The method of testing the viscosity of food-grade cellulose ethers usually involves preparing solutions, measuring the viscosity, and analyzing the results. The following are the specific steps and methods:

1. Sample preparation

• Dissolution process: Add the cellulose ether sample to an appropriate amount of deionized water, usually to prepare a 2% solution. For example, weigh 6.0g of cellulose ether and add it to 294g of water, stirring until it is completely dissolved.
• Temperature control: The dissolution process usually needs to be carried out at a specific temperature. For example, for hydroxypropyl methylcellulose (HPMC), the sample can be added to 60℃ hot water during dissolution. Stir until it swells. Then cool to room temperature and continue stirring until a homogeneous solution is formed.
• Constant temperature treatment: The prepared solution needs to be left at the experimental temperature (such as 20±2℃) for 3-4 hours. To ensure that the solution reaches a stable state.

2. Instruments and equipment

• Rotational viscometer: NDJ-1 or NDJ-4 rotational viscometers are commonly used. These devices comply with GB/T 1723 and ASTM D4212 standards. The measurement range is usually between 20 and 100,000 mPa·s.
• Constant temperature water bath: used to control the temperature of the solution. Ensure the consistency of the test conditions.
• Stirring equipment: such as a magnetic stirrer or an electric stirrer. Used in the dissolution and mixing process.

3. Viscosity test steps

• Solution preparation: Add the cellulose ether powder to a beaker filled with water and stir until it is completely dissolved. For example, for hydroxyethyl cellulose (HEC), the sample can be added to 60°C hot water. Stir until it swells. Then cool to room temperature and continue stirring until a homogeneous solution is formed.
• Constant temperature treatment: Place the prepared solution in a constant temperature water bath. Ensure that the temperature is stable within the range required by the experiment (such as 20±0.2°C).
• Viscosity measurement: Use a rotational viscometer to measure the viscosity of the solution. Select the appropriate rotor number and speed during the test. Ensure that the measured value is within the effective range of the instrument. It usually takes 3-5 minutes to stand before starting the measurement.

4. Result calculation and analysis

• Calculation of viscosity value: Calculate the viscosity value of the solution according to the reading of the viscometer, usually in mPa·s.
• Result analysis: The viscosity value reflects the molecular weight and thickening performance of the cellulose ether. The higher the viscosity, the stronger the thickening ability of the cellulose ether.

5. Notes

• Dissolution time: Ensure that the sample is fully dissolved to avoid deviation in the measurement results due to incomplete dissolution.
• Temperature control: Temperature has a great influence on viscosity, and the test temperature needs to be strictly controlled.
• Sample uniformity: Avoid local concentration differences in the solution due to uneven stirring, which affects the measurement results.
Through the above steps, the viscosity of food-grade cellulose ether can be accurately tested and its quality and performance can be evaluated. In specific operations, the dissolution temperature and stirring time can be adjusted according to the type of cellulose ether (such as HPMC, CMC-Na, etc.).