et al., 2003; Kazemi-Najafi and Englund, 2013). Reduction in crystallinity can be related to crosslinking which takes place in plastics during exposure to thermo or photo-oxidation, because the crystallinity of the solid polymer decreases with increases in the crosslinking (Tamboli et al., 2004). An increase in mechanical properties like the modulus of recycled PP and PE compared to virgin material can be ayyributed to crosslinking of the polymer chains by chain scission (NarasimhaMurthy, 2005). The recycled PP and PE contains smaller polymer chains (lower molecular weight) that are formed by chain-scission during the recycling process (may by crosslinking, too). These results show a change in the structure of the recycled plastics.