Method and system for preparing toughened impact-resistant injection molding material based on recycled GPPS (general purpose polystyrene)

Abstract

The invention discloses a preparation method and system of a toughening impact-resistant injection molding material based on recycled GPPS, and belongs to the technical field of high polymer material modification.The method specifically comprises the following steps that recycled GPPS particles are subjected to surface polarity activation treatment, the surfaces of the particles are subjected to infiltration treatment through a hydroxyl-containing polymer water solution under the heating condition, and the particles are subjected to surface polarity activation treatment; the surface polarity is increased; the interface compatibility with subsequent additives is improved; the recycled GPPS particles subjected to surface activation and a compound toughening agent are subjected to melt mixing, the compound toughening agent comprises a core-shell structure elastomer and long-chain fatty acid ester, stress dispersion and energy absorption are achieved through the core-shell structure, and molecular chain plasticizing and interface lubrication are achieved through the long-chain fatty acid ester; and adding the compatilizer and the lubricant into the mixed system. By introducing a novel composite modification system and optimizing the technological process, the mechanical property of the recycled GPPS material is improved, the preparation technology is simplified, and the production cost is reduced.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of high polymer material modification, and in particular to a toughened and impact-resistant injection molding material preparation method and system based on recycled GPPS. BACKGROUND

[0002] Toughening modification of recycled GPPS is a key way to improve its recycling value. Existing technologies mainly develop around two paths: one is to learn from the modification strategy of new GPPS, and the other is to develop complex nano-composite materials for the characteristics of recycled materials.

[0003] The invention patent with publication number CN103059432B (hereinafter referred to as: prior art 1) provides a typical modification idea for new materials. With new GPPS as the matrix, a transparent toughening color masterbatch is prepared by adding MBS (methyl methacrylate-butadiene-styrene copolymer) elastomer and oil-based toughening agent. The core of this scheme is to use elastomer particles as stress concentration points to induce silver lines and shear bands to absorb impact energy. However, this technical solution has obvious limitations: first, the design object is new material, the molecular chain is complete and the surface is clean, which is essentially different from the recycled GPPS whose chain segment structure has been damaged and the surface energy has changed after use and aging. Directly applying the toughening system for new materials to recycled materials will greatly reduce the interfacial bonding effect and toughening efficiency due to the inertness of the recycled material surface. Secondly, this scheme has high requirements for transparency, which limits the use of some efficient but may affect the transparency of the toughening agent, and does not fundamentally solve the demand for significantly improving the toughness of recycled GPPS.

[0004] The invention patent with publication number CN112341744B (hereinafter referred to as: prior art 2) represents another technical route, that is, to realize the high performance of recycled plastics by adding nanoparticles. Silicon carbide (SiC) nanoparticles are used to enhance and toughen recycled polystyrene. The principle is to use high-stiffness and high-hardness nanoparticles to bear the load and constrain the movement of polymer molecular chains, thereby improving the strength and toughness. However, this scheme introduces new complexity problems: first, nano-SiC is expensive and is prone to agglomeration in the polymer matrix, requiring harsh processing conditions such as high shear and surface modification to achieve uniform dispersion, which significantly increases the process complexity and production cost. Second, this scheme includes strict pretreatment of recycled materials such as cleaning and drying, which has a long process and high energy consumption. Third, the addition of nano-filler usually leads to a sharp increase in melt viscosity, which worsens the processing fluidity, making the material difficult to form, especially for complex structures, which is contrary to the original intention of low-cost and high-efficiency processing of recycled materials.

[0005] The existing technologies have not effectively solved the core contradictions of recycled GPPS modification as follows: First, there is a contradiction in interfacial compatibility: recycled GPPS has low surface energy and weak polarity, resulting in poor compatibility with most high-efficiency toughening agents and reinforcing fillers. Existing technologies either ignore this problem, such as existing technology 1 which directly applies the new material formulation, or existing technology 2 which uses complex surface treatment and dispersion technologies with high cost and high energy consumption, failing to provide a mild, efficient, and dedicated interfacial activation method for recycled GPPS.

[0006] Second, there is a conflict between toughening efficiency and cost: a single toughening mechanism (such as elastomers or nanoparticles) often requires a high addition amount to achieve the desired effect, which may lead to increased costs or sacrifice of other properties (such as stiffness and flowability). Existing technologies lack a compound system design that achieves efficient toughening with multiple mechanisms working synergistically and at low addition amounts.

