Epoxy Hardener Research Articles

EVALUATION OF THE CURING KINETICS OF A POLYMER MATRIX COMPOSITE USING A SENSOR CONTAINING AN ELECTRICALLY CONDUCTIVE FILLER

In this work, the kinetics of the curing of fabric GFRP was carried out by measuring the parameters of its electrical conductivity. A compound of epoxy resin (ED-20), plasticizer (DBF) and hardener (PEPA) with the addition of finely milled graphite (FMG) was used as a matrix. To en-sure high-quality mixing of FMG in epoxy resin, a planetary mixer was used. Plain weave glass tape 0.2 mm thick with two woven wires was impregnated with a matrix compound. This tape was placed onto a beam 4 mm thick made of typical GFRP as an external electrically conductive functional sensor (FS). During curing at room temperature, periodic measurements of the electrical conductivity of the FS and the stiffness of the beam with FS in three-point bending were carried out. The amount of FMG into the matrix compound was below the percolation threshold; there-fore, electrical measurements of FS required alternating current. The dependence of the imped-ance on the current frequency (from 10 Hz to 1 MHz) was recorded. Comparison of the change in FS electrical impedance with the change in the beam stiffness during the curing showed their close correlation. The proposed method of measuring the FS impedance can be used to assess the degree of curing of the polymer matrix in critical large-sized composite products during the manufacturing process.

Effect of silane‐modified SiO2@Ce3+ nanoparticles on the mechanical property and anti‐corrosion for steel of the epoxy coating

AbstractIn this work, nano‐SiO2 have been used as nanocarriers for loading Ce(III) ions (SiO2@Ce3+). After loading, silane coupling agent has been used to modify these nanocarriers (m‐SiO2@Ce3+). Then, these modified nanocarriers were added as green inhibitors into the inner epoxy coating matrix, which was based on the epoxy resin (DER 671X75) and hardener (polyamide Epicure 3125). Morphological study by FE‐SEM showed that the spherical nanoparticles (m‐SiO2@Ce3+) were in size < 100 nm and dispersed rather homogeneously into the polyme matrix. In addition, the addition of nanocarriers at a concentration of 2.5 wt.% into the epoxy polymer matrix enhanced significantly its mechanical property. Besides, the anticorrosion performance of the epoxy polymer matrix due to the presence of m‐SiO2@Ce3+ (at 2.5 wt. %) was proved by EIS analysis and salt spray tests.

Effect of Synthetic Low-Odor Thiol-Based Hardeners Containing Hydroxyl and Methyl Groups on the Curing Behavior, Thermal, and Mechanical Properties of Epoxy Resins

A novel thiol-functionalized polysilsesqioxane containing hydroxyl and methyl groups was synthesized using a simple acid-catalyzed sol–gel method to develop an epoxy hardener with low odor, low volatile organic compound (VOC) emissions, and fast curing at low temperatures. The synthesized thiol-based hardeners were characterized using Fourier transform infrared spectroscopy, nuclear magnetic resonance, thermogravimetric analysis (TGA), and gel permeation chromatography and compared with commercially available hardeners in terms of odor intensity and VOC emissions using the air dilution olfaction method and VOC analysis. The curing behavior and thermal and mechanical properties of the epoxy compounds prepared with the synthesized thiol-based hardeners were also evaluated. The results showed that synthetic thiol-based hardeners containing methyl and hydroxyl groups initiated the curing reaction of epoxy compounds at 53 °C and 45 °C, respectively. In contrast, commercial thiol-based hardeners initiated the curing reaction at 67 °C. Additionally, epoxy compounds with methyl-containing synthetic thiol-based hardeners exhibited higher TGA at a 5% weight loss temperature (>50 °C) and lap shear strength (20%) than those of the epoxy compounds with commercial thiol-based hardeners.

