Toughening aid suitable for melt extrusion molding and application method thereof in polyethylene

Abstract

The invention relates to the technical field of polyethylene modification, and discloses a toughening aid suitable for melt extrusion molding and an application method of the toughening aid in polyethylene. According to the invention, a matching mechanism between polyethylene with different length-diameter ratios and polyethylene with different densities of the toughening aid is found, and according to the density of polyethylene, the polyethylene resin raw material, the toughening aid with the corresponding length-diameter ratio and the composite antioxidant are subjected to melt blending according to a certain proportion to obtain the modified polyethylene composite material. Compared with the polyethylene resin raw material, the toughness of the obtained material can be improved by 20-300%.

Description

Technical Field

[0001] This invention relates to the field of polyethylene modification technology, and more specifically to a toughening agent suitable for melt extrusion molding and its application method in polyethylene. Background Technology

[0002] Polyethylene (PE), one of the five major synthetic resins, is widely used in films, packaging, pipes, sheets, and fibers due to its excellent processing performance, mechanical properties, chemical corrosion resistance, low-temperature resistance, and advantages such as wide availability and low price. However, despite its low cost and good processability, PE's insufficient impact strength and tensile strength are key bottlenecks restricting its widespread application in high-end fields. In automotive parts manufacturing, taking bumpers as an example, traditional polyethylene-based materials are prone to brittle fracture under low-to-medium speed collisions due to insufficient impact strength, failing to effectively absorb collision energy.

[0003] Polyethylene is a semi-crystalline polymer, and its crystallization behavior, the morphology and content of crystalline and amorphous regions directly affect the processing and application performance of polyethylene products. Nucleating agents are polymer modifiers mainly used to improve the performance of polyolefins. They can accelerate the crystallization rate, increase crystal density, and promote grain refinement, thereby shortening the molding cycle and improving the physical and mechanical properties of products such as transparency, surface gloss, tensile strength, impact resistance, heat distortion temperature, and creep resistance. They can be applied in food contact materials, medical devices, automotive parts, and building materials. In actual production, fillers used to fill polyethylene include calcium carbonate, talc, calcium silicate, stearate nucleating agents, and p-hydroxybenzoic acid nucleating agents. While polyethylene composites filled with common nucleating agents can reduce product costs and improve rigidity, heat resistance, and dimensional stability, they suffer from poor interfacial adhesion with non-polar polymers like polyethylene, poor dispersibility, and easy precipitation, leading to a decrease in the material's mechanical and flow properties. This results in significant limitations in application scenarios, raw material compatibility, and industrial operation.

[0004] Chinese patent CN117986717 A discloses a mixing process for high-density polyethylene and calcium carbonate. This scheme focuses on significantly improving the rigidity, hardness, and dimensional stability of the material, and has advantages such as good wear resistance and weather resistance. However, on the one hand, the particle size range of calcium carbonate in this scheme is 10-30μm, which is too narrow and limits the application scenarios. On the other hand, smaller particle size of calcium carbonate reduces the toughness of the product, failing to resolve the contradiction of simultaneously achieving rigidity and toughness. Chinese patent CN116355301 A discloses a straw fiber talc-modified polyethylene blown film composite material, which utilizes the compatibility between straw fiber and talc with organic polymer materials to reduce the surface polarity of talc. However, the process for preparing straw fiber is very complex, and the mechanical properties of the improved polyethylene film, such as tensile strength, elongation at break, yield strength, and elastic modulus, are not clearly described. Chinese patent CN108559164 A discloses a high-content calcium silicate-filled polyethylene masterbatch and its preparation method. The carrier is limited to low-density polyethylene and cannot be directly applied to other polyethylene categories such as high-density polyethylene and linear low-density polyethylene. The scope of application is narrow and there are shortcomings in performance improvement.

[0005] To address the shortcomings of traditional nucleating agent-filled polyethylene composites, such as poor interfacial adhesion, poor dispersibility, and easy precipitation, it is of great significance to research and develop a toughening agent suitable for polyethylene melt extrusion molding and its application method. Summary of the Invention

[0006] The purpose of this invention is to overcome the limitations of traditional nucleating agents in toughening and modifying polyethylene due to their poor interfacial adhesion, poor dispersibility, and easy precipitation. This invention provides a toughening agent suitable for melt extrusion molding and its application method in polyethylene. The resulting modified polyethylene composite material can improve its impact toughness and / or tensile toughness by 20% to 300%.

