Development of anioniic chitosan derivative as water soluble emulsiifier

Abstract

This research was dividing into two parts. Part 1, the emulsifying capability of sodium chitosan phosphate (PCTS) as anionic polymer was studied. In the prelimainary study, the Hydrophilic-Lipophilic Balance (HLB) and Critical Micelle Concentration (CMC) of sodium chitosan phosphate were determined and found those values around 19 and 0.13%w/v, respectively. These values indicated that PCTS was suitable for production oil-in-water emulsion. Then, the stability of emulsions was investigated. The results showed that emulsion using PCTS with degree of substitution (DS) around 0.04 at concentration of 1-3%w/v exhibited stable emulsion. Furthermore, the influence of ionic levels to emulsion stability was determined and found that emulsion using PCTS with high DS around 0.62 at concentration 4%w/v showed stable emulsion over wide range of pH. Part 2, the systematic conditions (pH, ionic strength, temperature) were set to investigate the physical mechanism which explained the destabilization phenomena of the stable emulsion emulsifying with 1%w/v PCTS and different ionic levels. The emulsion using PCTS with DS 0.04 (coding E85/0.1) exhibited positive surface charges, whilst that of using PCTS with DS 0.25 and 0.62 (coding E85/1 and E85/2) exhibited negative surface charges. Those emulsions showed isoelectric points (pI) which shifted to lower pH as increasing DS. E85/0.1 gradually increased its droplets size above pI, whereas E85/1 and E85/2 maintained constant in their size, except agglomerate below pI. With increasing electrolyte concentrations in the range of 0.1-4 mM or 0.1-1 mM, the droplet size for those E85/0.1, E85/1 and E85/2 maintained constant without considering the surface charges. With increasing electrolyte concentrations more than or equal 6 mM for E85/0.1 and 2 mM for E85/1, E85/2, may cause to compress the electric double layer in a consequence of agglomeration. The surface mean diameter of E85/0.1, E85/1, and E85/2 increased abruptly around 50℃ due to the water dehydration around PCTS molecule inducing more hydrophobic surface. The individual droplets became closer with hydrophobic interaction, resulting in agglomeration.