Crystallization kinetics – TTT curves The 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 test The 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 Introduction Year 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 6 PA6 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 preparations Plates 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). DRYDRY WETWET 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.