Resin Hardener Research Articles

Water absorption behavior and thermal-mechanical properties of epoxy resins cured with cardanol-based novolac resins and their esterified ramifications

To study the effect of chain flexibility and polarity on the water absorption and thermal-mechanical properties of epoxy materials, different kinds of bio-based novolac resin hardeners were synthesized by cardanol-formaldehyde condensation reaction and two esterified ramifications were synthesized by esterifying their corresponding phenolic resin. The cure behaviors were evaluated by differential scanning calorimeter, and the mechanical and thermal properties of cured samples were characterized by dynamic mechanical analyzer and thermogravimetric analysis. Water absorption process was monitored using gravimetric measurement, and time-resolved ATR-FTIR. The diffusion mechanism was also explained using 2D correlation analysis. The addition of cardanol into novolac resins was found to decrease the glass transition temperature due to the plasticizing effect of flexible aliphatic chain. On the other hand, water resistance ability was enhanced due to lower polarity. The effect of esterification on lowering water absorption is prominent for both esterified ramifications. The water absorption mechanism was then characterized and discussed using 2D correlation analysis of time-resolved ATR-FTIR.

Concentrating cesium-137 from seawater using resorcinol-formaldehyde resin for radioecological monitoring

Abstract A method of preconcentrating cesium-137 from seawater using a resorcinol-formaldehyde resin, which enables one to optimize the ecological monitoring procedure, has been suggested. Studies of sorption of cesium-137 from seawater by resorcinol-formaldehyde resin have been performed, and it has been demonstrated that the cation exchanger is characterized by high selectivity with respect to cesium-137. It was found that the selectivity depended on the temperature of resin solidification and the seawater pH value. The maximal value of the cesium-137 distribution coefficient is equal to 4.1–4.5×103 cm3 g−1. Under dynamic conditions, the ion-exchange resin capacity is 310–910 bed volumes depending on the seawater pH, whereas the efficiency of cesium removal exceeds 95%. The removal of more than 95% of cesium-137 has been attained using 1–3 M solutions of nitric acid: here, the eluate volume was 8–8.4 bed volumes. Application of 3 M solution of nitric acid results in resin degradation with the release of gaseous products.

Failure Behaviour of Concrete Prisms Strengthened by Various Bond Widths of Carbon Fibre Reinforced Polymer (CFRP)

The use of fibre reinforced polymers (FRP) for external strengthening of concrete structures in various forms such as laminates and sheets has become moderately common. FRP is more effective as it provides a better solution in terms of properties and application. The effectiveness of the FRP strengthening system lies in the bond between concrete and FRP which is affected by various factors such as bond length of FRP, bond width, resin hardening and surface preparation. In certain cases, bond width is a major factor which ensures that the structure can be strengthened properly. This paper focuses mainly on the failure behaviour of concrete prisms strengthened by various bond width ratios of carbon Fibre Reinforced Polymer (CFRP) which are 20mm (0.27), 40mm (0.53), 60mm (0.8) and 75mm (1) respectively. A total of fifteen strengthened prisms measuring 75 mm × 75 mm × 350 mm were cast for a three-point load test. Twelve strengthened prism specimens were externally strengthened with CFRP and three specimens were designated as control. The findings show that a greater width ratio of CFRP will strengthen concrete prisms greatly and will result in different types of failure modes.

A preliminary evaluation of bio-based epoxy resin hardeners for maritime application

A screening of different hardeners derived from cashew nut shell liquid (CNSL) was performed; they were compared to a conventional hardener in an epoxy resin system for composite production by infusion process. All samples were submitted to different post-curing processes before tensile strength and moisture uptake were evaluated. It was observed that the use of CNSL hardeners produced cured epoxies similar in Young’s Modulus (YM) to the conventional hardener with a lower moisture uptake however, the hardeners resulting in a low YM had a marked reduction in moisture uptake. Studies of the post-curing process showed that the moisture uptake of the conventional system can be improved but, depending on the temperature applied, the process can be detrimental to the CNSL hardeners, provided that moisture uptake was increased after post-curing. The results indicate that biobased content can be introduced to a conventional epoxy resin system by replacing the conventional hardener commonly used by a sustainable one derived from cashew nut shell liquid with an additional moisture uptake reduction.

