FRACTAL MECHANICS OF ORIENTED POLYMERS - Fractal Mechanics of Polymers - page 263

Thus, the stated above results demonstrated, that volume changes avail-
ability or absence in uniaxial tension process is due to structure type. If the
structure is Euclidean object (dimension d = 3, n = 0.5 [8]), then volume
changes are absent, if it is fractal object (2 < d f < 3.0 < n < 0.5 [7]), then
volume changes are obligatory [3].
In Ref. [5] it has been shown, that in solid-phase extrusion process of
polymerization-filled compositions on the basis of UHMPE structure sharp
change occurs, characterized by its fractal dimension d f , within the range of
extrusion draw ratio l = 1 ÷ 3, after that up to l = 9, the value d f remains
practically invariable. The same compositions structural changes analysis
shows, that sharp drop of local order regions (clusters) relative fraction j l.m.
change in the range of 1 ÷ 9 [7] and crystallinity degree K linear growth
in the same range of l [9] are observed. Therefore, the question arises on
mechanisms, defining such cardinal structural changes of polymerization-
filled compositions extrudates and, as consequence, their properties changes
[2, 10]. In Ref. [11] the indicated mechanisms analysis was fulfilled with-
in the frameworks of deformable body synergetics and fractal analysis on
the example of two polymerization-filled compositions - UHMPE-Al and
UHMPE-bauxite.
As it has been noted above, in the indicated compositions solid-phase
extrusion process the sharp drop of j cl (from ~0.26 up to ~0.05) within the
range of l = 1 ÷ 3 is observed, that results to corresponding d f increase from
2.63 up to ~2.87 [5]. As it is known [12], between the parameters d f and j cl
the intercommunication exists, expressed by the Eq. (1.12). In Fig. 14.1 the
dependences, calculated according to the Eqs. (1.9) and (1.12) comparison
is shown. As one can see, the good conformity between them is observed,
that confirms the made above conclusion - local order regions decay (j cl
decrease) in solid-phase extrusion process is the df f growth cause [11].
As it was shown earlier, both clusters [13] and crystallites [14] are dis-
sipative structures (DS). I n Fig. 14.2 , the dependences of crystallinity degree
K on l for both indicated compositions are adduced. The essential K increase
at l growth is observed. So, for compositions UHMPE-Al the value K in-
creases almost twice at l change from 1 up to 9. The plots of Figs. 14.1 and
14.2 show that the DS type change from local order regions to crystalline
regions occurs in solid-phase extrusion process, in addition this process is
expressed most strongly within the range of l = 1 ÷ 3. Therefore, it follows
to suppose, that shown in Fig. 14.1 sharp df f increase within the indicated l
range is due to DS type spontaneous change at polymers structure critical
state achievement in excess energy cumulation, when shape change cannot