Recycling Adhesives: A
Recycling Adhesives: A problem and solution in a circular economy Adhesives are compounds that are used to bond materials and hold them together once their surfaces come into contact. Their properties allow them to easily join materials of different natures. This has led to the development of myriad adhesive products for different sectors and applications, which is why these materials are of such indisputable value. But their very benefits sometimes lead to rejection in a society where sustainability and the circular economy are increasingly permeating all areas of our lives. These materials can become an obstacle when trying to recover components and separate materials to create pure flows and achieve adequate recycling. In some sectors such as construction, materials can be joined using other methods (dry connections), but this is not easy to implement in all sectors and much less in the packaging sector. As in other applications, adhesives in the packaging sector are a fundamental part of most products. Most food is now packaged in materials made of plastic due to properties such as lightness, easy transformation, and barrier properties. However, a single plastic material cannot meet all the requirements to guarantee proper food preservation. Therefore, a great deal of plastic packaging is made by combining different polymers on demand, depending on the products to be packaged. This is known as multilayer packaging. Currently, the main problem with these kinds of packaging is that they are very difficult to recycle because the polymer layers tend to be immiscible. Multilayer packaging makes up the greatest proportion of nonrecyclable packaging, around 20 % of all flexible packaging. Therefore, in order to increase the recycling rate, new strategies are required. Tackling this problem based on packaging design is a commonly used option and involves replacing heterogeneous multilayer packaging with singlematerial packaging. However, as mentioned, it is often not possible to provide the necessary properties for the proper preservation of some foods and this has a direct effect on food waste. Another option would be to join multilayer packaging materials in such a way that they could be separated again at the end of their shelf life. The individual components could then be recycled separately. It is here where adhesives can provide a solution for recycling multilayer packaging. As mentioned, the main function of adhesives is to join, but what would happen if these same adhesives could also help with separation? 18 bioplastics MAGAZINE [06/22] Vol. 17
Magnetic for Plastics www.plasticker.com • International Trade in Raw Materials, Machinery & Products Free of Charge. • Daily News from the Industrial Sector and the Plastics Markets. • Current Market Prices for Plastics. • Buyer’s Guide for Plastics & Additives, Machinery & Equipment, Subcontractors and Services. • Job Market for Specialists and Executive Staff in the Plastics Industry. Up-to-date • Fast • Professional Recycling But adhesives don’t only play an important role in recycling solutions for packaging. They are also of interest in compostable packaging solutions, given that not all packaging is designed to be recycled. Some applications and packaged foods require compostable solutions. Like conventional packaging, this packaging can be made of a mixture of biopolymers, it can be attached to other materials such as paper and the adhesive can even be on labels. In these cases, the adhesive used should not compromise the packaging’s compostability, which means that it should also be compostable. Companies such as BASF are working on the development of these adhesives and have launched some solutions on the market. In recent years, the study of this type of adhesives, called reversible adhesives, has generated great interest. These adhesives can be intrinsically reversible, that is, they are formulated so that, at the end of their shelf life, an external stimulus (UV radiation, IR, temperature, pH) produces a reversible reaction in the adhesive so it loses its binding function, and the materials are completely separated. Other types of adhesives can be formulated with additives sensitive to a specific stimulus (radiation, UV, IR, temperature, pH) so that, when they are subject to this stimulant, breakage points are created in the adhesive and the materials separate more easily. Reversible adhesives are therefore seen as the perfect solution for recycling multilayer packaging, but implementation of these solutions requires changes in current recycling systems and a firm commitment from recyclers. In recent years, in both Spain and Europe, there has been special interest in this type of solution due to the European Circular Economy strategy, which set the goal of recycling 100 % of European packaging by 2030. AIMPLAS, the Plastics Technology Centre, is aligned with the European Circular Economy strategy and its mission with society is to promote environmental sustainability and innovative product models that have impact. People at Aimplas, therefore, work intensely on the development of effective and environmentally sustainable solutions. One example of this is the ADHBIO Project, which is funded by the Valencian Innovation Agency (AVI). Its main goal is to obtain a hot-melt adhesive with 95 % of renewable content that provides the same functionality as conventional nonbiodegradable adhesives of fossil origin. This adhesive must do two things. It must allow the layers to be separated because it is removable or peelable, which represents an advantage when managing multilayer packaging that will be recycled at its end of life. It must also be possible to manage the adhesive jointly when both the adhesive and the packaging are compostable. Aimplas has also worked on the development of reversible adhesives for sectors other than packaging, although the knowledge acquired can be applied to this sector. /www.aimplas.net By: Jezabel Santomé, Packaging Researcher AIMPLAS, Plastics Technology Centre Paterna, Valencia, Spain bioplastics MAGAZINE [06/22] Vol. 17 19
