Juan Guan

Spider Silk: Super Material or Thin Fibre?

3] However, in order to judge whether silk is, in fact, an exceptional structural material that can deliver as a commercially attractive polymer replacement in engineering applications, we need direct com-parisons of silks with synthetic polymer fi bres on properties such as strength and toughness. This question has important consequences for industrial silk production routes such as silk reconstitution (RSF),

Thermally induced changes in dynamic mechanical properties of native silks.

Dynamic mechanical thermal analysis (DMTA) on individual native silk fibers demonstrates changes in the dynamic mechanical properties of storage modulus and loss tangent as a function of temperature and temperature history ranging from -100 to 250 °C. These property changes are linked quantitatively to two main types of change in the silk structure. First, the evaporation of water with increasing temperature up to 100 °C increases the storage modulus and removes two characteristic loss tangent peaks at -60 and +60 °C. Second, various discrete loss tangent peaks in the range 150-220 °C are associated with specific disordered silk structures that are removed or converted to a limiting high-temperature relaxed structure by the combination of increasing temperature and static load in the DMTA tests. The results identify important origins of silk filament quality based on the analysis of measurements that can be traced back to differences in production and processing history.

Two mechanisms for supercontraction in Nephila spider dragline silk.

Supercontraction in dragline silk of Nephila edulis spider is shown to have two distinct components revealed by single fiber measurements using dynamic mechanical thermal analysis. The first component relies on a contraction of maximum 13% and seems to be associated with relaxation processed through the glass transition, T(g), as is induced by increasing temperature and/or humidity. The second component is induced by liquid water to the total contraction of 30%. The T(g)-induced contraction is linearly correlated with the restraining stress on the fiber, and the mechanical properties of the partially contracted silk have mechanical profiles that differ from both native and fully supercontracted fibers. Here we present novel supercontraction data and discuss their structural origins, examining the relaxation of stretched orientation in the different primary structure sequences.

Linking naturally and unnaturally spun silks through the forced reeling of Bombyx mori.

The forced reeling of silkworms offers the potential to produce a spectrum of silk filaments, spun from natural silk dope and subjected to carefully controlled applied processing conditions. Here we demonstrate that the envelope of stress-strain properties for forced reeled silks can encompass both naturally spun cocoon silk and unnaturally processed artificial silk filaments. We use dynamic mechanical thermal analysis (DMTA) to quantify the structural properties of these silks. Using this well-established mechanical spectroscopic technique, we show high variation in the mechanical properties and the associated degree of disordered hydrogen-bonded structures in forced reeled silks. Furthermore, we show that this disorder can be manipulated by a range of processing conditions and even ameliorated under certain parameters, such as annealing under heat and mechanical load. We conclude that the powerful combination of forced reeling silk and DMTA has tied together native/natural and synthetic/unnatural extrusion spinning. The presented techniques therefore have the ability to define the potential of Bombyx-derived proteins for use in fibre-based applications and serve as a roadmap to improve fibre quality via post-processing.