Electron spectroscopy on plasma treated lignin and cellulose

Cellobiose and lignin were plasma treated in synthetic air and argon using a dielectric barrier discharge at atmospheric pressure. Changes due to the plasma modification of the surfaces were studied by the techniques of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy, and metastable impact electron spectroscopy. The combination of these techniques makes it possible to distinguish between hydroxyl and carbonyl groups at the surface, on the one hand, and conjugated and non-conjugated carbon bonds, on the other hand. This type of differentiation would not be easily possible based on XPS alone, even at very high resolution. The plasma treatment in oxygen containing atmospheres oxidizes the lignin surface by the generation of hydroxyl, carbonyl, and carboxyl groups and reduces cellulose surfaces by the degradation of hydroxyl groups and the formation of double bonds between carbon and oxygen. The plasma treatment in argon leads to the reduction of both lignin and cellulose by the formation of double bonds under degradation of hydroxyl groups.