Novel phosphorus-modified polysulfone as a combined flame retardant and toughness modifier for epoxy resins

A Nitrogen-Rich DOPO-Based Derivate for Increasing Fire Resistance of Epoxy Resin with Comparable Transparency

To endow synergistically epoxy resin (EP) with excellent fire resistance and high optical transparency, a nitrogen-rich DOPO-based derivate (named as FATP) was synthesized and incorporated into EP. It showed that the incorporation of the FATP reduced the fire hazard of the EP, as demonstrated by the fact that the EP/4% FATP blends gained a UL-94 V-0 rating and an LOI value of 35%, with the lowest values of the THR (86.7 MJ/m²), the PHRR (1059.3 kW/m²), and the TSP (89.6 MJ/m²). The presence of the FATP also reduced the thermal stability and the crosslinking density whilst improving the curing reaction and the storage modulus of the EP/FATP blends. The TG-FTIR spectra showed that •HPO/•PO free radicals and some nonflammable gases (HN₃ and NH₃) were produced during the pyrolysis, and the characterization (SEM, Raman spectroscopy, and XPS) of char residues confirmed that the FATP facilitated the formation of continuous and compact carbon layers of greater graphitization degree. It was thus concluded that the FATP played the flame-retardant roles in both the gas and condensed phases. Furthermore, the FREPs kept almost identical transparency as the pristine EP, and mechanical properties were also slightly enhanced. The FREPs presented in this work show promising applications in the fields of advanced optical technology.

Analysis of the Chemical Distribution of Self-Assembled Microdomains with the Selective Localization of Amine-Functionalized Graphene Nanoplatelets by Optical Photothermal Infrared Microspectroscopy

By incorporating 1-(2-aminoethyl)piperazine (AEPIP) into a commercial epoxy blend, a bicontinuous microstructure is produced with the selective localization of amine-functionalized graphene nanoplatelets (A-GNPs). This cured blend underwent self-assembly, and the morphology and topology were observed via spectral imaging techniques. As the selective localization of nanofillers in thermoset blends is rarely achieved, and the mechanism remains largely unknown, the optical photothermal infrared (O-PTIR) spectroscopy technique was employed to identify the compositions of microdomains. The A-GNP tends to be located in the region containing higher concentrations of both secondary amine and secondary alcohol; additionally, the phase morphology was found to be influenced by the amine concentration. With the addition of AEPIP, the size of the graphene domains becomes smaller and secondary phase separation is detected within the graphene domain evidenced by the chemical contrast shown in the high-resolution chemical map. The corresponding chemical mapping clearly shows that this phenomenon was mainly induced by the chemical contrast in related regions. The findings reported here provide new insight into a complicated, self-assembled nanofiller domain formed in a multicomponent epoxy blend, demonstrating the potential of O-PTIR as a powerful and useful approach for assessing the mechanism of selectively locating nanofillers in the phase structure of complex thermoset systems.

Investigation of the Structure-Property Effect of Phosphorus-Containing Polysulfone on Decomposition and Flame Retardant Epoxy Resin Composites

The flame retardant modification of epoxy (EP) is of great signification for aerospace, automotive, marine, and energy industries. In this study, a series of EP composites containing different variations of phosphorus-containing polysulfone (with a phosphorus content of approximately 1.25 wt %) were obtained. The obtained EP/polysulfone composites had a high glass transition temperature (Tg) and high flame retardancy. The influence of phosphorus-containing compounds (ArPN₂, ArPO₂, ArOPN₂ and ArOPO₂) on the thermal properties and flame retardancy of EP/polysulfone composites was investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), a UL-94 vertical burning test, and cone calorimeter tests. The phosphorus-containing polysulfone enhanced the thermal stability of EP. The more stable porous char layer, less flammable gases, and a lower apparent activation energy at a high degree of conversion demonstrated the high gas inhibition effect of phosphorus-containing compounds. Moreover, the gas inhibition effect of polysulfone with a P⁻C bond was more efficient than the polysulfone with a P⁻O⁻C bond. The potential for optimizing flame retardancy while maintaining a high Tg is highlighted in this study. The flame-retardant EP/polysulfone composites with high thermal stability broaden the application field of epoxy.

Flame-retardant halogen-free polymers using phosphorylated hexaglycidyl epoxy resin

Flame-retardant halogen-free epoxy resin, containing phosphorus and nitrogen atoms in the main chain, was synthesized through the curing of tris(3-(bis(oxiran-2-ylmethyl)amino)phenyl)phosphine oxide (HGE, hexaglycidyl epoxy monomer), starting from tris(3-aminophenyl) phosphine oxide (TAPO) and epichlorohydrin. The molecular structure of HGE with molecular weight 660 was confirmed using Fourier transform infrared, nuclear magnetic resonance, and liquid chromatography–mass spectrometry techniques. Epoxy equivalent weight determined by titration method was 120. The thermal curing behavior of the HGE/TAPO was investigated by differential scanning calorimetry. An intense exotherm due to curing reaction was observed in the temperature range from 123°C to 215°C. The HGE cured with TAPO, 4,4′-diaminodiphenylsulfone (DDS), and 1,5-diaminonaphthalene (DAN) and the thermal behaviors were studied by thermogravimetric analysis. The flame retardancy properties of the HGE/TAPO, DDS, and DAN were evaluated by vertical burning test (UL-94 V). The high performance cured epoxy resins showed high thermal stability and UL-94 V-0 flame retardancy rating.

