A recycled high-melt-index high-impact PP granule and a preparation method thereof

Abstract

The application discloses a recycled high-melt-index high-impact PP granular material and a preparation method thereof, and relates to the technical field of recycled plastic modification and processing.The application realizes the synergistic promotion of the high-melt-index and high-impact performance of a recycled PP base material by adopting a series of technical means such as modification by compounding of high-temperature peroxide and a crosslinking aid, deep purification treatment of the recycled PP base material, and one-step segmented feeding extrusion granulation, and simultaneously reduces the modification cost, improves the base material purity, and simplifies the production process.Detection shows that the melt flow rate of the recycled PP granular material prepared by the application is 20-30g / 10min, the cantilever beam impact strength is greater than or equal to 40kJ / m2, the tensile strength is greater than or equal to 23MPa, the bending strength is greater than or equal to 23MPa, and the bending modulus is 1000-1200MPa, so that the problem that the flowability and toughness of traditional materials cannot be considered simultaneously is solved, and the efficient injection molding and extrusion molding processing requirements are met.

Description

Technical Field

[0001] This invention relates to the field of recycled plastic modification and processing technology, and in particular to a recycled high melt index and high impact PP granules and its preparation method. Background Technology

[0002] Polypropylene (PP), as one of the most widely used general-purpose plastics, is extensively used in household appliance casings, industrial paint buckets, and daily necessities. With the increasing volume of discarded plastic products year by year, recycling and reusing waste PP has become a core direction for achieving a circular economy in plastics. Currently, the performance control of recycled PP materials faces many technical bottlenecks, and existing technologies have significant shortcomings in the synergistic improvement of both high melt flow index and high impact resistance.

[0003] Traditional recycled PP modification often uses simple physical blending methods. Mechanical blending alone cannot achieve precise control of the PP molecular chain structure, making it difficult to simultaneously obtain high melt flow rate (melt index) and high impact strength. The material is prone to problems where fluidity and toughness are mutually restrictive, failing to meet the performance requirements of efficient molding processes such as injection molding and extrusion. To improve the impact resistance of recycled PP, the industry commonly uses elastomers such as ethylene-octene copolymer (POE) and ethylene propylene diene monomer (EPDM) for toughening modification. For example, patent CN 115975294 A describes a high-impact rPP material and its preparation method. To address the problem of insufficient toughness in existing recycled polypropylene (PP) materials (rPP), this paper uses recycled polypropylene battery shells and washing machine materials as the matrix, and adds toughening agents (SBS+POE), EPDM elastomer powder masterbatch, antioxidants, lubricants, and odor absorbers. The mixture is then granulated by twin-screw extrusion. This method improves the impact strength of rPP by using three elastomers, SBS, POE, and EPDM, to synergistically toughen the material. However, the raw materials for such elastomers are expensive, significantly increasing the production cost of modified recycled materials. Furthermore, adding large amounts of these elastomers reduces the melt flowability of the material, requiring additional degradation agents to adjust the melt index, further increasing the complexity of the process and cost pressure, making it difficult to achieve large-scale production of economical and cost-effective recycled PP granules. For example, patent CN 103254509 A discloses a special material for recycled polypropylene washing machine plastic and its preparation method. It uses recycled polypropylene washing machine plastic as a matrix, adds POE, active calcium carbonate, peroxide DCP (dicumyl peroxide), antioxidants (1010 and 168) and calcium stearate, and granulates it by high-mixing twin-screw extrusion. Although the melt flow rate of the recycled special material is 25-30g / 10min, the cantilever beam impact strength is only 7-9kJ / m², and the impact strength needs to be further improved.

[0004] Meanwhile, recycled materials such as waste PP washing machine drums and paint buckets have complex compositions, containing impurities such as aluminum foil, oil, glue, and other small organic molecules in plastics. Existing sorting and cleaning processes are crude and incomplete in removing impurities, resulting in low purity of recycled PP substrates and significantly deteriorated mechanical properties, falling far short of the performance levels of virgin materials and limiting the high-end applications of recycled materials. Furthermore, in existing PP modification and granulation processes, peroxide degrading agents and antioxidants are prone to antagonism and free radical depletion, preventing the two agents from working simultaneously and efficiently. This necessitates a multi-step granulation process, resulting in a long production cycle, high energy consumption, and poor material performance stability.

