EP Composites Research Articles

Cyclotriphosphazene hyperbranched P/N/Si prepared flame retardants improve mechanical properties and flame retardancy of epoxy resins

AbstractIn this study, a cyclotriphosphazene hyperbranched P/N/Si prepared flame retardant (HBPPSi) was synthesized, and the effects of different loadings of HBPPSi on the mechanical properties, thermal stability and flame retardancy of epoxy resin were investigated. The mechanical property studies showed that the addition of HBPPSi could effectively improve the strength and toughness of epoxy resin, in which the strength and toughness of 5% HBPPSi/EP composites were improved by 43% and 59%, respectively. Meanwhile, thermogravimetric analysis and combustion performance test analysis indicated that the loading of HBPPSi could significantly improve the carbon formation rate, flame retardancy, and smoke suppression performance of EP composites. 5% HBPPSi/EP composites achieved a V‐1 grade in the UL‐94 test, and the LOI value increased to 28.3%. Compared with the pure EP material, the maximum heat release rate (PHRR) and total smoke release (TSP) of the 5% HBPPSi/EP composite were reduced by 47% and 32%, respectively. In addition, the release of toxic smoke CO was also significantly reduced. More importantly, the mode of action of the effect of HBPPSi on the mechanical properties, flame retardant properties, and smoke suppression properties of EP materials was investigated.

Synthesis of a vanillin‐based curing agent and its application in wood to improve dimensional stability and flame retardancy

AbstractA novel multifunctional phosphorus‐containing curing agent monomer (PPBMBA) was designed and prepared based on vanillin by the nucleophilic substitution reaction and Pinnick oxidation with phenylphosphonic dichloride (PPDCL). Then a series of epoxy resin (EP) impregnated reinforced wood samples were prepared by combining PPBMBA to improve the dimensional stability and flame retardancy of wood. Differential scanning calorimetry results showed that the curing ability of PPBMBA to EP formulations is equivalent to that of industrial amine curing agents, while simultaneously being flame retardant and environmentally friendly. Scanning electron microscopy (SEM) observation found that the cured EP composite was widely distributed in the wood. Besides, the water uptake rate and volumetric swelling (S) of the impregnated wood sample W‐EP‐0.10 were 59.8% and 67.8% lower than that of pure wood respectively, while the anti‐swelling efficiency (ASE) value was as high as 67.7%. The parallel‐to‐grain compression strength (CS) of the W‐EP‐0.10 was increased by up to 78.3% compared to that of pure wood, while the limiting oxygen index increased from 21.7% to 26.8%, and UL 94 reached V‐0 level. TGA‐FTIR and SEM analysis demonstrated that the thermal stability and flame retardancy of the impregnated wood samples were improved by generating non‐flammable gases and forming an insulating char layer synergistically. From a practical standpoint, this work has significant engineering application value for the development of value‐added wood products with high‐efficiency fire safety and dimensional stability from relatively low‐cost wood.

A novel phosphorus-, nitrogen- and sulfur-containing macromolecule flame retardant for constructing high-performance epoxy resin composites

Epoxy resin (EP) has two shortcomings: flammability and brittleness. Previous studies have improved brittleness or flame retardancy but they will compromise the glass transition temperature (Tg) and thermal stability. Herein, a novel DOPO based phosphorus-, nitrogen- and sulfur-co-contained macromolecular flame retardant (DOPONH2-S) was synthesized and incorporated into EP to improve its flame retardancy and toughness with not damaging Tg and thermal stability. After curing, both Tg and the tensile strength of EP-2 improved at the addition of DOPONH2-S is 6.75 wt%. Simultaneously, the thermogravimetric analysis (TGA) results showed DOPONH2-S is helpful increasing the thermal stability of EP composites and protecting the polymer from further decomposition. In the fire safety test, EP-2 achieved V-0 rating in the vertical burning test and obtained a limiting oxygen index value of 30.5%. In comparison with pure EP, the peak heat release rate, total heat release and effective heat of combustion of EP-4 incorporated with 10.0 wt% DOPONH2-S were reduced by 59.1%, 58.5% and 46.3%, respectively. A two-phase mechanism was discussed to explain the combination effect in DOPONH2-S. In condensed-phase, rich char residue prevents the exchange of mass and heat during combustion. It also obstructs the release of combustible gases into the combustion zone. In gas-phase, the produced phosphorus- and sulfur-containing free radicals can capture active free radicals (H· and OH·), thus ending the chain reaction of combustion. Moreover, the addition of DOPONH2-S apparently improved the impact strength (62.5%). This work provided ideas for the development of multifunctional EP.

