Volume 2, Issue 8 (September 2005)
New Technique for Measuring Extended Viscosity Ranges - Gel Times, Pot Life, or Cure Monitoring - with Programmable Rotational Viscometers or Rheometers
A new algorithm written in commercially available software controls programmable viscometers and rheometers so that multiple decades of apparent viscosity data may be acquired. This work is new and important because previous methods involved either: (1) very simple instrumentation providing (a) single-point viscosity data or (b) equipment providing “gel times” but no viscosity data, or (2) complicated instrumentation costing at least $20 000. Isothermal cure of a common epoxy system was successfully monitored in this work. Apparent viscosities measured during one room-temperature cure experiment ranged from approximately 1000 mPa·s to 50 000 000 mPa·s. Good repeatability of data was found for different batches prepared with similar stoichiometry. Viscosities measured at approximately 167 min of cure time, during multiple tests, differed by less than 1 %. Various test geometries were used, including disposable cylindrical spindles and sample chambers, to allow easy cleanup, with samples 10 mL or less in size. Samples were also successfully tested at 50 and 60°C. Aspects of the algorithm and its implementation are discussed. It is hoped that this new method will help personnel testing adhesives.