Mono-material, a ray of hope

The world of packaging is undergoing a radical change. The looming consequences of the climate crisis are a reason to rethink the materials and substances used in packaging and to examine tried and tested packaging materials with an eye towards the circular economy. One measure that more and more companies are taking is to switch to mono-materials. However, this can also be challenging.

First, let’s have a look at the history and status quo of packaging materials. Before the widespread rise of plastic-based packaging in the second half of the 20th century, the predominant packaging materials were paper, cardboard, wood, glass and metal. Plastics, particularly in the field of packaging, had their breakthrough in the 70s of the last century at the very latest, and opened up unprecedented opportunities for packaging manufacturers. The novel material combined flexibility in design, comparatively negligible weight, water-repellent effects and the possibility to hermetically seal products, particularly foodstuffs.

The practical implementation combined the various packaging materials in the form of compounds. Beverage cartons are an excellent example of this. While the packaging exterior consists of relatively low-cost and easily printable plastic, an interior aluminium layer ensures impermeability to oxygen and thus a longer shelf life of the packaged product. If needed, an integrated plastic spout can also ensure easier handling for end consumers. Purely from the perspective of product protection and convenience, this is a successful form of packaging all round.

However, that unfortunately doesn’t solve every problem. Despite all its advantages, composite packaging has a clear downside: recycling it is either impossible or requires a great deal of time and energy. That is because, in order to make the intended product protection fully effective, the packaging layers have to be glued together until they are practically inseparable. If you were to recycle them as-is, the foreign substances would render the final product unusable or, in the worst case, cause irreparable damage to the machine in question. Therefore, this type of non-recyclable packaging is generally separated out and either burned to generate energy (for example in cement mills) or downcycled, not into new packaging, but into other products made of rough plastic bars.

In this context, a real circular economy is difficult to create. That is why today many companies rely on packaging made of mono-materials. Even if you haven’t studied ancient Greek, this term is self-explanatory: Packaging made of mono-material is packaging that consists of one single material. This has the following advantage: As there are no different materials that have to be separated in a laborious process, mono-material packaging is much easier to recycle and turn into new packaging. This leads to less actual packaging waste, and less new material that needs to be brought into circulation to meet the demand for materials. In short, using mono-materials can reduce a company’s carbon footprint in terms of production and thus combat global warming.

Beverage bottles that can be made of PET or glass are a classic example of a mono-material application. In the case of PET bottles, the bottles minus the caps can be recycled to new PET, or rPET, after use (reusable PET bottles can be reused up to 25 times). Glass bottles can be melted down and formed into new containers in a similarly efficient process – always provided that they are sorted correctly. The paper cycle works just as smoothly in many countries. Paper packaging, brochures and old notepaper all land in the paper bin as waste paper and are subsequently reused as new brochures, shipping boxes or office paper. According to the German Environment Agency, over 92 percent of collected waste paper in Germany was reused in 2020.

In addition to these already established raw material cycles, the packaging industry is mainly turning to polypropylene (PP) and polyethylene (PE) in terms of mono-material. These materials combine the general advantages of plastic (individual design, low weight) with a relatively high degree of recyclability. Common applications of these plastics in the food packaging sector include yoghurt pots, bags of chips and food storage containers.

So far, so good. However, switching to mono-materials confronts packaging manufacturers with various challenges. On the one hand, even the best mono-material can’t offer all the functions that a composite material does. That’s simply due to its nature. We need other solutions to ensure the material’s recyclability. One possibility, for example in the area of flexible food packaging, is special coating that gives packaging airtight or waterproof characteristics but does not impair the recycling process. Similarly, some manufacturers are turning to packaging that consists of multiple materials that can be easily separated by consumers after use and thus returned to the different reusable material cycles.

Choosing the right machinery is another aspect that companies interested in mono-materials should consider. Not every material can be used in every filling system, for example in the case of tube bags. However, in the past few years, the mono-material trend has reached mechanical engineering companies as well as packaging manufacturers. Many new packaging machines can be converted for processing modern mono-material packaging with little or no effort, and upgrades are offered for older models. As a result, there are also opportunities for smaller companies that do not want to or cannot make a substantial investment right away to incorporate mono-materials into the production of packaging and thus expand their portfolio.

Finally, we want to point out one potential criticism: Despite the recyclability of PE and PP, the recycled materials cannot simply be used for new food packaging. This sector has high standards when it comes to food safety of materials, as specified by the European Food Safety Authority or the US Food and Drug Administration (FDA), for example. Their guidelines determine how many components of a material that comes into contact with food, for example primary packaging, can “migrate” to the packaged product. When using recycled materials, due to the possible proportion of foreign substances, the degree of migration is larger than when using new plastics. However, by more efficiently sorting packaging waste and using detachable barrier layers, this problem can also be counteracted. Either way, the use of mono-materials is better for the environment when compared with composite materials.