Bio-based melamine formaldehyde resins for flame-retardant polyurethane foams.

The polyurethane (PU) foams can be functionally tailored by modifying the formulation with different additives. One such additive is melamine (MA) formaldehyde resin for improving their flame-retardant properties. In this work, the glycerol-modified (GMF), sodium alginate (SGMF)- and lignosulfonate-modified melamine formaldehyde (LGMF) were prepared and used as flame retardants reacting with isocyanate to prepare the corresponding rigid polyurethane foams (GMF-PU, SGMF-PU and LGMF-PU). The thermomechanical properties and flame-retardant properties of the foams were characterized. The results showed that the specific compression strength of GMF-PU, SGMF-PU and LGMF-PU increased substantially compared to the foams from physical addition of MA, sodium alginate and lignosulfonate, all of which were greater than that of the foam without any flame retardant (PPU). Meanwhile, the cell wall of the foam pores became thicker and the closed pore ratio increased. The sodium alginate and lignosulfonate played a key role in enhancing foam thermal stability. The limiting oxygen index values and cone calorimetry results indicated the flame-retardant efficiency of GMF-PU, SGMF-PU and LGMF-PU was significantly enhanced relative to PPU. Meanwhile, the heat and smoke release results indicated sodium alginate and lignosulfonate could reduce the amount of smoke generation to different degrees during the combustion of the foam.

Novel Oligo-Ester-Ether-Diol Prepared by Waste Poly(ethylene terephthalate) Glycolysis and Its Use in Preparing Thermally Stable and Flame Retardant Polyurethane Foam.

Rigid polyurethane foam (PUF) was successfully prepared from a novel oligo-ester-ether-diol obtained from the glycolysis of waste poly(ethylene terephthalate) (PET) bottles via reaction with diethylene glycol (DEG) in the presence of ZnSO4·7H2O. The LC-MS analysis of the oligodiol enabled us to identify 67 chemical homologous structures that were composed of zero to four terephthalate (T) ester units and two to twelve monoethylene glycol (M) ether units. The flame retardant, morphological, compression, and thermal properties of rigid PUFs with and without triphenyl phosphate (TPP) were determined. The Tg values showed that TPP played a role of not only being a flame retardant, but also a plasticizer. PUF with a rather low TPP loading had an excellent flame retardancy and high thermal stability. A loading of 10 wt % TPP not only achieved a UL-94 V-0 rating, but also obtained an LOI value of 21%. Meanwhile, the PUF without a flame retardant did not achieve a UL-94 HB rating; the sample completely burned to the holder clamp and yielded a low LOI value (17%). The fire properties measured with the cone calorimeter were also discussed, and the results further proved that the flame retardancy of the PUF with the addition of TPP was improved significantly. The polymeric material meets the demands of density and compression strength for commercial PUF, as well as the needs of environmental development. The current study may help overcome the drawback of intrinsic high flammability and enlarge the fire safety applications of materials with a high percentage of recycled PET.