A method for modifying a high-strength polypropylene composite material and applications thereof

Abstract

The application belongs to the field of polymer composites, and particularly relates to a modification method and application of high-strength polypropylene composite material; aiming at the problems of high requirements on the anti-aging performance and low-temperature impact resistance of materials of pallets used outdoors or in complex environments; the application prepares a toughening agent by taking hydrogenated styrene-isoprene-styrene block copolymer as a core, layered double hydroxide and polymer as a shell, and loading high-efficiency hindered phenolic antioxidant in the shell layer sandwich, to form a nano core-shell particle with stable structure; the core-shell toughening agent is mixed with part of PP and lubricant through double-screw extrusion to prepare high-concentration masterbatch, so as to protect the core-shell structure of the toughening agent from being sheared and damaged; then the masterbatch is melt-blended and granulated with the remaining PP, high-density polyethylene, pre-dispersed glass fiber and other additives to obtain a material with anti-aging performance and low-temperature impact resistance, so as to realize the application in aspects such as plastic pallets.

Description

Technical Field

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

[0002] Polypropylene (PP) is widely used in products such as logistics pallets due to its advantages of light weight, chemical resistance, ease of processing, and low price. However, standard PP materials are easily affected by environmental factors when used outdoors for extended periods: on the one hand, ultraviolet radiation and heat-oxidation can cause the material to age and become brittle, reducing its service life; on the other hand, PP has a high glass transition temperature at low temperatures, and its impact toughness decreases sharply below 0°C, making it prone to cracking.

[0003] Traditional solutions typically involve adding antioxidants and light stabilizers to PP to improve its aging resistance, and adding rubber elastomers to enhance its low-temperature impact resistance. However, simply adding these additives and elastomers often has limitations: small molecules of antioxidants and UV absorbers may migrate and be lost during use, making it difficult to provide long-term stable protection; while directly adding elastomers can significantly reduce the material's rigidity and strength, decreasing the load-bearing capacity of the product. For example, adding an aging-resistant polypropylene composition utilizes nano-TiO2 and UV absorbers to block ultraviolet rays, improving its outdoor lifespan. However, due to the lack of elastomer components, the improvement in low-temperature impact toughness of this type of material is limited. Furthermore, research on improving PP toughness (CN120829648A) shows that adding elastomers such as ethylene-octene copolymer (POE) and ethylene propylene diene monomer (EPDM) can lower the brittle-tough transition temperature, thereby improving low-temperature impact performance to some extent. However, the improvement in toughness often comes at the cost of stiffness; excessive rubber addition can lead to a significant decrease in material strength, causing increased deformation of the pallet under load at room temperature.

[0004] In summary, existing technologies still have significant room for improvement in the anti-aging properties and low-temperature impact resistance of polypropylene materials, and there is an urgent need for a modification method to prepare high-strength polypropylene composite materials. Summary of the Invention

[0005] This invention provides a method for modifying high-strength polypropylene composite materials and its application. By preparing a special core-shell toughening agent and using a masterbatch blending process, the anti-aging properties and low-temperature impact properties of polypropylene materials are synergistically improved.

[0006] The specific technical solution is as follows:

[0007] A method for modifying high-strength polypropylene composite materials and its application are as follows:

[0008] S1: Preparation of core-shell toughening agent.

[0009] S11: Dissolve hydrogenated styrene-isoprene-styrene block copolymer (SEPS) in toluene solution and stir until dissolved to obtain SEPS oil phase solution; dissolve antioxidant 1010 in a mixed solution of ethanol and water in a volume ratio of 4:1, then add magnesium nitrate and aluminum nitrate, heat and stir until dissolved to obtain aqueous phase solution (LDH, layered bimetallic hydroxide).

[0010] S12: Add the SEPS oil phase solution prepared in S11 to the aqueous phase solution prepared in S11, stir, adjust the pH to 10, cool to room temperature, centrifuge, wash, dry, and grind to obtain SEPS nuclei.

[0011] S13: Dissolve the SEPS core prepared in S12 in deionized water and sonicate to obtain a SEPS core suspension; add the SEPS core suspension to an aqueous solution of polydiallyldimethylammonium chloride (PDDA) containing 0.1 mol / L NaCl, stir to adsorb, centrifuge, and wash to obtain SEPS@PDDA.

