Plastic recovery method for polyvinylchloride

Abstract

The present invention provides a plastic recovery method for polyvinylchloride, which uses a solvent in combination with a dissolution step to dissolve polyvinylchloride, and separates the solvent and recovers the polyvinylchloride by means of negative pressure. The plastic recovery method for polyvinylchloride of the present invention has a high plastic recovery rate and high recovery efficiency. Since the solvent can be recovered and reused, not only are costs reduced, but also derivative environmental problems can be further avoided.

Description

Polyvinyl chloride plastic recycling methods Technical Field

[0001] The invention relates to a method for recycling polyvinyl chloride plastics. Background Art

[0002] Plastics were invented in the 19th century. Their high quality, low price, and versatility have made them a common raw material for a wide range of products. For example, polyvinyl chloride (PVC), known for its acid and alkali resistance, flame retardancy, and durability, is widely used in bank cards, doors and windows, plastic wrap, imitation leather, and cable insulation.

[0003] Because plastics are difficult to decompose in nature, the plastic products that are ubiquitous in our daily lives have gradually become a serious environmental problem as they are replaced over time. Current plastic recycling methods include: (1) melt recycling: recycling clean scraps left over from processing plants and reshaping them into recycled plastics; or recycling mixed plastic products for composite recycling; and (2) thermal cracking: recycling specific plastics into fuel, such as Taiwan Patent Publication No. TWI254115B, which cracks waste plastics into liquid oil and combustible gas.

[0004] Although countries are gradually implementing plastic reduction policies, the environmental problems caused by plastic waste still need to be solved urgently, so it is necessary to develop new plastic recycling methods.

[0005] Summary of the Invention

[0006] To solve the above problems, the present invention provides a method for recycling polyvinyl chloride plastics, comprising:

[0007] (1) Preparation step: preparing a plastic-containing material, wherein the plastic-containing material comprises a plastic, and the plastic comprises polyvinyl chloride (PVC);

[0008] (2) a mixing step of mixing the plastic-containing material and a solvent to obtain a first mixture, wherein the plastic is soluble in the solvent;

[0009] (3) a dissolving step of stirring the first mixture at a temperature of 20° C. to 110° C. to dissolve the plastic in the solvent to obtain a solution; and

[0010] (4) Separation step: filtering the second mixture through a filter.

[0011] According to the present invention, first, a solvent is used to dissolve the plastic being recycled, resulting in a high plastic recovery rate. Second, stirring prevents the plastic-containing materials from adhering to each other or adhering to the surface of the container containing the first mixture, and facilitates dissolution, thereby improving plastic recycling efficiency. Third, evaporating the solvent in a negative pressure environment not only effectively separates the solvent from the plastic being recycled, but also prevents deterioration of the solvent or plastic due to overheating. The recovered solvent can then be reused, further reducing recycling costs. This not only attracts more manufacturers to invest in the plastic recycling industry, but also avoids the increased costs and potential environmental issues caused by solvent discharge, thereby doubly reducing environmental concerns.

[0012] The plastic-containing material of the present invention comprises a polymer, a mixture or a combination thereof.

[0013] In one embodiment, if the plastic-containing material includes a material other than polyvinyl chloride, the dissolving solution includes not only the polyvinyl chloride dissolved in the solvent but also a portion insoluble in the solvent, such as a precipitate or a suspended substance.

[0014] Preferably, the temperature of the dissolving step is 25°C to 105°C, for example, 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C or 105°C.

[0015] In one embodiment, the separation step further includes a heat preservation step: the solution is kept warm at a temperature of 40°C to 110°C, for example, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, or 110°C. The present invention lowers the boiling point of the solvent by creating a negative pressure environment, and maintains the solvent in a boiling state through heat preservation, thereby facilitating accelerated and stable solvent recovery and reducing energy consumption.

[0016] In one embodiment, in the separation step, after the insulation step is completed to obtain a recycled semi-finished product, a drying step is further performed: the recycled semi-finished product is dried at a temperature of 70°C to 90°C, for example, 70°C, 75°C, 80°C, 85°C, or 90°C, to obtain the plastic. The present invention further removes any solvent that may remain in the recycled semi-finished product through the drying step.

