Modifier with core-shell structure and application of modifier in dry recovery of wet diaphragm of lithium battery

Abstract

The invention provides a modifier with a core-shell structure and application of the modifier in dry recovery of a wet diaphragm of a lithium battery. The preparation method of the modified material for the dry-method recycled lithium battery wet-method diaphragm comprises the following steps: carrying out dry-method recycling process pretreatment on a lithium battery wet-method diaphragm waste material; a novel core-shell structure toughening and reinforcing modifier is prepared, and the modifier is prepared by melt blending of maleic anhydride and styrene grafted polyolefin elastomer as a soft shell and co-polypropylene as a hard core. And carrying out melt blending granulation on 85-87 parts of the pretreated reclaimed material, 10 parts of homo-polypropylene, 3-5 parts of a core-shell modifier and an auxiliary agent to obtain the modified polypropylene material. Through the innovative diaphragm waste dry pretreatment process and the core-shell structure modifier, the problems of high white oil content, poor fluidity and difficulty in balancing rigidity and toughness in the UHMWPE-based reclaimed material are effectively solved, and the low-value industrial waste is converted into a high-value-added modified material with high impact toughness, high tensile strength and good processing performance.

Description

Technical Field

[0001] This invention belongs to the field of wet-process separator recycling and polymer material modification technology in lithium batteries, specifically involving a modifier with a "core-shell" structure and its application in the dry recycling of wet-process separators in lithium batteries. Background Technology

[0002] As a core energy storage component in modern electronic devices and new energy vehicles, lithium-ion batteries are experiencing continuous market demand growth. The lithium battery separator is one of the four key materials used in lithium batteries, and its performance directly affects the battery's capacity, cycle life, and safety.

[0003] The manufacturing process of lithium-ion battery separators directly determines their microscopic pore structure and macroscopic material properties. Currently, the commercial production of lithium-ion battery separators mainly adopts two mainstream technical routes: dry process and wet process. At the same time, in order to meet specific performance requirements, modification processes such as coating have also been developed, further expanding the application scenarios of separators. Among them, the dry process, also known as melt stretching, is a process that forms a microporous structure on a polymer film through physical means. The core principle is to utilize the difference between the crystalline and amorphous regions of the polymer (mainly polypropylene PP), and stretch it at a specific temperature to deform the amorphous regions, thereby forming narrow slit-like micropores between the crystalline regions. The wet process, also known as thermally induced phase separation (TIPS), is currently the mainstream technology for lithium-ion battery separator manufacturing, accounting for 85-90% of the market. Its core process involves uniformly mixing polyolefins (mainly a blend of ultra-high molecular weight polyethylene (UHMWPE) and high-density polyethylene (HDPE)) with a pore-forming agent, white oil (paraffin oil), at high temperatures. This mixture is then extruded and stretched to form a microporous structure. The white oil is then extracted and removed using an extractant, leaving a uniformly distributed three-dimensional network of microporous structures, resulting in a wet-process separator with excellent performance. The main components of the finished wet-process separator are polyolefin materials such as UHMWPE and HDPE. UHMWPE, with its long molecular chains and high entanglement, gives the separator excellent mechanical strength and puncture resistance, ensuring that it is not easily damaged during battery charge-discharge cycles, thus broadening its application scenarios.

[0004] In the current wet-process separator production technology, white oil, as a pore-forming agent, directly affects the micropore quality and production cost of the separator through its addition, efficient extraction, and recycling, making it a core control point in the wet process. However, in the actual production process of wet-process separators, a large amount of waste is inevitably generated in each stage, from extrusion molding, biaxial stretching, white oil extraction to final slitting into finished products, as well as in the separators from the dismantling and recycling of used batteries. This includes scraps (offcuts) generated during slitting, defective products, and die head material generated during start-up and shutdown. The white oil content of these separator wastes varies greatly: defective separators that have not undergone extraction have an oil content as high as 60-70% because the white oil has not been removed; while scraps generated after extraction and slitting, although most of the white oil has been recovered, still retain some. The residual white oil poses several challenges to the subsequent treatment of diaphragm waste. On the one hand, the white oil makes the waste sticky and slippery, easily adhering to the inner wall of the equipment during crushing, leading to decreased crushing efficiency and increased equipment wear. At the same time, the sticky material is prone to clogging pipes during transportation, increasing production energy consumption. On the other hand, the residual white oil directly affects the purity and mechanical properties of the recycled granules. Especially during melt granulation, the white oil is easily volatilized when heated, producing small molecules that not only cause bubbles inside the granules but also easily release harmful gases, causing environmental pollution and safety risks.

