In the secondary cell wall, cellulose microfibrils are densely packed in a locally parallel arrangement and embedded in an amorphous matrix composed of hemicelluloses and lignin. Sample preparation often leads structural alteration, so a direct visualization of native structure is challenging. X-ray and neutron scattering are virtually free from sample preparation and thus can probe the structure without any modification to the structure. However, the interpretation of the data is not straightforward due to the overlaps of contribution from many structural features. We measured two-dimensional X-ray scattering on various wood samples covering a wide length scale of q = 0.006 to 2 Å<sup>-1</sup>, corresponding to 3 to 1000 Å spacing in real space. Here we focus on the equatorial scattering that represents the lateral arrangement inside the wood. In most samples, a shoulder appears at around q = 0.2 and a clear peak at q = 0.35. Those features could be explained if we consider a system composed of uniform hard cylinders that are parallel packed with a random lateral arrangement, at a volume fraction of 0.3-0.5. We propose a microfibril model with a diameter of 2.8 nm composed of 18 cellulose molecular chains. The 18-chain model gives good agreement in the wide-angle scattering profile reproducing the observed line-shapes.<br/>

Lateral arrangement of cellulose microfibrils in wood secondary cell wall

2019 Spring National Meeting

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