Vinyl Ester Matrix Research Articles

Luffa cylindrica fibres/vinylester matrix composites: Effects of 1,2,4,5-benzenetetracarboxylic dianhydride surface modification of the fibres and aluminum hydroxide addition on the properties of the composites

In this work we used a sequence of organic extraction and chemical modification treatments in order to increase the compatibility between the mat fibrous of the Luffa cylindrica ripe fruit and the vinyl ester resin for composites preparation. As observed from SEM and suggested from XRD analyses, these sequential treatments did not degrade the L. cylindrica fibres preserving their potential use as a reinforcement. The FTIR analyses and the conductometric titrations showed evidences of interactions between the fibres and the dianhydride. A fibre mass ratio of 15% was used for composites preparation decreasing the density of the composites at ca. 45% when compared with the vinylester matrix. The TG analyses showed that the aluminum hydroxide addition in the matrix increases the thermal stability of the composites. The DMA showed that the fibres did not influence the matrix cure kinetics, and a biphasic system was formed during pre-curing under environmental conditions. The tensile and Charpy impact strength tests showed an increase of the strength of the composites when compared with the matrix. The best results were obtained for PMDA treated fibres/vinyl ester matrix composites, which showed an increase of ca. 30% for tensile strength and 250% for impact strength.

Interfacial shear strength of cured vinyl ester resin-graphite nanoplatelet from molecular dynamics simulations

Interfacial adhesion between a three layer thick graphite nanoplatelet and a vinyl ester (VE) matrix was studied using molecular dynamics simulations. Polymer interphase formation near carbon surfaces influences interfacial bonding and carbon/matrix load transfer. A VE resin was equilibrated near the graphite surfaces and then cured using the Relative Reactivity Volume algorithm to form a crosslinked matrix while enforcing the correct regiochemistry and relative reactivity ratios within the free radical addition cure. The local styrene monomer concentration in both the liquid and cured resin was highest near the graphite sheets, affecting interfacial strength and near-surface crosslink density. The composite's glass transition temperature (466–502 K) was 50–100 K higher than pure VE. The interfacial shear strength was 141 MPa for resin with 87% monomer conversion and 106 MPa for 98% monomer conversion, indicating effective reinforcement/matrix load transfer. This computational methodology provides more chemically realistic predictions of interfacial surface adhesion than has been reported previously.

Tensile response and fracture and failure behavior of jute fabrics-flyash-vinylester hybrid composites

In this work, hybrid materials consisting on a vinylester matrix simultaneaously reinforced with jute woven fabrics and flyash particles were prepared. The tensile response and the fracture and failure behavior of these hybrid composites were investigated. Thermal stability of these materials was also studied. The aim was to obtain an environmentally friendly hybrid material with a good balance of tensile and fracture properties at relatively low cost. The effect of a novel treatment for the jute fabrics on the hybrids mechanical and fracture properties was investigated. The best balance of tensile and fracture properties was obtained for the hybrid consisting of fabrics treated with alkali under stress and fly ashes which also exhibited relatively high thermal stability.

Viscoelastic properties of hollow glass particle filled vinyl ester matrix syntactic foams: effect of temperature and loading frequency

Viscoelastic properties of hollow particle-reinforced composites called syntactic foams are studied using a dynamic mechanical analyzer. Glass hollow particles of three different wall thicknesses are incorporated in the volume fraction range of 0.3–0.6 in vinyl ester resin matrix to fabricate twelve compositions of syntactic foams. Storage modulus, loss modulus, and glass transition temperature are measured and related to the microstructural parameters of syntactic foams. In the first step, a temperature sweep from −75 to 195 °C is applied at a fixed loading frequency of 1 Hz to obtain temperature dependent properties of syntactic foams. In the next step, selected four compositions of syntactic foams are studied for combined effect of temperature and loading frequency. A frequency sweep is applied in the range 1–100 Hz and the temperature is varied in the range 30–140 °C. Time–temperature superposition (TTS) principle is used to generate master curves for storage modulus over a wide frequency range. The room temperature loss modulus and maximum damping parameter, Tanδ, are found to have a linear relationship with the syntactic foam density. Increasing volume fraction of particles helps in improving the retention of storage modulus at high temperature in syntactic foams. Cole–Cole plot and William–Landel–Ferry equation are used to interpret the trends obtained from TTS. The correlations developed between the viscoelastic properties and material parameters help in tailoring the properties of syntactic foams as per requirements of an application.

