Post-consumer polyolefin cleaning agent and recovery method

Abstract

The invention provides a cleaning agent and a method for recovering polyolefin resin after consumption. The cleaning agent provided by the invention can effectively reduce residual bisphenol A in polyolefin after consumption and effectively remove residual pollutants such as food, cleaning care, oil stains and the like on the surface of the polyolefin, so that the polyolefin has a clean and bright good appearance after consumption. The invention further provides a recovery method, residual bisphenol A in polyolefin and pollutants on the surface of the polyolefin are effectively removed by adopting the cleaning agent through abrasive cleaning, the BPA migration level of the obtained polyolefin is obviously reduced, the odor and the appearance are good, the BPA reduction rate is larger than or equal to 40%, the odor grade is smaller than or equal to 4, the BPA reduction rate is basically equivalent to that of a new polyolefin material, the b value is smaller than or equal to 6, and the BPA reduction rate is larger than or equal to 40%. And a clean and transparent appearance is presented.

Description

Technical Field

[0001] This invention belongs to the field of waste plastic cleaning, and specifically relates to a method for recycling post-consumer polyolefins. Background Technology

[0002] During the recycling of waste polyolefins, residual labels (containing ink, colorants, adhesives, etc.) on the plastic matrix, incompletely sorted polycarbonate, and pollutants introduced from the environment (water, environment) during processing may cause bisphenol A (BPA) residues to remain in the plastic.

[0003] Currently, there are two main types of methods for recycling plastics containing bisphenol A (BPA). The first type involves depolymerization of polyester containing BPA, where the polyester is alcoholyzed to obtain depolymerized monomers, which are then purified using various separation methods. The second type involves organic solvent dissolution of polyolefins containing BPA. Polyolefins and BPA are dissolved together in an extraction solvent under high temperature and pressure. The polyolefins then precipitate while the BPA remains in the solution. The precipitated polyolefins and the BPA-containing solution are then separated by filtration. CN 119744280 A discloses a method for purifying and regenerating polymers. First, contaminants, including BPA, are leached out using an organic solvent, followed by multiple complex extraction, sedimentation, filtration, and adsorption operations. The average removal efficiency of BPA is approximately 75%, while the average removal efficiency using only organic solvent leaching is approximately 55%.

[0004] All of the above methods require the use of high-temperature and high-pressure reactors for dissolution, sedimentation or depolymerization reactions. Furthermore, due to the use of large amounts of organic solvents, post-processing requires the recovery of these organic solvents. The processes are complex, costly, and difficult to replicate industrially.

[0005] While existing sorting and cleaning processes are simple and easy to scale up, there is no specific reduction process for bisphenol A compounds. Existing cleaning processes can reduce bisphenol A in polyolefins by less than 20%, which is difficult to meet the bisphenol A limit requirements of high-quality fields such as daily chemical packaging and home appliances, thus restricting the high-quality utilization of recycled polyolefins. Summary of the Invention

[0006] To address the technical problem that existing methods for reducing bisphenol A in post-consumer polyolefins cannot simultaneously achieve simple processes, low costs, and high bisphenol A reduction rates, this invention provides a cleaning agent and a method for recycling post-consumer polyolefins.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A cleaning agent, by weight, comprises the following components: Ester compounds: 5-10 parts, polyethylene glycol: 5-15 parts, inorganic base: 0.9-1.2 parts, ether compounds: 1-3 parts, water: 75-85 parts; The ester compound is R1-COO-R2, where R1 is selected from C1-C4 alkyl groups that are hydroxylated or unsubstituted, and R2 is selected from C2-C5 alkyl groups. The ether compound is R3-O-(CH2CH2O). n H and R3 are selected from C2~C18 alkyl groups, and n is not less than 1; The inorganic base is selected from one or more of NaOH and KOH.

[0008] The cleaning agent used in this invention uses ester compounds that cause polyolefins to swell to a certain extent, enhancing chain segment movement and accelerating the diffusion of bisphenol A from the polymer into the cleaning agent. Polyethylene glycol can accelerate the migration of bisphenol A from the polymer surface to the cleaning agent bulk. Inorganic bases can provide an alkaline environment preferred by bisphenol A. Ether compounds can assist the transfer of viscous polyethylene glycol from the polyolefin surface to the cleaning agent bulk. All four components work together to promote the reduction of bisphenol A.

