Hardener Agent Research Articles

Microstructural and main mechanical properties of novalac based carbon–carbon composites as the pyrolysis heating rate

In this study, the effects of pyrolysis heating rate on microstructural and main mechanical properties of Novalac-based carbon/carbon composites were investigated by CHNS, optical microscope, FE-SEM, BET N 2 adsorption, XRD, Raman, FT-IR, wear analyzing, three-point bending test, tensile and Vickers micro-hardness tests. Firstly, PAN-derived carbon nanofibers (reinforcing agent) was synthesized using electrospinning followed by the functionalizing via the wet chemical oxidation to improve the strength of nanofiber bonding to the matrix of composites. Firstly, novalac resin (acting as a matrix), hexamethylenetetramine (hardener agent) and carbon nanofibers (reinforcing agent) were mixed and hot-pressed at 180 °C under the compression load of 40 kN to produce compressed CNFs-Novolac composites. Carbon/Carbon composites were obtained from the pyrolysis of CNFs-Novolac composites up to 1000 °C by the various heating rates under the compression press of 400 bar, finally. Structural and mechanical studies confirmed that the heating rates below or equal to 10 °C.min −1 resulted in the production of low porosity (≤17%) carbon composite with high carbon content (>90 wt%), high fracture strength (≥270 MPa), high toughness (≥9 MPa m 1/2 ), high hardness (≥156 Hv), and low friction coefficient (<0.6).

Multifunctionality of structural nanohybrids: the crucial role of carbon nanotube covalent and non-covalent functionalization in enabling high thermal, mechanical and self-healing performance

This study proposes new kinds of functionalization procedures able to preserve specific properties of carbon nanotubes (CNTs) and to improve compatibility with the epoxy matrix. Through a covalent approach, for the first time, CNTs are functionalized with the same hardener agent, 4,4′-diaminodiphenyl sulfone, employed to solidify the epoxy matrix and capable to fulfill mechanical requirements of industrial structural resins. The same CNTs are non-covalently modified through the polymer wrapping mechanism with benzoxazine (Bz) terminated polydimethylsiloxane (PDMS). The comparison between electrical and mechanical properties of the nanocomposites highlights the success of the non-covalent functionalization in determining an increase in the glass transition temperature (Tg) and in better preserving the unfunctionalized CNT electrical conductivity. Besides, tunneling atomic force microscopy (TUNA), powerful to catch ultra-low currents, has been used for revealing the morphology on nanoscale domains and detecting the conductivity on the same location of CNT/epoxy resins. No electrical contacts to the grounds have been used for the TUNA analysis; a procedure that does not alter the results on the interface domains which experience contact areas with strong differences in their properties. The effectiveness of performed CNT functionalizations as a route to impart self-healing efficiency to the resin formulations has also been proved.

Comparative Evaluation of the Influence of Cast Hardening Agents on Surface Abrasion, Surface Hardness and Surface Detail Reproduction Properties of Refractory Investment Materials

Comparative Evaluation of the Influence of Cast Hardening Agents on Surface Abrasion, Surface Hardness and Surface Detail Reproduction Properties of Refractory Investment Materials

준설토와 친토양 경화재 혼합지반의 일축강도특성

준설토와 친토양 경화재 혼합지반의 일축강도특성

Evaluation of four curing agents of epoxy resin and their effects above their thermal and dinamomechanical properties

ABSTRACTWere synthesized four new hybrid hardener agents type amino tertiary functionalized with allyl groups from : l, 6-Hexanediamine, Diethylenetriamine, Trietilentriamine and Tris (2-aminoethyl) amine, using the basic nucleophilic substitution mechanism, replacing bromide by amino tertiary group in the presence of tetrabutylammonium bromide as phase transfer agent, producing allyl amine corresponding: ALA-4, ALA-5, ALA-6 and TRIS respectively, which were evaluated as a hardening of epoxy resin DGEBA through photopolymerization process by UV ligth curing, adding a 10, 20 and 40% molar percentage of hybrid materials and the thiol corresponding to carry out the thiol-ene reaction (TMP TMP, PTKMP) with DMPA as initiator. The resinic materials obtained, were evaluated by the technique of dynamic mechanical analysis (DMA) at a heating rate of 5° C/min in a range from - 50° C to 150° C in nitrogen atmosphere. The formulations with hybrid hardening agent ALA 4- 20% -PTKMP and TRIS 10% -PTKMP were the materials with modulus 2289, 2971 Mpa and tgs of 102,103°C, respectively.

