SAMPE Journal - May/June 2016 - 29
Feature Article
silk cocoons can be employed as innovative volumeoccupying reinforcements in polymer foams to facilitate
i) property enhancement, ii) cost reductions, and iii)
transitions into sustainable material technologies.
Replacing a substantial quantity (60-90% by weight
and 40-70% by volume) of the polymer matrix, silk
cocoons of both domesticated and wild silkworms
increased the density of the unreinforced foam from
45 kg/m3 to ~60 kg/m3 and ~120 kg/m3 respectively,
but also offered a marked increase in both absolute
and specific compressive properties.
Key insights of our study particularly demonstrate
the viability of silk cocoons as natural particulate
reinforcements. The prolate spheroid 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. Notably, the cocoon
reinforced foams can be thought of as useful hybrids
between honeycomb structures (that are anisotropic,
but difficult to form into complex shapes) and foams
(easy to form, but are isotropic). Attractively, the non-
SAMPE Journal, Volume 52, No. 3, May/June 2016
woven laminate structure of the silk cocoons imparts
a gradual damage mechanism, eliminating the typical
collapse plateau in the stress-strain curve of an
unreinforced foam, to the resulting syntactic foam.
Nonwoven and Woven Silk Laminate Composites
Silk: A Unique Natural Fibre for Reinforcing Polymers
Many of the properties of native silks (as opposed
to regenerated silks) also make them potential
sustainable alternative reinforcement materials,
alongside plant fibres, for engineering (i.e. nonbiomedical) composites. Table 2 compares the
economic, technical and ecological properties of silks
with plant and glass fibres. In general, the primary
disadvantages of silks in comparison to plant and glass
fibres are: i) higher cost, ii) lower annual production,
iii) higher moisture absorption, iv) lower softening
(and therefore processing) temperatures, v) poor
stiffness, and vi) high embodied energy for processed
materials (e.g. fabrics). However, they possess i) lower
density (than even plant fibres), ii) natural flame
resistance, iii) moderate strength, iv) unparalleled
toughness (higher than even Kevlar), and v) a
generally favourable environmental profile of the raw
material. Other technical advantages of silks specific
29
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Table of Contents for the Digital Edition of SAMPE Journal - May/June 2016
Contents
SAMPE Journal - May/June 2016 - Cover1
SAMPE Journal - May/June 2016 - Cover2
SAMPE Journal - May/June 2016 - Contents
SAMPE Journal - May/June 2016 - 2
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