Synergistic effect of phytic acid and eggshell bio-fillers on the dual-phase fire-retardancy of intumescent coatings applied on cellulosic substrates

Cellulosic substrates, including wood and thatch, have become icons for sustainable architecture and construction, however, they suffer from high flammability because of their inherent cellulosic composition. Current control measures for such hazards include applying intumescent fire-retardant (IFR) coatings that swell and form a char layer upon ignition, protecting the underlying substrate from burning. Typically, conventional IFR coatings are opaque and are made of halogenated compounds that release toxic fumes when ignited, compromising the roofing's aesthetic value and sustainability. In this work, phytic acid, a naturally occurring phosphorus source extracted from rice bran, was used to synthesize phytic acid-based fire-retardants (PFR) via esterification under reflux, along with powdered chicken eggshells (CES) as calcium carbonate (CaCO3) bio-filler. These components were incorporated into melamine formaldehyde resin to produce the transparent IFR coating. It was revealed that the developed IFR coatings achieved the highest fire protection rating based on UL94 flammability standards compared to the control. The coatings also yielded increased LOI values, indicative of self-extinguishing properties. A 17 °C elevation of the IFR coating's melting temperature and a significant ∼172% increase in enthalpy change from the control were observed, indicating enhanced fire-retardancy. The thermal stability of the coatings was improved, denoted by reduced mass losses, and increased residual masses after thermal degradation. As validated by microscopy and spectroscopy, the abundance of phosphorus and carbon groups in the coatings' condensed phase after combustion indicates enhanced char formation. In the gas phase, TG-FTIR showed the evolution of non-flammable CO2, and fire-retardant PO and P-O-C. Mechanical property testing confirmed no reduction in the adhesion strength of the IFR coating. With these results, the developed IFR coating exhibited enhanced fire-retardancy whilst remaining optically transparent, suggestive of a dual-phase IFR protective mechanism involving the release of gaseous combustion diluents and the formation of a thermally insulating char layer.

A Study of Isosorbide Synthesis from Sorbitol for Material Applications Using Isosorbide Dimethacrylate for Enhancement of Bio-Based Resins

Bio-based cross-linkers can fulfill the role of enhancing additives in bio-sourced curable materials that do not compare with artificial resin precursors. Isosorbide dimethacrylate (ISDMMA) synthesized from isosorbide (ISD) can serve as a cross-linker from renewable sources. Isosorbide is a bicyclic carbon molecule produced by the reaction modification of sorbitol and the optimal conditions of this reaction were studied in this work. The reaction temperature of 130 °C and 1% w/w amount of para-toluenesulfonic acid (p-TSA) were determined as optimal and resulted in a yield of 81.9%. Isosorbide dimethacrylate was synthesized via nucleophilic substitution with methacrylic anhydride (MAA) with the conversion of 94.1% of anhydride. Formed ISD and ISDMMA were characterized via multiple verification methods (FT-IR, MS, 1H NMR, and XRD). Differential scanning calorimetry (DSC) proved the curability of ISDMMA (activation energy Ea of 146.2 kJ/mol) and the heat-resistant index of ISDMMA (Ts reaching value of 168.9) was determined using thermogravimetric analysis (TGA). Characterized ISDMMA was added to the precursor mixture containing methacrylated alkyl 3-hydroxybutyrates (methyl ester M3HBMMA and ethyl ester E3HBMMA), and the mixtures were cured via photo-initiation. The amount of ISDMMA cross-linker increased all measured parameters obtained via dynamic mechanical analysis (DMA), such as storage modulus (E') and glass transition temperature (Tg), and the calculated cross-linking densities (νe). Therefore, the enhancement influence of bio-based ISDMMA on resins from renewable sources was confirmed.

Rethinking the pathway to sustainable fire retardants

Flame retardants are currently used in a wide range of industry sectors for saving lives and property by mitigating fire hazards. The growing fire safety requirements for materials boost an escalating demand for consumption of fire retardants. This has significantly driven both the industry and scientific community to pursue sustainable fire retardants, but what makes a sustainable flame retardant? Here an overview of recent advances in sustainable flame retardants is offered, and their renewable raw materials, green synthesis and life cycle assessments are highlighted. A discussion on key challenges that hinder the innovation of fire retardants and design principles for creating truly sustainable yet cost-effective fire retardants are also presented. This short work is expected to help drive the development of sustainable, cost-effective fire retardants, and expedite the creation of a more sustainable and safer society.

