Tuesday, 28 February 2012

Toxic Risk in Water?

Some plastic bottles continuously leach antimony into drinking water, claim geochemists in Germany.  Water contained in PET bottles contained up to 375 ppt antimony, whereas water in polypropylene bottles contained only 8.2 ppt antimony.  Three months later, the water in PET bottles contained up to 626 ppt antimony. PET is made using an antimony catalyst.

The antimony levels in the bottled water are lower than the US environmental protection agency’s maximum contamination level, set at six parts per billion. However, the researchers are more concerned that antimony continuously leaches into the water. However, the results need further scrutiny before any health implications can be discussed, partly because little is known about antimony’s toxicity.

Following reports of benzene in some soft drinks in the US, the Food Standards Agency asked the soft drinks industry to measure levels in the UK.  Benzene is a chemical that can cause cancer in humans. It is present in the air and has been detected at low levels in some soft drinks as a result of interaction between the preservative sodium benzoate and ascorbic acid (Vitamin C).

The Agency has received results of tests for benzene carried out on 230 drinks on sale in the UK. The results indicate that, where detectable, the levels of benzene are very low and are not a concern for the public health. The FSA is continuing to investigate and will be encouraging industry to make levels as low as possible.
Ozone is a powerful chemical reactant which needs special care.  A recent example has been the incidence of high bromate levels in remineralised reverse osmosis water, following ozone treatment, which converted bromide impurities in the salts to the toxic bromate.  

The lesson to learn from all this is that even minute amounts of impurities could be a possible health risk and these impurities can often form dangerous materials by subsequent chemical reactions.

Monday, 20 February 2012

How Do Bottlewash Detergents Work?

The best bottlewash detergents are formulated products, rather than a single chemical, such as nitric acid, preferred by some of our French colleagues.  Several bottlers were, or still are, from the farming community and nitric acid is ideal for some dairy applications, but not for washing polycarbonate bottles.

The most important consideration in formulating a product is to take account of the different types of water in which bottles are washed.  Often the actual spring water is used as the wash water and this may contain high levels of salts.  Calcium, magnesium and iron are the main elements which can affect wash performance.  Some bottling plants use a water softener, but this is the exception rather than the rule.

A major part of the formulated product has to contain water softening ingredients, otherwise soils will not be removed.  Remember, too, that the heaviest soiling is on the outside of the bottle.  For added wetting effectiveness on polycarbonate, the product should contain a detergent and some alkali to enhance soil removal.  If the product also contains a disinfectant component this will be an added bonus.  Formulating a disinfectant component into a bottle wash detergent can be difficult because of potential incompatibility problems, but it is possible.

Wednesday, 15 February 2012

Polycarbonate vs PET

If you read articles from manufacturers of polycarbonate and PET, the claims made for applications in bottle-making seem at odds. Data are produced to prove that PET or polycarbonate (depending on the origin of the article) is far superior for the production of 19 litre bottles. I have distilled information from several sources to try and provide a balanced picture.

In early history, water was stored in animal skins and large clay pots.  Although storage was temporary and the water was not always pure and sanitary, the containers served a need.  In more modern times water was bottled in glass containers, which were sanitary as well as clear, allowing consumers to see the contents.  However, they were also heavy and breakable.  As in all evolutionary trends, the industry began to look for a packaging material that would perform better than glass.

The search led to polycarbonate. Bottles made from polycarbonate were more durable than glass yet lighter.  Performance outweighed cost, hence the industry invested in new equipment and made the switch to polycarbonate.  Further searches for less expensive materials led to the use of PET, which transformed the convenience single-trip water market.  However, what about 19 litre, multiple-trip containers?

An important aspect is that the moulding techniques are completely different. This allows polycarbonate to have greater design flexibility such as integral moulded handles. PET bottles need a separately moulded solid handle (as shown).

However, PET has a better finish with smooth internal neck and no die lines or need for trimming. On the other hand, PET has a tendency to shrink at high wash temperatures which can cause leakage problems eventually.  PET is more flexible than polycarbonate and can often stand more impact punishment. The plastic distribution is better in PET bottles and the stress tendency is not dependent on manufacturing procedures such as annealing.

PET polymers provide a better barrier to gases when compared to polycarbonate and less tendency to allow odour elements through the bottle wall.  Polycarbonate has better scratch resistance and can be washed at temperatures between 60-70 degrees C without problems. You should obtain more return trips with polycarbonate compared with PET.  The cost of PET resin is less than polycarbonate, but the cost of equipment to make PET bottles is higher.  Polycarbonate can be recycled by grinding to make more bottles whereas PET does not retain the same degree of its original properties.

Other comparisons are possible, but hopefully this has provided you with some insight into the ongoing debate.