Influence of depolymerized lignin on resol synthesis

Abstract

Resole resins have been used for years as binders and adhesives in various wood products and in higher-value applications, such as in the automotive industry, toolmaking and household appliances. Alkaline resins based on phenol and formaldehyde are standard in the industry. These chemicals can cause health problems not only during the manufacture of the resins but also during the use of the products. The aim of this work was to investigate alternatives to the petroleum-based reactants with bio-based alternatives to create a more sustainable and less harmful alternative for phenol and formaldehyde in resin production and application. The used raw material was lignin, which was depolymerized to obtain fractions with higher reactivity. The formulation contained either the monomeric or oligomeric fraction. The depolymerization was carried out heterogeneously with a noble metal catalyst in an ethanol-water-solvent mixture. All resins were produced on a laboratory scale as alkaline resins. Formaldehyde and diformylfuran were used as crosslinking agents in the resin tests. The lignin fractions and the alkaline resins were then characterized. The most important resin property is the dynamic viscosity, which was determined by coneplate rheology. The molar mass distribution was analyzed by Gel Permeation Chromatography (GPC). In the heterogeneously catalyzed depolymerization, oligolignin was obtained as the largest mass fraction. The monomeric lignin showed a slower increase in mass average than the oligolignin, which is why oligolignin was used as starting material in the subsequent investigations. By changing the pH value between 9 and 12, an increase in dynamic viscosity and molar mass was observed. Different ratios of diformylfuran and formaldehyde showed that a higher polydispersity and higher temperature peaks were observed with increasing diformylfuran content. FTIR was used to assign structural elements. The results showed that oligolignin is well suited for resin synthesis on a laboratory scale due to its increase in dynamic viscosity and the molecular weight curve distribution. However, the resin formulations are not yet suitable for industrial applications as they are not reactive enough.

Datum der Bewilligung	2024
Originalsprache	Englisch
Betreuer/-in	Klaus Krennhuber (Betreuer*in)