[0007] The method provided by this invention reveals a matching mechanism between different aspect ratios of toughening additives and polyethylenes of different densities, specifically densities of 0.860~0.960 g / cm³. 3 Polyethylene exhibits different toughening responses to toughening agents with varying aspect ratios. Therefore, the matching mechanism between the aspect ratio of the toughening agent and polyethylene can be utilized to control the crystallization process and morphology of polyethylene, thereby altering its physical and mechanical properties. Furthermore, it has been found that nucleating agents, instead of crystal nuclei, reduce the free energy required for critical nucleus formation, bypassing the molecular chain nucleation process during polyethylene crystallization. This allows polyethylene molecular chains to grow crystals at higher temperatures. Therefore, this characteristic can be used to adjust processing conditions, optimize the manufacturing process, and reduce production costs.

[0008] To achieve the above objectives, this invention utilizes a matching mechanism between toughening additives with different aspect ratios and polyethylene densities. The toughening additives and polyethylene raw materials are melt-blended and then injection-molded to obtain modified polyethylene composite materials.

[0009] This invention discovers that during injection molding, polyethylene molecular chains undergo orientation in the flow direction. Toughening agents with an aspect ratio of 50~200:1 induce a density of 0.940~0.960 g / cm³ under the influence of the flow field. 3 High-density polyethylene (HDPE) exhibits a unique polymer crystal structure called a shish-kebab chain crystal, where the extended chain structure induced by a nucleating agent forms the central axis, surrounded by lamellae composed of folded chains, significantly improving its impact toughness. Later, it was discovered that toughening agents with aspect ratios of 20–49:1 only work for polyethylene with densities of 0.920–0.940 g / cm³. 3 Medium-density polyethylene (MDPE) exhibits a toughening response, while toughening additives with aspect ratios of 1–19:1 only work for densities of 0.860–0.920 g / cm³. 3 Low-density polyethylene (LDPE) exhibits a toughening response. However, the toughening mechanisms of the latter two (LDPE and PE) differ slightly from those of high-density polyethylene (HDPE). Because LDPE has a higher degree of branching than HDPE, nucleating agent particles with larger aspect ratios cannot induce molecular chain crystallization to form a shish structure, leading to toughening failure. Therefore, this invention shortens the aspect ratio of the toughening agent, enabling the LDPE molecular chains to interact with the toughening agent, adsorbing onto the nucleating agent surface to form a hybrid shish-kebab structure. The resulting high-toughness polyethylene material exhibits a 20%–300% increase in tensile toughness. Furthermore, this invention finds that, generally, improving material toughness may sacrifice some rigidity; however, during the toughening modification of polyethylene using the aforementioned toughening agent, the high-toughness polyethylene material still maintains high rigidity to ensure structural stability.

[0010] Based on the above findings, the present invention provides a method for melt extrusion molding of polyethylene based on toughening additives, which includes the following steps: 1) Select a toughening agent with an appropriate aspect ratio based on the density of the polyethylene resin raw material; wherein the density is 0.940~0.960 g / cm³. 3 For the polyethylene resin raw material, toughening additives with an aspect ratio of 50~200:1 are selected; the density is 0.920~0.940 g / cm³. 3 For the polyethylene resin raw material, toughening additives with an aspect ratio of 20~49:1 are selected; the density is 0.860~0.920 g / cm³. 3 For polyethylene resin raw materials, toughening additives with an aspect ratio of 1 to 19:1 are selected; 2) Mix the polyethylene resin raw material, the toughening agent and antioxidant prepared in step 1) evenly; 3) The mixture from step 2) is melt-extruded and granulated using a twin-screw extruder to obtain a modified polyethylene composite material.

[0011] The toughening agent of this invention has a melting point above the melt extrusion processing temperature; its length in the x, y, and z directions of three-dimensional space does not exceed 200 μm. Further, the toughening agent is one or more of the following: sorbitol nucleating agents, aliphatic carboxylic acid metal compounds, aromatic carboxylic acid metal compounds, organophosphates, lignin acids and their derivatives, metals, non-metallic solid oxides, and non-metallic elements. Preferably, the toughening agent is a sorbitol nucleating agent, such as one or more of 1,3-2,4-dimethylbenzylsorbitol, 1,3-2,4-diethylbenzylsorbitol, and di(3,4-dimethyldibenzyl)sorbitol.

