Method for analyzing the dynamic changes of biodegradable plastics and microplastics based on the dialysis bag method
Through in-situ degradation experiments and multiple characterization and analysis methods based on dialysis bag method, the degradation mechanism of biodegraded plastics in freshwater environment and the dynamic changes of microplastics are studied, and the problem of difficult to analyze the degradation of biodegraded plastics in freshwater environment and their potential ecological risks to the environment in the prior art is solved, and an in-depth understanding and prediction of its degradation mechanism and the formation mechanism of microplastics is achieved.
Patent Information
- Application Number
- CN202210886663.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-07-26
- Publication Date
- 2025-05-27
- Estimated Expiration
- 2042-07-26
AI Technical Summary
The prior art is difficult to effectively analyze the degradation of biodegradable plastics in freshwater environments and their potential ecological risks to the environment, especially the lack of methods to directly analyze the dynamic changes of microplastics.
The dialysis bag method is used to fix the dialysis bag in a freshwater environment through in-situ degradation experiments, and the degradation rate of biodegraded plastics, the formation and change patterns of microplastics are detected regularly. The degradation mechanism and the formation mechanism of microplastics are analyzed in combination with a variety of characterization and analysis methods (such as SEM-EDS, FTIR, XPS, multiple staining-laser confocal fluorescence microscopy, etc.).
In-depth analysis of the degradation mechanism of biodegradable plastics in freshwater environment and the study of the dynamic changes of microplastics, providing an important basis for evaluating their environmental behavior and ecological risks, and being able to reasonably predict the degradation rates of different biodegradable plastics.
Smart Images
Figure CN115236315B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of environmental analysis, and particularly to a method for analyzing the dynamic changes of biodegradable plastics and microplastics based on the dialysis bag method. Background Art
[0002] Globally, with the increasing severity of plastic and microplastic pollution, consumers and manufacturers are scrambling to find alternative materials, and the attention to using biodegradable plastics (BPs) to replace conventional plastics is increasing day by day. It is estimated that the global production capacity of bioplastics will increase from 2.11 million tons in 2018 to 2.62 million tons in 2023.
[0003] However, it is still uncertain whether BPs can solve the environmental crisis brought by plastics. Research shows that BPs can be biodegradable, but the degradation process requires specific conditions, and in natural ecosystems, there are no specific conditions, resulting in a significant slowdown in the biodegradation rate.
[0004] Although BPs decompose faster than traditional plastics, existing literature shows that BPs degrade slowly in soil and marine environments, and the microplastics generated by their decomposition have a negative impact on the ingested organisms and ecosystem functions. Compared with traditional microplastics, BPs even have a stronger ability to carry pollutants, microorganisms and resistance genes. If it cannot be ensured that the fragments generated by degradation are completely absorbed by microorganisms in a short time, the designed BPs may cause greater damage to the environment than non-biodegradable plastics.
[0005] Therefore, during the decomposition process of BPs, it is necessary to obtain information on the decomposition time and degree of decomposition, and this information is an important basis for understanding the environmental behavior and potential ecological risks of BPs. However, most current studies still stay in the laboratory, and the information on the in-situ degradation and fragmentation of plastics to generate microplastics in freshwater environments is very limited, and there is a lack of corresponding methods for analyzing microplastics, and it is impossible to directly obtain the microplastic degradation changes of BPs in freshwater habitats, as well as obtain the degradation mechanisms of different BPs and the key factors affecting degradation. Therefore, it is necessary to set up a method for analyzing the dynamic changes of biodegradable plastics and microplastics based on the dialysis bag method that can predict the degradation of BPs in the actual environment and better evaluate their behavior and ecological risks in the environment. Summary of the Invention
[0006] Aiming at the above deficiencies existing in the prior art, the purpose of the present invention is to provide a method for analyzing the dynamic changes of biodegradable plastics and microplastics based on the dialysis bag method that can predict the degradation of BPs in the actual environment and better evaluate their behavior and ecological risks in the environment.
