Tenacity, fibres

Polyacrylonitrile synthesized by radiation emulsion polymerization is used for manufacturing high tenacity fibres. 

Expansion of the hybridization between metals and eomposites has led to a re-examination of the role of metals in helmet systems. As expressed earlier, metals (namely steel) had been the armour material of ehoiee before the development of high-tenacity fibres. Since then, steel has been discarded from helmet material selection. While some have explored the rrse of alirminiirm, magnesium and titanium shells, the general performance gains were not substantial enough to justify the subsequent processing and interfacing, whilst concerns were also raised about their durability (Walsh et ai, 2008). 

Sikkema,D.J., Design,synthesis and properties of a novel rigid rod polymer,PIPD or M5 high modulus and tenacity fibres with substantial compressive strength, ... 

The optical properties of interest are refractive index and molecular refraction, polarisation, double refraction (birefringence) of isotropic and oriented PE, clarity, transparency, haze, and gloss (see Tables 3.1 and 3.9). PE granules are white and translucent, but the final appearance varies from hard, rigid, brightly coloured, glossy, flexible or transparent film to high-tenacity fibre. In the melt state the refractive index is 1.4297 and 1.4432 and the molar refractivity is 0.3297 and 0.32986 for HDPE and LDPE, respectively. 

The overall properties of the composites are dependent on the matrix properties, the fibre content (Figure 10.8), its modulus of elasticity, and the various means used to improve the fibre-matrix bond. A variety of different fibre types have been studied, including monofilaments of various diameters, fibres with buttons on their ends [21], twisted tapes [21], fibrillated mats [26], textile fabrics [18] and high tenacity fibres with frayed ends [7], Even with smooth monofilament... 

Hence, the main aim of the technological process in obtaining fibres from flexible-chain polymers is to extend flexible-chain molecules and to fix their oriented state by subsequent crystallization. The filaments obtained by this method exhibit a fibrillar structure and high tenacity, because the structure of the filament is similar to that of fibres prepared from rigid-chain polymers (for a detailed thermodynamic treatment of orientation processes in polymer solutions and the thermokinetic analysis of jet-fibre transition in longitudinal solution flow see monograph3. ... 

A recent approach was based on the DMAc/LiCl and N-methyl-2-pyrrohdone/IiCl solvent systems [252,253] that enabled better dry tensile strengths although they did not provide adequate wet tenacities, due to poor crystallinity and poor consohdation of the fibre. A further problem was the... 

The formation of crosslinks in silk fibroin increases the tenacity and resistance to deformation of the fibres, as reflected in the initial modulus and the yield point. This protective effect conferred by fixation of the bifunctional dye Cl Reactive Red 194 was not shown by the monofunctional Orange 16, which is unable to form crosslinks. The loss in tenacity of undyed silk that is observed on treatment at 90 °C and pH 7 for 2 hours is attributable to lowering of the degree of polymerisation (DP) by hydrolysis of peptide bonds. The crosslinking action of bifunctional dyes tends to compensate for this loss in DP and provides an intermolecular network that helps to maintain the physical integrity of the fibre structure [124] ... 

ISO 1346 2004 Fibre ropes - Polypropylene split film, monofilament and multifilament (PP2) and polypropylene high tenacity multifilament (PP3) - 3-, 4- and 8-strand ropes ISO 1873-1 1995 Plastics - Polypropylene (PP) moulding and extrusion materials - Part 1 Designation system and basis for specifications ISO 1873-2 1997 Plastics - Polypropylene (PP) moulding and extrusion materials - Part 2 Preparation of test specimens and determination of properties ISO 3213 1996 Polypropylene (PP) pipes - Effect of time and temperature on expected strength... 

PAN carbon fibres High tenacity High modulus Improved tenacity High modulus... 

Gun-cotton is considerably heavier than unprepared cotton, and may be distinguished therefrom by its harshness, and by tbe crepitating sound produced when pressed by the hand. When well made, there is scarcely any change in color or general appearance. It may also be known from common cotton by its electric condition for if a portion be pulled briskly between the finger and thumb of a dry hand, the fibres will adhere with great tenacity. If a strip of prepared paper ho thus treated, it will, on presenting one end to tho knuckle, be alternately attracted and repelled, and thus pait with its electricity. Gun-eottou Is also perfectly soluble in ether, and if the solution be poured on the surface of oold water, the xyloidin yields an opaque film thereon, which, when collected and dried, forms a remarkably explosive paper,... 

Thorough washing of the fibres is mandatory to remove traces of acid which otherwise have adverse effects on the tenacity. It is usual for the thread line to be sprayed with a weakly alkaline solution before final washing in water and subsequent drying. 

Annealing fibres melt-spun from nematic mesophases can produce very significant changes in some of the physical properties, notably increases in both tenacity and extension to break. Some of the values of tenacity attainable in this way are among... 

Most of the patents that claim thermotropic polymers also claim fibres made from them, although full spinning conditions and physical data for the products are not always provided. Tensile data for the samples of highest tenacity after annealing from some representative patents are fisted in Table 3. 

A very important diagram for fibres and yams is the stress—strain diagram, where the specific stress is plotted as a function of the elongation (extensional strain) in %. The curve starts at an elongation of zero and ends in the breaking point at the ultimate specific stress (=tensile strength or tenacity) and the ultimate elongation (=strain at break). 

Typical stress-strain curves are shown in Fig. 13.86. In addition Fig. 13.87 gives a survey of specific tenacity versus specific modulus for the modem high-performance filaments. The range of the specific modulus varies from 3 to 300 N/tex (i.e. modulus approximately from 3 to 500 GPa), that of tenacity from 0.2 to 3.5 N/tex (i.e. tenacity approximately from 0.2 to 5 GPa). Diagonal lines show the ratio average value is about 0.02. In comparison Fig. 13.88 shows the same parameters for the conventional man made fibres. Here the ranges are much smaller and the average value of [Pg.480]

FIG. 13.88 Diagram of the specific tenacity (ffb/p) versus the initial specific modulus (Ea/p) for conventional man made fibres. 0 is the limiting tangential slope in the stress-strain diagram for strain tending to zero. The diagonal lines show the indicated ffbr/ 0-ratio this varies from = 1 for elastomeric filaments and 0.2 for tyre yarns (ty) to 0.03 for yarns such as polyacrylonitrile. 

---