Influence of addition of Al2O3 and SiC on tensile and flexural characteristics of epoxy/glass fiber hybrid polymer composite

In today's world, hybrid polymer matrix composite is an extremely important component in manufacturing automobiles, aircraft, and sporting goods. This research paper describes the development of epoxy-based hybrid polymer composites (HPC) through a hand-lay technique. Hybrid polymer composite consists of Epoxy resin, E-glass fiber as reinforced materials, and Al2O3/SiC as filler material. The fabrication of a hybrid polymer composite with an equal proportion of Al2O3/SiC during which epoxy resin and hardener are mixed in 10:1 proportion. The tensile and flexural strength were investigated in this study. Experiment findings show that composite with four wt.% of Al2O3/SiC has optimum tensile and flexural behavior. It has an ultimate tensile strength of 170.84 MPa and flexural strength of 162.56 MPa, which is desirable in applications where epoxy-based composites are typically utilized, such as in tennis and badminton rackets.

Are ionic liquids effective curing agents for preparing epoxy adhesives?

This work compares for the first time the efficacy of using different ionic liquids (ILs) as epoxy hardeners in epoxy-based adhesives. Several phosphonium and imidazolium-based ionic liquids were tested as epoxy hardeners, and the thermal and mechanical properties and the lap shear strength of the cured epoxy resins were studied at different IL concentrations. Both the chemical structure and the concentration of ILs were found to impact the final properties of the epoxy resin, but among the ten different ILs studied, three of them cured the epoxy resin effectively and produced similar and even better mechanical properties and lap shear strength than those obtained with traditional amine-based curing agents. These results constitute an important step towards sustainability thanks to the non-volatility of ILs and the significantly lower amount needed for effectively curing epoxy resins.

Understanding cure and interphase effects in functionalized graphene‐epoxy nanocomposites

AbstractAgglomerations effects of graphene‐based nanofillers are often reported in the literature to be the main reason on the deterioration of the mechanical properties, especially at high filler loadings. In our study, we focused on the correlated effects of plasma‐treated graphene nanofillers on the curing reaction and mechanical properties of an epoxy matrix. Specifically, we explored the effect of dispersion state, planar size, filler content, surface functionalization and stoichiometric ratio on the epoxy curing process. The surface of the treated graphene nanofillers were studied in detail by X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy and X‐ray diffraction (XRD). The results indicated greater presence of oxygen containing groups with the crystallinity to be unaffected after the plasma process. Dynamic Mechanical Analysis (DMA) was used to assess the changes in both the Tg and the mechanical properties of graphene‐epoxy nanocomposites. Rheological and microscopic data showed that a well‐dispersed material was achieved at high filler loadings with the use of calendaring and plasma functionalization. Although, a well‐dispersed material was achieved on the bulk composite, no further mechanical reinforcement was observed at high filler loadings. The adsorption of epoxy groups onto the graphene nanofillers' surface, leading to a stoichiometric imbalance between the epoxy chains and hardener molecules, was proposed to explain the results.

Influence of Waste Filler on the Mechanical Properties and Microstructure of Epoxy Mortar

This paper presents experimental investigations on epoxy mortar produced using industrial wastes. In some recent studies, coal bottom ash and polyethylene terephthalate (PET) waste have been chosen as a filler to replace sand, and fly ash and silica fume have been chosen as micro fillers for epoxy mortar production; enhanced results in terms of compressive and tensile strengths and durability have been achieved. However, these approaches failed to boost the strength and durability compared to the epoxy steel slag, epoxy sand, epoxy marble dust, and epoxy polyvinyl chloride (PVC) waste. This present research work has investigated the influence of waste filler on the mechanical properties and microstructure of epoxy mortar, produced by using sand and industrial wastes, i.e., steel slag, marble dust, and polyvinyl chloride waste. Based on the composition ratio, the prepared samples of epoxy resin mortar containing 25% epoxy binder (epoxy resin plus epoxy hardener) and 75% filler (1:3) were compared to the cement mortar. However, each specimen of epoxy resin mortar was prepared by mixing with different fillers. The properties such as compressive strength, tensile strength, and microstructural changes were measured using different characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared radiation spectroscopy (FTIR), and scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDX). From the obtained results, it was found that the strength of the specimens increases when blended with steel slag and marble dust, which is attributed to their peak densities and enhanced particle interactions. The XRD, SEM, FTIR, and SEM-EDX analyses showed the formation of calcium, magnesium, and other phases in the microstructure of epoxy resin-based mortars. This resulted in lower water absorption and porosity, as well as improvements in both compressive and tensile strengths. This research can help in understanding the important role of different industrial wastes as feasible fillers in epoxy resin-based composites.

