An in-situ monitoring and distinguishing method for polymer aging free radical path based on chemiluminescence kinetics fitting

Abstract

The application discloses an in-situ monitoring and distinguishing method for polymer aging free radical path based on chemiluminescence kinetics fitting, and belongs to the field of polymer aging free radical reaction and path distinguishing. Chemiluminescence test is adopted, and a chemiluminescence kinetics curve is recorded to in-situ monitor a polymer aging process. For a data fitting module, a fitting equation of intensity I and time t is established based on RO termination reaction, a fitting equation is established based on ROO termination reaction, a measured kinetics curve is fitted, and the fitting degree is judged according to a correlation coefficient to distinguish two kinds of alkyl oxygen-containing free radicals. The method is rapid and effective, and provides a basis for understanding related reaction mechanisms such as polymer free radical reaction and aging path.

Description

Technical Field

[0001] This invention belongs to the field of free radical reactions and pathway differentiation in polymer aging, specifically involving a kinetic fitting strategy based on chemiluminescence for in-situ differentiation of alkoxy radical RO· and peroxyalkyl radical ROO· pathways during polymer aging, providing support for the study of free radical pathway monitoring and differentiation during polymer aging. Background Technology

[0002] Polymer aging occurs via a free radical chain reaction. Under oxygen-containing conditions, alkyl-related reactive oxygen species (RO·) are generated, primarily including alkoxy radicals (RO·) and peroxyalkyl radicals (ROO·). Different reaction pathways produce different products, ultimately affecting the polymer's structure and properties. The ROO·-dominated free radical pathway generates carbonyl compounds, leading to exponential growth in aging and severe degradation of the polymer structure. In contrast, the RO·-dominated free radical pathway exhibits lower reactivity, terminating aging by generating inert aldehydes or alcohols. Therefore, distinguishing between the RO· and ROO· free radical pathways in polymer aging is crucial for environmental sustainability and polymer recycling.

[0003] RO· and ROO· free radicals are characterized by short lifespans and extremely high reactivity; the self-reaction rate of RO· is 10. 2 -10 5 mol -1 L s -1 The self-reaction rate of ROO· reaches 10 3 -10 8 mol -1 L s -1 Electron paramagnetic resonance (EPR) is a common method for distinguishing free radicals; however, in practice, a suitable trapping agent is needed to convert transient free radicals into long-lived spin adducts. Furthermore, the addition of a trapping agent may affect the intrinsic free radical reactions of the polymer, making it impossible to accurately describe the aging pathway. While laser-induced fluorescence (LAFI) can detect free radicals by ionizing aging polymers with short-pulse lasers without the need for probes or trapping agents, the broadband fluorescence of scattered light and other trace components in the polymer matrix can severely interfere with the analysis of target free radicals.

[0004] Chemiluminescence (CL) is a sensitive method for recording the radiative transitions of luminescent organisms generated during chemical reactions, interpreting the types of luminescent organisms, and performing quantification. Accordingly, CL can be used as an in-situ strategy to record the kinetics of free radical termination during polymer aging. However, RO· and ROO· generated during polymer aging both have emission wavelengths in the 520-580 nm range, making it difficult to distinguish between them using overlapping CL spectra, thus hindering the accurate monitoring and differentiation of RO· and ROO· during polymer aging.

[0005] This invention proposes a method based on kinetic fitting to distinguish between alkyl oxygen-containing radicals RO· and ROO· during polymer thermal aging using an in-situ CL (Closing and Laying) method. For the CL testing module, the polymer aging process is monitored in situ by recording CL kinetic curves. For the data fitting module, a fitting formula for CL intensity I versus time t is established based on the RO· termination reaction. Based on the ROO-terminated reaction, a fitting formula for I and t is established: The kinetic curves of CL were fitted. The goodness of fit was determined based on the correlation coefficient, enabling the identification and differentiation of two types of alkyl oxygen-containing free radicals. The effects of oxygen content, temperature, and ROOH hydroperoxide content on the free radical pathway were evaluated using the obtained kinetic constants, and the transformation of the free radical pathway in polymer aging was achieved. This method is rapid and effective, providing a solid foundation for understanding the free radical-dominated aging mechanism of polymers. Summary of the Invention

[0006] Polymer aging occurs via a free radical chain reaction. Under oxygen-containing conditions, alkoxy radicals RO· and peroxyalkyl radicals ROO· are generated, producing different products through different reaction pathways, ultimately affecting the polymer's structure and properties. Distinguishing between the RO· and ROO· pathways in polymer aging is fundamental to understanding the polymer aging mechanism.