[0005] Therefore, developing a recycled high melt index and high impact PP granule material that combines low cost, high purity, and high performance to overcome the performance and cost limitations of traditional modification processes and realize the high-value utilization of waste PP recycled materials has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] To address the above shortcomings, this invention provides a recycled high melt flow index and high impact resistance PP granules and its preparation method, solving the technical problems in the prior art where recycled PP cannot simultaneously achieve high melt flow index and high impact resistance, and where large amounts of elastomer are required for toughening, resulting in high costs, incomplete impurity removal, and easy antagonism between additives. The specific technical solution is as follows:

[0007] A recycled high melt index and high impact PP granule material comprises the following components in parts by weight: 89-93 parts recycled PP substrate, 5-10 parts elastomer, 0.01-0.08 parts high temperature peroxide, 0.2-1 parts crosslinking aid, 0.2-0.5 parts composite antioxidant, and 0.5-1 parts color masterbatch.

[0008] Preferably, the recycled PP substrate includes one or a mixture of two types of PP material from waste washing machine drums and PP material from paint buckets.

[0009] Preferably, the elasticity is one or a mixture of two of ethylene-octene copolymer (POE) and polyolefin plasmon (POP).

[0010] Preferably, the high-temperature peroxide includes one or a mixture of two of dicumyl peroxide (DCP) and bis-tert-butyl peroxide (BIBP).

[0011] Preferably, the crosslinking aid comprises one or a mixture of two of glycidyl methacrylate (GMA) and trimethylolpropane triacrylate (TMPTA).

[0012] Preferably, the composite antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:(1-3).

[0013] This invention also provides a method for preparing the aforementioned recycled high melt index, high impact PP granules, comprising the following steps:

[0014] (1) Purification of recycled PP substrate: The recycled PP substrate is crushed into fragments and sent to an integrated photoelectric pre-sorting device to remove impurities, non-PP plastics and aluminum foil; then the fragments are sequentially sent to a pre-washing tank, a hot washing tank, a rinsing tank and a flotation tank for multi-layer cleaning. After cleaning, the substrate is dehydrated and dried to obtain recycled PP substrate with a purity ≥95% and a moisture content ≤0.5%.

[0015] (2) Extrusion granulation: The purified and dried recycled PP substrate from step (1) is added to a first-stage single-screw granulator for extrusion and filtration; the material extruded from the first-stage single-screw granulator is added to a second-stage twin-screw granulator; then, high-temperature peroxide, elastomer, crosslinking agent and color masterbatch are added at the overlap position of the first-stage single-screw granulator and the second-stage twin-screw granulator for shearing and mixing reaction; after the reaction is completed, composite antioxidant is added to the first two heating blocks of the vacuum section in the second-stage twin-screw granulator, and the vacuum degree is set to -0.08~-0.06MPa to remove small molecule volatiles; finally, after extrusion, strip drawing, cooling and pelletizing, recycled high melt index and high impact PP granules are obtained.

[0016] Preferably, in step (1), the pre-wash water temperature in the pre-wash tank is 40-50℃ and the pre-wash water pressure is 0.3-0.5MPa; the hot washing temperature in the hot washing tank is 60-80℃ and the washing time is 20-30min, and an alkaline cleaning agent is added during hot washing; the rinsing tank is rinsed with circulating clean water; and the flotation in the flotation tank is to remove residual impurities by density separation.

[0017] Preferably, in step (1), the particle size of the fragments is 6-20 mm.

[0018] Preferably, in step (2), the extrusion temperature of the single screw granulator is 210-230℃, the screw speed is 60-90r / min, the extrusion pressure is 8-12MPa, and the filter screen is 100 mesh.

