hydrolyze at an extremely slow rate and exchange with the PC end groups, continuously generating polar groups such as carboxyl groups. These newly generated polar groups continuously optimize the compatibility between the fiber and the PC matrix and repair microscopic interface damage caused by long-term use, keeping the material interface bonding force stable for a certain period of time. In the presence of open flame or high heat radiation, the temperature rises sharply to above 300°C. After reaching its rapid decomposition temperature threshold, the peroxide bonds undergo explosive homolytic cleavage, generating a high concentration of free radicals. These free radicals efficiently catalyze cross-linking reactions of adjacent PC molecular chains, instantly forming a dense and robust char layer around the glass fiber skeleton. This dense char layer insulates against heat and oxygen while firmly locking the molten PC onto the fiber, suppressing the "wick effect" and molten dripping. Some free radicals diffuse into the gas phase, acting as free radical scavengers, interrupting the chain reaction of combustion and improving the material's flame retardancy.

[0054] ② The cured fiber is immersed in a solution of low-melting-point coating material, pulled up and cooled to form a sacrificial protective layer on its surface, thus obtaining a reinforced fiber with a thermally responsive interface.

[0055] Specifically, the mass concentration of the low-melting-point coating material solution is 1% to 5%.

[0056] Understandably, during the mixing and granulation process, the low-melting-point protective layer rapidly melts, forming a uniform, viscous liquid film on the fiber surface. This liquid film effectively isolates the internal thermally responsive interface layer from the direct thermal shock of the high-temperature molten PC resin and the mechanical stress caused by screw shearing, reducing the damage of peroxide bonds. During daily use and service, the protective layer material re-cures at normal operating temperatures, forming a porous structure with numerous grain boundaries, defects, and micropores. Water molecules slowly diffuse through the microchannels to the interface layer, hydrolyzing the peroxide bonds in the thermally responsive interface layer, thereby maintaining this restorative reaction. The re-cured low-melting-point protective layer regulates the interface repair reaction at a gentler and more controllable rate, preventing excessive consumption of peroxide bonds and improving the long-term stability of interface performance. In the presence of open flames or high heat radiation, the protective layer material rapidly melts and decomposes, eliminating the physical barrier effect and preventing interference with the flame-retardant function of the thermally responsive interface layer.

[0057] ③Dry the polycarbonate resin until the moisture content is less than 0.02%, and mix the dried polycarbonate resin, flame retardant synergist, processing aid and reinforcing fiber with thermal response interface in a uniform manner according to the formula to obtain a mixture.

[0058] ④ The mixture is melt-blended using a twin-screw extruder, extruded, cooled, and then pelletized. The melt-blending temperature is controlled at 230-250℃.

[0059] The twin-screw extruder has a screw speed of 300-350 rpm, and the reinforcing fibers with a thermally responsive interface are added via side feeding.

[0060] Understandably, when reinforcing fibers with thermally responsive interfaces are added from the side feed, the PC resin has already been fully melted and plasticized into a uniform melt in the front section of the main cylinder. After the fibers enter, they can be more uniformly wrapped and wetted by the melt, achieving better dispersion under relatively mild shear. At the same time, when added from the downstream side feed, the fibers experience a shorter shearing process and can better maintain their initial length, thus more effectively exerting their reinforcing effect and enabling the composite material to obtain higher impact strength and rigidity.

[0061] ⑤ The composite material granules obtained after pelletizing are molded into products by injection molding machine. The injection temperature is controlled at 240-260℃ and the mold temperature is controlled at 80-100℃.

[0062] Specifically, by controlling the temperature below 260℃, the PC matrix can be melted and flowed while ensuring that the peroxide bonds are protected from being activated and decomposed in large quantities during the final processing step of injection molding.

[0063] To further understand the present invention, the PC composite material provided by the present invention will be described below with reference to the embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0064] Example 1

[0065] Preparation of reinforcing fibers with thermally responsive interfaces:

[0066] The glass fiber was heat-treated at 500℃ for 5 minutes, followed by oxygen plasma treatment at an oxygen concentration of 30% for 200 seconds to complete the pretreatment of the glass fiber. The activated glass fiber was then immersed in a 1 wt% solution of 3-(tert-butylperoxy)-1-propyltriethoxysilane and reacted at 40℃ for 4 hours. After grafting, the glass fiber was removed and dried and cured at 30℃ for 3 hours.

