Use Of New Renewable Resource For Low VOC Enamel
March 2016 www.coatingsworld.com Coatings World | 93
the initial study was carried out on white
paint, it has been extended further to formulations of colored enamels, e.g., Blue
(Phiroza Blue) and Grey (Smoke Grey)
based on a combination of organic and
inorganic pigments, wherein the extent of
flocculation was studied.
Experimental
Tree extract, or sap, is collected from
Date Palm trees and is normally sweet,
milky white and translucent, with nearly
neutral pH. Initially the sap is free of
microorganisms; however, environmental contamination leads to fermentation
converting it into acids and alcohol.2
Increased temperatures help in rapid
growth of the microorganisms; however,
even storage in lower temperatures do
not help once contaminated.
Although the Sweet Sap has been used
successfully in making emulsions, and
subsequently paints, the major challenge
was to stabilize it by preventing the initiation of fermentation. Three different
means were tried to stabilize the Sweet
Sap to prevent fermentation: (a) doping
with amino alcohol and maintaining at
higher pH; (b) addition of 5% methylated spirit (Trial 1); addition of 2% fungicides (Trial 2).
The first approach, caused a brown
coloration on storage and was discarded
after four months of storage. Studies have
continued with the other two routes.
Clearly it is different from the standard which is visible from the fingerprint
region. The same exercise was also carried out after ten months of sample preservation. The stability of the Sweet Sap
after 10 months was also checked by
FTIR analysis.
In this system of two immiscible liq-
uids, water molecules are dispersed in the
continuous phase of a long oil alkyd. The
experimental Sweet Sap is added to the
alkyd medium thinned with mineral tur-
pentine oil at 600 to 1000 rpm and run
for 15 minutes. The Sweet Sap, which is
partially soluble in the oil phase, is pref-
erentially adsorbed to the alkyd–water
interface. The water is added slowly at
1000 rpm to the system which causes the
water molecules to disperse and become
coated with hydrophilic Sweet Sap mol-
ecules. As the emulsion is sheared, larger
water droplets are stretched and ruptured
into smaller droplets. The sizes of the dis-
persed water droplets were in the range
of a few nanometers to a few microns and
are not visible to the unaided eye.
White pigment (rutile grade TiO2) was
dispersed in a long oil alkyd medium without using any dispersing/wetting additive
and the emulsion made was added during
letdown. Formulations are as shown in
Figure 2.
Results And Discussions
The performance of the sap was evaluated by:
1. FTIR re-evaluation of Sweet Sap
after 10 months storage;
2. Emulsion performance evaluation;
and
3. Performance evaluation of paint
made with respective emulsifiers and
paint long term storage stability.
As stated earlier the sap is very much susAs stated earlier, the sap is very much
susceptible to undergo fermentation
leading to acids and alcohol. It was thus
preserved with added amino alcohol,
methylated spirit and fungicide. The sample with amino alcohol turned reddish
after four months and was removed from
this re-evaluation study. FTIR analysis of
the other two was done after 10 months
of storage along with two available emulsifiers (Figures 3-6).
This emulsion basically has oil as
a continuous phase and is called an
‘inverse’ emulsion wherein water droplets
remain as a dispersed phase. The stability
has been evaluated by keeping the emul-
sion in a measuring cylinder and measur-
ing the extent of syneresis. Figure 7 shows
the level of separation after seven days.
The higher viscosity of the emulsion
made with sap can be attributed to bet-
ter emulsification of water in alkyd com-
pared to Additive 1.3 Poor emulsification
leads to the lowest viscosity for the emul-
sion made without emulsifier. Emulsions
prepared without emulsifier and with
commercially available emulsifier show
a higher extent of separation as com-
pared to emulsions based on Sweet Sap
indicating the higher efficiency of Sap as
an emulsifier and, hence, better emulsion
stability.
Emulsion stability can be attributed to
the homogeniety of the distribution and
sizes of the water droplets. The high shear
applied during emulsification causes
water to convert into smaller droplets;
however, sustainability of the size of the
droplets depends on the presence and ef-
ficiency of the emulsifier used. As report-
ed4, distribution of finer water droplets
can be depicted as shown in Figure 8.
In the absence of emulsifier, during the
emulsification stage water gets broken
into small droplets of size and distribu-
tion similar to that of emulsion prepared
in the presence of emulsifier. However,
with time, some of the smaller droplets
will merge into larger droplets due to the
absence of the stabilizing effect of the
emulsifier (Figure 8). In fact, two primary
mechanisms can destabilize the emulsion
Figure 2: Emulsion and paint formulations used for experimentation.
