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- Flame retardant (1)
- Flexible polyurethane foam (1)
- Foam (1)
- Layered double hydroxides (1)
- Lignin (1)
- Ligning (1)
- Polyurethane foam (1)
Organisationseinheit der BAM
Lignin has recently attracted the attention of the scientific community as a consequence of the potential depletion of fossil resources, being the most abundant biopolymer on earth after cellulose. Its industrial appeal lies on its renewability, facilitating the switch from fossil resources to environmentally friendly alternatives in terms of energy and chemicals production, materials engineering, and so on; and also on its abundant availability, since large amounts of lignin are obtained as a byproduct of the pulp and paper industry. Nevertheless, the main handicap of lignin consists on its variable structure, as it depends on the vegetable species of origin and on the production process from which it is isolated.
On the other hand, the biggest drawback of flexible polyurethane foams is represented by their bad demeanor against fire conditions. The use of effective halogenated flame retardants is more and more restricted due to their toxicity and their contribution to the destruction of the ozone layer. Latest efforts in improving this behavior have been focused on the synergy of different additives containing phosphorus and nitrogen and on the use of intumescent flame retardants. Lignin’s high carbon content and its phenolic crosslinked structure makes it the perfect candidate for addressing this issue.
Consequently, this work is focused on the effect of an industrially available lignin –softwood kraft lignin derived from southern pine- on the flame retardant properties of flexible polyurethane foams. Furthermore, seeking to improve the fire performance of these foams, the combined effect of lignin (L), layered double hydroxides (LDH) and a phosphorus containing flame retardant polyol (E) was also studied.
Water blown flexible polyurethane foams (PUF) were prepared using a polyether polyol and toluene diisocyanate (TDI) by one-shot free-rise method. A series of foams containing 5% by weight of lignin, 3 parts per hundred of polyol (pphp) of carbonate intercalated Mg-Al layered double and 5 pphp of a commercially available flame retardant (a phosphorus containing polyol) were prepared in order to study the effect on the properties of their introduction alone or in conjunction into the PUF formulation. For this purpose, different characterization techniques such as thermogravimetric analysis, cone calorimetry and limiting oxygen index were performed.
The high char residue obtained from the thermogravimetric analysis (TGA) of the lignin suggested that lignin could play a determinant role as a charring agent in the prepared PUF, which could be enhanced by the presence of an acid source such as phosphorus. On the other hand, its use in conjunction with LDH could help to improve the cohesion of the formed char layer, protecting more efficiently the underlying foam from combustion. Since the information provided by TGA is limited in terms of analyzing the contribution of lignin in the fire retardant properties of PUF, the potential charring effect of lignin and its combination with LDH and phosphorus containing polyol was furtherly studied by specific assays such as cone calorimeter and limiting oxygen index.
Flexible polyurethane foams with densities of 40 ± 2 kg m−3 were prepared by combining different ecofriendly fillers such as layered double hydroxides (LDH) and kraft lignin (a byproduct of the pulp and paper industry) with a phosphorous polyol (E560) in order to study their effect on the mechanical performance and fire behavior of the foams. Two series of foams were prepared, some containing lignin or LDH separately, and some with a combination of both: one of the series was prepared without E560 (0E foam series) and the other with 5 parts per hundred of E560 polyol (5E series). The use of fillers resulted in increased viscosity of the reactive mixture, requiring higher blowing agent content in order to hold the density of the foams constant. It was observed that urea phase segregation was favored in the series of 0E foams due to their lower viscosity than the 5E series. This had consequent effects on the resilience, compression force deflection and compression set of these foams. In terms of fire behavior it was observed that while the limiting oxygen index decreased, cone calorimeter results showed that the combination of lignin, LDH and E560 decreased the heat release of the foams. In addition, the combination of fillers and E560 contributed to increase the viscosity of the pyrolysis products, preventing the dripping of the molten polymer, which is a key factor in flame propagation towards adjacent objects in fire scenarios.