A method for testing the inherent molecular weight distribution type of natural rubber raw rubber

Abstract

The present invention relates to the technical field of molecular weight distribution of natural rubber, and in particular to a method for testing the inherent molecular weight distribution type of natural rubber. The testing method provided by the present invention comprises using a rotorless shear rheometer to sequentially subject the natural rubber to sample conditioning and frequency scanning to obtain a series of scanning frequencies and loss moduli; establishing a logarithmic relationship curve between the loss modulus and the scanning frequency, with the scanning frequency as the logarithmic horizontal coordinate and the loss modulus as the logarithmic vertical coordinate; and determining the inherent molecular weight distribution type of the natural rubber based on the relationship curve between the loss modulus and the scanning frequency: when the loss modulus increases with increasing scanning frequency, the inherent molecular weight distribution type of the natural rubber is bimodal; when the loss modulus decreases with increasing scanning frequency, the inherent molecular weight distribution type of the natural rubber is unimodal. The method can quickly and accurately identify the inherent molecular weight distribution type of natural rubber.

Description

Technical Field

[0001] The invention relates to the technical field of natural rubber raw rubber molecular weight distribution, in particular to a method for testing the inherent molecular weight distribution type of natural rubber raw rubber. Background Art

[0002] Natural rubber's superior comprehensive mechanical properties and irreplaceability stem from its unique molecular structure, endowed by biosynthesis. Among them, bimodal molecular weight distribution is one of the important structural characteristics of natural rubber. In fact, the molecular weight distribution type of natural rubber is related to the genotype of the rubber tree species, and is also affected by molecular chain crosslinking (gel formation) and oxidative chain scission (such as high-temperature drying) during the preparation of raw rubber from latex and the storage of raw rubber. Excluding the influence of molecular chain crosslinking and oxidative chain scission, the molecular weight distribution that can reflect the inherent characteristics of the rubber tree species is called the intrinsic molecular weight distribution. According to the different intrinsic molecular weight distribution types, rubber tree species can be divided into "unimodal family" and "bimodal family". Extensive research has shown that raw rubber prepared using latex produced by "unimodal family" or "bimodal family" rubber tree species has significantly different processing properties and application performance. Among them, natural rubber with a bimodal molecular weight distribution can obtain a better straightening force / elongation curve in the unprocessed state, thereby improving the performance of tire products. Therefore, understanding the direction of the molecular weight distribution type of natural rubber raw rubber is very meaningful for product users. During the preparation of raw rubber from latex and the storage of raw rubber, the natural rubber molecular chains will undergo structuring and produce gel. When using traditional methods (such as gel permeation chromatography) to test the molecular weight of natural rubber, the gel in the sample solution must first be filtered out, resulting in the test results not accurately reflecting the inherent molecular weight distribution. Summary of the Invention

[0003] The present invention aims to provide a method for testing the inherent molecular weight distribution type of natural rubber raw rubber. The method can quickly and accurately identify the inherent molecular weight distribution type of natural rubber raw rubber, and realize the traceability of the rubber tree "family" of the latex source adopted in the raw rubber preparation.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a method for testing the inherent molecular weight distribution type of natural rubber raw rubber, comprising the following steps:

[0006] Using a rotorless shear rheometer, the natural rubber raw rubber was subjected to sample conditioning and frequency scanning in sequence to obtain a series of scanning frequencies and loss moduli;

[0007] The logarithmic relationship curve between loss modulus and scanning frequency is established with scanning frequency as the logarithmic horizontal coordinate and loss modulus as the logarithmic vertical coordinate;

[0008] The inherent molecular weight distribution type of the natural rubber raw rubber is determined by the relationship curve between the loss modulus and the scanning frequency: when the loss modulus increases with the increase of the scanning frequency, the inherent molecular weight distribution type of the natural rubber raw rubber is bimodal; when the loss modulus decreases with the increase of the scanning frequency, the inherent molecular weight distribution type of the natural rubber raw rubber is unimodal.

[0009] Preferably, the natural rubber raw rubber is natural rubber raw rubber that has not been roller-molded.

[0010] Preferably, the sample is conditioned for 2 to 8 minutes, at a temperature of 80 to 130° C., at a frequency of 0.1 to 0.5 Hz, and at a strain of 2.8% to 7%.

[0011] Preferably, the sample is conditioned for 3 to 7 minutes, at a temperature of 90 to 120° C., at a frequency of 0.1 to 0.4 Hz, and at a strain of 3% to 6%.

