Method for recycling polypropylene waste into high-rigid high-tough polypropylene

Abstract

The application provides a method for recycling polypropylene waste into high-rigidity and high-toughness polypropylene polymer, and relates to the technical field of upgrading and recycling of waste plastics. The method comprises the following steps: S1, polypropylene waste is cleaned and sieved by a vibrating screen, and then is crushed into granular material with a particle size of less than or equal to 5 mm; S2, after the granular material is dried to a water content of less than 0.5%, 7% to 10% of glass fiber and 2.3% to 3% of elastomer are added to the granular material under a temperature of 200 DEG C to 230 DEG C and a pressure of 5 MPa to 15 MPa, and the mixture is melt-blended, extruded and granulated to obtain first polypropylene particles; and S3, after the first polypropylene particles are dried to a water content of less than 1%, 15% to 18% of nano calcium carbonate and 2% to 2.4% of a coupling agent are added to the granular material under a temperature of 200 DEG C to 220 DEG C and a pressure of 10 MPa to 14 MPa, and the mixture is melt-blended, extruded and granulated to obtain high-rigidity and high-toughness polypropylene polymer particles. The prepared polypropylene polymer has excellent toughness and rigidity.

Description

Technical Field

[0001] This invention relates to the field of waste plastic recycling technology, specifically to a method for recycling polypropylene waste into high-rigidity and high-toughness polypropylene polymer. Background Technology

[0002] Recycling polypropylene (PP) waste is an important direction for resource recycling and environmental protection. In existing technologies, the complex origins, high impurity content, and significant performance variations of PP waste make it difficult to simultaneously meet the requirements for toughening and stiffening in recycling processes, and the processing costs are also high. Therefore, there is an urgent need for a method to recycle PP waste into high-strength, high-toughness PP to achieve high-value-added transformation of PP waste. Summary of the Invention

[0003] (a) Technical problems to be solved

[0004] To address the shortcomings of existing technologies, this invention provides a method for recycling polypropylene waste into high-rigidity and high-toughness polypropylene polymers, solving the technical problem that existing recycling processes cannot simultaneously meet the requirements of toughening and stiffening.

[0005] (II) Technical Solution

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for recycling polypropylene waste into high-rigidity, high-toughness polypropylene polymer, comprising the following steps:

[0008] S1. After washing and vibrating screening, the polypropylene waste is crushed into granules with a particle size ≤5mm.

[0009] S2. After drying the granules to a moisture content of less than 0.5%, glass fiber of 7% to 10% of the mass of the granules and elastomer of 2.3% to 3% are added at a temperature of 200℃ to 230℃ and a pressure of 5MPa to 15MPa. The mixture is then melt-blended, extruded, and granulated to obtain the first polypropylene granules.

[0010] S3. The first polypropylene granules are dried to a moisture content of less than 1%. At a temperature of 200℃~220℃ and a pressure of 10MPa~14MPa, nano-calcium carbonate of 15%~18% of the granules mass and coupling agent of 2%~2.4% of the granules mass are added. The mixture is then melt-blended, extruded, and granulated to obtain high-rigidity and high-toughness polypropylene polymer granules.

[0011] This invention discloses a method for recycling polypropylene waste into a high-rigidity, high-toughness polypropylene polymer. The method involves treating the polypropylene waste with glass fiber, elastomer, nano-calcium carbonate, and a coupling agent. The synergistic effect of the glass fiber and elastomer improves the toughness of the prepared polypropylene polymer, while the synergistic effect of the nano-calcium carbonate and the coupling agent improves its rigidity. Therefore, the prepared polypropylene polymer possesses both excellent toughness and rigidity.

[0012] Preferably, the mass ratio of the amount of the granular material to the total amount of the glass fiber, elastomer, nano-calcium carbonate, and coupling agent is 100:30.

[0013] By controlling the mass ratio of the amount of the granular material to the total amount of glass fiber, elastomer, nano-calcium carbonate, and coupling agent, the prepared polypropylene polymer can possess both excellent rigidity and toughness.

[0014] Preferably, the mass ratio of glass fiber to elastomer is 10:3.

[0015] Preferably, the mass ratio of the nano-calcium carbonate to the coupling agent is 15:2.

[0016] Preferably, the mass ratio of the total amount of glass fiber and elastomer to the total amount of nano-calcium carbonate and coupling agent is 1:1.3 to 1:2.

