Polymer waste, sorting

It would appear that the use of laser-aided polymer waste sorting [137] (eventually in combination with LIBS) and fluorescent tracer systems (cfr. Chp. 1.4.2) [152] are technologically the most attractive, with the latter technology more geared towards the identification of polymers than additives. 

Automatic polymer waste sorting plants based on NIR identification are operative (c/r. Chp. 1.2.2). For identification and sorting of carpets a portable NIR spectroscopic system - CarPID - was developed [139]. Other reported NIRS applications are to be found in the quantitative analysis of copolymers or blends the near-IR range allows for accurately monitoring of the monomer ratio and residual monomer content. Ikeda [140] used near-IR spec-trochemical analysis in controlled manufacture of polyester plasticisers. Jones et al. [141] similarly described the use of NIR analysis for controlling plasticiser ester formation the esterification of phthalic anhydride by isodecyl alcohol was exemplified. 

Successful material recycling is dependent upon the purity and uniformity of the plastics waste. The properties of the recycled material depend upon the history of the synthesised polymer, the primary processing and application, and finally the recovery methods/equipment. Sorted, single polymer waste exhibiting low... 

Is the waste sorted with respect to colour and polymers contained in it ... 

The separation in a hydrocyclone, which works based on the principle of sorting by a centrifugal force field, using density difference of the various pol5rmers is one possible solution/ Sometimes, prior to separation, it becomes necessary to clean the polymer waste to remove contamination like dirt, food, and paper. 

Tertiary or quaternary recycling, (recovery of chemicals or energy), should only be considered when other types of recycling are not economically or technologically feasible. In tertiary recycling, waste plastics are converted to either monomers or fuels or petrochemical feedstocks. Conversion to monomers by solvolytic methods is feasible for condensation polymers but often requires pure polymer streams. Sorting and cleaning of the waste stream increases the cost of the process. 

Principles and Characteristics Industry requires both technically sound and economic waste sorting processes. According to EC directives polymers containing cadmium e.g. as CdS pigments) or bromine (e.g. PBDE) need to be eliminated from the recycling process. 

In contrast to Raman and IR spectroscopy, only few chemical functionalities (CH, OH, and NH) have a signature in the NIR spectra. Thus, the use of NIR spectra as stmctural interpretation tool is strongly limited. For raw material control or discrimination purposes, however, such as the sorting of polymer waste into a selected numher of commodities (e.g., polyethylene, polypropylene, polystyrene, poly(ethylene ter-ephthalate) (PET), and poly(vinyl chloride) (Figure 51), qualitative chemometric evaluation techniques (such as principal component analysis (PCA)) can he applied. ... 

Identification and sorting of plastics in waste materials were reviewed [19,31]. Garbassi [32] has stressed the important role played by polymer analysis and characterisation in plastics recycling. 

It is generally known that to obtain pure fractions from a mixture of different plastics is a more expensive process than separation of simple clean polymers, in plant. Therefore, it is anticipated that the separation of a municipal mixed plastic waste should be the most challenging. In such a fraction, traces of foods, labels, dirt (size mm), solvents (alcohols, petrol etc.), metals, low molecular weight products of different origins etc. could be found. Some of the sorting methods used are listed in Table 1. 

Generally the whole polymer recycling policy has to consider the problem in a holistic way. A combination of recycling methods has to be considered and polymer recycling has to be viewed in conjunction with recycling of other waste type. Issues such as sorting of waste into various waste types as well as separation issues have still to be tested. 

Waste plastics composition varies with collection area, sorting methods and time period, moreover several waste constituent polymer types occur in various waste categories. Nevertheless each customary plastic material will be discussed only in one of the three waste group included in this chapter. 

The methods that will be dealt with here are those used to obtain hydrocarbon vapours from this first phase. The treatment of plastic wastes of all sorts by pyrolysis, being still in its early stages, workers keeping practised procedures confidential, and often protects them by patents. As a consequence, this chapter deals exhaustively only with the procedures that have been personally tested and developed by the author. The general principle of polyolefin waste pyrolysis consists of heating plastic materials in isolation to a sufficient temperature such that the polymers decompose into small hydrocarbon molecules. 

Bulk agents included mustard (bis-2-chloroethyl sulfide, 12 tonnes), lewisite (2-chlorovinyl-dichloro arsine, 2.5 tonnes) and nerve agents in the G- and V-classes (0.3 tonne). The scrap (400 tonnes) consisted mainly of several thousand empty, mustard-contaminated 210 drums and ordnance casings stored in open pits. All of the lewisite and some of the mustard and nerve agents were stored in 1 ton containers. Nerve agents were also stored in non-explosive ordnance, primarily 105 and 155 mm artillery shells. Mustard which had aged or had been thickened with polymers was also contained in non-explosive ordnance. The waste previously had been sorted by type, collected and stored at four remote, protected sites on the EPG. 

Only a small number of the investigations summarized in this review addresses the obvious practical concern of mixed plastics waste. Higher performance products with multiple polymeric layers, the use of additives, fillers and colorants, and the expense of sorting individual polymers for subsequent processing all demand resource recovery strategies capable of handling a complex mixture of... 

Incineration of engineering and domestic wastes of inhibited plastics is inefficient in terms of energy production and leads to contamination of the atmosphere by harmful combustion products. In addition, incineration requires thorough sorting of waste, which is uneconomic. According to statistical information [25], incineration of a ton of polymer scrap is twice as expensive as recycling and five times expensive as burial. To obtain official permission to build an incineration plant is in fact improbable in many countries in the world today. 

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