Solubilization-emulsification mechanisms of detergency

C.A. Miller and K.H. Raney/Colloids Surfaces A: Physicochem. Eng. Aspects 74 (1993) 169-215 207
Fig. 45. Removal of triolein from 65/35 polyestercotton
fabric by washing with pure non-ionic
surfactants [48].
Above 50ºC, detergency drops off sharply. C 12E 5
yielded optimum detergency at still higher
temperatures, with a rather sharp peak in
performance occurring at 65ºC.
The optimum detergency temperature ranges
for both C 12E 4 and C 12E 5 are higher than the
ODTs found with hexadecane soil. At 65ºC with
C 12E 5, optimum detergency corresponds to the
temperature at which the D phase forms in that
system, i.e. the PIT. With C 12E 4, no sharp peak
in performance is noted because the D phase
forms in that system only for a very narrow
temperature range [48]. The decrease in
detergency at high temperatures (above 50ºC for
C 12E 4 and 65ºC for C 12E 5) corresponds to the
regime where the surfactant solubility in the
triolein phase increases significantly and a
water-in-oil microemulsion forms, i.e. where
little if any solubilization of oil into the washing
solution occurs.
Detergency studies have also been performed
in which TAA was added to the washing
solution at levels up to 20% relative to the
surfactant [52]. This study was performed to
determine if the addition of TAA could increase
triolein removal by promoting the formation of
the D phase during the washing process. The
levels of soil removal were found by extracting
the washed fabric swatches (both 100%
polyester and 65/35 polyester-cotton) with
hexane. For C 12E 4, triolein removal was poor at
50ºC and was unaffected by the addition of
TAA. Soil removal was much greater at 35ºC,
with the addition of 20% TAA providing only a
slight improvement when compared with
detergency with C 12E 4 alone. The lack of
significant performance enhancement was
attributed to the high water solubility of TAA,
which limits its effectiveness in highly dilute
surfactant solutions. Formation of the D phase
in the oil drop-contacting studies (see Fig. 31)
apparently occurred due to the higher
concentration of surfactant and TAA used in
that study.
A similar dependence of soil removal on
temperature was observed when the same
surfactants were used to remove a soil mixture
containing 1/1 hexadecane-triolein. In this
study, the triolein was labeled with tritium and
the hexadecane was labeled with carbon-14 to
allow independent measurement of the removal
of the two components. The results of that study
are shown in Fig. 46. When compared with the
results in Fig. 45, somewhat higher removal
levels of triolein were found from the soil
mixture. Also of interest is that removal of hexa-
Fig. 46. Removal of triolein and n-hexadecane from
65/35 polyester-cotton fabric by washing with pure
non-ionic surfactants [48]. Soil contains 50 wt.%
triolein.