Mechanical Properties Of Epoxy Resin Research Articles

Effect of Free-Volume Hole Fraction on Dynamic Mechanical Properties of Epoxy Resins Investigated by Pressure–Volume–Temperature Technique

Dynamic mechanical analysis experiments were carried out to investigate the mechanical properties of four types of chemically different epoxy resins. Pressure-volume-temperature (PVT) experiments were performed to determine the free-volume hole fraction (hPVT) of each epoxy resin using the Simha-Somcynsky lattice-hole theory. Using the Williams-Landel-Ferry equation, the correlations between the relative hole fraction (1 - hPVTTr/hPVT, where hPVTTr is the hole fraction at a reference temperature Tr) and four typical parameters reflecting dynamic mechanical properties [storage modulus (E'), loss modulus (E″), damping factor (tanδ), and complex viscosity (|η*|)] were studied in the temperature range from Tg(PVT) (the glass transition temperature determined by PVT data) to Tg(PVT) + 100 °C. In the temperature range from Tg(Eonset') (temperature corresponding to the intersection of the two tangent fitting lines in the E'(T) curve indicating the glassy-state and glass-transition stages) to Tg(PVT) + 100 °C, the variations in the four dynamic mechanical parameters with a relative hole fraction could be separated into two distinct categories: (i) log[E'(T)] and log[|η*|(T)] decreased linearly to their minimum values and then remained nearly unchanged with increasing relative hole fraction, and (ii) log[E″(T)] and log[tanδ(T)] first increased monotonically to their maximum values and then decreased linearly with the increasing relative hole fraction. This study demonstrates that the PVT technique is a feasible and reliable experimental method to determine the hole fractions of thermoset polymers.

Kinetics of partially depolymerized lignin as co-curing agent for epoxy resin

Lignin, which is crosslinked by ether and carbon‑carbon linkages, is a highly branched polymer consisting of phenyl propane units. And owing to the abundant phenolic hydroxyl groups and its structural heterogeneous characteristics, lignosulfonate, considered as a renewable aromatic macropolymer, can be used as co-curing agent in EP thermoset systems. In this study, kinetics of lignosulfonate (LS) and partially depolymerized lignosulfonate (DLS) as co-curing agents for applications to EP thermoset were discussed with the differential scanning calorimetry (DSC) measurement. The activation energy (Ea) and dynamic modeling of curing reaction were obtained by the methods of non-isothermal kinetic analysis reported by Kissinger and Ozawa. The glass transition temperature (Tg) was determined by DSC and mechanical properties of epoxy resins were carried out using the Universal Testing Machine. The LS dropped the exothermic peak temperature and Ea of curing reaction of EP thermoset. Those of DLS were more active than the higher molecular weight lignosulfonate. The EP thermoset cured with DLS (EP-DLS) exhibited much higher reactivity, and the curing reaction could be occurred at lower temperature. The Tg of EP-DLS has risen by 10 °C compared with the case without lignosulfonate. The tensile strength, elongation at break and impact strength of EP-DLS rose by 28.7%, 52.5% and 53.5%, respectively, than those of the epoxy resin cured with LS (EP-LS).Molecular weight of lignosulfonate could be an important factor of the curing reaction of EP thermoset. The high performance EP thermoset could be obtained by partially depolymerized lignin as co-curing agents.

Effect of free-volume holes on static mechanical properties of epoxy resins studied by positron annihilation and PVT experiments

The tensile, flexural, and fracture toughness properties of seven chemically different amine-cured epoxy resins were studied. Positron annihilation lifetime and pressure–volume–temperature (PVT) experiments were performed on each epoxy resin to characterize the average size and fraction, respectively, of free-volume holes. A negative correlation between hole fraction and hole size was revealed for these chemically different epoxy resins. Better tensile and flexural mechanical properties (higher tensile modulus and lower tensile strain at break; higher flexural modulus, higher flexural strength, and lower flexural strain at break) were clearly observed for epoxy resins with smaller hole size and higher hole fraction. However, no clear relationship between fracture toughness and hole properties was found. The correlations between (tensile and flexural) static mechanical properties and hole properties for chemically different epoxy resins should provide guidance for further improvements in the mechanical properties of carbon-fiber-reinforced polymers.

