Neat Resin Research Articles

Improved Melt Processabilities of Thermosetting Polyimide Matrix Resins for High Temperature Carbon Fiber Composite Applications.

With the goal of improving processability of imide oligomers and achieving of high temperature carbon fiber composite, a series of Thermosetting Matrix Resin solutions (TMR) were prepared by polycondensation of aromatic diamine (3,4′-oxybisbenzenamine, 3,4-ODA) and diester of biphenylene diacid (BPDE) using monoester of 4-phenylethynylphthalic acid (PEPE) as end-capping agent in ethyl alcohol as solvent to afford phenylethynyl-endcapped poly(amic ester) resins with calculated molecular weight (Calc’d Mw) of 1500–10,000. Meanwhile, a series of reactive diluent solutions (RDm) with Calc’d Mw of 600–2100 were also prepared derived from aromatic diamine (4,4′-oxybisbenzenamine, 4,4-ODA), diester of asymmetrical biphenylene diacid (α-BPDE) and monoester of 4-phenylethynylphthalic acid (PEPE) in ethyl alcohol. Then, the TMR solution was mixed with the RDm solution at different weight ratios to afford a series of A-staged thermosetting blend resin (TMR/RDm) solutions for carbon fiber composites. Experimental results demonstrated that the thermosetting blend resins exhibited improved melt processability and excellent thermal stability. After being thermally treated at 200 °C/1 h, the B-staged TMR/RDm showed very low melt viscosities and wider processing window. The minimum melt viscosities of ≤50 Pa·s was measured at ≤368 °C and the temperature scale at melt viscosities of ≤100 Pa·s were detected at 310–390 °C, respectively. The thermally cured neat resins at 380 °C/2 h showed a great combination of mechanical and thermal properties, including tensile strength of 84.0 MPa, elongation at breakage of 4.1%, and glass transition temperature (Tg) of 423 °C, successively. The carbon fiber reinforced polyimide composite processed by autoclave technique exhibited excellent mechanical properties both at room temperature and 370 °C. This study paved the way for the development of high-temperature resistant carbon fiber resin composites for use in complicated aeronautical structures.

Processing and properties of low-temperature cure carbon fiber-reinforced bismaleimide composite

Bismaleimide (BMI) resins are used in carbon fiber reinforced composites for high-temperature applications. Conventional BMI resins require high cure and post-cure processing temperatures, which limit fabrication methods and contribute to residual stress and microcracking. Recently, BMIs with lower cure temperatures have been developed; however, little data on the properties of low-temperature cure carbon/BMI composites are available in the open literature. In this study, processing and properties of a low-temperature cure BMI resin system, referred to here as BMI-2, were evaluated. Along with evaluation of neat resin properties, multi-directional woven carbon fiber reinforced BMI-2 composite laminates were fabricated by an out-of-autoclave, vacuum-bag-only resin infusion method. New data on the mechanical, thermal, and moisture absorption properties are presented. It was found that the resin infusion method produced laminates with fiber volume fraction of approximately 55% and immeasurably low void content. BMI-2 was found to attain a degree of cure of 96% and glass transition temperature of 366°C following a 163°C cure cycle. Cured laminates did not suffer from process-induced cracking at the inter- or intra-laminar levels. Tensile strength and modulus of quasi-isotropic specimens with woven AS4 carbon fiber were 443 MPa and 47.6 GPa, respectively, and failure under quasi-static tension occurred by delamination. Compression strength was stable across a wide temperature range, with quasi-isotropic specimens retaining 60% of their room temperature compression strength at 260°C. Equilibrium moisture content of composite specimens was 1.2% by weight.

