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This paper presents experimentally determined compression sets and compression behaviour of two closed-cell, crosslinked foam materials; ZOTEK N B50 (Nylon 6) and ZOTEK N A30 (nylon/polyolefin alloy). This work forms the basis of future investigations into the post-impact behaviour of these foams. Compression set performance was measured at 25.0, 37.5 and 50.0% strain at nine temperatures ranging from −5 to 90 °C. Compression tests at constant strain rates were conducted at four temperatures between 23 to 90 °C. Finally compression tests at 23 °C were repeated at four strain rates between 0.3 and 550 hr−1 to determine strain rate dependency. The Nagy and Williams-Landel-Ferry scaling factor for strain rate and temperature were applied to the experimental results and equations were derived which allowed the performance of the two polyamide based foams to be interpolated over the strain rate and temperature range of study. The required material properties of interest of the base polymers have been assessed and are presented and discussed in relation to the performance of the foam materials.

It is a fundamental response of any polymeric foam material to undergo non-recoverable deformation following the application of a defined compressive strain, exacerbated by temperature and humidity. This process is commonly referred to as compression set. The ability to predict recovery after the application of a compressive strain is crucial to both the manufacturers and end users of foam materials. Specific compression set test procedures have been established to quantify the extent of non-recoverable deformation in specific foam types but to date no general predictive approach exists. In this work, compression set (fixed strain) tests were undertaken on a cellular polyamide-6 material at various temperatures (-5°C to 90°C) and the foam recovery monitored over time periods in excess of those dictated by standard methods (ISO 1856 [1]). An empirical formula has been proposed to allow the prediction of recovery after compressive strain, covering recovery periods from 10 minutes to 24 hours (up to 168 hours at 23°C).