Effect of moisture on the dynamic mechanical relaxation of polyamide-6/clay nanocomposites

This article investigates the effect of moisture on the dynamic mechanical behavior of polyamide-6 (PA6)/clay nanocomposites with dynamic mechanical analysis from -130 to 110 degreesC. The storage moduli increase with the clay loading for dried and moisture-absorbed samples because of the enhancing effect from the high-aspect-ratio nanoclay. Storage moduli for moisture-exposed samples are lower than those for dried samples; the longer the moisture absorption period is, the lower the moduli are for neat PA6 and PA6/clay nanocomposites. At temperatures below about 10 degreesC, however, samples exposed to moisture for longer periods tend to be stiffer than dried samples, probably because of the stiffening effect of ice. The peak temperature of the 0 relaxation shifts from -53 to -65 degreesC as the moisture content increases. The glass-transition temperature (T-g) or a relaxation dramatically shifts; its position is significantly lowered from 62 to 17 degreesC as the moisture content increases (longer moisture absorption period) and from 62 to 50 degreesC as the clay loading increases. The observed depression of the storage modulus and T-g may be attributed to the plasticization effect of moisture absorption. (C) 2004 Wiley Periodicals, Inc.