Even before weight loss in the low-temperature pyrolysis of cellulose becomes significant, the average degree of polymerization of the partially pyrolyzed samples drops sharply. The gel permeation chromatograms of nitrated derivatives of the samples can be described in terms of a small number of mixed size populations—each component fitted within reasonable limits by a Weibull distribution function. The modal value of each component is taken as an integral multiple of a “macromonomer” of nominal degree of polymerization 228.4. Thus, the data are consistent with a model in which the degradation process is assumed to involve bond rupture at specific “weak links” into particularly favored molecular sizes. Such a mechanism provides a plausible alternative to the commonly assumed random breakdown along the length of the molecule.

The molecular weight distribution of a linear homologous polymer is usually obtained empirically for any particular sample. Sample-to-sample comparisons are made in terms of the weight- or number-average molecular weights and graphic displays of the distribution curves. Such treatment generally precludes data interpretations in which a distribution can be described in terms of differing proportions of mixed populations. However, a statistical continuous univariate distribution function such as the Weibull can be applied to the molecular weight distributions measured for cellulose nitrate samples. The size distributions of samples degraded under some gentle stress may then be indentified as consisting of differing proportions of populations with similar characteristic distributions. Analyzing data in this way should permit interpretation of the results as for breakdown of oligomers in a small-molecule system.

Whether the pyrolysis of cellulose is conducted in an inert medium or in air, partial pyrolysis at a lower temperature increases the char yield subsequently obtained after 1 h at 370°C. The results are consistent with a pyrolysis scheme in which two competing sequences of cellulose pyrolysis reactions are initiated by (1) an intermolecular dehydration leading to char formation and, in air, to glowing combustion; and (2) a char-free depolymerization leading, in air, to flaming combustion.

Although 1,6-anhydro-3,4-dideoxy-,β-d-glycero-hex-3-enopyranos-2-ulose (2) is produced by the acid-catalyzed pyrolysis of both cellulose and 1,6-anhydro-β-d-glucopyranose (1), data presented here show that the principal mechanism of its formation in the pyrolysis of cellulose is not via 1. Furthermore, the data provide evidence that 1 itself is not a primary product of cellulose pyrolysis, so that the principal mechanism of its formation must involve a precursor as yet unidentified.

Autoradiographs of mature cotton bolls which earlier had radioglucose introduced via a thin incision into their peduncles show a marked asymmetry in distribution of the label. Radio assay shows the specific activity of the cotton fibres on the treated side to be as much as 30-fold that on the opposite side.

Die Struktur des aus Cellulose und ähnlichen Kohlenhydraten bei der sauren Zersetzung gebildeten Lävoglucosans (I) wird bestimmt.

An earlier numerical analysis showed that the second approximate method of Horowitz and Metzger can be rendered exceedingly accurate for reduction of thermogravimetry data. It is demonstrated here that this result can be justified on the basis of an asymptotic expansion with a nondimensional activation energy as the large parameter. The order of magnitude of the error is ascertained for this and two other approximate methods. Higher-order terms in the approximation are developed.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLevoglucosenone (1,6-anhydro-3,4-dideoxy-.DELTA.3-.beta.-D-pyranosen-2-one). Major product of the acid-catalyzed pyrolysis of cellulose and related carbohydratesY. Halpern, R. Riffer, and A. BroidoCite this: J. Org. Chem. 1973, 38, 2, 204–209Publication Date (Print):January 1, 1973Publication History Published online1 May 2002Published inissue 1 January 1973https://pubs.acs.org/doi/10.1021/jo00942a005https://doi.org/10.1021/jo00942a005research-articleACS PublicationsRequest reuse permissionsArticle Views970Altmetric-Citations153LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Cellulose samples which have undergone various stages of thermal decomposition were characterized for changes in molecular weight and molecular weight distribution using gel permeation chromatography (GPC) and viscometry. Calculation of cellulose molecular weights (as cellulose nitrate) from the chromatogram and polystyrene calibration curves using the extended chain length-retention volume relationship (Q factor) resulted in very poor agreement between GPC and viscometric molecular weight values. Molecular weight averages determined by GPC were approximately five times greater than those obtained by viscometric technique. Application of various hydrodynamic considerations completely corrected this problem. The effects of calibration standard distribution and range are also discussed.

AbstractSamples of ordinary “ash‐free” cellulose papers and similar samples decrystallized by swelling in liquid ammonia were pyrolyzed in vacuo to a weight loss ranging from <0.1% to nearly 20%. The samples were then nitrated and their molecular weight distributions determined by gel permeation chromatography. When weight loss reached 1%, both the ordinary and the ammonia‐swelled celluloses showed a large drop in average degree of polymerization (D.P.). However, the ordinary cellulose showed this sharp drop long before there was any measurable weight loss; the ammonia‐swelled cellulose changed D.P. only gradually in the early stages. Further, x‐ray diffraction measurements showed that by the time the D.P. of the ammonia‐swelled cellulose had dropped appreciably, the material had developed a significant crystalline pattern. These results support the suggestion that initial rupture of the cellulose molecule occurs at strain points at the crystalline–amorphous boundaries.

By providing continuous weight measurement, thermogravimetry, even for isothermal experiments, offers a major advantage over the classical methods of determining weight-change curves in complex pyrolysis reactions. Thus, even minor weight changes, readily detectable on a continuous record, furnish clues concerning the reaction sequences and indicate conditions under which confirmatory experiments may be undertaken. Unfortunately, such perturbations are frequently ignored, being considered part of the “experimental error” which they often represent in the traditional experiments. This paper illustrates the utility of looking at the minor weight deviations, too large to be random experimental error, in a 1,000-hour isothermal pyrolysis experiment on high purity cellulose paper at 226°C. Resolution of the curve into the minimum number of consecutive and competing reactions required to fit within instrumental accuracy yields previously unrecognized characteristics of the pyrolysis behavior, applicable at other temperatures as well.

During pyrolysis of pure cellulose, the Crystallinity Index (Crl) remained fairly constant over more than 50% weight loss before dropping rapidly as the X-ray pattern deteriorated. With samples first treated with trace quantities of inorganic salts, heating first increased the Crl—the results implying a preferentially catalyzed decomposition of the amorphous regions. Swelling cellulose in liquid ammonia eliminated the crystalline diffraction pattern, but heating restored a considerable degree of order. The initial weight loss rate in the swelled material was considerably accelerated and the ultimate char residue reduced. The results support the suggestion that inter-ring cross-linking leading to enhanced char formation will occur preferentially in the ordered rather than the disordered regions of natural cellulose.

Cellulose decrystallized by swelling in liquid ammonia produced a simpler thermogravimetric analysis curve than obtained from ordinary cellulose—presumably because of a decrease in the intermolecular char-forming reactions. By using a graphical procedure which permits a linear plot of the thermogram, it was possible to resolve the overall curve into two components: the principal reaction by which more than 90% of the weight loss occurred (activation energy = 54.9 kcal/mole; pre-exponential factor = 3.15 × 1019/min), and a second component which may be approximated by a first-order reaction leading to an ultimate 4% char.