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Gewählte Master / Diploma Thesis:

Maria Krahofer (2015): Characterisation of lignin-phenol-formaldehyde wood adhesives prepared from different types of lignin.
Master / Diploma Thesis - Institut für Holztechnologie und Nachwachsende Rohstoffe, BOKU-Universität für Bodenkultur, pp 84. UB BOKU obvsg

Data Source: ZID Abstracts
Abstract:
Due to similarities in the chemical structure of lignin and phenol already a lot of research attempts were done with the aim of a substantial substitution of phenol by lignin in phenol-formaldehyde adhesives. However no commercial lignin-phenol-formaldehyde (LPF) adhesive is available on the market up to now. One reason for the missing breakthrough is the lower reactivity of lignin compared to phenol and consequently a lower reactivity of the LPF adhesives. In the present work LPF resoles were synthesised partially substituting phenol with different types of lignin. In a next step selecting curing characteristics of the adhesives, which serve to a certain extent as an indicator for reactivity, were analysed. Four different technical lignins, namely pine kraft lignin, Sarkanda grass soda and wheat straw soda lignin as well as beech organosolv lignin were copolymerised with phenol and formaldehyde aiming at a degree of phenol replacement by lignin as high as 20 % and 40 %, respectively. Additionally to the screening of the curing behaviour of the adhesives, the lignins were modified by ammoxidation prior to copolymerisation in order to identify a potential improvement of the curing characteristics. Furthermore the influence of the initial pH of the cooking suspension and of a Fenton-type lignin pre-oxidation step on the reaction rate in terms time-dependent viscosity increase was studied. The adhesives and adhesive bonds were analysed by various methods, whereby the Automated Bonding Evaluation System (ABES) was identified to be the most appropriate testing methodology for analysing the curing behaviour of wood adhesives by evaluating the hot press time-dependent development of the bond strength. Furthermore two approaches for a faster wet bond strength test of wood adhesives bonds, based on ÖNORM EN 302-1, was analysed in course of the thesis. As main results pine kraft lignin turned out to be the most suitable type of lignin for incorporation into phenol based adhesives, which is in accordance with literature. Ammoxidation and Fenton-type oxidation of lignins did not significantly increase resole formation.

Beurteilende(r): Konnerth Johannes
1.Mitwirkender: Liebner Falk

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