Aliphatic Hardener Research Articles

Surface Degradation of DGEBA Epoxy Resins Cured with Structurally Different Amine Hardeners: Effects of UV Radiation.

In this study, the effects of three diamine curing agents (aromatic, cycloaliphatic, aliphatic) on the photochemical behavior of bisphenol A diglycidyl ether networks were comparatively examined. In order to monitor structural changes and study the curing agents' action mode, the cured epoxy resins were characterized before and after photoirradiation by means of Fourier-transform infrared spectroscopy, contact angle, differential scanning calorimetry, scanning electron microscopy, and energy-dispersive X-ray analysis, mass loss, and color modification measurements. Water absorption tests were also conducted. The cured epoxy resins are to be used in different multicomponent polymer materials for outdoor protection. The presence of the cycloaliphatic hardener led to reduced water absorption, and after UV irradiation, an increase in the glass transition temperature and lowest mass loss of the corresponding cured epoxy resin compared to the ones cured with aromatic and aliphatic hardener.

Hybrid Strategies for the Improvement of the Flame Retardancy of in-situ Silica-Epoxy Nanocomposites cured with Aliphatic Hardener

The aerospace industry requires materials showing good mechanical performance, durability, and thermal stability to satisfy very stringent requirements in several applications. Epoxy-based composites can be a suitable solution, due to the peculiar characteristics of the polymer matrix. Epoxy resins can be cured by aliphatic or aromatic hardeners. The use of aliphatic amines is preferable because of their lower toxicity, though these curing agents are easily flammable. Recently, hybrid systems conjugating in-situ modified epoxy matrix with organic and inorganic additives have been developed to flame retard aliphatic epoxy composites. This short review summarizes some applications of such strategies, which are based on the use of the sol-gel technique, DOPO-based flame retardants, bio-waste compounds and other synergists. The review describes the main concept of this approach and the preparation of no-dripping self-extinguishing silica-epoxy hybrid composites showing low phosphorus loadings, tailored interphases and good mechanical properties.

Vanillin-Based Epoxy Vitrimers: Looking at the Cystamine Hardener from a Different Perspective.

Epoxy vitrimers encompass many advantages compared to traditional epoxy materials such as recyclability, repairability, and reprocessability. These properties are induced by the incorporation of dynamic reversible covalent bonds. Recently, the incorporation of aromatic disulfide bridges that are dynamic has expanded the development of new eco-friendly epoxy materials. Herein, we studied a bio-based aliphatic disulfide based on cystamine as a hardener with a vanillin-derived bio-sourced epoxy to prepare fully bio-based epoxy vitrimers. This article provides a comparative study between cystamine and an aromatic disulfide benchmark hardener issued from petrol resources. This work demonstrated that the presence of this aliphatic hardener has a significant influence not only on the reactivity, but most importantly on the resulting dynamic properties. An interesting yet counterintuitive accelerating effect of the dynamic exchanges was clearly demonstrated with only 2 to 20% of molar fraction of cystamine added to the aromatic disulfide formulation. A similar glass transition was obtained compared to the purely aromatic analogue, but relaxation times were decreased by an order of magnitude.

Experimental and theoretical insights on the thermal oxidation of epoxy-amine networks

This paper reports an investigation of the oxidation of three epoxy-amine networks obtained from DGEBA cured with three sorts of aliphatic hardeners ethylene diamine (EDA), diethylene triamine (DETA), and triethylene tetraamine (TETA). Oxidation was monitored by FTIR with an innovative discussion of CH2 consumption. Methylene groups held by hardeners groups were shown to be more sensitive to oxidation, which was confirmed by a discussion of Bond Dissociation Energies (BDE) computed by a machine-learning approach.

