Preparation method of anhydride-containing modified polypropylene composite material and application thereof

Abstract

The application discloses a preparation method and application of anhydride-containing modified polypropylene composite material, relates to the technical field of polypropylene composite material preparation, and comprises the following steps: S1, preparation of anhydride grafting masterbatch; S2, pretreatment of reinforcing filler; and S3, preparation of the composite material by melt blending. The preparation method and application of the anhydride-containing modified polypropylene composite material introduce a bridged cyclic anhydride copolymerization monomer and maleic anhydride to form a double-anhydride grafting system in the preparation stage of the anhydride grafting masterbatch. The rigid bridged cyclic skeleton in the bridged cyclic anhydride molecule produces a significant steric hindrance effect in the melt grafting process, on the one hand, the continuous hydrogen abstraction attack of peroxide free radicals on adjacent carbon atoms on the polypropylene main chain is inhibited, the chain reaction rate of beta shear chain scission is reduced, the grafting reaction occurs more at chain ends or side chains rather than main chain fracture points, and therefore, the retention rate of the matrix molecular weight is increased by 15% to 30% compared with a single maleic anhydride system at the same grafting rate level.

Description

Technical Field

[0001] This invention relates to the field of polypropylene composite material preparation technology, specifically to a method for preparing anhydride-modified polypropylene composite material and its application. Background Technology

[0002] Polypropylene is one of the five major general-purpose plastics. Due to its advantages such as low density, good chemical corrosion resistance, easy processing and molding, and low cost, it is widely used in automotive parts, appliance casings, packaging materials, and building pipes. However, unmodified polypropylene also has several inherent defects: its tensile strength and flexural modulus are relatively low, which cannot meet the mechanical load-bearing requirements of engineering structural components; its low-temperature impact toughness is poor, and it is prone to brittle fracture in environments below zero degrees Celsius; the polypropylene molecular chain has a non-polar structure, resulting in weak interfacial bonding between polypropylene and polar fillers and polar matrix. When directly blended, the filler is unevenly dispersed and easily pulled out of the matrix under stress, which greatly reduces the reinforcing effect of the composite material.

[0003] To overcome the aforementioned problems, maleic anhydride-grafted polypropylene is widely used in industry as a compatibilizer or interfacial coupling agent. The principle is as follows: under melt processing conditions, a peroxide initiator generates free radical sites on the polypropylene backbone. Maleic anhydride monomers are then grafted onto the polypropylene molecular chain through free radical addition reactions, introducing polar anhydride groups. These anhydride groups can chemically react with active groups such as hydroxyl or amino groups on the filler surface or form strong hydrogen bonds, thereby constructing an effective interfacial bridging layer between the polypropylene matrix and the filler, improving stress transfer efficiency.

[0004] However, existing maleic anhydride-grafted polypropylene technologies still face several technical challenges in practical applications. First, the balance between grafting rate and matrix degradation is difficult to control precisely. While peroxide initiators initiate the grafting reaction, they also cause beta shearing of the polypropylene backbone, leading to a decrease in molecular weight, an abnormally high melt flow rate, and ultimately, a deterioration in the material's mechanical properties. Increasing the initiator dosage to improve the grafting rate is often counterproductive. Second, the functional groups in a single anhydride grafting system are limited. Relying solely on maleic anhydride groups for coupling certain special fillers is still insufficient, and there is a ceiling effect on interfacial layer strength improvement. Third, conventional melt grafting processes often use single-screw or twin-screw extruders to complete grafting and blending in a single operation. This results in a wide distribution of material residence time in the barrel, leading to over-grafting and degradation in some areas while under-grafting occurs in others, resulting in significant quality fluctuations within and between product batches.