[0007] To solve the above technical problems, the present invention adopts the following technical solutions:
[0008] A method for analyzing the dynamic changes of biodegradable plastics based on the dialysis bag method, comprising the following steps:
[0009] Step 1. In-situ degradation experiment: Select biodegradable plastics of different materials as plastic samples, place the plastic samples of different materials in the treated dialysis bags respectively, one plastic sample of one material corresponds to one dialysis bag, and fix the dialysis bags in the freshwater environment in-situ through a device, and the position is 0.5 - 1 m underwater, and sample at intervals for detection;
[0010] Step 2. Determine the sampling time: When sampling and detecting the plastic samples in Step 1 at intervals, take a period of time as the sampling and detection cycle, and the sampling cycle detection includes the early stage and the later stage. Among them, the early stage is detected once every two weeks, and the later stage is detected once a week;
[0011] Step 3. Analysis of the degradation mechanism of biodegradable plastics: Take out the plastic samples collected at different time periods in Step 2 from the dialysis bags, conduct drying treatment, and conduct characterization and analysis of the physical mechanism, chemical mechanism and biological mechanism of the degradation rate, biofilm, thermal properties and surface groups of biodegradable plastics of different materials changing with time; Then take a part of the water sample in the dialysis bag, after filtration and solid-phase extraction treatment, use a gas chromatograph-mass spectrometer to analyze the degradation macromolecules generated by the degradation of the plastic samples in the water sample, and combine the characterization and analysis results to analyze the relationship between the degradation macromolecules in the dialysis bag and the degradation and microbial growth characteristics of the corresponding biodegradable plastics of different materials, and speculate on the degradation mechanism of biodegradable plastics of different materials in the freshwater environment.
[0012] Further, in Step 3, the physical mechanism includes using weight loss, molecular weight change and thermogravimetric analysis methods to obtain the degradation rate characterization of biodegradable plastics of different materials; the chemical mechanism includes using SEM-EDS to observe the physical damage, structural changes and C / O ratio on the surface of biodegradable plastics to obtain the biofilm characterization of biodegradable plastics of different materials, and using FTIR and XPS to obtain the surface group change characterization of biodegradable plastics of different materials; the biological mechanism includes using multiple staining-laser confocal fluorescence microscopy to observe the growth and changes of the biofilm on the surface of biodegradable plastics, and using spectrophotometry to quantitatively characterize the biofilm, and combining 16S rDNA to analyze the main microbial communities of the biofilm.
[0013] Combined with the characterization results, speculate on the degradation mechanism of biodegradable plastics with different materials in the freshwater environment; analyze the relationships between the polymer characteristics of biodegradable plastics, the growth rate of biofilms, temperature, wet-dry state and other factors and the degradation and cracking of biodegradable plastics; use methods such as principal component analysis, correlation analysis and non-parametric multivariate analysis of variance for in-depth mining, screen the main factors, conduct data fitting, establish a mathematical model, clarify the key factors affecting degradation, and reasonably predict the degradation rates of different biodegradable plastics in the freshwater environment.
[0014] Furthermore, the surface groups are characterized by the changes of carbonyl, hydroxyl and carbon-carbon double bonds in different parts of the biodegradable plastics.
[0015] The method for analyzing the dynamic changes of microplastics based on the dialysis bag method includes the following steps:
[0016] Step 1, in-situ degradation experiment: Select biodegradable plastics with different materials as plastic samples, place the plastic samples with different materials in the treated dialysis bags respectively, one plastic sample of one material corresponds to one dialysis bag, and fix the dialysis bags in the freshwater environment in-situ through the device, and the position is 0.5-1 m underwater, and samples are taken at intervals for detection;
[0017] Step 2, determine the sampling time: When sampling and detecting the plastic samples in Step 1 at intervals, take a period of time as the sampling and detection cycle, and the sampling cycle detection includes the early stage and the later stage. Among them, the early stage is detected once every two weeks, and the later stage is detected once a week;
[0018] Step 3, analysis of the change rules of microplastics: During the sampling and detection at different time periods in Step 2, collect the plastic fragments decomposed from the plastic samples of different materials, filter them with a microporous filter membrane to obtain microplastics of different materials, and conduct characterization analysis on the physical and chemical properties of microplastics of different materials changing with time. Combined with the characterization analysis results, analyze the relationships between the microplastics of the corresponding materials and environmental factors and the formation rate, particle size distribution and surface properties of microplastics, and obtain the general rules of the formation and change of microplastics.
