Industrial Use of Oil Cakes for Material Applications - The Economic Utilisation of Food Co-Products - page 156

those of commercial starch-based composite materials. 62 These materials are
brittle when no external plasticiser is used, as in the case for all agromaterials. 50

7.6 Durability of SFOC-Based Materials
The main advantage of protein-based materials, which is related to protein
aggregation, is their high water resistance. While carbohydrate-based materials
are highly moisture sensitive, moulded samples from ESTOC do not disin-
tegrate when immersed in water at 25 1C and water absorption reaches a
maximum of absorption lower than 60% in 24 h, while the samples injected
from ESFOC cannot be handled after the same time (Figure 7.14). The protein
matrix seems to have a thermoset-like behaviour rather than a thermoplastic
behaviour. Heat- and shear-induced aggregation of proteins involving hydro-
phobic interactions, while the disulfide bridges generate a three-dimensional
network. 26,63 This phenomenon is also responsible for the low proportion of
water-soluble material

d n 9 r 3 n g | 5

d y y f n n 3 .

in sunflower protein-based films obtained by

thermomoulding. 37
This essential property can be used in injection-moulding only because
lignocellulosic fibres contained in the sunflower oil cake prevent the complete
crosslinking of the proteins in the injection screw, as occurs during the forming
of sunflower protein isolate when a temperature higher than its denaturation
temperature is used. 64,65
This specific property can be improved with a thermal treatment, which is
known to reduce the hydrophilicity of wood or proteic films. In the former case,
the treatment is based on the crosslinking of hemicelluloses and lignin
compounds at high temperature and under inert atmosphere (200 1C, under
nitrogen flow). 66 Above the glass-transition temperature of the amorphous

Figure 7.14 Mass gain in water at 25 1C of ESFOC and thermally treated ESTOC
samples. 57