Radiation attenuation effectiveness of polymer-based radiation shielding materials for gamma radiation

Polymer materials are increasingly being utilised in radiation shielding applications due to their unique characteristics such as flexibility, durability, and cost-effectiveness. These properties have attracted the attention of researchers who have been exploring the potential of these materials in such applications. Recently, new radiation shielding materials have been developed by incorporating elements into polymer matrices. The purpose of this study was to assess the effectiveness of lead-free polymer-based radiation shielding bricks in attenuating gamma radiation at 140 keV and 364 keV. The study evaluated the radiation shielding capability of five different polymer-based bricks, which were prepared using an open-mould casting technique with thicknesses of 0.7 cm and 1.4 cm. The bricks were fabricated by loading 90% filler powder and 10% epoxy resin and hardener. The filler powders used in this study were tungsten carbide, tungsten carbide cobalt, bismuth oxide, barium sulphate, and tin powder. The effectiveness of the fabricated bricks in attenuating gamma radiation was evaluated at 140 keV and 364 keV, and their microstructural properties were analysed using field emission scanning electron microscopy (FESEM). The study found that the newly developed polymer-based radiation shielding bricks can attenuate gamma radiation up to 98% at 140 keV and 65% at 364 keV of the incident gamma radiation. The FESEM analysis showed that the fillers were evenly distributed within the epoxy matrix. In conclusion, the incorporation of tungsten carbide, tungsten carbide cobalt, bismuth oxide, barium sulphate, and tin particles into the epoxy matrix improves the radiation shielding effectiveness of polymer-based materials, making them suitable for gamma radiation shielding applications.

Modeling and static modal analysis of lathe bed using conventional and composite materials using FEM

The bed has a significant impact on a machine tool's performance. The Bed of the Machine Tool has to be appropriately robust to absorb all vibrations and rigid enough to avoid deflections under different cutting forces transferred over the tool-post and carriage to the Lathe Bed. In general, the various permanent and moveable Lathe parts are supported by the Lathe bed. Typically, cast iron or mild steel are used to make lathe beds. When dealing with really large machinery, the bed may be constructed from two or more segments that are connected together to achieve the appropriate length. Large and robust, the lathe bed has a large ability to absorb machine vibrations during machining.This paper summaries, static structural and mode forms analysis are done on the lathe bed under maximum load circumstances. By incorporating ribs and reducing volume where loads and deflection are less caused, these simulated outcomes are utilized to lighten the lathe bed without sacrificing its structural integrity and dampening ability. As an alternative material, FEA analysis of a modified lathe bed is conducted using CAST IRON, MILD STEEL, and CFRP, this is a blend of epoxy resin hardener and granite. The efficiency of both materials is compared with regard to generated stresses, deformation, and weight reduction. CATIAV5 Modeling software was used to create lathe bed CAD Models. ANSYS 16.2 was used to generate the FE Model. ANSYS is used to perform the analysis. The observations are calculated and presented as contour plots to analyse the impact of reduced weight on the machine bed's structural strength prior to and after weight reduction, and decisions on the ideal design are made.

Engineered Conductive Green Epoxy Hardener: Star-Shaped Bio-based Core Functionalized with Conjugated Oligoaniline via Microwave Irradiation

Engineered Conductive Green Epoxy Hardener: Star-Shaped Bio-based Core Functionalized with Conjugated Oligoaniline via Microwave Irradiation

Investigation of chemical resistance of epoxy binders based on various hardeners

The chemical resistance of binders based on epoxy resins and hardeners IMTGFA, KhT-152 B and Ethal-450 has been investigated. The binder based on ED-20 and IMTGFA+UP606 / 2 has the best chemical resistance to nitric acid. The composition based on ED-20 and KhT-152 B showed the greatest chemical resistance to a sodium hydroxide solution. The binder based on Ethal-370 and Ethal-450 has the best chemical resistance to the water environment.

