Natural rubber molecular weight sample preparation and peak shape analysis method based on GPC

Abstract

The invention discloses a natural rubber molecular weight sample preparation and peak shape analysis method based on GPC, and relates to the technical field of chromatographic analysis and biomass energy product detection. Materials with different peak shapes have great significance in research on synthesis and termination mechanisms of long and short chains of natural rubber, framework control of rubber particle protein in synthesis of long-chain and short-chain rubber molecules can be disclosed, and a mechanism of excellent comprehensive performance of natural rubber can be analyzed. The peak shape analysis method comprises the steps of test sample preparation, peak value judgment and peak shape judgment, the peak shape of the natural rubber molecular weight sample can be rapidly and accurately judged through specific peak shape judgment conditions, and important influences are generated on subsequent specific processing of natural rubber with different peak shapes.

Description

Technical Field

[0001] The present invention relates to the technical fields of chromatographic analysis and biomass energy product detection, and particularly relates to a method for preparing a natural rubber molecular weight sample based on GPC and analyzing the peak shape. Background Art

[0002] Natural rubber (NR) is a natural polymer material mainly composed of cis-1,4-polyisoprene. Among its components, 91% - 94% is rubber hydrocarbon (cis-1,4-polyisoprene), and the rest are non-rubber substances such as proteins, fatty acids, ash, sugars, etc. Natural rubber is the most widely used general-purpose rubber. The physical properties of natural rubber, such as tensile properties, dynamic mechanics, vulcanization characteristics, processing properties, thermal stability, etc., are closely related to its relative molecular mass and distribution. Currently, there are many methods for testing the molecular weight of rubber, including viscosity method, osmotic pressure method, end group analysis method, ultracentrifugation sedimentation equilibrium method, etc. However, these methods all require specific instrument equipment and operation procedures, and take a long time. Currently, gel permeation chromatography (GPC) is one of the most widely used methods, which has the advantages of fast speed, simple operation, and automatic sampling. The parameters output by GPC testing include number average molecular weight (Mn), weight average molecular weight (Mw), viscosity average molecular weight (Mp), Z average molecular weight, molecular weight polydispersity index (PDI), etc. Among them, Mn is the average molecular weight statistically weighted by the number of molecules; Mw is the average molecular weight statistically weighted by the mass of molecular chains; Mp is the molecular weight corresponding to the peak value of the curve; Mz is the average molecular weight statistically calculated according to the Z quantity, which depends more on high molecular weight components and is therefore difficult to accurately measure. Different statistical methods reflect the diversity characteristics of polymer molecules. Among these molecular weight representation methods, the common ones are Mn and Mw. PDI is also calculated by the ratio of Mw to Mn. Generally, the larger the PDI, the wider the molecular weight distribution. However, these data cannot characterize the distribution of different sizes of molecular weights, while the peak shape can more intuitively characterize the distribution trend of different sizes of molecules. GPC testing does not output the specific types of peak shapes, and there are no peak shape judgment conditions in the prior art. Therefore, the present application discloses a new method for analyzing the peak shape of rubber, hoping to better characterize the state of rubber molecules and provide better parameters for improving the economic application value of natural rubber. Summary of the Invention

[0003] Aiming at the above-mentioned defects of the prior art, the present invention proposes a method for preparing a natural rubber molecular weight sample based on GPC and analyzing the peak shape to solve the problems raised in the above background art.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A peak shape analysis method for the molecular weight of natural rubber based on GPC. The peak shape analysis method includes the preparation of test samples, peak value determination, and peak shape determination.

[0006] The peak shape determination includes the following steps, where W is the mass of the test sample and M is the molecular weight of the test sample:

[0007] (1) Single peak: There is no peak valley, only one peak, and the difference between dW / dLogM at LogM = 5.6 and LogM = 5.3 is greater than 0.06.

[0008] (2) Atypical single peak: There is no peak valley, the low peak has a certain bulge, the difference between dW / dLogM at LogM = 5.6 and LogM = 5.3 is greater than 0.02 and less than or equal to 0.06.

[0009] (3) Atypical double peak: There is no peak valley, the low peak is in a flat shoulder state, the difference between dW / dLogM at LogM = 5.6 and LogM = 5.3 is greater than 0 and less than 0.02; or there is a peak valley, and the difference between dW / dLogM at LogM = the peak value of the low peak and LogM = the peak valley value is greater than 0 and less than or equal to 0.02.

[0010] (4) Typical double peak: There is a peak valley, the low peak protrudes significantly, the difference between dW / dLogM at LogM = the peak value of the low peak and LogM = the peak valley value is greater than 0.02, and the difference between dW / dLogM at LogM = the peak value of the high peak and LogM = the peak value of the low peak is greater than 0.06.

