Lignin chemistry and selected applications (Overview paper)
Internal work for ILI Umbrella 2010
Roger Malherbe, Alfred Abächerli
Thermosets, also called duroplasts, retain their form even when warming up and, furthermore, the heating of thermosets is part of the production process that hardens them. Also, the hardened thermosets do not melt but are simply destroyed at a certain temperature. As a classical example, the plastic Bakelite belongs to this group. The presence of various reactive groups, that can be used for chemical reactions, carboxyl, aromatic and aliphatic hydroxyl or others, is important for the reactivity and the properties in adhesive applications. Typical thermosets where lignin can be used are phenolic resins, polyurethanes and epoxies.
Lignin is an obvious candidate as a phenol substitute in phenol formaldehyde resins. Recent progresses have been reported with modified lignin powders originating from novel processes (like organosolv pulping and non-wood raw materials). These products can replace up to 50% of the phenol formaldehyde resin in adhesives in the different application fields of phenolic resins. If the phenol is replaced in the resin cooking up to 80% replacement rate is possible.
The use of lignin in polyurethane copolymers is exploiting the presence of hydroxyl groups (aliphatic and aromatic). Lignin can be used without any preliminary chemical modification. It then functions as crosslinker or additive (flame retardant) in polyurethane foam. Moreover, lignin oxypropylation can produce liquid polyol mixtures of lower viscosity that are of great interest in polyurethane.
Epoxy blends are other challenging applications, which have already been extensively studied. The latest was reported by a laboratory of IBM for the production of a printed wiring board that had all the required properties. The composition containing lignin, an epoxy resin and an initiator was utilized to prepare prepregs and then processed by conventional methods.
A big amount of publications is available on these topics (see references and overview in Malherbe – first paper under ‘View All’, pp. 5).
Summaries, Overviews and Priority Papers
- View All
- Overviews
- PUs
- Resoles
- Reactivity
- Fibre Boards
- Various
- Epoxies
- Projects
- Novolacs