[0005] Against the backdrop of the rapid development of the new energy vehicle industry, power battery modules place higher demands on the material properties of structural components. Components such as battery module end plates, side plates, and insulating separators not only require excellent mechanical strength and dimensional stability, but also must possess sufficient flame retardancy, resistance to electrolyte corrosion, and electrical insulation properties. Simultaneously, it is desirable to have the lowest possible material density to facilitate vehicle lightweighting and improve driving range. Traditional engineering plastics such as flame-retardant nylon, while possessing good overall performance, have high density and strong hygroscopicity, leading to significant changes in dimensional stability with environmental humidity. Polycarbonate lacks sufficient chemical corrosion resistance and is prone to stress cracking in electrolyte environments. Therefore, developing a modified polypropylene composite material that combines low density, high strength, high toughness, flame retardancy, and chemical corrosion resistance has significant engineering application value for lightweight manufacturing of new energy vehicles. To this end, we propose a method for preparing anhydride-modified polypropylene composite materials and their applications. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing anhydride-modified polypropylene composite materials and their applications, thus solving the problems mentioned in the background section.

[0007] To achieve the above objectives, the present invention provides a method for preparing an anhydride-modified polypropylene composite material and its application, comprising the following steps: S1. Preparation of anhydride grafted masterbatch: 100 parts by weight of polypropylene resin, 1.5-4.0 parts by weight of maleic anhydride, 0.8-2.5 parts by weight of bridged anhydride comonomer, 0.3-1.0 parts by weight of peroxide initiator, 0.2-0.8 parts by weight of anti-degradation agent and 0.5-2.0 parts by weight of lubricating dispersant are mixed in a high-speed mixer to obtain a premix; the premix is ​​fed into a twin-screw extruder for melt grafting reaction, and the extrudate is water-cooled and pelletized to obtain anhydride grafted masterbatch; S2. Pretreatment of reinforcing filler: 100 parts by weight of inorganic reinforcing filler and 1.5-3.5 parts by weight of aminosilane coupling agent are mixed in a high-speed mixer. During the mixing process, the material temperature is maintained at 70℃-95℃ by jacket heating, so that the aminosilane coupling agent can be fully spread on the surface of the filler and undergo a pre-condensation reaction to obtain surface amination pretreated reinforcing filler. S3. Melt blending to prepare composite materials: 30-55 parts by weight of the anhydride grafted masterbatch obtained in step S1, 45-70 parts by weight of polypropylene resin, 15-35 parts by weight of the surface-aminated pretreated reinforcing filler obtained in step S2, 5-15 parts by weight of the toughening elastomer, 8-18 parts by weight of the flame retardant and 0.3-1.5 parts by weight of the processing aid are fed into a twin-screw extruder for melt blending and extrusion granulation.

[0008] Furthermore, the bridged anhydride comonomer is any one or a combination of methylmethylenetetrahydrophthalic anhydride or methylmethylenetetrahydrophthalic anhydride.

[0009] Furthermore, the peroxide initiator is either 2,5-dimethyl-2,5-dihexane or dicumyl peroxide.

[0010] Furthermore, the anti-degradation aid is a mixture of dilauryl thiodipropionate and triphosphite in a mass ratio of 1:0.5 to 1:1.5.

[0011] Furthermore, the inorganic reinforcing filler is any one or a mixture of at least two of talc powder, wollastonite powder, or mica powder with an average particle size of 1-8 μm; the aminosilane coupling agent is any one of N-3-aminopropyltrimethoxysilane or 3-aminopropyltriethoxysilane.

[0012] Furthermore, the toughening elastomer is any one or a combination of ethylene-octene copolymer or styrene-ethylene-butadiene-styrene block copolymer.

[0013] Furthermore, the flame retardant is a phosphorus-nitrogen intumescent flame retardant formulated by compounding ammonium polyphosphate and melamine cyanuric acid in a mass ratio of 1.5:1 to 3:1.

[0014] Furthermore, before the reinforcing filler with surface amination pretreatment in step S2 is added to step S3, its surface primary amino content is 0.15-0.60 mmol / g. During the melt blending process in step S3, the surface primary amino groups undergo an in-situ ring-opening amidation reaction with the anhydride groups in the anhydride graft masterbatch obtained in step S1 to generate amide bonds or imide bonds, forming a chemically bonded interfacial bridging layer in the interfacial region between the polypropylene matrix and the reinforcing filler.

[0015] An application of a method for preparing an anhydride-modified polypropylene composite material, wherein the structural component is any one of a battery module end plate, a battery module side plate, a battery module insulating partition, or a battery module busbar support.

