Difference between revisions of "Polyester & Recycled Polyester"

Revision as of 08:54, 17 April 2015

Finding innovations that mitigate the ecological impacts of polyester will not only reduce environmental impacts, but has the potential to influence the textile industry as a whole. Over the last 45 years technical developments in polyester production have improved the fibre’s hand-feel, fineness and quality. Polyester is now the world’s favorite fibre, representing 79% [in 2009] of world synthetic fibre production, fuelled in part by its use in fast-fashion garments, the fastest growing sector of the fashion industry.[1][2][3] Europe’s share in the polyester industry accounted for 960,000 tonnes in 2009-2010. [1] Polyester is a man-made, synthetic fibre. To produce polyester, crude oil (petroleum) is broken down into petrochemicals, which are then converted with heat and catalysts such as antimony into polyethylene terephthalate (PET). This is the same type of plastic used in plastic soda bottles.

Benefits

Polyester fabrics are readily available, strong, resistant to stretching and shrinking, resistant to most chemicals, and don’t easily succumb to wrinkling, mildew or abrasion. So, when polyester fabrics are used in robustly constructed garments, they have the potential to last and to be worn many times, optimizing the embodied energy and resources in the garment. see comment in Potential Impacts below for counterpoint to this benefit. Polyester’s positive attributes for clothing lie mostly in the consumer use phase of its lifecycle, which accounts for 50-80% of a polyester garment’s total ecological footprint. Polyester garments are generally washed in cold water and drip-dried, thereby minimizing water and energy use associated with garment care.[4] In comparison to other synthetic fibres, there is currently more research and innovation when it comes to sustainability and improving polyester’s environmental impact.

Potential impacts

Processing

Petroleum, the main ingredient in manufacturing polyester, is a non-renewable resource and mining for petroleum destroys natural habitats. That is to say that petroleum takes millions of years to form, and is currently being extracted from the earth for industrial uses faster than it can be replenished. The declining petroleum supply is the source of much debate—British Petroleum (BP) reports that there are 1,333 billion barrels still available to pump (enough for 40 years at current usage rates).[5] Other sources state that supply is overestimated and that reserves are about 30% lower than widely reported.[6]

The manufacturing process for polyester is fully chemical, energy intensive and releases greenhouse gasses into the environment.7 In the production of polyester, the main ingredients used are terephthalic acid (TA) or dimethyl terephthalate, which are reacted with ethylene glycol, based on bromide-controlled oxidation.7 The production of polyester emits emissions to air and water, which include: heavy metal cobalt; manganese salts; sodium bromide; antimony oxide; and titanium dioxide.

Antimony is of particular concern, since it is a toxic heavy metal known to cause cancer under certain circumstances and is a suspected reproductive toxin.[7] The function of antimony in the production of polyester is as a catalyst in the oxidation process. But it is not absolutely necessary for polyester production, and alternate non-antimony catalysts are available. Europe meets its oil consumption/needs by importing from foreign sources: 41% from the Russian Federation, 26% from Africa, 16% from the Middle East—14% comes from Europe—thus requiring transportation over long distances.[8][9] Fuel released by vehicles used to transport the oil causes pollution and CO2 emissions.

Dyeing and finishing

Certain types of dyes are suspected carcinogens and mutagens, while other dyes are known to have a sensitizing effect on skin and should be avoided. Untreated dye water can negatively impact receiving water bodies and harm aquatic ecosystems if left untreated before its release.

Consumer care/washing

Certain at-home detergents have been reported to have detrimental effects on humans and the environment, contributes to ozone depletion and can pollute wastewater.

End of use

Polyester has durability to last the wearer several years, however it is typically used in inexpensive, fast-fashion garments that are worn and quickly discarded. Synthetic fibres are from a carbon-based chemical feedstock and are considered non-biodegradable.[10]

There are conflicting opinions about how long polyester takes to decompose and estimates range from 40 years to 1000 years. This is because degradability is dependent upon a number of conditions including how much air, temperature and sunlight the fibre is exposed to.

Discarded polyester products increase load on landfills, contribute to water contamination and possibly toxic emissions into the air.[11] According to a study done by Mark Browne, an ecologist at University College Dublin, microscopic fragments of polyester, acrylic, polyethylene, polypropylene, and polyamide have been discovered in increasing quantities across the northeast Atlantic, as well as on beaches in Britain, Singapore and India. A chemical analysis revealed that nearly 80% of the filaments contained polyester or acrylic.[12]

Alternatives to virgin polyester

Recycled polyester

Using recycled polyester achieves two main ecological benefits: 1) it slows the depletion of virgin natural resources, and 2) it reduces textile waste building in landfills. Polyester can be recycled into new versions of the same product or into entirely different products. Post-consumer waste from used and discarded products and post-industrial waste from material collected during the product manufacturing can be recycled. There are two processes for recycling polyester: mechanical and chemical.

Mechanical recycling

Since polyester is a thermoplastic and is melt-spun, it can be effectively re-melted and remolded to make yarns. However, in this manner the fibre is “downcycled”: its physical structure breaks down, and eventually the product must be discarded to landfill.[13]

Collection, sorting and purifying discarded synthetic garments (i.e., post-consumer waste) is currently cumbersome. Infrastructure for labeling, collection and sorting needs to be improved so that the post-consumer raw material source can scale to be economically viable.

Polymer resins come in a variety of forms and some are relatively easy to collect and recycle. The most well known source is soda bottles, which can be used to make new PET (polyethylene terephthalate) fibre. The bottles are collected, sorted by colour (green vs. clear), thoroughly inspected to ensure that no caps (often polypropylene), bases or PVC bottles are present. (This is critical, because one stray PVC bottle in a melt of 10,000 PET bottles can ruin the entire batch of new fibre.) Following inspection, the bottles are sterilized, dried and crushed into flakes, which are washed again, bleached and dried. The flakes are then emptied into a vat, heated, melted and extruded through spinnerets, to form long polyester fibres. Flakes from green bottles are generally used for fibres that will be dyed in dark colours, though some companies take advantage of the green colour in the new fabric developed.

Chemical recycling

Chemical recycling involves breaking the polymer into its molecular parts and reforming the molecules into a yarn of equal strength and quality as the original, in perpetuity.[14] In this process, the chemical building blocks are separated (depolymerization) and reassembled (repolymerization), forming what is known as a “closed loop” where the final stage of the product lifecycle (disposal) forms the first stage of the next product (raw fibre). Closed loop recycled polyester processing is expensive in part because it is a relatively new technology. In addition, the infrastructure to label, collect, sort and purify discarded garments at scale is being developed.

In 2002, the Japanese company Teijin launched ECO CIRCLETM, the first closedloop chemical recycling system for polyester. Teijin works with fabric suppliers and apparel brands to manufacture products using recycled and recyclable materials, and is also helping to develop post-consumer clothing collection programs.

Teijin recently established a joint venture with one of China’s largest fibre producers, bringing the manufacture of chemically processed recycled polyester to China.[15]

Alternatives to virgin polyester

Biopolymer fibres

Polylactide (PLA)

Optimize sustainability benefits

Availability

Applications

Marketing opportunities

Innovation opportunities

Company opportunities

Sources