Melt-spun polyamide

Melt spinninq is the most economical method. The polymer granulate is fed into a heated reservoir. The melt is then pumped or extruded through spinnerets and the filaments arc allowed to cool in the air. The filaments are produced at rates of up to 1200 m/min. Only thermally stable or stabilized polymers that give a melt can be melt spun. Polyamides, polyesters, poly-(olefins), and glass are spun in this way (Figure 12- ). 

Sandler, J. K. W. et al. A comparative study of melt spun polyamide-12 fibres reinforced with carbon nanotubes and nanofifares. Polymer 45, 2001-2015 (2004). 

As Figure 9 shows, aliphatic polyketone fibers position well as compared to melt-spun polyamide-66 and poly(ethylene terephthalate) fibers. 

Sandler, J.K.W. Pegel, S. Cadek, M. Gojny, F. Es, M.V. Lohmar, J. Blau W.J. Schulte, K. Windle, A.H. Shaffer, M.S.P. A comparative study of melt spun polyamide-12 fibres reinforced with carbon nanotubes and nanofibres. Polymer 2004, 45, 2001-2015. 

Comparative SEM micrographs of melt-spun polyamide-12 nanocomposite fibres containing (a) 10 wt% CNFs, (b) 10 wt% entangled catalytic MWCNTs, (c) 5 wt% aligned CVD MWCNTs, and (d) 5 wt% arc-grown MWCNTs. Reproduced from Ref. 92. 

Plots summarising the relationship between (a) tensile modulus and (b) yield stress of melt-spun polyamide-12 nanocomposites and nanoscale filler weight fraction for CNFs, arc-grown (aMWCNT) entangled (eMWCNT) and aligned (aMWCNT) multiwall structures. (Tensile tests were based on a constant force ramp. )... 

More recentiy, melt-spun biconstituent sheath—core elastic fibers have been commercialized. They normally consist of a hard fiber sheath (polyamide or polyester) along with a segmented polyurethane core polymer (11,12). Kanebo Ltd. in Japan currentiy produces a biconstituent fiber for hosiery end uses called Sideria. 

Among melt-spun fibers, those based on thermotropic liquid-crystalline melts have the highest strength and rigidity reported to date, and appear comparable to polyamides spun from lyotropic liquids-crystalline solutions. This was a very active field of research in the 1970s and later, and many comonomers have been reported. Obviously, these compositions must contain three components at a minimum, but many have four or five com-... 

It was, however, observed that such systems under appropriate conditions of concentration, solvent, molecular weight, temperature, etc. form a liquid crystalline solution. Perhaps a little digression is in order here to say a few words about liquid crystals. A liquid crystal has a structure intermediate between a three-dimensionally ordered crystal and a disordered isotropic liquid. There are two main classes of liquid crystals lyotropic and thermotropic. Lyotropic liquid crystals are obtained from low viscosity polymer solutions in a critical concentration range while thermotropic liquid crystals are obtained from polymer melts where a low viscosity phase forms over a certain temperature range. Aromatic polyamides and aramid type fibers are lyotropic liquid crystal polymers. These polymers have a melting point that is high and close to their decomposition temperature. One must therefore spin these from a solution in an appropriate solvent such as sulfuric acid. Aromatic polyesters, on the other hand, are thermotropic liquid crystal polymers. These can be injection molded, extruded or melt spun. 

The excellent properties of fiber melt spun from nylon 6,6 led to research by would-be competitive companies to produce similar polymers that did not infringe on the Du Pont patent. Nylon 6 was such a product developed by I.G. Farbenindustrie, a German company, who started production of this resin in 1940. Nylon 6 is a single monomer polyamide of the AB type made by the ring-opening cyclization of caprolactam (Eq. 21.8). Nylon 6,6 and nylon 6 were initially, and remain, the dominant commercial polyamides. 