Synergistic Flame Retardancy of Phosphatized Sesbania Gum/Ammonium Polyphosphate on Polylactic Acid

Phosphating sesbania gum (DESG) was obtained by modifying sesbania gum (SG) with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and endic anhydride (EA). The structure of DESG was determined using Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance spectroscopy (¹H-NMR). Flame-retardant polylactic acid (PLA) composites were prepared by melt-blending PLA with DESG, which acted as a carbon source, and ammonium polyphosphate (APP), which acted as an acid source and a gas source. The flame retardancy of the PLA composite was investigated using vertical combustion (UL-94), the limiting oxygen index (LOI) and the cone calorimeter (CONE) test. Thermal properties and morphology were characterized via thermogravimetric analysis (TGA) and field emission scanning electron microscopy (FESEM), respectively. Experimental results indicated that when the mass ratio of DESG/APP was equal to 12/8 the LOI value was 32.2%; a vertical burning test (UL-94) V-0 rating was achieved. Meanwhile, the sample showed a lowest total heat release (THR) value of 52.7 MJ/m², which is a 32.5% reduction compared to that of neat PLA. Using FESEM, the uniform distribution of DESG and APP in the PLA matrix was observed. The synergistic effect of DESG and APP effectively enhanced the flame retardancy of PLA. Additionally, the synergistic mechanism of DESG and APP in PLA was proposed.

Green Sorbitol- and Isosorbide-Based Flame Retardants for Cotton Fabrics

Flame retardancy is often required in various textile applications. Halogenated flame retardants (FR) are commonly used since they have good FR performance. Several of these components are listed under REACH. Halogen-free FR compounds have been developed as alternatives. So far, not many biobased FR have made it to the market and are being applied in the textile sector, leaving great opportunities since biobased products are experiencing a renaissance. In this study, renewable FR based on sorbitol and isosorbide were synthesised. The reaction was performed in the melt. The resulting biobased FR were characterised via FT-IR, thermogravimetric analysis (TGA) and X-ray fluorescence (XRF). Cotton fabrics functionalized with the developed biobased FR passed ISO 15025 FR test. After washing, the FR properties of the fabrics decreased (longer afterflame and afterglow time) but still complied with ISO 15025, indicating the biobased FR were semi-permanent. The amount of residue of modified sorbitol and isosorbide measured at 600 °C in air was 31% and 27%, respectively. Cotton treated with biobased modified FR showed no ignition during cone calorimetry experiments, indicating a flame retardancy. Furthermore, a charring of the FR containing samples was observed by means of cone calorimetry and TGA measurements.

Effect of a Novel Flame Retardant on the Mechanical, Thermal and Combustion Properties of Poly(Lactic Acid)

Poly(lactic) acid (PLA) is one of the most promising biobased materials, but its inherent flammability limits its applications. A novel flame retardant hexa-(DOPO-hydroxymethylphenoxy-dihydroxybiphenyl)-cyclotriphosphazene (HABP-DOPO) for PLA was prepared by bonding 9,10-dihydro-9-oxy-10-phosphaphenanthrene-10-oxide (DOPO) to cyclotriphosphazene. The morphologies, mechanical properties, thermal stability and burning behaviors of PLA/HABP-DOPO blends were investigated using a scanning electron microscope (SEM), a universal mechanical testing machine, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), limiting oxygen index (LOI), vertical burning (UL-94) and a cone calorimeter test (CCT). The LOI value reached 28.5% and UL-94 could pass V-0 for the PLA blend containing 25 wt% HABP-DOPO. A significant improvement in fire retardant performance was observed for PLA/HABP-DOPO blends. PLA/HABP-DOPO blends exhibited balanced mechanical properties. The flame retardant mechanism of PLA/HABP-DOPO blends was evaluated.

