Nylon Polymer

Caprolactam is an amide and, therefore, undergoes the reactions of this class of compounds. It can be hydrolyzed, Ai-alkylated, O-alkylated, nitrosated, halogenated, and subjected to many other reactions (3). Caprolactam is readily converted to high molecular weight, linear nylon-6 polymers. Through a complex series of reactions, caprolactam can be converted to the biologically and nutritionally essential amino acid L-lysine (10) (see Amino acids). 

Prodnction of Nylon-6 from caprolactam is an important global industrial process. Of the several billions of pounds of caprolactam produced armually, most is polymerized to Nylon-6 [1]. Nylon-6 polymer is used in the manufacture of carpets, automotive parts and sporting goods as well as in films and packaging. 

The details of the anionic polymerization of nylon 6 have been extensively reviewed (1-8) and will only be discussed briefly as they affect the star-polymerization of nylon 6. Nylon 6 is polymerized anionically in a two-step process (Figure 1). The first step, creation of the activated species 3, is the slow step. The e-caprolactam monomer reacts in the presence of a strong base (such as sodium hydride) to form the caprolactam anion 2. This anion reacts with more caprolactam monomer to form 3. The reaction of this activated species with lactam anions occurs rapidly to form the nylon 6 polymer 4. 

CycUc polyamides were reported to be isolated from Nylon 6 polymers in 1956 [18,19]. Thermal polycondensation of co-amino acid (carbon number > 6) gave a cycUc and linear polymer [82]. Moreover, upon heating polyamide in the presence of a transamidation catalyst, the cyclization equilibrium is eventually reached, and both Unear and cyclic constituents are present [83]. The proportion of the latter depends on the concentration, and cycUc compounds predominate in high dilute solutions. 

Nylon, an aliphatic polyamide, was introduced as a commercial tire cord in 1947 and grew in usage to 5.4 billion kg/yr ( 2 billion lb/yr) in the 1990s (10,11). Nylon-reinforced tires use nylon-6 polymer (polycaprolactam) fibers as well as nylon-6,6 (poly(hexamethylenediamine adipamide)) fibers. Nylon tire cords are characterized by extremely good fatigue resistance in compression and good adhesion to most mbber compounds with simple RFL adhesives. 

Melting behaviour and spherulitic crystallization of polycaproamid (nylon 6). Polymer 3, 43—51 (1962). 

Similarly, treatment of discarded nylon 6 polymer with NH3 cleaves the polyamide backbone, forming e-caprolactam, which can be purified and re-converted to nylon 6. 

Gogolewski S, Peimings AJ (1973) Crystallization of polyamides under elevated pressure. Nylon 6. Polymer 14 463 see also 18 647, 654 (1977)... 

Garda et al. [204] prepared composites of nylon-6 polymer with nanometer-sized silica (Si02) filler by compression molding. The addition of 2wt% Si02 resulted in a friction reduction from 0.5 to 0.18 when compared with neat nylon-6. This low silica loading led to a reduction in wear rate by a factor of 140, whereas the influence of higher silica loadings was less pronounced. 

Andrews JM, Jones FR, Semlyen JA. Equihbrium ring concentrations and the statistical conformations of polymer chains part 12. CycHcs in molten and soHd nylon-6. Polymer. 1974 15 420-424. 

Figure 12. Edge view of pure nylon 6 polymer efter SCEPTRE agtosure.

Sodium montmorillonite (Na-MMT) was originally modified with pro-tonated amino acids with different numbers of carbon atoms and subsequently swollen with e-caprolactam. Then it underwent polymerization to produce nylon-6 polymer-clay nanocomposite [18]. Later, this technique was also extended to manufacture other thermoplactics. One advantage of this in-situ polymerization technique is the tethering effect, which enables the organic chemical such as 12-aminododecanoic acid (ADA) situated at the surface of the nanoclays to link with nylon-6 polymer chains during polymerization. 

Vitchuli et al. [174] used the combined technologies to prepare a multifunctional ZnO/nylon-6 nanofiber mat with antibacterial and detoxifying properties for use in protective applications. Nylon-6 polymer solution and a ZnO NP dispersion were loaded into two separate syringes and placed side-by-side on a two-syringe pump. In the resulting material, ZnO particles were attached to the nanofiber surface and were distributed throughout the entire mat. 

Table 10.1 The effect of an amino acid based nano-clay in a Nylon 6 polymer ...

Polymer Blends.—In addition to the work on polyester—polyamide blends reported in Section 2, several other papers describe the characteristics of various polymer formulations with polyamides. Biconstituent fibres have been formed from nylon-6 and poly(ethylene terephthalate). The same polyamide and nylon-12 have been blended with acrylonitrile-butadiene-styrene copolymer and the temperature and the concentration dependence of the dynamic modulus evaluated. The rheological properties of acrylonitrile-styrene copolymer/nylon-6 mixture have also been reported. Fourier transform infrared studies of nylon-6 and PVC have indicated the presence of specific interactions between the two polymers in both the molten and solid states. Finally X-r y studies carried out on injection-moulded blends of nylon-6, -12, and -66, have revealed that the addition of small amounts of the second component initiates formation of the y-crystalline phase within the nylon-6 polymer matrix. ... 