[0019] Furthermore, in Step 3, the changes in physical properties include observing the change in the number of microplastics using a fluorescence microscope and a particle counter, and observing the morphology and particle size distribution of microplastics using SEM-EDS; the changes in chemical properties include observing the changes in the surface groups and charges of microplastics using XPS, a microscopic infrared system, and zeta potential, and measuring the soluble organic carbon and insoluble organic carbon produced by plastic degradation using a total organic carbon analyzer to indirectly characterize the mass released by microplastics.
[0020] Based on the characterization results, methods such as principal component analysis, correlation analysis, and nonparametric multivariate analysis of variance are used to obtain the relationships between plastic composition, environmental factors, etc. and the formation rate, particle size distribution, and surface properties of microplastics, further clarify the general laws of microplastic formation and change, estimate the cumulative rate of microplastics in the environment, and reasonably predict the change trend of microplastics in the freshwater environment.
[0021] Furthermore, in step one, a wire cage with a rectangular frame structure is prepared. Multiple dialysis bags are filled with the aqueous solution in the in-situ freshwater environment, and adjacent dialysis bags are arranged at intervals. Then the wire cage is placed in the water body of the in-situ freshwater environment and stabilized for 4 hours. Then the wire cage is taken out, biodegradable plastics of different materials are cut into plastic films, and the plastic films of different materials are respectively placed into the dialysis bags. After sealing, the wire cage is fixed in the in-situ freshwater environment again.
[0022] This design cuts biodegradable plastics of different materials into plastic films of different materials to facilitate sampling during the experiment. Since the dialysis bag has certain pores, it is convenient for the water body to penetrate into the dialysis bag. When the plastic film in the dialysis bag degrades, it is convenient for macromolecules inside and outside the dialysis bag to freely enter and exit, realizing the exchange of matter and energy. However, the microplastics degraded from the plastic film will not be lost and will be retained in the dialysis bag. The dialysis bag is placed in the water body of the in-situ freshwater environment and stabilized for 4 hours to allow the dialysis bag to adapt to the water body.
[0023] Furthermore, in step one, the dialysis bags are dialysis bags with a molecular cut-off of 3.5KD, 10KD, and 500KD, and each plastic film is respectively placed into three dialysis bags with different molecular cut-offs.
[0024] Since different molecular weight macromolecules may be produced during the degradation of biodegradable plastics, dialysis bags with 3.5KD, 10KD, and 500KD can intercept macromolecules with different molecular weights.
[0025] Furthermore, in step one, the dialysis bags are regenerated fiber dialysis bags or polyvinylidene fluoride dialysis bags.
[0026] Furthermore, in step two, during each sampling, the temperature, pH value, dissolved oxygen, and conductivity data of the water body in the in-situ freshwater environment are recorded and measured.
[0027] In Step 2, during each sampling, the temperature, pH value, dissolved oxygen, and conductivity data of the water body in the in-situ freshwater environment are recorded and measured. This is because the temperature, pH value, dissolved oxygen, and conductivity data of the water body will affect the growth of the biofilm on the surface of the biodegradable plastic. By recording, the relationship between the growth rate of the biofilm on the surface of the biodegradable plastic and the degradation and cracking of the biodegradable plastic is analyzed; secondly, the temperature, pH value, dissolved oxygen, and conductivity data of the water body will also affect the physical and chemical degradation of the biodegradable plastic. By recording, the relationship between the formation rate, particle size distribution, and surface properties of the microplastics corresponding to the biodegradable plastic and environmental factors is analyzed.
[0028] Compared with the prior art, the present invention has the following beneficial effects:
[0029] 1. The present invention collects plastic samples at different time intervals, records and measures the environmental conditions and basic water quality indicators during sampling. By combining weight method, mechanical property testing, thermogravimetric analysis, molecular weight change, infrared spectrogram change and other characterizations, the changes of surface morphology, surface biofilm, microbial community, surface C / O ratio, functional groups, etc. of biodegradable plastics of different materials during the degradation process are analyzed; spectrophotometry, multiple staining-laser confocal fluorescence microscopy analysis, 16S rDNA and other characterizations are used to analyze the growth of the biofilm on the surface of biodegradable plastics of different materials and the changes of the microbial community.
[0030] Based on the comprehensive analysis of the characterization results, the action mechanism of the degradation and cracking of biodegradable plastics of different materials is speculated; methods such as principal component analysis and correlation analysis are used to screen the main factors from various factors (molecular composition, surface biofilm, dry-wet state, temperature, etc.), analyze the key influencing factors for the degradation of biodegradable plastics of different materials, and reasonably predict the degradation and cracking rates of biodegradable plastics of different materials.