A vanillin-derived hardener for recyclable, degradable and self-healable high-performance epoxy vitrimers based on transimination

Development of high-performance and reprocessable thermosets based on sustainable feedstocks is particularly desirable due to the issues of sustainability and resources. Herein, a simple single-step process between vanillin and xylene diamine was used to produce a sustainable vanillin-imine containing hardener (VIH). The VIH-cured epoxy vitrimer exhibits flexural strength (125 MPa) equivalent to commercially available counterparts and significantly higher storage modulus (3448 MPa) at ambient temperature. The hardened vitrimer can be repetitively recycled as like thermoplastics because of the substantial number of reversible imine linkages in the thermoset structures and the recovering of flexural properties near about 100 % even after three reprocessing cycles. Meanwhile, the glass transition temperature (Tg) and thermal properties of the recycled vitrimer maintain nearly identical to those of the pristine vitrimer. Furthermore, the VIH-cured epoxy vitrimer degrades quickly in acidic solution (HCl, 1 M) within 12 h at 50 ᵒC, but it totally resists degradation in other organic solvents over a period of 2 days. Taken together, this study offers a facile procedure for developing a renowned vanillin-imine based hardener for epoxy resins having excellent mechanical properties, recyclability, and degradability.

Synthesis of novel vanillin-amine hardeners fully derived from renewable bio feedstocks and their curing with epoxy resins to produce recyclable reprocessable vitrimers

Biobased epoxy vitrimers have reached intense interest in recent decades. The triggerable reverse bonds can be introduced into these crosslinked epoxy vitrimers through epoxy resins or hardeners. This study synthesized two imine hardeners, such as vanillin-butanediamine (V-BDA) and vanillin-hexanediamine (V-HDA), using biobased vanillin, butanediamine, and hexanediamine and their chemical structures were ensured by FTIR, 1HNMR, 13CNMR, and TOF-MS. The two novel hardeners were used to cure epoxy resins, rendering vitrimers with good reprocessability, self-healing, recyclability, and solvent resistance due to the reversible imine bonds. The flexural strengths and modulus of these cured resins were consistent with those of epoxy resins that were hardened with traditional amine-based hardeners. The cured resins maintained 100% of their Tg and flexural properties after being reprocessed up to three times. It was revealed that the cured epoxy vitrimers could be degraded entirely in a particular acidic solution capable of bond-exchanging reactions within 12 h at 50 ᵒC, allowing the thermoset matrix to be chemically recycled and the monomers regenerated. This versatile recyclability, combined with the use of fully biobased feedstocks to prepare the hardeners, provides an attractive approach to help achieve a sustainable circular composite economy.

Experimental Analysis of the Performance of Doweled Connections Reinforced with Glass-Fiber-Reinforced Polymer (GFRP) in Wood Pinus spp.

In line with technological advancements, the construction industry worldwide has sought more efficient building systems in relation to aspects such as increased productivity, reduced material waste and meeting the growing demand. The objective of this research was to use structural joints composed of composite dowels in laminated wood beams as an alternative to connect pieces of wood. Composite materials are composed of a matrix phase and a reinforcement phase and, in civil engineering, are generally applied as reinforcements in concrete structures. This article presents the structural performance of laminated pine timber with composite dowels made of fiber-reinforced polymeric resin (epoxy resin, hardener and glass fiber) (glass-fiber-reinforced polymer, GFRP) with a diameter of 12.5 mm, which was subjected to tensile force in the direction of the connection. For this, an experimental program was carried out that included characterization of the GFRP dowel, characterization of the woods used to make the connection and a tensile test of the connections with the dowels reinforced with fiberglass through a prototype designed specifically for the test. Subsequently, the results were compared with those observed in the literature. In the comparisons, it was possible to conclude that the joints with FRP pins exhibited better performance in terms of shear strength per section than those such as common nails, helical nails (Ardox) and composite structural pins (half-lap, 90°), which were 3.8 mm, 3.4 mm and 6 mm in diameter, respectively. This indicates that this composite material has potential for application in these types of connections. As an original contribution, it proves the feasibility of using this material in dowel joints for wooden structures.

