Recycled polyolefin single-screw extruder, application thereof, modified polyolefin and preparation method of modified polyolefin

Abstract

The invention relates to the field of recycled polyolefin films, and discloses a recycled polyolefin single-screw extruder and application thereof, modified polyolefin and a preparation method thereof.The single-screw extruder comprises at least one stage of screw, and each stage of screw comprises a melting area and a melt conveying area in the material flowing direction; the melting area and the melt conveying area are each provided with a barrier structure, the barrier structure of the melting area is parallel to the axial direction of the screw rod, and an included angle is formed between the barrier structure of the melt conveying area and the axial direction of the screw rod. By adopting the recycled polyolefin single-screw extruder disclosed by the invention, the mixing uniformity of the raw materials can be effectively improved, and the tensile strength, the bending strength and the simply supported beam notch impact strength of the final modified polyolefin can be improved particularly aiming at the reutilization of the recycled polyolefin.

Description

Technical Field

[0001] The invention relates to the field of recycled polyolefin films, in particular to a recycled polyolefin single-screw extruder and application thereof, and modified polyolefin and a preparation method thereof. Background Art

[0002] As the global plastic market scale steadily increases, plastics are widely used in various fields due to their own characteristics, and the problem of plastic pollution is becoming more and more serious. Traditional methods of recycling plastics include natural degradation, conventional landfill and incineration. Although natural degradation and conventional landfill require less investment and are simple to operate, they will occupy a large amount of land and cause land pollution. Although incineration technology can achieve the reduction requirements and recover some energy at the same time, this process is prone to release a large amount of hydrocarbons, nitrogen compounds, sulfides and highly toxic dioxins, which directly threaten human and ecological health. Therefore, it is urgent to realize the recycling of waste plastics.

[0003] In recent years, with the large-scale application of mulch film technology in the agricultural field, while increasing crop yields and agricultural production efficiency, the issue of mulch film recycling has gradually received attention. After the mulch film is recycled, some of it remains in the farmland and is difficult to recycle. A large amount of residual plastic film will significantly change the physical and chemical properties of the soil and the population structure and number of microorganisms, so mulch film recycling technology came into being.

[0004] At present, after the mulch materials are collected, impurities such as straw and dust account for a large proportion. Usually, the mulch materials need to be initially inspected, screened, cleaned, washed, dehydrated and dried. Subsequently, different melting technologies need to be used for granulation for different mulch materials. However, the current melting treatment of recycled mulch materials usually focuses on adding additives for modification, and the equipment used is a conventional single-screw extruder. However, conventional single-screw extruders often have uneven mixing, which leads to poor mechanical properties of the final modified material, affecting the recycling value of the mulch materials. Summary of the invention

[0005] The purpose of the present invention is to overcome the problem of uneven mixing in the conventional single-screw extruder used in the prior art, which leads to poor mechanical properties of the final modified material. A single-screw extruder, method and modified polyolefin for recycling polyolefin are provided. The single-screw extruder for recycling polyolefin has uniform mixing and is particularly suitable for the reuse of recycled polyolefin. It can significantly improve the mechanical properties of the final modified polyolefin, such as tensile strength, flexural strength and simply supported beam notched impact strength, so as to obtain modified polyolefin with excellent comprehensive mechanical properties, and realize high-value recycling of waste polyolefin materials such as mulch materials.

[0006] In order to achieve the above-mentioned objectives, the first aspect of the present invention provides a single-screw extruder for recycling polyolefins, which single-screw extruder includes at least one-stage screw, and the screw of each stage includes a melting zone and a melt conveying zone along the material flow direction, and the melting zone and the melt conveying zone are both provided with a barrier structure, wherein the barrier structure of the melting zone is arranged parallel to the axial direction of the screw, and the barrier structure of the melt conveying zone is arranged at an angle to the axial direction of the screw.

[0007] The second aspect of the present invention provides the use of the above-mentioned single-screw extruder for recycling polyolefins in olefin recovery.

