A high-strength polypropylene composite material and its preparation method

Abstract

This invention discloses a high-strength polypropylene composite material and its preparation method, belonging to the field of polymer composite technology. It aims to solve the contradiction between the decreased load-bearing capacity of waste polypropylene due to oxidative degradation and the difficulty of conventional toughening systems in simultaneously achieving high toughness and high creep modulus. This invention uses waste polypropylene as a matrix, introduces modified talc powder modified with gallic acid, and synthesizes a reactive structural toughening compatibilizer that combines a flexible skeleton with a rigid structure. Through an in-situ reactive melt extrusion process, an interfacial cross-linked force-transfer network is constructed, effectively maintaining the rigid support within the material while significantly absorbing external impact deformation energy. This improves the material's long-term constant-load creep resistance and can be widely applied in heavy-duty logistics packaging and structural support components.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials technology, specifically relating to a high-strength polypropylene composite material and its preparation method. Background Technology

[0002] Polypropylene (PP) is widely used in logistics packaging and automotive parts due to its low density, ease of processing, and resistance to chemical corrosion. Utilizing recycled polypropylene (R-PP) to replace virgin polypropylene in the production of heavy-duty logistics pallets has become an industry trend. However, during its initial service life and mechanical crushing, recycled PP undergoes photothermal oxidation at the tertiary carbon sites of its main chain, accumulating a large amount of carbonyl groups and trace amounts of polar aging products such as hydroxyl groups. Simultaneously, due to the physical degradation of the molecular chains, the intrinsic modulus and impact toughness of recycled PP are severely degraded. To meet the dual requirements of impact resistance and creep resistance for heavy-duty pallets, existing technologies typically employ a composite modification route combining elastomers with rigid inorganic fillers and grafted compatibilizers.

[0003] Existing patent CN121628247A discloses a talc-filled polypropylene composite material and a method for suppressing injection molding pitting defects based on surface modification and process synergy. This scheme utilizes acid salt-titanium ester to composite modify talc powder and introduces copolymerized polypropylene, polyolefin elastomer, and maleic anhydride-grafted polypropylene compatibilizer for blend modification. However, this modification method is essentially a physical encapsulation, and the surface of the modified filler lacks highly reactive groups, resulting in weak interfacial bonding between it and the matrix and easy debonding. At the same time, the introduction of a large amount of elastomer will seriously weaken the intrinsic modulus of the material, making it difficult to meet the requirements of high strength and long-term creep resistance for heavy-duty components.

[0004] In summary, there is an urgent need for a waste polypropylene composite system containing a combination of rigid-flexible block crosslinked oligomers and surface-modified talc to resolve the core contradiction between high impact toughness and high creep modulus in conventional physical toughening systems without significantly sacrificing the basic rigidity and load-bearing capacity of the material. Summary of the Invention

[0005] The present invention aims to solve the contradiction between the decrease in load-bearing capacity of waste polypropylene due to oxidative degradation and the difficulty of conventional toughening systems in achieving both high toughness and high creep modulus.

[0006] The specific technical solution is as follows: A high-strength polypropylene composite material is made from the following raw materials in parts by weight: 65-80 parts of waste polypropylene mixture, 15-25 parts of modified talc, 4-10 parts of reactive structural toughening compatibilizer, 5-10 parts of highly crystalline homopolymer polypropylene, 0.3-0.6 parts of composite antioxidant, and 0.1-0.5 parts of flow modifier; the reactive structural toughening compatibilizer has a molecular structure comprising a flexible skeleton and a rigid structure, with glycidyl groups at both ends of the molecule; the flexible skeleton is a C36 dimer fatty acid skeleton, and the rigid structure is hydrogenated bisphenol A; the modified talc is surface-modified with gallic acid.

[0007] Furthermore, the preparation method of the reactive structural toughening compatibilizer is as follows: 1.0 molar equivalent of C36 dimer fatty acid and 2.1 molar equivalent of hydrogenated bisphenol A are taken, and 0.1% of tetrabutyl titanate is added according to the total weight of the reaction substrate. Under nitrogen protection, the system is heated to 180°C at a heating rate of 3°C / min, and the reaction is maintained at this temperature with stirring for 4 hours. Subsequently, the temperature is raised to 220°C to continue the reaction, and the water generated during the reaction is continuously collected until the acid value drops to 5 mg. KOH concentration below 1 g; stop the reaction, cool the resulting intermediate oligomer system to 60°C, add 2.5 molar equivalents of epichlorohydrin, and add 1.5% tetrabutylammonium bromide by weight of epichlorohydrin; then heat the system to 70°C, stir for 2 hours, and add sodium hydroxide aqueous solution dropwise; after the addition is complete, continue to keep the reaction at the temperature for 3 hours, let it stand to separate into layers, collect the organic phase and wash it with deionized water at 90°C until neutral, remove excess epichlorohydrin by evaporation under normal pressure, and then vacuum devolatilize at -0.09 MPa and 120°C for 2 hours to obtain the reactive toughening compatibilizer.

