Recycling method of thermoplastic elastomer

Abstract

The invention relates to a thermoplastic elastomer recycling method, which comprises: crushing a waste thermoplastic elastomer containing a plasticizer A into powder, carrying out extrusion granulation to form colloidal particles with an average particle size of 0.5-1.5 mm, and spraying a modification liquid containing a plasticizer B to the surface of the colloidal particles when the average surface temperature of the colloidal particles is 100-120 DEG C so as to obtain the thermoplastic elastomer. The mass fraction of the plasticizer B in the modification liquid is 10-20%, and when the temperature of the colloidal particles is 20-40 DEG C, cleaning and drying the colloidal particles to obtain the regenerated thermoplastic elastomer. According to the scheme, the usage amount of the plasticizer in the recovery process can be reduced, so that the problem that the surface of the material is sticky due to the excessive usage of the plasticizer is avoided, a regenerated material with the uniformly distributed plasticizer can be formed, and better mechanical properties are obtained.

Description

Technical Field

[0001] The present invention relates to the field of thermoplastic elastomers, and particularly to a method for recycling thermoplastic elastomers. Background Art

[0002] Thermoplastic elastomer (also known as TPE) is a polymer material that combines the elasticity of rubber and the processing performance of thermoplastic plastics. It exhibits rubber elasticity at room temperature and can flow like a plastic at high temperatures. It contains a hard segment (such as polystyrene, polyester) to provide physical cross-linking points and a soft segment (polybutadiene, polyether, etc.) to endow it with elasticity. Thermoplastic elastomers do not require vulcanization and can be directly molded in various ways. The waste can be 100% recycled, making it a green material. The ratio of the hard segment / soft segment, plasticizer or filler of the thermoplastic elastomer determines the properties such as hardness and transparency of the material containing the thermoplastic elastomer. Among them, the mass fraction of the plasticizer is relatively low, but it has a significant impact on the mechanical properties of the material. The compatibility between the plasticizer and the TPE matrix is insufficient, and it is prone to migration during long-term use, especially the migration rate will increase by two orders of magnitude in a high-temperature environment. After the plasticizer migrates, it will cause an increase in the hardness of the material and a decrease in flexibility. Therefore, products made of recycled TPE materials are prone to brittle fracture. When these recycled TPE materials are mixed with other non-polar materials, the migrated plasticizer may penetrate into the interior of other materials, resulting in a decrease in the mechanical properties of other materials. Generally, the problem of plasticizer migration to the surface is solved by improving the formula of the TPE material to reduce the exudation of the plasticizer, or by cleaning the plasticizer migrated to the surface of the material during the recycling process. However, the method of modifying the TPE material is not applicable to the recycling of conventional TPE materials, and the method of cleaning the plasticizer migrated to the surface of the material cannot solve the problem of the decrease in the material properties caused by the reduction of the plasticizer inside the material.

[0003] Therefore, it is necessary to provide a method for recycling thermoplastic elastomers. Summary of the Invention

[0004] In order to solve the problems caused by plasticizer migration during the recycling process of TPE materials, it is necessary to provide a method for recycling thermoplastic elastomers.

[0005] A method for recycling thermoplastic elastomers includes the following steps: crushing waste thermoplastic elastomers containing plasticizer A into powder and then extruding and pelletizing to form rubber pellets with an average particle size of 0.5 - 1.5 mm. When the average surface temperature of the rubber pellets is 100 - 120 °C, spraying a modified liquid containing plasticizer B on the surface of the rubber pellets. The mass fraction of plasticizer B in the modified liquid is 10 - 20%. When the temperature of the rubber pellets is 20 - 40 °C, cleaning the rubber pellets, and then drying to obtain recycled thermoplastic elastomers.

