Flame-retardant reinforced polycarbonate composite material and preparation method thereof

Abstract

The invention discloses a flame-retardant reinforced polycarbonate composite material and a preparation method thereof, and belongs to the technical field of polycarbonate composites.The flame-retardant reinforced polycarbonate composite material comprises 70%-90% of polycarbonate resin, the polycarbonate resin is aromatic polycarbonate with the viscosity average molecular weight ranging from 20000 to 35000; the glass fiber is alkali-free chopped E glass fiber, and the surface of the glass fiber is treated by an amino silane coupling agent; the flame retardant comprises 5-15% of a phosphorus-nitrogen-silicon composite flame retardant, the composite flame retardant is a synergistic system formed by physically premixing a phosphate ester compound, a nitrogen charring agent and a silicone polymer, and the phosphate ester compound plays a role in gas-phase flame retardance and partial condensed-phase flame retardance during combustion. By adopting a phosphorus-nitrogen-silicon composite flame-retardant synergistic system, high flame-retardant efficiency is realized under the condition of low additive amount, the halogen-free and environment-friendly effects are realized, and the environmental and health hidden dangers of the traditional brominated flame retardant are overcome.

Description

Technical Field

[0001] This invention relates to the field of polycarbonate composite materials technology, and more specifically, to a flame-retardant reinforced polycarbonate composite material and its preparation method. Background Technology

[0002] Polycarbonate (PC) is a thermoplastic engineering plastic with excellent overall performance. Due to its high impact strength, good transparency, heat resistance, and dimensional stability, it is widely used in electronics, automotive parts, and building materials. However, pure polycarbonate has limited flame retardant properties, a low limiting oxygen index, and is prone to melting and dripping during combustion, posing a certain fire hazard. To meet increasingly stringent flame retardant safety standards, flame retardant modification is usually required. Furthermore, to further improve its mechanical properties and heat distortion temperature, high-performance composite materials are often prepared by adding reinforcing materials such as glass fibers.

[0003] Currently, flame-retardant modification of polycarbonate composites mostly employs halogenated flame retardants, such as bromine-based flame retardant systems. While these systems offer good flame-retardant efficiency, they easily release toxic and corrosive gases during combustion, posing potential hazards to the environment and human health. Furthermore, traditional phosphorus-nitrogen flame-retardant systems, although possessing certain environmental advantages, tend to lead to a decline in the material's mechanical properties at high addition levels, and their flame-retardant efficiency is limited, making it difficult to simultaneously achieve high flame-retardant ratings and good overall performance at low addition levels. In existing technologies, problems such as poor compatibility between flame retardants and the matrix, uneven dispersion of glass fibers, and fiber breakage during processing also restrict further improvements in the performance of composite materials.

[0004] Based on this, the present invention designs a flame-retardant reinforced polycarbonate composite material and its preparation method to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a flame-retardant reinforced polycarbonate composite material and its preparation method, so as to solve the problems mentioned in the background art.

[0006] A flame-retardant reinforced polycarbonate composite material, comprising: 70%-85% polycarbonate resin, wherein the polycarbonate resin is an aromatic polycarbonate with a viscosity-average molecular weight in the range of 20,000-35,000, which serves as the continuous phase matrix of the composite material and provides basic mechanical strength, toughness and heat resistance. 10%-20% glass fiber, wherein the glass fiber is alkali-free short-cut E glass fiber, and its surface is treated with an aminosilane coupling agent to enhance the rigidity, strength and heat distortion temperature of the polycarbonate resin matrix, and to form a strong bond with the matrix through interface modification; A phosphorus-nitrogen-silicon composite flame retardant of 4.5%-15% is provided. The composite flame retardant is a synergistic system composed of phosphate ester compounds, nitrogen-based charring agents, and silicone polymers through physical premixing. The phosphate ester compounds play a gas-phase flame retardant and partly condensed-phase flame retardant role during combustion. The nitrogen-based charring agents expand and foam with the phosphate ester compounds at high temperatures to form a dense heat-insulating char layer. The silicone polymers migrate to the material surface to form a stable silicon ceramic-like protective layer. The three are compounded in a weight ratio of (1-3):(0.5-2):(0.2-1) to achieve high flame retardant efficiency and maintain good comprehensive performance of the matrix with low addition amount. The anti-dripping agent is 0.1%-0.5%, which is a core-shell polytetrafluoroethylene-coated acrylonitrile-styrene copolymer. This anti-dripping agent can form a network structure when the material is burning, effectively preventing molten dripping, and does not have a significant negative impact on the mechanical properties of the material. The sum of the weight percentages of the polycarbonate resin, glass fiber, phosphorus-nitrogen-silicon composite flame retardant, and anti-dripping agent is 100%.