[0007] The technical solution of this invention is as follows: The aging process of the polymer membrane is monitored using a CL (Closing Chromium Fluorescence) testing module. The prepared polymer membrane is cut and fixed in the reaction chamber of a chemiluminescence instrument, and the CL kinetic curve is recorded. A data fitting module is used to distinguish the polymer aging reaction pathways in situ. Based on the RO· and ROO· termination reactions, fitting formulas for CL intensity I versus time t are established separately to fit the CL kinetic curves. The goodness of fit is determined based on the correlation coefficient to distinguish the RO· and ROO· aging pathways. The influence of aging conditions on the free radical pathway is evaluated by combining kinetic constants. By changing conditions such as oxygen content, temperature, and ROOH (hydroperoxide) content, the transformation of the polymer aging free radical pathway is achieved. This method is rapid and effective, providing a solid foundation for understanding the polymer free radical-dominated aging mechanism.

[0008] A method for distinguishing polymer aging free radical pathways based on in-situ chemiluminescence kinetic fitting, characterized by the following steps:

[0009] (1) A polymer film with a thickness of 0.25-2 mm is prepared by extrusion, mixing, pressing and other methods, and then cut into rectangles with a length of 2-5 cm and a width of 0.5-1 cm.

[0010] (2) Fix the cut polymer film onto the ceramic heating rod, place it in the reaction chamber, and then place it in the dark chamber of the chemiluminescence instrument for aging experiment. During the aging process, data intensity I is collected, and the integration time of the data collection interval is 0.1-1s. The CL kinetic curve with a total reaction time of 0-60min is recorded with the peak as the standard. Nitrogen, air, or other nitrogen / oxygen mixtures are used as carrier gases to simulate different environments in the reaction chamber. The gas is continuously pumped into the reaction chamber at a flow rate of 50-300mL / min. The temperature of the ceramic heating rod temperature controller is set to 60-300℃ and the working voltage is -100--1000V.

[0011] (3) Based on the RO·termination reaction, the fitting formula between CL intensity I and the corresponding time t is established as follows:

[0012]

[0013] Where A is the proportionality constant, Y is the ratio of the difference between the concentration of hydrogen peroxide [ROOH] in the equilibrium state and the initial state to the concentration of [ROOH] in the initial state, and k RO Expressed as the rate constant of the RO termination path;

[0014] (4) Based on the ROO·termination reaction, the fitting formula between CL intensity I and the corresponding time t is established as follows:

[0015]

[0016] Where B is another proportionality coefficient, and k ROO Represented as the rate constant of the ROO termination path;

[0017] (5) Based on the measured intensity I and time t, fit the data according to formulas (1) and (2) respectively. In the fitting process, set the initial values ​​of the parameters in the fitting formula as follows: A = 10000-1000000, B = 10000-1000000, Y = 1-100, k = 10000-1000000. RO For values ​​between 0.00001 and 0.001, k ROO For values ​​ranging from 0.000001 to 0.0001, the recorded CL dynamic curves are fitted using the Levenberg-Marquardt algorithm to obtain the specific k values. RO and correlation coefficient R1 2 Specific k ROO and correlation coefficient R2 2 ;

[0018] (6) The distinction is based on the correlation coefficient R1 between the fitting formula and the CL dynamic curve. 2 and R2 2 R1 2 and R22 The one closer to 1 has a better fit, and the polymer aging path is determined to be the free radical path with a higher correlation coefficient that is closer to 1.

