Chemistry Reference
In-Depth Information
FIGURE 2.8
The dependences of elasticity modulus
E
(1) and equilibrium modulus
E
∞
(2)
on macromolecular entanglements cluster network density n
cl
for HDPE. The corresponding
Let us consider the reasons of structural relaxation mechanism assumed
change. It has been shown earlier [55, 56], that in amorphous polymers de-
formation process two mechanisms are possible: the appearance and “freez-
ing” of macromolecules nonequilibrium conformations (the mechanism I)
and mutual motion of the connected by tie chains supramolecular structures
(the mechanism II). As a matter of fact, relaxation processes are opposite to
deformation processes and therefore, the indicated treatment can be used for
the obtained results explanation. It is obvious, that at glassy loosely packed
matrix structural relaxation by clusters motion is difficult (or, in any case, re-
quires very large duration) and therefore, relaxation is realized by reversion
of chains in nonequilibrium configurations to equilibrium ones (the mecha-
nism I). This process is realized easily enough at stress application in loosely
packed matrix, where values
f
g
are large. In case of devitrificated loosely
packed matrix (PC and PAr at
T
>
T
'
g
and HDPE) relaxation processes in it
occur very rapidly, its viscosity reduces significantly [2] and clusters motion
possibility appears, that defines now structural relaxation process. In Fig.
2.8, the plots
E
(n
cl
) and
E
¢
(n
cl
) for PC are traced at
T
>
T
'
g
and, as one can
see, they coincide practically with the corresponding plots for HDPE that
confirms relaxation processes identity.
One more confirmation of the indicated identity can be obtained from the
