Phase systems of starch acetate and cellulose acetate in acetone:water

Starch acetate (SA) with a degree of substitution (ds) of 2.1–3.0 can be blended with cellulose acetate (CA) with a ds ∼2.5 to make 25–30 wt.% blended solutions in acetone:water to dry spin fibers. To develop solubility and phase information, a modified CCF/CCC statistical designed experiment at 5 to 10 wt.% solids was completed. This was based on five factors: (1) acetyl value, (2) acetone vs. water concentration, (3) ratio of SA to CA, (4) total weight of solids in the solution, and (5) mixing temperature. The resulting solubility information can be used to predict the stability of SA:CA blends at the higher concentration and temperature ranges that are commonly used for fiber spinning. The data were divided into two sets, A and B, based on whether the SA:CA solutions formed one or two phases. Both sets contained 60 experimental runs and only four responses will be discussed in this paper. The phase type (one or two), percent of SA in each phase measured at 25°C and 35°C, and haze. The most significant factors influencing phase type is SA concentration and the interaction of SA percent and the total solids concentration. This is a nonlinear response. Low amounts of SA (<20%) or large amounts (>90%) are predicting to have a one phase system and amounts between 20 to 90% will tend to give a two phase systems. These results are consistent with microscopy and differential scanning calorimetry (DSC), measurements on SA:CA fibers.