Magazine July 2016

Focus on the textile world: from recycling to networking

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From bottle to needled textile

The billions of polyethylene terephthalate (PET) water bottles worldwide represent a vast source of secondary raw materials that can be recycled several times over. Thanks to its high quality, the bottle material can be reintroduced into the production process – and the raw material for the bottles can be reused several times over without any significant loss in terms of quality.

In addition to the ecological benefits, this also has a positive effect on costs: The cost of recycling old PET bottles is significantly lower than for new PET, which has to be obtained from crude oil.

According to market analyses, Germany produces 470,200 tons of PET bottles annually, around 97 percent of which can be recycled. Roughly one third of that amount (about 152,000 tons) goes to the textile industry, a further third is used again for the production of PET bottles, and the final third is distributed across several different fields of application such as plastic film manufacture or the packaging industry.

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The lifecycle of a PET disposable bottle

1: Pellets – 2: Preform – 3: Full PET bottle – 4: Pressed PET bottle – 5: PET flakes – 6: PET fibers

  • 1) Preparation of the PET pellets

    The raw material used for production of PET pellets is crude oil. In PET manufacturing, a thermoplastic resin is prepared by means of polycondensation – with properties that predestine it for the food industry.

  • 2) Manufacture and transportation of the preform

    To optimize transportation cost and efficiency, PET bottles are not shipped in their final shape but in so-called "preforms". This makes it possible to transport around 700,000 preforms on a truck in place of 15,000 bottles.

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  • 3) Preparation of PET bottles

    At their destination, the preforms are turned into finished PET bottles by means of the so-called stretch blow process. Here, the blanks are heated up to processing temperature and then pressed into the negative mold of the bottle by means of compressed air.

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  • 4) Filling and sale of PET bottles

    After the bottles have been produced they are filled and sealed, and then released for sale.

  • 5) Recycling of non-returnable PET bottles

    Prior to the actual recycling process, the bottles have to be transported to the recycler. For this, they are pressed into bales.

    In the first step of the multi-stage recycling process, the bales are opened and the PET bottles are subjected to a mechanical as well as manual pre-sorting process. Here, foreign substances such as metals or cans are removed. In addition, the bottles are already pre-sorted according to color, because only transparent bottles are used in the process for food-grade PET. Colored bottles are separated, and are often used in the production of recycled fibers.

    The PET bottles, including their polypropylene (PP) lids, are then comminuted in a shredder to a defined dimension. In this recycling step, the so-called "flakes" are created.

    Now the PET and PP are separated in a separation bath. During this process step, the flakes from the PP lids float on the surface, while the heavier PET sinks to the bottom. The flakes are then cleaned and dried, to remove all dirt or contamination, and packaged inside Big Bags. Now the PET and PP flakes are ready for the raw material cycle.

The PET bottle – reborn as fiber

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The recycled PET flakes can not only be used to produce new bottles, but also as a raw material for polyester fiber production. To this end, the recycled pellets are mixed together with so-called virgin pellets produced directly from crude oil. Depending on the mixing ratio, the quality level of the fibers can be influenced in different ways. The slight greenish or bluish tint that can occur in recycled fibers results from use of cheaper flakes originating from green or blue bottles.

Polyester is one of the most popular fiber materials. Its special characteristics, such as its high formability, enable numerous applications. Moreover, the thickness of the fibers and the feel of the fabric can be brought into line with the end-product requirements. Polyester also has the highest tear and abrasion resistance as well as dry and wet strength, and is extremely resistant to breakage and bleaching.

The potential of recycled PET bottles for production of (needled) nonwovens is huge: Experts believe that a 2-liter PET bottle (about 40 grams) can be turned into around 1 square meter of nonwoven fabric. A typical application for nonwovens of such weight range are coverstocks for sanitary products and incontinence articles.

So if the approximately 152,000 tons of PET bottles supplied to the textile industry in Germany were used to produce nonwoven fabric of around 40 gsm, that fabric would cover a total area of ​​3,800,000 square kilometers – even larger than the surface area of India (3,287,590 sq km).

The above reasons clearly show that because of its high availability, its properties and its lower price, recycled PET is a very interesting raw material for the production of nonwovens – indeed, it has already become an indispensable part of it.

Polyester fibers from PET bottles

Polyester fibers are produced by a melt spinning process. Here, the virgin pellets are mixed together with the recycled flakes. The material is then fed to an extruder and melted, until a viscous mass is formed that can be spun. The extruder pushes the spun material through a spinning beam with spinnerets. Depending on the gauge that needs to be achieved in the subsequent fiber product, the spinnerets have a suitably predefined nozzle diameter. During this process step it is also possible to give the fiber strands special cross-sections, such as a triangle or star shape.

The filaments are then passed through a cooling shaft. Here, the spinning process is completed and the filaments are cooled.

Now the fiber cable is fed into several pairs of rollers running at different speeds, so that the fibers are stretched. The interaction between the hole size of the spinneret, the stretching in the cooling shaft, and the pairs of rollers ultimately results in the final level of fiber fineness and crystallinity.

After this production step it is also possible to crimp the fiber cable, using a crimping chamber. Following these process steps, the fiber cables are cut to the desired staple length and compressed into bales.

A second life for environmental protection

The recycled PET flakes processed into polyester fibers are now ready to complete an additional lifecycle in a manufacturing process of the nonwoven industry. Through the use of recycled PET bottles, manufactured textiles can make a significant contribution to climate protection and to conservation of resources.

Moreover, the fibers can be integrated into products that are already making a contribution to environmental protection. Examples here include needled air filters for cleaning, or high-density geotextiles for counteracting erosion.

Other fields of application are also conceivable, of course, such as:

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  • Acoustic insulation boards
  • Automotive interiors (visible and invisible)
  • Artificial leather substrate
  • Carpets (floor coverings)
  • Hygiene products
  • Insulation felts
  • Towels and cloths
  • Highly fluffy and needled nonwoven products

The applications and cases are exceptionally diverse and varied.

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The processing of polyester fibers from virgin pellets or regranulated PET flakes puts reliable production of nonwovens to a severe test, due to the different fiber qualities in the needling process. Depending on the field of application, Groz-Beckert can provide needles and products that significantly stabilize the factors influencing the production process.

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The GEBECON® needle, for example, with its increased stability and therefore long service life, can be used in areas where, despite increased production speed and load, no needle breakage may occur.

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The twisted needle can contribute significantly to the effectiveness of the needling process, achieving higher densification and improvement of physical properties in comparison to a standard needle.

Groz-Beckert also offers a felting needle with a projectile point, especially for needling of abrasive fibers and recycled polyester. The advantage of this shape and geometry is that it specifically counteracts bifurcation of the needle point.