For production of a cellulosic filler that is compatible with thermoplastic polymers, a primarily nonpolar or lignin surface is needed. In order to allow quantitative measurement of the cellulose-to-lignin ratio on the surface of the fillers, infrared reflectance techniques and computer curve-fitting were employed. By the use of this method of analysis, relative quantitation was obtained, and it was possible to determine that careful control of certain parameters during the production of thermomechanical pulps produced a more nonpolar lignin-like surface that was compatible with the thermoplastic polymers.
Kathryn S. Kalasinsky, George R. Lightsey, Paul H. Short, and James R. Durig, "Quantitative Analysis of Cellulosic Fillers Using Infrared Reflectance Spectroscopy," Appl. Spectrosc. 44, 404-407 (1990)