Biodegradable lignin nanocontainers†

Lignin is one of the most abundant renewable biomaterials which can be extracted from plants and which represents approximately 15–30% of their total mass besides cellulose. In spite of these high amounts and its ready availability, lignin is normally considered as a non-preferred byproduct from the paper industry for example with over 30 mio tons per annum. A major reason for this is probably the complexity of the lignin structure with very broad molecular weight distributions and limited solubility, thus only 2% of lignin (mainly lignosulfonates) are applied in industry or in agricultural uses as binders for animal feed pellets, bricks, ceramics, or road dust, dispersants for oil well drilling products etc. The main structural elements of lignin, a phenolic polymer, are three basic structural elements (4-hydroxyphenyl, guaiacyl, and syringyl residues) which are connected via aromatic and aliphatic ether bonds that build up a hyperbranched, i.e. irregularly branched polymer. Because lignin has both phenolic and aliphatic hydroxyl groups, its further modication is obvious and was investigated in various publications. Recently, lignin doped with multi-walled carbon nanotubes were studied as chemical