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
Devansh Gupta
M.Sc 2nd
Semester

2. Introduction
Para rubber tree (Hevea brasiliensis) is a major commercial
source of natural rubber, which is used as a raw material for
various industries, owing to its unique properties which cannot
be replaced entirely by synthetic rubber. The latex tapped from a
Para rubber tree is composed of two main phases, hydrocarbon
(poly-isoprene) and non-rubber constituting mainly
carbohydrates, proteins and lipids in aqueous serum phase.
Bacterial infection of fresh Natural Rubber latex can arise from
many sources such as the atmosphere, the bark of the tree, and
utensils used for tapping and the bacteria can grow rapidly,
producing volatile fatty acids from carbohydrates present in the
latex.
An increase in volatile fatty acid causes latex to deteriorate,
which affects the stability of latex. Therefore, preservation of latex
quality is necessary. Ammonia and Potassium Hydroxide are
generally used as the main preservative in both field and
concentrated latex.
Concentrated latex can be categorised into three types
based on ammonia content or alkalinity, calculated as the
percentage of ammonia in latex. Low ammonia latex contains
ammonia not more than 0.29%, medium ammonia latex has
ammonia between 0.30-0.59%, and high ammonia latex contains
ammonia at least 0.60%.
Each type of latex is suitable for use in a different process
because the alkalinity content in latex has an effect on such
properties as colour, shelf-life and colloidal stability.
In the latex industry, alkalinity is determined by a standard
analytical method, acid-based titration, this method requires
chemicals and skilled analysts, as it is difficult to identify the
end-point. When the pH of the reaction changes the methyl red
indicator from red to yellow. Complete method is shown below.
Exactly What Happens In This 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.

3. REQUIREMENTS
1) pH Meter - equipped with glass electrode cell and saturated
calomel and capable of being read to the accuracy 0.02 unit.
2) Digital Balance
3) Weighing Bottle, Burette, beakers & Glass rod
4) 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
5) 0.1 N Sulphuric acid or Hydrochloric acid
6) Methyl red as indicator solution
Procedure
1) In the first step Take 5 to 10 gram of the well-mixed sample
of latex in a weighing bottle.
2) Take a 500 ml beaker and add 200 ml water in it.
3) Mix 10 ml stabilizer in this water and stir with a glass rod
for better distribution.
4) Pour the latex into the beaker from the weighing bottle and
Stir to distribute it in the stabilizer solution.
5) Insert the electrodes of a calibrated pH meter in the solution
and start continuous stirring.
6) Set up a burette with 0.1N Sulphuric acid or Hydrochloric
acid in it.
7) 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.
8) 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.
9) Here the objective of the stabilizer is to prevent coagulation
of the latex on addition of acid.

4. Calculation Of % Of Alkalinity
On the basis of preservative added in the latex there are two
ways to calculate the alkalinity.
1) If the latex is preserved with ammonia, calculate its
alkalinity as grams of ammonia (NH3) 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)
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.
2) 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.
Alkalinity (As NH3) =
1.7 × N × V
m
Alkalinity (As KOH) =
5.61 × N × V
m