72 / 2021-06-07 21:29:55

In-situ regulating of bacterial cellulose with starch: properties evaluation and regulation mechanism for oil-water separation

Bacterial cellulose; Nanocellulose; starch; network structure; oil-water separation

Bacterial cellulose is a novel biomaterial biosynthesized by the bacteria Komagataeibacter xylinus, with an annual production scale of several billion tons. Bacterial cellulose has raised great attention, owing to its unique interconnected network structure and robust physical properties, such as high-water holding capacity, large specific surface area, good chemical stability, environmental friendliness and remarkable mechanical strength. In fact, the applications of bacterial cellulose in biomedicine and environmental fields are closely related to its three-dimensional network structure. Although bacterial cellulose networks are highly interwoven, their mesh density is low, which is not conducive to cell infiltration and liquid penetration. Furthermore, the low compression modulus perpendicular to the bacterial cellulose fibril layer limits its applications. After the drying processes, irreversible compressive deformations are formed orthogonal to the plane of the bacterial cellulose membrane due to the H-bonding between the cellulose nanofibers. Therefore, it is necessary to control its network structure and mechanical properties perpendicular to fibrils. The morphology and properties of bacterial cellulose can be altered by including additives not specifically required for growth of the bacteria in liquid media. In this study, starches from different plant sources, and with different amylose / amylose contents, were added to the culture medium to regulate the network structure and mechanical properties of bacterial cellulose. After sterilization, the degree of gelatinization of starch granules was different, resulting in differences in the soluble components in the medium. The viscosity of the medium was determined by the type of starch. This affected the movement of bacteria, which influenced the speed and direction of cellulose production. Soluble matter also adhered to the microfibers, which affected their differentiation and polymerization. Consequently, there were differences in the network structure of the final bacterial cellulose membranes. After regulation, the anisotropy of the bacterial cellulose was changed, and the cross-sectional structures of the membranes were significantly different. The regulated bacterial cellulose membranes were immersed in an aqueous solution of silanol derived from tetraethoxysilane to generate silica nanoparticles. After coating with hexadecyltrimethoxysilane, the composite membranes were converted into superhydrophobic membranes for oil-water separation. The water contact angle of composite membrane was 167°, and the flux for kerosene was 8113 Lm^-2h^-1MPa^-1, which was 2.8 times higher than that of the original bacterial cellulose membrane. This preliminarily study provides a foundation for the development of methods to regulate the network structure of bacterial cellulose.