GB/T 46232-2025Rubber, unvulcanized — Determination of bound-rubber content (English PDF)

3.1 Combined with rubber-bound rubber

In rubber compounding, the portion of rubber that is tightly bonded to the filler.

Note. Chemical methods measure the portion of rubber that cannot be dissolved by common solvents; low-field NMR methods measure adsorption through physical and chemical bonding. That part of the rubber.

[Source. GB/T 9881-2008, 2.56, with modifications]

4.1 Low-field nuclear magnetic resonance (NMR)

Uncured rubber containing bound rubber comprises two components. a bound rubber component and an unbound rubber component (containing molecular chain physical entanglement,...

(Two parts of the free chain). The movement of rubber molecular chain segments in the bound rubber component is more restricted, resulting in faster transverse relaxation decay; the unbound rubber component...

These molecules exhibit certain molecular motion characteristics, and their transverse relaxation decay is relatively slow. The low-field nuclear magnetic resonance analyzer uses Hahn Echo sequences for acquisition.

The percentage of the combined rubber signal in the total signal indicates the content of the combined rubber. The schematic diagram of the test principle is shown in Figure 1.

Note. The Hahn Echo sequence is based on a 90°-tau-180°-tau radio frequency pulse sequence. The spin phase is flipped by a 180° pulse, correcting the phase distortion caused by magnetic field inhomogeneity.

The dispersed echoes reconverge at echo time (2tau) to form a spin echo. Indexing symbol explanation.

X --- Lateral relaxation time;

Y --- Nuclear magnetic resonance signal intensity;

A< sub>total< /sub> --- Total signal intensity of uncured rubber;

A. Signal intensity of non-bound rubber components;

A1---Binding rubber signal strength;

A2 --- Signal intensity of physical entanglement of rubber molecular chains;

A3 --- Signal intensity of free chain in rubber molecules;

t1 --- Start time of non-bonded rubber signal.

Figure 1.Schematic diagram of the low-field NMR testing principle.

4.2 Chemical Method

Uncured rubber filled with carbon black and/or silica is immersed in a solvent (usually toluene), because the rubber molecules react with the carbon black and/or silica...

The physical adsorption and chemical bonding forces on the surface of silica prevent the bound rubber in uncured rubber from being dissolved by solvents, while the unbound rubber...

It can be dissolved. The content of the bound rubber is calculated by the change in mass before and after soaking.

5.1 Reagents

Standard viscosity fluid. GB W13609, National Standard Material (NCRM).

5.2 Instruments and Equipment

5.2.1 Low-field nuclear magnetic resonance analyzers shall meet the following technical requirements.

— Magnetic field strength. 0.48T~0.52T;

— Effective spacing between magnets. not less than 35mm;

— Hydrogen probe coil inner diameter. not less than 12mm;

— Overall dead time. less than 15µs;

— Nuclear magnetic resonance analysis application software. includes pulse sequences such as FID and HahnEcho;

— Data processing software. includes Gaussian fitting algorithm;

— Magnetic field uniformity. The relaxation time of the FID signal at 50% of its original value is not less than 1ms.

5.2.2 Connector. Diameter not greater than 12mm, length not less than 180mm, no hydrogen signal.

5.2.3 Sample vial. 11.6 mm in diameter, 32 mm in height, no hydrogen signal.

5.2.4 Dry thermostat. Temperature control range is room temperature to 160°C, accuracy is 0.1°C.

5.3 Sample Preparation

Cut an appropriate amount of sample into two cylindrical specimens with a diameter of about 5 mm and a height of less than 2 cm.

5.4 Analysis Steps

5.4.1 Equipment Calibration

Before each power-on test, the standard viscosity fluid (5.1) provided by the manufacturer was used, according to the instruction manual of the low-field nuclear magnetic resonance analyzer (5.2.1). Perform calibration.

5.4.2 Test Conditions

Create a new HahnEcho sequence and set the specific parameters. Recommended device analysis conditions are as follows.

a) Sampling frequency SW. 5000kHz;

b) Cumulative count NS. 32;

c) Number of echoes TE. 40, echo time. 0.03ms~50ms.

5.4.3 Sample Determination

Set the dry thermostat to 32.0°C, connect the sample vial containing the sample to the connector (5.2.2), and place it in the dry thermostat (5.2.4).

Dry in medium for at least 5 minutes. Remove the sample vial and place it into the sample chamber of the low-field NMR analyzer. Call the Hahn Echo sequence and automatically...

Acquire signals and export raw data after acquisition.

5.4.4 Parallel Tests

Perform the above steps twice in parallel.

5.5 Result Calculation

The raw data was automatically fitted with Gaussian to obtain the signal quantities of the three components A1, A2, and A3.Combined with the mass fraction of rubber wbr, the signal quantities were calculated according to the formula... Calculate using formula (1). wbr= A1 A1 A2 A3x 100% (1) In the formula.

A1---Binding rubber signal strength;

A2 --- Signal intensity of physical entanglement of rubber molecular chains;

A3 --- Signal intensity of free chain in rubber molecules.

The average of the two test results is taken as the experimental result, and it is retained to two decimal places.

6.1 Reagents or materials

6.1.1 Toluene. Analytical grade as specified in GB/T 684.

6.1.2 Stainless steel mesh. 6µm.