[0008] Furthermore, the concentration of the sodium hydroxide aqueous solution is 30 wt%, and the molar amount of sodium hydroxide is 1.1 times the molar amount of epichlorohydrin.

[0009] Furthermore, the preparation method of the modified talc powder is as follows: 100 parts by mass of deionized water and 50 parts by mass of ethanol are mixed and heated to 70°C. 1.5 parts by mass of gallic acid are added and stirred until dissolved. The stirring speed is increased to 1500 rpm, and 100 parts by mass of 2500-mesh ultrafine talc powder are added in batches. After the addition is complete, the ultrasonic generator is turned on, the power is set to 1000W, the frequency is 25kHz, and the reaction is carried out at 70°C for 2 hours. Subsequently, nitrogen is introduced into the system to replace the air and maintain an initial positive pressure of 1.5MPa. The temperature is raised to 120°C and the reaction is carried out for 4 hours. After the reaction is completed, the resulting suspension is filtered. The filter cake is washed three times with a warm water-ethanol mixture and dried in a 110°C forced-air drying oven for 12 hours. The obtained material is depolymerized and pulverized to obtain the modified talc powder.

[0010] Furthermore, the isotacticity of the highly crystalline homopolymer polypropylene is ≥95%; the composite antioxidant is composed of a hindered phenolic antioxidant and a phosphite antioxidant in a weight ratio of 1:1, wherein the hindered phenolic antioxidant is antioxidant 1010 and the phosphite antioxidant is antioxidant 168; the flow modifier is a low molecular weight fatty acid ester or a polyether additive, including glyceryl trioctyl ester or polyoxyethylene / polyoxypropylene block copolymer.

[0011] Furthermore, the method for preparing the high-strength polypropylene composite material includes the following steps: S1: Take the waste polypropylene mixture, the high crystallinity homopolymer polypropylene, the modified talc, the composite antioxidant and the flow modifier according to the formula and put them into a mixer for dry mixing and pre-dispersion. Then add the reactive structural toughening compatibilizer and continue friction mixing to coat the surface to obtain a premix. S2: The premixed material is added to a twin-screw extruder for in-situ interfacial bonding reaction and melt extrusion; S3: The melt obtained by extrusion is subjected to vacuum degassing, extruded into strips, cooled in a water tank, granulated and dried to obtain the high-strength polypropylene composite material.

[0012] Furthermore, the operating conditions for dry mixing and pre-dispersion in step S1 are mixing at 1000 rpm for 5 minutes; the processing time for continued friction mixing is 3 minutes.

[0013] Furthermore, in step S2, the length-to-diameter ratio of the twin-screw extruder is set to 40:1, and the screw speed is set to 350 rpm.

[0014] Furthermore, the temperature control curve of the twin-screw extruder in step S2 is set as follows: 160°C to 180°C for zones 1 to 2, 200°C to 210°C for zones 3 to 5, 205°C to 195°C for zones 6 to 7, and the die head temperature is 195°C.

[0015] Furthermore, the drying process described in step S3 is specifically carried out at 80°C for 4 hours.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention synthesizes and introduces a reactive toughening compatibilizer, whose macromolecular network is composed of a highly flexible long carbon chain backbone and a highly rigid spatially saturated cyclic end group. During the compounding process, the highly reactive end group can effectively play the role of interfacial bridging, establishing a chemical bond interface between the resin matrix and the inorganic filler. Based on this microscopic interface feature, the long-chain flexible soft segment greatly improves the damping and dissipation efficiency of the material for external impact kinetic energy; at the same time, the spatial steric hindrance effect of the rigid structure at both ends and the rigid network restrict the slippage of the molecular side chains.

