Recycling of waste polyurethane shoe sole via aminolysis route

Motivation towards developing an eco-friendly sustainable environment demands extensive research in the field of polyurethane (PU) recycling which has resulted in the most published research area in last few decades. A newer class of PU waste i.e., PU shoe sole was aminolyzed using two novel amines—4,7,10-trioxatridecan-1,13-diamine (1,13-diamine—A) and 1,3-propanediamine (1,3-diamine—B) either alone (A/B) or in combination (A:B = 70:30/60:40/50:50/40:60) in presence of a base catalyst (NaOH–0.2 wt.% of shoe sole) at a temperature of 140 °C (comparatively lower temperature than that needed for other recycling techniques) for 3 h. The amine and hydroxyl functionalities of the aminolyzed products were investigated by amine and hydroxyl value analysis and FTIR spectroscopy. The products depolymerized were further used as hardeners for epoxy coatings considering only amine equivalent weight (AS) and both amine and hydroxyl equivalent weight (ASH) and the mechanical, chemical, thermal and anticorrosion properties of applied coatings were evaluated as per ASTM standards. PU shoe sole depolymerized using amine combination (A:B = 60:40) as aminolyzing agent offered improved qualities when taking into account both amine as well as hydroxyl equivalent weight while curing with commercial epoxy resin.