| Ordered porous silica materials were developed in 1992. These materials possess a uniform pore size in the mesoporous region (2--50 nm), which is in addition also variable. They are also characterized by a large pore volume and a high surface area. These ordered mesoporous silica materials are synthesized by the use of a supramolecular assembly of surfactant molecules (micelles) as the structure-directing agent for the porous structure.;SBA-15 possesses hexagonally ordered mesopores with microporous pore walls. By using a high silica precursor/surfactant ratio in the SBA-15 synthesis, a material of which part of the channels contain internal microporous nanocapsules or 'plugs' was synthesized. The first results showed these PHTS (Plugged Hexagonal Templated Silica) materials are more stable than the conventional micellar templated structures known so far, the amount of open and plugged pores can be varied and they possess a very high micropore volume. Four important parameters of the synthesis were investigated: the amount of silica precursor (tetraethylorthosilicate or TEOS), the stirring and aging temperature, and the stirring time. The adsorption of hydrocarbons (n-hexane, n-heptane, 3-methylpentane, c-hexane, toluene, 1-hexene) onto PHTS and its plug-free analogue SBA-15 was investigated to further characterize the structure.;Next to these smaller hydrocarbons, also the adsorption and desorption behavior of larger molecules, like antioxidants (thymol, chitosan, dodecyl gallate, Na-ascorbate, ascorbyl palmitate, alpha-tocopherol, origanox WS) and antimicrobial agents (nisin and lysozyme), was tested on several porous materials (laponite, SyloblockRTM, SBA-15, PHTS and MCF). These compounds can prevent food deterioration through lipid oxidation and micro-organisms. Control of the release rate of the active component from the plastic wrapping can result in an extension of the shelf-life of the food product. By inserting a porous material loaded with e.g. antioxidant into a packaging material, such an active system could be created. The adsorbent, loaded with active component, was modified in two ways to investigate the influence on the release rate: by mechanical compression and by silylation with silicon tetrachloride (SiCl4) and a commercial silicon oil. Both procedures cause obstructions in the pore channels of the adsorbent, consequently hampering diffusion of the molecules, which can delay their release. |