[0017] In one embodiment, during the separation step, the pressure of the negative pressure environment is greater than or equal to 0 mbar and less than or equal to 90 mbar, for example, 1 mbar, 10 mbar, 30 mbar, 50 mbar, 70 mbar, or 90 mbar. Preferably, the pressure of the negative pressure environment is greater than or equal to 0 mbar and less than or equal to 20 mbar. More preferably, the pressure of the negative pressure environment is the same as the pressure during the insulation step. The drying step can be performed under normal atmospheric pressure.

[0018] In one embodiment, the holding time is from 5 minutes to 1 hour. Preferably, when the pressure of the negative pressure environment is greater than or equal to 0 mbar and less than or equal to 20 mbar, the holding time is from 10 minutes to 20 minutes.

[0019] In one embodiment, the polyvinyl chloride plastic recycling method of the present invention does not use a precipitant to separate the plastic.

[0020] In one embodiment, the solvent comprises any one of butanone, cyclohexanone and tetrahydrofuran (THF) or a combination thereof.

[0021] Preferably, when the solvent comprises butanone, the temperature in the dissolving step is 60°C to 80°C, for example, 60°C, 65°C, 70°C, 75°C or 80°C; and / or the temperature in the keeping step is 40°C to 70°C, for example, 40°C, 50°C, 60°C or 70°C.

[0022] Preferably, when the solvent comprises cyclohexanone, the temperature in the dissolving step is 20°C to 100°C, for example, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C; and / or the temperature in the keeping step is 70°C to 110°C, for example, 70°C, 80°C, 90°C, 100°C or 110°C.

[0023] Preferably, when the solvent comprises tetrahydrofuran, the temperature in the dissolving step is 20°C to 60°C, for example, 20°C, 30°C, 40°C, 50°C or 60°C; and / or the temperature in the keeping step is 40°C to 70°C, for example, 40°C, 50°C, 60°C or 70°C.

[0024] In one embodiment, the solvent comprises butanone and cyclohexanone.

[0025] In one embodiment, the solvent comprises butanone and tetrahydrofuran.

[0026] In one embodiment, the solvent comprises cyclohexanone and tetrahydrofuran.

[0027] Preferably, when the solvent comprises butanone and cyclohexanone, the temperature in the dissolving step is 60° C. to 80° C., for example, 60° C., 63° C., 66° C., 69° C., 72° C., 75° C., 78° C., or 80° C., and / or the temperature in the holding step is 70° C. to 110° C., for example, 70° C., 80° C., 90° C., 100° C., or 110° C. More preferably, when the solvent comprises butanone and cyclohexanone, the temperature in the dissolving step is 68° C. to 72° C., and / or the temperature in the holding step is 80° C. to 100° C.

[0028] Preferably, when the solvent comprises butanone and tetrahydrofuran, the temperature in the dissolving step is 20° C. to 80° C., for example, 20° C., 30° C., 40° C., 50° C., 60° C., 70° C., or 80° C.; and / or the temperature in the holding step is 40° C. to 70° C., for example, 40° C., 50° C., 60° C., or 70° C. More preferably, based on the total volume of the solvent, the content of butanone is 40 volume percent to 60 volume percent, and the content of tetrahydrofuran is 40 volume percent to 60 volume percent.

[0029] Preferably, when the solvent comprises cyclohexanone and tetrahydrofuran, the temperature in the dissolving step is 20° C. to 80° C., for example, 20° C., 30° C., 40° C., 50° C., 60° C., 70° C., or 80° C.; and / or the temperature in the holding step is 70° C. to 110° C., for example, 70° C., 80° C., 90° C., 100° C., or 110° C. More preferably, based on the total volume of the solvent, the cyclohexanone content is 40 volume percent to 60 volume percent, and the tetrahydrofuran content is 40 volume percent to 60 volume percent.

[0030] In one embodiment, the volume ratio of butanone to cyclohexanone is 0.28 to 3.5, for example, 0.28, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8, 2.1, 2.4, 2.7, 3.0, 3.3, or 3.5. For example, when the volume of butanone is 60 ml and the volume of cyclohexanone is 20 ml, the volume ratio of butanone to cyclohexanone is 3. Preferably, the volume ratio of butanone to cyclohexanone is 0.28 to 3.05. More preferably, the volume ratio of butanone to cyclohexanone is 0.28 to 1.6.

[0031] In one embodiment, based on the total volume of the solvent, the content of butanone is 20 volume percent to 80 volume percent, for example, 20 volume percent, 30 volume percent, 40 volume percent, 50 volume percent, 60 volume percent, 70 volume percent, or 80 volume percent, and the content of cyclohexanone is 20 volume percent to 80 volume percent, for example, 20 volume percent, 30 volume percent, 40 volume percent, 50 volume percent, 60 volume percent, 70 volume percent, or 80 volume percent. Preferably, the content of butanone is 20 volume percent to 62 volume percent, and the content of cyclohexanone is 38 volume percent to 80 volume percent.

