Advanced rheological and physicochemical characterization and their correlation with morphology for microcellular HDPE foams
Résumé
The growing demand for lightweight materials with optimal mechanical properties has driven the development of innovative techniques such asmicrocellular foaming, applied here to high-density polyethylene (HDPE). This study highlights the importance of advanced characterizations toestablish correlations between the rheological and physicochemical properties of the polymer, process parameters, and foam morphology.Rheological tests were conducted under two configurations: in a nitrogen atmosphere without pressure and under pressure in supercriticalconditions using a rheometer equipped with a high-pressure cell. These measurements simulated foaming conditions and examined the effects ofpressure and gas type (Sc.CO2 ,Sc.N2) on the polymer's viscosity. The results reveal significant changes in viscoelastic properties depending onthe pressure and the presence of a supercritical fluid, providing essential data for process control. These rheological analyses are complementedby PVT and surface tension measurements performed using the pendant drop method under pressure, as well as by high-pressure calorimetricstudies (HP-DSC) to evaluate the impact of Sc.N2 on the structural evolution of the polymer. Additionally, sorption and density measurements(via the Sieverts method and a magnetic suspension balance) were used to characterize the polymer/Sc.N2 mixture. These data were leveraged tostudy the influence of process parameters on the cellular morphology and mechanical properties of the resulting foams. Finally, a numericalsimulation, enriched with experimental results, was conducted to optimize weight reduction and control microcellular structures. This integrativeapproach provides a comprehensive understanding of the mechanisms governing the microcellular foaming of HDPE, paving the way for thedesign of lightweight materials with superior properties.