[0011] (5) Symmetric double peak: There is a peak valley, the protrusion degrees of the high peak and the low peak are close, the difference between dW / dLogM at LogM = the peak value of the low peak and LogM = the peak valley value is greater than 0.02, and the difference between dW / dLogM at LogM = the peak value of the high peak and LogM = the peak value of the low peak is greater than 0 and less than or equal to 0.06.

[0012] (6) Trans peak: There is a peak valley, the low peak is higher than the high peak, and the difference between dW / dLogM at LogM = the peak value of the low peak and LogM = the peak value of the high peak is greater than 0.

[0013] Preferably, according to the test results of a large number of materials, LogM = 5.3, and its molecular weight is about 200,000; LogM = 5.6, and its molecular weight is about 400,000. This range basically overlaps with the distribution range of the number average molecular weight. LogM = 6.15, and its molecular weight is about 1.4 million, covering the starting range of the weight average molecular weight.

[0014] Preferably, the peak value determination includes the determination of the peak value of the low peak, the determination of the peak valley value, and the determination of the peak value of the high peak.

[0015] Preferably, the determination of the low peak value includes the following steps: Scan and search for dW / dLogM corresponding between LogM = 5.0 and LogM = 5.6. If it has been in an upward trend, this value is null (invalid); if the first decreasing value is encountered;

[0016] ① If it does not decrease thereafter, this value is the low peak value;

[0017] ② If the second decrease is encountered thereafter and it does not decrease anymore, this value is the low peak value;

[0018] ③ If it decreases continuously twice thereafter, this value is the low peak value.

[0019] Preferably, the determination of the peak valley value includes the following steps: Scan and search for dW / dLogM corresponding between LogM = 5.6 and LogM = 6.15. If it has been in an upward trend, this value is null (invalid); if it starts to decrease and the first increase is encountered:

[0020] ① If it does not decrease thereafter, this value is the peak valley value;

[0021] ② If the second increase is encountered thereafter and it does not decrease anymore, this value is the peak valley value;

[0022] ③ If two consecutive increases are encountered thereafter, this value is the peak valley value.

[0023] Preferably, the determination of the high peak value includes the following steps: Scan and search for dW / dLogM corresponding between LogM = 6.15 and LogM = 6.6. If it has been in an upward trend, this value is null (invalid); if the first decreasing value is encountered;

[0024] ① If it does not decrease thereafter, this value is the high peak value;

[0025] ② If the second decrease is encountered thereafter and it does not decrease anymore, this value is the high peak value;

[0026] ③ If it decreases continuously twice thereafter, this value is the high peak value.

[0027] Preferably, the test sample is a natural rubber sample.

[0028] Preferably, the preparation method of the natural rubber sample includes the following steps:

[0029] (1) After the fresh latex is sieved, a constant viscosity agent is added, and it is placed in an air-conditioned room at a temperature of 18 - 22 °C for dehumidifying and drying to obtain a rubber film;

[0030] (2) Cut the rubber film obtained in step (1) into granules and store them in a brown bottle for later use.

[0031] Preferably, it is best to perform mixed sampling on the sampling material for the fresh latex;

[0032] Preferably, the temperature of the air-conditioned room in step (1) is 20 °C.

[0033] Preferably, the constant viscosity agent in step (1) is one of hydroxylamine hydrochloride or hydroxylamine sulfate.

[0034] Preferably, the addition amount of the constant viscosity agent in step (1) is 0.09% ± 0.001% of the mass of the fresh latex.

[0035] Preferably, the peak shape analysis method disclosed in the present application is applied to determine the non-typical single peak, typical single peak, non-typical double peak, typical double peak, symmetric double peak and trans peak in the peak shape of the natural rubber molecular weight sample.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] (1) Currently, the samples used in gel permeation chromatography (GPC) generally come from rubber primary processing plants. After the latex is collected, ammonia is added to keep the pH value in a slightly alkaline state to maintain the stability of its colloidal state. After the primary processing plant measures the pH value of the latex, a certain amount of sulfuric acid is added to promote the rapid coagulation of the latex. After coagulation, it undergoes operations such as passing through a creping machine and crushing, and then drying. The drying is carried out by heating methods such as smoking and microwave, with a temperature of 50 - 60 °C. After drying, it is packed into standard rubber bales. Generally, there is also a process of storage and release after the bales are made, that is, the collected latex is made into rubber bales through a series of processes such as filtration, coagulation, drying, and packing. From the above process, it can be seen that during the processes of adding ammonia and acid to the latex, it may affect the molecular chains and the non-rubber components therein, thereby affecting the determination of the molecular weight; the relatively high temperature for a long time during the drying process has a certain destructive effect on the natural rubber molecular chains; during the storage process of the latex, crosslinking of the natural rubber molecular chains will also occur. These steps will cause changes in the molecular weight of the latex. However, the test samples used in the present application can well maintain the freshness of the latex and reduce the molecular weight change through a specific preparation method. As a biological macromolecule, the molecular weight of natural rubber should be measured as much as possible to eliminate adverse effects and make its molecular chains be measured in a natural state as much as possible to reflect its biological body characteristics.

