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Recycling And Resource Recovery

Nov 12, 2018

In many municipalities, the favoured method of disposing of solid waste is in sanitary landfills, in which layers of refuse alternate with layers of soil. However, concerns over the wisdom of such land use has encouraged efforts to dispose of various materials by recycling them for re-use or to derive some positive benefits. Paper as well as glass and aluminum containers have been recycled to some degree for many years, and in more recent years plastic recycling has become common. There are several technical and economic problems in the recycling of plastics; they fall into two general categories: (1) identification, segregation (or sorting), and gathering into central stations and (2) the economics of recovering value.  Game supply and game card sleeve and trading card sleeve and soft card holder.

Identification, segregation, gathering

Since plastics used in packaging form a highly visible part (approximately 20 percent by volume but less than 10 percent by weight) of the waste stream, most recycling efforts have focused on containers. Almost all bottles, foodtrays, cups, and dishes made of the major commodity plastics now bear an identifying number enclosed in a triangle together with an abbreviation. Game supply and game card sleeve and trading card sleeve and soft card holder.

In addition to such labeling, in many localities consumers are encouraged to return empty beverage containers to the place of purchase by being required to pay a deposit on each unit at the time of purchase. This system helps to solve two of the major problems associated with economical recycling, since the consumer seeking return of the deposit does the sorting and the stores gather the plastics into central locations. An added attraction of deposit laws is a notable decrease in roadside litter. However, while such measures have helped to raise dramatically the recycling rate of plastic bottles—especially those made of polyethylene terephthalate (PET) and high-density polyethylene (HDPE)—less than 5 percent of all plastic products are recycled after first use. (On the other hand, most plastics are used in long-term applications such as construction, appliances, and home furnishings, for which efficient recycling is difficult.) Game supply and game card sleeve and trading card sleeve and soft card holder.

Economic recovery of value

In general, thermoplastic materials can be recycled more readily than thermosets. Still, there are inherent limitations on the recycling of even these materials. First, a recyclable plastic may be contaminated by nonplastics or by different polymers making up the original product. Even within a single polymer type, there are differences in molecular weight. For instance, a supplier of polystyrene may produce a material of high molecular weight for sheet-formed food trays, since that forming process favours a high melt viscosity and elasticity. At the same time, the supplier may offer a low-molecular-weight polystyrene for the injection molding of disposable dinnerware, since injection molding works best with a melt of low viscosity and very little elasticity. If the polymers from both types of product are mixed in a recycling operation, the mixed material will not be very suitable for either of the original applications. Game supply and game card sleeve and trading card sleeve and soft card holder.

Another complication to the recycling of plastics is the mixing together of pigments or dyes of different colours, and yet another is the problem of quality control. Almost all plastics change either slightly or greatly as a result of initial fabrication and use. Some, for instance, undergo changes in molecular weight due to cross-linking or chain scission (breaking of the chemical bonds that hold a polymer chain together). Others undergo oxidation, another common reaction that can also change the properties of a plastic. Game supply and game card sleeve and trading card sleeve and soft card holder.