An Effective Package of Antioxidants for Avoiding Premature Failure in Polypropylene Random Copolymer Plastic Pipes under Hydrostatic Pressure and High Temperature

Abstract

Pipes of polypropylene random (PP-R) copolymers are the best choice for hot- and cold-water networks. Validation of a severe test, accomplishing the ISO 1167 standard, is mandatory to assess their service lifetime expectancy. This work evaluates the behavior shown by three commercial pipes, either the original ones (new pipes) or after being subjected to a hydrostatic pressure test at elevated temperature (aged pipes). Several features with relevance for the final performance have been examined: crystalline characteristics, phase transitions in crystalline regions, effect of high temperature and pressure on these transitions, and oxidation induction time. Moreover, the presence of inorganic fillers, and the content of different antioxidants together with their depletion, have also been analyzed. Films from the new pipes were also prepared for replication of the different environments in order to achieve a better and complete understanding of the phase transitions in the crystalline regions and of the consumption of antioxidants. Distinct environments surrounded the inner and outer parts of the pipes exposed to the failure aging test at 110 °C: hot water and warm dry air, respectively. These features play a key role in the loss of additives and in the subsequent initiation of degradation. Even if the crystalline characteristics are appropriate in the polymeric matrix, the success of a pipe lies in the homogeneous dispersion of components for avoiding damage at interfacial properties, and in a correct package of antioxidants used in its formulation.

Recycling of metallocene isotactic polypropylene: importance of antioxidants

“…In order to get a deeper insight on the effectiveness of antioxidants in the degradation state of these recycled HMRec materials, experiments of oxidation induction time have been performed [16,50,51]. It should be reminded at this point that a rather similar content of Irganox 1076 was found (see Fig.…”

Improvement of Thermal Protection in Recycled Polyolefins through Hybrid Mesoporous Silica–Antioxidant Particles

“…This result is even better in the case of using hybrid MCM-41@antioxidant particles, suggesting a synergistic action between antioxidant and mesoporous particles. In order to estimate the global antioxidant activity in the blends, tests for determining the oxidation induction time [54,55] have been also performed. Figure 11 represents the DSC curves obtained after switching the purge gas from nitrogen to oxygen at 180 • C, which was the temperature that was kept constant during rest of the experiment.…”

β-Nucleated Polypropylene: Preparation, Nucleating Efficiency, Composite, and Future Prospects

“…However, the coexistence of different polymorphic forms will still affect the main crystal form, just as it is difficult to obtain a 100% β-crystal PP [ 43 , 82 ]. It is possible to obtain γ-crystals [ 95 , 96 ] under different crystallization conditions in both polymers and composites. Certain nucleating agents, including β-nucleating agents, with a strong crystallization induction ability also have a dual nucleation ability [ 11 , 97 , 98 ].…”