On the interaction of UV screens with the lignocellulosic matrix

nIn this report, we describe our attempt to understand the photochemical in teractions that occur between dihydroxybenzophenone (DHB)-based UV screens and Lignin when high-yield pulps are treated with such materials. Milled wo od lignin (MWL) and filter paper were used as models, and various irradiati on protocols were carried out in the presence and absence of UV screens. Af ter irradiation, the lignin and the UV screen were extracted and the produc ts analyzed. These experiments showed that upon irradiation, fragments of M WL-containing chromophores were linked to cellulose via an acid-labile link age. In the presence of UV screens, these reactions were minimized. Molecul ar weight measurements of the extracted lignin showed that the MWL is degra ded upon solid-state irradiation. The samples that contained UV screens sho wed a reduced tendency to degrade. Using quantitative P-31 NMR, it was poss ible to probe further the detailed structural changes that occurred in MWL during irradiation. In general, DHB-based UV screens and derivatives were f ound to interact actively with MWL when irradiated.