[0005] Currently, the industry's methods for treating oily waste membranes all have certain limitations. Physical methods such as crushing and extrusion, and high-speed centrifugation, generally suffer from poor white oil separation. Solvent extraction, while offering higher separation efficiency, faces challenges related to organic solvent evaporation pollution and high recycling costs. Water washing processes consume large amounts of water, and subsequent oily wastewater treatment is difficult and costly. Therefore, how to achieve high-value, high-performance, and environmentally friendly recycling of high-value-added polyolefin materials from lithium-ion battery wet-process separator waste, while properly treating the paraffin oil within, remains a critical technological bottleneck that urgently needs to be overcome in the field of polymer materials.

[0006] Meanwhile, to improve the performance of recycled polyolefin materials, existing technologies typically employ blending modification with the addition of compatibilizers. However, for membrane recycled material systems containing a large amount of UHMWPE, conventional compatibilizers struggle to simultaneously achieve toughening effects, system processing flowability, and material rigidity, resulting in unbalanced product performance that fails to meet the demands of high-performance applications.

[0007] Therefore, developing an innovative recycling and modification technology specifically for wet-process lithium battery separator waste, especially a dry recycling pretreatment technology and designing a novel compatibilizer that can simultaneously achieve toughening, enhancement, and improved compatibility, is of great theoretical significance and commercial value for improving resource utilization efficiency and promoting the development of a circular economy. Summary of the Invention

[0008] This invention aims to solve the problems of low recycling rate, poor performance of recycled products, and low added value of wet-process lithium battery separator waste in existing technologies. Specifically:

[0009] (1) In view of the contradiction that conventional compatibilizers cannot effectively balance the toughness, rigidity and processability of recycled materials, the present invention provides a novel toughening and reinforcing compatibilizer with special structure and excellent performance and its preparation method.

[0010] (2) In view of the problem that UHMWPE / HDPE based membrane waste has high white oil content, poor melt flowability and is difficult to process directly, this invention provides an efficient dry recycling pretreatment process and a subsequent melt blending modification method.

[0011] (3) This invention uses waste from wet-process lithium battery separators as raw materials to prepare high-performance recycled modified materials with excellent mechanical and processing properties. In many mechanical properties, it even surpasses the level of some virgin modified plastics, achieving a perfect balance of toughness, rigidity and processing fluidity, making it widely applicable in many technical fields.

[0012] This invention provides a toughening and reinforcing modifier with a "core-shell" structure, comprising the following components by weight: 65-75 parts of maleic anhydride-styrene co-grafted polyolefin elastomer POE-g-MAH(St) and 25-35 parts of copolymer polypropylene PPB.

[0013] The modifier exhibits a dispersed phase structure in its microstructure, with copolymer polypropylene as the "hard core" and POE-g-MAH(St) as the "soft shell".

[0014] In a preferred embodiment, the total weight of maleic anhydride-styrene co-grafted polyolefin elastomer POE-g-MAH(St) and copolymer polypropylene PPB is 100 parts.

[0015] In a preferred embodiment, the preparation method of POE-g-MAH(St) includes: mixing polyolefin elastomer (POE), maleic anhydride (MAH), styrene (St) monomer and initiator at high speed, and then performing a melt grafting reaction through a twin-screw extruder; the reactants are then cooled and granulated to obtain the final product; the total grafting rate of maleic anhydride and styrene in POE-g-MAH(St) is 1.0-1.2%;

[0016] Preferably, in the preparation method of POE-g-MAH(St), by weight, it includes 95-105 parts of polyolefin elastomer, 1.0-3.0 parts of maleic anhydride, 0.9-2.7 parts of styrene monomer, and 0.1-0.5 parts of initiator; more preferably, the initiator includes dicumyl peroxide (DCP).

