Abstract
bark extracts obtained by lixiviation with water or alkaline solutions followed by spray drying. Extract yield was 2.5- to 6-fold higher with alkaline extractant solutions than with water. Within the ranges of temperature (T), NaOH dose (NaOH) and solid/liquid ratio (S/L) that were studied, the formaldehyde-condensable polyphenols content of spray-dried extracts obtained with NaOH as extractant was highest (27.3%) at T=90 °C, NaOH=5%, S/L=1/6. Polyphenols content fell with increasing particle size due to both diffusion limitations and the variation of particle composition with size, which is attributable to the dependence of both the chemical composition of the bark and its response to grinding on its anatomical origin. All the spray-dried extracts had Stiasny numbers high enough to allow their use in adhesives, although this application may require prior chemical modification to reduce the rapid rise in the viscosity of their aqueous solutions with increasing solids content. The reactivity of the extracts with formaldehyde is readily controlled by varying pH.
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