Moisture Effect on Structure and Mechanical Property of Nylon 6 as Studied by the Time-Resolved and Simultaneous Measurements of FT-IR and Dynamic Viscoelasticity under the Controlled Humidity at Constant Scanning Rate

Abstract

Time-resolved simultaneous measurement of infrared spectra and complex Young’s modulus was made for nylon 6 films by using the combined system of FT-IR spectrometer and dynamic viscoelastometer under the control of humidity scanned at a constant rate and at a constant temperature. The complex Young’s modulus of nylon 6 films annealed at various temperatures was found to decrease with increasing relative humidity. This behavior could be reproduced well by applying the complex mechanical model of the crystalline and amorphous phases with the humidity dependence of the amorphous modulus taken into consideration. The moisture effect on the infrared bands of crystalline and amorphous phases was investigated, from which the moisture-induced disordering in the crystalline region was speculated. The complex Young’s modulus was measured at the various strain frequencies under the stepwisely-scanned humidity at 35°C, from which the master curves of the real and imaginary parts of the modulus could be produced successfully. The humidity dependence of the thus evaluated shift factor was found to be fitted quite well to the theoretical equation concerning the free volume in the amorphous region. The characteristic features of the dynamic viscoelatometer system used in this experiment were also investigated in detail.