Polymer float-sink

Stage I - Dried chips from a mechanical, density based, float-sink system (such as the Rutgers BBRP process) are fed in, where they are washed with the process solvent at a temperature sufficient to remove insoluble impurities (up to 130 C), but insufficient to dissolve the intended polymer. For example, in the PET train, this washing will remove any adhesives, PS or PVC which may be present from use in 2 liter bottles or from sortation error. 

A carpet separation process is illustrated in Fig. 13.1. First the carpet is sorted by face fiber. A near infrared sensor can identify the face fiber within a second even though nylon 6 and nylon 66 have similar infrared spectra. These two types of nylon carpet must be separated since they are incompatible. Next a guillotine is used to cut the carpet into small enough pieces to feed a shredder. After shredding some of the latex, calcium carbonate and dirt will separate from the carpet. To improve the purity of the carpet, fine grinding is necessary. Then a density separator can be used to remove more filler and dirt. Since there is a significant difference in the densities of nylon and polypropylene, a density separator can be used to separate nylon face fibers from polypropylene backing fabrics. Hydrocyclones can separate these polymers rapidly. Sink-float baths can accomplish this... 

Polyperfluorohexane-coated sulfur floats on ethylene glycol for hours, whereas sulfur samples coated with the other two polymers sink after minutes, especially acrylic-acid-coated sulfur. As the surface energy of sulfur after encapsulation with a plasma polymer is brought closer to those of the rubbers, better compatibility with these rubbers is to be expected. 

If a 2-liter bottle waste is assumed to be compose of 70 wt% PET and 30 wt% HDPE and this waste is exposed to NMP at 175°C for 30 minutes followed by flotation/sedimentation, filtration, and precipitation, the resulting polymer would be 99.91 wt% PET. If the NMP treatn nt had been preceded by a sink-float stage capable... 

Magnetic fluids can be used as a high-density solution for the sink-and-float separation of solids in suspension. This separation technique for non-ferrous metals is based on the anomalous viscosity increase of a magnetic suspension as a function of applied field. The magnetic fluid consists typically of magnetite particles with an average diameter of 100 A in water, with 15-25 wt% of ferrite. To prevent particle aggregation, a surfactant such as kerosene and oleic acid, or a polymer is usually... 

Three methods are common, viz, the liquid displacement method, the sink-float method and the density gradient column method. Each of these is a common, standard technique and is fully described in ISO 10119, 1992 (for the determination of the density of carbon fiber), and also in ASTM D 276-87 (reapproved in 1993), which in fact also refers to ASTM D 1505, ASTM D 792, and AATCC, Method 20 (1990) (Fiber identification), each of which deals with the above techniques. ISO 10119 is a very good and concise description of the techniques. However the measurement liquids specified in ISO 10119 of ethanol, methanol, acetone, tricloroethane, and carbon tetrachloride, although suitable for carbon fibers, are not at all suitable for the general range of textile polymers, with the exception perhaps of ethanol and methanol. ASTM D 276 87 recommends the use of / -Heptane for universal application, except, of course for the olefins, such as polyethylene. A range of typical fiber densities is given in Table 4. 

Furthermore, various acid-promoted reactions proceed to give the desired products in high yields by passing a solution of reactants through a reaction column packed with (2) and Celite (eqs 12-14). The polymer catalyst can be isolated from a mixture of (2) and Celite based on the difference in their specific gravity while (2) floats on water, Celite sinks. 

Several wash-sink/float processes are in use and readily available for secondary recycling operations and, in addition to the action of water and detergents, function on the basis that polyolefins float inwater and most contamination and other polymers sink. Wash granulators which combine comminution and washing are also available. 

Polyhydroxyalkanoates (PHAs) are also biodegradable polymers. These are condensation polymers of 3-hydroxycarboxyhc acids. Thus, like PLA, they are polyesters. The most common PHA is PHB, a polymer of 3-hydroxybutyric acid it can be used for many of the things that polypropylene is now used for. Unlike polypropylene that floats, PHB sinks. PHBV, a PHA marketed under the trade name Biopol, is a copolymer of 3-hydroxybutyric acid and 3-hydrox5rvaleric acid. It is being used for such things as wastepaper baskets, toothbrush holders, and soap dispensers. PHAs are degraded by bacteria to CO2 and H2O. 

The polyolefin fractions (PP, LDPE, HDPE) all have densities below 1 g/cm. This allows a process called float-and-sink to be used to separate them from the other polymer fractions. Separation is carried out in a flotation tank using water as the separation medium. 

Processes have been developed to separate the mixed plastics in the waste. The simplest of these is a sink-float scheme that takes advantage of density differences among various plastics. Unfortunately, many plastic items are foamed, plated, or filled (mixed with nonpolymer components), which complicates density-based separations. Other separation processes are based on solubility differences between various polymers. An intermediate approach chemically degrades the waste polymer to the starting materials from which new... 

Typical data shown in Tables 6 and 7 for an E-CO and a corresponding LDPE homo-polymer, demonstrates the similarities between the two resins. In appearance, as film or extruded items, they are also seemingly identical. It is now known that the C=0 groups fit into the PE crystal lattice and hence have little effect on the overall crystallinity. However, E-CO density increases with increases in CO content. It has been noted that at around 16 % CO, E-CO will not float in fresh water, and at about 20% CO, the copolymer will sink in salt water. For rapid photodegradability of marine litter, those CO levels are the upper limitations to assure exposure to the light necessary for photodegradation. 

Once a mixture of plastics is reduced to chips on the order of 0.6 cm in diameter, liquids with intermediate densities can be used to differentiate polymers, assuming that the polymers do not contain fillers that alter their density. A mixture of the six plastics listed in Table 15.6 can be separated into two groups using water. The polyolefins (numbers 2,4, and 5) will float and the others (numbers 1, 3, and 6) will sink. 

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