Rational design of a functionalized silicone polymer for modifying epoxy-based composites

In this work, a new compound, N-TMSPrVaC, was synthesized using 3-aminopropyltrimethoxysilane (ATPMS) and valeryl chloride (C5H9ClO). Furthermore, it was grafted onto the silicone polymer (PSOL) to obtain a new epoxy resin modifier. Infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (1H NMR) were used to characterize the composition and structure of the compound N-TMSPrVaC. The mechanical properties and dynamic thermomechanical analysis (DMA) of PSOL-(N-TMSPrVaC)/EP composites were systematically studied. PSOL-(N-TMSPrVaC) can significantly improve the tensile properties and impact properties of composites by 8.9% (0.5 phr) and 18.2% (3.0 phr), respectively, according to the results. The distribution of PSOL-(N-TMSPrVaC) in the epoxy was studied using the scanning electron microscope and X-ray spectrometry (SEM-EDS). The DMA test showed that the functionalized silicon polymer retained the heat resistance of the epoxy composite material to a certain extent while toughened the epoxy.

Synergistic Effect of Multifunctional Layered Double Hydroxide-Based Hybrids and Modified Phosphagen with an Active Amino Group for Enhancing the Smoke Suppression and Flame Retardancy of Epoxy.

To improve the fire hazard of epoxy resin (EP), phosphomolybdate (PMoA), as a classical Keggin cluster, was successfully intercalated into Mg, Al, and Zn layered double hydrotalcite (LDH) by the reconstruction method, and it was denoted as MgAlZn-LDH-PMoA. The structure and morphology of MgAlZn-LDH-PMoA were characterized by X-ray diffraction and Fourier transform infrared spectroscopy. Subsequently, hexa(4-aminophenoxy)cyclotriphosphazene (HACP) was prepared and characterized as a high-performance organic flame retardant, which is rich in flame elements phosphorus and nitrogen. The synergistic effects of MgAlZn-LDH-PMoA and HACP on the fire safety of EP composites loaded with different amounts of flame retardant hybrids were studied in detail. Thermogravimetric analysis showed that the char residue of these EP composites increased significantly. Compared with the EP matrix filled with only MgAlZn-LDH-PMoA or HACP, the incorporation of MgAlZn-LDH-PMoA and HACP had a synergistic effect on promoting char formation of EP composites. Particularly, the char yield of EP7 is as high as 29.0%. Furthermore, the synergistic effects of incorporation of MgAlZn-LDH-PMoA with HACP were investigated using the cone calorimeter combustion tests. The results showed that the total heat release and peak heat release rate of the EP composites remarkably declined by 35.2 and 50.9%, respectively, with a loading of 7 wt % hybrid flame retardant. Moreover, the hybrid flame retardants also showed an obvious inhibitory effect on the total smoke production and the release of toxic CO gas. The detailed analysis of the residual char indicated that the main mechanism for improving the flame retardancy and smoke suppression performance is due to both the catalytic carbonization of MgAlZn-LDH-PMoA and phosphoric acid compounds and physical barrier function of the char layer. In addition, the molybdenum oxides produced from [PMo12O40]3– during combustion can not only increase the yield and compactness of the char layer but also reduce the release of CO through a redox reaction, which has important application value to reduce the fire hazard.

Toughness Improvement of Epoxy Composites Using a Kind of Environment-Friendly Bio-Based Polyester Polyol

Epoxy resin (EP) is a thermosetting resin with prominent performances and wide applications. However, the inherent brittleness limits its development in the engineering materials area. A liquid bio-based polyester polyol (LLP) with flexible long chains was synthesized in this study by melt polycondensation of corn straw lignin. After being compounded with EP (LLP/EP), the mechanical property, micromorphology and thermal behavior of the composite were evaluated. The experimental result indicated that the fracture brittleness of EP composite was decreased by importing the LLP. The bending and impact strength were up to 113.67 MPa and 51.29 kJ/m2 for 10%-LLP/EP, which were 5.25% and 27% higher than those of unmodified EP. The results of this work build new avenues for the efficient utilization of lignin and the development of low-cost, high-performance and well environmentally adaptable EP composite by renewable resources.Graphical Abstract

Facile Construction of Polypyrrole Microencapsulated Melamine-Coated Ammonium Polyphosphate to Simultaneously Reduce Flammability and Smoke Release of Epoxy Resin.

