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 maleicanhydride is not only used to modify fiber surface but also the PP matrix to achieve better interfacialbonding and mechanical properties in composites [55–57].
The PP chain permits maleicanhydride to be cohesive and produce maleicanhydridegrafted polypropylene (MAPP).
Then the treatment of cellulose fibers with hot MAPP copolymersprovides 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 andhigher 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 maleicanhydride
treatment reduced the water absorption to a great extent in banana, hemp and sisal fiber-reinforcednovolac composites.
Mechanical properties like Young’s modulus, flexural modulus, hardness and impact strength of plant fiber-reinforced composites increased after maleicanhydride treatment.