New rheometer speeds testing.

A dynamic mechanical test system said to be the first rheometer to perform unattended sample conditioning and rheological testing on plastic melts has been launched by Rheometrics, Inc., Piscataway, N.J.

The Rheometrics Automated Melt Analyzer (RAMA) eliminates manual sample conditioning and testing by way of reusable cartridges in which a sample is melted, tested and cooled. Technical marketing engineer Leon Suttner says RAMA measures dynamic mechanical properties of polymer melts five times faster and also more accurately than current methods, which are typically labor-intensive. requiring extensive sample preparation and, in some cases, contact with hazardous solvents. The RAMA instrument requires no sample weighing and no operator attention, so reproducible tests on up to 10 samples per hour can be achieved, versus up to a maximum of four samples per hour in conventional dynamic mechanical testing.

WHAT IT TELLS YOU

By obtaining measurements on the viscoelastic properties of a polymer, RAMA can help determine how the material's processing properties are affected by molecular weight, molecular-weight distribution, and the degree of crosslinking and chain branching. These data allow study of such effects as die swell after extrusion, warpage after injection molding, minimum running thickness in blown films, and maximum drawdown in fiber applications. Such information can be used for product development and to monitor and control product quality and production processes.

The new laboratory instrument has five components: a sample loading station, sample conditioning station, dynamic-mechanical test station, robotic transfer system, and computer controlled operating and data-analysis station. The operator loads samples of plastic pellets or powder into small, reusable aluminum cartridges. Each sample is melted, tested, and cooled in its own cartridge. As a result, different materials can be tested consecutively without having to clean the instrument between tests and with no fear of sample-to-sample contamination. As a cartridge is placed in the loading station (which holds up to 18 at a time), the operator enters the material type, a sample identification number, and the desired tests into the computer. After these preparatory steps, RAMA automatically conducts the test and collects, stores and analyzes data.

Rheometrics says the RAMA system has more accurate temperature control than other rheometers. Its probe and cartridges are electrically heated and are said to result in minimal temperature gradient within the sample. Automated sample conditioning is also said to be more consistent than manual methods, another factor leading to more accurate results, according to Rheometrics.

At the start of each test cycle the robotic arm transfers a cartridge from the loading station to the conditioning station. In about 6 min, the material is heated to the desired testing temperature, and entrapped air, moisture, and voids in the melt are removed. After conditionting, cartridges are transferred to the testing station for dynamic mechanical analysis. Samples are tested in a sealed system at precisely controlled temperatures to prevent exposure to atmospheric conditions and to avoid degradation. The sample temperature is controlled by an external heater and a patented transducer probe, which measures the material's rheological properties. Data are transferred to the analysis station. After testing, the cartridges are cooled to solidify the samples. The robotic arm then removes them and drops them into a recycling bin where they are emptied and reused.

Although RAMA was developed primarily for quality-control laboratories at resin suppliers, compounders, and processors, it can be used for research and product development and modified for on-line process monitoring. The instrument is currently priced at $200,000. Although that's more expensive than other rheometers (generally $60,000 to $140,000), Suttner says users can realize much faster payback, as RAMA is five times more productive and runs unattended. He estimates that labs running two 8-hr shifts per day could achieve payback in nine months. (CIRCLE 1)