[0019] Preferably, in step (2), the extrusion process parameters of the twin-screw granulator are: temperature of each zone of the twin screw 150-170℃, screw speed 200-300r / min, extrusion pressure 8-12MPa, and filter screen 150 mesh.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. This invention achieves a synergistic improvement in high melt flow rate and high impact resistance of recycled PP substrates through a series of technical means, including high-temperature peroxide and crosslinking agent compound modification, deep purification treatment of recycled PP substrates, and one-step segmented feeding extrusion granulation. Simultaneously, it reduces modification costs, improves substrate purity, and simplifies the production process. Testing shows that the recycled PP granules obtained by this invention have a melt flow rate of 20-30 g / 10 min, cantilever beam impact strength ≥40 kJ / m², tensile strength ≥23 MPa, flexural strength ≥23 MPa, and flexural modulus of 1000-1200 MPa. It is evident that the recycled PP granules obtained by this invention achieve high cantilever beam impact strength while maintaining a high melt flow rate, solving the problem of traditional materials' inability to simultaneously achieve both flowability and toughness, and meeting the requirements of efficient injection molding and extrusion molding.

[0022] 2. This invention employs a combination of high-temperature peroxides and crosslinking aids, along with a small amount of elastomers, to replace the traditional method of regenerated modified PP that relies entirely on elastomers for toughening. The free radicals generated by the thermal decomposition of high-temperature peroxides (DCP, BIBP) can induce moderate degradation of the PP molecular chains, improving the melt flowability of the material. The crosslinking aids (GMA, TMPTA) can capture free radicals to form branched, lightly crosslinked structures, inhibiting excessive molecular chain breakage and compensating for the impact strength loss caused by degradation, thus achieving simultaneous optimization of high melt flow index and high impact resistance. This invention uses extremely low amounts of peroxides and crosslinking aids, while the amount of elastomers (POE, POP) added is only 30-50% of that in traditional toughening modification methods, reducing raw material costs by more than 30% and achieving economical high-performance modification.

[0023] 3. This invention employs a one-step extrusion granulation production line combining a single-screw and a twin-screw extruder. Segmented feeding solves the problem of mutual repulsion and loss caused by direct contact between peroxides and antioxidants. A first side-feeding device is installed at the junction of the first-stage single-screw granulator and the second-stage twin-screw granulator to precisely add peroxides, crosslinking aids, and masterbatches, ensuring uniform dispersion and chemical reaction of the modified additives during the initial shearing and mixing stage of the twin-screw granulator. A second side-feeding device is installed in the vacuum section of the second-stage twin-screw granulator to add antioxidants and other processing aids, preventing direct contact between antioxidants and peroxide free radicals, reducing ineffective additive loss, and ensuring that both additives function efficiently. Through one-step continuous extrusion granulation, the production process is simplified, energy consumption is reduced, product performance stability is improved, and continuous large-scale production is achieved.

[0024] 4. This invention employs an integrated photoelectric pre-sorting and multi-layer cleaning purification process to deeply remove impurities such as non-PP plastics and aluminum foil from the substrate. The integrated photoelectric pre-sorting equipment, based on near-infrared spectroscopy and visual recognition technology, can quickly separate mixed non-PP plastics and metallic impurities, initially purifying the substrate. Subsequently, multi-layer cleaning is performed sequentially: pre-washing, hot washing, rinsing, and flotation. Pre-washing removes surface mud and large particles using high-pressure water jets; hot washing uses an alkaline cleaning solution heated and stirred at 60-80℃ to remove small molecules of organic matter such as oil and glue; rinsing removes residual cleaning agents through circulating clean water; and flotation separates remaining light and heavy impurities based on density differences. Ultimately, the purity of the recycled PP substrate is ≥95%, and the material's mechanical properties reach more than 85% of those of virgin PP materials of the same specifications, meeting the substrate selection requirements for high-performance modified granulation. Detailed Implementation

[0025] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0026] Example 1

[0027] A recycled high melt index and high impact PP granule material comprises the following components in parts by weight: 93 parts recycled PP substrate, 5 parts elastomer, 0.08 parts high temperature peroxide, 1 part crosslinking agent, 0.5 parts composite antioxidant and 1 part color masterbatch.

[0028] In recycled PP substrates, the ratio of PP material from waste washing machine drums to PP material from paint buckets is 5:5 by mass.

[0029] The elastomer is POE.

[0030] The high-temperature peroxide is DCP (dicumyl peroxide).