Screen-Printable Cu–Ag Core–Shell Nanoparticle Paste for Reduced Silver Usage in Solar Cells: Particle Design, Paste Formulation, and Process Optimization

Copper–silver (Cu–Ag) core–shell nanoparticles are promising for replacing the silver particles and flakes used in printed conductors in current solar cells since they deliver good conductivity, chemical stability, and optical performance, while also reducing the silver content, thus significantly impacting the cost. The bare nanoparticles offer excellent air stability thanks to the silver-covered copper structure. We demonstrate a screen-printable paste for use in solar cell conductor applications. We report a printed morphology and light reflection properties similar to those achieved with commercial silver pastes. The reported Cu–Ag core–shell paste is uniquely formulated with an epoxy binder and an aliphatic hardener, delivering significantly improved electrical conductivity, while simultaneously reducing the overall silver content by ∼36 wt %. This is attributable to the cross-linked polymeric structure, low-temperature conversion, and improved loading of conductive core–shell nanoparticles. As needed for contact formation in conventional top-contact silicon solar cells, the paste is additionally loaded with lead bisilicate and delivers conductivity on par with that of commercial silver paste. Thus, by combining the reduction of the silver content with excellent electronic and optical properties, this Cu–Ag nanoparticle-based paste becomes attractive for low-cost printed-conductor applications, including photovoltaics and electronics.

Macromolecular Mobility Changes Induced by Thermal Aging of Epoxy‐amine Polymer Networks

AbstractChanges in macromolecular mobility during the thermal oxidation of epoxy‐amine thermoset networks are addressed in this study. Three epoxy‐amine systems, cured with DGEBA and three similar aliphatic hardeners – ethylenediamine (EDA), diethylenetriamine (DETA), and triethylenetetramine (TETA) – aged at 160°C are characterized by dynamic mechanical analysis (DMA). Results show a split of the single initial α relaxation peak with aging, which may imply that chain scissions are preferred at certain oxidizable sites in the network. A β relaxation can be identified around ‐60°C and does not seem to evolve much with aging, while another sub‐glass transition around 30°C decreases with it. Implications of this work both with mechanical fracture properties and with segmental mobility of radical chemical functions involved in bimolecular oxidation reactions have yet to be confirmed.

Fire safe epoxy composite with low dielectric properties from a combination of fluoro-phosphonium salt, melamine and copper hydroxystannate

A phosphorus-fluorine containing compound tetraphenylphosphine hexafluorophosphate (Ph4PPF6) was synthesized by one-step method and characterized by FTIR, NMR, SEM, and EDX. Epoxy resin (EP) cured with an aliphatic hardener and Ph4PPF6 as a multifunctional additive were fabricated. The combined effects of Ph4PPF6 with melamine (MEL) and copper hydroxystannate (CuHS) on the fire safety, thermal stability, smoke toxicity and dielectric performances of EP were investigated. It is found that EP containing 2 wt% P (from Ph4PPF6) combined with 10 wt% MEL (sample EP 2P 10M) and EP with 2 wt% P from Ph4PPF6 combined with 5 wt% MEL, 5 wt% CuHS (sample EP 2P 5M5C) pass V0 classification in UL-94 VB tests. The cone calorimetric tests on these composites reveal that the peak heat release rate of sample EP 2P 5M5C is reduced by 64.2% in comparison to pure EP. The toxic gases including HF, CO, HCN are reduced to different extent when MEL and CuHS used as co-additives. The dielectric loss of sample EP 2P 10M is reduced by 26.3% in comparison to pure EP.

Improving flame retardancy of in-situ silica-epoxy nanocomposites cured with aliphatic hardener: Combined effect of DOPO-based flame-retardant and melamine

Silica-epoxy nanocomposites were prepared via an “in-situ” sol-gel synthesis process and a phosphorus (P) flame-retardant i.e. 6H-dibenz[c,e][1,2]oxaphosphorin,6-[(1-oxido-2,6,7-trioxa-1-phosphabicyclo[2.2.2]oct-4-yl)methoxy]-, 6-oxide (DP) and melamine (Mel) were further added to the matrix to improve its fire performance. The main components of epoxy resin were bisphenol A diglycidyl ether (DGEBA) and isophorone diamine (IPDA) hardener. The addition of DP as well as silica alone into the epoxy system stopped the melt dripping phenomena in the vertical fire test (UL 94), however, the addition of melamine was crucial for achieving the highest fire classification (UL 94-V0 rating). The presence of DP and Mel in the silica-epoxy nanocomposite promoted a large reduction (ranging from 53% up to 80%) in the heat release rate (HRR) and a delay (up to 31%) in the ignition time in the cone calorimetry experiments. Improved fire performance of the epoxy system was attributed to i) a condensed phase activity of silica, DP and melamine to form a protective thermal barrier during combustion and ii) a minor gas phase flame inhibition activity of DOPO component of DP. The mechanical characterization of the epoxy nanocomposites through tensile tests showed that the addition of DP increases the stiffness of the epoxy resin, resulting in a strong increase of Young modulus (up to 32%) and in a slight decrease of fracture strength, elongation at break and toughness. An increased glass transition temperature (up to 8%) of the epoxy system possibly due to hydrogen bonds and polar interactions of DP with the matrix was also observed.

