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I. Why Epoxy?
Composite Polymer Design manufactures a variety of epoxy resin
systems that are well suited to the infusion
process. Before delving into specifics, let’s take a moment
to consider why you should select an epoxy.
A. Adhesion to Reinforcement
The supreme advantage of epoxy is its excellent adhesion
to almost any surface. Epoxy adheres
tenaciously to a broad range of substrates, particularly
those that are frequently used as
reinforcement in composite parts and structures.
1. Carbon Fiber
Carbon fiber commonly has an epoxy binder. This binder
further promotes the adhesion of epoxy to the substrate
and makes an epoxy the ideal resin system for the fabrication
of
carbon fiber composites.
2. Kevlar®
Kevlar® typically does not have a binder. In this
case, the superior adhesion characteristics of epoxy
make it preferable to other organic polymers for the
fabrication of Kevlar® composites.
3. Fiber Glass
More so than carbon fiber and Kevlar® composites,
fiber glass composites are susceptible to attack by
water vapor. Water vapor attacks the interface between
resin and reinforcement, and leads to degradation of
the composite structure. In the long term, epoxy provides
a barrier against water vapor that is superior to other
organic polymers and can be used to fabricate more durable
fiber glass composites. Fiber glass is available with
a wide variety of binders. A number of these binders
have been formulated to promote the adhesion of specific
organic polymers to fiber glass. As such, it is important
to select a grade of fiber glass with an epoxy compatible
binder when using an epoxy resin system to construct
fiber glass composites.
4. Core Material
Where core material has been incorporated into the design
of a laminate to produce a light weight composite structure,
using an epoxy resin system can provide further weight
savings. The superior adhesion characteristics of epoxy
eliminate the need for a resin rich mat between the
structural reinforcement and the core material.
B. Versatility
Epoxy resin systems can be formulated with various curing
agents, diluents, fillers and other additives to produce
an almost unlimited range of properties. The tremendous
versatility of epoxy makes it possible to tailor the handling
and mechanical properties of an epoxy resin system to what
is needed.
C. Low Shrinkage
Epoxy resin systems exhibit little shrinkage during cure
and allow for the precise reproduction of mold surfaces.
The dimensional stability provided by an epoxy resin system
gives rise to the fabrication of composite parts and structures
with lower ingrained stress levels. As a result, finished
pieces are stronger and more durable than those produced
using organic polymers that exhibit higher values of shrinkage.
D. Chemical Resistance
Properly cured epoxy resin systems have excellent chemical
resistance to acids, bases and solvents. In contrast to
other organic polymers, epoxy resin systems are particularly
resistant to caustic substances.
E. No Volatile Loss
Epoxy resin systems formulated for the fabrication of structural
composites are typically 100 percent solids. No byproducts,
volatile or otherwise, are formed as these systems polymerize.
By and large, there are no VOC issues associated with the
handling of epoxy resin systems.
II. Selecting An Epoxy Resin System For Infusion
Several issues need to be weighed when selecting an epoxy resin
system for the infusion process. The
considerations that need to be made fall into two categories,
end product requirements and processing
requirements.
A. End Product Requirements
End product requirements are those requirements that apply
to the function and/or use of the composite part or structure
to be manufactured.
1. Operating Temperature
One requirement that is paramount to the selection of
an epoxy resin system is the operating temperature or
service temperature of the article to be manufactured.
The heat deflection temperature (HDT) of the epoxy resin
system selected must be greater than or equal to this
intended operating temperature.
a. Less Than 210°F
If the intended operating temperature of a composite
part or structure is less than 210°F, one of
the Composite Polymer Design (CPD) room temperature
infusion systems found in Table 1 should be considered.
b. Between 210°F and 310°F
If the intended operating temperature of a composite
part or structure is between 210°F and 310°F,
one of the CPD medium temperature infusion systems
found in Table 2 should be considered.
c. Greater Than 310°F
If the intended operating temperature of a composite
part or structure is greater than 310°F, one
of the CPD high temperature infusion systems found
in Table 3 should be considered.
2. Other Physical Properties
Other physical properties, such as the desired compressive,
flexural and tensile strengths, should be taken into
account when selecting an epoxy resin system for infusion.
Please refer to the physical properties listed in the
lower half of Table 1, Table 2 and Table 3 to determine
if one of the CPD infusion systems meets your end product
requirements. In the event that one of these systems
does not meet your end product requirements, Composite
Polymer Design can custom tailor an epoxy resin system
to meet your needs.
B. Process Requirements
Process requirements are those requirements that apply to
the act of manufacturing a composite part or structure.
