Recyclable polypropylene material and preparation method thereof

Abstract

The invention relates to a recyclable polypropylene material and a preparation method thereof, and belongs to the technical field of high polymer materials. According to the invention, the basalt fiber is subjected to isocyanate group modification and then is modified by partial ester group terminated hyperbranched polyester polyol, hydroxyl in the polyol is chemically bonded with the isocyanate group on the surface of the fiber, and a hyperbranched polyester structure is chemically bonded on the surface of the fiber, so that the fluidity of the fiber can be effectively improved; and the reduction of the performance caused by the damage of the fiber due to shear force in the melting processing process is avoided. The recyclable polypropylene material prepared by the invention has better initial mechanical properties, the polypropylene material obtained by crushing after standing at a high temperature for a certain time and reprocessing also has better mechanical properties, and the retention rates of tensile strength, impact strength and wear resistance are not less than 95%; the excellent cyclic utilization performance is shown.

Description

Technical Field

[0001] This invention relates to a recyclable polypropylene material and its preparation method, belonging to the field of polymer materials technology. Background Technology

[0002] Polypropylene, with its low density, good balance of rigidity and toughness, and excellent thermal and acid / alkali resistance, has been widely used in automotive interior and exterior trim products and other industrial fields. However, with increasingly harsh operating environments, higher requirements are being placed on the mechanical strength and heat-resistant and flame-retardant properties of polypropylene. Basalt fiber, due to its advantages such as high and low temperature resistance, acid and alkali resistance, electrical insulation, and low moisture absorption, is widely used in military, construction, and aerospace industries. Basalt fiber reinforced composite materials possess high strength, high temperature resistance, and high corrosion resistance, and can be used to manufacture aircraft parts, petrochemical pipelines, and high-temperature filter materials.

[0003] As polypropylene production continues to grow, the challenge of polypropylene waste disposal is becoming increasingly prominent. Currently, the main methods for treating polypropylene fiber composites are incineration or landfill, which have adverse environmental impacts. This is because when inorganic fiber materials are subjected to shearing forces in the screw, the fiber structure is damaged, leading to a decline in the mechanical properties of the composite material, making it unable to meet usage requirements and thus unable to be recycled.

[0004] Therefore, there is an urgent need to develop a recyclable polypropylene material and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to provide a recyclable polypropylene material and its preparation method, in order to solve the problem that the current method of using basalt fiber reinforced polypropylene is prone to structural damage due to the shearing action of basalt fibers in the screw, which makes it impossible to recycle and reuse the material.

[0006] This invention provides a method for preparing recyclable polypropylene material, comprising the following steps: (1) Basalt fibers are modified with isocyanate groups to obtain isocyanate-modified basalt fibers; (2) React some of the hydroxyl groups in the hyperbranched polyester polyol with an acyl chloride compound to obtain a partially ester-terminated hyperbranched polyester polyol; wherein the molar ratio of the hydroxyl group in the hyperbranched polyester polyol to the molar ratio of the acyl chloride compound is 1:0.5~0.7; the acyl chloride compound is a monobasic saturated fatty acyl chloride with 6~12 carbon atoms. (3) Isocyanate-modified basalt fiber and a portion of ester-terminated hyperbranched polyester polyol are mixed and reacted in a solvent to obtain hyperbranched polyester-modified basalt fiber; wherein the molar ratio of the isocyanate group of the isocyanate-modified basalt fiber to the molar ratio of the hydroxyl group of the portion of ester-terminated hyperbranched polyester polyol is 0.7~0.8:1; (4) After mixing polypropylene, hyperbranched polyester modified basalt fiber and maleic anhydride grafted polypropylene evenly, melt extrusion granulation is carried out to obtain recyclable polypropylene material.

[0007] Preferably, the basalt fibers have an average length of 5-8 mm and an average diameter of 6-10 μm.

[0008] Preferably, the method for isocyanate-modified basalt fiber is as follows: basalt fiber, 3-isocyanate-propyltrimethoxysilane and anhydrous toluene are mixed and reacted at 100~105℃ for 12~15h to obtain isocyanate-modified basalt fiber; wherein the mass ratio of basalt fiber to 3-isocyanate-propyltrimethoxysilane is 1:1~1.3.

[0009] Preferably, the acyl chloride compound is nonanoyl chloride, hexanoyl chloride, or lauroyl chloride.

[0010] Preferably, the hyperbranched polyester polyol is Boltorn P1000.

[0011] Preferably, in step (3), the temperature of the mixing reaction is 85~90℃ and the time is 5~8h.