[0008] The third aspect of the present invention provides a method for recycling polyolefins using the aforementioned single-screw extruder for recycling polyolefins, the method comprising:

[0009] The recycled polyolefin, inorganic whisker, antioxidant and toughening agent are added into a recycled polyolefin single-screw extruder and sequentially flow through the melting zone and melt conveying zone of each stage screw for melt extrusion.

[0010] The fourth aspect of the present invention provides a modified polyolefin prepared by the above method.

[0011] Through the technical solution of the present invention, by respectively arranging barrier structures with specific structures in the melting zone and the melt conveying zone of the recycled polyolefin single-screw extruder, the uniformity of raw material mixing can be effectively improved, especially for the reuse of recycled polyolefin, the tensile strength, bending strength and simply supported beam notched impact strength of the final modified polyolefin can be improved.

[0012] Other features and advantages of the present invention will be described in detail through the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 2 is a schematic structural diagram of a two-stage single-screw extruder according to a preferred embodiment of the present invention;

[0014] Figure 2 is a structural schematic diagram of a screw showing a barrier structure according to a preferred specific embodiment of the present invention;

[0015] Figure 3 (a) and (b) are scanning electron microscope images of the modified polypropylene obtained in Example 4;

[0016] Figure 4 (a) and (b) are scanning electron micrographs of the modified polypropylene obtained in Comparative Example 2.

[0017] Description of Reference Numerals

[0018] 1 Barrel 2 Screw 3 Barrel

[0019] 4 Side feed port 5 Single section barrier 6 Side rectangular barrier DETAILED DESCRIPTION

[0020] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0021] As described above, the first aspect of the present invention provides a single-screw extruder for recycling polyolefins, which single-screw extruder includes at least one-stage screw, and each stage of the screw includes a melting zone and a melt conveying zone along the material flow direction, and the melting zone and the melt conveying zone are both provided with a barrier structure, wherein the barrier structure of the melting zone is arranged parallel to the axial direction of the screw, and the barrier structure of the melt conveying zone is arranged at an angle to the axial direction of the screw.

[0022] According to a preferred embodiment of the present invention, the barrier structure of the melting zone is a single-section barrier. Preferably, the single-section barrier is located at the feed end of the melting zone and occupies 1 / 3-1 / 2 of the length of the melting zone.

[0023] According to another preferred specific embodiment of the present invention, the barrier structure of the melt conveying zone is a lateral rectangular barrier. Preferably, the lateral rectangular barrier is arranged at an angle of 5-45 degrees with the axial direction of the screw along the material flow direction. Preferably, the lateral rectangular barrier is located at the discharge end of the melt conveying zone and occupies 1 / 3-1 / 2 of the length of the melt conveying zone.

[0024] Preferably, the barrier body of each barrier structure is selected from at least one of a pin type, a solid groove type, and a recessed type, and is more preferably a pin type.

[0025] According to the present invention, by adding parallel single-section barriers (preferably longitudinal pins) in the melting zone of each stage screw, the mixing effect of the material in the material can be effectively increased. At the same time, by cooperating with the lateral rectangular barriers (preferably lateral rectangular pins) set up at the head of the single-screw extruder located in the melt conveying zone, the whiskers can follow the laminar flow direction of the material to achieve the filling and strengthening effect. The whisker material does not undergo shear friction, and the whisker aspect ratio loss is small, which can not only meet the filling and achieve the strengthening effect, but also establish a material pressure zone at the head. The pin direction is in the same direction as the material direction, and the material mixing effect is increased without shearing the material. Compared with the commonly used pin screw, the barrier-type screw mainly has diamond, tooth, groove, etc., which makes up for the disadvantage of poor mixing effect of the single screw.

[0026] Preferably, the single screw extruder is a single-stage, double-stage or triple-stage single screw extruder, preferably a double-stage single screw extruder.

[0027] According to the present invention, when the single-screw extruder is a multi-stage screw, the adjacent two-stage screws are preferably arranged vertically, so that the material obtained by the upper-stage screw located upstream of the material can enter the lower-stage screw through the side feed port located in the melting zone of the adjacent downstream screw to continue melt extrusion.