[0019] Further, by changing the oxygen content of the carrier gas in step (2), oxygen is mixed with nitrogen at a volume percentage of 5%-100%, and the oxygen content is adjusted to 0.5MPa-10.0MPa, preferably 1.0MPa, 2.1MPa, and 4.0MPa. The CL kinetic curve of the polymer aging is monitored, and the CL kinetic curves under different oxygen contents are fitted with fitting formulas based on the RO·termination reaction and the ROO·termination reaction, respectively, and the correlation coefficients R1 for different oxygen contents are obtained. 2 and R2 2 Based on the goodness of fit, the dominant free radical pathways of polymer aging under different oxygen content atmospheres were distinguished, and the regulatory effect of oxygen content on the dominant free radicals of polymer aging pathways was evaluated.

[0020] Further, by adjusting the temperature controller in step (2) to different temperatures (but generally between 60-300℃), preferably 110℃, the aging CL kinetic curves of the polymer at different temperatures are monitored, and fitting formulas based on RO·termination reaction and ROO·termination reaction are obtained at different temperatures. The correlation coefficients R1 at different temperatures are obtained by fitting the CL kinetic curves at different temperatures. 2 and R2 2 Based on the goodness of fit, the dominant free radical pathways of polymer aging at different temperatures are distinguished, the influence of different temperatures on the polymer aging pathway is evaluated, and the aging rate of the polymer is further evaluated by combining the rate constant obtained from the fitted curve.

[0021] Further step (1) involves controlling the ROOH content of the obtained film by plasma treatment under air or oxygen conditions for 0-10 min, preferably 2 min. The ROOH content after plasma treatment is quantitatively compared relative to the integral area of ​​the non-isothermal CL kinetic curve under nitrogen conditions. Then, the CL kinetic curve for polymer aging monitoring is further monitored. Based on the RO·termination reaction and ROO·termination reaction formulas, the CL kinetic curves after plasma treatment for different times are fitted. According to the goodness of fit, the dominant free radical pathway of polymer aging with different ROOH contents is distinguished, the influence of ROOH content on polymer aging pathway is evaluated, and the aging rate of polymer is further evaluated by combining the rate constant obtained from the fitted curve.

[0022] Furthermore, step (2) includes one or more aging methods under different conditions, such as thermal aging (by adjusting the temperature), thermo-oxidative aging (by adjusting the temperature and gas atmosphere), light aging (by using different light sources), photo-oxidative aging (by adjusting the gas atmosphere and light conditions), post-radiation aging (by increasing radiation), and stress aging (by increasing different stresses during winding).

[0023] Furthermore, the polymer can be selected from polyolefins such as polyethylene (PE) and polypropylene (PP), polyesters, and their blends.

[0024] Furthermore, the accuracy of the in-situ CL dynamic curve fitting strategy was verified through electron spin resonance testing.

[0025] Furthermore, based on the curve of the collected data intensity I versus time t, the number of peaks corresponds to the number of fitting equations (1) and (2), and the correlation coefficient R1 of the corresponding peaks is calculated. 2 and R2 2 Based on the goodness of fit, the corresponding aging paths can be determined.

[0026] Advantages of this invention: This method is fast and effective, providing a foundation for understanding polymer free radical reactions and aging pathways, and also providing a method for exploring aging conditions. Attached Figure Description

[0027] Figure 1 The table shows the kinetic curves and fitted curves of ultra-high density polyethylene (UHDPE) film under air thermal aging. (A) is the kinetic curve of air thermal aging, (B) is the curve fitted based on RO· termination, and (C) is the curve fitted based on ROO· termination.

[0028] The curve that terminates the fitting.

[0029] Figure 2 Figure 1 shows the CL kinetic curves and fitting curves of UHDPE membrane under different oxygen conditions for thermal aging. (A) is the CL kinetic curve under low oxygen and high oxygen conditions, (B) is the curve fitted according to RO· under low oxygen conditions, (C) is the curve fitted according to ROO· under low oxygen conditions, (D) is the curve fitted according to RO· under high oxygen conditions, and (E) is the curve fitted according to ROO· under high oxygen conditions.

