Epoxy Samples Research Articles

Curing and thermal comparative study of rosin epoxy thermosets with bio-based imidoamines and commercial curing agents

This paper includes the curing of previously synthesized multifunctional bio-based epoxy resins (PEMPAE/TMPAE) with rosin-based imidoamine curing agents (IAMDK/IASDK/IAEDK) which are nucleophilic addition reaction products of diamino diphenyl ether (DDE) and dimaleopimaryl ketone (DMPK), a dehydrodecarboxylated derivative of MPA. Curing dynamics of rosin-based epoxy resins (PEMPAE/TMPAE) with rosin-based imidoamine curing agents (IAMDK/IASDK/IAEDK) were evaluated using differential scanning calorimetry. For comparison, the bio-based epoxy resins were also cured with rosin derivative dimaleopimaryl ketone (DMPK) and commercial-based diamino diphenyl ether (DDE). The universal testing machine and thermogravimetric analyzer) were used to measure the mechanical properties and thermal stability of the cured epoxy samples. The samples’ chemical resistance was assessed by calculating the weight loss in percent after they were submerged in solutions of NaOH, HCl, and NaCl. We also used scanning electron microscopy (SEM) to examine the morphological changes. Rosin-based epoxy cured with imidoamine curing agents outperformed the commercial epoxy in terms of performance.

Electron irradiation damage of amorphous epoxy resin at low electron doses.

The mechanisms of electron irradiation damage to epoxy resin samples were evaluated using their electron diffraction patterns and electron energy-loss spectra. Their electron diffraction patterns consisted of three indistinct halo rings. The halo ring corresponding to an intermolecular distance of ∼6.4 Å degraded rapidly. Such molecular-scale collapse could have been caused by cross-linking between molecular chains. The degree of electron irradiation damage to the samples changed with the accelerating voltage. The tolerance dose limit of the epoxy resin estimated from the intensity of the halo ring was found to be improved at a higher accelerating voltage. Changes in low-loss electron energy-loss spectra indicated that the mass loss of the epoxy resin was remarkable in the early stage of electron irradiation.

Effects of Ion Beam Treatment on DC Flashover Characteristics of Epoxy

The effect of ion beam treatment on surface flashover characteristics of epoxy is evaluated and explored. Epoxy samples are prepared and ion beam treatment is carried out for 10-, 15-, 20-, 25-, and 30-min durations using an end-Hall ion source. Flashover test of both pristine and treated samples is conducted at negative dc voltage in air. The results indicate the effectiveness of ion beam treatment to enhance the flashover properties of epoxy. The flashover voltage of the epoxy resin increased to 21.35% after ion beam treatment for a duration of 20 min. Optical microscopic images, scanning electron microscopy (SEM) images, and results from Fourier transform infrared spectroscopy reveal the change in physicochemical characteristics of epoxy resin after treatment. The obtained surface potential from the surface potential decay (SPD) test shows a faster decay rate of surface charges for treated samples than the pristine epoxy. Moreover, from the trap distribution characteristics, it is found that ion beam treatment reduces the surface trap depth, which increases the surface conductivity of the epoxy insulator and helps to promote the charge migration and transport along the insulator surface.

Preparation of self-healing epoxy resin coatings based on dynamic disulfide bonds

Defects and mechanical damage that lead to peeling, corrosion and other potential hazards during practical applications are inevitable in epoxy coatings due to the high cross-link density of the epoxy network. Herein, the authors synthesized a self-healing polythiourethane (SPTU) material containing dynamic disulfide bonds for the design and preparation of an SPTU–epoxy coating. Fourier transform infrared spectroscopy, proton (1H) nuclear magnetic resonance spectroscopy and scanning electron microscopy showed that 2-hydroxyethyl disulfide was successfully introduced into the polythiourethane system. Due to the fracture and reattachment of double sulfur bonds, the 3% SPTU–epoxy coating exhibited good self-healing properties in scratch treatment, the scratch being repaired completely after 2 h at 85°C. Meanwhile, 75.7% of the tensile performance of the completely fractured 3% SPTU–epoxy sample was retained after self-healing. The Tafel polarization curve and electrochemical impedance spectroscopy results showed that the 3% SPTU–epoxy coating had excellent corrosion resistance and still provided considerable corrosion resistance after 19 days of immersion corrosion tests. The self-healing coating exhibited good self-healing ability under heating conditions, which is attributed to the bond breaking and reconnection of dynamic bonds provided by the self-healing component. The self-healing properties and corrosion resistance of the prepared coating effectively improve the service life of the epoxy coating and provide some guidance for corrosion protection of epoxy coatings.

