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Organophosphorus heteroaromatic compound towards mechanically reinforced and low-flammability epoxy resin
... Jian et al. [60] synthesized an organophosphorus heteroaromatic compound (DMBT) derived from DOPO and 2mercaptobenzothiazole (MBT) and incorporated it into a DGEBA based resin cured with DDM hardener ( Scheme 7 ). The idea to use MBT in the modification of DOPO came out from some recent works, which used this compound to improve the adhesion, toughness and curing behavior of epoxy resins [ 61 , 62 ]. ...
... ππ interactions and hydrogen bonds) like bridges to connect the epoxy macromolecular chains, leading to the strengthening of epoxy thermosets ( Fig. 6 ). Due to this strengthening effect of the DMBT additive, epoxy composites containing 10 wt% of the DOPO derivative resulted in an increase in the tensile strength, flexural strength and modulus compared to pure EP [60] . ...
... The epoxy composite containing 10 wt% DMBT (EP-2) passed UL-94 V1 rating, possessed a LOI value of 33.5% and had reduced PHRR and THE values during combustion ( Tables 5 and 17 ). Jian et al. [60] also calculated the FIGRA value of the sample. It is defined as the ratio of "PHRR" to "tp" and is recognized as an important parameter to assess the hazard of developing fire [63] . ...
Epoxy resins are widely used in the manufacturing of fire safety products in the industry. 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is a commercially available non-toxic reactive flame retardant and its incorporation improves the fire behavior of epoxy systems by releasing active phosphorus species to the gas phase. The reaction between DOPO and oxirane moieties negatively affects the glass transition temperature of epoxy-based composites and thus to overcome this drawback, it is usually modified to obtain non-reactive derivatives (i.e. mono- and multi DOPO derivatives). Besides, DOPO can also interact with the surface of silica- and carbon based nanostructures, leading to hybrid DOPO additives (“hybrid” term is referred to the organic-inorganic structure of such derivatives, which do not react directly with the polymer matrix). Non-reactive DOPO derivatives allow effective hybrid flame retardant mechanism and, in some hybrid –DOPO derivatives, good mechanical performances for the resin can be realized. This review focuses primarily on the technological advances in the last ten years (2011 onwards) on non-reactive DOPO derivatives for epoxy systems. Though DOPO is quite a common flame retardant additive in the polymer industry, for commercial exploitation of its derivatives, there is a need to develop economical alternative synthesis methodologies.
... Meanwhile, the peak at 1275 cm −1 is due to the CH 2 wagging. The characteristic peaks at 1065 and 1214 cm −1 are associated with the C-O-C asymmetric and symmetric stretching absorptions, respectively [29,30]. The particular peak of 1133 cm −1 results from the vibrations of the asymmetric stretching of the chemical bonds in C-N-C groups of the oxazine ring. ...
... while, the peak at 1275 cm −1 is due to the CH2 wagging. The characteristic peaks at 1065 and 1214 cm −1 are associated with the C-O-C asymmetric and symmetric stretching absorptions, respectively [29,30]. The particular peak of 1133 cm −1 results from the vibrations of the asymmetric stretching of the chemical bonds in C-N-C groups of the oxazine ring. ...
Polybenzoxazine (PBa) composites based on phosphorous-containing bio-based furfurylamine type benzoxazines (D-fu) and bisphenol-A type benzoxazines (Ba) were developed for flame retardation. The structure of D-fu was analyzed by Fourier transform infrared (FTIR) spectroscopy and ¹H-NMR spectroscopy. The curing temperature of Ba/D-fu mixtures was systematically studied by differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) demonstrated the excellent char formation ability of the PBa composites with the addition of phosphorous-containing D-fu. The flame retardancy of the PBa composite materials was tested by the limited oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter (CONE). The LOI and UL-94 level of PBa/PD-fu-5% reached 34 and V0 rate, respectively. Notably, the incorporation of 5% D-fu into PBa led to a decrease of 21.9% at the peak of the heat-release rate and a mass-loss reduction of 8.0%. Moreover, the fire performance index increased, which demonstrated that the introduction of D-fu can diminish fire occurrence. The role of D-fu in the condensed and gas phases for the fire-resistant mechanism of the PBa matrix was supported by SEM-EDS and TGA/infrared spectrometry (TG-FTIR), respectively. Dynamic mechanical analysis (DMA) revealed that the Tg of PBa flame-retardant composites was around 230 °C. Therefore, PBa composites are promising fire-retardant polymers that can be applied as high-performance functional materials.
... Nowadays, ame-retardant epoxy resin composites are rapidly developed so as to meet the high re-safety requirements. [4,5] For the commercial ame-retardant epoxy resin composites, both organic phosphorous ame retardants, such as DOPO and DOPO-derives, [6,7] and inorganic ame retardants, such as ATH and ammonium polyphosphate (APP), etc. [8,9] are used to enhance the re performance of epoxy resin composites. However, the complex prepared process, the massive use of organic solvents in preparation as well as the low smoke suppression capacity of the DOPO-based ame retardants during combustion are still a challenge. ...
Concerning inorganic flame retardants, the facile fabrication and high-efficiency fire safety without compromising the mechanical property of matrix are still significant challenges. Here, nano-layered double hydroxide containing boron constructed on the surface of ammonium polyphosphate complexes (B-LDH@APP) is prepared by a simple in-situ coprecipitation technology to reduce the fire hazard and improve mechanical performances of epoxy resin (EP). The as-obtained 4B-LDH@APP/EP achieves the UL-94 V-0 rating and presents superior flame-safety performance. With respect to the 4APP/EP, the fire growth rate, the peak heat release rate, and the peak smoke production rate of 4B-LDH@APP/EP decrease by 77.8%, 57.3%, and 52.6%, respectively. The reason is mainly contributed to excellent synergistic flame-retardant effect among boron, LDH, and APP, which can accelerate the generation of compact charring residual with good microstructure during combustion of B-LDH@APP/EP composites. Furthermore, B-LDH@APP slightly affects the mechanical performances of EP matrix due to the upgraded interfacial interaction.
... Adding a flame retardant or introducing a functional group responsible for triggering a flame retardant in the matrix polymer backbone or end group is a promising method for enhancing a thermoset's flame resistance. For example, halogen [69,70], organophosphorus [11,[71][72][73][74][75][76][77][78][79][80][81][82][83], intumescent effects [84][85][86][87][88][89][90], silicon-containing compounds [91,92], nanocomposites [93][94][95][96] and metal-containing compounds [97][98][99] are common flame retardants used in thermoset materials. Flame retardant approaches, such as addition and reactive approaches are often utilized in thermosets. ...
Thermosets are widely used in the polymer, composite, automobile, aerospace, and electronic industries due to their excellent mechanical, thermal, light weight, and dimensional stability performances. However, most thermosets are made from petroleum resources that deplete petroleum reservoirs and cannot be reused due to their stable linkages, resulting in many waste and environmental problems after their service life. Therefore, repairable, reprocessable, and reworkable thermosets can be produced by incorporating dynamic covalent linkages into polymeric thermosets, which can extend the lifetime and reduce waste. Nevertheless, when a product is recycled multiple times, it is unavoidable that it will decay and become a disposal problem. The use of green and sustainable biomass resources as raw materials for polymer products can assist in mitigating environmental issues by lowering petroleum usage and carbon dioxide emissions. Moreover, thermosets or recyclable biomass thermosets are extremely flammable, limiting their application in automobiles, railways, aircraft, buildings, and electrical products. As a result, flame retardant properties are needed. The purpose of this review paper is to impart a broad summary of the subject by emphasizing and addressing recent advancements as well as future prospects for inherently recyclable flame retardant biomass thermosets. Moreover, synthesis methods have been highlighted to develop the design of internally recyclable fire retardant biomass thermosets. A distinct emphasis will be given on recyclable and inherently fire retardant biomass thermosets in terms of flame retardancy, recycling property, physical properties, and thermal stability. Finally, we will explore the importance and threats that intrinsically recyclable flame retardant biomass thermosets face in the future.
... DOPO derivatives can be used as curing agents to produce flame-retardant epoxy resins including biologically based hardeners [40,41]. Several studies have demonstrated that DOPO or its derivatives as phosphorus-containing flame retardants demonstrate excellent thermal stability and flame retardancy [42][43][44][45]. ...
The interaction of glycidyl esters of phosphorus acids (GEF) with aromatic amine hardeners has been studied. A comparative analysis of the reactivity of different GEF (triglycidyl phosphate (TGFT), diglycidyl methyl phosphate (DGMFT), diglycidyl methyl phosphonate (DGMFN)) has been carried out. The activity of amine hardeners in interaction with GEF has been also compared. Kinetic parameters for the curing reaction have been calculated using Thermokinetics software, and the mode of the interaction of phosphorus-containing epoxy oligomers with aromatic amines has been assessed. Complex structures have been optimized using DFT computations at the CAM-B3LYP/TZVPP level with accounting for solvent effects using the C-PCM model. Thermophysical and flame-retardant characteristics of cured phosphorus-containing epoxy polymers have been investigated. It has been shown that epoxy polymers based on GEF and amine aromatic hardeners have high values glass transition temperature. The resulting binder is self-extinguishing and displays promise for use in the RTM process.
... Nevertheless, DOPO always needs a high additive amount to realize satisfied flame retardancy, and it shows poor smoke suppression, when it is used alone. According to the flame retardant synergism, the combination of DOPO and other flame retardants is an effective way to achieve highly-effective flame-retardant systems [17][18][19]. Boron-containing FRs (BFRs) can form a glassy protective layer on the polymer surface during combustion, thus retarding the smoke generation and heat transfer [20,21]. Additionally, nitrogen-containing FRs (NFRs) can release noncombustible gases to dilute the flammable pyrolysis products and oxygen in the burning process [22,23]. ...
Flame-retardant epoxy resins (EPs) with superior optical, mechanical and dielectric properties are highly desired in high-tech industries. In this work, a multifunctional hyperbranched additive (BDHDP) was synthesized for EPs. Our results showed that BDHDP catalyzed the curing of epoxy resin because of its tertiary amine and hydroxyl. At a low addition (<3.0 wt%), BDHDP increased the glass-transition temperature and maintained the transmittance of epoxy thermoset. As expected, BDHDP improved the mechanical robustness and toughness, and reduced the dielectric constant and loss of EP because of the rigid phosphaphenanthrene groups and intra-molecular cavities. Moreover, BDHDP retarded the heat release and smoke generation during the combustion of the EP matrix. Adding 1.5 wt% of BDHDP increased the UL94 rating to V-0, and reduced the total smoke production by 16.4%. Hence, this study offers an effective method to create transparent EP thermosets with outstanding mechanical, dielectric and fire-retardant properties via incorporating a P/N/B-containing hyperbranched oligomer.
... Phosphorus-based flame retardants can produce phosphoric acid, polyphosphoric acid during heating. These acid products promote the dehydration and carbonization of substrate to form the char layer, which prevents the transfer of oxygen, heat and mass between the burning zone and the inner, unburnt area [23][24][25]. In addition, phosphorus-containing radicals produced by the decomposition of phosphorous flame retardant can capture radicals in the gas phase and terminate chain reaction, as well as reducing the further decomposition of polymer materials [26,27]. ...
Phosphated cellulose (PCF) was synthesized based on urea, phosphated acid and cellulose. The structure of the PCF was confirmed by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy coupled with the Energy Dispersive Spectrometer (SEM-EDS). Benzoxazine (Ba)/PCF hybrid materials were fabricated and thermally cured to prepare polybenzoxazine composites (PBa/PCF). The effects of PCF on the curing temperature of Ba were analyzed through differential scanning calorimetry (DSC). The thermogravimetric (TGA) results demonstrated an increased char residue of 50% for the PBa composites incorporating PCF-5% compared with the pure PBa. The peak heat release rate (PHRR) and total heat release (THR) values of the PBa/PCF-5% composites clearly decreased by 58.1% and 16.5% compared to those of the pristine PBa. The smoke released from the PBa/PCF system significantly reduced with the loading of PCF. Moreover, the limited oxygen index (LOI) and vertical burning test level (UL-94) of PBa/PCF-5% reached up to 31 and V0. The flame retardant mechanism of the PCF in the PBa matrix was investigated TG-FTIR and char residues analysis. Finally, the dynamical mechanical analysis (DMA) results demonstrated that the Tg of the PBa/PCF composites was approximately 230 °C, which does not affect further applications of PBa composites.