[0031] The crosslinking aid is GMA (glycidyl methacrylate).

[0032] The compound antioxidant is composed of antioxidant 1010 and antioxidant 168 in a 1:1 mass ratio.

[0033] The preparation method of the recycled high melt index and high impact resistance PP granules includes the following steps:

[0034] (1) Purification of recycled PP substrate: The recycled PP substrate is crushed into fragments with a particle size of 6-20mm and sent to an integrated photoelectric pre-sorting device (TOMRA photoelectric sorting machine) to remove impurities, non-PP plastics and aluminum foil; then the fragments are sequentially sent to a pre-washing tank, a hot washing tank, a rinsing tank and a flotation tank for multi-layer cleaning; the pre-washing water temperature of the pre-washing machine is 40℃ and the pre-washing water pressure is 0.3MPa; the hot washing temperature of the hot washing machine is 60℃ and the washing time is 30min, and an alkaline cleaning agent is added during hot washing; the rinsing machine uses circulating clean water to rinse and uses ultrasonic vibration to peel off the surface ink colloid; the flotation of the flotation machine removes residual impurities by density separation; after cleaning, the recycled PP substrate is dehydrated and dried to obtain a purity ≥95% and a water content ≤0.5%;

[0035] (2) Extrusion granulation: The purified and dried recycled PP substrate from step (1) is added to a first-stage single-screw granulator for extrusion. The extrusion temperature is 210℃, the screw speed is 90r / min, the extrusion pressure is 12MPa, and the filter screen is 100 mesh. The material extruded from the first-stage single-screw granulator is added to a second-stage twin-screw granulator. Then, high-temperature peroxide, elastomer, crosslinking agent and color masterbatch are added to the overlap position of the first-stage single-screw granulator and the second-stage twin-screw granulator for shearing and mixing reaction. After the reaction is completed, composite antioxidant is added to the first two heating blocks of the vacuum section in the second-stage twin-screw granulator. The vacuum degree is set to -0.08MPa to remove small molecule volatiles. Finally, after extrusion, strip drawing, cooling and pelletizing, recycled high melt index and high impact resistance PP granules are obtained. The extrusion process parameters for the twin-screw granulator are: temperature of each zone of the twin screw 170℃, screw speed 300r / min, extrusion pressure 12MPa, and filter screen 150 mesh.

[0036] Example 2

[0037] A recycled high melt index and high impact PP granule material comprises the following components in parts by weight: 89 parts recycled PP substrate, 10 parts elastomer, 0.01 parts high temperature peroxide, 0.2 parts crosslinking agent, 0.2 parts composite antioxidant, and 0.5 parts color masterbatch.

[0038] In recycled PP substrates, the ratio of PP material from waste washing machine drums to PP material from paint buckets is 7:3 by mass.

[0039] The elastomer is POP.

[0040] The high-temperature peroxide is BIBP (di-tert-butyl peroxide diisopropylbenzene).

[0041] The crosslinking aid is TMPTA (trimethylolpropane triacrylate).

[0042] The compound antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:3.

[0043] The preparation method of the recycled high melt index and high impact resistance PP granules includes the following steps:

[0044] (1) Purification of recycled PP substrate: The recycled PP substrate is crushed into fragments with a particle size of 6-20mm and sent to an integrated photoelectric pre-sorting device (TOMRA photoelectric sorting machine) to remove impurities, non-PP plastics and aluminum foil; then the fragments are sequentially sent to a pre-washing tank, a hot washing tank, a rinsing tank and a flotation tank for multi-layer cleaning; the pre-washing water temperature of the pre-washing machine is 40℃ and the pre-washing water pressure is 0.3MPa; the hot washing temperature of the hot washing machine is 60℃ and the washing time is 30min, and an alkaline cleaning agent is added during hot washing; the rinsing machine uses circulating clean water to rinse and uses ultrasonic vibration to peel off the surface ink colloid; the flotation of the flotation machine removes residual impurities by density separation; after cleaning, the recycled PP substrate is dehydrated and dried to obtain a purity ≥95% and a water content ≤0.5%;

