SAMPE Journal - September/October 2020 - 39
Figure 9. The molecular structure of diglycidyl ether of bisphenol-A (DGEBA" or "Bis A")
type epoxy. This epoxy was chosen as a component of the resin system for the adhesive
and laminated patch.
Figure 10. Tetraethylene pentaamine (TEPA) was one of two curing agents using in the
laminating resin and adhesive.
of TEPA is shown in Figure 10. Because of its low
molecular weight and relatively high number of
amine hydrogens, TEPA creates a stiff matrix when
used to cure epoxy.
Polyamide curing agents are natural products,
derived from the oils of plants and trees. A wide variety of products are derived from plant oils, which
are hydrolyzed to their acid components. Natural
products are unusual in resin, adhesives, and coatings industries, but polyamides are an exception
and have been used for several decades in these
applications. Most notably, polyamides are major
components in many aerospace adhesives. For
polyamide curing agents, oleic and linoleic acid
are used. These components are reacted together
as shown in Figure 11 to form the high molecular
weight "dimer acid". The double bond in the dimer
acid prevents the curing agent from crystalizing (as
they do in plant oils). The acid end-groups are then
reacted with triethylene tetraamine (TETA), shown
in Figure 12. The reaction between an acid and an
amine results in an amide linkage, and since there
are more than one such linkage per molecule, the
product is a "polyamide". Polyamides were selected for bicycle frame repair because, due to their
high molecular weight and relatively fewer amine
groups per molecule (compared to TEPA) they result in a more compliant cured resin. In addition,
their high viscosity prevents drain-out from the
fabric reinforcement in the patch, and their longer
working life allows ample time to complete the layup sequence. The particular polyamide selected
was Versamid 140, which has a viscosity of approximately 9,000 cP at room temperature8, and provides approximately 2 hours of pot life when mixed
with epoxy at room temperature.
w w w. s a m p e . o r g
Figure 11. Formation of the dimer acid used to synthesize polyamide curing
agents.
Figure 12. Triethylene tetraamine (TETA) is reacted with dimer acid to form
polyamide curing agents. Polyamides are widely used in aerospace adhesives, and a polyamide was included in the bicycle frame repair resin formulation for its good adhesive properties and high viscosity.
S E P T E M B E R /O C TO B E R 2 0 2 0
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http://www.sampe.org
SAMPE Journal - September/October 2020
Table of Contents for the Digital Edition of SAMPE Journal - September/October 2020
Table of contents
SAMPE Journal - September/October 2020 - Cover1
SAMPE Journal - September/October 2020 - Cover2
SAMPE Journal - September/October 2020 - Table of contents
SAMPE Journal - September/October 2020 - 2
SAMPE Journal - September/October 2020 - 3
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SAMPE Journal - September/October 2020 - Cover3
SAMPE Journal - September/October 2020 - Cover4
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