Silane Modification of the Flax/Epoxy System Interface

Natural fibres (NF) are normally subjected to pre-treatment to ensure good fibre to matrix bonding and consequent mechanical properties and durability. To enhance the sustainability of NF composite systems, it would be sensible to minimise processes that incur environmental burdens. This research considers that addition of silane coupling agent to epoxy resin hardener may be an alternative to the direct chemical pre-treatment of NF before composites manufacture. The current study indicates that silane-in-hardener can eliminate the pre-treatment of fibres and generates composites with optimum mechanical properties.

Ballistic impact response of Kevlar Composites with filled epoxy matrix

Impact resistance and weight are important features for ballistic materials. Kevlar fibres are the most widely reinforcement for military and civil systems due to its excellent impact resistance and high strength-to-weight ratio. Kevlar fibres or spectra fiber composites are used for designing personal body armour to avoid perforation. In this study, the ballistic impact behaviour of Kevlar/filled epoxy matrix is investigated. Three different fillers, nanoclay, nanocalcite and nanocarbon, were used in order to increase the ballistic impact performance of Kevlar-epoxy composite at lower weight. The filler, nanoclay and nanocalcite, content employed was 1 wt.% and 2 of the epoxy resin–hardener mixture while the nanocarbon were dispersed into the epoxy system in a 0.5%, 1% and 2% ratio in weight relating to the epoxy matrix. Specimens were produced by a hand lay-up process. The results obtained from ballistic impact experiments were discussed in terms of damage and perforation. The experimental tests revealed a number of damage mechanisms for composite laminated plates. In the ballistic impact test, it was observed whether the target was perforated completely penetrated at the back or not. The presence of small amounts of nanoclay and nanocalcite dispersed into the epoxy system improved the impact properties of the Kevlar/epoxy composites. The laminates manufactured with epoxy resin filled by 1 wt.% of nanoclay and 2 wt% nanocalcite showed the best performance in terms of ballistic performance. The addition of nanocarbon reduced ballistic performance of Kevlar-epoxy composites when compared the results obtained for laminates with 0% nanoparticles concentration.

Stabilization of electrical sensing properties of carbon fiber sensors using pre-tensioning approach

Owing to fabrication defects in carbon fiber (CF) tows, the unevenness of fiber roves, such as local bends, misalignments, and skewness, results in irregular distribution of the electrical resistance in the transverse direction along the gauge length of a sensor, which affects its performance. In this study, a pre-tension approach was developed according to the creep mechanism of composites to straighten the CFs. In addition, the resin relaxation was controlled by tensioning the fibers during and after hardening of the epoxy resin using a double-tension method to enhance the electrical sensing properties of long gauge carbon fiber line (CFL) strain sensors. Different levels of sustained tensile stresses were studied to obtain the optimal tensile stress level both during and after hardening to be applied in the double-tension method. The results of static and dynamic tests showed that the double-tension technique could significantly straighten the fibers, and stabilize the transverse connections of CFL sensors in the case of tensioning the fibers during and after hardening under a sustained stress of 60% of the ultimate tensile stress of the CFs. The proposed double-tension method was utilized to improve the response of the CFL sensors with short gauge lengths.

Effect of Nanoparticles on Wettability of Nanocoating on Carbon Steel

Nanocoatings plays an important role in coating industry. The solution was being prepared through copolymerization of epoxy resin hardener and with the incorporation of metal oxide nanoparticles, Zinc Oxide (ZnO) and Silica (SiO2). ZnO and SiO2 were synthesized using sol-gel. Epoxy hardener acted as host while the metal oxide nanoparticles as guest components. The formulation of nanocoatings with excellent adhesion strength and corrosion protection of carbon steel was studied. The performance of wetting ability with different medium was analysed using contact angle. Water medium showed the addition of 3wt% of hybrid between ZnO and SiO2 was the best nanocoating to form hydrophobic surface and was also the best nanocoating surface to form hydrophilic surface with vacuum oil dropping. In oil dropping, the contact angle was smaller than 90° and the water drop tends to spreads on surface.