[0006] In the prior art, plasticizer is supplemented during the extrusion granulation process. On the one hand, the plasticizer will decompose during the high-temperature extrusion process, thereby reducing the utilization rate of the plasticizer. Therefore, it is necessary to add an excessive amount of plasticizer, which is likely to cause the surface of the material to become sticky. On the other hand, the plasticizer may agglomerate locally during the extrusion mixing process, so that it cannot be evenly dispersed, resulting in local differences in the mechanical properties of the material. Therefore, an excessive amount of plasticizer also needs to be added. In this solution, after the rubber particles are extruded, when the residual temperature is 100-120°C, a modified liquid containing plasticizer is sprayed on the surface of the rubber particles. At this temperature, the plasticizer is not easily degraded, so there is no need to add an excessive amount of plasticizer due to this; the plasticizer in the modified liquid has a high migration efficiency at this temperature, and the plasticizer with a high concentration (the mass fraction of the plasticizer in the conventional thermoplastic elastomer material is about 5%) in the modified liquid migrates into the rubber particles, forming a gradient distribution from the surface to the inside. During the migration process of the plasticizer, it is gradually fixed in the polymer network of the material, making the mechanical properties of the recycled material uniform; during the cleaning process of the rubber particles, on the one hand, the components of the residual modified liquid on the surface are removed, and at the same time, the mass fraction of the plasticizer on the outer layer of the rubber particles is reduced, thereby forming a surface layer that restricts the precipitation of the plasticizer. At the same time, because the temperature of the rubber particles is relatively low, it is not easy to cause the precipitation of the internal plasticizer. This solution can reduce the usage amount of the plasticizer during the recycling process through the above method, thereby avoiding the problem of the surface of the material becoming sticky due to the use of an excessive amount of plasticizer, and can form a recycled material with a uniform distribution of the plasticizer, obtaining better mechanical properties.

[0007] Further, the average particle size of the rubber particles is 0.5-1.5 mm. High temperature can significantly increase the migration rate of the plasticizer, but it is difficult for the plasticizer to penetrate through thick rubber particles. The rubber particles with the above particle size can allow the plasticizer to penetrate to the core of the rubber particles.

[0008] Further, the rubber particles are placed in an incubator and cooled to 60-80°C at a rate of 1-4°C / min. Using a slower cooling rate helps to relieve the stress concentration during the transformation of the thermoplastic elastomer from the molten state to the glassy state, avoid material catalysis, and at the same time provide a longer migration window period for the plasticizer. Further, the rubber particles cooled to 60-80°C are placed in an incubator and cooled to 20-40°C at a rate of 5-10°C / min. Rapid cooling can promote the rapid solidification of the body to avoid the reverse migration of the plasticizer, resulting in a decrease in the plasticizer content in the core.

[0009] Further, the mass fraction of plasticizer A in the rubber particles is 1-5%. This solution needs to form a certain concentration gradient inside and outside the rubber particles to drive the plasticizer to migrate into the rubber particles. Therefore, the plasticizer concentration in the rubber particles should not be too high, but it should not be too low either. Otherwise, after being treated by this method, the plasticizer content in the rubber particles will be significantly higher than its designed value, resulting in excessive softening of the material.

[0010] Furthermore, the plasticizers A and B have the same composition. Plasticizers with different compositions are prone to phase separation. Using plasticizers with the same composition can ensure the uniformity of the microstructure of the rubber particles.

[0011] Furthermore, the molecular weight of plasticizer B in the modification liquid is less than 1000. Plasticizers with low molecular weight have stronger migration ability at 80 - 120 °C, and can achieve rapid penetration from the surface to the core.

[0012] Furthermore, the plasticizer A is a polyol ester plasticizer. Polyol ester plasticizers have better environmental protection and safety, meeting the requirements of the composite recycling material market.

[0013] Furthermore, the thermoplastic elastomer is a styrenic thermoplastic elastomer. Styrenic TPEs (such as SBS, SEBS, etc.) are widely used in fields such as automotive sealing strips and wire and cable. According to the usage requirements, the appropriate hardness can be obtained by adjusting the hard segment / soft segment ratio and the plasticizer content.

[0014] Furthermore, the rubber particles are cleaned with a polar solution. Polar solutions, such as ethanol and acetone, have better cleaning effects on the modification liquid on the surface of the rubber particles, and can also reduce the plasticizer content on the surface of the rubber particles, thus avoiding the precipitation of plasticizers to the surface during long-term use of the material, resulting in stickiness on the material surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic flow chart of a recycling method for an embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] To facilitate the understanding of this application, the following will provide a more comprehensive description of this application. This application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosure content of this application more thorough and comprehensive.

[0017] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the application, "a plurality of" means at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terms used in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0019] In this application, among the technical features described in an open-ended manner, it includes a closed technical solution composed of the listed features, and also includes an open technical solution containing the listed features.

