134
5
used as adhesive, is diglycidyl ether of bisphenol ‘ A’ . It is
manufactured from the condensation reaction of bisphenol ‘ A’
(BPA) and epichlorohydrin (ECH) in the presence of sodium
hydroxide. The condensate comes out in the form of sodium
chloride and water. The resin is used in the form of a prepolymer. Fluoro-epoxy resins are used for fire- resistant applications. Elastomer-toughened epoxy resins are also available, and
they improve the toughness of the composite product. The
general properties of epoxy resins have been mentioned in
7 Chap. 1. The major processability factors for epoxy resins are
as follows:
5 The viscosities of epoxy resins can be controlled by
diluents.
5 Room-temperature curing hardeners, such as diethylene
triamine or triethylenetetramine, provide a processing
window of approximately 10 minutes, which is its gelation
time.
5 High-temperature curing hardeners, such as diamino
diphenyl sulfones (DDS) or diamino diphenyl methane
(DDM), are cured at 160–180 °C and provide a long
processing window of 2–3 hours.
5 Epoxy resins have low shrinkage (<0.5%).
2. Unsaturated Polyester (UPE) Resins—There are two types of
unsaturated polyester resins. One is a general-purpose resin
made from a condensation reaction of phthalic anhydride,
propylene glycol, and maleic anhydride. The other is an
isophthalic resin made out of a condensation reaction of acid,
propylene glycol, and maleic anhydride.
An isophthalic grade of UPE has superior properties over
a general-purpose UPE. These resins are mixed with α-methyl
styrene (which is cheaper in cost than styrene) to make the
resin in a liquid form. For curing, an initiator, such as methyl
ethyl ketone peroxide (MEKP), and a catalyst, such as cobalt
naphthenate, are mixed in the resin. Benzoyl peroxide along
with a tertiary amine is also used as an initiator for the curing
of UPE resins at room temperature. The catalyst is mixed after
the initiator is mixed in the resin; otherwise an excessive exothermic reaction may lead to an explosion. The cross-linking
and curing reactions in UPE resins are governed by free radical polymerization. During a cross-linking reaction, the double bond of maleic anhydride gets saturated with styrene. This
makes the cross-linked network with the styrene. The general
properties of UPE resins have been mentioned in 7 Chap. 1.
The major processability factors for UPE resins are given
here.
5 The molecular weight of UPE resin is in the range of
1200–3000 g/mol.
5 The viscosities of UPE resins are low.
5 UPE resins are curable at room temperature only. The
processing window is approximately 10–15 minutes, which
is its gelation time.
5 UPE resins have high shrinkage (approximately 1.5%).
Chapter 5 · Processability of Thermosetting Composites
5
used as adhesive, is diglycidyl ether of bisphenol ‘ A’ . It is
manufactured from the condensation reaction of bisphenol ‘ A’
(BPA) and epichlorohydrin (ECH) in the presence of sodium
hydroxide. The condensate comes out in the form of sodium
chloride and water. The resin is used in the form of a prepolymer. Fluoro-epoxy resins are used for fire- resistant applications. Elastomer-toughened epoxy resins are also available, and
they improve the toughness of the composite product. The
general properties of epoxy resins have been mentioned in
7 Chap. 1. The major processability factors for epoxy resins are
as follows:
5 The viscosities of epoxy resins can be controlled by
diluents.
5 Room-temperature curing hardeners, such as diethylene
triamine or triethylenetetramine, provide a processing
window of approximately 10 minutes, which is its gelation
time.
5 High-temperature curing hardeners, such as diamino
diphenyl sulfones (DDS) or diamino diphenyl methane
(DDM), are cured at 160–180 °C and provide a long
processing window of 2–3 hours.
5 Epoxy resins have low shrinkage (<0.5%).
2. Unsaturated Polyester (UPE) Resins—There are two types of
unsaturated polyester resins. One is a general-purpose resin
made from a condensation reaction of phthalic anhydride,
propylene glycol, and maleic anhydride. The other is an
isophthalic resin made out of a condensation reaction of acid,
propylene glycol, and maleic anhydride.
An isophthalic grade of UPE has superior properties over
a general-purpose UPE. These resins are mixed with α-methyl
styrene (which is cheaper in cost than styrene) to make the
resin in a liquid form. For curing, an initiator, such as methyl
ethyl ketone peroxide (MEKP), and a catalyst, such as cobalt
naphthenate, are mixed in the resin. Benzoyl peroxide along
with a tertiary amine is also used as an initiator for the curing
of UPE resins at room temperature. The catalyst is mixed after
the initiator is mixed in the resin; otherwise an excessive exothermic reaction may lead to an explosion. The cross-linking
and curing reactions in UPE resins are governed by free radical polymerization. During a cross-linking reaction, the double bond of maleic anhydride gets saturated with styrene. This
makes the cross-linked network with the styrene. The general
properties of UPE resins have been mentioned in 7 Chap. 1.
The major processability factors for UPE resins are given
here.
5 The molecular weight of UPE resin is in the range of
1200–3000 g/mol.
5 The viscosities of UPE resins are low.
5 UPE resins are curable at room temperature only. The
processing window is approximately 10–15 minutes, which
is its gelation time.
5 UPE resins have high shrinkage (approximately 1.5%).
Chapter 5 · Processability of Thermosetting Composites