Microstructural Dependency of Diffusion in Glass Flake-Reinforced Vinyl Ester Resins

Vinyl ester resins are utilized for long-term corrosion protection of metal, alloy, and concrete substrates against concentrated acids, alkalis, and solvents at high temperature. Glass flakes are usually added as fillers to reduce chemical diffusion within the vinyl ester matrix. A common industry practice is to use glass flakes with large aspect ratio, high volume fraction, and in parallel alignment to surface in chemical contact for barrier applications. During processing and curing of glass flake-filled vinyl ester resins, irregular microstructures such as reduced flake aspect ratio and random orientation of flakes are commonly observed. Such microstructures can affect the overall chemical diffusion, resulting to barrier properties less predictable by simple diffusion models. Therefore, in this study, a simple 2D random walk simulation procedure is used in attempt to estimate the microstructural dependency of diffusion in glass flake-reinforced vinyl ester resins. While the random walk simulations are in good agreement with the tortuosity-based diffusion models in terms of microstructural effects, in most cases the simulation results are inconsistent with the experimental measurements of acid diffusion in glass flake-filled vinyl ester resins. A possible cause for this is the poor adherence of vinyl ester resin to glass flakes. Osmotic cracks are also formed during immersion which also influences overall diffusion through the material.

Deformation and fracture behaviors of vinylester/fly ash composites

AbstractIn this work, the deformation and fracture behaviors of a commercial vinylester resin reinforced with fly ash were investigated. Tensile, compressive, and fracture tests were performed on the matrix and the composites with different ash content. Most composites exhibited improved stiffness, tensile strength, and fracture properties in comparison to the vinylester matrix. From scanning electron microscopic analysis of fracture surfaces, the toughening mechanisms of crack pinning, crack deflection, particle debonding, and localized shear yielding were identified. In addition, the dependence of tensile and compressive modulus and fracture energy toward ash content was adequately fitted by simple models available in the literature. From the results of these models and energy‐dispersive X‐ray spectroscopy analysis, some interaction between vinylester and ash seemed to exist. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

A modified short beam shear specimen for characterization of interfacial strength in nanocomposites

Abstract Analysis and design of a modified short beam shear (MSBS) specimen for interfacial strength characterization of nanocomposites was investigated using finite element analysis and testing. The MSBS specimen is a sandwich beam which consists of two relatively thick aluminum beams bonded to a thin core made of the nanocomposite material under test. To examine the specimen experimentally, polymer nanocomposites consisting of a thermosetting vinylester resin reinforced with multi-walled carbon nanotubes (MWCNTs), with and without chemical functionalization, were tested using the MSBS specimen. The failure mode observed for these nanocomposites is a result of a combination of shear and normal stresses, mainly due to the high brittleness of the vinylester matrix. Although the stress state existing in the nanocomposite is not pure shear, the mechanical strength measured by the MSBS specimen is sensitive to the chemical functionalization of MWCNTs.

Properties of thermo-chemically surface treated carbon fibers and of their epoxy and vinyl ester composites

Abstract Carbon fibers were surface treated by a continuous gas phase thermo-chemical treatment. The surface and the mechanical properties of the fibers were investigated before and after treatment and compared to the properties obtained with a conventional industrial electro-chemical surface treatment. The increase of the oxygen atomic content was much sharper, the surface chemistry was better controlled, and the tensile strength of the fibers increased slightly with the thermo-chemical surface treatment. The thermo-chemical surface treatment created a topography which amplitudes were under 10 nm, thus creating some mechanical interlocking with the matrix. The electro-chemical surface treatment did not generate such a topography. The improvement of interfacial adhesion with a vinyl ester matrix was limited, revealing that oxidation of the carbon fiber surface alone cannot tremendously improve the mechanical properties of carbon fiber–vinyl ester composites.