Low Velocity Impact and Mechanical Behaviour of Shot Blasted SiC Wire-Mesh and Silane-Treated Aloevera/Hemp/Flax-Reinforced SiC Whisker Modified Epoxy Resin Composites

In this research the effect of adding silicon carbide nano whiskers (SiCw) into epoxy resin and the impact of reinforcing surface treated SiC wire-mesh (SiCwm) and woven aloevera/hemp/flax fibers (NF) were studied. The principal aim of this work was demonstrating the importance of adding SiCw (0.5 and 1.0 vol.%) and SiC wire-mesh with economical natural fibres (50 vol.%) and silane surface treatment on natural fibres in mechanical and low velocity impact behavior. The SiCw and natural fibres were surface treated by 3-Aminopropyltriethoxysilane whereas SiC wire-mesh was shot blasted. The composites were cured at room temperature using an aliphatic hardener Triethylenetetramine (TETA). The strength factor results showed that the silane surface modified composite designation ‘H4’ gave highest normalized strength of 98%. The highest tensile and flexural strength of 141 and 240 MPa was observed for silane surface modified composite designation ‘H4’. The low velocity impact damage behavior of ‘H4’ composite designation showed higher resistance against to penetration. Transmission electron microscope (TEM) morphological images showed uniform dispersion of surface-modified SiCw in epoxy resin. Similarly the silane treated natural fibre and shot blasted SiC wire-mesh given improved adhesion with matrix. These high damping polymer composites offers their application in automobile, structural and domestic sector.

A comparative study of structural and dielectric properties of diglycidyl ether of bisphenol A (DGEBA) cured with aromatic or aliphatic hardeners

This study aims to present structural and dielectric comparisons between two epoxy polymers. These polymers are realized by curing diglycidyl ether of bisphenol A (DGEBA) resin with either aliphatic 1,3-diaminopropane (PDA) or aromatic 4,4′-diaminodiphenyl sulfone (DDS) hardeners. They are called DGEBA/PDA and DGEBA/DDS. Several complementary techniques have been used in the present study. The structural analysis was performed using grazing incidence X-ray reflectometry. It reveals the presence of a locally ordered nanostructure in the DGEBA/DDS polymer and an amorphous character for the DGEBA/PDA one. Dielectric characterization was carried by means of dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization current (TSDC) and time domain spectroscopy (TDS). DRS measurements performed over wide ranges of temperature (−80 to 160 °C) and frequency (10−1–106 Hz) showed the presence of dipolar γ and α relaxations in both polymers. Nevertheless, the interfacial Maxwell–Wagner–Sillars (MWS) relaxation appeared only in DGEBA/DDS. This can be related to the local nanostructure within this polymer, which can give rise to interfaces. Relaxation parameters were deduced from the best fits of experimental data with the Havriliak–Negami model. The calculated fragility index indicates that DGEBA/DDS is more fragile than DGEBA/PDA. The loss factor e′′(f) was calculated from the isothermal discharging current measurements, using Hamon approximation. Thanks to this e′′ calculation an interfacial relaxation was revealed in the frequency range of 10−3–10−1 Hz for each investigated polymer.

Thermo-mechanical characterization of siliconized E-glass fiber/hematite particles reinforced epoxy resin hybrid composite