[0030] Figure 3 The CL kinetic curves and fitting curves of UHDPE film under thermal aging at different temperatures are shown, where (A) represents 100-130℃.

[0031] The kinetic curves of CL under aging, (B)-(E) are the curves fitted according to RO· termination at 100-130℃, (F)-

[0032] (I) is the curve fitted according to ROO at 100-130℃.

[0033] Figure 4 Figure 1 shows the CL kinetic curves and fitted curves for thermal aging of UHDPE membranes with different ROOH contents. (A) shows the CL kinetic curves after plasma treatment for different times; (B) shows the quantitative ROOH content of the UHDPE membrane after plasma treatment for different times; (C)-(F) show the fitted curves based on ROOH content after plasma treatment for 1-4 min; Figure (G)-

[0034] (J) is the curve fitted according to ROO after plasma treatment for 1-4 min.

[0035] Figure 5 The electron spin spectrum (EPR) of UHDPE films with different ROOH contents after thermal aging is shown in Figure (A), which is the EPR spectrum after thermal aging without plasma treatment, and Figure (B), which is the EPR spectrum after thermal aging with plasma treatment.

[0036] Figure 6 The figures show the chemiluminescence kinetic curves and fitted curves of PP film before and after plasma treatment. (A) is the CL kinetic curve after thermal aging before and after plasma treatment; (B) is the curve fitted to the first CL peak without plasma treatment based on RO· termination; and (C) is the curve fitted to the first CL peak without plasma treatment based on RO· termination.

[0037] (D) is the curve fitted to the second CL peak after plasma treatment according to RO·, and (E) is the curve fitted to the second CL peak after plasma treatment according to ROO·. Detailed Implementation

[0038] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0039] Example 1:

[0040] (1) Preparation of UHDPE membrane

[0041] After pouring 5g of UHDPE granules into a mold, the mold containing the UHDPE granules is placed in an electric tablet press. The temperature is set to 150℃ based on the polymer's melting point. Pre-press for 1 minute, degas 5 times, pressurize for 1 minute, and cool for 1 minute. Finally, a UHDPE film with a thickness of 0.25mm is formed. For subsequent testing, the pressed UHDPE film is cut into rectangles with a length of 4cm and a width of 0.5cm.

[0042] (2) CL test

[0043] The cut UHDPE membrane was fixed onto a ceramic heating rod and placed in the reaction chamber, which was then placed in the darkroom of the chemiluminescence instrument. Air (21% oxygen content) was used as the carrier gas and continuously pumped into the reaction chamber at a flow rate of 100 mL / min. The temperature was controlled at 110℃ by a temperature regulator, the operating voltage was set to -1000V, the data integration time was 1 s, and the CL kinetic curve was recorded for a total reaction time of 60 min.

[0044] (3) Data Fitting

[0045] Data processing was performed using Origin software.

[0046] Based on the RO termination reaction, the fitting formula for CL intensity I versus time t is established as follows:

[0047]

[0048] Where A is the proportionality constant, Y is the ratio of the concentration difference of hydroperoxide ([ROOH]) between the equilibrium state and the initial state to the initial concentration, and k RO It is expressed as RO·terminal path total rate constant.

[0049] Based on the ROO termination reaction, the fitting formula for CL intensity I versus time t is established as follows:

[0050]

[0051] Where B is another proportionality coefficient, and k ROO It is expressed as ROO·Terminal Path Total Rate Constant.

[0052] The initial values ​​for the parameters in the formula are set as follows: A = 10000-1000000, B = 10000-1000000, Y = 1-100, and k = 1. RO For values ​​between 0.00001 and 0.001, k ROO The range is 0.000001-0.0001. The recorded CL dynamic curves are fitted using the Levenberg-Marquardt algorithm.

[0053] The distinction is based on the correlation coefficient R1 between the fitted formula and the CL dynamic curve. 2 and R2 2 R1 2 and R2 2 The one closer to 1 has a better fit, and the polymer aging path is determined to conform to R. 2 Higher free radical pathways.

