Chemistry Reference
In-Depth Information
at 543
◦
C was the best to show a Young's modulus of 39.7 GPa, a tensile
strength of 1,176 MPa, and an elongation to break of 5.70%, the best com-
posite fiber processed at the same condition showed a Young's modulus of
120 GPa, a tensile strength of 1,363 MPa, and an elongation at break of
1.61%. The high modulus displayed by the 30/70 PBT/ABPBI compos-
ite fiber suggested that the modulus (310 GPa) of the reinforcing PBT was
about fully utilized in the composite. Using the observed
E
c
= 120 GPa and
E
m
=39
.
7 GPa, and assuming
E
f
= 310 GPa
,V
f
=0
.
3, the reinforcement
− V
f
)
was
f
=0
.
99. On the other hand, the morphology and structure studies
using scanning electron microscopy and wide-angle x-ray diffraction tech-
niques showed no phase segregation in the as-spun fibers of the composites.
A molecular level composite was obtained.
In a more detailed study by Krause
et al
. (1986), the heat-treated fiber
and film processed from an optically homogeneous solution (C
<
C
cr
)of
30/70 PBT/ABPBI exhibited no large-scale phase separation. The fiber
and film contained crystallites of both PBT and ABPBI with lateral dimen-
sions no larger than 3 nm which were well oriented in the fiber and planar
isotropically oriented in the film. The PBT homopolymer was dispersed
in the matrix at the molecular level in ordered regions at a scale no
larger than 3 nm, resulting in a rigid-rod molecular composite. However,
if the solution was more concentrated with C
>
C
cr
the resulted fiber
and film contained brittle, 100 nm-4,000 nm long ellipsoidal particles which
were phase-separated from the surrounding matrix material. The parti-
cles in such a film were larger (2,000 nm-4,000 nm) than that in the fiber
(100 nm-200 nm). The shearing on the phase-separated domains during
fiber spinning broke the particles and reduced their size. Because of the
phase separation and to a lesser extent the lower degree of orientation, the
fiber and film prepared from the concentrated solution showed much lower
mechanical properties as shown in Table 5.15.
Although the concept of the molecular composite was demonstrated by
the work on PBT/ABPBI, the resulted composite was not melt-processible
since the melting points (if there is one) of the two component polymers
are well above 800
◦
C. Efforts were then put on systems with a ther-
moplastic polymer as the matrix. One such system was PBT/nylon 66
(Chuah
et al
., 1987). Thus, the PBT/nylon 66 in different ratio was dis-
solved in methane sulphonic acid to make 2 wt-%-3 wt-% (
<
C
cr
) solutions.
They were processed by extrusion and rapid coagulation into thin films.
The films were optically clear and did not show gross phase separation in
E
c
=
fE
f
V
f
+
E
m
(1
e
ciency factor calculated from the equation
