Behavior Of Epoxy Composites Research Articles

Study of Thermal Behavior of Epoxy Composites Filled with Different Natural Zeolites

One of the ways to enhance thermal stability and reduce the flammability of polymers is the introduction of fillers with flame retardant properties. The paper studies the effect of natural zeolites of the Sakhaptinsk and Shivyrtuysk deposits on the thermal stability and flame retardancy of epoxy composites. The thermal stability of epoxy composites was characterized by thermogravimetric analysis in oxidizing (air) and inert (argon) atmospheres. The parameters of thermo-oxidative degradation and thermal degradation of the samples with a filler concentration of 0, 1, 5, and 10 wt% were studied. Flame retardancy of epoxy composites filled with zeolite was evaluated using the limiting oxygen index. The limiting oxygen index increases with increasing concentration of natural zeolites in the epoxy matrix. The study revealed some differences in the first and second stages of heating the epoxy composites depending on zeolite type and did not reveal significant difference in the thermal behavior of the epoxy composites in the third stage of the heating. Thermal stability and flame retardant properties are more dependent on the zeolite content in the epoxy matrix than zeolite type.

Effect of Polypropylene (PP)/Glass fibers on the Mechanical behaviour of Epoxy composites with Al2O3 and Mg(OH)2 fillers

Effect of Polypropylene (PP)/Glass fibers on the Mechanical behaviour of Epoxy composites with Al2O3 and Mg(OH)2 fillers

Experimental and theoretical study of the rubbing process of epoxy composites against steel

Abstract In this study, the tribological behavior of epoxy composites was experimentally studied and analytically modeled using finite element techniques. Wear test and modeling were carried out for pin-on-disk configuration and under identical boundary and test conditions. The tribological elements consisted of Al2O3 filled epoxy composite pin and a steel disk. The tribological system was modeled two-dimensionally and a quasi-static analysis was performed. The wear amount and the developed stresses during the rubbing process were predicted and compared with the experimentally determined results. A good correlation between the experimental and analytical results were observed.

Desorption Behavior of Epoxy/Amine-Coated Polyester Triangular Bar Composites Pre-Exposed to Acid Environment

Epoxy/amine-coated polyester triangular bar composites were fabricated and exposed to 5 wt% hydrochloric acid (HCl) solution at 40 °C. The weight loss characteristics of pre-exposed composites in heated air at 40 °C under forced convection were studied as function of size, spacing, alignment, and orientation of triangular bars. The diffusion coefficient of composites during desorption increases when the bars are oriented flat and are aligned in parallel. The same result is observed when the size of triangular bars is increased, and when spacing between bars is decreased. These results are attributed to the presence of epoxy/polyester interphase regions, which are more accessible when the triangular bars are oriented flat and aligned parallel, have larger size, and have smaller spacing. These interphase regions are preferred conduits of water during desorption of composites. The diffusion coefficients of composites being higher than the values of epoxy and polyester resins further confirm the effect of interphase regions. Among the factors, orientation of triangular bars has the highest influence on the desorption behavior of epoxy composites.

Tribological Properties of Organic Functionalized ZrB2–Al2O3/Epoxy Composites

The tribological behaviors of epoxy composites filled with organic functionalized ZrB2–Al2O3 were environmentally investigated and compared with those with as-received fillers under both dry and oil sliding conditions in this work. The worn surfaces and the transfer films on the counterparts were characterized by scanning electronic microscope (SEM), and the frictional temperature rising was investigated by infrared thermometer. The results demonstrated that the coefficient of friction (CoF), the wear rate, as well as the frictional temperature rise of the epoxy composites were all decreased due to the introduction of ZrB2–Al2O3 fillers. And with the increase in filler content, similar variation tendencies of CoF and wear rate of epoxy composites were observed under the different sliding conditions. Besides, the organic functionalization of ZrB2–Al2O3 fillers, which made the epoxy composites exhibit lower CoF and wear rate than those with as-received fillers, lowered the frictional temperature as well. In comparison, the epoxy composites filled with 5 vol% modified fillers presented better tribological properties, suggesting a stronger interfacial bonding between modified fillers and epoxy matrix. The dominant wear mechanisms of filled composites under dry and oil sliding conditions could be inferred as the combination of adhesive wear and abrasive wear and the fatigue wear, respectively, on the basis of SEM images of worn surfaces.

Sorption and Degradation Behaviour of Epoxy Composites Reinforced with Amine-Coated Polyester Triangular Bars in Acid Environment

Sorption and degradation characteristics of epoxy composites reinforced with amine-coated polyester triangular bars in acid environment were studied. The following aspects of amine-coated triangular bars were varied during preparation of epoxy composites: orientation (flat or pointed), alignment (parallel or staggered), spacing (1 or 5 mm), and size (5 or 7 mm). Composites were tested using a one-side acid exposure test in 5 wt% hydrochloric (HCl) acid solution at 40°C for 308 h. Weight change curves of composites with pointed orientation show continuous sorption of acid solution with square root of time, while composites with flat orientation display an initial increase in weight followed by continuous weight loss. This can be attributed to the large interfacial area of triangular bars exposed to diffusing acid in flat orientation. Since the bars are amine-coated, the acid preferentially diffuses in the interfacial region, resulting to early degradation of composite. The following parameters were measured from the weight curves for data analysis: initial sorption rate (% - h-0.5), maximum weight change during sorption (%), and weight loss due to degradation (%). Analysis of variance (ANOVA) shows maximum weight change and weight loss due to degradation of epoxy composites are significantly affected by orientation and spacing.

