Combustion-modified polyurethane foam

These criteria were developed by the UK PU foam industry and were intended to differentiate the melamine or exfoliated graphite containing combustion modified PU foams from the standard, high resilience and flame retarded (chloro and bromo phosphate) containing PU foams (Table IV). This distinction was required because large scale burning tests of real arm chairs and furnished rooms had demonstrated the superiority of the combustion modified polyurethane foams. 

After the introduction of combustion-modified polyurethane foam into the upholstery and bedding market, a wet compression set method, BS 4443, Part 7. Method 18, has become much more widely used. This is carried out by using a humidity cabinet set at 40 C and 95 100% relative humidity. Apart from recommending the use of a stainless steel compression apparatus, the only major difference from EN ISO 1856, 1996 is that the compression is carried out at 70% of the original thickness as opposed to the more normal 75%. This slight discrepancy arises becau.se of the original test methods devised by the automotive trade. 

The next major improvement was the development of combustion modified PU foam. The original CMHR polyurethane foam was developed in the USA (26) and contained hydrated alumina and halogenated flame retardants but was made in a single operation. It was used in institutions, public buildings, hotels etc. but its high density and less than optimum physical properties... 

Polyurethane foams must also be of the specified as combustion modified types which in the UK include foams containing melamine and exfoliated graphite. 

Lee, F. T., Green, J., and Gibilisco, R. D., Recent developments using phosphorus-containing diol as a reactive combustion modifier for rigid polyurethane foams 3, J. Fire Sci., 1984, 2, 439-453. 

One of the additives being used in combustion-modified flexible polyurethane foams is melamine. Small-scale tests conducted at NIST indicated that a melamine-treated flexible polyurethane foam generated six times more HCN than an equal amount of foam that did not contain melamine. The presence of CuiO reduced the HCN from the melamine foam by 90%. Melamine-treated flexible polyurethane foam is one of two flexible polyurethane foams currently allowed in Great Britain. 

Introduction of up to 30 parts by weight of either of these two modifiers into the composition of the rigid polyurethane foams leads to an improvement of the combustion resistance and increase in the tanperature of softening for these materials. 

The availability of PMDI also led to the development of polyurethane-modified isocyanurate (PUIR) foams by 1967. The PUIR foams have superior thermal stability and combustibility characteristics, which extend the use temperature of insulation foams well above 150°C. The PUIR foams are used in pipe, vessel, and solar panel insulation glass-fiber-reinforced PUIR roofing panels having superior dimensional stability have also been developed. More recently, inexpensive polyester polyols based on residues obtained in the production of dimethyl terephthalate (DMT) have been used in the formulation of rigid polyurethane and PUIR foams. 

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