[0038] (2) For large-scale tree tests, it is necessary to simplify the preparation process from latex to dry rubber and the sample submission for testing to ensure the comparability of data between different germplasm resources and different batches. For example, the number of germplasm resources preserved in the National Rubber Germplasm Repository exceeds 6,000, and there are also a large number of breeding materials. In a large number of materials, it is very important to ensure homogeneity and uniformity by standardizing the preliminary preparation of samples. This method takes advantage of the low-temperature drying characteristics of the air-conditioned room. By placing shelves in the air-conditioned room, a large number of samples can be processed in the same batch, ensuring that different materials can be sampled at the same time and the comparability of data; hydrochloric hydroxylamine / hydroxylamine sulfate is added during processing to conduct constant viscosity treatment on the molecular chain, so that cross-linking does not occur in the short term, ensuring that the samples have sufficient waiting time for testing.

[0039] (3) For the output parameters of GPC equipment, it is difficult to comprehensively reflect the molecular weight and its distribution of natural rubber from a single parameter alone. However, there is a large amount of information in the peak shape, which can directly give the proportion and distribution of high and low molecular weights. The display of the peak shape is relatively intuitive and has strong stability, so it can be considered as one of the molecular weight characterization indicators to provide support for the quality control and processing development of natural rubber.

[0040] (4) This application discloses a peak determination method different from the prior art, which can efficiently and conveniently determine the low peak value, peak valley value and high peak value of rubber, and will play a crucial role in studying the correlation with the processing performance of natural rubber. Different peak shapes can reflect the differences between high and low molecular weights and are used for the overall performance analysis of materials, providing theoretical support for the precision processing, quality control and development and utilization of natural rubber.

[0041] (5) The molecular weight of natural rubber has a distribution of high and low molecular weights and shows continuity, presenting a unique distribution trend that is significantly different from synthetic rubber. Materials with different peak shapes provide good materials for studying the synthesis and termination mechanisms of long and short chains of natural rubber, revealing the control of the rubber particle protein in the architecture of long and short chain rubber molecules, analyzing the mechanism of excellent comprehensive performance of natural rubber, and providing material support for the study of natural rubber biosynthesis.

[0042] (6) In previous studies, it was found that the molecular weight of natural rubber shows two situations: single-peak and double-peak distributions, which were not further subdivided, and the situation where the low molecular weight peak is higher than the high molecular weight peak was not found. The processing properties of single-peak and double-peak distributions are different. The high molecular weight part gives the rubber high elasticity and tear resistance, while the low molecular weight part gives it better processing properties. Through specific peak shape determination conditions, this application can quickly and accurately judge the peak shape of natural rubber molecular weight samples, which is beneficial to subsequent control of the polymerization reaction conditions during rubber processing and provides a rich variety of natural rubber products. Description of the Drawings

[0043] Figure 1 Molecular weight peak shape changes of Reyan 88-13 before and after storage without adding constant viscosity agent;

[0044] Figure 2 Molecular weight peak shape changes of Reyan 88-13 measured by the method of the present invention and after 3 months;

[0045] Figure 3 Molecular weight diversity of rubber tree germplasm resources, where A is Mn, B is Mw, and C is PDI;

[0046] Figure 4 Continuous change peak shape diagrams of different rubber tree germplasm resources;

[0047] Figure 5 Peak shape diagrams of Reyan 88-13 and XJ001202;

[0048] Figure 6 Mn distribution of different peak shapes;

[0049] Figure 7 Mw distribution of different peak shapes;

[0050] Figure 8 PDI distribution of different peak shapes;

[0051] Figure 9 Percentage of different peak shapes in rubber tree germplasm resources;

[0052] Figure 10 Single peak distribution comparison diagram of material XJ003468;

[0053] Figure 11 Single peak distribution comparison diagram of material XJ003747;

[0054] Figure 12 Single peak distribution comparison diagram of material XJ004034;

[0055] Figure 13 Single peak distribution comparison diagram of material XJ004712;

[0056] Figure 14 Single peak distribution comparison diagram of material XJ004723;

[0057] Figure 15 Single peak distribution comparison diagram of material XJ005206;

[0058] Figure 16 Atypical single peak distribution comparison diagram of material XJ000683;

[0059] Figure 17 Atypical single peak distribution comparison diagram of material XJ001230;

[0060] Figure 18 It is a contrast graph of the atypical unimodal distribution of material XJ001619;

