Partially derivatized cellulose esters were prepared from dissolving-grade wood pulp fibers by reaction with a mixed p-toluene sulfonic/hexanoic anhydride system in a nonswelling (cyclohexane-based) reaction medium. The partially derivatized pulp fibers, which failed to undergo a significant change in shape or appearance during the modification, proved to be resistant to swelling (in water), were thermally deformable, and retained their biodegradability. Because X-ray diffractometry provided evidence for the presence of unsubstituted, ordered cellulose with cellulose I morphology, the thermally reshaped and consolidated sheets were found to consist of commingled mixtures of cellulose esters and cellulose I. The transparent or semitransparent consolidated sheets (depending on the degree of substitution) were found to represent composites in which cellulose I serves as a discontinuous inclusion that reinforces a continuous, partially ordered cellulose ester matrix. The composites, which revealed cohesive or adhesive failure at rupture, depending on the degree of substitution, had modulus values and tensile strengths as high as 1.3 GPa and 25 MPa, respectively.