Synthesis and characterization of SPDSCD and its flame retardant application on epoxy resins

In this study, a flame retardant agent, 2,4,8,10-tetraoxo-3,9-diphosphospiro[5.5]undecane spirophosphate-4,4-diaminopair benzene disulfone-1,3,5-himetriazine (SPDSCD), is synthesized through a direct polycondensation reaction. SPDSCD is a chemically expanded phosphorus-containing flame retardant in epoxy resins (EP). The molecular structure of SPDSCD and thermal stability are characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, and thermogravimetric analysis, and EP/SPDSCD composites were investigated in detail. These properties are associated with the phosphorus-containing spiro structure on the main molecular chain which can promote condensation polymerization into carbon during pyrolysis, the new nitrogen-containing carbon source, and the triazine structure. SPDSCD shows good thermal stability and low flammability, the weight loss from 500 to 800 °C was only 6.1 wt%, and the residual mass at 800 °C was 48.9 wt%. With the addition of SPDSCD, the flame retardant quality of the composites was gradually enhanced, the carbon residue becomes denser, which isolates heat transfer and inhibits the volatilization of flue gas. The addition of 20 wt% SPDSCD in the EP sample was associated with a limited oxygen index (LOI) value of 26% and a vertical burning V-0 rating. Cone calorimeter test shows that the peak heat release rate is reduced by 75%; the heat release rate curve enters the heat release platform area with a value lower than the first peak, TSP is reduced by 24%, the ac-CO₂Y value reduced by 25.6%, indicating that SPDSCD/EP produced less CO₂, which obviously prevented the combustion of volatile gas. SPDSCD exerted a charring and barrier effect in the condensation phase. Using basic characterization and flame retardancy testing, this work determined that SPDSCD has good flame retardancy when added to EP.

In this study, a flame retardant agent, 2,4,8,10-tetraoxo-3,9-diphosphospiro[5.5]undecane spirophosphate-4,4-diaminopair benzene disulfone-1,3,5-himetriazine (SPDSCD), is synthesized through a direct polycondensation reaction.

Biodegradable Flame Retardants for Biodegradable Polymer

To improve sustainability of polymers and to reduce carbon footprint, polymers from renewable resources are given significant attention due to the developing concern over environmental protection. The renewable materials are progressively used in many technical applications instead of short-term-use products. However, among other applications, the flame retardancy of such polymers needs to be improved for technical applications due to potential fire risk and their involvement in our daily life. To overcome this potential risk, various flame retardants (FRs) compounds based on conventional and non-conventional approaches such as inorganic FRs, nitrogen-based FRs, halogenated FRs and nanofillers were synthesized. However, most of the conventional FRs are non-biodegradable and if disposed in the landfill, microorganisms in the soil or water cannot degrade them. Hence, they remain in the environment for long time and may find their way not only in the food chain but can also easily attach to any airborne particle and can travel distances and may end up in freshwater, food products, ecosystems, or even can be inhaled if they are present in the air. Furthermore, it is not a good choice to use non-biodegradable FRs in biodegradable polymers such as polylactic acid (PLA). Therefore, the goal of this review paper is to promote the use of biodegradable and bio-based compounds for flame retardants used in polymeric materials.

The preparation of starch derivatives reacted with urea-phosphoric acid and effects on fire performance of expandable polystyrene foams

A novel bio-based flame retardant, ammonium phosphate starch carbamates (APSC) was synthesized from starch, phosphoric acid and urea to achieve better thermal stability and char formation. Flame retardant expandable polystyrene foams (EPS) were prepared by coating method with APSC. The fire resistance evaluation of EPS composites by limiting oxygen index (LOI), vertical burning (UL-94) and cone calorimeter tests indicated that the addition of 47 wt.% of APSC enhanced the LOI from 17.6%-35.2%, with V-0 rating in UL-94, and decreased the peak heat release rate from 666 kW/m² to 316 kW/m². Moreover, the total smoke production was also sharply decreased from 70 m² of pure EPS to 17 m². By the presence of APSC, the substantial char formation prevented the heat and oxygen transfer, and interrupted the releasing of flammable products, thus protecting the EPS foam from burning.