[0054] like Figure 1As shown in Figure A, the CL kinetics of UHDPE membrane aging in air exhibits a "single S"-shaped curve, with the CL intensity continuously increasing to 3800 cts within 3200 s. The I and t values ​​in the CL kinetic curve are fitted according to formulas (1) and (2), and based on R... 2 The fitting results were evaluated to determine the pathways of aged RO· and ROO· free radicals. Figure 1 As shown in B, according to the formula (1) for RO termination, R1 2 The rate constant (k) of the RO termination path is 0.9930. RO The value is 0.0022s. -1 ;like Figure 1 As shown in C, according to the formula (2) for ROO termination, R2 is obtained. 2 The rate constant (k) of the ROO termination path is 0.7225. ROO The value is 0.0012s. -1 The results show that the RO· termination pathway provides a better fit, therefore, it is determined that the RO· termination reaction dominates the free radical pathway of UHDPE thermal aging in air.

[0055] (4) Kinetic testing and fitting of CL under different oxygen contents

[0056] By mixing oxygen in nitrogen at volume percentages of 10% and 40%, and adjusting the O2 content to 1.0 MPa and 4.0 MPa, the CL kinetic curves of UHDPE membranes at 110 °C with different O2 contents were recorded to evaluate the effect of O2 on the free radical pathway of UHDPE aging. Figure 2 Figure A shows the CL kinetic curves of UHPDPE at O2 contents of 1.0 MPa and 4.0 MPa.

[0057] like Figure 2 As shown in Figure B, under a low O2 content of 1.0 MPa, the kinetic curve of CL fits well according to the formula (1) for RO·termination reaction, and R1 2 The value is 0.9521, k RO The value is 0.0006s -1 In contrast, the formula (2) for the ROO-terminated reaction showed poor fitting, with R2... 2 It is 0.8804, k ROO The value is 0.0003s -1 ( Figure 2 (C) This demonstrates that under low O2 content, the thermal aging of UHDPE proceeds along the RO· pathway. Conversely, under high O2 content (4.0 MPa), R1 is obtained by fitting the formula (1) for the RO· termination reaction. 2 The value is 0.6451, k RO The value is 0.0003s-1 ( Figure 2 (D); and by fitting the formula (2) for the ROO-terminated reaction, we obtain R2. 2 It is 0.9794, k ROO The value is 0.0010s -1 ( Figure 2 The study (E) demonstrated that the dominant free radical terminates the RO· reaction under low O2 content by transforming it into the ROO· termination reaction under high O2 content.

[0058] (5) CL dynamics test and fitting at different temperatures

[0059] The test temperature was adjusted to 100-130℃, and the CL kinetic curve of the UHDPE film under thermal aging was monitored. For example... Figure 3 As shown in Figure A, with increasing temperature, the intensity of the CL kinetic curve of UHDPE membrane aging increases significantly, and the peak time gradually advances. The CL kinetics of UHDPE aging at 100, 110, 120, and 130℃ were fitted using formula (1) for the RO·termination reaction and formula (2) for the ROO·termination reaction. The CL kinetics of UHDPE aging at 100, 110, 120, and 130℃ were fitted using formula (1) for the RO·termination reaction, as shown in Figure A. Figure 3 As shown in Figure B, R1 in the fitted curve at 100℃ 2 It is 0.9726; for example Figure 3 As shown in Figure C, R1 in the fitted curve at 110℃ 2 It is 0.9722; for example Figure 3 As shown in Figure D, R1 in the fitted curve at 120℃ 2 It is 0.9953; for example Figure 3 As shown in Figure E, R1 in the fitted curve at 130℃ 2 The value is 0.9775. Based on the ROO·termination reaction formula (2), the CL kinetics of UHDPE aging at 100, 110, 120, and 130 °C were fitted, as follows: Figure 3 As shown in Figure F, the R² value in the fitted curve at 100℃ 2 It is 0.8963; for example Figure 3 As shown in Figure G, the R² value in the fitted curve at 110℃ 2 It is 0.7983; for example Figure 3 As shown in Figure H, the R² value in the fitted curve at 120℃ 2 It is 0.9126; for example Figure 3 As shown in Figure I, the R² value of the fitted curve at 130℃ is... 2The value is 0.9183. The results show that at different temperatures, the fitting result according to formula (1) for the RO·termination reaction is better, while the fitting result according to formula (2) for the ROO·termination reaction is worse, indicating that the free radical pathway of UHDPE aging is mainly dominated by the RO·termination reaction. Accordingly, k is obtained by fitting the formula (1) for the RO·termination reaction. RO The value increases with increasing temperature; the k values ​​at 100℃, 110℃, 120℃, and 130℃ are 0.0028s. -1 0.0065s -1 0.0104s -1 0.0184s -1 This indicates that the polymer aging rate increases continuously with increasing temperature.

