A method for laboratory preparation of micro-sized thin film-like microplastics

Abstract

The present application relates to the technical field of microplastics, and specifically relates to a method for preparing micron-sized film-shaped microplastics in a laboratory, comprising: cutting modified polypropylene plastic film into fragments; mixing the plastic fragments with grinding medium quartz sand, and then adding the mixture into a grinding disc; cutting the film fragments by high-speed rotation of the quartz sand; collecting the sample; placing the ground sample into a beaker, adding deionized water, and then cleaning the sample in an ultrasonic cleaner to separate the ground grinding medium from the microplastics; using a siphon method to suck the sample floating in the beaker; transferring the sucked sample to another beaker containing deionized water, and repeating the ultrasonic cleaning step; repeating the siphon floating and cleaning operations until the cleaning liquid is clear and transparent; collecting the final purified floating sample, and drying the sample to obtain the film-shaped microplastics with a desired particle size range; and the present application provides a low-cost, simple-to-operate laboratory preparation method suitable for film-shaped microplastics.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of microplastics, in particular to a method for preparing micron-sized thin film microplastics in a laboratory. BACKGROUND

[0002] With the widespread use of agricultural mulching films, the pollution of soil by sheet microplastics caused by residual mulching films is increasingly common.

[0003] The current main methods for preparing microplastics in the laboratory have the following limitations:

[0004] Freeze grinding method: cut the plastic into small pieces, freeze in liquid nitrogen, and then crush; the crushed material is ground again in a mortar with liquid nitrogen; and finally, the sample is obtained by sieving. This method consumes a large amount of liquid nitrogen.

[0005] Tableting-crushing-sieving method: use a tablet press to compress the plastic, then use a crusher to crush it; the crushed sample is filtered and classified by a nylon filter screen to obtain microplastics of different particle sizes. This method relies on expensive equipment such as a tablet press.

[0006] Wet crushing-centrifugation-filtration method: cut the plastic into small pieces, crush it with a crusher, mix it with water, and further crush it in a blender; the resulting mixture is centrifuged to separate the supernatant, which is filtered through a filter membrane with a specific pore size, and the filter membrane residue is dried to obtain microplastics of the target particle size. This method is complex and requires expensive equipment such as a blender, centrifuge, etc.

[0007] Common defects of existing methods:

[0008] High cost: freeze grinding method consumes a large amount of liquid nitrogen, and tableting-crushing-sieving method and wet crushing-centrifugation-filtration method require expensive equipment (tablet press, crusher, blender, centrifuge).

[0009] Complex operation: tableting-crushing-sieving method and wet crushing-centrifugation-filtration method have complicated steps.

[0010] Morphological limitations: the above methods are more suitable for preparing granular or fragmented microplastics, and it is difficult to effectively prepare thin film microplastics. SUMMARY

[0011] The purpose of the present application is to provide a laboratory preparation method that is low in cost, easy to operate, and suitable for thin film microplastics.

[0012] The purpose of the present application can be achieved by the following technical solution: a method for preparing micron-sized thin film microplastics in a laboratory, comprising the following steps:

[0013] Fragment preparation: cut the modified polypropylene plastic film into fragments;

[0014] Mechanical grinding: the plastic fragments are mixed with the grinding medium quartz sand, and then added into the grinding disc. The quartz sand cuts the film fragments by high-speed rotation, and the sample is collected;

[0015] The ground sample is placed in a beaker, deionized water is added and mixed, and then placed in an ultrasonic cleaner for cleaning to separate the ground grinding medium and microplastics. The sample floating in the beaker is sucked by siphon method. The sucked sample is transferred to another beaker containing deionized water, and the ultrasonic cleaning step is repeated.

[0016] The siphon floating and cleaning operation is repeated until the cleaning liquid is clear and transparent, and the finally purified floating sample is collected and dried to obtain the film-shaped microplastics in the required particle size range.

[0017] As a further scheme of the present application: the quartz sand is 40-80 mesh, and the mass ratio of plastic fragments to quartz sand is 1:30.

[0018] As a further scheme of the present application: the preparation process of the modified polypropylene plastic comprises the following steps:

[0019] The polypropylene base material, ethylene-terminated polydimethylsiloxane and maleic anhydride grafted PP are premixed to obtain a premix;

[0020] The premix is added into a twin-screw extruder with a processing temperature of 155-192℃, and the initiator dicumyl peroxide is added from the middle of the twin-screw extruder to mix with the premix and then extruded to obtain the modified polypropylene plastic.

