Vinyl Ester Matrices Research Articles

Enhancing GFRP fatigue durability for chassis component applications through glass fiber coupling variation

As the landscape of mobility trends continues to evolve, concerted efforts have been made to incorporate Carbon Fiber Reinforced Plastic (CFRP) into automotive components. However, the substantial increase in cost relative to the achieved weight reduction has limited its widespread adoption. Consequently, research endeavors have focused on exploring alternative composite materials, adapting fibers such as glass fibers, natural fibers, and recycled fibers, to reduce the cost of composite components. Of particular interest in the automotive industry is the utilization of Glass Fiber Reinforced Plastic (GFRP) in chassis components like leaf springs. Nevertheless, the development of GFRP leaf springs encounters a significant challenge related to the adhesive strength at the interface between epoxy resin and glass fibers, which is crucial for enhancing fatigue durability. While glass fibers were traditionally paired with unsaturated polyester or vinyl ester matrices, the pursuit of improved durability has led to the adoption of epoxy matrices. Regrettably, this transition has not consistently yielded the expected gains in interfacial adhesion.In light of these challenges, this study systematically compares the interfacial adhesion strength and fatigue endurance performance. For comparison, two coupling agents widely used commercially, amino silane and epoxy silane, were selected. Glass fibers treated with each coupling agent were purchased commercially, and glass fiber-reinforced plastic (GFRP) specimens were fabricated using the HP-RTM (High-Pressure Resin Transfer Molding) method. Static property evaluations and fatigue durability assessments were conducted using the fabricated specimens. The results showed that when epoxy silane was used as the coupling agent, the interlaminar shear strength (ILSS) increased by approximately 7 %. Furthermore, SEM(Scanning Electron Microscopes) analysis confirmed a significant enhancement in interfacial adhesion, providing support for the ILSS evaluation results. Consequently, the fatigue durability performance improved by approximately six-fold. This confirms that the improvement in interfacial adhesion due to the change in coupling agents led to enhanced fatigue durability performance.

Degradation of GFRP Bars with Epoxy and Vinyl Ester Matrices in a Marine Concrete Environment: An Experimental Study and Theoretical Modeling

Degradation of GFRP Bars with Epoxy and Vinyl Ester Matrices in a Marine Concrete Environment: An Experimental Study and Theoretical Modeling

Optimization of Pyro‐gasification of Carbon Fiber Reinforced Polymers (CFRPs)

AbstractThis work focuses on the optimization of pyro‐gasification process of carbon fiber reinforced polymers (CFRPs) with the aim of recovering carbon fibers (CFs) with properties suitable for the production of new more sustainable composites with high performances. In particular, the pyro‐gasification process is carried out on cured CFRPs panels based on both epoxy (EC) and vinyl ester (VC) matrices, which are the two most used resins for CFRPs. The matrix degradation is evaluated via sample's weight loss measurement and the recovered CFs obtained after different time of treatment are analyzed to identify convenient pyro‐gasification conditions to avoid damaging of the recovered CFs. The obtained results highlight the importance of the thickness of the composites to be treated for the identification of the more suitable pyro‐gasification conditions.

Long-Term Compressive Strength of Polymer Concrete-like Composites with Various Fillers.

The durability of building composites with polymer matrix, such as polymer concretes, is considered high or excellent. However, very few studies are available that show the properties of such composites tested long after the specimens’ preparation, especially composites with fillers other than traditional rock aggregates. The paper presents the long-term compressive strength of polymer concrete containing common and alternative fine fillers, including quartz powder (ground sand) and by-products of the combustion of Polish fossil fuels (coal and lignite), tested nine or 9.5 years after preparation. The results were compiled with the data for respective specimens tested after 14 days, as well as 1.5 and 7 years. Data analysis confirmed the excellent durability of concrete-like composites with various fillers in terms of compressive strength. Density measurements of selected composites showed that the increase in strength was accompanied by an increase in volumetric density. This showed that the opinion that the development of the strength of composites with polymer matrices taking place within a few to several days was not always justified. In the case of a group of tested concrete-like composites with vinyl-ester matrices saturated with fly ashes of various origins, there was a further significant increase in strength over time.