[0012] Preferably, in step (4), the polypropylene includes high melt index polypropylene and low melt index polypropylene. The melt index of high melt index polypropylene is 1500~2000g / 10min under test conditions of 230℃ and 2.16kg load, and the melt index of low melt index polypropylene is 25~50g / 10min under test conditions of 230℃ and 2.16kg load.

[0013] Preferably, in step (4), the maleic anhydride content of the maleic anhydride-grafted polypropylene is 0.8-1%, and the melt index is 5-8 g / 10 min under test conditions of 230°C and 2.16 kg load.

[0014] Preferably, in step (4), the mass ratio of high melt index polypropylene, low melt index polypropylene, hyperbranched polyester modified basalt fiber and maleic anhydride grafted polypropylene is 35~45:18~24:40~50:8~10.

[0015] This invention provides a recyclable polypropylene material prepared by the method described above.

[0016] The beneficial effects of this invention are as follows: This invention modifies basalt fibers with isocyanate groups and then further modifies them with partially ester-terminated hyperbranched polyester polyols. The hydroxyl groups in the polyol chemically bond with the isocyanate groups on the fiber surface, and the hyperbranched polyester structure is chemically bonded to the fiber surface. This effectively improves fiber fluidity and prevents fiber damage due to shear force during melt processing, thus avoiding performance degradation. The recyclable polypropylene material prepared by this invention has excellent initial mechanical properties. The polypropylene material obtained after being pulverized at high temperature for a certain period and then reprocessed also exhibits excellent mechanical properties, with tensile strength, impact strength, and abrasion resistance retention rates of no less than 95%, demonstrating excellent recyclability. Detailed Implementation

[0017] The following examples are intended to further illustrate the content of the present invention, rather than to limit the scope of protection of the present invention. Example 1

[0018] The method for preparing recyclable polypropylene material in this embodiment includes the following steps: (1) Basalt fiber (average length 5 mm, average diameter 6 μm), 3-isocyanate-propyltrimethoxysilane and anhydrous toluene were added to a reaction vessel, heated to 100 °C, stirred for 12 h, cooled to room temperature and filtered. The filter cake was washed with anhydrous toluene and anhydrous tetrahydrofuran, respectively. The washed filter cake was vacuum dried to obtain isocyanate-modified basalt fiber. The mass ratio of basalt fiber, 3-isocyanate-propyltrimethoxysilane and anhydrous toluene was 1:1:70.

[0019] (2) Add hyperbranched polyester polyol (Boltorn P1000) and anhydrous toluene in a mass ratio of 1:15 to a reaction vessel, then introduce nitrogen into the reaction vessel, cool the material in the reaction vessel to 0°C, and then add a mixed solution containing triethylamine, nonanoyl chloride and anhydrous toluene (the mass fraction of toluene in the mixed solution is 60%) to the reaction vessel dropwise. After the dropwise addition is completed, stir the reaction at room temperature for 10 h, filter, distill the filtrate under reduced pressure to remove the solvent toluene, and dry to obtain a partially ester-terminated hyperbranched polyester polyol; wherein, the molar ratio of the hydroxyl group of the hyperbranched polyester polyol to the molar ratio of nonanoyl chloride is 1:0.5, and the molar ratio of triethylamine to nonanoyl chloride is 1.2:1.

[0020] (3) Isocyanate-modified basalt fiber and anhydrous toluene with a mass ratio of 1:40 were added to the reactor. Nitrogen gas was then introduced into the reactor. A mixed solution containing a portion of ester-terminated hyperbranched polyester polyol and anhydrous toluene (the mass fraction of toluene in the mixed solution was 50%) was added to the reactor. The mixture was heated to 85°C and stirred for 5 hours. After cooling to room temperature, the mixture was filtered. The filter cake was washed with toluene and ethanol in sequence and dried to obtain hyperbranched polyester modified basalt fiber. The molar ratio of the isocyanate group of the isocyanate-modified basalt fiber to the molar ratio of the hydroxyl group of the portion of ester-terminated hyperbranched polyester polyol was 0.7:1.

