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     

Effect of the delignification of wood fibers on the mechanical properties of wood fiber–polypropylene composites

The effect of the delignification of hornbeam fibers on the mechanical properties of wood fiber–polypropylene (PP) composites was studied. Original fibers and delignified fibers at three levels of delignification were mixed with PP at a weight ratio of 40:60 in an internal mixer. Maleic anhydride (0.5 wt %) as the coupling agent and dicumyl peroxide (0.1 wt %) as the initiator were applied. The produced composites were then hot‐pressed, and specimens for physical and mechanical testing were prepared. The results of the properties of the composite materials indicate that delignified fibers showed better performance in the enhancement of tensile strength and tensile modulus, whereas the hardness of the composites was unaffected by delignification. Delignified fibers also exhibited better water absorption resistance. Notched impact strength was higher for delignified fiber composites, but it was reduced at higher delignification levels. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4759–4763, 2006     

Effect of absorbed water on dynamic modulus for short fiber–CR composites

Short fiber–elastomer composites with 10 vol % fiber, nylon 6–CR and PET–CR composites, absorbed water either in the moisture atmosphere or in water. The effect of absorbed water on the viscoelastic properties for these composites was investigated. The temperature dependence of tan σ for the nylon–CR composite showed that the α-dispersion peak of nylon shifted to lower temperatures with increasing absorbed water content and that after displacement of the α-dispersion peak the additional small hump appeared at about 90°C. For the PET composite, the α-dispersion peak of PET shifted slightly to lower temperatures and the small shoulder at 90°C diminished with increasing absorbed water. The additional dispersion probably was caused by the interface between fiber and CR matrix and was independent of fiber orientation. The results suggested that nylon fiber absorbed a larger amount of water than CR matrix, while the water absorption for PET fiber was considerably less than for nylon fiber. The absorbed water in nylon fiber bonded stronger than that in CR matrix and was only slightly diminished by heat treatment under 100°C.     

Improvement of mechanical properties of natural fiber–polypropylene composites using successive alkaline treatments

The use of natural fibers (NFs) in polymer composites for structural applications has increased greatly in the last years, owing to their abundance and biodegradability. In this work, an innovative and simple successive alkali treatment has been developed to improve the mechanical properties of NFs/polypropylene (PP) composites. Three different cellulosic fibers (curauá, jute, and flax) were used, with a fixed proportion of 10 wt %. The fibers were immersed several times in a 5 wt % NaOH solution. Thermogravimetric analysis data showed an improvement in thermal properties of the fibers, as well as the increase of the crystallinity degree was measured by X‐ray diffraction. By Fourier transform infrared spectroscopy, disappearance of characteristics peaks of hemicelluloses and lignin was observed. Finally, mechanical behavior of the NF/PP composites was examined, using dynamic mechanical analysis. The results revealed that the curauá/PP mechanical properties were significantly improved, showing the positive effect of the successive alkali treatments. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41710.     

Effect of prolonged water absorption on mechanical properties in cellulose fiber reinforced vinyl‐ester composites

With the increasing of worldwide societal awareness about environmental impact, sustainability, and renewable energy sources, the polymer natural fiber composites recently have attracted the attention of researchers due to the fact that they are recyclable and biodegradable. This study conducted a new infiltration method that involved very thin sheets of recycled cellulose fibers (RCF) being fully soaked in vinyl‐ester resin for the development of natural fiber reinforced polymer composites. The effect of prolonged water absorption on the mechanical behavior of cellulose fiber (0–50 wt%) reinforced vinyl‐ester composites was investigated. The elastic modulus of these composites was measured and the data were validated with various mathematical models. The modeling results revealed that the experimental data matched the prediction data obtained by the Cox–Krenchel model. Prolonged exposure of these composites to water absorption caused a reduction in elastic modulus, strength, and toughness. POLYM. ENG. SCI., 55:2685–2697, 2015. © 2015 Society of Plastics Engineers     

Influence of coupling agents and treatments on the mechanical properties of cellulose fiber–polystyrene composites