[0012] Preferably, the sample is conditioned for 4 to 5 minutes, at a temperature of 100 to 110° C., at a frequency of 0.2 to 0.3 Hz, and at a strain of 4% to 5%.

[0013] Preferably, the frequency of the frequency sweep is 0.1-20 Hz, the temperature is 80-130° C., and the strain is 2.8%-7%.

[0014] Preferably, the frequency of the frequency sweep is 0.1-20 Hz, the temperature is 90-120° C., and the strain is 3%-6%.

[0015] Preferably, the frequency of the frequency sweep is 0.1-20 Hz, the temperature is 100-110° C., and the strain is 4%-5%.

[0016] The present invention provides a method for testing the inherent molecular weight distribution type of natural rubber raw rubber, comprising the following steps: using a rotorless shear rheometer, sequentially subjecting the natural rubber raw rubber to sample conditioning and frequency scanning to obtain a series of scanning frequencies and loss moduli; establishing a logarithmic relationship curve between the loss modulus and the scanning frequency, with the scanning frequency as the logarithmic horizontal coordinate and the loss modulus as the logarithmic vertical coordinate; and determining the inherent molecular weight distribution type of the natural rubber raw rubber based on the relationship curve between the loss modulus and the scanning frequency: when the loss modulus increases with increasing scanning frequency, the inherent molecular weight distribution type of the natural rubber raw rubber is bimodal; when the loss modulus decreases with increasing scanning frequency, the inherent molecular weight distribution type of the natural rubber raw rubber is unimodal. The testing method of the present invention utilizes a rheological method for testing, uses solid raw rubber as the sample, and does not require liquid phase separation, thereby achieving the purpose of identifying the inherent molecular weight distribution type of the natural rubber raw rubber. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 : This is a logarithmic relationship curve between the scanning frequency and the loss modulus G" of IAN873-RSS, IAN873-RSSCV, IAN873-TSR and IAN873-TSRCV in Example 1;

[0018] Figure 2 : is a logarithmic relationship curve between the scanning frequency and the loss modulus G" of Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV in Example 1;

[0019] Figure 3 : This is a logarithmic relationship curve between the scanning frequency and the loss modulus G" of IAN873-RSS, IAN873-RSSCV, IAN873-TSR and IAN873-TSRCV in Example 2;

[0020] Figure 4 The logarithmic relationship curve between the scanning frequency and the loss modulus G" of Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV in Example 2;

[0021] Figure 5 : This is a logarithmic relationship curve between the scanning frequency and the loss modulus G" of IAN873-RSS, IAN873-RSSCV, IAN873-TSR and IAN873-TSRCV in Example 3;

[0022] Figure 6 The logarithmic relationship curve between the scanning frequency and the loss modulus G" of Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV in Example 3;

[0023] Figure 7 The chromatograms of IAN873-RSS, IAN873-RSSCV, IAN873-TSR, and IAN873-TSRCV in Comparative Example 1 are shown;

[0024] Figure 8 The chromatograms of Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV in Comparative Example 1 are shown. DETAILED DESCRIPTION

[0025] The present invention provides a method for testing the inherent molecular weight distribution type of natural rubber raw rubber, comprising the following steps:

[0026] Using a rotorless shear rheometer, the natural rubber raw rubber was subjected to sample conditioning and frequency scanning in sequence to obtain a series of scanning frequencies and loss moduli;

[0027] The logarithmic relationship curve between loss modulus and scanning frequency is established with scanning frequency as the logarithmic horizontal coordinate and loss modulus as the logarithmic vertical coordinate;

[0028] The inherent molecular weight distribution type of the natural rubber raw rubber is determined by the relationship curve between the loss modulus and the scanning frequency: when the loss modulus increases with the increase of the scanning frequency, the inherent molecular weight distribution type of the natural rubber raw rubber is bimodal; when the loss modulus decreases with the increase of the scanning frequency, the inherent molecular weight distribution type of the natural rubber raw rubber is unimodal.

[0029] In the present invention, unless otherwise specified, all preparation raw materials are commercially available products well known to those skilled in the art.

[0030] The present invention adopts a rotorless shear rheometer to sequentially perform sample adjustment and frequency scanning on natural rubber raw rubber to obtain a series of scanning frequencies and loss moduli.

[0031] In the present invention, the natural rubber raw rubber is preferably natural rubber raw rubber that has not been roller-masticated.

[0032] In the present invention, the amount of the natural rubber is preferably 4.0 to 5.0 g.