[0012] S14: Add the SEPS@PDDA prepared in S13 to the aqueous solution prepared in S11, stir to adsorb, centrifuge, and wash to obtain SEPS@(PDDA-LDH).

[0013] S2: Masterbatch preparation: Polypropylene resin, SEPS@(PDDA-LDH) prepared in S1 and calcium stearate lubricant are mixed, and then melt-extruded through a twin-screw extruder, cooled, and pelletized to obtain masterbatch.

[0014] S3: Composite material preparation, polypropylene resin, masterbatch prepared in S2, high-density polyethylene, light stabilizer, and UV stabilizer are mixed to obtain a premix; the premix is ​​fed into an extruder through the main feeder for melt plasticization, pre-dispersed glass fiber is added from the side feed port, vacuum degassing is performed, then homogenization extrusion is carried out, cooling and shaping is performed, and pelleting is performed to obtain polypropylene composite material.

[0015] Furthermore, the SEPS described in S11 has a mass-to-volume ratio of 1:80 to 1:125 g / mL with toluene.

[0016] The antioxidant 1010 described in S11 has a mass-to-volume ratio of 1:250 g / mL to the mixed solution.

[0017] The molar ratio between magnesium nitrate and aluminum nitrate described in S11 is 2:1.

[0018] The heating and stirring described in S11 has the following parameter settings: temperature 60℃, rotation speed 200rpm.

[0019] The stirring described in S12 has the following parameters: temperature 65℃, speed 500rpm, and duration 12h.

[0020] The centrifugation described in S12 has the following parameters: rotation speed 8000 rpm, duration 10 min.

[0021] The washing described in S12 involves washing five times with a mixed solution of deionized water and anhydrous ethanol in a 1:1 volume ratio.

[0022] The ultrasonic treatment described in S13 has the following parameter settings: power 50-150W, duration 10-30min.

[0023] The stirring adsorption described in S13 has the following parameter settings: rotation speed 50-150 rpm, duration 15-20 min.

[0024] The centrifugation described in S13 has the following parameters: rotation speed 8000 rpm, duration 5 min.

[0025] Furthermore, the melt extrusion described in S2 has the following parameter settings: zone 1 temperature 170-180℃, zone 2 temperature 175-185℃, zone 3 temperature 180-190℃, zone 4 temperature 185-195℃, die head temperature 185-195℃, and screw speed 200-350rpm.

[0026] The cooling described in S2 uses a water tank with a water temperature of 20°C.

[0027] The masterbatch described in S2 has the following composition of raw materials in the following mass ratios: SEPS@(PDDA-LDH) 15-30%, polypropylene resin 69.5-84.5%, and lubricant 0.5-1.5%.

[0028] Furthermore, the mixing described in S3 has the following parameter settings: rotation speed 400-600 rpm, duration 5-7 min.

[0029] The melting and plasticizing process described in S3 has the following parameter settings: Zone 1 temperature 180-190℃, Zone 2 temperature 185-195℃, Zone 3 temperature 190-200℃, Zone 4 temperature 195-205℃, die head temperature 195-205℃, and screw speed 250-400rpm.

[0030] The vacuum exhaust described in S3 has the following parameter settings: vacuum degree -0.06 to -0.08 MPa.

[0031] The polypropylene composite material described in S3 has the following raw material composition in the following mass ratio: 50-70% polypropylene resin, 5-15% high-density polyethylene, 15-25% pre-dispersed glass fiber, 3-8% SEPS@(PDDA-LDH), 0.5-2% light stabilizer, and 0.5-1% lubricant.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. This invention prepares a core-shell toughening agent, utilizing SEPS to absorb and disperse impact energy; by alternately depositing LDH and PDDA on the SEPS core surface, it can effectively block the penetration of ultraviolet rays, oxygen and moisture, and delay the diffusion path of aging factors.

[0034] 2. This invention employs a two-step processing technique, first preparing a high-concentration masterbatch, which minimizes the shear damage to the fine core-shell structure during final blending, thus ensuring the preservation of the functional structure. Attached Figure Description

[0035] Figure 1 This is a process flow diagram of a modification method for high-strength polypropylene composite materials.

[0036] Figure 2 This is a comparison chart of the impact strength at 23°C and -30°C of the polypropylene composite materials finally prepared in Examples 1-4 and Comparative Examples 1-2.

