X-ray Diffractometer

X-ray diffraction (XRD) is a phenomenon of cooperative interference between photons and electrons strongly bound to atoms within a material. XRD is widely used as a standard crystallography technique. Given the crystalline nature of cellulose arrangements, XRD can be applied as an indirect, yet robust and rapid method to estimate various structural parameters of cellulose in wood—particularly the microfibril angle (MFA) and degree of crystallinity. Unlike crystallinity measurements on powdered materials, MFA measurement is performed on intact wood specimens, as the microscopic structure of the cell wall must be preserved. Samples are cut according to the anisotropy planes of wood, and the incident X-ray beam is directed perpendicular to the sample surface. Depending on beam cross-section and sample thickness, several hundred cells contribute to diffraction. For crystallinity measurements, powdered samples are required, obtained by milling wood specimens.

Cellulose Structure Analysis / Microfibril Angle Measurement

The diffractometer we use is the SUPERNOVA model developed by Oxford Diffraction (UK). The monochromatic X-ray source is generated by a microfocus copper anode (50 keV / 1 mA) and passes through the sample with a beam diameter of approximately 300 µm. The specimen is positioned vertically, with the LT plane perpendicular to the beam and located 43 mm from the detector. By applying an empirical model, we establish a correlation between the X-ray diffraction profile and the actual microfibril angle. X-ray diffraction measurements also allow the determination of the cellulose crystallinity index and the crystallite size, notably using the Segal method.

Results are provided as: raw diffraction profiles for each sample or interpretation files produced within the SILVATECH facility

Service Options

• Partial: supervised access to the equipment
• Full: from acquisition to interpretation (sample machining not included, unless within a collaborative project)

Strong relationships between MFA and wood properties make MFA measurement highly valuable. This technique is also applicable to other plant-derived fibres.
 

Contact:

• Equipment and unit coordinator: Julien Ruelle julien.ruelle@inrae.fr