SAMPE Journal - November/December 2021 - 75
Figure 5. The peel loads between the skin layers and the PPF composite cores (a) and the peel loads
between the PPF layers and the honeycomb cores (b).
If the PPF layers were considered as the " core "
section, the peel load between the " core " and the
GF or CF " skin " sections were evaluated by the
climbing drum approach. The results are provided
in Figure 5a. The peel load between the GF layers
and the new PPF composite core is 122.78 N. Once
the core is replaced to the used PPF composites,
the peel load increases 13.9%. Similar results are
also observed between the CF skin layers and the
PPF composite core. The used PPF composite
core offers an 11.4% higher peel load. Compared
to the affinity to the GF skin layers, the new and
used PPF composite cores show higher interfacial
adhesions to the CF skin layers (24.8% and 22.1%).
It is probably due to the effective transfer of stress
from the matrix to the carbon fibers via the better
bonded interface and the excellent mechanical
properties (stiffness and strength) of CF compared
to GF.
Figure 5b exhibits the peel loads between
the new or used PPF layers and the honeycomb
cores. Since the interfacial area between the PPF
layers and the honeycomb cores are much smaller
than the composite projection area, the peel
loads are much lower than the values between
the GF or CF skin layers and the PPF composite
cores, but the trend is similar. The used PPF layer
shows higher affinity to the honeycomb cores.
The incorporation of the skin layers can enhance
the peel loads. The reason might be that the skin
layers can substantially increase the stiffness of
the PPF layers, and it requires for a higher force to
dissociate the interface between the PPF layers and
the honeycomb cores.
Flame Retardancy of Composites
Figure 6 gives the LOIs of the PPF composites with
and without the honeycomb cores. In general, an
LOI value less than 22% indicates that the material
is flammable. If a LOI value is between 22 and
27%, the material is combustible and if the LOI
value is over 27, the material is flame-retardant13
.
The new PPF composites show a low LOI value of
22.5 %, indicating that it is easy to be burned and
has a high fire propagation rate. Although the new
PPF is flame retardant (LOI: 49.6%), the matrix is
poor in flame retardancy. The flame resistance
was enhanced to 28.3% by replacing the prepregs
from new PPF to used PPF, probably because the
filter bag had been used at high temperatures for a
Figure 6. LOI results of the PPF composites (a) and the honeycomb core PPF composites (b) with the
GF or CF skin layers.
www. sampe.org
NOVEMBER/DECEMBER 2021
|
SAMPE JOURNAL |
75
http://www.sampe.org
SAMPE Journal - November/December 2021
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