Advanced 3D printed mini-vascular network for self-healing concrete

Recently, the development of 3D mini-vascular networks has demonstrated their ability to facilitate self-healing in concrete structures. These 3D printed polylactide (PLA) hollow ligament tetrahedral shaped units (TETs) can heal multiple occurrences of damage by releasing a single-component healing agent stored within. To improve the healing efficacy of the concrete-TET system whilst overcoming the potentially short shelf life of single-component healing agents, the TETs design was modified. TETs with co-axial hollow ligaments (d-TETs) suitable for storing bi-component healing agents were manufactured. Different healing agents, including epoxy resin (i.e. cycloaliphatic epoxy resin plus hardener) and sodium silicate in isolation or in combination with either nanosilica or nanolime solution were explored. The d-TETs were effective in storing these bi-component healing agents without them undergoing premature mixing and curing. Moreover, the d-TETs successfully ruptured and released healing agents at a crack width of 0.35 mm. After one damage-healing cycle, significant strength and stiffness recovery was achieved: d-TETs hosting sodium silicate and nano-lime yielded the best strength recovery (25%), whilst most other sodium silicate-based healing agent combinations demonstrated stiffness recoveries of approximately 40%. This demonstrates the efficiency of the d-TETs concept as a system, which allows strength and stiffness recovery despite the limited volume of healing agent.

Synthesis of multitask star‐shaped oligoaniline: Introducing a novel, efficient epoxy hardener

AbstractMultitask star‐shaped oligoaniline (S‐TAH) was synthesized using microwave irradiation in three steps: preparation of phthalic acid‐ capped tetra‐aniline (as the arm), synthesis of a tetrafunctional biobased core, and subsequently, coupling arms to the core, using a divergent approach. A biobased core was synthesized through a direct condensation reaction of pentaerythritol, with l‐lactic acid. The chemical structures were extensively characterized using Fourier‐transform infrared and proton nuclear magnetic resonance spectroscopy. The performance of S‐TAH, as a multitask hardener for bisphenol A‐based epoxy resin (EP), was evaluated using differential scanning calorimetry, thermal gravimetric analysis, dynamic thermomechanical analyses (DMTA), and four‐prob conductometry. Peaks of cure exotherms for S‐TAH/EP (1:1) systems appear at 135°C with a tail‐like peak around 175°C. Compared to conventional amine‐cured EP, the thermal stability of the S‐TAH/EP cured was significantly higher, that is, ~ 40°C enhancement in half weight loss temperature (T50). A three‐fold improvement in char yield was observed. From DMTA, the material cured with S‐TAH displays representative storage moduli in glassy (9.4 GPa) and rubbery (5.2 GPa) states reflecting a uniform network and viscoelastic behavior. The electrical conductivities (σ) of the pure S‐TAH and the epoxy systems cured with S‐TAH/EP are 4.3 × 10−4, and 2.65 × 10−4, respectively. T star‐shaped oligoaniline is a promising multitask hardener—functioning as hardener, thermal stabilizer, electrically conductive and toughening agents—which can be versatilely applied in thermal resistance anticorrosive coatings and conductive adhesives.

Use of Lignin-Containing Waste of the Pulp and Paper Industry in Obtaining Lign-Epoxy Composite Materials

The possibility of processing lignosulfonates to obtain composite materials using ED-20 epoxy resin as a binder was considered. It was shown that powdered lignosulfonates (PLS) play the role of a hardener for epoxy resins and reduce the toxicity of polyethylenepolyamine (PEPA), which is widely used as an industrial hardener, by 50–68 %. The article assesses the possibility of using PLC as a hardener and filler composition. The optimal composition of lignoepoxy compounds was revealed: ED-20 – 60–70 % by weight; PLS – 30–40 % by weight; PEPA – 6–7 % by weight. Biotesting proved that the resulting material does not have toxic properties. It was discovered that these compositions have longterm biostability while maintaining physical and mechanical properties. It was concluded that it is expedient to process powdered lignosulfonates to obtain lignoepoxy compositions suitable as building material and alternatives to wood chip and wood fiber materials.

