Plasticizer loss in a complex system (polyamide 12): Kinetics, prediction and its effects on mechanical properties

Abstract

Plasticizer migration is a major concern for plasticized polymers because it leads to unwanted changes in mechanical properties and, in many cases, contamination of the environment. In cases of slow migration, it is of practical importance to be able to perform accelerated testing and estimate migration rates from high temperature experiments. Despite the importance, a critical evaluation of different ways of extrapolating mass loss data has hitherto not been reported. Therefore, in this article, three different methods (involving for the first time a master-curve approach to mass loss data) to estimate low temperature migration from high temperature data are presented and critically evaluated. The system chosen was a plasticized polyamide 12 pipe, an important component in vehicle fuel-line systems. This system was challenging since the lower part of the temperature range in which the material is used overlaps with the glass transition region. All three methods (using data at 80–145 °C) over-estimated, although to different extents, the low-temperature mass loss rate (60 °C). The main reason for the over-estimation was the partial overlap with the glass transition region. Hence, there is a built-in safety factor when predicting plasticizer loss over glass transition regions, and the predictions are conservative. It was observed that plasticizer loss and annealing effects were the main reasons for changes in mechanical properties (increase in flexural stiffness/strength) during ageing.