From waste stream to film performance: mechanical properties, process stability, and use criteria for recycled LLDPE

Essay. Recycled Plastic Film. Chapter 4: Recycled LLDPE: Structure, Behavior, and Industrial Design in Flexible Packaging

Linear low-density polyethylene (LLDPE) occupies a unique position within the landscape of polymers used for flexible packaging. Unlike LDPE, whose behavior is strongly influenced by the presence of long branches, LLDPE has a molecular structure characterized by short branches, distributed more evenly along the polymer chain. This architecture gives the material a set of distinctive mechanical properties, particularly high tensile and tear strength, which has favored its adoption in more technically demanding applications.

In the context of recycling, LLDPE presents different characteristics and critical issues compared to LDPE. The greater mechanical strength of virgin material, combined with its widespread use in high-stress applications, directly influences the quality and behavior of post-consumer waste. Analyzing the types of LLDPE waste therefore means considering not only the material's origin, but also the stress conditions to which it was subjected during its previous life cycle.

One of the most significant post-consumer LLDPE streams is the stretch film used for palletizing and load securing. This material is designed to operate under high elongation conditions, with elastic-plastic behavior that allows it to maintain tension over time. During use, the stretch film is subjected to intense and prolonged mechanical stress, which induces significant orientation of the polymer chains. Upon recovery, this residual orientation represents one of the key factors influencing the behavior of the recycled material.

From a recycling perspective, LLDPE stretch film is a highly attractive raw material due to its high volumes and relative chemical homogeneity. However, the mechanical properties of the recovered material are strongly influenced by the degree of deformation it undergoes during use.

In many cases, recyclate derived from stretch film exhibits an altered molecular weight distribution and is more sensitive to process conditions, requiring careful qualification before use in new applications.

Along with stretch film, another significant type of LLDPE waste is represented by drums and large-format flexible packaging, used to contain and transport industrial materials. These products, while formally classified as flexible packaging, are designed to withstand high mechanical stress and are often thicker than traditional films. The LLDPE used in these applications is formulated to ensure strength and puncture resistance, characteristics that are also partially reflected in the recycled material.

Waste from drums and flexible bags generally has a lower level of contamination than domestic flows, especially when it comes from controlled industrial circuits.

A third highly significant stream is made up of so-called LLDPE technical films. This category includes materials used in specialized applications, such as barrier films, coextruded films, and multilayer structures in which LLDPE performs a specific function within the system. The waste from these applications can be of both post-consumer and post-industrial origin and is more complex in composition than monolayer films......

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