Environmental Engineering Reference
In-Depth Information
3.3.5 Adhesive Properties
The use of adhesives, i.e., materials that can join surfaces (similar or dissimilar)
together is widely spread across the construction industry, both in structural and
nonstructural situations. Adhesives are used for example to join and attach internal
building panels and elements, to attach brick slips, ceramic tiles, and flooring or to
produce plywood. A large proportion of these adhesives are based on organic
solvents and polymeric resins like polyesters, polyurethanes, and acrylics.
Replacing these petroleum-based materials for more benign, water-based adhesives
would definitely contribute to environmental sustainability. Nature offers a vast
array of solutions to promote adhesion that are worth exploring in this context, as
described next with a few examples.
Marine-inspired adhesives. Marine organisms like the sandcastle worm
(Phragmatopoma californica, Shao et al.
2008
), limpets (Diodora aspera, Ellem
et al.
2002
), sea cucumbers (Holothuroidea, Flammang et al.
2009
), barnacles
(Megabalanus spp., Knight
2009
), mussels (Mytilus edulis, Lee et al.
2006
,
2007
),
and sea urchins (Santos and Flammang
2012
) secrete protein-based glues unri-
valled by any man-made adhesive. Moreover, unlike common adhesives, they
resist humidity and are produced using water-based chemistry. For example,
mussels secrete a cocktail of proteins rich in lysine and 3,4-dihydroxyphenylala-
nine (DOPA) amino acids, which solidify at the pH of sea water (around 8.2)
(Flammang et al.
2009
). DOPA residues are able to establish strong coordinate
bounds with metal ions of inorganic substrate and covalent bounds with the
molecules of organic substrates (Lee et al.
2006
). This versatility provides out-
standing permanent adhesion for defying the power of ocean waves.
If technically and economically feasible, the substitution of traditional glues
like the ones based on the recognized carcinogen formaldehyde by water-based
and water-resistant glues formulated with DOPA mimetic molecules could revo-
lutionize the adhesive market. Excellent results have already been obtained by
manipulating the abundant and inexpensive soy proteins to resemble marine
adhesive cocktails. The plywood manufacturer Columbia Forest Products
9
reduced
the use of carcinogenic components and the emission of hazardous air pollutants
by successfully introducing these soy-based, formaldehyde-free adhesives in the
manufacturing of hardwood plywood (PureBond
technology
10
).
Velcro. One of the most famous biomimetic products, Velcro, was conceived
back in 1948 by George de Mestral following the observation that the seeds of the
burdock plant (Arctium lappa) relied on hook-like structures to stick to clothes or
animal fur as a strategy for dispersion (Bhushan
2009
). Mestral ultimately patented
a process for producing the well-known fabric fastener and named it Velcro. Since
then, the production of Velcro has grown, its applications ranging from textiles,
9
Columbia Forest Products, Greensboro, North Carolina.
10
PureBond Technology. Ask Nature, Biomimicry 3.8. Accessed on the 20th March 2014,
http://www.asknature.org/product/22aa5601fcdb68b5d2dc9e3d3a22f7f1
.
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