Oxford, United Kingdom -- A study of foams made with a bio-based polyurethane matrix and silkworm cocoons fillers found that the latter significantly reinforces the structure.
A team from the University of Oxford’s Zoology department claim that creating a polymer matrix with a cocoon composition of 60% to 90% and cocoon volume of 40% to 70% increases the foam’s density.
Domesticated and wild silk cocoons will increase unreinforced foam density from 45 kg/m3 to 60 kg/m3 and 120 kg/m3 respectively, while also offering a marked increase in both absolute and specific compressive properties, the research concluded.
In fact, a materials property chart demonstrated that the mechanical properties of the cocoon reinforced foams were comparable to cork and very low density rigid polymer foams.
A report about the study stated: “The shape of the cocoon not only enables high filler fractions in a cast processing technique but also imparts the foam with anisotropic properties.
If the anisotropy is aligned in the principal loading direction, for instance perpendicular to the surface in a crash helmet, the high specific properties of the cocoon reinforced foams can be effectively utilised.”
The researchers found that the cocoon’s non-woven laminate structure “imparts a gradual damage mechanism, eliminating the typical collapse plateau in the stress–strain curve of an unreinforced foam.”
It also gave “comparable environmental resistance” to unreinforced foam, the team said.
Work is ongoing, with a study into “silk-based sandwich-structured composites” on the horizon, according to an article the team published in Vol 56 of Elsevier’s Polymer journal.