Cellulosic materials thermal degradation

The complex three-dimensional structure of these materials is determined by their carbon-based polymers (such as cellulose and lignin), and it is this backbone that gives the final carbon structure after thermal degradation. These materials, therefore, produce a very porous high-surface-area carbon solid. In addition, the carbon has to be activated so that it will interact with and physisorb (i.e., adsorb physically, without forming a chemical bond) a wide range of compounds. This activation process involves controlled oxidation of the surface to produce polar sites. 

The normal degradation of cellulose to the flammable tar, levoglucosan, is reduced and the charring of this compound is promoted. Shafizadeh and coworkers used thermogravimetric (TG) and thermal evolution analysis (TEA) data, to confirm two different mechanisms involved in flameproofing cellulosic materials ... 

The response of the cotton fiber to heat is a function of temperature, time of heating, moisture content of the fiber and the relative humidity of the ambient atmosphere, presence or absence of oxygen in the ambient atmosphere, and presence or absence of any finish or other material that may catalyze or retard the degradative processes. Crystalline state and DP of the cotton cellulose also affect the course of thermal degradation, as does the physical condition of the fibers and method of heating (radiant heating, convection, or heated surface). Time, temperature, and content of additive catalytic materials are the major factors that affect the rate of degradation or pyrolysis. 

One important thermal degradation mechanism of cellulose fibres (cotton, rayon, linen, etc.) is the formation of the small depolymerisation product levoglucosan (Fig. 8.7). Levoglucosan and its volatile pyrolysis products are extremely flammable materials and are the main contributors to cellulose combustion. Compounds that are able to hinder levoglucosan formation are expected to function as flame retardants for cellulose. The crosslinking and the single type of esterification of... 

Thermal degradation of cellulosic materials proceeds through a complex series of concurrent and consecutive chemical reactions. Fig. 1 provides an outline of the general sets of the degradation reac-... 

A number of experiments and observations have been made on various aspects of heating cellulosic materials at temperatures ranging from slightly above ambient conditions up to 250° (when rapid volatilization occurs). At the lower temperatures, it is difficult to draw a line of demarcation between the thermal degradation and the normal... 

The rate and kinetics of the thermal degradation of cellulosic materials have been investigated under a variety of conditions. However, these studies often relate to one of the physical effects produced by the overall process of heating or pyrolysis, instead of the kinetics of the individual chemical reactions involved. Consequently, the results are controversial and confusing. The variation of the results obtained under different conditions provides a vivid indication of the complexity of the reactions involved and the limited value of the overall kinetic data. 

Rate and Energy of Activation for Thermal Degradation of Cellulosic Materials ... 

Detrimental effects in WPC, 96 Thermal degradation, 95 Hemicellulosic materials, 77, 92, 94, 95, 180 Hemp fiber, 82, 83, 86, 101, 110 Cellulose content, 110 Eiber diameter, 110 Lignin cintent, 110 Specific gravity, 110 Heteropolysaccharides, 92 High density polyethylene (HDPE), 52, 55, 67, 68, 363, 371,... 

From both a physical and chemical basis cellulose is a rather intractable material. It cannot be converted into different shapes by injection molding, or melt extrusion as due to its high melting point it thermally degrades prior to obtaining the ability to flow. 

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