Tensile Behavior of Epoxy Composites Reinforced with Thinner Sisal Fibers

The use of natural fibers as reinforcement in polymer matrix composites is replacing the use of synthetic fibers, especially from an environmental standpoint. Indeed, natural fibers are biodegradable and renewable, with no aggression to the environment. Moreover, they are worldwide abundant with relatively low cost. It was found that fine fibers of sisal, with the thinnest diameters can achieve tensile strength on the order of 1000 MPa. In this work, tensile specimens were prepared with 30% in volume of sisal fibers with diameters between 0.1 and 0.10mm incorporated in a continuous and aligned way into epoxy matrix. The results showed a significant increase in tensile strength and elastic modulus of the composites as a function of the incorporated amount of thinner sisal fibers.

Frequency Characterizations of Epoxy/CNTs Composites under Compression at Different Strain Rates

This paper reports the compression behavior of epoxy composites with various carbon nanotubes (CNTs) contents, under quasi-static and high strain rate compression. The compression behaviours of epoxy composites with various CNTs contents under quasi-static and high strain rate compression were compared and analyzed in the frequency domain using the fast Fourier transform (FFT) method. The results show that the compression behavior, amplitude spectrum and phase spectrum of the epoxy/CNTs composite are strain rate sensitive. The epoxy/CNTs composites can absorb higher energy in a specific frequency range.

Morphological dissimilarities of ZnO nanoparticles and its effect on thermo‐physical behavior of epoxy composites

The work demonstrated the effect of ZnO nanoparticles with varied morphology on the thermal stability of epoxy composites. Optimization of three key parameters such as the molar ratio of ZnSO4/NaOH, reaction time, and calcination temperature was performed using Taguchi design method. The ZnO nanostructures of three categories such as nanoplatelets (PZs), nanospheres (SZs), and nanoplatelets/nanorods (CZs) were successfully grown by controlled process parameters. Field emission electron microscope, transmission electron microscopy, and X‐ray diffraction were used to determine the size, morphology, and crystallite size of ZnO nanostructures. The effect ZnO nanoparticle morphology on thermal properties of epoxy composites was investigated by thermogravimetric analysis. The TGA analysis demonstrated the significant effect of PZs on the enhancement of thermal stability of epoxy composites. This work, thus, exposed the ability of PZs for its symptomatic espousal as reinforcement in polymer to improve thermo‐physical behavior. POLYM. COMPOS., 39:135–145, 2018. © 2016 Society of Plastics Engineers

Graphene nanoplatelets thickness and lateral size influence on the morphology and behavior of epoxy composites

Graphene nanoplatelets/epoxy nanocomposites were prepared using a high shear toroidal mixer as dispersion technique. Suitable dispersions were obtained. Several graphene nanoplatelets, with different thickness and lateral dimensions, were added in order to analyze the influence of these parameters in the final properties. An important nanofiller concentration gradient was found from the top to the bottom in nanocomposites reinforced with large nanoplatelets due to a natural deposition by gravity. This phenomenon is not appreciable when the nanoplatelets size decreased. However, the small nanoplatelets have a greater tendency to agglomerate in packages of several parallel particles. In general, graphene nanoplatelets addition caused an increment in glass transition temperature, stiffness and thermal stability compared to the epoxy resin. However, it was also found that graphene nanoplatelets dimensions significantly affect to these enhancements. Nanocomposites reinforced with larger and thicker nanoplatelets presented lower glass transition temperature, higher modulus and higher decomposition temperature.

Kinetic model study of moisture sorption–desorption–resorption in triangular-shaped vinyl ester filler/epoxy composites

A phenomenological diffusion model was used to study and describe moisture sorption–desorption–resorption kinetics in triangular-shaped vinyl ester filler/epoxy composites at 80 °C. The model was derived to predict the experimental anomalous weight gain behaviors of epoxy composites during moisture sorption and resorption, and estimate the degree of material degradation and loss observed as negative weight change during desorption. To verify the applicability of the model, acid anhydride–cured epoxy composites were prepared at varied alignment (parallel or staggered), spacing (1 or 5 mm), and orientation (pointed or flat) of triangular-shaped vinyl ester fillers. Moisture sorption–desorption–resorption experiment was performed by immersion of specimens in deionized water for 1200 h, followed by vacuum drying for 300 h, and water reimmersion for 300 h. The parameters of the model were calculated from nonlinear regression of percent weight change versus time experimental data. The model was found to be in good agreement with the weight change kinetic curves of all specimens. Results of three-way analysis of variance of model parameters showed the degree of material degradation and moisture diffusion coefficients during sorption, desorption, and resorption to be significantly affected by triangular-shaped filler alignment, spacing, and orientation. Using staggered over parallel alignment and 5-mm over 1-mm spacing decreased material degradation and moisture transport rate during desorption in composites. Increasing the spacing from 1 to 5 mm decreased moisture diffusion during sorption. Orienting the fillers from pointed to flat decreased moisture diffusion during resorption. Effect of interaction of filler spacing and orientation was also found to be statistically significant on the diffusion rate during sorption.

Wear behavior of Al(OH)3-GF/epoxy composites in low velocity

Effects of fiber content, size, and weave form, and addition of particles on wear behaviors of epoxy composites are studied widely, while little investigation is paid on thermal effect in friction. In this study, effects of Al(OH)3 powder on wear behavior of glass fiber reinforced epoxy composites are investigated. The experimental results show that within 6 wt%, the addition of Al(OH)3 powder could decrease the friction surface temperature, friction coefficient, and wear mass loss of the composites. The decrease is attributed to the heat absorption when Al(OH)3 powder decomposes. However, when the content of Al(OH)3 powder increases to 9 wt%, the temperature, the friction coefficient, and the wear mass loss increase to nearly equal to those of pure epoxy resin-based composites. It is considered resulting from the decrease in mechanical property, which could lead to more serious fatigue wear. In a word, within a proper content, the addition of Al(OH)3 powder in epoxy could increase the resistance to wear and friction.