목재칩을 활용한 포장재의 현장 적용성 평가

Construction materials using soil which is the most common material around us have many advantages, but their long-term durability and sensation of walking as pavements have problems. Therefore, they are used after compaction or mixed with various hardening agents such as lime and cement for strength enhancement. However, studies on the behavior of pavement materials mixed with environment-friendly hardening agents or admixtures to improve walking property are still insufficient. In this study, therefore, in order to evaluate the appropriate mixing ratio and field application characteristics of pavement materials using mixed soils with environment-friendly hardening agents and natural materials such as wood chips, mechanical tests were performed to evaluate the rational mixing ratios and the ball test was performed as an elasticity test to evaluate the field applicability. The results suggest that the content of wood chips should be selected at 1.5% or lower according to the purpose of the structure, and the hardening agent at 10~15%. The evaluation results for GB/SB coefficient ratio which indicates the walking property show that the appropriate mixing ratio of the hardening agent in terms of the sensation of walking is 15% of lower, but different mixing ratios should be chosen according to the proportion of wood chips.

Influence of rubber on the curing kinetics of DGEBA epoxy and the effect on the morphology and hardness of the composites

The influence of the end groups of two liquid rubbers on curing kinetics, morphology, and hardness behavior of diglycidyl ether of bisphenol-A based epoxy resin (DGEBA) has been studied. The rubbers are silyl-dihydroxy terminated (PDMS-co-DPS-OH) and silyl-diglycidyl ether terminated (PDMS-DGE). Crosslinking reactions, investigated by shear rheometry, ranged 90–110 °C, using a constant concentration (5 phr) of liquid rubbers and 1,2-Diamino cyclohexane (1,2-DCH) as hardener agent. The gel time, tgel, of the neat epoxy significantly decreased when adding the elastomers, more so for the silyl-dihydroxy terminated elastomer; at 110 °C the reaction was nearly complete before rheological test started. The results suggest that the elastomers induced a catalytic effect on the curing reaction. Scanning electron microscopy revealed phase separation of the elastomer during the curing reaction with rubber domains about 5 μm size. However, the DGEBA/dihydroxy terminated elastomer composite cured at 110 °C exhibited a homogenous morphology, that is, the rapid reaction time would not allow for phase separation. Water contact angle tests evidenced either more hydrophilic (silyl-diglycidyl ether terminated rubber) or more hydrophobic (silyl-dihydroxy terminated rubber) behavior than the neat epoxy. The latter effect is attributed to the presence of aromatic rings in the backbone structure of PDMS-co-DPS-OH. Microindentation measurements show that the elastomers significantly reduced the hardness of the epoxy resin, the DGEBA/ether terminated composite exhibiting the lowest hardness values. Moreover, hardness increased as reaction temperature did, correlating with a reduction of microdomains size thus enabling the tuning of mechanical properties with reaction temperature.

Competition of diffusion and crosslink on the interphase region in carbon fiber/epoxy analyzed by multiscale simulations

ABSTRACTMolecular diffusion and crosslink between sizing, epoxy, and hardener agent were simulated to elucidate forming process of interphase in carbon fiber/epoxy composite, by using a multiscale method, in which fully atomistic molecular dynamics (MD), coarse‐grained dissipative particle dynamics (DPD) and Monte Carlo‐like polymerizing models are used in combination. It shows that mutual diffusions of the three components tend to result in gradient distributions in the fiber vicinity crossing the interphase transition region. The diffusion behavior is extremely restrained by the crosslink reactions. The results indicate that a period of diffusion before the initiation of chemical reaction is necessarily important to obtain sufficient crosslink within the interphase. The sizing amount and the sizing compositions have significant influence on the interphase region. Thicker sizing layer leads to less crosslink and wider transition region, whereas existence of hardener agent in the sizing layer can generate higher crosslink density without changing the width of the interphase. These results deepen our understanding on molecular formation and optimization of the three‐dimensional interphase region in carbon fiber/epoxy composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40032.

Investigation the interphase formation process of carbon fiber/epoxy composites using a multiscale simulation method

Abstract A multiscale simulation method is newly developed to investigate the competition and interplay between diffusion and crosslink reactions during the formation process of interphase in carbon fiber/epoxy composite. The simulations are conducted by using fully-atomistic molecular dynamics (MD), coarse-grained dissipative particle dynamics (DPD) and Monte Carlo-like polymerizing models in combination. The distributions of each component molecules and functional groups are predicted as function of time and of distance from the fiber surface, respectively. The concentration profiles indicate a gradient transition region in vicinity of the carbon fiber. The profiles of the unreacted functional groups demonstrate that, nearby the fiber surface, the amount of hardener agent is chemically inadequate to react with epoxide from the resin and the sizing. Therefore, the crosslink density within the interphase transition zone is much lower than that in the matrix bulk. Accordingly, width of the interphase region is estimated, and is consistent with the experimental result.