[0061] Figure 19 It is a contrast graph of the atypical unimodal distribution of material XJ004557;

[0062] Figure 20 It is a contrast graph of the atypical unimodal distribution of material XJ004631;

[0063] Figure 21 It is a contrast graph of the atypical unimodal distribution of material XJ004672;

[0064] Figure 22 It is a contrast graph of the atypical bimodal distribution of material XJ001598;

[0065] Figure 23 It is a contrast graph of the atypical bimodal distribution of material XJ002420;

[0066] Figure 24 It is a contrast graph of the atypical bimodal distribution of material XJ002475;

[0067] Figure 25 It is a contrast graph of the atypical bimodal distribution of material XJ003420;

[0068] Figure 26 It is a contrast graph of the atypical bimodal distribution of material XJ003856;

[0069] Figure 27 It is a contrast graph of the atypical bimodal distribution of material XJ004085;

[0070] Figure 28 It is a contrast graph of the typical bimodal distribution of material XJ000060;

[0071] Figure 29 It is a contrast graph of the typical bimodal distribution of material XJ000201;

[0072] Figure 30 It is a contrast graph of the typical bimodal distribution of material XJ000377;

[0073] Figure 31 It is a contrast graph of the typical bimodal distribution of material XJ001088;

[0074] Figure 32 It is a contrast graph of the typical bimodal distribution of material XJ001200;

[0075] Figure 33 It is a contrast graph of the typical bimodal distribution of material XJ001225;

[0076] Figure 34 It is a comparative graph of the symmetric bimodal distribution of material XJ000636;

[0077] Figure 35 It is a comparative graph of the symmetric bimodal distribution of material XJ001287;

[0078] Figure 36 It is a comparative graph of the symmetric bimodal distribution of material XJ002486;

[0079] Figure 37 It is a comparative graph of the symmetric bimodal distribution of material XJ003165;

[0080] Figure 38 It is a comparative graph of the symmetric bimodal distribution of material XJ003654;

[0081] Figure 39 It is a comparative graph of the symmetric bimodal distribution of material XJ004040;

[0082] Figure 40 It is a comparative graph of the trans-peak distribution of material XJ000407;

[0083] Figure 41 It is a comparative graph of the trans-peak distribution of material XJ0001025;

[0084] Figure 42 It is a comparative graph of the trans-peak distribution of material XJ001957;

[0085] Figure 43 It is a comparative graph of the trans-peak distribution of material XJ001981;

[0086] Figure 44 It is a comparative graph of the trans-peak distribution of material XJ002262;

[0087] Figure 45 It is a comparative graph of the trans-peak distribution of material XJ002351. Specific embodiments

[0088] The technical solution of the present invention will be further described in detail below in conjunction with specific embodiments.

[0089] Example 1

[0090] The preparation method of the natural rubber sample includes the following steps:

[0091] (1) Sampling of fresh latex: Use a centrifuge tube or a self-sealing bag. The sampling volume is about 50 ml. Bring it back in an ice bath. After passing the fresh latex through an 80-mesh sieve, use a petri dish with a diameter of 10 - 12 mm. Pour about 10 g of latex into each dish, add hydroxylamine sulfate accounting for 0.09% of the mass of the fresh latex, gently rotate the petri dish to mix evenly, and make the latex spread flat on the bottom of the dish. Place the petri dish flat on the rack and put it in an air-conditioned room. Set the temperature at 20 °C for dehumidifying and drying to obtain a rubber film;

[0092] (2) Wait until the drying reaches constant weight, peel off the rubber film, put it into a self-sealing bag, stick a variety name label on the bag, and store it in a dark, cool and dry place to prevent the rubber film from absorbing moisture and getting moldy. The storage time should not be longer than 3 months.

[0093] (3) Adopt the three-point sampling method. Cut 3 small strips of film from the rubber film, with a weight of 0.1 g ± 0.0005 g. Use scissors to cut the weighed rubber strips into granular form, cut into about 100 small grains, put them into a 40-ml brown bottle for storage, and then conduct GPC testing.

[0094] Example 2

[0095] The preparation method of the natural rubber sample includes the following steps:

[0096] (1) Sampling of fresh latex: Use a centrifuge tube or a self-sealing bag. The sampling volume is about 50 ml. Bring it back in an ice bath. After passing the fresh latex through an 80-mesh sieve, use a petri dish with a diameter of 10 - 12 mm. Pour about 10 g of latex into each dish, add hydroxylamine hydrochloride accounting for 0.09% of the mass of the fresh latex, gently rotate the petri dish to mix evenly, and make the latex spread flat on the bottom of the dish. Place the petri dish flat on the rack and put it in an air-conditioned room. Set the temperature at 18 °C for dehumidifying and drying to obtain a rubber film;

[0097] (2) Wait until the drying reaches constant weight, peel off the rubber film, put it into a self-sealing bag, stick a variety name label on the bag, and store it in a dark, cool and dry place to prevent the rubber film from absorbing moisture and getting moldy. The storage time should not be longer than 3 months.