[0045] (2) Extrusion granulation: The purified and dried recycled PP substrate from step (1) is added to a first-stage single-screw granulator for extrusion. The extrusion temperature is 230℃, the screw speed is 60r / min, the extrusion pressure is 8MPa, and the filter screen is 100 mesh. The material extruded from the first-stage single-screw granulator is added to a second-stage twin-screw granulator. Then, high-temperature peroxide, elastomer, crosslinking agent and color masterbatch are added to the overlap position of the first-stage single-screw granulator and the second-stage twin-screw granulator for shearing and mixing reaction. After the reaction is completed, composite antioxidant is added to the first two heating blocks of the vacuum section in the second-stage twin-screw granulator. The vacuum degree is set to -0.06MPa to remove small molecule volatiles. Finally, after extrusion, strip drawing, cooling and pelletizing, recycled high melt index and high impact resistance PP granules are obtained. The extrusion process parameters for the twin-screw granulator are: temperature of each zone of the twin screw 150℃, screw speed 200r / min, extrusion pressure 8MPa, and filter screen 150 mesh.

[0046] Example 3

[0047] A recycled high melt index and high impact PP granule material comprises the following components in parts by weight: 92 parts recycled PP substrate, 7 parts elastomer, 0.04 parts high temperature peroxide, 0.5 parts crosslinking agent, 0.3 parts composite antioxidant, and 0.8 parts color masterbatch.

[0048] In recycled PP substrates, the ratio of PP material from waste washing machine drums to PP material from paint buckets is 6:4 by mass.

[0049] The elastomers are POE and POP, with a POE:POP ratio of 5:2.

[0050] In high-temperature peroxides, the mass ratio of DCP (dicumyl peroxide) to BIBP (bis-tert-butyl peroxide) is 1:1.

[0051] In the crosslinking aid, the mass ratio of GMA (glycidyl methacrylate) to TMPTA (trimethylolpropane triacrylate) is 1:1.

[0052] The compound antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:2.

[0053] The preparation method of the recycled high melt index and high impact resistance PP granules includes the following steps:

[0054] (1) Purification of recycled PP substrate: The recycled PP substrate is crushed into fragments with a particle size of 6-20mm and sent to an integrated photoelectric pre-sorting device (TOMRA photoelectric sorting machine) to remove impurities, non-PP plastics and aluminum foil; then the fragments are sequentially sent to a pre-washing tank, a hot washing tank, a rinsing tank and a flotation tank for multi-layer cleaning; the pre-washing water temperature of the pre-washing machine is 40℃ and the pre-washing water pressure is 0.3MPa; the hot washing temperature of the hot washing machine is 60℃ and the washing time is 30min, and an alkaline cleaning agent is added during hot washing; the rinsing machine uses circulating clean water to rinse and uses ultrasonic vibration to peel off the surface ink colloid; the flotation of the flotation machine removes residual impurities by density separation; after cleaning, the recycled PP substrate is dehydrated and dried to obtain a purity ≥95% and a water content ≤0.5%;

[0055] (2) Extrusion granulation: The purified and dried recycled PP substrate from step (1) is added to a first-stage single-screw granulator for extrusion. The extrusion temperature is 220℃, the screw speed is 80r / min, the extrusion pressure is 10MPa, and the filter screen is 100 mesh. The material extruded from the first-stage single-screw granulator is added to a second-stage twin-screw granulator. Then, high-temperature peroxide, elastomer, crosslinking agent and color masterbatch are added to the overlap position of the first-stage single-screw granulator and the second-stage twin-screw granulator for shearing and mixing reaction. After the reaction is completed, composite antioxidant is added to the first two heating blocks of the vacuum section in the second-stage twin-screw granulator. The vacuum degree is set to -0.07MPa to remove small molecule volatiles. Finally, after extrusion, strip drawing, cooling and pelletizing, recycled high melt index and high impact resistance PP granules are obtained. The extrusion process parameters for the twin-screw granulator are as follows: temperature of each zone of the twin screw 160℃, screw speed 250r / min, extrusion pressure 10MPa, and filter screen 150 mesh.

[0056] Comparative Example 1: This comparative example does not contain crosslinking aids, and the other components and preparation methods are the same as in Example 1.