[0007] Third, there is a conflict between processing performance and mechanical properties: the introduction of reinforcing components often leads to poor processing flowability. In existing technologies, especially nanocomposite material solutions, the relationship between the mechanical properties of the final material and the injection molding processability has not been well balanced. Summary of the Invention

[0008] The purpose of this invention is to provide a method and system for preparing toughened and impact-resistant injection molding materials based on recycled GPPS. By introducing a novel composite modification system and optimizing the process flow, the mechanical properties of recycled GPPS materials are improved, the preparation process is simplified, and the production cost is reduced.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for preparing toughened and impact-resistant injection molding materials based on recycled GPPS includes the following steps: Step 1: Surface polarity activation treatment is performed on the recovered GPPS particles. The particle surface is wetted with an aqueous solution of hydroxyl-containing polymer under heating conditions to increase surface polarity and improve interfacial compatibility with subsequent additives. Step 2: The surface-activated recycled GPPS particles are melt-mixed with a compound toughening agent, which contains a core-shell structured elastomer and a long-chain fatty acid ester. The core-shell structure achieves stress dispersion and energy absorption, while the long-chain fatty acid ester achieves molecular chain plasticization and interface lubrication. Step 3: Add compatibilizer and lubricant to the mixture. The compatibilizer strengthens the interfacial bonding, and the lubricant improves the processing fluidity. Step 4: The surface-modified nanofiller is melt-blended with the aforementioned mixture to provide rigidity enhancement and dimensional stability control through the nanofiller; Step 5: The final modified material is processed into structural parts through injection molding.

[0010] In one embodiment of the present invention, the hydroxyl-containing polymer in step one is low molecular weight polyvinyl alcohol with a weight average molecular weight of 20,000 to 50,000, the mass fraction of the treatment solution is 0.5% to 2%, the treatment temperature is 60 to 80°C, and the treatment time is 2 to 3 hours.

[0011] In one embodiment of the present invention, the core layer of the core-shell elastomer in step two is cross-linked acrylate rubber, and the shell layer is methyl methacrylate-styrene copolymer; the long-chain fatty acid ester is butyl stearate or isopropyl palmitate.

[0012] In one embodiment of the present invention, the compatibilizer in step three is maleic anhydride-grafted polystyrene with a grafting rate of 0.5% to 2%; the lubricant is zinc stearate.

[0013] In one embodiment of the present invention, the nanofiller in step four includes nano-silica and nano-calcium carbonate modified with a silane coupling agent, wherein the silane coupling agent is γ-aminopropyltriethoxysilane.

[0014] In addition, this invention also discloses a system for preparing toughened and impact-resistant injection molding materials based on recycled GPPS, comprising the following modules: A surface activation treatment device is used to regulate the surface polarity of recycled GPPS particles; A toughening blending device is used to achieve uniform mixing of compound toughening agents and matrix; An additive and dispersion device for adding compatibilizers and lubricants and achieving uniform dispersion; A nano-reinforcement modification device is used to achieve the composite and dispersion of nanofillers in a matrix; Injection molding equipment is used for the molding and processing of final structural parts.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention fundamentally solves the core problems of poor interfacial compatibility, insufficient toughness, and deteriorated thermal stability in recycled GPPS through a triple synergistic mechanism of surface polar activation, compound toughening, and nano-reinforcement. Polyvinyl alcohol surface treatment enhances interfacial bonding, the synergistic effect of core-shell elastomers and long-chain fatty acid esters improves impact strength, and nano-filler composite reinforcement achieves a flexural strength of 57.3 MPa and a heat distortion temperature of 86.4℃. The entire process achieves performance improvement while reducing energy consumption, balancing mechanical properties, thermal stability, and processing fluidity, providing a reliable solution for the high-value utilization of recycled GPPS. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0017] Fig. 1 This is an overall flowchart of the preparation method described in this invention.

[0018] Fig. 2 This is a simplified flowchart of the overall process steps of the present invention. Detailed Implementation

[0019] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0020] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0021] Example 1, see Figs. 1-2 This embodiment discloses a method for preparing a toughened and impact-resistant injection molding material based on recycled GPPS, including the following steps: Step 1: Surface polarity activation treatment is performed on the recovered GPPS particles. The particle surface is wetted with an aqueous solution of hydroxyl-containing polymer under heating conditions to increase surface polarity and improve interfacial compatibility with subsequent additives. Step 2: The surface-activated recycled GPPS particles are melt-mixed with a compound toughening agent, which contains a core-shell structured elastomer and a long-chain fatty acid ester. The core-shell structure achieves stress dispersion and energy absorption, while the long-chain fatty acid ester achieves molecular chain plasticization and interface lubrication. Step 3: Add compatibilizer and lubricant to the mixture. The compatibilizer strengthens the interfacial bonding, and the lubricant improves the processing fluidity. Step 4: The surface-modified nanofiller is melt-blended with the aforementioned mixture to provide rigidity enhancement and dimensional stability control through the nanofiller; Step 5: The final modified material is processed into structural parts through injection molding.

