Nylon separation methods

The problem of carpet recycling is considered and the different methods being proposed or commercially utilised are discussed. The main component of the carpet waste is fibres of nylon-6 and nylon-66. The review of the literature includes a limited amount of journal publications, which focus primarily on fundamental aspects, and a large number of patents, which describe the available technologies. The most promising recycling techniques (depolymerisation, extraction, melt blending and mechanical separation) are described. 48 refs. 

Filters. HN03 is efficiently trapped out on nylon filters. Typically, two or more filters are connected in series. A schematic of such a filter pack was shown in Fig. 11.22 (Anlauf et al., 1988). A Teflon filter first removes particles from the airstream and a nylon filter then removes gaseous HNO,. In this particular system, a third filter (Whatman 41 impregnated with an aqueous solution of glycerol and citric acid) was used to trap NH3. After sample collection, each of the filters is extracted separately and nitrate, ammonium, and additional particle components collected on the Teflon filter are measured by ion chromatography. The sensitivity of this method for nitric acid and the other species is determined in part by filter blank values (i.e., nitrate on unexposed filters) and by the total amount collected and hence the sampling time used. Times of... 

Another variant of the hybridization assay is the Northern blot. Here it is RNA, not DNA, that is separated on a slab gel and transferred to a membrane. In the original version of the method, a special chemically treated cellulose membrane was used to hold the RNA, since nitrocellulose does not normally bind RNA. However, conditions have now been found where nitrocellulose will indeed retain RNA molecules. Nylon membranes can also be used. Radiolabeled DNA probes and autoradiography are then employed as above in the Southern blot method. The method is often useful in studying how levels of RNA species in a cell vary with stages of development and differentiation. 

Reverse osmosis is nsed as a method of desalting seawater, recovering wastewater from paper mill operations, pollution control, industrial water treatment, chemical separations, and food processing. This method involves application of pressure to the surface of a saline solution, thus forcing pure water to pass from the solution through a membrane that is too dense to permit passage of sodium and chlorine ions. Hollow fibers of cellulose acetate or nylon are used as membranes, since their large surface area offers more efficient separation. 

Steuerle and HUle (1959) and Hille (1960) developed a method for the quantitative determination of the N-terminal residues normally present in wool. After treatment with l-fluoro-2,4-dinitrobenzene the wool is hydrolyzed and the ether-soluble DNP derivatives applied to a column of nylon 66 powder and developed with phosphate buffer at 60°C. The DNP derivatives of aspartic acid, glutamic acid, serine, threonine, glycine, alanine, and valine separate cleanly and can be readily determined in the eluates. Hence, it is well suited to the determination of N-terminal residues in normal animal fibers. In its present form, however, it is not suitable for general use with proteins or modified wool fibers as some DNP derivatives, such as those incorporating two DNP groups, are bound so strongly by the nylon that they cannot be eluted. 

Bicomponent fibres are sjmthetic fibres composed of two firmly but separately combined polymers of different chemical and physical structures. The structure of the bieomponent depends on the shape of the spinnerette orifice (side-by-side, sheath eore, matrix - fibril and multi-fibrillary) and the type of spinning method. Due to the structural differences, the two components shrink differently on heat treatment and form crimp and greater bulk in the fibre. The first fully synthetic bicomponent was an acrylic (Sayelle, Orion 21). The use of sheath-core fibres composed of nylon 6,6 and nylon 6 (Heterofil, ICI) for floor coverings is described. 

A convenient random-priming method is labeling on a nylon membrane. Template can be spotted on the membrane, but it is also possible to use DNA restriction fragments transferred after electrophoretic separation onto nylon membranes (Chapter 9). DNA fixed on nylon membranes can serve as a template and the unincorporated precursors can be removed by simple washing for 1-2 min. The probe is then eluted from the membrane in formamide or in water. These membrane-bound DNAs can be reused. The probes synthesized by this method are as efficient in detecting nucleic acid as those synthesized in solution (Bhat, 1990). Similar methods have been proposed earlier for the synthesis of ij DNA probes from M13 templates (Ashley and MacDonald, 1984 Hansen et al., 1987). 

Later, it was possible to improve substantially the separation of deuterated olefins. Atkinson et al. [67], for example, separated all ethylene isomers differing by one unit of mass. It was shown that the accuracy of the gas chromatographic analysis of deuterium-labelled ethylene isotopes is the same as that in the mass spectral method. Silver nitrate solution in ethylene glycol (5M), saturated at room temperature, was used as the stationary phase [67]. This solution was added to Chromosorb P (45—60 mesh) in the ratio of 1 4 and this mixture was mechanically stirred for 4 h. The sorbent obtained was packed into nylon tube sections of length 15 m and diameter 3 mm. A flame-ionization detector was used. 

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