Postconsumer recycled plastics processing

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. 

Table 8 Some of the Markets and Products Made from Processing of Postconsumer Recycled Plastics...

Most end-use markets of recycled plastics require that they be separated by resin type and color. For postconsumer bottles, all lids, caps, and closures should also be removed because they are often of different colors, and made of different resins than the bottle. The goal of any sorting process is to obtain the highest purity, consistency, and quantity of a particular consumer resin type. This ensures the highest end-use value for new products incorporating substantial amounts of the recycled resin. 

When discussing many subjects it is important that they be properly identified by definitions such is the case in recycling. Different definitions exist to meet different industry and commercial requirements. ASTM defines a recycled plastics as those plastics composed of postconsumer material and recovered material only, or both, that may or may not have been subjected to additional processing steps of the types used to make products such as recycled regrind, or processed or reconstituted plastics. The industry scrap includes what is commonly referred to as trim or regrind in plastic production, is not considered recycled material. 

This book presents an overview of mixed plastics recycling technology. In addition it characterizes mixed plastics wastes, and describes collection methods, costs, and markets for reprocessed plastics products. While these studies were done for the State of Illinois, with the current national concern about recycling, the information presented will be of interest to anyone involved in municipal re( ciing, and the subsequent processing of postconsumer mixed plastics. 

Post-industrial recycled plastics occur in most plastic products, wherein the plastics from the sprues runners, extrudate, etc. are added back into the virgin plastic at the plastic manufacturing plant. Postconsumer resin (PCR) refers to plastics that were made into products, for example, bottles, bags, film, packaging, used by a consumer, collected by a waste disposal company, processed into recycled pellets at an MRF, where the recycled plastic parts are converted into recycled plastic pellets. The plastic pellets are then sold to plastic companies. 

Recychng single resin plastics from postindustrial or postconsumer sources typically utihzes standard processing equipment. Plastics are melted, extruded, pelletized, and then formed into a final product. Additives may be added that compensate for prior use, additional processing caused thermal histories or new product needs but the use of these additives is minimized to control the overall cost of the recycled plastic and thereby increase the overall profitability of the process. The next section addresses some of the technical issues associated with recychng specific individual plastic streams. 

Similarly, Dow has entered into a joint venture agreement with Dom-tar of Canada to operate what the companies hope will be by 1990 a self-sustaining PET and HDPE recycling business. The North American company is expected to take postconsumer plastics and, using a proprietary Dow process, convert them into resins for use in Domtar s manufacturing or to be sold by Dow. 

Recycling of postconsumer plastics involves the process of collection, cleaning, separation, and then processing them into various products. These different steps will be elaborated in the following sections. 

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... 

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