BEHAVIOR OF AN AGROMATERIAL BASED ON NEEM SEED EXTRUSION RAFFINATE IN RELATION TO WATER - MODELING OF THE ADSORPTION ISOTHERM

The valorization of neem seed extrusion raffinate, a co-product of the oilseed agro-industry that remains largely untapped offers promising prospects for the development of bio-based agromaterials. The water adsorption isotherms of the agromaterial were modeled using several commonly used semi-empirical and empirical mathematical models (GAB, BET, Henderson, Oswin, Peleg). The resulting curve exhibits the characteristic profile of a Type III isotherm according to the Brunauer-Emmett-Teller (BET) classification. This type of isotherm, which reflects weak water-material interaction at low water activities and adsorption that intensifies as water activity increases, is characteristic of multimolecular (multilayer) adsorption and is consistent with the predominantly fibrous composition of the agromaterial. A comparison of the statistical fit criteria (coefficient of determination and Mean Squared Deviations) shows that Peleg’s four-parameter model most accurately describes the material’s adsorption behavior. The three-parameter GAB model ranks second, yet offers the advantage of providing physically interpretable quantities, notably the water content of the monolayer, which is useful for estimating optimal storage conditions. These results confirm the hygroscopic nature of the neem raffinate based agromaterial, even though adsorption is low (approximately 6.61% at 75% relative humidity) compared to most bio-based materials, and highlight the relevance of the Peleg model for predicting its water behavior under varying relative humidity conditions.