Effect of α-methyl styrene on curing behaviour and interfacial properties of glass fibre-reinforced vinyl ester resins

The curing behaviour of bismethacryloyl derivative of diglycidyl ether of bisphenol A (vinyl ester VE resin) containing styrene and α-methyl styrene (MS) as reactive diluents was studied. Delayed curing was observed in samples containing increasing proportions of MS. Interfacial shear stress of untreated as well as γ-methacryloyloxy-propyl trimethoxy silane (MTS) treated, glass fibre-reinforced VE resin composites were measured by single fibre technique. In comparison to untreated glass fibres, a 30 – 50% increase in interfacial shear stress was observed in composites based on MTS treated glass fibres. Addition of up to 5 wt.-% MS to VE resin did not affect the interfacial shear strength (ILSS). This behaviour was observed by using ILSS measurement of both glass fabric-reinforced composites as well as single fibre specimens. Further increase in MS to 15 wt.-% resulted in an increase in ILSS and bending stiffness as well as flexural strength.     

Vinyl ester resins. II. Effect of styrene on electrical properties

Bisglycidyl methacrylate of bisphenol A (vinyl ester resin) having systematically varying styrene content was cured by using benzoyl peroxide as a initiator. Thermally stimulated discharge current (TSDC) and ac dielectric measurements of the cured resins were carried out. The polarization of these resins depended on the presence of polar groups and space charge. The lowest dielectric constant was observed with the resin having 30% styrene.     

MMA对乙烯基酯树脂及其复合材料性能的影响

通过粘度分析和力学性能、阻燃性能测试,研究了以甲基丙烯酸甲酯(MMA)作活性稀释剂的乙烯基酯树脂的流变性能及其对复合材料性能的影响。结果表明:常温下MMA能有效降低乙烯基酯树脂的粘度,20~40℃下,添加量>30%时,树脂体系的粘度在450 mPa.s以内,可应用于RTM工艺;固化后该复合材料的拉伸、弯曲强度、抗冲击性能、层间剪切强度和阻燃性能优异,可应用于高性能阻燃型复合材料构件的制备。     

Curing kinetics and thermal properties of vinyl ester resins

The curing kinetics of dimethacrylate-based vinyl ester resins were studied by scanning and isothermal DSC, gel time studies, and by DMTA. The rate of polymerization was raised by increased methyl ethyl ketone peroxide (MEKP) concentration but the cocatalyst, cobalt octoate, retarded the reaction rate, except at very low concentrations. By contrast, the gel time was reduced for all increases in either peroxide or cobalt concentration. This contradictory behavior was explained by a kinetic scheme in which the cobalt species play a dual role of catalyzing the formation of radicals from MEKP and of destroying the primary and polymeric radicals. The scanning DSC curves exhibited multiple peaks as observed by other workers, but in the present work, these peaks were attributed to the individual influence of temperature on each of fundamental reaction steps in the free radical polymerization. Physical aging appeared to occur during the isothermal polymerization of samples cured below the “fully cured” glass transition temperature (T_g). For these undercured materials, the difference between the DSC T_g and the isothermal curing temperature was approximately 11°C. Dynamic mechanical analysis of a partially cured sample exhibited anomalous behavior caused by the reinitiation of cure of the sample during the DMTA experiment. For partially cured resins, the DSC T_g increased monotonically with the degree of cure, and this dependence was fitted to an equation related to the Couchman and DiBenedetto equations. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 769–781, 1997     

Synthesis of vinyl ester resins

Summary The reaction of diglycidyl ether of bisphenol A with methacrylic acid was carried out in the presence of an amine catalyst (imidazole) or a chromium chelate (chromium diisopropylsalicylate). The resin products were analyzed by gel permeation chromatography and¹³C nuclear magnetic resonance spectroscopy. With both catalysts the reaction is characterized by an isomerization of the hydroxy-ester. The imidazole-catalyzed reaction product gave transesterification species in addition to isomerization product whereas these were absent with the chromium derivative catalyst.     

Low temperature cure of vinyl ester resins

Vinyl ester resins are well known for their versatility as a composite matrix. With the development of a promising room temperature molding technology, vacuum-assisted resin transfer molding, e.g. Seemann Composite Resin Infusion Molding Process (SCRIMP), the processability of vinyl ester resins at low temperatures has attracted considerable attention from the composite industry. The objective of this paper is to provide a better understanding of the reaction kinetics of this resin system at low temperatures. In this study, a differential scanning calorimeter (DSC) coupled with a Fourier transform infrared (FTIR) spectrometer was employed to measure the reaction profile of a vinyl ester resin with different promoter and styrene contents. A kinetic model based on the free radical co-polymerization mechanism was developed for simulating the reaction rates and conversions of styrene vinyl and vinyl ester vinylene groups. The model parameters were determined from several FTIR experiments under isothermal conditions. This model, in conjunction with heat transfer analysis, was able to successfully predict the temperature profiles during curing in two SCRIMP molding cases based on groove type resin distribution system.     