Synthesis, structure–property and flame retardancy relationships of polyphosphonamide and its application on epoxy resins

A series of polyphosphonamides (PPDA) with heteroatoms and phosphonamide structures are proposed as highly effective flame retardants in epoxy resins (EP).

Simultaneously enhancing the flame retardancy and toughness of epoxy by lamellar dodecyl-ammonium dihydrogen phosphate

Lamellar dodecyl-ammonium dihydrogen phosphate flame retardant was synthesized in one-pot. Its incorporation into epoxy leads to the simultaneous enhancement of flame retardancy and impact toughness for the resulting epoxy composites.

Simple green synthesis of solid polymeric bisphenol A bis(diphenyl phosphate) and its flame retardancy in epoxy resins

A simple and green method for the preparation of solid polymeric bisphenol A bis(diphenyl phosphate) (PBDP), aimed at improving the flame retardancy of epoxy resins (EP) is presented.

A study on glass fiber reinforced composites from 2,3-epoxypropyl-3-(2-furyl) acrylate and methyl methacrylate

2,3-Epoxypropyl-3-(2-furyl) acrylate (EPFA) was synthesized from 3-(2-furyl) acrylic acid (FAA) and epichlorohydrin, followed by copolymerization of EPFA with methyl methacrylate (MMA) by varying the mole ratio of EPFA:MMA at different reaction times using benzoyl peroxide as an initiator at 80°C in toluene. The FAA, EPFA and copolymers were characterized by Fourier transform infrared (FTIR) spectroscopy, 1H nuclear magnetic resonance (1H NMR) spectroscopy, viscosity measurement, gel permeation chromatography (GPC) as well as epoxy equivalent weight (EEW). Mechanical properties, electrical properties and chemical resistance of the selected glass fiber reinforced composites were determined according to the ASTM method and discussed in light of copolymer composites.

Preparation of phosphorus-containing epoxy emulsion and flame retardancy of its thermoset

In this study, the effects of the opening ratio and neutralization degree of diethanolamine to the formation of epoxy emulsion were examined. o-Cresol formaldehyde epoxy resin was modified with 9,10-dihydro-9-xa-10-phosphaphenanthrene-10-oxide and diethanolamine and was then neutralized by acetic acid to obtain a phosphorus-containing epoxy emulsion by the phase inversion method. The microstructure and size distribution of the epoxy latex were characterized using transmission electron microscopy and the Malvern particle sizer, respectively. The glass transition temperatures of epoxy resins and their thermosets were characterized using differential scanning calorimetry. The flame retardancy of the phosphorus-containing epoxy thermosets was tested by the UL-94 test method, limiting oxygen index (LOI), and thermogravimetric analysis (TGA). The result shows that when the diethanolamine opening ratio was 22.5% and neutralization degree was 100.0%, a stable epoxy emulsion was obtained. When the phosphorus content of the epoxy resin was 2.5 wt%, the LOI value of the epoxy thermoset can reach 36.8 and pass the V-0 rating of the UL-94 test. TGA and scanning electron microscopy images of char residue of epoxy thermosets show that the flame-retardant mechanism of the phosphorus-containing epoxy thermoset was mainly attributed to a condensed-phase mechanism.

Phosphorus-containing Polysulfones - A Comparative Study

A comparative study of the influence of 2-(10-oxo-10H-9-oxa-10 λ5-phosphaphenanthrene10-yl)-benzene-1,4-diol (DOPO-HQ) and 2-(2,8-dimethyl-10-oxo-10H-10 λ5-phenoxaphosphine-10-yl)benzene-1,4-diol (DPPO-HQ) on their ability to form polysulfones (PSU) with 4,4′ -difluorodiphenylsulfone (DFDPS) as well as the properties of the aromatic phosphorus-containing polysulfones (P-PSU) is reported. These properties are also compared to bisphenol A-based polysulfone. Both diols have the phosphorus unit as substituent and differ in the number of oxygen atoms within the environment of the phosphorus changing from DOPO-HQ (phosphinate structure, Ar2 OP(=O)) to DPPO-HQ (phosphine oxide structure, Ar3PO). The nucleophilic aromatic polycondensation was carried out successfully using both phosphorus-containing aromatic diols instead of bisphenol A and was followed by ATR-FTIR in-line monitoring. The use of DPPO-HQ decreased the number of side reactions and enhanced slightly the molecular weight. The thermal stability of DPPO-HQ-based PSU is slightly better than DOPO-HQ-based PSU. Thermal decomposition schemes for PSU and for both P-PSUs are proposed based on thermogravimetric analysis and Pyrolysis GC-MS results.