[0017] Preferably, the high-speed mixing speed is 1000-2000 rpm, the mixing temperature is below 60℃, and the mixing time is 5-15 min;

[0018] Preferably, the extrusion conditions include: the extruder is a twin-screw extruder with a length-to-diameter ratio of 48:1; the temperatures of each zone of the extruder are 150℃, 170℃, 190℃, 200℃, 200℃, 195℃, and 190℃; and the screw speed is 250-350 rpm.

[0019] Preferably, the prepared POE-g-MAH(St) is a cylindrical particle with a length of 2-4 mm.

[0020] In a preferred embodiment, the melt mass flow rate of the copolymer polypropylene PPB is 10-15 g / 10 min at 230°C and 2.16 kg, and the ethylene content is greater than 7.5%.

[0021] This invention designs an extrusion process for POE-g-MAH(St) and copolymerized PP. Based on the principle of melt-state chemical reaction, high-flowability copolymerized polypropylene (PPB) rich in ethylene end groups enters the POE phase of the high-viscosity POE-g-MAH(St) component. This achieves POE encapsulation of PPB while improving the flowability of the POE-g-MAH(St) / copolymerized PP product, acting as a "bridge" for subsequent blending of incompatible high-viscosity wet-process membrane recycled materials with high-flowability homopolymer polypropylene (PPH). The resulting toughening and reinforcing modifier has a "core-shell" structure of "elastic shell-rigid core," exhibiting excellent toughening effects while ensuring material rigidity and processing flowability. This solves the technical pain point of conventional compatibilizers, which struggle to balance material toughness and rigidity.

[0022] This invention also provides a method for preparing a toughening and reinforcing modifier with a "core-shell" structure, comprising the following steps:

[0023] POE-g-MAH(St) and copolymer polypropylene PPB are mixed evenly. The resulting mixture is melt-blended in a parallel co-rotating twin-screw extruder with an aspect ratio of (44-48):1. After water cooling, the mixture is drawn into strands and granulated to obtain a toughening and reinforcing modifier with a "core-shell" structure.

[0024] In a preferred embodiment, the mixing speed is 500-800 rpm, the mixing temperature is 70-90℃, and the mixing time is 1-10 min.

[0025] In a preferred embodiment, the extrusion conditions include: the extruder temperature is set to 170°C, 185°C, 200°C, 210°C, 210°C, 200°C; and the screw speed is set to 350-450 rpm.

[0026] This invention also provides a method for dry recycling of wet-process separators from lithium batteries, comprising the following steps:

[0027] Dry recycling pretreatment: Waste from the wet process of lithium battery separator production is processed through a dry process, including hydraulic guillotine cutting, spiral extrusion degreasing, multi-stage crushing, functional granulation, and vibrating screen sorting, to obtain dry process pretreatment recycled material;

[0028] Melt blending: The obtained dry process pretreated recycled material, homopolymer polypropylene (PPH), the toughening and reinforcing modifier with the "core-shell" structure, and processing aids are mixed at high speed and then melt-extruded and granulated through a twin-screw extruder to obtain high-performance recycled modified material.

[0029] In a preferred embodiment, in the dry recycling pretreatment step, the waste from the lithium battery wet separator production includes one or more of the following: scraps, offcuts, defective products, and machine head materials from the lithium battery wet separator production process.

[0030] In a preferred embodiment, during the dry recycling pretreatment step, the material length after being cut by the hydraulic guillotine is 20-30 cm. Preferably, bundled or block-shaped mixed waste is cut using a gantry hydraulic guillotine with a pressure of 8-12 MPa and a cutting speed of 0.5-5.0 m / min. Cutting it into 20-30 cm lengths facilitates the stable operation of subsequent conveying equipment and provides relatively uniform feed to the screw extrusion deoiler, preventing material blockage or uneven processing efficiency.

[0031] In a preferred embodiment, the screw extrusion deoiling step in the dry recycling pretreatment process specifically includes: the screw speed of the screw extruder is 30-50 rpm, and the barrel temperature is segmented as follows: 60-80℃ for the feeding section, 90-110℃ for the compression section, and 80-95℃ for the discharge section. The mechanical pressure of the screw extrusion forces the white oil out of the pores within the material. Simultaneously, the appropriate barrel temperature reduces the viscosity of the white oil, improving deoiling efficiency. Furthermore, the temperature is controlled below 110℃ to prevent thermo-oxidative aging of the polyolefin material. The extruded white oil has high purity and, after simple filtration and sedimentation, can be recycled as an auxiliary raw material for wet-process diaphragm production, achieving resource recovery. After this step, the oil content of the material is reduced from the initial 10-70% to below 5%. The remaining white oil is deeply embedded or adsorbed within the microporous structure of the polymer material and requires further processing.