Wood fibers of aspen in the form of chemithermomechanical pulp (CTMP) and Tembec 6816 have been used as reinforcing fillers in different varieties of polystyrene. The tensile strength, elongation, and energy at maximum point, as well as tensile modulus at 0.1% strain is reported. Also revealed is the optimum condition of compression molding. The influence of different coupling agents, such as poly[methylene(polyphenyl isocyanate)], silanes (A-172, A-174, A-1100), and grating on the mechanical properties of composites is discussed. The extent of increase in mechanical properties depends on the weight percentage of fibers, the concentration of coupling agents, and the grafting level (add-on %). Coating followed by an isocyanate treatment appears to be the best treatment. In addition, the isocyanate treatment and grafting are superior to the silane treatment. Experimental results are explained on the basis of possible interactions among cellulose fiber-coupling agent-polymer in the interfacial area.     

Processing and mechanical properties of bio‐derived vinyl ester resin‐based composites

A “green” vinyl ester resin (GVER) is investigated for use in structural applications. The GVER was formulated using a monodisperse vinyl ester created via a novel synthetic route capable of using bio‐waste material from paper and biodiesel industries. The GVER was used either as a neat resin or as blended with a commercial vinyl ester resin. The processing viscosity and gel times are investigated. The GVER reaches a similar viscosity as the commercial resin with only half the styrene monomer content, thereby reducing the volatile organic compounds associated with manufacturing. Composites of the GVER matrix reinforced by carbon fabric were tested for their tensile and flexural properties. The mechanical performance of the GVER compares favorably with commercial resin and provide a route for composites manufacturing from sustainably sourced vinyl ester matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44642.     

Effect of hygrothermal fatigue on dynamic mechanical properties and morphology of neat and glass-reinforced vinyl ester composites

A neat vinyl ester and a series of glass-reinforced vinyl-ester composites were prepared and investigated. All specimens were exposed to various syclic hygrothermal fatigue treatments, which differed from one another by the temperature and the duration of a cycle. Changes induced by the hygrothermal fatigue were studied by weight-gain measurements, dynamic-mechanical analysis, and electron microscopy. The T_g of fatigued composites were found to be determined by the amount of moisture absorbed within the resin network. The overall weight gain, however, also includes the moisture absorbed within the resin-reinnforcement interphase and is a function of the type of composite, the surface treatment of the reinforcement, and the temperature and duration of the fatigue cycle. A semiquantitative concept of the mechanism of water absorption in themoset-matrix composites has been advanced on the morphological level in order to interpret the experimental results.     

Metal ion adsorption behavior of lignocellulosic fiber–ethylene vinyl acetate composites

This study describes the applicability of lignocellulosic fiber dispersed in ethylene vinyl acetate (EVA) to adsorb Pb(II), Cr(III), and Cr(VI) ions in aqueous solutions. Water absorption studies revealed that metal‐ion uptake does not only take place on the surface of the adsorbent but ions can also diffuse into the composite. The adsorption of the metal ions under different experimental conditions was studied. Solute concentration, pH, and contact time were used to assess the adsorption capacity and efficiency. The amount of metal adsorbed increased to 7 mg/g with an increase in solute concentration but compromising the efficiency. Adsorption equilibrium was reached after 3 h, when the maximum lead adsorption was above 80%. The optimum pH for the adsorption of Pb(II) and Cr(III) was 6.5, and pH 2.5 was used for the adsorption of Cr(VI). Competitive adsorption revealed the order of adsorption to be: Pb(II) > Cr(VI) > Cr(III). POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Effect of hyperbranched epoxy resin on mechanical properties of short carbon fiber‐reinforced epoxy composites