... Given that the 1% P-MOF epoxy demonstrated a V1 rating, the effect of the organophosphorus compound in improving fire retardancy can be justified as reported in the literature. 65,66 3.2.4. Thermal Stability of MOF Reinforced Composites. ...
A new flame retardant derivatives based on cyclotriphopshazene were successfully synthesized and characterized. The chemical structure of these compounds was characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), and CHN elemental analysis. The flame retardant properties and thermal degradation behavior were investigated using limiting oxygen index (LOI) and thermogravimetric analysis (TGA). For the dielectric properties, the dielectric strength of the synthesized compound, 5a-b, incorporated with epoxy resin was measured using alternating current breakdown voltage. The result revealed that the LOI value of both synthesis compounds show LOI value 25.53 and 25.90%, respectively. The LOI results demonstrate an increase in value compared to the epoxy resin alone, suggesting that both synthesized compounds are promising candidates for improving the fire retardant properties of epoxy resin. The TGA results show that compound 5b, with the longest chain length, produces the highest char residue at 1.70%. This is because the compound promotes early decomposition of the epoxy resin matrix and accelerates char formation, leading to greater residual char and enhanced thermal stability of the epoxy resin at high temperatures. The TGA results for compound 5b reveal a compact and strong char layer, which protects the surface of the epoxy resin from further degradation and combustion, resulting in efficient fire retardancy. Finally, the dielectric strength of both synthesized compounds is 23.51 kV/mm. This reduction in dielectric strength is attributed to the increase in side chain length, which deteriorates charge transport and creates unfavorable intermolecular interactions.
Currently, the flame retardancy of epoxy resin (EP) was achieved at the expenses of the transparency and/or toughness. In the present work, a phosphorus/nitrogen‐containing compound (FDNP) was synthesized by one‐pot method using 9,10‐dihydro‐9‐oxa‐10‐phospha‐phenanthrene‐10‐oxide, furfural and N‐phenyl‐p‐phenylenediamine as raw materials, and further adopted as a functional agent for epoxy resin. The results demonstrated that the FDNP remarkably improved the fire safety of EP. The incorporation of 4 wt% FDNP enabled EP to pass UL‐94 V‐0 rating test and achieve a limiting oxygen index value of 35.5%; meanwhile, the peak heat release rate, total heat release rate and total smoke release were significantly reduced by 41.3%, 41.6% and 72.5% as compared with the pure EP, respectively. What is more, the EP/4 wt% FDNP composite kept almost the same transparency of the pure EP, simultaneously its impact strength was more than doubled as that of the pure EP. Herein, the improved flame retardancy is contributed to a synergistic biphasic flame retardant effect including the formation of a compact protective carbon layer and the release of both non‐combustible gases and phosphorus‐containing radicals.
Under the premise of ensuring the flame retardancy and heat resistance of flame-retardant epoxy resin (FREP), the development of bio-based reactive flame retardants has a broad application prospect.
This work reported a flame‐retardant, single‐component epoxy resin (EP) via introducing diphenylphosphine (DPP) and benzimidazolyl‐substituted cyclotriphosphazene (BICP) into EP. The differential scanning calorimetry (DSC) test showed that the onset curing temperature of DPP/BICP‐15/10 was 50°C lower than that of BICP‐12 due to the catalytic decomposition effect of DPP toward BICP under heating. Besides, the shelf life of DPP/BICP‐15/10 at room temperature reached ~14 days, demonstrating good storage stability. EP/DPP/BICP maintained satisfactory thermal properties and showed excellent flame retardancy with a UL‐94V‐0 classification. Compared with the unmodified EP sample, the peak heat release rate (PHRR) and total heat release (THR) of DPP/BICP‐15/13 were decreased by ~68.1% and ~55.1%, respectively. Hence, this flame‐retardant, single‐component epoxy resin with satisfactory comprehensive properties exhibited great potential for versatile industrial applications.
Fire is a typical disaster in the processing industry. Ionic liquids, as a type of green flame retardant, play an important role in process safety. In order to grasp the current research status, hotspots, and frontiers in the field of ionic liquids in flame retardancy, the bibliometric mapping method is applied to study the relevant literature in Web of Science datasets from 2000–2022 in this paper. The results show that the research on ionic liquids in flame retardancy is multidisciplinary and involves some disciplines such as energy science, material science, and environmental protection. Journal of Power Sources, Polymer Degradation and Stability, ACS Applied Materials and Interfaces, and Chemical Engineering Journal are the core journals in the field. The results of keyword co-occurrence indicate that the hotspots of research can be divided into five components: the improvement and application of pure ionic liquids electrolytes, the research of gel polymer electrolytes, applying ionic liquids to enhance the polymer materials’ flame retardancy properties, utilizing ionic liquids and inorganic materials to synergize flame retardant polymers, and using ionic liquids flame retardant to improve material’s multiple properties. The burst terms and time zone diagram’s results point out the combination of computational quantum chemistry to study the flame retardancy mechanism of ionic liquids, the study of fluorinated electrolytes, ionic liquids for smoke suppression, phosphorus-containing ionic liquids for flame retardant, and machine learning-assisted design of ILs flame retardants are the research frontiers and future research trends.
For inorganic flame retardants, facile fabrication and high-efficiency fire safety without compromising the mechanical property of the matrix are still significant challenges. Here, nanolayered double hydroxide containing boron constructed on the surface of ammonium polyphosphate (APP) complexes ([email protected]) is prepared by a simple in situ coprecipitation technology to reduce the fire hazard and improves the mechanical performances of epoxy resin (EP). The as-obtained [email protected]/EP achieves the UL-94 V-0 rating and presents superior flame-safety performance. With respect to the 4APP/EP, the fire growth rate (FIGRA), the peak heat release rate (pHRR), and the peak smoke production rate (pSPR) of [email protected]/EP decrease by 77.8, 57.3, and 52.6%, respectively. This is mainly attributed to the excellent synergistic flame-retardant effect among boron, LDH, and APP, which can accelerate the generation of compact charring residual with a good microstructure during combustion of [email protected]/EP composites. Furthermore, [email protected] slightly affects the mechanical performances of the EP matrix due to the upgraded interfacial interaction.
The integration of high mechanical toughness, impact strength as well as excellent flame-retardant properties toward epoxy resins (EPs) have always been a dilemma. The inadequate overall performance of EPs severely restricts their sustainable utilization in engineering aspects over long-term. Herein, a new bio-based agent (diglycidyl ether of magnolol phosphine oxide, referred as DGEMP) derived from magnolol (classified as lignan), extracted from natural plants Magnolia officinalis, was successfully synthesized and further employed as a flame-retardant reactive additive to diglycidyl ether of bisphenol A (DGEBA). As demonstration, the composite resin, DGEBA/15DGEMP (15 wt% DGEMP), achieved an Underwriters Laboratories-94 V-0 rating with a high limiting oxygen index (LOI) value (41.5%). In cone calorimeter tests, it showed that heat release and smoke production were effectively inhibited during combustion, wherein the peak heat release rate (PHRR) value of DGEBA/15DGEMP was reduced by 50% compared to neat DGEBA. Additionally, it exhibited a superior tensile strength (82.8 MPa), toughness (5.11 MJ/m3) and impact strength (36.5 kJ/m2), much higher than that of neat DGEBA (49.7 MPa, 2.05 MJ/m3 and 20.9 kJ/m2). Thus, it is highly anticipated that DGEMP imparts significantly improved mechanical and fire-retarded properties to conventional EPs, which holds a great potential to address the pressing challenges in EP thermosets industry.
A compound containing phosphorus/nitrogen/sulfur (named as DOVNPT) was synthesized by the reaction of p‐toluenesulfonamide, vanillin and 9,10‐dihydro‐9‐oxo‐10‐phosphophenanthrene‐10‐oxide, and was adopted to prepare flame retardant epoxy resins (FREPs) using 4,4‐diaminodiphenylmethane as the curing agent. The chemical structure of DOVNPT was verified using Fourier‐transform infrared spectroscopy, ¹H and ³¹P nuclear magnetic resonance. The influence of the DOVNPT content on the thermal stability, fire performance, combustion behaviors, transparency and mechanical properties of the FREPs was investigated in detail. The DOVNPT promoted the decomposition of EP on advance whilst lowered the maximum decomposition rate. With the incorporation of 4 wt% DOVNPT (0.49 wt% phosphorus content), the FREP‐4 achieved a LOI value of 34.4% and a UL‐94 V‐0 rating. The FREP‐4 also gave the lowest peak heat release rate, total heat release and total smoke release, with a reduction of 40.4%, 24.8%, and 28.6% as compared with the pure EP, respectively. The comprehensive analysis of the char residues and gaseous pyrolysis products demonstrated that the DOVPNT displayed good flame retardant effect in both gas phase and condensed phase. Simultaneously, the FREPs presented a comparable transparency and slightly improved mechanical properties as compared with the pure EP.
So far, discussions on the effects of elements on flame retardant properties have been widespread in flame retardant‐related fields, but reports on the effects of specific structures on flame retardant properties are rare. In this work, two novel phosphorus‐nitrogen flame retardants were synthesized from diphenylphosphinyl chloride and diphenyl chlorophosphite. It was proved that the POC structure of the DOAT flame retardant is beneficial to form a more stable carbon layer with high phosphorus content and reduce the total amount of smoke, while the PC structure of DPAT flame retardant is conducive to produce a large amount of phosphorus‐containing substances in the gas phase, while the phosphorus content in the residual carbon is very low. Therefore, the DOAT flame retardant mainly plays a flame retardant role in the condensed phase. The DPAT flame retardant mainly plays a flame retardant role in the gas phase. The flame retardant action mechanism of the combustion process was also investigated by using scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and Thermogravimetric analysis/infrared spectrometry (TG‐IR).
In this study, the first magnetic ceramic nanoparticles were produced utilizing the hydrothermal method. The properties of the nanoparticles were studied utilizing a variety of distinct analytical tools, including an X-ray diffraction pattern, a scanning electron microscope, an infrared absorption spectrometer, and a vibration sample magnetometer. Then, the polymer matrix nanocomposite (PMNC) was fabricated using epoxy resin and made into nanoparticles. In the next step, various analyses, such as microhardness, tensile strength, and flame tests, were taken from the PMNC samples, and the results were compared. The results showed that nanoparticles with a fine and uniform structure and high purity are produced and also have magnetic properties. Furthermore, by adding nanoparticles to epoxy resin and improving surface and mechanical properties, flame resistance is also improved.
In order to improve the flame‐retardant properties of epoxy resin (EP) without sacrificing the mechanical properties, a high‐efficient P/N/S‐containing reactive flame retardant (VTZD) was synthesized by a facile one‐pot method from vanillin, 2‐aminobenzothiazole and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO), and used in epoxy‐amine thermosets. When 5 wt% of VTZD was added with merely 0.31 wt% of phosphorus, the LOI value of cured resins increased to 32.7%, and the thermosets achieved a UL‐94 V‐0 rating. Furthermore, the peak heat release rate and the total heat release of the VTZD‐modified EP decreased by up to 34.66% and 32.49%, respectively, in comparison to those of the original EP. Subsequently, the residual char morphology and structure of epoxy thermosets were investigated, as well as the pyrolysis behavior of VTZD. The flame‐retardant mechanism was discussed in detail, and it confirmed that VTZD exhibited a bi‐phase flame retardant effect. In addition, the mechanical properties of the cured products were well maintained and even improved. All the results demonstrated that the VTZD was a bio‐based high‐efficiency flame retardant for EP with a broad prospect in practical applications.
