Prediction method for weight-average molecular weight of natural rubber and application of prediction method

Abstract

The invention relates to the technical field of analysis and testing, in particular to a prediction method for the weight-average molecular weight of natural rubber and application thereof.The prediction method at least comprises the following steps that S1, a fresh latex sample of a rubber tree is collected, and the mercaptan content in latex is measured; s2, calculating the measured mercaptan content in the latex through a prediction model function to predict the weight-average molecular weight of the natural rubber in the sample; the function of the prediction model is as follows: Y is equal to 1491339 to 306242x; x is the content of mercaptan in the latex. According to the method disclosed by the invention, the index of the weight-average molecular weight of the natural rubber can be predicted based on the mercaptan content of the fresh latex of the rubber tree by constructing the model function equation, and various equipment instruments are not needed, so that the problems that the original test period is long, the cost is relatively high and certain manpower and material resources are needed for supporting are solved; the method can rapidly, simply, economically and effectively predict the weight-average molecular weight of the natural rubber.

Description

Technical Field

[0001] The present invention relates to the technical field of analysis and testing, and in particular to a method for predicting the weight-average molecular weight of natural rubber and application thereof. Background Art

[0002] Natural rubber, derived from the latex produced by tapping rubber trees, is primarily composed of rubber hydrocarbons. As an important industrial raw material, it is widely used in daily life, healthcare, transportation, defense, and specialized equipment. Natural rubber is a typical natural polymer material primarily composed of cis-1,4-polyisoprene. Its molecular weight is a key indicator of the properties of polymer composites, making molecular weight testing a key method for assessing its quality. Furthermore, weight-average molecular weight, a key performance indicator of natural rubber, influences its physical and processing properties. Therefore, testing its weight-average molecular weight is beneficial for evaluating its quality.

[0003] Prior art CN110501478A discloses a method for predicting the molecular weight of natural rubber using a rubber processing analyzer (RPA2000). This method is highly reproducible and accurate. By measuring the molecular weight of natural rubber, the quality of different natural rubbers can be accurately compared. Furthermore, the quality of different brands of peptizers can be compared using the same natural rubber through the same mastication process.

[0004] At present, the weight-average molecular weight of natural rubber is mainly measured by gel permeation chromatography using the light scattering method. The measurement cycle is long and requires certain manpower and material resources to support it. There are certain difficulties in scientifically and quickly obtaining the weight-average molecular weight indicator of natural rubber. Summary of the Invention

[0005] In order to solve the problems in the prior art, the present invention provides a method for predicting the weight-average molecular weight of natural rubber, which comprises at least the following steps:

[0006] S1: Collect fresh latex samples from rubber trees and determine the thiol content in the latex;

[0007] S2: The measured mercaptan content in the latex is calculated using a prediction model function to predict the weight-average molecular weight of the natural rubber in the sample;

[0008] The prediction model function is Y=1491339-306242x, wherein x is the mercaptan content in the latex.

[0009] In one embodiment, the construction of the prediction model function includes at least:

[0010] a. Obtain the mercaptan content parameter value;

[0011] b. Obtaining the weight average molecular weight parameter value;

[0012] c. Build a prediction model;

[0013] d. Model diagnosis.

[0014] In one embodiment, the method for obtaining the mercaptan content parameter value in a comprises the following steps:

[0015] A fresh latex sample is placed in a test tube, stirred, and the extract is centrifuged to obtain a supernatant as a test sample; tris(hydroxymethylaminomethane) and 5,5'-dithiobis(2-nitrobenzoic acid) solution are added to the test sample in sequence for reaction, and the corresponding optical density of the sample is measured by a spectrophotometer to calculate the thiol content in the latex.

[0016] In one embodiment, the centrifugation condition in step a is: centrifugation in a 4000 r / min centrifuge for 10 minutes.

[0017] In one embodiment, the specific steps of obtaining the weight-average molecular weight parameter value in b include: taking the fresh latex sample from the same batch as in a, acidifying and coagulating it, tableting, air-drying, and baking it to obtain a test sample, randomly sampling and mixing at multiple points, taking 30 mg of the sample and placing it in a tetrahydrofuran solution, standing and dissolving it for 7 days, filtering it through a filter membrane, and the resulting filtrate is the sample to be tested, and measuring it using a gel permeation chromatography instrument to obtain the weight-average molecular weight parameter value.

