Effect of Paraffin Oil Plasticization on the Thermal Stability and Recyclability of Styrene–Butadiene Copolymer Blends

Paraffin oil is routinely mixed into commercial styren block copolymers, yet its effect on how the as-received material responds to repeated heating is rarely examined. Two linear and one branched styrene–butadiene–styrene (SBS) grade and a linear styrene–ethylene/butylene–styrene (SEBS) grade were mixed at room temperature with 0–80 wt% paraffin oil and studied by chemiluminescence (CL), three-cycle differential scanning calorimetry (DSC; 30–250 °C, air and nitrogen) and ATR-FTIR spectroscopy before and after heating. ATR-FTIR revealed silica and calcium stearate on two as-received grades and a 45 % higher vinyl content in one of two nominally identical linear grades. The first heating showed an enthalpy-recovery endotherm of the polystyrene-rich phase (66–80 °C) and an irreversible, induction-type exotherm from 187–213 °C (SBS) and 229–240 °C (SEBS) that continued through cooling and later cycles. Branched SBS released 2–2.5 times more heat and lost 82 % of its trans-butadiene double bonds. Heat per gram of polymer rose with oil content in all grades; in SEBS the oil itself reacted. Infrared carbonyl growth followed the DSC heat, whereas the CL emission yield differed up to 35-fold between grades. Architecture, midblock chemistry and grade-specific additives, more than oil content, govern the thermal behaviour of oil-extended commercial grades.