Short carbon fiber‐reinforced composites (SCFRCs) have attracted increasing attention owing to their comprehensive performance and easy processing route. However, the imperfect interfacial adhesion and serious stress concentration at the fiber/matrix interface have hampered their engineering application. In this article, we first report the preparation of SCFRC modified by a low‐viscosity liquid hyperbranched epoxy resin (Hyper E102). We then investigated the effect of Hyper E102 content on thermal and mechanical properties. The results show that the overall performance of the SCFRC first increases and then decreases with the increasing content of Hyper E102. With the incorporation of 12 phr Hyper E102, the tensile strength, fracture toughness, notched, and unnotched impact strength of SCFRC were increased by 16.7, 74.9, 95.3, and 194.5%, respectively. The toughening and reinforcing mechanisms were attributed to the following three aspects. First, the Hyper E102 improves the impregnation property of epoxy matrix against fibers, which helps form a better interfacial adhesion. Second, the incorporation of Hyper E102 reduces the internal stress level and stress concentration of the SCFRC. Finally, the critical crack length inside the SCFRC can be remarkably increased with the incorporation of Hyper E102, which can enhance the damage tolerance of a composite. POLYM. COMPOS., 37:2727–2733, 2016. © 2015 Society of Plastics Engineers     

Effect of layering pattern on dynamic mechanical properties of randomly oriented short banana/sisal hybrid fiber–reinforced polyester composites

Dynamic mechanical test methods have been widely employed for investigating the structures and viscoelastic behavior of polymeric materials to determine their relevant stiffness and damping characteristics for various applications. Randomly oriented short banana/sisal hybrid fiber–reinforced polyester composites were prepared by keeping the volume ratio of banana and sisal 1 : 1 and the total fiber loading 0.40 volume fraction. Bilayer (banana/sisal), trilayer (banana/sisal/banana and sisal/banana/sisal), and intimate mix composites were prepared. The effect of layering pattern on storage modulus (E′), damping behavior (tan δ), and loss modulus (E″) was studied as a function of temperature and frequency. Bilayer composite showed high damping property while intimately mixed and banana/sisal/banana composites showed increased stiffness compared to the other pattern. The Arrhenius relationship has been used to calculate the activation energy of the glass transition of the composites. The activation energy of the intimately mixed composite was found to be the highest. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2168–2174, 2005     

Effect of epolene E‐43 as a compatibilizer on the mechanical properties of palm fiber–poly(propylene) composites

Composites of palm fibers and poly(propylene) (PP) were compounded in an extruder at 200°C. The composites were subsequently injection molded into standard tensile specimens for mechanical characterization. The fracture morphology of the specimens was analyzed by scanning electron microscopy. It was observed that the composite modulus increased with the increase of fiber content, indicating the existence of adhesion between PP and the much stiffer palm fibers. However, the adhesion was not satisfactory and resulted in a decrease in the composite tensile strength with fiber addition. The compatibilizer Epolene E‐43 was used to minimize this incompatibility between the wood fibers and the PP matrix. The maleated PP additive enhanced the fiber–matrix adhesion, resulting in an improvement in composite performance. Also, small fibers showed better mechanical properties than those of long fibers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2581–2592, 2004     

Comparison between microwave and thermal curing of glass fiber–epoxy composites: Effect of microwave‐heating cycle on mechanical properties

The objective of this study was to compare the mechanical properties between epoxy composites cured by thermal heating and microwave heating. Epoxy‐anhydride resins reinforced with glass fiber were cured in a domestic microwave oven and in a thermal oven. Hardening agents included methyl tetrahydrophthalic anhydride and methyl hexahydrophthalic anhydride. Microwave curing was carried out at various conditions, including 1‐, 2‐, and 3‐step heating cycle, whereby each cycle employed different power level and time. Mechanical properties were tested according to ASTM standards. It is found that the microwave‐cured composites produced mechanical properties as good as the thermally cured composites. The 2‐ and 3‐step heating cycle used in the microwave curing process produced better mechanical properties higher than those obtained from the microwaved 1‐step and thermally curing process. This is attributed to the slow increase in temperature during the beginning of the microwave curing process whereby the very low power level was applied in the first cycle of the multistep heating process. This affected the slower rate of viscosity increment, resulting in better wettability of the glass fiber with enhanced interfacial adhesion between the fibers and the resins. The viscosity of resins affected the homogeneity of the crosslinked structure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1059–1070, 2006     

