DETERMINATION OF DRY RUBBER CONTENT (DRC)

IS: 3708(PART 1)-1985

DETERMINATION OF DRY RUBBER CONTENT

1. SCOPE

1.1 This standard method (part 1) prescribes a method for the determination of dry rubber content
of natural rubber latex of hevea brasiliensis, uncompounded and unvulcanized, and subjected to
some type of concentration process other than heat concentration and which may contain
preservatives.
1.2 The method is not necessarily suitable for compounded or vulcanized natural rubber latex and
is not applicable to synthetic rubber lattices.

2. OUTLINE OF THE METHOD

2.1 The latex is diluted to approximately 20 percent and then coagulated with a suitable coagulating
agent. The coagulum is dried at constant temperature and weighed.

3. APPARATUS

3.1 Chemical Balance
3.2 Air Oven- capable of being maintained at a temperature of 70 ±2 °C
3.3 Water Bath
3.4 Desiccator

4. REAGENTS

4.1 Acetic Acid-Two percent solution(m/v)(see IS:695-1975)
4.2 Rectified Spirit-see IS : 323-1959

5. PROCEDURE

5.1 Duplicate determination shall be done on each sample.
5.2 Weigh by difference from a weighing bottle, about 10 g of the well-mixed sample accurately to 1
mg into a suitable container such as beaker. Add water until the total solids content of the latex
is about 20 percent. Add up to 8 ml of acetic acid per gram of sample, gently stirring over a
period of 5 minutes. Keep the solution undisturbed for about 15 minutes at a temperature a
little below boiling. If the serum remains milky, add 5 ml of rectified spirit and gently stir. When
the serum s clear, collect any small particles of coagulum by rubbing with the main bulk. Wash
the coagulum with running water or with at least six changes of water until neutral to litmus.
Press the coagulum to expel water and to obtain a uniform sheet not exceeding 2 mm in
thickness, either by hand roller or mechanical rollers. Dry the coagulum at a temperature of
approximately 70 ± 2 °C until it has no white patches. Cool in desiccator and weigh. Repeat drying
operation until the loss in mass s less than 1 mg
Note-freshly preserved latex may be coagulated with 0.5 percent acetic acid by adding up to 15 ml of acid per gram of
sample.

6. CALCULATION

6.1 Calculate the dry rubber content (DRC) of the sample as follows:
Dry Rubber Content, percent by mass = M1 ×100
M2
Where,
M1= mass in grams of dry coagulum, and
M2= mass in grams of the sample taken for the test.
Note—A difference of 0.2 percent between the results of duplicate determinations on sample is not considered significant.

IS: 3708 (Part 4) – 1986

DETERMINATION OF VOLATILE FATTY ACID

1. SCOPE

1.1 This standard prescribes a method for the determination of volatile fatty acid number of
natural rubber latex which contains preservative agents and has been subjected to same type
of concentration process.
1.2 This method is not necessarily suitable for lattices from natural sources, sources other than
Hevea brasiliensis and is not applicable to compounded latex, vulcanized latex, artificial
dispersions of rubber or synthetic rubber lattices.

2. TERMINOLOGY

2.0 For the purpose of this test, the following definition shall apply.
2.1 Volatile Fatty Acid (VFA) Number of Latex - the number of grams of potassium hydroxide
equivalent to the volatile fatty acid in latex containing 100g of total solids.

3. OUTLINE OF THE METHOD

3.1 The latex is coagulated with ammonium sulphate and the resultant serum is separated and
acidified with sulphuric acid. The serum is steam distilled the volatile acids percent in the latex
are determined by acidimetric titration of the distillate.

4. APPARATUS

4.1 Stream jacketed distillation apparatus (Markham still) conforming essentially to figure 1. As
an alternative to the one –piece apparatus illustrated, a ground glass joined may be inserted
between the distillation vessel and the condenser.

