When formulating materials containing an hydraulic binder and plant particles, the setting of the binder may be slowed or prevented by the compounds extracted from the plant. In this article, a methodology is fixed to analyse three types of hemp shiv and to study the variability of the composition of extractives and their influence on the hydration of cement. Isothermal calorimetric measurements have shown that one type of shiv caused a greater delay in the setting of the cement. Analysis of free compounds extracted from the plant has shown that this shiv has a higher content of extractives, and in particular, of sugar. By using the same quantities of standard sugars, it was found that the measured sugar content could not, in and of itself, account for the delay in hydration measured in the presence of shiv. Other extracted molecules, such as phenolic compounds, also play a part in the hydration of the cement.
We review the studies on the wetting of soluble polymeric substrates by their solvents, both in the literature and conducted in our group in the past decade. When a droplet of solvent spreads on a soluble polymer layer, its wetting angle can strongly vary with the contact line velocity even at capillary numbers smaller than unity, in contrast to non-soluble substrates. The solvent content in the polymer is a key parameter for the spreading dynamics; that content is set by the initial conditions, but also by the transfers occurring from the droplet to the polymer layer during spreading. We focus on hydrophilic amorphous polymers that are glassy at room temperature, and we discuss the consequences on wetting of the very large changes in the polymer physical properties induced by solvent sorption. We finally present new results on polymers of varying molar masses, and show how they open new perspectives for a better understanding of powder dissolution.
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