Relationship between the network morphology and properties of commercial vinyl ester resins

Two commercial vinyl ester resins, Derakane 411‐350 (resin D) and Derakane 411‐350 Momentum (resin M), were characterized. Despite the large quantity of publications in the literature about vinyl ester resins, few experimental results have been reported for resin M. The effect of the styrene content on the mechanical properties and morphological structure was studied. An increase in the styrene content produced a network with a low storage modulus in the rubber state and a glass‐transition temperature. The apparent average molecular weight between crosslink points and glass‐transition temperature were slightly higher for resin D than for resin M. The Fourier transform infrared spectra and molecular weight distributions were similar. However, resin M was tougher than resin D, and this may have been due to the closer structure in the fully cured state. Atomic force microscopy was performed for each cured resin and confirmed the difference in the nanostructures. The main reason for the differences in the developed structures was the use of an accelerator, which influenced the final morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3895–3903, 2006     

Use of allyl‐functional benzoxazine monomers as replacement for styrene in vinyl ester resins

New vinyl ester systems are prepared using allyl‐functional benzoxazine monomers, 3‐allyl‐6‐methyl‐3,4‐dihydro‐2H‐benzo[e][1,3]oxazine (pC‐ala) or bis(3‐allyl‐3,4‐dihydro‐2H‐benzo[e][1,3]oxazin‐6‐yl)methane (BF‐ala), as reactive diluents for vinyl ester resins derived from an epoxy resin, diglycidyl ether of bisphenol A, instead of using styrene. Different initiators are used to investigate the copolymerization of allyl function from pC‐ala with vinyl function from vinyl ester resin prepolymer. The temperature dependence of viscosity is studied to demonstrate the retention of processability of the new vinyl ester resins. Dynamic mechanical and thermogravimetric analyses are used to investigate the dynamic mechanical properties and thermal stability of the new resins. Copyright © 2012 Society of Chemical Industry     

Curing kinetics of divinyl ester resins with styrene

The curing reaction of a divinyl ester resin with different proportions of styrene—4, 20, and 40% by weight—was investigated by differential scanning calorimetry (DSC) using isothermal and dynamic modes. The different constraints on the reaction rate was globally considered, taken the reaction as divided in two regimens: below the vitrification regimen and during the vitrification regimen. Below the vitrification regimen, the autocatalytic model developed by Kamal was used to perform the analysis of the curing kinetics of divinyl ester resin with styrene. Experimental data from dynamic and isothermic runs, at a fixed composition, were simultaneously considered, while the actual temperature records (measured during the DSC runs) were also taken into account. The adjusted kinetic parameters took into account the gel effect on the radicals' termination rate and the structure constraints on the reactivity of pendant vinyls groups, present during this stage. During the vitrification stage, the diffusion control due to the low mobility of the reactive groups and molecules was incorporated into the overall rate constant according to the Rabinowitch model, which considers the two regimen contributions to the overall reaction rate kinetic. The Vogel–Fulcher relationship was adopted to express the temperature dependence of the rate constant during the vitrification stage. The method presented here has been satisfactorily applied to dynamic and isothermal curing reactions, allowing a simple and general kinetic expression useful in the design, optimization, and control of the processing of composites based on these thermoset polymers to be obtained. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1044–1053, 1999     

Effect of structure on mechanical properties of vinyl ester resins and their glass fiber‐reinforced composites

The article describes the effect of structure of vinyl ester resins (VE) on the mechanical properties of neat sheets as well as glass fabric‐reinforced composites. Different samples of VE were prepared by reacting ester of hexahydrophthalic anhydride (ER) and methacrylic acid (MAA) (1 : 1 molar ratio) followed by reaction of monomethacrylate terminated epoxy resin with glutaric (E) or adipic (F) or sebacic acid (G) (2 : 1 molar ratio). The neat VE were diluted with styrene and sheets were fabricated by using a glass mold. A significant reduction in the mechanical properties was observed by increasing the methylene content of resin backbone (i.e., sample E to G). Glass fabric‐reinforced composites were fabricated by vacuum assisted resin transfer molding (VARTM) technique. Resin content in the laminates was 50 ± 5 wt %. Increase in the number of methylene groups in the vinyl ester resin (i.e., increasing the bridge length) did not show any significant effect on limiting oxygen index (LOI) value (21 ± 1) of the laminates but tensile strength, tensile modulus, flexural strength, and flexural modulus all increased though these values are significantly lower than observed in laminates based on resin B. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermokinetics of unsaturated polyester and vinyl ester resins

