Very short fibres

The cotton fibres are removed from seeds by a process called "ginning . The recovered fibres are called "lint . The seeds, to which very short fibres called "linters are still attached, are sent to a cotton-seed mill where the seeds and "linters are separated from each other... 

Reinforcement with short fibres is important for thermoplasts and thermosets. With the former, very short fibres (glass or other) are blended into the polymer the latter allow the use of longer fibres. The effect is a 3- to 5-fold increase of the stiffness and a 1.5 to 3-fold increase in strength. 

It may be shown that fibres used for reinforcement should be as small in diameter and as high in aspect ratio as possible. Very short fibres simply act as stress concentrators in all modes of stressing except compression. The upper limit to fibre length is purely a matter... 

The wood used in WPC is most often in particulate form, e.g., wood flour, or very short fibres, rather than longer individual wood fibres. Products typically contain approximately 50% wood, although some composites contain very little wood and others as much as 70%. The relatively high bulk density and free-flowing nature of wood flour compared with wood fibres or other longer natural fibres, as well as its low cost, familiarity, and availability, is attractive to WPC manufacturers and users. Common species used include pine, maple, and oak. Typical particle sizes are 10 to 80 mesh. 

Very short fibres this type of fibre is often referred to as tow. 

The primary class is seen also as the ultra-cleaned material. Cut lengths can be from 13 mm to 152 mm long, and can be suitably converted into nonwovens, woven textiles and composites products for the automotive, furniture, and construction industries. The secondary and very short fibre classes are general purpose grades having 50-70% cleaned fibre. These are used for hydro mulch, as cement fillers, in insulation and for geo-matting. 

It is usual to distinguish between fillers and fibres, the latter being traditionally a separate subject, although this distinction becomes difficult to maintain at very short fibre lengths. Nevertheless it can be noted that there are separate entries on Reinforcing fibres and (more relevant to fillers) on Fibres the effect of short glass fibres on the mechanical properties of thermoplastics. ... 

Reinforcing fibres have diameters varying from 7 /im to 1(X) /im. They may be continuous or in the form of chopped strands (lengths 3 mm-50 mm). When chopped strands are used, the length to diameter ratio is called the Aspect Ratio. The properties of a short-fibre composite are very dependent on the aspect ratio - the greater the aspect ratio the greater will be the strength and stiffness of the composite. 

In the manufacture of man-made and synthetic textiles the base materials are extruded through tiny orifices producing continuous lengths of very fine fibres or filaments. The textiles are mostly used in this continuous filament form, but for some purposes the filaments may be cut up into short fibres and spun into a yam. 

A large variety of hose constructions are produced by the rubber industry for a wide range of applications. To contain transported liquids, usually under pressure, it is necessary to reinforce the hose construction with fabric, yam or short fibres to constrain expansion of the rubber. Although hand-built construction using fabric still represents a proportion of the production, it is also very common to use yams either braided or knitted directly onto the hose liner. For heavy duty purposes it is also necessary to use wire, in a braided form, to either reinforce or protect the hose from external damage. Use of short fibres as reinforcement represents a small proportion of hose production and requires specialised dies for extrusion to orientate the fibres circumferentially. 

In fact, microscopic examination of a woollen fabric, especially if carded, often reveals the presence of a considerable proportion of fibres whioh do not show the finely toothed outline and the sharply cut ends of natural wool fibres but have evidently undergone profound change (Fig. 86, Plate IX). These fibres may be free from scales either entirely or for more or less of their length, or the scales may be so worn as to be visible only with difficulty. Further, owing to the loss of the outer scales and consequent wearing of the lower fibrous layer, such fibres, which are sometimes very short (scarcely 1-2 mm.) and of irregular diameter, exhibit ends split like a brush. 

Reinforcements in the form of continuous fibres, short fibres, whiskers or particles are available commercially. Continuous ceramic fibres are very attractive as reinforcements in high-temperature structural materials. They provide high strength and elastic modulus with high temperature-resistant capability and are free from environmental attack. Ceramic reinforcement materials are divided into oxide and non-oxide categories, listed in Table 3.1. The chemical compositions of some commercially available oxide and non-oxide reinforcements are given in Table 3.2 and Table 3.3. 

In-plane alignment of the fibres Due to the very nature of the technique used for processing the NW composites, inplane alignment of the NWs is a realistic possibility. From the Krenchel theory of short-fibre reinforcements [20], the orientation and length effects can be incorporated using an efficiency factor to evaluate E,... 

When thermoplastics are reinforced with short fibres, both stiffness and strength may be increased, but these improvements are accompanied by a reduction of the ultimate strain for high concentrations of fibres [1-5]. This brittle behaviour is incompatible with growing engineering applications in which tlie parts are subjected to cyclic loadings or impacts, as in automotive under-the-hood applications. Thus, very tough nylon thermoplastics with enhanced creep and impact resistances have been produced by the introduction of a rubbery phase to the... 

Filtration of the Solution. — When a substance has been dissolved, the solution must next be filtered from the insoluble impurities like by-products, filter-fibres, inorganic compounds, etc. For filtration a funnel with a very short stem is generally used, i.e. an ordinary funnel the stem of which -has been cut off dose to the conical portion (Fig. i). 

Bark has very little meehanieal strength on aeeount of its lack of fibres. The bark of softwoods has no thiekened axially-elongated cells, but the bark of some hardwoods do sometimes eontain small numbers of short fibres similar to wood fibres. 

The overall model of a P-CVI process is as shown in Figure 5.43. During a P-CVI process the mass transport of gaseous species can be divided into two stages. In the first stage mass transport takes place by forced convection within a very short period of a few hundredths or tenths of a second. In the second stage of the duty cycle the mass transport is dominated by the diffusion from the free space of the reaction chamber into the pores of the fibre preform. The temperature is kept... 

The individual cells of jute are very short. Table 1.11 compares the dimension of ultimate from several sources. The cross-section of jute fibre is polygonal, usually with five or six sides. It has thick walls and a broad lumen of oval cross-section. By contrast with the regular lumen of flax, that of jute is irregular it becomes narrow in plaees quite suddenly. The lengths of various vegetable fibres varies considerably, whereas the diameter is moderately constant from fibre to fibre. 

---