Demineralization Enables Reeling of Wild Silkmoth Cocoons

Abstract

Wild Silkmoth cocoons are difficult or impossible to reel under conditions that work well for cocoons of the Mulberry silkmoth, Bombyx mori. Here we report evidence that this is caused by mineral reinforcement of Wild Silkmoth cocoons and that washing these minerals out allows for the reeling of commercial lengths of good quality fibers with implications for the development of the "Wild Silk" industry. We show that in the Lasiocampid silkmoth Gonometa postica, the mineral is whewellite (calcium oxalate monohydrate). Evidence is presented that its selective removal by ethylenediaminetetraacetic acid (EDTA) leaves the gum substantially intact, preventing collapse and entanglement of the network of fibroin brins, enabling wet reeling. Therefore, this method clearly differs from the standard "degumming" and should be referred to as "demineralizing". Mechanical testing shows that such preparation results in reeled silks with markedly improved breaking load and extension to break by avoiding the damage produced by the rather harsh degumming, carding, or dry reeling methods currently in use, what may be important for the development of the silk industries not only in Asia but also in Africa and South America.

Structure and physical properties of silkworm cocoons

“…In order to understand the original contribution of fibres in the cocoon, we investigated the tensile behaviour of composite fibres covered with sericin rather than industrial degummed fibres, and hence a destoning method was used for unravelling the cocoons. This method uses ethylenediaminetetraacetic acid (EDTA) and has been found to succeed in unravelling the cocoon and causes less damage to both the sericin and the fibres [26]. EDTA powders from Fisher Scientific were dissolved to make a 1 mol l 21 solution, and sodium hydroxide pellets (Sigma) were dissolved in the liquid to get a pH value of 7.…”

Chemical, structural and thermal properties of Gonometa postica silk fibroin, a potential biomaterial

“…Their potential in biomedical and biotechnological fields can only be understood and explored if characteristics relating to applications are well investigated. These characteristics include procedures involved in the processing of the silks such as degumming and demineralization [18], as well as chemical and physical properties of the silks. Freddi et al studied the chemical and physical properties of G. rufobrunnea proteins [19].…”

Silk cocoons as natural macro-balloon fillers in novel polyurethane-based syntactic foams

“…Some species, such as the wild African silkworm Gonometa postica, are also known to include a small fraction (<5 wt%) of particulate minerals, namely calcium oxalate crystals, on the outermost surface of the cocoon structure ( Fig. 1) [17]. The columnar crystals (20e30 mm long) do not enhance interlaminar adhesion (in the outer layers) or fracture toughness, but owing to their high hardness of around 2 GPa, the crystals are known to improve the indentation hardness of the cocoon [18,19].…”