[0017] (2) This invention introduces interface-modified talc (GA-Talc). On the one hand, the organic modification layer formed on the surface of the talc significantly improves the melt dispersibility of the multiphase system and inhibits the risk of filler sedimentation and agglomeration, thereby providing a dense and tough physical framework support; on the other hand, the active functional structure retained in the organic layer endows the filler with excellent free radical scavenging ability. Through the endogenous antioxidant protection barrier provided by this structure, the tendency of polypropylene molecular chains to undergo photothermal oxidative degradation in subsequent heat setting and long-term service environments can be effectively mitigated, thereby ensuring the safe service life and mechanical durability of the structural material. Attached Figure Description

[0018] Figure 1 This is a synthetic route diagram for the reactive toughening compatibilizer of the present invention; Figure 2 The above is the 1H NMR spectrum of the reactive toughening compatibilizer obtained in Example 1 of this invention; Figure 3 Comparison of Fourier transform infrared spectra of modified talc, talc, gallic acid, and a physical mixture of talc and gallic acid. Detailed Implementation

[0019] The present invention proposes a high-strength polypropylene composite material, which is made from the following raw materials in parts by weight: 65-80 parts of waste polypropylene mixture (R-PP), 15-25 parts of GA-Talc, 4-10 parts of reactive structural toughening compatibilizer, 5-10 parts of high crystallinity homopolymer polypropylene (H-PP), 0.3-0.6 parts of composite antioxidant, and 0.1-0.5 parts of flow modifier.

[0020] The R-PP is a polypropylene material derived from industrial or domestic recycling. During its use and reprocessing, it undergoes a certain degree of thermo-oxidative degradation, forming oxygen-containing functional groups on its molecular chain, including polar end groups such as carbonyl, hydroxyl, and carboxyl groups.

[0021] The GA-Talc surface is constructed with an organic interface layer containing phenolic hydroxyl groups, which is used to adjust the surface polarity of talc and enhance its interfacial bonding performance with the polymer matrix. Simultaneously, the polyphenolic structural units retained by the gallic acid molecules possess a certain free radical scavenging ability, thereby inhibiting the thermo-oxidative aging of the material during processing and use.

[0022] The reactive toughening compatibilizer has a flexible backbone derived from C36 dimer fatty acids, rigid end groups derived from hydrogenated bisphenol A, and glycidyl groups at both ends, which can participate in interfacial reactions or chain extension processes during melt processing.

[0023] The H-PP is polypropylene with an isotacticity ≥95%, which serves as a crystallization regulating component to improve the crystallization rate and crystallization perfection of the system, thereby enhancing the rigidity and dimensional stability of the composite material. The composite antioxidant is a 1:1 weight ratio compound of hindered phenolic antioxidant 1010 and phosphite antioxidant 168, used to inhibit the thermo-oxidative degradation of the polypropylene matrix during processing and stabilize material properties. The flow modifier is a low molecular weight fatty acid ester or polyether additive, including glyceryl trioctyl ester or polyoxyethylene / polyoxypropylene block copolymer, used to improve melt flowability, reduce melt viscosity, and ensure uniform dispersion and coating of the reactive structural toughening compatibilizer on the surface of R-PP and GA-Talc particles.

[0024] Synthesis of reactive toughening compatibilizers, the synthetic route is shown in the attached figure. Figure 1 As shown, the details are as follows: (1) 1.0 mol equivalent of C36 dimer fatty acid and 2.1 mol equivalent of hydrogenated bisphenol A were added to a three-necked flask equipped with a condenser and a stirrer. 0.1% by weight of tetrabutyl titanate was added as a catalyst, and high-purity nitrogen was introduced for protection. The oil bath was turned on, and the temperature was increased to 180°C at a rate of 3°C / min. The mixture was kept at this temperature and stirred for 4 hours. The temperature was then increased to 220°C to continue the reaction, during which the water generated was continuously collected until the acid value dropped below 5 mg KOH / g. The reaction was stopped to obtain the intermediate oligomer. The highly flexible 36-carbon long chain in the dimer acid molecule provides excellent impact damping for the composite matrix. The hydrogenated bisphenol A has two saturated six-membered carbon rings, which serve as rigid end groups, providing high rigidity and steric hindrance at room temperature, thus enhancing the mechanical support properties of the composite material.

[0025] (2) The above intermediate oligomer system was cooled to 60°C, and 2.5 molar equivalents of epichlorohydrin were added, along with 1.5% tetrabutylammonium bromide by weight of epichlorohydrin as a phase transfer catalyst. The system was then heated to 70°C for etherification and ring-opening reaction. After stirring for 2 hours, a 30wt% sodium hydroxide aqueous solution was slowly added dropwise for ring-closing reaction. The molar equivalent of sodium hydroxide was 1.1 times that of epichlorohydrin. After the addition was complete, the reaction was continued for 3 hours. After the reaction was completed, the mixture was allowed to stand and separate into layers. The upper aqueous phase was discarded, and the organic phase was repeatedly washed with hot deionized water at 90°C until neutral. Unreacted excess epichlorohydrin was then evaporated under normal pressure. Finally, the mixture was vacuum-devoured at -0.09 MPa and 120°C for 2 hours to obtain a reactive toughening compatibilizer with the following structural formula: .