A unique mono-component intumescent flame retardant, named PPy-MAPP, of which melamine-coated ammonium polyphosphate (MAPP) was microencapsulated by polypyrrole (PPy), was synthesized and carefully characterized. The obtained PPy-MAPP was applied to epoxy resin (EP) for obtaining flame-retarded EP composites. The results show that PPy-MAPP imparts better flame retardancy and smoke suppression properties to EP compared to the same addition of MAPP. The EP composite with 15 wt% PPy-MAPP easily passes the UL94 V-0 rating and achieves an LOI value of 42.4%, accompanied by a 61.9% reduction in total heat release (THR) and a 73.9% reduction in total smoke production (TSP) when compared with pure EP. The char residue analysis shows that PPy-MAPP can promote a generation of more phosphorus-rich structures in the condensed phase that improve the integrity and intumescence of char against fire. The mechanical test indicates that PPy-MAPP has a less negative effect on the tensile strength and elastic modulus of epoxy resin due to the good compatibility between PPy-MAPP and the EP matrix, as supported by differential scanning calorimetry (DSC) analyses. In this paper, these attractive features of PPy-MAPP provide a new strategy to prepare satisfactory flame retardant and super flame retarding EP composites.

Metal-doped 2D rGO nano-sheets fabrication utilizing plant source bio-molecules and application in the epoxy anti-corrosive coating: Combined experimental and DFT-D modeling investigations

Recently, graphene-filled polymeric composites have been utilized for achieving durable active corrosion protection properties in seawater solutions. The utilization of reduced graphene oxide (rGO) is highly recommended for this purpose. Although the traditional reductants can successfully reduce the GO layers, employing green active agents is far more affordable. In the present study, Mustard seed extract was introduced as a novel cost-effective, and green reductant for GO layers since it includes active agents like arabinose, allyl isothiocyanate, galactose, xylose, diallyl trisulfide, and rhamnose molecules. For boosting the active protection property, the rGO nano-sheets were doped with Zn (II) ions (Zn@rGO) as the inorganic inhibitor. The synthesized nanosheets' anti-corrosion impacts in the solution phase were illustrated by polarization and EIS techniques. The obtained results have proved that the Zn@rGO containing saline solution exposed steel samples resulted in 88% degree of inhibition in mixed mode. The EIS assessments carried out over the scratched epoxy composite reflected that the coating resistance was raised from 12,491 Ω cm2 to 47,480 Ω cm2, affirming the inhibitive corrosion prevention potency of the Zn@rGO/EP composite. The FE-SEM captures have displayed that the inhibitive layer filled the scratched zones successfully. Besides, the intact coating's high resistance (over 30 GΩ.cm2) indicated that the constructed nano-filler could effectively promote the EP coating barrier index. The optical captures after conducting a salt-spray test have demonstrated that after the EP anti-corrosion performance was significantly improved in the presence of Zn@rGO nano-layers. The coating delamination diameter reduction from 28 mm for the neat epoxy to 11 mm for the Zn@rGO loaded coating was recorded in the cathodic disbondment test. In addition, the theoretical findings ensured the affinity of the zinc ions/ME compounds for adsorption on the GO layers.

