Lewis acid‐base properties of cellulose acetate butyrate by inverse gas chromatography

The dispersive component of the surface‐free energy, $\gamma_{S}^{d}$ , of cellulose acetate butyrate (CAB) has been determined using the net retention volume, V N , of n‐alkanes (C 5 C 8 ) probes in the temperature range 323.15–393.15 K. The $\gamma_{S}^{d}$ values decrease nonlinearly with increase in temperature, and the temperature coefficients of $\gamma_{S}^{d}$ are − 0.32 (mJ/m 2 K) and − 0.10 (mJ/m 2 K) in the range 323.15–353.15 K and 353.15–393.15 K, respectively. This variation in $d\gamma_{S}^{d}\big/dT$ has been attributed to the structural changes that take place on the surface of CAB at ∼353.15 K. The specific components of the enthalpy of adsorption, ${\Delta}H_{a}^{S}$ , and entropy of adsorption, ${\Delta}S_{a}^{S}$ , calculated using V N of polar solutes are negative. The ${\Delta}H_{a}^{S}$ values are used to evaluate Lewis acidity constant, K a , and Lewis basicity constant, K b , for the CAB surface. The K a and K b values are found to be 0.126 and 1.109, respectively, which suggest that the surface is predominantly basic. The K a and K b results indicate for the necessary surface modifications of CAB which act as biodegradable adsorbent material. Copyright © 2010 John Wiley & Sons, Ltd.