Tribological and thermal characteristics of an epoxy-based composite containing polyaryletherketone

Current research work focuses on the tribological and thermal properties of epoxy resin matrix composites, which were modified by polyaryletherketone (PAEK-C). The results of the infrared spectra and morphologies of fracture surfaces experiments corroborate the successful synthesis of the materials. From the tribological experiments, it can be known that when the mass fraction of PAEK-C was 10 phr., the corresponding composite exhibited the outstanding wear performances, which could be ascribed to the higher H/E ratio. Based on the results of tribological experiments, it could be obtained that the main wear mechanism is governed by combination of the plastic deformation, creation of vertical cracks in the sliding track, separation of debris, and material waves due to adhesions. In addition, the glass transition temperatures ( Tg) and heat-resistance index ( THRI) of the PAEK-C/epoxy resin higher than those of pure epoxy resin matrix, respectively. Furthermore, when the mass fraction of PAEK-C increased, the heat resistance index ( THRI) of the corresponding composite is 196.3°C, which is higher than that of neat epoxy resin (180.9°C). Also, according to the results of thermogravimetric analysis experiments, it could conclude that the activation energy of the curing process is situated in the range of 150–160 kJ mol−1 depending on the mass fraction of epoxy resins.

Effect of expanded glass particle size on compressive properties of vinyl ester syntactic foams

AbstractThe most common fillers for syntactic foam development are glass microballoons or fly ash cenospheres. However, the need for improved properties and reduced cost requires exploring other possibilities. In this work, syntactic foams of vinyl ester resin reinforced with expanded glass particles (EG) were fabricated and compressive properties of the composites were studied. The foam EGS was reinforced with smaller particles of size 0.04–0.125 mm in 15, 30, and 45 vol.% and EGL had larger particles of size 0.25–0.5 mm in 15 and 30 vol.%. Compression testing reveals that 45 vol.% smaller particles enhance the modulus of the EGS foam by up to 48% with a 3.4% reduction in yield strength compared to neat resin. Strain rate sensitivity was observed in both the modulus and yield strength values for all composites. Composite EGS with 15 and 30 vol.% filler showed better strength and modulus than the neat resin at 0.01 s−1 strain rate, which is an overall improvement in the material. When compared with the literature data, the foams made in the present work have the highest compressive strength and modulus for the same density.

On the Mechanism of the Steady-State Gamma Radiolysis-Induced Scissions of the Phenyl-Vinyl Polyester-Based Resins.

The major societal problem of polymeric waste necessitates new approaches to break down especially challenging discarded waste streams. Gamma radiation was utilized in conjunction with varying solvent environments in an attempt to discern the efficacy of radiolysis as a tool for the deliberate degradation of model network polyesters. Our EPR results demonstrated that gamma radiolysis of neat resin and in the presence of four widely used solvents induces glycosidic scissions on the backbone of the polyester chains. EPR results clearly show the formation of alkoxy radicals and C-centered radicals as primary intermediate radiolytic products. Despite the protective role of the phenyl groups on the backbone of the radiation-induced polyester chains, the radiolytic-glycosidic scissions predominate. Among the following three solvents used in this study (water, isopropyl alcohol, and dichloromethane), the highest radiolytic yield of glycosidic scission was achieved using water. The •OH radicals produced in the radiolysis of phenyl unsaturated polyester aqueous suspensions very rapidly abstract H atoms from the methylene group, which is followed by a very rapid glycosidic scission. The lowest glycosidic yield was found in the dichloromethane solutions of these polyester resins due to scavenging by the fast electron capture reactions.

Βio-Based Epoxy/Amine Reinforced with Reduced Graphene Oxide (rGO) or GLYMO-rGO: Study of Curing Kinetics, Mechanical Properties, Lamination and Bonding Performance.