Enhanced thermal conductivity of epoxy resin by incorporating pitch-based carbon fiber modified by Diels-Alder reaction

The ever-increasing power density and high integration of electronic devices and components greatly promotes the demand for thermal management materials. Herein, we report a lightweight and thermal conductive polymer composite based on the epoxy resin (EP) and high graphitized pitch-based carbon fiber (CF). To address the problem of the surface inertness of the raw CF (RCF), a Dies-Alder reaction was introduced after a conventional oxidation by AgNO3/K2S2O8. The results of the X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscopy showed that the oxygen content of the modified CF (OCF-MA) surface was significantly increased but its structure was not damaged after the Dies-Alder reaction with the maleic anhydride. Because of the superior thermal conductivity and improved surface activity of the RCF-MA, the OCF-MA/EP composites showed a remarkably high thermal conductivity of 4.43 W/m·K at a relatively low CF loading of 11.5 vol%, which is 2.34 times that of the RCF/EP composite (1.89 W/m·K). The infrared thermal imaging method further demonstrated the excellent heat transfer advantage of the RCF-MA/EP composites over the neat EP and RCF/EP composites. The thermogravimetric analysis showed that the addition of OCF-MA has no adverse effect on the thermal stability of the EP composites. In addition, the tensile test showed that the addition of OCF-MA into the EP had a positive effect on the tensile strength of the EP. This work demonstrates that grafting maleic anhydride via Diels-Alder reaction could be a feasible method to functionalize CF for advanced thermal management applications.

Significant Improvement in the Flame Retardancy and Thermal Conductivity of the Epoxy Resin via Constructing a Branched Flame Retardant Based on SI-ATRP Initiated by Dopamine-Modified Boron Nitride

The rapid development of integrated circuits and micro-devices has brought serious thermal failure and huge fire hazards to polymer composites due to the inefficient heat dissipation. Here, in order to simultaneously achieve the excellent thermal conductivity (TC) and flame retardancy (FR) of composites, we proposed a strategy of grafting a flame retardant on the surface of an exfoliated boron nitride nanosheet (BNNS). Briefly, the atom transfer radical polymerization (ATRP) reaction was initiated on the surface of the BNNS with predeposited polydopamine to obtain poly(glycidyl methacrylate) (PGMA) chain with high graft density, and then the flame-retardant molecule 6H-dibenz(C,E)(1,2)oxaphosphorin-6-oxide (DOPO) was further decorated to form a flame-retardant functionalized BNNS with branched structure. Due to the improvement of interfacial compatibility, the BNNS exhibits uniform dispersion and robust interfacial interaction with the epoxy resin (EP), which will further promote the formation of heat conduction paths and the reduction of interfacial thermal resistance (Rb). In particular, the EP composite containing 30 wt % BNNS-DOPO exhibits a TC of 1.25 W/m·K, exceeding that of the composite loaded with serious aggregated BNNS by 32%. Simultaneously, the EP composite with only 20 wt % BNNS-DOPO presents a superior FR with an obvious decrease in the values of peak heat release rate (PHRR), total heat release (THR), smoke production rate (SPR), and total smoke production (TSP) compared to EP, corresponding to a reduction of 47.6, 44.7, 46.5, and 50%, respectively. The enhanced FR is mainly ascribed to the catalytic carbonization of DOPO, and the continuous and compact protective layer formed by the char combined with the BNNS effectively prevents the exchange of heat, oxygen, and volatile gases. Therefore, this surface modification strategy of the BNNS provides a new idea for exploring thermally conductive and flame-retardant composites.

Cost-effective graphite felt and phosphorous flame retardant with extremely high electromagnetic shielding

With the advent of the 5G era, preparing conductive polymers to accomplish electromagnetic interference (EMI) shielding, mechanical enhancement, and flame retardancy are of vital importance. Graphite felt (GF) acts as a three-dimensional structure and organophosphorus derivatives containing different valences work as a flame retardant to form a novel EP composite. With GF incorporated into EP, EMI shielding effectiveness (SE) achieves around 60 dB, and absorption is dominated in the X band (8.2–12.4 GHz). Meanwhile, GF could exert a fiber reinforcement effect to enhance the mechanical properties of EP composites, tensile strength and impact strength of EP/GF are increased by 19.1% and 64.2%, respectively. However, owing to the “wick effect” of GF, 20 wt% DOPO-PEPA is added to acquire flame-retardant EP composites. Herein, a potential strategy broadens applications of EP composites in the high-end field and is provided to prepare polymer composites . • A cost-reasonable EP composites composed of 3D GF and two-valence phosphorous derivatives is successfully fabricated. • The EMI SE EP composites achieve around 60 dB in the X band. • The pHRR and THR of EP/GF/20FR are reduced by 53.4% and 35.3%, respectively. • EP composites exhibit potential promise for large-scale production and industrial applications.