[0032] In a preferred embodiment, the multi-stage pulverization process in the dry recycling pretreatment step includes coarse pulverization and fine pulverization until the material particle size is below 10 mm. The diaphragm material after extrusion deoiling is still in flake or block form. It is then processed into fragments smaller than 10 mm through two-stage pulverization (first coarse crushing using a low-speed, high-torque single-shaft shredder, then fine crushing in a crusher), creating conditions for subsequent uniform mixing, granulation, and extrusion granulation. Simultaneously, pulverization increases the specific surface area of ​​the material, providing a foundation for the subsequent adsorption of white oil by silica.

[0033] In a preferred embodiment, in the dry recycling pretreatment step, the functional agglomeration treatment specifically includes: conveying the pulverized material to an agglomerator, adding macroporous precipitated silica activated and modified by silane coupling agent KH-570, the amount of which is 1-5 wt% of the white oil content in the material, and stirring to agglomerate; preferably, first stirring at 500-800 rpm to 120-140°C, and then maintaining at 120-140°C and stirring at 100-200 rpm for 3-5 minutes to obtain agglomerates with a particle size of 3-5 mm;

[0034] Preferably, the preparation method of the macroporous silica modified by the silane coupling agent KH-570 includes: mixing macroporous silica with 1.5-3.0% by mass of the silane coupling agent, and activating by stirring at 100-120℃ to obtain the macroporous silica; the macroporous silica has a pore volume ≥1.8mL / g, a specific surface area of ​​200-400m² / g, and an average pore size of ≥20nm; more preferably, the silane coupling agent is silane coupling agent KH-570; the stirring activation speed is 100-500rpm, and the stirring activation time is 20-30min.

[0035] The core characteristics of macroporous silica are its high specific surface area and well-developed pore structure. Silica can effectively physically adsorb white oil remaining in the membrane fragments after extrusion, "fixing" the liquid oil onto the solid powder, thus eliminating its adverse effects in subsequent processing. However, when silica is used alone, its inorganic nature leads to poor compatibility with non-polar polyolefin matrices, causing stress concentration points during blending and granulation, severely degrading the material's mechanical properties. Therefore, this invention uses a silane coupling agent (KH-570) to modify the surface of silica, creating a "molecular bridge" between the inorganic filler (silica) and the organic matrix (PE). One end of the silane coupling agent reacts with the hydroxyl groups on the silica surface, while the organic functional groups at the other end can physically entangle or chemically bond with the polyolefin chains. During the agglomeration process, the above-mentioned design of the present invention simultaneously achieves: ① adsorption of residual oil: the silica adsorbs residual white oil that is harmful to subsequent processing; ② enhanced compatibility: the silane coupling agent binds the silica particles adsorbed with white oil to the membrane fragments, transforming them from a potential "impurity" into a "functional filler" compatible with the matrix; ③ improved material performance: the modified silica, as a reinforcing filler, effectively improves the mechanical properties and dimensional stability of the material.

[0036] In a preferred embodiment, in the dry recycling pretreatment step, the vibrating screen separation can be carried out using conventional methods known to those skilled in the art, such as setting the screen mesh size of the screening machine to 2-6mm, and using a vibration frequency of 15-20Hz to screen out granules with the required particle size, removing excessively fine dust and excessively large agglomerates, and obtaining recycled material with uniform particle size and good flowability.

[0037] In a preferred embodiment, the melt blending step comprises, by weight, 85-87 parts of the dry process pretreatment recycled material, 8-12 parts of homopolymer polypropylene PPH, 3-5 parts of the toughening and reinforcing modifier with a "core-shell" structure, and 0.5-5.0 parts of processing aid; more preferably, the total weight of the dry process pretreatment recycled material, homopolymer polypropylene PPH, and the toughening and reinforcing modifier with a "core-shell" structure is 100 parts.

