Dynamic melt flow of nanocomposites based on poly-epsilon-caprolactam

The dynamic flow behavior of polyamide-6 (PA-6) and a nanocomposite (PNC) based on it was studied. The latter resin contained 2 wt% of organoclay. The two materials were blended in proportions of 0, 25, 50, 75, and 100 wt% PNC. The dynamic shear rheological properties of well-dried specimens were measured under N-2 at T = 240 degreesC, frequency omega = 0.1-100 rad/s, and strains gamma = 10 and 0%.

At constant T, gamma, and omega the time sweeps resulted in significant increases of the shear moduli. The gamma and omega scans showed a complex rheological behavior of all clay-containing specimens. At gamma = 10% the linear viscoelasticity was observed for all compositions only at omega > 1 rad/s, while at gamma = 40% only for 0 and 25 wt% of PNC.

However, the effect was moderate, namely decreasing G' and G" (at omega = 6.28 rad/s; gamma = 50%) by 15 and 7.5%, respectively. For compositions containing > 25 wt% PNC two types of non-linearity were detected. At omega less than or equal to omega(c) = 1.4 +/- 0.2 rad/s yield stress provided evidence of a 3-D structure.

At omega > omega(c), G' and G" were sensitive to shear history - the effect was reversible. From the frequency scans at omega > omega(c) the zero-shear relative viscosity vs concentration plot was constructed. The initial slope gave the intrinsic viscosity from which the aspect ratio of organoclay particles, p = 287 9 was calculated, in agreement with the value calculated from the reduced permeability data, p = 286.