Novel exploration of the flame retardant potential of bimetallic MXene in epoxy composites

As a graphene-like material, MXene , represented by Ti 3 C 2 T x , has been found to possess promising flame retardant potential in polymers due to their excellent thermal and catalytic actions, as well as lamellar barrier effect. Thus, it is of great significance to explore whether MXene with double transition metal components has a higher flame retardant efficiency. Herein, Ti 3 C 2 T x and bimetallic MXene (Mo 2 Ti 2 C 3 T x ) were fabricated by acid-etching method and then introduced into epoxy resin (EP) for the comparative investigation of their flame-retardant effect. The results indicated that MXenes were homogeneously dispersed in EP matrix, which can contribute to the improvements of thermal and flame retardant properties of EP composites. Upon the incorporation of 1 wt% Mo 2 Ti 2 C 3 T x MXene, the EP composites achieved a significantly reduced maximum mass loss rate (R max ) by 39.4%, superb over EP/Ti 3 C 2 T x composites. Moreover, Mo 2 Ti 2 C 3 T x MXene endowed EP composites with a notable downward trend in fire risk, reflected by the decreasing PHRR of 34%, PSPR of 32.7%, TSP of 57.7%, PCO of 30.8%, along with significantly reduced SF value by 72.7%, which was superior to EP/Ti 3 C 2 T x composites. The strong catalytic attenuation and charring effect of transition metal Mo–Ti elements for bimetallic Mo 2 Ti 2 C 3 T x MXene, as well as nanosheet structure, imparted excellent fire retardant performance to EP composites. This work provides new insights into the application of bimetallic MXenes in flame retardant polymer composites .

Fabrication of two multifunctional phosphorus–nitrogen flame retardants toward improving the fire safety of epoxy resin

Abstract To improve the fire safety of epoxy resin (EP), two novel phosphorus–nitrogen flame retardants, which named as diphenyl allylphosphoramidate (DPCA) and N-allyl-P, P-diphenylphosphinic amide (DCA), were synthesized by acyl chloride reaction and introduced into EP for fabricating EP composites. The combustion tests showed that incorporation of 5 wt% DPCA or 5 wt% DCA into EP led to the exceptional limited oxygen index (LOI) value (27.1% or 31.6%). Besides, the peak of heat release rate of EP-5 wt% DPCA and EP-5 wt% DCA was reduced by 40.69% and 36.69%, respectively, compared to pure EP. The enhanced fire resistance of EP was ascribed to the trapping effect of fillers in the gas phase and the charring effect in the condensed phase. Furthermore, ultraviolet-visible spectra revealed that both EP-5 wt% DPCA and EP-5 wt% DCA have considerable transparency. This study is expected to broaden the application of EP in the industrial area.

Engineering two nitrogen-containing polyhedral oligomeric silsesquioxanes (N-POSSs) to enhance the fire safety of epoxy resin endowed with superior thermal stability

Despite remarkable advances in developing flame retardants and smoke suppressants for epoxy resin (EP), engineering nitrogen-containing polyhedral oligomeric silsesquioxane (N-POSS) to impart superior fire safety properties to EP has remained an intractable challenge. In this work, two nitrogen-containing polyhedral oligomeric silsesquioxanes (N-POSSs), namely, aminoethyl-aminopropyl-hepta-phenyl polyhedral oligomeric silsesquioxane (AEAP-POSS) and aminopropyl-hepta-phenyl polyhedral oligomeric silsesquioxane (AP-POSS), were synthesized through the “corner-capping” reaction. The molecular structures of N-POSSs were fully characterized by FTIR, 1H NMR, 29Si NMR and MALDI-TOF MS, and the synthesized AEAP-POSS and AP-POSS were introduced into EP to solve the shortcomings of flammability. TGA results showed that the incorporation of 4 wt% N-POSS nanoparticles distinctly improved the char residue at 800 °C, which significantly enhanced the thermal stability of the EP composites. When 4 wt% of AP-POSS was introduced into EP, reductions in the peak of heat release rate (p-HRR), fire growth index (FGI), peak of smoke production rate (p-SPR), and the peak of CO production rate (p-COP) reached to 60.6%, 70.2%, 52.3% and 60.4%, respectively. Subsequently, TG-FTIR and XPS were utilized to investigate the flame retardancy and smoke suppression mechanism. Our work presented a considerable advancement for the facile fabrication of flame retardants based on nitrogen-containing polyhedral oligomeric silsesquioxane compounds.

