137
5
carbon and glass fibres. Polyurethane matrix composites have
excellent strength coupled with toughness. PU matrix resins
can be used for automotive exteriors and sports goods (such as
tennis racquets, squash racquets, etc.) The general properties of
polyurethane matrix resins have been mentioned in 7 Chap. 1.
The major processability factors for polyurethane matrix resins
are the following:
5 Polyurethane matrix resins are low-viscosity resins and
cure at a moderately low temperature (T g = 120 °C). Thus,
they do not cause internal or residual stresses in the
component.
5 PU matrix resins may be demoulded at high temperatures
due to its thermal stability. Therefore, it enhances the
demoulding rate and thereby improves the rate of
production.
5 PU matrix resins are susceptible to UV degradation;
therefore, they need UV stabilizers in their formulations.
5 The inherently good surface finish and reactivity of PU
matrix resins facilitate printing on the finished composites.
5 These resins have an extraordinarily good interphase with
carbon fibres due to the reactivity of PU with the sizing of
carbon fibres.
5 PU matrix resins have low shrinkage (>0.2%).
8. Novolac Resins—Novolac resins are commonly known as
novolacs and are generally available in two types: phenolic
and epoxy. Novolacs are cured by an addition reaction and
do not release any condensate. They are used in the form of
prepregs, as described earlier in this chapter. Phenolic
novolacs are mostly used in the form of glass fibre CSM
prepregs and are processed using compression moulding.
The curing temperature of both phenolic and epoxy
novolacs are 160 °C and 180 °C, respectively. The general
properties of novolacs are similar to the properties of the
parent resins (such as phenolic or epoxies), as mentioned in
7 Chap. 1. The major processability factors for novolac
resins are given here.
5 Novolacs are made in powder form. Initially, they melt on
heating, and then subsequently—up to their curing temperature—they get cross-linked and cured.
5 They need post curing in a closed mould at 120 °C to
remove residual stresses in the composite product.
5 Novolacs have low shrinkage (>0.5%).
5.3.4 Selection Criteria for Reinforcement
Reinforcements, as we know, are the main building blocks of a composite as they are the load-bearing members and are responsible for
most of the major properties of composites [18]. Their properties,
size, and shape are important for processability. The processability
of reinforcements and matrices vis-à-vis processing methods is
shown in . Table 5.2. The selection criteria for the reinforcement of
5.3 · Thermosetting Composites
5
carbon and glass fibres. Polyurethane matrix composites have
excellent strength coupled with toughness. PU matrix resins
can be used for automotive exteriors and sports goods (such as
tennis racquets, squash racquets, etc.) The general properties of
polyurethane matrix resins have been mentioned in 7 Chap. 1.
The major processability factors for polyurethane matrix resins
are the following:
5 Polyurethane matrix resins are low-viscosity resins and
cure at a moderately low temperature (T g = 120 °C). Thus,
they do not cause internal or residual stresses in the
component.
5 PU matrix resins may be demoulded at high temperatures
due to its thermal stability. Therefore, it enhances the
demoulding rate and thereby improves the rate of
production.
5 PU matrix resins are susceptible to UV degradation;
therefore, they need UV stabilizers in their formulations.
5 The inherently good surface finish and reactivity of PU
matrix resins facilitate printing on the finished composites.
5 These resins have an extraordinarily good interphase with
carbon fibres due to the reactivity of PU with the sizing of
carbon fibres.
5 PU matrix resins have low shrinkage (>0.2%).
8. Novolac Resins—Novolac resins are commonly known as
novolacs and are generally available in two types: phenolic
and epoxy. Novolacs are cured by an addition reaction and
do not release any condensate. They are used in the form of
prepregs, as described earlier in this chapter. Phenolic
novolacs are mostly used in the form of glass fibre CSM
prepregs and are processed using compression moulding.
The curing temperature of both phenolic and epoxy
novolacs are 160 °C and 180 °C, respectively. The general
properties of novolacs are similar to the properties of the
parent resins (such as phenolic or epoxies), as mentioned in
7 Chap. 1. The major processability factors for novolac
resins are given here.
5 Novolacs are made in powder form. Initially, they melt on
heating, and then subsequently—up to their curing temperature—they get cross-linked and cured.
5 They need post curing in a closed mould at 120 °C to
remove residual stresses in the composite product.
5 Novolacs have low shrinkage (>0.5%).
5.3.4 Selection Criteria for Reinforcement
Reinforcements, as we know, are the main building blocks of a composite as they are the load-bearing members and are responsible for
most of the major properties of composites [18]. Their properties,
size, and shape are important for processability. The processability
of reinforcements and matrices vis-à-vis processing methods is
shown in . Table 5.2. The selection criteria for the reinforcement of
5.3 · Thermosetting Composites