How to reduce Acetaldehyde (“AA”) in PET bottles

WHAT IS AA?

Acetaldehyde (AA) is an organic compound, found as a colourless gas at room temperature. It has a strong fruity smell and a distinctive acidic taste. AA is produced by plants as part of their normal metabolism, and naturally occurs in many fruits and foodstuffs.

HOW AA AFFECTS PET PRODUCTS?

AA gives PET products an ‘off-taste’. In most cases the AA taste is masked by sweet or tangy flavours of the beverages contained in the PET bottles. The AA taste however is difficult to mask in pure water, and becomes very easy for the consumer to detect. Water companies are therefore challenged to ensure brand integrity of pure, high quality products, which means undetectable levels of AA in their products.

AA GENERATION IN PET RESINS

AA is generated in PET during the production and injection processing of PET bottles. During bottle manufacture, PET pellets are melt processed at high temperatures (> 260 0C) and injection moulded into preforms.

The preforms are further heated and stretch-blow moulded into containers. It is during the melt-processing stage that AA is generated. As a result it is difficult to avoid AA production and hence ALL PET resins have some residual AA after manufacture. Generation of AA during the melt processing of PET can however be controlled by making adjustments in the barrel of the machine. ]Thorough drying of the polymer material is also important for AA control, as this drives off some of the AA.

HOW TO REDUCE AA IN PET BOTTLES?

Optimization of the melt process by minimizing melt temperature and residence time, can help in minimizing AA generation, however it cannot be entirely eliminated. Residual AA is trapped in the polymer matrix of the bottle. AA trapped in the PET bottle eventually migrates into the atmosphere or packaged contents affecting taste as already mentioned. AA reducers or scavengers can be added to PET resins to reduce the amount of AA trapped in PET bottles. There are various compounds that can be used as AA reducers to decrease the content of AA in PET bottles, and examples of these are; anthranilamide, salicyclamide, salicylanilide, o-phenylenediamine, 3,4-diaminobenzoic acid, 1,8-diaminonaphthalene, and many others. Preferred additives include 1,8- diaminonaphthalene, salicylamide, salicylanilide and anthranilamide. The selection of an AA reducer not only depends on its efficacy, but also cost and ease of incorporation into PET. Tests are currently being done on trials that have various AA reducers, and mixtures of AA reducers incorporated in the PET melt process. The AA reducer product aimed for is one where yellowing of the bottle is not a problem. This means that the AA reducer is not used as the only additive, but in combination with other additives such as antioxidants, colorants, acid absorbers and AA scavengers. AA scavengers are organic compounds that chemically react with the AA to lock into the polymer matrix preventing its migration. Performance Colour Systems offers an AA reducer that is custom made for your application. Examples of AA reducers are PT-0098/1 (Oxford Blue) dosed between 0.03% and 0.1% and PT-0099/1 (Alto Blue) dosed between 0.02% and 0.1%. Performance and dose rates may vary according to application

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