5. REAGENTS

5.1 Ammonium sulphate solution – 30 percent (min) aqueous solution.
5.2 Sulphuric acid, Dilute – approximately 50 percent (min) aqueous solution.
5.3 Standard Barium Hydroxide Solution – 0.01 N. The solution is standardized by titration with
potassium hydrogen phthalate and stored in the absence of Carbon dioxide.
5.4 Indicator – The indicators bromo thymol blue or Phenolphthalein may be used. Bromo
thymol blue shall be used as 0.5 percent solution of the indicator in water and phenolphthalein
shall be used as 0.5 percent solution in a mixture of equal volumes of ethanol and water.
5.5 Anti foaming Agent – Silicone type.

6. PROCEDURE

6.1 Weigh about 50g of latex of known dry rubber and total solid content to the nearest 0.1gm
in to a beaker. Add 50ml of ammonium sulphate solution while stirring the latex. Either place
the beaker on a steam bath or immerse the beaker in a 70°C water bath, and continue stirring
the latex until its coagulates. Cover the beaker with a watch glass and leave it in the bath for
the total period of 15min. Decant the serum which exudes through a dry filter. Transfer the
coagulum in to a mortar and press out more serum by kneading it with a pestle. Filter this
serum through the same filter. Pipette 25ml of the filtered serum in to a dry 50ml conical flask
and acidify it by accurately adding 5ml of dilute sulphuric acid. Mix well by swirling the flask.
6.2 Pass steam through the apparatus for at least 15min. With steam passing through the outer
jacket of the apparatus, introduce in to the inner tube 10ml of the acidified serum by pipette. If
foaming is a difficulty, one drop of suitable anti foaming agent may be added. Place a 100ml of
graduated cylinder under the tip of the condenser to receive the distillate. Partially close the
steam outlet to divert steam in to the inner tube. Pass steam gently at first, then fully close the
steam outlet and continue distilling at a rate of 3 to 5ml/ min until 100ml of distillate has been
collected. Transfer the distillate to a 250ml conical flask and aerate the distillate by passing
through it a stream of air free from carbon dioxide at a rate of 200 to 300ml/min for
approximately 3min. Titrate with 0.01N barium hydroxide solution using one of the indicators
specified. Run a blank test by substituting 20ml of water for the 50g of concentrated latex.

7. CALCULATION

7.1 The volatile fatty acid (VFA) number is calculated as follows.
VFA = [67.32×N×V] × [50+ m (100-DRC)]
M ×TS 100 D
Where
N = normality of the barium hydroxide solution
V = final volume of barium hydroxide solution required to neutralize the distillate in
Milliliters, after correction for blank;
DRC = percentage dry rubber in the latex;
m = mass of the test portion in grams;
D = Density of the serum in gram/ ml;
= 1.02 for any latex except heat concentrated latex; and
TS = percentage total solids in the latex.
7.1.1 A difference in VFA number between duplicate determinations on the same sample is not
considered significant, if it is less than 0.01unit where the actual VFA number is 0.10 or less, or
if it is less than 10 percentage of actual VFA number where the VFA number is greater than 0.10
units.

IS: 9316 (Part 3)-1987

DETERMINATION OF COAGULAM CONTENT

(SIEVE RESIDUE)

1. SCOPE

1.1 This standard (part 3) prescribes a method for the determination of the coagulum content (sieve
residue) of natural rubber latex concentrate containing preservative agents and also for the
determination of the coagulum content (sieve residue) of synthetic rubber lattices.

2. TERMINOLOGY

2.0 For the purpose of this standard, the following definition shall apply.
2.1 Coagulum; Sieve Residue- The material, comprising pieces of coagulated rubber, latex skin and
coarse foreign matter, retained under the conditions of the test on a stainless steel wire cloth with
an average aperture width of 180± 10 μm.

3. APPARATUS

3.1 Test Filter- consisting of a disc of stainless steel wire cloth with an average aperture width of
180±10μm (180 micron IS Sieve)
(See IS: 460(part 1)-1978*)
3.2 Two Stainless Steel Rings- of equal internal diameter between 25 and 50 mm.
3.3 Oven- capable of being controlled at 105±2°c
3.4 Desiccators
3.5 Beaker- of capacity 600-ml which has a lip.