[0022] In one embodiment of the present invention, the hydroxyl-containing polymer in step one is low molecular weight polyvinyl alcohol with a weight average molecular weight of 20,000 to 50,000, the mass fraction of the treatment solution is 0.5% to 2%, the treatment temperature is 60 to 80°C, and the treatment time is 2 to 3 hours.

[0023] In one embodiment of the present invention, the core layer of the core-shell elastomer in step two is cross-linked acrylate rubber, and the shell layer is methyl methacrylate-styrene copolymer; the long-chain fatty acid ester is butyl stearate or isopropyl palmitate.

[0024] In one embodiment of the present invention, the compatibilizer in step three is maleic anhydride-grafted polystyrene with a grafting rate of 0.5% to 2%; the lubricant is zinc stearate.

[0025] In one embodiment of the present invention, the nanofiller in step four includes nano-silica and nano-calcium carbonate modified with a silane coupling agent, wherein the silane coupling agent is γ-aminopropyltriethoxysilane.

[0026] In addition, this embodiment also discloses a toughened and impact-resistant injection molding material preparation system based on recycled GPPS, including the following modules: A surface activation treatment device for controlling the surface polarity of recycled GPPS particles; the device specifically includes: Thermostatic water bath: Used to hold and heat aqueous solutions containing hydroxyl polymers for soaking recycled GPPS particles. It is equipped with a temperature control system, with a heating power of 2-5 kW, a temperature control accuracy of ±1℃, and a temperature adjustment range from room temperature to 100℃.

[0027] Solution circulation pump: Used to keep the treatment solution in the constant temperature water bath flowing and uniform in concentration, with a flow rate of 10-20 liters per minute.

[0028] Rinsing tank: Used to hold deionized water for rinsing the soaked particles.

[0029] pH online monitoring and adjustment unit: used to monitor and automatically adjust the pH value of the treated solution to maintain it within a set range, such as 6-7.

[0030] Drying chamber: Used to dry the washed granules. It is a forced ventilation drying chamber with a temperature adjustment range of 50-120℃ and an air velocity of 1-3 meters per second.

[0031] A toughening blending apparatus for achieving uniform mixing of the compounded toughening agent and the matrix; the apparatus specifically includes: High-speed heating mixer: This is the main mixing equipment. The impeller is of dual-speed or variable-speed configuration, with a main rotation speed range of 300–600 rpm. It is equipped with a heating jacket, and the temperature control range is room temperature to 200℃, with a temperature control accuracy of ±2℃. Observation windows and sampling ports are used to monitor the mixing process.

[0032] An additive and dispersion device for adding compatibilizers and lubricants and achieving uniform dispersion; the device specifically includes: Measuring and weighing unit: used for accurate weighing of compatibilizers and lubricants to be added, with an accuracy of ±0.1 grams.

[0033] Mixing and stirring unit: This unit can be integrated with the toughening blending device or set up independently. Its core is a high-speed shear mixing device; the stirring paddle is typically a high-shear dispersion disc or similar structure, and the shear rate can be adjusted within the range of 500–1000 rpm. This unit also has heating and temperature control functions.

[0034] A nano-reinforcement modification device is used to achieve the composite and dispersion of nanofillers in a matrix; the device specifically includes: Twin-screw extruder: co-rotating type, with a length-to-diameter ratio (L / D) of 30:1 to 40:1. The screw speed is adjustable from 200 to 300 rpm. The barrel is divided into multiple temperature zones with independent temperature control, ranging from 150 to 250°C. Equipped with a main feeder and side feeders for nanofillers, the feeding speed ranges from 5 to 10 kg per hour.

[0035] Cooling and granulation unit: connected to the extruder outlet, including a cooling water tank (or air-cooled conveyor belt) and a pelletizer. The cooling water flow rate is 5-10 liters per minute, used to rapidly cool the extruded molten strip and cut it into pellets.

