Epoxy resins cured with aminophenylmethylphosphine oxide—II. Mechanism of thermal decomposition

Aromatic vs. Aliphatic Hyperbranched Polyphosphoesters as Flame Retardants in Epoxy Resins

The current trend for future flame retardants (FRs) goes to novel efficient halogen-free materials, due to the ban of several halogenated FRs. Among the most promising alternatives are phosphorus-based FRs, and of those, polymeric materials with complex shape have been recently reported. Herein, we present novel halogen-free aromatic and aliphatic hyperbranched polyphosphoesters (hbPPEs), which were synthesized by olefin metathesis polymerization and investigated them as a FR in epoxy resins. We compare their efficiency (aliphatic vs. aromatic) and further assess the differences between the monomeric compounds and the hbPPEs. The decomposition and vaporizing behavior of a compound is an important factor in its flame-retardant behavior, but also the interaction with the pyrolyzing matrix has a significant influence on the performance. Therefore, the challenge in designing a FR is to optimize the chemical structure and its decomposition pathway to the matrix, with regards to time and temperature. This behavior becomes obvious in this study, and explains the superior gas phase activity of the aliphatic FRs.

Intumescent Phosphorus and Triazole-Based Flame-Retardant Polyurethane Foams from Castor Oil

Synthesis of a novel phosphorus and triazole-functionalized flame-retardant (FR) monomer (PTFM) using azide-alkyne "click" reaction between triprop-2-ynyl phosphate and 2-azidoethanol that can impart intumescent FR property to polyurethane foams (PUFs) has been reported. Polyurethane triazole foams (PUTFs) were prepared using the as-synthesized PTFM and a hydroxylated castor polyol with a hydroxyl value of ∼310 mg KOH/g for application as reactive FR rigid foams. PTFM and the castor polyol were characterized for structural elucidation using Fourier transform infrared and ¹H, ¹³C, and ³¹P NMR. PUTFs with a varying loading content of PTFM were subjected to the lab-scale flame test, cone calorimetry test, Underwriters Laboratory 94 Vertical burning test (UL 94V), and limiting oxygen index (LOI) test. A significant increase in the char yields, reduction in heat release rates, V-1 rating, and 27% of LOI were observed for PUTFs compared to PUFs and proportional to the percentage loading of PTFM. The cumulative effect of nitrogen and phosphorus in PUTFs on their intumescent behavior was evident from the thermogravimetric analysis and scanning electron microscopy micrographs, which were further supplemented by X-ray photoelectron spectroscopy studies, indicating expulsion of N₂ and overall improvement in compression strength as well. Such environment-friendly reactive FRs can be good replacements to the halogenated ones.

Curing behaviour and thermal properties of epoxy resin cured by aromatic diamine with carborane

A new kind of carborane-containing aromatic diamine, 1,2-bis (4-aminophenyl)-1,2-dicarba-closo-dodecaborane (HPPA), as a curing agent for epoxy resins was synthesized and confirmed by proton, carbon and boron nuclear magnetic resonance imaging, Fourier transform infrared spectroscopy and elemental analysis. The compatibility, thermal curing behaviour and thermal properties of HPPA/epoxy resin E51 system were investigated. HPPA exhibited good compatibility with E51. Compared with 4,4′-diaminodiphenylsulphone (DDS)/E51, HPPA/E51 system had higher reaction activity and lower curing temperature. When the ratio of amine protons versus epoxy groups was 1:1 in resin systems, the epoxy resin cured by HPPA exhibited the highest glass transition temperature of 207°C. The residual weight ratios of cured HPPA/E51 at 800°C under argon and in air atmospheres were 43.7% and 50.5%, respectively, which were 28.6% and 47.2% higher than that of DDS/E51, respectively, indicating that the HPPA/E51 system had good heat resistance.

The study on the compatibility of epoxy resin with liquid oxygen

Lightweight liquid oxygen (LOX) tank has attracted much attention recently, and epoxy resin is considered to be one of the most likely candidate materials. In this work, polymer wafer made from bisphenol-A epoxy resin was firstly treated with LOX, and then its macroscopic morphology, microscopic structure, and chemical composition were analyzed by atomic force microscopy and Fourier transformed infrared spectroscopy. Finally, its compatibility with LOX was studied by mechanical impact test. The results showed that LOX treatment has little influence on the macroscopic morphology and chemical composition of the epoxy resin wafer, but has a large influence on its microstructure and compatibility with LOX. With the increase of immersion time, the surface roughness, the number, length, and depth of the cracks appeared on the sample surface were all increased. The reaction caused by mechanical impact became more frequent and intense. Finally, possible damage mechanism was discussed.

Phosphorus-based Flame Retardancy Mechanisms-Old Hat or a Starting Point for Future Development?

Different kinds of additive and reactive flame retardants containing phosphorus are increasingly successful as halogen-free alternatives for various polymeric materials and applications. Phosphorus can act in the condensed phase by enhancing charring, yielding intumescence, or through inorganic glass formation; and in the gas phase through flame inhibition. Occurrence and efficiency depend, not only on the flame retardant itself, but also on its interaction with pyrolysing polymeric material and additives. Flame retardancy is sensitive to modification of the flame retardant, the use of synergists/adjuvants, and changes to the polymeric material. A detailed understanding facilitates the launch of tailored and targeted development.

Recent Developments in Halogen Free Flame Retardants for Epoxy Resins for Electrical and Electronic Applications

The recent implementation of new environmental legislations led to a change in the manufacturing of composites that has repercussions on printed wiring boards (PWB). This in turn led to alternate processing methods (e.g., lead-free soldering), which affected the required physical and chemical properties of the additives used to impart flame retardancy. This review will discuss the latest advancements in phosphorus containing flame retardants for electrical and electronic (EE) applications and compare them with commercially available ones. The mechanism of degradation and flame retardancy of phosphorus flame retardants in epoxy resins will also be discussed.