[0037] Figure 3 This is a comparison chart of the impact strength retention rate and tensile strength retention rate after UV aging of the polypropylene composite materials finally prepared in Examples 1-4 and Comparative Examples 1-2. Detailed Implementation

[0038] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0039] This invention proposes a method for modifying high-strength polypropylene composite materials and its application. A core-shell structured composite toughening agent is prepared, with a hydrogenated styrene-isoprene-styrene block copolymer as the core, a layered bimetallic hydroxide and a quaternary ammonium salt surfactant as the shell, and a hindered phenolic antioxidant loaded onto it. Next, this core-shell toughening agent, a portion of the polypropylene, and a lubricant are first prepared into a high-concentration masterbatch to protect its fine structure. Finally, the masterbatch is melt-blended and granulated with the remaining polypropylene, high-density polyethylene, pre-dispersed glass fiber, and other additives to obtain the final composite material. (See attached diagram) Figure 1 The diagram shows a method for modifying high-strength polypropylene composite materials, and its detailed technical solution is as follows:

[0040] 1. Preparation of core-shell toughening agents

[0041] Hydrogenated styrene-isoprene-styrene block copolymer was dissolved in toluene solution and stirred to obtain a SEPS oil phase solution. Antioxidant 1010 was dissolved in a mixed solution of ethanol and water in a volume ratio of 4:1, and then magnesium nitrate and aluminum nitrate were added. The mixture was heated and stirred to obtain an aqueous phase solution. The SEPS oil phase solution was then added to the aqueous phase solution, stirred, and the pH was adjusted to 10. The mixture was cooled to room temperature, centrifuged, washed, dried, and ground to obtain SEPS core particles. The SEPS core particles were dissolved in deionized water and sonicated to obtain a SEPS core suspension. This suspension was then added to an aqueous solution of PDDA containing 0.1 mol / L sodium chloride, stirred for adsorption, centrifuged, and washed to obtain SEPS@PDDA. Finally, SEPS@PDDA was added to the aqueous phase solution, stirred for adsorption, centrifuged, and washed to obtain SEPS@(PDDA-LDH).

[0042] In an alkaline coprecipitation environment, Mg 2+ And Al 3+ Formation [Mg 1-x Al x (OH)2] x+ The LDH consists of multiple layers. Simultaneously, antioxidant 1010 partially dissociates into anionic groups under alkaline conditions. These anions act as guests for balancing charges, being introduced and stably present in the interlayer channels of LDH through electrostatic interactions, achieving in-situ intercalation. This structure imparts higher thermal stability and migration resistance, achieving long-term anti-aging effects. SEPS spontaneously assembles into micelles in a toluene-water emulsion system, with its hydrophobic segments curled up in the core, while relatively hydrophilic portions such as styrene blocks tend to distribute on the micelle surface. This provides abundant interfacial sites for heterogeneous nucleation of LDH. When LDH precursors diffuse in solution, they preferentially react and nucleate on the surface of SEPS micelles, rather than undergoing homogeneous nucleation within the solution.

[0043] The SEPS core, PDDA, and LDH nanosheets carry negative, positive, and negative charges, respectively, at a specific pH. Thus, after each adsorption step, the charge on the particle surface reverses, providing sites for the adsorption of substances with opposite charges in the next step, thereby achieving precise layer-by-layer assembly. Simultaneously, LDH effectively extends the diffusion path of small molecules such as oxygen and water vapor within the material, acting as an excellent physical barrier; PDDA fills the gaps between LDH nanosheets, not only solving the interfacial compatibility problem between LDH nanosheets but also absorbing and dissipating energy through its own deformation, inhibiting the propagation of microcracks.

[0044] 2. Masterbatch preparation

[0045] PP resin, SEPS@ (PDDA-LDH) and calcium stearate lubricant are mixed, then melt-extruded through a twin-screw extruder, cooled, and pelletized to obtain masterbatch.

[0046] Core-shell toughening agents, with their soft SEPS core and brittle LDH shell, are prone to shell cracking, peeling, or core aggregation under intense shear and heat. Using the "masterbatch method," a first blend with pure PP is performed, eliminating the scraping effect of hard fillers. Through gentle process parameter control, this ensures that the majority of the core-shell structure is well embedded in the PP carrier. Directly mixing powdered functional additives with large amounts of resin and fillers at once easily leads to uneven dispersion due to uneven feeding and high interfacial energy. The "masterbatch method" achieves preliminary microscale dispersion of the high-concentration toughening agent within the masterbatch. During final blending, simply melting the masterbatch rapidly releases the pre-dispersed functional units, shortening the time required for uniform dispersion and improving efficiency and quality.

