Production of Cellulose Templated Mesoporous Silica Using Fibre Spinning
Examensarbete för masterexamen
Silica (or silicon dioxide, SiO2) occurs in abundance in nature, e.g. as the main constituent of sand, and there are many different existing uses for this material such as enzyme immobilisation, drug delivery and chromatography. There are also potential novel applications. This makes silica a very interesting and promising material to study more closely. For chromatographic purposes silica must be porous and more specifically mesoporous, i.e. with a pore size between 2 and 50 nm. The objective of this master thesis was to produce silica in this mesoporous state. As stated in the beginning of this paragraph one of the uses of mesoporous silica is to immobilise enzymes in the mesopores. By immobilising enzymes their stability can be increased and the cost, compared to using enzymes in their native form, can be reduced. Also, as mentioned, another application for mesoporous silica is for drug delivery by filling the pores with drugs that can then be transported into cells through endocytosis. If the pores instead of drugs are filled with e.g. a fluorescent dye the silica can aid in the identification of certain cell types. One possible way to produce mesoporous silica is to use a fibre spinning approach. However, since silica can not be spun alone additives are needed. The additive that was used was cellulose nanocrystals (CNC) or cellulose nanofibres (CNF). In this master’s thesis the properties and gelling behaviour of many different SiO2/CNC and SiO2/ CNF mixtures were studied to get a better understanding on how these materials interacted. From bulk gelling experiments it could be concluded that there was a clear synergy effect between CNC and silica where non-gelling samples of CNC and silica formed stable gels rapidly after being mixed at various pHs. The findings from these experiments were helpful later in the work when studying extrusion into a gelling bath. The gelling behaviour when extruding various CNC/silica mixtures into different gelling baths using a syringe and a needle was also explored. Subsequently, the fibre forming properties of the mixtures were examined to further understand the properties of the formed fibres; both on a physical macroscopic scale and later on a microscopical scale using Scanning Electron Microscopy (SEM) and nitrogen sorption analysis using the BrunauerEmmett-Teller (BET) method. These analyses were conducted to get an understanding of the surface of the samples as well as data about their porosity. In terms of mechanical stability it could be concluded that fibres composed of CNC and silica were generally very brittle whereas fibres with CNF and silica were generally robust. SEM analysis showed that fibres composed of CNC and silica did not produce highly porous fibres after calcination. This means that CNC is unsuitable as a template for producing mesoporous silica. Nitrogen sorption analysis was also used to study the surface area, pore volume and pore size of the (porous) silica. Overall, sorption analysis showed that the silica mixed with CNC did not produce very porous silica fibres after calcination. However, using CNF resulted in a much more porous silica after calcination with a surface area of 205 m2/g (sorption data). These values can be compared to the surface area of the pure silica used which was 123 m2/g. These results show that silica/CNF mixtures can be spun into stable enough fibres that upon drying and calcination can form a mesoporous silica material.