Nylon processing

Benzene was first isolated by Faraday in 1825 from the liquid condensed by compressing oil gas. It is the lightest fraction obtained from the distillation of the coal-tar hydrocarbons, but most benzene is now manufactured from suitable petroleum fractions by dehydrogenation (54%) and dealkylation processes. Its principal industrial use is as a starting point for other chemicals, particularly ethylbenzene, cumene, cyclohexane, styrene (45%), phenol (20%), and Nylon (17%) precursors. U.S. production 1979 2-6 B gals.  [c.55]

Nylon 6 and 6/6 possess the maximum stiffness, strength, and heat resistance of all the types of nylon. Type 6/6 has a higher melt temperature, whereas type 6 has a higher impact resistance and better processibility. At a sacrifice in stiffness and heat resistance, the higher analogs of nylon are useful primarily for improved chemical resistance in certain environments (acids, bases, and zinc chloride solutions) and for lower moisture absorption.  [c.1018]

In May 1992, the U.S. Pood and Dmg Administration estabUshed the following guidelines to help assure the consumer safety of plastics recycling processes (20). Primary recycling is the recycling of plastics that are plant scrap and have not been sold for consumer use. Secondary recycling is the physical cleaning and processing of post-consumer plastic products. Tertiary recycling is the chemical treatment of polymers. This treatment is usually depolymerization to produce monomers which are purified and then polymerized to produce new polymer. Using tertiary recycling, materials such as fillers and fibers can be physically removed from the monomer. The monomers can also be purified by distillation and other processes prior to polymerization. The leading example of tertiary recycling is poly(ethylene terephthalate). Tertiary recycling also has been suggested for nylon from discarded carpets (21).  [c.230]

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.  [c.240]

The continuing pursuit of a wide variety of alternate manufacturing processes indicates an effort by competitors to position themselves to take advantage of potential shifts in petrochemical feedstock prices. A large number of the reports concern the use of feedstocks, notably butadiene, although several major modifications to cyclohexane-based or benzene-based processes are included. The continued buildup of capacity in nylon-6,6 intermediates, especially in the Far East, attests to the confidence in continued growth by the major participants. Although the nylon-6 [25038-54-4] market currently is larger in Europe, both markets will share in the growth, especially in the developing areas of the world. The emergence of new polymers for specialized apphcations may tend to limit growth in certain areas. For example, polypropylene may take a significant share of the lower cost carpet market. Specialized polyamides such as nylon-4,6 [24936-71 -8] h.a.ve now appeared, although this one consumes adipic acid.  [c.245]

W. J. Nolan, in Proceedings Symposium on Processing Propellants, Explosives and Ingredients, AD PA, Washington, D.C., 1977, p. 1.3—1.  [c.56]

Thermoplastic, iaelastic fibers, such as nylon and polyester, may be processed to provide spring-like, hehcal, or zigzag stmctures. These fibers can exhibit high elongations as the hehcal or zigzag stmcture is stretched, but the recovery force is very low. This apparent elasticity results from the geometric form of the filaments as opposed to elastomeric fibers whose elastic properties depend primarily on entropy changes inherent within their polymer stmcture. Thus processed iaelastic fibers must comprise a significant portion of a stretch fabric whereas an elastomeric fiber provides the necessary stretch properties at 5—20% of fabric weight.  [c.304]

The film tube is collapsed within a V-shaped frame of rollers and is nipped at the end of the frame to trap the air within the bubble. The nip roUs also draw the film away from the die. The draw rate is controlled to balance the physical properties with the transverse properties achieved by the blow draw ratio. The tube may be wound as such or may be sHt and wound as a single-film layer onto one or more roUs. The tube may also be direcdy processed into bags. The blown film method is used principally to produce polyethylene film. It has occasionally been used for polypropylene, poly(ethylene terephthalate), vinyls, nylon, and other polymers.  [c.380]

Nitrite-Cured Meats. Ham, bacon, sausage, bologna, etc, are cured to reduce water activity, are spiced for flavor, and usually have ingredients to maintain the desired red color. Curing agents include salt, sodium nitrite, and sodium nitrate. Cured meats maintained in an absence of oxygen have refrigerated shelf Hves measured in weeks. Most processed meats are packaged under reduced oxygen on thermoform—vacuum—gas flush—seal systems, usually nylon-based, and are distributed under refrigeration. Small quantities of cured meats are packaged in oxygen barrier film pouches under inert atmosphere such as nitrogen (see also Eood additives).  [c.448]

