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What are the pros and cons of plastic and metal aerosol cans? Dr Nora Schiemann, Consultant for Technopolis Group on the evaluation of the European Aerosol Dispensers Directive on request of the European Commission, explains in her article in COSSMA.  She points out why plastic aerosols are on the rise and clarifies the common myths of plastic aerosols.

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Plastic aerosols on the rise

Lately, more plastic aerosol packs have been available in the market across Europe. Plastic seems to offer opportunities to create sustainable products. Looking a little bit closer, however, there are also some limitations that are even more restrictive than those for metal cans. After all, pressurised containers made of plastic need to comply with the same safety targets required for all aerosol packs:

  • All aerosols in Europe have to be temperature-resistant up to 50°C
  • No leakage
  • Mechanical resistance up to 50°C and even higher (e.g. to emerge unscathed from a hot water bath and other special conditions that might occur)

In addition, by no means must the mechanical resistance of the aerosol dispenser be impaired by the substances contained in it, even during prolonged storage. This applies to long-term resistance against ingredients and the environment (chemical and biological resistance, UV rays etc.).

Common myths on plastic aerosols

1. Plastic is much cheaper than metal:

However, plastic can be much more expensive than metal, as e.g. beverage bottles cannot be taken as a reference.

2. Plastic can be shaped more attractively:

However, shaping plastic cans in an appealing way is costly. The more complicated a shape, the more material is required to achieve a mechanically-resistant container. Production cost also increases due to higher tooling costs and slower line speed.

3. Plastic has better corrosion-resistance than metal.

However, permeation is a non-starter in many cases. UV rays can compromise the mechanical and chemical integrity of the container. Sometimes material blends are required, which involve higher costs than the round PET-bottle benchmark and are even higher than metal cans.

4. Enhanced decoration options: 

As plastic containers can be transparent, the appearance and decoration options are enhanced. However, the prescribed filling levels of less than 75% for the sake of safety, not to exceed 90% filling level at 50°C, may cause consumers to question the low visible filling level 

Design criteria for plastic aerosols

These are the design criteria for plastic aerosol packs:

  • Material shall not splinter on burst

  • Temperature resistance, but as water bath testing is difficult for plastic containers, particularly when drying with hot air afterwards, alternative testing methods to hot water bath are recommended. An additional high temperature test, e.g. at 60–65°C, is not included in legal proposals (to maintain alignment of legal requirements with those for metal cans). However, it reflects the expected temperature resistance during production and when used by consumers.

  • Long term stability against environmental impact, including stability tests on each individual aerosol product

The biggest disadvantage of plastic aerosol packs

The biggest disadvantage of plastic aerosol packs is the lack of full recyclability. Metal cans are proven to be fully recyclable. This is not the case with plastic cans as they tend to be composite packagings. Normally a plastic container is linked to a metal valve, which is a composite in itself. For metal cans this is not a problem, as minor plastic parts, coatings and imprints do not cause any problems in metal recycling, but in plastic recycling, metal pieces remain a challenge. This is an important aspect for the aerosol industry to keep in mind, particularly when considering that plastic pollution is a concern passed on to future generations.

AUTHOR:


Dr Nora Schiemann,
Consultant for Technopolis Group on the evaluation of the European Aerosol Dispensers Directive on request of the European Commission,
Cologne, Germany
nora.schiemann@imcd.de
www.imcdgroup.com

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