Dispersing sepiolite crystal bundles into nanofibers under expansion effect via steam pressure change and vacuum freeze-drying processes

Abstract

Sepiolite nanofibers mainly exist in the form of crystal bundles, and the crystal bundles often bond with each other to form aggregates, which makes it difficult to effectively display its nanometer characteristics. Based on the excellent water absorption characteristics of sepiolite, a new approach for dispersing the aggregates and crystal bundles into nanofibers was developed via steam pressure change and vacuum freeze-drying processes. The dispersion effect was evaluated using laser particle size analyzer, XRD, FTIR, SEM, TEM, and surface area porosity analyzer. The experiments found that finite times repeated using steam pressure change process improved the crystal bundles dispersion effect. Adding vacuum freeze-drying process further promoted the crystal bundles dispersion. The dispersion effect of the sample after two times of steam pressure change and one time of vacuum freeze-drying processes was optimal. Compared with the original sample, particle size corresponding to a cumulative volume percentage of 50 % and 90 % (D50 and D90) of the treated sample reduced by 84 % and 91 %, respectively. The crystal bundles with a width of 0–120 nm accounted for more than 90 %. The specific surface area (S_BET) increased by 62 %, reaching up to 237 m²g⁻¹, and the rotary viscosity increased from 584 mPa·s of original sample to 1635 mPa·s. The experimental results validated that the expansion effect of steam pressure change and vacuum freeze-drying processes can effectively achieve the non-destructive dispersion of sepiolite crystal bundles. The proposed method may provide a new idea for high value industrial production of fibrous clay.