[0026] Preparation of GA-Talc: In a high-pressure sealed reactor equipped with a high-speed shear mixer, 100 parts by weight of a mixture of deionized water and 50 parts by weight of ethanol were added, and the mixture was heated to 70°C. 1.5 parts by weight of gallic acid were slowly added to the mixed solvent, and the mixture was stirred at low speed until completely dissolved. The stirring speed was increased to 1500 rpm, and 100 parts by weight of 2500-mesh ultrafine talc powder were added in batches, ensuring thorough dispersion. After the addition was complete, an ultrasonic generator was turned on, with a power setting of 1000W and a frequency of 25kHz, and ultrasonic treatment was maintained at 70°C for 2 hours to enhance dispersibility and interfacial contact. Subsequently, the reactor was sealed, and nitrogen was introduced to replace the air, maintaining an initial positive pressure of 1.5 MPa. The system temperature was raised to 120°C, and the reaction was carried out for 4 hours, causing the carboxyl groups of gallic acid to undergo a condensation reaction with the hydroxyl groups on the surface of talc powder, forming a stable organic modification layer on the talc powder surface. This organic layer introduces phenolic hydroxyl functional groups onto the particle surface, regulating the surface chemical properties of talc powder and improving its interfacial compatibility with the polymer matrix. After the reaction, the resulting suspension was filtered, and the filter cake was washed three times with a warm water-ethanol mixture to remove free gallic acid from the surface. The washed filter cake was then dried in a 110℃ forced-air drying oven for 12 hours. The dried lumpy material was then depolymerized and pulverized using a high-speed air jet mill to restore its ultrafine powder morphology, ultimately yielding GA-Talc, which was collected and sealed for later use. This modification process was carried out in a water-ethanol mixed-phase system. Through high-temperature reflux and hydroxyl activation, covalent bonding of gallic acid on the surface of talc powder was achieved, while retaining the structural characteristics of natural polyphenols. This gave the inorganic powder both surface polarity regulation capabilities, free radical scavenging function, and resistance to thermo-oxidative aging. Compared with traditional organic solvent modification processes, this process avoids the use of highly volatile organic solvents, balancing environmental friendliness and functional performance.

[0027] Preparation process of high-strength polypropylene composite material of the present invention (1) Dry mixing pretreatment: R-PP, H-PP, GA-Talc, composite antioxidant and flow modifier are added to a high-speed mixer according to the ratio and dry mixed for 5 minutes at 1000 rpm to initially and uniformly disperse the solid components. Add reactive structural toughening compatibilizer and continue mixing for 3 minutes to soften the reactive structural toughening compatibilizer under the action of frictional heat and uniformly coat the polymer particles and filler surface to form a premix with an interfacial active layer, thereby avoiding local enrichment during subsequent extrusion.

[0028] (2) Segmented feeding and melt reaction extrusion: The premixed material is fed into the main feed port of a co-rotating parallel twin-screw extruder. The length-to-diameter ratio of the extruder is set to 40:1. The temperature profile of the extruder from zone 1 to the die head is set as follows: Zone 1 to zone 2 (solid conveyor belt): 160℃-180℃; Zone 3 to zone 5 (melting and high shear mixing reaction zone): 200℃-210℃; Zone 6 to zone 7 (curing and venting zone): 205℃-195℃; Die head temperature 195℃, screw speed set to 350 rpm. Under high shear and high temperature conditions in zones 3 to 5, the reactive toughening compatibilizer plays a rheological regulating role in the melt, improving the processing fluidity of the system. Its terminal epoxy groups react with the hydroxyl or carboxyl groups on the R-PP chain ends and GA-Talc surface in the system through ring-opening reactions or interfacial interactions, thereby constructing a stable interfacial bonding structure between the filler and the matrix, and to a certain extent realizing the extension or connection of molecular chains.

[0029] (3) Exhausting, granulation and post-processing: The obtained melt is subjected to vacuum exhaust to remove volatile small molecules and residual moisture generated during processing. It is then extruded into strips through a die head, cooled in a water tank, and granulated by a pelletizer. The resulting granules are dried at 80°C for 4 hours to obtain the high-strength polypropylene composite material, which can be directly used for injection molding to prepare plastic pallet products.

