Brookfield Engineering

Unsaturated Polyester Resins

Laboratory Viscometer Application Data Sheet


Viscosity can be used as pass/fail criteria for those UPRs that go through several reactions before they are put into pelletized, sheet, or granular form. These basic polymers then can be filled with fibers (typically spun glass) and formed into shapes like watercraft hulls or car fenders. Unfilled versions of these polymers can be pigmented or combined with other polymers to form composites which become solid objects like bowling balls and counter top surfaces.

Resin manufacturers tap their tanks at each stage of processing to determine the reaction progress by measuring viscosity. The Brookfield High Shear CAP viscometer replaces the Gardner-Holt tubes that were the industry standard. Information about the instrumentation and typical temperature and viscosity ranges are listed below. This in-process grab sample method has become more common in environments where the resin is cooked and added to, until it is solid at room temperature.

Required Equipment

Instrumentation used for single point in viscosity testing at elevated temperatures is the Brookfield CAP1000+ Viscometer with CAP-S-03 spindle or CAP-S-04 spindle (depending on processing stage and UPR formulation). Rotational speed is 900 rpm 115 VAC / 750 rpm 220VAC. Temperature set points are 130°C and 200°C.

  • small sample volume for test (<1 mL)
  • rapid temperature equilibration
  • clean in place
  • calculated display of viscosity in Poise or Pascal seconds
  • output to printer or external control through gather and analysis software

Test Method

The chart shows single data points collected from repeat testing of a fluid at on-going stages in the reaction process. Data is collected with minimal time to equilibrium and with small volume (24 - 124 microliters). The reaction tank is tapped, the sample brought to the Viscometer, allowed to equilibrate for 45 seconds, and then run at 900 rpm for 15 seconds, and data recorded. Upon acceptance of the viscosity data, the batch is released to the next reaction step. Before each reaction can proceed, the reaction tanks are tapped and samples taken.

The last three data points are taken on a resin that is solid at room temperature and must be heated to 225°C before being tested on the CAP. When grab samples are taken during production however, the fluid is in its liquid state. The data here demonstrates a marked difference in viscosity from the first data set (initial reaction) to the final data set (final reaction), thereby ensuring the end resin will perform as intended either at application, or before being filled, pigmented or shipped.


Ability to generate rheological flow curves can be accommodated by using a variable shear rate CAP2000+ and Brookfield data collection software, CAPCALC for Windows®