Before we use Sodium Carboxymethyl Cellulose, in order to ensure the performance of the product, we need to measure it in advance. There are many measurement methods for CMC-Na, and the ashing method is the most frequently used one. In order to ensure the accuracy of the measurement, specific knowledge can be obtained from the followings.
- Principle: The purified sodium carboxymethyl cellulose is burned and ashed at (700±25)°C to obtain residual sodium oxide. The sodium oxide content is then titrated with acid and alkali, and the degree of substitution is calculated based on the sodium oxide content.
- Instruments and reagents: high temperature furnace (0~1000℃), buret (50ml), beaker (300ml), 13# glass sand core crucible (30ml), suction flask (1000ml), air pump, 0.lmol/L NaOH standard solution, 0.1mol/L HCl standard solution, 0.1% methyl red.
- Operation steps: Weigh about 1.2g of sodium carboxymethyl cellulose into a 300ml beaker, add 20ml of 0.5mol/L HCl solution to acidify, stir thoroughly for 15min until there are no particles, add a few drops of phenolphthalein indicator and then add 0.5mol/L NaOH solution to neutralize until the solution becomes red. Continue stirring until the sample is dissolved and then add 3 drops of 0.5mol/L NaOH solution. Adding 95% ethanol solution dropwise while stirring. When white precipitate appears in the test solution, quickly add about 200ml 95% ethanol solution to precipitate. Stop stirring and heat on a water bath to make the precipitate clear and coarse.
Move the precipitate into a 3# glass sand core crucible, filter it, first wash it with 80% ethanol several times (about 100ml), then wash it with 95% ethanol three times (about 60ml), suck it dry, move it into the oven and dry it at 105℃ until the mass is constant (about 3 hours), cool and weigh.
Pour the weighed dry pure CMC into a dry 30ml porcelain crucible and slowly heat it to 700°C in a high-temperature furnace and keep it for 30 minutes, take it out and cool it to room temperature.
Moisten the burning object with a small amount of distilled water, wash it several times with 100 ml distilled water, transfer it to a 250 ml beaker, slowly heat it to boiling on an electric stove, and keep it for 5 minutes. Add 2 to 3 drops of methyl red indicator and titrate to the end point with 0.1mol/L HCl standard solution.
It is known from this that the operating principle and method of Sodium Carboxymethyl Cellulose ashing method should be strictly followed, which can ensure the accuracy of product measurement and facilitate subsequent work.