[0021] As a further scheme of the present application: the premixing process comprises: the ethylene-terminated polydimethylsiloxane and maleic anhydride grafted PP are put into a high-speed mixer and mixed for 5 minutes.

[0022] As a further scheme of the present application: the rotation speed of the high-speed mixer is 800-1000 rpm.

[0023] As a further scheme of the present application: the mass ratio of the polypropylene base material, ethylene-terminated polydimethylsiloxane, maleic anhydride grafted PP and dicumyl peroxide is 100:8:5:0.1-0.2.

[0024] As a further scheme of the present application: the twin-screw extruder comprises six zones.

[0025] As a further scheme of the present application: the six zones are specifically feeding zone, melting zone, reaction zone, mixing zone, devolatilization zone and homogenization extrusion zone.

[0026] As a further scheme of the present application: the temperature of the feeding zone is 160±5℃, the temperature of the melting zone is 180±5℃, the temperature of the reaction zone is 190±2℃, the temperature of the mixing zone is 185±5℃, the temperature of the devolatilization zone is 180±5℃, and the temperature of the homogenization extrusion zone is 175±5℃.

[0027] As a further scheme of the present application: the time of the feeding zone is 5-8s, the time of the melting zone is 10-15s, the time of the reaction zone is 40-60s, the time of the mixing zone is 20-25s, the time of the devolatilization zone is 25-30s, and the time of the homogenization extrusion zone is 15-20s.

[0028] The beneficial effects of the present application are:

[0029] Low cost: the main equipment (scissors, disc mill, ultrasonic cleaner) and consumables (quartz sand, beaker) are all laboratory routine or cheap and easy-to-get products (quartz sand as a high-efficiency and low-cost grinding medium), which significantly reduces the production cost.

[0030] Simple and efficient operation: compared with the existing methods (such as liquid nitrogen freezing-pulverizing, tabletting-pulverizing, crushing-wall breaking-centrifugation-filtering, etc.), the present method has simplified steps (fragment preparation, grinding, washing separation, flotation purification, drying and screening), and the process is intuitive, easy to implement, operate and repeat in the laboratory.

[0031] Excellent effect and wide applicability: multiple experiments have shown that the method can prepare target micron-sized thin film-shaped microplastics with ideal effect; at the same time, the method also has the potential to prepare other forms (such as granular, fragmented) of microplastics;

[0032] In addition, the present application forms a pre-grafted compatible phase by the premixing reaction (800-1000rpm high-speed mixing) of the vinyl-terminated polydimethylsiloxane (Vi-PDMS) and the maleic anhydride grafted PP (PP-g-MAH), so that the silicone is anchored in the PP molecular chain in the subsequent extrusion; the modified polypropylene plastic obtained can form a permanent lubricating layer on the surface of PP, which can effectively avoid the adhesion and grinding of polypropylene melt. The PP-g-MAH compatibilizer (5phr) inhibits phase separation, and the grafted silicone acts as a "molecular toughening agent", which can avoid the pulverization of fragments in mechanical grinding. DETAILED DESCRIPTION

[0033] In order to enable the personnel in the technical field to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely in combination with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the personnel in the field without creative labor should belong to the scope of protection of the present application.

[0034] Embodiment 1

[0035] The method for preparing micro-sized film-shaped microplastics in a laboratory provided by the embodiment of the present application specifically comprises the following steps:

[0036] S1, fragment preparation: using scissors to cut the modified polypropylene plastic film (20 microns thick) into fragments smaller than 1 cm x 1 cm;

[0037] S2, grinding preparation: taking out the grinding disc of the disc mill, washing it to remove impurities, drying it in an oven, and then taking it out and cooling it;

[0038] S3, mechanical grinding: uniformly mixing the plastic fragments and the preferred grinding medium quartz sand (quartz sand is 40-80 mesh) in a certain proportion (1:30), then putting them into the grinding disc, covering the grinding disc cover, fixing it on the disc mill and setting the grinding time (40 s) to start grinding, and through high-speed rotation, the quartz sand cuts the film fragments, after grinding, the grinding disc is taken out, and the sample is collected and put into a self-sealing bag. (During the grinding process, it is easy to heat, so if a large amount of microplastics needs to be prepared, the grinding disc needs to be cooled after each grinding to avoid high temperature);

[0039] S4, washing and separation: placing 250 microns, 75 microns and 45 microns of screen from top to bottom on the desktop, pouring the sample into the screen, and after fully sieving, washing the sample on the screen with clean water (since the quartz sand particles in the sample are fine, part of the quartz sand can be removed through the screen during washing), transferring the sample on the screen to a beaker with clean water, and placing it in an ultrasonic cleaner (during the cleaning process, a glass rod needs to be used for stirring to prevent the plastic sample from gathering into a group and reducing the cleaning effect), after the cleaning is completed, the beaker is taken out and the sample in it is poured into the corresponding screen, after the cleaning liquid is filtered out, the sample on the screen is washed into the beaker with clean water and then placed in the ultrasonic cleaner again. Repeat the above steps until the cleaning liquid is clear and transparent, and then collect the sample.

