Polypropylene composition, process for its preparation and injection-moulded foamed shaped body

Abstract

The present application relates to the technical field of high polymer materials, and provides a polypropylene composition, a preparation method thereof and an injection-molded foaming forming body.The polypropylene composition comprises modified polypropylene, acrylonitrile copolymer, plant fiber powder, nylon resin, a compatilizer and graphene, wherein the graphene has a micron-level flake diameter and an average length-height ratio of 100-5000.In the polypropylene composition, large-flake graphene is added to replace inorganic fillers, so that the mechanical properties of the base resin can be effectively improved at a low addition amount, the addition amount of fillers can be greatly reduced compared with conventional formulations, and the influence of the fillers on the cell structure is reduced; meanwhile, during the foaming process, the large-flake graphene can also function as a cell nucleating agent, so that more compact and uniform cells are induced to be generated, and the foaming performance of the polypropylene composition is improved.The polypropylene composition provided by the present application has very ideal injection-molded foaming performance, and can be widely applied to various existing injection-molded foaming processes.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and more specifically, to a polypropylene composition, its preparation method, and an injection-molded foamed product. Background Technology

[0002] As is well known, polypropylene foaming currently involves four main processes: autoclaving, compression molding, extrusion, and injection molding. Autoclaving, compression molding, and extrusion molding produce foamed materials with a thin-skinned, continuous honeycomb cell structure. Common products have a foaming ratio between 5 and 60 times. Autoclaved injection molded bodies, compression molded sheets, and extruded sheets all require secondary processing to obtain the final parts. Injection molding, on the other hand, has a unique "sandwich" core-skin structure. It has a relatively thick and dense skin layer, and the cell structure consists of discontinuously distributed "island-like cells." Currently, the common weight reduction ratio is between 3% and 10%, and parts can be formed in a single step. Because injection molded foam products have better mechanical properties, they can be used in some structural load-bearing components, hence the name "structural foaming."

[0003] Injection molding foaming technology creates a unique "sandwich" core-skin structure, resulting in excellent appearance quality, easy painting and coloring, and minimal loss of mechanical properties. The presence of uniform micropores not only reduces weight but also helps eliminate internal stress, thereby significantly reducing shrinkage and warpage of the parts and greatly improving dimensional accuracy. Furthermore, the presence of gas within the melt during injection molding eliminates the need for holding pressure during molding, effectively shortening the production cycle, increasing production efficiency, and reducing clamping force.

[0004] The current trend in the development of special materials for injection molding foam is to improve the weight reduction ratio of the product while maintaining or even enhancing its advantages in impact resistance, warpage resistance, and shrinkage resistance. Besides optimizing the injection molding foaming process, finding a special polypropylene material for injection molding foam that simultaneously possesses these advantages would be an even more ideal solution.

[0005] Polypropylene wood-plastic composites typically exhibit excellent impact toughness, good dimensional stability, and no warping. Chinese patent CN1105602098B discloses a modified polypropylene composite material and its preparation method. This method uses polypropylene, single-layer flake talc, long-fiber wollastonite, silane coupling agent, aluminate, and stearic acid to prepare a modified polypropylene composite material. The modified long-fiber wollastonite and flake talc enhance the tensile and flexural properties of the composite material. Chinese patent CN103937278B discloses a method for preparing polypropylene wood-plastic materials. Modified plant fibers are blended with fiber-grade polypropylene and extruded to form a fiber composite material. The wood-plastic material prepared by this method achieves a room-temperature impact strength of 3.66 KJ / m², showing some improvement in impact performance, but there is still room for further improvement. Chinese patent CN106380651B discloses a high-toughness wood-plastic composite material, whose components include polylactic acid, polyolefin, plant fiber powder, sodium tripolyphosphate, dipropylene glycol methyl ether acetate, and specific synthetic agents and starch synthetic agents. The method provided by this patent involves a multi-step process to prepare a synthetic agent, modify and crush plant fibers, and then blend and extrude them with polyolefins and processing aids to obtain a high-toughness polypropylene wood-plastic composite material. However, the process is complex and involves many types of additives. Chinese patent CN102276920A discloses a polypropylene composite material that modifies polypropylene using glass fiber, toughening agent, coupling agent, antioxidant, etc., resulting in a composite material with high mechanical strength and good creep resistance. Although the wood-plastic composite materials prepared by the above methods can have good application effects, they still suffer from poor compatibility between the matrix resin and fillers, and the addition of plant fibers significantly affects the formation of cells in injection-molded foamed products, failing to meet the requirements of injection molding foaming. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention proposes a polypropylene composition, a method for preparing the same, and an injection-molded foamed polypropylene composition.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention provides a polypropylene composition comprising modified polypropylene, acrylonitrile copolymer, plant fiber powder, nylon resin, compatibilizer and graphene, wherein the graphene has a micron-sized sheet diameter and an average length-to-height ratio of 100-5000.

[0009] In this invention, the "length-to-height ratio" refers to the ratio of the long side (diameter) of the graphene to its thickness.

[0010] As a preferred embodiment of the polypropylene composition provided by the present invention, the polypropylene composition comprises 100 parts by weight of the modified polypropylene, 1-20 parts by weight of the acrylonitrile copolymer, 2-80 parts by weight of the plant fiber powder, 10-100 parts by weight of the nylon resin, 1-12 parts by weight of the compatibilizer, 0.01-5.0 parts by weight of the graphene, and 0-10 parts by weight of the antioxidant.

