Relative Importance of the Effects of Seed and Feed Stage ...

Seed and Feed Stage Agitations of BMA and NMA 363
seed stages and feed stages (‘‘factor’’) was varied by varying the speed of the
agitator at two levels. When the values of x factors are varied at n levels, a
total of n x different experiments can be performed. Thus, the latexes were
prepared using all the 2 2 possible permutations of agitation speeds. No
monomer pooling was observed at any stage of the reaction, when the 8 cm
Rushton turbine was used. After their synthesis, the latexes were characterized
for the ‘‘responses’’, viz., the amount of coagulum, the particle
diameter, the amount of water-soluble polymer, and the viscosity. The agitation
conditions and the results are shown in Table 2.
Determination of Coagulum Amount
For the determination of the amount of coagulum (aggregated polymer
particles), the polymer on the reactor inserts were carefully scraped,
collected, washed using a sieve with 53 mm pore size, dried in an oven at
75°C, and weighed. The latex was also filtered through the sieve, but the
amount of coagulum in the latex was negligible.
Characterization of Serum-Polymer
Ultracentrifugation (Beckman, L8-55M ultracentrifuge) was used to
separate the aqueous phase of the latex, commonly called the serum,
from the polymer particles. It was found that ultracentrifugation of the
latex diluted with an equal mass of water resulted in a good separation
of the serum and the particles. Centrifugation was carried out at
37000 rpm and 4°C, for 6 h. Let x be the mass of a sample of the
original latex, w, the mass of water used for dilution, and y, the mass
fraction of solids in the aqueous phase of the diluted latex. The mass
fraction of solids in the serum of the original latex, f ws , was calculated
using Eq. 1:
f ws ¼
y
1 y
f w þ w
x
ð1Þ
where f w is the mass fraction of water in the original latex. If f a is
the mass-fraction of non-polymeric solids in the serum (SDS, NaHCO 3 ,
KPS, and unreacted NMA), the mass of water-soluble polymer in the
serum, M wsp (based on the total mass, M tot , of the recipe) is given by:
M wsp ¼ M tot ðf ws f a Þ ð2Þ