The Effect of Flame Retardant-Aluminum Trihydroxide on Mixed Mode I/II Fracture Toughness of Epoxy Resin.

Fire resistance is a major issue concerning composite materials for safe operation in many industrial sectors. The design process needs to meet safety requirements for buildings and vehicles, where the use of composites has increased. There are several solutions to increasing the flame resistance of polymeric materials, based on either chemical modification or physical additions to the material’s composition. Generally, the used flame retardants affect mechanical properties either in a positive or negative way. The presented research shows the influence of the mixed-mode behavior of epoxy resin. Fracture toughness tests on epoxy resin samples were carried out, to investigate the changes resulting from different inorganic filler contents of aluminum trihydroxide (ATH). Three-point bending and asymmetric four-point bending tests, with different loading modes, were performed, to check the fracture behavior in a complex state of loading. The results showed that the fracture toughness of mode I and mode II was reduced by over 50%, compared to neat resin. The experimental outcomes were compared with theoretical predictions, demonstrating that the crack initiation angle for higher values of KI/KII factor had a reasonable correlation with the MTS prediction. On the other hand, for small values of the factor KI/KII, the results of the crack initiation angle had significant divergences. Additionally, based on scanning electron microscopy images, the fracturing of the samples was presented.

High-voltage insulation and dielectric properties of ceramic-glass composites

ABSTRACT This paper reveals the high-voltage insulation properties – namely the dielectric constant, dissipation factor, breakdown strength, and voltage – of epoxy resin samples of various thicknesses containing the microadditives albite, potassium feldspar, lithium glass, and zinc glass in different concentrations. 0.1 wt% KAlSi3O8 ceramic powders as fillers in 1 mm epoxy composites designed for insulation is taken as the choice for highest breakdown strength 36.6491 kV/mm. After that, 5 wt% Li-Bi-B-O glass at 35.4687 kV/mm, 10 wt% Zn-Bi-B-O glass at 35.0432 kV/mm, and 10 wt% NaAlSi3O8 at 33.6504 kV/mm. The increase of thickness more than 1 mm is not recommended in the practical application due to the decrease of breakdown strength. Multi-layer thin structure is recommended for insulation purpose.

Analysis of the Influence of Organophosphorus Compounds and of Aluminium and Magnesium Hydroxides on Combustion Properties of Epoxy Materials

This paper presents the influence of selected flame retardant additives on heat release rate and thermokinetics properties of epoxy materials made of epoxy resin—Epidian 5. The epoxy resin underwent flame retardant modification with the use of organophosphorus compounds (Roflam F5, Roflam B7) and Al(OH)3, Mg(OH)2. The fire characteristics of the analysed epoxy resin were determined using the cone calorimeter method, and thermal analysis of epoxy resin and the surface morphology of the analysed epoxy materials was with the use of an SEM microscope with an EDS attachment. The lowest value of the heat release rate was recorded for hardened epoxy resin containing one component additive 5% by weight of Mg(OH)2, as well as two component additive 10% by weight of Roflam F5 and 5% by weight of Al(OH)3. Moreover, the initial temperature of thermal decomposition of phase I of the modified epoxy resin samples with Mg(OH)2 (sample 5M) or organophosphorus compounds and Mg(OH)2 (samples 5B + 10M and 5F + 10M) were higher compared to the unmodified epoxy resin for these samples. Considering the surface morphology of the samples with Mg(OH)2, it can be concluded that the additives cause a homogeneous charred layer.

