Over the last years glass bottles and jars have been replaced by plastic (mainly PET, PE or PP) and this change in packaging format will continue as currently a debate revolves around supplying baby food in plastic containers rather than glass jars, seeing as they are lighter and less likely to break. There are, however, a few problems with plastic containers that the consumer is concerned about. That’s not in the first place the environment, as the packaged consumer goods company might choose for a bio-plastic or rPET variant. But it’s like the BPA in cans and tins (which the industry is laughing away), the fossil-fuel migration in food products packaged in paperboard and with plastic bottles and jars the permeability to various gases and the risk of harmful substances contained in the packaging seeping into the food.
We know that plastics have a very poor gas barrier, i.e. they are permeable to air, which can pass through the material in both directions. “This is why water stored in PET bottles loses carbon dioxide and why food goes bad, for example by changing its flavour. A synthetic material that does not leak ingredients of some sort does not exist”, says Prof Dr-Ing. Peter Awakowicz of the Institute for Electrical Engineering and Plasma Technology, Faculty of Electrical Engineering and Information Technology of the Ruhr-Universität in Bochum, Germany.
Recent years have seen various technologies to improve the impermeability and diminish the risks of the influence of harmful substances inherent to plastic packaging material. I selected two recently published research results. The first is of the above mentioned university team of Prof Dr-Ing. Peter Awakowicz, the second is a story of a Brazilian company using silver micro-particles in plastic bottles to double the shelf life of milk.
Plasma-based coating processes
At the Institute for Electrical Engineering and Plasma Technology of the Faculty of Electrical Engineering and Information Technology at the Ruhr-Universität in Bochum/Germany, Prof Dr-Ing. Peter Awakowicz and his team developed processes for coating surfaces with protective layers that render the synthetic material less permeable.
The RUB engineers developed plasma-aided coating processes for PET bottles. A barrier layer inside the bottle makes the plastic less permeable.
The coating would make plastic packaging one hundred times more impervious than it is today. Consequently, the shelf life of food products would be prolonged, and they would be protected from substances that seep out from the synthetic material. With the coating, the volume of those substances could be reduced to 1% of the volume that usually seeps out.
The RUB team studies in what way an object with any chosen shape made from a specific synthetic material may be best coated using a plasma. For this purpose, the researchers utilise plasma enhanced chemical vapour deposition, i.e. PECVD. In the course of this process the substance hexamethyldisiloxane is vaporised, blended with oxygen and dispersed in plasma. Thus, silicon dioxide deposits on the synthetic material. The plasma provides the energy necessary for the process.
The barrier layer which is thus applied to the synthetic material has a thickness of a mere 50 nanometres. Thicker layers would tear and they would, moreover, disrupt the recycling process, because the silicon dioxide layer is nothing but wafer-thin glass. Negligibly small, the quantities in the coating layers are not relevant for recycling. They are not applied to the synthetic material directly, however, as the process begins with a protective layer. This is because tests have shown that the oxygenated plasma process for depositing silicon dioxide affects the synthetic surface. The result is a so-called weak boundary layer.
“No matter how great a barrier layer you apply to this damaged layer, it will never hold”, states Peter Awakowicz.
The plasma parameters ultimately determine how impervious, hard and elastic the barrier layer becomes. Different synthetic materials, such as PET, polypropylenes or polycarbonate, require different plasma properties. The item’s shape is likewise significant.
An argon plasma in a PET bottle – just the bottle bottom visible here. The plasma “cleans” and activates the interior bottle surface.
For more details about the plasma process read the full article: “Making synthetic materials more impervious”. (photos courtesy RUB)
Silver in plastic bottles to double shelf life of milk
Agrindus, an agricultural company in São Carlos, in São Paulo state/Brazil managed to increase the expiry date of fresh pasteurized milk type A from 7 to 15 days.
In Brazil the most consumed type of milk is the long-life (TetraPak, SIG), which passes through a sterilisation process at ultra-high temperatures (130 to 150°C for 2 to 4 seconds), in order to significantly decrease the number of bacterial spores from milk and allow the product to be marketed for a period of up to six months at room temperature.
But the very popular fresh milk, which is called “Tipo A”, undergoes a pasteurisation process of mild temperatures at the farm and requires refrigeration. By doubling the shelf life of this type of milk the farmer can make gains in logistics, warehousing, quality and product safety.
This shelf-life extension was achieved through the incorporation of silver-based micro-particles with bactericidal, antimicrobial and self-sterilising properties, in the rigid plastic bottles used to package the milk produced by the company.
Nanotechnology comprises technological developments within the nanoscale. Interdisciplinary, it falls within the field of nanoscience, which involves chemistry, physics, biology, computer science, engineering and environment.
Governed by the laws of quantum physics, the universe of nanoparticles causes the material to present very different behaviour than usual, on a macroscopic scale.
Known as intelligent materials, under the nanotechnology treatment, they present completely new properties or in combination with the originals, have multiple or adaptive functions and allow interfacing organic and inorganic materials, among other features.
The technology, developed by Nanox, a nanotechnology company also based in São Carlos, is mixing the micro-particles as a powder in the polyethylene matrix used for injection or blow moulding the plastic bottles. The micro-particles are inert, i.e., do not present the risk of detaching from the bottle and come in contact with the milk.
Note: As there is, at this moment, no clear legislation, neither in the US nor in Brazil, on the application of particles on the nanoscale (billionth of a metre) for products in contact with food, the company adopts nanotechnology processes that result in silver particles on micrometre scale.
The technology consists in the deposition of silver particles at the nanometre scale on the surface of ceramic particles (silica). The adhesion of the silver nanoparticles results in a ceramic matrix composite (composed of two different materials) in the micrometre range and with bactericidal properties.
The effect of the combination of silver particles with the ceramic matrix is synergistic, the company states, as silver has bactericidal property and silica not, but enhances this action and helps in controlling the release of silver particles to kill bacteria.
In addition to Agrindus, the material is also being tested by two other dairies, which distribute fresh milk in plastic bottles in São Paulo and Minas Gerais, and by companies in the Southern region of Brazil that sell fresh milk in flexible plastic packaging (pillow packs). For the flexibles the media is added to the inside of the bag without using any additives in the food product. For these packages the material is able to increase shelf life from 4 to 10 days.
Nanox plans to market the product in Europe and the United States, where much larger volumes of fresh milk are consumed than in Brazil.
Two interesting developments in enhancing the shelf-life of food packaged in plastic bottles. There is more going on in bottle manufacturing as well as we have seen some very interesting developments in packaging of milk products in cartons. But that’s all for a next time.
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