Potassium‐Based Geopolymer Composites Reinforced with Chopped Bamboo Fibers

Bamboo is a fast‐growing, readily available natural material with tensile specific strength equivalent to that of steel (250–625 MPa/g/cm³). In the pursuit of sustainable construction materials, a composite was made with potassium polysialate siloxo geopolymer as the matrix and randomly oriented chopped bamboo fibers (Guadua angustifolia) from the Amazon region as the reinforcement. Four‐point flexural strength testing of the geopolymer composite reinforced with bamboo fibers was carried out according to ASTM standard C78/C78M‐10^e1. Potassium‐based metakaolin geopolymer reinforced with 5 wt% (8 vol%) untreated bamboo fibers yielded 7.5 MPa four‐point flexural strength. Scanning electron microscopy and optical microscopy were used to investigate the microstructure. In addition, X‐ray diffraction was used to confirm the formation of geopolymer.     

The single fiber composite test: A comparison of E‐glass fiber fragmentation data with statistical theories

Novel difunctional and tetra functional organically modified ceramics with methacrylate functional groups were developed from liquid precursors using the sol–gel process. These novel inorganic–organic hybrid materials were characterized using various techniques and used for the preparation of visible light cure dental restoratives, which have good mechanical properties and excellent surface hardness. Effect of cure time on vickers hardness of cured composite was measured, and compared with that of the bisphenol A glycidyl methacrylate (Bis GMA) based composite. Statistical evaluation using analysis of variance (single factor) showed a significant (P < 0.05) difference in diametral tensile strength and hardness with variation in inorganic content. Also a significantly improved hardness was obtained for the new organically modified ceramic composite compared with BisGMA based composite at all exposure time. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Amorphous self-glazed,chopped basalt fiber reinforced,geopolymer-based composites

Geopolymer composites reinforced with refractory, chopped basalt fibers, and low melting glass were fabricated and heat treated at higher temperatures. K₂O·Al₂O₃·4SiO₂·11H₂O was the stoichiometric composition of the potassium-based geopolymer which was produced from water glass (fumed silica, deionized water, potassium hydroxide), and metakaolin. Addition of low melting glass (T_m ~815°C) increased the flexure strength of the composites to ~5 MPa after heat treatment above 1000°C to 1200°C. A Weibull statistical analysis was performed exhibiting how the amorphous self-healing and self-glazing effect of the glass frit significantly improved the flexure strength of the geopolymer and ceramic composites after exposure for 1 hour to high temperatures. At 950-1000°C, the K-based geopolymer converted to primarily a crystalline leucite ceramic, but the basalt fiber remained intact, and the melted glass frit flowed out of the surface cracks and sealed them. 1150℃ was determined to be the optimum heat treatment temperature, as at ≤1200°C, the basalt fibers melt and the strength of the reinforcement in the composites is significantly reduced. The amorphous self-healing and amorphous self-glazing effects of the glass frit significantly improved the room temperature flexure strength of the heat-treated geopolymer and ceramic composites.     

Investigation of mechanical properties of alumina nanoparticle‐loaded hybrid glass/carbon‐fiber‐reinforced epoxy composites

This research work investigates the tensile strength and elastic modulus of the alumina nanoparticles, glass fiber, and carbon fiber reinforced epoxy composites. The first type composites were made by adding 1–5 wt % (in the interval of 1%) of alumina to the epoxy matrix, whereas the second and third categories of composites were made by adding 1–5 wt % short glass, carbon fibers to the matrix. A fourth type of composite has also been synthesized by incorporating both alumina particles (2 wt %) and fibers to the epoxy. Results showed that the longitudinal modulus has significantly improved because of the filler additions. Both tensile strength and modulus are further better for hybrid composites consisting both alumina particles and glass fibers or carbon fibers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39749.     

