(A) study on crystallization kinetics and melt rheological properties of nylon 66

Abstract

The crystallization kinetics and melt rheological properties of nylon 66 were studied in this paper. The crystallization kinetics of nylon 66 was studied by the depolarized light intensity method. The effects of the crystallization temperature, the molecular weight, and the sodium phenylphosphinate on the rate of crystallization were evaluated. Avrami equation was used for the determination of the overall rate of crystallization, $t\frac{1}{2}^{-1}$. In the temperature range of 232-243℃, the overall rate of crystallization, $t\frac{1}{2}^{-1}$ varied from 0.0435 to 0.0125, and Avrami exponent, n were about 3-4. The overall rate of crystallization, $t\frac{1}{2}^{-1}$ varied from 0.0164 to 0.0204 as the number average molecular weight decreases from 16,500 to 15,500. This overall rate of crystallization was comparable to a commercial injection molding grade nylon 66, Leona 1300S. The overall rate of crystallization, $t\frac{1}{2}^{-1}$ varied from 0.0172 to 0.0278 in the presence of 1 wt.% sodium phenylphosphinate. The commercial injection molding grade Leona 1300S had $t\frac{1}{2}^{-1}$ value of 0.0200 which was equivalent to the synthesized nylon 66 with 0.25-0.5 wt% sodium phenylphosphinate. The Avrami exponent, n varied from 11.8 to 3 in the presence of 1 wt.% sodium phenylphosphinate. The melt rheological properties of nylon 66 were studied by capillary rheometer. The effects of three types of lubricant (Zn-Stearate, Na-Sterate, and Al-Stearate) on these properties were evaluated. Lubricants were compound with virgin nylon 66 using C.W. Brabender extruder. The lubricant efficiency was estimated by the moldability index (α$_{stv}$) value from the capillary rheometer data and the spiral mold flow test. The Zn-Sterate turned out to be the most effective lubricant of the three lubricants. Activation energy for viscous flow of virgin nylon was 16.5-17.8 kcal/mole, but that of nylon 66 containing lubricants was decreased to 14.8-15.2 kcal/mole. ...