This paper describes the synthesis of a phosphorus-based flame retardant that is a chemical analog of diglycidyl ether of bisphenol A (DGEBA), as well as its incorporation as a matrix into carbon fiber laminates. Carbon fiber composites, if used for structural applications in mass transport vehicles (aircraft, trains), will require some aspects of improved fire performance to be used safely in those applications. The first phase of work involved the development of two separate synthesis routes to produce the flame retardant monomer, referred to as Phosphorus-DGEBA or simply P-DGEBA. The second step was to determine the viability of the compound's polymerization behavior through various experimental mixing formulations and curing conditions with an aliphatic amine curing agent. Differential scanning calorimetry (DSC) was used to evaluate the curing behavior of P-DGEBA when mixed with DGEBA and an aliphatic amine curing agent and dynamic mechanical analysis (DMA) was used to observe the glass transition temperature (Tg) of the carbon fiber composites. Thermogravimetric analysis (TGA) was also used to investigate the thermal stability and thermal degradation behaviors of the P-DGEBA/DGEBA blends. The final step included the fabrication of composites and their flammability testing using a cone calorimeter. DMA testing for P-DGEBA measured a Tg that was 10°C higher than a DGEBA based carbon fiber composite, and DSC studies found that the P-DGEBA / DGEBA blend polymerized well with the amine curing agent. The TGA, MCC, and cone calorimeter data yielded mixed results with TGA and MCC suggesting a more condensed phase / char formation flame retardant activity for P-DGEBA, while cone calorimeter suggested a more vapor phase flame retardant activity. Overall, the P-DGEBA shows some promise as a reactive FR for epoxy + carbon fiber composites, but more study is needed.
A highly reactive intrinsic epoxy flame retardant FREP was successfully synthesized via ring‐opening reaction between DOPO and amino‐tetrafunctional epoxy resin (AG‐601), and the structure of the synthesized FREP was characterized by FTIR and MS. FREP was then introduced into the epoxy resin as an additive, aiming to improve fire safety. The flame‐retardant properties and thermal stabilities of epoxy thermosets were investigated by limiting oxygen index (LOI), vertical burning test (UL94) and cone calorimetry (CONE). The results indicated that EP/FREP‐4 thermoset passed UL94 V‐0 rating with a LOI value of 34.6%, where the phosphorus content was 1.5 wt%. When compared with neat EP, the peak heat release rate (pk‐HRR), total heat release (THR) and total smoke production (TSP) decreased by 63.1%, 42.6%, and 22.1%, respectively. Meanwhile, the lower av‐EHC of EP/FREP thermosets indicated that FREP plays a significant role in gas‐phase flame retardancy. Additionally, DMA analysis showed that FREP improved the crosslinking density of EP, which had little effect on the glass transition temperature (Tg). Thermogravimetric analysis (TGA), Py‐GC/MS analysis, and SEM were used to investigate the flame retardant mechanism. Excellent flame retardancy was attributed to phosphorus and nitrogen's synergistic effect in the gas and condensed phases.
Preparing biomass-based epoxy resin with high temperature resistance and flame retardancy is still an appealing yet challenging task. Now, a high-temperature resistant and flame-retardant resveratrol-based epoxy (RESEP) has been synthesized through a facile one-step method. The structure of RESEP was established using FTIR and NMR spectroscopy. RESEP and petroleum-based epoxy diglycidyl ether of bisphenol A (DGEBA) were each cured with 4,4-diaminodiphenyl methane (DDM) to prepare RESEP/DDM and DGEBA/DDM. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile testing, thermogravimetric analysis (TGA), thermogravimetric analysis-infrared spectroscopy (TG-IR), scanning electron microscopy (SEM), limiting oxygen index (LOI) and the UL-94 vertical burning test were used to systematically evaluate the properties of RESEP and RESEP/DDM. The glass transition temperature (Tg) of RESEP/DDM is 335 ℃, which is significantly higher than that of DGEBA/DDM (168 ℃). In addition, RESEP/DDM displays good thermogravimetric performance and flame retardancy. Typically, it displays a UL-94 V-0 rating, an LOI value was as high as 31.8%, and a char yield as high as 38.6% (800 ℃). The results reported indicate the possibility of preparing biomass-based epoxy resin with high temperature resistance, flame retardancy and mechanical properties, which is potential to be utilized in the fields of electronics and aerospace.
It is still challenging to simultaneously improve the strength and toughness of flame retardant epoxy resins. In this study, a new reactive flame retardant (DOPO-M) including bi-DOPO and biphenyl structures was successfully synthesized and applied as a co-curing agent. The introduction of DOPO-M accelerated the ring-opening reaction of epoxy resin. E51-DM-P composites exhibited improved transparency and retained good thermal resistance and thermal stability. Notably, the rigid biphenyl structure of DOPO-M and the in situ microphase separation effect created by DOPO-M-rich domains can both improve the tensile strength and toughness of composites by 28.6% and 24.4%, respectively. Meanwhile, the flame retardant property and fire safety of E51-DM-P composites have improved. With only 2.8 wt% DOPO-M (0.25 wt% of phosphorus), the E51-DM-P composites achieved UL-94 V-0 and a high LOI value of 30.2%. Furthermore, the peak heat release rate (PHRR) and total heat release (THR) of E51-DM-P0.5% decreased by 30.4% and 27.3%, respectively. All of these findings indicate that DOPO-M is a multifunctional and highly effective flame retardant that can be applied to manufacture epoxy resins with superior comprehensive properties.
As one of the most flammable common commercially resins, high flammability and heat/smoke release characteristics of unsaturated polyesters (UP) lead to severe casualties and irreparable property loss. To solve these problem, a flame-retardant approach via the multiple synergic effects of promoting char-ability, physically shielding heat/mass transfer, and quenching small molecular fragments in burning is proposed. Herein, a novel micro/nano rod flame retardant SDPPNi, composed of diphenylphosphinyl groups, Schiff base and Nickel (Ⅱ), are synthesized by self-assembly based on the coordination reactions. The UP with 25 wt% SDPPNi (UP/SDPPNi25), shows quite excellent fire-safety performance, and its limiting oxygen index (LOI) is as high as 38.0%, showing extremely high flame retardant efficiency. Meanwhile, its peak heat release rate (PHRR), total heat release (THR), fire growth rate (FIGRA), and maximum smoke density (Dsmax) values are significantly reduced by 69%, 40%, 72%, and 42%, respectively. During burning, the SDPPNi promotes UP to form compact char layers composed of pyridine derivatives, phosphoric-oxygenic compounds, and nickel-oxides, inhibiting the heat and mass transfer. Meanwhile, the SDPPNi also releases phosphorous-containing volatiles that can capture some small molecular fragments and break off the chain reaction of combustion. Therefore, a state-of-art strategy is proposed to endow UP resins with ultra-high fire-safety performance.
9,10‐Dihydro‐9‐oxa‐10‐phosphaphenanthrene (DOPO) is the star product in flame retard of epoxy resin (EP). However, its limited production capacity can hardly meet the market demand. In this work, a new phosphorus‐containing flame retardant named as methanephosphonite (MTA) was successfully synthesized to substitute the DOPO in EP. Due to the supreme efficiency of the gas phase mechanism, only 1.5 wt% of phosphorus is sufficient to achieve V0 rating and the LOI is as high as 31.4%. In addition, MTA can effectively suppress the heat release during combustion, and the peak of the heat release rate (pk‐HRR) of the MTA/EP‐2.0 decreases 50% than that of neat EP. Besides, the introduction of MTA does not significantly deteriorate the mechanical properties of the thermoset MTA/EP‐1.5, both of the flexural strength and impact strength reduce less than 15%, which shows a great value for EP material.
As an abundant natural resource, bamboo with enhanced flame retardancy and mildew resistance after surface treatment has a wider range of applications. Although several organic or metal oxide coatings have been used on bamboo, their basic properties such as transparency and durability are neglected, which limits their practical application. Herein, we prepared a new organic–inorganic coating by thermal curing between vanillin-derived epoxy (VEP) and hyperbranched siloxane (HPSi). The curing process of VEP/HPSi coating was analyzed with FTIR. When the mass ratio of VEP and HPSi was 20:28, the obtained Schiff base hybrid coating exhibited visible light transmittance over 90% and the highest pencil hardness of 9H. The mechanical properties of the coating were investigated by nanoindentation (hardness: 0.208 GPa, elastic modulus: 2.677 Gpa) and impact test. Impressively, the fabricated coating showed remarkable solvent wipe resistance (Xylene and ethanol: 1000 cycles) and continuous abrasion (cheesecloth test: 5000 cycles). In addition, the hydrophobic and dense coating endowed the coated bamboo excellent mildew resistance even in high humidity (97%). Due to the high thermal stability, the coated bamboo presented a significant enhanced flame resistance with a limiting oxygen index value of 29.1%. From a broader perspective, the Schiff base hybrid coating with excellent comprehensive performance and facile preparation process display great potential for practical application for bamboo or other substrates.
In this study, lignin-based epoxy resins (EP) were fabricated using lignin, phenol and glyoxal as crosslinking reagents. For improving the flame retardancy, a bi-DOPO compound with bi-hydroxyl structure was successfully synthesized, containing excellent quenching and charring capacities. Good pyrolysis behaviors of as-synthesized flame retardant resulted in significant quenching effect via structure decomposition to release PO and PO2 free radicals for capturing reactive H and OH radicals produced from epoxy combustion. With addition of 0.18 wt% phosphorus, epoxy composite (10% LPG-ER-4) passed V-0 rating with high limited oxygen index (LOI) value of 35.2%. Cone calorimeter tests showed that heat release (including heat release rate (HRR) and total heat release (THR)) from combustion was reduced with assistance of flame retardant. Char residue analyses illustrated that bi-hydroxyl structure in DOPO-based flame retardant benefited the formation of char layer with higher compactness and integrity to serve as a protective shell of interior epoxy matrix. Furthermore, exterior pore size of char residue was narrowed or blocked to avoid the release of heat and volatiles generated from combustion. This study provided a feasible method to improve flame retardancy of lignin-based EP and proposed flame-retardant mechanism both in gaseous and solid phases.
In this work, aiming to obtain multifunctional epoxy resin (EP) possessing flame retardancy and light smoke without compromising the mechanical properties, a novel nitrogen-rich phosphinic amide named D-5-AT was synthesized and then incorporated to EP. The results showed that UL-94 V-0 rating of EP with 7.5 wt% D-5-AT was available and limiting oxygen index (LOI) was up to 35.5%. Meanwhile, in the presence of D-5-AT, the heat release and smoke production of EP/D-5-AT materials were effectively suppressed during combustion as compared with EP. The improvement mentioned above was found related to the condensed and gaseous flame retardant effect of D-5-AT through the investigation on char residues of EP/D-5-AT materials and volatiles of D-5-AT. Besides, because of the existence of more hydrogen bonds and bulky group by virtue of the introduction of D-5-AT, the mechanical properties of modified EP were strengthened as well. This work offered a promising method to meet the ever-increasing requirement of multi-functionality of epoxy resins.