Particle swarm and simulated annealing based intuitive search optimization of flexural behaviors in bioparticles impregnated coir fiber–vinyl ester composites

The present investigation is focused on evaluation and optimization of flexural behaviors of bio‐particulates impregnated coir–vinyl ester composites. The bio‐particulates such as termite mound soil, groundnut and rice husk were selected and the composite fabrications were planned as per Design of Experiments with the different levels of fiber length, fiber content, and particulate content. The flexural strength of fabricated composites was evaluated as per ASTM D 790‐10. The fractography study was carried out on tested specimens using Scanning Electron Micrographs. The nonlinear regression models were developed for the prediction of flexural behaviors over the specified range of conditions. The fabrication parameters for the better value of flexural behaviors were determined using particle swarm and simulated annealing algorithms. The optimum conditions are further refined and validated experimentally using intuitive search algorithm. It was confirmed that the termite mound soil, ground nut and rice husk impregnated coir–vinyl ester composites exhibited better value of flexural strengths of 33.5 MPa, 36 MPa, and 38.4 MPa, respectively. POLYM. COMPOS., 37:1765–1774, 2016. © 2014 Society of Plastics Engineers     

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。     

Simultaneous effects of silanized coal fly ash and nano/micro glass fiber on fracture toughness and mechanical properties of carbon fiber‐reinforced vinyl ester resin composites

In this study, the simultaneous effects of both silanized coal fly ash (S‐CFA) and nano/micro glass fiber (nGF) on fracture toughness and mechanical properties of vinyl ester (VE) resin filled with carbon fiber‐based composite materials were investigated. The CFA was treated with (3‐trimethoxysilyl) propyl methacrylate to introduce the methacryloxy groups into the surface of CFA, and was confirmed by using FTIR technique. The nGF and S‐CFA with different weight ratios were well mixed with VE resin by using of high‐speed mechanical stirrer, and ultrasonic technique before using as matrices for fabrication of carbon fiber‐based composite materials via sheet molding compound (SMC) method and hot curing processing. Many characteristics of both cured VE resin composites and carbon fiber‐based composite were examined such as mechanical properties, fracture toughness, and morphology. The results showed that by adding of both 0.1 wt% nGF and 1 wt% S‐CFA into VE resin the tensile strength, tensile modulus, flexural strength, K_IC, impact strength as well as the Mode I interlaminar fracture toughness (G_IC) of VE composites and carbon fiber based composites get optimum values and increased about 61.39%; 39.83%; 36.21%; 103.1%; 81.79%; 48.61%, respectively when compared with pristine materials. POLYM. ENG. SCI., 59:584–591, 2019. © 2018 Society of Plastics Engineers     

Evaluation of mechanical and thermal properties of tamarind seed filler reinforced vinyl ester composites

This article deals with the usage of tamarind seed filler (TSF) as reinforcement in vinyl ester (VE) composites. The composite plates have been fabricated by compression molding machine with TSFs of varying wt% from 5 to 50 as reinforcement material, and their properties such as tensile, flexural, impact, hardness, water absorption, heat deflection tests, and thermogravimetric analysis are studied. The mechanical properties of TSF reinforced VE composites are optimum at 15 wt% filler. The tensile strength and flexural strength of TSF‐VE composites are estimated to be around 34.1 and 121 MPa, respectively. The better impact strength of TSF‐VE composites is found to be 14.02 kJ/m², and barcol hardness can hold a value up to 42.33. Thermo gravimetric analysis and heat deflection test of TSF reinforced VE composite have improved the thermal stability. The fiber matrix interaction of the fractured mechanical testing specimen has been analyzed by scanning electron microscope. The TSF‐VE composites are used to fabricate the wheel hubcap of heavy‐duty buses, bus seat backrest cover, and silencer guard of the motorcycle. J. VINYL ADDIT. TECHNOL., 25:E114–E128, 2019. © 2019 Society of Plastics Engineers     