[0021] (4) High melt index polypropylene (melt index of 1500 g / 10 min under test conditions of 230℃ and 2.16 kg load), low melt index polypropylene (melt index of 25 g / 10 min under test conditions of 230℃ and 2.16 kg load), hyperbranched polyester modified basalt fiber and maleic anhydride grafted polypropylene (maleic anhydride content of 0.8%, melt index of 5 g / 10 min under test conditions of 230℃ and 2.16 kg load) are mixed evenly in a mass ratio of 35:18:40:8 and then added to a twin-screw extruder. The mixture is melt-extruded and granulated at 210~220℃ to obtain recyclable polypropylene material. Example 2

[0022] The method for preparing recyclable polypropylene material in this embodiment includes the following steps: (1) Basalt fiber (average length 8 mm, average diameter 10 μm), 3-isocyanate-propyltrimethoxysilane and anhydrous toluene were added to a reaction vessel, heated to 105 °C, stirred for 15 h, cooled to room temperature and filtered. The filter cake was washed with anhydrous toluene and anhydrous tetrahydrofuran, respectively. The washed filter cake was vacuum dried to obtain isocyanate-modified basalt fiber. The mass ratio of basalt fiber, 3-isocyanate-propyltrimethoxysilane and anhydrous toluene was 1:1.3:90.

[0023] (2) Add hyperbranched polyester polyol (Boltorn P1000) and anhydrous toluene in a mass ratio of 1:18 to a reaction vessel, then introduce nitrogen into the reaction vessel, cool the material in the reaction vessel to 0°C, and then add a mixed solution containing triethylamine, nonanoyl chloride and anhydrous toluene (the mass fraction of toluene in the mixed solution is 80%) to the reaction vessel dropwise. After the addition is completed, stir the reaction at room temperature for 15 h, filter, distill the filtrate under reduced pressure to remove the solvent toluene, and dry to obtain a partially ester-terminated hyperbranched polyester polyol; wherein, the molar ratio of the hydroxyl group of the hyperbranched polyester polyol to the molar ratio of nonanoyl chloride is 1:0.7, and the molar ratio of triethylamine to nonanoyl chloride is 1.4:1.

[0024] (3) Isocyanate-modified basalt fiber and anhydrous toluene with a mass ratio of 1:60 were added to the reactor. Nitrogen gas was then introduced into the reactor. A mixed solution containing a portion of ester-terminated hyperbranched polyester polyol and anhydrous toluene (the mass fraction of toluene in the mixed solution was 50%) was added to the reactor. The mixture was heated to 90°C and stirred for 8 hours. After cooling to room temperature, the mixture was filtered. The filter cake was washed with toluene and ethanol in sequence and dried to obtain hyperbranched polyester modified basalt fiber. The molar ratio of the isocyanate group of the isocyanate-modified basalt fiber to the molar ratio of the hydroxyl group of the portion of ester-terminated hyperbranched polyester polyol was 0.8:1.

[0025] (4) High melt index polypropylene (melt index of 1500 g / 10 min under test conditions of 230℃ and 2.16 kg load), low melt index polypropylene (melt index of 25 g / 10 min under test conditions of 230℃ and 2.16 kg load), hyperbranched polyester modified basalt fiber and maleic anhydride grafted polypropylene (maleic anhydride content of 0.8%, melt index of 5 g / 10 min under test conditions of 230℃ and 2.16 kg load) are mixed evenly in a mass ratio of 45:24:50:10 and then added to a twin-screw extruder. The mixture is melt-extruded and granulated at 210~220℃ to obtain recyclable polypropylene material. Example 3

[0026] The method for preparing recyclable polypropylene material in this embodiment includes the following steps: (1) Basalt fiber (average length 5 mm, average diameter 6 μm), 3-isocyanate-propyltrimethoxysilane and anhydrous toluene were added to a reaction vessel, heated to 100 °C, stirred for 12 h, cooled to room temperature and filtered. The filter cake was washed with anhydrous toluene and anhydrous tetrahydrofuran, respectively. The washed filter cake was vacuum dried to obtain isocyanate-modified basalt fiber. The mass ratio of basalt fiber, 3-isocyanate-propyltrimethoxysilane and anhydrous toluene was 1:1:70.

[0027] (2) Add hyperbranched polyester polyol (Boltorn P1000) and anhydrous toluene in a mass ratio of 1:15 to a reaction vessel, then introduce nitrogen into the reaction vessel, cool the material in the reaction vessel to 0°C, and then add a mixed solution containing triethylamine, hexanoyl chloride and anhydrous toluene (the mass fraction of toluene in the mixed solution is 60%) to the reaction vessel dropwise. After the addition is completed, stir the reaction at room temperature for 10 h, filter, distill the filtrate under reduced pressure to remove the solvent toluene, and dry to obtain a partially ester-terminated hyperbranched polyester polyol; wherein, the molar ratio of the hydroxyl group of the hyperbranched polyester polyol to the molar ratio of hexanoyl chloride is 1:0.5, and the molar ratio of triethylamine to hexanoyl chloride is 1.2:1.