Investigation of Mechanical Behaviour of Sisal Epoxy Hybrid Composites

Objectives: The recent development in materials replaces automotive and aerospace components with composites. Among composites, natural fiber composites play a vital role due to their properties like bio-degradability, low strength to weight ratio and ease of manufacturing. Method: In this work, sisal epoxy hybrid composite was fabricated by hand layout process. Initially, releasing agent is applied on the top surface of the mould over which Glass Fiber Reinforced Plastic (GFRP) is placed. On GFRP, apply resin hardener mixer over which sisal is placed. Again GFRP layer is kept on sisal. Findings: The result shows that, breaking load of double shear test is increased from 1.02 to 1.43 kN. Hardness value increased from 76.2 to 88.2. The results of inter de lamination test also increased from s 7.96 to 8.52 kN. Above results proved that composite with equal fibre ratio of glass and sisal (50:50) has improved the mechanical properties than composite with minimum percentage of sisal fiber. Applications: The material developed is suitable for automotive bumper application. Also, it may be used as partition and load carrying medium in railway and marine application.

Effects of heat treatment on the properties of bamboo scrimber

This study aims to investigate physical characteristic, mechanical properties, and chemical composition of heat-treated bamboo scrimber. Specimens were heated at 50–230 °C in laboratory conditions for 2 h. Test results of heat treatment samples were compared with the controls. Moisture absorption decreased slightly and then increased as temperature increased. It was probably due to changes of crystallinity and chemical structure. Mechanical properties varied greatly according to different temperature levels. Failure types reflected treatment temperature to some extent. Compressive strength reached a maximum when fiber bundles fractured neatly at 170 °C, which is a turning point for physical, mechanical, and chemical properties under this heat treatment condition. Increasing mechanical properties of bamboo scrimber after heat treatment was due to solidification of phenolic resin.

Restructuring the surface of polyurethane resin enforced filter media to separate surfactant stabilized oil-in-water emulsions via coalescence

Abstract Reported here is a facile resin emulsification method of treating polyurethane enforced filter media by controlling the initial level of solvent volatilization for resin solidification. The treated media are endowed with varying degrees of lipophilicity as determined by their lipophilic to hydrophilic (L/H) values. An optimized treatment condition was pinned for coalescence separation of surfactant-stabilized oil-in-water emulsions using a surfactant free emulsion as the bench mark. The starting separation efficiency was found to depend on the type of surfactant involved in the order of non-ionic surfactant Tween 80 > cationic surfactant cetyl trimethyl ammonium bromide (CTAB) > anionic surfactant sodium dodecyl benzene sulfonate (SDBS). Quartz crystal microbalance (QCM) experiments showed that Tween 80 had the largest adsorption on the polyurethane coating, while least adsorption occurred to SDBS, and mediocre adsorption to CTAB. However, Tween 80 resulted in the lowest time-weighted averaged efficiency as compared to the other surfactants that barely caused any efficiency changes with filtration time. To make the resin emulsification treatment more environmental friendly, more polar solvents were tested, and ethanol was identified as a good alternative to isopropanol.

Epoxy-Filled Microcapsules by Interfacial Engineering

ABSTRACTIn this paper, we demonstrate the successful application of interfacial engineering toward the preparation of epoxy-filled microcapsules. The approach relies on the preferential reaction of polydimethylsilicone insoluble epoxy resin and amine-based hardener to form a cross-linked spherical shell at the interface. Among other features, tailorability is the biggest advantage of this route as both the core content and particle dimensions can be altered by varying the experimental parameters, i.e., stirring speed and resin:hardener ratio. Spherical microcapsules with a core content of 25% were obtained when the reaction was carried out under optimal conditions.