[0032] In one embodiment, the preparation step further includes a classification step: preparing classification solutions with different specific gravities to float out plastic-containing materials with different specific gravities.

[0033] Preferably, the classification step is to float out plastic-containing materials of different specific gravity ranges in the order of low to high specific gravity.

[0034] In one embodiment, the specific gravity is between 0.8 and 1.6, for example, 0.8, 1.0, 1.2, 1.4, or 1.6. For example, flotation is performed in the order of specific gravity: 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, and 1.6. Preferably, the specific gravity is between 1.3 and 1.5. More preferably, the specific gravity is between 1.35 and 1.45. The present invention effectively screens out non-PVC materials through flotation, thereby improving PVC recovery efficiency.

[0035] In one embodiment, the plastic-containing material is in granular form.

[0036] Preferably, the average diameter of the plastic-containing material is greater than 0 mm and less than or equal to 5 mm. More preferably, the average diameter of the plastic-containing material is greater than 0 mm and less than or equal to 3.1 mm, for example, 0.5 mm, 1 mm, 2 mm, 3 mm or 3.1 mm.

[0037] In one embodiment, the stirring speed of the dissolving step is 150 rpm to 200 rpm, for example, 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm, or 200 rpm. The present invention can maintain the plastic-containing material continuously suspended in the solvent through stirring, thereby improving dissolution efficiency and recovery rate.

[0038] In one embodiment, the dissolving step is performed for 15 to 120 minutes, for example, 15 minutes, 30 minutes, 45 minutes, 60 minutes, 90 minutes, or 120 minutes.

[0039] In one embodiment, the weight of the plastic-containing material is greater than 0 grams and less than or equal to 8 grams, for example, 0.05 grams, 0.1 grams, 0.5 grams, 1 gram, 2 grams, 3 grams, 4 grams, 5 grams, 6 grams, 7 grams, or 8 grams, based on 100 milliliters of the solvent. Preferably, the weight of the plastic-containing material is 6.8 grams to 7.2 grams, based on 100 milliliters of the solvent. According to the present invention, the ratio range of the volume of the solvent to the weight of the plastic-containing material can avoid the problem of excessively high viscosity and difficulty in stirring during the formation of the first mixture into a dissolved solution, thereby improving plastic recycling efficiency.

[0040] In one embodiment, the dissolving step (3) includes: (3-1): stirring the first mixture at a temperature of 20°C to 110°C to dissolve the plastic in the solvent to obtain a second mixture; and (3-2): filtering the second mixture through a filter to obtain a dissolved solution. This method can remove impurities insoluble in the solvent, thereby improving the purity of the recyclable material.

[0041] In one embodiment, step (3 / 2) further includes a precipitation step, i.e., after obtaining the second mixture, the second mixture is allowed to stand to obtain a settled second mixture; wherein the settled second mixture has a temperature lower than that of the first mixture and comprises a supernatant and a precipitate, and impurities in the supernatant are filtered through a filter to obtain the dissolved solution. In other words, the present invention can remove impurities by using a precipitation step, i.e., by allowing the second mixture to stand without heating, in conjunction with a filter to remove undissolved components and suspended matter.

[0042] Preferably, during the precipitation step, the second mixture is allowed to stand for 2 to 3 hours. The present invention allows the second mixture to stand at room temperature until the second mixture shows clear precipitation, and then filters the supernatant through a filter. This shortens the filtration time and reduces the amount of impurities in the solution compared to directly filtering the second mixture.

[0043] In one embodiment, the separation step can obtain a recovered solvent.

[0044] Preferably, the recovery solvent comprises a first solvent and a second solvent, and after the separation step, further comprises a solvent separation step: placing the recovery solvent in a recovery negative pressure environment, first boiling the recovery solvent at a first solvent recovery temperature, and condensing to obtain a first recovery liquid, and obtaining a first recovery residual liquid; then boiling the first recovery residual liquid at a second solvent recovery temperature, and condensing to obtain a second recovery liquid; wherein the first solvent recovery temperature is lower than the second solvent recovery temperature, and the first recovery liquid comprises the first solvent, and the second recovery liquid comprises the second solvent.