1. Cure Cycle
The first process requirements that should be considered
when selecting an epoxy resin system for infusion is
the desired cure cycle. Please review the capabilities
of your equipment, tooling and ancillary materials when
choosing a cure cycle. In particular, please consider
the temperature your mold will have to withstand.
a. Room Temperature Cure
Composite Polymer Design offers a variety of two
part epoxy resin systems that can be cured at room
temperature, 68-77°F (20-25°C).
b. Elevated Temperature Cure
CPD also offers one part and two part epoxy resin
systems that must be cured at an elevated temperature.
2. Post Cure Cycle
The second process requirement that should be considered
when selecting an epoxy resin system for infusion is
the post cure cycle. Not all epoxy resin systems require
a post cure. However, it is typically the case with
epoxy that a post cure is required to develop ultimate
properties. As with choosing a cure cycle, it is important
to review the capabilities of your equipment, tooling
and ancillary materials when choosing a post cure cycle.
Again, in particular, please consider the temperature
your mold will have to withstand.
a. Supported
In the first stage of a post cure cycle, a composite
part or structure made using an epoxy resin system
typically needs to be supported. That is, it should
remain in the mold to reduce the likelihood of any
deformation that may occur as a result of thermal
shock. A supported post cure is usually conducted
at temperatures less than or equal to 150°F to avoid
damaging the mold.
b. Unsupported
Prior to the latter stages of a post cure cycle,
a composite part or structure made using an epoxy
is typically removed from the mold and post cured
free standing. An unsupported post cure is usually
conducted at temperatures in excess of 150°F, but
should not exceed the heat deflection temperature
of the epoxy resin system.
3. Viscosity
Another process requirement to consider when selecting
an epoxy resin system for infusion is viscosity. Composite
Polymer Design offers a variety of low viscosity resins
that have been formulated specifically for infusion.
One advantage of using an epoxy versus other organic
polymers is that epoxy resin systems exhibit a latent
build in viscosity. That is, they typically remain low
in viscosity much longer than other organic polymers,
extending the work life without compromising gel time.
a. Input Resin Temperature
The input resin temperature is the temperature of
the resin at the point it is being infused. Typically,
the input resin temperature is equivalent to the
ambient temperature of the shop or facility in which
the resin system is being used. In some instances,
the input resin temperature is raised in order to
further reduce the viscosity of an epoxy resin system.
Composite Polymer Design reports viscosity at 77°F
(25°C). As a crude guide, heating to 100°F (38°C)
will reduce the viscosity of an epoxy resin system
by approximately 45%, heating to 120°F (49°C) will
reduce the viscosity by approximately 70% and heating
to 140°F (60°C) will reduce the viscosity by approximately
85%.
b. Mold Temperature
Ideally, the mold temperature should be the same
as the input resin temperature in order to maintain
a consistent viscosity.
4. Work Life
The work life required to infuse a composite part or
structure should also be considered when selecting an
epoxy resin system for infusion. Composite Polymer Design
does not report the work life of the epoxy resin systems
it manufactures, because work life generally varies
with mass and temperature. Rather, CPD reports the gel
time of each of its resin systems in a 150 gram mass
at 77°F (25°C).
a. Mass Dependent
The work life of an epoxy resin system is mass dependent.
In a large mass, the work life of an epoxy resin
system will be reduced and in a small mass, the
work life will be prolonged.
b. Temperature Dependent
The work life of an epoxy resin system is also temperature
dependent. At an elevated temperature, the work
life of an epoxy resin system will be shortened
and at a reduced temperature, the work life will
be extended. As a crude guide, heating to 100°F
(38°C) will reduce the work life of an epoxy resin
system by approximately 60%, heating to 120°F (49°C)
will reduce the work life by approximately 80% and
heating to 140°F (60°C) will reduce the work life
by approximately 90%.
5. Demold Time
The final process requirement that should be considered
when selecting an epoxy resin system for infusion is
the demold time. Demold time is the point at which the
resin system has cured to a degree that a composite
part or structure is strong enough to be removed from
the mold. In many cases, a composite part or structure
will be removed from the mold following the supported
stage of a post cure cycle and in others it will be
removed from the mold after a satisfactory time at room
temperature.
a. Mass Dependent
Much like the work life, the demold time of a composite
part or structure made using an epoxy resin is mass
dependent. In a large mass, the demold time will
be reduced and in a small mass, the demold time
will be prolonged.
b. Temperature Dependent
The demold time of a composite part or structure
made using an epoxy resin is also temperature dependent.
