Nylon monomer processes

The nylon casting process consists basically of four steps. These are the melting of the monomer, which is usually lactam flakes, the adding of the catalyst and activator, the mixing of the melts, and the casting process itself Cocatalyzed anionic polymerization is currently the most widely used nylon casting method. The cocatalysts are strong bases and their salts with imides and lactams. 

Most of the examples described hereabove have been selected in the fiels of nylon monomers, of polyalcohols and of the processing of natural feedstocks. 

The nylon-clay nanocomposites were prepared by in situ polymerization in the presence of organically modified, with aminolauric acid, montmorillonite. The reaction between nylon monomer and modified montmorillonite rendered nylon chains end-tethered though aminolauric acid to the silicate surface leading to exfoliated silicates (61). However, not all polymer nanocomposite systems could be produced via in situ polymerization processes because of the chemical sensitivity of polymerization catalysts. Direct melt blending of hydrophilic polymers with montmorillonite in its pristine state or polymers with surfactant-intercalated montmorillonite was found to be possible to deliver polymer intercalated or exfoliated nanocomposites (62,63). 

Despite the difficulties, the monomer process was eventually perfected at a Paris lab, by Kastner under the direction of Genas. In 1944 pilot production was begun in Normandy. 1950 saw the spinning of the first nylon 11 thread. Commercial production of monomer commenced in 1955 at Marseilles, where that plant continues today as the sole production unit of 11-aminoundecanoiC acid. Production of polymer continued in the tiny Normandy town of Serquigny this production constituted the total world capacity until 1971 when a U.S. subsidiary brought a 4000 T unit on-stream. 

They actually did produce the eight carbon capryllactam until about 1973 but never commerciallized Nylon 12. Their main monomer process points were ... 

Since adipic acid has been produced in commercial quantities for almost 50 years, it is not surprising that many variations and improvements have been made to the basic cyclohexane process. In general, however, the commercially important processes stiU employ two major reaction stages. The first reaction stage is the production of the intermediates cyclohexanone [108-94-1] and cyclohexanol [108-93-0], usuaHy abbreviated as KA, KA oil, ol-one, or anone-anol. The KA (ketone, alcohol), after separation from unreacted cyclohexane (which is recycled) and reaction by-products, is then converted to adipic acid by oxidation with nitric acid. An important alternative to this use of KA is its use as an intermediate in the manufacture of caprolactam, the monomer for production of nylon-6 [25038-54-4]. The latter use of KA predominates by a substantial margin on a worldwide basis, but not in the United States. 

Caprolactam Extraction. A high degree of purification is necessary for fiber-grade caprolactam, the monomer for nylon-6 (see Polyamides). Cmde aqueous caprolactam is purified by solvent extractions using aromatic hydrocarbons such as toluene as the solvent (233). Many of the well-known types of column contactors have been used a detailed description of the process is available (234). 

Rayon is unique among the mass produced man-made fibers because it is the only one to use a natural polymer (cellulose) directly. Polyesters, nylons, polyolefins, and acryflcs all come indirectly from vegetation they come from the polymerization of monomers obtained from reserves of fossil fuels, which in turn were formed by the incomplete biodegradation of vegetation that grew millions of years ago. The extraction of these nonrenewable reserves and the resulting return to the atmosphere of the carbon dioxide from which they were made is one of the most important environmental issues of current times. CeUulosic fibers therefore have much to recommend them provided that the processes used to make them have minimal environmental impact. 

Nylon-6 is the polyamide formed by the ring-opening polymerization of S-caprolactam. The polymerization of S-caprolactam can be initiated by acids, bases, or water. Hydrolytic polymerization initiated by water is often used in industry. The polymerization is carried out commercially in both batch and continuous processes by heating the monomer in the presence of 5—10% water to temperatures of 250—280°C for periods of 12 to more than 24 h. The chemistry of the polymerization is shown by the following reaction sequence. 

The process uses a catalyst and higher temperatures than nylon-6 (300—350°C) on account of the stabihty of the 13-membered ring. Again, there is Htde residual unreacted monomer. 

Ammonia is used in the fibers and plastic industry as the source of nitrogen for the production of caprolactam, the monomer for nylon 6. Oxidation of propylene with ammonia gives acrylonitrile (qv), used for the manufacture of acryHc fibers, resins, and elastomers. Hexamethylenetetramine (HMTA), produced from ammonia and formaldehyde, is used in the manufacture of phenoHc thermosetting resins (see Phenolic resins). Toluene 2,4-cHisocyanate (TDI), employed in the production of polyurethane foam, indirectly consumes ammonia because nitric acid is a raw material in the TDI manufacturing process (see Amines Isocyanates). Urea, which is produced from ammonia, is used in the manufacture of urea—formaldehyde synthetic resins (see Amino resins). Melamine is produced by polymerization of dicyanodiamine and high pressure, high temperature pyrolysis of urea, both in the presence of ammonia (see Cyanamides). 

Amorphous nylons are transparent. Heat-deflection temperatures are lower than those of filled crystalline nylon resins, and melt flow is stiffer hence, they are more difficult to process. Mold shrinkage is lower and they absorb less water. Warpage is reduced and dimensional stabiUty less of a problem than with crystalline products. Chemical and hydrolytic stabiUty are excellent. Amorphous nylons can be made by using monomer combinations that result in highly asymmetric stmctures which crystalline with difficulty or by adding crystallization inhibitors to crystalline resins such as nylon-6 (61). 

The basic RIM process is illustrated in Fig. 4.47. A range of plastics lend themselves to the type of fast polymerisation reaction which is required in this process - polyesters, epoxies, nylons and vinyl monomers. However, by far the most commonly used material is polyurethane. The components A and B are an isocyanate and a polyol and these are kept circulating in their separate systems until an injection shot is required. At this point the two reactants are brought together in the mixing head and injected into the mould. 

A process for depolymerizing nylon-6 and polyester-nylon-6 mixed scrap was patented by Allied Chemical Corporation in 19656 and 1967.7 Ground scrap was dissolved with high-pressure steam at 125-130 psig (963-997 kPa) pressure and 175-180°C for 0.5 h in a batch process and then continuously hydrolyzed with superheated steam at 350°C and 100 psig (790 kPa) to form -caprolactam at an overall recovery efficiency of 98%. The recovered monomer could be repolymerized without additional purification. 

Mond process The purification of nickel by the formation and decomposition of nickel carbonyl, monomer A small molecule from which a polymer is formed. Examples CH2=CH2 for polyethylene NH2(CH2)6NH2 for nylon, monoprotic acid A Bronsted acid with one acidic hydrogen atom. Example CH COOI I. monosaccharide An individual unit from which carbohydrates are considered to be composed. Example C6H(206, glucose, multiple bond A double or triple bond between two atoms. 

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