[0031] 2. Aiming at the problems that the time scale and degree of the degradation of biodegradable plastics in the freshwater ecosystem are not clear, and the potential ecological risks brought by the microplastics generated by cracking, through in-situ experiments in the river environment and combining direct and indirect characterization means, the action mechanism and change rules of the formation of microplastics by the degradation and cracking of different biodegradable plastics are studied. The purpose of the present invention is to reveal the degradation mechanism of different biodegradable plastics in the freshwater habitat and the main factors affecting degradation, clarify the change rules of the physical and chemical properties such as the formation rate, particle size distribution, surface groups, etc. of microplastics and the accumulation rate of microplastics during the degradation process, and provide an important basis for the environmental persistence and ecological risks of biodegradable plastics and their microplastics.
[0032] 3. The fate and ecological risks of biodegradable plastics in freshwater habitats are unknown. This invention focuses on typical biodegradable plastics and studies the mechanism and variation law of their in-situ degradation and fragmentation to form microplastics in freshwater habitats, providing important evidence for the environmental persistence and ecological risks of biodegradable plastics and their microplastics in actual freshwater ecosystems, and offering new ideas for the selection and development of biodegradable plastics.
[0033] 4. By cleverly setting up in-situ experiments and collecting and studying the microplastics generated during the degradation of biodegradable plastics in an actual freshwater environment, it is beneficial to track in-situ the degradation process of biodegradable plastics and the formation and change process of microplastics. BRIEF DESCRIPTION OF THE DRAWINGS
[0034] Figure 1 It is a flowchart of the method for analyzing the dynamic changes of biodegradable plastics based on the dialysis bag method in the present invention.
[0035] Figure 2 It is a flowchart of the method for analyzing the dynamic changes of microplastics based on the dialysis bag method in the present invention.
[0036] Figure 3 It is a schematic structural diagram of the experimental structure of the in-situ degradation experiment in the method for analyzing the dynamic changes of biodegradable plastics and microplastics based on the dialysis bag method in the present invention.
[0037] Figure 4 It is a mass loss diagram of biodegradable plastics polybutylene adipate / terephthalate (PLA / PBAT), polybutylene adipate / terephthalate / starch (PLA / PBAT / ST) and non-biodegradable plastic polyethylene (PE) in the method for analyzing the dynamic changes of biodegradable plastics based on the dialysis bag method in the present invention.
[0038] Figure 5 It is a microbial film change diagram of biodegradable plastics polybutylene adipate / terephthalate (PLA / PBAT), polybutylene adipate / terephthalate / starch (PLA / PBAT / ST) and non-biodegradable plastic polyethylene (PE) in the method for analyzing the dynamic changes of biodegradable plastics based on the dialysis bag method in the present invention.
[0039] Figure 6 It is a change diagram of the total organic carbon (TOC) of the degradation products of biodegradable plastics polybutylene adipate / terephthalate (PLA / PBAT), polybutylene adipate / terephthalate / starch (PLA / PBAT / ST) and non-biodegradable plastic polyethylene (PE) in the method for analyzing the dynamic changes of biodegradable plastics based on the dialysis bag method in the present invention.
[0040] Figure 7Microscopic pictures of microplastics generated from the biodegradable plastics polybutylene adipate terephthalate (PLA / PBAT), polybutylene adipate terephthalate / starch (PLA / PBAT / ST), and the non-biodegradable plastic polyethylene (PE) in the method for analyzing the dynamic changes of microplastics based on the dialysis bag method of the present invention.
[0041] Figure 8 Counting diagrams of microplastics generated from the biodegradable plastics polybutylene adipate terephthalate (PLA / PBAT), polybutylene adipate terephthalate / starch (PLA / PBAT / ST), and the non-biodegradable plastic polyethylene (PE) in the method for analyzing the dynamic changes of microplastics based on the dialysis bag method of the present invention.
[0042] In the figure: wire cage 1, dialysis bag 2, biodegradable plastic 3, lifting ring 4. Specific embodiments
[0043] The present invention will be further described below in conjunction with the drawings and embodiments.
