Acetaldehyde level in PET Bottles and Taste of water

Acetaldehyde is generated during the production and injection processing of poly (ethylene terephthalate), PET material. It can cause change of taste in bottled water.

Mostly acetaldehyde worries originate from the barrel during the injection process. All of PET resin manufactured, have some residual acetaldehyde based on the grade. Acetaldehyde is only generated while the PET resin is in its melt condition, therefore it can only be controlled by adjustments in the barrel (90%) and hot runner (10%) of the machine. The generation of acetaldehyde is not linked to moisture content of the material, although in the process of being dried, acetaldehyde can also be driven off. Therefore, correct drying is also important for acetaldehyde control.

Possible causes of likelihood and / or ease of correction:

Barrel / hot runner heater overriding Acetaldehyde A.A. in poly (ethylene terephthalate) processing. Confirming that all heating zones are operating correctly will reduce problems such as:

1. Thermocouples are seated correctly and are free of any damage.
2. All heaters are drawing correct amperage using a clip-on ammeter.
3. Wire connections are tight.

Melt temperature settings too high

Running the machine with the lowest practical melt temperature will reduce the risk of hydrolysis causing lowered I.V., and will limit degradation of the material that can lead to increased A.A. levels and other faults.

Using a melt temperature that is too low can cause problems such as:

1. Damage to screw tip
2. Broken low shear bolts
3. Very long screw charge time
4. Poor mixing of the material

Injection velocity too high

Maintaining a low injection speed can reduce the occurrence of shear forces in the material. Shear is the key factor influencing overheating material and IV reduced, thereby reducing the rate of PET resin to prevent excessive damage.

Screw rpm too high

Screw rotation speed will be reduced. This will prevent excessive shear and related friction heat occurs. The result will be improved control of acetaldehyde.

Insufficient temperature / airflow in dryer

Faulty dryer will cause hydrolysis of the material in the machine barrel. More than 60% of all the PET processing related failures can be traced back to the machine. Drier in the best condition will allow the molding machine with maximum efficiency and quality of performance.

Dew point

Correct dew point may vary according to the manufacturer of the dryer, consult the maker’s manual before assuming an error exists.

Incorrect choice of raw material

One way to alleviate this is to use a copolymer. CHDM or isophthalic acid comonomers lower melting temperature reduces the crystallinity of PET. Thus, the resin can be formed at lower temperatures and lower force.

Worn / damaged injection screw

If the injection screw wear, damage, or an old design, it may not properly plasticized material and can cause excessive shear forces.