Crystalline yarn

An interesting model of the possible structure of semi-crystalline yarns is that given by Prevorsek and Kwon (1976) and shown in Fig. 19.14. 

Figures 14.1(a,b) show typical CP/MAS spectra of two types of PET yarns, an amorphous yarn wound at relatively low speed and a 36% crystalline yarn wound at relatively high speed, respectively [2]. The ethylene and carbonyl carbon peaks of the amorphous yarn are shifted about 1 ppm downfield with respect to the semicrystalline yarn, as opposed to the aromatic carbons which are shifted slightly upheld. Besides differences in chemical shift, the spectrum of the 36% crystalline yarn shows narrower lines with a better S/N ratio than the spectrum of the amorphous yarn. The broader lines in Fig. 14.1(a) are attributed to a broader orientation distribution of polymer molecules, which results in a larger distribution of isotropic chemical shifts. Additional differences between both spectra are observed in the lineshape the ethylene and carbonyl carbon peaks in Fig. 14.1(a) have a symmetric lineshape, whereas, these lines in Fig. 14.1(b) are asymmetric. The asymmetric lineshape is resolvable into two partially overlapping resonances a relatively broad low-field component and a relatively narrow high-field...

Fig. 14.1. CP/MAS spectra of different PET yarns. Spinning sidebands are marked with an asterisk (a) Amorphous yarn (b) 36% crystalline yarn and (c) deconvolution spectra of carbonyl and ethylene resonances of Fig. 14.1(b).

Fig. 29 The observed strength as a function of the initial modulus of filaments taken from a single yarn of cellulose II spun from a liquid crystalline solution compared with the calculated curves [26]...

Spunbonded processes, 17 463 Spunbonded structures, novel, 17 466 Spunbound fibers, 11 236, 240-241 Spun fibers, 16 18, 20 Spunlaced nonwovens, 17 507 Spunlace fabrics, production of, 17 516 Spun yarn, 11 177, 178, 250. See also Yarn spinning technologies crystalline structure of, 11 237-238 Spurrite (5-calcium disilicate monocarbonate)... 

Accessible Cellulose in Wood Pulp, Linters and Regenerated Cellulose. Crystalline Reactivity and Yarn Properties2S... 

Unlike nylon, which is highly crystalline, PET fibers are amorphous after spinning. They are like the molecules shown at the top of Figure 22-6 in Chapter 22. In order to make a usable textile yarn or staple fiber our of PET, it must be drawn under conditions that result in orientation and crystallinity. This is accomplished by drawing at temperatures of about 175°F with stretch 300-400%. As with nylon, the conditions of draw (especially... 

The mechanisms by which materials change are of prime importance in determining the kinetics. Materials science and engineering emphasizes the role of a material s microstructure. Structure and mechanisms are the yarn from which materials science is woven [1]. Understanding kinetic processes in, for example, crystalline materials relies as much on a thorough familiarity with vacancies, interstitials, grain... 

Table II gives the crystallinity values for various kinds of polyamide yarns. In one case, the occurence of a relatively amorphous skin can be detected. There is also an example of the effect of an azimutal correction. Absolute crystallinity values do not agree well with X-ray based crystallinity values. Nevertheless, there is a general qualitative agreement in the difference between polyamide and polyester yarns (it is well known that crystallinity is generally higher for polyamide than for polyester commercial filaments).

The mechanical response of composites, as shown in these exploratory studies, indicates dependence on the ease with which fracture can occur between fibers, yarns, and plies. Poorly crystallized matrices result in composites that are strong and stiff but with little yield so that failure occurs catastrophically. In contrast, more crystalline matrices seem to be not quite as strong and to have a lower effective modulus, but their increased strain capability ensures that failure is not catastrophic the composited strength decays gradually as further strain is applied. Thus, the energy required for total failure is increased, and the composite with more crystalline matrix is more tolerant of defects or stress risers. 

Morphology Some polymers, like PETP, are spun in a nearly amorphous state or show a low degree of crystallinity. In other polymers, such as nylon, the undrawn material is already semi-crystalline. In the latter case the impact of extension energy must be sufficient to (partly) "melt" the folded chain blocks (lamellae) in all cases non-oriented material has to be converted into oriented crystalline material. In order to obtain high-tenacity yarns, the draw ratio must be high enough to transform a fraction of the chains in more or less extended state. 

PAN, a synthetic fiber, is a polymer of acrylonitrile monomers. Worldwide, 2.73 million tons of PAN are produced per year, of which over 98% are processed as filament yarn serving as material in the textile industry (Tauber et al., 2000). PAN usually has a molecular weight of 55,000-70,000 g mol and is most commonly a copolymer produced by radical polymerization from acrylonitrile, 5-10 mol% vinyl acetate (or similar nonionic comonomers) to disrupt the regularity and crystallinity, and ionic comonomers, such as sulfuric or sulfonic acid salts. PAN is a hydrophobic polymer that affects the processability of the fibers. The surface is not easily wetted. 

Another important application of thermoplastic fibers such as poly ether ether ketone (PEEK), Poly etherimide(PEI), and VectranM andHS (Vectranis the trade mark of Hoechst liquid crystalline polymer) is in making thermoplastic matrix composites. Commingled yams of the reinforcement and matrix such as quartz/PEEK, glass/PEI, Vectran HS/M are used to make the composites wherein the matrix yarn fuses to form the continuous phase of the composite. 

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