[0009] By limiting the weight of each component within the above-mentioned range, this invention can achieve both good cleaning effect, good bisphenol A reduction rate and low odor residue. Its bisphenol A reduction rate is more than 40% and can reach 60%, which is similar to the effect of pure organic solvent leaching. Moreover, it is green, environmentally friendly, non-toxic and odorless. The odor level of the polyolefin obtained by cleaning is close to that of virgin polyolefin, and its appearance is clean and bright.

[0010] Preferably, the ester compound is selected from at least one of butyl butyrate, butyl acetate, ethyl acetate, ethyl butyrate, ethyl propionate, ethyl lactate (ethyl 2-hydroxypropionate), and isoamyl acetate.

[0011] Specifically, the ester compound may be selected in quantities of 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, or 10 parts.

[0012] Preferably, the ether compound is selected from at least one of diethylene glycol butyl ether (CAS No. 112-34-5), diethylene glycol ethyl ether (CAS No. 111-90-0), triethylene glycol monobutyl ether (CAS No. 143-22-6), ethylene glycol monobutyl ether (CAS No. 111-76-2), C12-C18 fatty alcohol polyoxyethylene ether (CAS No. 68213-23-0), and C9-C11 fatty alcohol polyoxyethylene ether (CAS No. 68439-46-3).

[0013] Specifically, the ether compound may be selected in parts of 1, 2, or 3.

[0014] Specifically, the relative molecular weight of the polyethylene glycol is 200-1000, preferably 200-400. Within this range, the polyethylene glycol exhibits optimal cleaning and BPA reduction effects. If the relative molecular weight of the polyethylene glycol is too high, it will result in excessive viscosity, making it difficult to migrate from the polyolefin surface to the cleaning agent bulk.

[0015] Specifically, the polyethylene glycol can be selected in quantities of 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, or 15 parts.

[0016] Specifically, the water can be selected in quantities of 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, or 85 parts.

[0017] Specifically, the inorganic base may be selected in amounts of 0.9 parts, 1 part, 1.1 parts, or 1.2 parts.

[0018] This invention protects a method for recycling post-consumer polyolefins, comprising the following steps: Polyolefin fragments are thoroughly rubbed and cleaned in a friction cleaner with a cleaning agent and abrasive media, wherein the cleaning agent is the aforementioned cleaning agent; The polyolefin fragments that have undergone friction cleaning are sequentially rinsed, dried, and melt-extruded to obtain recycled polyolefin.

[0019] The recycling method of this invention uses a specific cleaning agent to abrasively clean polyolefin fragments, which can effectively reduce the residual bisphenol A in the polyolefin and remove contaminants from the surface of the polyolefin. The cleaning agent remaining in the polyolefin can be removed by simple cleaning and devolatilization operations such as rinsing, drying, and melt extrusion. The process is simple, and the recycled polyolefin has the same odor level and clean and bright appearance as the virgin polyolefin. It can be used to prepare packaging for chemicals that come into direct contact with the human body, such as toiletries and cosmetics.

[0020] The friction cleaning machine described in this invention can be any friction cleaning machine commonly used in the art, and the abrasive cleaning medium can be any abrasive cleaning medium commonly used in the art. The friction cleaning machine described in this invention can be kept in an open, normal pressure state, eliminating the need for high-pressure closed equipment.

[0021] Preferably, the friction cleaning can be performed at a temperature of 50°C or higher for better bisphenol A reduction. Considering the boiling point of water-based cleaning agents, the friction cleaning is performed at 60-75°C. Temperatures above this range can easily lead to water evaporation, causing changes in the concentration of various components in the cleaning agent, thus weakening the cleaning effect and the bisphenol A reduction effect.

[0022] Specifically, the friction cleaning rotation speed can be 100 rpm or higher. Preferably, the friction cleaning stirring speed can be 100~250 rpm. Within this range, the stirring speed can balance appearance, BPA reduction rate, and cost.

[0023] Specifically, the friction cleaning time can be 10-180 minutes. Preferably, the friction cleaning time is 20-40 minutes. Within this range, the friction cleaning time balances appearance, BPA reduction rate, and cost.

[0024] Preferably, the friction cleaning is performed under ultraviolet light irradiation at 240-280 nm. Ultraviolet light irradiation can accelerate the degradation of bisphenol A, thereby further reducing the bisphenol A content. The wavelength of ultraviolet light within this range allows for a good reduction rate of bisphenol A, while the structure of the polyolefin is unaffected or minimally affected.

[0025] Preferably, the ultraviolet irradiation time is 20-40 minutes. Within this range, the irradiation time allows for good reduction of bisphenol A while the structure of the polyolefin is unaffected or minimally affected.