[0067] The cured fiber is immersed in a 3% polyethylene wax solution, pulled up and cooled to form a sacrificial protective layer on its surface, thus obtaining a reinforced fiber with a thermally responsive interface.

[0068] Example 2

[0069] Preparation of reinforcing fibers with thermally responsive interfaces:

[0070] The glass fiber was heat-treated at 600℃ for 3 minutes, followed by oxygen plasma treatment at an oxygen concentration of 50% for 100 seconds to complete the pretreatment of the glass fiber. The activated glass fiber was then immersed in a 3 wt% solution of 3-(tert-butylperoxy)-1-propyltriethoxysilane and reacted at 60℃ for 2 hours. After grafting, the fiber was removed and dried and cured at 30℃ for 3 hours.

[0071] The cured fiber is immersed in a 5% polyethylene glycol solution, pulled up and cooled to form a sacrificial protective layer on its surface, thus obtaining a reinforced fiber with a thermally responsive interface.

[0072] Example 3

[0073] Preparation of reinforcing fibers with thermally responsive interfaces:

[0074] The glass fiber was heat-treated at 600℃ for 3 minutes, followed by oxygen plasma treatment at an oxygen concentration of 50% for 100 seconds to complete the pretreatment of the glass fiber. The activated glass fiber was then immersed in a 3 wt% solution of 3-(tert-butylperoxy)-1-propyltriethoxysilane and reacted at 60℃ for 2 hours. After grafting, the fiber was removed and dried and cured at 30℃ for 3 hours.

[0075] The cured fiber is immersed in a 1% zinc stearate solution, pulled up and cooled to form a sacrificial protective layer on its surface, thus obtaining a reinforced fiber with a thermally responsive interface.

[0076] Example 4

[0077] Preparation of flame-retardant PC composite materials with high-temperature interfacial crosslinking:

[0078] The polycarbonate resin was dried to a moisture content of less than 0.02%. 70 parts of polycarbonate resin, 3 parts of aluminum diethylphosphinate, 0.3 parts of pentaerythritol stearate, 0.2 parts of antioxidant 1010 and antioxidant 168 were melt-blended in a mass ratio of 1:2. 25 parts of the thermally responsive reinforcing fiber prepared in Example 1 were added from the side feed port and mixed evenly. After extrusion, cooling, and pelletizing, the masterbatch was obtained.

[0079] Example 5

[0080] Preparation of flame-retardant PC composite materials with high-temperature interfacial crosslinking:

[0081] The polycarbonate resin was dried to a moisture content of less than 0.02%. 85 parts of polycarbonate resin, 6 parts of aluminum diethylphosphinate, 0.5 parts of pentaerythritol stearate, 0.6 parts of antioxidant 1010 and antioxidant 168 were melt-blended at a mass ratio of 1.3:2. 15 parts of the thermally responsive reinforcing fiber prepared in Example 2 were added through the side feed port and mixed evenly. After extrusion, cooling, and pelleting, the masterbatch was obtained.

[0082] Example 6

[0083] Preparation of flame-retardant PC composite materials with high-temperature interfacial crosslinking:

[0084] The polycarbonate resin was dried to a moisture content of less than 0.02%. 80 parts of polycarbonate resin, 4 parts of aluminum diethylphosphinate, 0.4 parts of pentaerythritol stearate, 0.5 parts of antioxidant 1010 and antioxidant 168 were melt-blended at a mass ratio of 1.1:2. 15 parts of the thermally responsive reinforcing fiber prepared in Example 3 were added through the side feed port and mixed evenly. After extrusion, cooling, and pelleting, the masterbatch was obtained.

[0085] Comparative Example 1

[0086] Commercially available flame-retardant PC with glass fiber reinforcement, sourced from Chi Mei Plastics, model number Wonderlite. ® PC-500 series.

