Evaluation method of polyamide degradation behavior

Abstract

The invention discloses a polyamide degradation behavior evaluation method, and relates to the technical field of polyamide degradation behavior evaluation.The polyamide degradation behavior evaluation method comprises the following steps that S1, surface morphology observation is conducted on a polyamide degradation sample; s2, polyamide viscosity detection; s3, melting enthalpy and melting point detection; s4, polyamide degradation characteristic product detection; s5, analysis of degradation behaviors and characteristic degradation products, in the step S1, observation of the surface morphology of the polyamide degradation sample specifically comprises the following steps: S1-1, washing and drying a solid-phase residual sample before and after degradation; and S1-2, after drying, observing the change of the characterization surface morphology by using an electron scanning microscope. The scheme provided by the invention solves the problems that the release of carbon dioxide is affected by multiple aspects due to the complexity of the natural environment in the existing evaluation method, the influence factors are relatively large, and accurate judgment is very difficult.

Description

Technical Field

[0001] The invention relates to the technical field of polyamide degradation behavior evaluation, in particular to a method for evaluating polyamide degradation behavior. Background Art

[0002] Polyamide fiber (PA) is a type of polymer composed of amide bonds (-NH-CO-). It is also called nylon in my country and is generally called nylon, nylon, capron, etc. abroad. PA is the earliest industrialized synthetic fiber in the world. It has excellent toughness, wear resistance, cold resistance, heat resistance, self-lubrication, non-toxicity, easy molding, easy dyeing, high mechanical strength and other comprehensive properties. Therefore, it is widely used in many fields such as automobiles, textiles, instruments, machinery, communications, electronics, aerospace, national defense, clothing, food packaging, and daily consumer goods. With the growth of PA consumption demand, the corresponding waste materials are also increasing. PA is a plastic polymer with stable performance. It is difficult to degrade and decomposes slowly, which will pollute the environment and harm the ecosystem. For example, nylon waste has an adverse effect on the activity and diversity of soil microorganisms, the reproduction of soil organisms, and the leaching of soil invertebrates. With the widespread use of materials such as nylon, the damage they cause to the environment, especially the aquatic environment, is becoming increasingly significant. Investigations and studies have clearly shown that plastic waste interferes with the endocrine system of marine animals and causes physiological damage such as intestinal blockage and false satiety in aquatic animals.

[0003] Biodegradation is one of the main ways of degradation of polyamide fiber in the natural environment. Studies have shown that there are generally two ways of biodegrading organic matter. One is that microorganisms use the target compound as the carbon source for their growth, and sometimes as the only nitrogen source; the other is degradation through co-metabolism, that is, microorganisms obtain carbon sources and energy from other compounds, and convert the target compound into some organic matter that was originally unusable until it is completely degraded. The final products of these two degradation methods are water and carbon dioxide. At the same time, there are also studies showing the microbial degradation of polyamide in the environment. However, there are few studies on how to evaluate the degradation of polyamide in the environment. At present, the degradation of polyamide is almost centered around degradation methods and technologies, and there are very few aspects about detecting whether degradation has occurred. For example, "A Method for Degrading Polyamide in Soil" (CN 116921424 A) only describes a method of using an efficient and low-carbon heat-stabilizing system to achieve in-situ injection of bacterial agents or degradation liquids to improve the degradation efficiency of polyamide in soil, but does not involve a method for judging the degradation of polyamide. For polymer materials such as polyamide, the evaluation method of degradation performance is mostly based on the release of carbon dioxide. For example, in the "Evaluation Method of Degradation Performance of Polymer Materials" (CN 113671058 B), a preliminary judgment is first made based on molecular weight and weight loss, and finally a judgment is made based on whether the released carbon dioxide exceeds a preset threshold.

[0004] However, due to the complexity of the natural environment, the release of carbon dioxide is affected by many factors, and it is difficult to accurately judge. For this reason, we provide an evaluation method for the degradation behavior of polyamide. Summary of the invention

[0005] The purpose of the present invention is to provide a method for evaluating the degradation behavior of polyamide to solve the problem that the existing evaluation method proposed in the above background technology is difficult to accurately judge due to the complexity of the natural environment, the release of carbon dioxide is affected by many factors, and the influencing factors are large.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for evaluating the degradation behavior of polyamide, comprising the following steps:

[0007] S1: Surface morphology observation of polyamide degradation samples;

[0008] S2: polyamide viscosity test;

[0009] S3: Melting enthalpy and melting point detection;