[0033] In the present invention, the sample conditioning time is preferably 2 to 8 minutes, more preferably 3 to 7 minutes, and most preferably 4 to 5 minutes; the temperature is preferably 80 to 130°C, more preferably 90 to 120°C, and most preferably 100 to 110°C; the frequency is preferably 0.1 to 0.5 Hz, more preferably 0.1 to 0.4 Hz, and most preferably 0.2 to 0.3 Hz; the strain is preferably 2.8% to 7%, more preferably 3% to 6%, and most preferably 4% to 5%.

[0034] In the present invention, the frequency of the frequency sweep is preferably 0.1 to 20 Hz; the temperature is preferably 80 to 130°C, more preferably 90 to 120°C, and most preferably 100 to 110°C; the strain is preferably 2.8% to 7%, more preferably 3% to 6%, and most preferably 4% to 5%.

[0035] In the present invention, the logarithm in the logarithmic relationship curve between the loss modulus and the scanning frequency is preferably log10.

[0036] The test method for the inherent molecular weight distribution type of natural rubber provided by the present invention is described in detail below in conjunction with the examples, but they should not be understood as limiting the scope of protection of the present invention.

[0037] The test subjects of Examples 1 to 3 and Comparative Example 1 were all IAN873 (IAN873-RSS, IAN873-RSSCV, IAN873-TSR, and IAN873-TSRCV) of the "unimodal family" and Reyan73397 (Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR, and Reyan73397-TSRCV) of the "bimodal family";

[0038] Preparation of IAN873-RSS: Take fresh IAN873 latex → Filter → Pour 45 kg into a 100 kg insert coagulation tank → Dilute with water (control the coagulation concentration at 15%) → Add acid for coagulation (use 1.5% formic acid solution, the acid amount is calculated as neutralizing acid + 0.4% coagulation acid) → Stir evenly, insert the insert → Ripen for 5 hours → Tablet → Soak for 2 hours → Let the tablets air-dry for 2 days → Smoke dry (45°C × 1 day + 60°C × 3 days);

[0039] Preparation of IAN873-RSSCV: Take fresh IAN873 latex → Filter → Pour 45 kg into a 100 kg insert coagulation tank → Dilute with water (control the coagulation concentration to 15%) → Add constant viscosity agent NHS (prepare as a 5% aqueous solution) → Add acid for coagulation (use 1.5% formic acid solution, the amount of acid is calculated as neutralizing acid + 0.4% coagulation acid) → Stir evenly, insert the insert → Ripen for 5 hours → Tablet → Soak for 2 hours → Let the tablets air-dry for 2 days → Smoke dry (45°C × 1 day + 60°C × 3 days);

[0040] Preparation of IAN873-TSR: Take fresh latex of Reyan73397 → Filter → Pour 45kg into a plastic basin (over 80kg) → Dilute with water (control the coagulation concentration to 20%) → Add acid to coagulate (use 3% formic acid solution, calculate the acid amount as neutralizing acid + 0.4% coagulation acid) → Stir evenly → Ripen for 16 hours → Thin, crepe, and shred → Dry in an 83°C oven;

[0041] Preparation of IAN873-TSRCV: Take fresh IAN873 latex → Filter → Pour 45 kg into a plastic basin (over 80 kg) → Dilute with water (control the coagulation concentration to 20%) → Add constant viscosity agent NHS (prepare as a 5% aqueous solution) → Add acid to coagulate (use 3% formic acid solution, the acid amount is calculated as neutralizing acid + 0.4% coagulating acid) → Stir evenly → Ripen for 16 hours → Thin, crepe, and shred → Oven dry at 83°C;

[0042] Preparation of Reyan73397-RSS: Take fresh latex of Reyan73397 → Filter → Pour 45 kg into a 100 kg insert coagulation tank → Dilute with water (control the coagulation concentration at 15%) → Add acid for coagulation (use 1.5% formic acid solution, the amount of acid is calculated as neutralizing acid + 0.4% coagulation acid) → Stir evenly, insert the insert → Ripen for 5 hours → Tablet → Soak for 2 hours → Let the tablets air-dry for 2 days → Smoke dry (45°C × 1 day + 60°C × 3 days);

[0043] Preparation of Reyan73397-RSSCV: Take fresh latex of Reyan73397 → Filter → Pour 45 kg into a 100 kg insert coagulation tank → Dilute with water (control the coagulation concentration at 15%) → Add acid for coagulation (use 1.5% formic acid solution, the acid amount is calculated as neutralizing acid + 0.4% coagulation acid) → Stir evenly, insert the insert → Ripen for 5 hours → Tablet → Soak for 2 hours → Let the tablets air-dry for 2 days → Smoke dry (45°C × 1 day + 60°C × 3 days);

