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What is Acetaldehyde?

Acetaldehyde (short for AA) is a kind of compounds that exists naturally in many citrus fruits and other foods and has a distinctive acidic taste. Acetaldehyde in the PET bottle is generated in the melt-process of PET. During bottle manufacture the resin pellets are dried and melt at high temperatures (higher than 2600C) and are injection moulded into preforms. The preforms are then reheated and stretch-blow moulded to form a container. It is during the melt-processing stage that AA is generated.

How the AA affects PET container?

Generally speaking, the flavour of AA is barely detected during beverage consumption. Carbonated soft drinks, for example, have very sweet or tangy flavours that mask the slight taste of the plastic. But the taste of pure water is not strong enough to mask acetaldehyde, and so it is easier for the consumer to notice the presence of AA. Consumers rank taste as the number one criterion when selecting a water brand. Even minor differences in taste will affect sales.

How to minimize the AA generation?

There are a number of ways to reduce the AA level. First of all, choose the right PET resin. Resins are available with properties that are specifically tailored to the needs of water containers. For example, Voridian Aqua PET resins 18696 and 20837 are considered leaders in low AA levels. Each has a low intrinsic viscosity (IV) of 0.72 and 0.76 respectively. The low I.V. minimizes AA generation during melt-processing. However as the I.V increases, the chains become longer, the mechanical strength increase and the resistance to stress cracking is improved. For example, carbonated soft drinks require materials with an I.V. of 0.78 or higher because the internal gas pressure makes it susceptible to stress cracking. That is to say it is important to choose a PET solution with the proper balance between low AA levels and high performance.

Optimization of molding condition by minimizing melt temperature and residence time can also reduce the AA generation. However it cannot be entirely eliminated. Since AA boils at below room temperature, it eventually migrates out of the PET into the atmosphere or into the packaged contents, affecting taste. The amount of AA that migrates is directly related to storage time and temperature.

What is the recycle PET?

One of the most outstanding points about PET is recycle. Recycled PET can be used to make clothing and carpet fiber, as well as new bottles for non-food products such as cleaning products. Some PET bottle even can be refilled after many approved processes to ensure no pollutions and enough properties to meet the final quality requirement.

One of the simplest and the most popular way is use granulator to crush the PET products, and then mix the crushed PET granular with virginal PET resin, but no more than 20%.

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