[0007] Preferably, the phosphate ester compound is a halogen-free phosphate ester, selected from one or a mixture of two of bisphenol A-bis and resorcinol-bis. This type of phosphate ester has high thermal stability and low volatility, and can have good compatibility with polycarbonate matrix.

[0008] Preferably, the nitrogen-based char-forming agent is selected from melamine cyanurate or melamine polyphosphate, wherein melamine cyanurate has both heat absorption and cooling and char-forming functions, while melamine polyphosphate can further produce a PN synergistic effect with phosphate ester to enhance the char quality.

[0009] Preferably, the silicone polymer is a polydimethylsiloxane derivative with a number average molecular weight in the range of 3,000 to 10,000, and is a modified silicone containing reactive functional groups that can slightly react with the terminal hydroxyl or terminal carboxyl groups of polycarbonate at processing temperatures to improve its dispersibility and compatibility in the matrix.

[0010] Preferably, the modified silicone containing reactive functional groups is an epoxy-modified silicone or an amino-modified silicone. The epoxy-modified silicone can react with the end groups of polycarbonate, while the amino-modified silicone can interact with polycarbonate and also bind to the silanol groups on the surface of glass fiber, thus acting as a dual compatibilizer.

[0011] Preferably, the glass fiber is alkali-free chopped glass fiber with a single filament diameter of 9-13 micrometers and an initial length of 3-4.5 millimeters, and its surface is treated with an aminosilane or epoxysilane coupling agent to enhance its interfacial bonding with the polycarbonate resin matrix.

[0012] A method for preparing a flame-retardant reinforced polycarbonate composite material includes the following steps: S1. Premixing: Add the formulated amount of polycarbonate resin, phosphorus-nitrogen-silicon composite flame retardant and optional anti-dripping agent into a high-speed mixer and mix at a speed of 200-600 rpm for 3-10 minutes until all components are evenly dispersed to obtain a premix. S2. Melt blending and side feeding: The premixed material is continuously fed into a co-rotating twin-screw extruder through the main feeder. After the polycarbonate resin is completely melted, the formulated amount of glass fiber is precisely introduced into the melt through the side feeder located in the melting section. S3. Extrusion, Cooling and Granulation: The molten mixture containing glass fiber is homogenized in the subsequent mixing section of the extruder, extruded into strips through a die, cooled in a water tank, dried by a blower, and finally cut into uniform granules by a pelletizer to obtain the flame-retardant reinforced polycarbonate composite material.

[0013] Preferably, the screw configuration of the twin-screw extruder is optimized, with a length-to-diameter ratio of (36-48):1. The temperature of each heating zone of the twin-screw extruder from the feeding section to the die head is set to a gradient increase from 240°C to 280°C, and the screw speed is controlled at 200-400 rpm.

[0014] Preferably, the side feeder is located at 35% to 45% of the total screw length, calculated from the main feed port of the twin-screw extruder. This position ensures that the polycarbonate resin has been fully melted and plasticized, enabling it to immediately and effectively coat and impregnate the introduced glass fibers, while minimizing the phenomenon of excessive breakage of the glass fibers in a strong shear field due to premature addition.

[0015] Compared with the prior art, the advantages of this invention are: 1. This invention achieves high flame retardant efficiency (UL-94V-0 rating, LOI≥30%) with low addition amount by adopting a phosphorus-nitrogen-silicon composite flame retardant synergistic system, and is halogen-free and environmentally friendly, overcoming the environmental and health hazards of traditional bromine-based flame retardants.

