RELTEK BONDiT B-45/B-45TH TEST REPORT OF PROPERTIES

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A Study of the Physical Properties of B-45TH Epoxy

 1. Introduction

 A study of the physical and mechanical properties of B-45TH and B-45 was carried out
in order to better understand potential applications of the two-part epoxy system.

TMA, TGA and DSC were used to study the effect of curing method and mixing technique
on several important physical property characteristics. Table 1 summarizes the
experiments that were performed.

Analysis of the physical properties of B-45TH included for the resin mixed with a static
mixer¹ and by hand mix²:

Comparing the glass transition temperature of a hand mixed Vs a static mixed sample,

• The out gassing behavior of the epoxy using three curing methods and outgassing
  under elevated operational temperatures,
• The extent of curing reaction as a function of curing method,
• Environmental test of 85RH / 85°C with three curing methods,
• Moisture absorption, (hand mix)
• Oil absorption, (hand mix)
• Percent solid of hand mix epoxy compared to a static mix,
• Contact angle relative to static mix and hand mix,
• Joint strength relative to static mix and hand mix. 

Other tests included

• Tensile strength, (hand mix)
• Static fatigue strength, (hand mix)
• Tear strength, (hand mix)
• Velocity of sound, (hand mix)
• Thermal conductivity, (hand mix)
• Coefficient of thermal expansion, (hand mix)
• Lap shear tests on various substrates, (static mix)
• Peel tests on various substrates, (static mix)
• Bead length Vs bead width for B-45TH dispensed from a static mixer.

¹ Static mix = parts A & B measured 2:1 by a double-barreled cartridge dispensed
with a plunger in a hand actuated gun through a 6” helical 21 element static mixer
tube having a 1/16” exit nozzle.

² Hand mix = parts A & B measured in 2:1 ratio by weight and mixed by hand.

Table 1 TMA, TGA, DSC tests of B-45TH epoxy 

 2. Glass Transition by TMA Method

The glass transition temperature was not apparent in either the epoxy that was
hand mixed or sample that was mixed using a static mixer by analyzing with the DSC.
The TMA was then used to determine the Tg for the two samples.  

Theoretically, the glass transition temperature should be approximately 60°C.
Expanding the graphs from 40°C to 80°C did reveal that the Tg for the static mixed
sample is 64.93°C and the Tg for the hand mixed sample is 65.02°C. These values
are in agreement with the theoretical Tg. The difference in Tg between the two
samples is negligible.  

Figure 1 Glass Transmission temperature comparison - Hand Mix vs. Static Mixer Method

3. Outgassing 
   Thermo gravimetric Analysis (TGA) was used for the outgassing study.

 The initial outgassing study was performed on un-cured material from room temperature
to 300°C at a rate of 10°C/min.  This scan determines the amount of outgassing during
cure as a function of weight loss.  At 60°C, the weight loss due to outgassing is only
0.149%. Up to 220°C, were curing appears to end and before degradation, the total
weight loss is 7.225%.

Figure 2 Outgassing

Further testing by TGA indicates a correlation between weight lost during the thermal
cycle and curing technique. In Figure 3 and Table 2 the results are summarized.

Table 2. Percent weight loss as a function of curing method 

From the results, it is possible to conclude that when cured under lower temperatures
there is more free water and volatile material in the epoxy. There also is a significant
difference between the onset of out gassing temperature for the heat-cured methods
and the sample cured at ambient temperature.

Figure 3 Graph of epoxy outgassing profiles

In order to know the amount of outgassing at regular operating temperatures, an
isothermal scan at 60°C for four hours was performed and only 2.624% weight loss
was measured.  This relates to 0.66% outgas weight loss per hour.

Figure 4 Isothermal Cure Weight Loss

4. Degree of Cure
   
   Differential Scanning Calorimetry (DSC) was used for the cure study.

The adhesive was cured at typical (uncontrolled 16°C - 22°C) room temperature (RT)
for 24 hours.  It was observed in that period the surface remained somewhat tacky and
the bulk of the material is very flexible. 

An incomplete cure was suspected. To determine the cure schedule a DSC was performed
on un-cured material from room temperature to 300°C at a rate of 5°C/min.  Curing began
at 30°C, peaked at about 90°C and ended at about 170°C.  Degradation occurred at
temperatures greater than 170°C.  Normalized with respect to the sample amount,
the heat of reaction during cure was measured to be 156.25J/g, the area under bell curve. 

