| The role of lignin in a furfuryl alcohol-lignin adhesive was investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and nuclear magnetic resonance (NMR) spectrometry. Bulk lignin and lignin fractionated by polarity were used throughout the study.;Evidence of reaction between lignin and furfuryl alcohol was found in NMR results, primarily through line broadening in the regions of interest. Evidence of phenylic and furanic structures were found in all NMR spectra, despite repeated attempts to separate disparate compounds. Since it is unlikely that different compounds each with phenylic or furanic character would have the same polarity, it was concluded that these spectra supported other results of reaction. Thin layer chromatography (TLC) sample preparation for NMR found a product of furfuryl alcohol-vanillin reaction with unique Rf value, indicating a compound unique from either parent. Spectrometric results concluded that lignin reacted with furfuryl alcohol, but did not inform on whether lignin was a reactive component or a comonomer in the adhesive.;DSC results found that lignin did not self-react under the conditions of study. DSC found that activation energies at 1%, 10%, and 50% conversion, using the Vyazovkin method, were lower for adhesive reactions containing the principal lignin fraction than for catalysed furfuryl alcohol. Adhesive reactions typically exhibited more pronounced exotherms than catalysed furfuryl alcohol and at temperatures slightly lower and slightly higher than those of catalysed furfuryl alcohol. TGA demonstrated the greater thermal resistance of the adhesive to catalysed furfuryl alcohol, lignin, and catalysed lignin. Thermal analysis concluded that lignin not only reacts with furfuryl alcohol, but is a comonomer in the adhesive.;Lignin was concluded to be not only a reactive component but also a necessary comonomer without which a very different, and inferior, adhesive resulted. Contrary to conventional thinking, it was found that it is possible to include lignin in an adhesive formulation without greatly sacrificing either curing speed or bonding properties.;Results prompted the proposal of reaction mechanism and partial reaction product structure and the proposal that lignin's role as comonomer in the adhesive may be that of plasticising agent and energy sink. |