In this present work hybrid polymer (epoxy) matrix composite has been strengthened with surface modified E-glass fiber and iron(III) oxide particles with varying size. The particle sizes of 200nm and <100nm has been prepared by high energy ball milling and sol-gel methods respectively. To enhance better dispersion of particles and improve adhesion of fibers and fillers with epoxy matrix surface modification process has been done on both fiber and filler by an amino functional silane 3-Aminopropyltrimethoxysilane (APTMS). Crystalline and functional groups of siliconized iron(III) oxide particles were characterized by XRD and FTIR spectroscopy analysis. Fixed quantity of surface treated 15vol% E-glass fiber was laid along with 0.5 and 1.0 vol% of iron(III) oxide particles into the matrix to fabricate hybrid composites. The composites were cured by an aliphatic hardener Triethylenetetramine (TETA). Effectiveness of surface modified particles and fibers addition into the resin matrix were revealed by mechanical testing like tensile testing, flexural testing, impact testing, inter laminar shear strength and hardness. Thermal behavior of composites was evaluated by TGA, DSC and thermal conductivity (Lee’s disc). The scanning electron microscopy was employed to found shape and size of iron(III) oxide particles adhesion quality of fiber with epoxy matrix. Good dispersion of fillers in matrix was achieved with surface modifier APTMS. Tensile, flexural, impact and inter laminar shear strength of composites was improved by reinforcing surface modified fiber and filler. Thermal stability of epoxy resin was improved when surface modified fiber was reinforced along with hard hematite particles. Thermal conductivity of epoxy increased with increase of hematite content in epoxy matrix.

Rheological study of gel phenomena during epoxide network formation in the presence of sepiolite

AbstractThe dynamic behaviour during the crosslinking of an epoxy polymer near the gel point was monitored using rheological multiple frequency experiments. The influence of a needle‐shaped inorganic nanofiller, sepiolite, either non‐modified or organically surface modified during the cure process in the presence of an aliphatic and an aromatic hardener was investigated. The validity of various criteria for determining the gel point was examined for the crosslinking of these filled thermosets. The Winter–Chambon criterion at the gel point is obeyed by the unfilled and by the non‐modified sepiolite‐filled epoxy matrix with either of the two hardeners. However, physical gels are formed in the presence of the organically modified sepiolite and the Winter–Chambon criterion is not valid. For all the systems investigated, the nanofiller reduces the time to reach gelation. Critical relaxation exponents and gel strength have been determined indicating a more elastic and stronger gel in the presence of the aliphatic hardener. © 2012 Society of Chemical Industry

Effect of polyisocyanate hardener on adhesive force of waterborne polyurethane adhesives

A series of waterborne polyurethane (WBPU)/hardener adhesives were obtained from mixing of WBPU containing different types of polyol as a soft segment with aliphatic and aromatic polyisocyanates hardeners. By characterization of allophanate and biuret bonds formed from the reaction of hardener NCO with urethane/urea groups of WBPU using 1HNMR spectroscopy. It was found that the optimum number ratio (molar ratio) of NCO group of hardener to urethane/urea group of WBPU that shows the highest adhesion force was depended on the type of hardener (aliphatic/aromatic polyisocyanate) and dimethylol propionic acid (DMPA) content (total content of urethane/urea groups); however independent of the type of soft segment (polyol) of WBPU. The optimum number ratio (molar ratio) of NCO group of aromatic polyisocyanate hardener to urethane/urea was higher than that of aliphatic hardener to achieve the highest adhesion force of WBPU. The adhesive force increased with increasing hardener content up to the optimum point and then decreased. Poly(tetramethylene adipate glycol) (PTAd) based WBPUs with aliphatic hardener show higher adhesive force than Poly(tetramethylene oxide glycol) (PTMG) and aliphatic hardener-based WBPUs at the optimum number ratio (molar ratio) of NCO group of hardener to urethane/urea group of WBPU. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3663–3669, 2007

Ultimate properties of rubber and core-shell modified epoxy matrices with different chain flexibilities

Preformed polystyrene-co-butylacrylate (PScoBu) core-shell particles and polystyrene microspheres as well as amine-terminated butadiene nitrile (ATBN) rubber have been used for modification of both rigid and more flexible crosslinked DGEBA-based epoxy networks having significantly different crosslink densities. Some variations in cure kinetics have been shown by both thermal and rheological measurements. Independently of the crosslink density of the neat epoxy matrix, function of the cycloaliphatic or aliphatic hardener used, the toughening effect via core-shell modification has been found as good as that for rubber modification but with a better retention of thermal properties. Results are investigated as a function of the morphologies obtained by scanning electron microscopy (SEM) but also by atomic force microscopy (AFM). Larger fracture toughness was obtained for every-unmodified and modified- epoxy matrices cured with the aliphatic hardener as a consequence of the lower crosslink density of the corresponding mixtures.