[0060] (6) Kinetic testing and fitting of Cl under different ROOH contents

[0061] The UHDPE membrane was subjected to plasma treatment under air conditions. The membrane was vertically placed under plasma for 1-4 minutes, followed by 2 minutes in air to enhance ionization. Non-isothermal CL (Cl-Acoustic Coagulation) tests were performed on the plasma-treated UHDPE membrane at 110°C in an N2 atmosphere. The ROOH (hydroperoxide) content was represented by the integral area of ​​the non-isothermal CL kinetic curve under N2 atmosphere. Figure 4 As shown in Figure B, the integral area of ​​UHDPE gradually increases after 0-2 min of treatment. With further extension of the treatment time to 3-4 min, the integral area decreases, indicating a correlation between ROOH content and plasma treatment time.

[0062] The CL kinetic curves of UHDPE under air plasma treatment for different times were recorded at 110°C. Figure 4 As shown in Figure A, all curves exhibit a single "S" shape. As the treatment time increases from 0 min to 2 min, the CL intensity of UHDPE gradually increases, and the slope of the CL kinetic curve also gradually rises. However, plasma treatment for 3 to 4 min does not further enhance the CL intensity of UHDPE. To determine the dominant free radical pathway for UHDPE aging after plasma treatment, the CL kinetics of aging after 1-4 min of plasma treatment were fitted using formula (1) for the RO termination reaction, as shown... Figure 4 As shown in Figure C, the R1 curve after 1 minute of plasma treatment is... 2 It is 0.9880, k RO The value is 0.0018s -1 ;like Figure 4 As shown in Figure D, the R1 value in the fitted curve after 2 minutes of processing is... 2 It is 0.8491, k ROThe value is 0.0086s -1 ;like Figure 4 As shown in Figure E, R1 in the fitted curve after 3 minutes of processing 2 It is 0.9893, k RO It is 0.0038s -1 ;like Figure 4 As shown in Figure F, R1 in the fitted curve after 4 minutes of processing 2 The value is 0.9941, k RO The value is 0.0034s -1 The kinetics of CL aged after plasma treatment for 1-4 min were fitted according to the formula (2) for the ROO termination reaction, as follows: Figure 4 As shown in Figure G, the R² value in the fitted curve after 1 minute of plasma treatment is... 2 It is 0.9636, k ROO The value is 0.0010s -1 ;like Figure 4 As shown in Figure H, the R² value of the fitted curve after 2 minutes of processing is... 2 It is 0.6943, k ROO The value is 0.0011s -1 ;like Figure 4 As shown in Figure I, the R² value of the fitted curve after 3 minutes of processing is... 2 It is 0.8320, k ROO The value is 0.0011s -1 ;like Figure 4 As shown in Figure J, the R² value of the fitted curve after 4 minutes of processing is... 2 It is 0.8740, k ROO The value is 0.0011s -1 In contrast, the R1 of the fitted curve based on the formula (1) for the RO-termination reaction is... 2 The R² is better than that fitted by formula (2) based on the ROO·termination reaction. 2 The change in ROOH content indicates that the free radical pathway of UHDPE aging is still dominated by the RO· termination reaction.

