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
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.
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.
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.
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.
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.
beginning of stirring and the end-point.
6.2 The results of duplicate determinations shall agree within 5 percent of their mean value.
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