[0011] More preferably, based on 100 parts by weight of the modified polypropylene, the acrylonitrile copolymer is 1-10 parts by weight, the plant fiber powder is 2-50 parts by weight, the nylon resin is 20-70 parts by weight, the compatibilizer is 3-10 parts by weight, the graphene is 0.01-1.0 parts by weight, and the antioxidant content is 0.1-1.0 parts by weight.

[0012] More preferably, based on 100 parts by weight of the modified polypropylene, the acrylonitrile copolymer is 3-8 parts by weight, the plant fiber powder is 5-40 parts by weight, the nylon resin is 30-60 parts by weight, and the graphene content is 0.05-0.5 parts.

[0013] As another preferred embodiment of the polypropylene composition provided by the present invention, the graphene sheet has a diameter of 1-20 micrometers and an average length-to-height ratio of 300-2500.

[0014] As another preferred embodiment of the polypropylene composition provided by the present invention, the graphene has carboxyl-modified groups.

[0015] More preferably, the graphene has an oxygen content of 0.5wt%-20wt%, preferably 3wt%-10wt%; and a hydrogen content of 0.01wt%-1wt%, preferably 0.05wt%-0.5wt%.

[0016] As another preferred embodiment of the polypropylene composition provided by the present invention, the graphene has an electrical conductivity of 500-1000 S / m.

[0017] As another preferred embodiment of the polypropylene composition provided by the present invention, the modified polypropylene is polypropylene grafted with polar monomers. More preferably, the grafting rate is 0.5 wt%-10 wt%. More preferably, the grafting rate is 0.8 wt%-6 wt%.

[0018] More preferably, the polypropylene is homopolymer polypropylene or copolymer polypropylene.

[0019] More preferably, the polypropylene is an ethylene / propylene copolymer.

[0020] More preferably, the ethylene content in the ethylene / propylene copolymer is 0-8 wt%.

[0021] More preferably, the polar monomer includes at least one of polar monomers containing amino, hydroxyl, carboxyl, acid anhydride and / or epoxy groups.

[0022] More preferably, the polar monomer is selected from at least one of glycidyl methacrylate, maleic anhydride, acrylic acid, methacrylic acid, ethyl methacrylate and methyl acrylate.

[0023] More preferably, the polar monomer includes a polar monomer containing an epoxy group and / or an anhydride.

[0024] More preferably, the polar monomer is glycidyl methacrylate.

[0025] As another preferred embodiment of the polypropylene composition provided by the present invention, the modified polypropylene has a melt index greater than 5 g / 10 min at 230°C and 2.16 kg.

[0026] More preferably, the modified polypropylene has a melt index greater than 20 g / 10 min at 230°C and 2.16 kg.

[0027] As another preferred embodiment of the polypropylene composition provided by the present invention, the acrylonitrile copolymer is at least one of the acrylonitrile copolymers obtained by copolymerizing acrylonitrile with monomers selected from C2-C20 olefins and / or C2-C20 unsaturated esters.

[0028] More preferably, the acrylonitrile copolymer is selected from at least one of styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-methyl acrylate copolymer, methyl methacrylate-acrylonitrile copolymer, and vinyl acetate-acrylonitrile copolymer.

[0029] As another preferred embodiment of the polypropylene composition provided by the present invention, the particle size of the plant fiber powder is 600-3000 mesh.

[0030] As another preferred embodiment of the polypropylene composition provided by the present invention, the plant fiber powder is selected from at least one of poplar powder, pine powder, rice husk powder, coconut shell powder, walnut shell powder and bamboo powder.

[0031] As another preferred embodiment of the polypropylene composition provided by the present invention, the nylon resin is selected from at least one of nylon 6, nylon 12 and nylon 66.

[0032] More preferably, the nylon resin is nylon 6.

[0033] As another preferred embodiment of the polypropylene composition provided by the present invention, the compatibilizer is selected from at least one of oxazoline compatibilizers, acrylic compatibilizers, maleic anhydride compatibilizers, and isonitrile ester compatibilizers.

[0034] As another preferred embodiment of the polypropylene composition provided by the present invention, the antioxidant includes phenolic antioxidants and / or phosphite antioxidants.

[0035] More preferably, the antioxidant is selected from at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1076), 2,2'-methylenebis-(4-methyl-6-tert-butylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, tris(2,4-di-tert-butylphenyl) phosphite, pentaerythritol diphosphite (antioxidant 626), and bis(2,6-di-tert-butyl-4-tolyl) pentaerythritol diphosphite.

[0036] In a second aspect, the present invention provides a method for preparing the above-mentioned polypropylene composition, comprising: mixing the components according to the formula, then melt-extruding, cooling and drawing into fibers, and pelletizing.

[0037] As a preferred embodiment of the preparation method of the polypropylene composition provided by the present invention, the mixing stirring speed is 500-2000 rpm and the stirring time is 1-3 minutes.

[0038] As another preferred embodiment of the preparation method of the polypropylene composition provided by the present invention, the melt extrusion temperature is 180-250°C.

[0039] Further preferably, the melt extrusion employs a multi-stage heating process.

[0040] A further preferred multi-stage heating process includes: stage 190-230℃, stage 210-245℃, stage 310-260℃, stage 400-245℃, and stage 500-245℃.

[0041] Thirdly, the present invention provides an injection-molded foamed polypropylene composition, which is obtained from the polypropylene composition described above or the polypropylene composition prepared by the preparation method described above.

