Aerogéis hidrofóbicos de nanofibras de celulose

Abstract

The use of natural fibers from renewable and biodegradable sources, such as cellulose, in oleophilic sorbent formation has become an interesting alternative due to their excellent properties. However, chemical treatments are necessary to make the hydrophobic sorbents. In this study, sorbent materials called aerogels were developed from suspensions of unbleached softwood pulp (Pinus ellioti) and bleached and unbleached hardwood pulp (Eucalyptus sp.) through mechanical fibrillation in a grinder. Two methods for drying nanocellulose were used: freeze drying and supercritical drying. Chemical treatments with methyltrimethoxysilane (MTMS) through vapor deposition were used to obtain aerogels with hydrophobic and oleoliphic properties. Cellulose plates were characterized and the α-, β- and γ-cellulose and lignin contents were evaluated. The aerogels were characterized and their apparent density, porosity and compressibility. Aerogels were also characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy with field emission gun (FEG-SEM) and sorption tests. All cellulose samples presented α-cellulose contents varying from 57.34% to 92.57%. Unbleached cellulose samples showed a lignin content varying from 5.69% to 14.18%. The mechanical fibrillation, freeze drying and supercritical drying processes were effective for obtaining cellulose nanofibers with a diameter between 38 to 75 nm. The freeze dried aerogels showed no shrinkage, while the aerogels obtained by supercritical drying showed shrinkage of 12.18%. Contact angle measurements with water obtained for the aerogels were above 134°, confirming their hydrophobic character. The freeze-dried aerogels displayed a lower density and higher porosity, as well as higher compressive strength and sorption capacity when compared to supercritical-dried aerogels. Aerogels from unbleached cellulose (Pinus elliotti and Eucalyptus sp.) showed higher sorption capacities, ranging from 19.188 to 23.493 g.g-1 in heterogeneous medium (water and oil). Aerogels from bleached cellulose (Eucalyptus sp.) displayed a sorption capacity between 15.318 and 18.615 g.g-1 in the same medium. All aerogels had oil removal efficiency above 90%.