[0038] In a preferred embodiment, in the melt blending step, the processing aid includes one or more of antioxidants, dispersants, and lubricants; preferably, the antioxidant includes one or more of antioxidant 1010, antioxidant 168, and antioxidant 215B; the dispersant includes one or more of stearic acid, calcium stearate, and zinc stearate; the lubricant includes polyethylene wax and / or ethylene bis-stearamide (EBS); more preferably, the mass ratio of the antioxidant, dispersant, and lubricant is (0.2-0.4):(0.3-0.7):(0-1.0).

[0039] In a preferred embodiment, in the melt blending step, the high-speed mixing speed is 800-1000 rpm, the mixing temperature is 70-90℃, and the mixing time is 1-10 min.

[0040] In a preferred embodiment, in the melt blending step, the extrusion conditions include: the extruder is a parallel co-rotating twin-screw extruder with an aspect ratio of (44-48):1; the temperatures of each zone of the extruder are 180°C, 200°C, 220°C, 230°C, 230°C, and 225°C; and the screw speed is 400-500 rpm.

[0041] The present invention also provides a high-performance recycled modified material prepared by a wet-process separator dry-process recycling method for lithium batteries. The high-performance recycled modified material has a tensile strength of up to 38.5 MPa, an elongation at break of up to 220%, a flexural modulus of up to 1350 MPa, a cantilever beam notched impact strength of up to 58 kJ / m², and a melt mass flow rate (230℃, 2.16 kg) of up to 2.5 g / 10 min.

[0042] This invention also provides the application of the aforementioned high-performance recycled modified material in the fields of automotive interior and exterior parts, electronic and electrical housings, sheet and building materials, pipes, luggage accessories, and toy housings.

[0043] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0044] 1. This invention addresses the waste materials from wet-process lithium battery separator production, including scraps, defective products, and die head materials. From pretreatment, physical degreasing, crushing, functional granulation, vibrating sieving, to blending and granulation, a completely dry process is employed. This eliminates the need for organic solvents or large amounts of water, solving the wastewater treatment problem during oily waste recycling at its source and effectively reducing environmental pressure and processing costs. Furthermore, the extracted white oil can be further recycled, resulting in economic benefits.

[0045] 2. The novel toughening and reinforcing modifier prepared in this invention has a unique "core-shell" structure. The "soft shell" (POE-g-MAH(St)) provides excellent toughening effect and forms an effective interface with trace oxide groups or surfaces in UHMWPE / HDPE recycled materials through the grafted polar groups (MAH); the "hard core" (copolymer PP) has good compatibility with the homopolymer PP in the matrix, acting as an anchor to ensure uniform and stable dispersion of the toughening phase, while maintaining the overall rigidity and strength of the material and avoiding rigidity loss due to excessive toughening.

[0046] 3. This invention scientifically proportions and blends recycled membrane material, flow-improving homopolymer PP, and a specially designed "soft shell-hard core" modifier. The resulting recycled modified material achieves or even surpasses the levels of some virgin modified plastics in key mechanical properties such as tensile strength, elongation at break, and impact strength, achieving a perfect balance of toughness, rigidity, and processing flowability. In particular, its notched impact strength can reach 58 kJ / m², and its tensile strength can be maintained at 38.5 MPa. These performance effects are difficult to achieve with known recycled materials.

[0047] 4. The dry pretreatment, melt grafting and melt blending processes used in this invention are all based on mature equipment (such as twin-screw extruders), the process parameters are precisely controlled, and it is easy to achieve large-scale and continuous production, which has strong industrial production value.

[0048] 5. This invention transforms low-value, difficult-to-process lithium battery wet-process separator waste into high-performance modified materials with excellent comprehensive mechanical properties, significantly increasing its added value and meeting the requirements of circular economy and sustainable development. The resulting recycled modified materials can be widely used in injection molding, extrusion and other molding fields to manufacture high-quality automotive parts, electrical housings, pipes and other products. Detailed Implementation

[0049] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments. However, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0050] The technical solution of this application will be described in detail below through specific embodiments:

[0051] Unless otherwise specified, the technical means used in this invention are conventional means well known to those skilled in the art. All raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. Unless otherwise specified, all reagents used in this invention are of analytical grade. In this invention, the room temperature is 25±2℃.