Nylon films are used in lamination or coated form to ensure heat sealabiHty and enhance barrier properties. The largest uses are as thermoforming webs for twin-web processed meat and cheese packagiag under vacuum or in an inert atmosphere. Other uses include bags for red meat, boil-ia-bags, bag-in-box for wine, and as the outer protective layer for aluminum foil in cookie and vacuum coffee packages.  [c.452]

Some heavier gauge flexible materials, usually containing nylon, are thermoformed, ie, heated and formed into three-dimensional shapes. Such stmctures are used to provide high gas-barrier, heat-sealable containment for processed meat or cheese.  [c.453]

In a weU-designed multistage hydrogenation unit, operating costs are small as a result of recovery of the heat of hydrogenation between reactor stages by steam generation or integration with other process units, or by more efficient one- and two-stage processes (57,58). Consequentiy, the principal costs in cyclohexane manufacture are maintenance expenses, interest and return charges on the plant and working capital, and the cost of benzene and high purity hydrogen. The cost of hydrogen recovery from the gases produced from catalytic reforming of naphtha or from ethylene manufacture is included in the manufacturing cost. The price of cyclohexane is dependent on the price of benzene (qv). Virtually all cyclohexane goes to the production of nylon (see POLYAMDES).  [c.408]

Almost all of the cyclohexane that is produced in concentrated form is used as a raw material in the first step of nylon-6 and nylon-6,6 manufacture. Cyclohexane also is an excellent solvent for cellulose ethers, resins, waxes (qv), fats, oils, bitumen, and mbber (see Cellulose ethers Resins, natural Fats AND FATTY OILS Rubber, NATURAL). When used as a solvent, it usually is in admixture with other hydrocarbons. However, a small amount is used as a reaction diluent in polymer processes.  [c.409]

The cyclohexane in cmde oil has three primary dispositions. Some of it is included in a light fraction (35—75°C) that is distilled from cmde oil and is blended with other materials into motor gasoline (see Gasoline and other motor fuels). Alternatively, this fraction is used as a feed to ethylene manufacture, particularly in Europe. The third, and most important disposition, is as a feed to a catalytic reformer where the naturally occurring cyclohexane is converted to benzene by dehydrogenation (see BTX processing). The cyclohexane used in this fashion often is reconverted by hydrogenation for use in nylon manufacture after recovery of high purity benzene by solvent extraction of the Hquid product from the catalytic reformer. Direct recovery of cyclohexane from cmde oil for chemical appHcations is practiced to a limited extent because of the small volumes of cyclohexane needed and the difficulty in fractionally distilling it from the many hydrocarbons in cmde oil that boil at similar temperatures.  [c.409]

Membrane Sep r tion. The separation of components ofhquid milk products can be accompHshed with semipermeable membranes by either ultrafiltration (qv) or hyperfiltration, also called reverse osmosis (qv) (30). With ultrafiltration (UF) the membrane selectively prevents the passage of large molecules such as protein. In reverse osmosis (RO) different small, low molecular weight molecules are separated. Both procedures require that pressure be maintained and that the energy needed is a cost item. The materials from which the membranes are made are similar for both processes and include cellulose acetate, poly(vinyl chloride), poly(vinyHdene diduoride), nylon, and polyamide (see AFembrane technology). Membranes are commonly used for the concentration of whey and milk for cheesemaking (31). For example, membranes with 100 and 200 p.m are used to obtain a 4 1 reduction of skimmed milk.  [c.368]

The largest use of nitric acid (ca 74—78% of total U.S. production) is for the manufacture of ammonium nitrate. About 75% of ammonium nitrate [6484-52-2] is used in fertilizers (qv) the remainder is used for chemicals, explosives, and miscellaneous other uses. Partiy because of the increased popularity of urea, the use of ammonium nitrate as a fertilizer has declined. This has been offset to some extent by the growth in the use of ammonium nitrate for explosives and other chemical uses. Overall, the production of ammonium nitrate in the United States is expected to remain flat for several years. The next three largest uses for nitric acid are in the manufacture of cyclohexanone (ca 8—9%), dinitrotoluene (ca 4%), and nitrobenzene (ca 3—4%). Cyclohexanone [108-94-1/ is a raw material for manufacture of adipic acid, which reacts with hexamethylenediamine to make nylon-6,6. Dinitrotoluene [25321-14-6] is hydrogenated to toluenediamine [26764-44-3] which is used to make toluenediisocyanate [1321 -38-6] (I DI). Nitrobenzene [98-95-3] (qv) is hydrogenated to make aniline, which is a raw material for the manufacture of methylene diphenyl diisocyanate [101-68-8] (MDI). TDI is used to make flexible polyurethane foams, elastomers, and coatings, whereas MDI is used for rigid foams (see Amines, aromatic-methylenedianiline). Other uses of nitric acid are in the production of explosives, metal nitrates, nitrocellulose [9004-70-0] nitrochlorobenzene, metal treatments (eg, the pickling of stainless steels and metal etching), rocket propellants, and nuclear fuel processing (86,88).  [c.47]