[0018] In one embodiment, the solidified sample is placed for 24 hours before the tableting step in b.

[0019] In one embodiment, the drying temperature in step b is 70° C. and the drying time is 24 hours.

[0020] In one embodiment, the filter membrane in step b is a PTFE filter membrane.

[0021] In one embodiment, the gel permeation chromatography measurement conditions in step b are: setting the column temperature and detector temperature parameters to 40°C.

[0022] In one embodiment, the specific step of constructing the prediction model in c includes: constructing a prediction model by using the lm function based on the thiol content in the latex obtained in a and the weight average molecular weight parameter value obtained in b.

[0023] In one embodiment, the specific steps of model diagnosis in d include: performing model diagnosis on the prediction model using the shapiro.test function and the performance toolkit, evaluating the model performance based on the statistical values ​​of the prediction model, and constructing a prediction model function.

[0024] In one embodiment, the prediction model function is Y=1491339-306242x; wherein x is the thiol content in the latex.

[0025] In one embodiment, the confidence interval of the prediction model function parameter is set as:

[0026] The confidence interval of the model intercept is 1442708.3 to 1539969.6; the confidence interval of the regression coefficient is -454502.6 to -157980.5.

[0027] The second aspect of the present invention provides an application of the above prediction method in the field of predicting the weight-average molecular weight of natural rubber.

[0028] Beneficial effects

[0029] 1. The method of the present invention can quickly, simply and cost-effectively predict the weight-average molecular weight of natural rubber based on the mercaptan content of fresh latex from rubber trees by constructing a model function equation.

[0030] 2. The present invention is based on the weight-average molecular weight index of 132 natural rubber latex samples. Through regression analysis, it is determined that there is an extremely significant relationship between the thiol content in the latex and the weight-average molecular weight (p < 0.001). The present invention can predict the weight-average molecular weight, a quality index, based on the thiol content in the latex through a prediction model function equation.

[0031] 3. The present invention uses the shapiro.test function to perform a normality test on the prediction model, draws the residual graph of the model through the performance toolkit and performs residual diagnosis. The final constructed model function equation has high accuracy and strong reproducibility in detection results.

[0032] 4. The present invention is simple to process samples, has high sensitivity, short testing time, and no chemical reagent pollution.

[0033] 5. The invented testing method does not require a variety of equipment and instruments, which solves the problems of long conventional testing cycles, high costs, and the need for certain manpower and material resources to support. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a functional model diagram for predicting the weight-average molecular weight based on the thiol content in latex.

[0035] Figure 2This is a diagram showing the difference between the simulated and observed values ​​of the weight average molecular weight in Example 2.

[0036] Figure 3 This is a diagram showing the difference between the simulated and observed values ​​of the weight average molecular weight in Example 3. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the examples and drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. The experimental methods for which specific conditions are not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used for which the manufacturer is not specified are all conventional products that can be purchased commercially.

[0038] Example 1

[0039] This embodiment provides a method for predicting the weight-average molecular weight of natural rubber, comprising the following steps:

[0040] S1: Collect fresh latex samples from rubber trees and determine the thiol content in the latex;

[0041] S2: The measured mercaptan content in the latex is calculated using a prediction model function to predict the weight-average molecular weight of the natural rubber in the sample;

[0042] The prediction model function is Y=1491339-306242x, wherein x is the mercaptan content in the latex.

[0043] The construction of the prediction model function at least includes:

[0044] a. Obtain the mercaptan content parameter value;

[0045] b. Obtaining the weight average molecular weight parameter value;

[0046] c. Build a prediction model;

[0047] d. Model diagnosis.

