Crystallization kinetics – TTT curves The crystallization kinetics was investigated by Flash-DSC....
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Transcript of Crystallization kinetics – TTT curves The crystallization kinetics was investigated by Flash-DSC....
Crystallization kinetics – TTT curvesThe crystallization kinetics was investigated by Flash-DSC.
Both crystallization from melt and from amorphous
(annealing) have been performd, and TTT curves
(temperature-time-transformation) have been obtained
(Figure 3). With these results it is possible to determine the
time to crystallization at several temperatures.
In the case of crystallization from melt, the different kinetics
between α and γ phase are easily recognizable as shown
in Figure 3, and it is clear that the α kinetics dominates at
high temperature whereas the gamma kinetics start to
govern at temperature of about 80°C. Instead, the TTT
curve obtained from amorphous (cold crystallization), has
revealed a similar kinetics for both the phase as shown in
Figure 3.
Mechanical properties – Tensile testThe stress-strain curves measured on single phase
samples are presented in Figure 4 for both dry and wet
condition. In Figure 5 the rate dependence of the yield
stress is shown to be comparable for the different phases
at the same level of hydration. For the wet samples the
yield stress is much lower and the strain rate dependence
less pronounced. It should be noted that the degree of
crystallinity varies between the samples (α 40%, γ 17%).
Structure-property relations in polyamide 6
E. Parodi, L.E.Govaert, G.W.M. Peters
PolymerTechnology
/ department of mechanical engineering
IntroductionYear after year, polymers are getting more and more
importance in load-bearing applications. In this, high-
performance is the key word; therefore the optimization of
processing is required to achieve as best performance as
possible.
Nylon 6 is an aliphatic polyamide and, despite its strong
hydrophilic character (which tend to strongly decrease its
mechanical properties), it is largely used in several
applications.
Polymorphism in polyamide 6PA6 has a stable crystalline phase called α-phase
(monoclinic) which is obtainable by slow cooling from melt;
however, upon fast cooling from the melt the γ mesophase
(pseudo-hexagonal) may be formed. Upon very fast
cooling (quenching), it is even possible to obtain a fully
amorphous phase.
Samples preparationsPlates containing only a single phase were made by
compression molding following these production protocols: Alpha cooling in air (in between of hot steel plates,
thickness 3mm) Gamma cooling in “cold” press at 80ºC, force < 10 KN
(in between of hot steel plates, thickness 3mm) Amorphous quenching in ice-water bath (in between
of aluminium sheets) For all the phases, melting at 265ºC for 5 min and 100 KN.
Figure 1 – The first transmission cross beam made of nylon 6, is standard equipment in the new BMW M5.
Figure 3 – TTT curves for polyamide 6 crysatllized from melt (left), and crystallized from amorphous (right).
DRY
WET
Figure 4 – Stress-strain curves for samples in dry and
wet condition.
Figure 5 – Eyring plot for dry and wet samples.
Polyamide 6
Figure 2 – Schematic representation of alpha (left) and gamma (right) structures.