[0010] S4: Detection of characteristic products of polyamide degradation;

[0011] S5: Analysis of degradation behavior and characteristic degradation products;

[0012] In order to evaluate the degradation of polyamide in the environment, the physical properties and chemical changes before and after the degradation of polyamide are analyzed. When the surface morphology of the detected polyamide residue after degradation is significantly different from that of the sample before degradation, such as obvious pits or fractures on the surface, it can be preliminarily concluded that the polyamide has been damaged in the environment. Then the changes in the physical properties of polyamide such as viscosity, melting point, and melting enthalpy are analyzed. When the viscosity of the polyamide after degradation decreases relative to the sample before degradation, it can be shown that the molecular weight of the polyamide has decreased and the long-chain molecules of the polyamide have broken; when the melting point and melting enthalpy of the polyamide after degradation decrease, it proves that the internal crystalline area of ​​the polyamide is destroyed, and the polyamide has degraded in the environment. At the same time, after the degradation environment and the degradation solid phase residues are detected, the characteristic degradation products are analyzed by non-target and target, which verifies that the polyamide has been degraded in the environment.

[0013] Preferably, in step S1, the surface morphology observation of the polyamide degradation sample specifically comprises the following steps:

[0014] S1-1: Wash and dry the solid phase residual samples before and after degradation;

[0015] S1-2: After drying, the surface morphology was observed using a scanning electron microscope.

[0016] Preferably, in step S1-2, the magnification of the electron scanning microscope is 800-3000.

[0017] Preferably, in step S2, the specific steps of polyamide viscosity detection are as follows:

[0018] S2-1: Weigh the dried sample into a ground-mouth bottle to avoid moisture absorption, add concentrated sulfuric acid to make a 0.01 g / mL solution

[0019] S2-2: Stir the solution in step S2-1 in a shaking device or a magnetic stirring heater until the sample is completely dissolved (the dissolution temperature should not exceed 40° C., for about 4 hours or more), and after complete dissolution, cool to room temperature;

[0020] S2-3: using an Ubbelohde viscometer to test the relative viscosity of the solution treated in step S2-2, and testing the time it takes to flow through the Ubbelohde viscometer at 25° C.;

[0021] S2-4: Relative viscosity η of the sample r Calculate according to formula (1):

[0022]

[0023] Where:

[0024] η r ——Relative viscosity value of the sample;

[0025] t 2 ——The flow time of the solution, in seconds (s);

[0026] t 1 ——The flow time of the solvent, in seconds (s).

[0027] Preferably, in step S3, the specific steps of detecting the melting enthalpy and melting point are:

[0028] S3-1: Wash and dry the solid phase residual samples before and after degradation;

[0029] S3-2: Use a scanning differential calorimeter to detect the melting enthalpy and melting point of the dried sample.

[0030] Preferably, in step S3-2, the setting standard of the scanning differential calorimeter instrument is: 2 atmosphere, heating rate 10℃ / min, 10℃ to 280℃ and keep constant temperature for 3min, then cool to 30℃, and then heat to 280℃.

[0031] Preferably, in step S4, the process of detecting characteristic degradation products of polyamide is sample pretreatment and instrument detection, wherein the specific steps of solid phase pretreatment are as follows:

[0032] S4-1: Weigh a certain amount of solid phase residue sample and put it into a Teflon tube, add an organic reagent, and select reagents of different polarities;

[0033] S4-2: Perform ultrasonic extraction on the sample in step S4-1, repeating 3 times;

[0034] S4-3: Mix the extracts from step S4-2, blow nitrogen to dryness, and redissolve with 0.5 mL of the same reagent;

[0035] S4-4: Filter the solution in step S4-3 using a 0.22 μm organic phase nylon filter membrane, transfer it to a 1.5 mL brown injection vial, and store it at -20°C for subsequent testing.

[0036] Preferably, in step S4, the process of detecting characteristic degradation products of polyamide is sample pretreatment and instrument detection, wherein the specific steps of liquid phase pretreatment are as follows:

[0037] S4-1: Take a certain amount of environmental sample and put it into a Teflon tube, add an organic reagent that is immiscible with water, and select reagents of different polarities;

[0038] S4-2: Perform liquid-liquid extraction on the sample in step S4-1, repeating 3 times;

[0039] S4-3: Mix the extracts from step S4-2, blow nitrogen to dryness, and redissolve with 0.5 mL of acetone;

[0040] S4-4: Filter the solution in step S4-3 using a 0.22 μm organic phase nylon filter membrane, transfer it to a 1.5 mL brown injection vial, and store it at -20°C for subsequent testing.

