Teresina, Brazil – Scientists at the Federal University of Piauí’s interdisciplinary lab for advanced materials have investigated a flame retardant PU foam composite. Its flame retardant properties are imparted by the inclusion of vermiculite.
In recent years, the team says there has been interest in PU–clay composites because of their good thermomechanical properties. These composites can be made by incorporating inorganic clays dispersed in a polymer matrix.
One such clay, vermiculite, is a swelling hydrous phyllosilicate clay mineral containing magnesium and iron cations that is made up of thin crystal layers. At temperatures above 650°C it can expand to up to 30 times its original volume, and is commonly used as an additive in geopolymers and other materials to give better fire resistance and porosity.
The team looked more closely at the properties of foams containing vermiculite. Rigid PU foams were made via the one-step expandable foam method with casting moulding. Vermiculite was dispersed in the polyol, and then the MDI added before being poured into the mould. After keeping at room temperature for 24 hours, the foam was demoulded, and the hard surface removed. Five different foams were made, containing no vermiculite, and 5, 10, 15 and 20%.
The foam was characterised using scanning electron microscopy, and crystallinity reduced with the increase in vermiculite. The diameter and distribution of pores in the foam was altered by the presence of vermiculite, because of the increase in viscosity of the polyol when the clay is added.
The vertical flame test was used to look at its flame retardant properties, with an increase in residue mass that increased with the proportion of vermiculite. The best firing performance was seen with 15% vermiculite, and the team also said this level of incorporation gave better dispersibility and planar orientation of the clay layers.
They concluded that this 15% vermiculite foam is uniform, and gave reduced flammability. It showed better burn performance, and as a result better dispersibility and planar orientation of the layers of vermiculite.
The work has been published in the journal Polymers.