[0020] In this application, regarding numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0021] In this application, for the mass percentage involved, unless otherwise specified, for solid-liquid mixtures and solid-solid mixtures, it refers to the mass percentage, and for liquid-liquid mixtures, it refers to the volume percentage.

[0022] In this application, for the percentage concentration involved, unless otherwise specified, it all refers to the final concentration. The final concentration refers to the proportion of the added component in the system after adding this component.

[0023] For the temperature parameters in this application, unless otherwise specified, it allows both isothermal treatment and treatment within a certain temperature range. The isothermal treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument.

[0024] The "particles" mentioned in this application, or substances with a defined particle size distribution, do not necessarily have a spherical shape and may also be irregular. They can be primary particles or secondary particles. The particle size of irregular particles is calculated as the average of their maximum diameter and minimum diameter.

[0025] Example 1: A method for recycling a thermoplastic elastomer, comprising the following steps:

[0026] Cut the waste styrene-based TPE material (sole material, the plasticizer is dipentaerythritol ester, the designed value of the mass fraction of the plasticizer is 4.6%, and the actual value is 3.5%) into pieces of 5 - 10 cm 3The fragments are washed, dried and then crushed into powder. The powder is transferred to a twin-screw extruder and extruded (extrusion temperature: 190 °C, the same below) to form pellets with an average particle size of 1.5 mm. When the average surface temperature of the pellets reaches 120 °C, an ethanol solution of dipentaerythritol ester (Weilinna, product number w220, molecular weight 507) with a mass fraction of 10% is sprayed onto the surface of the pellets through a spraying device as a modification liquid to ensure that the modification liquid is evenly distributed on the surface of all particles. The pellets are placed in an incubator and cooled to 80 °C at a rate of 4 °C / min, and then cooled to 20 °C at a rate of 10 °C / min. The surface of the pellets is further cleaned with ethanol for 30 s and then centrifugally dried to obtain recycled thermoplastic elastomer pellets.

[0027] Example 2: A method for recycling thermoplastic elastomer, comprising the following steps:

[0028] The waste styrene-based TPE material (sole material, plasticizer is dipentaerythritol ester, the designed mass fraction of the plasticizer is 4.6%, the actual value is 3.5%) is cut into pieces of 5 - 10 cm 3 The fragments are washed, dried and then crushed into powder. The powder is transferred to a twin-screw extruder and extruded into pellets with an average particle size of 0.5 mm. When the average surface temperature of the pellets reaches 100 °C, an ethanol solution of dipentaerythritol ester (Weilinna, product number w220, molecular weight 507) with a mass fraction of 10% is sprayed onto the surface of the pellets through a spraying device as a modification liquid to ensure that the modification liquid is evenly distributed on the surface of all particles. The pellets are placed in an incubator and cooled to 60 °C at a rate of 1 °C / min, and then cooled to 20 °C at a rate of 5 °C / min. The surface of the pellets is further cleaned with ethanol for 30 s and then centrifugally dried to obtain recycled thermoplastic elastomer pellets.

[0029] Example 3: A method for recycling thermoplastic elastomer, comprising the following steps:

[0030] The waste styrene-based TPE material (sole material, plasticizer is dipentaerythritol ester, the designed mass fraction of the plasticizer is 4.6%, the actual value is 3.5%) is cut into pieces of 5 - 10 cm 3The fragments are washed, dried and then crushed into powder. The powder is transferred to a twin-screw extruder for extrusion granulation to form rubber pellets with an average particle size of 1 mm. When the average surface temperature of the rubber pellets reaches 120 °C, an ethanol solution of dipentaerythritol ester (Weilinna, product number w220, molecular weight 507) with a mass fraction of 10% is sprayed onto the surface of the rubber pellets through a spraying device as a modification liquid to ensure that the modification liquid is evenly distributed on the surface of all particles. The rubber pellets are placed in an incubator and cooled to 80 °C at a rate of 4 °C / min, and then cooled to 20 °C at a rate of 10 °C / min. The surface of the rubber pellets is further washed with ethanol for 30 s and then centrifugally dried to obtain recycled thermoplastic elastomer rubber pellets.