[0042] The beneficial effects of this invention are at least as follows:

[0043] This invention adds large-area, thin-film graphene to a polypropylene composition to replace commonly used inorganic fillers. This effectively improves the mechanical properties of the matrix resin even with low addition levels. Compared to conventional formulations, it significantly reduces the amount of filler needed, minimizing the impact of filler on the cell structure. Simultaneously, during foaming, the large-film graphene acts as a cell nucleating agent, inducing the formation of denser and more uniform cells, thus improving the foaming performance of the polypropylene composition. This invention also uses polar monomer-grafted modified polypropylene blended with nylon to improve the compatibility between the matrix resins. This significantly improves the impact resistance of the polypropylene composition at room temperature without negatively impacting foaming performance. Furthermore, the modified polypropylene facilitates the dispersion and reinforcement of fillers within the matrix resin. The uniformly distributed wood flour, large-film graphene, and micropores effectively reduce stress concentration within the material, resulting in injection-molded foams with excellent rigidity, toughness, and warpage resistance. The polypropylene composition provided by this invention has ideal injection molding foaming properties and can be widely used in various existing injection molding foaming processes. Moreover, depending on the needs of downstream applications, different process methods and different types of foaming agents can be used to prepare polypropylene composition injection-molded foamed articles with different foaming ratios, cell structures and mechanical properties. Attached Figure Description

[0044] Figure 1 This is a cross-sectional cell morphology diagram of the polypropylene composition injection-molded foam of Example 1 of the present invention.

[0045] Figure 2 This is a cross-sectional cell morphology diagram of the injection-molded foam of the polypropylene composition of Comparative Example 1 of the present invention.

[0046] Figure 3 This is a cross-sectional cell morphology diagram of the injection-molded foam of the polypropylene composition of Comparative Example 4 of the present invention. Detailed Implementation

[0047] To make the technical problem to be solved, the technical solution, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely for illustrating this patent and do not limit the scope of protection of this invention in any way.

[0048] The polypropylene composition proposed in this invention comprises modified polypropylene, acrylonitrile copolymer, plant fiber powder, nylon resin, compatibilizer and graphene, wherein the graphene has a micron-sized sheet diameter and an aspect ratio of 100-3000.

[0049] The addition of acrylonitrile copolymer to the polypropylene composition provided by this invention not only provides toughening, but also allows acrylonitrile to generate oxazoline during melt processing, which interacts with the active groups on nylon resin and modified polypropylene. This, along with the compatibilizer, promotes the bonding between multiple components such as nylon resin, modified polypropylene, and plant fiber powder, giving the material excellent impact and bending properties as well as good dimensional stability, and providing more material options for injection molding foaming processes.

[0050] The graphene used in this invention is a large-sheet graphene with a large surface area and thin thickness. When added to a mixture of modified polypropylene and acrylonitrile copolymer, a very small amount (below 1000 ppm) can effectively improve the mechanical properties of the matrix resin. Compared with conventional formulations, this significantly reduces the amount of filler needed, minimizing the impact of filler on the cell structure. Simultaneously, during the foaming process, the large-sheet graphene also acts as a cell nucleating agent, inducing the formation of denser and more uniform cells. Furthermore, the addition of large-sheet graphene helps eliminate internal stress within the material, improving the mechanical properties of the foamed product under room temperature conditions.

[0051] According to some embodiments of the present invention, the polypropylene composition further includes a lubricant; preferably, the lubricant is 0-5 parts by weight per 100 parts by weight of the modified polypropylene. For example, the lubricant may be 0, 1, 2, 3, 4, or 5 parts by weight, etc.

[0052] In this invention, since graphene acts as a cell nucleating agent, there is no need to add other cell nucleating agents. Depending on the specific application requirements, the polypropylene composition may also include various other additives commonly used in injection-molded foamed polypropylene compositions, such as light stabilizers, flame retardants, toughening agents, pigments, coupling agents, dispersants, etc. The types and amounts of the above-mentioned additives are all conventional choices in the art, and will be known to those skilled in the art, so they will not be elaborated upon here.

[0053] According to some embodiments of the present invention, the polypropylene composition comprises 100 parts by weight of the modified polypropylene, 1-20 parts by weight of the acrylonitrile copolymer, 2-80 parts by weight of the plant fiber powder, 10-100 parts by weight of the nylon resin, 1-12 parts by weight of the compatibilizer, 0.01-5.0 parts by weight of the graphene, and 0-10 parts by weight of the antioxidant.

[0054] For example, the acrylonitrile copolymer can be 1, 2, 3, 4, 5, 8, 10, 12, 15, 16, or 20 parts by weight.

[0055] The plant fiber powder can be in parts by weight of 2, 5, 10, 20, 30, 40, 50, 60, 70, or 80.

[0056] The nylon resin can be in parts by weight of 10, 20, 30, 40, 45, 50, 60, 70, 80, 90, or 100.

[0057] The compatibilizer can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 parts by weight.

[0058] The graphene content can be 0.01, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.8, 0.9, 1.0, 2.0, 3.0, 3.5, or 5.0 parts by weight.

[0059] The content of the antioxidant can be 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.5, 1.0, 1.5, 2.0, 4.0, 5.0, 8.0, or 10 parts by weight.

[0060] According to some embodiments of the present invention, based on 100 parts by weight of the modified polypropylene, the acrylonitrile copolymer is 1-10 parts by weight, the plant fiber powder is 2-50 parts by weight, the nylon resin is 20-70 parts by weight, the compatibilizer is 3-10 parts by weight, the graphene is 0.01-1.0 parts by weight, and the antioxidant content is 0.1-1.0 parts by weight.