In this work, we report the synthesis and study of nanocomposites with a biobased epoxy/amine (Epilok 60-600G/Curamine 30-952) matrix reinforced with reduced graphene oxide (rGO) or functionalised with 3-glycidoxypropyltrimethoxysilane (GLYMO-rGO). These graphene related materials (GRMs) were first dispersed into a Curamine hardener using bath ultrasonication, followed by the addition of epoxy resin. Curing kinetics were studied by DSC under non-isothermal and isothermal conditions. The addition of 1.5 wt% of GLYMO-rGO into the epoxy matrix was found to increase the degree of cure by up to 12% and glass transition temperature by 14 °C. Mechanical testing showed that the addition of 0.05 wt% GLYMO-rGO improves Young’s modulus and tensile strength by 60% and 16%, respectively, compared to neat epoxy. Carbon fibre reinforced polymer (CFRP) laminates were prepared via hand lay up, using the nanocomposite system GRM/Epilok/Curamine as matrix, and were cut as CFRP adherents for lap shear joints. GRM/Epilok/Curamine was also used as adhesive to bond CFRP/CFRP and CFRP/aluminium adherents. The addition of 0.1 wt% GLYMO-rGO into the adhesive and CRFP adherents showed improved lap shear strength by 23.6% compared to neat resin, while in the case of CFRP/Aluminium joints the increase was 21.2%.

Hydrophilic and hydrophobic silica‐based nanocomposites of chemically recyclable thermoset

AbstractIn this study we evaluated the effect of the addition of hydrophilic and hydrophobic silica nanoparticles on the electrical properties of polyhexahydro‐s‐triazine (PHT), a new chemically recyclable thermoset produced from 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane and paraformaldehyde. Chemical recycling as well as thermal and mechanical properties were also investigated. Regarding the electrical properties, electrical conductivity near 10−8 S m−1 at 100 Hz and dielectric constant close to 4.00 at 1 kHz were observed for neat PHT polymer. Better results for electrical properties were observed with the addition of hydrophobic silica nanoparticles. After the addition of the highest concentration (4.5 wt%) the dielectric constant increased about 8% at 1 kHz. Concerning the thermal properties, PHT polymer exhibited a glass transition temperature (Tg) of 185 °C. The addition of hydrophilic or hydrophobic nanoparticles into the neat matrix did not lead to significant variations of thermal properties, but Tg values were decreased compared to the neat resin. Additionally, for mechanical properties, values of reduced modulus (4.58 GPa) and nanohardness (0.38 GPa) were observed. Besides, for all nanocomposites, there was an increase in the reduced modulus for all samples studied. Finally, the chemical recycling of both neat polymer and all nanocomposites after acid treatment was successfully characterized via NMR analysis. © 2021 Society of Industrial Chemistry.

Experimental investigation of epoxy matrix and pine sawdust reinforced wood-polymer composite materials

Mechanical, thermal, and water absorption properties of the composites have been studied as a function of sawdust content, using different weight percentage. The characteristics properties of the composites were studied using differential scanning calorimetry and Fourier-transform infrared spectroscopy. Field emission scanning electron microscopy was used to understand the interfacial bonding. The obtained results showed that the 15 wt% composites exhibited the highest tensile strength (7.5 MPa) and flexural strength (8.9 MPa) compared with the 5 wt%, 30 wt%, 40 wt%, and 50 wt% composites. A good interfacial combination was formed between 15 wt% of sawdust and epoxy resin. In terms of the tensile and flexural strength, the differential scanning calorimetry analysis confirmed that matrix modification could improve the mechanical properties and thermal stability of the composites compared to neat resin. The Fourier-transform infrared spectroscopy spectrum showed the presence of functional groups pertaining to composites. The absorption data of the composite showed that the water uptake increased as the amount of sawdust in the composite increased. The 5 wt%, 15 wt%, 30 wt%, and 40 wt% sawdust composites also displayed less water absorption behavior (1.534%, 1.871%, 2.492%, and 4.127%, respectively) compared to the 50 wt% composite.

