Recycled Polyethylene Terephthalate (rPET)

• INTRODUCTION

Synthetic fibers are the most popular fibers in the world. They account for about 65% of world production versus 35% for natural fibers. Most synthetic fibers (approximately 70%) are made from polyester. The polyester most often used in textiles is polyethylene terephthalate (PET). When used in a fabric, it is most often referred to as “polyester” or “poly”.

The majority of the world’s PET production, about 60%, is used to make fibers for textiles, while the remaining 30% is used to make bottles. It is estimated that it takes about 104 million barrels of oil for PET production each year, i.e., 70 million barrels just to produce the virgin polyester used in fabrics. This means that most of the polyester – 70 million barrels worth – is manufactured specifically to be made into fibers, not bottles, as many people think.  Of the 30% of PET which is used to make bottles, only a tiny fraction is recycled into fibers. But the idea of using recycled bottles – ‘Diverting waste from landfills’ – and turning it into fibers has caught the public’s attention.

The reason recycled polyester (often written as rPET) is considered a green option in textiles today is two-fold:

1. Energy needed to make the rPET is less than what is needed to make virgin polyester in the first place; thus, energy is saved
2. The bottles and other plastics is kept out of the landfills

• Argument 1:

The energy needed to make the rPET is less than what is needed to make virgin polyester

It is true that recycling polyester uses less energy than what is needed to produce virgin polyester. Various studies agree that it takes from 33% to 53% less energy. If the higher estimate is considered, and take 53% of the total amount of energy needed to make virgin polyester (125 MJ per KG of ton fiber), the amount of energy needed to produce recycled polyester in relation to other fibers is:

                         Table 1: Embodied Energies used in production of various fibers 

rPET is also cited as producing far fewer emissions than virgin polyester; again estimates vary. But according to studies by the Stockholm Environment Institute, the CO2  emissions in producing rPET is estimated at 54.6% lesser than the case of Virgin Polyester.

   Table 2: KG of CO₂ emission per ton of Spun fiber 

• Argument 2:

Diverting bottles and other plastics from the landfills

rPET is divided into Post Consumer and Post Industrial

• Post Consumer:

Post consumer means that the polyester comes mainly from bottles.

It has been touted as the “greenest” option, and that has driven up demand for used bottles

• Post Industrial:

Post industrial might be the unused packaging in a manufacturing plant, or other byproducts of manufacturing

Indeed, the demand for used bottles, from which recycled polyester fibre is made, is now outstripping supply in some areas and certain cynical suppliers are now buying new, unused bottles directly from bottle producing companies to make polyester textile fiber that can be called recycled.

• WAYS OF RECYCLING

• Mechanical recycling

This is accomplished by melting the plastic and re-extruding it to make yarns.  However, this can only be done few times before the molecular structure breaks down and makes the yarn suitable only for the landfill where it may never biodegrade, may biodegrade very slowly, or may add harmful materials to the environment as it breaks down (such as antimony). This is also called as “Downcycling”.

• Chemical recycling

This means breaking the polymer into its molecular parts and reforming the molecule into a yarn of equal strength and beauty as the original.  The technology to separate out the different chemical building blocks, called Depolymerization, so that they can be reassembled, also called as Repolymerization, is very costly and almost nonexistent.

Most recycling is done mechanically (or as noted above, by actual people). Chemical recycling does create a new plastic which is of the same quality as the original, but the process is very expensive and is almost never done.

• RECYCLING PROCESS

Water bottles are collected and brought to a recycling facility. At the recycling facility the conversion process of turning waste into wearable fabric begins.

• A floatation and separation process removes the caps and labels from the bottles, as they are made of plastics with different characteristics
• Plastic bottles are then processed into flakes
• After being washed the flakes are melted
• Yarns are pulled from the melted polyester
• The result is a clean, valuable, and recycled raw material perfect for the textile industry
• The raw filament yarns are spun into yarn and ultimately woven into variety of different fabrics

Fig 1: The Complete Recycling Process of PET 

• LIMITATIONS OF rPET

Using recycled PET for fibers also creates some problems specific to the textile industry

• The base color of the recycled polyester chips vary from white to creamy yellow, making color consistency difficult to achieve, particularly for the pale shades. Some dyers find it hard to get a white, so they are using chlorine-based bleaches to whiten the base
• Inconsistency of dye uptake makes it difficult to get good batch-to-batch color consistency and this can lead to high levels of re-dyeing, another very high energy process.  Re-dyeing contributes to high levels of water, energy and chemical use
• Unsubstantiated reports claim that some recycled yarns take almost 30% more dye to achieve the same depth of shade as equivalent virgin polyesters
• Another consideration is the introduction of PVC into the polymer from bottle labels and wrappers
• Many rPET fibers are used in forgiving constructions such as polar fleece, where the construction of the fabric hides slight yarn variations.  For fabrics such as satins, there are concerns over streaks and stripes
• Once the fibers are woven into fabrics, most fabrics are rendered non-recyclable  because the fabrics almost always have a chemical backing, lamination or other finish, or they are blends of different synthetics (for example polyester and nylon)

• CONCLUSION

Bottles are now routinely recycled. Currently, the vision that most marketers have led us to believe, is that of a closed loop or cycle, in which the yarns never lose their value and can be recycled again and again.

Few manufacturers, such as Designtex (with their line of EL fabrics designed to be used without backings) and Victor Innovatex (who has pioneered EcoIntelligent™ polyester made without antimony) have taken the time, effort and money needed to accelerate the adoption of sustainable practices in the industry so we can one day have synthetic fabrics that are not only recycled but recyclable.

An Article by :- Chitranshu Katiyar

National Institute of Fashion Technology