Preparation and Tribological Properties of Self-Lubricating Epoxy Resins with Oil-Containing Nanocapsules.

The design and development of self-lubricating materials aid in enhancing the tribological performance and prolonging the service life of aero self-lubricating spherical plain bearings. Herein, monodisperse hollow mesoporous carbon nanospheres (HMCNs) with thin shell thickness and uniform particle size were synthesized. Afterward, oil-containing nanocapsules (Oil@HMCNs) were obtained by the impregnation method, which was an innovative approach to prepare nanoscale capsules. The Oil@HMCNs were monodispersed, and the oil content rate could reach 45 wt %. The nanocapsules were applied as additives to achieve the self-lubricating properties of epoxy resin (EP). It was revealed that the coefficient of friction (COF) and the wear rate of EP in dry friction can be decreased from 0.56 to 0.084 and from 50.15 × 10-6 to 0.27 × 10-6 mm3/N/m, respectively. The tribological properties of EP composites in dry friction are better than those of EP with external oil. According to the analysis of friction pairs, the antifriction performance was contributed by the released automatic transmission fluid 6HP (ATF6) from nanocapsules. Meanwhile, the presence of ATF6 effectively could inhibit fatigue wear, and the decrease of compressive strength and surface hardness led to plastic deformation and mechanical polishing. Both resulted in a lower wear rate of EP. In conclusion, this work explored the application possibility of hollow mesoporous materials in lubrication. The prepared EP composites exhibited excellent tribological performances and self-lubricating properties, which were expected to be applied to self-lubricating spherical plain bearings and other mechanical parts.

Novel design of MOFs-based hierarchical nanoarchitecture: Towards reducing fire hazards of epoxy resin

The inherent inflammability of epoxy resin (EP) has seriously limited its further application. The structural design of flame retardants has huge potential for boosting the fire safety properties of polymer materials. Herein, a novel MOFs-based hierarchical nanoarchitecture (ZIF-8@PA@SiO2) was constructed, composed of ZIF-8 nanoparticles, as well as in-situ grown phytic acid (PA) and silica. The results indicated that not only was ZIF-8@PA@SiO2 uniformly dispersed in the EP matrix, but it also formed a good interface bond, which was beneficial to boosting the thermal and fire safety properties of EP composites. The incorporation of ZIF-8@PA@SiO2 markedly decreased the maximum weight loss rate (MLRmax) and increased char residues. Compared with neat EP, the limiting oxygen index (LOI) value of EP/5% ZIF-8@PA@SiO2 increased from 23.4% to 28.8%. Furthermore, the peak heat release rate (PHRR), fire growth index (FGI), peak smoke production rate (PSPR), peak CO production rate (PCOPR) and smoke factor (SF) were decreased by 38.3%, 41.6%, 45.5%, 42.9% and 69.3%, respectively. The TG-FTIR results provided strong evidence for suppressed emissions of CO, aromatic, hydrocarbons and carbonyl, further corroborating the impeded heat release and the hindered fire toxicity, which were primarily ascribed to the barrier effect, free-radical scavenging and dilution effect of the multi-integrated P/N/Si-containing MOFs-based hierarchical nanoarchitecture.

Assembling MXene with bio-phytic acid: Improving the fire safety and comprehensive properties of epoxy resin

Phytic acid (PA)-modified MXene (P-MXene) was prepared combination selective etching with assemble method, and was mixed with epoxy resin (EP) to investigated its flame retardancy, thermal conductivity, conductivity and mechanical properties. P-MXene exhibited two-dimensional single layer structure and had good char-forming property with 86.7% char residue at 800 °C. The cone calorimetry test results showed that P-MXene endowed EP with excellent flame retardancy. Compared with pure EP, the peak heat release rate, peak smoke release rate, peak CO generation rate, and peak CO2 generation rate of EP composites with 2 phr P-MXene decreased by 38.6%, 31.6%, 38.7% and 40.6%, respectively. The flame retardant mechanism was attributed to physical barrier, catalyzing carbonization effect, oxidative thermal degradation and physical barrier effect. Additionally, the conductivity and mechanical properties of EP composites were slightly reduced. This work provides a promising method to design multifunctional polymers.

