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SynopsisCellulose linters with starting degreea of polymerization between 100 < DP, < 6OOO had been hydrolytidy degraded (0.5 M aqueous solution of KHSO,, degradation temperature 40 O C and 60° C) and the results compared with those obtained in a former study on pure cotton cellulose using the same degradation conditions. A complete coincidence in the degradation characteristics of both is shown, distinguishing the latter one by the following features: (1) different kinetic behavior according to the molecular weight range in which degradation takes place; (2) those corresponding to the very high as well as to the very low range of DP reveal a notable decrease of reaction rate; (3) a simultaneous systematic decrease of derivatization capacity occurs in the low molecular weight range; (4) There is no systematic increase of soluble material in the acidic medium with degradation time; (5) in the low molecular weight range, the polidispersity index derived from the molecular weight distributions remains near DP,/DP, = 2.0, except when the hydrolysis had been d e d out on already technologically digested materials, causing in these cases a certain increase. The possible reasons for the distinct features of degradation behavior are

Die Anyewandte Makromolekulare Chemic. 12 ( I 978) 161 -171 ( N r . 11 00)Divisi6n "Macromol6culas", Instituto de Investigaciones Fisicoquimicas Te6ricas y Aplicadas, Casilla de Correo 16,

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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 DP,,,, between 400 and 7500 dissolved in ethyl acetate were used. The resulting macromolecular properties were determined viscosimetrically as well as by SEC (DP, DP,, DP,, 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 DPo. At longer degradation times a limiting DP (DP,) is observed. Materials with a DP,(,, < 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 DP,. 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. ZUSAMMENFASSUNG:Der Ultraschallabbau von Cellulose rnit einem Bandelin-Sonopuls-HD-60-Gerat mit einer Frequenz von 20 kHz und einer Leistungsabgabe von 22 W wurder untersucht. Es wurden funf Celluloseproben polymeranaloger Nitrate mit Ausgangspolymerisationsgraden DP,(,, zwischen 400 und 7 500 untersucht, gelost in Ethylacetat.Die resultierenden makromolekularen Eigenschaften wurden viskosimetrisch bzw. mit SEC (DP, DP,, DP, und Verteilungen) bestimmt. Die Resultate zeigen folgende charakteristische Merkmale, von denen die meisten von synthetischen Polymeren her bekannt sind:Die Abbaugeschwindigkeit ist vom Polymerisationsgrad (DP) abhangig. Der Abbau ist urn so stiirker, je hoher der Ausgangspolymerisationsgrad (DP,) ist. Bei Ian-Hiithig & Wepf Verlag, Zug CCC 0003-3146/97/$07.00 85 M. Marx-Figini geren Abbauzeiten wird ein sich nicht mehr andernder DP (DP,) beobachtet. Cellulosen mit DP,(,, < 700 werden nicht mehr abgebaut. Wahrend des Abbaus tritt eine sehr rasche Verengung der Verteilung des DP ein, die um so schneller stattfindet, je hoher DP, ist. Entsprechend nimmt die Uneinheitlichkeit (U) der Proben ab. Die Verteilungen sind wahrend des gesamten Abbaus monomodal. Die angefiihrten Charakteristika geben Hinweise auf einen Spaltungsmechanismus der Molekiile. Die Moglichkeit, die Ultraschallbehandlung fur die Herstellung einheitlicher Cellulosematerialien zu benutzen, wird diskutiert.

A detailed study on the calibration of vapour pressure osmometry (VPO) using thirteen different samples (eight of them polystyrenes) in a range of molecular weights up to 50000 as solutes and chloroform, dichloromethane, ethyl methyl ketone, cyclohexane, and acetone as solvents is carried out. The results show that contrary to the commonly used calibration equation A4 = K . ( A V / C ) , .~~, the relationship between the measuring result ( A V / c ) , , , and molecular weight M obeys a function of the type M = K . ( A V / c ) , p , in which the exponent a differs from I . For each of the above mentioned solvents the values of K and a are determined.The limits of applicability of VPO with respect to polymers are discussed in view of these terms and recent theoretical considerations.

A recent suggestion by Bersted which takes into account the influence of the diffusion coefficient of the solute on the non-colligative behaviour in vapour pressure osmometry is studied. Its involvement on the kind of the resulting molecular weight average is derived.

The kinetics of the hydrolytic degradation of celluloses the molecular properties of which still correspond largely to those of the native state are studied. The hydrolytic agent has been 0,5 mol/l aqueous solution of KHSO,. The degrees of polymerization were determined viscosimetrically in copper ethylene diamine (CuEn) as solvent under standard conditions. In order to convert viscosity-average and weight-average degrees of polymerization DP, and DP, in the corresponding number-average DP,, a DP,/DP, calibration curve had been elaborated using polymer analogeous nitrates of a series of samples degraded under the same conditions. The results reveal that hydrolytic degradation of native cellulose takes place by two simultaneously occurring kinetic mechanisms, for which the following rate constants were derived: k , = 0,12 h-I, k, = 3,88.h-I, corresponding to a degradation temperature of 40°C and 60"C, respectively, and related to an initial degree of polymerization DP, = 13000. The number of faster cleaving bonds per molecule (J,) and the number average of normally splitting bonds being between two "weak links" Gs,) resulted in 8, = 3,5 and Dz = 3 600. The activation energies of the rapid and the slower reaction were found to be 20 kcal/mol (83,7 kJ/mol) and 24 kcal/mol (100,4 kJ/mol), respectively. Additional degradation experiments on the same, but pre-swollen or pre-reduced samples did not provoke any variations in the results. It can be excluded, therefore, that the simultaneous occurrence of two kinteic mechanisms is a consequence either of facts which involve diffusion control, or the existence of "stressed" bonds. The found relatively high activation energies rather permit to assume native modifications in the chemical structure of the cellulose molecule as the most probable reason for the faster bond splitting reaction.h-l, and k , = 0,79 h-I; k, = 38,35.0025-1 16X/8 l/0182/3603/$03.OO