[0041] Preferably, in step S4, the process of detecting characteristic degradation products of polyamide is sample pretreatment and instrument detection, wherein the instrument detection uses a gas chromatography-mass spectrometer and a high performance liquid chromatography tandem triple quadrupole mass spectrometer to detect the pretreated samples, and the mass spectrometer uses a full scan mode to perform non-target analysis. The detection results of the two instruments are mutually verified and supplemented, and standard samples are used for target analysis.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The present invention proposes a detection method for evaluating the degradation of polyamide, wherein surface morphology, viscosity and characteristic products are used as evaluation criteria, the degradation behavior of polyamide is preliminarily judged by changes in surface morphology, viscosity and the like, and the environmental degradation of polyamide is further judged by analysis of characteristic products. This method combines various detection results for evaluation, so that the degradation behavior of polyamide in the environment is judged more accurately, providing a favorable basis for its degradability. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the overall evaluation method of the present invention;

[0045] Figure 2 This is a scanning electron microscope characterization image of the sample before degradation in Example 1 of the present invention;

[0046] Figure 3 This is a scanning electron microscope characterization image of the sample after degradation in Example 1 of the present invention;

[0047] Figure 4 This is a graph showing the relative viscosity change during the degradation process of the sample in Example 1 of the present invention;

[0048] Figure 5 This is a DSC characterization diagram of the sample degradation process in Example 1 of the present invention; DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0050] See also Figure 1-5 The present invention provides an embodiment: a method for evaluating the degradation behavior of polyamide 6, comprising the following steps:

[0051] S1: Surface morphology of polyamide 6 degradation samples was observed. The samples that had been degraded in the laboratory seawater environment for about 100 days were characterized by scanning electron microscopy. The results showed that the surface of polyamide 6 had obvious damage, such as Figure 3 As shown;

[0052] S2: Polyamide 6 viscosity test. After the sample was tested for viscosity, the relative viscosity of polyamide 6 fiber was 2.10 before degradation; after 100 days of degradation, the relative viscosity decreased to 1.85; after 130 days of degradation, the relative viscosity decreased to 1.76; after 160 days of degradation, the relative viscosity decreased to 1.62; after 190 days of degradation, the relative viscosity decreased to 1.43; with the increase of degradation time, the relative viscosity of polyamide 6 fiber gradually decreased. Figure 4 As shown;

[0053] S3: Melting enthalpy and melting point detection, after differential scanning calorimeter DSC detection, after 100 days of degradation, the melting enthalpy dropped from 83.39 J / g to 76.49 J / g, and the melting point dropped from 210.69°C to 205.14°C; after 130 days of degradation, the melting enthalpy dropped to 69.45 J / g, and the melting point dropped to 204.19°C; after 160 days of degradation, the melting enthalpy dropped to 62.44 J / g, and the melting point dropped to 204.15°C; after 190 days of degradation, the melting enthalpy dropped to 42.29°C, and the melting point dropped to 202.28°C; with the increase of degradation time, the melting enthalpy and melting point gradually decrease. Figure 5 As shown;

[0054] S4: Detection of characteristic degradation products of polyamide 6. According to mass spectrometry, the characteristic products of polyamide 6 are polyamide 6 monomer caprolactam, cyclic dimer 1,8-diazacyclotetradecane-2,9-dione and (N-butylamino)acetonitrile. At the same time, target analysis was performed using caprolactam standard samples.

[0055] S5: Analysis of degradation behavior and characteristic degradation products. In order to evaluate the degradation of polyamide 6 in the environment, physical properties and chemical changes are analyzed.

[0056] According to the diagram, the surface morphology of the degraded polyamide 6 residues has been significantly different from that of the samples before degradation, and it can be preliminarily concluded that polyamide 6 has been damaged in the environment; at the same time, the viscosity, melting enthalpy and melting point of the degraded polyamide 6 samples are lower than those of the samples before degradation, indicating that the long-chain molecules of polyamide 6 have broken, and the internal crystalline region of polyamide 6 has been destroyed, and degradation has occurred in the environment. After testing the degradation environment and the degradation solid phase residues, the characteristic products found were caprolactam, cyclic 1,8-diazacyclotetradecane-2,9-dione and (N-butylamino) acetonitrile; at the same time, verification was carried out using a standard sample of caprolactam. Through the above analysis, it was verified that polyamide 6 has been degraded in the environment.

