Difference in reduction properties between longitudinal dimension and elastic modulus of wood induced with aqueous NaOH treatment: modeling and analysis

The dependence of the elastic modulus and the longitudinal contraction on the NaOH fractional concentration [NaOH], which differs from each other, was discussed based on a quantitative model analysis using the rule of mixtures, a cell wall model, and a dual-phase model consisting of crystal and amorphous phases. The elastic modulus was formulated as a function of the degree of crystallinity of the decrystallized microfibrils. The [NaOH] dependence of the calculated elastic modulus shows good agreement with the experimental results in that the [NaOH] dependence differs before and after at [NaOH] = 0.12. The model analysis illustrates that the reduction property of the elastic modulus is dependent on whether the amorphous region created with the treatment transverses the originally crystalline region of the microfibrils or not: the concentration is [NaOH] = 0.12. This is attributed to the difference in the reduction property between the elastic modulus and the dimensional changes along the longitudinal axis of a wood sample at [NaOH] < 0.12.