[0087] Comparative Example 2

[0088] Glass fibers were heat-treated at 500℃ for 5 minutes, followed by oxygen plasma treatment at an oxygen concentration of 30% for 200 seconds to complete the pretreatment of the glass fibers. The activated glass fibers were then immersed in a 1 wt% solution of 3-(tert-butylperoxy)-1-propyltriethoxysilane and reacted at 40℃ for 4 hours. After grafting, the fibers were removed and dried and cured at 30℃ for 3 hours to obtain thermally responsive interface fibers.

[0089] The polycarbonate resin was dried to a moisture content of less than 0.02%. 70 parts of polycarbonate resin, 3 parts of aluminum diethylphosphinate, 0.3 parts of pentaerythritol stearate, 0.2 parts of antioxidant 1010 and antioxidant 168 were melt-blended in a mass ratio of 1:2. 25 parts of thermally responsive interface fiber were added from the side feed port and mixed evenly. After extrusion, cooling, and pelleting, the control masterbatch was obtained.

[0090] Test example:

[0091] The materials of Examples 4 and 5, as well as Comparative Examples 1 and 2, were subjected to UL-94 vertical burning (1.6 mm) tests, and the specific results are shown in Table 1.

[0092] The limiting oxygen index (LOI) of the materials in Examples 4 and 5, as well as Comparative Examples 1 and 2, was tested according to ASTM D2863. The specific results are shown in Table 1.

[0093] Peak heat release rate tests were performed on the materials of Examples 4 and 5 and Comparative Examples 1 and 2 according to ISO 5660-1 standard. The specific results are shown in Table 1.

[0094] Tensile strength tests were performed on the materials of Examples 4 and 5 and Comparative Examples 1 and 2 according to ISO 527 standard, and the specific results are shown in Table 1.

[0095] Bending strength tests were performed on the materials of Examples 4 and 5 and Comparative Examples 1 and 2 according to ISO 178 standard. The specific results are shown in Table 1.

[0096] Cantilever beam notched impact strength tests were conducted on the materials of Examples 4 and 5 and Comparative Examples 1 and 2 according to ISO 180 standard. The specific results are shown in Table 1.

[0097] The heat distortion temperature of the materials in Examples 4 and 5, as well as Comparative Examples 1 and 2, was tested according to ISO 75 standard. The specific results are shown in Table 1.

[0098] Melt flow rate tests were performed on the materials of Examples 4 and 5, as well as Comparative Examples 1 and 2. The specific results are shown in Table 1.

[0099] The yellowing index (b-value) of the materials in Examples 4 and 5, as well as Comparative Examples 1 and 2, was tested according to ASTM E313 standard. The specific results are shown in Table 1.

[0100] Table 1. Statistical Table of Parameters for Examples and Comparative Examples

[0101]

[0102] In summary, this invention provides a flame-retardant PC composite material based on high-temperature interfacial crosslinking and its in-situ reinforcement process. During melt blending and granulation, the low-melting-point coating material melts at the processing temperature, forming a viscous liquid film encapsulating the fibers. This liquid film acts as a physical barrier, effectively isolating the high-temperature shear stress within the twin-screw extruder. As shown in the table, the MFR of Comparative Example 2 decreased sharply from its normal state to 6 g / 10 min after processing, and the yellowing index of the material reached as high as 8.0, indicating that its active components had largely decomposed during processing and triggered matrix degradation. In contrast, the MFR of Examples 4 and 5 remained stable at 13-14 g / 10 min, with a yellowing index <2.5, demonstrating that the liquid film barrier formed by the sacrificial protective layer ensured that the key peroxide bonds in the thermally responsive interfacial layer remained "dormant" during processing, laying the technological foundation for subsequent functional realization.

[0103] In daily use, the slow hydrolysis and exchange reactions of the interface layer continuously "repair" the micro-damage at the interface. This self-healing effect ensures that the glass fiber and the PC matrix maintain a strong interfacial bond. This results in the mechanical properties of Examples 4 and 5 being significantly superior to the comparative examples: their tensile strength, flexural strength, and cantilever beam notched impact strength are all significantly better than those of Comparative Examples 1 and 4, demonstrating a stronger interfacial bond and better long-term durability.

