Extension to break

The further step up to 6000 m/min or more led to flat yams that were sufficiently oriented and crystalline, of sufficiently low extension to break, and of sufficiently high tenacity to be used for many purposes without further drawing. 

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... 

A similar process has been used to make polypyrrole-poly(vinyl alcohol) composites by electropolymerization from aqueous solution into a cross-linked poly(vinyl alcohol) film301 . The conductivity decreased and the elongation to break increased 10x with respect to polypyrrole. A conducting composite of 6% polypyrrole in a vinyl-idenefluoride-trifluorethylene copolymer showed an extension to break of 120% 302). 

Morphological characterization can be conducted by light and electron microscope techniques and by X-ray diffraction and thermal analysis, often used to determine crystallinity. Standard mechanical tests can be used to determine strength, extension to break in tension, and toughness. Normally, a selection of characterization methods is used with samples exposed for selected periods. When mechanical tests are used, the exposure period increment must be fairly short, in case a recovery phenomenon is present (see the section Engineering Properties—Consequences of Photodegradation ). Other tests related to appearance. 

The polymerization potential has also been found to influence the mechanical properties of polyaniline PAn/HA emeraldine salt films.50 The most extensible films were formed at a polymerization potential of 0.65 V (versus Ag/Ag+), which displayed an extension to break of around 40%. Preparation of the PAn/HA films at 0.8 V and 1.0 V resulted in more brittle films. It was suggested that degradation of the PAn at polymerization potentials in excess of 0.8 V might explain the poor properties of the 1.0 V film. The difference in behavior of the films prepared at 0.65 V and 0.8 V was attributed to differences in their crosslink density. Unfortunately,... 

The low-speed mechanical properties of polymer blends have been frequently used to discriminate between different formulations or methods of preparation. These tests have been often described in the literature. Examples of the results can be found in the references listed in Table 12.9. Measurements of tensile stress-strain behavior of polymer blends is essential [Borders et al., 1946 Satake, 1970 Holden et al., 1969 Charrier and Ranchouse, 1971]. The mbber-modified polymer absorbs considerably more energy, thus higher extension to break can be achieved. By contrast, an addition of rigid resin to ductile polymer enhances the modulus and the heat deflection temperature. These effects are best determined measuring the stress-strain dependence. 

Other important parameters of load-elongation curves are the Hookean limit (Figure 8-2, Point A), the turnover point (Figure 8-2, Point B), the percentage extension to break, the stress to break (the tensile strength), the... 

The moisture content of human hair varies with relative humidity, increasing with increasing RH. Speakman [25] and Feughelman and Robinson [24] have conducted relatively extensive load-elongation studies at different relative humidities for wool fiber. These data show a regular increase in extensibility (percent extension to break) with increasing relative humidity. Although such extensive studies could not be found in the literature for human hair, a similar relationship undoubtedly exists because... 

The mechanical properties of both fibres and textile stmctures are important to determine the suitability of dmg-releasing textiles in various applications. Tensile strength and extension to break values can be determined using standard tensile testing equipment. These values provide a good indication of the mechanical durability of the textiles before and after treatment with bioactive agents. Kumar and co-workers have reported that the bioactive textiles used in regenerative medical applications... 

Initial modulus (g denier" ) = 900 b where b is the extension to break (%) for a single filament. ... 

P(3HB) has a ri d t-handed 2l helix with a fiber repeat of 0.596 mn [4]. The comparison of P(3HB) and polypropylene shows the similar structure and physical properties [2]. However, P(3HB) is a stiifer and more brittle material, which shows a very low value (about 5%) of extension to break. Alcaligenes eutrophus produces a random copolymer of 3-hydnnybutyrate (3HB) and 3-hydroxyvalerate (3HV) (Figure lb), when propionic [5,6] or pentanoic acid [7] was fed as the sole carbon source. This copolyester P(3HB-co-3HV) is tougher and more flexible than P(3HB) homopolymer, and more suitable for commercial use. Imperial Chemical Industries (ICI) in the United Kingdom has produced P(3HB-CO-3HV) commercially with a large fermentation process [5,8]. Its ICI s... 

The poly[3,5-(4-phenyl-l,2,4-triazole)-1,4-phenylene] (I), with a Tq of 260 C, that is produced here can be dry- and wet-spun from formic acid solution. At 300°C the fibers still retain 30% of their original extension to break. The elimination of water to give polyoxadiazole can be carried out on drawn or undrawn poly(phenylene hydrazide) fibers. Here (II) is poly[3,5(4-oxa-1,2-diazole)-1,4-phenylene]. 

For melt-crystallised samples, moduli decreased markedly with increasing PCL content from 20% PCL to 30% PCL and samples became very extensible (34% extension to break compared with 2% for PCL) and had reduced TgS. Then, with more PCL, moduli rose markedly and yield strengths increased, but samples with up to 50 wt % PCL had elongations to break of about 7%. With more PCL the moduli decreased and the elongation to break increased in general. In most cases, except at 30 wt % and 40 wt % PCL, melt crystallised samples have higher moduli than solvent-cast samples (Figs. 26 and 27) [105]. 

Addition of only 1 wt % LCP to PCL increased Young s modulus by a factor of two and reduced the extension to break from 600% to about 7%. The effect at high concentrations of LCP was proportionally less and 10 wt % LCP increased Young s modulus by a factor of four and reduced elongation to break to about 2% [156]. 

Semiciystalline Polymers There are two cases to be considered in the stress-strain relationships of semicrystalline plastics. If the amorphous portion is rubbery, then the plastic will tend to have a lower modulus, and the extension to break will be very large see polyethylene. Table 11.1. If the amorphous portion is glassy, however, then the effect will be much more like that of the glassy amorphous polymers. Orientation of semicrystalline polymers is also much more important than for the amorphous polymers. A special case involves fibers, where tensile strength is a direct function of the orientation of the chains in the fiber direction. 

Gels are soft materials, so we would expect elastic moduli to be below 10 MPa and we would expect the modulus to decrease as the volume fraction of solvent increases. As an example, a gelatin gel swollen to five times its dry weight, has a modulus of about 0.8 MPa and a fracture stress of about 70 kPa with an extension to break of 10 %. At a swelling of 40 times, the modulus is only 40 kPa and the strength 6 kPa with the extension to break 11%. This soft, weak, brittle behavior is characteristic of most simple gels. 

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