Toughening Effect of Rodlike Cellulose Nanocrystals in Epoxy Adhesive

Epoxy structural adhesives have been used extensively in the automotive and aerospace industries to bond assembly parts. Much effort has been devoted to enhancing the mechanical properties of epoxy resin by incorporating fillers. Among a variety of fillers investigated for this purpose, nanocelluloses are regarded as a promising type of emerging green filler material because of their excellent mechanical and physicochemical properties. Indeed, nanocelluloses have been used as a filler for polymer nanocomposites. However, the toughening and reinforcing effects of nanocelluloses on rigid epoxy adhesives have not yet been fully revealed, particularly from the perspective of adhesive bonded joints. Here we report that epoxy adhesive containing cellulose nanocrystal (CNC) aggregates produced using a solvent-free ball milling method achieves drastically improved adhesive strength and fracture toughness compared with that of the reference adhesive without CNCs. The epoxy adhesive containing CNC aggregates exhibi...

Studies on the curing behavior, thermal, and mechanical properties of epoxy resin‐co‐amine‐functionalized lead phthalocyanine

AbstractA high performance copolymer was prepared by using epoxy (EP) resin as matrix and 3,10,17,24‐tetra‐aminoethoxy lead phthalocyanine (APbPc) as additive with dicyandiamide as curing agent. Fourier‐transform infrared spectroscopy, dynamic mechanical analysis (DMA), differential scanning calorimetric analysis (DSC), and thermogravimetric analysis (TGA) were used to study the curing behavior, curing kinetics, dynamic mechanical properties, impact and tensile strength, and thermal stability of EP/APbPc blends. The experimental results show that APbPc, as a synergistic curing agent, can effectively reduce the curing temperature of epoxy resin. The curing kinetics of the copolymer was investigated by non‐isothermal DSC to determine kinetic data and measurement of the activation energy. DMA, impact, and tensile strength tests proved that phthalocyanine can significantly improve the toughness and stiffness of epoxy resin. Highest values were seen on the 20 wt% loading of APbPc in the copolymers, energy storage modulus, and impact strength increased respectively 388.46 MPa and 3.6 kJ/m2, Tg decreased 19.46°C. TGA curves indicated that the cured copolymers also exhibit excellent thermal properties.

Mechanical properties of natural fiber/particulate reinforced epoxy composites – A review of the literature

Abstract Natural fibers are one of the abundant resources that exist in nature. They are easily decomposable, bio degradable, renewable and cost efficient. It can be extorted from various plant & animal resources. They are used as reinforcement material in polymers for the growth of natural-fiber composites. The mechanical properties of epoxy resin, reinforced with various natural fiber materials/agricultural by product particles are compared in the present study. This review intends to provide basic and background information of the natural fibers and their composites to trigger new research activities and facilitate development of new variety polymer composites.

Phosphorous-jointed epoxidized soybean oil and rice husk-based silica as the novel additives for improvement mechanical and flame retardant of epoxy resin

The combined effects of phosphorous-jointed epoxidized soybean oil and rice husk–based silica on the flammability and mechanical properties of epoxy resin were examined in detail. The chemical structures of the epoxidized soybean oil, phosphorous-jointed epoxidized soybean oil, and rice husk–based silica were confirmed using Fourier transform infrared spectroscopy and proton nuclear magnetic resonance. Many characteristics of the obtained composite materials were examined, such as the tensile properties, impact strength, flexural strength, critical stress intensity factor (KIC), dynamic mechanical analysis, and flammability. The incorporation of both 10 phr phosphorous-jointed epoxidized soybean oil and 20 phr rice husk–based silica into the epoxy resin yielded the optimum values of the flexural strength, tensile strength, impact strength, and KIC, with increases of 87.78%, 67.23%, 109.34%, and 111.32%, respectively, compared with pristine samples. The limiting oxygen index increased from 23.1% to 29.3%, the peak heat-release rate decreased by up to 37.2%, and the sample satisfied the UL94 V-0 rating.