Development of Radiation-Resistant Warm Magnets Using Cyanate Ester Resin

We have been developing radiation-resistant warm magnets insulated by cyanate ester (CE) resins. A glass fiber cloth prepreg tape was fabricated using CE pre-polymers supplied by Mitsubishi Gas Chemical Company Inc. Proton beam irradiation tests were carried out for evaluation of the radiation hardness. We prepared cured resin samples of cyanate ester, bismaleimide triazine (BT), and epoxy resins using the same glass fiber cloth. The resin samples were irradiated by a 70-MeV proton beam at doses up to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> Gy at the Cyclotron and Radioisotope Center, Tohoku University. The results of tensile tests after irradiation showed that the radiation resistance of the CE resins was almost same as that of BT resins and more than 10 times as high as that of epoxy resins. We also developed a CE putty for use in coil moldings. A curing test was performed on a coil mock-up made of a stack of hollow conductors wrapped with the CE prepreg tapes and putty. We successfully cured the coil mock-up without causing thermal runaway.

The Effect of UV Exposure on the Service-life of Thermochromic Microcapsules Integrated into the Epoxy Matrix

The effect of ultraviolet (UV) exposure on the service-life of thermochromic microcapsules integrated into the epoxy matrix was investigated. The microcapsules of the formaldehyde shell contain the core of thermochromic leuco dye. Seven sets of epoxy resin samples filled with concentrations from 0 to 10 wt.% of microcapsules were investigated. The composite samples were exposed to UV for approximately 1000 h. For the quantitative evaluation of colour change under UV, a fast and simple original procedure based on samples’ image treatment was developed. With the exposure time intervals of 50 h, samples were taken out from the UV light chamber to evaluate the exposure effect on their reversible thermochromic ability and mechanical properties. Periodical evaluation of the UV light effect on mechanical properties during the exposure was performed by microhardness tests. Tensile tests of the samples till the fracture were performed every 200 h. The critical time under the exposure of the UV lamp that destroys the reversible thermochromic reaction of the microcapsules was defined as 200 h. At the same time, it has been found that the mechanical properties of the epoxy resin under the same UV source were not strongly affected after 1000 h of irradiance and changed in the frame of ~ 10 %.

Efficient flame retardancy, good thermal stability, mechanical enhancement, and transparency of DOPO-conjugated structure compound on epoxy resin

A novel multifunctional flame retardant EAD with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and conjugated structure was successfully synthesized via addition reaction of PH bond and alkynyl group. The structure was characterized by Fourier transform infrared (FTIR) spectra and nuclear magnetic resonance (NMR) spectra. Thermogravimetric analysis (TGA) showed that EAD possessed high thermal stability with 290 ℃ Tonset and 20.4% char yield at 700 ℃ due to the presence of rigid structure and crosslinking reaction. When incorporating 2 wt% EAD into epoxy resin, the results from TGA indicated that the modified sample had good thermal stability with a Tonset value of 354 ℃ and char-forming performance with 22.9% char yield at 700 ℃, as well as glass transition temperature without any deterioration was obtained. Compared with pure epoxy, the same EAD content with only 0.186 wt% phosphorus loading improved effectively the flame retardancy, reflected by the increased limiting oxygen index (LOI) value of 31.0% and V-0 rating in UL-94 vertical burning test. Results from cone calorimeter test (CCT) further confirmed the positive effect on the fire retardancy, which was expressed as the heat release reduction and smoke suppression. The high-efficient flame retardancy was investigated by analyzing the pyrolysis behavior and char residue, which demonstrated the multiple actions of EAD in gas and condensed phases. The low addition of EAD also brought out the reinforcing and toughening effect for epoxy resin. Moreover, the modified epoxy samples with no more than 2 wt% EAD presented good transparency and UV-shielding performance.