[0036] Injection molding equipment is used for the molding of final structural parts; the equipment specifically includes: Injection molding machine: Used to mold modified material granules into finished products. Its clamping force is selectable depending on the product size, ranging from 50 to 100 tons. The injection unit is equipped with a screw, allowing for multi-stage injection speed and multi-stage holding pressure control.

[0037] Mold assembly: Installed on the injection molding machine, the number of cavities can be 1 to 4. The mold is equipped with cooling water channels, and the mold temperature is controlled by a mold temperature controller at 40 to 60°C. To further improve the demolding effect, the surface of the mold cavity can be coated with polytetrafluoroethylene (PTFE) to reduce demolding resistance, and its surface roughness Ra value is controlled at 0.1 to 0.5 micrometers.

[0038] To facilitate a better understanding of the present invention by those skilled in the art, the present invention will be further described below in conjunction with specific embodiments.

[0039] A method for preparing toughened and impact-resistant injection molding materials based on recycled GPPS includes the following steps: Step 1, Surface polarity activation treatment: Take 1.0 kg of recovered GPPS granules (2-4 mm in diameter, melt flow rate 8 g / 10 min, 2.16 kg at 230℃) and place them in a 50 L stainless steel constant temperature water bath. Add 15 L of a 1.5% (w / w) aqueous solution of low molecular weight polyvinyl alcohol (PVA-1788), with a weight average molecular weight of 30000±2000. Monitor the pH of the solution using a pH meter and adjust it to 6.5±0.1 with dilute hydrochloric acid. Turn on the constant temperature control system and soak the GPPS granules at 74℃-76℃ for 2.5 hours, manually stirring every 30 minutes to ensure that PVA molecules are fully adsorbed onto the surface of the GPPS granules.

[0040] After processing, the granules were removed and repeatedly rinsed with deionized water in a rinsing tank until the pH of the effluent was 7.0±0.2. The washed granules were then evenly spread on a stainless steel tray and placed in a forced-ventilation drying oven at a temperature of 78℃-82℃ and an air velocity of 2.0m / s for 5 hours until the moisture content was below 0.1%. The moisture content was measured using a Karl Fischer moisture analyzer to obtain surface-activated recovered GPPS granules.

[0041] Step 2, toughening blending: Add the surface-activated recycled GPPS particles to a high-speed heated mixer and set the temperature to 150±2℃. After the temperature stabilizes, add the compound toughening agent, which includes: Core-shell elastomer, brand name EXL-2330, with a core layer of cross-linked butyl acrylate rubber and a shell layer of methyl methacrylate-styrene copolymer, average particle size 150±20nm; addition amount 100g, which is 10% of the total mass of GPPS; Long-chain fatty acid esters, such as butyl stearate, purity ≥99%, melting point 35℃: addition amount 20g, 2% of the total mass of GPPS; Set the mixer speed to 500 rpm and the mixing time to 15 minutes. Confirm through the observation window that the materials are mixed evenly and that the toughening agent is completely coated on the surface of the GPPS matrix.

[0042] Step 3, Addition and Dispersion of Additives: Maintain the mixer temperature and add the following to the mixing system: Compatibilizer: Maleic anhydride-grafted polystyrene, brand name CMG-9801, grafting rate 1.2%; addition amount 50g, 5% of the total mass of GPPS; Lubricant: Zinc stearate, average particle size 3μm, purity ≥99%; addition amount 10g, 1% of the total mass of GPPS; The temperature was raised to 170±2℃, the system was switched to high-speed shear mode, the shear rate was set to 800 r / min, and the mixture was stirred for 25 minutes. Sampling and observation confirmed that all components were uniformly dispersed, thus obtaining the preliminary modified material.

[0043] Step 4, Nano-reinforcement modification: After cooling the pre-modified material to 23℃-27℃, surface-modified nanofillers are added: Nano-silica modified with silane coupling agent, with a specific surface area of ​​200±10m² / g: added at 12g, which is 1.2% of the total mass of GPPS; the silane coupling agent is γ-aminopropyltriethoxysilane, KH-550.

[0044] Nano-calcium carbonate, average particle size 80nm, purity ≥99%: addition amount 20g, 2% of the total mass of GPPS.

[0045] A co-rotating twin-screw extruder, model TSE-35A, with an L / D ratio of 36:1, was used for melt blending. The extruder temperature zones were set as follows: Zone 1 185℃, Zone 2 195℃, Zone 3 205℃, and Die Head 210℃. The screw speed was 250 r / min, and the feed rate was 8 kg / h. After cooling in a water bath, the melt was pelletized to obtain cylindrical pellets with a diameter of 2–3 mm.

