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Odour problems in finished goods

If finished goods have an unpleasant odour on arrival, investigation can ascertain the source and eliminate the problem.

Many new products have an inherent, but not unpleasant odour that people readily associate with the individual items. For instance, new carpets, leather goods and car interiors all have their own distinct smell. In fact some fragrance manufacturers have now developed aromas that mimic these ‘new product’ odours in order to capitalise on consumer perceptions of luxury items.

However, some materials may develop odours which are not desirable and in many cases these are not apparent during the production and packaging stage but become evident only after a long period of transportation and storage in a sealed container. At SATRA we have investigated a wide variety of products with odour problems, from textile duvet covers and curtains, car mats and covers to upholstered furniture, carpets, clothing and footwear. This article looks at some of the potential causes of these malodours and the implications for the products affected.

For an item to have a smell it must contain some volatile compounds, which can be emitted from the product and detected by the human nose. This applies to items that are deliberately given an odour, such as an air freshener or scented candle, as well as those from which a smell is undesirable. The nose is a very sensitive organ and can often pick up odours at very low concentrations. Problems arise when the perceived odour is considered to be unpleasant. Such odours are often categorised by association with a potential origin: hydrogen sulphide is the smell associated with rotten eggs and organic amines are associated with fish.

Initial assessment

When an odour is discovered in a product or material it often raises health concerns, for example with the operatives who are unpacking the containers. An initial assessment by the SATRA odour panel (pictured left) can normally be carried out inhouse to broadly classify the type of odour.

If the smell is ‘damp’ and ‘musty’ then it is likely to be linked to the action of micro-organisms on the materials. This smell is often found in conjunction with visible signs of mould growth, although the absence of visible signs does not automatically discount the presence of micro-organisms. For micro-organisms to grow they require three things: food, moisture and warmth. Leather and other natural materials will provide the food and potentially the level of moisture and temperature in containers will be within the range to sustain growth. The unpleasant odour is actually caused by the bacteria or fungi eating and degrading the materials.

An ‘acrid’ smell can normally be linked to synthetic materials such as polyurethane (PU) or ethyl vinyl acetate (EVA) and is due to either process chemicals remaining in the material or degradation which has begun through poor storage. It is the breakdown of these materials that causes the smell. In some cases the cause of degradation may be microbiological in origin.

If the product has a strong ‘chemical’ odour (petrol or mothball type smells) then the origin is probably from the use of solvents and oils in production. For example, solvents are found in adhesives, cleaners and lacquers and oils in rubbers and leathers. Low boiling point solvents will evaporate quickly and any residual odour will often dissipate during transportation if the products are not packed in air-tight containers. However, high boiling point solvents, such as naphthalene (mothball odour), will not evaporate quickly at normal temperatures and so may remain in the product long after it has reached its destination and in some cases may never be entirely removed.

The gas chromatograph can separate and identify specific VOCs in a material

Where solvents are used in the production process, they should ideally be of a low boiling point and sufficient time should be given to allow solvents to air off before components are assembled prior to final packaging and sealing. Some solvents are odourless and these will evaporate with no associated smell. However, poor quality solvents could be contaminated with benzene, xylene and other potentially harmful chemicals and their presence should be investigated.

Laboratory assessment

In the laboratory we assess odour by dismantling the product into its component materials. The odour of each material is assessed on receipt and also after overnight storage at an elevated temperature in a sealed container. This will characterise the odour with respect to whether it is acceptable or not from a consumer’s point of view.

If items are received with a strong odour and there is no evidence of a physical reason for the odour, such as the presence of mould growth, a product or material can be stored in warm conditions to see if the odour diminishes. If the odour remains, it may be necessary to determine the cause by chemical analysis.

To identify the specific chemicals that are associated with an odour, we carry out what is known as a ‘headspace’ analysis. A sample of the material is sealed in a glass vial and heated to approximately 80°C to 120°C to drive off any volatile components. A portion of ‘headspace’ air taken from above the sample is then injected into a gas chromatograph with a mass selective detector (GC-MS). Using this machine we can separate, detect and identify the individual Volatile Organic Compounds (VOCs) present in the material.

It is also our practice to allow a material or product to air in the open laboratory, in a well-ventilated place, to determine the persistence of the odour. If the item is only lightly contaminated with very volatile solvents then the odour will reduce quickly on airing. If this is the case then allowing the products to air in a wellventilated area for a short period of time may remedy the problem, allowing the goods to be sold.

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Odour problems are known to occur when changing suppliers, or when suppliers change the material composition without informing the client company. These problems can arise suddenly without warning and can be costly to rectify. SATRA has considerable experience of tracking and identifying product odours and is able to assist members with their problems. Please email chemistry@satra.com if you require any further information or testing.