Phosphorus-Containing Flame Retardants from Biobased Chemicals and Their Application in Polyesters and Epoxy Resins

Phosphorus-containing flame retardants synthesized from renewable resources have had a lot of impact in recent years. This article outlines the synthesis, characterization and evaluation of these compounds in polyesters and epoxy resins. The different approaches used in producing biobased flame retardant polyesters and epoxy resins are reported. While for the polyesters biomass derived compounds usually are phosphorylated and melt blended with the polymer, biobased flame retardants for epoxy resins are directly incorporated into the polymer structure by a using a phosphorylated biobased monomer or curing agent. Evaluating the efficiency of the flame retardant composites is done by discussing results obtained from UL94 vertical burning, limiting oxygen index (LOI) and cone calorimetry tests. The review ends with an outlook on future development trends of biobased flame retardant systems for polyesters and epoxy resins.

Recent Advances in Bio-Based Flame Retardant Additives for Synthetic Polymeric Materials

It would be difficult to imagine how modern life across the globe would operate in the absence of synthetic polymers. Although these materials (mostly in the form of plastics) have revolutionized our daily lives, there are consequences to their use, one of these being their high levels of flammability. For this reason, research into the development of flame retardant (FR) additives for these materials is of tremendous importance. However, many of the FRs prepared are problematic due to their negative impacts on human health and the environment. Furthermore, their preparations are neither green nor sustainable since they require typical organic synthetic processes that rely on fossil fuels. Because of this, the need to develop more sustainable and non-toxic options is vital. Many research groups have turned their attention to preparing new bio-based FR additives for synthetic polymers. This review explores some of the recent examples made in this field.

Preparing the Degradable, Flame-Retardant and Low Dielectric Constant Nanocomposites for Flexible and Miniaturized Electronics with Poly(lactic acid), Nano ZIF-8@GO and Resorcinol Di(phenyl phosphate)

Degradable, flame retardant, and flexible nanocomposite films with low dielectric constant were prepared with poly (lactic acid) (PLA), nano ZIF-8@GO, and degradable flame-retardant resorcinol di(phenyl phosphate) (RDP). The SEM results of the fractured surfaces indicated that ZIF-8@GO and RDP were dispersed uniformly in the PLA matrix. The prepared films had good mechanical properties and the tensile strength of the film with 1.5 wt% of ZIF-8@GO was increased to 48.2 MPa, compared with 38.5 MPa of pure PLA. Meanwhile, the nanocomposite films were flexible due to the toughing effect of RDP. Moreover, above 27.0% of limited oxygen index (LOI) and a VTM-0 rating were achieved for the nanocomposite films. The effects of nano ZIF-8@GO hybrids and RDP on the dielectric properties were investigated, and the results showed that ZIF-8@GO and RDP were beneficial in reducing the dielectric constant and dielectric loss of the nanocomposites.

Renewable Isohexide-Based, Hydrolytically Degradable Poly(silyl ether)s with High Thermal Stability

Several degradable poly(silyl ether)s (PSEs) have been synthesized by dehydrogenative cross-coupling between bio-based 1,4:3,6-dianhydrohexitols (isosorbide and isomannide) and commercially available hydrosilanes. An air-stable manganese salen nitrido complex [Mn^V N(salen-3,5-tBu₂ )] was employed as the catalyst. High-molecular-weight polymer was obtained from isosorbide and diphenylsilane (M_n up to 17000 g mol^-1 ). Thermal analysis showed that these PSEs possessed high thermal stability with thermal decomposition temperatures (T_-5 % ) of 347-446 °C and glass transition temperatures of 42-120 °C. Structure-property analysis suggested that steric bulk and molecular weight have a significant influence to determine the thermal properties of synthesized polymers. Importantly, these polymers were degraded effectively to small molecules under acidic and basic hydrolysis conditions.