The development of new resins, plastics, fibers, elastomers, etc, which are processed at progressively higher operating and curing temperatures has created a need for pigments that stand up for relatively long periods of time to a hostile environment. They must remain essentially unaltered when incorporated into plastics such as polypropylene, ABS, or nylon at relatively high temperatures. In reaUty, in high temperature plastics most organic pigments partially dissolve and undergo particle ripening or growth thus changing color without chemical destmction. Some pigments can change to thermodynamically more stable polymorphic forms with consequent color change, and others simply decompose.  [c.23]

The packaging (qv) requirements for shipping and storage of thermoplastic resins depend on the moisture that can be absorbed by the resin and its effect when the material is heated to processing temperatures. Excess moisture may result in undesirable degradation during melt processing and inferior properties. Condensation polymers such as nylons and polyesters need to be specially predried to very low moisture levels (3,4), ie, less than 0.2% for nylon-6,6 and as low as 0.005% for poly(ethylene terephthalate) which hydrolyzes faster.  [c.136]

The magnitude of the intellectual achievement of Carothers often overshadows the tremendous effort and success that followed in building the necessary industrial infrastmcture and developing the numerous scientific and engineering innovations required to make nylon a successhil commercial venture. One of the first of these was the development of a route to produce the starting materials from "coal, air, and water," and the first intermediates plant was built at Belle, West Virginia (10). Another was the invention of the autoclave polymerisation process using balanced salt and acetic acid end termination to control the molecular weight of the final polymer. Because nylon-6,6 was insoluble in all common solvents, a new melt-spinning process was required to form fibers and wind them onto packages. Also, the two-step drawing process was invented to develop the hill strength of the fibers. Additional inventions were required for effective downstream processing of this new synthetic fiber in order to dye and form it into finished goods. Finally, strong markets were required to support the financial investment necessary for this revolutionary product fortunately, nylon was extremely well suited to compete in the high value sHk markets.  [c.219]

Adipic acid (qv) has a wide variety of commercial uses besides the manufacture of nylon-6,6, and thus is a common industrial chemical. Many routes to its manufacture have been developed over the years but most processes in commercial use proceed through a two-step oxidation of cyclohexane [110-83-8] or one of its derivatives. In the first step, cyclohexane is oxidized with air at elevated temperatures usually in the presence of a suitable catalyst to produce a mixture of cyclohexanone [108-94-1] and cyclohexanol [108-93-0] commonly abbreviated KA (ketone—alcohol) or KA oil  [c.232]

Polymer Production. Three processes are used to produce nylon-6,6. Two of these start with nylon-6,6 salt, a combination of adipic acid and hexamethylenediamine in water they are the batch or autoclave process and the continuous polymerisation process. The third, the soHd-phase polymerisation process, starts with low molecular weight pellets usually made via the autoclave process, and continues to build the molecular weight of the polymer in a heated inert gas, the temperature of which never reaches the melting point of the polymer.  [c.233]

The SPP process has the advantage of being able to produce polymer of very high molecular weight without increasing the thermal degradation of the polymer. Although this is useful for nylon-6,6, it can be essential for other types of polyamides that caimot be processed in the melt phase owing to thermal degradation, eg, many aromatic-containing polyamides. Unfortunately, this is done at the cost of long holdup times in the continuous process or a slow processing step in batch processing. In addition, thermooxidative damage is always increased in the polymer along with the accompanying increase in yellow color, because oxygen can never be completely excluded from the reactor at a practical cost. Another disadvantage is the additional capital investment above that needed for autoclaves or CP units.  [c.233]

Ingredients. Nylon-6 is produced commercially from caprolactam [105-60-2] which is the most important lactam industrially. AH industrial production processes for caprolactam are multistep and produce ammonium sulfate [7783-20-2] or other by-products. Approximately 95% of the world s caprolactam is produced from cyclohexanone oxime [100-64-1] via the Beckmann rearrangement (144). The starting material for cyclohexanone can be  [c.233]

