Progress in Organic Coatings: Kamakshi. R. Christopher, Amarjeet Pal, Girish Mirchandani, Tapan Dhar
Progress in Organic Coatings: Kamakshi. R. Christopher, Amarjeet Pal, Girish Mirchandani, Tapan Dhar
Progress in Organic Coatings: Kamakshi. R. Christopher, Amarjeet Pal, Girish Mirchandani, Tapan Dhar
C to
100
C using persul-
fate as the initiator and a pre-emulsion made of anionic/nonionic
combination surfactants with styrene and butyl acryate as co-
monomers. The addition was carried out for a period of 4h and
then cooled after a hold period of 1h.
To the styrene-acrylate core, organosiloxane intermediate
that contains methoxy linkages was added drop-wise into
kettle by using peristaltic pump and the reactions were pro-
cessed at room temperature until homogenous emulsions were
obtained. Finally the emulsion latex was ltered and polystyrene-
acrylate/polysiloxane hybridlatexwas obtained. Sevenexperimen-
tal sets wereprocessedusingtheabovemethodas showninTable1.
2.3. Preparation of white paints
White paints were made by stirring the millbase and polymer in
a 60:40 ratio as given in Table 2. The mill base was prepared using a
dispersion of pigments and extenders with a thickener and surfac-
tant. Paints were made with all the binders with different amounts
Table 1
Comparisons of synthesized binders and their physico-chemical properties.
Exp no. % Core % Siloxane Coagulum pH Solids MFFT (
C to 100
C with a ramp of 10
C per
min and the transitions of the styrene acrylic core emulsion and
PSA/PSi hybrid core shell polymer hybrid polymers are given in
Table 3. DSC analyses of styrene acrylic siloxane hybrid polymer
show that the T
g
of the polymer showing two transitions indica-
tive of heterogeneity in the hybrid (Fig. 5a and b). The major T
g
is
found to raise corresponding to increasing siloxane content while
the opposite is true for the minor T
g
. This is due to a more differ-
entiated structure in the polymer [22]. An increase in minimum
lmformation temperature (MFFT as in Table 1) is also attributed
this phase separation. The pure core particle does not showdouble
transition as expected.
Table 3
Glass transition temperatures of the PSA core and core shell polymers by DSC.
Latex Tg (major) Tg (Minor)
Pure SA core 17.8
Core shell (90:10) 22.6 2.6
Core shell (80:20) 25.4 3.6
Core shell (75:25) 26.8 8.2
3.5. Dynamic mechanical analysis
Dynamic mechanical analysis (DMA) was carried out on cured
paint lms (14 days) using a DMA Q800 (TA Instruments), which
can obtain the storage modulus E
, and the
loss factor (tan) over a temperature range from 50 to 100
C.
The isochronal tan curve at 1Hz as a function of temperature
is recorded using DMA. The DMA curves (Fig. 6) clearly show a
change inthe tan values of the polystyrene acrylic core andhybrid
latex particles (systems I & VII). There is a decrease in the storage
Fig. 6. DMA curves of PSA core (systemI)and PSA/Si (systemVII) depicting storage,
loss moduli and tan.
Kamakshi.R. Christopher et al. / Progress in Organic Coatings 77 (2014) 10631068 1067
Fig. 7. SEM-EDXS image of the hybrid polymer lm showing uniform presence of
silicon.
modulus of the hybrid polymer compared to the pure polystyrene-
acrylate whereas the tan has decreased from2.0 to 1.5. This may
be attributed to the T
g
difference between core and shell of the
hybrid latex. However, the effective tan (>0.5) of the core (from
15
to 60
to 100