[0012] When sorbitol-based nucleating agents are selected as toughening additives, this invention also provides several methods to obtain toughening additives with the desired aspect ratio, thereby matching polyethylene resin raw materials of corresponding densities. These methods include, but are not limited to, time-controlled recrystallization, solvent polarity adjustment, and physical grinding adjustment. Specifically, the time-controlled recrystallization method obtains the toughening additive with the desired aspect ratio by controlling the recrystallization time; the solvent polarity adjustment method obtains the toughening additive with the desired aspect ratio by selecting a solvent of suitable polarity and crystallizing it; and the physical grinding adjustment method obtains the toughening additive with the desired aspect ratio by controlling the grinding time.

[0013] According to a specific embodiment of the present invention, the specific implementation method for preparing toughening agents with different target aspect ratios can be as follows: (1) Time-controlled recrystallization method: Sorbitol nucleating agent raw materials are dissolved in N,N-dimethylformamide solvent and recrystallized at 80-100℃. The hot solution is filtered through a preheated funnel to remove insoluble impurities while hot. The filtrate is slowly cooled to 20-25℃ at a cooling rate of 1-2℃ / hour, and then allowed to stand at 0-5℃ for 12, 24, and 48 hours to obtain crystals with aspect ratios of 1-19:1, 20-49:1, and 50-200:1, respectively. The crystals are separated by vacuum filtration, washed 2-3 times with cold solvent (0-5℃), and then dried in a vacuum environment at 60℃ for 4-6 hours to obtain sorbitol nucleating agents with different aspect ratios. (2) Solvent polarity adjustment method: Sorbitol nucleating agent raw materials are dissolved in high polarity solvents (such as N,N-dimethylformamide, methanol), medium polarity solvents (such as ethanol, acetone), and low polarity solvents (such as cyclohexane, toluene).

[0014] Taking a highly polar solvent as an example, the preferred highly polar solvent is N,N-dimethylformamide. Sorbitol nucleating agent raw materials are added to N,N-dimethylformamide at a mass ratio of 1:8 to 1:10 and dissolved at 60-70°C for 1-1.5 hours until completely dissolved. The solution is cooled to 50°C, and 0.5-1% (by mass) of sorbitol nucleating agent seed crystals are added, with stirring continued for 30 minutes. The solution is cooled to 25°C at a rate of 1°C / hour, then to 15°C at a rate of 0.5°C / hour, and maintained at this temperature for 4-6 hours. Crystals are collected by centrifugation (4000 rpm, 15 minutes), washed twice with a small amount of cold N,N-dimethylformamide, and then washed three times with methanol to remove residual N,N-dimethylformamide. The crystals are dried in a vacuum environment at 60°C for 8-10 hours to prepare sorbitol nucleating agents with an aspect ratio of 50-200:1.

[0015] Taking a moderately polar solvent as an example, ethanol is preferred. Sorbitol nucleating agent raw materials are added to ethanol at a mass ratio of 1:8 to 1:10 and dissolved at 60-70°C for 1-1.5 hours until completely dissolved. The solution is cooled to 50°C, and 0.5-1% (by mass) of sorbitol nucleating agent seed crystals are added, with stirring continued for 30 minutes. The solution is cooled to 25°C at a rate of 1°C / hour, then to 15°C at a rate of 0.5°C / hour, and maintained at this temperature for 4-6 hours. Crystals are collected by centrifugation (4000 rpm, 15 minutes), washed twice with a small amount of cold ethanol, and then washed three times with methanol to remove residual ethanol. The crystals are dried in a vacuum environment at 60°C for 8-10 hours to prepare sorbitol nucleating agents with an aspect ratio of 20-49:1.