[0017] By controlling the mass ratio of glass fiber to elastomer to be 10:3, the mass ratio of nano-calcium carbonate to coupling agent to be 15:2, and the mass ratio of the total amount of glass fiber and elastomer to the total amount of nano-calcium carbonate and coupling agent to be 1:1.3 to 1:2, the rigidity and toughness of the prepared polypropylene polymer can be balanced.

[0018] Preferably, the elastomer is selected from polyolefin elastomers and ethylene propylene diene monomer (EPDM) rubber.

[0019] Preferably, the particle size of the nano-calcium carbonate is 50-100 nm.

[0020] Preferably, the coupling agent is selected from phthalate coupling agents, silane coupling agents, and maleic anhydride-grafted polypropylene coupling agents.

[0021] Preferably, the mass ratio of the total amount of glass fiber and elastomer to the total amount of nano-calcium carbonate and coupling agent is 1:1.3.

[0022] By controlling the mass ratio of the total amount of glass fiber and elastomer to the total amount of nano-calcium carbonate and coupling agent to 1:1.3, the rigidity and toughness of the prepared polypropylene polymer can be balanced.

[0023] Preferably, the mass ratio of the total amount of glass fiber and elastomer to the total amount of nano-calcium carbonate and coupling agent is 1:2.

[0024] By controlling the mass ratio of the total amount of glass fiber and elastomer to the total amount of nano-calcium carbonate and coupling agent to 1:2, both the rigidity and toughness of the prepared polypropylene polymer can be taken into account. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the notch on a specimen prepared for testing the impact strength of a simply supported beam. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] This application provides a method for recycling polypropylene waste into a high-rigidity and high-toughness polypropylene polymer, which solves the technical problem that existing recycling processes cannot simultaneously meet the requirements of toughening and stiffening, and achieves the preparation of a polypropylene polymer with both excellent rigidity and toughness.

[0029] The technical solution in this application is to solve the above-mentioned technical problems, and the general idea is as follows:

[0030] This invention provides a method for recycling polypropylene waste into high-rigidity, high-toughness polypropylene polymer, comprising the following steps:

[0031] S1. After washing and vibrating screening, the polypropylene waste is crushed into granules with a particle size ≤5mm.

[0032] S2. After drying the granules to a moisture content of less than 0.5%, glass fiber of 7% to 10% of the mass of the granules and elastomer of 2.3% to 3% are added at a temperature of 200℃ to 230℃ and a pressure of 5MPa to 15MPa. The mixture is then melt-blended, extruded, and granulated to obtain the first polypropylene granules.

[0033] S3. The first polypropylene granules are dried to a moisture content of less than 1%. At a temperature of 200℃~220℃ and a pressure of 10MPa~14MPa, nano-calcium carbonate of 15%~18% of the granules mass and coupling agent of 2%~2.4% of the granules mass are added. The mixture is then melt-blended, extruded, and granulated to obtain high-rigidity and high-toughness polypropylene polymer granules.

[0034] In some embodiments, polypropylene waste includes at least one of briquettes, water-reclaimed material, and fallen material. Briquettes are irregular solid lumps discharged from the start-up valve of a polypropylene extruder during start-up and shutdown due to poor temperature control and material flow. Water-reclaimed material consists of long strips, flakes, and fragments of polypropylene that adhere to each other during the washing and separation process of granules in underwater pelletizing. Fallen material is polypropylene material that falls to the ground and mixes with ground contaminants during conveying, screening, and packaging. Briquette pretreatment includes: shredding → crushing → washing, with a cutter speed of 400–600 rpm. Water-reclaimed material pretreatment includes: washing → vibrating screening → crushing → secondary washing → drying, controlling the moisture content to ≤0.5%. Fallen material pretreatment includes: washing → impurity separation → drying, optimizing the cooling time to 20–30 seconds to improve dimensional stability.

[0035] In some embodiments, the cleaning can be performed by any cleaning method known in the art. For example, physical cleaning of polypropylene (PP) materials can be performed using the cavitation effect of ultrasound and high-frequency mechanical vibration for efficient decontamination, degassing, or surface treatment.

[0036] In some embodiments, the particle size of the granules is 1 mm, 2 mm, 3 mm, 4 mm, 5 mm or any value between these values.