[0028] Preferably, when the single screw extruder is multi-stage, each stage screw of the single screw extruder is independently selected from a gradual-type screw, a sudden-type screw, an equal-depth and unequal-pitch screw, an equal-pitch and unequal-depth screw and an unequal-depth and unequal-pitch screw, more preferably a gradual-type screw.

[0029] Preferably, when the single-screw extruder is multi-stage, the number of screw threads of each stage of the single-screw extruder is independently selected from single thread, double thread and triple thread.

[0030] According to the present invention, when the single-screw extruder is multi-stage, the screw groove depths of each stage of the single-screw extruder can be the same or different. Preferably, the screw groove depth of the upper stage (upstream of the material) screw is smaller than that of the adjacent lower stage (downstream of the material) screw.

[0031] According to the present invention, preferably, the diameter of each stage screw is independently selected from 20-50 cm, and the aspect ratio is independently selected from 20-30.

[0032] According to the present invention, each stage screw of the single-screw extruder further comprises a solid conveying zone, and the solid conveying zone is located upstream of the melting zone.

[0033] According to a preferred specific embodiment of the present invention, the single-screw extruder of the present invention is a two-stage single-screw extruder, including a first-stage single-screw extruder and a second-stage single-screw extruder located downstream of the first-stage single-screw extruder, the first-stage single-screw extruder is connected to the feed port of the second-stage screw extruder, and the screws of each stage include a melting zone and a melt conveying zone along the material flow direction, and the melting zone and the melt conveying zone are both provided with barrier structures, wherein the barrier structure of the melting zone is arranged parallel to the axial direction of the screw, and the barrier structure of the melt conveying zone is arranged at an angle to the axial direction of the screw, and the barrier body of each barrier structure is preferably pin-shaped.

[0034] The following combination Figure 1 and Figure 2A preferred specific embodiment of the present invention is described. The recycled polypropylene extruder provided by the present invention is a two-stage single screw extruder, and the two-stage single screw extruder comprises a first-stage screw extruder 1 and a second-stage screw extruder 2, wherein the second-stage screw 2 is located downstream of the first-stage screw 1 and is connected to a feed port 4 of the melting zone of the second-stage screw extruder 2; Figure 2 Each stage of the screw extruder includes a barrel 3 and a screw 7. The screw 2 is arranged in the barrel 3, and the screw 7 includes a core and a spiral thread located on the surface of the core. The screw 7 of each stage is divided into a solid conveying zone, a melting zone and a melt conveying zone along the material flow direction. The melting zone is provided with a single-section barrier 5, which is located at the feed end of the melting zone and occupies 1 / 3-1 / 2 of the length of the melting zone. The single-section barrier 5 is arranged parallel to the axial direction of the screw; the melt conveying zone is provided with a lateral rectangular barrier 6, which has an angle of 5-45 degrees with the material flow direction, and is located at the discharge end of the melt conveying zone, occupying 1 / 3-1 / 2 of the length of the melt conveying zone.

[0035] According to the present invention, the recycled polyolefin single-screw extruder described in the present invention also includes other conventional components or structural parts of the existing screw extruder, such as a barrel, the screw is rotatably retained in the barrel, a feeder, a booster pump, and the screw includes a core and a spiral thread located on the surface of the core, the spiral thread, the core and the barrel together constitute a screw extrusion space, etc. The present invention will not be described one by one here. The present invention lists a specific choice in the subsequent specific embodiment part, which should not be understood by those skilled in the art as a limitation of the present invention.

[0036] The recycled polyolefin single-screw extruder provided by the present invention effectively improves the uniformity of raw material mixing by arranging specific barrier structures in the melting zone and the melt conveying zone, especially for the reuse of recycled polyolefin, and improves the tensile strength, bending strength and simply supported beam notched impact strength of the final modified polyolefin.

[0037] As mentioned above, the second aspect of the present invention provides the use of the aforementioned recycled polyolefin single-screw extruder in olefin recovery.

[0038] As mentioned above, the third aspect of the present invention provides a method for recycling polyolefins using the aforementioned single-screw extruder for recycling polyolefins, the method comprising:

[0039] The recycled polyolefin, inorganic whisker, antioxidant and toughening agent are added into a recycled polyolefin single-screw extruder and sequentially flow through a melting zone and a melt conveying zone for melt extrusion.