[0040] Among them, the sample floating in the beaker is sucked by siphon method. The sucked sample is transferred to another beaker containing deionized water, and the ultrasonic cleaning step is repeated. Repeat the siphon and cleaning operation until the cleaning liquid is clear and transparent. Collect the final purified floating sample.

[0041] S5, drying: drying the collected sample to obtain the film-shaped microplastics with the required particle size range.

[0042] The preparation process of the modified polypropylene plastic comprises the following steps:

[0043] S11, premix the polypropylene base material, vinyl-terminated polydimethylsiloxane and maleic anhydride grafted PP to obtain a premix;

[0044] That is, the vinyl-terminated polydimethylsiloxane and the maleic anhydride grafted PP are put into a high-speed mixer, and mixed for 5 minutes, wherein the rotating speed of the high-speed mixer is 800 rpm;

[0045] S12, the premix is added to a twin-screw extruder, and the processing temperature is 155℃; and the initiator dicumyl peroxide is added from the middle of the twin-screw extruder, mixed with the premix and then extruded to obtain the modified polypropylene plastic;

[0046] The mass ratio of the polypropylene base material, the vinyl-terminated polydimethylsiloxane, the maleic anhydride grafted PP and the dicumyl peroxide is 100:8:5:0.1;

[0047] The twin-screw extruder includes six zones, specifically a feeding zone, a melting zone, a reaction zone, a mixing zone, a devolatilization zone and a homogenization extrusion zone, wherein the temperature of the feeding zone is 155℃ and the time is 5s, the temperature of the melting zone is 175℃ and the time is 10s, the temperature of the reaction zone is 188℃ and the time is 40s, the temperature of the mixing zone is 180℃ and the time is 20s, the temperature of the devolatilization zone is 175℃ and the time is 25s, and the temperature of the homogenization extrusion zone is 170℃ and the time is 15s.

[0048] Example 2

[0049] The method for preparing microfilm microplastics in the laboratory provided by the embodiment of the application specifically comprises the following steps:

[0050] S1, fragment preparation: using scissors to cut the modified polypropylene plastic film (thickness of 20 microns) into fragments smaller than 1cm*1cm;

[0051] S2, grinding preparation: taking out the grinding disc of the disc mill, washing and drying in an oven, and then taking out and cooling;

[0052] S3, mechanical grinding: the plastic fragments and the preferred grinding medium quartz sand (quartz sand is 40-80 mesh) are uniformly mixed in a certain proportion (1:30) and then added to the grinding disc, the grinding disc cover is covered, the disc mill is fixed and the grinding time (40s) is set, and then the grinding is started, the quartz sand cuts the film fragments through high-speed rotation, the grinding disc is taken out after the grinding is completed, and the sample is collected and put into a self-sealing bag. (During the grinding process, it is easy to heat, so if a large amount of microplastics is to be prepared, the grinding disc needs to be cooled after each grinding is completed before the next grinding is continued to avoid high temperature);

[0053] S4, cleaning and separation: place the 250-micron, 75-micron, and 45-micron screens on the table from top to bottom, pour the sample into the screens, and after the sample is fully sieved, rinse the sample on the screens with clean water (since the quartz sand particles in the sample are fine, part of the quartz sand can be removed through the screens during the rinsing process), transfer the sample on the screens to a beaker with clean water, and place it in an ultrasonic cleaner (stir with a glass rod during the cleaning process to prevent the plastic sample from clumping together and reducing the cleaning effect), after the cleaning is complete, remove the beaker and pour the sample in it into the corresponding screens, and after the cleaning liquid is completely filtered out, rinse the sample on the screens into the beaker with clean water again and place it in the ultrasonic cleaner for cleaning. Repeat the above steps until the cleaning liquid is clear and transparent, and then collect the sample.

[0054] In the process, the sample floating in the beaker is sucked up by siphoning. The sucked sample is transferred to another beaker containing deionized water, and the ultrasonic cleaning step is repeated. The floating material is repeatedly siphoned and cleaned until the cleaning liquid is clear and transparent. The finally purified floating sample is collected.

