Hot air aging behavior of polypropylene random copolymers

Abstract

This article deals with the global aging behavior of three polypropylene random copolymer (PP-R) materials with varying primary structure and morphology. Hot air aging experiments at elevated temperatures from 95 to 135 C were carried out using micro-sized specimens with a thickness of 100 μm. Technological and analytical aging indicators were monitored for an exposure time of up to 750 days. Independent of comonomer type (ethylene vs. butylene) and morphology (α vs. β crystal form) a critical molar mass of 300 kg mol −1 was obtained. The consumption of antioxidants was slower for the β-nucleated PP-R grade with finer spherulitic structure. The β-grade outperformed the α-crystal PP-R grades resulting in about 20% higher time-to-embrittlement values.

Chlorinated Water Induced Aging of Pipe Grade Polypropylene Random Copolymers

“…As expected, the time-to-embrittlement values in hot air were found to strongly depend on the exposure temperature, with time-to-embrittlement values strongly decreasing with increasing temperature. For example, at 95 °C embrittlement times of higher than 15,000 h were determined, while at the highest exposure temperature of 135 °C, total embrittlement was obtained for both grades after about 3300 h. By comparison, the present study revealed time-to-embrittlement values for PP-Rα and PP-Rβ at 60 °C in chlorinated water of 1500 and 2000 h, respectively, both values being significantly below the numbers reported by Grabmann et al [7] for 95 °C and even 135 °C in air. Clearly, hot chlorinated water is a much more aggressive environment than hot air, with polymer degradation occurring even at low temperatures after shorter exposure times.…”

“…Clearly, hot chlorinated water is a much more aggressive environment than hot air, with polymer degradation occurring even at low temperatures after shorter exposure times. Simultaneously, Grabmann et al [7], as well as this study, revealed PP-Rβ as the material with improved aging resistance. The aggressive nature of chlorine in the liquid environment was also corroborated by the mechanical performance investigations, where PP-Rβ was found to outperform PP-Rα both in terms of tensile behavior after environmental exposure and in fatigue crack growth performance under superimposed mechanical-environmental loading.…”

“…Grabmann et al [7] investigated the aging behavior of alpha- and beta-nucleated polypropylene random copolymers in hot air. This environment was chosen based on previous studies by this group, where hot air was shown to be more severe in terms of aging of PP compared to hot non-chlorinated water [49,50,51,52].…”

“…According to the standard ISO 15874, the high-performance pipe material class PP-RCT is defined as a polypropylene random copolymer with distinct crystalline morphology and improved pressure and temperature resistance, allowing for the production of pipes for higher pressures or with thinner wall thicknesses at constant loads [2,3]. Indeed, beta-nucleated PP-R with its trigonal β crystal form and its fine spherulite structure is classified as PP-RCT material, and it is recommended for pressure pipes in hot water circulation systems and for other applications where materials with excellent impact strength, chemical resistance and crack growth resistance are required [1,4,5,6,7,8,9].…”

Global and Local Aging in Differently Stabilized Polypropylenes Exposed to Hot Chlorinated Water with and without Superimposed Mechanical-Environmental Loads

“…In this context, it is important to recognize that the applicability and effectivity of stabilizer systems not only depend on the environmental conditions but also on the molecular and morphological nature of the polymeric base material. Considering this complexity and the necessity for a manageable methodological approach to cover aspects of global and local aging, it is not surprising that only a limited amount of investigations exists on the effects of various stabilizer systems on the global and local aging behavior in polypropylene [4,5,6,7,12,13,14,15,16,17,19,20,39,40,41,42,43]. Nevertheless, regarding the methodological approach, novel test methods have been implemented in the laboratory of the Institute of Polymeric Materials and Testing at the Johannes Kepler University Linz to investigate such phenomena of pure environmental global aging (without stresses) and superimposed mechanical-environmental local aging in an efficient manner [4,5,6,7,12,13,14,15,17,20,40,42].…”