Polymer Production. Commercially the ring-opening polymerization of caprolactam to nylon-6 is accompHshed by both the hydrolytic and anionic mechanisms. However, the hydrolytic process is by far the most predominantiy used method because it is easier to control and better adapted for large-scale production. Like nylon-6,6, the polymerization process for nylon-6 via the hydrolytic mechanism can be batch or continuous however, the processes for the two polymers are significantly different. The hydrolytic process for nylon-6 contains the foUowiag steps caprolactam and additives addition, hydrolysis, addition, condensation, pelletizing (for remelt processiag), leaching/extraction of monomers, drying, and packagiag (for pellet sales) (147). Caprolactam is usually handled as a molten Hquid because its melting poiat is 69°C and it can be melted with hot water. Increasiagly caprolactam is being shipped as a molten Hquid vs a dried soHd for ease of handling. When deUvered as a soHd, it is melted and fed iato the first step of the process as a hquid.  [c.234]

Finally, there are significant differences in polymer production. Nylon-6 requires the extraction of caprolactam and other oligomers, which increases the capital investment as well as operating costs in polymerization. On the other hand, nylon-6,6 is plagued with a propensity to branch and gel when exposed to the required higher processing temperatures for extended periods of time. Proper management of gel deposits in nylon-6,6 manufacturing and processing steps in order to maintain high polymer quaUty requires skill and experience, which undoubtedly adds to its overall costs. Finally, nylon-6,6 can be readily processed from ingredients to final polymer in 2 h, whereas nylon-6 takes 12—24 h.  [c.235]

The use of preformed pellets of uniform size is important because the rate of soHd-phase polymerization and thus the uniformity of the degree of polymerization is dependent on particle size. This is especially important for nylon-4,6 because the polymer is not held in the melt long enough for transamidation to estabUsh a uniform molecular weight distribution, owing to the sensitivity of nylon-4,6 to thermal degradation. The excess diamine is removed from the nitrogen stream and recycled. The pellets of high molecular weight nylon-4,6 exit the soHd-phase reactor and are cooled and stored under nitrogen. Although this manufacturing process effectively minimizes any thermal degradation damage during polymer production, downstream melt-processing, such as injection mol ding or fiber spinning, requires increased care over what is necessary for nylon-6 or nylon-6,6, so as to avoid extended periods in the melt where further degradation damage could occur.  [c.235]

The usual starting materials for type AABB polyamides, diamines, and diacids or diacid chlorides, are hazardous materials because they are moderate-to-strong bases, acids, or highly reactive chemicals, respectively. However, there is rarely any detectable starting material in type AABB polyamides. The common starting materials for type AB polyamides, lactams, or aminoacids are generally less hazardous but can be present in the final products. The most significant case is the relatively high concentration of caprolactam in nylon-6. Although caprolactam can be an eye, skin, and respiratory irritant, this is rarely a problem in the final product where the concentrations are kept low (<2-3%) and the lactam is well below its melting point. Mechanical and thermal processing can generate higher levels of caprolactam in the air from nylon-6 or its copolymers and create dust from most polyamides, which can act as irritants and which are usually monitored and corrected in the workplace.  [c.240]

Environmental Aspects. In general, the polymerization processes for nylon-6,6 and nylon-6 generate Htde waste. However, because of economic advantages and governmental regulations, there has been a substantial increase in recycling of the starting materials for polyamides, especially hexamethylenediamine, caprolactam, and water and of the energy, most often as steam. The hexamethylenediamine and caprolactam are usually emitted as vapors during the polymerization process along with steam and can be condensed, purified, and reused. The caprolactam extracted from the finished polymer, usually in aqueous solution, is also recycled in a similar manner.  [c.240]

Molecular chains in a polyamide fiber are held in specific stmctural configurations by weak van der Waal and strong intermolecular hydrogen bonding forces between amide groups. An increase in the number of amide bonds raises the melting point in a homologous series as shown with AB and AABB polyamides in Eigure 1. Nylon-6 and nylon-6,6 are isomers that share the same empirical formula, C H NO density, 1.14 gm /cm refractive index n ]), 1.530 (unoriented fiber) and many other properties (24). However, they differ in melting point by 40°C because of differences in the alignment of molecular chains and crystallization behavior (23). These parameters are important in fiber formation in melt spinning, but are not as significant as the glass-transition temperature, T, in the downstream processing of the fiber into a specific end use article (25). The T, which signifies a transition from a glassy to a mbbery state, plays a role in the drawing, texturing, and dyeing of a fiber. By controlling melt spinning and downstream processing, the fiber properties of both nylon types can be adjusted to accommodate a variety of end use performance requirements.  [c.246]