Design of h-BN@boronate polymer core-shell nanoplates to simultaneously enhance the flame retardancy and mechanical properties of epoxy resin through the interficial regulation

In this report, we develop a simple and controllable coating strategy to decorate h-BN with a cyclotriphosphazene-containing boronate polymer (CPBP), thus forming h-BN-OH@CPBP core-shell nanoplates with different shell thicknesses. By introducing h-BN-OH@CPBPs into epoxy resin (EP), we have found that the thermal stability, flame retardant and mechanical performances of the as formed nanocomposites greatly relies on the CPBP shell thickness. Also, our design effectively improve the compatibility between h-BN nanoplates and polymer matrix and regulate the corresponding interface. The nanocomposites show the highest limiting oxygen index (LOI) of 28.7% and reach V-0 rating in the vertical burning test at loading amount of 2.5 wt%. Also the heat and smoke releases of nanocomposites during burning are significantly reduced. The flexural strengths and modulus of the nanocomposites are at most 42.12% and 27.85% higher than that of pure EP. The glass transition temperature and dynamic mechanical property of the nanocomposites are both improved.

Study of the effect of plasticizers and thermoplastics on the mechanical properties of epoxy and carbon fiber reinforced plastic (Review)

Increasing strength of epoxide resin (ER) and carbon fiber reinforced plastic (CFRP) is an aim up-to-date for many machinery sections: space, aviation, defense, automotive, and others. The aim is achieved via numerous methods of ER and carbon fiber reinforced plastic modifications. ER modifications is carried through injection of various chemical compounds. One of efficient modifications assumes introduction of plasticizers (tricresyl phosphate, oleic acid) or thermoplastics (polysulfone, polycarbonate, polystyrene, high impact polystyrene). The article contains experimental data of various types of modifiers influence on strength of ER and CFRP available in literature. The mechanism of modifying ER and CFRP with plasticizers and thermoplastics were analyzed. The introduction of plasticizers as ER modifiers leads to a twofold improvement in impact strength. The optimal input of plasticizers in ER is 15% and depends on the completeness of solubility in the binder, a further increase in the input of plasticizer leads to a decrease in the strength of the material. Modification of thermoplastics with CFRP can lead to an improvement in compression strength by 20% and impact strength by 2 times. With the introduction of thermoplastics over 20% in CFRP, strength indicators are reduced. The acquired data is necessary to elaborate domestic technology for production of high-impact CFRP.

Dielectric strength and mechanical properties of epoxy resin filled with self-propagating high-temperature synthesized Al2O3/SiC nanoparticles

In this study, the rice husk as a source of silica was used to synthesize the Al2O3/SiC composite via the self-propagation high-temperature synthesis (SHS) process. Then, the particle size of the synthesized product was reduced to the nanoscale using a planetary ball mill. Finally, different amounts (5, 10, and 15 wt.%) of Al2O3/SiC nanoparticles were incorporated into an epoxy resin in order to improve the mechanical properties and the dielectric strength of fabricated epoxy-based composites. The results indicated that the Al2O3/SiC composite was successfully synthesized by the SHS process from a mixture of the rice husk ash, Al, and carbon black powders as starting materials. The average size of the synthesized Al2O3/SiC particles decreased to 80 nm after 12-h ball milling. Also, the mechanical properties of the fabricated epoxy-based composite samples were improved with the addition of Al2O3/SiC nanoparticles in the investigated range in comparison with the pure epoxy sample. Additionally, the overall dielectric strength of the fabricated epoxy-based composites containing 5–15 wt.% of Al2O3/SiC nanoparticles was higher than that of the pure epoxy. These results were interpreted in terms of the synthesis mechanism of Al2O3/SiC composite via the SHS process, the rice husk ash structure, the interfacial bonding between the polymer chains and the surface of nanoparticles, and the insulation nature of the synthesized nanoparticles.