[0016] Taking a low-polarity solvent as an example, toluene is preferred. Sorbitol nucleating agent raw materials are added to toluene at a mass ratio of 1:8 to 1:10 and dissolved at 60-70°C for 1-1.5 hours until completely dissolved. The solution is cooled to 50°C, and 0.5-1% (by mass) of sorbitol nucleating agent seed crystals are added, with stirring continued for 30 minutes. The solution is cooled to 25°C at a rate of 1°C / hour, then to 15°C at a rate of 0.5°C / hour, and maintained at this temperature for 4-6 hours. Crystals are collected by centrifugation (4000 rpm, 15 minutes), washed twice with a small amount of cold toluene, and then washed three times with methanol to remove residual toluene. The crystals are dried in a vacuum environment at 60°C for 8-10 hours to prepare sorbitol nucleating agents with an aspect ratio of 1-19:1. (3) Physical grinding adjustment method: The raw materials of sorbitol nucleating agent are put into a ball mill and ground for 0-9min, 10-29min and 30-60min respectively to obtain sorbitol nucleating agents with aspect ratios of 50~200:1, 20~49:1 and 1~19:1.

[0017] According to a preferred embodiment of the present invention, the weight ratio of each component during mixing in step 2) is as follows: 98.5~99.7 wt% polyethylene resin raw material, 0.2~1.0 wt% toughening agent, and 0.1~0.5 wt% antioxidant. The antioxidant includes a first antioxidant and a second antioxidant, with a weight ratio of 0.5-2:1, preferably 1:1.

[0018] According to a preferred embodiment of the present invention, the temperature of the melt extrusion granulation is 170-230°C and the rotation speed is 50-300 rpm.

[0019] The present invention further provides a modified polyethylene composite material prepared by the aforementioned method. During the molding process, the molecular chains of the polyethylene resin raw material and the appropriate aspect ratio toughening agent synergistically form a tandem crystal structure in the modified polyethylene composite material, which can increase the crystallinity of the modified polyethylene composite material by 5-10% and improve its toughness by 20-300%.

[0020] The beneficial effects of the present invention through the above technical solution are as follows: (1) This invention has discovered the matching mechanism between the aspect ratio of the reinforcing and toughening additive and the molecular chains of polyethylene with different densities. Based on the matching mechanism, a polyethylene melt extrusion molding method is proposed. This method is simple to operate, has a wide range of applications, and all components are commercially available large-scale products with wide availability and low raw material costs.

[0021] (2) The toughening additives corresponding to the aspect ratio provided by the present invention, combined with the injection molding process of strong flow field, can change the crystal morphology of polymers of corresponding density, improve the crystallization rate and crystallinity of polymers, and the special shish-kebab structure enables the material to disperse stress when subjected to external force, avoid the formation of stress concentration points, improve the toughness of polyethylene composite materials, and make the obtained polyethylene material have excellent impact resistance / tensile resistance.

[0022] (3) The modified polyethylene composite material prepared by the method provided in this invention can improve its toughness by 20-300%. Detailed Implementation

[0023] 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.

[0024] It should be noted that this invention does not specifically limit the type of toughening agent. The toughening agent only needs to meet the set aspect ratio, a melting point above the melt extrusion processing temperature, and a length not exceeding 200 μm in the x, y, and z directions of three-dimensional space to meet the application requirements of this invention. The toughening agent can be an organic or inorganic material, typically, but not limited to, one or more of sorbitol nucleating agents, aliphatic carboxylic acid metal compounds, aromatic carboxylic acid metal compounds, organophosphates, lignin and its derivatives, metals, non-metallic solid oxides, and non-metallic elements. In the embodiments of this invention, sorbitol nucleating agents are used as an example to verify the technical effects of this invention; however, the above selection is merely exemplary and should not constitute a limitation on the selection of toughening agents in this invention.

[0025] The sorbitol nucleating agent in the examples can be one or more of 1,3-2,4-dimethylbenzylsorbitol, 1,3-2,4-diethylbenzylsorbitol, and di(3,4-dimethyldibenzylidene)sorbitol. The sorbitol nucleating agent is a non-toxic, tasteless, and odorless organic polymer crystalline powder. Scanning electron microscopy shows that the aspect ratio of the primary crystals is 50-200:1. The aspect ratio can be controlled by methods such as time-controlled recrystallization, solvent polarity adjustment, and physical grinding. Taking grinding as an example: putting the primary sorbitol nucleating agent into a ball mill and grinding for 10 min and 30 min can yield sorbitol nucleating agents with aspect ratios of 20-49:1 and 1-19:1.