[0098] (3) Adopt the three-point sampling method. Cut 3 small strips of film from the rubber film, with a weight of 0.1 g ± 0.0005 g. Use scissors to cut the weighed rubber strips into granular form, cut into about 100 small grains, put them into a 40-ml brown bottle for storage, and then conduct GPC testing.

[0099] Example 3

[0100] The preparation method of the natural rubber sample includes the following steps:

[0101] (1) Sampling of fresh latex: Use a centrifuge tube or a self-sealing bag. The sampling amount is about 50 ml. Bring it back in an ice bath. After passing the fresh latex through an 80-mesh sieve, use a petri dish with a diameter of 10 - 12 mm. Pour about 10 g of latex into each dish, add hydroxylamine sulfate accounting for 0.09% of the mass of the fresh latex, gently rotate the petri dish to mix evenly, and make the latex spread flat on the bottom of the dish. Place the petri dish flat on the rack and put it in an air-conditioned room. Set the temperature at 22°C for dehumidifying and drying to obtain a rubber film;

[0102] (2) Wait until the drying reaches constant weight. Peel off the rubber film, put it into a self-sealing bag, stick a label with the variety name on the bag, and store it in a shaded, cool and dry place to prevent the rubber film from absorbing moisture and getting moldy. The storage time should not be longer than 3 months.

[0103] (3) Adopt the three-point sampling method. Cut 3 small strips of rubber film from the rubber film, with a weight of 0.1 g ± 0.0005 g. Use scissors to cut the weighed rubber strips into granular form, cut into about 100 small grains, put them into a 40-ml brown bottle for storage, and then conduct GPC testing.

[0104] Comparative Example 1

[0105] The difference between this comparative example and Example 1 is that no constant-viscosity agent is added, and the other components and steps remain unchanged.

[0106] (1) Sampling of fresh latex: Use a centrifuge tube or a self-sealing bag. The sampling amount is about 50 ml. Bring it back in an ice bath. After passing the fresh latex through an 80-mesh sieve, use a petri dish with a diameter of 10 - 12 mm. Pour about 10 g of latex into each dish, gently rotate the petri dish to mix evenly, and make the latex spread flat on the bottom of the dish. Place the petri dish flat on the rack and put it in an air-conditioned room. Set the temperature at 20°C for dehumidifying and drying to obtain a rubber film;

[0107] (2) Wait until the drying reaches constant weight. Peel off the rubber film, put it into a self-sealing bag, stick a label with the variety name on the bag, and store it in a shaded, cool and dry place to prevent the rubber film from absorbing moisture and getting moldy.

[0108] (3) Adopt the three-point sampling method. Cut 3 small strips of rubber film from the rubber film, with a weight of 0.1 g ± 0.0005 g. Use scissors to cut the weighed rubber strips into granular form, cut into about 100 small grains, put them into a 40-ml brown bottle for storage, and then conduct GPC testing.

[0109] Change in molecular weight of the rubber film without adding a constant-viscosity agent before and after storage in Experimental Example 1

[0110] Test the changes of the rubber film prepared in Comparative Example 1 after 6 months of storage. The results are shown in Table 1 and Figure 1 as follows:

[0111] Table 1 Test results of molecular weight of Reyan 88 - 13 without adding a constant-viscosity agent before and after storage

[0112] Reyan 88-13 Determine immediately Determine after storage for 6 months Mn (g / mol) 253151 331723 Mw (g / mol) 1783847 2123174 PDI 7.05 6.40

[0113] By comparing the test results of the samples of Reyan 88-13 before and after storage, it was found that after 6 months of storage, the molecular weight increased, Mn increased by 31.0%, Mw increased by 19.0%, PDI decreased, and the peak shape changed from a typical bimodal distribution to a unimodal distribution. Therefore, it is urgent to effectively prepare the molecular weight test samples from the perspective of the planting end.

[0114] Change in molecular weight of the latex film sample added with the constant viscosity agent before and after storage in Experimental Example 2

[0115] Take the latex of Reyan 88-13, prepare a latex film by the preparation method of Example 1, and test the molecular weight and peak shape of the samples before storage and after 3 months of storage. See Table 2 and Figure 2 Using the above sample preparation method, the molecular weight and peak shape of the samples after 3 months of storage are well maintained, especially in the low molecular weight part. It shows that after adding the constant viscosity agent hydroxylamine hydrochloride or hydroxylamine sulfate, there is little difference in the molecular weight test results when measured immediately and when measured at 3 months, which can ensure sufficient time for the determination of a large number of samples.