An organic chemist can learn most from Nature. Detailed knowledge of biological molecules and processes is an essential prerequisite for this teaming process. An organic chemist nowadays, however, profits most from moving beyond Nature towards artiflcial analogues. This has been valuable for the development of synthetic reagents (e.g., metal complex catalysts instead of metalloproteins) and of industrial and academic target molecules (e. g., nylon instead of protein fibers, crown-type ligands instead of natural ion carriers). At the present time, the details of the architectures of cell membranes, proteins, and nucleic acids are elucidated by electron microscopy, crystal structure analysis, molecular biology, and modem spectroscopic methods. Attempts are then made to understand the construction principles and to apply them in syntheses of molecular systems or of supramolecules which arc held together by weak intermolecular forces. Alternatively, organic chemistry may be combined with biochemical expertise and computer-aided molecular modelling. In general it turns out, that with simple, repetitive reaction sequences and well-planned or luckily discovered self-assembly processes, molecular buildings and chemical machineries of astounding complexity may be synthesized on often surprisingly large scales.  [c.341]

Adiponitrile Synthesis. 1,6-Hexanediarnine, the second ingredient in the production of nylon-6,6 polyamide, is prepared by hydrogenation of adiponitrile [111-69-3J. In several large plants around the world, the nitrile is produced from adipic acid by dehydration of the ammonium salt. A significant percentage of adipic acid capacity in Western Europe currently is used for this purpose. The technology has been reviewed in the Hterature (196). Although this was the primary adiponitrile process for several years, new processes based on propylene and butadiene have supplanted this technology in the United States. Eor several years, Du Pont operated a process based on the chlorination and cyanation of butadiene, but this was shut down in 1983 (197,198). Du Pont produces adiponitrile at two large U.S. plants and one Erench joint venture by direct nickel(0)-catalyzed homogeneous hydrocyanation of butadiene (199). Monsanto and Asahi developed and practiced the electrolytic coupling of acrylonitrile process, used in the United States, Western Europe, and Japan (200,201).  [c.247]

The cross-sectional shape of fibers is an important characteristic that influences many end use properties. The cross-sectional shape of cotton fibers is essentially that of a flat ribbon, although there are cotton fibers that have circular cross sections. Wool fibers are eUiptical in shape, although again nearly circular shapes can be found. The earlier synthetic fibers were generally circular in cross-sectional shape, but it is now possible to produce fibers with modified cross sections. This is accomptished by designing the shape of the spinneret orifice used in melt spinning. Fibers (primarily nylon, polyester, and polypropylene) can be produced with ttilobal, multilobal, flat, triangular, and a variety of other shapes. These fibers have special optical effects, and are also useful in modifying mechanical properties of textile products. HoUow fibers can also be produced by special fiber extmsion processes.  [c.268]

Until the mid-1970s, acryhc fiber in 17—22 dtex (15 to 20 den) form was a primary competitor in the carpet market. Strict flammabihty regulations put in effect during this period provided the impetus for the development of flame-resistant acryhcs and modacryhcs. Fibers with high levels of vinyl chloride, vinyl bromide, or vinyhdene chloride were developed to pass government tests, such as the tunnel test and the methenamine pill test. These acryhc and modacryhc carpet fibers allow exceptional versatihty in styling and color patterns. Although acryhc carpets can also be superior to nylon aesthetically, dense and expensive constmctions are requited to match the pile height and durabihty of nylon carpets. In less dense constmctions acryhc carpets can develop wear patterns and lose resihence and pile height in the dye bath or in service under hot humid conditions. The carpet market is dominated by nylon staple fiber in the 1990s. A small market stiU exists in the United States and Europe in Japan acryhc carpets are stiU relatively popular. Numerous studies have been made to find ways of improving hot—wet and durabihty properties of acryhc carpet fibers. Fiber density and fibrillar stmcture can be improved by using modified compositions and spinning processes for high abrasion resistance. Producer dyed fibers and blends of acryhc and nylon have been developed to improve hot—wet performance.  [c.283]