Vinylester / glass fiber interface: Still a key component for designing new styrene-free SMC composite materials

Sheet molding compounds (SMC) allow to design high performance polymer-matrix composites increasingly used for structural applications in the automotive industry. SMC are usually based on an unsaturated polyester thermosetting resin diluted in styrene with chopped glass fibers and fillers. Due to international regulations linked with the potential risks of styrene, replacing such styrene-based reactive system compound is becoming more and more strategic in order to zero-VOC emission, while keeping similar (or displaying even better) mechanical properties and shrinkage control to conventional SMC-based composite materials. In this study, the same sized E-glass fiber was combined with two different vinylester matrices, a conventional styrene containing resin and a styrene free one. The second type fits more suitable for friendly environmentally purposes as it is based on a dimethacrylate diluent. The objective of this work is focused on interfacial adhesion in both systems as the fiber/matrix interface is a key parameter governing the mechanical properties of the final composite materials. A multiscale analysis was carried out from: i)the fiber scale by measuring the interfacial shear stress by using the microdebonding test; ii)the fibers bundle scale by studying the wettability of fibers by the uncured resin; iii)up to the mechanical characterization of unidirectional SMC composites by measuring the interlaminar shear strength (ILSS). As main results, it is demonstrated that the styrene-free composites have a suitable interfacial resistance compared to conventional systems whereas impregnation, i.e. specific fiber sizings which will be more soluble in the resin-dimethacrylate reactive system need to be designed.

Effects of oxygen and tetravinylsilane plasma treatments on mechanical and interfacial properties of flax yarns in thermoset matrix composites

This work is focused on the assessment of the effect of oxygen and polymer plasma tetravinylsilane (pp-TVS) treatments on the adhesion of flax yarns with epoxy and vinylester thermoset matrices. These low temperature plasma processes have been selected as more environmentally friendly alternatives to traditional chemical treatments. Tensile tests performed on single flax yarns revealed a reduction in their mechanical properties after plasma treatments. In particular, a tensile strength reduction of 36.4% was detected after the oxygen plasma treatment using 100 W of plasma power. The morphological analysis highlighted that this result is mainly ascribed to the ablation action produced by oxygen plasma process. In the case of pp-TVS, both morphological and Fourier transform infrared spectroscopy analysis confirmed the presence of a homogeneous tetravinylsilane film on the surface of the yarns. The interfacial adhesion of untreated, oxygen plasma treated, and plasma-polymer coated flax yarns has been determined by single fibre fragmentation test. The plasma polymer deposition can produce a significant improvement of the adhesion property of flax yarns with both epoxy and vinylester matrices. An increase of the interfacial shear strength values of 114% and 71% was found after the TVS film deposition in epoxy and vinylester composites, respectively. These results were confirmed by high-resolution micro-CT, photoelasticity analysis and FE-SEM observations.

Parameters affecting local buckling response of pultruded GFRP I-columns: Experimental and numerical investigation

This paper aims to investigate the performance of pultruded glass fiber reinforced polymer (pGFRP) I-section columns subject to short-term concentric compression, bringing up a discussion on the relevant parameters affecting their local buckling behavior and the interpretation of tests results. An experimental program was carried out, including a detailed material characterization and twenty-nine compression tests on short I-columns made of either polyester or vinyl ester matrices, with variable flange width-to-section depth ratios (bf/d), column lengths and local end conditions. The theoretical critical loads predicted using generalized beam theory (GBT) and finite element method (FEM) were compared to experimental results obtained by Southwell and Koiter techniques, with better agreements obtained for the latter. It is shown that, besides the length and local end conditions for loaded edges, post-buckling with associated non-linear elastic strains distribution throughout the cross-section and damage prior to buckling have relevant influence on the measured critical loads. On the other hand, the influence of the rotational stiffness of web-flange junctions were considered small for the material and cross-sections studied. Finally, results have shown that the usual boundary condition adopted in literature approaches a clamped condition instead of simply-supported one.

Study on Residual Stresses in Unidirectional Flax Fiber/Vinyl Ester Composites by XRD Technique

The development of flax fiber reinforced polymer composites with improved properties has been increasingly studied by many researchers because of their sustainability. However, the effects of thermal residual stresses on the interfacial properties of flax composites have not been evaluated or very well understood. In this study, the thermal properties of flax, vinyl ester matrices and their composites were accessed by different techniques, including thermomechanical analyzer, dynamic mechanical analyzer, and X-ray diffraction combined with aluminum particles. The effects of thermal properties of flax fibers and vinyl ester resin systems on the mechanical properties of their biocomposites were studied. The theory of modifying the thermal properties of flax and vinyl ester to improve the interfacial adhesion between them has been proven by the study of the thermal residual stresses in their composites.

