Biomedical Engineering Reference
In-Depth Information
critical SC transition parameters as the initial ceramic (T
c
=92K, and
Δ
C, T
c
remains
constant (91.6K) while the transition width increases sharply (
T
c
=8K). For PP under the same conditions at 180
8
8K). It
is known that the presence of tertiary atoms of carbon in the macro chain
weakens carbon-carbon bonds in that polymer, making it less thermo-stable
than polyethylene [31]. It is assumed that this inclination of the PP to
decompose under thermo-oxidation conditions, combined with the partici-
pation of oxygen from the SC orthorhombic phase in this process, are the
main causes of the observed phenomena.
To obtain confirmation of this supposition, antioxidants (Irganox
®
1010
and NG-2246) were additionally introduced into the matrix, which should
decrease the thermo-oxidative destruction rate of the polymer substantially.
However, the addition of Irganox
®
1010 contracted the width of the
temperature transition into the SC state up to the characteristic values of the
initial ceramic (
Δ
T
c
≥
T
c
of the
composites based on PP. This is because NG-2246 is not an effective
antioxidant for polyolefins.
Elevation of the pressing temperature of the composites based on PMMA
(content of ceramic 85% by weight) up to 160
Δ
T
c
≈
8 K), whereas NG-2246 did not affect the
Δ
8
C and a longer duration
(15min, cooling down to 40
8K), while T
c
remains steady (91.9-92.3K). When NG-2246 antioxidant was added or the
formation duration was cut down to the conventional time of 4min, the
characteristics (T
c
=91.5K and
8
C) increases
Δ
T
c
appreciably (
≥
T
c
=8 K) were restored.
Thus, all of the results outlined in Table 9.2 can be explained by the
competing action of two processes taking place in parallel:
Δ
.
interaction of separate elements or fragments of the macromolecule of
polymeric binder with the surface of the ceramic grain before their
intercalation into the interstitial layer of the ceramic
.
thermo-oxidative destruction of the polymeric binder.
In this case, factors that promote the interaction of the binder
macromolecule elements with the surface of the ceramic (flexibility of the
macro chains, elevation of the temperature, etc.), as well as the decrease of
the rate of thermo-oxidative destruction (reducing the temperature of
pressing, introduction of antioxidants), promote, or at least maintain, the
critical SC properties that they possess in the initial state. It is supposed that
oxygen contained in the ceramic grains plays an active role in the process of
thermo-oxidative destruction of the polymeric matrix. Nevertheless, to
determine whether thermo-oxidative destruction of the polymeric binder is a
governing factor responsible for the widening of
Δ
T
c
, the thermo-chemical
properties of the non-filled polymeric binder, as well as those of the
composites based on them, was investigated.