Environmental durability of banana‐fiber‐reinforced phenol formaldehyde composites

We explored the environmental aging behavior of banana‐fiber‐reinforced phenol formaldehyde (PF) composites. The composites were subjected to water aging, thermal aging, soil burial, and outdoor weathering. The effects of chemical modification and hybridization with glass fibers on the degradability of the composites in different environments were analyzed. The extent of degradation was measured by changes in the weight and tensile properties after aging. Absorbed water increased the weight of water‐aged composites, and chemical treatments and hybridization decreased water absorption. The tensile strength and modulus of the banana/PF composites were increased by water aging, whereas the strength and modulus of the glass/PF composites were decreased by water aging. As the glass‐fiber loading was increased in the hybrid composites, the increase in strength by water aging was reduced, and at higher glass‐fiber loadings, a decrease in strength was observed. The tensile properties of the composites were increased by oven aging. The percentage weight loss was higher for soil‐aged samples than for samples weathered outdoors. The weight loss and tensile strength of the glass/PF composites and banana/glass/hybrid/PF composites were much lower than those of the banana/PF composites. Silane treatment, NaOH treatment, and acetylation improved the resistance of the banana/PF composites on outdoor exposure and soil burial. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2521–2531, 2006     

Friction and wear behavior of glass fabric/phenolic resin composites with surface‐modified glass fabric

Untreated, air‐plasma‐bombarded, and β‐aminoethyltrimethoxylsilane‐silanized glass fabric (GF) was used to prepare GF/phenolic composites by dip coating in a phenolic adhesive resin and successive curing. The tribo‐performances of these GF/phenolic composites sliding against AISI‐1045 steel were evaluated with a pin‐on‐disc wear tester. The chemical composition of the untreated and surface‐treated GF was analyzed with Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy. The interfacial regions between the phenolic resin and GF and the worn surfaces of the composites were analyzed with scanning electron microscopy. The results show that the GF/phenolic composite with β‐aminoethyltrimethoxylsilane‐silanized GF had the highest load‐carrying capacity and best tribo‐performance, and it was followed by the composite with plasma‐treated GF. The improved tribo‐performance of the GF/phenolic composite made of surface‐treated GF was attributed to the strengthened interfacial bonding between the treated GF and the phenolic adhesive resin. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

Long jute fiber‐reinforced polypropylene composite: Effects of jute fiber bundle and glass fiber hybridization

Two types of long jute fiber pellet consisting of twisted‐jute yarn (LFT‐JF/PP) and untwisted‐jute yarn (UT‐JF/PP) pellets are used to prepare jute fiber–reinforced polypropylene (JF/PP) composites. The mechanical properties of both long fiber composites are compared with that of re‐pelletized pellet (RP‐JF/PP) of LFT‐JF/PP pellet, which is re‐compounded by extrusion compounding. High stiffness and high impact strength of JF/PP composites are as a result of using long fiber. However, the longer fiber bundle consequently affects the distribution of jute fiber. The incorporation of 10 wt % glass fibers is found to improve mechanical properties of JF/PP composites. Increasing mechanical properties of hybrid composites is dependent on the type of JF/PP pellets, which directly affect the fiber length and fiber orientation of glass fiber within hybrid composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41819.     

Mechanical behavior of agro‐residue‐reinforced polypropylene composites

In this research, fully environment‐friendly, sustainable and biodegradable composites were fabricated, using wheat straw and rice husk as reinforcements for thermoplastics, as an alternative to wood fibers. Mechanical properties including tensile, flexural, and impact strength properties were examined as a function of the amount of fiber and coupling agent used. In the sample preparation, three levels of fiber loading (30, 40, and 50 wt %) and two levels of coupling agent content (0 and 2 wt %) were used. As the percentage of fiber loading increased, flexural and tensile properties increased significantly. Notched Izod results showed a decrease in strength as the percentage of fiber increases. With addition of 50% fiber, the impact strengths decreased to 16.3, 14.4, and 16.4 J/m respectively, for wheat straw‐, rice husk‐, and poplar‐filled composites. In general, presence of coupling agent had a great effect on the mechanical strength properties. Wheat straw‐ and rice husk‐filled composites showed an increase in the tensile and flexural properties with the incorporation of the coupling agent. From these results, we can conclude that wheat straw and rice husk fibers can be potentially suitable raw materials for manufacturing biocomposite products. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Melt rheology of polypropylene reinforced with polyaniline‐coated short glass fibers

