Acid behavior of carboxylic derivatives of cellulose. Part I. Carboxymethylcellulose

The potentiometric and viscometric behavior of carboxymethylcellulose have been studied with solutions containing potassium chloride. It has been found that the titration results can be described by the modified form of the Henderson equation pH = pKm + nlog α/(1 — α), the values of pKm and n being dependent on the concentration of both carboxymethylcellulose and the concentration of potassium chloride in the system. Extrapolation of the straight‐line pK versus α to α = 0 yields a value of 3.42 for pK0 which is identical with the pK value of galacturonic acid. The concentration dependence of pH for any given value of α can be described by the equation [pH]cα = [pH]0α – 0.52√c where [pH]0α is the pH at a concentration c and degree of dissociation α, and [pH]0α is the corresponding value extrapolated to infinite dilution. Both the viscosity and the potentiometric results show that the carboxyl groups in CMC are not free from electrostatic interactions but that at a salt concentration of 1M electrostatic effects almost disappear.