Bond Strength of Reline Resins to Aged-simulated Denture Base Acrylic Resin

ABSTRACT Objectives The aim of this study was to evaluate the bond strength of different direct reliners to acrylic resin for denture base. Materials and methods Double-cone specimens were made: HA-heat-cured acrylic resin-(n = 20); U-Ufi Gel Hard C-(n = 10); K: Kooliner-(n = 10); R-Rebase II Fast-(n = 10) and RH-Rebase II Fast + Resin Hardener-(n = 10). Ten HA samples were immediately submitted to cohesive test. The remaining HA samples and others were submitted to thermal aging (HAaged, 1000 cycles, 5.55oC), followed by tensile test. For tensile strength, 50 single cone-shaped samples were made of heat-cured acrylic resin and aged (HAaged, 1000 cycles, 5.55oC). After surface treatment, relining resin cones were build up using silicon molds, and stressed to failure. Values of cohesive and tensile strength were submitted to one-way ANOVA and Tukey's test (α = 5%). Results Bond strength were: HA/HAaged: 21.17 (±4.89)a, U/HAaged: 11.56 (±1.98)b, R/HAaged: 9.69 (±2.37)b, RH/ HAaged: 9.38 (±1.78)bc and K/HAaged: 5.98 (±1.90)c. The cohesive strength were: KCoe: 22.29(±4.06)a; RCoe: 23.99 (±3.29)a; RHCoe: 24.84 (±3.88)a; UCoe: 25.62 (±3.03)a; HAaged: 36.06 (±8.65)b and HA:42.29 (±7.68)b. Groups followed by the same letters do not show differences. Conclusion Bond strength of acrylic resin to acrylic denture base material is higher than the reliners and Ufi Gel Hard C showed the higher bond strength. How to cite this article Zanatta RF, Batista GR, Crastechini É, Bresciani E, Borges AB, Torres CRG. Bond Strength of Reline Resins to Aged-simulated Denture Base Acrylic Resin. World J Dent 2016;7(1):1-5.

Effects of Long-Term Dry Curing on Strength Development of Initially Combined Wet/Dry-Cured and Steam-Cured Hardener-Free Epoxy-Modified Mortars

It is clarified by the previous studies that even without any hardener epoxy resin can harden in the presence of hydroxide ions from calcium hydroxide in the cement mortars and concretes at ambient temperature. The strength development through the long-term curing of hardener-free epoxy-modified mortars and concretes has hardly been examined till now. Hardener-free epoxy-modified mortars using an epoxy resin (diglycidyl ether of bisphenol A) without any hardener are prepared with various polymer-cement ratios, subjected to (1) initial combined wet/dry curing plus long-term dry curing and (2) initial steam curing plus long-term dry curing, and tested for hardening degree of epoxy resin and strength development. As a result, the application of the initial steam curing rather than the initial combined wet/dry curing causes a marked strength development with increasing polymer-cement ratio and additional dry curing period. The flexural and compressive strengths of the initially steam-cured plus 336-d dry-cured hardener-free epoxy-modified mortars with polymer-cement ratios of 10% or more are about 1.5 to 2.0 times higher than those of the initially steam-cured unmodified mortar. This is proved by a marked increase in the degree of hardening of the hardener-free epoxy resin in the epoxy-modified mortars with additional dry curing period.

KENAF AS MATERIAL FOR LABORATORY TABLETOP

Nowadays, kenaf are gaining attention in the development and is used in many types of engineering application. This new type of composite also contribute towards the green technology making it favorable in various applications. This research is focused on making a laboratory tabletop by utilizing the unidirectional oriented kenaf fiber as the main material which is layered with woven fiberglass. The project methodology is divided into three sections; preparing the specimen, conducting the experiment and testing as well as data analysis. The mould that contains a layer of woven fiberglass and kenaf fiber were poured from a mixture of polyester resin and polyester hardener. The specimen was then compressed and left to dry completely before further testing. Tensile test was carried out by following the ASTM D3039, ASTM D7264 standard for flexural test and ASTM D7136 for drop weight impact test. The results data obtained was found to be suitable for lightweight use only.