[0048] The method for obtaining the thiol content parameter value in the above method a comprises the following steps: taking a fresh latex sample and placing it in a test tube, stirring it, taking the extract and centrifuging it, and obtaining the supernatant as the test sample; adding 0.8 mL of 0.5 M / L tris(hydroxymethylaminomethane) and 0.1 mL of 5,5'-dithiobis(2-nitrobenzoic acid) solution to the test sample for reaction, measuring the corresponding optical density value of the sample using a spectrophotometer, and calculating the thiol content in the latex.

[0049] The specific steps of obtaining the weight-average molecular weight parameter value in the above-mentioned step b include: taking the fresh latex sample of the same batch as the above-mentioned step a, acidifying and coagulating it for 24 hours, pressing it into sheets using a sheeting machine, drying it, setting the temperature at 70° C. in a drying room, and drying it for about 24 hours to obtain a test sample; after random sampling and mixing at multiple points, taking 30 mg of the sample and placing it in a tetrahydrofuran solution, standing and dissolving it for 7 days, filtering it through a PTFE filter membrane, and obtaining the filtrate as the sample to be tested; using a gel permeation chromatograph, setting the column temperature and detector temperature parameters at 40° C., and measuring the above-mentioned filtrate to obtain the weight-average molecular weight parameter value.

[0050] The specific step of constructing the prediction model in c includes: constructing a prediction model by using the lm function based on the thiol content in the latex obtained in a and the weight average molecular weight parameter value obtained in b.

[0051] The specific steps of the model diagnosis in d include: using the shapiro.test function and the performance toolkit to perform model diagnosis on the prediction model, evaluating the model performance based on the statistical values ​​of the prediction model, and constructing a prediction model function.

[0052] The confidence interval of the prediction model function parameters is set as:

[0053] The confidence interval of the model intercept is 1442708.3 to 1539969.6; the confidence interval of the regression coefficient is -454502.6 to -157980.5.

[0054] The second aspect of the present invention provides an application of the above prediction method in the field of predicting the weight-average molecular weight of natural rubber.

[0055] Figure 1 This is a functional model diagram for predicting the weight average molecular weight based on the thiol content in latex.

[0056] Performance Testing

[0057] Accuracy test

[0058] Test 1: Rubber latex was sampled from a field test site in a rubber forest at the Chinese Academy of Tropical Agricultural Sciences. The latex samples were analyzed using the DTNB reagent method. The optical density of the samples was measured using a spectrophotometer to calculate the thiol content of the latex. The filtrate of the sample was analyzed using gel permeation chromatography to determine the weight-average molecular weight.

[0059] The weight average molecular weight index value of natural rubber was predicted using the prediction model function equation Y=1491339-306242x based on the mercaptan content and weight average molecular weight in latex. The mercaptan contents in latex were 0.3883333, 0.1023333, 0.426, 0.271, 0.3123333, 0.276, 0.2503333, 0.2146667, 0.3343333, 0.2843333, 0.525, 0.55, 0.3803333, 0.2323333, 0.3366667 and 0.1596667, respectively. The prediction model function, the simulated values ​​of the weight average molecular weight of natural rubber are 1372415, 1460000, 1360880, 1408347, 1395689, 1406816, 1414676, 1425599, 1388952, 1404264, 1330562, 1322906, 1374865, 1420189, 1388238 and 1442442. The R software ggpubr toolkit was further used to perform a T test on the weight average molecular weight test values ​​and the simulated weight average molecular weight test values. The results are shown in Figure 2 .

[0060] The T-test result showed that p=0.1>0.05, that is, the simulated value of the weight average molecular weight was not significantly different from the observed value, indicating that the prediction model has statistical significance and the method of the present invention can predict the weight average molecular weight index value of natural rubber.

[0061] Test 2: Rubber latex was sampled from a field test site in a rubber forest at the Chinese Academy of Tropical Agricultural Sciences. The latex samples were analyzed using the DTNB reagent method. The optical density of the samples was measured using a spectrophotometer to calculate the thiol content of the latex. The filtrate of the sample was analyzed using gel permeation chromatography to determine the weight-average molecular weight.