[0046] Step 5, Injection Molding: The final modified material is injection molded into standard test specimens and complex structural parts, thin-walled shells with an average wall thickness of 1.5 mm. The standard test specimens refer to ISO527-2 / 1A.

[0047] The injection molding process parameters are as follows: barrel front section temperature 215℃, middle section temperature 210℃, rear section temperature 205℃, mold temperature 50℃. A three-stage injection control is used: first stage injection speed 65mm / s, filling the cavity to 85%; second stage injection speed 40mm / s, filling to 98%; third stage injection speed 15mm / s, for final filling and holding pressure. Injection pressure 100MPa, holding pressure 80MPa, holding time 8 seconds, cooling time 12 seconds.

[0048] Example 2, Step 1, Surface polarity activation treatment: Take 1.0 kg of recycled GPPS granules and place them in a constant temperature water bath. Add 15 L of a 0.8% (w / w) aqueous solution of low molecular weight polyvinyl alcohol (PVA1788), with a weight average molecular weight of 40000±2000. Adjust the pH of the solution to 6.8±0.1. Soak at a constant temperature of 64℃-66℃ for 3 hours, stirring manually every 30 minutes. After treatment, remove the granules and rinse with deionized water until the pH of the effluent is 7.0±0.2. Place them in a drying oven at 73℃-77℃ with an air velocity of 1.5 m / s and dry for 6 hours.

[0049] Step 2, Toughening Blending: Add the surface-activated recycled GPPS particles to a high-speed mixer, setting the temperature to 143℃-147℃. Add the compound toughening agent: Core-shell elastomer, grade EXL-2330: addition amount 80g; Isopropyl palmitate, melting point 42℃: 15g added; set speed 450r / min, mixing time 18 minutes.

[0050] Step 3, Addition and Dispersion of Additives: Add the following to the mixture: Compatibilizer: Maleic anhydride-grafted polystyrene, grafting rate 0.8%; addition amount 40g; Lubricant: Zinc stearate: 8g; Raise the temperature to 163℃-167℃, set the shear rate to 600r / min, and stir for 28 minutes.

[0051] Step 4, Nano-reinforcement modification: Adding nanofillers: Modified nano-silica: 8g added; Nano calcium carbonate: 15g added; A twin-screw extruder is used, with the following temperature settings: Zone 1 180℃, Zone 2 190℃, Zone 3 195℃, and Die Head 200℃. The screw speed is 280 r / min, and the feeding speed is 7 kg / h.

[0052] Step 5, Injection Molding: Injection temperature: front section 205℃, middle section 200℃, rear section 195℃, mold temperature 45℃, injection pressure 90MPa, holding pressure 70MPa.

[0053] It should be noted that the items not described in this embodiment are the same as those in Embodiment 1.

[0054] Example 3, Step 1, Surface polarity activation treatment: A 2.0% PVA aqueous solution with a weight average molecular weight of 25000±2000 was used and treated at 79℃-81℃ for 2 hours. The rest of the treatment was the same as in Example 1.

[0055] Step 2, toughening blending: The amount of core-shell elastomer added was 120g, the amount of long-chain fatty acid ester (butyl stearate) added was 25g, the mixing temperature was 155±2℃, and the mixing time was 12 minutes.

[0056] Step 3, Addition and Dispersion of Additives: The compatibilizer grafting rate was 1.8%, the addition amount was 70g, the lubricant addition amount was 12g, the shear rate was 900r / min, the mixing temperature was 173℃-177℃, and the time was 22 minutes.

[0057] Step 4, Nano-reinforcement modification: The amount of nano-silica added is 18g, the amount of nano-calcium carbonate added is 28g, the extrusion temperature is 190℃ in zone 1, 200℃ in zone 2, 215℃ in zone 3, 220℃ at the die head, and the screw speed is 220r / min.

[0058] Step 5, Injection Molding: Injection temperature: front section 225℃, middle section 220℃, rear section 215℃, mold temperature 55℃, injection pressure 110MPa.

[0059] Comparative Example 1: The surface polarity activation treatment in step one was not performed; the original recycled GPPS particles were used directly, and the remaining steps were the same as in Example 1.

[0060] Comparative Example 2: In step two, only a core-shell elastomer was used, with an addition amount of 120g. Long-chain fatty acid esters were not used. The rest was the same as in Example 1.