Phosphorylated Salicylic Acid as Flame Retardant in Epoxy Resins and Composites

A novel, versatile flame retardant substructure based on phosphorylated salicylic acid (SCP) is described and used in the synthesis of new flame retardants for HexFlow® RTM6, a high-performance epoxy resin used in resin transfer molding processes as composite matrix. The starting material salicylic acid can be obtained from natural sources. SCP as reactive phosphorus chloride is converted with a novolak, a novolak containing 9, 10-dihydro-9- oxa-10-phospha-phenanthrene-10-oxide (DOPO) substituents or DOPO-hydroquinone to flame retardants with sufficient thermal stability and high char yield. Additionally, these flame retardants are soluble in the resin as well as react into the epoxy network. The determined thermal stability and glass transition temperatures of flame retarded neat resin samples as well as the interlaminar shear strength of corresponding carbon fiber reinforced composite materials showed the applicability of these flame retardants. Neat resin samples and composites were tested for their flammability by UL94 and/or flame-retardant performance by cone calorimetry. All tested flame retardants decrease the peak of heat release rate by up to 54% for neat resin samples. A combination of DOPO and SCP in one flame retardant shows synergistic effects in char formation and the mode of action adapts to neat resin or fiber-reinforced samples, so there is efficient flame retardancy in both cases. Therefore, a tailoring of SCP based flame retardants is possible. Additionally, these flame retardants efficiently reduce fiber degradation during combustion of carbon fiber-reinforced epoxy resins as observed by scanning electron microscopy and energy dispersive X-ray spectroscopy.

Evaluation of Mechanical Properties of Nanofillers Glass Fiber Reinforced Composites

The usage of Glass Fibre Reinforced Polymer (GFRP) composites is gradually increasing day by day because of its unique properties over conventional metals. As weight to strength ratio is very high for GFRP materials, these are widely used in Aerospace, Marine, Automotive, Locomotive etc. industries. In this work, specimens were made by Nanosilica as a nanofiller, Epoxy as a resin and Glass fibre as reinforcement using hand lay-up process. The nano silica has dispersed into epoxy by three levels i.e, 1,2 and 3%. The addition of nanosillica with neat resin has enhanced the ultimate tensile strength by 7.02% and impact strength by 38%.

Fatigue damage propagation and creep behavior on sisal/epoxy composites

The lack of knowledge about the behavior under creep and fatigue limits the use of polymeric composites reinforced with natural fibers. Thus, this work assessed the behavior of epoxy composites reinforced with sisal fibers under tensile, fatigue, and creep tests. Also, thermogravimetry and scanning electron microscopy assessed the sodium hydroxide (NaOH) treatment efficiency in sisal fibers. Further, differential scanning calorimetry determined the degree of cure of the composites, and stereomicroscopy allowed the evaluation of the surface’s fracture. As a result, the tensile strength of the composite was 1.4 times the value of neat epoxy resin after 100,000 cycles in the fatigue test. Moreover, when loaded with 20% of the maximum tensile strength, it is estimated that the composite resists 200,000 h without rupturing by creep. To conclude, the efficient adhesion between sisal fibers and epoxy obtained by NaOH treatment allowed good mechanical behavior to the epoxy composite.

Processing, thermal and mechanical properties of composite laminates with natural fibers prepregs

This work manufactured prepregs by impregnating discontinuous curaua fibers with B-stage epoxy resin. The prepreg layers were then stacked to produce laminates by hot compression. Alkaline treatments were previously applied to the curaua fibers to improve their interface with the polymer matrix. Then, the prepregs and the final composites were studied regarding their thermal, dynamic mechanical, mechanical, and morphological behavior. The treatments promoted defibrillation by removing lignin and hemicellulose from the fibers, which allowed better impregnation of the treated fibers with epoxy resin. In general, laminates that used treated fibers exhibited the largest storage modulus in the glassy region. The mechanical results showed the laminates produced with treated fibers prepregs presented a highest tensile and flexural resistance than those manufactured with untreated fibers and neat epoxy resin. The NaOH-treated curaua/epoxy laminate exhibited high tensile strength (56.2 MPa) and modulus (3.3 GPa). Overall, fracture morphology indicated better fiber adhesion for the treated fiber composites. The results demonstrate that natural fibers prepregs can be successfully produced and present proper physical and mechanical behavior in components.

