Recycle plastics stream

In most cases, before attempts are made to recycle plastic resins, the used parts must first go through a series of sorting processes. The purpose of these sorting processes is to separate the desired recycle plastic from possible contaminants in the incoming stream. These contaminants can take many forms. They include dirt, paper, glue, and metal as well as other recyclable plastics and even the same desired plastic but of a different color. The most postconsumer recycled plastic today is PET. This is the plastic from which all plastic soft drink beverage bottles are made. 

Researchers at the Chehalis facility carried out 18-months of parametric study to assess the Conrad recycling process [9]. Their objective was to identify process bottlenecks, develop operating parameters and begin to assess product value and markets. For the initial experiments a base feed mixture of 60 20 20 high-density polyethylene, polypropylene and polystyrene (HDPE PP PS) was used as representative of the major constituents found in post-consumer plastic streams. 

Plastics (PL) comprise more than 8% of the total weight of the municipal waste stream and about 12-20% of its volume [ 146,147]. In 1992, approximately 30 mil-hon metric tons (33 milhon tons) of plastics were discarded in the United States only 14.7 million metric tons (16.2 milhon tons) were recycled. Current research on the use of recycled plastics in highway construction is wide and varied. 

A designer sometimes has an opportunity to use a material that provides no problem in the solid-waste stream or to use a design that lets lower-cost recycled plastics be used. In fact, blends of virgin (not previously processed) plastics with recycled plastics could permit the meeting of required product performance requirements. This approach has been used for the past century. However, the designer must take into account the possible lower performances that will occur with recycled plastics (Chapter 3). 

Mixed Waste Processing. Another approach to recycling plastics and other materials is not to ask consumers to do any special sorting or preparation bufi instead, to recover recyclables from the garbage stream. The advantage of these systems is that, since they do not require any particular cooperation by consumers, they have the potential to recover the largest amount of recyclables. 

The sources of HDPE in the U.S. MSW stream are shown in Fig. 8.24. For many years, HDPE was the second most recycled plastic, but it overtook PET several years ago. In the United States, the EPA reports that the recycling rate for HDPE milk and water bottles was 31.9 percent in 2003, a total of 460 million pounds. Other HDPE containers were recycled... 

As mentioned, one application for recycled commingled plastics is in plastic lumber. The plastic lumber business has grown rapidly in the last five years. Not aU plastic lumber is made using recycled plastics, but much of it is. Some companies using recycled plastics for plastic lumber use mixed plastics, and others use relatively pure streams of material. Some use primarily postconsumer materials, while others use mostly industrial scrap. 

PE represents the largest constituent of plastics in the municipal waste stream and the fraction is mainly composed of high-density polyethylene (HDPE) packaging materials. Recycling this type of waste packaging material yields a stream of recycled plastic that is highly homogeneous and consistent [8]. 

Figure 5.1 illustrates the industrial recycling of discarded waste into raw material. In municipal waste, postconsumer plastic represents a small percentage however, it occnpies about 25% of the waste stream volume. Recycled plastics can be transformed into pellets which can be used as raw materials to either partially or fully replace virgin material in many plastic mannfactnring operations. 

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