Caprolactam, Polycaprolactam

PatentNumber US 5869654 A 19990209 PROCESS FOR DEPOLYMERISING POLYCAPROLACTAM PROCESSING WASTE TO FORM CAPROLACTAM... 

The polycaprolactam waste is contacted with superheated steam in the absence of added catalyst at a temperature of about 250 to 400C and a pressure in the range of about 1.5 to 100 atm. and substantially less than the saturated vapour pressure of water at the temperature at which a caprolactam-containing vapour stream is formed. The resulting caprolactam may then be used in the production of engineered resins and fibres. 

The ring opening polymerization of cyclic monomers that yield thermoplastic polymers of interest in composite processing is reviewed. In addition, the chemistry, kinetics, and rheology of the ring opening polymerization of caprolactam to nylon 6 are presented. Finally, the rheo-kinetics modelsfor polycaprolactam are applied to the composite process of reaction injection pultrusion. 

The rheokinetics of polycaprolactam polymerizing in the monomer shows that below 50 percent conversion, the relative complex viscosity versus conversion of the nylon 6 homopolymerization is defined by the phenomenological equation ri / t]Q = exp(19.6 X), where // is the complex viscosity of nylon 6 anionically polymerizing in its monomer, 0 is the viscosity of caprolactam monomer, and X is fractional conversion. 

According to the 1981-83 National Occupational Exposure Survey (NOES, 1997), approximately 25 000 workers in the United States were potentially exposed to caprolactam (see General Remarks). Occupational exposures to caprolactam may occur in the manufacture of the chemical and of polycaprolactam (nylon 6) fibres and resins. 

Platinum complexes, 161 Polarographic studies, 153, 154 of 2-aminothiazoles, 29 of 2-anilinothiazoles, 30 of 2-azothiazoles, 107, 108 Polyacrylonitrile, 105, 163, 164, 167 Polyamines, 156-168 Polycaprolactam, 156-168 Polyesters, 163, 165, 166, 167 Polyhalogenothiazole. reactivity of, 408-409 Polymers, e-caprolactam, butadiene, 438 Polymorphism, of sulfathiazole, 116 Positive colored image, 440 Postemergence activity, 134 Potassium salts, of acetamido thiazoles, 90 Potentiometric measurements, and amido-imido equilibrium, 116 and amino-imino equilibrium, 21 P.P.P. approximation, charge diagrams calculations by, 17... 

The manufacture of the large variety of polyamides (commonly referred to as nylons) occurs through polycondensation of amino carboxylic acids (or functional derivatives of them, e.g. lactams) and from diamines and dicarboxylic acids. Labeling the amino groups with A and the carboxyl groups with B allows differentiation of the different chemical structures between the two types AB (from amino carboxylic acids) and AA-BB (from diamines and dicarboxylic acids). The number of C atoms in the monomers acts as a code number for the identification of the polyamides. The polycaprolactam manufactured from caprolactam (type AB) is then called polyamide 6 (PA 6). The number of carbon atoms in the diamine is given first for type AA-BB followed by the number of atoms in the dicarboxylic acid, e.g. PA 66 for polyhexamethylenedia-dipic amide from hexamethylenediamine and adipic acid. For copolymers the components are separated by a slash, e.g. PA 66/6 (90 10) is a copolymer composed of 90 parts PA 66 and 10 parts PA 6. 

Note also that nylon-6 was listed in Table 2-2 as the product of the ringopening polymerization of the cyclic monomer caprolactam. So here is an example of the same polymer that can be made from (at least) two different monomers by two different mechanisms. This illustrates the complexity of our classification and nomenclature schemes, because polycaprolactam,... 

POLYCAPROAMIDE see PJY500 POLY(e-CAPROAMIDE) see PJY500 POLYCAPROLACTAM see PJY500 POLY(e-CAPROLACTAM) see PJY500 POLYCAT 8 see DRF709 POLYCHLORCAMPHENE see CDVIOO POLYCHLORINATED BIPHENYL (AROCLOR 1221) see PJMOOO... 

Scheme 1.29. Polycaprolactam polymerization from ring-opening of caprolactam. After Brown (1992).