[0044] In this embodiment: Refer to Figure 1 And Figure 2 For the method of analyzing the dynamic changes of biodegradable plastics based on the dialysis bag method, it includes the following steps:
[0045] Step 1. In-situ degradation experiment: Select biodegradable plastics 3 of different materials as plastic samples, which can be polylactic acid, polybutylene adipate terephthalate, polybutylene adipate terephthalate, starch, polyhydroxyalkanoates, etc. Put the biodegradable plastics 3 of different materials into the treated dialysis bags 2 respectively, with one plastic sample of one material corresponding to one dialysis bag, and fix the dialysis bags 2 in the freshwater environment in-situ through the device. Place the plastic samples in the in-situ freshwater environment and at a position 0.5 - 1 m underwater, and take samples at intervals for detection;
[0046] Step 2. Determine the sampling time: When taking samples of the plastic samples in Step 1 at intervals for detection, take a period of time as the sampling and detection cycle. The sampling cycle detection includes the early stage and the later stage. Among them, the early stage is to detect once every two weeks, and the later stage is to detect once every week;
[0047] Step 3. Analysis of the biodegradation mechanism of biodegradable plastics: Take out the plastic samples collected at different time periods in Step 2 from the dialysis bag 2, conduct drying treatment, and perform characterization and analysis of the physical mechanism, chemical mechanism, and biological mechanism of the degradation rate, biofilm, thermal properties, and surface groups of biodegradable plastics 3 of different materials over time; then take a part of the water sample in the dialysis bag 2, conduct filtration and solid-phase extraction treatment, and use a gas chromatography-mass spectrometry instrument to analyze the degradation macromolecules generated by the degradation of the plastic sample in the water sample. Combine the characterization and analysis results to analyze the relationship between the degradation macromolecules in the dialysis bag and the degradation and microbial growth characteristics of the biodegradable plastics 3 of the corresponding materials, and speculate on the degradation mechanism of biodegradable plastics 3 of different materials in a fresh water environment.
[0048] Preferably, in Step 3, the physical mechanism includes using weight loss, molecular weight change, and thermogravimetric analysis methods to obtain the degradation rate characterization of biodegradable plastics 3 of different materials; the chemical mechanism includes using SEM-EDS to observe the physical damage, structural changes, and C / O ratio on the surface of biodegradable plastics 3 to obtain the biofilm characterization of biodegradable plastics 3 of different materials, and using FTIR and XPS to obtain the surface group change characterization of biodegradable plastics 3 of different materials; the biological mechanism includes using multi-staining-laser confocal fluorescence microscopy to observe the growth and changes of the biofilm on the surface of biodegradable plastics 3, and using spectrophotometry to quantitatively characterize the biofilm, and combining 16S rDNA to analyze the main microbial communities of the biofilm.
[0049] Combine the characterization results to speculate on the degradation mechanism of biodegradable plastics 3 of different materials in a fresh water environment; analyze the relationship between the polymer characteristics of biodegradable plastics 3, the growth rate of the biofilm, temperature, dry-wet state and other factors and the degradation and cleavage of biodegradable plastics 3; use methods such as principal component analysis, correlation analysis, and non-parametric multivariate analysis of variance for in-depth mining, screen the main factors, conduct data fitting, establish a mathematical model, clarify the key factors affecting degradation, and reasonably predict the degradation rate of different biodegradable plastics 3 in a fresh water environment.
[0050] Preferably, the surface groups are the change characterizations of carbonyl, hydroxyl, and carbon-carbon double bonds at different parts of the biodegradable plastics 3.
[0051] A method for analyzing the dynamic changes of microplastics based on the dialysis bag method, characterized by including the following steps:
[0052] Step 1. In-situ degradation experiment: Select biodegradable plastics 3 made of different materials as plastic samples, which can be polylactic acid, polybutylene adipate terephthalate, polybutylene adipate terephthalate, starch, polyhydroxyalkanoates, etc. Place the biodegradable plastics 3 made of different materials into the treated dialysis bags 2 respectively. One plastic sample of a material corresponds to one dialysis bag. Fix the dialysis bags 2 in the fresh water environment in-situ through the device. Place the plastic samples in the in-situ fresh water environment and at a position 0.5 - 1 m underwater. Take samples at intervals for detection;
[0053] Step 2. Determine the sampling time: When taking samples of the plastic samples in Step 1 at intervals for detection, take a period of time as the sampling and detection cycle. The sampling cycle detection includes the early stage and the later stage. Among them, the early stage is to detect once every two weeks, and the later stage is to detect once every week;
[0054] Step 3. Analysis of the change law of microplastics: During the process of sampling and detecting at different time periods in Step 2, collect the plastic fragments decomposed from the plastic samples of different materials, filter them with a microporous filter membrane to obtain microplastics of different materials, conduct characterization analysis on the physical and chemical properties of the microplastics of different materials changing with time, and combine the characterization analysis results to analyze the relationship between the microplastics of the corresponding materials, environmental factors and the formation rate, particle size distribution and surface properties of microplastics, so as to obtain the general law of the formation and change of microplastics.