Effect of Different DC Prestressed Time on Flashover Characteristics of Epoxy Resin Under Polarity Reversal Voltage

DC wall bushing is one of the key equipment in high-voltage direct current (HVDC) transmission project. At present, post insulators based on epoxy composites are widely used for supporting insulation in SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> -insulated apparatus. However, the flashover faults caused by surface charge accumulation can be a severe threat to the long-term operation of the post insulators under dc field. Therefore, the issue of charge accumulation on epoxy post insulators in HVDC wall bushing and its effect on flashover has been widely concerned. Aiming at this problem, the flashover characteristics of epoxy samples in SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas under polarity reversal conditions with dc voltage prestressed for 10–600 min were measured in this article. The flashover process is analyzed through surface charge distribution measurement and electric field computation. The results show that with the increase of prestressed time, the accumulated negative charge density could reach <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-14.8\,\,\mu \text{C}/\text{m}^{{2}}$ </tex-math></inline-formula> , which led to a 12% increase in maximum field strength. As a result, the polarity reversal flashover voltage could decrease by 12% and the flashover time delay could decrease by 84.6%. This article can offer as a reference for the effect of surface charge accumulation on flashover in SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas-insulated equipment.

Water ageing effects on the elastic and viscoelastic behaviour of epoxy-based materials used in marine environment

Both experimental tests and numerical simulations have been performed in this study to analyze the influence of long-term immersion (over 500 days) on the hygro-elastic and hygro-viscoelastic behaviour of epoxy resin samples. First, a diffusive and swelling campaign was carried out with water immersion at 25 °C and 60 °C. Various experimental tests have also been undertaken at different stages of ageing to highlight and quantify the influence of water diffusion on elastic and viscoelastic properties. A model is then proposed to simulate the hygro-viscoelastic behaviour of the studied material through finite element simulations. A good agreement between the experimental and numerical results is observed.

Space Charge Dynamics in Epoxy Resins Under the Influence of a Long-Term High Electric Field at Various Temperatures.

As the main insulating material of an ultra-high voltage (UHV) resin impregnated paper (RIP) bushing, epoxy resin accumulates space charge under the DC voltage, which would affect the insulation properties of the bushing. In this article, the evolution of space charge accumulation and dissipation within the epoxy resin samples was measured under the influence of a long-term (24 h) electric field of 60 kV/mm at 40°, 60°, 80°, and 100°C. The experimental results show that the space charge transport in the epoxy sample was a long-time dynamic process. When the temperature was not greater than 60°C, only homocharge accumulation was observed within the samples, and the space charge distribution did not reach a stable state even after 24 h of voltage application. When the temperature was not lower than 80°C, the positive heterocharge accumulation was observed at the interface between cathode and epoxy. Through analysis by fitting and numerical simulation, it was verified that the positive heterocharge accumulation was caused by the limitation of the hole extraction, and the transport of holes within the samples obeyed the jump conductance model.

DC Flashover Performance of GIS Spacers Fluorinated at Different Temperatures

In order to verify the effectiveness of direct fluorination in improving the dc flashover performance of gas insulated switchgear (GIS) actual spacers and explore the effect of fluorination conditions, 126-kV disk spacers were surface fluorinated in the laboratory at the different temperatures of 35 °C, 55 °C, or 80 °C. The evaluation of surface physicochemical characteristics and basic electrical properties of the fluorinated disk spacers are realized by using the epoxy samples of the same material and simultaneously fluorinated with the disk spacers. Flashover tests indicate that direct fluorination significantly increases the dc flashover voltage of the actual spacer in SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas and reduces the dispersion of flashover voltage, fluorination temperature has a significant effect on the enhancement of the flashover voltage, and the fluorination at higher temperatures can produce a larger improvement in the flashover performance. In addition, these fluorinated spacers can withstand heat treatment at 120 °C, with unchanged flashover performance. Infrared analysis and scanning electron microscopy observation show that the fluorination at different temperatures changes surface chemistry of the disk spacer substantially, forming the fluorinated layers with different thicknesses, compositions, and structures. Measurements of surface conductivity and surface potential decay consistently show that direct fluorination increases surface conduction of the spacer, and the fluorination at higher temperatures leads to a more significant increase in surface conduction. The improvement in dc flashover performance, caused by direct fluorination, is mainly attributed to the suppression of surface charge accumulation by the increase in surface conduction of the spacer.

