Studies on the ultrasonic degradation of cellulose macromolecular properties

The ultrasonic degradation of cellulose was investigated using a Bandelin‐Sonopuls‐HD 60 equipment with a frequency of 20 kHz and an output power of 22 W. As cellulose samples five polymeranalogous nitrates with an initial degree of polymerization DPη(0) between 400 and 7500 dissolved in ethyl acetate were used. The resulting macromolecular properties were determined viscosimetrically as well as by SEC (DPw, DPη, DPn, and distributions). The results show the following characteristics, some of them have already been known for the ultrasonic degradation of synthetic polymers: The rate of degradation is the more rapid the higher is DP0. At longer degradation times a limiting DP (DP∞) is observed. Materials with a DPη(0) < 700 do not degrade further. During degradation a very rapid narrowing of the distribution of DP takes place which is the more rapid the higher is DP0. Correspondingly the polydispersity U decreases. The distributions show one maximum only during the whole degradation. The behaviour of polydispersity and distribution gives indications about the mechanism of scission of the molecules. The possibility to use ultrasonication to produce cellulose samples with narrow distributions is discussed.