Quantitative Investigation of Free Radicals in Bio‐Oil and their Potential Role in Condensed‐Phase Polymerization

Abstract We report on the quantitative analysis of free radicals in bio‐oils produced from pyrolysis of cellulose, organosolv lignin, and corn stover by EPR spectroscopy. Also, we investigated their potential role in condensed‐phase polymerization. Bio‐oils produced from lignin and cellulose show clear evidence of homolytic cleavage reactions during pyrolysis that produce free radicals. The concentration of free radicals in lignin bio‐oil was 7.5×10 20 spin g −1 , which was 375 and 138 times higher than free‐radical concentrations in bio‐oil from cellulose and corn stover. Pyrolytic lignin had the highest concentration in free radicals, which could be a combination of carbon‐centered (benzyl radicals) and oxygen‐centered (phenoxy radicals) organic species because they are delocalized in a π system. Free‐radical concentrations did not change during accelerated aging tests despite increases in molecular weight of bio‐oils, suggesting that free radicals in condensed bio‐oils are stable.