| Cellulose acetate (CA), a derivative of cellulose is a cellulose esters that is partially or fully substituted at the C-2, 3 and 6-positions of the anhydro-D-glucopyranose residue. Their solubility in various solvents depends on the degree of substitution (DS) of the acetyl groups. CA is soluble in water at low DS of between 0.5--1 but insoluble in aqueous solutions at higher degree of substitution (DS > 1). Applications involving cellulose acetate often exploit semi- to concentrated solutions. In this regard, the main objectives of our study are as follows---to develop a semi- to concentrated ternary mixed solvent system comprising of cellulose acetate, N,N dimethylacetamide and water and manipulate the system to form aggregated structures leading to phase separated gel network. The tools employed in this project to investigate and characterize the macroscopic and microstructural property changes are rheology, scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM).; The first part of this study involves addition of water-N,N dimethylacetamide solutions in different ratios to bulk 20% cellulose acetate- N,N dimethylacetamide solutions with emphasis on increasing water content in the system. The steady state viscosity was found to increase with water content increase and above critical water concentrations, typically greater than 19%, there is a solution to gel transition. The SEM and LSCM micrographs showed microstructural formation with more open network or voids at lower water content, whiles a more compact homogenous structure was exhibited for higher water content gel samples.; The second part of this study, addition of cellulose acetate to different ratios but constant weight of N,N dimethylacetamide/water solutions. The systems phase separates into two layers consisting of a clear solution on top of a viscous bottom layer above 19wt% water content. Heating the two-phase system to 100°C and cooling back to room temperature led to the formation of a one-phase physical gel matrix. All the gels showed increase in elastic and viscous moduli at constant cellulose concentration with water content increment. |
