NIST instrumentation installed at plastics film manufacturing facility - News Briefs - National Institute of Standards and Technology - Brief Article

Journal of Research of the National Institute of Standards and Technology, Sept, 2001

Instrumentation developed at NIST has been installed in a polymer processing plant to facilitate development of manufacturing conditions for polymer films. The instrumentation addresses the need of polymer film producers for a more rapid measurement of molecular orientation and temperature during film production to avoid costly time delays and rejected product runs. The performance properties of biaxially stretched films are determined by their molecular orientation (or anisotropy) and the temperature at which they are processed. Currently, film processors measure orientation in post processing quality control experiments that are carried out with a considerable time delay after processing.

Under an arrangement with a private company, NIST scientists have developed a sensor and measurement system for real-time monitoring of temperature and molecular orientation during processing of biaxially stretched polypropylene film. At the private company facility, film processing is carried out in a continuous manner using a tenter stretching frame in an oven that stretches a plastic ribbon in two perpendicular directions: the process flow direction (machine direction) and the direction perpendicular to the process flow (transverse direction).

The NIST measuring technique relies on the presence of a fluorescent dye molecule that is doped into the polymer resin at very low concentrations. Temperature monitoring is carried out by measuring temperature induced changes in the shape of the fluorescence spectrum. Molecular orientation is determined by measuring fluorescence anisotropy of the fluorescent probe molecule whose orientation mimics the orientation of the resin matrix. A sensor head containing optical fibers, focusing lenses, and polarization elements is lowered into the stretching oven and is positioned directly above the processed film. The optical fibers transmit light from the light source to the film and collect fluorescence light for transmission to the detectors. As the film is transported past the sensor, three quantities are measured: orientation in the machine direction, orientation in the transverse direction, and temperature. Private company scientists are using this new information to develop processing strategies that are designe d to tailor product performance to specific applications.

CONTACT: Anthony Bur, (301) 975-6748; anthony. bur@nist.gov.