[0061] According to some embodiments of the present invention, based on 100 parts by weight of the modified polypropylene, the acrylonitrile copolymer is 3-8 parts by weight, the plant fiber powder is 5-40 parts by weight, the nylon resin is 30-60 parts by weight, and the graphene content is 0.05-0.5 parts.

[0062] According to some embodiments of the present invention, the graphene sheet has a diameter of 1-20 micrometers and an average length-to-height ratio of 300-2500.

[0063] According to some embodiments of the present invention, the graphene has carboxyl-modified groups.

[0064] According to some embodiments of the present invention, the graphene has an oxygen content of 0.5wt%-20wt%, preferably 3wt%-10wt%; and a hydrogen content of 0.01wt%-1wt%, preferably 0.05wt%-0.5wt%.

[0065] According to some embodiments of the present invention, the electrical conductivity of the graphene is 500-1000 S / m.

[0066] The graphene used in this invention is prepared by mechanical exfoliation, the specific method of which is as follows:

[0067] (a) Add flake graphite powder and / or expanded graphite powder with a particle size of 10-80 mesh to the reactor.

[0068] (b) Carbon dioxide is introduced into the reactor, and the temperature is controlled to be greater than 31.26℃ and the pressure to be greater than 7.29MPa, so that it is in a supercritical state to form a mixture of graphite powder and supercritical carbon dioxide, with a weight ratio of graphite powder to carbon dioxide of 1:5-40. The mixture is then ground in the reactor at a rotation speed of 500-3000 r / min, a reactor temperature of 35-200℃, and a pressure of 75-300 atm.

[0069] (c) After grinding for a certain period of time, the pressure inside the reactor is rapidly reduced to normal pressure to obtain graphene.

[0070] According to some embodiments of the present invention, the modified polypropylene is polypropylene grafted with polar monomers. Preferably, the grafting rate is 0.5 wt%-10 wt%. More preferably, the grafting rate is 0.8 wt%-6 wt%.

[0071] The modified polypropylene used in this invention introduces polar monomer side chains through a grafting process, which not only improves the mechanical properties of the polypropylene matrix itself, but also facilitates the dispersion and reinforcement of fillers in the matrix resin. At the same time, the active groups on the modified polypropylene also help to improve the interaction between the modified polypropylene and nylon resin at the interface, thereby giving the material better mechanical properties.

[0072] According to some embodiments of the present invention, the polypropylene is homopolymer polypropylene or copolymer polypropylene.

[0073] According to some embodiments of the present invention, the polypropylene is an ethylene / propylene copolymer.

[0074] According to some embodiments of the present invention, the ethylene content in the ethylene / propylene copolymer is 0-8 wt%.

[0075] According to some embodiments of the present invention, the polar monomer includes at least one of polar monomers containing amino, hydroxyl, carboxyl, acid anhydride and / or epoxy groups.

[0076] According to some embodiments of the present invention, the polar monomer is selected from at least one of glycidyl methacrylate, maleic anhydride, acrylic acid, methacrylic acid, ethyl methacrylate and methyl acrylate.

[0077] According to some embodiments of the present invention, the polar monomer comprises a polar monomer containing an epoxy group and / or an anhydride.

[0078] According to some embodiments of the present invention, the polar monomer is glycidyl methacrylate.

[0079] According to some embodiments of the present invention, the modified polypropylene has a melt index greater than 5 g / 10 min at 230°C and 2.16 kg.

[0080] According to some embodiments of the present invention, the modified polypropylene has a melt index greater than 20 g / 10 min at 230°C and 2.16 kg.

[0081] The modified polypropylene used in this invention can be prepared by grafting polar monomers using an aqueous suspension grafting method. Specific preparation methods include:

[0082] (a) Mix 100 parts by weight of polypropylene, 0.06-0.26 parts by weight of initiator, and an appropriate amount of organic solvent at room temperature for 10-60 min to obtain a mixture. The initiator may be a peroxide initiator and / or an azo initiator. The organic solvent may be at least one of C2-C5 alcohols, C2-C4 ethers, and C3-C5 ketones.

[0083] (b) Remove the organic solvent from the mixture obtained in step (a) and add 2-10 parts by weight of polar monomer to swell for 10-120 min.

[0084] (c) Add 150-300 parts by weight of water to the swollen material obtained in step (b), heat to 60-120°C to carry out the reaction, and the reaction time is 1-10 hours.

[0085] (d) Wash and dry the reaction product obtained in step (c).

[0086] (e) The dried reaction product obtained in step (d) is placed in a benzene-based substance, heated until dissolved, and then mixed with ketone and / or ester solvents to precipitate. The precipitate is then dried to obtain modified polypropylene.

[0087] In the above preparation process, all raw materials must be deoxygenated beforehand, and nitrogen protection is required throughout the feeding and reaction process.

[0088] According to some embodiments of the present invention, the acrylonitrile copolymer is at least one of the acrylonitrile copolymers obtained by copolymerizing acrylonitrile with monomers selected from C2-C20 olefins and / or C2-C20 unsaturated esters.

[0089] According to some embodiments of the present invention, the acrylonitrile copolymer is selected from at least one of styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-methyl acrylate copolymer, methyl methacrylate-acrylonitrile copolymer, and vinyl acetate-acrylonitrile copolymer.

[0090] According to some embodiments of the present invention, the particle size of the plant fiber powder is 600-3000 mesh.

[0091] According to some embodiments of the present invention, the plant fiber powder is selected from at least one of poplar powder, pine powder, rice husk powder, coconut shell powder, walnut shell powder and bamboo powder.

