Chemical treatment mercerization

The effect of chemical treatment is dominant in the low frequency range, i. e. from lO Hz to 1 kHz. It can be opposite for various kinds of lignocellulosic fillers. Figs. 16 and 17 show the frequency dependences of dielectric permittivity sf obtained at room temperature for the polypropylene composites containing crude, mercerized and modified lignocellulosic fillers derived from pine and beech wood as well as two kinds of rapeseed straw. The effect observed for the pine and beech wood (Fig. 16) consists in the increase of the dielectric permittivity s value. The modification with maleic anhydride causes greater increase than the mercerization. In the case of both kinds of rapeseed straw Kaszub and Californium (Fig. 17), the mercerization decreases the dielectric permittivity s value several times and the modification with maleic anhydride reduces s value to that measured for composites with crude pine and crude beech. One should take into account the location of the / wet- relaxation in the vicinity of room temperature to explain the opposite influence of chemical treatment... 

There are some treatment methods that are partially physical and chemical in nature, among which alkaline treatment (mercerization) (Kozlowski and Wladyka-Przybylak 2004 Bledzld et al. 2000 Paukszta 2000) and hquid ammonia treatment (Yanai) should be mentioned. 

Alkaline treatment or mercerization is one of the most used chemical treatments of natural fibers when used to reinforce thermoplastics and thermosets. Mercerization leads to the increase in the amoxmt of amorphous cellulose at the expense of crystalline cellulose. The important modification expected here is the removal of hydrogen bonding in the network structure. 

Alkaline treatment (mercerization) is one of the most common chemical methods applied to plant fibers which are used as reinforcement in biocomposites. Alkalization partially removes lignin, wax and oils covering the surface of fiber cell wall [3]. Thus, alkalization improves the surface adhesion of fiber to the polymeric matrix with the removal impurities which results in a rough surface topography [8]. 

Alkaline treatment or mercerization is one of the best used chemical treatment for natural fibers. 

However, after chemical treatment of C. indica fibers, dielectric constant values of finally fabricated biocomposites have been found to be lowered, which could be due to the decrease in orientation polarization of polymer composites containing surface-modified fiber. We have reported earlier that benzoylation reduces the moisture absorption behavior of fibers because of blockage of —OH groups on cel-lulosic fiber backbone. Thus resultant decrease in hydrophUicity of the polymer composites leads to lowering of orientation polarization and ultimately dielectric constant value [22]. It has also been observed that mercerization is one of the most effective methods in the reduction of dielectric constant values of the obtained biocomposites. 

Dusenbury, J.H. Mercer, E.H. Wakelin, J.H. 1954. The Influence of Chemical Treatment on the Properties of Wool— I. Alkali Solubility as a Measure of Sulfuric Add Degradation. Textile Research Journal 890-899. 

Coir fiber-NR Mechanical properties Mercerization TDI HR Good adhesion for composite containing fibers subjected to a chemical treatment with alkali, TDI, and NR solutions along with the HR system. [17]... 

To impart the required functional properties to fibers, yams, and fabrics, it is customary to subject textile materials to different types of physical and chemical treatments. For example, wash-and-wear finish for a cotton fabric is necessary to make it crease- or wrinkle-free. In a similar way, mercerizing, singeing, flame-retardant, water-repellent, waterproof, antistatic, and peach finishing achieve various fabric properties desired by consumers. 

Alkali treatment Mercerization or alkali treatment with strong alkali bases was developed as a method for cotton fibre modification by John Mercerin 1850 [55], It is a common method to produce high quality natural fibres, by removing the natural and artificial impurities from the fibre surface. The chemical treatment reduces the fibre diameter and thereby increases the aspect ratio [26]. Mercerization is usually performed applying aqueous solutions of sodium hydroxide (NaOH), at reaction times of 30 min up to 3 hr. 

An important chemical finishing process for cotton fabrics is that of mercerization, which improves strength, luster, and dye receptivity. Mercerization iavolves brief exposure of the fabric under tension to concentrated (20—25 wt %) NaOH solution (14). In this treatment, the cotton fibers become more circular ia cross-section and smoother ia surface appearance, which iacreases their luster. At the molecular level, mercerization causes a decrease ia the degree of crystallinity and a transformation of the cellulose crystal form. These fine stmctural changes iacrease the moisture and dye absorption properties of the fiber. Biopolishing is a relatively new treatment of cotton fabrics, involving ceUulase enzymes, to produce special surface effects (15). 

The swelling of cotton with an aqueous solution of sodium hydroxide is an important com mercial treatment. It is called mercerization after its discoverer, John Mercer, who took a patent on the process in 1850 [308]. Other alkali metal hydroxides, notably lithium hydroxide and potassium hydroxide, will also mercerize cotton, but normally sodium hydroxide is used. Mercerization is utilized to improve such properties as dye affinity, chemical reactivity, dimensional stability, tensile strength, luster, and smoothness of the cotton fabrics [309]. The treatment is normally applied either to yarn or to the fabric itself either in the slack state to obtain, for example, stretch products, or under tension to improve such properties as strength and luster. The interaction of alkali metal hydroxides and cellulose has been extensively reviewed. Earlier reviews can be traced from relatively recent ones [99,310,311]. 

The preceding discussion of the industrial products obtained from cellulose while not complete nor in technical detail emphasizes the striking fact that cellulose, a widely distributed natural substance, complex in its constitution and inactive in its properties, may, by either mechanical treatment or chemical reaction, be converted into such important products as thread, string and rope wearing apparel (cotton and linen). Mercerized cotton, artificial silk collodion, celluloid, smokeless powders and high explosives. 

Cellulose undergoes chemical, physico-chemical and structural modifications on treatment with caustic soda solution of mercerizing strength [5]. Chemical reactions lead to the formation of alkali cellulose, physical reactions, to a change in arrangement of units of cellulose. The optimum modifications in the properties of... 

Native cellulose are commonly modified by physical, chemical, enzymic, or genetic means in order to obtain specific functional properties, and to improve some of the inherent properties that limit their utility in certain application. Physical/surface modification of cellulose are performed in order to clean the fiber surface, chemically modify the surface, stop the moisture absorption process, and increase the surface roughness. " Among the various pretreatment techniques, silylation, mercerization, peroxide, benzoylation, graft copolymerization, and bacterial cellulose treatment are the best methods for surface modification of natural fibers. 

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