The effects of silica aerogel on the rheological behaviour and polymer matrix structure of Rigid Polyurethane foams

[Display omitted] •Rigid polyurethane-aerogel foams are produced using isocyanate-aerogel dispersions of different concentrations.•Rheology shows that for concentrations above 2.5 wt% of aerogel the dispersion is in a percolated gel-like state.•The addition of aerogel progressively slows down the vi...

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Bibliographic Details
Published in:European polymer journal 2022-08, Vol.176, p.111398, Article 111398
Main Authors: Cimavilla-Román, Paula, Perez-Tamarit, Saul, Vananroye, Anja, Moldenaers, Paula, Ángel Rodriguez-Pérez, Miguel
Format: Article
Language:English
Subjects:
Fractions
Isocyanates
Newtonian fluids
Plastic foam
Plastic foams
Polyurethane
Polyurethane foam
Reaction kinetics
Rheological properties
Rheology
Silica aerogel
Silica aerogels
Struts
Viscosity
Vitrification
X-ray tomography
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Summary:[Display omitted] •Rigid polyurethane-aerogel foams are produced using isocyanate-aerogel dispersions of different concentrations.•Rheology shows that for concentrations above 2.5 wt% of aerogel the dispersion is in a percolated gel-like state.•The addition of aerogel progressively slows down the viscosity build-up and curing of the foam.•Percolated dispersions show less drainage of the reactive polymer and, in turn, lower fraction of mass in the struts of the final foam. The incorporation of silica aerogel particles into the isocyanate used to prepare Rigid Polyurethane composite foams drastically modifies its rheological behaviour. The isocyanate changes from being a Newtonian fluid of constant viscosity (0.3 Pa s at 25 °C) to a non-linear power-law material with complex viscosity decreasing from 104 to 101 Pa s with a slope −1 versus frequency. The change in response is caused by the formation of a percolated network of particles at contents above 2.5 wt% of aerogel. Moreover, the addition of aerogel significantly slows down the modulus-build up kinetics and vitrification of the matrix by approximately 4.5 min with every 1 wt% of aerogel added. For the foam with 3.0 wt% of aerogel, the combination of high viscosity at early reaction times coupled with the slow modulus build-up impedes the drainage which leads to a decrease in the fraction of material in the struts of the matrix.
ISSN:0014-3057
1873-1945
DOI:10.1016/j.eurpolymj.2022.111398