Photostabilizing Milled Wood Lignin with Benzotriazoles and Hindered Nitroxide†¶

Abstract

The inhibitory processes operating when a 2(-2-hydroxyphenyl) benzotriazole-based ultraviolet absorber (UVA) and a hindered nitroxide free radical are applied to highyield pulps were studied using milled wood lignin and filter paper as a model. Using quantitative 31 P NMR it was determined that the UVA is almost completely photostable during irradiation, suggesting that its protective mechanism is based primarily on ultraviolet absorption. Furthermore, the nitroxide was found to protect the UVA from photodegradation. Analysis of irradiated lignin samples involved derivatization followed by reductive cleavage of ␤-arylether groups. The phenolic-OH groups thus released were quantified using 31 P NMR. The benzotriazole/nitroxide stabilizing system was found to cooperatively inhibit the cleavage of ␤-arylether groups. Furthermore, this system was found to have a synergistic inhibitory effect on the formation of catechol structures. These results suggest that the synergism observed between benzotriazole-based UV screens and nitroxyl radicals on the inhibition of yellowing could be a result of their ability to slow the formation of catechol structures and ␤-O-4 cleavage in addition to the possibility of a UVA-regeneration mechanism.

New approaches in wood coating stabilization

“…According to this new concept an optimized wood protection can be achieved, when the lignin stabilizer is applied as a dilute aqueous solution or in an already utilized primer formulation directly onto wood. 26 To obtain durable protection effects, the treatment has to be associated with selected UVA (for indoor applications) or UVA/HALS (for outdoors) in the same treatment (internal UV filter effect) or better in a subsequently applied topcoat (external filter effect). Besides the improved aesthetical aspects other benefits of the better wood surface protection can be extended retention of properties such as coating adhesion and resistance to failures as flaking and cracking and therefore resulting in higher durability and extended maintenance intervals.…”

Photostabilization of Poly (Vinyl Chloride) by Some Schiff Base Derivedfrom 2-amino pyridine

“…[ This is also suggested for benzophenon [26][27], benzotriazole [28][29] and aromatic Schiff base photostabilizer [15]. These stabilizerstability and a provide very good long time stability and are usually offered to these mechanism.…”

Studies on photostability of butyrylated, milled wood lignin using spectroscopic analyses

“…The MWL has been used as a representative source of native lignin. Therefore, the photochemistry of lignin has been frequently studied with MWL [6,11,20]. In this paper we report the chemical changes of MWL during photo-oxidation by FT-IR and ESR spectroscopies, the chemical characteristics of MWL after butyrylation, and the photo-stabilising effect on milled wood lignin of butyrylation.…”