4. REAGENTS

4.1 Potassium Oleate or Ammonium Laurate- surfactant solution 5 percent (m / m), of pH 10 (for
use with natural rubber lattices).
4.2 Water Soluble Ethoxylated Alkyl Phenol- surfactant solution 5 percent (m/ m) (for use with
synthetic rubber lattices).
4.3 Litmus paper

5. PROCEDURE

5.1 Weigh 200 1g of the laboratory sample into the beaker. Add 200ml of the appropriate surfactant
solution and mix thoroughly. Dry the test filter to constant mass in the oven, controlled at 105 ±2 °c
and weigh to the nearest milligram. Record the mass (m1). Firmly clamp the test filter between the
stainless steel rings.
Note – if the wire cloth is not clean, immerse it for 2 min in boiling nitric acid (density 1.42 g/ml) and wash it with water
before drying it to constant mass and weighing
5.2 Wet the test filter with the same surfactant solution and pour the latex-surfactant mixture into
the test filter. Wash the residue on the wire cloth with the same surfactant solution until it is free
from latex. With natural rubber latex concentrate, wash with water until the washings are neutral to
litmus. With synthetic rubber latex, wash with 200ml of water. Carefully remove the wire cloth
containing the wet coagulum from the clamp and swab the underside with filter paper.
5.3 Heat the wire cloth and coagulum for 30 min in the oven, controlled at 105± 2 °c allow cooling in
the desiccator and weighing. Return to the oven at 105± 2 °c for a further period of 15 min, allow to
cool and re-weigh. Repeat the drying for 15 min periods until the loss in mass between successive
weightings is less than 1 mg.

6. CALCULATION

6.1 The coagulum content, expressed as a percentage by mass of the latex, is given in the following
formula:
M2― M1 × 100
M0
Where,
M0 = Mass, in grams, of the test portion;
M1 = Mass, in grams, of the wire cloth; and
M2 = Mass, in grams, of the wire cloth plus the dried coagulum.
6.2 If the results of duplicate determination do not agree to within 0.01 percent (m/m), carry out
two further determinations.

IS: 3708 (part 6)-1985

DETERMINATION OF MECHANICAL STABILITY

1. SCOPE

1.1 This standard (part6) prescribes a method for the determination of the mechanical stability of
natural rubber latex which contains preservative agents and which has been subjected to some
type of concentration process. it is also applicable to vulcanized natural rubber latex.
1.1.1 This method is not necessarily suitable for lattices preserved with potassium hydroxide,
lattices from natural sources other than hevea brasiliensis,or for compounded latex, or
artificial dispersions of rubber, and is not applicable to synthetic rubber lattices

2. OUTLINE OF THE METHOD

2.1 Latex is stirred at a high speed and the time required to produce obvious signs of clotting is
recorded as a measure of mechanical stability.

3. APPARATUS

3.0 The apparatus shall consist of the following.
3.1 Container- a latex container consist of a flat-bottomed cylindrical vessel 127 mm high and having
a diameter of 56 to 60 mm. the inner surface shall be smooth and a transparent container is
preferred.
3.2 Stirring Device- The stirring device consist of a vertical stainless steel shaft 15.2 cm long and
tapering to 6.35 mm at its lower end, where a horizontal smooth stainless steel disk 21 ±0.025 mm
in diameter and 1.55± 0.05 mm thick is attached by means of a threaded stud at the exact centre of
the disk.
3.3 Holding Device- An arrangement, for holding the latex container so that the axis of rotating shaft
is concentric with that of the latex container and the bottom of the stirring disk, is 12.5 ±2.5 mm
from the bottom inside of the latex container.
3.4 The apparatus is designed to maintain a stirring speed of 14000±200rev/min throughout the
test. The speed should be checked while a test is progress. At this speed the shaft shall not run more
than 0.25 mm out of true
3.5 Stainless steel sieves- 180-micron IS sieve [see IS; 460(PART 1)-1978*]
3.6 Heating Device- Any one of the following devices may be used.
3.6.1 A water bath, capable of maintaining a temperature of 60 to 80°c
3.6.2 A glass tube, bent to a shape suitable for inspection in the latex, together with a means of
circulating water at a temperature of 60 to 80°c through the tube.

4. REAGENTS

4.1 Ammonia solution—if the latex has an alkalinity above 0.30 percent (calculated relative to the
latex), a 1.6 percent aqueous ammonia (NH₃) solution shall be used. If the latex has an alkalinity
of less than 0.30 percent (calculated relative to the latex), a0.6 percent aqueous ammonia (NH₃)
solution shall be used.