[0055] As Figure 3 shown, preferably, in Step 1, prepare an iron wire cage with a rectangular frame structure, put multiple dialysis bags into the aqueous solution in the in-situ fresh water environment, set adjacent dialysis bags at intervals, and then place the iron wire cage in the water body of the in-situ fresh water environment and stabilize it for 4 hours; then take out the iron wire cage, cut the biodegradable plastics of different materials to obtain plastic films, put the plastic films of different materials into the dialysis bags respectively, seal them, and then fix the iron wire cage in the in-situ fresh water environment.
[0056] The iron wire cage 1 is also provided with a lifting ring 4 for convenient lifting, which is convenient for the operator to operate.
[0057] With such a design, cutting the biodegradable plastics 3 of different materials to obtain plastic films of different materials is for the convenience of sampling during the experiment. Since the dialysis bag 2 has certain pores, it is convenient for the water body to immerse into the dialysis bag 2. When the plastic film in the dialysis bag 2 degrades, it is convenient for the macromolecules inside and outside the dialysis bag to freely enter and exit, realizing the exchange of matter and energy. However, the microplastics degraded from the plastic film will not be lost and will be retained in the dialysis bag 2.
[0058] Preferably, in step one, the dialysis bag 2 is a dialysis bag 2 with molecular cut-off values of 3.5 KD, 10 KD, and 500 KD respectively. Each plastic film is placed into three dialysis bags 2 with different molecular cut-off values respectively.
[0059] Preferably, in step one, the dialysis bag 2 is a regenerated fiber dialysis bag 2 or a polyvinylidene fluoride dialysis bag 2.
[0060] Preferably, in step two, during each sampling, the temperature, pH value, dissolved oxygen, and conductivity data of the water body in the in-situ fresh water environment are recorded and measured.
[0061] Preferably, in step three, the changes in physical properties include observing the change in the number of microplastics using a fluorescence microscope and a particle counter, and observing the morphology and particle size distribution of microplastics using SEM-EDS; the changes in chemical properties include observing the changes in the surface groups and charges of microplastics using XPS, a microscopic infrared system, and zeta potential, and measuring the soluble organic carbon and insoluble organic carbon generated by plastic degradation using a total organic carbon analyzer to indirectly characterize the mass of microplastics released.
[0062] Through the characterization results, methods such as principal component analysis, correlation analysis, and non-parametric multivariate analysis of variance are used to obtain the relationships between plastic composition, environmental factors, etc. and the formation rate, particle size distribution, and surface properties of microplastics, further clarify the general laws of microplastic formation and change, estimate the cumulative rate of microplastics in the environment, and reasonably predict the change trend of microplastics in the fresh water environment.
[0063] This invention considers the influence of plastic composition and environmental conditions on plastic degradation and microplastic formation, and selects four typical biodegradable plastics - polybutylene adipate / terephthalate (PLA / PBAT), polybutylene adipate / terephthalate / starch (PLA / PBAT / ST), and non-biodegradable plastic polyethylene (PE) as plastic samples. It is planned to select a certain section of the Yangtze River in the main city of Chongqing as the research site.
[0064] In order to facilitate the collection of microplastics during the in-situ degradation process of the water body and simulate the real environment as much as possible, the test sample is placed in a dialysis bag with a certain pore size, allowing the exchange of substances and energy, but the microplastics will not be lost. First, prepare a wire cage of about 30 cm × 30 cm. Select a dialysis bag with appropriate material and size (it is planned to use a polyvinylidene fluoride dialysis bag, assuming that the degradation of the polyvinylidene fluoride dialysis bag can be ignored during the experiment, and the change in the shape of the dialysis bag will be monitored during the experiment). After treatment, fill the dialysis bag with the actual river water at the test location and place it in the river for 4 hours to balance. Place the plastic film cut into a certain shape into the dialysis bag, seal it, and then fix it in the device. Place the device at a position 0.5 m underwater and fix it. Sample at regular intervals.