[0040] Preferably, the reaction conditions of the melting zone in each stage of the screw independently include: temperature 180-235°C, screw speed 30-40rpm; the reaction conditions of the melt conveying zone in each stage of the screw independently include: temperature 220-235°C, screw speed 35-45rpm.

[0041] Preferably, the recycled polyolefin is recycled polyethylene or recycled polypropylene.

[0042] And / or, the inorganic whisker is selected from at least one of calcium stearate, potassium hexatitanate, calcium sulfate, calcium carbonate, zinc oxide and magnesium borate.

[0043] And / or, the antioxidant is selected from at least one of antioxidant 1010, antioxidant 168, antioxidant B900, antioxidant 300, antioxidant 1076 and calcium stearate, more preferably a combination of antioxidant 1010 and antioxidant 168. Preferably, in the combination, the weight ratio of the antioxidant 1010 to the antioxidant 168 is 1:1-3.

[0044] And / or, the toughening agent is POE (polyolefin elastomer).

[0045] And / or, relative to 100 parts by weight of the recycled polyolefin, the content of the inorganic whisker is 10-45 parts by weight, the content of the antioxidant is 0.05-0.5 parts by weight, and the content of the toughening agent is 5-20 parts by weight.

[0046] According to a preferred specific embodiment of the present invention, the recycled polyolefin single screw extruder is a two-stage single screw extruder, including a first-stage single screw extruder and a second-stage single screw extruder located downstream of the first-stage single screw extruder. Part of the toughening agent is added to the reaction system through the first-stage single screw extruder, and the remaining part of the toughening agent is directly added to the reaction system through the second-stage single screw extruder, which means that all the recycled polyolefins, all the inorganic whiskers, all the antioxidants and part of the toughening agent are mixed and added to the first-stage single screw extruder, and the material is sent to the second-stage single screw extruder after the first-stage single screw extruder is melt-extruded. At the same time, the remaining part of the toughening agent is directly added to the second-stage single screw extruder through the feeding port of the second-stage single screw extruder and continues to react with the molten extruded material from the first-stage single screw extruder. The inventor of the present invention found that, in particular, by adopting this preferred specific embodiment, the thermal history of the toughening agent POE is reduced, and the mechanical properties such as tensile strength, flexural strength and simply supported beam notched impact strength of the final modified polyolefin are improved. According to the present invention, when the toughening agent POE is added in batches, the toughening agent POE added in batches can be added through the same port or different addition ports.

[0047] Preferably, part of the toughening agent accounts for 50-90 wt % of the total toughening agent.

[0048] As mentioned above, the fourth aspect of the present invention provides a modified polyolefin obtained by the above method.

[0049] Preferably, the modified polyolefin has a tensile strength of 25-35 MPa, a flexural strength of 30-45 MPa, and a simply supported beam notched impact strength of 8-30 kJ / m 2 (Tested at 23°C).

[0050] In the present invention, unless otherwise specified, room temperature refers to 25±2° C. and pressure refers to gauge pressure.

[0051] The present invention will be described in detail below by way of examples. In the following examples and comparative examples,

[0052] Tensile strength: measured according to standard ISO / R527;

[0053] Bending strength: measured according to standard ISO / R178;

[0054] Heat deformation temperature: measured according to standard ASTMD648;

[0055] Charpy notched impact strength: measured according to standard ISO / R179.

[0056] The raw materials used in the examples and comparative examples are all commercially available.

[0057] Example 1

[0058] This embodiment is used to illustrate the polyolefin recycling single screw extruder, method and modified polyolefin of the present invention.

