Fibres surface-related properties

The dry strength of paper relates strongly to the distribution of fibres and bonds (controlled by the formation process) and the mechanical properties of the fibres. Surface chemistry plays the main role in the development and strength of fibre-fibre bonds. Fibres are often chemically and/or mechanically refined to increase bond areas and strength. This is not always desired since it may slow down drainage and decrease the paper porosity, which may result in loss of bulk, and detrimentally affect stiffness, tearing resistance and opacity. 

As the formation of disulfide bridges between proximate cysteine residues plays a particularly important role in physical properties of wool, any reagents or conditions that interfere with these bonds will have a significant effect on the fibres. A particular and related problem associated with the deterioration of wool fibres is the release of volatile sulfur compounds, which may then attack adjacent materials many of the silver-containing metal threads found on the Tree of Jesse tapestry show signs of surface corrosion, in the form of silver sulfide. 

A tentative model has been proposed to relate the interfacial shear strength at the fibre-matrix interface, measured by a fragmentation test on single fibre composites, to the level of adhesion between both materials. This last quantity has been estimated from the surface properties of both the fibre and the matrix and was defined as the sum of dispersive and acid-base interactions. This new model clearly indicates that the micromechanical properties of a composites are mainly determined by the level of physical interactions established at the fibre-matrix interface and, in particular, by electron acceptor-donor interactions. Moreover, to a first approximation, our model is able to explain the stress transfer phenomenon through interfacial layers, such as crystalline interphases in semi-crystalline matrices and interphases of reduced mobility in elastomeric matrices. An estimation of the elastic moduli of these interphases can also be proposed. Furthermore, recent work [21] has shown that the level of interfacial adhesion plays a major role on the final performances (tensile, transverse and compressive strengths and strains) of unidirectional carbon fibre-PEEK composites. 

Si ieha and cowoikers [67] found that the degree of surface treatment of cellulose fibres can be determined from the electrical conductance of a distilled water suspension of the treated fibres. The measured conductance is a function of treatment c iditi( s such as discharge current, treatment time and availability of oxygm, and under certain conditions can be related to the mechanical properties of resulting composites, see Hg. 13. Increased conductance obviously results fiom the increasing concentration of water-soluble itmic species, for example the acids listed in section 32.2. 

Chrysotile and croci-dolite asbestos, erion-ite, man made fibres Rat pleural meso-thelial cells Cytotoxicity assessed by the 3-(4,5-dimethyl-tniazol-2-yl)-2,5-diphenyltetrazolium bromide assay The tumorigenic potency of fibres may be related to the fibre dimensions, to their surface properties on in vivo biopersistence. Renier et al. (1992)... 

The surface energy of fibres is closely related to the hydrophility of the fibre. Some investigations are concerned with methods to decrease hydrophility. The modification of wood-cellulose fibres with stearic acid [49] causes those fibres to become hydrophobic and improves their dispersion in PR As can be observed in jute reinforced unsaturated polyester resin composites, treatment with polyvinylacetate increases the mechanical properties [50] and moisture repellence. Silane coupling agents may contribute hydrophilic properties to the interface, especially when amino-functional silanes, such as epoxies and urethane silane are used as primers for reactive polymers. The primer may supply much more amine functionality than can possibly react with the resin at the interphase. Those amines, which could not react, are hydrophilic and therefore responsible for the poor water resistance of the bonds. An effective way to use hydrophilic silanes is to blend them with hydrophobic silanes such as phenyltrimethoxysilane. Mixed siloxane primers also have an improved thermal stability, which is typical for aromatic silicones [48]. 

New applieations and improved applicability of many fibres used for clothing, industrial materials and interior decoration require the provisions of new properties in areas sueh as dyeability, static resistance, current control, stain resistance, water absorption, hydrophilicity, water repellency, adhesive ability and so on. There are surface treatment methods that additionally increase the value of textile materials. The methods can be classified as chemical treatment (wet) methods and physieal treatment (dry) methods. Chemical treatment methods are most often used in actual practice. Because of the large amount of energy involved and the high consumption of water and consequently increase of pollution, these techniques are costly and not eco-fiiendly. In addition, these processes treat the fabric in bulk, something which is uimecessaiy and may adversely affect overall product performance. Problems related to toxicity and other health hazards have resulted in the replacement of chemical processing by more eco-friendly physical methods. The physical treatment processes are dry, which makes it possible to preserve certain properties intrinsic to textile materials they are likely to affect the surface of the materials. Therefore the researchers are extensively studying the possibilities of physical surface treatments as alternatives to the chemical treatments. 

Mechanical softening treatments may involve fibre displacement, web buckling, and affect the absorbency of the resulting structure. Embossing, calendering surface glazing and other mechanical treatments can be utilized to modify web properties and the related absorbency characteristics. 

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