Thermal x‐ray diffraction study of highly acetylated cotton cellulose

Cotton cellulose in the form of scoured yarn was acetylated at 15°C. in a mixture of isopropyl acetate and acetic anhydride in the presence of perchloric acid catalyst to various degrees from 1.1 to 2.9 acetyl groups per anhydroglucose unit. For comparative purposes some of the yarn was acetylated at 20°C. by a more conventional method with a 3:1 mixture of acetic acid and acetic anhydride, also with perchloric acid as catalyst. The products were studied by x‐ray diffraction, both at room temperature and, with the aid of a specially controlled diffractometer furnace, at elevated temperatures. Diffractograms of the products show that as acetylation proceeds, the crystal structure of native cellulose disappears progressively until at a substitution of 2.93 acetyls per anhydroglucose unit it is nearly all gone. Examination with the diffractometer furnace shows in an impressive way the acetyl content and temperature at which cellulose acetate first begins to crystallize, the progressive increase in crystallizable acetate as acetylation proceeds, the temperature range over which the crystal structure is stable, the temperature at which it melts, and finally the temperature at which the acetate eventually carbonizes.