Silk for light-weight syntactic foams and tough textile composites

Growing interest in bio-based materials has powered the recent industrial uptake of plant fibre reinforced plastics. In contrast, nature's wonder-fibre silk has had no commercial applications and only limited scientific investigations as a composite reinforcement in addressing the question 'are silks suitable as polymer reinforcements?', we explored two routes to silk composites: i) syntactic foams, where silk cocoons were employed as natural, macroballoon, particulate reinforcements in a bio-based polyurethane foam, and ii) laminate composites, where nonwoven mats and woven textiles of silk were fibre reinforcements in an epoxy matrix. In the syntactic foams, cocoons were effective volume-occupying, structural fillers; the cocoons replaced 60-90 wt% (40-70 v%) of the polymer foam, and yet a marked increase in compressive properties was observed. Notably, the cocoon reinforced foams were useful hybrids between honeycomb structures (that are anisotropic, but difficult to form into complex shapes) and foams (easy to form, but are isotropic). As a fibre reinforcement, silk was a superior alternative to flax, and a potential sustainable option against glass, in appropriate applications, viz. i) light-weight, impact-critical components, such as high-performance helmets and drones, and ii) light-weight, flexural stiffness- or strength-critical components, such as construction beams, automotive load-floors, and sporting equipment.