Fibre properties density

Properties such as density, electrical resistance, ultimate tensile strength and initial modulus are related to the internal structure and chemical composition of the fibres. Properties may also vary according to variations in diameter along with the length of individual filaments, size and maturity, as well as the processing methods used for the extraction of fibres. These fibres are biodegradable and non-abrasive. However, incompatibility of the fibres and poor resistance to moisture often reduces the potential of natural fibres and these drawbacks have become a critical issue in their development." ... 

Virtually every fibre, both namral and manufactured, has been used in absorbent nonwoven structures. Being the structural element, fibres making up a nonwoven have a major influence on the absorbency characteristics. The major fibre properties exerting such an influence include polymer type, linear density or denier, fibre cross-section shape, crimp, fibre finish and fine stmcture. 

Figure 6 (A) A fibre optic probe for reflectometry. The light scattered from a single excitation fibre is detected by a linear array of collection fibres. Tilting the excitation fibre shifts the profile along the surface by an amount that is determined by the sample s optical properties. (B) A fibre optic probe with a circular fibre arrangement for reflectometry. A 2 cm probe head consist of a central calibration fibre, an excitation fibre and non-equally spaced fibres. Neutral density (ND) filters adapt the light intensity in a transfer array to a smaller dynamic range.

The degree of needling or punch density, specified as punches per square centimetre or square metre, is important for the fabric s properties. The mass per unit area, fibre orientation in the web and fibre properties also affect the final properties of the fabric. Needling gives cohesion, compaction and strength to the resulting nonwoven fabric. 

Composites need not be made of fibres. Plywood is a lamellar composite, giving a material with uniform properties in the plane of the sheet (unlike the wood from which it is made). Sheets of GFRP or of CFRP are laminated together, for the same reason. And sandwich panels - composites made of stiff skins with a low-density core - achieve special properties by combining, in a sheet, the best features of two very different components. 

The properties of a foam are determined by the properties of the polymer, and by the relative density, p/p - the density of the foam (p) divided by that of the solid (p ) of which it is made. This plays the role of the volume fraction Vf of fibres in a composite, and all the equations for foam properties contain p/p. It can vary widely, from 0.5 for a dense foam to 0.005 for a particularly light one. 

Fig. 26.2. The microstructure of wood. Woods ore foams of relative densities between 0.07 and 0.5, with cell walls which ore fibre-reinforced. The properties ore very anisotropic, partly because of the cell shape and partly because the cell-wall fibres ore aligned near the axial direction.

Wood, then, is a foamed fibrous composite. Both the foam cells and the cellulose fibres in the cell wall are aligned predominantly along the grain of the wood (i.e. parallel to the axis of the trunk). Not surprisingly, wood is mechanically very anisotropic the properties along the grain are quite different from those across it. But if all woods are made of the same stuff, why do the properties range so widely from one sort of wood to another The differences between woods are primarily due to the differences in their relative densities (see Table 26.1). This we now examine more closely. 

Typical applications for nylon include small gears, bearings, bushes, sprockets, housings for power tools, terminal blocks and slide rollers. An important design consideration is that nylon absorbs moisture which can affect its properties and dimensional stability. Glass reinforcement reduces this problem and produces an extremely strong, impact resistant material. Another major application of nylon is in fibres which are notoriously strong. The density of nylon is about 1100 kg/m. ... 

This is an important relationship. It states that the modulus of a unidirectional fibre composite is proportional to the volume fractions of the materials in the composite. This is known as the Rule of Mixtures. It may also be used to determine the density of a composite as well as other properties such as the Poisson s Ratio, strength, thermal conductivity and electrical conductivity in the fibre direction. 

Example 3.2 PEEK is to be reinforced with 30% by volume of unidirectional carbon fibres and the properties of the individual materials are given below. Calculate the density, modulus and strength of the composite in the fibre direction. 

The pH optical fiber sensor without any pH-sensitive dye was also described70. Porous silica layer made by the sol-gel method was cladded onto optical fibre core and was exploited as the optical transducer. Acid-base properties of silica surface caused that the surface charge of silica changed with pH of the solution. For example saturation of the sol-gel layer with cations leads to an increase of the electron density of the film, hence, the refractive index of the film. Since the surface charge of silica depends on pH, the refractive index of silica film varies also with pH. Thus, changes of... 

Korai (2001) also considered the importance of density profile of composites made from acetylated fibres in determining mechanical properties. Fibres of yellow cedar were acetylated with vapour-phase acetic anhydride and fibreboards were made from these, bonded with melamine formaldehyde resin. The results from this study indicated that bonding between fibres was the most important property determining mechanical properties. 

Barsberg and Hassingboe (2003) noted that the use of enzymes for surface activation of fibres for board production can produce highly variable results and that the reasons for this are not understood. In order to further understand the process, they treated TMP fibres with a laccase from Trametes villosa for 1 hour and dried the fibres. A control set of fibres was subjected to an identical protocol, but with no enzyme present. Air-laid fibre mats were produced from the fibres, which were then hot-pressed to form 3 mm thickness boards. Varying amounts of wax were sprayed on to the fibres prior to board production. Both the MOE and the MOR of the composites increased with board density. Boards produced from enzyme-treated or control fibres exhibited no difference in MOE, but the MOR of boards formed from enzyme-treated fibres was higher above a density of 800 kg m . Wax addition resulted in a decrease in mechanical properties. At a board density of c. 930 kg m , the MOR was of the order of 23 MPa and the MOE 11 GPa. 

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