Post-consumer flow analysis, processing behavior, and application limitations of low-density polyethylene in flexible packaging

Manual. Recycled Plastic Film. Chapter 3: Recycled LDPE. Origin of waste, technical properties, and industrial criteria for use.

Low-density polyethylene (LDPE) is one of the most widely used and strategic materials in the flexible packaging sector, both in terms of volumes sold and its variety of applications. Its flexibility, tear resistance, sealability, and ability to be transformed into thin films have made it, over the decades, the go-to material for bags, pouches, packaging films, and protective wraps. This widespread use is precisely the basis for the abundant availability of post-consumer waste, which today constitutes one of the main sources of recycled LDPE.

Analyzing the origins of post-consumer LDPE waste means examining the relationship between the product's end use, consumption patterns, and the quality of the recoverable material. Unlike other, more rigid or structural polymers, LDPE is primarily used in short-life applications, often related to everyday consumption. This generates a large amount of waste, but also introduces significant variability in terms of the material's composition, contamination, and degradation.

Post-consumer LDPE waste largely comes from flexible packaging intended for direct or indirect contact with various goods. Shopping bags, food packaging films, and protective wrappings for industrial and agricultural goods constitute a significant portion of this flow. Each of these applications leaves a specific imprint on the material, influencing its chemical and physical characteristics upon collection.

A key factor in evaluating post-consumer waste is the material's exposure to degradation factors. During the use phase, LDPE film can be subjected to mechanical, thermal, and environmental stresses that affect the length of the polymer chains and the material's stability. Exposure to sunlight, particularly in agricultural or logistics contexts, can trigger photo-oxidation phenomena that partially compromise the polymer's mechanical properties. Contact with greasy substances, detergents, or organic residues also contributes to altering the profile of the recovered material.

From a recycling perspective, not all post-consumer LDPE waste offers the same potential for recovery.

The quality of recoverable material depends significantly on the collection methods and the conditions in which the waste is disposed of. Household waste sorting, for example, generates highly heterogeneous LDPE flows, both in terms of origin and level of contamination. Conversely, post-consumer waste from more controlled circuits, such as large-scale retail trade or industrial logistics, tends to have more uniform characteristics.

An often overlooked aspect is the presence of foreign materials within post-consumer LDPE streams. Labels, inks, residues of other polymers, and inorganic contaminants pose a significant challenge for subsequent sorting and regeneration stages. Even small percentages of incompatible materials can negatively impact melt behavior during extrusion, making it more difficult to produce consistently high-quality recycled films.

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