Application Oriented Rheological Characterization of Sealants using the Physica MCR 300 Rheometer by Anton Paar

Topics Covered

Background
Rheological Measurements of Sealants
Sealant Samples
Solution
     Amplitude Sweep
     Thixotropy Test - 3 Interval Thixotropy Test (3ITT)
Results and Discussion
Summary

Background

Anton Paar GmbH produces high-end measuring and laboratory instruments for industry and research. It is the world leader in the measurement of density, concentration and CO₂ and in the field of rheometry. Anton Paar GmbH is owned by the charitable Santner Foundation.

Over 1180 employees at the headquarters in Graz and the thirteen sales subsidiaries worldwide ensure that Anton Paar products live up to their excellent reputation. The core competence of Anton Paar – high -precision production – and close contact to the scientific community form the basis for the quality of Anton Paar's instruments.

Rheological Measurements of Sealants

Application oriented rheological measurements were carried out on three sealant samples. The measurements were conducted using a Physica MCR 300 rheometer, the Peltier temperature control unit TEK150P, and a plate-plate measurement system PP25 (ø 25 mm). The temperature was 20°C for all tests.

Sealant Samples

It is known that one sealant (S1) has good rheological properties, whereas the other two sealants (S2 and S3) lead to different problems. S2 is still flowing after the force is removed from the cartridge whereas S3 requires a higher force than S1 or S2 to begin flowing from the cartridge.

Solution

Due to large filler particles and other large structures in sealants, which are highly filled polymer systems, a plate-plate measuring system with a gap size of 1 mm has been used.

Oscillation tests are used to measure the sealants for two reasons:

1. Rotational tests are limited for these kinds of samples since the sealants tend to move out of the gap at higher shear rates.
2. Oscillatory tests give the additional information on the elastic behavior of the sample, i.e. it can be distinguished between viscous (G’’) and elastic (G’) properties.

Amplitude Sweep

Presetting:

Fixed frequency f = 1Hz; Strain as logarithmic ramp: γ = 0.00015 % – 500% (strain sweep), 40 measuring points.

Thixotropy Test - 3 Interval Thixotropy Test (3ITT)

By presetting three measurement intervals the following conditions during the application of a sealant are simulated:

rest / pressing out of the cartridge / rest

Presetting:

Constant frequency 5 Hz, strain controlled test, measurement point duration 1s in all three intervals

1. Interval: strain γ = 0.01 %; 30 measuring points
2. Interval: strain γ = 30 %; 30 measuring points
3. Interval: strain γ = 0.01 %, 120 measuring points

Results and Discussion

Figure 1 shows the results of AS of the three sealants. Although the AS was measured in strain control the results are plotted versus the shear stress. All three sealants have a linear visco-elastic plateau (LVEP). As can be seen S1 and S2 have an almost similar behavior with S1 having a slightly higher G’’ values than S2. For both sealants the LVEP end at around 100 Pa, i.e. the structure is stable at stress values below 100 Pa and is broken at higher stresses. In a presentation versus the strain (not shown here) the LVEP ends at around 0.1% strain for these two samples. However, S3 exhibits a very different behavior. The G’ and G’’ values are around a factor of 10 higher as for S1 and S2. Additionally, the LVEP lasts up to stress values of approximately 1000 Pa, i.e. 10 times higher as for the other 2 sealants. This result is directly related to the application problem of S3: The force required to press S3 out of the cartridge is greater than for the sealants S1 and S2.

Figure 1. Amplitude Sweeps (AS) of the three different sealants

Figure 2. Interval Thixotropy Test (3ITT) – Structure decomposition and recovery of the sealants S1 and S2

In figure 2 the results of the structure decomposition and recovery test (3ITT) on S1 and S2 are presented. The most interesting part in this test is the step from interval 2 (large amplitude oscillation) to interval 3 (small amplitude oscillation). This is a direct simulation of the movement due to the pressing out of the container and the behavior directly after the force is removed. As can be seen the elastic part (G’) is almost immediately above the viscous part (G’’) for S1, whereas for S2 G’ stays for approximately 80 s below G’’ after the cessation of the high shear in interval 2. This means the structure rebuilds much faster in S1 compared to S2, and S1 will not flow after the pressing out of the cartridge, whereas S2 still flows for a significant amount of time resulting in the described application problem.

For both samples the G’ and G’’ values are lower in the 3rd interval than in the 1st interval, indicating that the structure recovers only partially after the cessation of the high shear and that it takes a much longer time for the full recovery.

Summary

The discussed results show clearly that it is possible to correlate the known application problems of different sealants to the results of rheological measurements. The amplitude sweep shows that a sealant requiring a higher applicaton force also has a much higher structure strength compared to other sealants, which are easily applicable.

A three interval thixotropy test in oscillation is able to give valuable information on whether a sample is still flowing after the pressing force is removed or not. It is possible to distinguish clearly between a good sealant and a sealant, which shows the not wanted flow after the force is removed.

Source: Anton Paar GmbH.

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