MISCELLANEOUS TECHNIQUES
2
MISCELLANEOUS TECHNIQUES
*
MT 36.3 EMULSION CHARACTERISTICS AND
RE-EMULSIFICATION PROPERTIES
SCOPE
The method is suitable for determining the emulsification stability of emulsion
formed by the dispersion of emulsifiable concentrates (EC), or emulsions, oil in
water (EW) at dilution rates of 0.1 % to 5 % (Note 1).
OUTLINE OF METHOD
An emulsion of known concentration in standard water is prepared. The stability
of this emulsion is then assessed in terms of amounts of free 'oil' and/or 'cream',
which separates while the emulsion is allowed to stand undisturbed for 24 h. The
ability of the system to re-emulsify at the end of the 24 h period is also
determined.
REAGENTS
Standard Water D MT 18.1.4 unless otherwise specified
APPARATUS
Measuring cylinders 100 ml, glass stoppered. The volume between the 100 ml
graduation mark and the bottom of the stopper should be not more than 40 ml
and not less than 30 ml. The apparatus must be clean and free from grease.
Water bath capable of maintaining a specified temperature (Note 2) and large
enough to allow several 100 ml measuring cylinders to be immersed in an
upright position in the water to the 100 ml mark (Note 3).
Adjustable lamp fitted with a bulb of sufficient brightness.
Measuring cylinders or pipettes graduated up to 5 ml
*
CIPAC method 2000. Prepared by the German Formulation Panel (DAPF). Chairman: G Menschel.
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MISCELLANEOUS TECHNIQUES
PROCEDURE
(i) Initial emulsification. Fill a measuring cylinder (100 ml) approximately to the
95 ml mark with Standard water at the specified temperature. Pour the
emulsifiable formulation (ml-amount to meet the recommended concentration
for the use as specified (Note 1) at the same temperature as the standard water)
gently onto the surface of the water and fill up the cylinder to 100 ml with
standard water. Replace the stopper and invert the cylinder once (Note 4). After
30 s observe whether the mixture has emulsified spontaneously giving 100 ml of
an emulsion which appears, on visual examination, to be uniform or incomplete.
(ii) Emulsion stability on standing. Invert the cylinder 10 times (Note 4) and
allow the cylinder and its contents to stand undisturbed in the constant
temperature bath at the specified temperature for 24 h (Note 2). Record the
volume (Note 5), if any, of free oil (Note 6), and/or cream formed either at the
top or the bottom of the emulsion, after standing for 30 min, 2 h and 24 h.
(iii) Re-emulsification after standing for 24 h. At the end of the 24 h period
invert the cylinder 10 times (Note 4). Allow to stand for 30 s, then observe
whether any free 'oil', and/or 'cream' or solid matter (Note 7) found after
standing for 24 h is re-emulsified, giving 100 ml of an emulsion which appears,
on visual examination (Note 6), to be uniform.
(iv) Final emulsion stability. Allow the cylinder to remain undisturbed for a
further period of 30 min. Record the volume, if any, of free 'oil', and/or 'cream'
or solid matter present at the end of the 30 min period.
Note 1 As test concentration the concentration should be used, which is
recommended in the directions for use supplied with the product.
Where several concentrations are recommended, the highest and lowest
concentrations, coming with the scope of the method, should be used.
Note 2 The temperature should be consistent with the use conditions of the
product. Often 30° ± 2° C is readily maintained in a thermostated water
bath. Generally, however. Lower test temperatures (e.g. ambient
temperature) are more relevant to practical conditions. For testing at
ambient temperatures no water bath is needed.
Note 3 Any vibration can alter the properties of the dilute emulsion in the
cylinder. The cylinder should therefore be supported or clamped in
such a way that it is not in contact with the body of the water bath. The
stirrer assembly should preferably be clamped independently of the
water bath.
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MISCELLANEOUS TECHNIQUES
Note 4 The expression 'invert the cylinder' implies that the stoppered cylinder
is tipped by hand 180 degrees, and is then brought back to its original
position, the whole operation being completed in approximately
2 seconds.
Note 5 An adjustable lamp, fitted with a 60 watt pearl bulb, should be used to
illuminate the cylinder. The position and angle of the light should be
adjusted for optimum viewing of the phase boundary. It is often easier
to see this by reflected, rather than by transmitted light.
Note 6 If initially, difficulty is experienced in distinguishing between oil and
cream, a dye soluble in the oil phase may be used, but the final tests
should be carried out without the addition of the dye. It has been found
out that dyes which give a deep blue solution in aromatic hydrocarbon
solvents, e.g. Oil Blue SWS, 1,4-bis(isopropylamino)anthraquinone
(CI 61551), are most suitable fort his purpose. The dye (0.1 g/100 ml)
should be added to the emulsion concentrate before carrying out the
test.
If oil is present, then the dye will colour it deep blue; if extensive
creaming has occurred, the dye will give a pale blue layer; if little or no
creaming has occurred, then no definite colour band will be produced.
Note 7 If solid matter is observed, it is advisable to confirm that under
practical use conditions, no adverse effects are generated.
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