Thermo-rheological behaviour of native silk feedstocks

The rheology of native silk protein feedstock specimens was characterised by shear and oscillatory measurements, over the temperature range from 2 to 55 �C, producing no evidence of thermally-driven phase change behaviour. All specimens exhibited flow characteristics typical of a concentrated polymer solution, with visco-elastic behaviour dominated by two main relaxation modes exhibiting time constants around 0.44 and 0.055 s at 25 �C. The specimens showed well-behaved temperature dependence following the Arrhenius equation, consistent with the kinetics being governed by an activation energy of flow, which ranged from 30.9 to 55.4 kJ mol�1 based on oscillatory data. Consequently, for the first time, it was possible to compile master-curves for native silk feedstock specimens following the principles of time-temperature superposition, using oscillatory data demonstrating visco-elastic behaviour typical of a polymer solution across a wide temperature range. Our work has highlighted the processing range of natural silks and furthered our stance on the molecular mechanisms governing the flow behaviour of these interesting and important materials