[0047] 3. Preparation of composite materials

[0048] Polypropylene resin, masterbatch, high-density polyethylene (HDPE), light stabilizer, and UV inhibitor are mixed to obtain a premix. The premix is ​​fed into an extruder through a main feeder for melt plasticization. Pre-dispersed glass fibers are added from the side feed port, the air is degassed under vacuum, and then homogenized and extruded. After cooling and shaping, the material is pelletized to obtain a polypropylene composite material.

[0049] Glass fiber, as a rigid filler, significantly enhances the material's strength and modulus; while the core-shell toughening agent and high-density polyethylene (HDPE), as flexible phases, absorb impact energy by inducing crazing and shear banding. After melt blending, PP and HDPE form a "sea-island" structure. The HDPE dispersed phase acts as a stress concentration point, inducing matrix yielding and plastic deformation, while also possessing good low-temperature toughness. Working synergistically with the core-shell toughening agent, it further pushes the brittle-ductile transition temperature of the material towards lower temperatures. Pre-dispersed glass fiber forms a good interfacial bond with the polymer matrix, ensuring that stress is effectively transferred from the relatively soft PP matrix to the high-strength glass fiber, thus achieving efficient reinforcement. Antioxidants slowly released from the core-shell toughening agent, along with directly added light stabilizers, form a combined internal and external defense. The light stabilizer primarily captures free radicals generated by ultraviolet radiation, while antioxidant 1010 mainly prevents thermo-oxidative aging during processing and use. Together, they provide dual protection for the material's long-term use in harsh outdoor environments.

[0050] Example 1

[0051] A method for modifying high-strength polypropylene composite materials and its application are as follows:

[0052] Table 1 Main Raw Materials

[0053]

[0054] A method for modifying high-strength polypropylene composite materials and its application are as follows:

[0055] S1: Preparation of core-shell toughening agent.

[0056] S11: Dissolve SEPS in toluene solution and stir until dissolved to obtain an oil phase solution of SEPS; dissolve antioxidant 1010 in a mixed solution of ethanol and water with a volume ratio of 4:1, then add magnesium nitrate and aluminum nitrate, and heat and stir at 200 rpm at 60°C until dissolved to obtain an aqueous phase solution. The mass-to-volume ratio of SEPS to toluene is 1:100 g / mL, the mass-to-volume ratio of antioxidant 1010 to the mixed solution is 1:250 g / mL, and the molar ratio of magnesium nitrate to aluminum nitrate is 2:1.

[0057] S12: The SEPS oil phase solution prepared in S11 was added to the aqueous phase solution prepared in S11, stirred, the pH was adjusted to 10, cooled to room temperature, centrifuged, washed 5 times with a 1:1 volume ratio of deionized water and anhydrous ethanol, dried, and ground to obtain SEPS core particles. The stirring parameters were set as follows: temperature 65℃, rotation speed 500 rpm, duration 12 h; centrifugation speed 8000 rpm, duration 10 min.

[0058] S13: The SEPS cores prepared in S12 were dissolved in deionized water and sonicated to obtain a SEPS core suspension. The SEPS core suspension was added to a PDDA aqueous solution containing 0.1 mol / L NaCl, stirred for adsorption, centrifuged at 8000 rpm for 5 min, and washed to obtain SEPS@PDDA. The sonication parameters were set as follows: power 100 W, duration 20 min; stirring adsorption parameters were set as follows: rotation speed 100 rpm, duration 18 min.

[0059] S14: Add the SEPS@PDDA prepared in S13 to the aqueous solution prepared in S11, stir to adsorb, centrifuge, and wash to obtain SEPS@(PDDA-LDH).

[0060] S2: Masterbatch preparation: Polypropylene resin, SEPS@(PDDA-LDH) prepared in S1, and calcium stearate lubricant are mixed, then melt-extruded through a twin-screw extruder, cooled at 20°C with water, and pelletized to obtain masterbatch. The melt extrusion parameters are set as follows: Zone 1 temperature 175°C, Zone 2 temperature 180°C, Zone 3 temperature 185°C, Zone 4 temperature 190°C, die head temperature 190°C, and screw speed 280 rpm. The masterbatch's raw material composition is as follows: SEPS@(PDDA-LDH) 23%, polypropylene resin 76%, and lubricant 1%.