[0016] Furthermore, the anhydride-modified polypropylene composite material has a density of 0.98-1.08 g / cm³, a tensile strength of 45-60 MPa, a flexural modulus of 2500-3800 MPa, a notched impact strength of 8-15 kJ / m² at 23°C, a flame retardancy rating of UL94 V-0, and an electrical insulation strength higher than 18 kV / mm at a thickness of 1.5 mm.

[0017] This invention provides a method for preparing an anhydride-modified polypropylene composite material and its application, which has the following beneficial effects: the method for preparing anhydride-modified polypropylene composite material and its application; I. This invention introduces a dual-anhydride grafting system composed of a bridged-ring anhydride comonomer and maleic anhydride during the preparation stage of the anhydride grafting masterbatch. The rigid bridged-ring skeleton in the bridged-ring anhydride molecule generates a significant steric hindrance effect during melt grafting. On the one hand, it inhibits the continuous hydrogen-depleting attack of peroxide free radicals on adjacent carbon atoms on the polypropylene main chain, reduces the chain reaction rate of beta shear chain breaking, and causes the grafting reaction to occur more at the chain ends or side chains rather than at the main chain breakage point. As a result, the retention rate of the matrix molecular weight is increased by 15% to 30% compared with the single maleic anhydride system at the same grafting rate level. On the other hand, after the cyclic structure of the bridged-ring anhydride is grafted onto the polypropylene molecular chain, its steric hindrance causes the anhydride groups to be distributed in a more extended posture at the filler-matrix interface, increasing the contact probability and reactivity with the amino groups on the filler surface, and increasing the density of effective chemical bonding sites at the interface by about 20% to 40%.

[0018] II. This invention employs a two-step process: The first step involves a high-grafting-rate masterbatch prepared by specifically performing an anhydride grafting reaction under high-temperature, high-shear conditions. The second step involves blending the grafted masterbatch with virgin polypropylene, pretreated fillers, and other additives under relatively mild conditions. This two-step separation design ensures that the harsh conditions of the grafting reaction are applied only to the grafted masterbatch, while the virgin polypropylene and toughening elastomer, which constitute the majority of the formulation, remain completely isolated from the peroxide initiator. This avoids the molecular weight loss caused by the initiator to the entire matrix resin in a full-volume, one-time blending process. The resulting composite material achieves excellent interfacial bonding strength while maintaining good overall melt flow rate and impact toughness, overcoming the contradiction between increased grafting rate and deteriorated overall performance in traditional one-step processes.

[0019] III. This invention employs an aminosilane coupling agent instead of conventional epoxy or vinylsilane coupling agents in the pretreatment of the reinforced filler surface. After the aminosilane spreads and condenses on the filler surface, the filler surface is covered with a layer of organic molecular brushes containing primary amino groups. When the pretreated filler encounters the anhydride grafted masterbatch during the melt blending stage, the primary amino groups on the filler surface undergo an in-situ ring-opening amidation reaction with the anhydride groups in the grafted masterbatch, first generating an amic acid intermediate, which then further closes the ring in the high-temperature section of the extruder to form stable imide bonds. The bond energy of this chemical bond is much higher than that of physical adsorption or hydrogen bonding, ensuring that the filler-matrix interface transition layer does not preferentially debond and fail under stress, but effectively transfers the stress to the filler particles, fully leveraging the reinforcing effect of the filler. This in-situ chemical reaction occurs during the melt blending process, requiring no additional catalysts or post-treatment steps, making the process simple and controllable.

[0020] IV. This invention utilizes dilauryl thiodipropionate and triphosphite as synergistic anti-degradation agents. The former interrupts chain-linked oxidative degradation reactions by decomposing peroxide free radicals, while the latter prevents the initiation of new free radicals by decomposing hydroperoxides. The two work synergistically in the high-temperature, high-shear environment of the grafting reaction, further inhibiting unnecessary degradation of the polypropylene backbone and tilting the grafting reaction selectivity towards a direction favorable to grafting rather than chain breaking. This combination of anti-degradation agents, along with the steric hindrance protection effect of the bridged-ring anhydride comonomer, provides dual protection, significantly improving the quality and batch-to-batch consistency of the anhydride grafted masterbatch.

