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O. Liske, S. Baudis, S. Knaus:
"Post-modification of wheat straw soda lignin for light-induced radical polymerization process";
Poster: 4th European Symposium of Photopolymer Science, Leipzig; 11.09.2016 - 14.09.2016; in: "ESPS 2016", (2016), S. P-67.

Lignin, the second most abundant natural polymer in wood and annual plants, is an amorphous and highly branched heteropolymer with a complex and sporadic structure built primarily of phenylpropanoic units. Its content varies with the wood species and extraction method. Annually, 50 million[1] tonnes of lignin is obtained worldwide as a waste product from paper and pulp industry. Lignin can be modified through an oxyalkylation reaction with propylene oxide. This process not only liquefies the lignin but also improves the solubility, decreases the viscosity and homogenizes the different functional groups. In fact, both the substrate and the reagent are based on renewable resources, since propylene oxide can be prepared from glycerol[2, 3]. Acrylation of propoxylated lignin is already known from literature[4] but light-induced polymerization of high absorptive acrylated lignin is to our best knowledge unknown.
Wheat straw soda lignin was modified and characterized via several qualitative and quantitative methods such as 31P-NMR, 1H-NMR, Photo-DSC and photorheology to evaluate its potential in 3D-printing. Chemical modification was performed in two steps. In the first step, wheat straw soda lignin was reacted with propylene oxide to produce lignopolyol by direct oxyalkylation under alkaline conditions with potassium hydroxide in a solvent-free procedure. The chain-length of grafted polymer was calculated by means of 1H-NMR and the hydroxyl number was estimated by 31P-NMR. In the second step, the propoxylated soda lignin was modified with acrylated, methacrylated, and some unsaturated longer chained carbon acid halides. Modification of propoxylated soda lignin with different types of unsaturated compounds leads to a change in viscosity and reactivity. This was confirmed by rheological measurements before and after light emission. The post-modificated lignopolyols with different acrylates open a new field of application for lignin to use it in a radical polymerization process induced by light.