Recycling of polymers

One of the main causes of the high costs of recycling is sorting. It is essential to separate collected postconsumer waste in order to obtain plastics of one single type to feed the recycling process. The addition of chemical additives and new granular plastics can 

A NIR spectrometer system has been described based on optical fibres for absorption and reflexion measurements, an AOTF and a transputer system. It is able to detect 1,000 spectra per second and to identify 20 pieces per second (209). The identification system was implemented and tested for a real-world application of plastic identification in municipal solid waste. 

Automated sorting of post-consumer plastic waste was achieved using a combination of fixed-filter NIR and neural network data analysis. Rapid and reliable identification of polymers can be made. The effectiveness of the method was demonstrated for sorting PET, HDPE, and PVC (261). 

The composition of recycled HDPE/virgin PP blends prepared in a single-screw extruder have been monitored in-line at three different points by NIR (247). 

The suitability of Raman spectroscopy for computerised classification of post-consumer plastics was evaluated. Plastics investigated were PET, PP, PS, PVC, HDPE and LDPE. It was found that Raman spectroscopy could be used to identify both HDPE and LDPE (81). 

Recovery and reuse of synthetic polymers is by far the most acceptable way of dealing with the problem of waste. Items can rarely be reused as such but instead the polymers from which they are fabricated can be recycled. In principle, polymers can be recycled without any significant loss of their properties. For example, polycarbonate bottles can be recycled into automobile bumpers and then into articles for high performance housing. 

In America there are promising signs for certain polymers. For example, poly(ethylene terephthalate) drinks bottles can be cleaned and recycled to give an acceptable grade of PET resin in a process that is economically viable. The recycled polymer is used as carpet fibre, furniture stuffing, or insulation. Waste nylon can also be recycled profitably. 

The quantity of these materials is relatively small compared with the amount of waste high-density poly(ethylene) produced each year. Containers made from HDPE are widely used for detergents, oil, and antifreeze, and enormous amounts of material are used in disposable applications aimually. In principle recycled poly(ethylene) could be used for drain pipes, flower pots, dustbins, and plastic crates. The problem remains, however, that economics do not favour recycling of these polymers and in the absence of Government intervention little or nothing can be done to alter commercial attitudes towards recycling. 

One technical difficulty that does beset recycling is that in many applications a variety of polymers are employed together in a complex way. It therefore becomes essential to distinguish between the various types of polymer in order to separate them. One system proposed (but not yet introduced anywhere in the world) is for the individual polymer components of complex articles such as automobiles to be identified using computer-scannable bar codes on each individual polymer component. 

Recycling can include chemical recycling. This involves plastics waste being processed chemically, either by cracking or depolymerisation, to 

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The Committee of Recycling Technology. Recycling of polymer recycling, Tokyo Jpn. J. Publ. House, 121, 1982. 

The main methods for the recycling of polymer-based packaging wastes are ... 

The review is not meant to promote degradable plastics, but rather to highlight them as one possible route to a cleaner environment. In many applications, recycling of polymers or incineration of waste products may offer more protection to the environment. The final decision for any application requires careful deliberation and not emotional judgements. 

In analogy to the enzyme membrane reactors (EMRs) [8], a chemzyme membrane reactor (CMR) is used to retain a polymer-enlarged chemical catalyst of this kind. Tremendous progress could be made in the recycling of polymer-enlarged catalysts (Fig. 3.1.3) by employing different types of catalysts for both the enan-tioselective C-C bond formation and redox reactions. 

Recycling of polymers has become an important environmental issue. Not surprisingly, given its relatively high cost, such studies are underway on silicone elastomers as part of a general effort addressed to various types of elastomeric materials, including ones that are heavily filled with silica 208-211... 

Chemical recycling of polymers is an important target of modem society that consumes a great deal of petroleum-based polymeric materials. Although the chemical recycling of thermosetting polymers is also required, it is difficult because of their inherent insoluble and infusible properties. 

Professor Walter Kaminsky was bom 1941 in Hamburg and studied chemistry at the University of Hamburg. His thesis was in the field of metallocene chemistry and his habilitation in the field of recycling of polymers by pyrolysis. Since 1979, he has occupied the role of Full Professor of Technical and Macromolecular Chemistry at the University of Hamburg. 

Y. Sakata, Catalytic Degradation of Polyethylene and Polypropylene into Fuel Oil in Recycling of Polymers, J. Kabovec, ed., (Wiley-VCH, Weinheim Germany), pp 7-18 (1998). 

W. Kaminsky, M. Predel and A. Sadiki Feedstock Recycling of Polymers by Pyrolysis in a Fluidised Bed Reactor. Polym. Degrad. Stabil, 85, 1045 (2004). 

W. Kaminsky, Thermal recycling of polymers, J. Anal. Appl. Pyrolysis, 8, 439-448, (1985). 

After the first oil crisis in 1975, there was great interest in feedstock recycling of polymers to recover oil and gas from this hydrocarbon source. Another goal was to protect the environment from landfilling of plastic materials that decompose very slowly. 

F. Sasse and G. Emig, Chemical Recycling of Polymer Materials, Chem. Eng. Tech-nol, 21, 10 (1998). 

W. Kaminsky, Pyrolysis of Polymers, ACS Symposium Series, 513, 60-72 (1992). W. Kaminsky, Recycling of polymers by pyrolysis, Journai of Physique IV, 3, 1543-1552 (1993). 

PET is useful polymer used for fiber, film, and plastic containers such as carbonated beverage bottles. Recently, the recycling of polymers such as PET after use is attracting the attention of many researchers aware of environmental problems and wishing to find ways to save earth resources. Previous studies showed that unsaturated polyester resins can be economically prepared from recycled PET and the resins may be useful for resin concretes (1 4). However, there is little information on the molecular features of the UPE resins. Thus, we synthesized various UPE resins from PET. Especially, the PET content, chain flexibility and degree of unsaturation of the resins were systematically varied and the effects of those variables on the mechanical properties of the cured resins and polymer mortars made therefrom were studied. 

Valenza, A. La Mantia, F.P. Recycling of polymers. Part 1. Photo-oxidized polypropylene. Polym. Degrad. Stab. 1987,19, 135-145. 

The development of polymer-immobilized ligands and catalysts for asymmetric synthesis is a rapidly growing field [1], which has great importance due mainly to the easy separation and recyclability of polymer-supported catalysts. The polymeric catalysts also represent one of the most powerful tools for green sustainable chemistry, in the sense that they can be easily recovered and reused many times. 

Recycling of polymers saves resources, since no new crude oil is required -... 

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