Municipal solid waste, polymers

Another approach for overcoming the problems posed by conventional cracking catalysts has been disclosed recently by Reverse et al. [101]. In this case, direct cracking is performed by using as catalyst a molten bed of pure metal or a metal mixture (mainly lead, zinc, tin) at a temperature of 460-550°C wherein the waste polymer is loaded inside the reactor at a certain depth. The authors point out that the products are indeed a result of the combination of both thermal and catalytic cracking. The catalyst composition may also include some acidic component such as metal silicates, metal carbonates and their mixtures. The process can be applied to pure and mixed polymers (PE, PET, PP, PVC), as well as to the plastic fraction of municipal solid wastes. 

Plastic polymers make up a high proportion of waste and the volume and range used is increasing dramatically. The two main types of plastic are thermoplastics which soften when heated and harden again when cooled and thermosets which harden by curing and cannot be remoulded. The six main plastics in municipal solid waste are, high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) and polyethylene terephthalate (PET). In addition there are... 

Biomass-derived polymers are often touted as "green" alternatives to polyethylene and other plastics used for packaging. However, not all biopolymers are biodegradable (2). Moreover, as we shall see in section 8.5, degradability of biopolymers is sometimes overstated (3). In this chapter, we will quantify the contribution of plastics to municipal solid waste in the USA and examine some of the realities about biodegradability of "bioplastics."... 

Most of the effort at China Lake was directed toward demonstrating, at the bench scale, that polymer gasoline could indeed be made noncatalytically from the olefins formed by the selective pyrolysis of municipal solid waste (MSW). Funding for the bench-scale demonstration was provided by the Industrial Environmental Research Laboratory (IERL) of the Environmental Protection Agency, beginning in 1975 (EPA-IAG-D6-0781). 

The same technique can be used to dye a material that is otherwise difficult to dye. An ethylene-propylene copolymer rubber was reacted first with maleic anhydride, then with an aromatic amine dye in an extruder to produce a dyed rubber.81 Dye sites can also be inserted into polyolefins by grafting them with dimethylaminoethyl methacrylate, using azo or peroxide catalysts in an extruder.82 jV-Vinylimidazole has been grafted to polyethylene in an extruder with the help of dicumylperoxide.83 The product was mixed with an acrylic acid-modified polypropylene and used to compatibilize polyethylene and polypropylene. This could be helpful in the recycling of mixed polyolefins from municipal solid waste. Recycling of cross-linked (thermoset) polymers is more of a problem because they cannot be remelted in an extruder. However, they can be if... 

Plastics and rubber are essential materials in today s industrialized societies. The consumption of plastics has grown by a factor of about 60 in the past 30 years, which has led to a corresponding increase in the generation of plastic wastes. One of the most valuable properties of plastics, their low density, is one of the major limitations in the recycling of plastic wastes. Thus, to recover one tonne of plastics it is necessary to collect about 20 000 plastic bottles. Plastic wastes are mainly found in municipal solid wastes (MSW). As a consequence of their low density, plastics account for just 8 wt% of the MSW, but this value increases to over 20% in volume terms. In spite of the great diversity of plastic materials, plastic wastes are made up of a relatively small number of polymers polyethylene, polypropylene, polystyrene, polyvinyl chloride and polyethylene terephthalate. These resins account for more than 90% of total plastic wastes. 

Industry is under great pressure to improve its practices. The polymer industry is particularly under fire, no doubt due to the short lifespan of many plastics-based consumer products, the high visibility of polymers in municipal solid waste and the rapid increase of plastics consumption. 

Due to its sensitivity to contamination from other polymers and from impurities, solvolysis will most likely find application within well-defined product areas with efficient collection and sorting infirastructures. Thermolysis, on the other hand, shows high potential for treating mixed plastics waste such as municipal solid waste and automotive shredder residue which otherwise would go to landfill. Not all thermolytic processes are suited for the generation of new polymers, and a certain amount of the oils, gases and solid residues from these processes is used to replace fuel. 

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