[0026] According to the present invention, the application of toughening and reinforcing additives in polyethylene via melt extrusion molding is a matching mechanism. Specifically, the sorbitol-based nucleating agent with an aspect ratio of 50 to 200:1 is suitable for applications with densities of 0.940 to 0.960 g / cm³. 3 The polyethylene is toughened; the sorbitol-based nucleating agent with an aspect ratio of 20~49:1 is suitable for toughening polyethylene with a density greater than 0.920 g / cm³. 3 But less than 0.940 g / cm³ 3 The polyethylene is toughened; the sorbitol-based nucleating agent with an aspect ratio of 1 to 19:1 is suitable for densities of 0.860 to 0.920 g / cm³. 3 The polyethylene is toughened.

[0027] According to the present invention, HDPE is high-density polyethylene, a non-toxic, odorless, and tasteless polymer. In this invention, the HDPE has a melt index of 0.5-20 g / 10 min at 190°C and a density of 0.940-0.960 g / cm³. 3 The molecular weight distribution shows a low molecular weight content ≤ 5.0%; more preferably, a low molecular weight content ≤ 0.2%. According to the present invention, MDPE is medium-density polyethylene. In this invention, the MDPE has a melt index of 0.5-10 g / 10 min at 190°C and a density of 0.920-0.940 g / cm³. 3 ; According to the present invention, LDPE is low-density polyethylene. In this invention, the LDPE has a melt index of 0.5-10 g / 10 min at 190°C and a density of 0.860-0.920 g / cm³. 3 ; According to the present invention, based on the total weight of the modified polyethylene composite material, the weight ratio of the content of the polyethylene, the sorbitol nucleating agent, and the composite antioxidant is (98.5~99.7):(0.2~1.0):(0.1~0.5).

[0028] According to the present invention, the composite antioxidant comprises a first antioxidant and a second antioxidant, wherein the weight ratio of the content of the first antioxidant to the content of the second antioxidant is 1:1.

[0029] According to the present invention, the antioxidant is not specifically limited, as long as it is applicable to most PE and UHMWPE. In the present invention, preferably, the antioxidant can be selected from one or more of antioxidant 264, antioxidant 1010, antioxidant 1024, antioxidant 1076, antioxidant B225 and antioxidant B215.

[0030] As mentioned above, the present invention provides a polyethylene melt extrusion molding method based on toughening additives, comprising the following steps: (1) Select a toughening agent with an appropriate aspect ratio based on the density of the polyethylene resin raw material; wherein the density is 0.940~0.960 g / cm³. 3 For the polyethylene resin raw material, toughening additives with an aspect ratio of 50~200:1 are selected; the density is greater than 0.920 g / cm³. 3 But less than 0.940 g / cm³ 3 For the polyethylene resin raw material, toughening additives with an aspect ratio of 20~49:1 are selected; the density is 0.860~0.920 g / cm³. 3 For polyethylene resin raw materials, toughening additives with an aspect ratio of 1 to 19:1 are selected; (2) Mix 98.5 to 99.7 parts by weight of polyethylene, 0.2 to 1.0 parts by weight of sorbitol nucleating agent with an appropriate aspect ratio, and 0.1 to 0.5 parts by weight of antioxidant evenly; (3) The mixture in step (2) is melt-extruded and granulated in a mixer with the screw speed controlled at 50~200 rpm and the temperature controlled at 170~230℃ to obtain toughened modified polyethylene masterbatch.

[0031] According to the present invention, the granulation is carried out by melt extrusion granulation equipment. In the present invention, a twin-screw extruder can be used for melt extrusion granulation.

[0032] Characterization methods for the mechanical properties of modified polyethylene composites: (1) Density: determined according to GB / 1033 1986 method.

[0033] (2) Impact strength: determined according to GB / T 1843 2008, wherein the impact specimen is formed by injection molding.

[0034] (3) Tensile strength: determined according to GB / T 1040.1 2018, wherein the tensile specimen is formed by injection molding.

[0035] According to the present invention, the injection molding can be performed using a micro-sample injection molding machine. The injection molding process includes: feeding the toughened modified polyethylene masterbatch into an injection molding machine and performing injection molding. The injection molding process conditions are: injection temperature of 170~190℃, mold preheating temperature of 40~60℃, injection pressure of 100~550 bar, mold holding pressure of 50~250 bar, and holding time of 5~10 s. Example

[0036] This embodiment illustrates the preparation of modified polyethylene composite materials using the compositions and preparation methods of the present invention.