[0092] According to some embodiments of the present invention, the nylon resin is selected from at least one of nylon 6, nylon 12 and nylon 66.

[0093] According to some embodiments of the present invention, the nylon resin is nylon 6.

[0094] According to some embodiments of the present invention, the compatibilizer is selected from at least one of oxazoline compatibilizers, acrylic compatibilizers, maleic anhydride compatibilizers, and isonitrile ester compatibilizers.

[0095] According to some embodiments of the present invention, the compatibilizer is a maleic anhydride type compatibilizer and an oxazoline type compatibilizer.

[0096] According to some embodiments of the present invention, the antioxidant includes phenolic antioxidants and / or phosphite antioxidants.

[0097] According to some embodiments of the present invention, the antioxidant is selected from at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1076), 2,2'-methylenebis-(4-methyl-6-tert-butylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, tris(2,4-di-tert-butylphenyl) phosphite, pentaerythritol diphosphite (antioxidant 626), and bis(2,6-di-tert-butyl-4-tolyl) pentaerythritol diphosphite.

[0098] In a second aspect, the present invention provides a method for preparing the above-mentioned polypropylene composition, comprising: mixing the components according to the formula, then melt-extruding, cooling and drawing into fibers, and pelletizing.

[0099] According to some embodiments of the present invention, the mixing speed is 500-2000 rpm and the mixing time is 1-3 minutes.

[0100] According to some embodiments of the present invention, the melt extrusion temperature is 180-250°C.

[0101] According to some embodiments of the present invention, melt extrusion employs a multi-stage heating process.

[0102] According to some embodiments of the present invention, the multi-stage heating process includes: a first stage at 190-230°C, a second stage at 210-245°C, a third stage at 210-260°C, a fourth stage at 200-245°C, and a fifth stage at 200-245°C.

[0103] The polypropylene composition injection-molded foam provided by the present invention is obtained from the polypropylene composition described above or the polypropylene composition prepared by the preparation method described above.

[0104] According to some embodiments of the present invention, the polypropylene composition injection-molded foamed article can be prepared by injection molding foaming process.

[0105] The injection molding foaming process conditions used in this invention can all be conventional choices in the field, and the specific processes are known to those skilled in the art, so they will not be described in detail here.

[0106] According to some embodiments of the present invention, when the polypropylene composition is formed into an injection-molded foam, a foaming agent needs to be added.

[0107] The foaming agent used in this invention can be a chemical foaming agent or a physical foaming agent. The chemical foaming agent includes, but is not limited to, at least one of azoformamide (AC foaming agent), p-toluenesulfonyl hydrazine, aminoureas, tetrazolium, sodium bicarbonate, and sodium citrate. The physical foaming agent can be an organic physical foaming agent or an inorganic physical foaming agent. Organic physical foaming agents include, but are not limited to, aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane; alicyclic hydrocarbons such as cyclobutane and cyclohexane; and halogenated hydrocarbons such as at least one of chlorofluoromethane, trifluoromethane, 1,2-difluoroethane, 1,2,2,2-tetrafluoroethane, methyl chloride, ethyl chloride, and dichloromethane. The inorganic physical foaming agent includes, but is not limited to, at least one of air, nitrogen, carbon dioxide, oxygen, and water.

[0108] In this invention, the foaming agent used for injection molding foaming is either a chemical foaming agent or a physical foaming agent, which does not have a significant impact on the various properties of the injection-molded foamed polypropylene composition.

[0109] The polypropylene composition and injection-molded foamed articles provided by the present invention will be described in detail below with reference to specific embodiments.

[0110] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the reagents used in the following embodiments are conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or by existing methods; unless otherwise specified, the reagent dosages are those used in routine experimental operations; unless otherwise specified, the experimental methods are conventional methods.

[0111] In the various embodiments and comparative examples of the present invention, the performance data were tested according to the following test methods:

[0112] (1) Impact strength, shrinkage rate, and heat distortion temperature of injection-molded foam mechanical specimens:

[0113] The notched impact strength of simply supported beams shall be determined according to the method specified in GB / T1043-2008;

[0114] Shrinkage shall be determined according to the method specified in GB / T 17037.4-2003;

[0115] The heat distortion temperature shall be determined according to the method specified in GB / T1634.

[0116] (2) Density testing method for injection-molded foam:

[0117] The density of the injection-molded polypropylene composition was obtained using the density accessory YDK01 of a Satorius CPA225D balance (Germany) via the displacement method, measured according to the methods described in national standard GB / T1033.1-2008 and ISO1183-1:2012. The foaming weight loss ratio of the obtained injection-molded polypropylene composition was calculated using the following formula:

[0118] r = ρ2 / ρ1 * 100%

[0119] Where r is the foaming weight loss ratio, ρ1 is the density of the base resin, and ρ2 is the apparent density of the injection-molded foam.

[0120] (3) Cell structure inside the injection-molded foam body and average sheet diameter and aspect ratio of graphene:

[0121] The foamed material was quenched with liquid nitrogen, and the fracture surface was sprayed with gold. The results were then tested using a scanning electron microscope (XL-30, FEI Corporation, USA).

[0122] (4) Melt Flow Index (MI):

[0123] The test was conducted according to the method specified in GB / T3682-2000, with a test temperature of 230℃ and a load of 2.16 kg.

[0124] (5) Surface resistivity of injection-molded foam:

[0125] According to the method specified in GB / T1410-2006.

[0126] (6) Oxygen and hydrogen content of graphene:

[0127] Characterized by X-ray photoelectron spectroscopy (XPS).