[0037] In some embodiments, the length of the glass fiber is 3 mm, 4 mm, 5 mm or any value between them.

[0038] In some embodiments, the glass fiber length is 3 mm to 5 mm, which gives the prepared polypropylene polymer excellent toughness.

[0039] In some embodiments, the amount of glass fiber is 5%, 8%, 9%, 10%, 11%, 12%, 15% or any value between thereof, of the mass of the granules, and the amount of elastomer is 2%, 3%, 4%, 5% or any value between thereof, of the mass of the granules.

[0040] In some embodiments, the amount of nano-calcium carbonate added accounts for 10%, 13%, 14%, 15%, 16%, 17%, 20% or any value between these percentages of the mass of the granules, and the amount of coupling agent added accounts for 1%, 2%, 3% or any value between these percentages of the mass of the granules.

[0041] In some embodiments, S2 is performed by melt blending using a twin-screw extruder, for example, with an aspect ratio of 44, a nominal diameter of 71 mm, and a rotation speed of 500–600 rpm.

[0042] In some implementations, a segmented temperature control process is used in S3, for example, the first segment is 220°C and the second segment is 200°C, to ensure uniform dispersion of nano-calcium carbonate.

[0043] In some embodiments, the pelletizing system for preparing the high-rigidity, high-toughness polypropylene polymer particles uses nitrided steel cutters with a die orifice diameter of 4 mm, resulting in particle sizes of 3–5 mm. The vacuum dehydration system for preparing the high-rigidity, high-toughness polypropylene polymer particles has an ultimate vacuum of -0.09 MPa, a polypropylene polymer particle moisture content ≤0.3%, and a polypropylene polymer particle uniformity of over 95%, resulting in an efficiency increase of 2000 yuan per ton. The toughened grade exhibits a 40% increase in impact strength, while the rigidified grade shows a 30% increase in flexural modulus.

[0044] The present invention discloses a method for recycling polypropylene waste into a high-rigidity and high-toughness polypropylene polymer. The method involves treating the polypropylene waste with glass fiber, elastomer, nano-calcium carbonate, and coupling agent. The toughness of the prepared polypropylene polymer is improved by the synergistic effect of glass fiber and elastomer, and the rigidity of the polypropylene polymer prepared by the present invention is improved by the synergistic effect of nano-calcium carbonate and coupling agent.

[0045] Preferably, the mass ratio of the amount of the granular material to the total amount of the glass fiber, elastomer, nano-calcium carbonate, and coupling agent is 100:30.

[0046] By controlling the mass ratio of the amount of the granular material to the total amount of glass fiber, elastomer, nano-calcium carbonate, and coupling agent, the prepared polypropylene polymer can possess both excellent rigidity and toughness.

[0047] Preferably, the mass ratio of glass fiber to elastomer is 10:3.

[0048] Preferably, the mass ratio of the nano-calcium carbonate to the coupling agent is 15:2.

[0049] In some embodiments, the mass ratio of the total amount of glass fiber and elastomer to the total amount of nano-calcium carbonate and coupling agent is 1:1.3, 1:1.5, 1:2 or any value between them.

[0050] By controlling the mass ratio of glass fiber to elastomer to be 10:3, the mass ratio of nano-calcium carbonate to coupling agent to be 15:2, and the mass ratio of the total amount of glass fiber and elastomer to the total amount of nano-calcium carbonate and coupling agent to be 1:1.3 to 1:2, the rigidity and toughness of the prepared polypropylene polymer can be balanced.

[0051] Preferably, the elastomer is selected from polyolefin elastomers and ethylene propylene diene monomer (EPDM) rubber.

[0052] Preferably, the particle size of the nano-calcium carbonate is 50-100 nm.

[0053] Preferably, the coupling agent is selected from phthalate coupling agents, silane coupling agents, and maleic anhydride-grafted polypropylene coupling agents.

[0054] Preferably, the mass ratio of the total amount of glass fiber and elastomer to the total amount of nano-calcium carbonate and coupling agent is 1:1.3.

[0055] By controlling the mass ratio of the total amount of glass fiber and elastomer to the total amount of nano-calcium carbonate and coupling agent to 1:1.3, the rigidity and toughness of the prepared polypropylene polymer can be balanced.

[0056] Preferably, the mass ratio of the total amount of glass fiber and elastomer to the total amount of nano-calcium carbonate and coupling agent is 1:2.