At an elevated temperature, the demold time will
be shortened and at a reduced temperature, the demold
time will be extended.
c. Type of Structural Reinforcement
Another factor that impacts demold time is the type
of structural reinforcement used to build a composite
part or structure. Fiber glass is a good conductor
of heat, while carbon fiber and Kevlar® are
better insulators. This means that, all other factors
being equal, the demold time of fiber glass composites
will be greater than the demold time of a carbon
fiber or Kevlar® composites.
Disclaimer
The information contained in this guide is believed to be reliable.
We do not guarantee the accuracy of the information or make
any warranty of merchantability or any warranty of fitness for
a specific purpose or use. In no event shall Epoxical, Inc.
be liable for incidental or consequential damages.
Table 1 – CPD Room Temperature
Infusion Systems
| System |
2110/9218 |
2110/9226 |
2110/9283 |
2110/9287 |
2110/9297 |
2110/9298 |
| Elevated Temperature Cure Required In Mold1
|
No |
No |
No |
No |
No |
No |
| Post Cure Required1 |
Yes |
No |
No |
No |
No |
No |
| Post Cure Recommended1 |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
| Handling Properties |
| Resin Viscosity @ 77°F, cps |
1,200 |
1,200 |
1,200 |
1,200 |
1,200 |
1,200 |
| Hardener Viscosity @ 77°F, cps |
40 |
25 |
30 |
15 |
30 |
120 |
| Mixed Viscosity @ 77°F, cps |
290 |
200 |
250 |
200 |
300 |
750 |
| Mix Ratio By Weight |
100:30 |
100:33 |
100:33 |
100:33 |
100:26 |
100:22 |
| Mix Ratio By Volume |
2.3:1 |
2.5:1 |
2.5:1 |
2.5:1 |
3.1:1 |
4:1 |
| Gel Time @ 77°F, 150g, min. |
85 |
450 |
180 |
600 |
290 |
45 |
| Physical Properties |
| Color |
Amber |
Amber |
Amber |
Clear |
Amber |
Amber |
| Shore Hardness |
86D |
78D |
83D |
75D |
82-85D |
86D |
| Tensile Strength, psi |
12,600 |
9,300 |
11,300 |
9,300 |
11,700 |
10,500 |
| Tensile Modulus, psi |
499,000 |
410,000 |
452,000 |
401,000 |
468,000 |
457,000 |
| Tensile Elongation, % |
5.8 |
7.3 |
7.4 |
7.2 |
6.9 |
3.8 |
| Compressive Strength, psi |
16,700 |
11,700 |
15,900 |
11,700 |
16,200 |
12,500 |
| Flexural Strength, psi |
19,500 |
15,000 |
18,700 |
14,700 |
19,000 |
15,000 |
| Flexural Modulus, psi |
494,000 |
460,000 |
492,000 |
440,000 |
492,000 |
511,000 |
| HDT, Post Cured, °F |
210 |
185 |
160 |
150 |
200 |
210 |
| Izod Impact, Notched, ft-lb/in |
1.06 |
1.01 |
1.12 |
1.01 |
1.18 |
0.92 |
| Shrinkage, in/in |
<0.002 |
<0.002 |
<0.002 |
<0.002 |
<0.002 |
<0.002 |
1Tooling must be able to withstand the temperatures it will
be exposed to during the cure cycle and the supported stage(s)
of a post cure cycle.
Table 2 – CPD Medium Temperature
Infusion Systems
|
System |
4310/9231 |
4310/9234 |
4310/9235 |
| Elevated Temperature Cure Required In Mold1 |
Yes |
No |
No |
| Post Cure Required1 |
Yes |
No |
No |
| Post Cure Recommended1 |
Yes |
Yes |
Yes |
| Handling Properties |
| Resin Viscosity @ 77°F, cps |
1,200 |
1,200 |
1,200 |
| Hardener Viscosity @ 77°F, cps |
100 |
15 |
20 |
| Mixed Viscosity @ 77°F, cps |
500-700 |
400-600 |
400-600 |
| Mix Ratio By Weight |
100:35 |
100:25 |
100:26 |
| Mix Ratio By Volume |
2.33:1 |
3.2:1 |
3:1 |
| Gel Time @ 77°F, 150g, min. |
500 |
60 |
200 |
| Minimum Recommended |
| Cure Temperature2 (In Mold) |
150°F |
68°F |
68°F |
| Physical Properties |
|
|
|
| Color |
Amber |
Amber |
Amber |
| Shore Hardness |
89D |
87D |
88D |
| Tensile Strength, psi |
7,100 |
12,600 |
11,900 |
| Tensile Modulus, psi |
367,000 |
419,000 |
427,000 |
| Tensile Elongation, % |
2.5 |
4.1 |
3.9 |
| Compressive Strength, psi |
13,500 |
16,700 |
15,400 |
| Flexural Strength, psi |
14,100 |
19,500 |
18,900 |
| Flexural Modulus, psi |
411,000 |
454,000 |
448,000 |
| HDT, Post Cured, °F |
310 |
312 |
314 |
| Izod Impact, Notched, ft-lb/in |
0.54 |
1.28 |
1.25 |
| Shrinkage, in/in |
<0.001 |
<0.001 |
<0.001 |
1Tooling must be able to withstand the temperatures it will
be exposed to during the cure cycle and the supported stage(s)
of a post cure cycle.