Novel Dihydroxy-Containing Ammonium Phosphate Based Poly(Lactic Acid): Synthesis, Characterization and Flame Retardancy

The aim of this work is to prepare flame-retardant biobased poly(lactic acid) materials through incorporating a novel flame retardant dihydroxy-containing ammonium phosphate (DAP) derived from 2-chloro-5,5-dimethyl-1,3,2-dioxaphosphinane-2-oxide (DOP) and 2-amino-2-methyl-1,3-propanediol (AMPD). Interestingly, PLA modified with only 0.5% DAP passed UL-94 V-0 rating, and possessed a limiting oxygen index (LOI) value of 24.6%, which would further increase with the increasing loading of DAP. PLA/DAP did not exhibit obviously improved results in terms of heat release rate (HRR), as the loading of DAP was relatively low. It was found that DAP showed little effect on the thermal stability of PLA and the onset decomposition temperatures of PLA and PLA/DAP blends were very close. Besides, the degree of crystallization increased because of the plasticized effect of DAP. Based on the analyses of flame-retardant mechanism of DAP, it disclosed that DAP decomposed to generate incombustible compounds, such as water and ammonia, to dilute the concentration of oxygen and fuels, and then release some phosphorus-containing fragments that could produce phosphorus-containing free radicals to interrupt free-radical reactions, and finally noncombustible melt dripping was produced so as to bring away large amount of heat and stop the feedback of heat to the matrix.

Mechanically Robust, Flame-Retardant Poly(lactic acid) Biocomposites via Combining Cellulose Nanofibers and Ammonium Polyphosphate

Expanding the application range of flame-retardant polymer biocomposites remains a huge challenge for a sustainable society. Despite largely enhanced flame retardancy, until now the resultant poly(lactic acid) (PLA) composites still suffer reduced tensile strength and impact toughness due to improper material design strategies. We, herein, demonstrate the design of a green flame retardant additive (ammonium polyphosphate (APP)@cellulose nanofiber (CNF)) via using the cellulose nanofibers (CNFs) as the green multifunctional additives hybridized with ammonium polyphosphate (APP). The results show that PLA composite with 5 wt % loading of APP@CNF can pass the UL-94 V-0 rating, besides a high limited oxygen index of 27.5%, indicative of a significantly enhanced flame retardancy. Moreover, the 5 wt % of APP@CNF enables the impact strength (σi) of the PVA matrix to significantly improve from 7.63 to 11.8 kJ/m2 (increase by 54%), in addition to a high tensile strength of 50.3 MPa for the resultant flame-retardant PLA composite. The enhanced flame retardancy and mechanical strength performances are attributed to the improved dispersion of APP@CNF and its smaller phase size within the PLA matrix along with their synergistic effect between APP and CNF. This work opens up a facile innovative methodology for the design of high-performance ecofriendly flame retardants and their advanced polymeric composites.

Synthesis of DOPO-HQ-functionalized graphene oxide as a novel and efficient flame retardant and its application on polylactic acid: Thermal property, flame retardancy, and mechanical performance

The fabrication of biodegradable polymer nanocomposites with improved flame retardancy has been an urgent task in practical because of the huge benefits of biodegradable polymers. In this work, 10-(2,5-dihydroxyl phenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-HQ)-functionalized graphene oxide (GO) (FGO-HQ) was used as a novel and highly efficient flame retardant (FR) to improve the flame retardancy of polylactide (PLA) nanocomposites. Contributed by the bi-phase flame retardant action, including the physical barrier char in solid phase and the decreased flammable volatiles in gas phase, the resultant PLA/FGO-HQ nanocomposites presented excellent flame resistance at the loading of 6 wt% FR: UL-94 reached V-0 rating; peak heat release rate (PHRR) and total heat release (THR) decreased by 24.0% and 43.0%, respectively; smoke production rate (SPR) and total smoke release (TSR) decreased by 46% and 83%, respectively. For further confirming its flame-resistance mechanism, thermogravimetric analysis/infrared spectrometry (TG-IR) and Fourier transform infrared spectra (FT-IR), scanning electron microscope (SEM), and Raman spectroscopy were employed. Results indicated that the incorporation of FGO-HQ can effectively reduce the evaporation of flammable gaseous product in gas phase through quenching free radicals. Meanwhile, graphitized carbons are formed in the residual char and PLA/FGO-HQ sample can achieve a good thermal stability in the combustion with phosphorus-containing compounds and aromatic structure in the solid phase. Furthermore, the tensile strength of PLA nanocomposites presented good mechanical properties with the addition of FR as well. These results suggested that the incorporation of FGO-HQ FR not only improve the flame retardancy and thermal stability of biodegradable polymer nanocomposites but also without sacrificing their mechanical properties.

