Determination of Hansen Solubility Parameters for the Solid Surface of Cellulose Acetate Butyrate by Inverse Gas Chromatography

The specific retention volumes, , for adsorption of 21 solute probes on the solid surface of cellulose acetate butyrate (CAB) were determined in the temperature range 343.15 to 403.15 K by inverse gas chromatography (IGC). The weight fraction activity coefficients, , and Flory–Huggins interaction parameters, , were evaluated using . Both and values decreased with increase of temperature in all the solutes. Further, the values increased with increase of chain length in n-alkanes, but in the case of alcohols the trend was reversed. values were less than 0.5 in polar solutes and greater than 0.5 in 1-alkanes and alcohols. The Hansen solubility parameters (HSP) were calculated by relating with the cohesive energy of adsorption of the solutes on the surface of CAB. The adsorption model proposed by Snyder and Karger was used to determine the HSP for the CAB. The dispersive, , polar, , and hydrogen bonding components of HSP decreased with increase of temperature and the relative error associated with these parameters increased with increase of temperature. The characterization of the solid surface of CAB in terms of the three solubility parameter components was analyzed and is discussed.     

Characteristic Shear Rate for Nonlinear Viscoelastic Behavior in a Polydisperse Polymer Solution

The characteristic shear rate for nonlinear viscoelastic behavior in a polydisperse polymer system was investigated by the study of the stress overshoot behavior of polybutadiene solutions. The frequency at the crossing point of the dynamic moduli () was determined by oscillation frequency sweeps. For the stress overshoot observed in the shear flow at a fixed rate, the dependency of the stress drop, , defined as the difference between the stress at the peak and the stress at the steady state, on the shear rate can be well described by a fitting function: , and a critical shear rate () can be obtained using this fitting function. The correlation between and for the solutions can be expressed as and the proportionality factor is dependent on the degree of chain interpenetration. When the shear rate was normalized by , the dependency of the stress drop on this normalized shear rate for the solutions with different concentrations can be superposed well. This observation indicates that can be viewed as a characteristic shear rate for nonlinear viscoelastic behavior in a polydisperse polymer solution.