The removal of particles that would block the spinneret holes occurs in several stages. The traditional plate-and-frame first-filters dressed with disposable multilayers chosen from woven cotton, cotton wadding, or wood pulp have now been replaced by durable nylon needlefelts that can be cleaned by automatic backwashing (17). Second filtration, usually after deaeration, is also changing to fully automatic systems with sintered steel elements that do not need manual cleaning. Third-stage filtration, close to the spinning machines, is used to provide a final polishing of viscose quaUty, but is only justifiable for the premium quaUty fibers. AH processes nevertheless use small filters in each spinneret to catch any particulate matter which may have eluded, or been formed after, the main filter systems.  [c.347]

Lead nitrate is used in many industrial processes, ranging from ore processing to pyrotechnics (qv) to photothermography. Thus lead nitrate is used as a flotation agent in titanium removal from clays (92) in electrolytic refining of lead (93) in rayon delustering (94) in red lead manufacture (95) in matches, pyrotechnics, and explosives (96) as a heat stabilizer in nylon (97) as a coating on paper for photothermography (98) as an esterification catalyst for polyesters (99) as a rodenticide (see Pesticides) (100) as an electroluminescent mixture with zinc sulfide (101) as a means of electrodepositing lead dioxide coatings on nickel anodes (102) and as a means of recovering precious metals from cyanide solutions (103).  [c.70]

Shordy after the commercial introduction of nylon, Wodd War 11 began and most of the nylon produced was used for military purposes such as in ropes, parachutes, and tires. After the war, nylon production expanded rapidly, first into the apparel and tire markets, and then into carpets and plastic parts. During the following three decades (1950—1980), numerous technical developments were achieved to provide increased nylon capacity and cost effectiveness. These include the development of intermediates production from petroleum-based feedstocks the invention of the continuous polymerisa tion (CP) and soHd-phase polymerisa tion (SPP) processes coupled dra w-spinning and the invention of interlace to replace twisting of the fiber bundle and the invention of numerous additives to improve the performance of nylon in special end uses, such as thermal and photostabiLisers and mbber tougheners. This development of technology continues where high productivity—low cost, intensely competitive worldwide markets, and environmental friendliness are key factors driving the development of the polymer industry.  [c.219]

Figure 2 shows the unit cell for nylon-6,6, and Table 8 presents the crystaHographic constants for several polyamides. The semicrystalline nature of polyamides and their high melting point ate generally attributed to the high degree of hydrogen bonding between adjacent chains in the crystals. The apparent crystal size in polyamides has been determined by wide-angle x-ray scattering (waxs) (20) and small-angle x-ray scattering (saxs) (21). The average size depends on the mechanical and thermal history of the polymer, and in commercial samples it is typically 5—7 nm on each side, but the size disttibution is very broad. Chain-folded lameUat, single crystals of polyamides have been formed from dilute solution (22) and from the melt (23). It is generally accepted that such lamellar stmctures ate present as crystaUites in isotropic samples (24), though extended chain crystals may be formed in highly oriented systems such as fibers. The crystaUites can form ordered three-dimensional superstmctures called spheruHtes which ate detectable by optical microscopy using polarized light. In drawn fibers and films the crystaUites as well as the polymer chains in the amorphous regions ate preferentially oriented in the direction of the appHed strain. The large-scale stmcture in bulk polyamides is usually unoriented and spheruHtic, though some orientation can occur at the surface and elsewhere in the polymer where stresses were induced by flow during melt processing such as injection mol ding. A comprehensive review of crystallinity and stmcture in polyamides has been pubflshed (25), and extensive crystaHographic data ate also available (26).  [c.220]

Photodegradative Processes. Polymers can undergo two types of photodegradative processes one in the presence of oxygen, photooxidation, and one in its absence, photodegradation. Additive-free, noncontaminated nylons appear to have only one significant chromophore in the uv-visible region, a strong, log e > 4.0, at approximately 185 nm, which is assigned to the tt — tt transition of the amide group. There may also be a much weaker n — tt at slightly longer wavelengths, but its presence is usually masked by absorption resulting from thermooxidative impurities or the carbonyl absorption of the acid ends. The strongly forbidden ground singlet state to first excited triplet state absorption, Sq — Tj, can He as low as 285 nm, based on low temperature phosphorescence excitation—emission spectra of model alkyl-bis(hexanamides) (102). A weak, predominantiy continuum absorption by the thermooxidative degradation products occurs from about 235 to at least 400 nm, where they are the primary source of yeUow color in polyamides. Thermal degradation products can also show a continuum-like absorption in this region however, nylon-6,6 shows a weak but discernible absorption peak at 290 nm (103) which has been assigned to the foUowing chromophore (104)  [c.229]

