Developing Polypropylene Bonded Hindered Phenol Antioxidants for Expanding Polypropylene Applications in High Temperature Conditions

Abstract

Polypropylene (PP) represents about a quarter of commercial plastics produced around the world. Despite its huge commercial success, PP polymer is not suitable for the applications that require long-term exposure to high temperatures (>80°C), due to its chemical and physical stability. The PP chain is prone to the oxidative chaindegradation and exhibits a relatively low material softening temperature. This paper discusses a new research approach by developing the PP-bonded hindered phenol (PP-HP) antioxidants to address this scientifically challenging issue. We have investigated two PP-HP structures, one with two methylene units adjacent to the hindered phenol group (HP-L) and one without this spacer (HP-S). In general, PP-HP polymers are advantaged with the ability to incorporate a suitable concentration of HP antioxidant groups with homogeneous distribution along the polymer chain, which provide effective protection to the PP chains from oxidative degradation. In addition, the specific PP-HP-L structure can also engage in a facile crosslinking reaction to form a 3-D network during the oxidation reaction. In one accelerated oxidation test in air at 190-210°C, the regular commercial PP polymer (containing common antioxidants and stabilizers) degrades within a few minutes; a PP-HP-L copolymer with about 1 mol% HP-L group shows almost no detectable weight loss after 24 hrs. In an ASTM endurance test at 140°C in air, the commercial PP shows 1% weight loss within about 10 days. On the other hand, the PP-HP-L polymer lasts for more than 30 years. Overall, the experiment results present the potential of expanding PP applications into a much higher temperature range (>140°C) under oxygen oxidative environments.

A Study of the Friction Stir Lap Welding of AA5052 and Polypropylene

“…It was measured using Differential Scanning Calorimetry (DSC) and was found to be around 30 min. Commercial PP, on the other hand, has an onset temperature of 235 • C and an induction time of 15 min [28,29]. This suggests that the antioxidant additive package in the PP material used can protect the material from thermo-oxidation for approximately half an hour at the test temperature.…”