[0128] (7) Electrical conductivity of graphene:

[0129] The resistivity and conductivity were measured using a powder resistivity and conductivity tester according to the method specified in DB13 / T 2768.3-2018.

[0130] (8) Calculation method for grafting rate of modified polypropylene:

[0131] The Ag graft monomer was added to Bg polypropylene for grafting reaction. The resulting product was washed with n-heptane and dried to finally obtain Cg substance. The grafting rate of this modified polypropylene is then:

[0132] Grafting rate % = (A + BC) * 100 / B.

[0133] The materials and amounts used in the various embodiments and comparative examples of this invention are as follows:

[0134] (1) Acrylonitrile copolymer: Acrylonitrile-butadiene-styrene copolymer, produced by Chi Mei Corporation in Taiwan, China, grade PA-765A high flow V0 flame retardant ABS.

[0135] (2) Plant fiber powder: Pine wood powder, with a particle size of 600-1000 mesh, provided by Kingfa Wood Plastics Co., Ltd.

[0136] (3) Nylon resin: PA6 product from BASF, with a relative viscosity of 3.4 and a density of 1.13 g / cm³. 3 .

[0137] (4) Compatibilizer: Maleic anhydride-type compatibilizer and oxazoline-type compatibilizer were mixed in a 1:1 weight ratio. The maleic anhydride-type compatibilizer (maleic anhydride-grafted polypropylene, PP-g-MAH) was purchased from Jia Yi Rong Company, brand name CMG9801; the oxazoline-type compatibilizer was purchased from Dow Chemical Company, and was copolymer PS grafted with oxazoline (RPS) (oxazoline 1 wt%, molecular weight 20000). The amount of compatibilizer added was 5.0 parts.

[0138] (5) The antioxidant is a mixture of 1010 and 168 in a 1:1 ratio, produced by BASF in Germany, with an addition amount of 0.5 parts.

[0139] (6) Lubricant: Erucamide, produced by Guangzhou Haozhao Chemical Co., Ltd., 1.0 part added.

[0140] (7) Nanoscale chemically exfoliated graphene (CGO): Nanoscale chemically exfoliated graphene (CGO): sheet diameter 100-200nm, thickness 10nm, aspect ratio 10-20, oxygen content 32wt%, hydrogen content 0, electrical conductivity 75S / m, purchased from Nanjing Jicang Nanotechnology Co., Ltd.

[0141] (8) Reinforcing filler: Single-layer flaky talc powder MTalc, purchased from Mingzheng Plastics Co., Ltd., grade: ultrafine talc powder-3000 mesh.

[0142] (9) Graphene GO1#: sheet diameter 10-20 micrometers, thickness 10nm, length-to-height ratio 1000-2000, oxygen content 5.3wt%, hydrogen content 0.30wt%, electrical conductivity 870S / m;

[0143] The preparation method of graphene GO1# is as follows: Adjust the gap between the upper and lower grinding discs to 1 mm, and then place 100 g of 32 mesh flake graphite powder into the reactor; inject 2.5 kg of carbon dioxide into the reactor through the air inlet, and the pressure inside the reactor is 60 atm; heat the reactor to 55℃ through the jacket heating; then set the grinding disc rotation speed to 1000 rpm and turn on the magnetic rotation component; the pressure inside the reactor rises to 120 atm; stop the experiment after 24 h; open the air inlet and reduce the pressure inside the reactor to 1 atm within 10 s, and discharge the material from the discharge port at the bottom of the reactor to obtain graphene GO1#.

[0144] (10) Graphene GO2#: sheet diameter 5-10 micrometers, thickness 10nm, length-to-height ratio 500-1000, oxygen content 7.8wt%, hydrogen content 0.42wt%, electrical conductivity 530S / m;

[0145] The preparation method of graphene GO2# is as follows: Adjust the gap between the upper and lower grinding discs to 3 mm, and then place 50 g of 32 mesh expanded graphite powder into the reactor; inject 2.5 kg of carbon dioxide into the reactor through the air inlet, and the pressure inside the reactor is 60 atm; heat the reactor to 70℃ through the jacket heating; then set the grinding disc rotation speed to 2000 rpm and turn on the magnetic rotation component; the pressure inside the reactor rises to 160 atm; stop the experiment after 48 h; open the air inlet and reduce the pressure inside the reactor to 1 atm within 10 s, and discharge the material from the discharge port at the bottom of the reactor to obtain graphene GO2#.

[0146] (11) Modified polypropylene 1#: glycidyl methacrylate grafted polypropylene (PP-g-GMA), produced by Beijing Research Institute of Chemical Industry. The polypropylene matrix is ​​a copolymer polypropylene produced by Sinopec, grade SP179; the grafting rate of glycidyl methacrylate is 5.6wt%, and its melt flow rate is 6.0g / 10min under the test conditions of 230℃×2.16kg.

[0147] (12) Modified polypropylene 2#: It is ethyl methacrylate grafted polypropylene (PP-g-EA), produced by Beijing Research Institute of Chemical Industry. The polypropylene matrix is ​​a copolymer polypropylene produced by Sinopec, grade SP179; the ethyl methacrylate grafting rate is 2.5wt%, and its melt flow rate is 7.5g / 10min under the test conditions of 230℃×2.16kg.

[0148] (13) Modified polypropylene 3#: Maleic anhydride-grafted polypropylene, produced by Beijing Chemical Research Institute. The polypropylene matrix is ​​homopolymer polypropylene produced by Sinopec, grade T03s; the grafting rate is 0.9wt%, and its melt flow rate is 3.8g / 10min under the test conditions of 230℃×2.16kg.