[0030] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0031] The preferred embodiments of the present invention are described in detail below; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

[0032] Example 1 Synthesis of reactive toughening compatibilizer: 56.5 parts of dimer acid and 50.5 parts of hydrogenated bisphenol A were added to a reactor. 0.1 parts of tetrabutyl titanate were added, and nitrogen gas was introduced for protection. The system was heated to 180°C at a heating rate of 3°C / min and stirred for 4 hours. The temperature was then increased to 220°C to continue the reaction, with water continuously collected during the process. After 2 hours of reaction, the acid value of the system decreased to 4.5 mg KOH / g, at which point the reaction was stopped, yielding an intermediate oligomer. The system was cooled to 60°C, and 23 parts of epichlorohydrin and 0.3 parts of tetrabutylammonium bromide were added. The system was then heated to 70°C and stirred for 2 hours. Subsequently, 36 parts of a 30 wt% sodium hydroxide aqueous solution were slowly added dropwise to initiate a ring-closing reaction. After the addition was complete, the reaction was continued at this temperature for 3 hours. After the reaction was complete, the mixture was allowed to stand and separate into layers. The organic phase was collected and washed with hot deionized water at 90°C until neutral. Unreacted epichlorohydrin was evaporated under normal pressure. Finally, the mixture was vacuum devolatilized at -0.09 MPa and 120°C for 2 hours to obtain the reactive toughening compatibilizer. (See attached image) Figure 2 The following is its 1H NMR spectrum: deuterated chloroform (CDCl3, 400MHz): δ (ppm) 5.40-5.36 (m, 2H), 4.76-4.72 (m, 2H), 3.87-3.85 (m, 2H), 3.72-3.45 (m, 4H), 3.26-3.23 (m, 2H), 2.94-2.70 (m, 4H), 2.33-2.29 (t, 4H), 2.08-1.98 (m, 3H), 1.96-1.88 (m, 1H), 1.85-1.42 (m, 33H), 1.40-1.34 (m, 12H), 1.33-1.19 (m, 40H), 1.14-1.05 (m, 3H), 0.92-0.87 (m, 18H).

[0033] Preparation of GA-Talc: 100 parts deionized water and 50 parts ethanol were added to a reactor and heated to 70°C. 1.5 parts gallic acid were added and stirred at low speed until completely dissolved. The stirring speed was then increased to 1500 rpm, and 100 parts of 2500-mesh ultrafine talc powder were added in batches. After the addition was complete, an ultrasonic generator was turned on at 1000W power and 25kHz frequency, and the reaction was maintained at 70°C for 2 hours. The reactor was then sealed, and nitrogen was introduced to replace the air, maintaining an initial positive pressure of 1.5 MPa. The system temperature was raised to 120°C, and the reaction was continued for 4 hours. Subsequently, the resulting suspension was filtered, and the filter cake was washed three times with a warm water-ethanol mixture. The filter cake was collected and dried in a 110°C forced-air drying oven for 12 hours. The dried lumpy material was then depolymerized and pulverized using a high-speed air jet mill to obtain GA-Talc, which was collected and sealed for later use.

[0034] The high-strength polypropylene composite material was prepared with the following formulation: 70 parts R-PP, 20 parts GA-Talc, 7 parts reactive structural toughening compatibilizer, 8 parts H-PP (isotacticity ≥95%), 0.25 parts antioxidant 1010, 0.25 parts antioxidant 168, and 0.3 parts trioctyl glycerol. The specific preparation process is as follows: (1) R-PP, H-PP, GA-Talc, antioxidant 1010, antioxidant 168 and glyceryl trioctyl ester were added to a high-speed mixer according to the specified ratio and dry-mixed for 5 minutes at 1000 rpm. Then, a reactive structural toughening compatibilizer was added and the mixture was continued for 3 minutes to obtain a premix.

[0035] (2) Feed the premixed material into the main feed port of the co-rotating parallel twin-screw extruder. The length-to-diameter ratio of the extruder is 40:1. Extruder temperature settings: Zone 1 to Zone 2: 170℃; Zone 3 to Zone 5: 205℃; Zone 6 to Zone 7: 200℃; Die head temperature 195℃, screw speed 350rpm.

[0036] (3) The obtained melt is vacuum degassed, extruded into strips by die head, cooled, granulated and dried at 80°C for 4 hours to obtain a high-strength polypropylene composite material.

[0037] Examples 2 to 8 Based on Example 1, the addition ratio or type of each macroscopic component of the composite material were changed to verify the applicability and robustness of the formulation parameters of the present invention. All examples were prepared using the same process as in Example 1.

[0038] Table 1 Examples 2 to 8 Comparative Example 1 This comparative example uses a traditional polyolefin elastomer (POE) and polypropylene grafted maleic anhydride (PP-g-MAH) compound instead of a reactive structural toughening compatibilizer. The formulation is as follows: 70 parts R-PP, 20 parts GA-Talc, 4 parts POE, 2 parts PP-g-MAH, 8 parts H-PP, 0.25 parts antioxidant 1010, 0.25 parts antioxidant 168, and 0.3 parts trioctyl glycerol. The preparation process is the same as in Example 1.

