Rheological behaviour of native silk feedstocks

Abstract

a b s t r a c tWhilst much is known about the properties of silks, the means by which native silk feedstocks are spun still represent a gap in our knowledge. Rheology of the native silk feedstocks is germane to an understanding of the natural spinning process. Yet, an overview of the literature reveals subtle limitations and inconsistencies between studies, which has been largely attributed to sample-to-sample variation when testing these exquisitely flow-sensitive materials. This ambiguity has prevented reliable, consistent inferences from standard polymer rheology and constitutes an obstacle to further development.To address this challenge, we present the largest study to date into the rheological properties of native silk feedstocks from Bombyx mori larvae. A combination of shear and oscillatory measurements were used to examine in detail the relationships between concentration, low shear viscosity, relaxation times, complex modulus and estimates of the molecular weights between entanglements. The results from this highly detailed survey will provide a sound basis for further experimental or theoretical work and lay the foundations for future bio-inspired processing of proteins.

The Rheology behind Stress-Induced Solidification in Native Silk Feedstocks

“…This was similar to the behavior reported previously [59,60,61]. The initial peak was ascribed to “stress overshoot”, which is a non-linear rheological effect commonly observed with polymeric systems and generally ascribed to the changes in coil shape at the onset of steady flow [83,84,85,86,87,88].…”

“…Although previous work demonstrated considerable natural variation between specimens of silk feedstock from B. mori , this value was close to the median value expected during the early stages of cocoon construction [61]. …”

“…Nevertheless, the importance of a flow-induced phase change at a critical shear rate or stress has motivated a considerable number of rheological investigations [36,37,59,60,61,62,63,64,65,66,67,68,69,70,71,72]. Amongst these, recent work has demonstrated that B. mori silk feedstock behaves as a typical polymer solution [59,60,61].…”

“…Amongst these, recent work has demonstrated that B. mori silk feedstock behaves as a typical polymer solution [59,60,61]. Its flow behaviour was found to be dominated by a relatively small number of relaxation modes and followed an Arrhenius-type temperature dependence [59].…”

Applicability of biotechnologically produced insect silks

“…Rheological measurements revealed that native spinning dopes of spider dragline and silkworm cocoon silk proteins show many similarities although they evolved separately; both dopes are visco-elastic with properties of typical polymer melts with high viscosities [36,37]. Such a material in principle could challenge the animals due to the relatively high forces needed for processing.…”