Assessing the feasibility of mechanical recycling for plastic tree shelters used in agriculture and forestry: degradation and contamination of waste

Plastic tree shelters are widely used in agriculture and forestry to protect young plants from predators and generate a favorable microclimate, thus increasing survival and growth rates. Considering that several thousand tons of plastic tree shelters (mostly polypropylene, PP) are used each year in Europe and that discarded aged shelters can release microplastics, residues of additives, and even pesticides, the destination of this material after use is a matter of concern. Mechanical recycling is the best option for these residues, but its technical feasibility depends on the polymer degradation level and its contamination, both by inorganic materials and by residues of additives and/or agrochemicals. Therefore, not all tree shelter waste is suitable for recycling. The main objective of this work is to characterize the degradation and contamination of PP tree shelters used in agriculture and forestry, to obtain information on the feasibility of their mechanical recycling. The results show the presence of fungicide residues only in some tubes used in agriculture. Although the external faces of the tubes appear strongly degraded, the degradation of the overall tube material is much less due to a dilution effect. Thus, we can conclude that most PP tree shelters, even those used for several years in harsh climates, could be successfully subjected to mechanical recycling.