Batch processiag of nylon-6 is generally used only for the production of specialty polymers such as very high molecular weight polymer or master batch polymers for special additives. In a typical modem batch process (147—150), the caprolactam is mixed ia a hoi ding tank with the desired additives and then charged to an autoclave with a small amount (2—4%) of water. During the two-stage polymeriza tion cycle, the temperature is raised from 80 to 260°C. In the first stage, water is held ia the reactor, the pressure rises, and the hydrolysis and addition steps occur. After a predetermined time the pressure is releasedand the final condensation reaction step occurs. The molecular weight of the polymer can be iacreased by means of a vacuum finishing step, if desired. The entire process can take three to five hours. The final polymer is then drained, often with a forcing pressure of iaert gas, through a die to form ribbons of polymer, which are then cooled ia water and cut iato pellets. Because nylon-6 has such a high monomer and oligomer content, 10—12% by weight, ia the cast pellets, which would significantly reduce the quaUty of the final fiber or resia products, it must be extracted. This is usually done ia hot water under pressure at 105—120°C for 8—20 h. Most of the caprolactam and higher oligomers that are released with the steam from the autoclave or extracted from the pellets ia hot water are then recycled. The pellets must be carefully dried because excess water decreases the molecular weight of the polymer duting subsequent melt processiag. The fiaal polymer processed through water extractioa and drying can have an oligomer level of <0.2% and a moisture level of <0.05%. Alow level of total oligomers is necessary because on remelting and further processiag, the oligomers coateat will iacrease owiag to the reestabUshmeat of the equiUbrium distributioa of molecular species that occurs for all coadeasatioa polymers (151). Because the approach to equihbrium progresses at a moderate rate, it is possible to utilize extracted ayloa-6 ia a remelt process without increasing the oligomer coaceatratioa above 2—3% and thus avoiding any significant drop ia fiaal properties.  [c.234]

Table 9 shows the similarity of properties however, a few differences between the two polyamides do exist in melting point, in ingredients preparation, and in polymer manufacturing. The melting point of nylon-6,6 is about 40°C higher than that for nylon-6. This is an advantage for nylon-6,6 in those end uses where high temperature performance is required, such as under-the-hood appHcations for automobiles, high speed thermal processing of fibers and films, and high temperature fatigue resistance in industrial tire cords (qv). On the other hand, the lower processing temperatures for nylon-6 result in slightly lower energy costs and could potentially permit the use of some additives which would decompose at the higher temperatures necessary for processing nylon-6,6. Nylon-6 appears to have a definite advantage in ingredients preparation because it requires the capital investment and handling costs for only one monomer, whereas nylon-6,6 requires the same for two monomers. However, the added cost of ammonium sulfate production, handling, and sales increases the cost of caprolactam production. Also hexamethylenediamine is increasingly being made from three- or four-carbon petroleum-based hydrocarbons vs higher cost six-carbon feedstocks for caprolactam (and adipic acid). In general, the nylon-6,6 ingredients are made in very large plants by a few producers, which allows for substantial economy-of-scale. This has an unexpected consequence for the relative growth of the two polymers. Although caprolactam and adipic acid are commodity chemicals, hexamethylenedi amine is not, since almost its entire world production is consumed internally to produce nylon-6,6. Thus nylon-6 can be made from its monomer, purchased on the open market without the investment in an ingredients faciUty, whereas nylon-6,6 caimot. This probably accounts for the growth of nylon-6 in such developing areas as Asia/Paciftc.  [c.235]

Nylon-6,9, Nylon-6,10, and Nylon-6,12. These related polyamides ate produced in a process similar to that used for nylon-6,6, where a salt of hexamethylenediamine and the appropriate diacid is formed in water. The solution is heated in an autoclave until polymerisation is complete. Processing times, pressures, and temperatures are adjusted for the slightly different melting points and viscosities of these polymers. Because of the lower melting points, ie, nylon-6,9 (T = 210° (7), nylon-6,10 (T = 220 (7), and nylon-6,12 (T = 212" (7), and the perhaps greater chemical stabihty of the diacids, these polymers generally experience less thermal degradation in processing than nylon-6,6. They ate generally used as engineering resins for specialty appHcations where reduced moisture regain and chemical resistance are important. Nylon-6,12 [24936-74-1] and its copolymers are also used in the manufacture of toothbmsh btisties and fishing line.  [c.236]

