Characterisation of polyacrylonitrile yarns by thermal analysis

Six polyacrylonitrile yarns of different linear density were characterised by both differential scanning calorimetry and thermomechanical analysis. The DSC technique, when working with a sealed pan, showed a step-like change around 80°C, which was associated with a glass-transition temperature, and a small cold crystallisation peak around 200°C. The DSC thermograms, when working with perfored pans, showed a single glass transition temperature around 95°C in the cooling scan (210 -0°C) and two breaks of the slope in the range 85-105°C in the reheating curve (0-210°C). The TMA scan exhibited two thermal transitions at ≈ 95°C and ≈ 160 °C. The former was very reproducible and was identified with the step-like change observed in the DSC scan. The latter was not very reproducible and, as with the DSC exothermic peak, seemed to be affected by the linear density of the yarn.