X-ray nanoimaging of a transversely embedded carbon fiber in epoxy matrix under static and cyclic loads

The initial stage of fatigue failure has not been thoroughly clarified for carbon fiber reinforced plastics (CFRPs). Although the initiation of fatigue cracks has been regarded to be interfacial debonding between the carbon fiber and polymer matrix, their detection among numerous carbon fibers, whose diameter is only 7 µm, is extremely difficult. In this study, a single carbon fiber was transversely embedded in a dumbbell-shaped epoxy sample to focus on the interfacial debonding and was observed using synchrotron radiation (SR) X-ray computed tomography (CT). A tabletop fatigue testing machine driven by a piezoelectric actuator was developed to apply static and cyclic loads along the beamline. SR X-ray multiscale CT imaging was conducted by switching between an absorption-contrast projection method (micro-CT) and a phase-contrast imaging-type X-ray microscopic CT (nano-CT). The carbon fiber was entirely captured by micro-CT and then magnified at both ends on the free surfaces. Nano-CT clearly visualized the interfacial debonding under 30 MPa static tensile load and the implication of the coalescence of nano-voids along the interface under 50 MPa. Under cyclic loads, the interfacial debonding gradually progressed under a 8–40 MPa sinusoidal stress after 10,000 cycles, whereas it did not propagate under a stress below 30 MPa.

Thermal degradation behavior of 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide modified epoxy resin with liquid oxygen compatibility

The phosphorus-containing epoxy resin, 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB) modified epoxy resin, has been proved compatible to liquid oxygen, and it is prospective to be used as the matrix in composites for liquid oxygen tanks. It is considered that impact energy would be partially converted into heat and concentrated in small regions to form “hot spots”, which cause the degradation of polymer molecular chains to produce large quantities of free radicals and combustible products, thus initiating sensitive reactions of polymer with liquid oxygen. In the present paper, the temperature of the hot spot was estimated and the thermal degradation behavior of ODOPB modified epoxy resin was investigated simultaneously in gas and solid phases, and then on the base of that, the mechanism of its compatibility with liquid oxygen was proposed. The calculated results showed that the theoretical temperature of hot spots could be instantaneously raised up to 810 K (537 °C) under the impact energy of 98 J, which is sufficient to result in the degradation of epoxy resin. In the investigation of degraded gas products from epoxy resin samples, thermogravimetric-Fourier transform infrared spectroscopy-mass spectrometry (TG-FTIR-MS) results revealed that the incorporation of ODOPB effectively reduced the generation of free radicals and combustible volatiles. On the other hand, in the solid phase, the FTIR results demonstrated that the introduction of ODOPB could endow epoxy resin with preferable char-forming ability, which effectively hindered the diffusion of oxygen, flammable volatiles, and free radicals. The quenching effects of phosphorus-containing radicals and favorable char-forming ability of ODOPB played key roles in the transformation of epoxy resin from sensitive to compatible with liquid oxygen. This work provides a series of experimental evidence for revealing the mechanism of compatibility of ODOPB modified epoxy resin with liquid oxygen, which is important for the development of composites for liquid oxygen tanks.

Epoxy resin/graphene nanoplatelets composites applied to galvanized steel with outstanding microwave absorber performance

Abstract The necessity of new electromagnetic interference shielding materials has expanded scientific research, especially with regard to microwave frequency range (X-band). In this context, polymer-based composites with nanoparticles – such as graphene – are promising electromagnetic interference shielding materials. In this work, epoxy resin/graphene nanoplatelets (NPG) composites with 0.10, 0.25 and 0.5% w/w were developed and applied to galvanized steel substrates. Dynamic-mechanical tests showed that the addition of NGPs increased the resin rigidity due to molecular restrictions of the organic chains imposed by the NPG. With the increase of the NPG concentration to 0.50%, the impact strength and the adhesion of the composites significantly decreased due to the formation and propagation of large cracks, followed by delamination. The epoxy resin sample containing 0.25% NPG presented the best microwave absorber performance with an increase of 48% in the attenuated energy and 80% in the reflection loss, respectively. Moreover, this sample extended the microwave absorption range to 10 GHz.

