The onset of climate change as a direct result of CO2 gas emissions has fueled a need to produce CO2-negative composite building materials. Lignin and lignite currently serve as fillers in wood plastic composites which are then used to make building materials. Carboxylation of lignin has shown enhanced blending with the polymer matrix and increase the overall mechanical performance. Traditional carboxylation methods are cost prohibitive, thus captured CO2 in the form of carboxylic acids will serve as a feedstock. Infrared spectroscopic (IR) information of the lignin before and after carboxylation is used to determine the extent of carboxylation and serve as an experimental guide to optimize the carboxylation process. Quantitative analysis of carboxyl groups through IR is commonly performed through the transmission method; however, this technique encounters challenges derived from sample preparation. The reflection technique, commonly performed through Attenuated Total Reflectance spectroscopy (ATR) and Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTs), provide quantitative information through the Kubelka-Munk equation which is highly dependent on the grain size (i.e., particle diameter). Through careful sample preparation and well-defined methodology, each of these methods can be used to successfully quantify the extent of carboxylation on the lignin surface. The use of ultraviolet-visible (UV-Vis) spectroscopy to determine the extent of carboxylation will also be discussed.

Spectroscopic techniques for carboxylic acid quantification on lignin

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