In order to broaden the application field of epoxy resin (EP), it is significant to heighten the fire safety without deteriorating the comprehensive performance. A high-efficiency reactive phosphorus/nitrogen/sulfur flame retardant (SAD) derived from 2-Thenaldehyde, 9,10-dihydro-9-oxa-10-phosphaphenanthrene10-oxide (DOPO) and 3-amino-1H-1,2,4-triazole (ATA) was designed, acting as the co-curing agent for DGEBA/DDM system. Fourier transform infrared (FTIR) spectra and nuclear magnetic resonance (NMR) were used to confirmed the chemical structure of SAD. Besides, the glass transition temperature (Tg) was gradually increased from 150.4 ℃ for EP to 156.9 ℃ for EP-7.5 and the maximum thermal decomposition rate was decreased after the introduction of SAD. The samples exhibited excellent thermal stability. Meanwhile, SAD promoted cross-linking reaction during curing process. Compared with EP, EP-5 (phosphorus content was 0.39 wt%) reached V-0 rating in vertical burning (UL-94) test and acquired a remarkable enhancement from 25.7% to 34.7% in the limited oxygen index (LOI) value, an obvious blowing out effect occurred when the samples burned. Furthermore, from the data of cone calorimeter (CC) tests, there was a reduction of 19.1% and 16.6% for EP-7.5’s the total heat release (THR) and the peak heat release rate (PHRR) compared with EP. And the analysis of char residue and incomplete combustion products indicated that SAD displayed bi-phase flame-retardant effect. It is very meaningful that the mechanical properties of materials were slightly enhanced after the introduction of SAD. The results showed that SAD has a broad prospect in practical application.
Because of the highly inherent flammability of epoxy resin (EP), its application especially in high‐performance fields that have demands on flame retardancy was greatly limited. Herein, a novel Si/N/P‐containing flame retardant (PMBZ) was prepared to solve the flammability defects of EP. In particular, the sample with 10.0 wt% PMBZ reached a limiting oxygen index (LOI) of 32.4 % and could successfully pass UL‐94 V‐0 rating. Meanwhile, there was a 16.1 % and 22.4 % decrease in total smoke production (TSP) and total heat release (THR), respectively. The satisfactory flame retardancy and smoke suppression were due to the introduction of PMBZ, which could function both in condensed and gas phases through forming a compact and coherence self‐extinguishing char layer and inducing a dilution effect. More importantly, the tensile strength, impact strength and flexural strength had also increased by 33.0 %, 53.7 % and 20.7 %, respectively, which indicated the incorporation of PMBZ could also maintain its desired mechanical properties due to the excellent compatibility and enhanced intermolecular interactions. This work provides an exploitable flame retardant additive for epoxy resin to guarantee a superior flame retardancy, favorable smoke suppression and mechanical properties.
The aggregation and plasticizing of most 9,10-dihydro-9-oxa-10-phosphaphenanthrene −10-oxide (DOPO) derived additives often result in deteriorating the glass transition temperature and mechanical properties of epoxy resins (EP). To address this issue, an imide-DOPO derivative (BMP) with bulky aromatic structure was successfully synthesized. Benefitting from the space hindering and intermolecular interaction (π-π stacking) of BMP, it does not lead to the loss of glass transition temperature, and only a minor damage of tensile and impact strengths is caused. Additionally, with only 0.78 wt% loading of phosphorus (10 wt% BMP), the EP/BMP10% achieves UL-94 V-0 and high LOI value of 35%. Simultaneously, both the heat release rate and total smoke production are markedly reduced. More excitingly, BMP exhibits aggregation-induced emission enhancement of fluorescence in the N, N-dimethylformamide/water mixed solution as well as epoxy resin. This work provides a new insight in simultaneously imparting flame retardancy and fluorescence to epoxy resins without losing glass transition temperature.
Epoxy resins (EP) possessing superior flame retardancy, mechanical properties and glass transition temperature are urgently needed to meet the ever-increasing requirement of high performance for the practical application of EP. Herein, lamellar-like phosphorus-based triazole-zinc complex (Zn-PT) was firstly constructed through coordination reaction in a facile condition to address the above issue. The results revealed that Zn-PT was well dispersed in epoxy matrix, and with 3 wt% Zn-PT, the tensile strength, flexural strength and modulus of epoxy composites were remarkably increased from 71, 112 and 2982 MPa of neat epoxy resin (EP) to 80, 162 and 3482 MPa respectively. The glass transition temperature was higher than EP. Besides, the limiting oxygen index (LOI) increased to 28.3%, and UL-94 V-1 level was available. Meanwhile, the cone calorimeter test (CCT) results showed that epoxy composites displayed less heat release and smoke production. Generally, this work provides a feasible strategy to prepare high-performance epoxy composites, which has the potential to satisfy the requirement of epoxy in the practical application.
It is still a great challenge to develop flame-retardant epoxy resins (EP) with high transparency. Herein, a reactive P/N/S-containing compound (DOPT) was designed and synthesized by the Atherton-Todd reaction between p-toluenesulfonamide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. The addition of DOPT simultaneously improved the flame retardancy, fire safety and mechanical strength meanwhile kept the better transparency of the EP At 5 wt% DOPT loading, the modified EP (FREP-5) achieved a LOI value of 37.5% and UL-94 V-0 rating, with maintaining almost the same transmittance of the pure EP. Meanwhile, the FREP-5 also gave the lowest values of the peak heat release rate, total heat release, total smoke production and fire growth rate, revealing the enhanced fire safety of the flame-retardant EP. The significant improvement of flame retardancy of FREP thermosets was ascribed to the physical barrier effect of phosphorus-rich char in condensed phase, and the quenching and diluting effects of abundant phosphorus-containing free radicals and nitrogen/sulfur-containing inert gases in gaseous phase. Furthermore, the results of dynamical mechanical analysis and mechanical performance test revealed that the incorporation of DOPT improved the tensile and flexural strength of epoxy thermoset. In summary, DOPT is a novel highly efficient flame retardant for EP, which enables EP to maintain its potential application in the optical fields.
9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and DOPO derivatives had always been regarded as main candidates for improving the flame retardancy of epoxy resin (EP). In this paper, a novel reactive flame retardant DOPOMAH was synthesized from the reaction between DOPO and cis‐butenedioic anhydride (MAH), thereafter acted as a co‐curing agent for EP to remarkably improve the flame retardancy of matrix. The effects of DOPOMAH and DOPO on comprehensive performance of EP were systematically investigated and compared through dynamic mechanical analysis, mechanical performance testing, limiting oxygen index (LOI), vertical burning (UL‐94), and cone calorimetry test. These results indicated that the excellent dispersion of DOPOMAH in EP makes the EP modified by DOPOMAH has good mechanical properties. When the content of phosphorus is 2.0 wt%, compared with the EP modified by DOPO (ED), the LOI of the EP modified by DOPOMAH (EDM) increased from 30.6% to 32.8%, and the UL‐94 was also improved from no rating to V‐0. Meanwhile, the peak heat release rate of EDM was only 51% of that of pure EP, which was slightly less than that of ED. Finally, a flame‐retardant mechanism comparison between DOPOMAH and DOPO was discussed in detail to reveal the reasons why the flame reatardant effect of DOPOMAH was better than that of DOPO.
With the aim to reduce the flammability of poly(lactic acid) (PLA), herein, Tris‐phosphaphenanthrene based phosphonate (DOT) originated from 10‐hydroxy‐9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO‐OH) and trihydroxymethyl aminomethane (Tris) was incorporated. Interestingly, DOT showed superior flame‐retardant efficiency for PLA, that was, PLA with 1 wt% DOT displayed a LOI value at 29.0%, about 49.0% increment as compared to virgin PLA, and passed a UL‐94V‐0 rating. Apart from the mentioned, cone calorimeter tests clearly demonstrated that DOT was beneficial for reducing the heat release in the whole combustion to some extent, for example, the peak heat release rate and the maximum average values of heat emission with a reduction of 15% and 17%, respectively. It was speculated that the improved flame retardance of PLA containing DOT was related to the melting droplet‐promotion effect and the vapor‐phase activity of DOT. Meanwhile, thermal stabilities of PLA/DOT were well maintained as compared to virgin PLA. Moreover, the existence of DOT promoted the crystallization of PLA owing to the nucleating effect of DOT.
High-performance and multifunctional epoxy resins (EPs) are of great use in the booming electric & electronic and 5G fields, however their fabrication shows huge challenges. Herein, through a facile strategy by simply incorporating a functional molecule DPI (phosphaphenanthrene polyethylenimine), which possessed a unique structure with hyperbranched polyethyleneimine as flexible inner core and phosphaphenanthrene groups as rigid outer shell, a high-performance and multifunctional epoxy resin was successfully fabricated. The hyperbranched rigid-flexible structure of DPI endowed the resultant thermoset EP-DPI with superb mechanical performance and high glass transition temperature, for which, at a low DPI content (≤ 4 wt%), EP-DPI exhibited 160%, 40%, and 31% improvement in impact toughness, tensile strength, and flexural strength compared with neat EP. At the same time, the good compatibility between DPI and the EP matrix enabled EP-DPI to be highly transparent, and the aromatic phosphorus structure endowed EP-DPI with excellent UV-shielding effect in the UV-A band. The dielectric performance of EP-DPI was enhanced due to the unique structure of DPI and its interaction with the EP matrix. Furthermore, the phosphaphenanthrene groups endowed EP-DPI with excellent anti-ignition, self-extinguishing, and low heat release during combustion. This work opens up a new strategy for developing novel high-performance and multifunctional EPs with potential versatile applications.
In order to obtain an efficient flame retardant without sacrificing mechanical properties and transparency of epoxy resin (EP), a P/N/S-containing flame retardant (STP) by combining 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) with Schiff base intermediate synthesized by the reaction of sulfathiazole and 2-thenaldehyde was successfully synthesized. The synthesis of STP was verified and the properties of modified EP were studied. The test results indicated that STP slowed down the degradation rate of EP. The glass transition temperature (Tg) of the flame-retardant epoxy resin (FREP) samples were well maintained and even improved after introducing a certain amount of STP. Furthermore, FREP with low phosphorus content exerted excellent flame retardant ability, EP/5%STP (phosphorus content: 0.27 wt%) obtained the V-0 rating of UL-94 test with the value of limiting oxygen index (LOI) 33.5%. In contrast with EP, the peak heat release rate (PHRR), total heat release (THR) and total smoke production (TSP) of EP/7.5%STP were respectively decreased by 33.31%, 26.04% and 28.75%. Mechanical performance tests show that STP improved the tensile and flexural strength of EP. It is worth mentioning that the EP modified with STP still maintains good transparency.
It is difficult to strengthen and toughen epoxy resin (EP) and concurrently obtain good flame retardancy. A novel flame retardant marked as TFD was prepared by tyrosine (Tyr), furfuraldehyde (FA) and 9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) and co-cured with EP. Only 6 wt% TFD makes EP achieve UL-94 V⁰ and limited oxygen index (LOI) value 32.4 vol% revealing the high flame retardant efficiency. Furthermore, the tensile and impact strength of EP-8TFD are 29.3 % and 84.4 % higher than that of EP indicating strengthening and toughening effect of TFD. TFD can chemically bond into EP networks via its carboxyl and phenolic hydroxyl reacting with EP leading to good tensile properties. The high rigidity of DOPO forms holes between molecular chains, which eliminates stress concentration and improves impact strength. The strength, toughness and flame retardancy of EP are regulated by simple molecular structure, which provides a good idea for integration of structure and performance.
A novel phosphorus-containing, nitrogen-containing, and sulfur-containing reactive flame retardant (BPD) was successfully synthesized by 1-pot reaction. The intrinsic flame-retardant epoxy resins were prepared by blending different content of BPD with diglycidyl ether of bisphenol-A (DGEBA). Thermal stability, flame-retardant properties, and combustion behaviors of EP/BPD thermosets were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), limited oxygen index (LOI) measurement, UL94 vertical burning test, and cone calorimeter test. The flame-retardant mechanism of BPD was studied by TGA/infrared spectrometry (TGA-FTIR), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), morphology, and chemical component analysis of the char residues. The results demonstrated that EP/BPD thermosets not only exhibited outstanding flame retardancy but also kept high glass transition temperature. EP/BPD-1.0 thermoset achieved LOI value of 39.1% and UL94 V-0 rating. In comparison to pure epoxy thermoset, the average of heat release rate (av-HRR), total heat release (THR), and total smoke release (TSR) of EP/BPD-1.0 thermoset were decreased by 35.8%, 36.5% and 16.5%, respectively. Although the phosphorus content of EP/BPD-0.75 thermoset was lower than that of EP/DOPO thermoset, EP/BPD-0.75 thermoset exhibited better flame retardancy than EP/DOPO thermoset. The significant improvement of flame retardancy of EP/BPD thermosets was ascribed to the blocking effect of phosphorus-rich intumescent char in condensed phase, and the quenching and diluting effects of abundant phosphorus-containing free radicals and nitrogen/sulfur-containing inert gases in gaseous phase. There was flame-retardant synergism between phosphorus, nitrogen, and sulfur of BPD.