[0116] Table 2 Test results of the molecular weight of the latex film sample of Reyan 88-13 added with the constant viscosity agent before and after storage

[0117] Reyan 88-13 Determine immediately Determine after storage for 3 months Mn (g / mol) 242414 247547 Mw (g / mol) 1755261 1766258 PDI 7.24 7.14

[0118] Experimental Example 3 Peak shape diversity of different germplasm resources of rubber trees

[0119] Using Example 1, perform GPC tests on the molecular weights of 500 materials in the germplasm resource nursery. Use a polystyrene (CAS 9003-53-6) standard sample with a weight average molecular weight (Mw) in the range of 2×10 3 ~2×10 7 which can cover the entire molecular weight range of natural rubber. The Mn, Mw, and PDI of the 500 materials are all normally distributed. See Figure 3 In the study of its peak shape, it was found that the peak shape of the molecular weight of natural rubber shows diversity. Some materials show a unimodal distribution, some materials show an atypical unimodal or bimodal distribution, some materials show a typical bimodal distribution, some materials show a symmetric bimodal distribution, and some materials have a lower molecular weight peak higher than the higher molecular weight peak, that is, a reverse peak. See Figure 4 This diversity far exceeds the previous understanding obtained from a small number of varieties, and it is necessary to conduct a subdivision for further in-depth study of its relationship with processing performance in the future.

[0120] Example 4 Rubber trees with similar molecular weight parameters but different peak shapes

[0121] The research found that when the number-average, weight-average, and PDI data are similar, there are also obvious differences in the peak shape, especially in the low-peak part, indicating different proportions of large and small molecules. Two materials, Reyan 88-13 and XJ001202, were selected for GPC testing using Example 1. From the molecular weight parameters of the measurement results, the two are relatively close, as shown in Table 3. However, from the peak shape, the two are significantly different. Especially in the low molecular weight part, Reyan 88-13 has an obvious low peak, while the low peak part of XJ001202 is not obvious, as shown in Figure 5 . It shows that the existing parameters cannot reflect the distribution of molecular weights of different sizes.

[0122] Table 3 Molecular weight test results of Reyan 88-13 and XJ001202

[0123]

[0124] Example 5 Distribution of molecular weight parameters corresponding to different peak shapes of rubber trees

[0125] The test results of the Mn distribution corresponding to different peak shapes are as shown in Figure 6 . The test results of the Mw distribution corresponding to different peak shapes are as shown in Figure 7 . The test results of the PDI distribution corresponding to different peak shapes are as shown in Figure 8 . It can be seen from Figures 6-8 that there are overlapping situations in the PDI, Mn, and Mw parameters for different peak shape distributions, especially for Mw. When Mw is 1.7 million Daltons, all six peak shape situations may exist. Therefore, the molecular weight distribution of natural rubber cannot be reflected by the existing parameters.

[0126] Example 6 Peak shape analysis

[0127] 6.1 Peak determination

[0128] In peak shape determination, it is crucial to determine the differential value of the low molecular weight peak, the differential value of the peak valley, and the differential value of the high molecular weight peak. Only after determination can the peak shape situation be judged accordingly. Since the Slice table data output by GPC is not smooth, it can be considered to re-fit and analyze in groups of 8-10 data to obtain a smooth curve.

[0129] 6.1.1 The determination of the low peak value includes the following steps: Scan and search for dW / dLogM corresponding between LogM = 5.0 (100,000) and LogM = 5.6 (about 400,000). If it is always in an upward trend, this value is null; if the first decreasing value is encountered;

[0130] ① If it no longer decreases afterwards, this value is the low peak value;

[0131] ②After encountering the second decline and no further decline afterwards, this value is the peak-to-peak value;

[0132] ③After two consecutive declines, this value is the peak-to-peak value.

[0133] 6.1.2 The determination of peak and valley values includes the following steps: Scan and search for dW / dLogM corresponding to LogM = 5.6 (about 400,000) and LogM = 6.15 (about 1.4 million). If it has been in an upward trend, this value is null; if it starts to decline and encounters the first rise:

[0134] ①After no further decline, this value is the peak and valley value;

[0135] ②After encountering the second rise and no further decline afterwards, this value is the peak and valley value;

[0136] ③After encountering two consecutive rises, this value is the peak and valley value.

[0137] 6.1.3 The determination of the peak peak value includes the following steps: Scan and search for dW / dLogM corresponding to LogM = 6.15 (about 1.4 million) and LogM = 6.6 (about 4 million). If it has been in an upward trend, this value is null; if it encounters the first decline value;

[0138] ①After no further decline, this value is the peak peak value;

[0139] ②After encountering the second decline and no further decline afterwards, this value is the peak peak value;

[0140] ③After two consecutive declines, this value is the peak peak value.

