[en] Foams are versatile materials encountered in our daily life for a wide variety of uses such as cushioning, thermal and acoustic insulation or medical applications. The combination of the mixed properties between a continuous matrix and gas cells and the diversity of pore structures represent a powerful tool for the design of new materials. Among the different polymer foam fabrication processes, the use of supercritical CO2 has been one of the most investigated in the past decade. Nevertheless, the design of crosslinked polymer foams with high foaming ratio still remains a challenge. Various crosslinking processes mainly based on heating, irradiation with the addition of an external agent have been applied after foaming but remain difficult to perform due to mass transfer issues of the crosslinking agent. When crosslinking occurs before foaming, it dramatically limits the material expansion.
In order to overcome these drawbacks, the present work aims taking advantage of the thermoreversible Diels-Alder cycloaddition to elaborate foams of poly(ε-caprolactone) (PCL) covalent networks. Based on this reaction, we considered to induce cross-linking after the foam expansion by playing on the thermal equilibrium of the thermoreversible Diels-Alder cycloaddition. Therefore, low molar mass star-shaped PCL end-capped by furan or maleimide were impregnated with CO2 under supercritical conditions and then foamed under appropriate control of the pressure and temperature. Annealing about 2h at 40°C allows Diels-Alder adducts to be formed and a stable PCL network keeping at least 80% of the expanded volume is obtained. The resulting foam possesses a much higher volume expansion than a pre-crosslinked sample foamed in the same conditions, thanks to the low crosslinking ratio during foaming. These foams exhibit also improved thermal stability thanks to its chemical crosslinking as compared to non-crosslinked PCL foams. Interestingly, these foams possess shape memory properties due to the semi-crystallinity of the PCL. Thermal stability and shape memory properties were evaluated by dynamic mechanical analysis in both tensile and compression testing with controlled force mode, stress and temperature ramps.
Research Center/Unit :
Complex and Entangled Systems from Atoms to Materials (CESAM) Research Unit MolSys Research Unit Center for Education and Research on Macromolecules (CERM), Belgium
Disciplines :
Chemistry Materials science & engineering
Author, co-author :
Houbben, Maxime ; University of Liège (ULiège), Complex and Entangled Systems from Atoms to Materials (CESAM), Center for Education and Research on Macromolecules (CERM), Belgium
Malherbe, Cédric ; University of Liège (ULiège), Laboratory of Inorganic Analytical Chemistry, MolSys Research Unit, Belgium
Thomassin, Jean-Michel ; University of Liège (ULiège), Complex and Entangled Systems from Atoms to Materials (CESAM), Center for Education and Research on Macromolecules (CERM), Belgium > )
Jérôme, Christine ; University of Liège (ULiège), Complex and Entangled Systems from Atoms to Materials (CESAM), Center for Education and Research on Macromolecules (CERM), Belgium
Language :
English
Title :
Supercritical CO2 foaming of PCL covalent networks : taking benefit from the thermo-reversible Diels-Alder cycloaddition
Publication date :
27 May 2019
Event name :
Belgian Polymer Group (BPG) Annual Meeting
Event place :
Houffallize, Belgium
Event date :
27/05/2019 - 28/05/2019
Funders :
ULiège - University of Liège [BE]
Funding text :
The University of Liège in the frame of the ARC program