[0057] Comparative Example 2: This comparative example uses the traditional POE toughening solution. The raw materials are: 79.5 parts of recycled PP substrate, 20 parts of POE, 0.2 parts of composite antioxidant (168:1010=1:1), and 0.3 parts of color masterbatch; the recycled PP substrate is waste washing machine drum material.

[0058] The preparation method is a conventional one-step blending granulation: After purifying the recycled PP substrate according to the method in Example 1, the purified and dried recycled PP substrate is added to a first-stage single-screw granulator for extrusion. The extrusion temperature is 220℃, the screw speed is 80 r / min, the extrusion pressure is 10 MPa, and the filter screen is 100 mesh. The material extruded from the first-stage single-screw granulator is added to a second-stage twin-screw granulator, followed by the addition of composite antioxidants, elastomers, and color masterbatches for shearing and mixing reaction. Finally, the material is extruded, stretched, cooled, and pelletized to obtain the final product. The extrusion process parameters of the twin-screw granulator are: temperature of each zone of the twin screw 160℃, screw speed 250 r / min, extrusion pressure 10 MPa, and filter screen 150 mesh.

[0059] Comparative Example 3: This comparative example uses the traditional POE toughening solution. The raw materials are: 84.5 parts recycled PP substrate, 15 parts POE, 0.2 parts composite antioxidant (168:1010=1:1), and 0.3 parts color masterbatch. The recycled PP substrate is in the following mass ratio: waste washing machine drum material: paint drum material is 85:15.

[0060] The preparation method is a conventional one-step blending granulation: After purifying the recycled PP substrate according to the method in Example 1, the purified and dried recycled PP substrate is added to a first-stage single-screw granulator for extrusion. The extrusion temperature is 220℃, the screw speed is 80 r / min, the extrusion pressure is 10 MPa, and the filter screen is 100 mesh. The material extruded from the first-stage single-screw granulator is added to a second-stage twin-screw granulator, followed by the addition of composite antioxidants, elastomers, and color masterbatches for shearing and mixing reaction. Finally, the material is extruded, stretched, cooled, and pelletized to obtain the final product. The extrusion process parameters of the twin-screw granulator are: temperature of each zone of the twin screw 160℃, screw speed 250 r / min, extrusion pressure 10 MPa, and filter screen 150 mesh.

[0061] Performance testing:

[0062] The melt flow rate (230℃, 2.16 kg), cantilever beam impact strength (room temperature), tensile strength, flexural strength, and flexural modulus of the granules prepared in Examples 1, 2, 3, Comparative Examples 1, 2, and 3 were tested respectively. The melt flow rate (230℃, 2.16 kg) was tested according to the method in GB / T 3682.1-2018; the tensile strength was tested according to the method in GB / T 1040-2025; the flexural strength and flexural modulus were tested according to the method in GB / T 9341-2008; and the cantilever beam impact strength was tested according to the method in GB / T 1843-2008. The results are shown in Table 1.

[0063] Table 1 Performance of the pellets in each embodiment and comparative example

[0064] The data in the table above from Examples 1 to 3 show that, through a series of technical means such as high-temperature peroxide and crosslinking agent compound modification, deep purification treatment of recycled PP substrate, and one-step segmented feeding extrusion granulation, the present invention achieves a melt flow rate of 20-30 g / 10 min, cantilever beam impact strength ≥40 kJ / m², tensile strength ≥23 MPa, flexural strength ≥23 MPa, and flexural modulus of 1000-1200 MPa for the recycled PP substrate. This achieves a synergistic improvement in the high melt flow rate and high impact resistance of the recycled PP substrate, that is, it can obtain a high cantilever beam impact strength while ensuring a high melt flow rate, solving the problem that traditional materials cannot simultaneously achieve both fluidity and toughness, and meeting the requirements of efficient injection molding and extrusion molding.