[0039] Comparative Example 2 The formulation of this comparative example is the same as that of Example 1, except that no reactive structural toughening compatibilizer was added. The preparation process is the same as that of Example 1.

[0040] Comparative Example 3 This comparative example uses unmodified 2500-mesh ordinary talc powder instead of the GA-Talc of this invention. The formulation is as follows: 70 parts R-PP, 20 parts ordinary talc powder, 7 parts reactive structural toughening compatibilizer, 8 parts H-PP, 0.25 parts antioxidant 1010, 0.25 parts antioxidant 168, and 0.3 parts trioctyl glycerol. The preparation process is the same as in Example 1.

[0041] Comparative Example 4 The formulation of this comparative example is the same as that of Example 1, except that GA-Talc is not added. The preparation process is the same as that of Example 1.

[0042] Performance testing: 1. Tensile property test Refer to GB / T 1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics".

[0043] Sample preparation: The sample particles were injection molded into standard dumbbell-shaped specimens of type 1A. The specimens were then left to stand for 48 hours.

[0044] Test procedure: Under the condition of 23±2℃, the sample is installed on the electronic universal testing machine and tested at a tensile rate of 50mm / min until the sample breaks; the tensile strength (MPa) and elongation at break (%) of the sample are automatically recorded by the instrument. Each group of samples is tested 5 times and the average value is taken.

[0045] 2. Bending performance test Refer to GB / T 9341-2008 "Determination of Flexural Properties of Plastics".

[0046] Sample preparation: Inject the sample particles into standard specimens with dimensions of 80mm×10mm×4mm.

[0047] Test procedure: Under the condition of 23±2℃, the sample is placed in a three-point bending device with a span of 64mm and a loading rate of 2mm / min. The bending modulus (MPa) is recorded. Each group of samples is tested 5 times and the average value is taken.

[0048] 3. Cantilever beam notched impact strength test Refer to GB / T 1843-2008 "Determination of Impact Strength of Plastic Cantilever Beams".

[0049] Sample preparation: The sample particles are injection molded and prepared into standard specimens with dimensions of 80mm×10mm×4mm, and a V-shaped notch is machined in the middle.

[0050] Test procedure: The test was conducted using a cantilever beam impact testing machine at 23±2℃, and the notched impact strength (kJ / m) was recorded. 2Each group of samples was tested 5 times, and the average value was taken.

[0051] 4. Creep performance test Refer to GB / T 11546.2-2022 "Determination of creep properties of plastics - Part 2: Three-point bending creep".

[0052] Sample preparation: The sample particles were injection molded into standard rectangular specimens with dimensions of 80mm×10mm×4mm. The specimens were conditioned for 24 hours at 23±2℃ and 50±5% relative humidity before use.

[0053] Test Procedure: Under conditions of 23±2℃, the specimens were installed in a three-point bending creep testing apparatus with a span of 64mm. A constant bending stress was applied to the specimens according to the three-point bending stress mode, with the applied stress being 30% of the bending strength of each group of specimens. Continuous testing was conducted under constant load, and the deflection of the specimens over time was recorded until 100 hours. The creep strain was calculated based on the change in deflection, and the creep modulus (MPa) was further calculated. Each group of specimens was tested 3 times, and the average value was taken.

[0054] 5. Fourier Transform Infrared Spectroscopy (FTIR) Characterization (1) Parameter setting and detection process: The chemical structure and inorganic-organic interface bonding characteristics of GA-Talc, pure talc, pure gallic acid, and the physical mixture of talc and gallic acid (GA / Talc) obtained in the examples were analyzed using Fourier transform infrared spectroscopy (FTIR). Test parameters: A powder attenuated total reflectance ATR accessory was used for detection, and the scanning wavenumber range was set to 4000-500 cm⁻¹. -1 The resolution is set to 4cm. -1 The data was collected at room temperature.

