Low-melt Fibers

Non-crystalline polymers or copolymers can also be used to generate fibers with relatively low softening temperatures. Such fibers can be blended with regular fibers, e.g. staples, and bonded together by applying sufficient heat to melt the low-temperature component. Such fibers need not be exotic. The use of undrawn, amorphous fibers suffices for many such purposes, for example, bonded nonwo-ven webs formed from a mix of drawn and undrawn PET staple fibers. Without crystalline structure, the undrawn fibers will soften and become tacky at relatively low temperatures, so providing bond sites. 

Bico fibers are a new class of fibers, rather than a sub-set of PET fibers. Such fibers are formed from two different polymers, which are melted separately, and then combined into a single fiber at the last moment before extrusion. In some cases, the fibers are actually extruded separately, and then combined beneath the spinneret while they are still molten, so that they fuse together after spinning. 

The side-side configuration is typically used to impart crimp to the fiber. If the fiber is formed from polymers with different shrinkage characteristics, and 

Bico fibers have been available for at least 30 years, but only recently have they developed widespread applications. Bico production equipment is relatively more complex and expensive, and so the fibers require higher selling prices. As these fibers become more common in specialty markets, production cost is decreasing, so that they are now beginning to find uses in commodity applications. 

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Finally, the use of low-melting polyesters for low-melt fibers (melting point, 110-180 °C) should be pointed out, where TPA is replaced partly by IPA or adipic acid for bond fiber application. 

Webs produced with the above described processed have limited strength in their unbonded form and need to be consolidated. There are three basic types of bonding thermal, mechanical and chemical. The thermal bonding uses the thermoplastic properties of certain synthetic fibers to form bonds under controlled heating. In some cases the web fiber itself can be used, but often a low melt fiber or bi-compo-nent fiber is introduced at the web formation stage to perform the binding function later in the process. 

However, because of the low melting poiats and poor hydrolytic stabiUty of polyesters from available iatermediates, Carothers shifted his attention to linear ahphatic polyamides and created nylon as the first commercial synthetic fiber. It was nearly 10 years before. R. Whinfield and J. T. Dickson were to discover the merits of poly(ethylene terephthalate) [25038-59-9] (PET) made from aromatic terephthaUc acid [100-21-0] (TA) and ethylene glycol [107-21-1] (2G). 

Thermoplastic Fibers. The thermoplastic fibers, eg, polyester and nylon, are considered less flammable than natural fibers. They possess a relatively low melting point furthermore, the melt drips rather than remaining to propagate the flame when the source of ignition is removed. Most common synthetic fibers have low melting points. Reported values for polyester and nylon are 255—290°C and 210—260°C, respectively. 

C. Characteristically, these nematic melts show the persistence of orientational order under the influence of elongational flow fields which result in low melt viscosities under typical fiber formation conditions even at high molecular weights. 

Nylon-11. Nylon-11 [25035-04-5] made by the polycondensation of 11-aminoundecanoic acid [2432-99-7] was first prepared by Carothers in 1935 but was first produced commercially in 1955 in France under the trade name Kilsan (167) Kilsan is a registered trademark of Elf Atochem Company. The polymer is prepared in a continuous process using phosphoric or hypophosphoric acid as a catalyst under inert atmosphere at ambient pressure. The total extractable content is low (0.5%) compared to nylon-6 (168). The polymer is hydrophobic, with a low melt point (T = 190° C), and has excellent electrical insulating properties. The effect of formic acid on the swelling behavior of nylon-11 has been studied (169), and such a treatment is claimed to produce a hard elastic fiber (170). 

The polyamide copolymer of dodecanoic acid with methylenedi(cyclohexylamine) (MDCHA, PACM) was sold as continuous filament yam fiber under the tradename QIANA. As late as 1981, over 145,000 t was produced using high percentages, typically 80%, of trans, trans MDCHA isomer. The low melting raffinate coproduct left after t,t isomer separation by fractional crystallisation was phosgenated to produce a Hquid aUphatic diisocyanate marketed by Du Pont as Hylene W. Upon terrnination of their QIANA commitment, Du Pont sold the urethane intermediate product rights to Mobay, who now markets the 20% trans, trans—50% cis, trans—30% cis, cis diisocyanate isomer mixture as Desmodur W. In addition to its use in polyamides and as an isocyanate precursor, methylenedi (cyclohexyl amine) is used directiy as an epoxy curative. The Hquid diamine mixture identified historically as PACM-20 is marketed as AMICURE PACM by Anchor Chemical for performance epoxies. 

Polymeric isocyanates or PMDI ate cmde products that vary in exact composition. The main constituents are 40—60% 4,4 -MDI the remainder is the other isomers of MDI, trimeric species, and higher molecular weight oligomers. Important product variables are functionaHty and acidity. Rigid polyurethane foams are mainly manufactured from PMDI. The so-called pure MDI is a low melting soHd that is used for high performance polyurethane elastomers and spandex fibers. Liquid MDI products are used in RIM polyurethane elastomers. 

Narrow molecular weight distribution Difficult extrusion except where NMWD resins are used. Low melt strength, good melt drawability Fiber/nonwovens Fiber/nonwovens... 

Improvements in melt spinning techniques and film filament processes have made polypropylene accessible for fiber production. Low-cost fibers made from polypropylene are replacing those made from sisal and jute. 

Polyesters are the most important class of synthetic fibers. In general, polyesters are produced by an esterification reaction of a diol and a diacid. Carothers (1930) was the first to try to synthesize a polyester fiber by reacting an aliphatic diacid with a diol. The polymers were not suitable because of their low melting points. However, he was successful in preparing the first synthetic fiber (nylon 66). In 1946, Whinfield and Dickson prepared the first polyester polymer by using terephthalic acid (an aromatic diacid) and ethylene glycol. 

Evaporation is used extensively for the deposition of aluminum and other low melting-point metals as well as hard coatings such as TiN for cutting tools, decorative coatings (jewelry), and for the metallization of paper and fibers. It is also a major coating... 

The char layer from a burning polymer, while it exerts protective action, is itself vulnerable to oxidation. This can manifest itself either during flaming combustion as a constant destruction of the char as it forms, or as afterglow. Means for prevention of this undesired char destruction have been reported. In studies on preventing combustion of carbon fibers, incorporation of borates, phosphates, or low melting glasses has been shown to be effective (12, 13). 

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