EFFECT OF ALKALI TREATMENT ON MECHANICAL PROPERTIES AND MICROSTRUCTURAL ANALYSIS OF LUFFA CYLINDRICA AND SNAKE GRASS FIBER-REINFORCED EPOXY COMPOSITES

This study investigates the mechanical properties of Luffa cylindrica and snake grass fiber composites prepared with different combinations of fiber and resin. Fibers are produced from natural sources having good mechanical properties and eco-friendly that can be used in various engineering applications such as automobile, aerospace and automotive industries. The Luffa cylindrica and snake grass fibers will be treated for 3[Formula: see text]h with alkali (NaOH) chemical treatment. The treated fibers are then developed as Laminate composites using compression molding technique. The composites have been made in five different compositions by varying the weight percentage (wt.%) of the chemically treated Luffa cylindrica and snake grass fibers (combination of maximum 30[Formula: see text]wt.%) mixed with epoxy resin and hardener (maximum of constant 70[Formula: see text]wt.%). Bonding between the fiber and matrix plays a vital role in influencing the mechanical characteristics of composites. The five samples have been prepared from the five different compositions and undergone various studies to find its mechanical properties such as ultimate tensile test (UTS), impact test, flexural test and water absorption test. It is found that the UTS and flexural strength have been considerably enhanced by sample 2 and impact strength has been notably increased by sample 3. The microstructure of tensile-tested specimen is observed by using the Scanning Electron Microscopy (SEM). It is reported that the better bonding between the fibers and matrix has been observed by SEM microstructural analysis.

High-performance and fully recyclable epoxy resins cured by imine-containing hardeners derived from vanillin and syringaldehyde

Increasing concerns about environmental protection have driven the rapid development of recyclable and sustainable thermosetting polymers. Herein, two biobased epoxy hardeners containing imine bonds were prepared from lignin-derived aromatic aldehydes (vanillin and syringaldehyde). The epoxy resins cured by these two hardeners showed comparable mechanical performances in comparison to traditional epoxy resins. Owing to the dynamic feature of incorporated imine bonds, both cured epoxy resins could be repeatedly reprocessed via hot pressing like thermoplastics, and were degradable in the amine solution. It is noteworthy that a closed-cycle chemical recycling process could be realized by utilizing the degradation products to prepare fresh epoxy resins. Notably, the flexural strength and modulus of the chemically recycled and thermally reprocessed epoxy resins were nearly 100% recovered. In addition, both cured epoxy resins showed acceptable glass-transition temperature, thermal stability and chemical resistance. Taken together, our work offered a simple method to develop biobased epoxy resins with versatile recyclability and high performance recovery rates.

Imidazolium Ionic Liquids as Compatibilizer Agents for Microcrystalline Cellulose/Epoxy Composites

Four imidazolium-based ionic liquids (IL; 1-butyl-3-methylimidazolium chloride, 1-carboxymethyl-3-methylimidazolium chloride, 1,3-dicarboxymethylimidazolium chloride and 1-(2-hydroxyethyl) -3-methylimidazolium chloride) were tested as compatibilizers of microcrystalline cellulose (MCC). Subsequently, ethanolic IL solutions were prepared; MCC was mixed, and the mixtures were left to evaporate the ethanol at ambient conditions. These modified MCC were characterized and applied as reinforcements (5.0 and 10 phr) in an epoxy resin aiming to manufacture biobased composites with enhanced performances. The IL did not significantly modify the morphological and structural characteristics of such reinforcements. Regarding the thermal stability, the slight increase was associated with the MCC-IL affinity. The IL-modified MCC-epoxy composites presented improved mechanical responses, such as flexural strength (≈22.5%) and toughness behavior (≈18.6%), compared with pure epoxy. Such improvement was also obtained for the viscoelastic response, where the storage modulus at the glassy state depended on the MCC amount and IL type. These differences were associated with stronger hydrogen bonding between IL and epoxy hardener or the IL with MCC, causing a "bridging" effect between MCC and epoxy matrix.