We report the results of an investigation by differential scanning calorimetry (DSC) of two mobility controlled processes
in the amorphous phas e of semicrystalline PEEK — enthalpy relaxation below the glass transition (Tg) and secondary crystallization aboveTg. Both result in the observation of an endothermic peak just above the annealing temperature in the DSC scan of the polymer
— the enthalpy recovery peak and the low temperature melting peak, respectively. There is a striking similarity in the time
and temperature dependence of the endothermic peak for these two processes. These results are reminiscent of those obtained
from small strain creep studies of “physical aging” of semicrystalline PEEK below and aboveTg.
The reinforcement of nano-barium titanate in ferrite filled poly-ether-ether-ketone (PEEK) composites caused a shift in the
decomposition temperature, at which maximum mass loss occurred, to higher side and enhancement in char yield in thermogravimetric
analysis. Loss tangent and glass transition temperature of ferrite filled PEEK composites were also found to be increased
with the reinforcement of nano barium titanate. The effect of nano barium titanate on the melting behaviour of ferrite filled
PEEK composites was negligible.
Authors:P. Rajagopalan, L. Kandpal, A. Tewary, R. Singh, K. Pandey, and G. Mathur
PEEK is characterised by high impact and fatigue resistance andTg of 145‡C. Blends of PEEK and PEI have been made and scanning electron micro-graphs of the broken specimen show that the two
polymers are completely miscible in all proportions. The study also shows that PEEK∶PEI 50∶50 blend, can be used as matrix
for composite applications with appreciable enhancement ofTg to 177‡C.
Positron lifetime measurements have been performed on differently manufactured PEEK samples of different molecular weights. Our measurements confirmed an old assumption: the o-Ps lifetime changes linearly with the molecular weight of the polymer. We have found that both the size of the free volumes and their number increase with increasing molecular weight of the investigated polymers.
Authors:M. Mourgues-Martin, A. Bernes, and C. Lacabanne
Thermally Stimulated Current (TSC) spectroscopy and Differential Scanning calorimetry (DSC) have been applied to the characterization
of the microstructure of Poly (Ether Ether Ketone)/PEEK. the dielectric relaxation spectra show two modes, dependent upon
* for the mode stuated in the vicinity of the glass transition temperature, two components have been distinguished and attributed
to the molecular mobility in the ‘true amorphous phase’ and in the ‘rigid amorphous region’.
* below 0°C, two sub-modes appear, situated around-110°C and-75°C, due to the two different crystal entities, beads and laths.
This investigation demonstrates that polyphenylene sulfide (PPS) crystallizes in a unique dual-mechanistic fashion in which
8% of the material by volume crystallizes instantaneously, while the remaining material crystallizes in a time dependent fashion.
These rapid melt-crystallization kinetics are quantitatively modeled using a dual-mechanistic model approach which is based
on the methodology first observed by Velisaris and Seferis in polyetheretherketone (PEEK) crystallization. The crystallization
model is then used to accurately predict both isothermal and for the first time non-isothermal crystallization behavior over
a wide spectrum of cooling rates utilizing the same model parameters. Specifically, this work identifies and models the initial
fast crystallization kinetics of PPS. Additionally, the versatility of the Velisaris and Seferis dual-mechanistic model has
been established with PPS, by simply showing that it is a special case of the generalized dual-crystallization kinetics methodology.
Measurement of the degree of crystallinity of the polymer matrix in a composite is complicated by the presence of the reinforcing
additive. This is particularly the case in APC-2 in which as much as 70% can be carbon fibre. A First Law procedure, developed
for determining the degree of crystallinity of PEEK, which involves direct measurement of the enthalpy changes associated
with melting, crystallization and heat capacity changes, has found to be an effective method for the determination of the
crystallinity of the PEEK matrix. The procedure has been applied to carbon fibre and glass fibre PEEK composites.