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.