the diffuse reflectance spectra of the paper sheets were mea-sured with a Perkin–Elmer 860 Spectrophotometer equipped witha 15 cm diameter integrating sphere bearing the holder in the bot-tom horizontal position. They were recorded at room temperaturein steps of 1 nm, in the range 350–600 nm with a bandwidth of2 nm. The instrument was calibrated with a certified Spectralonwhite standard (Labsphere, North Sutton, USA) and spectra wereacquired by inserting before the detector a visible short-wave passfilter (LOT-Oriel 450FL07–50, 450 cut-off wavelength) in order toremove the fluorescence component of the chitosan derivative.The reflectance of both sides of the sheet was measured, whichprovided two spectra for each sample.The Kubelka–Munk model (Kubelka & Munk, 1931) describesthe light penetration in porous media using only two parame-ters (both with units of cm1), namely an absorption coefficient,k, and an isotropic scattering coefficient, s. This leads to a verysimple relationship between infinite reflectance and absorptionand scattering coefficients, known as the remission function,viz.