[0061] Comparative Example 3: In step four, nano-silica and nano-calcium carbonate that have not been modified by silane coupling agent were used, and the rest was the same as in Example 1.

[0062] Performance testing and results analysis: The materials obtained in the above embodiments and comparative examples were subjected to performance tests, and the test standards and methods are as follows: Tensile strength: ISO527-2 / 1A, 50 mm / min; Bending strength: ISO178, 2 mm / min; Notched impact strength: ISO179 / 1eA, pendulum energy 4J; Heat distortion temperature: ISO75-2, load 0.45MPa; Melt flow rate: ISO 1133, 230℃ / 2.16kg; The material performance test results are shown in Table 1:

[0063] The test results show that the materials prepared in Examples 1-3 of this invention exhibit excellent and balanced comprehensive performance in terms of mechanical properties, thermal properties, and processing fluidity. In contrast: Comparative Example 1, due to the lack of surface polar activation treatment, has poor interfacial bonding, resulting in a significant decrease in various properties of approximately 25-40%; Comparative Example 2, lacking the synergistic toughening effect of long-chain fatty acid esters, experiences a decrease in impact performance of approximately 30% and a reduction in fluidity of 40%; Comparative Example 3, due to the lack of surface modification of the nanofiller, suffers from uneven dispersion in the matrix, forming stress concentration points, leading to a significant decrease in its mechanical properties and heat distortion temperature, and negatively impacting processing fluidity. The above examples fully verify that this invention, through the synergistic effect of multiple technical means such as surface polar activation, compound toughening, and nano-reinforcement, effectively solves the problem of performance degradation of recycled GPPS materials, achieving high-performance recycling.

[0064] Example 4: Although the PVA aqueous solution heating and immersion method used in Examples 1-3 can effectively improve the surface polarity of recovered GPPS, this method mainly relies on molecular thermal motion and concentration gradient-driven physical adsorption. For severely aged and highly contaminated recovered GPPS particles, there is still room for improvement in processing efficiency and the ability to remove deep contaminants. Some contaminants or weak boundary layers may still remain on the particle surface, becoming potential defects affecting the final performance.

[0065] This embodiment is a further optimization based on Embodiment 1, which adds ultrasonic treatment: the immersion treatment in step one is carried out under ultrasonic assistance, with an ultrasonic frequency of 20~40kHz, a power of 100~500W, and a treatment time of 10~30 minutes.

[0066] Furthermore, the ultrasound treatment is divided into two stages: first, low-frequency treatment at 20-25kHz for 10-15 minutes, followed by high-frequency treatment at 35-40kHz for 5-15 minutes.

[0067] The above operation can thoroughly remove oil, dust and aging degradation layer attached to the surface of recycled GPPS particles, form a micron / nano-scale rough structure on the particle surface, significantly increase the specific surface area, accelerate the diffusion and adsorption process of PVA molecules to the GPPS surface, and form a denser and stronger polar modification layer.

[0068] In practice, the recovered GPPS particles and a 1.5% PVA aqueous solution were placed in an ultrasonic-assisted constant-temperature water bath. The ultrasonic device was turned on, and a two-stage ultrasonic treatment was adopted: the first stage was set with an ultrasonic frequency of 25kHz and a power of 300W for 12 minutes, mainly for macroscopic cleaning and peeling; the second stage was switched to a frequency of 38kHz and a power of 200W for 8 minutes, mainly for microscopic activation and adsorption promotion. The entire treatment process was carried out simultaneously at 74℃-76℃, and the post-treatment operation was the same as in Example 1.

[0069] The material performance test results are shown in Table 2:

[0070] Example 1 employed conventional activation, while Comparative Example 1 was unactivated. The comparison with Comparative Example 1 further demonstrates the extreme importance of surface activation treatment, with all properties showing orders-of-magnitude improvements. Compared to Example 1: after ultrasonic-assisted treatment, the material's impact strength increased from 18.5 to 20.1 kJ / m², and its heat distortion temperature increased from 86.4 to 89.5 °C. This indicates that more thorough cleaning and more effective interface modification further strengthen the interfacial bond between the matrix and the toughening agent / filler, enabling the material to more effectively transfer and dissipate energy under impact and thermal loads. Simultaneously, the melt flow rate also improved, indicating better material processing fluidity, possibly due to improved surface lubricity and the removal of low-molecular-weight contaminants. In Example 5, while the combination of core-shell elastomer and long-chain fatty acid ester in Examples 1-3 effectively toughens the matrix, the interaction between the two and the GPPS matrix is ​​still primarily physical blending, leaving room for strengthening the interfacial interaction forces. Under high temperature or high stress, the elastomer particles may slip off the matrix interface, leading to a decrease in toughening efficiency. The key to further improving the toughening limit is to further "anchor" the elastomer particles and strengthen the interface without sacrificing processing fluidity. Therefore, in this example, step two also includes adding a vulcanizing agent, with the amount added being 0.5% to 2% of the total mass of the compounded toughening agent, achieving dynamic vulcanization during the melt mixing process.

