Resins recycled plastics

These lower prices make it more difficult for recycled plastics to compete with virgin resins in the absence of legislation mandating plastics recycling. 

Recycled poly(ethylene terephthalate) (PET), which offers excellent properties at potentially lower cost, is finding wider use as a raw material component and meeting increasing demands for environmentally compatible resins (see POLYESTERS,THERMOPLASTIC Recycling, PLASTICS). 

Contaminants in recycled plastic packaging waste (HDPE, PP) were identified by MAE followed by GC-MS analysis [290]. Fragrance and flavour constituents from first usage were detected. Recycled material also contained aliphatic hydrocarbons, branched alkanes and alkenes, which are also found in virgin resins at similar concentration levels. Moreover, aromatic hydrocarbons, probably derived from additives, were found. Postconsumer PET was also analysed by Soxhlet extraction and GC-MS most of the extracted compounds (30) were thermally degraded products of additives and polymers, whereas only a few derived from the original contents... 

To efficiently use recycled plastics in molded parts, it is beneficial to work with several recycling suppliers to obtain a resin that is as close to the color of the product as possible. The resin that most closely matches the product may cost more per pound due to special sorting necessary to obtain a special color. This resin will probably cost less to use since it will require less corrective colorant to adjust the recycled resin to match the target. Recycled resins that are farther off color will require much more pigment to overpower the colorants in the recycled resin. 

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. 

In 1976 plastic became the most widely used material in the United States. It represents a 140-billion-per-year industry8, greater than steel and aluminum combined. Unfortunately the increase in the use of plastic has affected the problem of waste plastic disposal at about the same rate. The need to recycle plastics to reduce the use of virgin resins and to reduce the amount of waste materials has become a subject of considerable interest. 

Engelmann, P.V., Monfore, M.D., Dawkins, E.W., Mclnemey, J.A. (1992) Recycling Extrusion-Compression of Commingled Resins Blends, Plastic Engineering, February 1992, pp. 27-31. 

Innovation in the fabric softener business not only focused on compositions, but also on packaging. As an alternative to plastic bottles, heat-sealed flexible polyethylene pouches were introduced to the market in the early 1980s [7], followed by several other containers free-standing flexible pouches with a solid base, different bag in a box rigid units, and refill cartons coated with chemically resistant polymers. These novelties led to a 40% reduction in plastic bottle consumption, the use of more biodegradable, renewable, easily recycled material, and a decrease in the packaging and distribution cost. New bottles made of 100% post consumer recycled plastic sandwiched between two layers of virgin resin also became available [7],... 

Recycling plastic is now a popular issue. In 1989,58 x 10 lb of resin were produced in the United States. Of this, it is estimated that 14 x 10 lb were used for packaging and 29 x 10 lb became solid waste. At that time, only 340 to 400 X 10 Ib were recovered. 

Therefore, recycled polymers usually exhibit lower properties and performance than the virgin material, and are useful only for undemanding applications. Recycling plastics without prior separation by resin produces a material with mechanical properties similar to timber, hence it is often used for the replacement of timber in certain applications. A higher quality of recycled plastics is achieved when separation by resin is carried out prior to the remoulding step. However, even in this case, recycled plastics cannot be used in food containers, unless direct content with the food can be avoided. 

Resin/grade Price for prime resin Lowest price in the plastic grades Price for recycled plastics, pellets... 

Recycled resins (all commodity and some engineering ones) are commercially available. A comparative list of prices of the virgin and recycled resins is shown in Table 16.5. The prices of recycled plastics are quite competitive. Evidently, while the quoted prices of commodity resins are reasonably close to these of virgin materials, the situation vis-a-vis condensation polymer is atrocious. The only way to make profit on the latter materials is to upgrade them by the recyclers ABC and supply compounds with well-defined and reproducible set of properties to a specific market niche. As it will be discussed later, the addition-type polymers can be reused after restabilization and compounding, whereas the condensation-type ones may require molecular repair to bring up... 

Recycled plastics need to be re-stabilized. Since the resin may already suffer from degradation, a higher concentration of stabilizer may need to be added than that introduced during the initial pelletization [Herbst et a/., 1995, 1997]. 

The use of virgin polyethylene as an additive to asphalt concrete is not new however, two new processes also use recycled plastic as an asphalt cement additive [ 146,147]. These latter two processes both use recycled low-density polyethylene resin, which is generally obtained from plastic trash and sandwich bags. The recycled plastic is made into pellets and added to asphalt cement at a rate of 4-7% by weight of binder [146-148]. 

As mentioned earlier, for some applications it is possible to use recycled plastics that contain a mixture of different types of resins. Since different plastic resins are generally not compatible with each other, such mixtures tend to contain small regions of individual types of polymers within a matrix of another polymer. Adhesion between these regions can be poor, resulting in a substantial decrease in performance. Two general approaches have been taken to producing usable materials from such mixtures. 

Most end-use markets for recycled plastic bottles require that they be separated by resin type and color. This ensures high end-use value for new products incorporating substantial amounts of the recycled resin. PVC bottles, like PET bottles, are very recyclable. Manual sorting of nonpigmented PVC and clear PET bottles is difficult because they look alike. When the two types are received commingled, the reprocessor can experience quality deficiencies due to rheological incompatibilities between these two resins. Therefore, all attempts to separate and remove these two resins must be made prior to recycling. 

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