[0061] S3: Composite material preparation involves mixing polypropylene resin, the masterbatch prepared in S2, high-density polyethylene, light stabilizer, and UV inhibitor to obtain a premix. The premix is ​​fed into an extruder via the main feeder for melt plasticization. Pre-dispersed glass fiber is added through a side feed port, vacuum degassing is performed, followed by homogenization extrusion, cooling and shaping, and pelletizing to obtain the polypropylene composite material. The mixing parameters are set as follows: speed 500 rpm, duration 6 min; melt plasticization parameters are set as follows: zone 1 temperature 185℃, zone 2 temperature 190℃, zone 3 temperature 195℃, zone 4 temperature 200℃, die head temperature 200℃, screw speed 380 rpm; vacuum degassing parameters are set as follows: vacuum degree -0.07 MPa; the composition of the polypropylene composite material is as follows: polypropylene resin 61.9%, high-density polyethylene 10%, pre-dispersed glass fiber 20%, SEPS@(PDDA-LDH) 6%, light stabilizer 1.3%, and lubricant 0.8%.

[0062] Example 2

[0063] The composition and preparation process are the same as in Example 1, except that:

[0064] In the preparation process S11, the mass-to-volume ratio of SEPS to toluene is 1:80 g / mL, and the other components are the same.

[0065] In step S13 of the preparation process, the ultrasonic treatment power is 50W and the duration is 10min; the stirring adsorption is performed with the following parameters: rotation speed 50rpm and duration 15min, and other steps are the same.

[0066] In the S2 melt extrusion process of the preparation process, the parameters are set as follows: zone 1 temperature 170℃, zone 2 temperature 175℃, zone 3 temperature 180℃, zone 4 temperature 185℃, die head temperature 185℃, screw speed 200rpm, and other steps are the same.

[0067] The masterbatch in the S2 preparation process has the following raw material composition ratio: SEPS@(PDDA-LDH) 15%, polypropylene resin 84.5%, lubricant 0.5%, and other components are the same.

[0068] The polypropylene composite material in preparation process S3 has the following raw material mass ratio composition: 50% polypropylene resin, 15% high-density polyethylene, 25% pre-dispersed glass fiber, 8% SEPS@(PDDA-LDH), 1.5% light stabilizer, 0.5% lubricant, and other components are the same.

[0069] In the S3 step of the preparation process, the parameters for melt plasticization are set as follows: zone 1 temperature 180℃, zone 2 temperature 185℃, zone 3 temperature 190℃, zone 4 temperature 195℃, die head temperature 195℃, and screw speed 250rpm; the vacuum exhaust parameters are set as follows: vacuum degree -0.06MPa, and other steps are the same.

[0070] Example 3

[0071] The composition and preparation process are the same as in Example 1, except that:

[0072] In the preparation process S11, the mass-to-volume ratio of SEPS to toluene is 1:125 g / mL, and the other components are the same.

[0073] In step S13 of the preparation process, the ultrasonic treatment power is 150W and the duration is 30min; the stirring adsorption is performed with the following parameters: rotation speed 150rpm and duration 20min, and other steps are the same.

[0074] In the S2 melt extrusion process of the preparation process, the parameters are set as follows: zone 1 temperature 180℃, zone 2 temperature 185℃, zone 3 temperature 190℃, zone 4 temperature 195℃, die head temperature 195℃, screw speed 350rpm, and other steps are the same.

[0075] The masterbatch in the S2 preparation process has the following raw material composition ratio: SEPS@(PDDA-LDH) 30%, polypropylene resin 69.5%, lubricant 0.5%, and other components are the same.

[0076] The polypropylene composite material in preparation process S3 has the following raw material mass ratio composition: 70% polypropylene resin, 8% high-density polyethylene, 18% pre-dispersed glass fiber, 3% SEPS@(PDDA-LDH), 0.5% light stabilizer, 0.5% lubricant, and other components are the same.