Effect of hybrid phenolic hollow microsphere and silica-filled vinyl ester composites

Study on phenolic hollow microspheres (PHMS)-filled vinyl ester (VE) composites has been carried out. Effect of adding PHMS fillers at different filler loading on flexural, impact, and thermal properties were studied. The impact strength increased with the addition of PHMS fillers but at the expense of flexural strength, flexural modulus, and thermal stability of the composites. The second stage of this article aims to study the effect of adding silica as second filler in PHMS-filled VE composite system, and the influence of silane treatment on the mechanical properties of silica/PHMS/VE hybrid composites. PHMS/VE composites filled with silane-treated silica were found to show an increase in flexural modulus with increasing filler content. On contrary, the untreated silica fillers were observed to provide reinforcing effect in PHMS/VE composites at rather low filler concentration. The flexural strengths of silica/PHMS/VE hybrid composites were found to decrease with addition of silica content in the composites, and further decreased with increasing in silica content for both untreated and treated silica/PHMS-filled VE composites. Addition of silane-treated silica in the composites also provided an increase in the impact resistance of the PHMS/VE composites. Interestingly, the addition of silica and PHMS fillers in VE matrix has resulting in low density composites with improved flexural modulus and impact resistance.

Modeling compression-after-impact response of polymer matrix composites subjected to seawater aging

This manuscript presents a computational investigation of the compression-after-impact (CAI) response of polymer matrix composites subjected to seawater-induced environmental degradation. A multiscale computational model that accounts for seawater-induced property degradation in composite constituents is proposed to predict the CAI response of E-glass reinforced vinyl-ester composites. Predictions of the CAI response as a function of specimen saturation are validated against experimental observations. The investigations revealed that partially-saturated vinyl-ester matrix composites undergo a significant reduction in the CAI strength, part of which is recovered upon full matrix saturation. The proposed computational model captures the response characteristics of partially- and fully-saturated specimens.

Energy Absorption of Nano-Reinforced and Sandwich Composites in Ballistic and Low-Velocity Punch-Shear

This paper presents an investigation on energy absorption characteristics of nano-reinforced panels, laminated face sheets and sandwich composites in high velocity ballistic and low velocity punch-shear experiments. The vinyl ester panels were reinforced with 1.25 and 2.5 wt. percent nanoclay and exfoliated graphite platelets. Three different face sheets were manufactured with E-glass, Owens Corning HP ShieldStrand? glass and T-700 Carbon woven fabric in vinyl ester; and one with the E-glass and graphite platelets impregnated vinyl ester matrix. The sandwich composites were fabricated with balsa, PVC foam, 3D-fiber reinforced Tycor? and fire resistant fly-ash based Eco-Core? cores in between E-glass/vinyl ester face sheets. Ballistic tests were conducted according to NIJ level III using a universal receiver equipped with a barrel to launch 0.308 caliber M80 ball round projectile at about 890 m/s. Low velocity punch-shear tests were performed at around 3 m/s according to ASTM D3763 Standard using a drop-weight impact test system. The tortuosity of the fractured surface in nanocomposite specimens has been investigated using digital microscope. In ballistic tests, the 3-D fiber reinforced Tycor? core provided the most resistance when projectile strikes at the web-flange interface region. The 2.5 wt. pct. graphite platelet reinforced nanocomposite, HP ShieldStrand? glass vinyl ester face sheets, and E-glass/Eco-Core? sandwich composite showed the best energy absorption under low velocity punch-shear.

