Chemistry Reference
In-Depth Information
The authors of Ref. [102] use the considered above model [93] for
branched polyethylenes (BPE) yielding process description. As it is known
[103], the crystallinity degree
K
, determined by samples density, can be ex-
pressed as follows:
K
= a
c
+ a
if
,
(4.65)
where a
c
and a
if
are chains units fractions in perfect crystallites and aniso-
tropic interfacial regions, accordingly.
The Eq. (4.59) with replacement of
K
by a
c
was used for the value
cr
s
s
is always small-
er than macroscopic yield stress s
Y
. In Fig. 4.27, the dependence of crystal-
line phase relative contribution in yield stress
estimation. Such estimations have shown that the value
cr
s
/s
Y
on a
c
is adduced. This
dependence is linear and at a
c
= 0 the trivial result
cr
cr
s
= 0 is obtained. Let us
note that this extrapolation assumes s
Y
≠ 0 at a
c
= 0. At large a
c
the crystal-
line phase contribution is prevailed and at a
c
= 0.75
cr
s
/s
Y
= 1 (Fig. 4.27).
s
/s
Y
in yield stress
cr
FIG. 4.27
The dependence of crystalline regions relative contribution
on perfect crystallites fraction a
c
for series of BPE [102].
The dependence a
if
(a
c
) showed a
if
linear reduction at a
c
growth. Such
a
if
change and simultaneous
cr
s
/s
Y
increasing (Fig. 4.27) at a
c
growth as-
sume local order degree reduction, determining noncrystalline regions con-
tribution in s
Y
, at crystallinity degree enhancement. Besides, the correlation
