Cotton fibres cellulose structure

It is worth noting that the mercerisation process, bom in the 19th century, produces a cellulose II structure too, but without dissolution of the fibres and therefore with no reshaping. Cotton fibres are soaked in a concentrated (19%) NaOH solution then washed. Mercerised cotton shows a softer touch and more brilliance than natural cotton. 

Cotton is single cell fibre and develops from the epidermis of the seed [4]. An elongation period continues for 17-25 days after flowering. Cotton consists of cellulosic and non-cellulosic material. A morphological structure of the cotton fibre is given in Fig. 1-1. The outer most layer of the cotton fibre is the cuticle, covered by waxes and pectins, and this surrounds a primary wall, built of cellu-... 

Figure 2.9 Structure of polysiloxanes (silicones), and polyethylene glycols. An inventory of all the compositions of this type of phase, used either for impregnation or bonding, would be lengthy. Treatment of the internal wall of a silica column with tetradimethylsiloxane will obtain a stationary phase bounded, polymerized and later reticulated. (The bonding resembles the fixing of indelible colours in order to create a brightly tinted fabric the colour contains an active site with which is able to attach itself, for example, to the alcohol functionality of cellulose on cotton fibres).

The wettability of various wood fibres was studied in [173], including bleached and unbleached, and alkyl ketene dimer sized and non-sized fibres. An improvement of the wettability with an increase of the surfactant concentration, except nonionics, was observed for all types of fibres. It has been noted in [174] that the electrokinetic potential of fibres determines considerably the efficiency of their washing and dying. Alkali mercerisation of cotton influences not only the fine structure, morphology and conformation of cellulose molecules, but also the negative electrokinetic potential of the cotton fibres. Based on this, the selection of mercerisation conditions due to changes in the NaOH concentration will allow to... 

Cellulose is found in the cell wall of plant cells and helps to give plants their structure. It is found in large amounts in trees and cotton fibres (which are nearly pure cellulose). Cellulose has many uses, including the making of paper. Cellulose molecules have many O-H bonds and the strength of wood is due, in part, to hydrogen bonding between nearby molecules. 

The fully developed cotton fibre consists of a waxy cuticle that envelopes it, a cell wall that is differentiated into primary (outer) and secondary (inner) layers and residual protoplasm called the lumen. Although this concept of the fibre structure persists, more recent ideas do not differentiate between the cuticle and the primary wall, which is less than half a micrometer thick and consists of around 50% cellulose, with pectin, waxes and proteins making up the remainder. The secondary wall, which differs considerably in chemical composition and structure from the primary wall, consists of up to 95% cellulose. ... 

The finer details of secondary and tertiary cellulose structure remain somewhat controversial and in any case will not concern us here. It will suffice to say that the chains align themselves side by side to form a substructure of microflbrils 35 A in diameter, and these in turn are linked together in more complex arrangements to form the main cellulose fibres. The microfibrils are believed to contain both amorphous and crystalline regions of aligned cellulose chains and the latter may adopt helical configurations. As a result of the presence of other components, differences exist between wood, cotton and synthetic cellulose fibres. 

In the dry state, with no absorbed water, the limit is the extension of the cellulose crystals. This is more difficult to calculate theoretically, because it depends on the position of the point of inflection in the plot of free energy versus extension, but would be expected to be at about 2% extension. Due to the helical structure, the extension in the cotton fibre will be greater and the other resulting stresses may influence the fracture. 

As shown above, flame retardants change the thermal decomposition of cellulose (fibres) to a more intensive char-formation which may be further increased by addition of intumescents [57], These substances not only lead to a thicker char barrier which is well-known as fire protection but also to "char-bonded" structures. They are resistant to air oxidation at elevated temperatures and thus form a second flame and heat barrier. As the thickness of the char layer has a strong influence on the thermal gradient between the surface and the fibre it improves the thermal protection of the material. TG, TMA and DSC were applied to four samples of cotton fabrics treated with different commercial flame retardants and two commercially available intumescents. The results show the interaction between flame-retardant cotton fibres and the intumescents, an enhanced char formation and the expected char-bonded structures [57]. 

McKelvey etal. (1959) investigated the reaction of epoxides with cellulose in alkaline conditions, reporting that alkaline cellulose reacted readily once the concentration of sodium hydroxide was sufficiently high. However, no evidence was found of reaction between cotton yarn and cellulose with a range of epoxides under a variety of reaction conditions. It was concluded that the apparent reactivity of cellulose with epoxides was primarily due to alkaline swelling of the cellulose, self-polymerization of the epoxide monomers then occurring within the interior structure of the fibres. It was also noted that the reactivity with phenol OH groups was very low (e.g. only 1 % conversion of ethylene oxide with various phenols). 

Much of our technology has been developed by observing and imitating the natural world. Synthetic polymers, such as those you just encountered, were developed by imitating natural polymers. For example, the natural polymer cellulose provides most of the structure of plants. Wood, paper, cotton, and flax, are all composed of cellulose fibres. Figure 2.15 shows part of a cellulose polymer. 

Cellulose is reputedly the most abundant organic material on Earth, being the main constituent in plant cell walls. It is composed of glucopyranose units linked pi 4 in a linear chain. Alternate residues are rotated in the structure, allowing hydrogen bonding between adjacent molecules, and construction of the strong fibres characteristic of cellulose, as for example in cotton. 

Dall Acqua et al.45 reported the development of conductive fibres made by cellulose-based fibres embedded with polypyrrole. Several efforts with cotton, viscose, cupro and lyonell have followed. The conductivity is directly related to the amount of polypyrrole, oxidant ratio and fibre structure with significant differences between viscose and lyonell. Polymerisation occurs uniformly inside the fibre bulk, by producing a coherent composite polypyrrole/cellulose. The mechanical and physical properties of cellulose fibres were not significantly modified as they are the best available45. 

Viscose rayon is inherently a weak fibre, particularly when wet, therefore it is highly susceptible to damage if enzymatic hydrolysis is not controlled. The enzymatic hydrolysis of viscose fibres causes a decrease of the intrinsic viscosity from 250 to 140 ml/g and an increase in crystallinity from 29 to 39% after 44 h [34]. Strong changes of the structure, however, are not typical for the enzymatic hydrolysis of cellulosic materials. Neither cotton nor wood pulp show an essential decrease of the DP during enzymatic hydrolysis [35-37]. The kinetics of the enzymatic hydrolysis of regenerated cellulose fibres before and after acid prehydrolysis changes the kinetics from a monophasic to a biphasic first order reaction [38]. 

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