[0026] The method of applying ultraviolet light irradiation is not limited; any method that ensures uniform ultraviolet light irradiation on the surface of the polyolefin fragments is acceptable. This invention applies ultraviolet light irradiation by adding a glass-covered ultraviolet device to the upper wall of the friction barrel.

[0027] Specifically, the drying temperature can be 100°C or higher. After friction cleaning, the shredded plastic pieces are dried by a heating drying module, which dries the water remaining on the plastic surface and removes some of the cleaning agent that has swollen into the plastic matrix.

[0028] Preferably, the drying temperature is 100~120℃. Within this temperature range, the cleaning agent can be effectively removed, while the structure of the polyolefin is unaffected or minimally affected.

[0029] Specifically, the temperature of the melt extrusion can be 200°C or higher. Melt extrusion can, to some extent, reduce bisphenol A and remove cleaning agents that have swollen into the plastic matrix.

[0030] Preferably, the melt extrusion temperature can be 200~250℃. A melt extrusion temperature within this range can effectively remove the cleaning agent that has swollen into the polyolefin, making the odor level of the recycled polyolefin comparable to that of virgin polyolefin, while the structure of the polyolefin remains unaffected or minimally affected.

[0031] The post-processing of the recycling method of the present invention is simple. The generated wastewater is introduced into a wastewater treatment tank for ozone treatment to remove bisphenol A compounds from the wastewater, and then other simple purification treatments are carried out.

[0032] Specifically, the post-consumer polyolefin includes PP or PE, PE further includes HDPE, LDPE, and LLDPE, and PP further includes copolymer PP, homopolymer PP, and random PP.

[0033] This invention also protects the application of the above-described recycling method in the recycling of post-consumer polyolefin products.

[0034] Specifically, the post-consumer polyolefin products include food packaging, personal care packaging, and cosmetic packaging.

[0035] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a cleaning agent that can effectively reduce bisphenol A in post-consumer polyolefins and remove contaminants from the surface of post-consumer polyolefins. The bisphenol A reduction rate is over 40%, and the cleaning effect is good. The post-consumer polyolefins after cleaning have low bisphenol A migration levels, a clean and bright appearance, and an odor level that is basically close to that of virgin polyolefins.

[0036] Based on this, the present invention further provides a recycling method. The above-mentioned cleaning agent can effectively reduce the residual bisphenol A in polyolefin and remove contaminants on the surface of polyolefin through simple friction cleaning. It does not require the use of high temperature and high pressure closed equipment. The process is simple, green and environmentally friendly, low cost and easy to scale up. The resulting recycled polyolefin has a clean and bright appearance, an odor level close to that of virgin polyolefin, and a significantly reduced bisphenol A migration. Detailed Implementation

[0037] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0038] The reagents used in the various embodiments and comparative examples of this invention are described below: Butyl butyrate: CAS number 109-21-7, commercially available; Ethyl octanoate: CAS No. 106-32-1, commercially available; Ethyl lactate: CAS number 97-64-3, commercially available; Ethyl acetate: CAS number 141-78-6, commercially available; PEG-400: Number average molecular weight ≈ 400, commercially available; PEG-1500: Number average molecular weight ≈ 1500, commercially available; Diethylene glycol butyl ether: CAS number 112-34-5, commercially available; C9-C11 fatty alcohol polyoxyethylene ether: CAS No. 68439-46-3, commercially available; NaOH: CAS No. 1310-73-2, commercially available; Na2CO3: CAS No. 497-19-8, commercially available; HDPE 5502: Huizhou CNOOC Shell, grade HDPE 5502, measured odor level 3.5~3.8; HDPE-100: HDPE 5502 was soaked in a mixture of milk, shampoo, and cooking oil for one month. After simple rinsing and drying, the dried HDPE was mixed with a known amount of BPA in a high-speed mixer, extruded, injection molded into sheets, and crushed to prepare HDPE fragments containing BPA. The b-value of the HDPE fragments was measured to be 11.7, the odor level was 5.1, and the BPA migration was 236.4 µg / kg. This was used to verify the BPA reduction and cleaning effects and reduce the errors caused by batch-to-batch fluctuations in post-consumer recycled plastics.

[0039] The cleaning agent formulation of the present invention is shown in Table 1, in parts by weight: Table 1 Cleaning agent formulation (unit: parts by weight)

[0040] Continued from Table 1

[0041] The cleaning agent of the present invention is prepared by the following process: Add each component to the water in the appropriate weight proportions, stir and heat to 55°C, then store in a storage tank for later use.