Dynamic mechanical behavior of vinylester matrix composites reinforced by Luffa cylindrica modified fibers

AbstractCurrently, there is a demand for new engineering materials presenting a combination of strength, low density, processing easiness, and reduced costs. In this context, polymer matrix composites reinforced by natural fibers have been studied in recent years due to their ecological and economic advantages. Some fibers are still little explored in literature despite presenting a great potential as reinforcement like Luffa cylindrica. The present work aims at the preparation and characterization of a vinylester thermoset matrix composite material reinforced by fibers of the natural L. cylindrica fruit after modification treatments. In this study, extraction treatments in organic solvents, mercerization, and a quite new esterification with BTDA dianhydrides were used and the results showed that in all cases, the composite materials reinforced by Luffa fibers have showed improvements in mechanical and thermal properties compared to the vinylester matrix. As an example, 50% tensile increase was obtained for the composite reinforced by fibers esterified with benzophenone tetracarboxylic dianhydride when compared with thermoset matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Investigation on Mechanical, Thermal and Morphological Behaviors of Turmeric Spent Incorporated Vinyl Ester Green Composites

This study aimed at utilizing nutraceutical industrial waste and reducing carbon footprints of plastics. Vinyl ester green composites (VEGCs) have been prepared with turmeric spent A (TS) and organically modified layered silicates (o-montmorilonite, MMT) (organoclays). Tensile behavior and impact strength of vinyl ester matrix thermoset composites were characterized. Thermal characteristics of the vinyl ester/MMT/TS green composites were evaluated by using differential scanning calorimetric (DSC), thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMA). Morphological behavior of nanocomposites has been studied by using scanning electron microscopy (SEM) and atomic force microscopy (AFM).

Influence of moisture absorption on flexural properties of syntactic foams

Abstract This work studies the influence of moisture absorption on the flexural properties of vinyl ester matrix–glass particle syntactic foams. The extent and the effect of moisture absorption are related to the wall thickness and volume fraction of the particles present in the composite. Four compositions of vinyl ester–glass systems are exposed to deionized and sea water conditions. Experimental findings are compared with results on virgin specimens. In general, the exposure of syntactic foams to a water environment yields a deterioration of Young’s modulus. This phenomenon is more prominent with deionized water as compared to sea water and increases with the particle volume fraction. In addition, results from water absorption tests show that syntactic foams have a lower diffusivity as compared to the neat resin. Experimental data are interpreted by using available modeling tools that allow for predicting the composite behavior from the properties of its constituents.

Post-Impact Mechanical Characterisation of Glass and Basalt Woven Fabric Laminates

Two woven fabric laminates, one based on basalt fibres, the other on E-glass fibres, as a reinforcement for vinylester matrix, were compared in terms of their post-impact performance. With this aim, first the non-impacted specimens were subjected to interlaminar shear stress and flexural tests, then flexural tests were repeated on laminates impacted using a falling weight tower at three impact energies (7.5, 15 and 22.5J). Tests were monitored using acoustic emission analysis of signal distribution with load and with distance from the impact point. The results show that the materials have a similar damage tolerance to impact and also their post-impact residual properties after impact do not differ much, with a slight superiority for basalt fibre reinforced laminates. The principal difference is represented by the presence of a more extended delamination area on E-glass fibre reinforced laminates than on basalt fibre reinforced ones.

Multi-axial fatigue life estimation of unidirectional GFRP composite

Abstract Aim of this work is to test and understand the mechanical behaviour, in multi-axial stress conditions, of a composite material (E-glass reinforce fibres and vinyl-ester matrix) used to build a structural component: a corner beam of bus cabin. A series of experimental tests is performed on specimens cut out from this beam. Different unidirectional (UD) fibres orientations with respect to the direction of load application are considered: longitudinal (0°), normal (90°), inclined at 30° and 45°. Static and fatigue characterization are carried out to identify the mechanical behaviour in terms of σ – N curves. Obtained fatigue data are then interpolated by fitting the parameters required for multi-axial models of fatigue life estimation. A final comparison with the literature data is included, proposing a simple tool to evaluate the damage evolution of E-glass reinforced composites during fatigue life.