[0052] In this invention, the weight parts can be weight units known in the art such as µg, mg, g, kg, or multiples thereof, such as 1 / 10, 1 / 100, 10 times, 100 times, etc.

[0053] Example 1

[0054] (1) Dry recycling pretreatment: Take 100kg of scrap (offcuts) and defective products collected from the production line of a certain brand of lithium battery wet process separator (brand name: Celgard2325 similar, material is UHMWPE, HDPE and white oil). First, cut them into strips with a length of about 25cm by a gantry hydraulic guillotine. Then, use a screw extruder with a screw speed of 50rpm and the barrel temperature set in stages of 60-90-95℃ for high-efficiency screw extrusion deoiling. Then, send the deoiled dense separator waste into a crusher for coarse crushing to obtain After fragments smaller than 30mm are fed into a high-speed pulverizer for further pulverization into 10mm fragments, they are then conveyed to a pelletizer. An adsorbent with a white oil content of 3.0wt% is added based on the white oil content of the material. The mixture is stirred at 500rpm to 120℃, and then maintained at 120℃ for 5 minutes at 150rpm to granulate. Finally, the material is discharged to a vibrating screen, where a small amount of dust and large particles are separated, resulting in a pretreated recycled material with a loose density of approximately 0.4g / cm³ and a particle size of 3-5mm. The adsorbent is macroporous silica modified with silane coupling agent KH-570. The specific preparation method includes mixing macroporous silica with a pore volume of 1.8mL / g and silane coupling agent KH-570 at a mass ratio of 100:3, and then mixing at 100℃ and 500rpm for 20 minutes.

[0055] (2) Preparation of toughening and reinforcing modifiers with a "core-shell" structure:

[0056] (A) Preparation of POE-g-MAH(St)

[0057] By weight, 100 parts of polyolefin elastomer (POE, Dow Chemical), 2.0 parts of maleic anhydride (MAH), 1.8 parts of styrene (St) monomer and 0.3 parts of dicumyl peroxide (DCP) initiator were mixed in a high-speed mixer at room temperature and 1500 rpm for 5 minutes.

[0058] The uniformly mixed material was fed into a parallel co-rotating twin-screw extruder (Anhui Tengda Extrusion Intelligent Equipment Co., Ltd., CTE-50) with a length-to-diameter ratio of 48:1 via a loss-in-weight feeder. The extruder temperature settings were: 150℃, 170℃, 190℃, 200℃, 200℃, 195℃, and 190℃; the screw speed was set to 300 rpm. After the material underwent a complete melting and grafting reaction in the extruder, it was extruded into strips through the die head. After cooling by an air-cooled conveyor belt, it was pelletized into granules of POE-g-MAH(St) graft material by a pelletizer. The total grafting rate was determined to be 1.15% by titration.

[0059] (B) Preparation of toughening and reinforcing modifiers with "core-shell" structure

[0060] Weigh 70 parts by weight of the POE-g-MAH(St) particles prepared in the previous step (A) and 30 parts by weight of the copolymer polypropylene (PPB, Korean SK, B380G, MFR of 12g / 10min, ethylene content of 8.0%) particles and mix them in a high-speed mixer at 80°C and 800rpm for 2min until homogeneous.

[0061] The resulting mixture was fed into a parallel co-rotating twin-screw extruder with a length-to-diameter ratio of 44:1. The temperatures of each zone of the extruder were set to 170℃, 185℃, 200℃, 210℃, 210℃, and 200℃; the screw speed was set to 400 rpm. After the material was melt-blended in the extruder, it was extruded into strips through the die head, cooled in a water tank, and then pelletized into granules by a pelletizer to produce a novel "core-shell" structure toughening and reinforcing modifier.

[0062] Microstructure characterization: A small amount of the modifier particles were taken and a thin slice of approximately 80 nm thickness was prepared at low temperature using an ultramicrotome. The slice was stained with ruthenium tetroxide vapor for 4 hours (preferably staining the POE phase), and then observed using transmission electron microscopy (TEM). The TEM images clearly showed that there were a large number of uniformly dispersed particles in the sample, and the particles exhibited a typical "core-shell" structure: the center was an unstained, light-colored copolymer PP "core", and the outer layer was wrapped with a dark-stained POE-g-MAH(St) "shell".