[0042] The performance testing methods and standards for the polyolefins obtained in the various embodiments and comparative examples of this invention are as follows: Appearance: The cleaned HDPE shreds are injection molded into standard color swatches, and the b-value of the color swatches is tested using a colorimeter (Datacolor Spectro1050); the b-value is the blue-yellow value, ranging from -120 to 120, and the higher the b-value, the more yellow it is; Bisphenol A (BPA) reduction rate: Referring to GB 31604.10-2016, the sample was immersed in 95% ethanol and migrated at 60℃ for 10 days. The migration amount was detected by LC-MS / MS. The detection limit of this method is 1 µg / kg and the quantitation limit is 3 µg / kg. If the detection result is less than the method detection limit, it is considered non-detectable (ND). BPA reduction rate = (BPA migration amount of unreduced HDPE - BPA migration amount of reduced HDPE) ÷ BPA migration amount of unreduced HDPE × 100%.

[0043] Odor: Following the German Association of the Automotive Industry (VDA) standard VDA270, samples were categorized into three sampling methods based on size, and 1 L odor bottles were used for testing. Test temperatures were 23±2℃, 40±2℃, and 80±2℃. Odor levels were described on a six-level scale, but a rating of 0.5 was allowed during evaluation. A minimum of five evaluators were required. The difference between each person's rating could not exceed two levels, and the final rating was the average. The level classifications are shown in Table 2 below. Table 2 Odor Rating Description

[0044] Examples and Comparative Examples The recovery methods of each embodiment and comparative example include the following steps: First rinsing: The solvent medium in the rinsing tank is water. Polymers such as polycarbonate and epoxy resin have a higher density than water. Non-polyolefin impurities such as polycarbonate, epoxy resin, and silt are removed by density sorting. Friction cleaning: The broken polyolefin fragments are poured into the friction cleaning machine, and the prepared cleaning agent is injected through the conveying pipe. The broken pieces are stirred and rubbed while being heated and kept warm. The temperatures used in each embodiment are shown in Table 3. A glass cover ultraviolet device is added to the upper wall of the friction barrel. The ultraviolet wavelengths used in each embodiment are shown in Table 3. This allows for sufficient friction with the cleaning agent and the grinding equipment, removing contaminants such as food, detergent, and oil stains from the surface of the broken pieces while reducing bisphenol A compounds. Second rinsing: After grinding and washing, the broken pieces are placed in the second rinsing tank. The solvent medium is water. The purpose is to remove the cleaning agent remaining on the plastic surface, and then remove non-polyolefin impurities such as polycarbonate and epoxy resin through density sorting. The third rinsing: After rinsing, the broken pieces are placed in a high-pressure spray conveyor device of not less than 10 meters to further remove contaminants and cleaning agents from the surface of the plastic substrate, and then conveyed to the baking equipment to be baked with hot air until dry. Drying: Dry the polyolefin fragments after the third rinse at 110°C to remove residual moisture on the surface of the polyolefin fragments and at least some of the ester compounds that have swollen into the interior of the polyolefin. Melt extrusion: The dried polyolefin fragments are melt-extruded through an extruder at a temperature of 200°C to remove ester compounds that have swollen into the interior of the polyolefin and to reduce BPA. Post-treatment: Wastewater from the friction cleaner and rinsing tank is collected in the wastewater treatment tank and treated with ozone for 30 minutes to remove bisphenol A compounds from the wastewater before further purification.

[0045] Table 3. Method parameters for each embodiment and comparative example.

[0046] Continued from Table 3

[0047] As shown in Table 3, the HDPE shredded sheets obtained by the recycling methods of each embodiment have significantly reduced BPA residue, good odor, and good appearance. The BPA reduction rate is ≥40%, the odor level is ≤4, which is basically equivalent to that of virgin polyolefin material, and the b value is ≤6, presenting a clean and bright appearance.

[0048] Comparative Example 1, which did not undergo UV irradiation during the grinding process, showed a poor BPA reduction rate; Comparative Example 2, which did not undergo heat preservation during the grinding process, showed a significantly reduced BPA reduction rate; it can be seen that UV irradiation and heating can promote the reduction of BPA in the plastic matrix.

[0049] In Comparative Example 3, the use of ethyl octanoate in the cleaning agent resulted in poor BPA reduction. Furthermore, the BPA swelled into the polyolefin and could not be completely removed by simple devolatilization steps such as rinsing, drying, and melt extrusion, leading to a strong, interfering odor in the cleaned fragments.