Prediction of thermal hazard of liquid organic peroxides by non-isothermal and isothermal kinetic model of DSC tests

Abstract Liquid organic peroxides (LOPs) have been widely used as initiators of polymerization, hardening, or cross-linking agents. We evaluated a beneficial kinetic model to acquire accurate thermokinetic parameters to help preventing runaway reactions, fires or explosions in the process environment. Differential scanning calorimetry was used to assess the kinetic parameters, such as kinetic model, reaction order, heat of reaction (ΔHd), activation energy (Ea), frequency factor (lnk0), etc. The non-isothermal and isothermal kinetic models were compared to determine the validity of the kinetic model, and then applied to the thermal hazard assessment of commercial package contaminated with LOPs. Simulations of a 0.5-L Dewar vessel and 25-kg commercial package were performed. We focused on the thermal stability of different liquid system properties for LOPs. From the results, the optimal conditions were determined for avoiding violent heat effects that can cause a runaway reaction in storage, transportation...

The chemical and dielectric properties of epoxy/(Ba 0.8Sr 0.2)(Ti 0.9Zr 0.1)O 3 composites for embedded capacitor application

Abstract The characteristics of epoxy/(Ba 0.8 Sr 0.2 )(Ti 0.9 Zr 0.1 )O 3 (BSTZ) composites are investigated for the further application in embedded capacitor device. The effects of BSTZ ceramic powder filler ratio on the chemical, physical and dielectric properties of epoxy/BSTZ composites are studied. Differential scanning calorimeter (DSC) thermal analysis is conducted to determine the optimum values of hardener agent, curing temperature, reaction heat, and glass transition temperature ( T g ). The hardener reaction process starts at about 115 °C and completes at about 200 °C, for that it is appropriate to process of epoxy/BSTZ composites in the range of temperature. The highest glass transition temperature ( T g ) of 155 °C is obtained at one equivalent weight ratio (hardener/epoxy). Only the BSTZ phase can be detected in the XRD patterns of epoxy/BSTZ composites. The more BSTZ ceramic powder is mixed with epoxy, the higher crystalline intensity of tetragonal BSTZ phase are revealed in the XRD patterns. The dielectric constant measured at 1 MHz increases from 5.8 to 23.6 as the content of BSTZ ceramic powder in the epoxy/BSTZ composites increases from 10 to 70 wt%. The loss tangents of the epoxy/BSTZ composites slightly increase with the increase of measurement frequency.

분말 폐타이어와 분말 수지를 함유한 환경친화적 고인성 시멘트계 무수축 그라우트재의 개발

Grouting materials are used for the unification of superstructural and substructural body like bridge seat (shoe) or machinery pedestal and e.t.c by filling their intercalary voids. Accordingly, grouting materials have been developed and used mainly with products of high strength because those materials are constructed specially in a part receiving large or impact load. In this situation, the structural body constructed by grouting materials with high stiffness-centered (caused by high strength) products is apt to cause brittle failure when receiving over a limit stress and to cause cracks according to cumulative fatigue by continuous and cyclic load. In addition, grouting materials are apt to cause cracks by using too much rapid hardening agents that give rise to high heat of hydration to maintain high strength at early age. In this study, to overcome these problems, cement type grouting materials including powder of waste tire and resin as elastic materials which aim to be more stable construction and to be improvement of mother-body`s unification are developed and endowed with properties of high toughness and high durability add to existing properties of high flowability, non-shrinkage and high strength. Besides, this study contribute to of for green construction materials for being possible recycling industrial waste like waste tire and flyash. On the whole, seven type mixing conditions are tested and investigated to choose the best mixing condition.

水酸化アルミニウムのメカニカル活性化による水和活性微粒子材料の調製とセメント速硬化機能

Milling of gibbsite by an agitation ball mill brought about mechanochemical dehydration and amorphization. A remarkable increase in hydration reactivity with Ca(OH)2 is demonstrated by using a conduction calorimeter. An integral heat of hydration from mechanically activated gibbsite is about 300 times larger than that from the intact gibbsite. We found high correlation between the integral heat of hydration and the 3h compressive strength of conventional Portland cement paste containing milled gibbsite with or without Ca(OH)2. Acquired high activity of milled gibbsite was sustained for at least 2 months under 50%RH. These properties warrant applicability of mechanically activated gibbsite to rapid hardening agents for Portland cement.