Figure 5 DSC Uncured B-45TH

A DSC scan was performed on a sample cured at room temperature (controlled 21°C)  
for 24 hours to measure the amount of cure.  Normalized to sample weight yielded a
heat of reaction of 3.60J/g thus making the sample 97.7% cured, meaning that a
24-hour, 21°C room temperature cure is sufficient for many applications. It is to be
expected that a three (3) day cure or longer will produce further cure and improvement
in physical properties for ambient cure applications.  

156.25J/g  -  3.60J/g   X  100  =  97.7% cure
         156.25J/g 

Figure 6 DSC Cured B-45TH

The extent of completion of the curing reaction can easy be evaluated by looking at the
heat released when the epoxy is put through a thermal cycle. Figure 7 shows the profiles
of the exothermic curing reaction for several curing methods. Table 3 lists the specific
heat for three curing methods and an uncured sample.

Table 3 Specific heats of cured epoxy and uncured epoxy

From the specific heat data, it can be seen that optimized curing is correlate with
curing temperature. For instance, at ambient temperature the material will never fully
cure, yet be sufficient for the application. Further studies by tensile strength tests
indicate optimal operational cure is approximately 100°C for three (3) hours. 

Figure 7 Extent of completion of curing as a function of cure method

5. Environmental Test 

The three curing methods were subjected to an environmental test. The test was an
85RH / 85°C for duration of approximately four days. Figure 8 shows the weight loss
of the tests processed using three curing methods. Table 4 lists the percent weight loss
of each of the tests. 

Table 4 Percent weight loss of three curing methods after a 85/85 humidity test 

The percent weight loss by EsTGA2 is the most significant. The weight lost by EsTGA1
and EsTGA3 are very similar. This result was not expected because of their very different
curing methods. However, the RT was uncontrolled and over all the difference between
the samples is relatively small. A larger statistical sampling would clarify the differences,
if any.

Figure 8 Weight lost for test runs after 4 days in an 85/85 chamber

6. Moisture Absorption 
   
   A moisture absorption test in DI water was conducted according to ASTM D570,
   showing an ultimate absorption of under 1% in equilibrium state after 51 days at
   uncontrolled lab room temperature (68-72°F days, 60-65°F nights).
   
   Figure 9 Moisture Absorption
   
   
   
7. Oil Absorption  
   
   Hand mixed samples were for oil absorption per ASTM D570 were also tested
   using Shell Oil Isopar M, resulting in an ultimate equilibrium of 0.73% in 60 days
   exposure.
   
   Figure 10 Oil Absorption
   
   
   
   
8. Contribution of Solids Content 

   The total solids content contribution from the resin and the hardener is very
   comparable. F igure 10 shows the graphs of the total mass lost by each of the tests.
   A direct comparison of the total solids content in the epoxy mixture, the resin and
   the hardener can be made by regarding Table 5. 

Figure 11 Pyrolization profiles of the resin, hardener, and epoxy

Table 5 Percent weight loss of epoxy materials and epoxy heated to 500°C
for ½-hour  

There is not a lot of filler in the B-45TH epoxy system. It is interesting to note that there
seems to be no appreciable difference between the solids content of the hand mixed and
the static mixed epoxy. There is little practical difference between B-45TH and B-45 due
to the small amount of thixotropic filler in the B-45TH.

9. Surface Energy of Cured Material 

   The surface energy of B-45TH prepared by using a static mixer and by hand was
   looked at. The surface energy of the epoxy side exposed to air while curing and
   the side that was on the Teflon surface was also compared. The data for the contact
   angle is shown in Figure 11. 

   The static mixed epoxy exposed to air while curing had an erratic contact angle profile.
   The standard deviation of the contact angle for the static, air set was approximately
   14°. The backside of the epoxy had a much lower standard deviation of only 3°.
   In general, the backside that was not exposed to air during curing (static and hand
   mixed) had much higher contact angle values. 

Figure 12 Plot of the Contact Angle Water on B-45TH

10. Mechanical Properties

Joint Strength 

The data collected from the joint strength testing did not reveal any great disparity
in strength between epoxy that is static mixed and hand mixed. Figure 13 shows the
joint strength for 20 samples of the static mixed epoxy and the hand mixed epoxy. 

Note the hand mixed sample had a higher standard deviation of .83 Kg compared to
static mix of .64 Kg. 

Figure 13 Joint Strength of 20 Samples of Static and Hand Mixed Epoxy

Table 6 Tensile Strength

Figure 14 Tensile Strength

Table 7 Static Fatigue and Tear Strength

Table 8 Velocity of Sound, Density, Thermal Conductivity, Coefficient of
Thermal Expansion

Table 9 Lapshear Test per ASTM D3163