Apparatus for investigating the burning and dripping of vertically oriented polyurethane foams

Abstract

The burning and dripping behaviour of polyurethane (PU) foam is crucial for upholstered furniture fires due to the melting and dripping behaviour of the foam that results in a pool fire under the furniture, which enhances the combustion. The sample feeding vertical cone is developed to investigate the two-dimensional small-scale burning and dripping behaviour of vertically oriented PU foams where a constant irradiance is maintained at the exposed surface by means of automatic sample compensation. Seven different PU foams were investigated and classified as conventional foam or char-forming foam according to the observed surface phenomena during exposure to heat fluxes. The burning and dripping behaviour is found to depend on the foam density as well as the solid-phase char formation by the presence of fire retardant additives. The total mass loss rate and the dripping rate increase with higher foam density and with the presence of char formation. In contrary, the vaporisation rate is favoured at lower foam density and with the absence of char formation. Flexible foams of low density without the ability to form char tend to achieve low dripping rate where majority of the mass loss is via vaporisation, contributing directly to the gas-phase combustion. K E Y W O R D S burning and dripping behaviour, fire retardant additives, polyurethane foam, sample feeding vertical cone 1 | INTRODUCTION Flexible polyurethane (PU) foam is a synthetic thermosetting polymer 1,2 that is commonly found in bedding and upholstered furniture. The flexible foam's expansive range of hardness and densities allows the material to be incorporated into different types of mattress and different paddings of the upholstered furniture. The end use of mattresses and upholstered furniture means that these products are often intimate with the users where life safety in event of fire is paramount. Non-fire retardant (NFR) flexible PU foams have relatively poor performance in fire, in terms of ignitability, flammability and toxicity, which challenge the occupants survival in the room of origin and beyond. 3,4 A number of researchers have focused on improving the understanding on the decomposition and burning behaviour of flexible PU foams. 5,6 Despite being a thermosetting polymer, flexible PU foams exhibit melting behaviour upon thermal decomposition, which resembles the characteristic of most thermoplastic polymers. The amount of melt produced depends on the type of flexible foams, and according to Ohlemiller et al, 2 this can be as high as 70%-90% of the original mass for certain foams, which is comparable to common thermoplastic polymers such as polypropylene and polystyrene. Flexible PU foam is formed by the polycondensation of polyfunctional isocyanates commonly diisocyanates, with polyfunctional alcohols or polyols commonly polyestherols or polyetherols. 3,7,8 The manufacturing process also includes a number of additives such as blowing or foaming agent, coupling agent, catalyst, chain extender, neutralizer, surfactant and cell opener. 1,7-10 Ch...

Bubbles and collapses: Fire phenomena of flame‐retarded flexible polyurethane foams

“…The main parameter influencing the dripping behavior of a polymer in a fire is its melting viscosity as a thermophysical property 34 . Viscosity, which characterizes dripping behavior during combustion, is consistent with the steady‐flow viscosity 52 ; therefore, dripping occurs at low shear rates 53 .…”

“…For the investigation of the dripping behavior, the cone calorimeter setup was changed to vertical orientation to ensure melt flow and to enhance dripping during the test 34,35 . The conical heater of the cone calorimeter was brought into an upright position and a foam specimen with dimensions of 100 × 100 × 50 mm 3 was placed in vertical orientation at a distance of 25 mm.…”