Chemistry Reference
In-Depth Information
Properties of composites of PPTA/nylon 6
∗
.
Table 5.14.
Sample
Mol. Wt.
of PPTA
PPTA/Nylon
Young's
modulus
Yield
stress
Ultimate
strength
Elongation
at break
Nylon 6
0/100
0.91 GPa
24 MPa
51 MPa
5.3%
Composite
980
5/95
1.45 GPa
40 MPa
52 MPa
2.7%
Composite
4,500
5/95
1.59 GPa
46 MPa
54 MPa
1.6%
Composite
12,300
5/95
1.67 GPa
58 MPa
59 MPa
0.6%
Oriented (drawn at 170
◦
C to three times its original length):
Nylon 6
0/100
1.18 GPa
220 MPa
28%
Composite
34,000
3/97
3.35 GPa
340 MPa
20%
∗
Source: Takayanagi
et al
., 1980.
large amount of water and washed with water and methanol. For mechan-
ical property measurements the specimens were prepared by compressing
at an appropriate temperature (240
◦
C for that of nylon 6 and 290
◦
Cfor
the blends of nylon 66) and quenched in ice-water. Electron microscopy
revealed that the rod-like molecules were dispersed in the matrix in the
form of microfibrils. The diameter is in the range of 15 nm to 30 nm depend-
ing on the molecular weight of the rod-like polymer. The PPTA molecules
of lower molecular weight (4,500 by viscosity-average) formed a thinner
microfibril (
∼
15 nm in diameter) than that (
∼
30 nm) of the higher molec-
ular weight (34,000). The diameters are much smaller (1
µ
m-10
µ
m) than
that of macroscopic fibers used in composites. Significant reinforcement was
achieved by the microfibrils as shown in Table 5.14. PPTA of higher molec-
ular weight resulted in a higher reinforcement. The Young's modulus of
nylon 6 was almost doubled by blending in only 5% of the high molecular
weight PPTA. The oriented sample with 3% of PPTA was found to show a
modulus of 3.35 GPa and a strength of 340 MPa. The calculated value for
the ultimate strength of the microfibrils of PPTA in the oriented composite
was 4.2 GPa if an additive rule was applied. This calculation suggested that
the tensile property of PPTA was fully developed in the composite.
Although the reinforcement by aromatic polyamides was remarkable, the
composites prepared by these researchers were not molecular. As mentioned
above, the molecules were coagulated into microfibrils of 15
m-30 nm in
thickness. Using the Halpin-Tsai equation modified by Nielsen (1975) and
the modulus values of E
1
=0
.
91 GPa and E
2
= 182 GPa for nylon 6 and
PPTA as well as the observed modulus of the composites, the calculated
L/D ratio was 15 for low molecular weight PPTA and 25 for high molecular
µ
