Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance

Area of Science:

• Materials Science
• Biochemistry
• Analytical Chemistry

Background:

• The crystallinity index (CI) is a key parameter for cellulose characterization.
• Existing CI measurement methods, particularly the widely used X-ray diffraction (XRD) two-height method, yield variable results.
• The relationship between CI and cellulose digestibility is not fully understood.

Purpose of the Study:

• To compare the accuracy of different methods for measuring the CI of cellulose.
• To evaluate novel XRD and solid-state 13C nuclear magnetic resonance (NMR) techniques.
• To clarify the correlation between CI and cellulose digestibility.

Main Methods:

• Comparison of four distinct CI measurement techniques.
• Utilized X-ray diffraction (XRD) and solid-state 13C nuclear magnetic resonance (NMR).
• Tested on eight diverse cellulose preparations, including Avicel PH-101.

Main Results:

• The simplest, most common XRD method (two-height measurement) significantly overestimated CI.
• Novel XRD and NMR methods, analyzing entire spectra, provide more accurate CI determination.
• Literature data for Avicel PH-101 supports the overestimation by the simple method.

Conclusions:

• Accurate CI measurement requires methods considering amorphous and crystalline contributions across spectra.
• Cellulose digestibility is influenced by CI but also by other factors like lignin, porosity, and particle size.
• Caution is advised when correlating minor CI changes with digestibility or predicting cellulase performance.