Abstract
X-ray diffraction (XRD) of cellulose acetate (CA; degree of substitution >2.4) fibers stretched in solvent suggests the existence of a third polymorph of cellulose triacetate (CTA). Comparison of these results with patterns from model structures indicates that it has an antiparallel two-chain unit cell with space group P21221. XRD, differential scanning calorimetry (DSC), and modeling results have shown that the polymorph forms small crystallites, which are less stable than CTA I and CTA II. DSC studies of CA with different degrees of substitution suggest that CTA III forms when the number of contiguous triacetylated monomers is less than the minimum sequence length required for formation of CTA II.
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