Browsing by Author "Nikkilä, Ida"

The literature review of this master’s thesis dealt with polysaccharide based hydro- and aerogels and their preparation methods and characterization. TEMPO/laccase-catalyzed oxidation was also included in the literature review. The aim of the experimental part of this thesis was to prepare hydrogels by TEMPO/laccase-catalyzed oxidation and study how the oxidation changed the rheological and chemical characteristics of the polysaccharides. The hydrogels were also dried to produce hydrogels via lyophilization and their characteristics were determined. The degree of oxidation of the hydrogels was analyzed by the GC-MS method. The viscoelastic properties of the hydrogels were studied by oscillation measurements. The compressive modulus of the aerogels was determined by means of a compression test. The morphology of the aerogels was studied with the help of a scanning electron microscopy (SEM). The studied polysaccharides were arabinoxylan, glucomannan, galactomannan and xyloglucan. Due to the oxidation, a change in the viscoelastic behaviour could be seen between the native and oxidised polysaccharides. The rheological test revealed that the native polysaccharides were viscous liquids (G' > G'') and oxidized polysaccharides formed elastic hydrogels (G' > G''). The degree of oxidation of the hydrogels varied 3,3–11,7 %. The hydrogels were dried using two different freezing methods, unidirectional and conventional, and they were freeze-dried into aerogels without significant shrinkage. The density of the aerogels varied 0,017–0,030 g/mm3. The compressive modulus of the aerogels was 108‒1184 kPa depending on the polysaccharide. The SEM images revealed that unidirectional freezing resulted in pores that were parallelly oriented with the freezing direction. Unidirectionally frozen aerogels were stronger than conventionally frozen aerogels when the compression was oriented against the freezing direction. This was the first time that TEMPO/laccase catalyzed oxidation was used to prepare arabinoxylan and glucomannan hydro- and aerogels. The arabinoxylan and glucomannan aerogels were mechanically stronger than previously studied aerogels that have been prepared by enzymatic oxidation.