[0016] 2. By optimizing the glass fiber surface treatment process and the side feeding process, this invention improves the interfacial bonding force between the fiber and the matrix, reduces fiber breakage during processing, and enables the composite material to maintain excellent flame retardant properties while possessing higher mechanical strength and thermal stability. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of a flame-retardant reinforced polycarbonate composite material and its preparation method proposed in this invention. Detailed Implementation

[0018] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example Before implementing the preparation method of the present invention, the main raw materials are pretreated as follows to ensure the stability of product quality: Drying of polycarbonate resin: It should be dried in a hot air circulating oven at 100–120°C for 4–6 hours to reduce its moisture content to below 0.02% to prevent hydrolytic degradation during melt processing.

[0020] Pretreatment of glass fiber: Alkali-free chopped E glass fiber with surface treated with aminosilane coupling agent. The treatment process is impregnation. After treatment, it is dried at 100-110℃ for 1-2 hours to ensure that the coupling agent is completely cured and effectively improve the interfacial bonding force with the resin matrix.

[0021] Pretreatment of flame retardants: It is recommended that phosphorus-nitrogen-silicon composite flame retardants be dried at 80°C for 2 hours to remove hygroscopic moisture, avoid agglomeration during the premixing process, and ensure uniform dispersion in the matrix.

[0022] Example 1 Material composition (based on total mass 100%): 80% polycarbonate resin (aromatic polycarbonate with a viscosity-average molecular weight of approximately 25,000); 15% glass fiber (alkali-free chopped E-glass fiber, monofilament diameter 10 μm, initial length 3 mm, surface treated with aminosilane coupling agent); 4.5% phosphorus-nitrogen-silicon composite flame retardant (composed of bisphenol A-bis(diphenyl phosphate), melamine cyanurate, and epoxy-modified silicone in a weight ratio of 2:1:0.5); 0.5% anti-dripping agent (core-shell structure polytetrafluoroethylene coated acrylonitrile-styrene copolymer).

[0023] Preparation method: Premixing: Add polycarbonate resin, phosphorus-nitrogen-silicon composite flame retardant and anti-dripping agent into a high-speed mixer and mix at 400 rpm for 5 minutes to obtain a premix.

[0024] Melt blending and side feeding: The premixed material is fed into a twin-screw extruder (L / D ratio 40:1) via the main feeder. The temperature gradient from the feed port to the die head is set to 240℃, 255℃, 265℃, 270℃, and 265℃, with a screw speed of 300 rpm. Glass fibers are introduced into the melt section (approximately 40% of the total screw length) via the side feeder.

[0025] Extrusion, cooling and granulation: The melt is extruded through a die, cooled in a water tank, dried by air, and then granulated to obtain composite material masterbatch.

[0026] Example 2 Material composition (based on total mass 100%): 75% polycarbonate resin; 18% glass fiber; 6.5% phosphorus-nitrogen-silicon composite flame retardant (composed of resorcinol-bis(diphenyl phosphate), melamine polyphosphate and amino-modified silicone in a weight ratio of 2.5:1.5:0.5); 0.5% anti-dripping agent.

[0027] Preparation method: Premixing: Add polycarbonate resin, phosphorus-nitrogen-silicon composite flame retardant and anti-dripping agent into a high-speed mixer and mix at 400 rpm for 5 minutes to obtain a premix.

[0028] Melt blending and side feeding: The premixed material is fed into a twin-screw extruder (L / D ratio 40:1) via the main feeder. The temperature gradient from the feed port to the die head is set to 245℃, 260℃, 270℃, 275℃, and 270℃, with a screw speed of 350 rpm. Glass fibers are introduced into the melt section (approximately 38% of the total screw length) via the side feeder.

[0029] Extrusion, cooling and granulation: The melt is extruded through a die, cooled in a water tank, dried by air, and then granulated to obtain composite material masterbatch.