[0149] The formulations of the polypropylene compositions prepared in each embodiment and comparative example are shown in Table 1.

[0150] The preparation method of the polypropylene composition is as follows:

[0151] After the wood flour is fully dried, the components are added to a high-speed mixer according to the formula ratio shown in Table 1 and mixed. Then, the mixture is added to a screw extruder for melt extrusion. The five heating temperatures are 210℃, 240℃, 245℃, 240℃ and 235℃, respectively, and the screw speed is 350 rpm. After extrusion, the mixture is cooled, drawn into fibers, and pelletized to obtain the polypropylene compositions of each example and comparative example.

[0152] Table 1 Formulation of Polypropylene Compositions

[0153]

[0154] In the various embodiments and comparative examples of the present invention, the injection molding process of the polypropylene composition used for injection-molded foamed articles is as follows:

[0155] On a dedicated injection molding machine for physical microfoaming, using the polypropylene compositions of each embodiment and comparative example as raw materials, 99.99% nitrogen gas is injected into the screw homogenization zone as a supercritical physical foaming agent. Under the shearing of the screw, the supercritical nitrogen gas is mixed with the polypropylene composition to form a single-phase melt. The single-phase melt is injected into the cavity of the national standard mechanical spline mold through a self-locking nozzle. When the mold is opened and the pressure is released, the gas escapes, and the polypropylene composition is injection molded into a foamed body.

[0156] The weight loss ratio, impact strength, heat distortion temperature, shrinkage rate and surface resistivity of the injection-molded foamed polypropylene composition were determined, and the results are shown in Table 2.

[0157] Table 2. Statistical Table of Performance Tests of Polypropylene Composition Injection Molded Foamed Articles

[0158]

[0159] The performance test results of the various embodiments and comparative examples show that the polypropylene composition of the present invention improves the compatibility of the two matrix resins by blending modified polypropylene with nylon, while also possessing the excellent rigidity of wood-plastic composites. During processing, acrylonitrile can generate oxazoline in the molten state, which can interact with the nylon molecular chains and the grafted chains of modified polypropylene, and synergistically promotes the compatibility between multiple components and the dispersion of wood flour and graphene in the matrix resin. As shown in Comparative Examples 5 and 6, if the polypropylene composition lacks the presence of ABS, it will be impossible to injection mold and foam due to uneven dispersion between the multiphases. The uniformly distributed wood flour, large-scale graphene, and micropores effectively reduce stress concentration inside the material, giving the injection-molded foam excellent rigidity, toughness, and warpage resistance.

[0160] Adding large-sheet graphene to polypropylene compositions as a cell nucleating agent and antistatic agent can improve the weight loss ratio of the foam, and also significantly improve the uniformity of the cell structure, mechanical properties, and antistatic properties. (Comparison) Figure 1 and Figure 2 It can be seen that the injection-molded foam of the polypropylene composition provided in Example 1 has a dense outer skin and fine cell morphology, with a pore size of approximately 10 μm and a relatively uniform size distribution. In contrast, no similar micropores can be observed on the cross-section of the injection-molded foam of the polypropylene composition provided in Comparative Example 1; only one large pore with a diameter of approximately 1 mm exists. The micron-sized cells inside the injection-molded foam of the polypropylene composition provided in Example 1 have regular shapes and uniform distribution, which can eliminate internal stress in the material and disperse and absorb impact force when subjected to external impact, effectively hindering crack propagation and improving the material's toughness. In contrast, the millimeter-sized large pores in the injection-molded foam of Comparative Example 1 not only fail to achieve the above effects but also become stress concentration points, thereby greatly reducing the material's mechanical properties.

[0161] The antistatic properties of polypropylene injection-molded foams increase with the addition of large-sheet graphene. However, too little large-sheet graphene will result in insufficient nucleation sites, while too much will cause agglomeration, both of which will adversely affect the weight reduction ratio and the mechanical properties of the injection-molded foam.

[0162] If talc is used as a cell nucleating agent, it can improve the mechanical properties and shrinkage of injection-molded foam to a certain extent, but the disadvantages are that the amount added is high, which has a great impact on the weight reduction ratio, and it has no antistatic ability.

[0163] Compared to antistatic agents using chemically exfoliated nanoscale graphene, injection-molded foams prepared from polypropylene compositions using large-sheet graphene showed little change in antistatic properties at the same addition level, but significantly improved mechanical properties and weight reduction ratio, and markedly reduced shrinkage. This indicates that large-sheet graphene more readily provides more inducing cell nucleation sites and cell nucleation sites within the melt. Figure 1 and Figure 3 It can be seen that the polypropylene composition provided in Example 1 has a dense outer skin and fine cell morphology with a pore size of about 10 μm and a relatively uniform size distribution. Although the cross-section of the polypropylene composition provided in Comparative Example 4 also has relatively uniform cells, the diameter of the cells is in the 100-micrometer range, and the cells are significantly less regular and fine in shape than those in the injection-molded foam of Example 1.

