Effects of structural changes on thermal properties and pyrolysis of modified cotton fibres

Abstract

The changes resulting in the supramolecular structure Of cotton fibres after mercerization at different temperatures were investigated by means of X-ray diffraction, sorption measurements and determination of the degree of polymerization. For comparison, corresponding measurements were also carried out after liquid ammonia treatment. Pyrolysis of the mercerized cotton samples showed that the levoglucosan yield of NaOH-treated samples is less than that of untreated or NH3-treated samples. Comparisons were made of the thermal stability of the modified cotton samples, as indicated by DTA and TG. A decrease in the percentage crystallinity was found to lower the onset and peak temperatures of the major decomposition reactions. An NH3-treated sample (acetone) was less thermally stable than untreated or mercerized samples.There are several reasons for studying the pyrolysis of cellulose. For example, such studies are important for the development of flame retardants for cotton fibres [1]. Thermal analysis is a useful technique for assessing the flammability of cellulosic materials. Thermoanalytical techniques can provide an insight into how a cellulosic material might react on exposure to fire, e.g. the nature and temperature of its decomposition, the amount of volatiles versus char residue, etc. The thermal degradation of cellulosic materials proceeds through a series of complex chemical reactions. The reactions are highly influenced by the nature and period of heating, the surrounding atmosphere and impurities. The postulated pyrolysis paths can be depicted as shown in Scheme 1. Heating at lower temperatures favours dehydration and subsequent char formation. Heating at higher temperatures favours the formation of gaseous combustible products. Theories about the pyrolysis mechanisms for cellulose have been based on the origin of two main pyrolysis products: tar and char. Several investigations have established that levoglucosan (1,6-anhydro-fl-D-glycopyranose) is the major tar component. A large number of other materials have been identified as cellulose pyrolysis products. However, Glassner and Pierce [2] demonstrated that the chromatograms obtained forJohn Wiley & Sons, Limited, Chichester AkadAmiai Kiadr, Budapest

Influence of Sequential Liquid Ammonia and Caustic Mercerization Pre-Treatment on Dyeing Performance of Knit Cotton Fabric

“…These were ascribed to the presence of a greater amount of amorphous cellulose, which underwent faster thermal decomposition than the crystalline phase [ 32 ]. All of these data indicate that the LA-treated sample showed less thermal stability, as confirmed by the TGA and DTG curves, which corresponds to the previous report [ 33 ]. Although the T max of untreated cotton fabric was higher among all samples, the amount of char residue was lower than that of treated fabrics ( Table 2 ).…”