Increasing Polypropylene High Temperature Stability by Blending Polypropylene-Bonded Hindered Phenol Antioxidant

Currently, hindered phenol (HP) antioxidants mixed in PP products provide thermal-oxidative protection during PP melt processing (homogeneous mixing). However, there are concerns about their effectiveness during applications. This paper presents computer simulation and experimental results to demonstrate a facile phase separation of HP molecules in the PP matrix and investigates a new approach that can dramatically improve PP thermal-oxidative stability under elevated temperatures. This technology is centered on a new PP–HP copolymer containing a few comonomer units with HP moieties, homogeneously distributed along the polymer chain. Because of the cocrystallization between the PP and PP–HP copolymer, all HP antioxidant groups are homogeneously distributed in the PP matrix (amorphous domains). The resulting PP/PP–HP blends demonstrate a thermal-oxidative stability nearly proportional to the HP content. While commercial PP products (containing regular antioxidants and stabilizers) degrade within a few minutes at 210 °C in air, the PP/PP–HP blend, with the same concentration of HP groups, demonstrates nearly no detectable weight loss after 1000 h. In an ASTM endurance test under a targeted application temperature (140 °C in air), the commercial PP shows 1% weight loss within 10 days. On the other hand, the new PP/PP–HP (5/1) blend with the same HP content lasts for about 2 years under the same constant heating condition. Overall, the experiment results of the PP–HP antioxidant present the potential of expanding PP applications into a far higher temperature range (>140 °C) under thermal-oxidative environments.