[0062] The weight-average molecular weight of natural rubber was predicted using the prediction model function equation Y=1491339-306242x based on the latex thiol content and weight-average molecular weight. The latex thiol contents were 0.2676667, 0.245, 0.1513333, 0.074, 0.232, 0.3376667, 0.2773333, 0.2936667, 0.3716667, 0.4066667, 0.238, 0.3203333, 0.351, 0.5093333, 0.4053333, 0.5246667 and 0.4446667, respectively. According to the prediction model function, the simulated values ​​of the weight average molecular weight of natural rubber are 1409368, 1416310, 1444994, 1468677, 1420291, 1387931, 1406408, 1401406, 1377519, 1366801, 1418453, 1393239, 1383848, 1335360, 1367209, 1330664 and 1355163. The R software ggpubr toolkit was further used to perform a T test on the weight average molecular weight test values ​​and the simulated weight average molecular weight test values. The results are shown in Figure 3. Figure 3 .

[0063] The T-test result showed that p=0.16>0.05, that is, the simulated value of the weight average molecular weight was not significantly different from the observed value, indicating that the prediction model has statistical significance, and the method of the present invention can predict the weight average molecular weight index value of natural rubber.

Claims

1. A method for predicting the weight average molecular weight of natural rubber, characterized in that: At least the following steps are included: S1: Collect fresh latex samples from rubber trees and determine the mercaptan content in the latex; S2: The measured mercaptan content in the latex is calculated by the prediction model function to predict the weight average molecular weight of the natural rubber in the sample; The prediction model function is Y=1491339-306242x; x is the mercaptan content in the latex.

2. The method for predicting the weight average molecular weight of natural rubber according to claim 1, characterized in that: The construction of the prediction model function at least includes: a. Obtain the mercaptan content parameter value; b. Obtaining the weight average molecular weight parameter value; c. Build a prediction model; d. Model diagnosis.

3. The method for predicting the weight average molecular weight of natural rubber according to claim 2, characterized in that: The method for obtaining the mercaptan content parameter value in a comprises the following steps: A fresh latex sample is placed in a test tube, and after stirring, the extract is centrifuged to obtain the supernatant as a test sample; tris(hydroxymethylaminomethane) and 5,5'-dithiobis(2-nitrobenzoic acid) solution are successively added to the test sample for reaction, and the corresponding optical density value of the sample is measured by a spectrophotometer to calculate the thiol content in the latex.

4. The method for predicting the weight average molecular weight of natural rubber according to claim 2, characterized in that: The specific steps of obtaining the weight average molecular weight parameter value in b include: The fresh latex samples from the same batch as described in a are acidified and coagulated, and then tabletted, air-dried, and baked to obtain test samples. After multi-point random sampling and mixing, 30 mg of the sample is placed in a tetrahydrofuran solution, allowed to stand and dissolve for 7 days, and then filtered through a filter membrane. The filtrate obtained is the sample to be tested, and the weight-average molecular weight parameter value is obtained by gel permeation chromatography.

5. The method for predicting the weight average molecular weight of natural rubber according to claim 3, characterized in that: Before the tableting step, the solidified sample is placed for 24 hours.

6. The method for predicting the weight average molecular weight of natural rubber according to claim 3, characterized in that: The drying temperature in b is 70° C. and the drying time is 24 h.

7. The method for predicting the weight average molecular weight of natural rubber according to claim 2, characterized in that: The specific step of constructing the prediction model in c includes: constructing a prediction model by using the lm function to calculate the thiol content in the latex obtained in a and the weight average molecular weight parameter value obtained in b.

8. The method for predicting the weight average molecular weight of natural rubber according to claim 2, characterized in that: The specific steps of the model diagnosis in d include: using the shapiro.test function and the performance toolkit to perform model diagnosis on the prediction model, evaluating the model performance based on the statistical value of the prediction model, and constructing a prediction model function.

9. The method for predicting the weight average molecular weight of natural rubber according to claim 1, characterized in that: The confidence interval of the prediction model function parameter is set as: The confidence interval of the model intercept is 1442708.3 to 1539969.6; the confidence interval of the regression coefficient is -454502.6 to -157980.

5.

10. Use of the method for predicting the weight average molecular weight of natural rubber according to claims 1 to 9 in the field of predicting the weight average molecular weight of natural rubber.

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