IN-LINE MONITORING OF TITANIUM-DIOXIDE CONTENT IN POLY(ETHYLENE-TEREPHTHALATE) EXTRUSION

Peak absorbance changes correlated to changes in species concentration have been the norm in applied spectroscopy, while baseline shifts hav e been more of an inconvenience. Taking the first or second derivative of the spectra eliminates these baseline shifts. However, with multiv ariate techniques becoming more readily available, repeatable baseline changes may now be monitored and correlated to specific physical chan ges. This concept has been studied by monitoring the concentration of titanium dioxide (TiO2), a white inorganic filler, in molten poly(ethy lene terepthalate) (PET). Various mixtures of filled and unfilled PET resins were run through a single-screw extruder, and near infrared spe ctra were collected in-line by using a flow cell, housing two fiber-op tic probes, and mounted downstream of the extruder. The presence of ti tanium dioxide caused the scattering of light that resulted in a syste matic baseline shift. The baseline shifts were correlated to the TiO2 concentration data. Multivariate techniques involving the use of singu lar value decomposition (SVD) to perform partial least squares regress ion (PLS) were applied to quantitatively determine TiO2 content in the PET melt stream. Standard error of prediction (SEP) values of about 1 % were obtained for a model based on two factors.