[0063] (7) Free radical pathway verification

[0064] To verify the accuracy of the proposed fitting strategy, electron paramagnetic resonance (EPR) tests were performed to verify the types of free radicals in untreated or plasma-treated UHDPE during aging at 110°C for 2 min. Spin trapping was performed using a DMPO / toluene solution to obtain EPR spectra. Figure 5 (A) and plasma treatment ( Figure 5 The EPR spectrum of post-B) UHDPE aging showed a sextuplet of peaks with the same intensity and uniform spacing, with a coupling constant of α. N =12.7G and αH =6.7G, indicating that the RO· pathway dominates the aging process of UHDPE before and after plasma treatment, which is consistent with the CL kinetic fitting results.

[0065] Example 2:

[0066] (1) Preparation of polypropylene (PP) film

[0067] After pouring 5g of PP granules into the mold, the mold containing the PP granules was placed in an electric tablet press. The temperature was set to 170℃ based on the polymer's melting point. Pre-press for 1 minute, degas 5 times, pressurize for 1 minute, and cool for 1 minute. Finally, a PP film with a thickness of 0.25mm was formed. For subsequent testing, the pressed UHDPE film was cut into rectangles with a length of 4cm and a width of 0.5cm.

[0068] (2) Kinetics and fitting of Cl under different ROOH contents

[0069] The PP film was subjected to plasma treatment under air conditions. The PP film was placed vertically under plasma for 2 minutes and then placed in air for 2 minutes to enhance the ionization effect. The CL kinetic curves of thermal aging of PP in air at 110°C after different times of air plasma treatment were recorded. Figure 6 The CL kinetic curves of the PP membrane before and after plasma treatment in Figure A show a "double S" shape. For the untreated PP membrane, the aging CL kinetic curve has two peaks at 0-600s and 1100-3000s. These peaks are fitted according to the formula (1) for the RO termination reaction. The R1 value of the first CL peak... 2 It is 0.9956, k RO The value is 0.0160s -1 ( Figure 6 (B) The R2 of the second peak 2 It is 0.9925, k ROO The value is 0.0002s -1 ( Figure 6 The results showed that both CL peaks were dominated by the RO· termination reaction. The aging CL kinetic curve of the PP membrane after 2 min of plasma treatment was fitted. For the first CL peak, the formula (1) for the RO· termination reaction was used to fit the curve, yielding R1. 2 It is 0.9940, k RO The value is 0.0124s. -1 This indicates that the RO-termination reaction plays a dominant role in the early stage of PP aging. Figure 6 (D); For the second CL peak, the fit is better according to the formula (2) for the ROO·termination reaction, R2 2 It is 0.9536, k ROOThe value is 0.0051s. -1 ( Figure 6 The presence of E in the middle indicates that the free radical pathway changed during the later stages of PP aging.

Claims

1. A method for in-situ monitoring and differentiation of polymer aging free radical pathways based on chemiluminescence kinetic fitting, characterized in that, Includes the following steps: (1) A polymer film with a thickness of 0.25-2 mm is prepared by extrusion, mixing, pressing and other methods, and then cut into rectangles with a length of 2-5 cm and a width of 0.5-1 cm. (2) Fix the cut polymer film onto the ceramic heating rod, place it in the reaction chamber, and then place it in the dark chamber of the chemiluminescence instrument for aging experiment. During the aging process, data intensity I is collected, and the integration time of the data collection interval is 0.1-1s. The CL kinetic curve with a total reaction time of 0-60min is recorded with the peak as the standard. Nitrogen, air, or other nitrogen / oxygen mixtures are used as carrier gases to simulate different environments in the reaction chamber. The gas is continuously pumped into the reaction chamber at a flow rate of 50-300mL / min. The temperature of the ceramic heating rod temperature controller is set to 60-300℃ and the working voltage is -100--1000V. (3) Based on the RO·termination reaction, the fitting formula between CL intensity I and the corresponding time t is established as follows: Where A is the proportionality constant, Y is the ratio of the difference between the concentration of hydrogen peroxide [ROOH] in the equilibrium state and the initial state to the concentration of [ROOH] in the initial state, and k RO Expressed as the rate constant of the RO termination path; (4) Based on the ROO·termination reaction, the fitting formula between CL intensity I and the corresponding time t is established as follows: Where B is another proportionality coefficient, and k ROO Represented as the rate constant of the ROO termination path; (5) Based on the measured intensity I and time t, fit the data according to formulas (1) and (2) respectively. In the fitting process, set the initial values ​​of the parameters in the fitting formula as follows: A = 10000-1000000, B = 10000-1000000, Y = 1-100, k = 10000-1000000. RO For values ​​between 0.00001 and 0.001, k ROO For values ​​between 0.000001 and 0.0001, the recorded CL dynamic curves are fitted using the Levenberg-Marquardt algorithm to obtain the specific k values. RO and correlation coefficient R1 2 Specific k ROO and correlation coefficient R2 2 ; (6) The distinction is based on the correlation coefficient R1 between the fitting formula and the CL dynamic curve. 2 and R2 2 R1 2 and R2 2 The one closer to 1 has a better fit, and the polymer aging path is determined to be the free radical path with a higher correlation coefficient that is closer to 1.

