Hydrogen Bonding in Lignin:  A Fourier Transform Infrared Model Compound Study

Abstract

Hydrogen bonding plays an important role in the thermal and mechanical properties of biopolymers. To investigate hydrogen bond formation in lignin, an abundant natural polymer found in plants, Fourier transform infrared (FTIR) analysis of various lignin model compounds was performed. Four monomeric model compounds and one dimeric model compound were studied under various conditions. FTIR analysis revealed aliphatic hydroxyl groups form stronger hydrogen bonds than phenolic hydroxyl groups. Further, the dimeric biphenyl-type structure formed significantly stronger intermolecular hydrogen bonds as compared to the other monomeric model compounds. Results from the model compound studies were used to explain the observed complex hydrogen-bonding system present in both softwood and hardwood technical lignins. Together with chemical analysis, we discuss the difference in hydrogen bonding between hardwood and softwood lignin and the observed differences in the glass transition temperature.

Materials produced from plant biomass: part III: degradation kinetics and hydrogen bonding in lignin

“…Lignin is a natural polymer found in wood, being one of the most abundant biomacromolecules, second only to cellulose in natural abundance 1,2 . Lignin is a complex threedimensional network polymer that serves as a continuous matrix component in plant cell walls 2 .…”

“…Lignin is a complex threedimensional network polymer that serves as a continuous matrix component in plant cell walls 2 . Depending on the extraction method used and original source the physicalchemical characteristics differ considerably 2,3 .…”

“…Lignin is a complex threedimensional network polymer that serves as a continuous matrix component in plant cell walls 2 . Depending on the extraction method used and original source the physicalchemical characteristics differ considerably 2,3 . Various methods have been developed to separate lignin from the other constituents of the lignocellulosic materials [1][2][3][4] .…”

“…Depending on the extraction method used and original source the physicalchemical characteristics differ considerably 2,3 . Various methods have been developed to separate lignin from the other constituents of the lignocellulosic materials [1][2][3][4] . Since each separation method modifies to some degree the chemical structure of the naturally occurring lignin, so lignin is conventionally named after the method of separation used.…”

“…The method separates lignin as an insoluble material by depolymerization of cellulose and hemicellulose in 72% sulfuric acid followed by hydrolysis of the dissolved polysaccharides in boiling 3% sulfuric acid 4,5 . The wood species also affects the properties of lignin 2,3 . Chemically, softwood lignins consist largely of guaiacylpropane units, while hardwood lignins are basically composed of both guaiacyl-and syringylpropane units 2,3 .…”