[0071] Furthermore, the vulcanizing agent is dicumyl peroxide (DCP) or a sulfur system, the vulcanization temperature is 160~180℃, and the vulcanization time is 1~3 minutes.

[0072] In practice, the surface-activated recycled GPPS particles were added to a high-speed heated mixer, and the temperature was set to 170±2℃. After the temperature stabilized, 100g of the compound toughening agent EXL-2330 and 20g of butyl stearate were added, along with 1.2g of dicumyl peroxide (DCP), which is 1% of the total mass of the compound toughening agent. The mixer speed was set to 500r / min, and the mixture was mixed at 170℃ and dynamically vulcanized for 2 minutes. Subsequent steps were the same as in Example 1.

[0073] The material performance test results are shown in Table 3:

[0074] In this embodiment, the cross-linked elastomer particles, as the dispersed phase, are firmly fixed in the GPPS continuous phase. Under the action of the vulcanizing agent, a small number of covalent bonds may be generated between the elastomer and the GPPS molecular chains, which greatly enhances the interfacial bonding force. When the material is impacted, these firmly anchored, partially cross-linked elastomer particles can more effectively initiate, terminate, and dissipate crazes and shear bands, prevent crack propagation, and thus absorb impact energy more efficiently.

[0075] This embodiment, compared with Comparative Example 2, further demonstrates the necessity of synergistic toughening of long-chain fatty acid esters and elastomers. Compared with Example 1, this embodiment shows a remarkable improvement in impact strength after dynamic vulcanization, from 18.5 to 21.5 kJ / m². Simultaneously, flexural strength and heat distortion temperature also increased. This proves the significant effect of interfacial chemical crosslinking on improving toughening efficiency. The melt flow rate decreased slightly but remained significantly higher than in Comparative Example 2, indicating that dynamic vulcanization, while greatly improving toughness, effectively balanced processing fluidity and did not lead to deterioration in processability due to crosslinking. Dynamic vulcanization technology, through chemical bonding, upgrades the physical blend system to a physical-chemical synergistic toughening system, strengthening the interface and achieving a significant breakthrough in impact strength.

[0076] This invention fundamentally solves the performance degradation problem caused by chain breakage and surface inertness in recycled GPPS by organically combining three technical approaches: molecular interface design, multiphase synergistic toughening, and nano-reinforcement, achieving significant technological progress.

[0077] This invention employs a surface polar activation treatment, using a low molecular weight polyvinyl alcohol solution to gently treat recycled GPPS particles. The hydroxyl groups on the PVA molecular chain form hydrogen bonds with the GPPS surface, significantly enhancing surface polarity and interfacial energy. This fundamentally improves the compatibility of recycled GPPS with subsequent polar additives, increasing the interfacial bonding strength between the surface-activated GPPS and the toughening agent, thus laying a solid foundation for subsequent modification.

[0078] This invention employs a toughening system combining a core-shell elastomer and a long-chain fatty acid ester. The core-shell elastomer achieves stress dispersion and energy absorption through its rubber core, while the shell layer exhibits good compatibility with the matrix. The long-chain fatty acid ester effectively improves the mobility of molecular chain segments through molecular chain penetration and plasticization. The synergistic effect of these two components results in a notched impact strength exceeding 18.5 kJ / m², a significant improvement compared to unmodified recycled GPPS, while maintaining good rigidity.

[0079] More importantly, this invention achieves uniform dispersion of the reinforcing phase through surface-modified nanofillers. Silane coupling agent-modified nano-silica provides strong interfacial bonding, while nano-calcium carbonate effectively fills the gaps between molecular chains. This multi-scale reinforcement effect enables the material to achieve a flexural strength of 57.3 MPa and a heat distortion temperature of 86.4 °C, significantly improving the material's dimensional stability and heat resistance.