[0059] The recycled polypropylene extruder used in this embodiment is a double-stage single-screw extruder, the number of thread heads is double, the screw is a gradual screw, the diameter of the screw is 25 cm, the aspect ratio is 25, and its specific structure is as follows: Figure 1 and Figure 2 As shown. Combined Figure 1 The extruder comprises a first-stage screw extruder 1 and a second-stage screw extruder 2, wherein the second-stage screw 2 is located downstream of the first-stage screw 1 and is connected to a feed end 4 of a melting zone of the second-stage screw extruder 2, and the screw groove depth of the first-stage screw is less than that of the second-stage screw. Figure 2The screw 7 is divided into a solid conveying zone, a melting zone and a melt conveying zone in the material flow direction. The melting zone is also provided with a single-section barrier 5 (barrier body is a pin type), which is located at the feed end of the melting zone and occupies 1 / 3 of the length of the melting zone. The melt conveying zone is also provided with a lateral rectangular barrier 6 (barrier body is a pin type), which is 30 degrees with the axial direction of the screw along the material flow direction, and is located at the discharge end of the melt conveying zone, occupying 1 / 3 of the length of the melt conveying zone.

[0060] The two-stage single-screw extruder is used to recycle polypropylene. Specifically, the recycled polypropylene, inorganic whiskers, antioxidants and toughening agents (the types and amounts of each component are shown in Table 1) are all sent to the first-stage screw extruder 1 of the two-stage single-screw extruder for melt mixing and extrusion, and then flow into the second-stage screw extruder 2 for melt mixing and extrusion (reaction conditions are shown in Table 1) to obtain modified polypropylene S1.

[0061] The tensile strength, flexural strength, heat deformation temperature and simply supported beam notched impact strength of S1 are shown in Table 2.

[0062] Example 2

[0063] This embodiment is used to illustrate the polyolefin recycling single screw extruder, method and modified polyolefin of the present invention.

[0064] The difference between this embodiment and embodiment 1 is that the raw material content used for the recycled polypropylene is different. The types and amounts of each component are specifically shown in Table 1. The modified polypropylene S2 is obtained after extrusion granulation using this method.

[0065] The tensile strength, flexural strength, heat deformation temperature and simply supported beam notched impact strength of S2 are shown in Table 2.

[0066] Example 3

[0067] This embodiment is used to illustrate the polyolefin recycling single screw extruder, method and modified polyolefin of the present invention.

[0068] The difference between this embodiment and embodiment 1 is that the content of the raw materials used for the recycled polypropylene is different. The types and amounts of each component are specifically shown in Table 1. The modified polypropylene S3 is obtained after extrusion granulation using this method.

[0069] The tensile strength, flexural strength, heat deformation temperature and simply supported beam notched impact strength of S3 are shown in Table 2.

[0070] Example 4

[0071] This embodiment is used to illustrate the polyolefin recycling single screw extruder, method and modified polyolefin of the present invention.

[0072] The difference between this embodiment and embodiment 1 is that the toughening agent POE is added in a different way. Specifically, 5 parts of the 10 parts of the toughening agent POE are added through the first-stage single-screw extruder, and the other 5 parts are directly added through the feed port of the second-stage single-screw extruder. The modified polypropylene S4 is obtained after extrusion granulation using this method. The scanning electron microscope image of the modified polypropylene S4 is as follows: Figure 3 shown.

[0073] The tensile strength, flexural strength, heat deformation temperature and simply supported beam notched impact strength of S4 are shown in Table 2.

[0074] Example 5

[0075] A method similar to that of Example 1 was adopted, except that: the structure of the two-stage single-screw extruder used was different, specifically: the lateral rectangular barrier arranged in the melt conveying zone of each stage single-screw extruder had an angle of 60 degrees with the screw axis along the material flow direction; the rest was the same as that of Example 1, and the modified polypropylene S5 was obtained after extrusion granulation using this method.

[0076] The tensile strength, flexural strength, heat deformation temperature and simply supported beam notched impact strength of S5 are shown in Table 2.

[0077] Comparative Example 1

[0078] This comparative example uses a conventional twin-screw extruder to recycle polypropylene.

[0079] Specifically, recycled polypropylene, inorganic whiskers, antioxidants and toughening agents (the types and amounts of each component are shown in Table 1) are mixed and then sent into a twin-screw extruder for melt mixing (mixing conditions are shown in Table 1). However, due to the irregular shape of the recycled polypropylene material, bridging occurs during feeding and screw feeding, so the preparation of inorganic whiskers filled recycled polypropylene materials by the twin screw is restricted and the sample work cannot be completed. Therefore, the comparative example 1 cannot test the properties such as tensile strength, flexural strength, heat deformation temperature and simply supported beam notched impact strength.

