A fiber-optic-assisted, charge-coupled device spectrometer was used to monitor the color of molten polymer concentrates during extrusion. Color coordinates L*, a* and b* were calculated from each of the reflectance spectra as polyethylene color concentrate was replaced by a purge material and as the purge material was replaced by another color concentrate. A method of calculating replacing component residence time distributions and component washout residence time distributions from the spectra was developed and applied. Results with a red and a blue concentrate showed that dimensionless time (time/average residence time) superimposed both residence time distributions and color coordinate variations during changeover from two different extruder screw speeds. X = k S(h) R(h) x(h) d h 780 I, 380 r 780 k x S ( X ) R(X) x(h) AX (11 S(h) R(X) y(X) d hk x S(X) R(X) y(X) AX (2) 380 780 S(X) R(h) %(A) d hk x S(X) R(X) :(A) AX (3) 380where S(X) is the spectral power distribution of the standard illuminant selected, R(h) is the reflectance spectrum of the sample X(X). y ( h ) , Z(X) are the color matching functions for the standard observer selected and k is a constant (1).However, although color can be matched and compared by using the tristimulus values, there are several 356
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