This research deals with the melt rheology of isotactic polypropylene (iPP) reinforced with short glass fibers (SGF) coated with electrically conductive polyaniline (PAn). Composites containing 10, 20, and 30 wt % PAn‐SGF were studied. Moreover, a composite of 30 wt % PAn‐SGF was also prepared with a blend of iPP and PP‐grafted‐maleic anhydride (iPP/PP‐gMA). The composites showed linear viscoelastic regime at small strain amplitudes. The onset of nonlinearity decreased as the concentration of filler increased. The time‐temperature superposition principle applied to all composites. The filler increased the shear moduli (G′, G″) and the complex viscosity η*. Steady‐state shear experiments showed yield stress for the composites with 20 and 30 wt % PAn‐SGF. Strikingly, the 10 wt % composite showed higher steady state viscosity than the 20 wt %. Rheo‐optics showed that shear induced disorder of microfibers at a concentration of 10 wt %. However, at 20 wt % concentration shear aligned the microfibers along the flow axis, this would explain the anomalous steady state viscosity values. The viscosity exhibited a shear thinning behavior at high shear rates for all composites. Creep experiments showed that the filler induced greater strain recovery in the composites and that the amount of strain recovery increased as the PAn‐SGF concentration increased. However, the enhancement of strain recovery (as well as shear viscosity) was more significant when using the iPP/PP‐gMA blend, suggesting greater adhesion between this matrix and the filler PAn‐SGF. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Tensile stress relaxation of short‐coir‐fiber‐reinforced natural rubber composites

The stress relaxation behavior of natural rubber (NR) and its composites reinforced with short coir fibers under tension was analyzed. The rate of stress relaxation was a measure of the increase in the entropy of the compounds: the higher the rate was, the greater the entropy was. At lower strain levels, the relaxation mechanism of NR was independent of strain level. However, the rate of relaxation increased with the strain level. Also, the strain level influenced the rate of stress relaxation considerably in the coir‐reinforced NR composites. However, the relaxation mechanisms of both the unfilled compound and the composite were influenced by the strain rate. The rate of relaxation was influenced by fiber loading and fiber orientation. From the rate of stress relaxation, we found that fiber–rubber adhesion was best in the composite containing fibers subjected to a chemical treatment with alkali, toluene diisocyanate, and NR solutions along with a hexaresorcinol system as a bonding agent. In this study, the stress relaxation curves could not be viewed as segments with varying slopes; however, a multitude of inflection points were observed on the curves. Hence, we propose neither a two‐step nor three‐step mechanism for the coir‐fiber‐reinforced NR composites as reported for some other systems. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 96–104, 2004     

Non‐traditional lightweight polypropylene composites reinforced with milkweed floss

Lightweight composites are preferred for automotive applications due to the weight restrictions and also due to the presence of inherent voids that can enhance the sound absorption of these composites. The density of the reinforcing materials plays a crucial role in such lightweight composites. Milkweed is a unique natural cellulose fiber that has a completely hollow center and low density (0.9 g cm^?3) unlike any other natural cellulose fiber. The low density of milkweed fibers will allow the incorporation of higher amounts of fiber per unit weight of a composite, which is expected to lead to lightweight composites with better properties. Polypropylene (PP) composites reinforced with milkweed fibers have much better flexural and tensile properties than similar PP composites reinforced with kenaf fibers. Milkweed fiber‐reinforced composites have much higher strength but are stiffer than kenaf fiber‐reinforced PP composites. Increasing the proportion of milkweed in the composites from 35 to 50% increases the flexural strength but decreases the tensile strength. The low density of milkweed fibers allows the incorporation of higher amounts of fibers per unit weight of the composites and hence provides better properties compared to composites reinforced with common cellulose fibers with relatively high density. This research shows that low‐density reinforcing materials can more efficiently reinforce lightweight composites. Copyright © 2010 Society of Chemical Industry     

Melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites. II. Chemical modification

The effect of chemical modification of both fiber and matrix on melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites was studied with an Instron capillary rheometer. The variations of melt viscosity with different shear rate and shear stress values for different temperatures were studied. A temperature range of 130 to 150°C and shear rates of 16.4 to 5468 s^?1 were chosen for the analysis. Chemical modifications with stearic acid, maleic anhydride, silane, and peroxides were tested for their ability to improve the interaction between the matrix and fiber. The viscosity of the hybrid composites increases with every chemical modification. In the case of peroxide‐treated composites, the increase can be attributed to the peroxide‐induced grafting of the polyethylene matrix to the fiber surface and to the crosslinking of the polyethylene matrix. These phenomena are both activated by temperature, whereas temperature causes a reverse effect for all other chemical modifications. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 443–450, 2003     

Short‐term effects of sea water on E‐glass/vinylester composites

The use of ambient cured E‐glass/vinylester composites is increasingly being considered for infrastructure applications both along the shore and offshore, thereby exposing the composite to a marine aqueous environment. The use of ambient cure potentially results in incomplete polymerization and susceptibility for degradation early in life. This study characterizes the mechanical response of E‐glass/vinylester quadriaxial composites immersed in deionized water, sea water, and synthetic sea water. It is seen that there are substantial differences based on the solution type, with deionized water immersion causing the maximum drop in interlaminar shear performance and sea water causing the maximum reduction in tensile performance. The effect of cycling, simulating the tidal zone or the splash zone, is seen to be more pronounced in a resin‐dominated response. Drying of specimens, even over prolonged periods of time, is not seen to result in complete regain of performance degradation due to sorption processes. A clear competition is seen between the phenomena of moisture‐induced residual cure/postcure and physical (fiber‐matrix debonding, microcracking, plasticization) and chemical (hydrolysis) aging. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2760–2767, 2002     

Low‐temperature hygrothermal degradation of ambient cured E‐glass/vinylester composites

Freeze and freeze‐thaw durability characteristics of fiber reinforced polymer (FRP) composites, especially in the presence of moisture, need to be investigated prior to the widespread implementation of these materials in civil, polar, and offshore structural components and systems. The hygrothermal degradation characteristics of an ambient cure E‐glass/vinylester system due to exposure to ?10°C conditions and conditions of freeze‐thaw, including in the presence of water and seawater, was investigated. Changes in mechanical characteristics such as strength and modulus, and thermo‐mechanical dynamic characteristics such as storage and loss moduli, and glass‐transition temperature were measured, and short‐term effects of environmental exposure were assessed. It is seen that the presence of moisture/solution has a significant effect; both in terms of physical and chemical aging, and in terms of microcracking and fiber–matrix debond initiation. Results indicate the critical importance of cure characteristics and diffusion related phenomena. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2255–2260, 2002     

Amorphous self-healed,chopped basalt fiber-reinforced,geopolymer composites

Geopolymer composites containing refractory, chopped basalt fibers and low-melting glass were made and systematically heat-treated at higher temperatures. Potassium-based geopolymer of stoichiometric composition K₂O·Al₂O₃·4SiO₂·11H₂O was produced by high shear mixing from fumed silica, deionized water, potassium hydroxide, (i.e., water glass) and metakaolin. With the addition of low-melting glass (T_m ~815°C) the flexure strengths of the composites increased to ~6 MPa after heat treatment above 900°C to 1100°C. A Weibull statistical analysis was performed showing how the amorphous self-healing effect of the glass frit significantly improved the flexure strength of the geopolymer and ceramic composites after high-temperature exposure. At temperatures up to 900°C, the geopolymer-basalt composite remained amorphous and the low-melting glass frit flowed into the dehydration cracks in the geopolymer matrix. This type of composite could be described as amorphous self-healed geopolymer (ASH-G). At ~1000°C, the geopolymer converted to primarily a crystalline leucite ceramic, but the basalt fiber remained intact, and the melted glass frit flowed and sealed the cracks developed at that temperature. This type of composite could then be described as amorphous self-healed ceramic (ASH-C). A temperature of 1150°C was determined to be optimum as at 1200°C the basalt fibers melted and the strength of the reinforcement was lost in the composites. The amorphous self-healing effect of the glass frit significantly improved the room temperature flexure strength of the heat-treated geopolymer-based composites.     

