er:

$2$

$4\mathrm{.}2$ Three polypropylene polymer with different volume fractions F of rubber particles were tested for

yield stress measurements at $20\backslash$deg C$.$

The yield stress sy as a function of $$ and F were given in the table below. Calculate V$*$ for each polymer and

suggest why V$*$ varies with F$.$

$($s$-1)10-510-3$

F$=023\mathrm{.}130\mathrm{.}2$

F$=0\mathrm{.}119\mathrm{.}724\mathrm{.}9$

F$=0\mathrm{.}215\mathrm{.}519\mathrm{.}7$