Investigation of the effect of Graphene Nanoplatelet content on Flexural Behavior, Surface Roughness and Water Absorption of a Graphene Nanoplatelets Reinforced Epoxy Nanocomposites

In the present work, the effect of Graphene nanoPlatelets (GnP) content on the flexural, surface roughness, and water absorption behavior of a GnP reinforced epoxy composite was investigated. Different wt.% of GnP (0.25, 0.5, 0.75, and 1 wt.%) was added into the epoxy matrix through the sonication method followed by the ball milling. The results indicate a significant enhancement in the flexural properties of the epoxy nanocomposite with the addition of GnP in the epoxy matrix. The optimum enhancement in the properties was obtained at 0.25 wt.% GnP incorporated epoxy composites. The increase in flexural strength and flexural modulus results were noticed as 42.7% and 49.2% when compared with neat epoxy. The surface roughness value for the loading of 0.25 wt.% of GnP into the epoxy showed a drop of 48.7% when compared with that of the neat epoxy sample. The loading of 0.25 wt.% of GnP into the epoxy also reduces the water absorption from 0.125% for the neat epoxy sample to 0.067% for the composite sample. The Scanning Electron Microscope (SEM) images of the fractured surface (flexural samples) of the GnP embedded epoxy composites show the river like pattern, which is the result of the better dispersion of the GnP in the epoxy matrix and thus shows improvement in flexural behaviour of such composite materials.

Study on the species and stability of free radicals in bisphenol-A based epoxy resin induced by γ irradiation up to 1000 kGy

Epoxy resins are radiation-resistant polymers that are widely employed in aerospace and nuclear facilities; however, free radicals formed by ionizing radiation may lead to changes in their physicochemical properties. In this study, bisphenol-A based epoxy resin samples in both air and vacuum environments were subjected to gamma irradiation with doses up to 1000 kGy and the generated free radicals were investigated by electron spin resonance (ESR). Four radicals, namely cyclohexadienyl-type radicals, phenoxy radicals, peroxy radicals, and alkyl radicals, were formed in epoxy resin in both environments after gamma irradiation. The ESR spectra showed that the free radicals yield produced in the air was significantly larger than that produced in a vacuum. The radical concentration of the EP increased until a dose of 500 kGy and approached saturation upon increasing the dose to 1000 kGy. The ESR spectra of the EP annealed between 50 and 160 °C indicated that the radical concentration decreased with increasing temperature. The radicals in the EP samples irradiated in air disappeared at an annealing temperature of 130 °C, close to the glass transition temperature of the EP. The radicals in the EP irradiated in vacuum still remained even at 160 °C, which can be attributed to the stable phenoxy radicals. The free radical reaction mechanism was also developed for the bisphenol-A based EP irradiated by gamma-ray in different atmospheres.

Epoxy resin matrix integrating epoxy‐polydimethylsiloxane based self‐healing microcapsules: Healing efficiency, mechanical and thermal stability

AbstractEnvironmental factors such as climate change, temperature fluctuations, and mechanical forces hinder long‐term space, transportation, and research missions due to structural damage. We report an innovative system to overcome this problem. The self‐healing structure under examination is an epoxy as a polymeric matrix, which includes microcapsules embedded with epoxy‐polydimethylsiloxane (PDMS), as a healing agent, separately combined by microcapsules embedded with triethylenetetramine (TETA) as a hardener or curing agent. Scanning electron microscopy confirmed the presence and size of the microcapsules. It was shown that the rough appearance of microcapsules improves mechanical bonding. The diameter of microcapsules varied between 40 and 200 μm, with an average diameter of ~100 μm. The information of microcapsules and their structures were scrutinized through Fourier transformed infrared spectroscopy for chemical structure confirmation. It was determined that epoxy‐PDMS practical liquids have been effectively encapsulated. The thermal performance of the microcapsules was investigated utilizing thermogravimetric analysis. The results showed that the microcapsules have thermal stability up to 220°C without degradation and decomposition. Additionally, the flexural test was used to evaluate the samples manually scratched with blade and compared with the pure epoxy sample. The results showed the sample containing 15% microcapsules has 105% recovery efficiency after 55 h.