[0055] (2) Characterization results: as shown in the appendix Figure 3 The image shows a comparison of Fourier transform infrared (FTIR) spectra of Talc, GA, a physical mixture (GA / Talc), and the modified product GA-Talc prepared in this invention. The comparative features are assigned as follows: Talc is located at 3675 cm⁻¹. -1 The presence of a characteristic, extremely sharp absorption peak at 10¹⁸ cm⁻¹ is attributed to the free inorganic polar metal hydroxyl groups on its surface. -1 With 670cm -1 The peaks at 1610 cm⁻¹ represent the vibrational peaks of the Si-O-Si and Si-O frameworks. GA and GA / Talc show peaks at 1610 cm⁻¹. -1 and 1530cm -1 The absorption peak at this point is attributed to the C=C stretching vibration of the aromatic ring skeleton; 3675 cm⁻¹ in GA / Talc -1The hydroxyl peak on the talc surface remained sharp, indicating that simple physical mixing did not trigger a chemical reaction. In contrast, GA-Talc showed a peak at 3675 cm⁻¹. -1 The surface hydroxyl peak at 1735 cm⁻¹ was significantly weakened, indicating that the hydroxyl groups on the talc surface had been consumed and participated in the reaction; simultaneously, at 1735 cm⁻¹... -1 A new characteristic absorption peak appears at 1610 cm⁻¹, attributed to the C=O stretching vibration of the esterification condensation product. -1 1530cm -1 The C=C vibration peak of the aromatic ring at 3000-3500 cm⁻¹ -1 The polyphenol hydroxyl absorption peak at the flask was retained in GA-Talc, indicating that the polyphenol structure of gallic acid was not destroyed after modification. In summary, the FTIR results show that gallic acid has been covalently bonded to the surface of talc powder, achieving chemical coating modification of the powder.

[0056] Table 2 Comparison of tensile strength, elongation at break, and flexural modulus results for each embodiment and comparative example. Table 3 Comparison of notched impact strength and 100h creep modulus results for each embodiment and comparative example Results analysis: (1) As can be seen from Tables 2 and 3, all embodiments maintain a high level in terms of tensile strength, flexural modulus, and creep modulus, while balancing good impact performance and elongation at break, demonstrating a balance between rigidity and strength. Embodiment 1 exhibits the best overall performance, with outstanding performance in flexural modulus and creep modulus, indicating that the material has better resistance to deformation under load conditions. The performance of the other embodiments fluctuates consistently under different formulation conditions, but the overall differences are not significant, indicating that the system has good formulation stability within a certain range. In summary, the system of the present invention can provide good impact resistance while maintaining rigidity and significantly improve creep resistance under long-term use conditions.

[0057] (2) Comparative Example 1 uses a traditional elastomer toughening system without adding a reactive structural toughening compatibilizer. Although it can significantly improve the notched impact strength and elongation at break, the flexural modulus and creep modulus decrease significantly, resulting in insufficient flexural support and easy longitudinal deformation creep failure. Comparative Example 2 does not add a reactive structural toughening compatibilizer, resulting in weak chemical bonding between multiphase interfaces. Its tensile strength, impact performance and creep performance all decrease significantly, indicating that the reactive structural toughening compatibilizer plays a key role in improving the interface structure and enhancing the overall performance of the material.

[0058] (3) Comparative Example 3 used unmodified talc. Although it showed a certain improvement in flexural modulus compared to pure resin, the stress transmission was hindered due to the polarity mismatch at the inorganic interface, resulting in lower elongation at break, notched impact strength, and creep resistance compared to the embodiments of the present invention. Comparative Example 4 did not add GA-Talc, resulting in the complete absence of its internal load-bearing network, further reducing its overall rigidity and creep resistance. In summary, GA-Talc not only provides a strong rigid support base but also promotes the interfacial crosslinking effect with polymer segments, thereby achieving efficient dissipation of kinetic energy.

[0059] In summary, this invention introduces reactive structural toughening compatibilizers and surface-modified talc into a polypropylene composite matrix, and triggers interfacial coupling and polymer long-chain extension mechanisms during the melt composite processing stage. This enables the composite material to achieve effective synergy between structural rigidity and impact toughness, while maintaining reasonable ductility and significantly improving the bending load resistance of the molded parts as well as the creep resistance and dimensional stability under long-term pressure conditions.

