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

366 Krishnan et al.
F LO ¼ y 1 þ y 2
2
F HI ¼ y 3 þ y 4
2
m f ¼ F HI F LO
2
h ¼ y 1 þ y 2 þ y 3 þ y 4
4
The experimental error is calculated as follows:
E LO ¼ y 2 þ y 3
2
E HI ¼ y 1 þ y 4
2
m e ¼ E HI E LO
2
error ¼ absðm e Þ
ð6Þ
ð7Þ
ð8Þ
The calculation of the first order effect involves all four experimental
data. The averaging reduces the influence of an error in any datum. The
coefficients m s and m f can be directly compared to determine the relative
importance of each independent variable. For a measured effect to be
significant, it has to be greater than the experimental error. The error also
includes the deviation of the experimental effect from the simple model
assumed (Eq. 4).
RESULTS
Effect of Agitation on Coagulum Formation
Shear-induced coagulation in latexes has been studied by several
researchers (Ali and Zollars, 1987, 1988; Husband and Adams, 1992;
Kusters et al., 1997; Lowry et al., 1984, 1986; Matejicek et al., 1988;
Utracki, 1973; Zollars and Ali, 1986). Smoluchowski’s expression for
orthokinetic (shear-induced) flocculation is normally used to describe the
rate of shear-induced aggregation. The collision frequency in the absence of
interparticle forces, for uniform particles approaching each other along
rectilinear paths, was predicted by Smoluchowski to be (16/3)N 2 p a3 g where
N p is the number of particles per unit volume, a is the particle radius, and g
is the shear rate (von Smoluchowski, 1917). If each collision results in