[0141] 6.2 Peak shape determination

[0142] 6.2.1 Conduct peak shape analysis by judging the presence or absence of peak and valley and comparing the situation between the low peak and the high peak. The peak shapes can be divided into six types: typical single peak, atypical single peak, atypical double peak, typical double peak, symmetric double peak, and reverse peak. First, by determining the presence or absence of peak and valley values, if there is no peak and valley, single peak, atypical single peak can be separated from other types; Select logM as 5.6 (molecular weight 400,000) and logM as 5.3 (molecular weight 200,000), and judge by the difference between the differential values of the two points to distinguish single peak and atypical single peak; In the case of the existence of peak and valley values, the difference between the differential values of the high peak and the low peak can be used to distinguish atypical double peak, typical double peak, symmetric double peak, and reverse peak.

[0143] 6.2.2 Peak shape determination conditions

[0144] (1) Single peak: There is no peak and valley, only one peak, and the difference between dW / dLogM at LogM = 5.6 and LogM = 5.3 is greater than 0.06;

[0145] (2) Atypical single peak: Without peak valley, there is a certain bulge in the low peak, and the difference between dW / dLogM at LogM = 5.6 and LogM = 5.3 is greater than 0.02 and less than or equal to 0.06;

[0146] (3) Atypical double peak: Without peak valley, the low peak is in a flat shoulder state, and the difference between dW / dLogM at LogM = 5.6 and LogM = 5.3 is greater than 0 and less than 0.02; or there is a peak valley, and the difference between dW / dLogM at LogM = the peak value of the low peak and LogM = the peak valley value is greater than 0 and less than or equal to 0.02;

[0147] (4) Typical double peak: There is a peak valley, the low peak is significantly protruded, and the difference between dW / dLogM at LogM = the peak value of the low peak and LogM = the peak valley value is greater than 0.02, and the difference between dW / dLogM at LogM = the peak value of the high peak and LogM = the peak value of the low peak is greater than 0.06;

[0148] (5) Symmetric double peak: There is a peak valley, the protrusion degrees of the high peak and the low peak are close, the difference between dW / dLogM at LogM = the peak value of the low peak and LogM = the peak valley value is greater than 0.02, and the difference between dW / dLogM at LogM = the peak value of the high peak and LogM = the peak value of the low peak is greater than 0 and less than or equal to 0.06;

[0149] (6) Trans peak: There is a peak valley, the low peak is higher than the high peak, and the difference between dW / dLogM at LogM = the peak value of the low peak and LogM = the peak value of the high peak is greater than 0.

[0150] The above peak shape determination conditions are summarized in Table 4 as follows:

[0151] Table 4 Peak Shape Determination Conditions

[0152]

[0153] 6.3 Testing

[0154] In August and October 2023, the molecular weights of 335 materials in the National Rubber Germplasm Repository were measured respectively. For details, see Figure 9 , and from the results of the two measurements, it shows that there is rich diversity in the peak shapes among the materials. From the perspective of the proportion of different peak shapes, the typical double peak accounts for an absolute advantage, reaching 41.2%; the proportions of the atypical single peak, atypical double peak, and symmetric double peak are similar, being 15.1%, 15.4%, and 14.3% respectively; the distributions of the single peak and trans peak account for 8.4% and 5.7%.

[0155] Example 7 Accuracy Test

[0156] Plot the peak shapes of the SLICE TABLE for the test outputs. Randomly select 6 materials for each peak shape and compare them with the analysis results of this application. For the comparison of the single-peak distribution, see in detail Figures 10-15 For the comparison of the atypical single-peak distribution, see in detail Figures 16-21 For the comparison of the atypical double-peak distribution, see in detail Figures 22-27 For the comparison of the typical double-peak distribution, see in detail Figures 28-33 For the comparison of the symmetric double-peak distribution, see in detail Figures 34-39 For the comparison of the trans-peak distribution, see in detail Figures 40-45 From the comparison results, it can be seen that the peak shape analysis method of this application has high accuracy.

[0157] Repeatability test of Example 8

[0158] Compare and analyze the two measurement results of 335 materials, and it is found that the peak shape stability between the two measurements is good. Among them, the typical single peak is assigned 1, the atypical single peak is assigned 2, the atypical double peak is assigned 3, the typical double peak is assigned 4, the symmetric double peak is assigned 5, and the trans peak is assigned 6. Subtract the assignment in August from the assignment in October.

[0159] The test results show that the assignments of 180 materials are completely consistent, 60 are +1, and 95 are -1. For the materials with inconsistent assignments, most of them are near the critical value of peak shape determination. In addition, the month may also have a certain impact on the measurement results. To sum up, under the same measurement conditions, the peak shapes measured by the method of this application have strong stability.

