RT info:eu-repo/semantics/article
T1 Role of air bubble inclusion on polyurethane reaction kinetics
A1 Brondi, Cosimo
A1 Santiago Calvo, Mercerdes
A1 Di Maio, Ernesto
A1 Rodríguez Pérez, Miguel Ángel
K1 Polimers
K1 Polyurethanes
K1 Plastic foams
K1 Foamed materials
K1 Espumas poliméricas de poliuretano - Propiedades mecánicas
K1 Nucleation
K1 Air bubble
K1 Gels
K1 Materials science
K1 Condensed Matter Physics
K1 Física de la materia condensada
K1 2206.10 Polímeros
K1 2304.21 Poliuretanos
K1 3312 Tecnología de Materiales
AB In this study, we investigated the influence of mixing conditions on the foaming process of water blown polyurethane (PU) foams obtained at different mixing speeds (50, 500, 1000 and 2000 rpm). In particular, the morphological evolution during the foaming process, in terms of the bubble size and bubble density, was studied via optical observations, while the effects on the reaction kinetics were monitored using in situ FTIR spectroscopy. At the slow mixing speed (50 rpm), no air bubbles were included and the early foaming process was characterized by the formation of new bubbles (CO2 nucleation), provided by the blowing reaction. Later on, it was observed that the coalescence affected the overall foaming process, caused by the gelling reaction, which was inhibited by the indigent mixing conditions and could not withstand the bubbles expansion. As a result, a PU foam with a coarse cellular structure and an average bubble size of 173 µm was obtained. In this case, the bubbles degeneration rate, dN/dt, was −3095 bubble·cm−3·s−1. On the contrary, at 500 rpm, air bubbles were included into the PU reaction system (aeration) and no formation of new bubbles was observed during the foaming process. After this, the air bubbles underwent growth caused by diffusion of the CO2 provided by the blowing reaction. As the gelling reaction was not strongly depleted as in the case at 50 rpm, the coalescence less affected the bubble growth (dN/dt = −2654 bubble·cm−3·s−1), leading to a PU foam with an average bubble size of 94 µm. For the foams obtained at 1000 and 2000 rpm, the bubble degeneration was first affected by coalescence and then by Ostwald ripening, and a finer cellular structure was observed (with average bubble sizes of 62 µm and 63 µm for 1000 rpm and 2000 rpm, respectively). During the first foaming stage, the coalescence was less predominant in the bubble growth (with dN/dt values of −1838 bubble·cm−3·s−1 and −1601 bubble·cm−3·s−1, respectively) compared to 50 rpm and 500 rpm. This occurrence was ascribed to the more balanced process between the bubble expansion and the PU polymerization caused by the more suitable mixing conditions. During the late foaming stage, the Ostwald ripening was only responsible for the further bubble degeneration (with dN/dt values of −89 bubble·cm−3·s−1 and −69 bubble·cm−3·s−1, respectively).
PB MDPI
SN 1996-1944
YR 2022
FD 2022
LK https://uvadoc.uva.es/handle/10324/63070
UL https://uvadoc.uva.es/handle/10324/63070
LA eng
NO Materials, 2022, Vol. 15, Nº. 9, 3135
NO Producción Científica
DS UVaDOC
RD 25-nov-2024