[0077] In the S3 step of the preparation process, the parameters for melt plasticization are set as follows: zone 1 temperature 190℃, zone 2 temperature 195℃, zone 3 temperature 200℃, zone 4 temperature 205℃, die head temperature 205℃, and screw speed 400rpm; the vacuum exhaust parameters are set as follows: vacuum degree -0.08MPa, and other steps are the same.

[0078] Example 4

[0079] The composition and preparation process are the same as in Example 1, except that:

[0080] In the preparation process S11, the mass-to-volume ratio of SEPS to toluene is 1:120 g / mL, and the other components are the same.

[0081] In step S13 of the preparation process, the ultrasonic treatment power was 130W and the duration was 25min; the stirring adsorption parameters were set as follows: rotation speed 120rpm and duration 19min, and other steps were the same.

[0082] In the S2 melt extrusion process of the preparation process, the parameters are set as follows: zone 1 temperature 171℃, zone 2 temperature 179℃, zone 3 temperature 182℃, zone 4 temperature 188℃, die head temperature 192℃, screw speed 260rpm, and other steps are the same.

[0083] The masterbatch in the S2 preparation process has the following raw material composition ratio: SEPS@(PDDA-LDH) 20%, polypropylene resin 78.8%, lubricant 1.2%, and other components are the same.

[0084] The polypropylene composite material in preparation process S3 has the following raw material mass ratio composition: 65.5% polypropylene resin, 12% high-density polyethylene, 17% pre-dispersed glass fiber, 3% SEPS@(PDDA-LDH), 0.6% light stabilizer, 1.9% lubricant, and other components are the same.

[0085] In the S3 step of the preparation process, the parameters for melt plasticization are set as follows: Zone 1 temperature 183℃, Zone 2 temperature 1892℃, Zone 3 temperature 194℃, Zone 4 temperature 202℃, die head temperature 203℃, and screw speed 390rpm; the vacuum exhaust parameters are set as follows: vacuum degree -0.075MPa, and other steps are the same.

[0086] Comparative Example 1

[0087] The composition and preparation process are the same as in Example 1, except that:

[0088] In step S3 of the preparation process, no core-shell toughening agent is added. Instead, an equal amount of ordinary SEBS (YH-501T) is used as the toughening agent, and the other steps are the same.

[0089] Comparative Example 2

[0090] The composition and preparation process are the same as in Example 1, except that:

[0091] In step S2 of the preparation process, the masterbatch method is not used. The core-shell toughening agent prepared in Example 1 is mixed with all other raw materials at once, and then the final blending and granulation are carried out directly. The other steps are the same.

[0092] Based on Examples 1-4 and Comparative Examples 1-2, samples of the finally prepared polypropylene composite material were taken and subjected to tensile strength testing: the polypropylene composite material was prepared into a dumbbell shape and tested using a universal testing machine, referring to the standard GB / T1040.1-2025 "Determination of tensile properties of plastics - Part 1: General".

[0093] Based on Examples 1-4 and Comparative Examples 1-2, samples of the finally prepared polypropylene composite material were taken for flexural modulus testing: the polypropylene composite material was prepared into rectangular strips and tested using a universal testing machine, referring to the standard GB / T9341-2008 "Determination of Flexural Properties of Plastics".

[0094] Based on Examples 1-4 and Comparative Examples 1-2, samples of the finally prepared polypropylene composite material were taken for impact strength testing: the polypropylene composite material was prepared into rectangular strips and treated in environments of 23℃ and -30℃ for 4 hours respectively, and then tested using a cantilever beam impact testing machine, referring to the standard GB / T 1843-2008 "Determination of impact strength of plastic cantilever beam".

[0095] Based on Examples 1-4 and Comparative Examples 1-2, samples of polypropylene composite material specimens after impact strength testing were taken and subjected to impact strength retention rate testing after UV aging: the impact specimens were placed in an aging test chamber and exposed to alternating cycles of UV radiation (8h) and condensation (4h) for two weeks. The specimens were then removed and the impact strength was tested, referring to the standard GB / T 1843-2008 "Determination of Impact Strength of Plastic Cantilever Beams".

[0096] Based on Examples 1-4 and Comparative Examples 1-2, samples of polypropylene composite material specimens after tensile strength testing were taken and tensile strength retention rate after thermo-oxidative aging was tested: the tensile specimens were placed in an oxygen pressure aging test chamber at 150℃ for aging, and the cycle was repeated once. Then the specimens were taken out and the tensile strength was tested, referring to the standard GB / T 1040.1-2025 "Determination of tensile properties of plastics - Part 1: General".