[0065] The differences in the degradation rates and microbial film growth of biodegradable plastics polybutylene adipate / terephthalate (PLA / PBAT), polybutylene adipate / terephthalate / starch (PLA / PBAT / ST), and non - biodegradable plastic polyethylene (PE) were obtained through the method for analyzing the dynamic changes of biodegradable plastics based on the dialysis bag method and the method for analyzing the dynamic changes of microplastics based on the dialysis bag method. As Figure 4 shown, there are obvious differences in the weight loss of the three plastics before and after degradation. From Figure 3 it can be seen that as the degradation time increases, the weight loss of biodegradable plastics increases.
[0066] The biofilm growth of the three plastics PLA / PBAT, PLA / PBAT / ST, and PE was obtained in the method for analyzing the dynamic changes of biodegradable plastics based on the dialysis bag method. As Figure 5 shown, there are a large number of microorganisms and algae in natural environmental water bodies, which attach to biodegradable plastics to form biofilms, and crystal violet staining was used to measure the total amount of biofilms. From Figure 5 it can be known that the biofilms growing on biodegradable plastics increase with the increase of degradation time in water bodies, and the biofilm weight of biodegradable plastics after long - term degradation is significantly higher than that of traditional refractory plastics.
[0067] The mass concentrations of macromolecules and microplastics decomposed from the three plastics PLA / PBAT, PLA / PBAT / ST, and PE were obtained in the method for analyzing the dynamic changes of biodegradable plastics based on the dialysis bag method, and total organic carbon (TOC) was used to characterize them. From Figure 6 it can be known that biodegradable plastics PLA / PBAT, PLA / PBAT / ST, and traditional refractory plastic PE all decomposed to form microplastics in natural water bodies, and the TOC of microplastics produced by biodegradable plastics is higher than that of traditional refractory plastic PE.
[0068] In the method for analyzing the dynamic changes of microplastics based on the dialysis bag method, as Figure 7 shown, an optical microscope was used to observe microplastics. From Figure 8 shown, graphic software was used to count the number of microplastics decomposed from the three plastics. From Figure 8 it can be known that the microplastic concentration in the 16th week is much greater than that in the 4th week, and the number of microplastics produced by biodegradable plastics is significantly higher than that of traditional refractory plastics.
[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Those of ordinary skill in the art should understand that any modifications or equivalent replacements made to the technical solutions of the present invention without departing from the purpose and scope of the present technical solutions shall be covered by the scope of the claims of the present invention.
Claims
1. Method for analyzing dynamic changes of biodegradable plastics based on dialysis bag method, Characterized in that, It includes the following steps: Step 1. In-situ degradation experiment: Select biodegradable plastics of different materials as plastic samples, place plastic samples of different materials in the treated dialysis bags respectively, one plastic sample of one material corresponds to one dialysis bag, and fix the dialysis bags in the fresh water environment in-situ through a device, and the position is 0.5 - 1 m underwater, and sample and detect at intervals; Step 2. Determine the sampling time: When sampling and detecting the plastic samples in Step 1 at intervals, take a period of time as the sampling and detection cycle. The sampling cycle detection includes the early stage and the later stage. Among them, the early stage is to detect once every two weeks, and the later stage is to detect once every week. Each time sampling, record and measure the temperature, pH value, dissolved oxygen and conductivity data of the water body in the in-situ fresh water environment; Step 3. Analysis of the degradation mechanism of biodegradable plastics: Take out the plastic samples collected at different time periods in Step 2 from the dialysis bags, perform drying treatment, and conduct characterization and analysis of the physical mechanism, chemical mechanism and biological mechanism of the degradation rate, biofilm, thermal properties and surface groups of biodegradable plastics of different materials changing with time; Then take a part of the water sample in the dialysis bag, after filtration and solid phase extraction treatment, use a gas chromatograph-mass spectrometer to analyze the degradation macromolecules generated by the degradation of the plastic sample in the water sample, and combine the characterization and analysis results to analyze the relationship between the degradation macromolecules in the dialysis bag and the degradation and microbial growth characteristics of the corresponding material of biodegradable plastics, and speculate on the degradation mechanism of biodegradable plastics of different materials in the fresh water environment.