Response surface predictions of the viscoelastic properties of vapor‐grown carbon nanofiber/vinyl ester nanocomposites

AbstractA full factorial design of experiments and response surface methodology were used to investigate the effects of formulation, processing, and operating temperature on the viscoelastic properties of vapor‐grown carbon nanofiber (VGCNF)/vinyl ester (VE) nanocomposites. Factors included VGCNF type (pristine, oxidized), use of a dispersing agent (DA) (no, yes), mixing method (ultrasonication, high‐shear mixing, and a combination of both), VGCNF weight fraction (0.00, 0.25, 0.50, 0.75, and 1.00 parts per hundred parts resin (phr)), and temperature (30, 60, 90, and 120°C). Response surface models (RSMs) for predicting storage and loss moduli were developed, which explicitly account for the effect of complex interactions between nanocomposite design factors and operating temperature on resultant composite properties; such influences would be impossible to assess using traditional single‐factor experiments. Nanocomposite storage moduli were maximized over the entire temperature range (∼20% increase over neat VE) by using high‐shear mixing and oxidized VGCNFs with DA or equivalently by employing pristine VGCNFs without DA at ∼0.40 phr of VGCNFs. Ultrasonication yielded the highest loss modulus at ∼0.25 phr of VGCNFs. The RSMs developed in this investigation may be used to design VGCNF‐enhanced VE matrices with optimal storage and loss moduli for automotive structural applications. Moreover, a similar approach may be used to tailor the mechanical, thermal, and electrical properties of nanomaterials over a range of anticipated operating environments. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Effects of ZnS:Mn concentrated vinyl ester matrices under flexural loading on the triboluminescent yield

This paper investigates the feasibility of using zinc sulfide manganese (ZnS:Mn) concentrated vinyl ester resin as a photon emitter for damage monitoring of polymer composites under flexural loading. Unreinforced vinyl ester resins doped with optical emitting materials (ZnS:Mn phosphors) in ratios of 5–50% by weight were cast, and subjected to flexural loading using standard 3-point bend tests. The intent of this work was to observe the transient response of triboluminescence (TL) throughout the failure cycle. Results indicate TL crystals emit light at various intensities corresponding to crystal concentration and imminent matrix fracture. Consequently, concentrated samples showed nearly 50% reductions of mechanical moduli. Scanning electron microscopy (SEM) revealed particulate inclusions with shearing bands and semblance of particle to resin adhesion. Despite significant parasitic effect to mechanical properties, the triboluminescent properties occur at yielding and point of matrix fracture.

Preparation, characterization, and improvement of hollow epoxy particle‐toughened vinyl ester composites for high‐end applications

AbstractSpherical hollow epoxy particles (HEPs) that can serve as advanced reinforcing fillers for vinyl ester thermosets were prepared using the water‐based emulsion method. The HEP fillers were incorporated into the vinyl ester matrices at different loading amounts, ranging from 0 to 9 wt %, to reinforce and toughen the vinyl ester composite. The optimum mechanical properties of the HEP‐toughened epoxy composite can be achieved by the addition of 5 wt % HEP filler into the vinyl ester matrices. The toughening and strengthening of the epoxy composites involved the interlocking of vinyl ester resins into the pore regions on the HEP fillers. The toughening and interlocking mechanisms of HEP‐toughened vinyl ester composites were also proposed and discussed. The addition of HEP fillers into vinyl ester matrices increased the glass transition temperature (Tg) and thermal stability of the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Toughening vinyl ester networks with polypropylene meso-fibers: Interface modification and composite properties

Polymer–polymer composites comprised of vinyl ester matrices (VE) and polypropylene (PP) fiber meshes were fabricated and tested in this investigation. Results indicated that PP fibers greatly enhanced fracture toughness; however, strength of the VE was significantly reduced as voids were observed at the interface of the PP and VE. A two-step surface modification, oxygen plasma treatment followed by grafting vinyltrimethoxysilane (VTMS), was conducted on PP fibers in an effort to improve interfacial strength. Interfacial discontinuities of composites were improved after surface modification of PP. The oxygen plasma treatment added hydrophilic functional groups but caused surface roughness. Surface treatment of PP slightly increased fracture toughness of the PP-VE composite by enhancing energy absorption capacity at the interface. However, mechanical strength and modulus did not significantly increase for the composite using VTMS grafted PP fibers due to the weak fiber material. Small PP fibers with higher strength may attain the expected improvement in mechanical properties after surface treatment.

Polyester composites for shipbuilding

The composites with polyester or vinylester matrices as the most widespread shipbuilding nonmetallic materials are reviewed. Mechanical, physical, technological and operating characteristics of glass reinforced plastics and their relationship with component properties are discussed. The influence of aggressive environmental factors on the properties of the composites, polymer aging, and time dependence of destructive stress are considered. Rheological properties of the polymers and composites used in shipbuilding are evaluated. A new view on the polymer properties scale effect is discussed.