[0021] V. The anhydride-modified polypropylene composite material prepared by this invention exhibits comprehensive performance advantages in the application of power battery module structural components for new energy vehicles: its density is only 0.98~1.08g / cm³, which is about 25%~30% lighter than flame-retardant nylon, which is beneficial to the overall lightweighting of the battery pack; its tensile strength reaches 45~60MPa, its flexural modulus reaches 2500~3800MPa, and its notched impact strength of simply supported beam reaches 8~15kJ / m², which meets the mechanical load-bearing and impact resistance requirements of battery module structural components. Detailed Implementation

[0022] A method for preparing an anhydride-modified polypropylene composite material and its application, comprising the following steps: Example 1: Preparation of anhydride grafted masterbatch in step S1: Weigh 100 parts by weight of homopolymer polypropylene resin, 2.5 parts by weight of maleic anhydride, 1.2 parts by weight of methylenetetrahydrophthalic anhydride, 0.5 parts by weight of 2,5-dimethyl-2,5-dihexane, 0.3 parts by weight of dilauryl thiodipropionate, 0.3 parts by weight of triphosphite, and 0.8 parts by weight of calcium stearate. Premix the above components in a high-speed mixer at 1200 rpm for 5 minutes to obtain a powdered premix.

[0023] The premixed material was fed into the main feed port of a co-rotating twin-screw extruder via a loss-in-weight metering feeder. The temperatures of each section of the extruder from the feeding section to the die head were sequentially set to 160℃, 180℃, 195℃, 200℃, 200℃, 195℃, 195℃, 190℃, 185℃, and 185℃, with the screw speed set to 260 rpm. The average residence time of the material in the barrel was controlled to approximately 60 seconds by adjusting the feeding rate. A vacuum pump with a pressure of -0.08 MPa was connected to the extruder's vacuum exhaust port to remove unreacted monomers and volatile small molecules. After cooling in a water bath, the extrudate was pelletized into cylindrical particles approximately 2.5 mm in diameter and 3 mm in length, yielding anhydride grafted masterbatch. The anhydride grafting rate of the masterbatch was determined to be 1.35 wt% by acid-base titration; the melt flow index (MFR) of the masterbatch was 28 g / 10 min.

[0024] Step S2: Pretreatment of the reinforcing filler: 100 parts by weight of talc powder with an average particle size of 3.5 μm were weighed and added to a high-speed mixer. Under stirring, 2.2 parts by weight of N-3-aminopropyltrimethoxysilane were evenly sprayed through an atomizing nozzle. The mixer speed was 800 rpm, and hot water was circulated through the jacket to maintain the mixing temperature at 80℃±5℃. Mixing was continued for 15 minutes. After mixing, the material was discharged and dried in a 110℃ forced-air oven for 30 minutes to obtain talc powder with surface amination pretreatment. The primary amine content on the surface of the treated talc powder was determined to be 0.38 mmol / g by ninhydrin colorimetry.

[0025] Step S3: Melt blending to prepare the composite material: Weigh 40 parts by weight of the anhydride grafted masterbatch obtained in step S1, 60 parts by weight of homopolymer polypropylene resin, 25 parts by weight of the surface-aminated pretreated talc obtained in step S2, 10 parts by weight of the ethylene-octene copolymer toughened elastomer, 12 parts by weight of the intumescent flame retardant premixed with ammonium polyphosphate and melamine cyanuric acid at a mass ratio of 2:1, and 0.5 parts by weight of the processing aid compounded with antioxidant 1010 and antioxidant 168 at a mass ratio of 1:1. Add all the above components to a high-speed mixer and mix at 800 rpm for 5 minutes, then feed the mixture into the main feed port of a twin-screw extruder. The temperatures of each section of the extruder are 165℃, 185℃, 200℃, 205℃, 205℃, 200℃, 200℃, 195℃, 195℃, and 190℃, respectively, with a screw speed of 280 rpm. The extrudate was water-cooled, granulated, and dried at 90°C for 2 hours to obtain an anhydride-modified polypropylene composite material.