5. PROCEDURE

5.1 Carry out the determination within 24 h of first opening the sample bottle. If the total solid
content and alkalinity of the latex are not known, determine them in accordance with
IS:9316(Part 4)-1979¥ and IS :3708(Part 4 )-1985 ¥ respectively
Note- If the concentration of the carbon dioxide in the atmosphere in the vicinity of the mechanical stability
measuring apparatus (3.1) is above normal [above 0.03 percent (v/v)], the mechanical stability time of the latex will be
reduced. This effect may be pronounced at carbon dioxide concentrations as low as0.05 percent (v/v). High carbon dioxide
concentration in the atmosphere may be caused by the proximity of any apparatus which generates carbon dioxide, such
as certain gas heaters or oil heaters.
5.2 Dilute100 g of well-mixed sample, in a glass beaker, to 55.0 ±0.2 percent total solids content
with the appropriate ammonia solution as specified in 4.1 without delay, warm the diluted latex
with gentle stirring quickly to 36 to 37°c by one of the means of heating specified in 3.6.
Immediately filter the diluted and warmed latex through the stainless steel sieve and weigh
80.0± 0.5 g of the filtered latex into the container. Check that the temperature of the latex is
35± 1°c. Place the container in position and stir the latex, ensuring that the speed of the stirrer is
14000±200 rev/min throughout the test, until the end-point is reached. The arrival of the endpoint
is preceded by a marked decreased in the depth of the latex at the vertex around the
stirring shaft. Determine the end-point by dipping a clean glass rod into the latex at intervals of
approximately 15 seconds and drawing it gently over the palm of the hand. Take the end-point
as the first appearance of flocculum. Confirm the end-point by the presence of an increased
amount of flocculum in a sample taken after stirring the latex for an additional 15 seconds.

6. EXPRESSION OF RESULTS

6.1 Express the mechanical stability time of the latex as the number of seconds between the
beginning of stirring and the end-point.
6.2 The results of duplicate determinations shall agree within 5 percent of their mean value.

IS: 3078 (Part 4) – 1985

DETERMINATION OF TOTAL ALKALINITY

1. SCOPE

1.1 This standard prescribes a method for the determination of total alkalinity of natural rubber
latex of Hevea brasiliensis, uncompounded and unvulcanized and subjected to some type of
concentration process other than heat concentration and which may contain preservatives.

2. OUTLINE OF THE METHOD

2.1 Latex is titrated to pH 6.0 in the presence of a stabilizer, either electrometrically, or
alternatively with methyl red as visual indicator and its alkalinity calculated from the quantity of
acid which is required

3. APPARATUS

3.1 PH Meter-equipped with glass electrode and saturated calomel cell and capable of being
read to .02unit.
3.2 Chemical balance
3.3 Weighing bottle
3.4 Burette

4. REAGENTS

4.1Emulsion stabilizer- 5 percent solution of a non-ionic stabilizer of the ethylene oxide
condensate type .Before use, the PH of the solution shall be adjusted to a value of 6.0±0.1.
4.2 Sulphuric acid or Hydrochloric acid- 0.1N

5. PROCEDURE

5.1 Take between 5gm and 10 gm of well mixed sample in a weighing bottle fitted with a
stopper. Weigh to the nearest .01g. To a 500ml squat beaker add 200 ml of water. Mix with
water 10 ml of stabilizer solution. Stir the water with a glass road to distribute the stabilizer.
Pour the latex in to the beaker from the weighing bottle, restopper the bottle and re weigh to
obtain the mass of latex added by difference. Stir to distribute the latex in the stabilizer
solution. Insert the electrodes of the standardized PH meter and, with continual stirring, add
from a burette the sulphuric acid or hydrochloric acid solution until the PH is reduced to a value
of 6.0±.05.Add the acid drop by drop on approaching the end point.
5.2 As an alternative to electrometric titration, use methyl red as visual indicator, taking the
end point as the colour change to pink.