[0097] The specific test results are shown in Table 2. Figure 2 , Figure 3 As shown:

[0098] Table 2 Comparison of core performance of Examples 1-4 and Comparative Examples 1-3

[0099]

[0100] The comparison results above show that Example 1 has the best overall performance, thanks to the good pre-dispersion of the core-shell toughening agent in the masterbatch and the excellent interfacial bonding with polypropylene resin and glass fiber during the final composite process. This allows it to maintain toughness while also fully utilizing rigidity, indicating that Example 1 successfully solves the problem of high requirements for the anti-aging performance and low-temperature impact resistance of materials when pallets are used outdoors or in complex environments. The overall performance of Examples 2 to 4 is slightly lower than that of Example 1, but still maintains a high level, indicating that high strength is still achieved under a wide range of parameter variations. Comparative Example 1 uses ordinary SEBS instead of the core-shell toughening agent, resulting in a significant decrease in anti-aging performance and low-temperature impact resistance. Comparative Example 2 does not use the masterbatch method and directly mixes all raw materials, resulting in uneven dispersion of the toughening agent, and the impact strength and aging retention rate are significantly lower than those of Example 1.

[0101] In summary, it is clear from the above embodiments and comparative examples that the high-strength polypropylene composite material provided by the present invention has significantly better anti-aging performance and low-temperature impact resistance than traditional solutions. This is attributed to the construction of a core-shell toughening agent, which improves the material's anti-aging performance and low-temperature impact resistance.

Claims

1. A high-strength polypropylene composite material, comprising a matrix resin, a toughening agent, reinforcing fillers, and additives, characterized in that: The toughening agent has a core-shell structure, with its core phase being a SEPS hydrogenated block copolymer and its shell phase being a composite multilayer structure of layered bimetallic hydroxide and quaternary ammonium salt surfactant. The composite multilayer structure also contains a highly efficient hindered phenolic antioxidant. The toughening agent is premixed and dispersed in the matrix resin via masterbatch, ensuring that the core-shell structure of the toughening agent is not damaged by shear. The reinforcing filler is an inorganic rigid fiber, forming a stress transfer network between the dispersed phase resin in the additive and the matrix resin. The hydrogenated block copolymer is a hydrogenated styrene-isoprene-styrene block copolymer, abbreviated as SEPS. The layered bimetallic hydroxide is a lamination constructed from magnesium and aluminum bimetallic ions, abbreviated as LDH. The quaternary ammonium salt surfactant is polydiallyldimethylammonium chloride, abbreviated as PDDA. The inorganic rigid fiber is a predispersed glass fiber. The toughening agent preparation process is as follows: S11: Dissolve SEPS in toluene solution and stir until dissolved to obtain SEPS oil phase solution; dissolve antioxidant 1010 in a mixed solution of ethanol and water with a volume ratio of 4:1, then add magnesium nitrate and aluminum nitrate, heat and stir until dissolved to obtain aqueous phase solution; S12: Add the SEPS oil phase solution prepared in S11 to the aqueous phase solution prepared in S11, stir, adjust the pH to 10, cool to room temperature, centrifuge, wash, dry, and grind to obtain SEPS core particles. S13: Dissolve the SEPS core prepared in S12 in deionized water and sonicate to obtain a SEPS core suspension; add the SEPS core suspension to a PDDA aqueous solution containing 0.1 mol / L NaCl, stir to adsorb, centrifuge, and wash to obtain SEPS@PDDA; S14: Add the SEPS@PDDA prepared in S13 to the aqueous solution prepared in S11, stir to adsorb, centrifuge, and wash to obtain SEPS@(PDDA-LDH).

2. The high-strength polypropylene composite material according to claim 1, characterized in that: The masterbatch has the following composition of raw materials in the following mass ratios: core-shell toughening agent 15-30%, polypropylene resin 69.5-84.5%, and lubricant 0.5-1.5%.

3. The high-strength polypropylene composite material according to claim 1, characterized in that: The polypropylene composite material has the following composition of raw materials in the following mass ratio: 50-70% polypropylene resin, 5-15% high-density polyethylene, 15-25% pre-dispersed glass fiber, 3-8% toughening agent, 0.5-2% light stabilizer, and 0.5-1% lubricant.

