synopsisThe effects of crystallinity, orientation and degree of polymerization on the vacuum pyrolysis of cellulose have been investigated. Natural, modified and manmade celluloses were characterized and the kinetics of their pyrolysis a t 251OC studied. The hightemperature pyrolysis of these samples was also investigated by means of DSC and TGA. At 251°C all of the samples showed a rapid, initial weight loss followed by a linear (weight loss)1/2 versus time dependency. Both the initial weight loss and the subsequent reaction rate were dependent upon the crystallinity of the sample. The reaction rate was shown to be inversely proportional to (DP)'/' and related to the orientation. Effects of crystallinity and orientation could also be seen in the DSC thermograms and in the apparent energies of activation. Results are interpreted in terms of probable mechanisms of the uncatalyzed pyrolysis of cellulose.

The effects of orientation upon the pyrolysis of cellulose were investigated by using a series of rayon fibers which differed only in orientation. The initial weight loss seen in low‐temperature vacuum pyrolysis is due to crosslinking in the less ordered regions and was shown to be a first‐order reaction whose rate varies directly with the degree of orientation. The extent of this reaction decreases with increasing orientation and is directly related to the amount of char formed at higher temperatures. The bulk pyrolysis rate increases with increasing orientation. DSC, air pyrolysis rates, and levoglucosan formation were also studied.

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synopsisThe pyrolysis of purified celluloses in air at 251OC was studied. The pyrolysis was found to obey first-order kinetics, and the.rate constants correlated with the crystallinities, orientations and accessibilities of the samples. The results are interpreted in terms of an oxygen-catalyzed decomposition, with the accessibility of oxygen to the cellulose determining the rate of pyrolysis. The production of levoglucosan under conditions approaching combustion was shown to be a function of the crystallinity and orientation of cellulose. Some levoglucosan appears to be produced from the less ordered regions.

The relative efficiencies of phosphorus and sulfur-based flame-retardant systems have been compared on cotton, ramie, and rayon. Sulfur-based systems were found to be equally effective on all the substrates tested. Phosphorus-based flame retardants were significantly less effective on rayon than on cotton or ramie. The flame-retardant fabric systems were also studied by differential scanning calorimetry. The differences observed are ascribed to different mechanisms by which sulfur and phosphorus-based flame retardants operate and to the influence of cellulosic fine structure upon these mechanisms.