| Abstract
| - Lignin is a highly branched polymer consisting of phenylpropane units, and it is one of the ingredientsof the supporting matrix in plant cell walls. The morphology of several lignins extracted from plant cellwalls using different methods was studied by small-angle and ultra-small-angle X-ray scattering. A power-law type intensity was observed for the dry lignins, but on the basis of the power-law exponent the fractalapproach often applied to lignins is not fully justified. However, the intensity of kraft lignin did show apower law with surface fractal dimension Ds = 2.7 ± 0.1. The specific surface area of the lignins rangedfrom about 0.5 to 60 m2/g with 20% relative accuracy. The radius of gyration was determined from small-angle X-ray scattering data for aqueous solutions of kraft lignin. The shape of the particles in NaCl andNaOH solutions was found to be elongated. The particles were about 1−3 nm thick, while the length (5−9nm) depended on the solvent and on the lignin concentration. The size of these primary particles wasapproximately the same as the size of the pores in the fractal aggregates of the dry kraft lignin. Their sizewas determined to be about 3.5 nm.
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