2. The method for analyzing dynamic changes of biodegradable plastics based on dialysis bag method according to claim 1, Characterized in that, In Step 1, prepare a wire cage with a rectangular frame structure, put multiple dialysis bags into the aqueous solution in the in-situ fresh water environment, set adjacent dialysis bags at intervals, and then place the wire cage in the water body of the in-situ fresh water environment and stabilize for 4 hours; Then take out the wire cage, cut the biodegradable plastics of different materials to obtain plastic films, put the plastic films of different materials into the dialysis bags respectively, seal them, and then fix the wire cage in the in-situ fresh water environment.
3. The method for analyzing dynamic changes of biodegradable plastics based on dialysis bag method according to claim 1, Characterized in that, In Step 1, the dialysis bags are dialysis bags with a molecular cut-off of 3.5 KD, 10 KD and 500 KD, and each plastic film is put into three dialysis bags with different molecular cut-offs respectively.
4. The method for analyzing dynamic changes of biodegradable plastics based on dialysis bag method according to claim 1, Characterized in that, In Step 1, the dialysis bags adopt regenerated fiber dialysis bags or polyvinylidene fluoride dialysis bags.
5. The method for analyzing dynamic changes of biodegradable plastics based on dialysis bag method according to claim 1, Characterized in that, In Step 3, the physical mechanism includes using weight loss, molecular weight change, and thermogravimetric analysis methods to obtain the degradation rate characterization of biodegradable plastics of different materials; the chemical mechanism includes using SEM-EDS to observe the physical damage, structural changes, and C / O ratio on the surface of biodegradable plastics to obtain the biofilm characterization of biodegradable plastics of different materials, and using FTIR and XPS to obtain the surface group change characterization of biodegradable plastics of different materials; the biological mechanism includes using multiple staining-laser confocal fluorescence microscopy to observe the growth and changes of biofilms on the surface of biodegradable plastics, and using spectrophotometry to quantitatively characterize the biofilms, and analyzing the main microbial communities of the biofilms in combination with 16S rDNA analysis.
6. The method for analyzing the dynamic changes of biodegradable plastics based on the dialysis bag method according to claim 5, wherein, the surface groups are the change characterizations of carbonyl, hydroxyl, and carbon-carbon double bonds at different parts of the biodegradable plastics.
7. The method for analyzing the dynamic changes of microplastics based on the dialysis bag method, wherein, it includes the following steps: Step 1, in-situ degradation experiment: Select biodegradable plastics of different materials as plastic samples, place the plastic samples of different materials in the processed dialysis bags respectively, one plastic sample of one material corresponds to one dialysis bag, and fix the dialysis bags in the freshwater environment in-situ through the device, and the position is 0.5 - 1 m underwater, and sample at intervals for detection; Step 2, determine the sampling time: When sampling and detecting the plastic samples in Step 1 at intervals, take a period of time as the sampling and detection cycle, and the sampling cycle detection includes the early stage and the later stage. Among them, the early stage is to detect once every two weeks, and the later stage is to detect once every week. Each time sampling, record and measure the water temperature, pH value, dissolved oxygen, and conductivity data of the in-situ freshwater environment; Step 3, analysis of the change law of microplastics: During the process of sampling and detecting at different time periods in Step 2, collect the plastic fragments decomposed from the plastic samples of different materials, filter them with a microporous filter membrane to obtain microplastics of different materials, conduct characterization analysis on the physical and chemical properties of microplastics of different materials changing with time, and combine the characterization analysis results to analyze the relationship between the microplastics of the corresponding materials, environmental factors, and the formation rate, particle size distribution, and surface properties of microplastics, so as to obtain the general law of the formation and change of microplastics.
8. The method for analyzing the dynamic changes of microplastics based on the dialysis bag method according to claim 7, wherein, in Step 3, the change in physical properties includes observing the change in the number of microplastics using a fluorescence microscope and a particle counter, and observing the morphology and particle size distribution changes of microplastics using SEM-EDS; the change in chemical properties includes observing the change in surface groups and charges of microplastics using XPS, a microscopic infrared system, and zeta potential, and using a total organic carbon analyzer to measure the soluble organic carbon and insoluble organic carbon generated by plastic degradation, and indirectly characterizing the mass released by microplastics.