POLYMERS AS NATURAL COMPOSITES: STRUCTURE AND PROPERTIES - Fractal Mechanics of Polymers - page 333

The stated above data give a clear example of large possibilities of poly-
mer properties operation through its structure change. From the plots of f Fig.
15.29 it follows that annealing of REP extruded up to ε e = 0.52 results to
elasticity modulus increase in more than 8 times and from the data of f Fig.
15.30 y ield stress increase in 6 times follows. From the practical point of
view the extrusion and subsequent annealing of rarely cross-linked epoxy
polymers allow to obtain materials, which are just as good by stiffness and
strength as densely cross-linked epoxy polymers, but exceeding the latter
by plasticity degree. Let us note, that besides extrusion and annealing other
modes of polymers nanostructure operation exist: plasticization [70], filling
[26, 71], films obtaining from different solvents [72] and so on.
Hence, the stated above results demonstrated that neither cross-linking
degree nor molecular orientation level defined cross-linked polymers final
properties. The factor, controlling properties is a state of suprasegmental
(nanocluster) structure, which, in its turn, can be goal-directly regulated by
molecular orientation and thermal treatment application [62].
In the stated above treatment not only nanostructure integral character-
istics (macromolecular entanglements cluster network density ν cl or nano-
cluster relative fraction φ cl ), but also separate nanocluster parameters are
important (se e Section 15.1 ). In this case of particulate-filled polymer nano-
composites (artificial nanocomposites) it is well-known, that their elasticity
modulus sharply increases at nanofiller particles size decrease [17]. The sim-
ilar effect was noted above for REP, subjected to different kinds of process-
ing (se e Fig. 15.28 ). Therefore, the authors of Ref. [73] carried out the study
of the dependence of elasticity modulus E on nanoclusters size for REP.
It has been shown earlier on the example of PC, that the value E p is de-
fined completely by natural nanocomposite (polymer) structure according to
the Eq. (15.32) (see Fig. 15.26 ).