Impact of multiple extrusion on LLDPE cast stretch film performance in pallet wrapping

Abstract

The upcoming European Packaging and Packaging Waste Regulation (PPWR) mandates at least 35% post-consumer recyclate in non-food packaging by 2030, increasing to 65% by 2040. Consequently, linear low-density polyethylene (LLDPE), the dominant material in stretch films, will likely be subjected to multiple extrusion cycles during recycling. This study investigates the impact of multiple extrusion cycles on film quality via a controlled closed-loop recycling approach. Virgin LLDPE was re-extruded up to 15 times and incorporated into the core of three-layer cast stretch films, with virgin polymer in the outer layers. Seven films (16–27 µm) were produced: a virgin reference and six films containing 35% or 60% regranulate derived from 5, 10, or 15 extrusion cycles. Mechanical performance was evaluated through small-scale testing, film-on-roll evaluation, and full-scale pallet wrapping with transport simulation. Complementary chemical analyses (DSC, GPC, GC-MS) assessed polymer degradation. Results revealed severe deterioration in machine-direction tear resistance, dropping from 5.33 N (virgin film) to 0.70 N (60% regranulate, 15 cycles). Visual inhomogeneities (“gels”) surged from six defects per meter in the virgin film to 139 defects per meter in the 60% 15x film. Chemical characterization confirmed progressive degradation dominated by chain scission and structural heterogeneity, coinciding with a 90% depletion of the Irganox 1076 antioxidant after 15 cycles. Despite this degradation, most films allowed for stable pallet wrapping and transport tests showed no visible decline in performance. The only exception was the 60% 15x film, which failed even at a modest 100% pre-stretch. These findings demonstrate that adequately designed stretch films with high regranulate content can ensure load stability, providing a scientific foundation for meeting future PPWR targets.