Processability and Properties of Re‐Graded, Photo‐Oxidized Post‐Consumer Greenhouse Films

Abstract

Summary: The recycling of post‐consumer plastics leads, in general, to secondary materials having properties worse than those of the reclaimed material and certainly worse than those of the same virgin polymer. This is because of the degradation undergone by the objects during their use and because of the thermo‐mechanical degradation undergone during the reprocessing operations. The change of the molecular architecture is responsible for this worsening of properties. The use of stabilizing systems can slow the degradation during the melt processing but cannot give any improvement of the final properties of the material. In order to enhance the properties of the recycled plastics, some rebuilding of the molecular structure is necessary. The use of suitable additives can enlarge the molecular weight distribution or can create branching and cross‐linking during the melt processing of the photo‐oxidized PE. The processability in film blowing and the mechanical properties of these secondary materials are reported in this work. The rheological behavior, the filmability and most of the mechanical properties of the secondary PE with the rebuilt molecular structure are better than those of the post‐consumer material and similar to those of the virgin polymer.

Quality Concepts for the Improved Use of Recycled Polymeric Materials: A Review

“…The addition of new stabilisers during recycling (restabilisation) may help to both protect the thermo‐mechanical degradation during processing and enhance the long‐term stability of the recycled products, but is not enough to improve their mechanical properties and performance. Modification of the chemical structure and molecular architecture of the recyclates is needed to upgrade effectively the properties of recycled products; this approach has been inspiringly designated as “rebuilding” by La Mantia and co‐workers 89–92. The use of certain additives during mechanical recycling, such as radical generators or compounds with reactive functional groups, can be effective in inducing branching or crosslinking reactions in the degraded polymeric chains from waste materials during melt reprocessing (reactive extrusion); this increases the molecular weight of the chains and improves rheological and mechanical properties.…”

“…The use of certain additives during mechanical recycling, such as radical generators or compounds with reactive functional groups, can be effective in inducing branching or crosslinking reactions in the degraded polymeric chains from waste materials during melt reprocessing (reactive extrusion); this increases the molecular weight of the chains and improves rheological and mechanical properties. This procedure has been successfully applied to upgrade degraded post‐consumer PE from greenhouse films89, 90, 92 and pipes 91…”

“…The mechanical recycling of waste plastic from agriculture may be limited, however, because of high degree of degradation (in this case, photo‐degradation due to extensive exposure to UV‐radiation), moisture and mud content, and due to the presence of dangerous agrochemical residues such as pesticides and fertilisers. Despite these inconveniences, some researchers have reported successful recycling of greenhouse PE films by employing restabilisation techniques,77, 121, 122 rebuilding the molecular structure,89, 92 and adding organic fillers115, 117…”

The role of the disposition of the recycled polymer on the properties of films for greenhouses coverage

“…Different strategies have been adopted to decrease the negative effect of the degradation on the final properties of postconsumer plastics, like stabilization,11–18 regradation,19–21 etc.…”

“…Indeed the synergistic effect of oxygen, temperature, and UV radiation during the lifetime cause relevant damages in the chemical structure and morphology and, consequentely, in the mechanical and optical properties of the postconsumer material, while the combined effect of temperature and stress gives rise more degradation. [4][5][6][7][8][9][10] Different strategies have been adopted to decrease the negative effect of the degradation on the final properties of postconsumer plastics, like stabilization, [11][12][13][14][15][16][17][18] regradation, [19][20][21] etc.…”