High-temperature processing nylon

Unlike the high-temperature process where about 8 to 10% cyclics are generated, the equilibrium monomer content of nylon 6 resulting from polymerization at temperature lower than 200 C (i.e., low-temperature polymerization) can be less than 2%. The polymer therefore does not usually require any additional purification. Also, the maximum rate of crystallization of rylon 6 falls within the range of... 

New Product Technical Bulletin NP-31, Properties and Processing of Nomex High Temperature Resistant Nylon Paper, E.I. du Pont de Nemours Co. Inc., 1964. 

The result of elemental analysis of PVA oxidized by KMn04 indicates the presence of 1.5% of Mn remaining in this polymeric structure [212], Thus, we suggest that this catalytical amount of chelated Mn-structure incorporated in the polymer may provide the rapid high-temperature process of carbonization and formation of char. The fire tests at 50 kW/m for Nylon 6,6 and PVA(80 20%) compositions are shown in Table 5.2. 

The by-product of this process, pelargonic acid [112-05-0] is also an item of commerce. The usual source of sebacic acid [111-20-6] for nylon-6,10 [9008-66-6] is also from a natural product, ticinoleic acid [141-22-0] (12-hydroxyoleic acid), isolated from castor oil [8001-79-4]. The acid reacts with excess sodium or potassium hydroxide at high temperatures (250—275°C) to produce sebacic acid and 2-octanol [123-96-6] (166) by cleavage at the 9,10-unsaturated position. The manufacture of dodecanedioic acid [693-23-2] for nylon-6,12 begins with the catalytic trimerization of butadiene to make cyclododecatriene [4904-61-4] followed by reduction to cyclododecane [294-62-2] (see Butadiene). The cyclododecane is oxidatively cleaved to dodecanedioic acid in a process similar to that used in adipic acid production. 

Oxidation. AH polyamides are susceptible to oxidation. This involves the initial formation of a free radical on the carbon alpha to the NH group, which reacts to form a peroxy radical with subsequent chain reactions leading to chain scission and yellowing. As soon as molten nylon is exposed to air it starts to discolor and continues to oxidize until it is cooled to below 60°C. It is important, therefore, to minimize the exposure of hot nylon to air to avoid discoloration or loss of molecular weight. Similarly, nylon parts exposed to high temperature in air lose their properties with time as a result of oxidation. This process can be minimized by using material containing stabilizer additives. 

However, some semiaromatic nylons can give problems as a result of the high melt viscosity. A process for produciag polymers of hexamethylenediamine, adipic acid, terephthaUc acid, and isophthaUc acid has been developed, which iavolves vaporising the salt mixture ia a high temperature flash reactor followed by molecular weight iacrease ia a twia-screw extmder with efficient moisture removal (17). 

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). 

A method for the depolymerisation of PETP fibres using quarternary ammonium salt phase transfer catalysts in saponification processes at atmospheric pressure and temperatures as low as room temperature is reported. Terephthalic acid was produced in yields as high as 93%. Also reported are similar processes for the depolymerisation of nylon 66 and nylon 46 fibres. Nylon 46 oligomers produced were repolymerised using solid-state polymerisation to produce high molecular weight nylon 46. Nylon 66 was depolymerised to produce oligomers and adipic acid in reasonable yields. 11 refs. USA... 

TPEs prepared from rubber-plastic blends usually show poor high-temperature properties. This problem could be solved by using high-melting plastics like polyamides and polyesters. But, often they impart processing problems to the blends. Jha and Bhowmick [49] and Jha et al. [50] have reported the development and properties of novel heat and oil-resistant TPEs from reactive blends of nylon-6 and acrylate rubber (ACM). The properties of various thermoplastic compositions are shown in Table 5.4. In this kind of blend, the plastic phase forms the continuous phase, whereas... 

The development of resins, plastics, fibers, elastomers, etc. that 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. 

Homolytic liquid-phase processes are generally well suited to the synthesis of carboxylic acids, viz. acetic, benzoic or terephthalic acids which are resistant to further oxidation. These processes operate at high temperature (150-250°C) and generally use soluble cobalt or manganese salts as the main catalyst components. High conversions and selectivities are usually obtained with methyl-substituted aromatic hydrocarbons such as toluene and xylenes.95,96 The cobalt-catalyzed oxidation of cyclohexane by air to a cyclohexanol-cyclohexanone mixture is a very important industrial process since these products are intermediates in the manufacture of adipic acid (for nylon 6,6) and caprolactam (nylon 6). However, the conversion is limited to ca. 10% in order to prevent consecutive oxidations, with roughly 70% selectivity.97... 

If one were to choose more reactive monomers, it would be possible to carry out polycondensations at considerably lower temperatures in solution. For example, consider the reaction of a diamine and a diacid to make a polyamide (nylon), a polymerization that requires relatively high temperatures (see Equation 9). A much faster reaction would occur between the diamine and a corresponding diacid chloride (see Equation 10). Both reactions would produce the same polymer, although the reaction conditions would be much different, and the byproduct HC1 from the acid chloride reaction would have to be carefully trapped. One technique for performing a polymerization such as that in Equation 10 is to dissolve the monomers in different, immiscible solvents, forcing the polymerization to occur only at the interface of the two solvents, a process called interfacial polymerization. Because of the high reactivity of an acid chloride, these reactions can be carried out at very low temperatures. This polymerization can be carried out rather dramatically in a beaker and is known as the nylon rope trick (see Section 4). 

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