As is known to all, the reduced flammability of modified epoxy resin is always accompanied with damaged mechanical properties. Surprisingly, in this work, we synthesized a novel Lewis base, namely D–AZ sourced from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 2-aminothiazole to modify epoxy resin, and found that it could not only impart excellent flame retardance to epoxy resin, but also improve the strength of epoxy resin simultaneously. For instance, epoxy resin with 5% loading of D–AZ possessed limited oxygen index as high as 34.7%, and it passed V-0 rating. By comparison with neat epoxy resin, tensile strength of epoxy resin with 10% loading of D–AZ increased by 20%, flexural strength by 38%, and izod unnotched impact strength by 92%. Besides, D–AZ also played an important role in inhibiting the heat release of epoxy resin during combustion, thanks to its gaseous phase and condensed-phase flame-retardant mechanism. Imperfectly, it exhibited that the addition of D–AZ caused some decrease in the thermal stability of epoxy resin, especially in the initial decomposition temperature. Nevertheless, epoxy resin with 10% loading of D–AZ still displayed glass transition at 157 °C, and there was not much difference in the storage and loss modulus of epoxy resins in the low temperature. Briefly, epoxy resins containing D–AZ possessed excellent flame retardance and outstanding mechanical properties with comparison to neat epoxy resin, showing high promise for application.
The combination of DOPO and 2-aminobenzothiazole (ABZ) was designed to develop P/N/S-containing flame retardant DOPO-ABZ, and its chemical structure was confirmed by HRMS, FTIR, 1H and 31P NMR. The reduced thermal-stability of EP/DOPO-ABZ formulations were found through DSC and TGA, as compared to that of EP. Fire properties were evaluated by LOI, UL-94, and cone calorimeter tests, respectively. The results indicated that DOPO-ABZ imparted flame retardance to EP, that EP/7.5wt%DOPO-ABZ passed V-0 rating, and acquired a LOI value of 33.5%; moreover, when the loading of DOPO-ABZ increasing to 10 wt%, it could further suppress the heat release and smoke release of the curved epoxy resin. Finally, the flame-retardant mechanism was studied by TG-FTIR and py-GC/MS, disclosing that DOPO-ABZ exerted predominant gaseous phase activity of fire inhibition via generating phosphorus-containing free radicals and nitrogen/sulfur-containing volatiles.
Recent advances in macromolecular chemistry have revolutionized the way we perceive the synthesis of polymers. Polymerization, to be modern, must be "controlled", which usually means capable of producing macromolecules of well-defined structure. The purpose of this review is to examine how the chemistry of epoxy resins, an almost century-old chemistry, is also involved in this movement.Epoxy resins are characterized by both the flexibility of implementation and the qualities of the polymers obtained. Key materials in health-, mobility- and energy related technologies, these resins are heavily present in high-performance composites, electronic boards, adhesives and coatings. Currently, a large number of resins and hardeners are available on the market or described in the literature and an interesting point is that almost any combination of the two is possible. Common to all these recipes and processes is that a liquid (or soluble) resin at some point becomes insoluble and solid. It is very important to know how to manage this transition, physically known as the gel point, as it is the point after which the shape of the object is irreversibly set. Taking into account the variety of epoxy polymerization processes - polyaddition, anionic or cationic polymerization - we detail a number of methods to program the occurrence of the gel point and how this type of control affects the structure of the growing network.
Harvesting biobased epoxy resins with improved thermomechanical properties (e.g., glass transition temperature Tg and storage modulus), mechanical and dielectric similar and even superior to that of bisphenol A epoxy resin (DGEBA) is vital to many applications, yet remains a substantial challenge. Here we develop a novel eugenol-based epoxy monomer (TEU-EP) with a branched topology and a very rich biobased retention (80 wt %). TEU-EP can be well cured by 3,3′-diaminodiphenyl sulfone (33DDS) and the resultant TEU-EP/33DDS system can be considered as a "single" epoxy component, exhibiting adequate reactivity at high processing temperatures. Importantly, compared with DGEBA/33DDS, TEU-EP/33DDS achieves a 33 °C, 39% and 55% increment in the glass transition temperature, Youngs modulus, and hardness, respectively, and shows the improved creep resistance and dimensional stability. TEU-EP/33DDS is also characterized by the considerably reduced permittivity, dielectric loss factor, and flammability with high yield of pyrolytic residual. Overall, TEU-EP endows the cured epoxy with a number of the distinguished properties outperforming its DGEBA counterpart, and therefore may find practical applications in demanding and even cutting-edge areas.
In order to develop a multi-element synergistic flame retardant system, the combination of DOPO, POM and POSS was achieved by using the classical Kabachnik-Fields reaction. The as designed POSS-bisDOPO was characterized by FT-IR, 1H NMR, 13C NMR, 31P NMR, 2D NMR, and MS. POSS-bisDOPO was introduced into epoxy resins to obtain flame retardant materials. The LOI value can reach up to 34.5% with a 20 wt% content of POSS-bisDOPO. TGA results showed that the char yield could be significant improved in cured POSS-bisDOPO/EP. The ATR-FTIR, optical images and SEM analyses indicated that the residual char had a compact and coherent appearance in inner layer, while the outer sider structure was intumescent and multi-porous. Therefore, by isolating heat and oxygen more efficiently, the char played an important role in improving the excellent thermal stability and flame retardancy of cured POSS-bisDOPO/EP. The three point bending test results showed that the mechanical strength of the POSS-bisDOPO/EP was higher than that of pure EP and POSS-NH2/EP, owning to the outstanding reinforced effect from the unique nano-structure of POSS-bisDOPO assembled in EP matrix. These data indicated that POSS-bisDOPO could not only obviously enhance the flame retardancy, but also improve the mechanical properties of epoxy resins.
In this paper, the thermal stability and fire retardant behavior of epoxy resin (ER) composites filled with graphene nanosheets (GNS) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were investigated. Addition of GNS and DOPO changed the decomposition pathway of ER. During combustion, DOPO played a key flame retardancy role in the gas phase and the char enhancement in the condensed phase, while GNS played an effect in the condensed phase. Addition of 5 wt% GNS and DOPO separated, the peak heat release rate (PHRR) of ER was reduced from 1194 kW m−2 to 513.9 kW m−2 and 937.1 kW m−2, respectively. With the combined addition of GNS and DOPO, the flame retardancy of ER composites was significantly improved. The PHRR was reduced to 396 kW m−2 at the addition of 2.5% GNS and 2.5% DOPO. The same tendency was obtained for the total heat release (THR), showing a synergistic effect between GNS and DOPO in improving the flame retardancy of ER composites. The combined addition of GNS and DOPO extended the diffusion path for heat and combustible gas while DOPO captured the free radicals which further retarded ER degradation.
Graphene is regarded as a prominent multi-functional flame retardant for the use in halogen-free flame retardant polymer simultaneously with improved integrated properties and special functionalities. However, its flame retardant efficiency is not impressive enough due to the weak resistance to thermo-oxidative decomposition. In order to overcome this problem, the surface of graphene oxide was covered with large amounts of non-flammable silicas through a sol–gel and surface treatment process, and then used to modify the epoxy (EP) resin. Results show the incorporation of as-prepared nanosilica/graphene oxide (m-SGO) hybrid to EP resin not only obviously increases the flame retardancy, mechanical, and thermal stability properties, but also endows EP resin with high thermal conductivity, low dielectric loss, and high dielectric constant. Specifically, the peak of heat release rate and total heat release of modified EP resin with 1.5 wt.% m-SGO are only 39 and 10 % of that of neat EP resin, respectively. These attractive features of m-SGO/EP nanocomposites are attributed to the unique structure and high resistance to oxidative degradation of m-SGO as well as their good interactions with EP resin. The investigation provides a new approach to preparing novel core-shell flame retardants through surface wrapping with other flame retardants on the SGO and related high performance flame retardant resins.
There is little consensus within the fire science community on interpretation of cone calorimeter data, but there is a significant need to screen new flammability modified materials using the cone calorimeter. This article is the result of several discussions aiming to provide guidance in the use and interpretation of cone calorimetry for those directly involved with such measurements. This guidance is essentially empirical, and is not intended to replace the comprehensive scientific studies that already exist. The guidance discusses the fire scenario with respect to applied heat flux, length scale, temperature, ventilation, anaerobic pyrolysis and set-up represented by the cone calorimeter. The fire properties measured in the cone calorimeter are discussed, including heat release rate and its peak, the mass loss and char yield, effective heat of combustion and combustion efficiency, time to ignition and CO and smoke production together with deduced quantities such as FIGRA and MARHE. Special comments are made on the use of the cone calorimeter relating to sample thickness, textiles, foams and intumescent materials, and the distance of the cone heater from the sample surface. Finally, the relationship between cone calorimetry data and other tests is discussed. Copyright © 2007 John Wiley & Sons, Ltd.
Aiming to imparting epoxy resin (EP) matrix with highly efficient fire safety and mechanical strength, the organically intercalated layered double hydroxide nanosheets (LDH-DBS) were functionalized by silica via electrostatic assembly. EP nanocomposite with resultant nanohybrid [email protected] was constructed and verified. Results showed that 3wt% [email protected] endowed EP matrix with self-extinguishment (close to V-1) in contrast to burning-to-clamp of EP/3LDH-DBS (EP with 3wt% LDH-DBS). Meanwhile, EP/[email protected] (EP with 3wt% [email protected]) possessed 63.3% and 29.2% lower peak heat release rate than EP and EP/3LDH-DBS separately, accompanied by remarkably reduced smoke and CO production. The mechanism study illustrated that the optimization of intumescent char accounted for improved fire safety due to the interfacial charring reaction toward stable cordierite (5SiO2·2Al2O3·2MgO) and smaller microcrystalline carbon. The spatially preferential assembly of silica on LDH nanosheets was proposed to contribute to the dynamic char reconstruction. In parallel, [email protected] enhanced glass transition temperature of EP by 8 °C. The more silica endowed EP matrix with progressively increased non-notched impact strength. In perspective, the interfacial engineering of LDH nanosheets offered an effective approach to strengthening fire safety of polymers.
In this paper, we have reported a facile way to functionalize graphene oxide (GO) via assembling a supermolecular aggregate of piperazine (PiP) and phytic acid (PA) onto the GO surface (PPGO) without using any organic solvent. The functionalization of GO is confirmed by the X-ray photoelectron spectrum (XPS), transmission electron micrographs (TEM) and Raman spectrum. The introduction of 3 wt% PPGO into epoxy resin (EP/PPGO3) results in notable suppression on the fire risk of epoxy resin. In addition, cone calorimeter tests showed that the peak heat release rate (pHRR) was decreased from 727.4 kW/m² to 367.5 kW/m² (49%), and the peak smoke production rate (pSPR) was decreased from 0.2316 m²/s to 0.1379 g/s (40%). The improved flame-retardant performance of EP nanocomposites is most likely due to a tripartite cooperative effect from the key components (piperizine, phytic acid, and GO). This strategy demonstrates a facile and efficient approach for fabricating highly effective graphene-based flame retardants for polymers.
