Aromatic material constituents derived from renewable resources are attractive for new biobased polymer systems. Lignin, derived from lignocellulosic biomass, is the most abundant natural source of such structures. Technical lignins are, however, heterogeneous in both structure and polydispersity and require a refining to obtain a more reproducible material. In this paper the ethanol-soluble fraction of Lignoboost Kraft lignin is selectively allylated using allyl chloride by means of a mild and industrially scalable procedure. Analysis using 1 H-, 31 P-, and 2D HSQC NMR give a detailed structural description of lignin, providing evidence of its functionalization and that the suggested procedure is selective toward phenols with a conversion of at least 95%. The selectively modified lignin is subsequently cross-linked using thermally induced thiol−ene chemistry. FT-IR is utilized to confirm the cross-linking reaction, and DSC measurements determined the T g of the thermosets to be 45−65 °C depending on reactive group stoichiometry. The potential of lignin as a constituent in a thermoset application is demonstrated and discussed.
The
need for renewable alternatives for fossil-based aromatic material
constituents is evident for a more sustainable society. Lignin is
the largest source of naturally occurring aromatic compounds but has
mainly been considered as waste material or energy source in the pulp
and paper industry. Developments in extracting lignin from these processes
provide a large source for renewable aromatic structures to be used
in various applications. Producing thermosets out of lignin is a very
promising route to utilize this raw material toward, for example,
composite application. The buildup of the molecular network based
on oligomeric lignin segments will be different from traditional thermoset
analogues, where the constituents often are smaller molecules, and
will have an effect on the material properties. In this work LignoBoost
Kraft lignin is refined, chemically modified, and used to produce
freestanding thermosets with different architectures and properties.
These different thermosets are evaluated, and the possibilities to
tailor the material properties through work-up and modification are
demonstrated. Morphological studies on the formed thermosets using
X-ray scattering show systematic differences in molecular stacking
and aggregate sizes.
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