The diacids for these polymers are prepared via different processes. A2elaic acid [123-99-9] for nylon-6,9 [28757-63-3] is generally produced from naturally occurring fatty acids via oxidative cleavage of a double bond in the 9-position, eg, from oleic acid [112-80-1]  [c.236]

An emerging development is the introduction of high temperature polyamide resins for automotive, under-the-hood use and in some electrical end uses, such as cores for transformer windings. At first glance, nylon-6,T appears to be an excellent candidate, because it has a very high melting point (365°C) and its components, hexamethylenediamine and terephthaUc acid, are low in cost and readily available. However, its high melting point requires even higher processing temperatures, which in turn lead to substantial thermal degradation. The attempt to produce copolymers with nylon-6 or nylon-6,6 in a melt process is thwarted by the formation of macroscopic portions of high melting blocks of nylon-6,T that can act as nucleating agents for sphemUte (microscopic particles) formation, as particulate contamination (visible particles), and as nonmelting reactor fouling (bulk material). In addition, when nylon-6,6 is blended with nylon-6,T, the required higher processing temperatures accelerate the rate of branching and gel formation to such an extent that the process is inoperable above 300°C. Since nylon-6,T and nylon-6,6 are isomorphic, they maintain a high degree of crystallinity in the copolymer, but when nylon-6 is used, its copolymer with nylon-6,T demonstrates the usual eutectic-like drop in melting point. Thus, a high ratio of nylon-6,T to nylon-6 is required to attain a significant increase in melting point. At high ratios, the copolymer can lose much of its crystallinity, but at a lower ratio it is stiU semicrystalline, and a satisfactory nylon-6,T/6 copolymer has been introduced by BASF. Amoco has introduced a proprietary process that allows the production of terephthaUc acid-based copolymers which also contain isophthaUc acid (192). These materials have been named polyphthalamides and show many desirable properties, such as a high melting point, high T, and low moisture regain (193).  [c.238]

Polymer recycle has been practiced as part of the manufacturing process for nylon-6,6 (219) and nylon-6 (220) almost from the beginning of the iadustry. Acid hydrolysis by Du Pont and base hydrolysis by BASF and Rhc ne-Poulenc of relatively pure nylon-6,6 waste streams, followed by separation of iagredients, purification, and reuse, has been practiced for many years. Also, phosphoric acid-cataly2ed hydrolysis and steam distillation of caprolactam from pure nylon-6 is still used by BASF, Rhc ne-Poulenc, and SNIA. However, it is the challenge of recycling post-consumer waste that has generated the greatest activity siace 1990. Stimulated by more stringent governmental regulations for recycling plastic packagiag and automotive plastic components la Germany and the growing landfill problem ia the United States, the nylon iadustry has developed several technologies to address the issue of recycling post-consumer waste. One of the greatest economic challenges is the collection and separation of nylon from other wastes, including other polymers. The ultimate solution to this problem may await the development of a cost-effective waste handling iafrastmcture for all recycled materials, at which poiat relatively pure, high volume, low cost, post-consumer nylon will become available. Recycled nylon carpets constitute the largest single supply of potentially recyclable nylon. A patent has appeared for the preparation of a thermoplastic composite by remelting all the components of a nylon carpet and forming it iato bulk plastic parts (221). Unfortunately, because of the thermo- and photooxidative products formed ia nylon during manufacture and use, and the thermal degradation and thermooxidative products formed during further melt processiag, any direct remelt processiag of nylon results ia a low grade product, even with the use of currentiy available thermal stabilizers. Other approaches have focused on depolymerization and separation of the iagredients. Several patents and articles have appeared regarding the recovery of caprolactam from post-consumer waste nylon-6 via hydrolysis (222) or polymer pyrolysis (223), and the recovery of polymer via solvent dissolution of nylon-6 from nonpolyamide contamination (224) however, these technologies are limited to waste streams that contain nylon-6 as the only polyamide. In particular, nylon-6,6 significantly iaterferes with these processes. Several technologies have appeared which attempt to separate nylon-6,6 and nylon-6, and convert them simultaneously to usehil monomers (225,226). The most promising technology to date appears to be the ammonolysis of nylon-6,6—nylon-6 mixtures, which converts all three iagredients to bexametbylenedi amine (227,228).  [c.241]

See pages that mention the term Nylon processing : [c.475]    [c.507]    [c.875]    [c.906]    [c.274]    [c.155]    [c.226]   
Plastics materials (1999) -- [ c.500 , c.501 , c.505 ]