Most flame retardants used in epoxy resin (EP) inevitably affect its curing process, mechanical properties as well as transparency. To solve this problem, a novel phosphorus-containing halogen-free ionic liquid ([Dmim]Tos), composed of imidazole cation modified with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and tosylate anion, has been designed and used as a flame retardant for EP. DSC non-isothermal curing scans show that [Dmim]Tos has accelerating effect on the curing of EP. The addition of [Dmim]Tos enhances not only the crosslinking density but also the modulus of EP. The unnotched izod impact strength and the glass transition temperatures (Tgs) of EP/[Dmim]Tos are a little lower than pure EP because of the plasticization of unreacted [Dmim]Tos. Due to the good affinity with epoxy resin, low [Dmim]Tos addition almost has no effect on the transparency of EP. Besides, incorporation of 4 wt% [Dmim]Tos into EP makes it pass UL-94 V-0 level and increases the LOI value to 32.5%. Cone calorimeter test indicates the peak heat release rate (p-HRR) of EP/4.0[Dmim]Tos reduces by 37% compared with EP. The flame-retardant mechanism of EP/[Dmim]Tos has been investigated in detail. It is found that the flame-retardant action of [Dmim]Tos on EP is in the gas phase for quenching effect of phosphorus-based radicals and the condensed phase for dehydration of phosphorous fragments.
The aim of this work was to study the influence of a high efficient halogen-free phenylphosphonic amide flame retardant (FP1) to epoxy resin (brand name RTM6) on the rheological, mechanical and water absorption properties of the carbon fiber/RTM6 epoxy composite (CFR). With a 8 wt% loading FP1 in RMT6, the processing of CFR/FP1 was able to use the equal condition with that of CFR since the viscosity of RTM6 was maintained at a similar level in the minimum viscosity temperature region. The addition of FP1 showed negligible impacts on the interlayer share strength (ILSS) and in-plane share strength (IPSS) of CFR. The interfacial strength between RTM6 matrix and carbon fiber was decreased due to the impact of FP1 on cross-linking density and polarity of RTM6. The flame retardant efficiency of FP1 showed difference in presence of carbon fiber or not in RTM6. RTM6/FP1 (8 wt%) had a LOI value of 38%, achieved a V-0 rating at thickness of 3.2 mm in UL 94 test and showed 60% reduction in peak of heat release rate. RTM6/carbon fiber/FP1 (8 wt%) had a LOI of 43%, while it showed reduced performance in UL 94 and cone calorimeter tests.
This work investigates the synergetic effect of zinc aluminum polyphosphate (ZAPP) and 2-mercaptobenzimidazole (MBI) on the corrosion protection of mild steel coated with a solvent-borne epoxy-polyamide layer. The magnitude and trend of electrochemical impedance spectroscopy data over 70-d immersion in 3.5 wt.% NaCl solution indicate superior corrosion protection of the combined inhibitors compared to those containing either just ZAPP or MBI. Pull-off tests show that the combined inhibitor system provides an improved adhesion strength. The enhanced corrosion performance is correlated to precipitation of a protective layer at the coating/metal interface verified by SEM and electrochemical studies upon exposure to electrolytes.
To obtain a latent curing epoxy system with satisfactory thermal stability, flame retardance and dielectric properties, imidazolium dibenzo[c,e][1,2]oxaphosphate (IDOP) was synthesized by a facile way and utilized as a latent flame-retardant curing agent for epoxy resins (EP). It was confirmed that IDOP/EP one-pack system kept reactive inert near room temperature and cured efficiently under heating with a moderate heat release. The curing procedure was explored by X-ray photoelectron spectroscopy (XPS), confirming that the flame-retardant group was incorporated into epoxy chains by covalent and/or ionic bonds, hence the intrinsic flame retardance and excellent thermal stability were given to the cured resins finally. With only 15 wt% IDOP additions, the limiting oxygen index (LOI) increased to 37.0% from 20.5% of the reference sample, and UL-94 V-0 rating was achieved. The results of cone calorimetry test further certified that IDOP/EP showed satisfactory flame retardance dominating in gaseous phase, which was confirmed by the results of thermogravimetric analysis/infrared spectrometry (TG-IR). The thermal mechanical behavior of IDOP/EP was also evaluated by dynamic mechanical analysis (DMA). Especially, the incorporation of the flame-retardant group didn’t deteriorate the dielectric properties of the cured resin. Benefiting from the advances, the latent curing epoxy system with excellent comprehensive performance exhibited potential for versatile applications.
Aiming to impart epoxy resin (EP) with super-efficient fire safety, organically modified layered double hydroxide (LDH-DBS) nanosheets were surface-assembled by ultrafine Ni(OH)2 nanocatalyst via the circular coordination-induced growth. The design of LDH-DBS@Ni(OH)2 was to exploit a spatial-dependent catalytic strategy to strengthening interfacial structure between LDH nanosheets and EP matrix during dynamic charring process. Adaquate characterizaitons verfied the susscessful preparation of LDH-DBS@Ni(OH)2 with Ni(OH)2 nanocrystals uniformly distributed on LDH nanosheets. LDH-DBS@Ni(OH)2 presented better nano-dispersion in EP matrix relative to LDH-DBS. Results illustrated that merely 3wt% LDH-DBS@Ni(OH)2 imparted EP matrix with UL-94 V-0. The peak heat release rate and total smoke prodcution at 200s were reduced by 60.6% and 66.5% respectively with the addition of 3wt% LDH-DBS@Ni(OH)2, accompanied by tremendously suppressed CO production. In parallel, the thermal degradation analysis revealed that the interfacial growth of Ni(OH)2 nancatalyst resulted in the significant reduction of volatiles including CO, aliphatic and aromatic compounds. The further mechanism investigation by dynamic charring analysis revealed the remarkable contribution of interfacial-charring catalysis to the reinforcement of intumescent char structure and fire safety. In perspective, the interface-catalysis assembly of nanomaterials without traditional fire-retardant elements opened a novel and up-scaling window toward super-efficient fire safety.
Traditional cured epoxy resin (EP) usually loses its transparency once it encounters the requirement of flame retardance. To obtain the EP with simultaneous excellent transparency and flame retardancy, a novel multi-functional polymeric curing agent named DPPEI was synthesized via a reaction between diphenylphosphinic chloride (DPPC) and polyethylenimine (PEI) in this work. Different measurements confirmed that the DPPEI was prepared successfully. After incorporation of the DPPEI into EP, the cured EP (DPPEI-EP) material with simultaneous excellent transmittance and flame retardancy was obtained after a mild curing process. The transmittance of the resulting DPPEI-EP was kept at about 90% in the visible region at a loading of 35 wt% DPPEI, meanwhile, the DPPEI-EP sample with the thickness of only 1.6 mm passed the V-0 rating in vertical burning test, had no dripping, and achieved the limiting oxygen index of 29.8%. In combustion test, both total heat release and total smoke production of the DPPEI-EP containing 30 wt% DPPEI were respectively greatly decreased by 69.5% and 78.3% compared with the corresponding value of the reference sample PEI-EP, showing high flame-retarding and smoke-suppressing efficiency. The transparent and flame-retardant mechanisms of DPPEI-EP were investigated insightfully through different tests. All these results demonstrate that the DPPEI is a novel multi-functional polymeric curing agent for EP, which has efficient curing ability and meanwhile endows the cured EP with simultaneous excellent flame retardancy and transparency.
Corrosion is a natural phenomenon which significantly deteriorates metal properties. The existing corrosion protection methods are costly and require a regular replacement of sacrificial metals or inevitable use of toxic chemicals. So far, various extrinsic self-healing approaches have been attempted to prevent metal corrosion, which have facilitated the corrosion protection at a reasonable cost and non-toxicity level. Here, we review the existing and the recent novel corrosion-protective extrinsic self-healing technologies, focusing on the capsule-based and the fiber-based self-healing approaches, while looking at the pros and cons of these methods. In addition, by introducing potential ways, this review aims to provide insights for the further development of extrinsic self-healing technologies.
To further study the effect of the phosphorus, sulfur, and nitrogen-containing flame retardant on epoxy resin, a DOPO-based phenol derivative 4-[(benzothiazolyl 2-amino)(6-oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl) methyl] phenol namely D-P-A, was successfully synthesized from 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), p-hydroxybenzaldehyde (PHBA), and 2-aminobenzothiazole (ABZ), and used to flame retard epoxy resin (EP). As expected, D-P-A imparted flame retardance to epoxy resin. For example, with 7.5 wt% loading of D-P-A, epoxy thermoset passed a UL-94 V-0 rating, and got a LOI value of 29.6%. Besides, D-P-A played an effective role in inhibiting heat release of EP, that EP/7.5% D-P-A showed a peak of heat release rate (PHRR) of 713 kW/m² much lower than 1137 kW/m² of EP. However, it decomposed in advance owing to the lower thermal stability of D-P-A. Finally, through Scanning electron microscopy (SEM), Raman spectra and X-ray photoelectron spectroscopy (XPS) and pyrolysis-gas chromatograph/mass spectrometer (Py-GC/MS), it disclosed that D-P-A exerted its flame-retardant activity both in the vapor and condensed phase.
Liquid epoxy resins (EP), curing agents, as well as other additives such as flame retardants are preferred to be formulated as one-pack materials rather than being mixed just prior to their applications. Therefore, they suffer premature curing with increasing of viscosity during storing and operating. To address the above challenging problem, we designed and synthesized a novel latent flame-retardant curing agent named 1-(diphenylphosphinyl)-1H-imidazole oxide (DPPIO) for EP, which was proved exhibiting not only long pot life during storing and fast curing as operating, but also excellent flame retardance after curing. It was observed from dynamic rheometry that, DPPIO/EP kept stable near room temperature for a long time but quickly gelated within only 6.5 min at 150 °C. With only 15 wt% addition of DPPIO, the limiting oxygen index (LOI) of the cured sample increased to 38.0% from 21.0% of the contrast sample, and UL-94 V-0 rating at 1.6 mm thickness was successfully achieved. Peak of heat release rate (PHRR) and total heat release (THR) obtained from cone calorimetry further certified excellent flame retardance of DPPIO/EP. Another typical flame-retardant group with different chemical environment was designed for modifying imidazole to obtain a derivative named diphenyl 1H-imidazol-1-ylphosphonate (DPIPP) in the same way. It was verified that DPIPP/EP showed acceptable latent curing efficiency and satisfactory flame retardance as DPPIO/EP did. Therefore, it's a generally effective and facile approach to develop latent flame-retardant curing agents for EP by modifying imidazole with appropriate flame-retardant groups. Taking advantage of the features, these one-pack flame-retardant epoxy materials can bring more chances for widespread applications.
In past few decades, heterocyclic compounds and their derivatives have gained popularity due to their prominent medicinal importance. Keeping in view of their multiple applications, the versatile and synthetically accessible 2-aminobenzothiazole scaffolds are quite fascinating in both synthetic organic chemistry and biological field due to their potent pharmacological activities. A large number of efforts were made to develop a wide range of methodologies for the synthesis of 2-aminobenzothiazole and its derivatives. On other hand, 2-aminobenzothiazole significantly serve as reactants or reaction intermediates for affording various fused heterocycles, since NH2 and endocyclic N functions of 2-aminobenzothiazole are suitably situated to assist the reactions with common bis electrophilic reagents to form a diverse fused heterocyclic scaffold. This review highlights on various synthetic methodologies and chemical reactions of 2-aminobenzothiazole.