[0057] By controlling the mass ratio of the total amount of glass fiber and elastomer to the total amount of nano-calcium carbonate and coupling agent to 1:2, both the rigidity and toughness of the prepared polypropylene polymer can be taken into account.

[0058] The rigidity of polypropylene polymer is a well-known concept in the art and can be tested using methods known in the art, such as a polypropylene tensile strength tester, as per GB / T 1040.1-2018 Determination of tensile properties of plastics and GB / T 1040.2-2022 Determination of tensile properties of plastics.

[0059] The toughness of polypropylene polymer is a well-known concept in the art and can be tested using methods known in the art, such as a pendulum simply supported beam impact tester, as per GB / T 1043.1-2008 Determination of impact properties of simply supported beams in plastics.

[0060] To better understand the above technical solution, the following will provide a detailed explanation of the above technical solution in conjunction with specific implementation methods.

[0061] I. Preparation Method

[0062] Example 1

[0063] This embodiment provides a method for recycling polypropylene waste into high-rigidity and high-toughness polypropylene polymer, including the following steps:

[0064] S1. After washing and vibrating screening, the water-washed material is crushed into granules with a particle size of 5mm.

[0065] S2. After drying the granules to a moisture content of 0.3%, take 100 parts by weight and feed them into a twin-screw extruder. Adjust the temperature of the twin-screw extruder to 210℃, the pressure to 10MPa, and the speed to 550rpm. Add 10% of the granules by weight of glass fiber with a length of 4mm and 3% of polyolefin elastomer POE. Blend and extrude to granulate to obtain the first polypropylene granules.

[0066] S3. Dry the first polypropylene granules to a moisture content of 0.5%, feed them into a twin-screw extruder, adjust the front section temperature of the twin-screw extruder to 220℃, the rear section temperature to 200℃, the pressure to 12MPa, and the rotation speed to 550rpm. Add 15% of the granule mass of 80nm nano-calcium carbonate and 2% of the granule mass of titanate coupling agent, and co-extrude and granulate to obtain high-rigidity and high-toughness polypropylene polymer granules.

[0067] Examples 2-6

[0068] The difference between Examples 2-6 and Example 1 is that the total amount of glass fiber and POE used in the preparation of high-rigidity and high-toughness polypropylene polymer particles is different from the total amount of nano-calcium carbonate and titanate coupling agent by mass ratio, as shown in Table 1. Other aspects are the same as in Example 1.

[0069] Table 1. Amount of raw materials used in the preparation of Examples 2-6

[0070] Example 2 Example 3 Example 4 Example 5 Example 6 Granular material 100 copies 100 copies 100 copies 100 copies 100 copies Total amount of glass fiber, POE, nano-calcium carbonate, and titanate coupling agent 30 copies 30 copies 30 copies 30 copies 30 copies The ratio of glass fiber to POE mass 10:3 10:3 10:3 10:3 10:3 Mass ratio of nano-calcium carbonate to titanate coupling agent 15:2 15:2 15:2 15:2 15:2 Mass ratio of total glass fiber and POE usage to total nano-calcium carbonate and titanate coupling agent usage 1：1 1：1.5 1：2 1：0.8 1：2.5

[0071] Comparative Example 1

[0072] The difference between this comparative example and Example 1 is that no glass fiber is added, and the amount of POE added accounts for 13% of the mass of the granules. The rest is the same as in Example 1. The specific dosage is shown in Table 2.

[0073] Comparative Example 2

[0074] The difference between this comparative example and Example 1 is that POE is not added, and the amount of glass fiber added accounts for 13% of the mass of the granules. Other aspects are the same as in Example 1. The specific dosage is shown in Table 2.

[0075] Comparative Example 3

[0076] The difference between this comparative example and Example 1 is that no nano-calcium carbonate is added, and the amount of titanate coupling agent added accounts for 17% of the mass of the granules. The rest is the same as in Example 1. The specific dosage is shown in Table 2.

[0077] Comparative Example 4

[0078] The difference between this comparative example and Example 1 is that no titanate coupling agent is added, and the amount of nano-calcium carbonate added accounts for 17% of the mass of the granules. Other aspects are the same as in Example 1. The specific dosage is shown in Table 2.

