The aim of this study was to show that multilayer fractal Brunauer−Emmett−Teller (mfBET) theory can be
used as a tool to obtain information about the distribution of water in cellulose powder particles of varying
crystallinity. Microcrystalline cellulose, agglomerated micronized cellulose, low-crystallinity cellulose, and
cellulose powders from green and brown algae were characterized by scanning electron microscopy and mfBET
analysis on water and nitrogen adsorption isotherms. The distribution of water in the cellulose materials was
found to be characterized by a fractal dimension smaller than 1.5 for all powders. The results showed that for
highly crystalline cellulose materials, such as Cladophora cellulose, the cellulose−water interactions take
place mainly on cellulose fibril surfaces adjacent to open pores without causing any significant swelling of
the material. For less ordered celluloses the water interaction was found to take place inside the bulk material
and the water uptake process caused the pore volume to swell between 1 and 2 orders in magnitude. For the
Cladophora cellulose, the thickness of the adsorbed water layer at the outer cut off of the fractal region was
found to coincide very well with the average pore size obtained from nitrogen adsorption measurements. The
multilayer fractal BET analysis on nitrogen adsorption isotherms showed that the particles could be characterized
by fractal dimensions between 2.13 and 2.50. We conclude that water adsorption has the ability to alter the
structure of the studied material and reveal a sorption-induced, “apparent” fractal structure over a relatively
narrow length scale interval, while nitrogen adsorption probes the substrate morphology over a wide range of
length scales and reveals the “true” fractal structure.
The surface are and crystallinity was measured on a cellulose powder made from Cladophora sp. algae. The algae cellulose powder was found to have a very high surface area (63.4 m2/g, N2 gas adsorption) and build up of cellulose with a high crystallinity (approximately 100%, solid state NMR). The high surface area was confirmed by calculations from atomic force microscope imaging of microfibrils from Cladophora sp. algae.
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