[0050] The cleaning agent used in Comparative Example 4 contained too many ester compounds, which were difficult to remove through simple devolatilization steps such as rinsing, drying, and melt extrusion, resulting in the cleaned fragments exhibiting a strong, interfering odor.

[0051] The cleaning agent used in Comparative Example 5 contained too much PEG, making it too viscous and resulting in poor cleaning performance. Contaminants could not be completely removed, and the b-value and odor level of the recycled polyolefin fragments were inferior to those in Example 2.

[0052] The cleaning agent in Comparative Example 6 did not contain any ether compounds. On the one hand, the cleaning effect was worse, and the b-value and odor level of the recycled polyolefin fragments were inferior to those in Example 1. On the other hand, the BPA reduction effect was also reduced.

[0053] The cleaning agent in Comparative Example 7 did not contain any inorganic alkali, which resulted in a poorer cleaning effect, with the b-value and odor level of the recycled polyolefin fragments being inferior to those in Example 1. Furthermore, the BPA reduction effect was also reduced.

[0054] The cleaning agent in Comparative Example 8, which does not contain ester compounds, showed significantly reduced cleaning performance and BPA reduction, with its b-value, odor rating, and BPA reduction rate all inferior to those in Example 1.

[0055] In Comparative Example 9, the cleaning agent without polyethylene glycol significantly reduced BPA, and the BPA reduction rate was significantly worse than that of Example 1.

[0056] In Comparative Example 10, Na2CO3 was used instead of NaOH in the cleaning agent, resulting in a decrease in both cleaning effect and BPA reduction effect. The b-value and BPA reduction rate were inferior to those in Example 1.

[0057] The cleaning agent used in Comparative Example 11 was polyethylene glycol 1500, which significantly reduced BPA, and the BPA reduction rate was significantly worse than that in Example 1.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A cleaning agent, characterized in that, By weight, it includes the following components: Ester compounds: 5-10 parts, polyethylene glycol: 5-15 parts, inorganic base: 0.9-1.2 parts, ether compounds: 1-3 parts, water: 75-85 parts; The ester compound is R1-COO-R2, where R1 is selected from C1-C4 alkyl groups that are hydroxylated or unsubstituted, and R2 is selected from C2-C5 alkyl groups. The ether compound is R3-O-(CH2CH2O). n H and R3 are selected from C2~C18 alkyl groups, and n is not less than 1; The inorganic base is selected from one or more of NaOH and KOH.

2. The cleaning agent according to claim 1, characterized in that, The relative molecular weight of the polyethylene glycol is 200-1000, preferably 200-400.

3. The cleaning agent according to claim 1, characterized in that, The ester compound is selected from at least one of butyl butyrate, butyl acetate, ethyl acetate, ethyl butyrate, ethyl propionate, ethyl lactate, and isoamyl acetate.

4. The cleaning agent according to claim 1, characterized in that, The ether compound is selected from at least one of diethylene glycol butyl ether, diethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol monobutyl ether, C12-C18 fatty alcohol polyoxyethylene ether, and C9-C11 fatty alcohol polyoxyethylene ether.

5. A method for recycling post-consumer polyolefins, characterized in that, Includes the following steps: Polyolefin fragments are thoroughly rubbed and cleaned in a friction cleaning machine with a cleaning agent and abrasive media. The cleaning agent is any one of the cleaning agents described in claims 1 to 4. The temperature of the friction cleaning is 50°C or higher, and the friction cleaning is carried out under ultraviolet light irradiation of 240 to 280 nm. The polyolefin fragments that have undergone friction cleaning are sequentially rinsed, dried, and melt-extruded to obtain recycled polyolefin.

6. The recycling method according to claim 5, characterized in that, The friction cleaning speed is 100 rpm or higher, and the friction cleaning time is 10 minutes or higher.

7. The recycling method according to claim 5, characterized in that, The ultraviolet light irradiation time is 20~40 minutes.

8. The recycling method according to claim 5, characterized in that, The drying temperature is 100°C or higher, and the melt extrusion temperature is 200°C or higher.

9. The recycling method according to claim 5, characterized in that, The post-consumer polyolefins include PP or PE, PE further includes HDPE, LDPE, and LLDPE, and PP further includes copolymer PP, homopolymer PP, and random PP.

10. The application of the cleaning agent according to claims 1 to 4 or the recycling method according to claims 5 to 9 in the recycling of post-consumer polyolefin products, wherein the post-consumer polyolefin products include food packaging, personal care packaging, and cosmetic packaging.

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