Combination of a bio-based polyphosphonate and modified graphene oxide toward superior flame retardant polylactic acid

Superior flame retardant polylactic acid (PLA) composites were prepared using bio-based polyphosphonate (BPPT) and polyethyleneimine-modified graphene oxide (M-GO) to be used as a flame retardant, the total amount of which is only 3 wt%.

Making a Supertough Flame-Retardant Polylactide Composite through Reactive Blending with Ethylene-Acrylic Ester-Glycidyl Methacrylate Terpolymer and Addition of Aluminum Hypophosphite

Biocompatible and biodegradable polylactide (PLA) composites with supertough mechanical property and sufficient flame retardancy were fabricated by employing a facile approach involving reactive blending of PLA and ethylene-acrylic ester-glycidyl methacrylate terpolymer (EGMA), with the addition of aluminum hypophosphite (AHP) as an effective flame retardant. In consideration of the balance between mechanical property and flame retardancy, the optimal formula was taking a PLA/EGMA 80/20 blend (supertough STPLA) as the matrix and adding 20 wt % of AHP (relative to the mass of STPLA) as the flame retardant, coded as STPLA/20AHP. The mechanical property test showed that for STPLA/20AHP the elongation at break was increased by about 22 times and the notched Izod impact strength was enhanced by approximately 11 times as compared to those for neat PLA. The flame-retardant property test showed that for STPLA/20AHP the limiting oxygen index value reached 26.6% and the UL-94 V0 rating test was passed. Thermogravimetric analysis, microscale combustion calorimetry, and cone calorimeter were further applied to reveal the thermal stability and combustion behaviors of STPLA/xAHP, respectively, where x indicated the mass content of AHP in percentage. The phase separation morphology, dispersion of AHP particles in STPLA matrix, and fracture surfaces and char residues after flame burning were examined by phase contrast optical microscopy and scanning electron microscopy, respectively, which helped comprehend the results obtained from the mechanical property and flame retardancy tests. The supertough STPLA/xAHP, with sufficient flame retardancy as prepared in this work, could have a potential for engineering applications.

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

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

Synthesis of a highly efficient phosphorus-containing flame retardant utilizing plant-derived diphenolic acids and its application in polylactic acid

A highly efficient phosphorous-containing flame retardant for PLA is synthesized from plant-derived diphenolic acids.

Synthesis of biosafe isosorbide dicaprylate ester plasticizer by lipase in a solvent-free system and its sub-chronic toxicity in mice

The biosafety isosorbide dicaprylate ester plasticizer was synthesized with bubbling dried air in solvent-free system.

Hyper-branched polymer grafting graphene oxide as an effective flame retardant and smoke suppressant for polystyrene

A well-defined functionalized graphene oxide (FGO) grafted by hyper-branched flame retardant based on N-aminoethyl piperazine and phosphonate derivative was synthesized to reduce flammability and toxicity of polystyrene (PS). The chemical structure, morphological and thermal properties were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and thermogravimetric analysis, respectively. Micro combustion calorimeter and steady state tube furnace were employed to evaluate the heat and non-heat fire hazards of PS nanocomposites. The incorporation of FGO into PS matrix effectively improved the flame retardancy and restrained the toxicity of the volatiles escaped, which is attributed to that the homogeneous dispersion of FGO in the PS matrix enhanced barrier effect that reduced peak heat release rate, total heat release and toxic gas release during combustion. Furthermore, PS-FGO nanocompsites obviously decreased the amount of flammable and toxic volatiles evolved, such as the aromatic compounds, carbonyl compounds, carbon monoxide, indicating suppressed fire hazards of the PS composites.

Structure and thermal properties of phosphorus-containing polyol synthesized from cardanol

P-Containing cardanol polyol (PCP), a novel cardanol derivative, was synthesized.

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

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