[0080] Furthermore, the entire preparation process of this invention is meticulously designed, with parameters for each step perfectly matched. From the mild surface treatment conditions of 60-80℃ to the temperature control of the blending process of 140-220℃, further degradation of the molecular chains is avoided. The use of multi-stage injection molding ensures the molding quality of complex structural parts. Compared with traditional methods, energy consumption and production costs are reduced. This invention not only significantly improves the mechanical and thermal properties of recycled GPPS materials but also successfully resolves the contradiction between processing fluidity and mechanical properties, providing a reliable technical solution for the high-value reuse of recycled GPPS.

[0081] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing toughened and impact-resistant injection molding materials based on recycled GPPS, characterized in that, Includes the following steps: Step 1: Surface polarity activation treatment is performed on the recovered GPPS particles. The particle surface is wetted with an aqueous solution of hydroxyl-containing polymer under heating conditions to increase surface polarity and improve interfacial compatibility with subsequent additives. Step 2: The surface-activated recycled GPPS particles are melt-mixed with a compound toughening agent, which contains a core-shell structured elastomer and a long-chain fatty acid ester. The core-shell structure achieves stress dispersion and energy absorption, while the long-chain fatty acid ester achieves molecular chain plasticization and interface lubrication. Step 3: Add compatibilizer and lubricant to the mixture. The compatibilizer strengthens the interfacial bonding, and the lubricant improves the processing fluidity. Step 4: The surface-modified nanofiller is melt-blended with the aforementioned mixture to provide rigidity enhancement and dimensional stability control through the nanofiller; Step 5: The final modified material is processed into structural parts through injection molding.

2. The method for preparing toughened and impact-resistant injection molding material based on recycled GPPS according to claim 1, characterized in that: The hydroxyl-containing polymer mentioned in step one is low molecular weight polyvinyl alcohol with a weight average molecular weight of 20,000 to 50,000. The mass fraction of the treatment solution is 0.5% to 2%, the treatment temperature is 60 to 80°C, and the treatment time is 2 to 3 hours.

3. The method for preparing toughened and impact-resistant injection molding material based on recycled GPPS according to claim 1, characterized in that: In step two, the core layer of the core-shell elastomer is cross-linked acrylate rubber, and the shell layer is methyl methacrylate-styrene copolymer; the long-chain fatty acid ester is butyl stearate or isopropyl palmitate.

4. The method for preparing toughened and impact-resistant injection molding material based on recycled GPPS according to claim 1, characterized in that: The compatibilizer mentioned in step three is maleic anhydride-grafted polystyrene with a grafting rate of 0.5% to 2%.

5. The method for preparing toughened and impact-resistant injection molding material based on recycled GPPS according to claim 1, characterized in that: The nanofiller mentioned in step four includes nano-silica and nano-calcium carbonate modified with a silane coupling agent, wherein the silane coupling agent is γ-aminopropyltriethoxysilane.

6. The method for preparing toughened and impact-resistant injection molding material based on recycled GPPS according to claim 1, characterized in that: The immersion treatment described in step one is performed under ultrasonic assistance, with an ultrasonic frequency of 20~40kHz, a power of 100~500W, and a treatment time of 10~30 minutes.

7. The method for preparing toughened and impact-resistant injection molding material based on recycled GPPS according to claim 6, characterized in that, The ultrasonic treatment is divided into two stages: first, low-frequency treatment at 20-25kHz for 10-15 minutes, and then high-frequency treatment at 35-40kHz for 5-15 minutes.

8. The method for preparing toughened and impact-resistant injection molding material based on recycled GPPS according to claim 7, characterized in that, The ultrasonic treatment is divided into two stages: first, low-frequency treatment at 25kHz for 12 minutes, and then high-frequency treatment at 38kHz for 8 minutes.

9. The method for preparing toughened impact-resistant injection molding material based on recycled GPPS according to claim 4, characterized in that: The lubricant is zinc stearate.

10. A system for preparing a toughened impact-resistant injection molding material based on recycled GPPS as described in any one of claims 1-9, characterized in that, include: A surface activation treatment device is used to regulate the surface polarity of recycled GPPS particles; A toughening blending device is used to achieve uniform mixing of compound toughening agents and matrix; An additive and dispersion device for adding compatibilizers and lubricants and achieving uniform dispersion; A nano-reinforcement modification device is used to achieve the composite and dispersion of nanofillers in a matrix; Injection molding equipment is used for the molding and processing of final structural parts.

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