[0044] Preparation of Reyan73397-TSR: Take fresh Reyan73397 latex → Filter → Pour 45kg into a plastic basin (over 80kg) → Dilute with water (control the coagulation concentration to 20%) → Add acid to coagulate (use 3% formic acid solution, calculate the acid amount as neutralizing acid + 0.4% coagulation acid) → Stir evenly → Ripen for 16 hours → Thin, crepe, and shred → Dry in an 83°C oven;

[0045] Preparation of Reyan73397-TSRCV: Take the fresh latex of Reyan73397 → filter → take 45kg and pour it into a plastic basin with more than 80kg → dilute with water (control the coagulation concentration at 20%) → add constant viscosity agent NHS (prepare to make a 5% aqueous solution) → add acid to coagulate (use 3% formic acid solution, calculate the amount of acid based on neutralizing acid + 0.4% coagulating acid) → stir evenly → mature for 16h → press, crepe and tear into particles → dry in an 83℃ oven.

[0046] Example 1

[0047] 4.0 g of IAN873-RSS, IAN873-RSSCV, IAN873-TSR, IAN873-TSRCV, Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV were weighed respectively and placed in a rotorless shear rheometer for testing: the sample adjustment conditions were: frequency 0.5 Hz, strain 2.8%, temperature 80°C, and time 8 min; the frequency scanning conditions were: 0.1-20 Hz, strain 7%, and temperature 80°C; the loss modulus G" (as shown in Table 1) under different frequency scans was recorded, and the scanning frequency was used as the logarithmic horizontal axis and the loss modulus G" as the logarithmic vertical axis to establish a logarithmic relationship curve between the scanning frequency and the loss modulus G" (as shown in Table 1). Figure 1 and Figure 2 As shown, Figure 1 The logarithmic relationship curve between the scanning frequency and the loss modulus G" of IAN873-RSS, IAN873-RSSCV, IAN873-TSR and IAN873-TSRCV is shown in Figure 2. Figure 2 The logarithmic relationship curve (log10) between the scanning frequency and the loss modulus G" of Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV;

[0048] Table 1IAN873-RSS, IAN873-RSSCV, IAN873-TSR, IAN873-TSRCV, Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV

[0049] Loss modulus G" under different frequency sweeps

[0050]

[0051] Depend on Figures 1-2It can be seen that the loss modulus G" of IAN873-RSS, IAN873-RSSCV, IAN873-TSR and IAN873-TSRCV decreases with increasing frequency, and the intrinsic molecular weight distribution type of IAN873-RSS, IAN873-RSSCV, IAN873-TSR and IAN873-TSRCV is unimodal, which is consistent with the actual situation; the loss modulus G" of Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV increases with increasing frequency, and the intrinsic molecular weight distribution type of Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV is bimodal, which is consistent with the actual situation.

[0052] Example 2

[0053] 4.0 g of IAN873-RSS, IAN873-RSSCV, IAN873-TSR, IAN873-TSRCV, Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV were weighed respectively and placed in a rotorless shear rheometer for testing: the sample adjustment conditions were: frequency 0.5 Hz, strain 2.8%, temperature 100 ° C, and time 8 min; the frequency scanning conditions were: 0.1-20 Hz, strain 7%, and temperature 100 ° C; the loss modulus G" (as shown in Table 2) under different frequency scans was recorded, and the scanning frequency was used as the logarithmic horizontal axis and the loss modulus G" was used as the logarithmic vertical axis to establish a logarithmic relationship curve between the scanning frequency and the loss modulus G" (as shown in Table 2). Figure 3 and Figure 4 As shown, Figure 3 The logarithmic relationship curve between the scanning frequency and the loss modulus G" of IAN873-RSS, IAN873-RSSCV, IAN873-TSR and IAN873-TSRCV is shown in Figure 2. Figure 4 The logarithmic relationship curve (log10) between the scanning frequency and the loss modulus G" of Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV;

[0054] Table 2IAN873-RSS, IAN873-RSSCV, IAN873-TSR, IAN873-TSRCV, Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV

[0055] Loss modulus G" under different frequency sweeps

[0056]

[0057] Depend on Figures 3-4 It can be seen that the loss modulus G" of IAN873-RSS, IAN873-RSSCV, IAN873-TSR and IAN873-TSRCV decreases with increasing frequency, and the intrinsic molecular weight distribution type of IAN873-RSS, IAN873-RSSCV, IAN873-TSR and IAN873-TSRCV is unimodal, which is consistent with the actual situation; the loss modulus G" of Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV increases with increasing frequency, and the intrinsic molecular weight distribution type of Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV is bimodal, which is consistent with the actual situation.