[0028] (3) Isocyanate-modified basalt fiber and anhydrous toluene with a mass ratio of 1:40 were added to the reactor. Nitrogen gas was then introduced into the reactor. A mixed solution containing a portion of ester-terminated hyperbranched polyester polyol and anhydrous toluene (the mass fraction of toluene in the mixed solution was 50%) was added to the reactor. The mixture was heated to 85°C and stirred for 5 hours. After cooling to room temperature, the mixture was filtered. The filter cake was washed with toluene and ethanol in sequence and dried to obtain hyperbranched polyester modified basalt fiber. The molar ratio of the isocyanate group of the isocyanate-modified basalt fiber to the molar ratio of the hydroxyl group of the portion of ester-terminated hyperbranched polyester polyol was 0.7:1.

[0029] (4) High melt index polypropylene (melt index of 1500 g / 10 min under test conditions of 230℃ and 2.16 kg load), low melt index polypropylene (melt index of 25 g / 10 min under test conditions of 230℃ and 2.16 kg load), hyperbranched polyester modified basalt fiber and maleic anhydride grafted polypropylene (maleic anhydride content of 0.8%, melt index of 5 g / 10 min under test conditions of 230℃ and 2.16 kg load) are mixed evenly in a mass ratio of 35:18:40:8 and then added to a twin-screw extruder. The mixture is melt-extruded and granulated at 210~220℃ to obtain recyclable polypropylene material. Example 4

[0030] The method for preparing recyclable polypropylene material in this embodiment includes the following steps: (1) Basalt fiber (average length 5 mm, average diameter 6 μm), 3-isocyanate-propyltrimethoxysilane and anhydrous toluene were added to a reaction vessel, heated to 100 °C, stirred for 12 h, cooled to room temperature and filtered. The filter cake was washed with anhydrous toluene and anhydrous tetrahydrofuran, respectively. The washed filter cake was vacuum dried to obtain isocyanate-modified basalt fiber. The mass ratio of basalt fiber, 3-isocyanate-propyltrimethoxysilane and anhydrous toluene was 1:1:70.

[0031] (2) Add hyperbranched polyester polyol (Boltorn P1000) and anhydrous toluene in a mass ratio of 1:15 to a reaction vessel, then introduce nitrogen into the reaction vessel, cool the material in the reaction vessel to 0°C, and then add a mixed solution containing triethylamine, lauroyl chloride and anhydrous toluene (the mass fraction of toluene in the mixed solution is 60%) to the reaction vessel dropwise. After the dropwise addition is completed, stir the reaction at room temperature for 10 h, filter, distill the filtrate under reduced pressure to remove the solvent toluene, and dry to obtain a partially ester-terminated hyperbranched polyester polyol; wherein, the molar ratio of the hydroxyl molar of the hyperbranched polyester polyol to the molar molar of lauroyl chloride is 1:0.5, and the molar ratio of triethylamine to lauroyl chloride is 1.2:1.

[0032] (3) Isocyanate-modified basalt fiber and anhydrous toluene with a mass ratio of 1:40 were added to the reactor. Nitrogen gas was then introduced into the reactor. A mixed solution containing a portion of ester-terminated hyperbranched polyester polyol and anhydrous toluene (the mass fraction of toluene in the mixed solution was 50%) was added to the reactor. The mixture was heated to 85°C and stirred for 5 hours. After cooling to room temperature, the mixture was filtered. The filter cake was washed with toluene and ethanol in sequence and dried to obtain hyperbranched polyester modified basalt fiber. The molar ratio of the isocyanate group of the isocyanate-modified basalt fiber to the molar ratio of the hydroxyl group of the portion of ester-terminated hyperbranched polyester polyol was 0.7:1.

[0033] (4) High melt index polypropylene (melt index of 1500 g / 10 min under test conditions of 230℃ and 2.16 kg load), low melt index polypropylene (melt index of 25 g / 10 min under test conditions of 230℃ and 2.16 kg load), hyperbranched polyester modified basalt fiber and maleic anhydride grafted polypropylene (maleic anhydride content of 0.8%, melt index of 5 g / 10 min under test conditions of 230℃ and 2.16 kg load) are mixed evenly in a mass ratio of 35:18:40:8 and then added to a twin-screw extruder. The mixture is melt-extruded and granulated at 210~220℃ to obtain recyclable polypropylene material.