2. The method according to claim 1, characterized in that, By changing the oxygen content of the carrier gas in step (2), oxygen is mixed with nitrogen at a volume percentage of 5%-100%, and the oxygen content is adjusted to 0.5MPa-10.0MPa, preferably 1.0MPa, 2.1MPa, and 4.0MPa. The CL kinetic curve of the polymer aging is monitored, and the CL kinetic curves under different oxygen contents are fitted with fitting formulas based on the RO·termination reaction and the ROO·termination reaction, respectively, and the correlation coefficients R1 for different oxygen contents are obtained. 2 and R2 2 Based on the goodness of fit, the dominant free radical pathways of polymer aging under different oxygen content atmospheres were distinguished, and the regulatory effect of oxygen content on the dominant free radicals of polymer aging pathways was evaluated.

3. The method according to claim 1, characterized in that, By adjusting the temperature controller in step (2) to different temperatures, preferably 110°C, the aging CL kinetic curves of the polymer at different temperatures are monitored. Fitting formulas based on RO·termination reaction and ROO·termination reaction are obtained at different temperatures. The correlation coefficient R1 at different temperatures is obtained by fitting the CL kinetic curves at different temperatures. 2 and R2 2 Based on the goodness of fit, the dominant free radical pathways of polymer aging at different temperatures are distinguished, the influence of different temperatures on the polymer aging pathway is evaluated, and the aging rate of the polymer is further evaluated by combining the rate constant obtained from the fitted curve.

4. The method according to claim 1, characterized in that, Step (1) The ROOH content of the obtained film is controlled by plasma treatment under air or oxygen conditions. The treatment time is 0-10 min, preferably 2 min. The ROOH content after plasma treatment is relatively quantitatively compared by the integral area of ​​the non-isothermal CL kinetic curve under nitrogen conditions. Then, the CL kinetic curve of polymer aging monitoring is continued. Based on the RO·termination reaction and ROO·termination reaction formulas, the CL kinetic curves after plasma treatment for different times are fitted. According to the goodness of fit, the dominant free radical pathway of polymer aging with different ROOH contents is distinguished, the influence of ROOH content on polymer aging pathway is evaluated, and the aging rate of polymer is further evaluated by combining the rate constant obtained from the fitted curve.

5. The method according to claim 1, characterized in that, Step (2) Aging methods include one or more aging methods under different conditions such as thermal aging (by adjusting temperature), thermo-oxidative aging (by adjusting temperature and gas atmosphere), light aging (by using different light), photo-oxidative aging (by adjusting gas atmosphere and light conditions), post-radiation aging (increasing radiation), and stress aging (increasing different stresses during winding).

6. The method according to claim 1, characterized in that, The polymers can be selected from polyolefins such as polyethylene (PE) and polypropylene (PP), polyesters and their blends.

7. The method according to claim 1, characterized in that, Based on the curve of the collected data intensity I versus time t, the number of peaks corresponds to the number of fitting equations (1) and (2), and the correlation coefficient R1 of the corresponding peaks is calculated. 2 and R2 2 Based on the goodness of fit, the corresponding aging paths can be determined.

Images