An experimental study was carried out to investigate the isothermal and non-isothermal curing kinetics of unsaturated polyester and vinyl ester resins, using differential scanning calorimetry (DSC). Emphasis was put on investigating the effect of low-profile additives on the curing kinetics of the thermo-setting resins. For the study, a general-purpose polyester resin and a vinyl ester resin were used, together with polyvinyl acetate (PVAc) as low-profile additive, benzoyl peroxide as initiator, and N,N-dimethyl aniline as promoter. It has been found that (1) the addition of the low-profile thermoplastic-additive decreases the rate of cure and, also, the final degree of cure of the resins, (2) the total heat of cure generated by isothermal cure is lower than that generated by non-isothermal cure, and (3) the resin/initiator mixture with promoter exhibits two major exotherm peaks during non-isothermal cure, but only a single exotherm peak during isothermal cure.     

Effect of oxirane groups on curing behavior and thermal stability of vinyl ester resins

The effects of oxirane groups in vinyl ester (VE) resin and reactive diluent on curing characteristics and thermal behavior of cured resins are described. Stoichiometric (0.5:1, sample A) as well as nonstoichiometric (0.5:0.85, sample B) ratios of the diglycidyl ether of bisphenol-A (DGEBA) and methacrylic acid (MA) were used for the synthesis of VE resins. Resin sample B had more residual epoxy groups because of the stoichiometric imbalance of the reactants. VE resins thus obtained were diluted with methyl methacrylate (MMA; 1:1, w/w), and controlled quantities of epoxy groups were introduced by partial replacement of MMA with glycidyl methacrylate (GMA), keeping the overall ratio of resin and reactive diluent constant. Increase of GMA content in resin A or B resulted in a decrease in gel time, indicating that the curing reaction is facilitated by the presence of epoxy groups. An increase in initiator content also reduced the gel time. In the differential scanning calorimetry (DSC) scans, a sharp curing exotherm was observed in the temperature range 107 ± 3–150 ± 1 °C. The onset temperature (T_onset) and peak exotherm temperature (T_exo) decreased with increase in GMA content. Heat of curing (ΔH) also increased with increase in GMA content. A broad exotherm was observed after the initial sharp exotherm that was attributed to the etherification reaction. Cured VE resins were stable up to 250–260 °C, and started losing weight above this temperature. Rapid decomposition was observed in the temperature range 400–500 °C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 416–423, 2001     

Hybrid resins from polyisocyanate,vinyl ester,melamine formaldehyde and water glass: structure and properties

Abstract

Hybrid thermosets were produced from polymeric methylene diphenyl isocyanate (PMDI), styrene cross-linkable vinyl ester (VE) and water glass (WG) using melamine formaldehyde (MF) resin as additional reactive emulsifier. Vinyl ester (VE) was added to the PMDI/MF mixture in which the WG was dispersed next. The content of MF in the resin formulation was varied between 0·5 and 15 wt-%. The resulting water in oil type (W/O) emulsion (water=WG, oil=organic phase composed of PMDI+VE+MF) was cured at room temperature for 24 h followed by post-curing at T=100°C for 4 h. The chemorheology of the hybrid resins was assessed by plate/plate rheometry. Information on the morphology of the cured hybrid resins was received from scanning electron microscope (SEM), atomic force microscopic (AFM) and dynamic mechanical thermal analysis (DMTA) studies. The mechanical and fracture mechanical properties as well as the resistance to thermal degradation of the hybrid thermosets were determined and discussed.     

Morphology and fracture properties of modified bisphenol A and novolac type vinyl ester resins

The morphology–toughness relationship of vinyl ester resins was studied as a function of their modification. Bisphenol A based and novolac‐based vinyl ester resins were modified by a star‐shaped polyether polymer with vinyl and hydroxyl functionalities and/or by a polyisocyanate. The polyisocyanate‐containing systems were termed vinyl ester/urethane hybrids. The morphology of the crosslinked resins was studied with dynamic mechanical thermal analysis and atomic force microscopy with ion‐eroded specimens and discussed. The toughness of the crosslinked resins was assessed by the linear elastic fracture mechanics with compact tension specimens. The fracture toughness and energy changed fairly linearly as functions of M_c and M_c^0.5, respectively, where M_c is the mean molecular mass between crosslinks. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4012–4022, 2006     