[0030] Example 3 Material composition (based on total mass 100%): 85% polycarbonate resin; 10% glass fiber; 4.8% phosphorus-nitrogen-silicon composite flame retardant (composed of bisphenol A-bis(diphenyl phosphate), melamine cyanurate, and epoxy-modified silicone in a weight ratio of 2:1.2:0.6); 0.2% anti-dripping agent.

[0031] Preparation method: Premixing: Add polycarbonate resin, phosphorus-nitrogen-silicon composite flame retardant and anti-dripping agent into a high-speed mixer and mix at 400 rpm for 5 minutes to obtain a premix.

[0032] Melt blending and side feeding: The premixed material is fed into a twin-screw extruder (L / D ratio 40:1) via the main feeder. The temperature gradient from the feed port to the die head is set to 250℃, 265℃, 275℃, 280℃, and 275℃, with a screw speed of 280 rpm. Glass fibers are introduced into the melt section (approximately 40% of the total screw length) via the side feeder.

[0033] Extrusion, cooling and granulation: The melt is extruded through a die, cooled in a water tank, dried by air, and then granulated to obtain composite material masterbatch.

[0034] Comparative Example 1 (Traditional Brominated Flame Retardant System) Material composition (based on total mass, 100%): 80% polycarbonate resin; 15% glass fiber; 4.5% conventional brominated flame retardant (a mixture of decabromodiphenyl ether and antimony trioxide in a mass ratio of 3:1); 0.5% anti-dripping agent.

[0035] Preparation method: Premixing: Add polycarbonate resin, conventional brominated flame retardant and anti-dripping agent into a high-speed mixer and mix at 400 rpm for 5 minutes to obtain a premix.

[0036] Melt blending and side feeding: The premixed material is fed into a twin-screw extruder (L / D ratio 40:1) via the main feeder. The temperature gradient from the feed port to the die head is set to 240℃, 255℃, 265℃, 270℃, and 265℃, with a screw speed of 300 rpm. Glass fibers are introduced into the melt section (approximately 40% of the total screw length) via the side feeder.

[0037] Extrusion, cooling and granulation: The melt is extruded through a die, cooled in a water tank, dried by air, and then granulated to obtain composite material masterbatch.

[0038] Comparative Example 2 (Silicone-free synergistic effect) Material composition (based on total mass, 100%): 80% polycarbonate resin; 15% glass fiber; 4.5% phosphorus-nitrogen composite flame retardant (bisphenol A-bis(diphenyl phosphate) and melamine cyanurate are compounded in a weight ratio of 2:1); 0.5% anti-dripping agent.

[0039] Preparation method: Premixing: Add polycarbonate resin, phosphorus-nitrogen composite flame retardant and anti-dripping agent into a high-speed mixer and mix at 400 rpm for 5 minutes to obtain a premix.

[0040] Melt blending and side feeding: The premixed material is fed into a twin-screw extruder (L / D ratio 40:1) via the main feeder. The temperature gradient from the feed port to the die head is set to 240℃, 255℃, 265℃, 270℃, and 265℃, with a screw speed of 300 rpm. Glass fibers are introduced into the melt section (approximately 40% of the total screw length) via the side feeder.

[0041] Extrusion, cooling and granulation: The melt is extruded through a die, cooled in a water tank, dried by air, and then granulated to obtain composite material masterbatch.

[0042] I. Experimental Objective The flame retardant properties, mechanical properties, and thermal stability of the flame-retardant reinforced polycarbonate composite materials prepared in Examples 1-3 of this invention were comprehensively evaluated.

[0043] By comparing with Comparative Example 1 (traditional bromine-based flame retardant system) and Comparative Example 2 (silicone-free synergistic system), the synergistic effect of the phosphorus-nitrogen-silicon composite flame retardant system in this invention and its effect on improving the overall performance of the material are verified.