Strength properties and molecular composition of epoxy-modified mortars

Even without hardener, epoxy resin is able to harden in the presence of hydroxyl ions produced during cement hydration process. In this study commercially available Bisphenol A-type epoxy resin without hardener was used as a polymeric admixture to prepare epoxy-modified mortars, whose properties and chemical composition were then investigated. The mortars were prepared with a mass ratio of 1:3 (cement:fine aggregate), water-to-cement ratio (W/C) of 0.48, and epoxy content of 5%, 10%, 15% and 20% of cement. The specimens were subjected to dry and wet–dry curing. Workability, setting time, compressive strength, flexural strength, and tensile splitting strength tests were conducted. A Fourier transformation infrared spectroscopy test was also administered to determine the molecular composition and structure of mortars. Results showed an inverse relationship between workability and setting time of mortars versus epoxy content. The compressive, flexural, and tensile splitting strengths of epoxy-modified mortars were noted to be the highest for mortars containing 10% epoxy in wet–dry curing. A significant improvement in strength development of mortars without hardener had been achieved through dry curing due to gradual hardening of epoxy resin with hydrated cement.

Degree of Hardening of Epoxy-Modified Mortars without Hardener in Tropical Climate Curing Regime

Previous studies show that the epoxy resin will harden in the presence of calcium hydroxide from cement hydration process under steam curing. In this study, commercially available epoxy resin without any hardener was used as a polymeric admixture to prepare epoxy-modified mortars subjected to dry, and 5 day wet followed by dry curing in tropical environment. The mortars were prepared with a mass ratio of cement to fine aggregate 1:3, water-cement ratio of 0.48 and epoxy content of 5, 10, 15 and 20% of the cement. The tests conducted were workability, setting time, compressive strength, flexural strength, and degree of hardening of epoxy resin. The results of the study show that the optimum epoxy content that produced the highest strength was 10% under wet-dry curing. However, the degree of epoxy hardening starts to decrease with an increase in epoxy content above 10%. It was also found that a significant improvement in strength development is achieved along with additional dry curing period due to gradually hardening reaction of epoxy resin with cement hydrates.

Epoxy 수지 경화제에 따른 Putty 개발에 관한 연구

Epoxy 수지 경화제에 따른 Putty 개발에 관한 연구

In Situ Analysis of the Relationship between Cure Kinetics and the Mechanical Modulus of an Epoxy Resin

The cure kinetics of epoxy cured with an amine hardener is investigated using a combination of light scattering techniques. Concurrent Raman and Brillouin scattering are used to monitor the formation of epoxy networks over time in terms of both the structural connectivity of the network and the evolution of chemical bonding configurations. The relationship between the elastic properties of the network and the degree of cure was found to depend on the cure temperature and the resin–hardener stoichiometry. A numerical model was created to determine the degree of cure and elastic modulus as a function of time and cure conditions. Accordingly, the modulus of the epoxy comprises two contributions: one directly related to the concentration of covalent bonds that form and another one due to nonbonding interactions that arise as the network relaxes into an optimally packed configuration.

Emulsion-templated porous carbon monoliths derived from tannins

Tannin-based, carbonised, polymerised High Internal Phase Emulsions (polyHIPEs) are described in detail for the first time. Such highly porous materials were prepared by emulsion-templating, using an aqueous phase made of tannin and a low amount of hexamine dissolved in water, sunflower oil, and ethoxylated castor oil. After hardening of the tannin-based resin, the oil was leached out and the resultant monoliths were pyrolysed. The porous structure of carbon polyHIPEs prepared with an initial oil fraction ranging from 43 to 80vol.% has been investigated, as well as their mechanical and thermal properties. We show that the most homogeneous materials, having the smallest pores, the narrowest pore size distributions and also the highest mechanical properties, are those made with an initial oil fraction around 70vol.%. Such value is close to random and hexagonal close packing fractions: 64% and 74%, respectively.