[0055] S5, drying: dry the collected sample to obtain a film-shaped microplastic in the desired particle size range.

[0056] In the preparation process of the modified polypropylene plastic, the following steps are included:

[0057] S11, premixing the polypropylene base material, the vinyl-terminated polydimethylsiloxane, and the maleic anhydride grafted PP to obtain a premix;

[0058] That is, the vinyl-terminated polydimethylsiloxane and the maleic anhydride grafted PP are put into a high-speed mixer, and mixed for 5 minutes, wherein the rotation speed of the high-speed mixer is 900 rpm;

[0059] S12, adding the premix to a twin-screw extruder with a processing temperature of 172℃, and adding the initiator dicumyl peroxide from the middle of the twin-screw extruder to mix with the premix after extrusion to obtain the modified polypropylene plastic;

[0060] The mass ratio of the polypropylene base material, the vinyl-terminated polydimethylsiloxane, the maleic anhydride grafted PP, and the dicumyl peroxide is 100:8:5:0.15;

[0061] In the process, the sample floating in the beaker is sucked up by siphoning. The sucked sample is transferred to another beaker containing deionized water, and the ultrasonic cleaning step is repeated. The floating material is repeatedly siphoned and cleaned until the cleaning liquid is clear and transparent. The finally purified floating sample is collected.

[0062] Example 3

[0063] The method for preparing micro-sized film-shaped microplastics in the laboratory according to the embodiment of the present application specifically comprises the following steps:

[0064] S1, fragment preparation: using scissors to cut the modified polypropylene plastic film (thickness of 20 microns) into fragments smaller than 1 cm x 1 cm;

[0065] S2, grinding preparation: remove the grinding disc of the disc mill and wash it to remove impurities, and then take it out, dry it in an oven, and cool it down;

[0066] S3, mechanical grinding: mix the plastic fragments and the preferred grinding medium quartz sand (quartz sand of 40-80 mesh) in a certain proportion (1:30) and then add them to the grinding disc, cover the grinding disc cover, fix it on the disc mill and set the grinding time (40s) to start grinding, and through high-speed rotation, the quartz sand cuts the film fragments, after grinding, take out the grinding disc, collect the sample, and put it into a self-sealing bag. (During the grinding process, it is easy to heat, so if a large amount of microplastics needs to be prepared, the grinding disc needs to be cooled down after each grinding to avoid high temperature);

[0067] S4, washing and separation: place the 250-micron, 75-micron, and 45-micron sieves from top to bottom on the table, pour the sample into the sieves, and after sieving, wash the sample on the sieves with clean water (since the quartz sand particles in the sample are fine, part of the quartz sand can be removed through the sieves during washing), transfer the sample on the sieves to a beaker with clean water, and place it in an ultrasonic cleaner (stir with a glass rod during cleaning to prevent the plastic sample from clumping together and reducing the cleaning effect), after cleaning, take out the beaker and pour the sample in it into the corresponding sieves, after the cleaning liquid is filtered out, wash the sample on the sieves into the beaker again and clean it in the ultrasonic cleaner. Repeat the above steps until the cleaning liquid is clear and transparent, and then collect the sample.

[0068] Among them, the sample floating in the beaker is sucked by siphon method. The sucked sample is transferred to another beaker containing deionized water, and the ultrasonic cleaning step is repeated. Repeat the siphon and cleaning operation until the cleaning liquid is clear and transparent. Collect the final purified floating sample.

[0069] S5, drying: dry the collected sample to obtain the desired particle size range of film-shaped microplastics.

[0070] The preparation process of the modified polypropylene plastic comprises the following steps:

[0071] S11, premix the polypropylene base material, ethylene-terminated polydimethylsiloxane, and maleic anhydride grafted PP to obtain a premix.

[0072] Namely, the vinyl-terminated polydimethylsiloxane and the maleic anhydride grafted PP are put into a high-speed mixer, and mixed for 5 minutes, wherein the rotating speed of the high-speed mixer is 1000 rpm;

[0073] S12, the premix is added into the twin-screw extruder, the processing temperature is 192℃; and the initiator dicumyl peroxide is added from the middle part of the twin-screw extruder, mixed with the premix and then extruded to obtain the modified polypropylene plastic;

[0074] The mass ratio of the polypropylene base material, the vinyl-terminated polydimethylsiloxane, the maleic anhydride grafted PP and the dicumyl peroxide is 100:8:5:0.2;

[0075] The twin-screw extruder includes six zones, specifically a feeding zone, a melting zone, a reaction zone, a mixing zone, a devolatilization zone and a homogenization extrusion zone, wherein the temperature of the feeding zone is 165℃ and the time is 8s, the temperature of the melting zone is 190℃ and the time is 15s, the temperature of the reaction zone is 192℃ and the time is 60s, the temperature of the mixing zone is 190℃ and the time is 25s, the temperature of the devolatilization zone is 185℃ and the time is 30s, and the temperature of the homogenization extrusion zone is 180℃ and the time is 20s.

