Industrial Use of Oil Cakes for Material Applications - The Economic Utilisation of Food Co-Products - page 154

on the ESFOC. The evolution of the ESFOC viscosity according to the amount
of reducing agent is similar to that observed in a previous study of the rheo-
logical properties of sunflower protein isolate. 28 The increase of the sodium
sulfite ratio with regard to the mass of protein from 0 to 5% results in a
progressive decrease of the apparent ESFOC viscosity. Then, when the addition
is increased above 5%, the viscosity does not decrease further (Figure 7.5), and
even increased when a low shear stress rate was applied to the mixture. This
result is attributed to the consequence of the structural changes in proteins
during the

d n 9 r 3 n g | 5

chemical attack, however, the mechanism explaining this

phenomenon has not yet been elucidated.
Extruded sunflower oil cake treated with 5% sodium sulfite (ESTOC) has an
optimal rheological behaviour. The addition of the reducing agent leads to a
large decrease in the consistency coecient K and an increase of the pseudo-
plasticity index m (Figure 7.13). At a moisture content of 25% and a
temperature of 120 1C, the coecients of consistency and pseudoplasticity are
respectively, 310 958 and 0.04 for the ESFOC and 9145 and 0.54 for the
ESTOC. The rheological behaviour of ESTOC is particularly interesting and as
such, it would be possible to decrease its moisture content further. Therefore,
while the treatment via extrusion results in a 5% decrease of the moisture
content of the cake, treatment with sodium sulfite reduces it more eciently
(Figure 7.13).

d y y f n n 3 .

7.5 Injection Moulding of SFOC
Injection moulding of 100% natural biopolymers and biocomposites is not well
documented. It still belongs mainly to industrial know-how, which stands as a
major retarding issue for the development of agromaterials. Only two German
papers 61,62 from the 1990s compare the operating conditions for the moulding
of such materials. From these works and according our experience, particular
issues have been raised and are summarised in Table 7.5. There are three main
differences for their processing when compared to classic thermoplastic
materials:

the occurrence of adsorbed water: agrobased compounds should never be
dried;
the heat sensitivity of biopolymers: high shear, long residence time and
high temperature should be avoided;
the high viscosity of these materials: high injection pressure and wide gaps
should be used.

For the processing of SFOC, injection moulding at different stages of the
destructuring process has been studied. Raw SFOC with 30% moisture content
can be formed by injection moulding. However, due to its lack of ''plasticity'',
the use of a screw without a backflow stop valve is necessary. The mechanical
constraint engendered by this valve resulted in a local temperature rise and