Ice-regenerated flame retardant and robust film of Bombyx mori silk fibroin and POSS nano-cages.

Luca Valentini,Silvia Bittolo Bon,Nicola M Pugno

doi:10.1039/c7ra13708g

Luca Valentini, Silvia Bittolo Bon + Show 1 more

Open Access

https://doi.org/10.1039/c7ra13708g

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Abstract

In this study, we present a simple method to prepare and control the structure of regenerated hybrid silkworm silk films through icing. A regenerated hybrid silk (RHS) film consisting of a micro-fibrillar structure was obtained by partially dissolving amino-functionalized polyhedral oligomeric silsesquioxanes (POSS) and silk fibers in a CaCl2–formic acid solution. After immersion in water and icing, the obtained films of RHS showed polymorphic and strain-stiffening behaviors with mechanical properties that were better than those observed in dry or wet-regenerated silk. It was also found that POSS endowed the burning regenerated silk film with anti-dripping properties. The higher β-sheet content observed in the ice-regenerated hybrid micro-fibrils indicates a useful route to fabricate regenerated silk with physical and functional properties, i.e. strain-stiffening, similar to those observed to date in natural spider silk counterpart and synthetic rubbers, and anti-dripping of the flaming melt. Related carbon nanotube composites are considered for comparison.

Highlights

Silk is a fascinating natural material that combines exceptional mechanical properties in terms of strength, stiffness, and resilience;[1,2] there is an increasing interest to emulate the properties of natural silk by mimicking the natural process in regenerated silk.[3,4,5]
Previous studies have indicated the importance of the complete dissolution of silk in several solvents that destroys the hierarchy once the lms are dried.[20,21,22,23,24]
The results indicate that both ice and polyhedral oligomeric silsesquioxanes (POSS) addition have a signi cant in uence on the formation of the silk I structure

Summary

Introduction

Silk is a fascinating natural material that combines exceptional mechanical properties in terms of strength, stiffness, and resilience;[1,2] there is an increasing interest to emulate the properties of natural silk by mimicking the natural process in regenerated silk.[3,4,5]It is generally believed that the exceptional mechanical properties of silk originate from the combination of a hierarchical architecture of the b-sheet crystal and brillar structures. The methods adopted to reassemble silk broin in thin lms resulted in lms that became brittle once dried or had low strength in the wet state.[9,10] A recent study demonstrates that the partial dissolution of silk bers can be the hidden ingredient to obtain hierarchical micro- brils with a high content of b-sheet crystals.[8] Recent advances on the structure of regenerated liquid silk broin help us gain a deeper understanding of the effect of ber dissolution on the properties of silk broin and provide important experimental data for using silk protein as advanced functional biomaterials.[11,12,13]

Results

Conclusion