Effects of pH of medium and molecular weight on polyelectrolyte complex formation between pectin and chitosan
The effects of pH of medium and molecular weight of chitosan on polyelectrolyte complex (PEC) formation between pectin and chitosan was investigated using capillary viscometry. The intrinsic viscosity of the polymers was determined using Huggin's plot. PECs were formed between pectin and chitosan in the pH range 2.9-5.6, but no PEC was formed at pH 1.5. The proportion of pectin in pectin-chitosan PEC varied with pH of the medium due to different levels of ionisation of the polymers and also probably due to the flexibility of pectin molecule. The amount of pectin in the PEC increased with a decrease in pH while that of chitosan increased with an increase in pH of medium. Linear relationships were established between the pH of media used and the weight fraction of pectin required for optimal PEC formation with molecular weight grades of chitosan. Molecular weight of chitosan appeared to have no effect (p>0.05) on the optimal ratio of pectin:chitosan required for PEC formation but intrinsic viscosity of chitosan was molecular weight dependent with a rank order of intrinsic viscosities being: high molecular weight chitosan >medium molecular weight chitosan > low molecular weight chitosan.