[0031] Example 4: A method for recycling thermoplastic elastomer, comprising the following steps:

[0032] The waste styrene-based TPE material (sole material, plasticizer is dipentaerythritol ester, the designed value of the mass fraction of the plasticizer is 4.6%, and the actual value is 3.5%) is cut into pieces of 5-10 cm 3 The fragments are washed, dried and then crushed into powder. The powder is transferred to a twin-screw extruder for extrusion granulation to form rubber pellets with an average particle size of 1.5 mm. When the average surface temperature of the rubber pellets reaches 120 °C, an ethanol solution of dipentaerythritol ester (Weilinna, product number w220, molecular weight 507) with a mass fraction of 20% is sprayed onto the surface of the rubber pellets through a spraying device as a modification liquid to ensure that the modification liquid is evenly distributed on the surface of all particles. The rubber pellets are placed in an incubator and cooled to 80 °C at a rate of 4 °C / min, and then cooled to 20 °C at a rate of 10 °C / min. The surface of the rubber pellets is further washed with ethanol for 30 s and then centrifugally dried to obtain recycled thermoplastic elastomer rubber pellets.

[0033] Example 5: A method for recycling thermoplastic elastomer, comprising the following steps:

[0034] The waste styrene-based TPE material (sole material, plasticizer is dipentaerythritol ester, the designed value of the mass fraction of the plasticizer is 4.6%, and the actual value is 3.5%) is cut into pieces of 5-10 cm 3 The fragments are washed, dried and then crushed into powder. The powder is transferred to a twin-screw extruder for extrusion granulation to form rubber pellets with an average particle size of 1.5 mm. When the average surface temperature of the rubber pellets reaches 120 °C, an ethanol solution of dipentaerythritol ester (Weilinna, product number w220, molecular weight 507) with a mass fraction of 10% is sprayed onto the surface of the rubber pellets through a spraying device as a modification liquid to ensure that the modification liquid is evenly distributed on the surface of all particles. The rubber pellets are placed in an incubator and cooled to 80 °C at a rate of 4 °C / min, and then cooled to 20 °C at a rate of 10 °C / min. The surface of the rubber pellets is further washed with acetone and then centrifugally dried to obtain recycled thermoplastic elastomer rubber pellets.

[0035] Comparative Example 1: A method for recycling thermoplastic elastomer, comprising the following steps:

[0036] Cut waste styrene-based TPE material (sole material, plasticizer is dipentaerythritol ester, the designed value of the mass fraction of plasticizer is 4.6%, and the actual value is 3.5%) into pieces of 5 - 10 cm 3 After cleaning and drying, crush it into powder, transfer the powder to a twin-screw extruder for extrusion granulation to form pellets with an average particle size of 1.5 mm. When the average surface temperature of the pellets reaches 120 °C, place the pellets in an incubator and cool them to 80 °C at a rate of 4 °C / min, then cool them to 20 °C at a rate of 10 °C / min, and then centrifuge and dry to obtain recycled thermoplastic elastomer pellets.

[0037] Comparative Example 2: A method for recycling thermoplastic elastomer, comprising the following steps:

[0038] Cut waste styrene-based TPE material (sole material, plasticizer is dipentaerythritol ester, the designed value of the mass fraction of plasticizer is 4.6%, and the actual value is 3.5%) into pieces of 5 - 10 cm 3 After cleaning and drying, crush it into powder, transfer the powder to a twin-screw extruder for extrusion granulation to form pellets with an average particle size of 5 mm. When the average surface temperature of the pellets reaches 120 °C, spray an ethanol solution of dipentaerythritol ester (Weilinna, product number w220, molecular weight 507) with a mass fraction of 10% on the surface of the pellets as a modification liquid through a spraying device to ensure that the modification liquid is evenly distributed on the surface of all particles. Place the pellets in an incubator and cool them to 80 °C at a rate of 4 °C / min, then cool them to 20 °C at a rate of 10 °C / min, further wash the surface of the pellets with ethanol for 30 s, and then centrifuge and dry to obtain recycled thermoplastic elastomer pellets.

[0039] Test the hardness and plasticizer exudation rate of the above recycled thermoplastic elastomer pellets. The hardness test method refers to the method of ASTM D2240, and the test method of plasticizer exudation rate refers to the method of ASTM D1239, and record the test results in Table 1.