Pressure Field Assisted Polycondensation Nonaqueous Precipitation Synthesis of Mullite Whiskers and Their Application as Epoxy Resin Reinforcement.

Mullite whiskers were novelty prepared via pressure field assisted polycondensation nonaqueous precipitation method. The precipitate phase transition in heating process, phase compositions and microstructure of samples calcined at different temperatures, effect of pressure field on precursors polycondensation and AlF3 amount on sample morphology, the structure and the growth mechanism of whiskers were investigated. The results indicate that pressure field caused by kettle treatment promotes the polycondensation reaction between AlF3 and tetraethyl orthosilicate (TEOS), the excess aluminum fluoride coordinates with the precipitate skeleton of the =Al–O–Si≡, which brings about the low mullitization temperature (900 °C). The sample prepared with the optimal amount of aluminum fluoride (1.3 of the theoretical amount) calcined at 1100 °C presents high yield and aspect ratio (>15, 100 nm in diameter) of mullite whiskers. Growth of whiskers prepared via pressure field assisted polycondensation nonaqueous precipitation method is attributed to a vapor-solid (VS) mechanism with the inducement of screw. These mullite whiskers with the structure of multi-needle whiskers connected in the same center can be distributed evenly in epoxy resin, which greatly improves the mechanical properties of epoxy resin.

Synthesis of a novel graphene conjugated covalent organic framework nanohybrid for enhancing the flame retardancy and mechanical properties of epoxy resins through synergistic effect

A novel graphene conjugated covalent organic framework (AGO@COF) nanohybrid was synthesized by solvothermal method and used to enhance the flame retardancy and mechanical performances of epoxy resins (EP) through synergistic effect firstly. It is deduced from thermogravimetric analysis and cone calorimeter results that the obtained AGO@COF nanohybrid improves the flame retardancy of EP significantly. The time to peak heat release rate of EP increases by 17 s, the peak heat release rate and total heat release of EP decrease by 43.6 and 24.3% due to incorporation of 2 wt% AGO@COF. It is referred from thermogravimetric analysis-fourier transform infrared spectrometry results that the release of toxic gases and combustible volatiles during pyrolysis is also suppressed. As for mechanical performance of EP nanocomposites, the storage modulus of EP/2 wt% AGO@COF (34.66 GPa) in the glassy state increases by 23.8% compared with the neat epoxy (28.00 GPa). The possible mechanism for enhanced flame retardant and mechanical performances is proposed according to the test results. This work has opened up a new application for AGO@COF nanohybrid in the field of flame-retardant polymers.

Epoxidized soybean oil grafted with CTBN as a novel toughener for improving the fracture toughness and mechanical properties of epoxy resin

We prepared epoxidized soybean oil (ESO) grafted with carboxyl-terminated poly(acrylonitrile-co-butadiene) (CTBN) (ESO-g-CTBN) by a ring-opening reaction between the epoxide group and the carboxyl group. The structural features of the resulting product were determined using modern analytical techniques, such as Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (1H NMR) spectroscopy, and gel permeation chromatography (GPC). The ESO-g-CTBN was applied as a toughener for an epoxy resin-based composite that was fabricated by blending the epoxy resin with diethylenetriamine (DETA) as the curing agent. The main aim of this procedure is to simultaneously improve the mechanical properties and fracture toughness of a bisphenol A-based epoxy resin. When 15 phr of ESO-g-CTBN was added to the EP/DETA mixture, the resin fracture toughness (KIC) and tensile strength increased from 0.65 to 1.09 MPa m1/2 and from 34.42 to 42.55 MPa, respectively. The ESO-g-CTBN existed in the EP matrix as a separate phase and induced an increase in the KIC via stopping crack growth or changing the crack direction. The epoxydized soybean oil grafted with CTBN (ESO-g-CTBN) was synthesized from ring opening reaction between epoxide group and carboxyl group. The ESO-g-CTBN help to improve the fracture toughness of epoxy resin by the mechanism as shown in the figure.

