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O. Liske, P. Dorfinger, R. Gmeiner, S. Baudis, J. Stampfl, R. Liska, S. Knaus:
"Modification of Wheat Straw Soda Lignin for Light-Induced Radical Polymerization Process";
Talk: Bypos Workshop 2017, Zemplínská Sírava, Slovakia; 06-12-2017 - 06-16-2017; in: "Bypos Workshop Book 2017", (2017), 55.

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 plant species and extraction method and is a vastly under-utilized and low-cost natural polymer. Annually, 50 million[1] tons of lignin are obtained worldwide as a waste product from paper and pulp industry, where 98 %[2] are used for combustion. Especially sulfur-free lignins (soda and organosolv lignin) are interesting classes for the use in polymeric materials compared to the traditional sulfur-based kraft and sulphite lignins.
In this work, a sulfur-free wheat straw soda lignin was taken as an alternative renewable resource for photo-curable polymers. Untreated lignin show poor solubility properties and low reactivity which are a restriction to many industrial applications. Oxyalkylation of hydroxyl functionalities of lignin (aliphatic-OH, phenolic-OH and carboxylic-OH) with propylene oxide (PO) not only improves the solubility, decreases the viscosity and homogenizes the different hydroxyl-functional groups but also increases the reactivity and liquefies the polymer.
The length of grafted chains was estimated by 1H-NMR and the hydroxyl number was determined by 31P-NMR spectroscopy. Subsequently, the modified lignin was equipped with photopolymerizable (meth)acrylate groups and successfully processed by lithography-based additive manufacturing to obtain arbitrary parts in high resolution.

Lignin, natural polymer, heteropolymer, wheat straw soda lignin