A nitrogen heterocyclic/phosphaphenanthrene derivative as a reactive additive for simultaneous improvement of flame retardancy, mechanical and dielectric properties of epoxy resins

Various approaches have been successfully applied to solve the flammability of epoxy resin (EP) materials, but enhanced flame retardance of EP is often along with deteriorated glass transition temperature (Tg) and mechanical property. In order to prepare EP composites with good comprehensive performance, we synthesized a phosphorus-containing triazole derivative named TBO from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 3,5-diamino-triazolz and salicylaldehyde, and attached it into epoxy framework. With 0.75 wt% phosphorus loading, the 0.75-TBO/EP composite had a V-0 rating and a limiting oxygen index of 33%. 1.0-TBO/EP composite also had a V-0 rating and acquired a decrease of 37.6% in peak heat release rate. In addition, the tensile strength and flexural strength of 0.75-TBO/EP increased to 63.9 MPa and 146 MPa from 59 MPa and 134 MPa of EP respectively. Meanwhile, the Tg values of TBO/EP elevated to some certain compared to EP. In a word, EP modified with TBO composites owned strong mechanical property, higher Tg and excellent flame retardance, indicating great potential for application.

Effect of cyclophosphazene nucleated hyperbranched polyester on flame retardancy and mechanical properties of epoxy resins

AbstractHexakis(4‐hydroxyphenoxy) cyclotriphosphazene (PN‐OH) was synthesized by a nucleophilic substitution and aldehyde reduction reaction of hexachlorocyclotriphosphazene with p‐hydroxybenzaldehyde, and then cyclophosphazene nucleated hyperbranched polyesters (HBP) were prepared via a one‐pot esterification reaction of PN‐OH and dimethylolpropionic acid. The chemical structure and molecular weight distribution of HBP were confirmed by 1H‐NMR, FTIR, and GPC. The HBP was applied to epoxy resin (EP) to improve its mechanical properties and flame retardancy. The cone calorimeter test revealed that the maximum heat release rate, total heat release and total smoke release of HBP/EP composites were reduced by 35.9%, 21.6%, and 27.3%, respectively, when 7 wt% HBP was added to the EP matrix compared with pure EP. Meanwhile, when 7 wt% HBP was added to EP composites, the limiting oxygen index value was increased from 24.6% to 27.7% and the UL‐94 test reached a V‐1 rating. More importantly, the thermal stability and mechanical properties of the HBP/EP composites were enhanced. The flame retardant mechanism analysis showed that HBP primarily acted as a flame retardant in the condensed phase. These results indicate that the HBP/EP composites have exceptional overall performance and a broad range of applications in critical fields.

Facile strategy to synthesize MXene@LDH nanohybrids for boosting the flame retardancy and smoke suppression properties of epoxy

The creation of high-efficient MXene-based flame retardants to cope with the fire hazards of polymer composites remained an intractable challenge. Hence, this work explored a facile strategy to synthesize MXene-based nanohybrids (MXene@LDH) by in situ growth of layered double hydroxides (CoAl-LDH) on the surface of MXene in anticipation of constructing an efficient flame retardant system. The results indicated that the integration of LDH prevented the stacking of MXene nanosheets and enhanced the dispersion of MXene in EP matrix, endowing EP composites with excellent thermal properties and flame retardancy. With the addition of 2 wt% MXene@LDH, EP composites exhibited reduced the maximum mass loss rate (Rmax) of 28.5%, increased residual char and led to 25.3% reduction in PHRR and a drop of 24.4% in THR, compared to those of neat EP. Furthermore, EP/2 wt% MXene@LDH composites also demonstrated superior smoke suppression performance, mainly reflected by the 38.5%, 37.8%, 33.8% and 31.2% reduction in PSPR, TSP, PCO and PCO2, respectively, together with a 52.0% decline in smoke factor (SF), compared to those of pure EP. The improved fire safety of EP composites was attributed to the catalytic charring and attenuation effect of the transition metal oxides, coupled with the barrier effect of the nanosheets and the cooling effect, gas-phase dilution effect of LDH.