Kenaf Bast Fiber Bundle–Reinforced Unsaturated Polyester Composites. II: Water Resistance and Composite Mechanical Properties Improvement

Water resistance properties of kenaf bast fiber bundle (KBFB)–reinforced composites with either unsaturated polyester (UPE) or vinyl ester (VE) matrices, developed in previous research, were studied. The effects of styrene content in UPE resin on the neat UPE resin tensile properties and molding pressure on composite flexural properties were evaluated. The effect of laser and plasma radiation on fiber-matrix interfacial shear strengths was studied. The composites exhibited high water uptake during short- and long-term water immersion. Encapsulation by surface coating and edge sealing improved composite water resistance. Statistical analyses indicated that molding pressures of 5 to 7 MPa were preferable to achieve the maximum composite mechanical properties, and 37.6 percent (wt/wt) styrene in the UPE resin gave the highest UPE matrix tensile properties in the studied range. Laser and plasma radiation of the KBFBs significantly improved fiber-matrix interfacial bonding.

The Transfer of Matrix Toughness to Composite Mode I Interlaminar Fracture Toughness in Glass-Fibre/vinyl Ester Composites

The transfer of matrix toughness to composite mode I interlaminar fracture toughness (GIc) has been investigated in unidirectional glass-fibre reinforced composites with brittle and rubber-toughened vinyl ester matrices. Single-edge-notch bend (SENB) and double cantilever beam (DCB) specimens were used for matrix and composite GIc characteristion, respectively. The initial crack opening displacement rate was used as the parameter for comparison of GIc results. Matrix GIc was completely transferred to composite GIc for crack initiation (GIc -init) in the brittle-matrix composites, but in the toughened composites transfer was only partial due to the presence of fibres. The conclusion is that the maximum contribution to energy absorption by the matrix is more accurately reflected by GIc -init, and should be used for further assessment of the enhancing effect of fibre bridging during steady-state crack propagation, instead of matrix GIc. A plot of composite GIc for steady-state crack propagation, GIc -prop versus GIc -init indicates that the enhancing effect of fibre bridging is greater in the toughened composites. This enhancement is related to a larger deformation zone size in the toughened matrices.

Effect of matrix toughness on the shear strength of brittle and rubber-modified glass-fiber/vinyl ester composites

Due to its superior mechanical properties and corrosion resistance, vinyl ester resin is increasingly used as the matrix for fiber-reinforced composites instead of polyester [1]. Corrosion resistance in particular is an important attribute for composites used in applications such as marine structures, where the environment is highly corrosive. However, while vinyl ester is also tougher than polyester, with a mode I strain energy release rate (GIc) of 0.13 kJ/m2 compared to 0.06 kJ/m2 for isophthalic polyester [2], it is still relatively brittle. This brittleness makes the composite susceptibel to delamination through interlaminar fracture. In response to this delamination problem, recent work investigated interlaminar fracture toughness for unidirectionally reinforced glass-fiber composites with brittle and rubber-modified vinyl ester matrices [3, 4]. There was a considerable increase in toughness with a GIc of nearly 2 kJ/m2 reported for the toughest neat resin and, under mode I tensile loading, a GIc of 2.4 kJ/m2 for steady-state crack propagation in the composite counterpart [3]. However, under mode II shear loading, there was no significant matrix effect on composite interlaminar fracture toughness, GIIc [4]. The absence of a matrix effect on shear induced interlaminar fracture toughness is surprising, which led to the next step in the characterization of these composites; to study the matrix effect on the shear strength properties. This letter presents the results from short beam shear and compression induced shear tests, and discusses them in relation to the previously obtained fracture toughness results. The influence of loading pin diameter on short beam shear strength is also addressed. The composite laminates were made by hand lay-up using 24 plies of unidirectional E-glass fiber (Owens

The effect of matrix toughness and loading rate on the mode-II interlaminar fracture toughness of glass-fibre/vinyl-ester composites

