Maleated Coupling Gents
Maleated coupling agents are widely used to strengthen
composites containing fillers and fiber reinforcements
[51–54]. The difference with other chemical
treatments is that maleic anhydride is not only used to
modify fiber surface but also the PP matrix to achieve
better interfacial bonding and mechanical properties in
composites [55–57]. The PP chain permits maleic
anhydride to be cohesive and produce maleic anhydride
grafted polypropylene (MAPP). Then the treatment
of cellulose fibers with hot MAPP copolymers
provides covalent bonds across the interface (Fig. 1).
The mechanism of reaction of maleic anhydride with
PP and fiber can be explained as the activation of the copolymer by heating (170C) before fiber treatment
and then the esterification of cellulose fiber [58]. After
this treatment, the surface energy of cellulose fibers is
increased to a level much closer to the surface energy
of the matrix. This results in better wettability and
higher interfacial adhesion of the fiber.
Mohanty et al. [59] used MAPP as coupling agent
for the surface modification of jute fibers. It has been
found that a 30% fiber loading with 0.5% MAPP
concentration in toluene and 5 min impregnation time
with 6 mm average fiber lengths gave the best results.
A 72.3% increase in flexural strength was observed
with the treated composites. In addition to PP matrix,
Mishra et al. [60] reported that maleic anhydride
treatment reduced the water absorption to a great
extent in banana, hemp and sisal fiber-reinforced
novolac composites. Mechanical properties like
Young’s modulus, flexural modulus, hardness and
impact strength of plant fiber-reinforced composites
increased after maleic anhydride treatment.