In both NR and SBR, a broad -OH stretching band is observed between 3660 cm -1 and 3125 cm in the unaged material due to hydroxyl groups present in the additives. The signal intensity increases up to 168 h, possibly due to oxidation or hydration, but reduces thereafter as the additives are consumed. A direct result of weathering in both materials is the occurrence of a carbonyl band at about 1713 cm -1 (see * in Figure ) after 168 h of weathering and is prominently present in the skin at 504 h, but disappears in the core. In NR, the asymmetric =C-H stretching band at 3035 cm -1 (i) decreases from 0 h to 504 h, while the skin shows its complete loss at 504 h. Likewise, the asymmetric -CH3 stretching (2959 cm -1 , ii) and asymmetric -CH2stretching (2918 cm -1 , iii) bands also reduce with weathering.