[0079] Table 2. Raw material usage for Comparative Examples 1-4

[0080] Fiberglass POE Nano calcium carbonate titanate coupling agent Comparative Example 1 0 13% 15% 2% Comparative Example 2 13% 0 15% 2% Comparative Example 3 10% 3% 0 17% Comparative Example 4 10% 3% 17% 0

[0081] II. Testing Methods

[0082] The properties of the high-rigidity and high-toughness polypropylene polymer particles prepared in Examples 1-6 and Comparative Examples 1-4 were tested using the following methods:

[0083] 1 Impact strength of simply supported beam

[0084] 1.1 Sample Preparation

[0085] 1.1.1 Sample Preparation

[0086] In accordance with ISO 2818:1994, the high-rigidity and high-toughness polypropylene polymer particles prepared in Examples 1-6 and Comparative Examples 1-4 were used to prepare sample plates with a length * width * thickness of 80±2mm * 10±0.2mm * 4±0.2mm.

[0087] 1.1.2 Sample Inspection

[0088] The specimen material should be free from distortion and have mutually perpendicular parallel surfaces. The surfaces and edges should be free from scratches, pits, dents, and burrs. Visually inspect the specimen using a ruler, straightedge, and flat plate, and measure it with a micrometer to ensure compliance with requirements. If any one or more of the observed and measured specimens fail to meet the requirements, the specimen should be discarded or machined to a suitable size and shape.

[0089] 1.1.3 Machining shall be performed according to ISO 2818:1994 to process the sample into... Figure 1 The shape and depth shown indicate that the notch is a type A notch with a bottom radius of r. N =0.25mm±0.05mm, and perpendicular to the spindle.

[0090] 1.2 The samples were kept at a constant temperature of 23℃ and 50% humidity for 24 hours, and then tested at 23℃ and 50% humidity. A pendulum impact tester (model 6967, manufactured by Ceast) was used to test the samples according to the standard GB / T 1043.1-2008 "Determination of Impact Properties of Simply Supported Plastic Beams". The sample was placed on the tester support with the impact blade facing the center of impact. The notched sample was carefully positioned so that the center of the notch was exactly on the impact plane. The pendulum was released, and the impact energy absorbed by the sample was recorded. The test results are shown in Table 3.

[0091] 2 Tensile strength

[0092] 2.1 Sample Preparation

[0093] In accordance with GB / T 1040, the high-rigidity and high-toughness polypropylene polymer particles prepared in Examples 1-6 and Comparative Examples 1-4 were made into dumbbell-shaped sample plates with a total length ≥150mm, a gauge length (parallel section) of 50mm, a width of 10mm, and a thickness of 4±0.2mm.

[0094] 2.2 Sample Testing

[0095] The sample sheets were tested using an Instron 5566 tensile strength testing machine according to the standard GB / T 1040.1-2018 Determination of Tensile Properties of Plastics. The test results are shown in Table 3.

[0096] 3. Flexural modulus

[0097] 3.1 Sample Preparation

[0098] According to ISO 2818, the high-rigidity and high-toughness polypropylene polymer particles prepared in Examples 1-6 and Comparative Examples 1-4 were made into samples with a length l*width b*thickness h of 80±2mm*10±0.2mm*4±0.2mm.

[0099] 3.2 Sample Inspection

[0100] The specimen must not be twisted; opposing surfaces should be parallel to each other, and adjacent surfaces should be perpendicular to each other. All surfaces and edges should be free of scratches, pits, dents, and burrs. Visually inspect the specimen for compliance with the above requirements using a ruler, gauge, and plate, and measure with vernier calipers. Before testing, specimens that do not meet one or more of the above requirements should be rejected, or they should be machined to acceptable dimensions and shape.

[0101] 3.3 The flexural modulus tester manufactured by Instron (model 5566) was used to test the sample sheets according to the standard GB / T 1040.1-2018 Determination of tensile properties of plastics. The test results are shown in Table 3.

[0102] III. Test Results

[0103] The test results of the above embodiments and comparative examples are shown in Table 3.