[0160] The test results are shown in Table 5:

[0161] Table 5 Peak shape repeatability analysis

[0162] <![CDATA[Assignment 10月 - Assignment 8月 > Portion Percentage -1 95 28.4％ 0 180 53.7％ ﹢1 60 17.9％ Total 335 100％

[0163] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A peak shape analysis method for natural rubber molecular weight based on GPC, characterized in that, The peak shape analysis method includes test sample preparation, peak value determination and peak shape determination; The peak shape determination comprises the following steps, wherein W is the mass of the test sample and M is the molecular weight of the test sample: (1) Single peak: no valley, only one peak, the difference of dW / dLogM between LogM=5.6 and LogM=5.3 is greater than 0.06; (2) Atypical single peak: no peak valley, low peak has a certain bulge, the difference of dW / dLogM when LogM=5.6 and LogM=5.3 is greater than 0.02, and less than or equal to 0.06; (3) Atypical double peaks: no peaks and valleys, the low peak is flat, the difference of dW / dLogM when LogM=5.6 and LogM=5.3 is greater than 0 and less than 0.02; or there are peaks and valleys, the difference of dW / dLogM when LogM=low peak value and LogM=peak-to-valley value is greater than 0 and less than or equal to 0.02; (4) Typical double peaks: There are peaks and valleys, the low peak is obviously protruding, the difference of dW / dLogM when LogM=low peak value and LogM=peak-to-valley value is greater than 0.02, and the difference of dW / dLogM when LogM=high peak value and LogM=low peak value is greater than 0.06; (5) Symmetrical double peaks: There are peaks and valleys, the high peak and the low peak have similar protrusions, the difference between dW / dLogM when LogM=low peak-to-peak value and LogM=peak-to-valley value is greater than 0.02, and the difference between dW / dLogM when LogM=high peak-to-peak value and LogM=low peak-to-peak value is greater than 0, and less than or equal to 0.06; (6) Trans peak: There are peaks and valleys, the low peak is higher than the high peak, and the difference of dW / dLogM is greater than 0 when LogM = low peak-peak value and LogM = high peak-peak value.

2. The peak shape analysis method according to claim 1, characterized in that: The peak value determination includes low peak-to-peak value determination, peak-to-valley value determination and high peak-to-peak value determination.

3. The peak shape analysis method according to claim 2, characterized in that: The low peak-to-peak value determination comprises the following steps: scanning and searching for the dW / dLogM corresponding to between LogM=5.0 and LogM=5.6, if it is always in an upward trend, this value is null; if the first decreasing value is encountered; ①It will not decrease after that, and this value is the low peak-to-peak value; ②After that, it encounters the second drop and then stops dropping. This value is the low peak-to-peak value. ③After that, it drops twice in succession, and this value is the low peak-to-peak value.

4. The peak shape analysis method according to claim 2, characterized in that: The peak-to-valley value determination includes the following steps: Scan and search for the dW / dLogM corresponding to LogM=5.6 and LogM=6.

15. If it is always in an upward trend, this value is null; if it starts to decrease and encounters the first increase: ①It will not decrease after that, and this value is the peak-to-valley value; ②After that, it encounters the second rise and no longer decreases. This value is the peak-to-valley value; ③After that, there are two consecutive rises, and this value is the peak-to-valley value.

5. The peak shape analysis method according to claim 2, characterized in that: The determination of the peak value comprises the following steps: scanning and searching for the dW / dLogM corresponding to between LogM=6.15 and LogM=6.6, if it is always in an upward trend, this value is null; if the first decreasing value is encountered; ①After that, it will not decrease any more, and this value is the peak value; ②After that, it encounters the second decline and then stops declining. This value is the peak value; ③After that, it drops twice in succession, and this value is the peak value.

6. The peak shape analysis method according to claim 1, characterized in that: The test sample is a natural rubber sample.

7. The peak shape analysis method according to claim 6, characterized in that: The method for preparing the natural rubber sample comprises the following steps: (1) After the fresh latex is sieved, a constant viscosity agent is added, and the latex is placed at a temperature of 18 to 22° C. and dehumidified to obtain a film; (2) Cut the film obtained in step (1) into granules and store them in a brown bottle for later use.

8. The peak shape analysis method according to claim 7, characterized in that: The constant viscosity agent in step (1) is one of hydroxylamine hydrochloride or hydroxylamine sulfate.

9. The peak shape analysis method according to claim 7, characterized in that: The amount of the constant viscosity agent added in step (1) is 0.09%±0.001% of the mass of the fresh latex.

10. Application of the peak shape analysis method according to any one of claims 1 to 9 in determining single peak, atypical single peak, atypical double peak, typical double peak, symmetrical double peak and trans peak in the peak shape of a natural rubber molecular weight sample.

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