[0037] Weigh 34.65g of HDPE1 (density 0.960g / cm³) at room temperature. 3 0.175g of sorbitol nucleating agent with an aspect ratio of 50:1 and 0.175g of composite antioxidant (antioxidant 1010: antioxidant 168 = 1:1) were mixed evenly. Then, the mixture was melt-mixed for 5 minutes in a twin-screw extruder at 170℃ and 50 rpm. After that, the mixture was manually pelletized to obtain masterbatch S1. Masterbatch S1 was then fed into a micro-injection molding machine for injection molding.

[0038] During injection molding, the mold preheating temperature is 60℃, the injection hopper temperature is 190℃, the injection pressure is 550 bar, the mold holding pressure is 250 bar, and the holding time is 5 seconds. Example

[0039] This embodiment illustrates the preparation of modified polyethylene composite materials using the compositions and preparation methods of the present invention.

[0040] Weigh 34.65g of HDPE2 (density 0.955g / cm³) at room temperature. 3 0.175g of sorbitol nucleating agent with an aspect ratio of 50:1 and 0.175g of composite antioxidant (antioxidant 1010: antioxidant 168 = 1:1) were mixed evenly. Then, the mixture was melt-mixed in an internal mixer at 170℃ and 50 rpm for 5 minutes. After that, the mixture was manually granulated to obtain masterbatch S2. Masterbatch S2 was then fed into a micro-injection molding machine for injection molding.

[0041] During injection molding, the mold preheating temperature is 60℃, the injection hopper temperature is 190℃, the injection pressure is 550 bar, the mold holding pressure is 250 bar, and the holding time is 5 seconds. Example

[0042] This embodiment illustrates the preparation of modified polyethylene composite materials using the compositions and preparation methods of the present invention.

[0043] Weigh 34.65g of MDPE1 (density 0.934g / cm³) at room temperature. 3 0.175g of sorbitol nucleating agent with an aspect ratio of 20:1 and 0.175g of composite antioxidant (antioxidant 1010: antioxidant 168 = 1:1) were mixed evenly. Then, the mixture was melt-mixed in an internal mixer at 170℃ and 50 rpm for 5 minutes. After that, the mixture was manually granulated to obtain masterbatch S3. Masterbatch S3 was then fed into a micro-injection molding machine for injection molding.

[0044] During injection molding, the mold preheating temperature is 60℃, the injection hopper temperature is 190℃, the injection pressure is 550 bar, the mold holding pressure is 250 bar, and the holding time is 5 seconds. Example

[0045] This embodiment illustrates the preparation of modified polyethylene composite materials using the compositions and preparation methods of the present invention.

[0046] Weigh 34.65g of MDPE2 (density 0.921g / cm³) at room temperature. 30.175g of sorbitol nucleating agent with an aspect ratio of 20:1 and 0.175g of composite antioxidant (antioxidant 1010: antioxidant 168 = 1:1) were mixed evenly. Then, the mixture was melt-mixed in an internal mixer at 170℃ and 50 rpm for 5 minutes. After that, the mixture was manually granulated to obtain masterbatch S4. Masterbatch S4 was then fed into a micro-injection molding machine for injection molding.

[0047] During injection molding, the mold preheating temperature is 60℃, the injection hopper temperature is 190℃, the injection pressure is 550 bar, the mold holding pressure is 250 bar, and the holding time is 5 seconds. Example

[0048] This embodiment illustrates the preparation of modified polyethylene composite materials using the compositions and preparation methods of the present invention.

[0049] Weigh 34.65g of LDPE1 (density 0.902g / cm³) at room temperature. 3 0.175g of sorbitol nucleating agent with an aspect ratio of 10:1 and 0.175g of composite antioxidant (antioxidant 1010: antioxidant 168 = 1:1) were mixed evenly. Then, the mixture was melt-mixed in an internal mixer at 170℃ and 80 rpm for 5 minutes. After that, the mixture was manually granulated to obtain masterbatch S5. Masterbatch S5 was then fed into a micro-injection molding machine for injection molding.

[0050] During injection molding, the mold preheating temperature is 40℃, the injection hopper temperature is 190℃, the injection pressure is 350 bar, the mold holding pressure is 150 bar, and the holding time is 5 seconds. Example

[0051] This embodiment illustrates the preparation of modified polyethylene composite materials using the compositions and preparation methods of the present invention.