4. A method for modifying a high-strength polypropylene composite material according to any one of claims 1-3, characterized in that, Includes the following steps: S1: Preparation of core-shell toughening agents; S11: Dissolve SEPS in toluene solution and stir until dissolved to obtain SEPS oil phase solution; dissolve antioxidant 1010 in a mixed solution of ethanol and water with a volume ratio of 4:1, then add magnesium nitrate and aluminum nitrate, heat and stir until dissolved to obtain aqueous phase solution; S12: Add the SEPS oil phase solution prepared in S11 to the aqueous phase solution prepared in S11, stir, adjust the pH to 10, cool to room temperature, centrifuge, wash, dry, and grind to obtain SEPS core particles. S13: Dissolve the SEPS core prepared in S12 in deionized water and sonicate to obtain a SEPS core suspension; add the SEPS core suspension to a PDDA aqueous solution containing 0.1 mol / L NaCl, stir to adsorb, centrifuge, and wash to obtain SEPS@PDDA; S14: Add the SEPS@PDDA prepared in S13 to the aqueous solution prepared in S11, stir to adsorb, centrifuge, wash, and obtain SEPS@(PDDA-LDH). S2: Masterbatch preparation: Polypropylene resin, SEPS@(PDDA-LDH) prepared in S1 and calcium stearate lubricant are mixed, and then melt-extruded through a twin-screw extruder, cooled, and pelletized to obtain masterbatch; S3: Composite material preparation, polypropylene resin, masterbatch prepared in S2, high-density polyethylene, light stabilizer, and UV stabilizer are mixed to obtain a premix; the premix is ​​fed into an extruder through the main feeder for melt plasticization, pre-dispersed glass fiber is added from the side feed port, vacuum degassing is performed, then homogenization extrusion is carried out, cooling and shaping is performed, and pelleting is performed to obtain polypropylene composite material.

5. The modification method for a high-strength polypropylene composite material according to claim 4, characterized in that: The SEPS described in S11 has a mass-to-volume ratio of 1:80 to 1:125 g / mL with toluene. The antioxidant 1010 described in S11 has a mass-to-volume ratio of 1:250g / mL to the mixed solution; The molar ratio of magnesium nitrate and aluminum nitrate described in S11 is 2:1; The heating and stirring described in S11 has the following parameter settings: temperature 60℃, rotation speed 200rpm.

6. The modification method for a high-strength polypropylene composite material according to claim 4, characterized in that: The stirring described in S12 has the following parameters: temperature 65℃, speed 500rpm, and duration 12h. The centrifugation described in S12 has the following parameters: rotation speed 8000 rpm, duration 10 min; The washing described in S12 involves washing five times with a mixed solution of deionized water and anhydrous ethanol in a volume ratio of 1:

1. The ultrasonic treatment described in S13 has the following parameter settings: power 50-150W, duration 10-30min. The stirring adsorption described in S13 has the following parameter settings: rotation speed 50-150 rpm, duration 15-20 min; The centrifugation described in S13 has the following parameters: rotation speed 8000 rpm, duration 5 min.

7. The modification method for a high-strength polypropylene composite material according to claim 4, characterized in that: The melt extrusion described in S2 has the following parameter settings: Zone 1 temperature 170-180℃, Zone 2 temperature 175-185℃, Zone 3 temperature 180-190℃, Zone 4 temperature 185-195℃, Die head temperature 185-195℃, and screw speed 200-350 rpm. The cooling described in S2 uses a water tank with a water temperature of 20°C.

8. The modification method for a high-strength polypropylene composite material according to claim 4, characterized in that: The mixing described in S3 has the following parameter settings: rotation speed 400-600 rpm, duration 5-7 min; The melting and plasticizing process described in S3 has the following parameter settings: Zone 1 temperature 180-190℃, Zone 2 temperature 185-195℃, Zone 3 temperature 190-200℃, Zone 4 temperature 195-205℃, die head temperature 195-205℃, and screw speed 250-400 rpm. The vacuum exhaust described in S3 has the following parameter settings: vacuum degree -0.06 to -0.08 MPa.

9. The application of the high-strength polypropylene composite material according to claim 1, characterized in that, The high-strength polypropylene composite material is used for injection molding of pallets and is obtained through injection molding.

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