We all know that polyolefins are incredibly versatile materials that have application in many kinds of packaging and other products. However, they are hydrophobic and it can be difficult to compatibilize their surfaces with other materials or interfaces. This is one reason that additives for polyolefins are used. For example, British company Polymer Interfaces’ series of Polarfin© additives are compatible with polypropylene and/or polyethylene but also include polar groups. When added to the plastic, the polar groups will migrate to the surface based on surface energy. This enables a number of things – changes in surface properties and the ability to make modifications more easily.
A more hydrophilic polyolefin surface has applications such as agriculture and food packaging. Bulk bags of produce such as apples or carrots are often sold in the store, and if water condenses on the interior surface it can promote rot. By changing the surface energy and making it more hydrophilic, condensation is reduced and produce can last longer. In an agricultural setting, greenhouses often use a thick, clear plastic sheeting. Condensation can be deleterious by blocking light. Before additives, this might have been addressed with a multilayer film. Additives are an easier (and less costly) method. In another use, surface modifications of polyolefins often require a treatment step such as corona discharge or a chemical etch to temporarily put polar groups on the surface. These treatments generally only are temporary, and can be uneven, and must be done immediately before whatever final modification. Additives that permanently put these chemical groups on the plastic surface create more flexibility for this modifications.
What does all of this have to do with the circular economy? Polyolefins (mostly polyethylene and polypropylene and often in the form of single use packaging) make up something like 2/3 of plastics waste. One of the problems in recycling these materials is in sorting. They are chemically similar, and with similar densities, so sorting can be expensive. At the same time, although they are similar, they still cannot be mixed, and simply regrinding a mix of the two and re-extruding it will result in a product with poor optical and mechanical properties. This is where these Polarfin© additives may have a role. Recently, Evonik has invested in Polymer Interfaces specifically for these additives as a mean to help increase plastics recycling and circularity. If these additives have groups compatible with both polyethylene and polypropylene, they can be used to make blends of the materials with superior mechanical properties. Then sorting becomes unnecessary, and costs of recycling go down. This shows the potential of existing technologies to be repurposed in order improve recycling and materials’ circularity goals.