[0076] Comparative Example 1

[0077] The difference between Comparative Example 1 and Example 1 is that the polypropylene plastic used in Comparative Example 1 is not modified;

[0078] The film-shaped microplastics of Examples 1-3 and Comparative Example 1 are subjected to performance tests, and the test results are as follows:

[0079] It can be seen from the above table that the film-shaped microplastics of the present application have good friction coefficient and anti-attrition pulverization capacity. The above describes one embodiment of the present application in detail, but the content described is only the preferred embodiment of the present application, and cannot be considered as limiting the implementation scope of the present application. Any equivalent changes and improvements made according to the scope of the present application should still belong to the patent coverage scope of the present application.

Claims

1. A method for preparing micron-sized thin-film microplastics in the laboratory, characterized in that, Includes the following steps: Fragment preparation: Cut the modified polypropylene plastic film into fragments; Mechanical grinding: Plastic fragments are mixed evenly with grinding media quartz sand and then added to a grinding disc. The quartz sand is used to cut the film fragments by high-speed rotation, and the samples are collected. The ground sample was placed in a beaker, mixed with deionized water, and then placed in an ultrasonic cleaner to separate the pulverized grinding media from the microplastics. The sample floating in the beaker was then siphoned off. The sample was then transferred to another beaker containing deionized water, and the ultrasonic cleaning steps were repeated. Repeat the siphoning and washing process until the washing solution is clear and transparent. Collect the finally purified floating sample and dry it to obtain membrane microplastics in the desired particle size range. The preparation process of modified polypropylene plastic includes the following steps: A premix of polypropylene base material, vinyl-terminated polydimethylsiloxane and maleic anhydride-grafted PP is obtained. The premixed material is added to a twin-screw extruder at a processing temperature of 155–192°C; and the initiator dicumyl peroxide is added from the middle of the twin-screw extruder, mixed with the premixed material, and then extruded to obtain modified polypropylene plastic.

2. The method for preparing micron-sized thin-film microplastics in the laboratory according to claim 1, characterized in that, The quartz sand is 40-80 mesh, and the mass ratio of plastic fragments to quartz sand is 1:

30.

3. The method for preparing micron-sized thin-film microplastics in the laboratory according to claim 1, characterized in that, The premixing process includes: putting vinyl-terminated polydimethylsiloxane and maleic anhydride-grafted PP into a high-speed mixer and mixing for 5 minutes.

4. The method for preparing micron-sized thin-film microplastics in the laboratory according to claim 3, characterized in that, The high-speed mixer operates at a speed of 800-1000 rpm.

5. A method for preparing micron-sized thin-film microplastics in the laboratory according to claim 1, characterized in that, The mass ratio of polypropylene base material, vinyl-terminated polydimethylsiloxane, maleic anhydride-grafted PP, and dicumyl peroxide is 100:8:5:0.1-0.

2.

6. A method for preparing micron-sized thin-film microplastics in the laboratory according to claim 5, characterized in that, The twin-screw extruder consists of six zones.

7. A method for preparing micron-sized thin-film microplastics in the laboratory according to claim 6, characterized in that, The system consists of six zones: feeding zone, melting zone, reaction zone, mixing zone, devolatilization zone, and homogenization extrusion zone.

8. A method for preparing micron-sized thin-film microplastics in the laboratory according to claim 7, characterized in that, The temperature of the feeding zone is 160±5℃, the temperature of the melting zone is 180±5℃, the temperature of the reaction zone is 190±2℃, the temperature of the mixing zone is 185±5℃, the temperature of the devolatilization zone is 180±5℃, and the temperature of the homogenization extrusion zone is 175±5℃.

9. A method for preparing micron-sized thin-film microplastics in the laboratory according to claim 8, characterized in that, The feeding zone time is 5-8s, the melting zone time is 10-15s, the reaction zone time is 40-60s, the mixing zone time is 20-25s, the devolatilization zone time is 25-30s, and the homogenization extrusion zone time is 15-20s.

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