Ghorbani Masoumeh, Konnerth Johannes, Budjav Enkhjargal, Silva Ana Requejo, Zinovyev Grigory, Van Herwijnen Hendrikus W G, Edler Matthias, Griesser Thomas, Liebner Falk
Department of Material Sciences and Process Engineering, Institute of Wood Technology and Renewable Materials; University of Natural Resources and Life Sciences Vienna, University and Research Center Tulln, Konrad-Lorenz-Strasse 24, 3430 Tulln an der Donau, Austria.
Department of Chemistry, Division of Chemistry of Renewable Resources, University of Natural Resources and Life Sciences Vienna, University and Research Center Tulln, Konrad-Lorenz-Strasse 24, 3430 Tulln an der Donau, Austria.
Polymers (Basel). 2017 Jan 28;9(2):43. doi: 10.3390/polym9020043.
Ammoxidation of pine kraft lignin in aqueous 5 wt % ammonia affords a novel type of phenol substitute that significantly accelerates resole synthesis and curing as demonstrated for 40 wt % phenol replacement. Compared to non-ammoxidized lignin, which already shortens significantly the cooking time required to reach a resole viscosity of 1000 Pa·s (250 vs. 150 s) and reduces the typical curing B-time by about 25% at 100 °C, the use of ammoxidized lignin has an even more pronounced impact in this respect. Activation of lignin by Fenton-type oxidation prior to ammoxidation further boosts both synthesis and curing of the resole. This is presumably due to the intermediary formation of polyvalent cross-linkers like N,N,N-tris (methylol) trimethylene triamine triggered by saponification of a larger fraction of nitrogenous moieties present in such a treated lignin (ammonium salts, amide-type nitrogen, urea) and reaction of the released ammonia with formaldehyde. Except for the fact that phenol replacement by ammoxidized lignin results in a somewhat less brittle cured adhesive polymer and higher elastic modulus, the aforementioned acceleration in curing could no longer be observed in the presence of wood, where a significantly delayed wood-adhesive bond formation was observed for the lignin-containing adhesives as evident from the automated bonding evaluation system.