[0104] Under high-temperature fire conditions, the sacrificial protective layer rapidly decomposes and fails. The peroxy bonds in the thermal response interface layer absorb a large amount of heat and undergo explosive breakage, generating a high concentration of free radicals. These free radicals efficiently catalyze cross-linking reactions of adjacent PC molecular chains, instantly forming a dense and robust char layer on the material surface. Examples 4 and 5 not only achieved UL-94 V-0 ratings and were completely drip-free, but also had a limiting oxygen index as high as 38% and a peak heat release rate significantly lower than 180 kW / m². This contrasts sharply with Comparative Examples 1 and 2, demonstrating that their rapid interfacial charring mechanism effectively suppresses the "wick effect" and achieves highly efficient flame retardancy.

[0105] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A flame-retardant PC composite material based on high-temperature interfacial crosslinking, characterized in that, The components include the following parts by weight: 70-85 parts of polycarbonate resin; 15-25 parts of reinforcing fiber with a thermally responsive interface; 3-6 parts of flame retardant synergist; Processing aids: 0.5–1.1 parts; The reinforcing fiber with a thermally responsive interface is a glass fiber with a thermally responsive interface layer and a sacrificial protective layer sequentially constructed on its surface. The thermally responsive interface layer is formed by reacting a pretreated glass fiber surface with a silane coupling agent containing peroxy bonds. The sacrificial protective layer is a low-melting-point coating material that covers the outside of the thermal response interface layer. The low-melting-point coating material is any one of polyethylene wax, polyethylene glycol, or zinc stearate. The melting point of the sacrificial protective layer is lower than the processing temperature of the polycarbonate composite material, and its thermal decomposition temperature is higher than the triggering decomposition temperature of the peroxy bond in the thermally responsive interface layer.

2. The flame-retardant PC composite material based on high-temperature interfacial crosslinking according to claim 1, characterized in that, The silane coupling agent containing peroxy bonds is 3-(tert-butylperoxy)-1-propyltriethoxysilane.

3. The flame-retardant PC composite material based on high-temperature interfacial crosslinking according to claim 1, characterized in that, The flame retardant synergist is aluminum diethylphosphonate.

4. The flame-retardant PC composite material based on high-temperature interfacial crosslinking according to claim 1, characterized in that, The processing aids include a lubricant and an antioxidant. The lubricant is pentaerythritol stearate, and the antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1-1.3:

2.

5. The flame-retardant PC composite material based on high-temperature interfacial crosslinking according to claim 1, characterized in that, The preparation steps of the reinforced fiber with a thermally responsive interface include: ① Pre-treat the glass fiber to activate its surface. Immerse the activated glass fiber in a 1-3 wt% peroxysilane coupling agent solution and react at 40-60℃ for 2-4 hours. After grafting, remove the glass fiber and dry and cure it. The pretreatment includes heat-treating the glass fiber at 500-600℃ for 3-5 minutes, followed by oxygen plasma treatment for 100-200 seconds. ② The cured fiber is immersed in a solution of a low-melting-point coating material, pulled up and cooled to form a sacrificial protective layer on its surface, thus obtaining the reinforced fiber with a thermally responsive interface.

6. An in-situ reinforcement process for PC composite materials, characterized in that, The preparation step for preparing the PC composite material according to any one of claims 1-5 includes: ①Dry the polycarbonate resin until the moisture content is less than 0.02%, and mix the dried polycarbonate resin, flame retardant synergist, processing aid and reinforcing fiber with thermal response interface in a uniform manner according to the formula to obtain a mixture; ② The mixture is melt-blended using a twin-screw extruder, and then extruded, cooled, and pelletized. The melt-blending temperature is controlled at 230-250℃.

7. The in-situ reinforcement process for PC composite materials according to claim 6, characterized in that, The twin-screw extruder has a screw speed of 300-350 rpm, and the reinforcing fiber with a thermally responsive interface is added via side feeding.

8. The in-situ reinforcement process for PC composite materials according to claim 6, characterized in that, It also includes the product molding step: the composite material granules obtained after pelletizing are molded into products by injection molding machine, with an injection temperature of 240-260℃ and a mold temperature of 80-100℃.

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