[0034] Comparative Example 1 The only difference between the preparation method of the recyclable polypropylene material in this comparative example and the preparation method of the recyclable polypropylene material in Example 1 is that in step (4) of the preparation method of the recyclable polypropylene material in this comparative example, the hyperbranched polyester modified basalt fiber is replaced with the isocyanate-modified basalt fiber prepared in step (1) of Example 1.

[0035] Comparative Example 2 The difference between the preparation method of the recyclable polypropylene material in this comparative example and the preparation method of the recyclable polypropylene material in Example 1 is that in step (4) of the preparation method of the recyclable polypropylene material in this comparative example, the hyperbranched polyester modified basalt fiber is replaced with the isocyanate-modified basalt fiber prepared in step (1) of Example 1 and the partially ester-terminated hyperbranched polyester polyol prepared in step (2). The ratio of the molar amount of isocyanate groups in the isocyanate-modified basalt fiber to the molar amount of hydroxyl groups in the partially ester-terminated hyperbranched polyester polyol is 0.7:1.

[0036] Comparative Example 3 The difference between the preparation method of the recyclable polypropylene material in this comparative example and the preparation method of the recyclable polypropylene material in Example 1 is that nonanoyl chloride is replaced with butyryl chloride in step (2) of the preparation method of the recyclable polypropylene material in this comparative example.

[0037] Comparative Example 4 The difference between the preparation method of the recyclable polypropylene material in this comparative example and the preparation method of the recyclable polypropylene material in Example 1 is that in step (2) of the preparation method of the recyclable polypropylene material in this comparative example, nonanoyl chloride is replaced with palmitoyl chloride.

[0038] Experimental Example This experimental example was used to evaluate the recycling performance of the recyclable polypropylene materials prepared in each embodiment and comparative example. First, the prepared recyclable polypropylene materials were molded into standard test strips using a compression molding process. The tensile strength, notched impact strength, and abrasion resistance of the recyclable polypropylene materials were tested. Then, the standard test strips were placed in an 85℃ constant temperature chamber for 90 days and crushed into particles with an average particle size of 5 mm. These particles were then fed into a twin-screw extruder and melt-extruded into granules at 210~220℃. The samples were then molded again to form standard test strips. The tensile strength, impact strength, and abrasion resistance of the reused polypropylene materials were tested. Based on the original data, the retention rates of tensile strength, notched impact strength, and abrasion resistance were calculated. The experimental results are shown in Table 1. Tensile strength was tested according to the method in standard ISO 527, notched impact strength was tested according to the method in standard ISO 179-1, and abrasion resistance was tested using an abrasion meter, characterized by abrasion loss.

[0039] Table 1 Tensile strength and impact strength of polypropylene materials Strength, abrasion resistance, and performance retention after repeated use polypropylene material Tensile strength (MPa) <![CDATA[Izod impact strength (kJ / m 2 )]]> Abrasion resistance (mg) Tensile strength retention rate (%) Notched impact strength retention rate (%) Abrasion resistance retention rate (%) Example 1 133 19.5 6.5 98.6 99.1 97.8 Example 2 128 18.1 7.6 98.2 97.5 98.1 Example 3 125 17.2 7.2 98.9 98.3 97.1 Example 4 129 17.7 7.9 97.8 98.5 96.3 Comparative Example 1 94 11.3 14.7 67.4 68.3 63.7 Comparative Example 2 108 13.6 12.6 75.9 77.1 68.6 Comparative Example 3 114 14.1 10.5 78.2 79.5 75.2 Comparative Example 4 121 13.8 11.7 81.4 83.6 73.9 As shown in Table 1, the recyclable polypropylene material prepared by this invention exhibits excellent initial mechanical properties. The polypropylene material obtained after being pulverized at high temperature for a certain period and then reprocessed also possesses excellent mechanical properties, with tensile strength, impact strength, and abrasion resistance retention rates of no less than 95%, demonstrating superior recyclability. This is because this invention modifies basalt fibers with isocyanate groups followed by further modification with partially ester-terminated hyperbranched polyester polyols. The hydroxyl groups in the polyol chemically bond with the isocyanate groups on the fiber surface, and the hyperbranched polyester structure is chemically bonded to the fiber surface. This effectively improves fiber fluidity and prevents fiber damage due to shear force during melt processing, thus avoiding performance degradation.

[0040] As can be seen from Example 1 and Comparative Example 1, when the hyperbranched polyester polyol modification step is omitted, the basalt fiber surface lacks a hyperbranched polyester structure with good flowability, which makes it susceptible to shear force and damage during melt processing, resulting in a decline in performance.