[0063] (3) Preparation of high-performance recycled modified materials

[0064] Weigh 86 parts by weight of the pretreated recycled material obtained in step (1), 10 parts of homopolymer polypropylene (PPH, Korean SK, Y130, MFR 30g / 10min), 4 parts of the "core-shell" modifier prepared in step (2), 0.2 parts of antioxidant 1010 and 0.3 parts of calcium stearate lubricant, and mix them in a high-speed mixer at 80°C and 1000rpm for 2min until homogeneous.

[0065] The final mixture is fed into a parallel co-rotating twin-screw extruder with a length-to-diameter ratio of 48:1. The temperatures of each zone of the extruder are set to 180℃, 200℃, 220℃, 230℃, 230℃, and 225℃; the screw speed is set to 450 rpm. After sufficient plasticization, shearing, and dispersion, the material is directly granulated through a water ring die-cutting system to obtain the final high-performance modified material for wet-process separators of recycled lithium batteries.

[0066] Performance testing

[0067] The modified material granules obtained in Example 1 were dried at 80°C for 4 hours, then injection molded into standard test strips using an injection molding machine. Performance tests were conducted according to national standards, and the results are as follows:

[0068] Tensile strength (GB / T1040.2-2006): 38.5 MPa

[0069] Elongation at break (GB / T1040.2-2006): 220%

[0070] Flexural modulus (GB / T9341-2008): 1350 MPa

[0071] Notched impact strength of cantilever beam (GB / T1043.1-2008, 23℃): 58kJ / m²

[0072] Melt mass flow rate (MFR, 230℃, 2.16kg): 2.5g / 10min.

[0073] Test results show that the recycled modified material prepared by this invention has high strength, high toughness and good processing fluidity, and excellent comprehensive performance.

[0074] Comparative Example 1

[0075] The only difference from Example 1 is that in the formulation of step (3), 4 parts of the "core-shell" modifier prepared in step (2) are replaced with 4 parts of homopolymer polypropylene (PPH).

[0076] The formulation is as follows: 86 parts of the pretreated recycled material obtained in step (1), 14 parts of homopolymer polypropylene (PPH, Korean SK, Y130, MFR 30 g / 10 min), 0.2 parts of antioxidant 1010, and 0.3 parts of calcium stearate lubricant. The remaining steps are completely consistent with those in Example 1.

[0077] The obtained material was subjected to the same performance tests, and the results were as follows:

[0078] Tensile strength: 32.1 MPa, elongation at break: 25%, flexural modulus: 1380 MPa, notched impact strength of cantilever beam (23℃): 8.2 kJ / m² (brittle fracture).

[0079] Comparative Example 2

[0080] The only difference from Example 1 is that in the formulation of step (3), 4 parts of the "core-shell" modifier prepared in step (2) are replaced with 4 parts of conventional POE-g-MAH (grafting rate of 1.0%, no St, and not blended with PPB for granulation).

[0081] The formulation is as follows: 86 parts of the pretreated recycled material obtained in step (1), 10 parts of homopolymer polypropylene (PPH, Korean SK, Y130, MFR 30 g / 10 min), 4 parts of POE-g-MAH, 0.2 parts of antioxidant 1010, and 0.3 parts of calcium stearate lubricant. The remaining steps are completely consistent with those in Example 1.

[0082] The obtained material was subjected to the same performance tests, and the results were as follows:

[0083] Tensile strength: 34.5 MPa, elongation at break: 250%, flexural modulus: 950 MPa, notched impact strength of cantilever beam (23℃): 65 kJ / m².

[0084] Results analysis and discussion:

[0085] As can be seen from Example 1 and Comparative Example 1, without adding any compatibilizer, the recycled material has extremely poor compatibility with PPH when diluted only with PPH, resulting in a severe deterioration of the material's impact performance and making it brittle. As can be seen from Example 1 and Comparative Example 2, although the use of conventional POE-g-MAH can improve the impact toughness of the material, it leads to a significant decrease in the material's stiffness (flexural modulus) and strength (tensile strength), resulting in over-toughening.

