I am close to completing a book about Silk to be published by the SSRL. All going well it will be out early/mid 2021. The content is based around my Lecture series presented in Rivera, Uruguay in 2018. Here’s a small preview:
What is silk?
Silk is a natural proteinaceous secretion of many kinds of invertebrates. It is usually secreted as a fibre, although may be secreted as a glue or other substance. Some silk fibres are woven into textiles by humans. The fibre is usually secreted as a liquid or gel and rapidly self-assembles into a fibre. The vast majority of a silk fibre is composed primarily of a protein called fibroin or, in the case of spider silk, spidroin (which is a derivation of spider fibroins)2. It has, despite being a fairly transparent fibre, a shiny appearance owing to its triangular or prism-like shape. Silks have a density of around 1.3 g cm-3. While this is lower than many other natural fibres (e.g. wool or cotton, at ~1.5 g cm-3), it is greater than synthetic fibres (e.g. polyester, nylon, at 1.1-1.2 g cm-3 g cm-3). Nevertheless, it is much less dense than most of the high performing synthetics, like carbon fibre (at 2 g cm-3). Despite its low density, silk (in particular silkworm moth cocoon silk and spider dragline silk) has a greater strength, elasticity, and toughness than most natural or synthetic materials (see Table 1). The significance of this I will explain later when I discuss the uses of and properties of silk. Needless to say, silk has a particularly low mass per unit volume for a high performing material. It is the hierarchical structure of silk, from its sub-molecular order through to the bulk fibre (for which I’ll give more details later), that enables such a high performing material to be developed while maintaining a low density.
<TABLE 1: STRENGTH, ELASTICITY AND TOUGHNESS OF SOME NATURAL AND SYNTHETIC FIBRES>