[0045] Preferably, the pressure of the recycling negative pressure environment is greater than or equal to 0 mbar and less than or equal to 90 mbar, for example: 1 mbar, 10 mbar, 30 mbar, 50 mbar, 70 mbar or 90 mbar. Preferably, the pressure of the recycling negative pressure environment is greater than or equal to 0 mbar and less than or equal to 20 mbar.

[0046] Preferably, the first solvent comprises butanone, and the second solvent comprises cyclohexanone, and the first solvent recovery temperature is 70°C to 80°C, and the second solvent recovery temperature is 90°C to 100°C.

[0047] Preferably, the first recovery liquid and / or the second recovery liquid is used as a recovery solvent, and the solvent separation step is performed again. According to the present invention, performing the solvent separation step again can improve the purity of the first recovery liquid and / or the second recovery liquid.

[0048] In summary, the polyvinyl chloride plastic recycling method of the present invention has a high plastic recovery rate and high recovery efficiency, and the solvent can be recycled and reused, which not only reduces costs but also avoids derivative environmental problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG1 and FIG2 are flow charts of the polyvinyl chloride plastic recycling method of the present invention. DETAILED DESCRIPTION

[0050] Several operating modes are provided below to illustrate the implementation methods of the present invention. Those skilled in the art can easily understand the advantages and effects that can be achieved by the present invention through the contents of this specification, and make various modifications and changes without departing from the spirit of the present invention to implement or apply the contents of the present invention.

[0051] As shown in Figure 1 , the polyvinyl chloride (PVC) plastic recycling method of the present invention first proceeds to step S1: a preparation step. A plastic-containing material is prepared, comprising a plastic material containing polyvinyl chloride (PVC). Specifically, the plastic-containing material is industrial waste containing PVC, which is crushed and then sieved to obtain a powder. For example, the powder is sieved through a 10-mesh sieve to obtain plastic-containing material particles with a diameter of less than 2 mm.

[0052] Next, step S2: mixing is performed: the plastic-containing material and a solvent are mixed to obtain a first mixture, wherein the plastic is soluble in the solvent. Specifically, the solvent is selected from butanone and cyclohexanone, and the plastic-containing material, butanone and cyclohexanone are mixed to obtain the first mixture.

[0053] Then, S3: dissolving step is performed: the first mixture is stirred at a temperature of 20°C to 110°C to dissolve the plastic in the solvent to obtain a solution. Specifically, the dissolving step is performed at a temperature of 70°C, a stirring speed of 150 rpm to 200 rpm, and a time of 20 minutes to 40 minutes.

[0054] Finally, S4: Separation Step: The solution is placed in a negative pressure environment to separate the solvent, thereby obtaining the plastic. Specifically, the solution is sealed in a vacuum concentration device, where vacuum is created by pumping air, causing the solution to boil and separate butanone and cyclohexanone, resulting in polyvinyl chloride flakes or granules.

[0055] Referring to Figures 1 and 2 , when the plastic-containing material is industrial waste containing polyvinyl chloride, since it contains components that are insoluble in the solvent, the S3 dissolution step includes: S3-1: stirring the first mixture at a temperature of 20°C to 110°C to dissolve the plastic in the solvent to obtain a second mixture; and S3-2: filtering the second mixture with a filter to obtain a dissolved liquid. Specifically, the filter is used to remove undissolved solids to remove impurities. Furthermore, before removing undissolved solids with the filter, the second mixture can be allowed to stand at room temperature. After the second mixture shows obvious precipitation, the supernatant can be filtered.

[0056] Example 1 to Example 14

[0057] As shown in FIG1 , the polyvinyl chloride plastic recycling method of the present invention first proceeds to step S1: a preparation step: a plastic-containing material is prepared, the plastic-containing material comprising a plastic, and the plastic comprises polyvinyl chloride. Specifically, the plastic-containing material used in Examples 1 through 14 is commercially available polyvinyl chloride pellets (approximately 0.5 cubic centimeters in volume).

[0058] Next, step S2: Mixing: The plastic-containing material and a solvent are mixed to obtain a first mixture, wherein the plastic is soluble in the solvent. Specifically, the solvents are listed in Table 1. 7 grams of commercially available polyvinyl chloride granules and 100 milliliters of solvent are weighed using a graduated cylinder and mixed in a vacuum concentrator to obtain the first mixture.