[0052] Weigh 34.65g of LDPE2 (density 0.868g / cm³) at room temperature. 3 0.175g of sorbitol nucleating agent with an aspect ratio of 10:1 and 0.175g of composite antioxidant (antioxidant 1010: antioxidant 168 = 1:1) were mixed evenly. Then, the mixture was melt-mixed in an internal mixer at 170℃ and 100 rpm for 5 minutes. After that, the mixture was manually pelletized to obtain masterbatch S6. Masterbatch S6 was then fed into a micro-injection molding machine for injection molding.

[0053] During injection molding, the mold preheating temperature is 40℃, the injection hopper temperature is 190℃, the injection pressure is 200 bar, the mold holding pressure is 100 bar, and the holding time is 5 seconds.

[0054] Comparative Example 1 The modified polyethylene composite material was prepared using the same method as in Example 1, except that no sorbitol nucleating agent was added during the preparation steps.

[0055] The result was the raw material DS1-1.

[0056] Comparative Example 2 The modified polyethylene composite material was prepared using the same method as in Example 1, except that a sorbitol nucleating agent with an aspect ratio of 10:1 was added during the preparation step.

[0057] The result was the formation of the complex DS1-2.

[0058] Comparative Example 3 The modified polyethylene composite material was prepared using the same method as in Example 2, except that no sorbitol nucleating agent was added during the preparation steps.

[0059] The result was the raw material DS2-1.

[0060] Comparative Example 4 The modified polyethylene composite material was prepared using the same method as in Example 2, except that a sorbitol nucleating agent with an aspect ratio of 10:1 was added during the preparation step.

[0061] The result was the formation of the complex DS2-2.

[0062] Comparative Example 5 The modified polyethylene composite material was prepared using the same method as in Example 3, except that no sorbitol nucleating agent was added during the preparation steps.

[0063] The resulting masterbatch was DS3-1.

[0064] Comparative Example 6 The modified polyethylene composite material was prepared using the same method as in Example 3, except that a sorbitol nucleating agent with an aspect ratio of 50:1 was added during the preparation step.

[0065] The result was the formation of the complex DS3-2.

[0066] Comparative Example 7 The modified polyethylene composite material was prepared using the same method as in Example 4, except that no sorbitol nucleating agent was added during the preparation steps.

[0067] The resulting masterbatch was DS4-1.

[0068] Comparative Example 8 The modified polyethylene composite material was prepared using the same method as in Example 4, except that a sorbitol nucleating agent with an aspect ratio of 50:1 was added during the preparation step.

[0069] The result was the formation of the complex DS4-2.

[0070] Comparative Example 9 The modified polyethylene composite material was prepared using the same method as in Example 5, except that no sorbitol nucleating agent was added during the preparation steps.

[0071] The resulting masterbatch was DS5-1.

[0072] Comparative Example 10 The modified polyethylene composite material was prepared using the same method as in Example 5, except that a sorbitol nucleating agent with an aspect ratio of 20:1 was added during the preparation step.

[0073] The result was the formation of the complex DS5-2.

[0074] Comparative Example 11 The modified polyethylene composite material was prepared using the same method as in Example 6, except that no sorbitol nucleating agent was added during the preparation steps.

[0075] The resulting masterbatch was DS6-1.

[0076] Comparative Example 12 The modified polyethylene composite material was prepared using the same method as in Example 6, except that a sorbitol-based nucleating agent with an aspect ratio of 20:1 was added during the preparation step.

[0077] The result was the formation of the complex DS6-2.

[0078] Application examples The modified polyethylene composite materials prepared in the embodiments and comparative examples of this invention were processed by injection molding to obtain mechanical property test strips for mechanical property evaluation. Due to the material properties of Examples S3-S6, the impact strips could not be broken by impact, therefore their impact strength could not be accurately determined. Tensile toughness tests were used instead to illustrate the tensile properties of the compositions. The test results are shown in Table 1 (tensile strength test), Table 2 (tensile toughness test), and Table 3 (simply supported beam impact strength test).

[0079] Table 1 Table 2 As can be seen from the results in Tables 1 and 2, the high-toughness polyethylene materials prepared using Examples 1-6 of the present invention possess excellent tensile properties.