[0164] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A polypropylene composition, characterized in that, The material comprises modified polypropylene, acrylonitrile copolymer, plant fiber powder, nylon resin, compatibilizer, and graphene, wherein the graphene has a micron-sized sheet diameter and an average aspect ratio of 100-5000; the aspect ratio is the ratio of the long side to the thickness of the graphene; and the graphene has carboxyl-modified groups. The polypropylene composition comprises 100 parts by weight of the modified polypropylene, 1-20 parts by weight of the acrylonitrile copolymer, 2-80 parts by weight of the plant fiber powder, 10-100 parts by weight of the nylon resin, 1-12 parts by weight of the compatibilizer, 0.01-5.0 parts by weight of the graphene, and 0-10 parts by weight of the antioxidant. The modified polypropylene is polypropylene grafted with polar monomers; the polypropylene is homopolymer polypropylene or copolymer polypropylene; the polar monomer includes at least one of polar monomers containing amino, hydroxyl, carboxyl, acid anhydride and / or epoxy groups. The acrylonitrile copolymer is at least one of the acrylonitrile copolymers obtained by copolymerizing acrylonitrile with monomers selected from C2-C20 olefins and / or C2-C20 unsaturated esters; The particle size of the plant fiber powder is 600-3000 mesh.

2. The polypropylene composition according to claim 1, characterized in that, Based on 100 parts by weight of the modified polypropylene, the acrylonitrile copolymer is 1-10 parts by weight, the plant fiber powder is 2-50 parts by weight, the nylon resin is 20-70 parts by weight, the compatibilizer is 3-10 parts by weight, the graphene is 0.01-1.0 parts by weight, and the antioxidant content is 0.1-1.0 parts by weight.

3. The polypropylene composition according to claim 2, characterized in that, Based on 100 parts by weight of the modified polypropylene, the acrylonitrile copolymer comprises 3-8 parts by weight, the plant fiber powder comprises 5-40 parts by weight, the nylon resin comprises 30-60 parts by weight, and the graphene comprises 0.05-0.5 parts by weight.

4. The polypropylene composition according to any one of claims 1-3, characterized in that, The graphene sheets have a diameter of 1-20 micrometers and an average length-to-height ratio of 300-2500.

5. The polypropylene composition according to any one of claims 1-3, characterized in that, The graphene contains 0.5 wt% to 20 wt% oxygen and 0.01 wt% to 1 wt% hydrogen. And / or, the electrical conductivity of the graphene is 500-1000 S / m.

6. The polypropylene composition according to claim 5, characterized in that, The oxygen content of the graphene is 3wt%-10wt%; And / or, the hydrogen content of the graphene is 0.05wt%-0.5wt%.

7. The polypropylene composition according to any one of claims 1-3, characterized in that, The grafting rate of the modified polypropylene is 0.5wt%-10wt%; And / or, The polypropylene is an ethylene / propylene copolymer; And / or, The polar monomer is selected from at least one of glycidyl methacrylate, maleic anhydride, acrylic acid, methacrylic acid, ethyl methacrylate, and methyl acrylate.

8. The polypropylene composition according to any one of claims 1-3, characterized in that, The polar monomers include polar monomers containing epoxy groups and / or acid anhydrides.

9. The polypropylene composition according to claim 7, characterized in that, The grafting rate of the modified polypropylene is 0.8wt%-6wt%; And / or, The ethylene content in the ethylene / propylene copolymer is 0-8 wt%; And / or, The polar monomer is glycidyl methacrylate.

10. The polypropylene composition according to any one of claims 1-3, characterized in that, The modified polypropylene has a melt flow index greater than 5 g / 10 min at 230°C and 2.16 kg.

11. The polypropylene composition according to claim 10, characterized in that, The modified polypropylene has a melt flow index greater than 20 g / 10 min at 230°C and 2.16 kg.

12. The polypropylene composition according to any one of claims 1-3, characterized in that, The acrylonitrile copolymer is selected from at least one of styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-methyl acrylate copolymer, methyl methacrylate-acrylonitrile copolymer, and vinyl acetate-acrylonitrile copolymer.

13. The polypropylene composition according to any one of claims 1-3, characterized in that, The plant fiber powder is selected from at least one of poplar wood powder, pine wood powder, rice husk powder, coconut shell powder, walnut shell powder, and bamboo powder; And / or, the nylon resin is selected from at least one of nylon 6, nylon 12 and nylon 66; And / or, the compatibilizer is selected from at least one of oxazoline compatibilizers, acrylic compatibilizers, maleic anhydride compatibilizers, and isocyanate compatibilizers.

14. The polypropylene composition according to claim 13, characterized in that, The nylon resin is nylon 6.

15. The polypropylene composition according to any one of claims 1-3, characterized in that, The antioxidants include phenolic antioxidants and / or phosphite antioxidants.

16. The polypropylene composition according to claim 15, characterized in that, The antioxidant is selected from at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 2,2'-methylenebis-(4-methyl-6-tert-butylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, tris(2,4-di-tert-butylphenyl) phosphite, pentaerythritol diphosphite (2,4-di-tert-butylphenol), and pentaerythritol diphosphite (2,6-di-tert-butyl-4-tolyl).

17. A method for preparing a polypropylene composition according to any one of claims 1-16, characterized in that, include: The components are measured according to the formula and mixed, then melt-extruded, cooled and drawn into fibers, and then granulated.

18. The preparation method according to claim 17, characterized in that, The mixing speed is 500-2000 rpm, and the mixing time is 1-3 minutes; And / or, The temperature for melt extrusion is 180-250℃.

19. The preparation method according to claim 18, characterized in that, Melt extrusion employs a multi-stage heating process.

20. The preparation method according to claim 19, characterized in that, The multi-stage heating process includes: stage 190-230℃, stage 210-245℃, stage 310-260℃, stage 400-245℃, and stage 500-245℃.

21. A polypropylene composition injection-molded foam, obtained from a polypropylene composition as described in any one of claims 1-16 or a polypropylene composition prepared by any one of the preparation methods as described in claims 17-20.

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