[0059] Then, S3: Dissolution Step was performed: the first mixture was stirred at a temperature of 20°C to 110°C to dissolve the plastic in the solvent to obtain a solution. Specifically, the vacuum concentration bottle containing the first mixture was connected to a vacuum concentration device, and the pressure was maintained at normal atmospheric pressure. The vacuum concentration bottle containing the first mixture was then placed in a water bath and stirred. The stirring speed for each group was 170 rpm, and the temperature of each group during the stirring process was as shown in Table 1: wherein the room temperature was 25°C. After the commercially available polyvinyl chloride particles were completely dissolved, the dissolution time (i.e., the time required to obtain the solution) was recorded for each group. The results are shown in Table 1.

[0060] Finally, S4: Separation Step: The solution is placed in a negative pressure environment to separate the solvent, thereby obtaining the plastic. Specifically, the solution is allowed to stand until its temperature is approximately room temperature. The vacuum pump is then activated to reduce the pressure in the vacuum concentration device, lowering the pressure in the vacuum concentration bottle to between 0 and 20 mbar for the separation step. The solution is stirred at a speed of 20 rpm and heated in a water bath to accelerate solvent evaporation. Once boiling is observed, the heating temperature (i.e., the temperature for the insulation step) is maintained, as shown in Table 1. The vacuum pump is then closed, and the solvent vapor is condensed and recovered via a condenser, while simultaneously maintaining a constant pressure within the system.

[0061] After the solvent was completely evaporated and condensed, the volume of the recovered solution was recorded to calculate the solvent recovery rate. The results are shown in Table 2. Furthermore, when no solvent was visible in the vacuum concentration bottle and the recovered semi-finished product, in the form of a film, was approximately dry, it was placed in an oven at 80°C for approximately one hour to completely remove any residual solvent, thereby obtaining a polyvinyl chloride film. After the polyvinyl chloride film cooled to room temperature, its weight was measured to calculate the plastic recovery rate. The results are shown in Table 2. Fourier transform infrared spectroscopy (FTIR) analysis was also performed to confirm the plastic purity. The results are also shown in Table 2.

[0062] Table 1: Solvents used in Examples 1 to 14, the temperature of the dissolution step (hereinafter referred to as the dissolution temperature), the dissolution time, and the temperature of the holding step (hereinafter referred to as the holding temperature)

[0063] As can be seen from Table 1, first, the dissolution time of each group ranged from 15 minutes to 120 minutes. Among them, Example 5 had the shortest dissolution time, requiring only 15 minutes. This indicates that using tetrahydrofuran as the solvent and a temperature of 50°C in the dissolution step can dissolve polyvinyl chloride the fastest and has the highest dissolution efficiency.

[0064] Second, a comparison of Examples 2 and 3, 4 and 5, 6 and 7, and 13 and 14 shows that, using the same solvent, increasing the temperature of the dissolution step can significantly reduce the dissolution time. Specifically, the difference in dissolution temperature between Examples 2 and 3 is 65°C, resulting in a difference in dissolution time of 80 minutes; the difference in dissolution temperature between Examples 4 and 5 is 25°C, resulting in a difference in dissolution time of 25 minutes; the difference in dissolution temperature between Examples 6 and 7 is 45°C, resulting in a difference in dissolution time of 100 minutes; and the difference in dissolution temperature between Examples 13 and 14 is 45°C, resulting in a difference in dissolution time of 40 minutes. Furthermore, increasing the temperature of the dissolution step shortens the dissolution time to varying degrees with different solvents, with the greatest reduction in dissolution time achieved when using 50 weight percent each of butanone and tetrahydrofuran as the solvent.

[0065] Third, considering that tetrahydrofuran is relatively expensive, Example 7 mixes the solvents of Examples 1 and 5 to further understand the feasibility of mixing solvents to reduce costs. A comparison of Examples 1, 5, and 7 shows that when Example 5 uses only tetrahydrofuran as the solvent, the required dissolution time is the shortest. In other words, the dissolution efficiency of Example 7, which mixes butanone and tetrahydrofuran, is only slightly better than that of Example 1 (which uses only butanone). Similarly, Example 14 mixes the solvents of Examples 3 and 5. A comparison of Examples 3, 5, and 14 shows that the dissolution efficiency of Example 14, which mixes cyclohexanone and tetrahydrofuran, is also only slightly better than that of Example 3 (which uses only cyclohexanone). It can be seen that while mixing butanone or cyclohexanone with tetrahydrofuran can reduce costs, the dissolution efficiency is also reduced.