6. CALCULATION

6.0 Calculate the alkalinity of the latex as specified in 6.1 or 6.2 whichever is appropriate.
6.1 If the latex is preserved with ammonia, calculate its alkalinity as grams of ammonia per
100Kg of latex, as follows.
Alkalinity (as NH3) = 1.7×N×V
M
Where
N= normality of the acid used
V= volume in ml of acid used
m= mass in gm of the test portion
The result of the duplicate determinations shall not differ by more than .02 unit where the
actual alkalinity is above 0.5 unit, or shall not differ by more than .01 unit where the actual
alkalinity is 0.5 unit or less.

IS: 9316 (Part 4) – 1988

DETERMINATION OF TOTAL SOLID CONTENT

1. SCOPE

1.1 This standard prescribes a method for determination of total solid content of natural rubber
latex concentrates whi8ch contains preservative agent and which has been prepared by some
type of concentration process, and also for determination of total solids content of synthetic
rubber lattices.
1.1.1 The method is not necessarily suitable for lattices from natural sources other than Hevea
brasiliensis or for compounded latex, vulcanized latex or artificial dispersion of rubber.

2. METHOD FOR TAKING OUT SAMPLES

2.1 The method for taking out samples shall be in accordance with the method prescribed in IS :
9316 (part 5) – 1988.

3. OUTLINE OF THE METHOD

3.1 A test portion is heated to constant mass in an oven under specified condition, either at
atmospheric pressure or under vacuum, depending on the type of latex. The total solids
content is determined by weighing before and after heating.

4. APPARATUS

4.1 Glass Petri Dish
4.2 Oven – Capable of being maintained at 70 ± 2°C or 105 ± 2°C.
4.3 Vacuum Oven – Capable of being maintained at 125 ± 2°C.

5. PROCEDURE

5.1 For natural rubber latex concentrate, proceed according to 5.1.1 and for synthetic rubber
latex proceed according to 5.1.1 or 5.1.2.
5.1.1 Heating at Atmospheric Pressure – Weigh, to the nearest 1mg, a dish, together with its
cover. Pour in to the dish 2± 0.5g of latex replace the cover and weigh to the nearest 1mg.
gently swirl the contents of the dish to ensure that the latex covers the bottom. If desired,
approximately 1ml of distilled water or water of equivalent purity may be added mixed well
with the latex by swirling. Place the dish uncovered in the oven so that it is horizontal and heat
it at either 70± 2°C or 105 ± 2°C until the sample has lost its whiteness, or for 16h or 2h
respectively. Allow to cool in desiccators, replace the cover and weigh. Return the dish,
uncovered, to the oven for 30min if the drying temperature 70± 2°C or for 15min if the drying
temperature is 105± 2°C. Allow to cool in desiccators, replace the cover and reweigh. Repeat
the drying procedure at intervals of 30min or 15min, as appropriate, until the loss in mass
between two successive weightings is less than 1mg.
5.1.2 Heating at reduced pressure – Weigh, to the nearest 1mg, a dish together with its cover.
Pour in to the dish 1± 0.2gm of latex, replace the cover and weigh to the nearest 0.1mg.
Remove the cover add 1ml of distilled water or water of equivalent purity and mix well by
swirling to ensure that the latex covers the bottom of the dish.
Place the dish, uncovered in the vacuum oven so that it is horizontal. Reduce the
pressure slowly, to avoid foaming and splattering, and heat at 125 ± 2°C for 45 to 60min at a
pressure below 20kPa. Allow to cool in a desiccator, replace the cover and weigh. Repeat the
drying procedure at intervals of 15min until the loss in mass between two successive weighing
is less than 0.5mg.

6. CALCULATION

6.1 Calculate the total solids content (TSC), expressed as percentage by mass, using the
formula.
TSC, percentage by mass = M1 × 100
Where M0
M0 = mass, in g, of the test portion; and
M1 = mass, in g, of the dried material.
NOTE – The result of duplicate determinations shall not differ by more than 0.2%

7. TEST REPORT

7.1 The test report shall include the following particulars:
a) Reference to this standard;
b) Identification of the test sample;
c) The results, and the form in which they are expressed;
d) Any unusual features noted during the determination; and
e) Any operation not included in this standard to which reference is made, or regarded as
optional.