Effect of saline degradation on the mechanical properties of vinyl ester matrix composites reinforced with glass and natural fibers

One important application of polymeric composites reinforced with natural fibers is in the area of naval engineering design. The objective of this work was to study the influence of saline degradation on the mechanical properties of vinyl ester matrix composites reinforced with glass, sisal, and coconut fibers and natural fibers modified with bitumen. All samples presented mass loss after exposure in a salt spray chamber. All materials, except the composite reinforced with coconut–bitumen, showed a decrease in toughness after a salt spray test. The fracture of the vinyl ester resin with sisal and sisal–bitumen fibers showed a fiber bridging mechanism. These materials showed the highest value of toughness among the materials studied. The presence of fiber pullout was observed in the samples of vinyl ester resin reinforced with glass, coconut, and coconut fibers covered with bitumen. In these samples, poor adhesion between the fiber and matrix was observed. The treatment of fibers with bitumen increased the mass loss and decreased the stability of samples in a saline atmosphere. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Thermal,mechanical, and corrosion resistance properties of vinyl ester/clay nanocomposites for the matrix of carbon fiber‐reinforced composites exposed to electron beam

Vinyl ester/clay nanocomposites with 1, 3, and 5% nanoclay contents were prepared. X‐ray diffractography patterns and Scanning Electron micrographs showed that nanocomposites with the exfoliated structure were formed. Thermogravimetric analysis, water absorption test, and Tafel polarization method, respectively, revealed the improvements in thermal resistance, water barrier properties, and corrosion resistance properties of the samples with an increase in the amount of the incorporated nanoclay. Tensile tests showed that nanoclay also enhanced the mechanical properties of the polymer, so that the tensile strength of the samples with 5% nanoclay was more than 3 times higher than tensile strength of pure vinyl ester samples. Overall, the best properties were observed for the samples containing 5% nanoclay. Pure vinyl ester and nanocomposite with 5% nanoclay content were exposed to the electron beam radiation and their mechanical properties improved up to 500 kGy irradiation dose. Finally, pure vinyl ester and vinyl ester/nanoclay (5%) matrixes were reinforced with carbon fiber and the effect of electron beam irradiation on their mechanical properties was examined. The tensile strength and the modulus of the samples initially increased after exposure to the radiation doses up to 500 kGy and then a decrease was observed as the irradiation dose rose to 1000 kGy. Moreover, nanoclay moderated the effect of the irradiation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42393.     

Short fiber–elastomer composites. Effects of matrix and fiber level on swelling and mechanical and dynamic properties

The effects of different types of elastomeric matrix (NR, SBR, CR, NBR) and several levels (10, 15, and 20 parts phr) of short fibers on mechanical properties of uncured and cured composites and on swelling behavior of composites in hydrocarbon solvent are studied. The variation of the dynamic properties, E′, E″, and tan δ is determined as a function of deformation amplitude, temperature, and vibration frequency in composite materials subjected to dynamic deformation. The increase of fiber level does not limit the orientation ability of the fibers, which in all materials seemed to be above 70%. The addition of fiber markedly reduces maximum swelling and entails an increase in material stiffness. In addition, the amount of dissipated energy is increased and hence transformable into heat upon fiber incorporation, which can reach up to 16 times the value corresponding to the matrix alone, in addition to an increase with strain amplitude. The effect is most pronounced in the presumed direction of fiber orientation. The marked reduction of elongation at break (up to values of 7–9% of those of unfilled samples) and the shape of stress-strain curves point to a good fiber-matrix adhesion. Dynamic glass transition temperature is displaced toward higher values as a consequence of matrix-fiber interaction, which increases proportionally to fiber level, thus proving a linear relationship between thermal displacement and the number of interactions between the two phases. By the same token, the apparent activation energy of the relaxation process is enhanced for fiber-containing materials as compared to the fiber-free. The fiber composites present a less prominent yet broader transition zone.