[0080] Comparative Example 2

[0081] This comparative example uses a traditional barrier-free gradient single-screw extruder to recycle polypropylene.

[0082] Specifically, the recycled polypropylene, inorganic whiskers, antioxidants and toughening agents (the types and amounts of each component are shown in Table 1) are mixed and then sent into a gradient single-screw extruder for melt mixing (the mixing conditions are shown in Table 1), and the mixture is extruded and granulated to obtain modified polypropylene D2. The scanning electron microscope image of the modified polypropylene D2 is shown in FIG. Figure 4 shown.

[0083] The tensile strength, flexural strength, heat deformation temperature and simply supported beam notched impact strength of D2 are shown in Table 2.

[0084] Comparative Example 3

[0085] A similar method to Example 1 is adopted, except that the structure of the two-stage single-screw extruder used is different, specifically, the barrier structure of each melting zone is a lateral rectangular barrier; the rest is the same as Example 1, and the modified polypropylene D3 is obtained after extrusion granulation using this method.

[0086] The tensile strength, flexural strength, heat deformation temperature and simply supported beam notched impact strength of D3 are shown in Table 2.

[0087] Comparative Example 4

[0088] A similar method to Example 1 is adopted, except that the structure of the two-stage single-screw extruder used is different, specifically, the barrier structure of each melt conveying zone is a single-section barrier arranged parallel to the screw; the rest is the same as Example 1, and the modified polypropylene D4 is obtained after extrusion granulation using this method.

[0089] The tensile strength, flexural strength, heat deformation temperature and simply supported beam notched impact strength of D4 are shown in Table 2.

[0090] Comparative Example 5

[0091] A method similar to that of Example 1 is adopted, except that: the structure of the two-stage single-screw extruder used is different, specifically: the barrier structure of each melt conveying zone is a single-section barrier arranged parallel to the screw, and the barrier structure of each melting zone is a lateral rectangular barrier; the rest is the same as in Example 1, and the modified polypropylene D5 is obtained after extrusion granulation using this method.

[0092] The tensile strength, flexural strength, heat deformation temperature and simply supported beam notched impact strength of D5 are shown in Table 2.

[0093] Table 1

[0094]

[0095]

[0096] Note: The amounts in reference 1 are all by weight.

[0097] Table 2

[0098]

[0099] By comparing Example 1 with Comparative Example 1, it can be seen that when a conventional twin-screw extruder is used to recycle polypropylene, due to the irregular shape of the recycled polypropylene material, bridging occurs during the feeding and screw feeding, and therefore it is impossible to prepare inorganic whisker-filled recycled polypropylene material;

[0100] By comparing Example 1 with Comparative Example 2, it can be seen that the physical properties of the modified recycled polypropylene obtained by using the double-stage single-screw extruder provided with a specific barrier structure are significantly better than those of the conventional single-screw extruder without a barrier structure.

[0101] By comparing Example 1 and Example 4, it can be seen that the toughening agent is added in batches through the side feeding device, which breaks the current situation of fully enclosed two-stage screw granulation, and cooperates with the double-sided addition of the barrier head to achieve better blending and melting of the materials.

[0102] pass Figure 3 and Figure 4 By comparison, it can be seen that the barrier-type single screw provided by the present invention has an obviously better mixing effect on the filling material, and the material flow in the barrel forms better characteristics, that is, when mixing inorganic fillers, the barrier-type screw has a more significant extrusion rheological effect on the inorganic whiskers.

[0103] In summary, the melting zone and the melt conveying zone in the single-screw extruder for recycling polyolefins provided by the present invention are respectively provided with barrier structures, which effectively improves the uniformity of raw material mixing, realizes the regeneration and recycling of waste materials, and the recycled modified polyolefin has high tensile strength, high bending strength and high simply supported beam notched impact strength.