[0040] Table 1 Test results of hardness and plasticizer exudation rate of pellets in Examples 1 - 5 and Comparative Examples 1 - 2.

[0041] Item Elongation at break (%) Precipitation rate (%) Example 1 281 1.2 Example 2 290 1.0 Example 3 288 1.0 Example 4 293 1.5 Example 5 275 0.7 Comparative Example 1 162 4.8 Comparative Example 2 192 2.9

[0042] According to the data in Table 1, the fracture generation rates of Examples 1-5 are all higher than that of Comparative Example 1, and the precipitation rates of plasticizers in Examples 1-5 are significantly reduced. This is because after the rubber pellets are extruded, when the residual temperature is 100-120 °C, a modified liquid containing a plasticizer is sprayed onto the surface of the rubber pellets. At this temperature, the plasticizer is not easily degraded, so there is no need to add an excessive amount of plasticizer due to this; the plasticizer in the modified liquid has a high migration efficiency at this temperature. The plasticizer with a high concentration (the mass fraction of the plasticizer in the conventional thermoplastic elastomer material is about 5%) in the modified liquid migrates into the rubber pellets, forming a gradient distribution from the surface to the inside. During the migration process of the plasticizer, it is gradually fixed in the polymer network of the material, making the mechanical properties of the recycled material uniform; during the cleaning process of the rubber pellets, on the one hand, the residual components of the modified liquid on the surface are removed, and at the same time, the mass fraction of the plasticizer in the outer layer of the rubber pellets is reduced, thus forming a surface layer that restricts the precipitation of the plasticizer. At the same time, because the temperature of the rubber pellets is relatively low, it is not easy to cause the precipitation of the internal plasticizer. Through the above method, this solution can reduce the usage amount of the plasticizer in the recycling process, thereby avoiding the problem of the material surface becoming sticky due to the use of an excessive amount of plasticizer, and can form a recycled material with a uniform distribution of the plasticizer, obtaining better mechanical properties. In Comparative Example 2, rubber pellets with a larger average particle size were used, and the migration ability of the plasticizer was limited, making it difficult to reach the core of the rubber pellets, resulting in a poor elongation at break of the rubber pellets.

[0043] In Example 2, smaller particles were used, and better effects can also be achieved at lower temperatures and migration times; in Example 4, a modified liquid with a higher mass fraction of plasticizer was used, which can further increase the plasticizer content inside the rubber pellets. In Example 5, acetone was used, and the cleaning with a strong polar reagent was more thorough, with less residual plasticizer on the surface layer and the lowest precipitation rate, but at the same time, it would affect the toughness of the surface layer of the rubber pellets.

[0044] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0045] The above-described embodiments merely represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for recycling a thermoplastic elastomer, characterized in that: The method comprises the following steps: crushing waste thermoplastic elastomer containing plasticizer A into powder, extruding and granulating the powder to form rubber particles; when the average surface temperature of the rubber particles is 100-120°C, spraying a modification liquid containing plasticizer B onto the surface of the rubber particles, wherein the mass fraction of the plasticizer B in the modification liquid is 10-20%; when the temperature of the rubber particles is 20-40°C, washing the rubber particles, and drying to obtain the regenerated thermoplastic elastomer.

2. The recycling method according to claim 1, characterized in that: The average particle size of the colloid particles is 0.5-1.5 mm.

3. The recycling method according to claim 1, characterized in that: The colloid particles are placed in an incubator and cooled to 60-80°C at a rate of 1-4°C / min.

4. The recycling method according to claim 3, characterized in that: The colloid particles whose temperature is reduced to 60-80° C. are placed in an incubator and cooled to 20-40° C. at a rate of 5-10° C. / min.

5. The recycling method according to claim 1, characterized in that: The mass fraction of the plasticizer A in the granules is 1-5%.

6. The recycling method according to claim 1, characterized in that: The plasticizer A and the plasticizer B have the same composition.

7. The recycling method according to claim 1, characterized in that: The molecular weight of the plasticizer B in the modified liquid is less than 1000.

8. The recycling method according to claim 1, characterized in that: The plasticizer A is a polyol ester plasticizer.

9. The recycling method according to claim 1, characterized in that: The thermoplastic elastomer is a styrene-based thermoplastic elastomer.

10. The recycling method according to claim 1, characterized in that: The colloidal particles are washed with a polar solution.

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