Glass-fibre-reinforced composites are increasingly used for structural applications. However, like high-performance carbon-fibre composites, they are susceptible to mode-II-dominated delamination. In response to this problem, this paper investigates the effect of matrix toughness and loading rate on the mode-II interlaminar fracture toughness ( G IIc) of unidirectional glass-fibre composites with brittle and rubber-toughened vinyl ester matrices. Mode II tests were conducted σn end-notch-flexure (ENF) specimens at test rates ranging from 1 mm/min to 3 m/s. The G IIc results were compared to the order of matrix G Ic. There was no significant effect of loading rate or matrix toughness on G IIc. The absence of a loading rate effect is consistent with the bulk of the experimental data in the literature, but the absence of a matrix effect is not. Microscopic examination of fracture surfaces shows similar matrix deformation in each composite. The through-thickness matrix deformation zone size is also similar. These observations suggest similar energy absorption in each composite and hence support the G IIc test results. It is concluded that failure is interface controlled, whereby unstable fracture is initiated after a similarly short period of crack growth in each composite, and before an increase in G IIc as a result of increased matrix toughness becomes apparent. The G IIc results indicate that the use of rubber-toughened vinyl ester matrices in glass-fibre composites will not improve resistance to impact-induced mode II-delamination. However, through-thickness impact damage in composite structures is likely to result from mixed-mode (I/II) loading. Therefore, suggestions for future work include investigation of the matrix effect on mixed-mode (I/II) interlaminar fracture toughness, and on delamination resistance of plate structures subjected to transverse low-velocity impact.

Designed Interphase Regions in Carbon Fiber Reinforced Vinyl Ester Matrix Composites

Fiber-reinforced polymer matrix composites are finding increased use in structural applications where long-term mechanical and environmental durability are key issues. This has prompted impetus for fundamental studies to determine relationships between the structure of fiber/matrix “interphase” regions and eomposite durability in both our laboratories and those of others. This study describes initial interphase and composite properties for a series of carbon-fiber-reinforced vinyl ester matrix composites wherein the liber sizing chemical structure has been varied within a series of ductile poly(hydroxyethcr)s. The mechanical properties of the sizings were similar. The primary difference between the systems studied was the amount of sizing-matrix interdiffusion and, hence, the inicrostructure of the interphase regions. A number of techniques were used to evaluate both the “macro and micro” properties of the composites as a function of interphase structure. These include atomic force microscopy and nanoindentation to map sizing matrix interdilfusion compositional gradients and the resulting mechanical properties across bi-layer films comprised of the fiber “sizings” and vinyl ester matrices. Micro-debond tests were carried out by the Korean group to probe adhesion between the “sized” libers and matrices. Fatigue cycling proved to be particularly useful in highlighting the influence of the tailored interphases on the durability of the carbon fiber/vinyl ester composites. Composite fatigue properties of AS-4 vinyl ester composites having a tough, ductile polyhydroxyether thermoplastic in the “interphase” region were improved dramatically (relative to using unsized fibers) with < 1 wt.% of the sizing in the composite. The thermoplastic sizing dissolved in the thermoset at the cure temperature, but microphase separated into ∼90 nm diameter inclusions during matrix curing. A gradient in chemical composition and morphology resulted, which moved outward from the fiber into the thermoset matrix. It is hypothesized that the unusually good fatigue resistance of composites from these materials can be at least partially attributed to this interphase gradient.

Using XPS to Investigate FiberMatrix Chemical Interactions in Carbonfiberreinforced Composites

With the uses of composites expanding into areas from aerospace to recreation, different matrices are being investigated to tailor the composites to specific uses. The degree of adhesion between the fiber and matrix has been recognized to be a critical factor in determining the performance of fiber-reinforced composites. Indirect analysis of the matrix/fiber interface is possible using model compounds which represent functional groups present in the matrix system. Model compounds based on epoxy, polyimide, polyphenylene sulfide and vinyl ester matrices have been investigated to characterize the chemical reactions at the fiber/matrix interface. X-ray photoelectron spectroscopy has been used to characterize both the carbon-fiber surfaces and the reacted carbon-fiber surfaces. The model compounds for the polyimide and polyphenylene sulfide matrices have been found to show little chemical interaction with the fiber surfaces, while chemical reactions have been observed in the vinyl ester and epoxy resin model compound/fiber interfaces. © 1997 by John Wiley & Sons, Ltd.

Using XPS to Investigate Fiber/Matrix Chemical Interactions in Carbon-fiber-reinforced Composites

With the uses of composites expanding into areas from aerospace to recreation, different matrices are being investigated to tailor the composites to specific uses. The degree of adhesion between the fiber and matrix has been recognized to be a critical factor in determining the performance of fiber-reinforced composites. Indirect analysis of the matrix/fiber interface is possible using model compounds which represent functional groups present in the matrix system. Model compounds based on epoxy, polyimide, polyphenylene sulfide and vinyl ester matrices have been investigated to characterize the chemical reactions at the fiber/matrix interface. X-ray photoelectron spectroscopy has been used to characterize both the carbon-fiber surfaces and the reacted carbon-fiber surfaces The model compounds for the polyimide and polyphenylene sulfide matrices have been found to show little chemical interaction with the fiber surfaces, while chemical reactions have been observed in the vinyl ester and epoxy resin model compound/fiber interfaces.