Electrochemical and bioelectrocatalytical properties of polydimethylsiloxane carbon paste doped with glucose oxidase

Abstract The carbon paste electrodes (CPE) based on a mixture of graphite (C) and polydimethylsiloxane (PDMSi) were prepared. Effects of carbon paste (CP) modification with a hardening agent (HA) and glucose oxidase (GO) on the heterogeneous electron transfer (ET) rate and the electrochemically active surface area were investigated using chronoamperometry and cyclic voltammetry of ferricyanide. An evaluation of the chronoamperometric data permits one to conclude that the ET of ferricyanide at the CPE proceeds following the “pinhole” model. The surface coverage by the insulator and the radius of the pinholes depend on the CP nature and change from 0.88 to 0.69, and from 3.5 to 13.0 μm, respectively. The CPs comprising GO show larger electrode covering and a larger radius of pinholes, which was interpreted in relation to hydrophilization of modified graphite. In anaerobic conditions oxidation of glucose with CP containing GO proceeds at a potential of 0.2 V vs. SCE, when ferricyanide was used as a soluble mediator. The calibration graphs of the electrodes response show a slightly sigmoidal character and are saturated at 40 mM of glucose. The electrode response depends on the enzyme amount and the nature of the CP. The maximum current of the electrodes was 2.0, 2.7 and 4.5 μA cm−2 for HA-free CP containing 1, 2 and 5% of GO, respectively. The current decreases about two times after addition of 1% hardening agent that is related to limited enzyme inactivation.

Oxidized Starch as a Hardening Agent in the Gelatin‐Immobilization of Living Yeast Cells

AbstractPeriodate‐oxidized starch (oxystarch) was shown to be a good substitute for formaldehyde or glutaraldehyde as hardening agents in an immobilization procedure of microbial cells within gelatin. In fact, contrary to both aldehydes, oxystarch has no antimicrobial activity so that the immobilized cells retain their viability. Cell loading and mechanical stability of the immobilizates make them suitable for operations in continuous bioreactors.

Effect of a Novel Catechol Copolymer on Cuticle Sclerotization by the American Cockroach

A new biologically active copolymer containing catechol and succinic acid has been synthesized. This polymer is highly soluble in water and stable at neutral (physiological) pH. An injection of the copolymer into the haemocoel of American cockroaches was lethal. Newly-ecdysed (molted) cockroaches could tolerate only 0.6 mg while interecdysial animals died after injection of 1 mg. The copolymer contains catechol with a free beta carbon which is similar in structure to the natural cuticle sclerotization (hardening) agents. Experiments show that the copolymer appears to bind cuticle protein precursors which could be related to the lethal effect of this agent.

The use of chemical heat treatment in industry

The authors review the state of heat treating and diffusion coating of alloys in metals industry of the Soviet Union and offer specific information on the use of various metals, including aluminium, cerium, chromium, silicon, and zirconium, as hardening and corrosion-resistant agents for the protection of alloys from wear, temperature, and corrosion.

The fracture energy of some epoxy resin materials

The double cantilever beam technique has been used to measure the fracture energy of a series of cured epoxy resins. A range of materials was produced by varying the proportion of resin to hardener agent (Araldite CT200 and hardener HT901 — phthalic anhydride, CIBA Ltd) and by adding silica flour or aluminium powder as a filler.

Some Experiments on the Behavior of the Carbonic-acid-type High Molecular Hardening Agents

Some Experiments on the Behavior of the Carbonic-acid-type High Molecular Hardening Agents

Formalin as a Hardening Agent for Nerve Tissues

Formol, Formalin, or Formaldehyde was discovered by A. W. Hoffman in 1863 while passing wood spirit and air over a redhot platinum spiral. If the vapor is brought into water to its pzint of saturation, a forty per cent. solution of formaldehyde is obtained, which has long been known under the name of formol. That Formalin possessed antiseptic as well as hardening powers we owe to the investigations of Dr. F. Blum, and these facts induced the elder Blum to make an extended serints of investigations in the hardening of animal and vegetable tissues in the Senckenbergischen Institute at Frankfort, Germany. His preliminary report was published in the Zo6logischer Anzeiger, 1893, No. 434, and a more detailed report in the Berichte fiber die Senckenbergische Naturforscher Gesellschaft, I894, p. I95. Here he details his experience, which in brief is as follows: Several human embryos were finely preserved in formol diluted with ten to twenty parts of water. Small embryos with amnion intact were preserved and the amniotic fluid remained transparent, so