To achieve superior fire safety epoxy resins (EP), a novel multifunctional organic-inorganic hybrid, melamine-containing polyphosphazene wrapped ammonium polyphosphate (PZMA@APP) with rich amino groups was prepared and used as an efficient flame retardant. Thanks to the cross-linked polyphosphazene part, PZMA@APP exhibited high flame retardant efficiency and smoke suppression to the EP composites. Thermogravimetric analysis indicated that PZMA@APP significantly enhanced the thermal stability of EP composites. The obtained sample passed UL-94 V-0 rating with 10.0wt% addition of PZMA@APP. Notably, inclusion of incorporating PZMA@APP leads to significantly decrease on fire hazards of EP, for instance, bring about a 75.6% maximum decrease in peak heat release rate and 65.9% maximum reduction in total heat release, accompanied with lower smoke production rate and higher graphitized char layer. With regards to mechanical property, the glass transition temperature of EP/PZMA@APP10.0 was as high as 184.5°C. In particular, the addition of PZMA@APP did not worsen the mechanical properties, compared to pure APP. It was confirmed that the participation of melamine-containing polyphosphazene could significantly enhance the quality of char layer and thereby resulting the higher flame retardant efficiency of PZMA@APP.
In the study, the hierarchical nanohybrid (GO@MCM-41) with mesoporous MCM-41 nanospheres covalent assembling on graphene oxide (GO) nanosheets was successfully prepared, aiming to improve fire retardancy of epoxy resin (EP). Fourier transformation infrared spectra (FTIR), Raman spectra, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) verified GO@MCM-41. The nano-dispersion of GO@MCM-41 in EP was certified via TEM and XRD. Fire-retardant investigation (cone calorimeter test) revealed that EP nanocomposite with 2wt% GO@MCM-41 possessed a 40.0% drop of peak heat release rate (pHRR) and suppressed smoke production relative to EP/GO. Intriguingly, EP/GO@MCM-41 demonstrated lower pHRR than EP/GO-MCM-41 (direct addition of GO and MCM-41). TG analysis indicated GO@MCM-41 imparted EP with significantly reduced degradation rate and increased char yield, accompanied by reduced volatile in thermogravimetric analysis couple with Fourier transformation infrared spectra (TG-FTIR) and improved aromatization in variable-temperature FTIR. The impact strength of EP/GO@MCM-41 was enhanced by 38.8% compared with EP. Contrastive analysis proposed the mechanism of neighboring synergy of GO and MCM-41, which involved in GO nanosheets wrapped by enormous carbonaceous stuffs due to MCM-41 neighboring catalysis. In perspective, hierarchical nano-assembly with neighboring synergy offered a viable approach for fire-safe polymers.
Poly(ethylene terephthalate) (PET) is a fiber-forming polymer with the largest output and widest usage. Its flame retardation is well-achieved via a mechanism of promoting the melt dripping while ignited. However, the melt dripping leads to secondary damage and an immediate empyrosis during fire. How to address the contradiction between the flame retardation and the melt-dripping behavior of PET via an inherent flame-retardant approach becomes a real challenge. This feature article highlights the design and synthesis of novel PET-based copolyesters with flame-retardant and antidripping performance. Three approaches are used to design these copolyesters: “ionic aggregation,” “smart self-cross-linking,” and “rearrangement at high temperatures.” Some new conceptions are proposed accordingly. The synthesis, structure characterization, and properties of those copolyesters are discussed together with the ongoing challenges and limitations at this frontier.
A novel flame retardant, namely bisphenol-A bridged penta(phenoxy)cyclotriphosphazene (A-BP), was synthesized and characterized successfully. Obtained A-BP was mixed in different proportions with diglycidyl ether of bisphenol-A (DGEBA) in order to prepare a series of flame retardant epoxy resins (EP). The differential scanning calorimeter (DSC) results indicated that the glass transition temperatures (Tg) of EPs containing A-BP had only a slight decrease in comparison to EP. Thermogravimetric analysis (TGA) showed that the incorporation of A-BP improves the thermal stability of EP at a high temperature. Moreover, an increase of LOI value (33.9%) was achieved for EP contained with 9 wt% of A-BP. Furthermore, such sample passed UL-94 V-0 rating. Additionally, according to the cone calorimeter tests, in the whole combustion, the EP/9% A-BP material showed lower heat release and smoke production than neat EP. To elucidate the flame retardant actions of A-BP for EP, comprehensive measurement including Fourier transform infrared (FTIR), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) and TG-FTIR techniques were adopted to analyze the char layers and gaseous products. As a result, a bi-phase flame retardant mechanism was proposed showing the efficiency of inert gas dilution and quenching of existed free radicals in gaseous phase and char formation action in a condensed phase, respectively.
In order to develop safe electrical insulating epoxy nanocomposites with fast heat dissipation and low fire hazard, a “3D fabrication method” was proposed to employ acid-sensitive metal organic framework (MOF) as precursor to construct sandwich-type three-dimensional (3D) graphene/layered double hydroxide (LDH) hybrid structure ([email protected]) with NiCo-LDH platelets standing vertically or lying horizontally on both sides of graphene nanosheets which act as a high-performance nanofiller in epoxy nanocomposite. The LDH sheath encased the surface of graphene, impeding electrical conduction and effectively generating a 3D phonon transport channel prone to fast heat dissipation. A 2 wt% [email protected] epoxy nanocomposite sustained an electrical resistivity of 1.21 × 10¹⁴ Ω cm and its thermal conductivity was 0.421 W m⁻¹ K⁻¹, 81.4% higher than that of pure epoxy resin. Likewise, thanks to the physical barrier and catalytic effects of [email protected], the nanocomposite had low fire hazard indicated by cone calorimeter data showing that peak of heat release rate and total smoke production decreased strikingly compared with those of the pristine one. Moreover, the thermal stability and tensile strength of the nanocomposite were also enhanced in the presence of [email protected] This work advances progress on the development of highly safe multifunctional epoxy nanocomposite for practical use.
A novel P/N/S-containing flame retardant DHBAZ was synthesized with 9, 10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, p-hydroxybenzaldehyde and 2-aminothiazole, and used as a co-curing agent for epoxy resin (EP). With the aid of DHBAZ, EP/7.5% DHBAZ passed UL-94 V-0 rating, and owned a LOI value of 31.4%. Besides, DHBAZ also played a positive role in inhibiting the release of heat and the production of smoke. Through non-isothermal DSC tests it revealed that in the presence of DHBAZ, epoxy resin was cured at a lower temperature and showed lower curing-reaction activity energy. DMA analyses indicated that EP/7.5% DHBAZ showed an increased storage modulus, and it had a close glass transition temperature with EP. While, DHBAZ presented a decreased effect on the thermal stability of epoxy resin acquired from TG analyses. Finally, the flame-retardant mechanism studied by TG-FTIR and py-GC/MS deduced that DHBAZ worked in the gaseous phase by producing P·, PO· and incombustible gases.
Biomass-based thermally insulating and flame retardant polymer aerogels were fabricated from renewable pectin (PC) and aniline via polymerization-cogulation and supercritical drying process. The special physical cross-linking action existed between PC and polyaniline (PA). The resultant aerogels showed three-dimensional networks with hierarchical pores and high surface areas (103-205 m2/g). Benefitting from the cross-linking structure, the pectin-based aerogels exhibited good compressive strengths (4.7-9.2 MPa) and water resistance. The results from thermal conductivity measurements and thermogravimetric analysis revealed that these aerogels also had low thermal conductivity (0.033-0.038 W m−1 K−1) and considerable thermal stability. Limiting oxygen index, vertical burning tests, microscale combustion and cone calorimetry tests further confirmed that the inherently low flammability of the aerogels could be achieved by the flame retardancy of PA and the cross-linking action between PA and PC. These aerogels with good mechanical properties, water resistance, low thermal conductivity and flammability, show promising prospects in the field of thermal insulation.
A novel phenylphosphonic di-benzothiazolyl amide (PPDAB) and its imine-type tautomer were successfully synthesized via the amidation of phenylphosphonic dichloride (PPDC) with 2-aminobenzothiazole (ABZ), and used to flame-retard epoxy resin (EP). In the help of PPDAB-Amine as an additive-type flame retardant and PPDAB-Imine as a reactive-type flame retardant, PPDAB showed excellent general properties in epoxy resin. EP with 0.69 wt% of phosphorus achieved UL-94 V-0 rating, and the LOI value of it was increased to 31.0%. Compared with the EP, its performances in terms of the peak of heat release rate (PHRR), total heat release (THR), and smoke production rate (SPR) obtained from cone calorimeter were obviously improved. Besides, EP-PPDAB in which the amount of PPDAB was lower than 10 wt% also exhibited similar glass transition temperature (Tg) to EP, and well-maintained mechanical properties in terms of tensile strength and impact strength.
A bio-based flame retardant toughening agent, phosphaphenanthrene groups-containing triscardanyl phosphate (PTCP), was successfully synthesized via debydrochlorination, epoxidation and ring opening reaction from renewable resource cardanol. The chemical structure of PTCP was confirmed by the proton and phosphorus nuclear magnetic resonance. Epoxy resins (EPs) with different contents of PTCP were prepared through a simple mixing method. Thermogravimetric analysis results indicated that the earlier degradation of PTCP catalyzed the char formation of epoxy resins which was beneficial to protecting underlying polymers from further decomposition. The flame retardant properties were enhanced with the increase of the PTCP content. The EP composite containing 30 wt% PTCP showed a limiting oxygen index of 30.5%, and meanwhile, its peak heat release rate, total heat release and average effective heat of combustion values were decreased by 50%, 27% and 32%, respectively, in comparison to those of neat EP. The enhanced flame retardant behavior was attributed to the improved quality of char residue, which effectively inhibited the flammable volatiles, oxygen and heat transfer between degradation zone and flame zone. The impact strength was increased to 19.14 kJ/m2 for EP/PTCP-30% composite from 14.85 kJ/m2 for neat EP, indicating the toughening effect of PTCP on EP. The findings in this study demonstrated that PTCP could be used as a promising flame retardant toughening agent for epoxy resins to overcome their drawbacks of intrinsic brittle and high flammability.
The mechanical properties of two chemically distinct and complementary thermoset polymers were manipulated through development of thermoset blends. The thermoset blend system was composed of an anhydride-cured diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin, contributing high tensile strength and modulus, and polydicyclopentadiene (PDCPD), which has a higher toughness and impact strength as compared to other thermoset polymers. Ultra-small-angle and small-angle X-ray scattering analysis explored the morphology of concurrently cured thermoset blends, revealing a macroscopically phase separated system with a surface fractal structure across blended systems of varying composition. The epoxy resin rich and PDCPD rich phases exhibited distinct glass transitions (Tg's): the Tg observed at higher temperature was associated with the epoxy resin rich phase and was largely unaffected by the presence of PDCPD, whereas the PDCPD rich phase Tg systematically decreased with increasing epoxy resin content due to inhibition of dicyclopentadiene ring-opening metathesis polymerization. The mechanical properties of these phase-separated blends were in reasonable agreement with predictions by the rule of mixtures for the blend tensile strength, modulus, and fracture toughness. Scanning electron microscopy analysis of the tensile and fracture specimen fracture surfaces showed an increase in energy dissipation mechanisms, such as crazing, shear banding, and surface roughness, as the fraction of the more ductile component, PDPCD, increased. These results present a facile method to tune the mechanical properties of a toughened thermoset network, in which the high modulus and tensile strength of the epoxy resin can be largely retained at high epoxy resin content in the blend, while increasing the fracture toughness.
A review is presented of the recent developments concerning the use of polyhedral oligomeric silsesquioxane (POSS) for designing polymer nanocomposites endowed with enhanced fire retardancy. Emphasis is placed on the scientific and technological advances in the use of POSS as fire retardants, as well as on the achievements and challenges associated to the exploitation of POSS either alone or in combination with conventional fire retardants to provide the required fire retardancy to polymer materials. Polymer/POSS nanocomposites show a great potential to provide materials characterized by improved fire retardancy together with superior physical properties and environmental neutrality. Achievements obtained with POSS in fire retardancy are presented for the different types of polymer materials and critically discussed, especially in terms of the modes of fire retardant action, in the attempt to reveal attractive strategies for successful development of the next generation of polymer/POSS materials and applications.
