Lignin is the second most abundant organic compound on earth and is currently a highly underutilized natural resource and industrial byproduct. Among the many research steps taken toward new practical lignin applications is one involving the chemical modification of lignin to form processable thermoplastics. Such lignin-based materials could potentially be used as a direct substitute for petroleum based plastics. This preliminary research has studied specifically the esterification reactions of kraft and agricultural hydrolysis lignins, the byproducts of the kraft paper-making process and of ethanol production, respectively. These lignins were reacted with acetic, propanoic, butyric, and hexanoic acid anhydrides to form their respective lignin esters. The chemical structures of the resulting compounds were analyzed using proton nuclear magnetic resonance spectroscopy (1{sup left}H-NMR), diffuse reflectance Fourier transform infrared spectroscopy (DR-FTIR), and pyrolysis gas chromatography/mass spectrometry (GC-MS). Thermal transitions were detected using differential scanning calorimetry (DSC) and dynamic rheology. The results have shown that kraft lignin was easily modified by esterification into thermally processable plastics, though so far successful modification of the agricultural lignins has proven more difficult, due to their highly condensed structure. The effect of phenolation (to selectively depolymerize lignin) prior to esterification of the lignins is being examined as a possible solution to these difficulties. Results have also shown that the lignin ester thermal properties can be controlled by simple changes in esterification reaction parameters. Future work will look at the mechanical properties of the materials using dynamic mechanical analysis (DMA).
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