[0080] Table 3

[0081] As can be seen from the results in Table 3, the modified polyethylene composite materials prepared using Examples 1-2 of the present invention have excellent impact resistance.

[0082] The preferred embodiments of the present invention have been described in detail above; 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.

Claims

1. A method for melt extrusion molding of polyethylene based on toughening additives, characterized in that, Includes the following steps: 1) Select a toughening agent with an appropriate aspect ratio based on the density of the polyethylene resin raw material; wherein the density is 0.940~0.960 g / cm³. 3 For the polyethylene resin raw material, toughening additives with an aspect ratio of 50~200:1 are selected; the density is less than 0.940 g / cm³. 3 And greater than 0.920 g / cm 3 For the polyethylene resin raw material, toughening additives with an aspect ratio of 20~49:1 are selected; the density is 0.860~0.920 g / cm³. 3 For polyethylene resin raw materials, toughening additives with an aspect ratio of 1 to 19:1 are selected; 2) Mix the polyethylene resin raw material, the toughening agent and antioxidant prepared in step 1) evenly; 3) The mixture from step 2) is melt-extruded and granulated using a twin-screw extruder to obtain a modified polyethylene composite material.

2. The polyethylene melt extrusion molding method according to claim 1, characterized in that, The toughening agent has a melting point above the melt extrusion processing temperature; its length in the x, y, and z directions in three-dimensional space does not exceed 200 μm.

3. The polyethylene melt extrusion molding method according to claim 1, characterized in that, The toughening agent is one or more of the following: sorbitol nucleating agents, aliphatic carboxylic acid metal compounds, aromatic carboxylic acid metal compounds, organophosphates, lignin and its derivatives, metals, non-metallic solid oxides, and non-metallic elements.

4. The polyethylene melt extrusion molding method according to claim 3, characterized in that, The toughening agent is preferably a sorbitol-based nucleating agent, including one or more of 1,3-2,4-dimethylbenzylsorbitol, 1,3-2,4-diethylbenzylsorbitol, and di(3,4-dimethyldibenzylidene)sorbitol.

5. The polyethylene melt extrusion molding method according to claim 4, characterized in that, When sorbitol-based nucleating agents are selected as toughening aids, at least one of the following methods is further employed to obtain the toughening aid with the desired aspect ratio: (1) Time-controlled recrystallization method: Sorbitol nucleating agent raw material is dissolved in solvent and recrystallized at 80-100℃. The hot solution is filtered through a preheated funnel. The filtrate is slowly cooled to 20-25℃ at a cooling rate of 1-2℃ / hour. Then the filtrate is left to stand at 0-5℃ for different times. Sorbitol nucleating agent crystals with different aspect ratios are obtained by different standing times. (2) Solvent polarity adjustment method: Dissolve the sorbitol nucleating agent raw materials in solvents of the required polarity; add sorbitol nucleating agent seed crystals, cool and crystallize the solution, and obtain the toughening agent with the required aspect ratio according to the selection of solvent polarity; (3) Physical grinding adjustment method: The raw materials of sorbitol nucleating agent are put into a ball mill and the grinding time is adjusted to obtain the sorbitol nucleating agent with the required length-to-diameter ratio.

6. The polyethylene melt extrusion molding method according to claim 1, characterized in that, Step 2) The weight ratio of each component during mixing is as follows: polyethylene resin raw material 98.5~99.7 wt%, toughening agent 0.2~1.0 wt%, antioxidant 0.1~0.5 wt%.

7. The polyethylene melt extrusion molding method according to claim 6, characterized in that, The antioxidant is a composite antioxidant, comprising a first antioxidant and a second antioxidant, with a weight ratio of 0.5-2:1; The first antioxidant and the second antioxidant are selected from one or more of antioxidant 264, antioxidant 1010, antioxidant 1024, antioxidant 1076, antioxidant 168 and antioxidant B215, respectively.

8. The polyethylene melt extrusion molding method according to claim 1, characterized in that, The temperature of the melt extrusion granulation is 170-230℃, and the rotation speed is 50-300 rpm.

9. A modified polyethylene composite material prepared by the method according to any one of claims 1-8.

10. The modified polyethylene composite material according to claim 9, characterized in that, The modified polyethylene composite material has a 5-10% increase in crystallinity and a 20-300% increase in toughness compared to the unmodified polyethylene resin raw material.

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