Environmental Engineering Reference
In-Depth Information
Silk is also a fibre of major interest. Mimicking spider silk biosynthesis is still
a dream of many researchers [38] and classical silk finds many applications in
composites and biomedical devices such as tissue scaffolds [39].
6.3.6.6
Lignin Derivatives
A portfolio of biomaterials can be obtained from lignin derivatives. First the
lignophenol derivative, which contains a diphenylpropane unit formed by binding
a carbon atom at an ortho-position of a phenol derivative to a carbon atom at a
benzyl-position of a phenylpropane fundamental unit of lignin, and binding an
oxygen atom of the hydroxyl group and a β-positional carbon atom under alkali
conditions to obtain an arylcoumaran derivative [40]. The latter can be reticulated
to form polymers shaped under hot-moulding.
A similar strategy involves liquefying biomass with phenol under acidic condi-
tions to obtain phenolic monomers. The type of monomers obtained varies largely
[41] and these monomers can reticulate with the help of increased temperatures
or with formaldehyde to obtain novolac-type or resol-type resins.
Two commercial materials made from or including lignin are the blend
XyloBag™ marketed by the American company CycleWood Solutions Inc. and
Arboform® from German company Tecnaro.
6.4
Agromaterials, Blends and Composites
6.4.1
Agromaterials
The food-processing industry produces a large amount of waste and co-products
rich in fibres. The nature of these fibres and the types of biopolymers contained
within vary largely. The three main food industries (vegetable oil, starch and sugar)
produce millions of tons of oilcakes, stalks, pulp and bagasse. Most of these resi-
dues are often used for animal feed. However, their high cellulose content and their
low price make them the source of choice for the fabrication of materials known as
'agromaterials' [42].
The availability of these residues depends on regional agricultural productions
and on the commitment of agricultural cooperatives in favour of agromaterials. In
France for instance, there are currently corn crops dedicated exclusively to the
production of thermoplastic agromaterials.
In this case the biopolymers are directly plasticised by thermomechanical
means and transformed through the classical forming technologies of the plastic
industry: injection-moulding, extrusion and thermo-forming. These agromaterials
(e.g. wood) maintain a natural aspect and are sensitive to atmospheric conditions,
but have no shape restriction (Figure 6.23).
Agromaterials demonstrate that it is possible to profitably transform raw agri-
cultural products without separation (Table 6.5) and that almost all non-cellulosic