Claims

1. A high-strength polypropylene composite, characterized in that, The high-strength polypropylene composite material is made from the following raw materials in parts by weight: 65-80 parts of waste polypropylene mixture, 15-25 parts of modified talc, 4-10 parts of reactive structural toughening compatibilizer, 5-10 parts of high-crystallinity homopolymer polypropylene, 0.3-0.6 parts of composite antioxidant, and 0.1-0.5 parts of flow modifier; the reactive structural toughening compatibilizer has a molecular structure comprising a flexible skeleton and a rigid structure, with glycidyl groups at both ends of the molecule; the flexible skeleton is a C36 dimer fatty acid skeleton, and the rigid structure is hydrogenated bisphenol A; the modified talc is surface-modified with gallic acid; the molecular structure of the reactive structural toughening compatibilizer is: 。 2. The high-strength polypropylene composite of claim 1, wherein the polypropylene is a homopolymer of propylene. The specific preparation method of the reactive structural toughening compatibilizer is as follows: 1.0 mol equivalent of C36 dimer fatty acid and 2.1 mol equivalent of hydrogenated bisphenol A are taken, and 0.1% of tetrabutyl titanate is added according to the total weight of the reaction substrate. Under nitrogen protection, the system is heated to 180°C at a heating rate of 3°C / min, and the reaction is maintained at this temperature with stirring for 4 hours. Subsequently, the temperature is raised to 220°C to continue the reaction, and the water generated during the reaction is continuously collected until the acid value drops to 5 mg. KOH concentration below 1 g; stop the reaction, cool the resulting intermediate oligomer system to 60°C, add 2.5 molar equivalents of epichlorohydrin, and add 1.5% tetrabutylammonium bromide by weight of epichlorohydrin; then heat the system to 70°C, stir for 2 hours, and add sodium hydroxide aqueous solution dropwise; after the addition is complete, continue to keep the reaction at the temperature for 3 hours, let it stand to separate into layers, collect the organic phase and wash it with deionized water at 90°C until neutral, remove excess epichlorohydrin by evaporation under normal pressure, and then vacuum devolatilize at -0.09 MPa and 120°C for 2 hours to obtain the reactive toughening compatibilizer.

3. The high-strength polypropylene composite of claim 2, wherein the polypropylene is a homopolymer of propylene. The concentration of the sodium hydroxide aqueous solution is 30 wt%, and the molar amount of sodium hydroxide is 1.1 times the molar amount of epichlorohydrin.

4. The high-strength polypropylene composite material as described in claim 1, characterized in that, The preparation method of the modified talc powder is as follows: 100 parts by mass of deionized water and 50 parts by mass of ethanol are mixed and heated to 70°C. 1.5 parts by mass of gallic acid are added and stirred until dissolved. The stirring speed is increased to 1500 rpm, and 100 parts by mass of 2500-mesh ultrafine talc powder are added in batches. After the addition is complete, the ultrasonic generator is turned on, the power is set to 1000W, the frequency is 25kHz, and the temperature is kept at 70°C for 2 hours. Subsequently, nitrogen is introduced into the system to replace the air and maintain an initial positive pressure of 1.5MPa. The temperature is raised to 120°C and the reaction is carried out for 4 hours. After the reaction is completed, the resulting suspension is filtered. The filter cake is washed three times with a warm water-ethanol mixture and dried in a 110°C forced-air drying oven for 12 hours. The obtained material is depolymerized and pulverized to obtain the modified talc powder.

5. The high-strength polypropylene composite material as described in claim 1, characterized in that, The isotacticity of the highly crystalline homopolymer polypropylene is ≥95%; the composite antioxidant is composed of a hindered phenolic antioxidant and a phosphite antioxidant in a weight ratio of 1:1, wherein the hindered phenolic antioxidant is antioxidant 1010 and the phosphite antioxidant is antioxidant 168; the flow modifier is a low molecular weight fatty acid ester or a polyether additive, including glyceryl trioctyl ester or polyoxyethylene / polyoxypropylene block copolymer.

6. A method for preparing a high-strength polypropylene composite material according to any one of claims 1-5, characterized in that, Includes the following steps: S1: Take the waste polypropylene mixture, the high crystallinity homopolymer polypropylene, the modified talc, the composite antioxidant and the flow modifier according to the formula and put them into a mixer for dry mixing and pre-dispersion. Then add the reactive structural toughening compatibilizer and continue friction mixing to coat the surface to obtain a premix. S2: The premixed material is added to a twin-screw extruder for in-situ interfacial bonding reaction and melt extrusion; S3: The melt obtained by extrusion is subjected to vacuum degassing, extruded into strips, cooled in a water tank, granulated and dried to obtain the high-strength polypropylene composite material.

7. The method for preparing a high-strength polypropylene composite material as described in claim 6, characterized in that, The operating conditions for dry mixing and pre-dispersion in step S1 are mixing at 1000 rpm for 5 minutes; the processing time for continued friction mixing is 3 minutes.

8. The method for preparing a high-strength polypropylene composite material as described in claim 6, characterized in that, In step S2, the length-to-diameter ratio of the twin-screw extruder is set to 40:1, and the screw speed is set to 350 rpm.

9. The method for preparing a high-strength polypropylene composite material as described in claim 6, characterized in that, The temperature control curve of the twin-screw extruder in step S2 is set as follows: 160°C to 180°C for zones 1 to 2, 200°C to 210°C for zones 3 to 5, 205°C to 195°C for zones 6 to 7, and the die head temperature is 195°C.

10. The method for preparing a high-strength polypropylene composite material as described in claim 6, characterized in that, The drying process described in step S3 is specifically carried out at 80°C for 4 hours.

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