Toughening effects of interleaved nylon veils on glass fabric/low‐styrene‐emission unsaturated polyester resin composites

The effectiveness of using interleaved nylon veils to increase the interlaminar toughness of glass fiber reinforced, low‐styrene emission unsaturated polyester resin composites has been investigated. Samples were manufactured by a hand lay‐up technique followed by compression moulding. Nylon 66 veils were used, with the veil content varying from 0% to 4% by weight. Double cantilever beam, short beam shear, and three point bend tests were performed. The increasing levels of nylon veil content improved the interlaminar toughness of the composites, which was characterized by critical strain energy release rate (G_IC). The maximum G_IC for crack propagation of a nylon interleaved composite increased by almost 170% over the baseline glass fiber reinforced composite. Dynamic Mechanical Analysis revealed an increase in the damping parameter of up to 117%. Image analysis via Digital Image Correlation and Scanning Electron Microscopy revealed increased fiber bridging between adjacent plies as a key reason for these improvements. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41462.     

Synthesis and Characterization of Silicon Carbide Powders Converted from Metakaolin‐Based Geopolymer

Silicon carbide (SiC) ceramic powders were synthesized by carbothermal reduction in specific geopolymers containing carbon nanopowders. Geopolymers containing carbon and having a composition M₂O·Al₂O₃·4.5SiO₂·12H₂O+18C, where M is an alkali metal cation (Na⁺, K⁺, and Cs⁺) were carbothermally reacted at 1400°C, 1500°C, and 1600°C, respectively, for 2 h under flowing argon. X‐ray diffraction and microstructural investigations by SEM/EDS and TEM were made. The geopolymers were gradually crystallized into SiC on heating above 1400°C and underwent significant weight loss. SiC was seen as the major phase resulting from Na‐based geopolymer heated to ≥1400°C, even though a minor amount of Al₂O₃ was also formed. However, phase pure SiC resulted with increasing temperature. While a slight increment of the Al₂O₃ amount was seen in potassium geopolymer, Al₂O₃ essentially replaced cesium geopolymer on heating to 1600°C. SEM revealed that SiC formation and a compositionally variable Al₂O₃ content depended on the alkaline composition. Sodium geopolymer produced high SiC conversion into fibrous and globular shapes ranging from ~5 μm to nanosize, as seen by X‐ray diffraction as well as SEM and TEM, respectively.     

Melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites. I. Untreated fibers

The melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites was studied with an Instron capillary rheometer. The variation of melt viscosity with shear rate and shear stress at different temperatures was studied. The effect of relative composition of component fibers on the overall rheological behavior also was examined. A temperature range of 130 to 150°C and shear rate of 16.4 to 5470 s^?1 were chosen for the analysis. The melt viscosity of the hybrid composite increased with increase in the volume fraction of glass fibers and reached a maximum for the composite containing glass fiber alone. Also, experimental viscosity values of hybrid composites were in good agreement with the theoretical values calculated using the additive rule of hybrid mixtures, except at low volume fractions of glass fibers. Master curves were plotted by superpositioning shear stress and temperature results. The breakage of fibers during the extrusion process, estimated by optical microscopy, was higher for glass fiber than sisal fiber. The surface morphology of the extrudates was analyzed by optical and scanning electron microscopy. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 432–442, 2003