Recycling of waste polymer

Z. Zhibo, S. Nishio, Y. Morioka, A. Ueno, H. Ohkita, Y. Tochihara, T. Mizushima, and N. Kaknta, Thermal and chemical recycle of waste polymers, 29, 303 (1996). 

Symposium on Feedstock Recycling of Waste Polymers, Co-chairs, E. M. Eyring and J. W. Zondlo, ACS, Div. Fuel Chem. Preprints, 42(4) (1997). 

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. 

The reaction-catalysing properties of super-critical fluids are described, and some examples are demonstrated of the chemical recycling of waste plastics. 16 refs. Articles from this journal can be requested for translation by subscribers to the Rapra produced International Polymer Science and Technology. 

Progress in Rubber and Plastics Technology 16, No.l, March 2000, p.61-8 CHEMICAL RECYCLING OF WASTE SATURATED POLYESTERS AND URETHANE POLYMERS TO YIELD RAW MATERIALS FOR THE PRODUCTION OF POLYURETHANES Kacperski M Spychaj T Szczecin,Polytechnic... 

CHEMICAL DISSOCIATION OF AMIDE BONDS - RECYCLING OF PURE POLYMER WASTES... 

Polymers with hetero-atoms in the chain are suitable for chemical recycling of waste materials. In addition to depolymerisation (nylon 6) and solvolysis (nylon 6,6, PETP, PU) the degradation of aliphatic polyamides with dicarboxylic acids, diamines and cyclic anhydrides, especially trimellitic anhydride, becomes more and more important. The utilisation of the obtained fragments is described. 

Most of the work on feedstock recycling of plastic has focused on conversion of plastic to transportation fuels. Little has been reported on conversion of waste plastic to highervalued products. In this section, research on the conversion of waste polymers such as polyethylene to high-quality lubricant oils is summarized. A more detailed account of this research is available elsewhere [24]. 

T. Ernst R. Popp and R. van Eldik, Quantification of heavy metals for the recycling of waste plastics from electrotechnical applications, Talanta, 53, 347-357 (2000). W. Camacho and S. Karlsson, Quality-determination of recycled plastic packaging waste by identification of contaminants by CC-MS after microwave assisted extraction (MAE), Polymer Degradation and Stability, 71, 123-134 (2000). 

It can be shown that it is possible to recover high amounts of monomers from special polymers by pyrolysis in a tluidized-bed process. Up to 98 wt% of MMA can be recovered from filled or coloured PMMA wastes. In the case of polystyrene the rate of recovered styrene is limited to about 77 wt% the rest is oligomers. The high yields of TFE, HFP and C-C4F8 obtained from PTFE compounds in the experiments described show that tluidized-bed pyrolysis of pure PTFE or PTEE compounds is a feasible and interesting opportunity for the chemical recycling of this polymer. 

Apparently, AMSd is also useful in the reduction of the molecular weight of waste polymer.491 Heating polystyrene foam pieces recycled from food packaging materials at 160 °C for 1 h in the presence of AMSd reduced the Mn from approximately 70 000 to 10 000. The mode of action is unknown, but it is presumed that AMS radicals are generated and abstract hydrogen atoms from the polystyrene backbone, resulting in chain cleavage. 

The major disadvantage of chemical depolymerization is that it is almost completely restricted to the recycling of condensation polymers, and is of no use for the decomposition of most addition polymers, which are the main components of the plastic waste stream. Condensation polymers are obtained by the random reaction of two molecules, which may be monomers, oligomers or higher molecular weight intermediates, which proceeds with the liberation of a small molecule as the chain bonds are formed. Chemical depolymerization takes place by promoting the reverse reaction of the polymer formation, usually through the reaction of those small molecules with the polymeric chains. Several resins widely used on a commercial scale are based on condensation polymers, such as polyesters, polyamides, polyacetals, polycarbonates, etc. However, these polymers account for less than 15% of the total plastic wastes (see Chapter 1). 

Thermal processes are mainly used for the feedstock recycling of addition polymers whereas, as stated in Chapter 2, condensation polymers are preferably depolymerized by reaction with certain chemical agents. The present chapter will deal with the thermal decomposition of polyethylene, polypropylene, polystyrene and polyvinyl chloride, which are the main components of the plastic waste stream (see Chapter 1). Nevertheless, the thermal degradation of some condensation polymers will also be mentioned, because they can appear mixed with polyolefins and other addition polymers in the plastic waste stream. Both the thermal decomposition of individual plastics and of plastic mixtures will be discussed. Likewise, the thermal coprocessing of plastic wastes with other materials (e.g. coal and biomass) will be considered in this chapter. Finally, the thermal degradation of rubber wastes will also be reviewed because in recent years much research effort has been devoted to the recovery of valuable products by the pyrolysis of used tyres. 

The decomposition of waste polymer by means of chemical substances or heat and the decomposition products are monomers or mixture of compounds [25]. In chemical recycling, monomers are produced as a result of depolymerization or other secondary valuable materials are produced by partial degradation. Energy recovery by incineration is a successful way to decrease the volume of organic materials. 

K. Hamad, M. Kaseem, F. Deri, Recycling of waste from polymer materials An overview of the recent works. Polym. Degrad. Stab. 98(12), 2801-2812 (2013)... 

Foamed phenolic polymer appears to be an excellent insulator, stable and cheap. There is much competition for similar outlets between thermosets and thermoplastics—urea and melamine, ABS, acetal, PP and Nylon. The phenolics have the advantage of low price, and a good combination of general performance when appropriately composed. On the other hand, use of thermoplastics is frequently preferable due to improved processing in mass production, in addition to the recyclability of wastes. 

Pol mer waste management options are shown in Figure 1.2. The utilization of waste polymers by mechanical recycling and incineration has ecological limitations. 

Chitin and chitosan belong to a group of natural polymers produced by the shells of crab, shrimp, and lobster, but they have not been utilized effectively. Chitin ranks second to cellulose as the most plentiful organic compound on earth. Almost all of the estimated 10 °-10" tons of crab, shrimp, and lobster produced annually could be used as raw materials. Chitin and chitosan are, therefore, very beneficial natural resources when the economical recycling of wastes is considered. Accordingly,... 

The following section 1.2 is an overview of plastic resin production and the primary methods utilized in manufacturing consumer goods and recycling waste plastics into new products. Also discussed are factors influencing the recyclability of waste plastic mixtures and compatibility between polymer types. 

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