Danger in the Bottling Plant

In the UK, the noise level in bottling plants which requires employers to make hearing protection available to workers is 80 dB, and the level at which workers must wear hearing protection is set at 85 dB.  The Control of Noise at Work Regulations 2005, which come into force on 6 April 2006, require employers to do the following: assess the risks employees face from noise at work; take action to reduce noise exposure that produces such risks; provide employees with hearing protection if the noise exposure cannot be reduced sufficiently by other methods; ensure that legal limits on noise exposure are not exceeded; provide employees with information, instruction and training; and conduct health surveillance where there is a risk to health.

The Health and Safety Executive (HSE) has produced a free leaflet that provides useful information on a number of areas, including: how loud noise can damage hearing; how to assess and control noise at work; different types of hearing protection; when to inform and consult workers; and health surveillance.

Chemicals are often another of the major hazards to be found in a bottling plant and working with chemicals requires a risk assessment. Risk assessments, training in chemicals handling and COSHH issues should be provided by your supplier as part of the service.  Manual handling of chemicals creates a high potential risk, however dangerous handling of chemicals can be avoided by use of suitable proportioning and dosing devices, a range of which is available from several suppliers.

Hydrogen Peroxide or Peracetic Acid?

In the bottle wash process, peracetic acid is often used as terminal disinfectant before the final water rinse.  The reasons for choosing peracetic acid are well known, such as excellent activity gainst bacteria, spores, yeasts and moulds, a reasonable price (particularly for larger quantities), good efficacy even at low temperatures and harmless decomposition products (vinegar and water). Although, there has been some concern that if not rinsed adequately, vinegar could act as a bacterial nutrient.

However, if you have a concern about your chemical effluent and normally have to use special facilities to cope with it, hydrogen peroxide is the friendliest terminal disinfectant to use.  The breakdown products are water and oxygen, so, if released into ground water, they will actual have a beneficial effect by oxygenating the ground water.

Hydrogen peroxide is used at a similar concentration to peracetic acid and the efficacy against bacteria, yeasts and moulds is the same, with just a slight reduction in effect on bacterial spores. Pricing is not as different as you may imagine.  Normally, bulk hydrogen peroxide is sold as a 35% concentrate, whereas peracetic acid is normally delivered at 5%, hence although the drum price is very different, dilution of hydrogen peroxide down to the use concentration will easily offset the higher drum price.

Peracetic acid and hydrogen peroxide are commonly available from several suppliers.

Sell-By Dates for Chemicals

I have been asked by several customers about sell-by dates related to chemicals. This depends on the type of chemical. Products based on detergents and water softeners, for bottle washing, and descaling chemicals have a very long shelf life because generally there are no unstable elements in the formulations.

Shelf-life becomes more of an issue when oxidising disinfectants are considered such as peracetic acid and hydrogen peroxide-based disinfectants. These materials are inherently unstable (that is partly why they work well as bacteria killers) and require stabilizers in the formulation to lengthen the shelf-life.  Care should be taken in storing these materials so that the decomposition is not accelerated.

Conditions which can accelerate this are: excessive heat and light and contamination. The golden rules are therefore to store in a cool place and out of direct sunlight. The caps should never be left off, to prevent any possibility of contamination from the surroundings.

Most of these materials will retain there potency for over one year, but this is very dependent on storage conditions. The decomposition will occur slowly but gradually during the year, so if you have older stock it may be necessary to check concentrations in use and, if necessary, increase the concentration slightly to compensate for any loss. 

How to Wash Polycarbonate Bottles Without Stress

I have written about micro-cracks in polycarbonate bottles previously, but it is worth going into more detail here because this phenomenon can be avoided.  The consequences of not being aware of micro-cracks can be leaking bottles and contamination of water with unfiltered air while the bottle is on the cooler.

Polycarbonate bottles are produced using the extrusion blow moulding process in which a tube of hot plastic is extruded between two open halves of a mould.  When the tube, or parison, reaches the proper length, the mould halves clamp together and air is injected to force the parison to the shape of the mould.

Cooling water is then circulated inside the mould halves to cool the plastic until it is rigid.  The mould opens, the part is ejected, any excess flash is removed, and the bottle is almost ready for use.

The need for a high production rate dictates a rapid cool-down following the blowing operation.  Unfortunately this creates areas of unequal stress in the plastic, particularly at the clamping points where the mould comes together.

Bottle producers relieve the stress by re-heating the bottle to just below the softening point of the plastic and then allowing it to cool slowly.  If done properly, this succeeds in removing most of this induced stress.  If hurried, some of the stress remains.

The bottles then can easily form micro-cracks when subject to further stress.  This may be from the use of incorrect bottle-wash chemicals, the bouncing movement of bottles in the delivery truck, stress of pressurising during the filling operation or use of badly designed bottle racks.  The older the bottle, the more likely micro-cracks will appear.

These cracks are sometimes difficult to see (see the microscope view).  However, when the bottle is inverted on the cooler, after drawing water, a vacuum exists briefly and air can enter through the micro-cracks as well as through the filter.  Bacteria and algal spores also enjoy the haven of the micro-cracks during bottle washing.

Stress cracking with the wrong kind of detergent can can occur rapidly and reduce the number of viable wash cycles of the bottle while encouraging algal growth ("green bottles").  Test rigs can easily demonstrate the results of chosing the wrong bottle-wash detergent (see photo showing broken polycarbonate strips).

 Various bottle-wash detergents are available on the market that are specially formulated to avoid stress cracking of polycarbonate while ensuring a clean bottle. 

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.

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.

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.