105Plant Fiber–Based Composites
• Restrained layers: coupling agents develop a highly cross-linked interface
region, with a modulus intermediate between that of the substrate and of
the polymer
• Wettability: coupling agents improve the wetting between polymer and sub-
strate (critical surface tension factor)
• Chemical bonding: coupling agents form covalent bonds with both materials
• Acid–base effect: coupling agents alter the acidity of the substrate surface
The development of a denite theory for the mechanism of bonding by coupling
agents in composites is a complex problem. The main chemical bonding theory alone
is not sufcient. So the consideration of other concepts appears to be necessary,
including the morphology of the interface, the ...