Theoretical and experimental study on the oil sorption behavior of kapok assemblies

•The oil sorption behavior of kapok assemblies with relation of their pore structure was theoretically and experimentally studied.•A dual-scale model related the oil sorption behavior of kapok assemblies with kapok lumen and inter-fiber pores was developed.•The dual-scale model was proved fitting excellently well with the actual oil sorption behaviors of kapok assemblies, which were measured by the oil wicking tests.•Kapok lumen contributed considerably to the total oil absorption of kapok assemblies for tightly packed conditions.•The oil sorption rate of kapok assemblies was dominantly determined by inter-fiber pores.

Kapok fiber is a natural hollow fiber whose assemblies show high oil sorption capacity for various oils. In this article, a dual-scale model based on Washburn Capillary Theory was developed to study the oil sorption behavior of kapok assemblies with relation of their pore structure. The validity of this model was evaluated by oil sorption coefficient obtained from the curve of oil mass increase versus sorption time, which was measured by a wicking method. Diesel and motor oil were chosen as experimental oils. It turned out that theoretical values of sorption coefficients of the two oils were highly consistent with their experimental results. On the basis of theoretical analysis, we found that the big lumen of kapok fiber contributed considerably to the oil sorption capacity of kapok assembly, which was further enhanced with increasing kapok packing density. At the tightly packed condition of 0.10 g/cm3, oil absorbed by kapok lumens accounted for up to one fifth of the total oil absorption of kapok assembly for both test oils.