Molten polycaprolactam, at the end of equilibrium polymerization, contains 10 - 12 % low molecular-weight material consisting of unreacted monomer and of cyclic oligomers. For most end-uses, this low m.w. portion has to be removed. For this purpose, Hopff and Ufer developed a hot-water extraction process for nylon 6 chips [25], As an alternative process, vacuum demonomerization of the polymer melt in the autoclave was practiced as early as 1939/1943 [26], Hot-water leaching and vacuum extraction were further elaborated and incorporated in integrated, continuous processes for the manufacture of nylon 6 polymer (Fig. 5). In the case of vacuum extraction the integration may also include fiber manufacture by direct spinning [26]. 

Levchik, G.F. Levchik, S.V. Lesnikovich, A.I. Mechanisms of action in flame retardant reinforced nylon 6. Polym. Degrad. Stab. 1996, 54, 361-363. 

BH Stuart. A Fourier transform Raman study of water sorption by Nylon 6. Polym Bull 33 681-686, 1994. 

Laura, D.M., Keskkula, H., Barlow, J.W., and Paul, D.R. (2002) Effect of glass fiber surface chemistry on the mechanical properties of glass fiber-reinforced, rubber-toughened nylon 6. Polymer, 43, 4673-4687. 

E. Passaglia, M. Aglietto, G. Ruggeri, and F. Picchioni, Formation and compatibilizing effect of the grafted copolymer in the reactive blending of 2-diethylsuccinate containing polyolefins with poly-e-caprolactam (nylon-6), Polym. Adv. Technol, 9(5) 273-281, May 1998. 

Lincoln, D.M., Vaia, RA., Wang, Z.G., and Hsiao, B.S. (2001) Secondary structure and elevated temperature crystallite morphology of nylon-6. Polymer, 42,1621-1631. 

Evaluations of the exfoliation efficiency of the montmorillonite in the polymers and mechanical performance were identical to the protocol for evaluating the nylon 6-montmorillonite nanocomposite above. Data for the weight concentrations of montmorillonite in the three nylon 6 polymers were at approximately 3% and 7% and were reported in tabular form. Plots of mechanical performance versus wt.% montmorillonite concentration indicated that montmorillonite concentrations at approximately 1.5%, 4%, and 6.5% were also evaluated. 

In addition to the in situ polymerization method described above, anionic ring opening polymerization of -caprolactam can be utilized to prepare montmorillonite-nylon 6 polymer nanocomposites by in situ processing [18,19]. The polymerization process involves exfoliating an... 

At this point in the discussion of the mechanical properties of montmorillonite-nylon 6 polymer nanocomposites, a review of the work carried out by the Toyota Central Research Development Labs, Inc. that initiated an explosion of research and development of polymer-montmorillonite nanocomposite technology in relation to the subsequent work found above is provided. A series of three articles appeared in the Journal of Materials Research in 1993 in issue number 5. 

The last paper in this series [15] focused on the measurement of the mechanical properties of the nylon 6-montmorillonite nanocomposites prepared above. The control nylon 6 (1013B, Ube Industries) was reported to have a = 13 000. The montmorillonite content in the nylon 6 polymer nanocomposites varied from 1.9% to 7.1%. In the previous article, the montmorillonite content at 1.5% in the nylon 6 nanocomposite produced M = 62000 the nylon 6 nanocomposite at 6.8% produced M = 29 000. The influence of molecular weight on the Young s modulus was not compensated for in the comparisons of the pure nylon with the nylon nanocomposites. The Young s modulus values were measured at 23 °C and 120 °C. The modulus values at 120 °C increased from about 0.19 GPa for pure nylon to about 0.7 GPa for the nylon 6 nanocomposite with 6.8% montmorillonite content. The heat distortion temperature climbed from approximately 65 °C to approximately 150 °C for the polymer nanocomposite with a 6.8% montmorillonite content. The authors argue the applicability of the mixing law (Equation 5.3) coupled with a constrained polymer region associated with the montmorillonite as the mechanism for reinforcement. Identification of the proper mechanism for reinforcement of nylon 6-montmorillonite is provided above by Paul et al. [5j. 

Lim, J. et al. A novel preparation method of maleic anhydride grafted syndiotactic polystyrene and its blend performance with nylon 6. Polymer Bulletin (Berlin, Germany), 48(April 5), 397 05 (2002). 

Murthy NS, Kagan VA, Bray RG. Effect of melt temperature and skin-core morphology on the mechanical performance of nylon 6. Polym Eng Sci 2002 42 940-950. 

BASF s strongest product presence is nylon 6, in which it is highly integrated. The company makes caprolactam from cyclohexane and then nylon 6 polymer, at its integrated sites in Ludwigshafen, Germany, and Freeport, Texas. The polymer is next finished and fhen eifher compounded or sold direcfly to processors, independent compounders, and fiber producers. At one time, BASF made its own nylon 6 fibers, buf exited that business via a portfolio swap with Allied-Honey well in 2003, that sent the fibers business to Allied-Honeywell and the engineering plastics business to BASF. 

---