The degree of polymerization (DP) of cellulose in cellulosic biomass and how it changes during enzymatic and chemical transformations has remained a fundamental property of interest to numerous researchers. Currently, with increased interest in cellulosic biofuels, more attention is being focused on determining changes in cellulose DP before and during pre-treatment, as well as the effect of DP on enzymatic deconstruction of cellulose to glucose. Different sources of celluloses from woody and non-woody biomass have been isolated and the DP has been frequently examined as a key parameter contributing to effi cient biomass deconstruction. The isolation and derivatization/dissolution of cellulose are crucial steps in determining cellulose DP. This review summarizes approaches to measuring DP developed over the past six decades and highlights opportunities for further improvements.

Detailed chemical structural elucidation of ethanol organosolv lignin (EOL) of Buddleja davidii was performed to determine the fundamental structure released from an ethanol organosolv pretreatment (EOP). Several nuclear magnetic resonance (NMR) techniques were used to analyze the structure of EOL, including quantitative 13 C, 31 P NMR, and qualitative DEPT-135 13 C, 2D 1 H-13 C correlation NMR. As revealed by NMR, the aryl-O-ether linkage (β-O-4 0 ) of lignin was extensively cleaved via homolysis during pretreatment and led to the formation of stilbene structures. Other linkages, such as resinol (β-β 0 ) and phenylcoumaran (β-5 0 ), were resistant to degradation. The high degree of condensation of EOL indicated that condensation reactions occurred but did not impede the delignification efficiency of EOP. Both guaiacyl and syringyl lignin were found to be reactive toward condensation during pretreatment. The results from gel-permeation chromatography showed that the degree of polymerization (DP) of lignin significantly decreased by ∼85%, facilitating lignin solubilization in ethanol.

A compositional analysis was performed on Buddleja davidii to determine its general biomass characteristics and provide detailed analysis of the chemical structures of its cellulose and lignin using NMR. B. davidii is a new potential lignocellulosic bioresource for producing bioethanol because it has several attractive agroenergy features. The biomass composition of B. davidii is 30% lignin, 35% cellulose, and 34% hemicellulose. Solid-state CP/MAS (13)C NMR showed that 33% of the cellulose is para-crystalline and 41% is at inaccessible surfaces. Both quantitative (13)C and (31)P NMR were used to examine the structure of lignin. The lignin was determined to be guaiacyl and syringyl with an h:g:s ratio of 0:81:19.

Ethanol organosolv pretreatment was performed on Buddleja davidii to evaluate this bioresource as a potential feedstock for bioethanol production. B. davidii was pretreated and delignified, while 85% of the glucose content of the untreated material was retained in the pretreated solid fraction. The enzymatic hydrolysis showed that organosolv pretreatment produced solid substrates that were readily digestible by cellulases. Gel-permeation chromatography was used to determine the degree of polymerization (DP) of cellulose, and solid-state cross polarization/magic angle spinning 13C NMR experiments were conducted to study the changes in crystallinity and ultrastructure of cellulose. The results showed a decrease in DP along with an increase in the relative proportions of para-crystalline and amorphous cellulose and a decrease in cellulose Iα and Iβ. Removal of lignin and hemicellulose, reduction in DP, and decrease in the crystalline allomorphs (Iα and Iβ) increased the amenability of the biomass to enzymatic degradation.