[0058] Example 3

[0059] 4.0 g of IAN873-RSS, IAN873-RSSCV, IAN873-TSR, IAN873-TSRCV, Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV were weighed respectively and placed in a rotorless shear rheometer for testing: the sample adjustment conditions were: frequency 0.5 Hz, strain 2.8%, temperature 130 ° C, and time 8 min; the frequency scanning conditions were: 0.1-20 Hz, strain 7%, and temperature 130 ° C; the loss modulus G" (as shown in Table 3) under different frequency scans was recorded, and the scanning frequency was used as the logarithmic horizontal axis and the loss modulus G" was used as the logarithmic vertical axis to establish a logarithmic relationship curve between the scanning frequency and the loss modulus G" (as shown in Table 3). Figure 5 and Figure 6 As shown, Figure 5 The logarithmic relationship curve between the scanning frequency and the loss modulus G" of IAN873-RSS, IAN873-RSSCV, IAN873-TSR and IAN873-TSRCV is shown in Figure 2. Figure 6 The logarithmic relationship curve (log10) between the scanning frequency and the loss modulus G" of Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV;

[0060] Table 3IAN873-RSS, IAN873-RSSCV, IAN873-TSR, IAN873-TSRCV, Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV

[0061] Loss modulus G" under different frequency sweeps

[0062]

[0063] Depend on Figures 5-6 It can be seen that the loss modulus G" of IAN873-RSS, IAN873-RSSCV, IAN873-TSR and IAN873-TSRCV decreases with increasing frequency, and the intrinsic molecular weight distribution type of IAN873-RSS, IAN873-RSSCV, IAN873-TSR and IAN873-TSRCV is unimodal, which is consistent with the actual situation; the loss modulus G" of Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV increases with increasing frequency, and the intrinsic molecular weight distribution type of Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV is bimodal, which is consistent with the actual situation.

[0064] Comparative Example 1

[0065] Gel permeation chromatography (GPC) was used to characterize the molecular weight distribution of IAN873-RSS, IAN873-RSSCV, IAN873-TSR, IAN873-TSRCV, Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV. The test method was based on ISO16564-2004. The supernatant retained from the gel content test was filtered with a 1 μm filter membrane and injected into a 2 mL brown sample bottle. The molecular weight distribution was tested using gel permeation chromatography. The test conditions were: THF as the eluent, a column oven temperature of 40°C, an injection volume of 100 μL, and a flow rate of 1.0 mL / min. The test results are shown in Figure 2. Figures 7-8 As shown, Figure 7 The chromatograms of IAN873-RSS, IAN873-RSSCV, IAN873-TSR and IAN873-TSRCV are shown. Figure 8 is the chromatogram of Reyan73397-RSS, Reyan73397-RSSCV, Reyan73397-TSR and Reyan73397-TSRCV; Figures 7-8 It can be seen that the GPC test of the bimodal strain Reyan73397-RSS shows a unimodal distribution. Therefore, the present invention can trace the intrinsic molecular weight distribution of natural rubber, while the traditional method GPC test has errors.

[0066] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for testing the inherent molecular weight distribution type of natural rubber raw rubber, characterized in that: The following steps are involved: Using a rotorless shear rheometer, the natural rubber raw rubber was subjected to sample conditioning and frequency scanning in sequence to obtain a series of scanning frequencies and loss moduli; The logarithmic relationship curve between loss modulus and scanning frequency is established with scanning frequency as the logarithmic horizontal coordinate and loss modulus as the logarithmic vertical coordinate; The intrinsic molecular weight distribution type of the natural rubber raw rubber is determined by the relationship curve between the loss modulus and the scanning frequency: when the loss modulus increases with the increase of the scanning frequency, the intrinsic molecular weight distribution type of the natural rubber raw rubber is bimodal; when the loss modulus decreases with the increase of the scanning frequency, the intrinsic molecular weight distribution type of the natural rubber raw rubber is unimodal; The natural rubber raw rubber is natural rubber raw rubber that has not been roller-molded; The sample conditioning time is 8 minutes, the temperature is 80-130°C, the frequency is 0.5 Hz, and the strain is 2.8%; The frequency of the frequency sweep is 0.1-20 Hz, the temperature is 80-130° C., and the strain is 7%.

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