Toughening of vinyl ester resins by two-dimensional MXene nanosheets

Two-dimensional nanosheets are highly effective tougheners for vinyl ester resins. The toughening effect is related to the high specific surface area and unique two-dimensional planar structure of the nanosheets. In this study, a coupling agent γ-(2,3-epoxypropoxy) propytrimethoxysilane (Kh-560) was used to modify MXene nanosheets (M-MXene) for use in toughening vinyl ester resin. The mechanical properties, including the tensile strength, flexural strength, Young’s modulus and elongation, of neat vinyl ester resin and vinyl ester resin modified with MXene and M-MXene were investigated. The results showed that modification significantly improved the mechanical properties of the vinyl ester resin. The tensile and flexural strengths of the MXene-nanosheet-modified vinyl ester resin were 27.20% and 25.32% higher, respectively, than those of the neat vinyl ester resin. The coupling agent improved the interfacial compatibility between the MXene nanosheets and vinyl ester resin, which resulted in the tensile and flexural strengths of the M-MXene-nanosheet-modified vinyl ester resin being 52.57% and 54.60% higher, respectively, than those of the neat vinyl ester resin for a loading quantity of nanosheets of only 0.04 wt %, which is economically viable. The main mechanisms by which the nanosheets toughen the resin are crack deflection and crack pinning.     

Molecular relaxation behavior of fatty acid-based vinyl ester resins

The experimental characterization of the time-dependent properties of fatty acid-based vinyl ester resins with reduced styrene content and emissions was conducted and compared with that of various commercial vinyl ester (VE) resins. Constant heating rate and isothermal, multifrequency sweep experiments were conducted over a wide temperature range using dynamic mechanical analysis. Storage and loss modulus master-curves were formed using time–temperature superposition (TTSP) and analyzed to quantify the molecular relaxation behavior using accepted techniques and theories. Special attention was focused on determining the effect of reducing styrene weight percent on the derived viscoelastic properties. The fatty acid-based VE resins were found to have similar or slightly inferior thermomechanical properties and a more pronounced viscoelastic response compared with the commercial resins. However, the research definitively demonstrates that the evaluated fatty acid VE resins are a viable replacement to commercial resins in certain applications with concomitant attractive environmental benefits. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Polystyrene/vinyl ester resin/styrene thermoplastic elastomer composites: Miscibility,morphology, and mechanical properties

Polystyrene/Styrene‐Ethylene‐Propylene‐Styrene/Vinyl Ester Resin (PS/SEPS/VER) blends used as matrix of ultra high molecular weight polyethylene (UHMWPE) fiber‐reinforced composites, which included both physical crosslinking points of thermoplastic resin SEPS and chemical crosslinking network of thermosetting resin PS/VER, were prepared by solution blending and hot‐molding. Morphology and mechanical properties of the PS/SEPS/VER composites were investigated in this work. The microstructure of PS/SEPS/VER composites observed by means of scanning electron microscopy (SEM) was correlated with mechanical properties. It is worth noting that, stiffness increased sharply with the addition of VER within a certain range. Impact properties verified the structure that the physical crosslinking points of SEPS were immersed in the chemical crosslinking network of PS/VER. Dynamic mechanical analysis revealed that, incorporation of VER changed the storage modulus and loss tangent. In brief, addition of VER had improved mechanical properties, thermal stability, and fluidity of the composites during processing, indicating a successful result for preparing resin matrix material with outstanding comprehensive performances. Analog map was presented to facilitate better understanding of the special structure of PS/SEPS/VER. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Process cure monitoring of unsaturated polyester resins,vinyl ester resins,and gel coats by Raman spectroscopy

The curing process of unsaturated polyester resins, vinyl ester resins, and gel coats was studied by using a process Raman spectrometer, equipped with a remote fiber‐optic probe. The resins were cured and Raman spectra were recorded during the curing reaction. The spectral changes were identified and, from the intensities, the cure process could be monitored. Gel times given by the resin suppliers correlated well with the Raman results. It could also be seen that the curing process continues for a long time, up to several weeks. Postcuring will finally complete the curing process. White and lightly colored gel coats could easily be monitored by Raman spectroscopy, but fluorescent problems were encountered with heavily colored pigments. The curing of laminates containing 50–70 wt % glass fiber mat could also be followed by Raman spectroscopy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1285–1292, 2004     

Vinyl ester resins, 3. Effect of ethyl methacrylate on thermal and mechanical properties

This paper describes the effect of ethyl methacrylate (EMA) on the thermal and mechanical properties of glass fibre-reinforced laminates of vinyl ester resins derived from diglycidyl ether of bisphenol-A and methacrylic acid. The thermal stability and the curing characteristic of the resins were investigated by thermogravimetric analysis and differential scanning calorimetry. The glass transition temperature of the laminates decreased with increase in EMA content. Dilution of vinyl ester resin with EMA resulted in a decrease in flexural strength and flexural modulus of the laminates.