Shear rate ramps were one of the four experiments conducted
using the parallel plate rheometer. Shear rates started at 1 1
/s and
increased to a maximum that ranged from 50 to 150 1
/s, depending
on the adhesive type and temperature. Materials were tested
up to the highest shear rate that provided stable hysteresis loops.
The resultant viscosities ranged from 50 to 5000 Pa s. Fig. 3 shows
the viscosity–shear rate data with both increasing shear rate (from
1 to 200 1
/s) and decreasing shear rate (back to 1 1
/s) for Adhesive
B. Both tests were conducted 60 days after the adhesives were
manufactured. It was observed that the decreasing shear rate
viscosity data were lower, indicating a thixotropic behavior [5].
This was more evident at the lower temperature, with the final
decreasing viscosity being approximately 60% of the initial value.
When tested at 45 °C, the difference was substantially less, with
only a 10% decrease or 90% of the initial value.