Expanding Polyethylene and Polypropylene Applications to High-Energy Areas by Applying Polyolefin-Bonded Antioxidants

Despite a broad range of commercial applications, polyolefins, including polyethylene (PE) and polypropylene (PP), are not recommended for applications that require long-term exposure to elevated temperatures, high electric fields, organic solvents, and combinations of those, due to both chemical and physical stability concerns. This paper discusses current antioxidants/stabilizers and cross-linking technologies and their shortcomings under extreme application conditions. The incompatibility of polar antioxidants in nonpolar and semicrystalline polyolefin prevents homogeneous distribution with adequate concentration required for protecting the polymer chain from thermal-oxidative degradation. A new approach for incorporating hindered phenol (HP) antioxidant groups in the polyolefin chain offers a specific HP concentration homogeneously distributed in the polyolefin matrix, which not only shows effective antioxidation protection but also in situ forms a polymer network via a coupling reaction between two deprotonated HP groups. Instead of weakening the mechanical strength, the resulting cross-linked PE-HP and PP-HP copolymers become stronger after high-energy exposure. Furthermore, PE-HP and PP-HP can serve as the antioxidant in PE and PP products, respectively. In a comparative endurance test at 140 degrees C in air, the well-formulated PP shows significant weight loss within 10 days. On the other hand, the new PP/PP-HP blend with similar HP content can last more than 2 years (<1% weight loss). The overall experimental results suggest the potential of expanding the PE and PP applications into high-energy areas by applying this polyolefin-bonded antioxidant technology.