Explorations with homogeneous membranes quickly showed that the flux-selectivity requirements for water desalination membranes would demand more than a simple melt-spun hollow fiber. In fact, it has been necessary to work out structure-property relationships on all levels of structure to bring RO membrane technology involving aromatic polyamides to its current status. 

Polymers from Table II that are typically wet or dry spun are aramids, acrylics, modacrylics, and cellulosics. The polyesters, polyamides, and polyolefins are melt spun fibers. 

The polycondensation of terephthalic acid with hexamethylene diamine produces a high melting temperature polyamide which can only be spun from concentrated sulfuric acid because of the high melting temperature of 370 C. If, however, terephthalic acid is polycondensed with a 1 1 mixture of 2,2,4-and 2,4,4-trimethyl hexamethylene diamine, I and II, an easily processed glass-clear amorphous polyamide is obtained. Glass-clear polyamides are also produced by the polycondensation of terephthalic acid with a mixture of the... 

Polyamide monofilament sutures show smooth surhices wifti a circular cross-section before implantation (see Fig. lb). No fibrous tissue cqisule was observed on the suture surface or around the knot post implantation. This is contributed to its smooth surface characteristic. However a closer examination of the opened knot shows flattening of the knot region (see Fig. 7). This is attributed to the ductile structure of polyamide sutures. It shows permanent deformation due to lateral forces exerted during loading. The rupture of the melt-spun synthetic fibres like polyamide is dominated by yield. Plastic yield of material causes the crack to open into a V-notch, vduch propagates steadily into the specimeiL This typical ductile fixture was seen at the broken ends, alter tmisile tests, both before and er implantation (see Fig. 8). 

Flat-sheet asymmetric-skinned membranes made from synthetic polymers (also copolymers and blends), track-etched polymer membranes, inorganic membranes with inorganic porous supports and inorganic colloids such as Zr02 or alumina with appropriate binders, and melt-spun thermal inversion membranes (e.g., hollow-fiber membranes) are in current use. The great majority of analytically important UF membranes belong to the first type. They are usually made of polycarbonate, cellulose (esters), polyamide, polysulfone, poly(ethylene terephtha-late), etc. 

Vibrational spectroscopy makes it possible to assess morphological parameters (e.g. order and orientation) of the blend constituents separately. This has, for instance, been demonstrated with PP/polyamide melt spun fibers. The composition and morphology of microdomains in PP... 

Wallace H. Carothers and his research team at DuPont discovered nylon-6,6, which is covered in his patents issued in 1937 and 1938. Diamines from C2 to Cis were synthesized and reacted with aliphatic and aromatic dicarboxylic acids to make polyamides, which were then melt spun and evaluated as fibers. Nylon-6,6 was ultimately selected for scale-up and development because of its favorable... 

Soin et al. (2014) have produced a 3D-knitted spacer piezo fabric. Melt-spun PVDF yams as spacer yams are incorporated between two knitted faces made of silver-coated polyamide yams. They claim the piezo fabric that can produce a power output density of 1.10-5.10 pW cm at applied impact pressures in the range of 0.02-0.10 MPa. 

Crystallization in step-growth polymers such as polyesters and nylons is known to assist their subsequent solid-state polymerization because exclusion of reactive end-groups from crystalline domains enhances their effective concentration in the amorphous domains [14,15]. However, the condensation reaction between the last fraction of end-groups may be hindered by crystallization [16, 17]. The possibility and rate of crystallization can also be enhanced by processes that enhance orientation, such as shearing and fiber drawing [18]. For example, partial replacement of terephthalic units with isophthalic units in PET reduces crystallinity, so that no crystallization in seen in 70 30 random poly(ethylene terephthalate-co-ethylene iso-phthalate) under quiescent conditions. However, heating its amorphous fiber above its Tg under a moderate tensile force results in rapid stress-induced crystallization [19]. The reduction in crystallization by copolymerization has been employed to enhance drawability of melt-spun polyester and polyamide fibers [20]. 

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