Analysis of mechanical properties of pineapple leaf/glass fiber-vinyl ester hybrid composite

Pineapple and glass fibers reinforced vinyl ester hybrid composites were prepared in both the dispersed and skin-core types at 40 wt% using hand lay-up technique, and their mechanical properties were studied based on the content of glass fibers (5, 11, 16, and 19 wt%). The effects of the glass fiber addition on mechanical properties were discussed with varying the fiber content by keeping the overall fiber content as constant. The fractographic studies on the fracture surface of tested composite specimens were examined by using scanning electron microscopy. The results were compared with the neat resin samples and pineapple-alone composites. The results show that the mechanical properties of composites increased with an increase in glass fiber addition. Hybrid composite having the pineapple fiber of 21 wt% and the glass fiber 19 wt% show the maximum level of mechanical properties in both types of hybrid composites. The dispersed type hybrid composites show inferior performance than the skin-core type hybrid composites. The theoretical model was used to predict and compare the experimental results and was also found to be in good agreement.

UV durability assessment of a thermoplastic epoxy-based hybrid composite rod for structural reinforcement and retrofitting

Recently, a hybrid composite cable has been developed for external strengthening of structures in seismically active zones, containing a novel thermoplastic epoxy matrix. While this resin has advantageous properties such as processability, the UV resistance for outdoor service conditions has not been studied. This paper examines the accelerated UV degradation behavior by using a xenon arc source, and reporting the changes in chemical structure and mechanical properties of both the resin and FRP rods. While the neat resin is susceptible to photo-oxidation and a sharp decline in strength, the hybrid FRP shows no significant changes in tensile properties even after nearly 2000 MJ/m2 of UV radiation (equivalent to seven years in Florida, USA). This was attributed to the fiber-dominant nature of unidirectional composites, further supported by a Curtin-type analytical model.

Cure mechanism and kinetic prediction of biobased glass/polyfurfuryl alcohol prepreg by model-free kinetics

This paper explains the cure reaction mechanisms of a novel bio-based glass/Polyfurfuryl prepreg using an experimental and numerical approach. It suggests optimized parameters of rapid curing for isothermal curing conditions. Dynamic scanning calorimetry (DSC) under non-isothermal conditions was used to determine parameters for the two model-free kinetic methods Friedman and Ozawa Flynn Wall. The average activation energy (88.9 ± 4.9 kJ/mol) was found to be higher than that reported for neat resin in literature. The validated models were used to gain insight into reaction mechanisms and were used to predict the evolution of reaction time under isothermal conditions for the PFA prepreg. This suggested that the curing time can be reduced to half by rapidly heating and maintaining isothermal conditions at 160°C, which provides faster curing using hot-press. In addition, dynamic mechanical analysis (DMA) was carried out to compare the manufacturer recommended cure cycle with the rapid cycle suggested.

Influence of Cenosphere on Compression After Impact Strength of Glass Epoxy Laminates

Under controlled lab settings, two distinct laminates, one containing cenosphere and the other with neat resin, were evaluated for impact strength using a Fractovis impact machine, compression, and Compression After Impact (CAI) strengths through Tinus Olsen UTM. The GFRP laminates were prepared with 16 layers of glass fiber combined with epoxy resin reinforced Cenospheres at concentrations of 1, 3 and 5 wt%, according to ASTM specifications. The dominant failure mode controlling the specimen’s compression ultimate load resistance, and other failure modes of impacted specimens such like fiber pull-out and debonding, were found to be the effects of delamination using coupled coustic emission (AE) monitoring and compression tests. On specimens with a 3 wt% filler additive, there was a noticeable increase in strength. Both impacted and non-impacted samples exhibited significant compression ultimate load resistances, with the 3 wt% filler impregnated specimen having the maximum.

The Influence of Sonication Processing Conditions on Electrical and Mechanical Properties of Single and Hybrid Epoxy Nanocomposites Filled with Carbon Nanoparticles.