2A post cure at temperatures in excess of the minimum recommended
cure temperature is required to develop ultimate properties.
Table 3 – CPD High Temperature Infusion Systems
| System |
2134/4307 |
2134/9282 |
2135/9529 |
4305 |
4309/4309 |
4310/9232 |
| Elevated Temperature Cure Required In Mold1 |
Yes |
No |
Yes |
Yes |
Yes |
No |
| Post Cure Required1 |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
| Post Cure Recommended1 |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
| Handling Properties |
|
|
|
|
|
|
| Resin Viscosity @ 77°F, cps |
7,500 |
7,500 |
8,000 |
NA |
400 |
1,200 |
| Hardener Viscosity @ 77°F, cps |
200 |
50 |
6,500 |
NA |
300 |
40 |
| Mixed Viscosity @ 77°F, cps |
1,800 |
1,800 |
1,800 |
5,700 |
330 |
620 |
| Mixed Viscosity @ 100°F, cps |
860 |
1,000 |
1,100 |
2,900 |
NA |
340 |
| Mixed Viscosity @ 120°F, cps |
380 |
550 |
600 |
500 |
NA |
NA |
| Mixed Viscosity @ 140°F, cps |
270 |
300 |
320 |
200 |
NA |
NA |
| Mix Ratio By Weight |
100:92 |
100:14 |
100:6 |
NA |
100:150 |
100:20 |
| Mix Ratio By Volume |
100:89 |
5.8:1 |
13.8:1 |
NA |
100:144 |
4:1 |
| Gel Time @ 77°F, 150g, min. |
1,440 |
120 |
720 |
NA |
1,440 |
75 |
| Gel Time @ 100°F, 150g, min. |
NA |
48 |
240 |
NA |
NA |
35 |
| Gel Time @ 120°F, 150g, min. |
360 |
24 |
90 |
>480 |
NA |
NA |
| Gel Time @ 140°F, 150g, min. |
NA |
12 |
45 |
>240 |
NA |
NA |
| Minimum Recommended |
| Cure Temperature2 (In Mold) |
160°F |
68°F |
150°F |
200°F |
200°F |
68°F |
| Physical Properties |
| Color |
Brown |
Brown |
Brown |
Brown |
Green |
Brown |
| Shore Hardness |
90D |
90D |
92D |
87D |
84D |
88D |
| Tensile Strength, psi |
12,200 |
12,900 |
10,200 |
8,600 |
12,000 |
12,900 |
| Tensile Modulus, psi |
472,000 |
457,000 |
470,000 |
527,000 |
500,000 |
431,000 |
| Tensile Elongation, % |
2.3 |
3.6 |
2.8 |
2.1 |
2.5 |
3.1 |
| Compressive Strength, psi |
21,300 |
22,900 |
27,100 |
NA |
30,000 |
16,900 |
| Flexural Strength, psi |
17,900 |
15,200 |
15,600 |
NA |
23,000 |
17,900 |
| Flexural Modulus, psi |
488,000 |
464,000 |
485,000 |
NA |
580,000 |
448,000 |
| HDT, Post Cured, °F |
385 |
350 |
450 |
425 |
360 |
356 |
| Izod Impact, Notched, ft-lb/in |
1.01 |
1.21 |
1.01 |
NA |
1.01 |
1.23 |
| Shrinkage, in/in |
<0.003 |
<0.003 |
<0.002 |
<0.002 |
<0.01 |
<0.001 |
1Tooling must be able to withstand the temperatures it will
be exposed to during the cure cycle and the supported stage(s)
of a post cure cycle.
2A post cure at temperatures in excess of the minimum recommended
cure temperature is required to develop ultimate properties.
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