[0026] Example 2: The difference between this example and Example 1 is as follows: In step S1, the amount of maleic anhydride was adjusted to 3.5 parts by weight, the bridged anhydride comonomer was adjusted to 1.8 parts by weight of methylindimethylenetetrahydrophthalic anhydride, the peroxide initiator was adjusted to 0.6 parts by weight of dicumyl peroxide, the screw speed was adjusted to 300 rpm, and the residence time was controlled at approximately 50 seconds. The resulting anhydride grafting rate of the anhydride grafted masterbatch was 1.62 wt%, and the MFR was 35 g / 10 min. In step S2, the filler was replaced with wollastonite powder with an average particle size of 5 μm, and the aminosilane coupling agent was replaced with 2.8 parts by weight of 3-aminopropyltriethoxysilane. After treatment, the primary amino content on the filler surface was 0.28 mmol / g. In step S3, the amount of anhydride grafted masterbatch was adjusted to 35 parts by weight, the amount of polypropylene resin was adjusted to 65 parts by weight, the toughening elastomer was replaced with 8 parts by weight of SEBS, and the ratio of ammonium polyphosphate to melamine cyanuric acid in the flame retardant was adjusted to 2.5:1. The rest was the same as in Example 1.

[0027] Example 3: The difference between this example and Example 1 is as follows: In step S1, the bridged anhydride comonomer was adjusted to 2.0 parts by weight of a mixture of methylindolemethyltetrahydrophthalic anhydride and methylindolemethyltetrahydrophthalic anhydride in a 1:1 mass ratio, and the anti-degradation agent was adjusted to 0.25 parts by weight of dilauryl thiodipropionate and 0.35 parts by weight of triphosphite. The resulting anhydride grafting masterbatch had an anhydride grafting rate of 1.48 wt% and an MFR of 30 g / 10 min. In step S2, the filler was replaced with mica powder with an average particle size of 2 μm, the amount of aminosilane coupling agent was adjusted to 1.8 parts by weight, the mixing temperature was maintained at 90℃±5℃, and the primary amino content on the filler surface after treatment was 0.52 mmol / g. In step S3, the amount of anhydride grafting masterbatch was adjusted to 50 parts by weight, the amount of polypropylene resin was adjusted to 50 parts by weight, the amount of reinforcing filler was adjusted to 30 parts by weight, and the amount of flame retardant was adjusted to 15 parts by weight. The rest is the same as in Example 1.

[0028] Performance testing The composite material granules obtained in each embodiment were injection molded into standard test strips on an injection molding machine, and the performance was tested according to the following standards: tensile strength according to GB / T 1040.2 standard, flexural modulus according to GB / T 9341 standard, notched impact strength of simply supported beam according to GB / T 1043.1 standard, density according to GB / T 1033.1 standard, flame retardancy according to UL94 vertical burning test, electrical insulation strength according to GB / T 1408.1 standard, and electrolyte resistance according to GB / T 11547 standard.

[0029] The properties of the composite material obtained in Example 1 are as follows: density 1.02 g / cm³, tensile strength 52 MPa, flexural modulus 3200 MPa, notched impact strength of simply supported beam 12 kJ / m², flame retardant rating UL94 V-0, electrical insulation strength 21 kV / mm, and tensile strength retention rate of 93% after immersion in electrolyte.

[0030] The properties of the composite material obtained in Example 2 are as follows: density 1.05 g / cm³, tensile strength 55 MPa, flexural modulus 3500 MPa, notched impact strength of simply supported beam 10 kJ / m², flame retardant rating UL94 V-0, electrical insulation strength 20 kV / mm, and tensile strength retention rate of 91% after immersion in electrolyte.

[0031] The properties of the composite material obtained in Example 3 are as follows: density 1.08 g / cm³, tensile strength 48 MPa, flexural modulus 3800 MPa, notched impact strength of simply supported beam 9 kJ / m², flame retardant rating UL94 V-0, electrical insulation strength 22 kV / mm, and tensile strength retention rate of 94% after immersion in electrolyte.

[0032] The above embodiments demonstrate that the anhydride-modified polypropylene composite material prepared by the present invention achieves a good balance of mechanical strength, impact toughness, flame retardancy, and electrolyte corrosion resistance while maintaining the low density advantage of polypropylene. Its comprehensive performance meets the requirements for use in structural components of power battery modules for new energy vehicles.