[0104] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A single screw extruder for recycling polyolefins, characterized in that: The single-screw extruder comprises at least one stage of screws, and each stage of the screws comprises a melting zone and a melt conveying zone along the material flow direction, and the melting zone and the melt conveying zone are both provided with barrier structures, wherein the barrier structure of the melting zone is arranged parallel to the axial direction of the screw, and the barrier structure of the melt conveying zone is arranged at an angle to the axial direction of the screw.

2. The recycled polyolefin single screw extruder according to claim 1, wherein: The barrier structure of the melting zone is a single-section barrier; Preferably, the single-section barrier is located at the feed end of the melting zone and occupies 1 / 3-1 / 2 of the length of the melting zone.

3. The recycled polyolefin single screw extruder according to claim 1, wherein: The barrier structure of the melt conveying zone is a lateral rectangular barrier; Preferably, the lateral rectangular barrier is arranged at an angle of 5-45 degrees with the axial direction of the screw along the material flow direction; Preferably, the lateral rectangular barrier is located at the discharge end of the melt conveying zone and occupies 1 / 3-1 / 2 of the length of the melt conveying zone.

4. The recycled polyolefin single screw extruder according to any one of claims 1 to 3, wherein: The single screw extruder is a single-stage, double-stage or three-stage single screw extruder, preferably a double-stage single screw extruder; And / or, each stage screw of the single screw extruder is independently selected from a gradual screw, a sudden screw, an equal-depth unequal-pitch screw, an equal-pitch unequal-depth screw, and an unequal-depth unequal-pitch screw; And / or, the number of screw threads of each stage of the single-screw extruder is independently selected from single thread, double thread and triple thread; And / or, the barrier body of each barrier structure is selected from at least one of a pin type, a solid groove type and a recessed type, and is more preferably a pin type.

5. The recycled polyolefin single screw extruder according to claim 4, wherein: The single screw extruder is a two-stage single screw extruder, comprising a first-stage single screw extruder and a second-stage single screw extruder located downstream of the first-stage single screw extruder; Preferably, the screw groove depth of the first-stage single-screw extruder screw is smaller than that of the second-stage single-screw extruder.

6. Use of the recycled polyolefin single screw extruder according to any one of claims 1 to 5 in olefin recovery.

7. A method for recycling polyolefins using the single-screw extruder for recycling polyolefins according to any one of claims 1 to 5, characterized in that: include: The recycled polyolefin, inorganic whiskers, antioxidant and toughening agent are added into the recycled polyolefin single screw extruder and sequentially flow through the melting zone and melt conveying zone of each stage screw for melt extrusion; Preferably, the reaction conditions of the melting zone in each stage of the screw independently include: temperature 180-235°C, screw speed 30-40rpm; the reaction conditions of the melt conveying zone in each stage of the screw independently include: temperature 220-235°C, screw speed 35-45rpm.

8. The method according to claim 7, wherein: The recycled polyolefin is recycled polyethylene or recycled polypropylene; And / or, relative to 100 parts by weight of the recycled polyolefin, the content of the inorganic whisker is 10-45 parts by weight, the content of the antioxidant is 0.05-0.5 parts by weight, and the content of the toughening agent is 5-20 parts by weight; And / or, the inorganic whiskers are selected from at least one of calcium stearate, potassium hexatitanate, calcium sulfate, calcium carbonate, zinc oxide and magnesium borate; and / or, the antioxidant is selected from at least one of antioxidant 1010, antioxidant 168, antioxidant B900, antioxidant 300, antioxidant 1076 and calcium stearate, more preferably a combination of antioxidant 1010 and antioxidant 168; And / or, the toughening agent is POE.

9. The method according to claim 7 or 8, wherein: The recycled polyolefin single screw extruder is a two-stage single screw extruder, comprising a first-stage single screw extruder and a second-stage single screw extruder located downstream of the first-stage single screw extruder; Preferably, part of the toughening agent is added to the reaction system through the first-stage single-screw extruder, and the rest of the toughening agent is directly added to the reaction system through the second-stage single-screw extruder.

10. The modified polyolefin prepared by the method according to any one of claims 7 to 9; Preferably, the modified polyolefin has a tensile strength of 25-35 MPa, a flexural strength of 30-45 MPa, and a simply supported beam notched impact strength of 8-30 kJ / m 2 .

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