Influence of the nigrosine dye on the thermal behavior of polyamide 66

Abstract To reveal the effect of the nigrosine dye, that the addition of the dye lowers the crystallization point ( T c ) of molten polyamide resins with substantially no shift in the melting point ( T m ), thus suppressing the crystallization enhancement of the crystalline nucleation agents, the characteristics of polyamide 66 (PA‐66) containing nigrosine dye EX (N‐EX) were investigated. Differential scanning calorimetry (DSC) analysis showed that the addition of N‐EX reduced the crystallization rate and T c of molten PA‐66 with substantially no shift in T m , and the crystallization enthalpy per unit of weight of PA‐66 was substantially constant. T c of molten PA‐66 was lowered with an increase in the amount of N‐EX and reached its maximum at 13 wt % N‐EX. Dynamic mechanical analysis showed that the glass‐transition temperature and the secondary glass‐transition temperature increased with an increasing amount of the dye. On the other hand, the DSC and X‐ray diffraction results indicated that no dye molecule was present in the crystal structure of PA‐66. This effect of the nigrosine dye on PA‐66 is in contrast to those of crystalline nucleation agents, plasticizers, and antiplasticizers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3270–3274, 2006