[0066] In contrast, a comparison of Examples 1, 3, and 8 shows that when Example 8 uses a mixture of butanone from Example 1 and cyclohexanone from Example 3, the dissolution time in Example 8 is only 40 minutes, significantly shorter than the 120 minutes in Example 1, provided that the temperature (70°C) of the dissolution step in Example 8 is the same as that in Example 1. Furthermore, the dissolution time in Example 8 is the same as the 40 minutes in Example 3, provided that the temperature (70°C) of the dissolution step in Example 8 is lower than that in Example 3, provided that the temperature (90°C) is lower than that in Example 3. It can be seen that when butanone and cyclohexanone are mixed as solvents, an unexpected improvement in dissolution efficiency can be achieved.

[0067] Finally, a comparison of Example 8 and Examples 9 to 12 shows that, under the premise that the temperature of the dissolution step is the same, the dissolution time of Example 8 is 40 minutes, while the dissolution time of Examples 9 to 12 is only 20 minutes, which is half the dissolution time of Example 8. It can be seen that when the content of butanone is 25 volume percent to 60 volume percent and the content of cyclohexanone is 40 volume percent to 75 volume percent based on the total volume of the solvent, the dissolution efficiency can be further improved.

[0068] Table 2: Plastic recovery rate, plastic purity and solvent recovery rate of Examples 1 to 14

[0069] As shown in Table 2, the plastic recovery rate for each group reached approximately 100%, and the FTIR spectra were free of additional noise, indicating that the recovered product (i.e., polyvinyl chloride film) was of high purity. Furthermore, the solvent recovered in each group was clear and free of impurities, demonstrating the high purity of the recovered solvent. Finally, the relatively low solvent recovery rates in Examples 6 through 14 indicate that mixing solvents can lead to a slight decrease in solvent recovery.

[0070] In summary, the polyvinyl chloride plastic recycling method of the present invention does have a high plastic recovery rate and high recovery efficiency, and the solvent can be recycled and reused, which not only reduces costs but also avoids derivative environmental problems.

Claims

1. A method for plastic recycling of polyvinyl chloride, comprising: (I) Preparation step: Prepare a plastic-containing material, the plastic-containing material contains a plastic, and the plastic contains polyvinyl chloride; (II) Mixing step: Mix the plastic-containing material and a solvent to obtain a first mixture, wherein the plastic is soluble in the solvent; (III) Dissolving step: Stir the first mixture at a temperature of 20°C to 110°C to dissolve the plastic in the solvent to obtain a solution; and (IV) Separating step: Place the solution in a negative pressure environment to separate the solvent, and obtain the plastic.

2. The method for plastic recycling of polyvinyl chloride according to claim 1, wherein in the separating step, it further comprises a heat preservation step: Keep the solution warm, and the temperature is 40°C to 110°C.

3. The method for plastic recycling of polyvinyl chloride according to claim 1, wherein the solvent comprises any one or a combination of methyl ethyl ketone, cyclohexanone, and tetrahydrofuran.

4. The method for plastic recycling of polyvinyl chloride according to claim 3, wherein the solvent comprises methyl ethyl ketone and cyclohexanone.

5. The method for plastic recycling of polyvinyl chloride according to claim 4, wherein the temperature in the dissolving step is 68°C to 72°C.

6. The method for plastic recycling of polyvinyl chloride according to claim 4, wherein the volume ratio of methyl ethyl ketone to cyclohexanone is 0.28 to 3.

5.

7. The method for plastic recycling of polyvinyl chloride according to claim 4, wherein based on the total volume of the solvent, the content of methyl ethyl ketone is 20 volume percentages to 80 volume percentages, and the content of cyclohexanone is 20 volume percentages to 80 volume percentages.

8. The method for plastic recycling of polyvinyl chloride according to claim 1, wherein the plastic-containing material is in granular form, and the average diameter of the plastic-containing material is greater than 0 mm and less than or equal to 5 mm, the stirring speed in the dissolving step is 150 rpm to 200 rpm, and the time of the dissolving step is 15 minutes to 120 minutes.

9. The method for plastic recycling of polyvinyl chloride according to claim 1, wherein the pressure of the negative pressure environment is greater than or equal to 0 mbar and less than or equal to 90 mbar.

10. The method for plastic recycling of polyvinyl chloride according to claim 1, wherein based on 100 ml of the solvent, the weight of the plastic-containing material is greater than 0 g and less than or equal to 8 g.

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