[0086] Example 1 uses the "core-shell" structure compatibilizer of the present invention, which effectively maintains the tensile strength and flexural modulus of the material while maintaining extremely high impact toughness, thus achieving an excellent balance of rigidity and toughness.

[0087] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A toughening and reinforcing modifier with a "core-shell" structure, characterized in that, By weight, it includes the following components: 65-75 parts of maleic anhydride-styrene co-grafted polyolefin elastomer POE-g-MAH(St) and 25-35 parts of copolymer polypropylene PPB. The modifier exhibits a dispersed phase structure in its microstructure, with copolymer polypropylene as the "hard core" and POE-g-MAH(St) as the "soft shell".

2. The toughening and reinforcing modifier with a "core-shell" structure as described in claim 1, characterized in that, The preparation method of POE-g-MAH(St) includes: mixing polyolefin elastomer, maleic anhydride, styrene monomer and initiator at high speed, and then carrying out melt grafting reaction through a twin-screw extruder, and cooling and granulating the reactants to obtain the product; the grafting rate of POE-g-MAH(St) is 1.0-1.2%.

3. The toughening and reinforcing modifier with a "core-shell" structure as described in claim 1, characterized in that, The copolymer polypropylene PPB has a melt flow rate of 10-15 g / 10 min at 230℃ and 2.16 kg, and an ethylene content greater than 7.5%.

4. The method for preparing the toughening and reinforcing modifier with a "core-shell" structure as described in any one of claims 1-3, characterized in that, Includes the following steps: POE-g-MAH(St) and copolymer polypropylene PPB are mixed evenly. The resulting mixture is melt-blended in a parallel co-rotating twin-screw extruder with an aspect ratio of (44-48):

1. After water cooling, the mixture is drawn into strands and granulated to obtain a toughening and reinforcing modifier with a "core-shell" structure.

5. A method for dry recycling of wet-process separators in lithium batteries, characterized in that, Includes the following steps: Dry recycling pretreatment: Waste from the wet process of lithium battery separator production is processed through a dry process, including hydraulic guillotine cutting, spiral extrusion degreasing, multi-stage crushing, functional granulation, and vibrating screen sorting, to obtain dry process pretreatment recycled material; Melt blending: The obtained dry process pretreated recycled material, homopolymer polypropylene (PPH), toughening and reinforcing modifier with "core-shell" structure as described in any one of claims 1-3, and processing aids are mixed at high speed and then melt-extruded and granulated through a twin-screw extruder to obtain high-performance recycled modified material.

6. The method for dry recycling of lithium battery wet separators as described in claim 5, characterized in that, In the dry recycling pretreatment step, the functional granulation treatment specifically includes: conveying the crushed material to a granulator, adding macroporous silica activated and modified by silane coupling agent KH-570, the amount of which is 1-5 wt% of the white oil content in the material, and stirring and granulating.

7. The method for dry recycling of lithium battery wet separators as described in claim 6, characterized in that, The preparation method of the macroporous silica modified by the silane coupling agent KH-570 includes: mixing macroporous silica with 1.5-3.0% by mass of the silane coupling agent KH-570, and stirring and activating at 100-120℃ to obtain the macroporous silica; the macroporous silica has a pore volume ≥1.8mL / g, a specific surface area of ​​200-400m² / g, and an average pore size of ≥20nm.

8. The method for dry recycling of lithium battery wet separators as described in claim 5, characterized in that, In the melt blending step, by weight, it includes 85-87 parts of dry process pretreatment recycled material, 8-12 parts of homopolymer polypropylene PPH, 3-5 parts of toughening and reinforcing modifier with "core-shell" structure as described in any one of claims 1-3, and 0.5-5.0 parts of processing aid.

9. The high-performance recycled modified material prepared by the wet-process and dry-process recycling method for lithium battery separators as described in claim 5, characterized in that, The high-performance recycled modified material has a tensile strength of 38.5 MPa, an elongation at break of 220%, a flexural modulus of 1350 MPa, a notched cantilever beam impact strength of over 58 kJ / m², and a melt flow rate (230℃, 2.16 kg) of 2.5 g / 10 min.

10. The application of the high-performance recycled modified material as described in claim 9 in the fields of automotive interior and exterior parts, electronic and electrical housings, sheet and building materials, pipes, luggage accessories, and toy housings.