Thermal Properties and Fire Resistance of Jute-Reinforced Composites

The thermal behaviour, fire resistance and mechanical properties of jute-reinforced composites with vinylester and resol matrix were studied. Organically modified clay was added to the polymeric matrix in order to enhance the properties of the composites. An inhomogeneous distribution of the nanoreinforcement in the polymer was observed by X-ray diffraction. Thermogravimetric analyses revealed that the addition of clay to the resol resin by sonication enhanced the thermal resistance of the jute-reinforced composite at temperatures higher than 300°C. The fire resistance of the composites was evaluated by means of a cone calorimeter. A diminution in the peak of the heat release rate was observed when clay was added to the polymeric matrix. On the other hand, neither the time to ignition nor the total heat evolved was significantly reduced by the clay addition. Additionally, an increment in the flexural modulus as well as in the flexural strength of the resol composites was observed when the clay was added to the matrix. The fiber–matrix interface of the composites was studied by scanning electron microscopy. It was observed that as the clay dispersion degree was increased the interface quality was diminished in the resol composites.

Free Vibrations of Pultruded FRP Elements: Mechanical Characterization, Analysis, and Applications

The research shows the results of experimental tests to establish the dynamic parameters of fiber-reinforced polymer (FRP) structural elements in the free vibration field. The tests and the analysis consider the simply supported configuration of pultruded elements characterized by glass fiber reinforcement, glass fiber-reinforced polymer (GFRP) and the thermosetting vinylester matrix subjected to flexural, transversal, and torsional vibrations. Comparison between the experimental results and numerical analysis and the finite element method is also presented. The dynamic response of GFRP structural elements is compared with the behavior of steel and aluminum elements. The results show a good performance, especially in the case of open cross-sectional profiles, considering the advantages deriving from the ratio between the dead load and total load of fiber reinforced composite material. Finally, the use of pultruded GFRP elements for new-built decks is investigated to detect possible resonance phenomena due...

Novel functionalized carbon nanotubes as cross-links reinforced vinyl ester/nanocomposite bipolar plates for polymer electrolyte membrane fuel cells

In this study, the novel functionalized multi-walled carbon nanotubes (MWCNTs) are used as cross-links between MWCNTs–vinyl ester interfaces to achieve homogeneous dispersion and strong interfacial bonding for developing fully integrated MWCNTs–vinyl ester nanocomposite bipolar plates. POAMA (i.e. poly(oxyalkylene)-amines (POA) bearing maleic anhydride (MA)) are grafted onto the MWCNTs by amidization reaction, forming MWCNTs-POAMA. In the MWCNTs-POAMA/vinyl ester nanocomposites, MWCNT-POAMAs react with vinyl ester and become part of the cross-linked structure, rather than just a separate component. It is found that the MWCNTs-POAMA exhibited better dispersion in the vinyl ester matrix than those of pristine MWCNTs. Moreover, the results demonstrate that the mechanical and electrical properties of the vinyl ester nanocomposite bipolar plate are improved dramatically. The ultimate flexural strength, unnotched impact strength, in-plane electrical conductivity and contact resistance of the MWCNTs-POAMA/vinyl ester nanocomposite bipolar plate are increased by 45%, 90%, 315% and 28%, respectively. In addition, the maximum current and power densities of the single fuel cell test using the MWCNTs-POAMA/vinyl ester nanocomposite bipolar plates is enhanced from 1.03 to 1.23 A cm−2 and from 0.366 to 0.518 W cm−2, respectively, which suggested that a higher electron transfer ability for polymer electrolyte membrane fuel cell applications can be achieved.

Influence of moisture absorption on the interfacial strength of bamboo/vinyl ester composites

Moisture absorption is a major concern for natural fibers used as reinforcement in structural composites. This paper reports a detailed study on the moisture sorption characteristics of bamboo strips and their influence on the interfacial shear strength (IFSS) of bamboo/vinyl ester composite. The IFSS determined by pull-out test decreased dramatically as the fabrication humidity increased. The bamboo strips provide a reservoir of moisture which diffuses into the interfacial region and inhibits the hardening of vinyl ester matrix. The interface of the bamboo/vinyl ester composite can also be damaged due to moisture exposure after fabrication. Post-fabrication exposure of composites to moisture was found to be less damaging than the moisture exposure during the composite fabrication. The IFSS of the composite decreased by nearly 40% in the first 9 d of water immersion. Further immersion up to 100 d did not cause any further reduction in interfacial shear strength.