[0044] II. Experimental Samples Test group: Example 1, Example 2, Example 3 Control group: Comparative Example 1 (conventional brominated flame retardant), Comparative Example 2 (silicone-free synergistic effect) III. Experimental Methods and Standards 1. Limiting Oxygen Index Test Test standard: ASTM D2863 Testing equipment: Oxygen index meter Sample specifications: Length 80-150mm, width 6.5±0.5mm, thickness 3.0±0.5mm Test procedure: Fix the sample vertically in the combustion chamber and adjust the oxygen / nitrogen mixture flow rate to 4±1cm / s; ignite it from the top with an igniter, and use the lifting method to determine the minimum oxygen concentration required for the material to burn continuously for 3 minutes or for the burning length to reach 50mm, and record it as the LOI value.

[0045] 2. Vertical Burning Test (UL-94) Test standard: ASTM D3801 Testing equipment: Vertical combustion tester Sample specifications: Length 125±5mm, Width 13.0±0.5mm, Thickness 1.6mm Test procedure: Clamp the upper end of the sample and place degreased cotton at the lower end; apply Bunsen burner flame (blue flame height 20mm) twice, 10 seconds each time, and record the afterflame time t1, t2 and whether the degreased cotton is ignited; determine the UL-94 rating based on the total afterflame time and dripping condition.

[0046] 3. Tensile property test Test standard: ASTM D638 Testing equipment: Universal testing machine Sample specifications: Type I dumbbell-shaped specimen Test procedure: Stretch at a rate of 50 mm / min until fracture, record the stress-strain curve, and calculate the tensile strength, elongation at break, and tensile modulus.

[0047] 4. Bending performance test Test standard: ASTM D790 Testing equipment: Universal testing machine (three-point bending fixture) Sample specifications: Length 80mm, width 10.0±0.5mm, thickness 4.0±0.5mm Test procedure: Set the span to 16 times the thickness of the specimen, apply the strain at the corresponding strain rate, and calculate the bending strength and bending modulus.

[0048] 5. Cantilever beam impact strength test Test standard: ASTM D256 Testing equipment: Cantilever beam impact testing machine Sample specifications: length 63.5±2.0mm, width 12.7±0.2mm, thickness 3.2mm, with V-shaped notch. Test procedure: Release the pendulum to impact the specimen, read the absorbed energy, and calculate the impact strength (kJ / m). 2 ).

[0049] 6. Heat distortion temperature test Test standard: ASTM D648 Testing equipment: Heat distortion tester Sample specifications: Length 127mm, Width 13mm, Thickness 3.2mm Test procedure: Apply a bending stress of 1.82 MPa, increase the temperature at 2°C / min, and record the temperature at which the sample deflection reaches 0.25 mm, which is the HDT value.

[0050] 7. Thermogravimetric analysis Test standard: ASTM E1131 Testing equipment: Thermogravimetric analyzer Test procedure: Under nitrogen atmosphere, the temperature is increased from 30°C to 800°C at a rate of 10°C / min, the TGA curve is recorded, and the temperature at which the weight loss is 5% (Td5%) and the char residue at 700°C are analyzed.

[0051] IV. Experimental Results and Analysis The composite materials prepared in the above examples and comparative examples were subjected to performance tests, and the results are shown in the table below: ; Results analysis: Flame retardant performance: All examples achieved UL-94 V-0 rating and LOI values ​​were all above 30%, significantly better than Comparative Example 1 (bromine-based flame retardant) and Comparative Example 2 (silicone-free), indicating that the phosphorus-nitrogen-silicone composite flame retardant system has a highly efficient synergistic flame retardant effect, and the addition of silicone significantly improves char quality and flame retardant efficiency.

[0052] Mechanical properties: The tensile strength, flexural strength, and impact strength of the embodiment are all higher than those of the two comparative examples. This indicates that the flame-retardant system of the present invention has better compatibility with the matrix, less negative impact on the mechanical properties of the material, and better preservation of the reinforcing effect of glass fiber.

[0053] Thermal properties: The heat distortion temperature (HDT) and char residue at 700°C of the embodiment are higher than those of the comparative example, indicating that the composite material has better thermal stability and heat resistance, which is due to the stable protective layer formed by silicone in the condensed phase.