Graphene nanoplatelets (GNP) and carbon nanotubes (CNT) are used to enhance electrical and mechanical properties of epoxy-based nanocomposites. Despite the evidence of synergetic effects in the hybrid GNP-CNT-epoxy system, there is still a lack of studies that focus on the influence of different dispersion methods on the final properties of these ternary systems. In the present work, direct and indirect ultrasonication methods were used to prepare single- and hybrid-filled GNP-CNT-epoxy nanocomposites, varying the amplitude and time of sonication in order to investigate their effect on electrical and thermomechanical properties. Impedance spectroscopy was combined with rheology and electron microscopy to show that high-power direct sonication tends to degrade electrical conductivity in GNP-CNT-epoxy nanocomposites due to damage caused in the nanoparticles. CNT-filled samples were mostly benefitted by low-power direct sonication, achieving an electrical conductivity of 1.3 × 10−3 S·m−1 at 0.25 wt.% loading, while indirect sonication was not able to properly disperse the CNTs and led to a conductivity of 1.6 ± 1.3 × 10−5. Conversely, specimens filled with 2.5 wt. % of GNP and processed by indirect sonication displayed an electrical conductivity that is up to 4 orders of magnitude higher than when processed by direct sonication, achieving 5.6 × 10−7 S·m−1. The introduction of GNP flakes improved the dispersion state and conductivity in hybrid specimens processed by indirect sonication, but at the same time impaired these properties for high-power direct sonication. It is argued that this contradictory effect is caused by a selective localization of shorter CNTs onto GNPs due to strong π-π interactions when direct sonication is used. Dynamic mechanical analysis showed that the addition of nanofillers improved epoxy’s storage modulus by up to 84%, but this property is mostly insensitive to the different processing parameters. Decrease in crosslinking degree and presence of residual solvent confirmed by Fourier-transform infrared spectroscopy, however, diminished the glass transition temperature of the nanocomposites by up to 40% when compared to the neat resin due to plasticization effects.

Facile construction of lamellar-like phosphorus-based triazole-zinc complex for high-performance epoxy resins

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-94V-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.

Probing the charge injection and dissipation in graphene oxide–epoxy composite

The inorganic filler can modify the electrical and dielectric properties of polymeric composites. However, it is challenging to understand the local charge injection and dissipation in composites through traditional characterization at nanoscale. In this work, we provide a potential mapping of the charge injection and dissipation in the local area of graphene oxide/epoxy resin (GO/EP) composite under various biases by Kelvin probe force microscopy (KPFM) with high spatial resolution. Thus, an improved KPFM experimental setup is used to inject charges at the fixed point to demonstrate surface charge dissipation around the interface between GO and EP. It is found that the charge is more easily injected into the GO/EP nanocomposites and dissipates more quickly in nanocomposite than in neat epoxy resins. Meanwhile, the electrons diffuse more rapidly than holes in pure EP and nanocomposites. The faster charge injection and dissipation of GO/EP composite are ascribed to the filler of GO which has much higher conductivity than that of neat epoxy. This work offers significant insights into the understanding of charge injection and dissipation in dielectric composites.

Effect of ZrO2 Nanofiller on the Physical Properties of Epoxy Composites: Mechanical, Thermal and Dielectric

Abstract: In this present work, Zirconia nanoparticles were prepared by precipitation method, Zirconium Oxychloride (ZrOCl2.8H2O) and ammonia (NH3) as starting materials. The synthesized Zirconia nanoparticles were characterized by XRD and the grain size in nanoscale was confirmed. The sheets of neat epoxy resin and epoxy with addition of ZrO2 nanoparticles are primed by solution casting method. The structures of epoxy polymer and hardener were found out using FTIR analysis. The thermal properties were analyzed using Thermo Gravimetric Analysis (TGA) and Differential Thermal Analysis (DTA). Thermo gravimetric analysis has been employed to investigate the thermal characteristics and their mode of thermal degradation. Differential thermal analysis has been used to determine the glass transition temperature of epoxy nanocomposites. The mechanical properties like tensile and flexural studies were analyzed and thus influences of nanofiller loading on these parameters were found to be very low. Keywords: Epoxy, ZrO2 nanoparticles, Nanocomposites, Thermal stability, Dielectric properties, Tensile strength, Flexural strength.