Nylon resin

Nylon resins are important engineering thermoplastics. Nylons are produced by a condensation reaction of amino acids, a diacid and a diammine, or by ring opening lactams such as caprolactam. The polymers, however, are more important for producing synthetic fibers (discussed later in this chapter). 

---

Fig. 1. (a) World production of nylon fiber (11) (b) world consumption of nylon resins (12). 

The principal worldwide manufacturers of nylon resins are given in Table 6. Total sales of nylon plastics in the United States and Canada in 1993 were 331,000 metric tons (37). West European sales were 352,000 t and Japanese sales 220,000 t (37). Figure 7 shows how sales in the United States have steadily increased since 1967 (38) and also how the price of nylon-6,6 has changed (39). The effect of the oil price rises, the boom of the mid-1980s, as well as the oil price reduction and the recession that followed are clearly evident. Table 7 shows the variation of price across different polyamide types. 

Nylon. Nylons comprise a large family of polyamides with a variety of chemical compositions (234,286,287). They have excellent mechanical properties, as well as abrasion and chemical resistance. However, because of the need for improved performance, many commercial nylon resins are modified by additives so as to improve toughness, heat fabrication, stabiUty, flame retardancy, and other properties. 

Nylon Resins. Nylon engineering thermoplastic resins have the foUowing polyamide stmctures ... 

Commercial engineering thermoplastic nylons are mainly crystalline resins. Nylon-6,6 [32131 -17-2] is the largest volume resin, followed by nylon-6 (48). Other commercially available but much lower volume crystalline nylons are -6,9, -6,10, -6,12, -11, and -12. The crystallinity of the molded part decreases with chain size (49). A few truly amorphous commercial nylon resins contain both aromatic and ahphatic monomer constituents (50). For example, Trogamid T resin is made from a mixture of 2,2,4- and 2,4,4-trimethylhexamethylenediamines and terephthahc acid (51). 

In the United States, 11 companies manufacture nylon resin Du Pont, Monsanto, Hoechst-Celanese, and AUied-Signal are the leaders. In Europe, there are 22 manufacturers, and in Japan, six (52). 

Nylon resins are made by numerous methods (53) ranging from ester amidation (54) to the Schotten-Baumann synthesis (55). The most commonly used method for making nylon-6,6 and related resins is the heat-induced condensation of monomeric salt complexes (56). In this process, stoichiometric amounts of diacid and diamine react in water to form salts. Water is removed and further heating converts the carboxylate functions to amide linkages. Chain lengths are controlled by small amounts of monofunctional reagents. The molten finished nylon resin can be dkectly extmded to pellets. 

The preparation of nylon resins from lactam precursors involves ring opening, which is facihtated by a controlled amount of water in the reaction mixture. The salt complex condenses internally to produce the polyamide (57). The synthesis of nylon-6 [25038-54-4] from S-caprolactam is as follows ... 

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). 

Over 565,000 t/yr of nonftber crystalline nylons is sold worldwide (63). Since markets are controUed by the economy, a modest growth of 5—8%/yr is expected. Although currently only ca 900 t/yr of amorphous nylons is sold worldwide (64), a growth rate of 10% is expected because of increased research activity. Currently, the amorphous nylon resins compete with PEI and polyesters in many appHcations. 

Modified nylons are blends of nylon resins and specially grafted nylon resins. In the Du Pont family of Zytel resin, certain blends have been designated Supertough to emphasize the improvement in impact that blends provide over standard resins. General Electric s Noryl GTX resins consist of a nylon matrix resin and a PPO resin in dispersed form. A highly sophisticated blend, it maintains a filled nylon s HPT with no sacrifice of impact resistance. 

Currently, over 110,000 t/yr of engineering resin blends are consumed worldwide, primarily in the transportation, business-machine, hardware, electrical, and appHance industries. Annual growth is projected to be ca 17%/yr. New blends based on PC, terephthalate, and nylon resins are experiencing the greatest expansion (122). These projections could be surpassed if large-volume metal appHcations such as automotive panels are replaced by engineering resin blends which are currently being field-tested. 

Liquid-crystal (79), advanced polyimide, and amorphous-nylon resin technologies (60) will be appHed. 

Rotational Molding with Capron Nylon Resins... 

PBT will absorb very little water (0.08 %), and its mechanical properties are not affected in the short term. Polyamides, on the other hand, may absorb up to 12% of water. In nylon resins, the water acts as a plasticizer it lowers the Tg, decreases the flexural modulus, and may cause part growth. Based on these criteria alone, polyesters are often a better choice than nylons for many applications (less variation of properties). 

Polyamides, commonly known as nylons, may safely be used to produce articles intended for application in processing, handling, and packaging of food, including for products intended to be cooked directly in their packages. Nylon resins are manufactured by condensation of hexyamethylenediamine and adipic acid (nylon 66) or sebacic acid (nylon 610), by the polymerization process, e.g., of co-laurolactam (nylon 12), or by condensation and polymerization, e.g., nylon 66 salts and s-caprolactam. 

Nearly all cyclohexane is used to make three intermediate chemicals. About 85% goes for caprolactam, and adipic acid. Another 10% goes for hexamethylene diamine (HMD). All three are the starting materials for Nylon 6 or Nylon 66 synthetic fibers and resins. Nylon fiber markets include the familiar applications hosiery, upholstery, carpet, and tire cord. Nylon resins are engineering plastics and are largely used to manufacture gears, washers, and similar applications where economy, strength, and a surface with minimum friction are important. 

Nylon (polyamide fibers). The chemical structure of the nylon fiber looks just like the nylon resin. The polymerization processes are the same the numbering systems are the same and the two most important nylon fibers are the same nylon, 6 and 66. The difference is the length of the molecule in comparison to the cross-section. Thats regulated by the polymerization process conditions. 

Zytel Nylon Resins, Product Guide and Properties, E-96368, E. I. du Pont de Nemours Co., Inc., Wilmington, Del., Sept. 1991. 

Nylon resins usually arc supplied in the form of cylindrical or rectangular diced pellets. Most commercial nylon molding, resins are... 

Some of the monomers commonly used to prepare the nylon resins are shown in Ihe accompanying table. Both petrochemical and vegetable products provide the source materials that are transformed into the reactive intermediates. Tile table correctly suggests that there is a wider choice in diacids than in diamines. The most important commercial polyamide resins are nylons-66 and -6. Other commercial nylons include 610, 612, 11, and 12. 

---