Claims

1. A method for preparing an anhydride-modified polypropylene composite material, characterized in that, Includes the following steps: S1. Preparation of anhydride grafted masterbatch: 100 parts by weight of polypropylene resin, 1.5-4.0 parts by weight of maleic anhydride, 0.8-2.5 parts by weight of bridged anhydride comonomer, 0.3-1.0 parts by weight of peroxide initiator, 0.2-0.8 parts by weight of anti-degradation agent and 0.5-2.0 parts by weight of lubricating dispersant are mixed in a high-speed mixer to obtain a premix; the premix is ​​fed into a twin-screw extruder for melt grafting reaction, and the extrudate is water-cooled and pelletized to obtain anhydride grafted masterbatch; S2. Pretreatment of reinforcing filler: 100 parts by weight of inorganic reinforcing filler and 1.5-3.5 parts by weight of aminosilane coupling agent are mixed in a high-speed mixer. During the mixing process, the material temperature is maintained at 70℃-95℃ by jacket heating, so that the aminosilane coupling agent can be fully spread on the surface of the filler and undergo a pre-condensation reaction to obtain surface amination pretreated reinforcing filler. S3. Melt blending to prepare composite materials: 30-55 parts by weight of the anhydride grafted masterbatch obtained in step S1, 45-70 parts by weight of polypropylene resin, 15-35 parts by weight of the surface-aminated pretreated reinforcing filler obtained in step S2, 5-15 parts by weight of the toughening elastomer, 8-18 parts by weight of the flame retardant and 0.3-1.5 parts by weight of the processing aid are fed into a twin-screw extruder for melt blending and extrusion granulation.

2. The method for preparing an anhydride-modified polypropylene composite material according to claim 1, characterized in that, The bridged anhydride comonomer is any one or a combination of methylmethylenetetrahydrophthalic anhydride or methylmethylenetetrahydrophthalic anhydride.

3. The method for preparing an anhydride-modified polypropylene composite material according to claim 1, characterized in that, The peroxide initiator is any one of 2,5-dimethyl-2,5-dihexane or dicumyl peroxide.

4. The method for preparing an anhydride-modified polypropylene composite material according to claim 1, characterized in that, The anti-degradation aid is a mixture of dilauryl thiodipropionate and triphosphite in a mass ratio of 1:0.5 to 1:1.

5.

5. The method for preparing an anhydride-modified polypropylene composite material according to claim 1, characterized in that, The inorganic reinforcing filler is any one or a mixture of at least two of talc powder, wollastonite powder or mica powder with an average particle size of 1-8 μm; the aminosilane coupling agent is any one of N-3-aminopropyltrimethoxysilane or 3-aminopropyltriethoxysilane.

6. The method for preparing an anhydride-modified polypropylene composite material according to claim 1, characterized in that, The toughening elastomer is any one of ethylene-octene copolymer or styrene-ethylene-butadiene-styrene block copolymer, or a combination of both.

7. The method for preparing an anhydride-modified polypropylene composite material according to claim 1, characterized in that, The flame retardant is a phosphorus-nitrogen intumescent flame retardant formulated by compounding ammonium polyphosphate and melamine cyanuric acid in a mass ratio of 1.5:1 to 3:

1.

8. The method for preparing an anhydride-modified polypropylene composite material according to claim 1, characterized in that, Before being added to step S3, the surface-aminated pretreated reinforcing filler in step S2 has a surface primary amino content of 0.15-0.60 mmol / g. During the melt blending process in step S3, the surface primary amino groups undergo an in-situ ring-opening amidation reaction with the anhydride groups in the anhydride graft masterbatch obtained in step S1 to generate amide bonds or imide bonds, forming a chemically bonded interfacial bridging layer in the interfacial region between the polypropylene matrix and the reinforcing filler.

9. The application of the method for preparing an anhydride-modified polypropylene composite material according to any one of claims 1-8, characterized in that, The structural component is any one of the following: battery module end plate, battery module side plate, battery module insulating partition, or battery module busbar bracket.

10. The application according to claim 9, characterized in that, The anhydride-modified polypropylene composite material has a density of 0.98-1.08 g / cm³, a tensile strength of 45-60 MPa, a flexural modulus of 2500-3800 MPa, a notched impact strength of 8-15 kJ / m² at 23°C, a flame retardancy rating of UL94 V-0, and an electrical insulation strength higher than 18 kV / mm at a thickness of 1.5 mm.