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.

The Degradation and Repolymerization Analysis on Solvolysis Liquefaction of Corn Stalk.

One of the most effective and renewable utilization methods for lignocellulosic feedstocks is the transformation from solid materials to liquid products. In this work, corn stalk (CS) was liquified with polyethylene glycol 400 (PEG400) and glycerol as the liquefaction solvents, and sulfuric acid as the catalyst. The liquefaction conditions were optimized with the liquefaction yield of 95.39% at the reaction conditions of 150 °C and 120 min. The properties of CS and liquefaction residues (LRs) were characterized using ATR-FTIR, TG, elemental analysis and SEM. The chemical components of liquefied product (LP) were also characterized by GC-MS. The results indicated that the depolymerization and repolymerization reaction took place simultaneously in the liquefaction process. The depolymerization of CS mainly occurred at the temperature of <150 °C, and the repolymerization of biomass derivatives dominated at a higher temperature of 170 °C by the lignin derivatives repolymerization with cellulose derivatives, hemicellulose derivatives and PEG400 and self-condensation of lignin derivatives. The solvolysis liquefaction of CS could be classified into the mechanism of electrophilic substitution reaction attacked by the hydrogen cation.

Anti-flammability, mechanical and thermal properties of bio-based rigid polyurethane foams with the addition of flame retardants.

Adding efficient and environmentally friendly flame retardants to polyurethane foams is the preferable way to improve their flame resistance ability. In this work, bio-based rigid polyurethane foams (RPUFs) were prepared with the addition of dicyclohexyl aluminium hypophosphate (DAH) or aluminium diethyl phosphinate (ADP) as the flame retardant. The mechanical properties, thermal degradation and flammability behavior of the obtained RPUFs were evaluated by means of compressive strength tests, thermogravimetry analysis, vertical burning test and scanning electron microscopes. The characterization results indicate that, with the same content of flame retardant, the compressive strength at the deformation of 10% for each RPUF prepared with the addition of DAH is higher than that of the foams with ADP addition, which fully meets the specifications for building insulation materials. Moreover, the average flame height of each RPUF with the addition of flame retardants is less than 250 mm, whereas the average burning time of RPUF with 15 wt% addition of DAH is only 4.4 s, far less than that (12.5 s) of the foam with the same addition amount of ADP. The RPUFs with DAH addition have the potential advantages for thermal insulation applications in various fields.