Civil Engineering Reference
In-Depth Information
coupling is thought to occur via alcoholysis, surface chelation or coordination exchange.
h e monoalkoxy- and neoalkoxy-type titanium-derived coupling agents react with
the hydroxyl groups present on the surface of the substrate to form a monomolecular
layer [165, 166]. Nair and his partners [167] used phenyl isocyanates and alkenyl suc-
cinic anhydride to improve the quality of the interface between natural rubber and
chitin whiskers with presence of 3-isopropenyl-R, R¢-dimethylbenzyl isocyanate. h e
expected chemical reactions that occur in the alternative chemical modii cations are
given in Figure 22 [167].
11.6.4
Grat ing
h ere are three methods reported by Stenstad
et al.
[40] for modii cation of MFC
by heterogeneous reactions in both water and organic solvents to produce cellulose
nanoi bers with a surface layer of moderate hydrophobicity. Epoxy functionality was
introduced onto the MFC surface by oxidation with cerium (IV) followed by grat ing
with glycidyl methacrylate. Reactive epoxy groups served as a starting point for further
functionalization with ligands, which typically do not react with the surface hydrox-
yls present in native MFC. As the reaction is conducted in aqueous media, the use of
organic solvents and laborious solvent exchange procedures can be avoided, which is
the major advantage of this technique. In the same research conducted by these authors,
grat ing of hexamethylene diisocyanate followed by reaction with amines yield a far
more hydrophobic MFC surface. Succinic and maleic acid groups can be introduced
directly onto the MFC surface as a monolayer by a reaction between the corresponding
anhydrides and the surface hydroxyl groups of the MFC. Also, noctadecyl isocyanate
(C
18
H
37
NCO) has been applied as the grat ing agent in order to improve MFC compat-
ibility with polycaprolactone [168].
Apart from this, i ve dif erent chemicals, ethylene acrylic acid, styrene maleic anhy-
dride, guanidine hydrochloride, and Kelcoloids HVF and LVF stabilizers (propylene
glycol alginate), were used to prepare bionanocomposites from PLA and PHB as matri-
ces by Wang and Sain [169] in order to explore the potential use of chemically coated
O
OH
NH
O
HO
O
O
HO
O
NH
n
OH
O
O
O
NCO
O
R
R
O
O
R
R
NH
CH
2
COOH
O
O
O
O
NH
O
NH
O
HO
O
HO
O
O
HO
HO
O
O
OH
O
OH
NH
NH
n
n
O
O
Figure 11.22
Chemical reactions that occur in the alternative chemical modii cations of chitin
whiskers with phenyl isocyanate, alkenyl succinic anhydride and 3-isopropenyl-R, R¢-dimethylbenzyl
isocyanate [167] .
