Advances and opportunities in synthesis of flame-retardant polymers via reversible deactivation radical polymerization

Progress of flame retardant research on flexible polyurethane foam

To broaden the applications of wood, it is necessary to prepare flame-retardant coatings that can protect wood substrates during combustion. In this study, a bio-based, intumescent, flame-retardant phytic acid–melamine polyelectrolyte (PM) was prepared using phosphorus-rich biomass phytic acid and nitrogen-rich melamine as raw materials through an ion crosslinking reaction. Subsequently, a series of bio-based, flame-retardant wood coatings were prepared by optimizing the structure of urea–formaldehyde resin with the addition of melamine, sodium lignosulfonate, and PM as a flame-retardant curing agent. Woods coated with PM-containing coatings displayed significantly improved flame-retardant performances in comparison to uncoated woods. For PM-cured woods, the measured values of total heat release and total smoke production were 91.51% and 57.80% lower, respectively, compared with those of uncoated wood. Furthermore, the fire growth index decreased by 97.32%, indicating a lower fire hazard. This increase in flame retardancy and smoke suppression performance is due to the dense expanded carbon layer formed during the combustion of the coating, which isolates oxygen and heat. In addition, the mechanical properties of the flame-retardant coatings cured with PM are similar to those cured with a commercial curing agent, NH4Cl. In addition, the prepared flame-retardant coating can also stain the wood. This study proves the excellent flame-retarding and curing effect of ammonium phytate in urea–formaldehyde resin coatings and provides a new approach for the application of bio-based flame retardants in wood coatings. 

Preparation of a Flame-Retardant Curing Agent Based on Phytic Acid–Melamine Ion Crosslinking and Its Application in Wood Coatings

Urea–formaldehyde (UF) resin is the most widely used adhesive resin. However, it is necessary to improve its flame-retardant performance to expand its applications. In this study, exploiting electrostatic interactions, anionic phytic acid and cationic chitosan were combined to form a bio-based intumescent flame-retardant, denoted phytic acid–chitosan polyelectrolyte (PCS). The molecular structure of the urea–formaldehyde resin was optimized by crosslinking with melamine and plasticizing with polyvinyl alcohol-124. Thus, by combining PCS with the urea–formaldehyde resin and with ammonium polyphosphate and ammonium chloride as composite curing agents, flame-retardant urea–formaldehyde resins (FRUFs) were prepared. Compared to traditional UF resin, FRUF showed excellent flame retardancy and not only reached the UL-94 V-0 level, but the limit of oxygen index was also as high as 36%. Compared to those of UF, the total heat release and peak heat release rate of FRUF decreased by 86.44% and 81.13%, respectively. The high flame retardancy of FRUF originates from the combination of oxygen and heat isolation by the dense carbon layer, quenching of phosphorus free radicals, and dilution of oxygen by a non-flammable gas. In addition, the mechanical properties of the FRUF remained good, even after modification. The findings of this study provide a reference for the flame-retardant application of FRUF for applications in multiple fields. 

Preparation of a Highly Flame-Retardant Urea–Formaldehyde Resin and Flame Retardance Mechanism

Incorporating flame‐retardant compounds into polymeric composites is a key area of materials research. Halogenated flame‐retardants are currently the most widely used, however they are under scrutiny due to health and environmental concerns increasing interest in the pursuit of eco‐friendly alternatives. Tannic acid (TA) is a naturally occurring polyphenol with intumescent flame‐retardant properties. To overcome current challenges incorporating TA into polymer composites at high concentrations, non‐woven mats of nylon/tannic acid composite nanofibers are fabricated using electrospinning. TA is incorporated into nylon nanofibers at concentrations up to 50 rel. wt% while maintaining uniform fiber morphology and fibers were characterized using scanning electron microscopy (SEM), optical microscopy, IR spectroscopy, differential scanning calorimeter (DSC), and thermogravimetric analysis (TGA). Analysis using TGA shows that TA within the nanofibers begins to degrade at ca. 230 °C and the polymer begins to degrade at ca. 400 °C, irrespective of the initial concentration of TA. The char yield increases with respect the concentration of tannic acid, resulting in a maximum of 25% for fibers containing 50 rel. wt% TA. The flame resistance is further characterized using microscale combustion calorimetry (MCC) which shows composite fibers have reduced heat capacity and total heat release (THR) indicating flame resistance at ≥ 75 rel. wt% TA.. Finally, ignition tests and condensed phase analysis show that TA acts as an intumescent material when embedded within the polymer matrix that produces an insulating foam‐like char under direct heat that eliminates flaming melt dripping and results in self‐extinguishing nanofibers.This article is protected by copyright. All rights reserved.

Flame‐Retardant Properties and Characterization of Nylon/Tannic Acid Electrospun Fibers

The synergistic flame-retardant behaviors of soybean oil phosphate-based polyols and modified ammonium polyphosphate in polyurethane foam

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The synergistic flame-retardant behaviors of soybean oil phosphate-based polyols and modified ammonium polyphosphate in polyurethane foam