To obtain highly fire-safe epoxy resin (EP), piperazine-modified ammonium polyphosphate (PAz-APP) with multiple active –NH– groups was prepared and utilized as a highly effective flame-retardant hardener. After curing by PAz-APP as a monocomponent hardener, cross-linked networks containing both tertiary amino and ether linkages were obtained, which resulted in two glass transitions. Thanks to the phosphorus-containing inorganic part, PAz-APP brought excellent flame retardance and smoke suppression efficiency to the EP system. The cured sample passed V-0 rating (UL-94) with only 7.5 wt% addition of PAz-APP. Cone calorimetric results suggested that, compared with PAz/EP (as a reference sample), both the peak-heat release rate (PHRR) and total smoke production (TSP) of PAz-APP 15/EP (15 wt% addition) sharply dropped by 81.5% and 80.0%, respectively. By analyzing the chemical constitution of the decomposing residues at different temperatures, it was noticed that PAz-APP mainly acted as a flame retardant in the condensed phase via the formation of phosphorus-rich char. Dynamic mechanical analysis (DMA) illustrated that the main glass transition temperature (Tg) of PAz-APP 15/EP was as high as 162.4 °C. Furthermore, the incorporation of PAz-APP did not worsen the mechanical properties, but contrarily, improved the impact strength.
ABSTRACT Layered double hydroxide (LDH) is regarded as a prominent flame retardant nano-additive for polymers. However, the flame retardant efficiency of LDH depends strongly upon its dispersion state and composition. Usually, modification or functionalization of LDH is crucial to obtain the high performance polymer nanocomposites. In order to develop multifunctional epoxy nanocomposites, in this study LDH was firstly modified by bio-based flame retardant species, phytic acid (Ph) and hydroxypropyl-sulfobutyl-beta-cyclodextrin sodium (CDBS), and subsequently decorated by Fe3O4 nano-particles to obtain Fe3O4 nano-sphere@LDH hybrid. Results obtained from size distribution and TEM revealed that the Fe3O4 nano-particles with average size of 8 nm were well decorated on the LDH platelet. The Fe3O4 decorated LDH hybrids facilitated their dispersion within epoxy matrix, as indicated in XRD. The incorporation of the as-prepared Fe3O4@Ph-CDBS-LDH hybrid into EP not only improved the flame retardant properties, but also endowed EP resin with increased thermal conductivity. Specifically, the peak heat release rate and total smoke production of the EP composite with 8 wt% Fe3O4@Ph-CDBS-LDH were decreased by 55% and 34%, respectively, in comparison to those of pristine EP, and UL-94 V0 rating requirement can be met. The investigation provides a promising approach for the preparation of multi-functional LDH hybrids and related high performance polymer nanocomposites by just using functionalized nanomaterial.
Cu-doped graphene (graphenit-Cu) was successfully prepared through chemical reduction method, and its surface morphology, crystalline structure and Cu content in graphenit-Cu were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), inductive couple plasma (ICP) and electrochemical cyclic voltammetry, respectively. Graphenit-ox/epoxy systems and graphenit-Cu/epoxy systems were prepared, and the contents of graphenit-ox and graphenit-Cu were kept as 1 and 3 wt%, respectively. The effect of graphenit-ox or graphenit-Cu on the flame retardancy, combustion properties, thermal degradation and thermomechanical properties of epoxy resin was investigated systematically by limiting oxygen index (LOI), cone calorimeter (Cone), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Compared to graphenit-ox, the addition of graphenit-Cu reduced the heat release rate (HRR), total smoke production (TSP) and smoke production rate (SPR), and improved LOI values of epoxy composites. Moreover, the addition of graphenit-ox also had little flame retardant effect on epoxy composite. The possible synergistic effect between graphene and Cu was confirmed in the flame retardant epoxy composites. TGA and DMA results also indicated the considerable effect on the thermal degradation and thermomechanical properties of epoxy composites with the addition of graphenit-Cu. The results supplied an effective solution for developing excellent flame retardant epoxy composites.
Currently, anticorrosive coatings find a large number of applications and can be effectively used for corrosion protection of many corrosion-prone metals like aluminum, iron, etc. Nanocontainers have the ability to encapsulate large amounts of guest molecules within their core, and releasing them in a controlled way can aid in providing self-healing abilities to the coating, thus providing active protection. In the present study, a novel approach of synthesis of nanocontainers using carbon nanotubes (CNTs) and corrosion inhibitor 2-mercaptobenzothiazole has been discussed with their applications in corrosion protection of mild steel (MS). It is a three-step procedure involving layer-by-layer deposition of the CNT, inhibitor, and polyelectrolytes, which thus provides enhanced corrosion protection when coated on MS plates. The thickness of the layer, surface charge, and functional groups present on each layer were identified using various analytic techniques such as particle size distribution, zeta potential, and FTIR analysis. X-ray diffractograms analyses of CNT and modified CNT were performed to evaluate their crystallographic properties. The morphological and particle size clearly indicate the development of a nanocontainer. The corrosion rate analysis of nanocontainer-epoxy coatings on MS panel has been performed by means of salt spray and DC polarization measurements. The corrosion resistance was measured after the immersion of the coated samples in alkali solution.
A flame retardant, tri-(3-DOPO-2-hydroxypropan-1-yl)-1, 3, 5-triazine-2, 4, 6-trione (TGIC-DOPO) containing both phosphaphenanthrene and triazine-trione groups, is introduced into diglycidyl ether of bisphenol-A (EP) thermosets respectively cured by 4,4′-diamino-diphenyl methane (DDM), 4,4′-diamino-diphenyl sulfone (DDS), and m-phenylenediamine (m-PDA). TGIC-DOPO exhibits excellent flame-retardant effects in EP/DDM compared with EP/DDS and EP/m-PDA. The thermoset cured with DDM with only 4%TGIC-DOPO reaches UL94 V-0 rating and possesses a limited oxygen index (LOI) value of 35.6%. The macroscopic and microscopic morphologies of the residues reveal that a cage-like char crown envelops the fire, thus hindering oxygen from permeating inside and inhibiting the release of PO and phenol free radicals with quenching effect. The char-cage hindering effect is the main reason for the high LOI values. TGIC-DOPO in EP/DDM not only locks more carbon components in condensed phase but also facilitates to release more pyrolyzed PO and phenol free radicals. The concentrated release of PO and phenol free radicals exert a strong quenching effect, which is the main mechanism for the high flame-retardant rating with the addition of relatively low amount of TGIC-DOPO. Therefore, the integration of char-cage hindering and free radical quenching effects enables excellent flame retardancy to epoxy thermosets.
Epoxy resins are very important and widely used thermosetting polymers that find many practical applications. Very often their properties can be effectively modified by an addition of reactive silanes, polysiloxanes, silsesquioxanes, silica, montmorillonite, and other fillers. This review considers the literature concerning: (a) synthesis of carbofunctional silanes (CFS), polysiloxanes (CFPS) and polyhedral silsesquioxanes (POSS); (b) properties of neat epoxy resins and their composites and nanocomposites, obtained by modifications with reactive silanes, silicon containing monomers and polymers, and silica based fillers, enabling improvement of their mechanical properties, thermal and flame resistance as well as providing corrosion and antimicrobial protection.
Aiming to develop multi-functional flame retardant for epoxy resins, a novel bio-based eugenol derivative containing silicon and phosphorus [((1,1,3,3-tetramethyldisiloxane-1,3-diyl)bis(propane-3,1-diyl))bis(2-methoxy-4,1-phenylene)bis(phenylphosphonochloridate), SIEPDP]was synthesized, and was further used to modify Mg-Al layered double hydroxide (SIEPDP-LDH). This modified SIEPDP-LDH was used as a novel nano flame-retardant for a bisphenol epoxy resins and compared with unmodified pristine LDH. X-ray diffraction (XRD) analysis justified that intercalation of SIEPDP into LDH increased interlayer distance to 2.95 nm. Morphological analysis (XRD and TEM) revealed that the SIEPDP-LDH was dispersed well in epoxy matrix in a partially exfoliated manner. Results in the cone calorimeter tests showed that even a low loading of SIEPDP-LDH into epoxy resin led to significantly decrease in heat release rate and total heat release compared to unmodified LDH/epoxy composites. More interestingly, SIEPDP-LDH/epoxy’s UL-94 classification was V-0 with only 8 wt% loading. Moreover, the addition of SIEPDP-LDH was able to increase the impact strength and modulus of the cured epoxy, indicating besides being nano flame retardant, SIEPDP-LDH was a good reinforcement agent as well.
Flame-retardant-free and thermo-cross-linkable copolyesters have been synthesized, and their flame retardation and anti-dripping behavior as a consequence of cross-linking during combustion were investigated in detail. TG-DSC simultaneous thermal analysis, rheological analysis, and TGA established the extent and rate of the cross-linking reaction. The extent of cross-linking depends on the content of cross-linkable monomer, PEPE, and the higher the extent of the cross-linking, the better the flame retardance and anti-dripping performance of copolyesters. The large melt viscosity caused by crosslinked networks at high temperature played the most important role in anti-dripping of copolyesters. TG-FTIR results confirmed that the flame-retardant activity of copolyesters mainly took effect in the condensed phase, and XPS results indicated that the carbonization process was aromatization-dominant. SEM and Raman analysis suggested that the char layers were constituted mainly of polyaromatic species with small and uniform microstructures at the surface. Consequently, both the large melt viscosity and the formation of an especially compact char with fine microstructure resulting from cross-linking were considered as the key to the flame retardance and anti-dripping performance of the polymer when subjected to the flame.
We found in our previous study that ethylenediamine- or ethanolamine-modified ammonium polyphosphates could be used alone as an intumescent flame retardant for polypropylene (PP), but their flame-retardant efficiency was not very high. In this present work, a novel highly-efficient mono-component polymeric intumescent flame retardant, piperazine-modified ammonium polyphosphate (PA-APP) was prepared. The oxygen index value of PP containing 22 wt% of PA-APP reached 31.2%, which increased by 58.4% compared with that of PP with equal amount of APP, and the vertical burning test (UL-94) could pass V-0 rating. Cone calorimeter (CC) results indicated that PP/PA-APP composite exhibited superior performance compared with PP/APP composite. For PP containing 25wt% of PA-APP, fire growth rate (FGR) and smoke production rate (SPR) peak were reduced by 86.4% and 78.2%, respectively, compared with PP blended with 25 wt% APP. The relevant flame-retardant mechanism of PA-APP was investigated by Fourier transform infrared spectroscopy etc. The P-N-C structure with the alicyclic amine was formed during the thermal decomposition of piperazine salt (-NH2+-O-P-), and the rich P-N-C structure facilitated the formation of stable char layer at the later stage, consequently improved the flame-retardant efficiency of APP.
The works undertaken to obtain either partially or fully biobased epoxide materials are studied. The reaction between the phenate ion and ECH 2 reveals two competitive mechanisms, one-step nucleophilic substitution with cleavage of the C-Cl bond and a two-step mechanism based on ring opening of ECH (2) with ArO- (1') followed by intramolecular cyclization (SNi) of the corresponding alcoholate, containing one atom of chlorine in the β-position, formed in situ. Depending on the substituent position or nature in the phenol, it takes 6-20 h at reflux or 24-26 h at room temperature to complete the reaction. The reaction of ECH with an alcohol is more difficult, with many side reactions, since this reaction generates new alcohol groups with similar pKa values which are able to react with the epoxy group of ECH, thus leading to its homopolymerization. Epoxies are able to react with (meth)acrylic acid to give formulations for coating applications or vinyl ester monomers and networks after radical polymerization.
Study on epoxy resin modified by M (2-Mercaptobenzothiazole) promoter
- Li
Li DF. Study on epoxy resin modified by M (2-Mercaptobenzothiazole) promoter.
China Adhes 1995;4.