A novel phosphorus-containing semi-aromatic polyester toward flame retardancy and enhanced mechanical properties of epoxy resin

Aiming to develop high performance flame-retardant epoxy resin (EP), a novel phosphorus-containing semi-aromatic polyester named poly[4,4′-bis(6-hydroxyhexyloxy)biphenyl 9,10-dihydro-10-[2,3-di(hydroxycarbonyl)propyl]-phosphaphenanthrene-10-oxide] (PBHDDP) was synthesized and employed as a multi-functional additive for EP with simultaneously flame retardation and mechanical enhancement. Appropriate thermodynamic compatibility between PBHDDP and the EP network made no phase separation occurred in the process of curing reaction. Compared with neat EP, the resultant EP thermoset containing barely 2.5 phr (2.44 wt%) of PBHDDP exhibited superior mechanical properties with 20.3% and 149% increase in tensile and impact strengths, respectively. Simultaneously, as increasing the content of PBHDDP, flame retardancy of the thermosets enhanced obviously as evidenced by the elevated anti-ignition and self-extinguishing performance, along with the reduced combustion rate and heat release. Whereas, obvious sacrifice of either transparency, glass transition temperature or thermal stability was absent. The exploration of this novel state-of-art that simultaneously improved the mechanical properties and flame retardancy of EP thermosets at a relatively low content of a single-component multi-functional additive provided a powerful basis for the technologies and potential industrial applications.

Influence of gamma irradiation on the molecular dynamics and mechanical properties of epoxy resin

The chemical structures, molecular dynamics and mechanical properties of diglycidyl ether of bisphenol-A (DGEBA)/triethylenetetramine (TETA) resins under gamma irradiation and physical ageing have been investigated. Fourier transform infrared (FTIR) spectroscopy results indicated that an amount of amines and oxidized carbonyl-containing products were generated during the irradiation process. The oxidized skin-like layer was confirmed via micro-FTIR, and the thickness of the oxidized layer increased linearly with irradiation dose. Dynamical mechanical analysis and broadband dielectric spectroscopy were used to analyze the molecular dynamics of DGEBA/TETA resins under different irradiation doses. Three distinct relaxations were observed for all polymers. The irradiation process resulted in an increase of local mobility corresponding to β and γ relaxations. The cooperative mobility associated with α relaxation was significantly shifted to lower temperature with irradiation. Meanwhile, α relaxation broadened considerably with increasing irradiation dose, demonstrating an increasingly heterogeneous environment. The gamma irradiation process resulted in an increase of threshold stress, but a decrease of strain at break, which was accounted for a destruction of the cross-linking networks associated with the increase of the heterogeneity environments. Meanwhile, the increase of the flexural and tensile modulus with the irradiation dose was due to the generation of the abundant hydrogen bonds acted as physical cross-linking points.

Influence of Naturally Occurring Fiber (Switchgrass) Reinforcement on the Mechanical Properties of Epoxy Resin

In the present era, lightweight composites are in great demand in various applications such as automobile, aerospace, as well as in recreational industries to enhance the efficiency and performance..

