Measurement Total alkalinity of rubber

The total alkalinity (TA) is a measure of how much of the alkaline substances present in the solution of sample rubber material.

1. Measurement Of Total Alkalinity Of Rubber & Latex Presented by Devansh Gupta M.Sc Polymer Science Semester 2

2. Introduction The total alkalinity (TA) is a measure of how much of the alkaline substances present in the solution of sample rubber material. In other words we can say that alkalinity refers to the capability of the solution of rubber material to neutralize acid. Ammonia (NH 3 ) or Potassium Hydroxide (KOH) are the main preservative that is added to concentrated latex to prevent the deterioration of properties and coagulation of latex . Almost all factories monitor NH 3   and KOH content or alkalinity during processing, as it is an important parameter for application purposes. Alkalinity is determined by the standard analytical method, acid-based titration.

3. How To Determine Alkalinity ? This standard IS : 3708 (Part 4) describes a method for the determination of total alkalinity of natural, uncom­pounded and unvulcanised rubber. OUTLINE OF THE METHOD Here in this method Natural rubber is titrated to pH 6.0 in the presence of a stabilizer, either electrometrically , or visually with methyl red as indicator, and the alkalinity is calculated from the quantity of acid which is required in the titration.

4. REQUIREMENTS pH Meter - equipped with glass electrode cell and saturated calomel and capable of being read to the accuracy 0.02 unit . Digital Balance, Weighing Bottle, Burette, beakers & Glass rod Emulsion Stabilizer – 5% solution of a non-ionic ethylene oxide, Before use the pH of the solution shall be adjusted to a value of 6.0 ± 0.1 0.1 N Sulphuric acid or Hydrochloric acid Methyl red as indicator solution

5. Method Of Determination In the first step Take 5 to 10 gram of the well-mixed sample of latex in a weighing bottle. Take a 500 ml beaker and add 200 ml water in it. Mix 10 ml stabilizer in this water and stir with a glass rod for better distribution. Pour the latex into the beaker from the weighing bottle and Stir to distribute it in the stabilizer solution. Insert the electrodes of a calibrated pH meter in the solution and start continuous stirring. Set up a burette with 0.1N Sulphuric acid or Hydrochloric acid in it.

6. Add the acid drop by drop in the beaker until the pH of the solution is reduced to a value of 6.0 ± 0.05. As an alternative to e1ectrometric titration, we can also use methyl red as visual indicator , taking the end-point as the colour change from red to yellow. Here the objective of the stabilizer is to prevent coagulation of the l atex on addition of acid .

7. Calculation On the basis of preservative added in the latex there are two ways to calculate the alkalinity. If the latex is preserved with ammonia, calculate its alkalinity as grams of ammonia ( NH 3 ) per 100 grams of latex, as follows: Where, N = normality of the acid used V = volume of acid used in titration ( v alue in ml) M = mass of test sample (value in gram) The results of each determinations shall not differ by more than 0.02 unit where the actual alkalinity is above 0.5 unit, or shall not differ by more than 0.01 unit where the actual alkalinity is 0.5 unit or less.  

8. If the latex is preserved with potassium hydroxide, calculate its alkalinity as grams of potassium hydroxide (KOH) per 100 grams of latex, as follows:   Where, N = normality of the acid used V = volume of acid used in titration (value in ml) M = mass of test sample (value in gram) Here, the results of each determinations shall not differ by more than 0.03 unit.

9. Sources Indian Standard 3708 (1985), Methods Of Test For Natural Rubber Latex Part 4 Determination Of Total Alkalinity