[0054] 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 reinforced polycarbonate composite material, characterized in that, include: 70%-85% polycarbonate resin, wherein the polycarbonate resin is an aromatic polycarbonate with a viscosity-average molecular weight in the range of 20,000-35,000. 10%-20% glass fiber, wherein the glass fiber is alkali-free chopped E glass fiber and its surface is treated with an aminosilane coupling agent; A phosphorus-nitrogen-silicon composite flame retardant of 4.5%-15% is provided. The composite flame retardant is a synergistic system composed of phosphate ester compounds, nitrogen-based charring agents, and silicone polymers through physical premixing. The phosphate ester compounds play a gas-phase flame retardant and partly condensed-phase flame retardant role during combustion. The nitrogen-based charring agents expand and foam with the phosphate ester compounds at high temperatures to form a dense heat-insulating char layer. The silicone polymers migrate to the material surface to form a stable silicon ceramic-like protective layer. The three are compounded in a weight ratio of (1-3):(0.5-2):(0.2-1). The anti-dripping agent is 0.1%-0.5%, wherein the anti-dripping agent is a core-shell polytetrafluoroethylene-coated acrylonitrile-styrene copolymer; The sum of the weight percentages of the polycarbonate resin, glass fiber, phosphorus-nitrogen-silicon composite flame retardant, and anti-dripping agent is 100%.

2. The flame-retardant reinforced polycarbonate composite material according to claim 1, characterized in that, The phosphate ester compound is a halogen-free phosphate ester, selected from one or a mixture of two of bisphenol A-bis and resorcinol-bis.

3. The flame-retardant reinforced polycarbonate composite material according to claim 1, characterized in that, The nitrogen-based char-forming agent is selected from melamine cyanurate or melamine polyphosphate. Melamine cyanurate has both heat absorption and cooling and char-forming functions, while melamine polyphosphate can further produce a PN synergistic effect with phosphate esters to enhance the quality of char formation.

4. The flame-retardant reinforced polycarbonate composite material according to claim 1, characterized in that, The silicone polymer is a polydimethylsiloxane derivative with a number average molecular weight in the range of 3,000 to 10,000, and is a modified silicone containing reactive functional groups.

5. The flame-retardant reinforced polycarbonate composite material according to claim 4, characterized in that, The modified silicone containing reactive functional groups is an epoxy-modified silicone or an amino-modified silicone.

6. The flame-retardant reinforced polycarbonate composite material according to claim 1, characterized in that, The glass fiber is an alkali-free chopped glass fiber with a single filament diameter of 9-13 micrometers and an initial length of 3-4.5 millimeters. Its surface is treated with an aminosilane or epoxysilane coupling agent.

7. A method for preparing a flame-retardant reinforced polycarbonate composite material, characterized in that, Includes the following steps: S1. Premixing: Add the formulated amount of polycarbonate resin, phosphorus-nitrogen-silicon composite flame retardant and optional anti-dripping agent into a high-speed mixer and mix at a speed of 200-600 rpm for 3-10 minutes until all components are evenly dispersed to obtain a premix. S2. Melt blending and side feeding: The premixed material is continuously fed into a co-rotating twin-screw extruder through the main feeder. After the polycarbonate resin is completely melted, the formulated amount of glass fiber is precisely introduced into the melt through the side feeder located in the melting section. S3. Extrusion, Cooling and Granulation: The molten mixture containing glass fiber is homogenized in the subsequent mixing section of the extruder, extruded into strips through a die, cooled in a water tank, dried by a blower, and finally cut into uniform granules by a pelletizer to obtain the flame-retardant reinforced polycarbonate composite material.

8. The method for preparing a flame-retardant reinforced polycarbonate composite material according to claim 7, characterized in that, The screw configuration of the twin-screw extruder has been optimized, with a length-to-diameter ratio of (36-48):

1. The temperature of each heating zone from the feeding section to the die head of the twin-screw extruder is set to a gradient increase from 240℃ to 280℃, and the screw speed is controlled at 200-400 rpm.

9. The method for preparing a flame-retardant reinforced polycarbonate composite material according to claim 7, characterized in that, The side feeder is located at 35% to 45% of the total screw length, calculated from the main feed port of the twin-screw extruder.

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