[0057] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A method for evaluating the degradation behavior of polyamide, characterized in that: The following steps are involved: S1: Surface morphology observation of polyamide degradation samples; S2: polyamide viscosity test; S3: Melting enthalpy and melting point detection; S4: Detection of characteristic products of polyamide degradation; S5: Analysis of degradation behavior and characteristic degradation products.

2. The method for evaluating the degradation behavior of polyamide according to claim 1, characterized in that: In step S1, the surface morphology of the polyamide degradation sample is observed, which specifically includes the following steps: S1-1: Wash and dry the solid phase residual samples before and after degradation; S1-2: Scanning electron microscopy was used to characterize the changes in surface morphology after drying.

3. The method for evaluating the degradation behavior of polyamide according to claim 2, characterized in that: In the step S1-2, the magnification of the electron scanning microscope is 800-3000.

4. The method for evaluating the degradation behavior of polyamide according to claim 3, characterized in that: In step S2, the specific steps of polyamide viscosity detection are as follows: S2-1: Weigh the dried sample into a ground-mouth bottle to avoid moisture absorption, add concentrated sulfuric acid to make a 0.01 g / mL solution; S2-2: Stir the solution in step S2-1 in a shaking device or a magnetic stirring heater until the sample is completely dissolved (the dissolution temperature should not exceed 40°C, for about 4 hours or more). After complete dissolution, cool to room temperature; S2-3: using an Ubbelohde viscometer to test the relative viscosity of the solution treated in step S2-2, and measuring the time it takes to flow through the Ubbelohde viscometer at 25° C.; S2-4: Relative viscosity η of the sample r Calculate according to formula (1).

5. The method for evaluating the degradation behavior of polyamide according to claim 4, characterized in that: In the step S3, the specific steps of melting enthalpy and melting point detection are as follows; S3-1: Wash and dry the solid phase residual samples before and after degradation; S3-2: Use a scanning differential calorimeter to detect the melting enthalpy and melting point of the dried sample.

6. The method for evaluating the degradation behavior of polyamide according to claim 5, characterized in that: In step S3-2, the setting standard of the scanning differential calorimeter instrument is N2 atmosphere, heating rate 10°C / min, heating from 10°C to 280°C and keeping the temperature constant for 3 min, then cooling to 30°C, and then heating to 280°C.

7. The method for evaluating the degradation behavior of polyamide according to claim 6, characterized in that: In step S4, the process of detecting characteristic degradation products of polyamide is sample pretreatment and instrument detection, wherein the specific steps of solid phase pretreatment are as follows: S4-1: Weigh a certain amount of solid residue sample into a Teflon tube, add an organic reagent, and select the reagent according to its polarity; S4-2: The sample of step S4-1 was subjected to ultrasonic extraction and repeated 3 times; S4-3: The extracts of step S4-2 were mixed and blown to dryness with nitrogen and refilled with 0.5 mL of the same reagent; S4-4: Filter the solution in step S4-3 using a 0.22 μm organic phase nylon filter membrane, transfer to a 1.5 mL brown injection vial, and store at -20°C for subsequent testing.

8. The method for evaluating the degradation behavior of polyamide according to claim 7, characterized in that: In step S4, the process of detecting characteristic degradation products of polyamide is sample pretreatment and instrument detection, wherein the specific steps of liquid phase pretreatment are as follows: S4-1: Take a certain amount of environmental sample and put it into a Teflon tube, add an organic reagent that is immiscible with water, and select the reagent according to its polarity; S4-2: The sample in step S4-1 was subjected to liquid-liquid extraction and repeated 3 times; S4-3: The extracts of step S4-2 were mixed and blown to dryness with nitrogen and re-filled with 0.5 mL of acetone; S4-4: Filter the solution in step S4-3 using a 0.22 μm organic phase nylon filter membrane, transfer to a 1.5 mL brown injection vial, and store at -20°C for subsequent testing.

9. The method for evaluating the degradation behavior of polyamide according to claim 8, characterized in that: In step S4, the process of detecting characteristic degradation products of polyamide is sample pretreatment and instrument detection, wherein the instrument detection uses a gas chromatography-mass spectrometer and a high performance liquid chromatography tandem triple quadrupole mass spectrometer to detect the pretreated samples, and the mass spectrometer uses a full scan mode to perform non-target analysis. The detection results of the two instruments are mutually verified and supplemented, and standard samples are used for target analysis.

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