[0041] As can be seen from Example 1 and Comparative Example 2, when the hyperbranched polyester modified basalt fiber is replaced with a mixture of isocyanate-modified basalt fiber and partially ester-terminated hyperbranched polyester polyol, although the isocyanate groups on the fiber surface and the hydroxyl groups in the polyol can react during the melt extrusion process, the hydroxyl groups will also react with the anhydride in the maleic anhydride-grafted polypropylene. Furthermore, the degree of material reaction during the melt extrusion process is limited, resulting in insufficient coating of the fiber surface with the hyperbranched polyester structure, which leads to a decrease in recyclability.

[0042] As can be seen from Examples 1, 3, 4 and Comparative Examples 3-4, the length of the ester aliphatic chain in the partially ester-terminated hyperbranched polyester polyol affects the recyclability of polypropylene materials. As the length of the aliphatic chain increases, the recyclability first improves and then deteriorates, which may be related to the lubricity of the ester group and the physical winding effect.

Claims

1. A method for preparing recyclable polypropylene material, characterized in that, Includes the following steps: (1) Basalt fibers are modified with isocyanate groups to obtain isocyanate-modified basalt fibers; (2) React some of the hydroxyl groups in the hyperbranched polyester polyol with an acyl chloride compound to obtain a partially ester-terminated hyperbranched polyester polyol; wherein the molar ratio of the hydroxyl group in the hyperbranched polyester polyol to the molar ratio of the acyl chloride compound is 1:0.5~0.7; the acyl chloride compound is a monobasic saturated fatty acyl chloride with 6~12 carbon atoms. (3) Isocyanate-modified basalt fiber and a portion of ester-terminated hyperbranched polyester polyol are mixed and reacted in a solvent to obtain hyperbranched polyester-modified basalt fiber; wherein the molar ratio of the isocyanate group of the isocyanate-modified basalt fiber to the molar ratio of the hydroxyl group of the portion of ester-terminated hyperbranched polyester polyol is 0.7~0.8:1; (4) After mixing polypropylene, hyperbranched polyester modified basalt fiber and maleic anhydride grafted polypropylene evenly, melt extrusion granulation is carried out to obtain recyclable polypropylene material.

2. The method for preparing recyclable polypropylene material as described in claim 1, characterized in that, The basalt fibers have an average length of 5-8 mm and an average diameter of 6-10 μm.

3. The method for preparing recyclable polypropylene material as described in claim 1 or 2, characterized in that, The method for isocyanate-modified basalt fiber is as follows: basalt fiber, 3-isocyanate-propyltrimethoxysilane and anhydrous toluene are mixed and reacted at 100~105℃ for 12~15h to obtain isocyanate-modified basalt fiber; wherein the mass ratio of basalt fiber to 3-isocyanate-propyltrimethoxysilane is 1:1~1.

3.

4. The method for preparing recyclable polypropylene material as described in claim 1, characterized in that, The acyl chloride compound is nonanoyl chloride, hexanoyl chloride, or lauroyl chloride.

5. The method for preparing recyclable polypropylene material as described in claim 1, characterized in that, The hyperbranched polyester polyol is Boltorn P1000.

6. The method for preparing recyclable polypropylene material as described in claim 1, characterized in that, In step (3), the temperature of the mixed reaction is 85~90℃ and the time is 5~8h.

7. The method for preparing recyclable polypropylene material as described in claim 1, characterized in that, In step (4), the polypropylene includes high melt index polypropylene and low melt index polypropylene. The melt index of high melt index polypropylene is 1500~2000g / 10min under the test conditions of 230℃ and 2.16kg load, and the melt index of low melt index polypropylene is 25~50g / 10min under the test conditions of 230℃ and 2.16kg load.

8. The method for preparing recyclable polypropylene material as described in claim 7, characterized in that, In step (4), the maleic anhydride content of the maleic anhydride-grafted polypropylene is 0.8-1%, and the melt index is 5-8 g / 10 min under the test conditions of 230℃ and 2.16 kg load.

9. The method for preparing recyclable polypropylene material as described in claim 8, characterized in that, In step (4), the mass ratio of high melt index polypropylene, low melt index polypropylene, hyperbranched polyester modified basalt fiber and maleic anhydride grafted polypropylene is 35~45:18~24:40~50:8~10.

10. A recyclable polypropylene material prepared by a method according to any one of claims 1-9.