Significant enhancement of fracture toughness and mechanical properties of epoxy resin using CTBN‐grafted epoxidized linseed oil

ABSTRACTCarboxyl‐terminated poly(acrylonitrile‐co‐butadiene) (CTBN)‐grafted epoxidized linseed oil (ELO) (CTBN‐g‐ELO) was synthesized and used as an effective toughener to simultaneously enhance the mechanical properties and fracture toughness of epoxy resin (EP). The ELO was fabricated from linseed oil via epoxidation processing. The characteristics of the ELO and CTBN‐g‐ELO, such as the average molecular weight and chemical structure, were determined using gel permeation chromatography, proton nuclear magnetic resonance, and Fourier transform infrared spectroscopy. The effects of the CTBN‐g‐ELO loading on the characteristics of the EP were investigated in detail. The test results indicated that by adding 15 phr CTBN‐g‐ELO, the tensile strength, impact strength, and critical stress intensity factor (KIC) were significantly increased, by approximately 23.62, 91.8, and 33.8%, respectively, compared with pristine EP. The glass‐transition temperature (Tg) and storage modulus, which were examined via dynamic mechanical thermal analysis and differential scanning calorimetry, respectively, exhibited decreasing trends. Scanning electron microscopy revealed that the CTBN‐g‐ELO existed as spherical particles in the EP, helping to stop the crack growth and change the crack growth directions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2020,137, 48276.

Effects of carbonized particles on microstructure and mechanical properties of epoxy resin

In this study, mechanical properties of epoxy resin were enhanced using carbonized cow bone (CCB) particulates due to changes in its microstructure and reduction in polymer chains’ mobility. The CCB particles were dispersed in epoxy matrix at 40 wt%, 50 wt%, and 60 wt% concentrations for particles size of 150 μm, 300 μm, and 600 μm by mechanical stirring. Scanning electron microscope (SEM) was used in microstructural study of the CCB and the composites. This study was designed with taguchi in minitab software, and the responses of the mechanical properties were investigated based on interactions and effects of concentration and particles size on the properties. From the results obtained, the mechanical properties varied with particle size but were generally better between 40 and 50 wt% at 150 μm.

Mechanical properties improvement of epoxy composites by natural hy-droxyapatite from fish scales as a fillers

This study was carried out to prepare epoxy/ natural hydroxyapatite composite for potential biomedical application. Natural hydroxyapatite (nHAp) powder was extracted from Tilapia fish scales via the thermal method. The natural hydroxyapatite was milled for 48 hours and dried by spray method. The nHAp particle size was determined using mastersizer 2000 particle size analyser and the chemical structure was confirmed using (XRD) and FTIR analysis. The particle size of nHAp was identified to be between 1 and 10 microns. Mechanical properties of epoxy/ natural hydroxyapatite were investigated by using impact and flexural test. The highest flexural strength of epoxy/nHAp composite was recorded when the nHAp filler was 10 wt% which is 77 % increment as compared to epoxy alone. The impact strength was increased up to two-fold as compared to neat epoxy. The scanning electron micrograph (SEM) and EDX analysis showed uniform dispersion of nHAp particles within the epoxy matrix for the composites with 10 wt% filler loading.

The effect of adding CoFe2O4–CdS nanoparticles on the mechanical properties of rice husk ash epoxy composite: an experimental approach

In this paper, first, cobalt ferrite and cadmium sulfide nanostructures were synthesized through precipitation method. Thereafter, CoFe2O4 nanocomposite as core–shell structure with magnetic cobalt ferrite core and cadmium sulfide shell was synthesized through chemical method. Afterward, the effect of the synthesized nanocomposites along with rice husk ash microparticles (RHAMPs) on the mechanical properties of epoxy resin (EP) has been investigated. Epoxy resin (Epikote 828) and polyamine hardener have been used to prepare the nanocomposite samples. CoFe2O4–CdS nanocomposites with weight percentages of 0, 0.5, 1, and 2% mixed with 3% of rice husk ash microparticles (RHAMPs) were distributed inside the epoxy resin (EP). The prepared products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and alternating force gradient magnetometer (AFGM). The mechanical properties of the epoxy nanocomposites/RHAMPs were also determined using uniaxial tensile standard and three-point bending tests. The results associated with the mechanical tests also showed improvement in tensile modulus, bending modulus, and strength of epoxy resin by adding nanoparticles along with rice husk ash to the epoxy matrix.