Nylons based on oj-aminocarboxylie acids, although briefly investigated by Carothers, were commercialized first in Germany around 1939 (Figure 1). Of particular interest to the plastic industry is nylon 6 (based on caprolactam), which became available in 19A6 in Europe. It was initially Introduced to the United States in 195A by Allied Chemical Company for fiber purposes. Polycaprolactam is crystalline, has a lower melting point than nylon... 

There are several satisfactory commercial ways to produce polycaprolactam (6-nylon). In one method, eaminocaproic iu id is used as a catalyst. Molten caprolactam with 1-5 per cent catalyst is heated at atmospheric pressure at 24Q-280°C for 6-8 hr. The vessel is blanketed with steam or nitrogen to prevent oxidation. At equilibrium, the pol3mier contains about 10 per cent of unreacted caprolactam. Use of a small amount of the monofunctional acid assists in stabilizing the molecular weight. 

Cyclohexanone, a six-membered carbon ring with a ketone as functional group, is almost exclusively applied as a precursor for the production of aliphatic polyamides. Pure cyclohexanone is mainly converted, via cyclohexanone oxime and caprolactam, to nylon-6 (also called polycaprolactam) [1]. Mixtures of cyclohexanone and cyclohexanol, often called K4 oil, are converted via oxidation into adipic acid that reacts with hexamethylene diamine (HMDA) to nylon-6,6 (poly-hexamethylene adipamide). Other applications of these products can be found in the field of polyurethane and polyester production. 

Nylon-6 is the generic name for polycaprolactam. It is almost exclusively synthesized from -caprolactam by a ring-opening reaction Equation 2.3... 

In the course of formation of polymers, some monomer remains in the cured adhesive. This monomer can diffuse to the boundary, plasticizing faulty surface layers of the polymer and adsorbing on the substrate surface [13]. Monomer at the boundary between the adhesive and the substrate inevitably decreases the adhesion strength. For example, by electron microscopy one can observe single crystals of caprolactam on the surface of PC-4 polycaprolactam [14], Removal of the polymer surface layer usually results in noticeable increase of the adhesion strength in the course of bonding [15],... 

Hydrolytic polymerizations are the smoothest of all three types of polymerization reactions, because the growing species are less activated than in either cationic or anionic polymerizations. Many commercial processes utilize it in c-caprolactam polymerizations. Formation of irregular structures, however, and even crosslinked material was detected. In addition, at elevated temperatures deamination and decarix)xylation of polycaprolactam can take place. Such reactions can result in formations of ketones and secondary amine groups The ketones, in turn, can react with amines and form Schiff bases. This leads to branching and crosslinking. 

Much of nylon 6 is used in producing fibers. Polycaprolactam prepared by water-catalyzed polymerizations is best suited for this purpose. It can also be used in molding, though anionically polymerized caprolactam can be used as well. The polymerizations are carried out both in batch and in continuous processes. Often, tubular flow reactors are employed. 

X—NHCOCHj ) (X = poly caprolactam chain) Mechanical degradation of polycaprolactam/ Solid polymer EPR/ 77 2H(a) 1.9 67Zakl... 

The same reaction can also be carried out on a copolymer of ethylene and carbon monoxide [266], Polycaprolactam can be treated with either SO2CI2, POCI3, or PCI5 at 70°C to introduce ionic chlorine groups [267]. The main product is poly(a,a-dichloro-caprolactam) ... 

Many impurities are present in commercial caprolactam that pass into the liquid wastes from polycaprolactam (PCA) manufacture from which caprolactam monomer may be recovered. Also, the products of the thermal degradation of PCA, dyes, lubricants, and other PCA fillers may be contained in the regenerated caprolactam. Identification of the contaminants by infrared (IR) spectroscopy has led to the detection of lower carboxylic acids, secondary amines, ketones, and esters. Aldehydes and hydroperoxides have been identified by polarography and thin-layer chromatography. 

Caprolactam must be very carefully purified to exclude small concentrations of (1) ferric ions, which would catalyze the thermal oxidative degradation of polycaprolactam and (2) aldehydes and ketones, which would markedly increase the oxidizabihty of caprolactam. The impurities in caprolactam may retard the rate of caprolactam polymerization as well as having a harmful effect on the properties of the polymer and liber. In the vacuum depolymerization of nylon 6, a catalyst must be used because in the absence of a catalyst, by-products such as cyclic olefins and nitrides may form, which affects the quality of the caprolactam obtained [3]. 

---