Extract yields of two commercially valuable wood species in Central Africa: Bilinga and Tali, their nature and role in water sorption activities

This paper aimed at determining the quantity, nature and role of extracts during the sorption behavior of two Central African hardwood species: Nauclea diderrichii (Bilinga) and Erythrophleum suaveolens (Tali) at 30, 40, 50, 60 and 70°C using relative humidities (RH) between 5.3% and 97%. For this purpose, extract contents and their nature were determined by solvent extraction and mass spectrometric analysis (MALDI-TOF/MS) respectively. The ABC model whose parameters were used to determine the monolayer moisture capacity (EMCm) also described type II sigmoidal sorption isotherms. The results showed that acetone extracts were the highest in Tali (7.88%) and Bilinga (6.92%). MALDI-TOF results found 10 new chemical components out of 24 in Tali (saponins, flavonoids, glycosides, alkaloids and stilbenes) while 16 were identified as saponins, acids and flavonoids in Bilinga. Acetone-soluble extracts had the most significant effect on the hygroscopic nature of wood. Extracted wood recorded higher equilibrium moisture contents (EMC), monolayer moisture capacities and lower sorption differences. For native wood, water-repellent polyphenols like alkaloids and stilbenes and newly identified components there in, rendered Tali less hygroscopic than Bilinga. The nature of extractives would be an effective alternative to explore the chemical compounds, which can best improve the hygroscopic response of wood.