129
5
5 Chemical Interaction with Reinforcement—Chemical
interaction between the resin and reinforcement for
making a chemical bond is preferred. The interphase of the
composite depends upon the reactivity of resin as well as
the reinforcement for each other. However, coupling agents
on the reinforcement play a major role in this. Normally,
thermosetting resins are reactive to the coupling agent on
reinforcements. The resin must be selected based on its
reactivity with the surface of the reinforcement to make a
good interphase.
5 Curing Reaction—Resins having additional reactions (such
as epoxy resins, polyester resins, etc.) are preferred for
composite processing. Resins undergoing condensation
reactions, such as phenolic resins, give byproducts in the
form of water, and PMR–PI resins give byproducts such as
methanol/ethanol and N-methylpyrrolidone/dimethylacetamide. This creates multifold challenges during moulding
of composites, such as the extraction of byproducts,
consolidation of matrix, correct volume fractions, etc.
5 Molecular Weight and Its Distribution—The high molecular
weight of resins restricts their ability to flow and thus their
percolation around the reinforcement. In the case of epoxy
resins, there are bifunctional resins, such as diglycidylether
of bisphenol ‘ A’ (DGEBA), which has molecular weight of
30,000–70,000 g/mol and a viscosity of 10,000–12,000 cps.
This viscosity comes down to 5000–7000 cps after mixing
with a hardener (i.e. amines or anhydrides). The molecular
weights of tri-functional and tetra-functional epoxy resins
are in the range of 50,000–120,000 g/mol and have viscosities in the range of 20,000–50,000 cps. These are hot melt
processed resins. The molecular weight distribution is quite
narrow at approximately 1.5 for epoxy resins.
Resin with low
surface tension
Resin with high
surface tension
Limited wetting
Good wetting
Fibre
Resin
. Fig. 5.6 a Limited wetting of fibre by resin having high surface tension
and b good wetting of fibre having low surface tension
5.3 · Thermosetting Composites
5
5 Chemical Interaction with Reinforcement—Chemical
interaction between the resin and reinforcement for
making a chemical bond is preferred. The interphase of the
composite depends upon the reactivity of resin as well as
the reinforcement for each other. However, coupling agents
on the reinforcement play a major role in this. Normally,
thermosetting resins are reactive to the coupling agent on
reinforcements. The resin must be selected based on its
reactivity with the surface of the reinforcement to make a
good interphase.
5 Curing Reaction—Resins having additional reactions (such
as epoxy resins, polyester resins, etc.) are preferred for
composite processing. Resins undergoing condensation
reactions, such as phenolic resins, give byproducts in the
form of water, and PMR–PI resins give byproducts such as
methanol/ethanol and N-methylpyrrolidone/dimethylacetamide. This creates multifold challenges during moulding
of composites, such as the extraction of byproducts,
consolidation of matrix, correct volume fractions, etc.
5 Molecular Weight and Its Distribution—The high molecular
weight of resins restricts their ability to flow and thus their
percolation around the reinforcement. In the case of epoxy
resins, there are bifunctional resins, such as diglycidylether
of bisphenol ‘ A’ (DGEBA), which has molecular weight of
30,000–70,000 g/mol and a viscosity of 10,000–12,000 cps.
This viscosity comes down to 5000–7000 cps after mixing
with a hardener (i.e. amines or anhydrides). The molecular
weights of tri-functional and tetra-functional epoxy resins
are in the range of 50,000–120,000 g/mol and have viscosities in the range of 20,000–50,000 cps. These are hot melt
processed resins. The molecular weight distribution is quite
narrow at approximately 1.5 for epoxy resins.
Resin with low
surface tension
Resin with high
surface tension
Limited wetting
Good wetting
Fibre
Resin
. Fig. 5.6 a Limited wetting of fibre by resin having high surface tension
and b good wetting of fibre having low surface tension
5.3 · Thermosetting Composites