(c) Copyright : 2016-18
Plastic recycling is the process of recovering scrap or waste plastics and reprocessing the material into useful products, sometimes completely different in form from their original state. For instance, this could mean melting down soft drink bottles then casting them as plastic chairs and tables. Typically a plastic is not recycled into the same type of plastic and products made from recycled plastics are often not recyclable.
When compared to other materials like glass and metal materials, plastic polymers require greater processing to be recycled. Plastics have a low entropy of mixing, which is due to the high molecular weight of their large polymer chains. A macromolecule interacts with its environment along its entire length, so its enthalpy of mixing is large compared to that of an organic molecule with a similar structure. Heating alone is not enough to dissolve such a large molecule; because of this, plastics must often be of nearly identical composition in order to mix efficiently.
When different types of plastics are melted together they tend to phase-separate, like oil and water, and set in these layers. The phase boundaries cause structural weakness in the resulting material, meaning that polymer blends are only useful in limited applications.
Another barrier to recycling is the widespread use of dyes, fillers, and other additives in plastics. The polymer is generally too viscous to economically remove fillers, and would be damaged by many of the processes that could cheaply remove the added dyes. Additives are less widely used in beverage containers and plastic bags, allowing them to be recycled more frequently.
The use of biodegradable plastics is increasing. If some of these get mixed in the other plastics for recycling, the reclaimed plastic is not recyclable because the variance in properties and melt temperatures.
Before recycling, plastics are sorted according to their resin identification code, a method of categorisation of polymer types, which was developed by the Society of the Plastics Industry in 1988. Polyethylene terephthalate, commonly referred to as PET, for instance, has a resin code of 1. They are also often separated by colour. The plastic recyclables are then shredded. These shredded fragments then undergo processes to eliminate impurities like paper labels. This material is melted and often extruded into the form of pellets which are then used to manufacture other products.
Yet another process that is gaining ground with start-up companies (especially in Australia, United States and Japan) is heat compression. The heat compression process takes all unsorted, cleaned plastic in all forms, from soft plastic bags to hard industrial waste, and mixes the load in tumblers (large rotating drums resembling giant clothes dryers). The most obvious benefit to this method is the fact that all plastic is recyclable, not just matching forms. However, criticism rises from the energy costs of rotating the drums, and heating the post-melt pipes.
Post-consumer polyethylene terephthalate (number 1), also known as PET, is often used as the raw material for a range of products. To obtain the pure PET, the recycled items, such as plastic bottles and containers(the main use for PET), are first inspected for any non PET materials. These materials are then removed and the PET items are sorted into different colour fractions, cleaned, and prepared for processing. This sorted post-consumer PET waste is crushed, chopped into flakes, pressed into bales, and offered for sale.
One use for this recycled PET that has recently started to become popular is to create fabrics to be used in the clothing industry. The fabrics are created by spinning the PET flakes into thread and yarn. This is done just as easily as creating polyester from brand new PET. The recycled PET thread or yarn can be used either alone or together with other fibres to create a very wide variety of fabrics. Traditionally these fabrics were used to create strong, durable, rough, products, such as jackets, coat, shoes, bags, hats, and accessories. However, these fabrics are usually too rough on the skin and could cause irritation. Therefore, they usually are not used on any clothing that may irritate the skin, or where comfort is required. But in today’s new eco-friendly world there has been more of a demand for “green” products. As a result, many clothing companies have started looking for ways to take advantage of this new market and new innovations in the use of recycled PET fabric are beginning to develop. These innovations included different ways to process the fabric, to use the fabric, or blend the fabric with other materials. Some of the fabrics that are leading the industry in these innovations include Billabong's Eco-Supreme Suede, Livity (http://www.livity.org/) 's Rip-Tide III, Wellman Inc (http://www.wellmaninc.com/) 's Eco- fi(formerly known as EcoSpun), and Reware (http://www.rewarestore.com/) 's Rewoven. Some additional companies that take pride in using recycled PET in their products are Crazy Shirt and Playback (http://www.playbackclothing.com/)
PVC- or Vinyl Recycling has historically been difficult to perfect on the industrial scale. But within the last decade several viable methods for recycling or up-cycling PVC plastic have been developed.
The most-often recycled plastic, HDPE or number 2, is down-cycled into plastic lumber, tables, roadside curbs, benches, truck cargo liners, trash receptacles, stationery (e.g. rulers) and other durable plastic products and is usually in demand.
In 2008, the price of PETE dropped from $370/ton in the US to $20 in November. PET prices had returned to their long term averages by May 2009.
Plastic recycling rates lag far behind those of other items, such as newspaper (about 80%) and corrugated fibreboard (about 70%). All plastic bottles were recycled at a rate of 24 percent in 2005.
The quantity of post-consumer plastics recycled has increased every year since at least 1990. In 2006 the amount of plastic bottles recycled reached a record high of 2.2 trillion pounds. The amount of PET bottles recycled in 2006 increased more than 102 million pounds compared to 2005. HDPE bottle recycling increased in 2005 to 928 million pounds.
Seven groups of plastic polymers, each with specific properties, are used worldwide for packaging applications (see table below). Each group of plastic polymer can be identified by its Plastic Identification code (PIC) - usually a number or a letter abbreviation. For instance, Low-Density Polyethylene can be identified by the number 4 and/or the letters "LDPE". The PIC appears inside a three-chasing arrow recycling symbol. The symbol is used to indicate whether the plastic can be recycled into new products.
The PIC was introduced by the Society of the Plastics Industry, Inc. which provides a uniform system for the identification of different polymer types and helps recycling companies to separate different plastics for reprocessing. Manufacturers of plastic products are required to use PIC labels in some countries/regions and can voluntarily mark their products with the PIC where there are no requirements. Consumers can identify the plastic types based on the codes usually found at the base or at the side of the plastic products, including food/chemical packaging and containers. The PIC is usually not present on packaging films, as it is not practical to collect and recycle most of this type of waste.