Environmental Engineering Reference
In-Depth Information
Figure 6.26
Film obtained by extrusion of sugar beet pulp.
characteristic for the biodegradation of the agromaterials, which reaches 100% in a
very short time. A particular application is to assist in the pricking out of seedlings. A
pot made of any of these agromaterials is strong enough to ensure the mechanical
support of growing small plants. When they are big enough, the plants can be trans-
planted to the soil without removing the pots. The latter will biodegrade and provide
nutrients to the plant, which has been demonstrated to grow faster and to a larger size.
In the particular case of protein-rich granulates (oilcakes), thermo-moulding is
often more suitable because it takes advantage of their cross-linking abilities [43].
The mechanical properties of these materials are lower, but the advantage is that
oilcake can be used as it is and the materials produced are more resistant to water.
Regarding its microstructure, sugar beet pulp is the best candidate to extrude
films (thickness >200 µm) [44]. Figure 6.26 depicts a film produced using sugar
beet pulp and glycerol as the external plasticiser.
6.4.2
Blends of Synthetic Polymers and Starch
Blends of starch and a synthetic polymer (usually polyethylene) are products of
commercial importance. Two families of blends are currently available: those
using dehydrated starch pellets and those using gelatinised or thermoplastic
starch. In both cases, the mixture is produced with the synthetic polymer by extru-
sion. Further processing by moulding or blowing is also possible, depending on
the kind of starch used.
Dehydrated starch
acts as a charge and diminishes the mechanics properties of
the polymer. It is not possible to add more than 20%; in practice, the rate oscillates
between 6 and 10%. In order to obtain a better compatibility between starch and
the polymer, starch might be rendered hydrophobic by chemical treatment as
described in Section 6.3.4.
One of the principal objectives in these systems is biodegradability. In this
regard, auto-oxidation agents and organometallic catalysts are often added to the