[0065] Data from Example 1 and Comparative Example 1 show that the combination of high-temperature peroxide and crosslinking aid can simultaneously improve melt flow rate and retain impact performance with only a small amount of modified components. When high-temperature peroxide is used alone to degrade and control melt index, although a higher melt flow rate can be obtained, the impact strength will decrease significantly and cannot meet the requirements for high impact resistance. This indicates that the introduction of crosslinking aid plays a key role in improving impact resistance, and the tensile strength and other properties are also improved to a certain extent compared with those without crosslinking aid.

[0066] The data from Example 1 and Comparative Examples 2 and 3 show that the impact resistance of the recycled material prepared by the method of the present invention is comparable to that of the traditional POE toughening scheme, but its flexural strength and flexural modulus are far superior to the latter, resulting in better overall performance. At the same time, the raw material cost is reduced by more than 30% compared with the traditional elastomer toughening scheme, which greatly reduces the modification cost and achieves economical high-performance modification.

[0067] 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 recycled high melt index, high impact PP granule, characterized in that, It includes the following components in parts by weight: 89-93 parts recycled PP substrate, 5-10 parts elastomer, 0.01-0.08 parts high-temperature peroxide, 0.2-1 parts crosslinking aid, 0.2-0.5 parts composite antioxidant, and 0.5-1 parts color masterbatch.

2. The recycled high melt flow index, high impact resistance PP granules according to claim 1, characterized in that, The recycled PP substrate includes one or a mixture of two types of PP material from waste washing machine drums and PP material from paint drums.

3. The recycled high melt flow index, high impact resistance PP granules according to claim 1, characterized in that, The elastomer includes one or a mixture of two of POE and POP.

4. The recycled high melt flow index, high impact resistance PP granules according to claim 1, characterized in that, The high-temperature peroxide includes one or a mixture of two of DCP and BIBP.

5. The recycled high melt flow index, high impact resistance PP granules according to claim 1, characterized in that, The crosslinking aid includes one or a mixture of two of GMA and TMPTA.

6. The recycled high melt flow index, high impact resistance PP granules according to claim 1, characterized in that, The composite antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:(1-3).

7. A method for preparing recycled high melt index, high impact PP granules as described in any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Purification of recycled PP substrate: The recycled PP substrate is crushed into fragments and sent to an integrated photoelectric pre-sorting device to remove impurities, non-PP plastics and aluminum foil; then the fragments are sequentially sent to a pre-washing tank, a hot washing tank, a rinsing tank and a flotation tank for multi-layer cleaning. After cleaning, the substrate is dehydrated and dried to obtain recycled PP substrate with a purity ≥95% and a moisture content ≤0.5%. (2) Extrusion granulation: The purified and dried recycled PP substrate from step (1) is added to a single-screw granulator for extrusion and filtration; the material extruded from the single screw is added to a twin-screw granulator; then, high-temperature peroxide, crosslinking agent and color masterbatch are added at the overlap position of the single-screw granulator and the twin-screw granulator for shearing and mixing reaction; after the reaction is completed, composite antioxidant is added to the first two heating blocks of the vacuum section in the twin-screw granulator, and the vacuum degree is set to -0.08~-0.06MPa to remove small molecule volatiles; finally, after extrusion, stretching, cooling and pelletizing, recycled high melt index and high impact PP granules are obtained.

8. The preparation method according to claim 7, characterized in that, In step (1), the pre-wash water temperature in the pre-wash tank is 40-50℃ and the pre-wash water pressure is 0.3-0.5MPa; the hot wash temperature in the hot wash tank is 60-80℃ and the washing time is 20-30min, and an alkaline cleaning agent is added during hot washing; the rinsing tank is rinsed with circulating clean water; the flotation in the flotation tank is to remove residual impurities by density separation.

9. The preparation method according to claim 7, characterized in that, In step (1), the particle size of the fragments is 6-20 mm.

10. The preparation method according to claim 7, characterized in that, In step (2), the extrusion temperature of the single screw granulator is 210-230℃, the screw speed is 60-90r / min, the extrusion pressure is 8-12MPa, and the filter screen is 100 mesh.

11. The preparation method according to claim 7, characterized in that, In step (2), the extrusion process parameters of the twin-screw granulator are: temperature of each zone of the twin screw 150-170℃, screw speed 200-300r / min, extrusion pressure 8-12MPa, and filter screen 150 mesh.

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