Other single-polymer PSW go through different schemes. Many
foams (namely polyurethane, PU) are powdered and grinded to a
particle size less than 0.2 mm using two-roll milling, cryogenic
grinders or precision knife cutters. Another process used in
mechanical recycling is re-bonding, in which recycled foam flakes
originating from flexible slab stock foam production waste are usually
blown from storage silos into a mixer that consists of a fixed
drum with rotating blades or agitators, where the foam flakes are
sprayed with an adhesive mixture (Zia et al., 2007). Fig. 4 shows
a schematic illustration of the re-bonding process. One of the main
advantages of this process is the ability to obtain a clean product
with new properties, i.e. higher density and lower hardness.