[0104] Table 3 Test results of the examples and comparative examples

[0105] Impact strength of simply supported beam / kJ / m² Tensile strength / MPa Flexural modulus / MPa Example 1 25 32 1800 Example 2 26 33 1445 Example 3 23 31 1810 Example 4 22 30 1820 Example 5 27 34 1430 Example 6 15 20 1890 Comparative Example 1 10 9 1832 Comparative Example 2 12 11 1790 Comparative Example 3 26 33 850 Comparative Example 4 23 30 910

[0106] According to Tables 1, 2, and 3, comparing Comparative Examples 1 and 2 with Example 1, it is evident that the polypropylene polymer prepared with both glass fiber and POE exhibits higher simply supported beam impact strength and tensile strength. Conversely, the polypropylene polymer prepared lacking either component shows lower simply supported beam impact strength and tensile strength. Therefore, glass fiber and POE have a synergistic effect in improving the toughness of the polypropylene polymer in this application. Comparative Examples 3 and 4 with Example 1, it is evident that the polypropylene polymer prepared with both nano-calcium carbonate and titanate coupling agent exhibits higher flexural modulus. The flexural modulus of polypropylene polymers prepared by lacking either of these components is relatively low. Therefore, nano-calcium carbonate and titanate coupling agent have a synergistic effect in improving the rigidity of the polypropylene polymer of this application. As can be seen from the comparison of Examples 1, 3, 4 and Examples 2, 5, 6, when the mass ratio of glass fiber to POE is 10:3 and the mass ratio of nano-calcium carbonate to titanate coupling agent is 15:2, the mass ratio of the total amount of glass fiber and POE to the total amount of nano-calcium carbonate and titanate coupling agent is 1:1.3 to 1:2, which can take into account both the rigidity and toughness of the prepared polypropylene polymer.

[0107] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0108] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0109] The present invention has been illustrated with the above embodiments to describe the detailed process flow of the present invention. However, the present invention is not limited to the above detailed process flow, that is, it does not mean that the present invention must rely on the above detailed process flow to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method of recycling polypropylene scrap into a high-rigid high-tough polypropylene polymer, characterized in that, It comprises the following steps: S1, the polypropylene waste is cleaned, vibrated and sieved, and then crushed to a particle size of ≤5mm; S2, after the granular material is dried to a moisture content of less than 0.5%, 7%-10% of glass fiber, 2.3%-3% of elastomer, and 2%-2.4% of coupling agent are added to the granular material under the conditions of a temperature of 200-230℃ and a pressure of 5-15MPa, and then the mixture is melt blended, extruded and granulated to obtain first polypropylene particles; S3, after the first polypropylene particles are dried to a moisture content of less than 1%, 15%-18% of nano calcium carbonate and 2%-2.4% of coupling agent are added to the granular material under the conditions of a temperature of 200-220℃ and a pressure of 10-14MPa, and then the mixture is melt blended, extruded and granulated to obtain high-rigidity and high-toughness polypropylene particles; The mass ratio of the glass fiber to the elastomer is 10:3; The mass ratio of the nano calcium carbonate to the coupling agent is 15:2; The mass ratio of the total amount of the glass fiber and the elastomer to the total amount of the nano calcium carbonate and the coupling agent is 1:1.3-1:

2. The mass ratio of the granular material to the total amount of the glass fiber, the elastomer, the nano calcium carbonate and the coupling agent is 100:

30.

2. The process for recycling polypropylene scrap into high stiffness and high toughness polypropylene polymer as claimed in claim 1 wherein, The elastomer is selected from polyolefin elastomers and ethylene-propylene-diene rubber.

3. The process for recycling polypropylene scrap into high stiffness and high toughness polypropylene polymer as claimed in claim 1 wherein, The particle size of the nano calcium carbonate is 50-100nm.

4. The process for recycling polypropylene scrap into high stiffness and high toughness polypropylene polymer as claimed in claim 1 wherein, The coupling agent is selected from phthalate coupling agents, silane coupling agents and maleic anhydride grafted polypropylene coupling agents.

5. The process for recycling polypropylene scrap into high stiffness and high toughness polypropylene polymer as claimed in claim 1 wherein, The mass ratio of the total amount of the glass fiber and the elastomer to the total amount of the nano calcium carbonate and the coupling agent is 1:1.

3.

6. The process for recycling polypropylene scrap into high stiffness and high toughness polypropylene polymer as claimed in claim 1 wherein, The mass ratio of the total amount of the glass fiber and the elastomer to the total amount of the nano calcium carbonate and the coupling agent is 1:

2.

7. The process for recycling polypropylene scrap into high stiffness and high toughness polypropylene polymer as claimed in claim 1 wherein, ​

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