Short- and long-term strength characteristics of particulate-filled cast epoxy resin

Particulate-filled thermosetting composites are widely used, yet little systematic work has been done on their long-term strength characteristics. In this study short-term tensile, flexural, and impact tests as well as tensile creep-rupture tests were made for unfilled and filled epoxy to clarify the effects of filler size, filler content, and temperature. Fillers used were silica, alumina particles, and glass beads. Test temperatures were varied from 25 to 110°C. As a result of short-term testing, it was found that the Petch relation held between strength and filler size if brittle fracture occurred, while a strength and filler size if brittle fracture occurred, while a strengthening effect existed when ductile fracture occurred. On creeprupture testing, a strengthening is observed with filler size and content for silica and glass beads. The Arrhenius plot of rupture time for various filler sizes and contents converges to a characteristic point corresponding to the glass transition temperature of the material. Using this relation, a modified Larson-Miller master rupture curve is proposed which can predict the long-term strength of particulate-filled thermosetting composites as functions of rupture time, temperature, filler size, and content.     

Effects of temperature and strain rate on the tensile behavior of polypropylene composites insulator coatings used in offshore deepwater pipelines

Polypropylene (PP) composites are being increasingly used as thermal insulation coatings in both onshore and offshore pipelines. In this study, the direct tensile behavior of pure PP, PP with glass microsphere filler, and PP with 65% glass filler were investigated at 22, 60, and 90 °C temperatures at various strain rates from 0.003/min to 0.300/min. Fourier transform infrared spectroscopy and scanning electron microscope studies were used to characterize the materials. Stress–strain relationships of the materials were nonlinear in the elastic and inelastic domains. Addition of glass fiber to the PP increased the elastic modulus, but the yield strength and yield strain were reduced along with the ductility. Based on the experimental results, constitutive models coupling the strain rate and temperature have been developed to predict the yield strength, the initial elastic modulus and secant modulus at yield for the PP composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45209.     

The unidirectional glass fiber reinforced furfuryl alcohol for pultrusion. II. Correlation of processing parameters for optimizing the process

Unidirectional glass fiber reinforced furfuryl alcohol (FA) composites have been prepared by the pultrusion processes. The optimum processing parameters of the glass fiber reinforced FA composites by pultrusion has been studied. The effects of the optimum processing parameters on the properties (flexural strength, flexural modulus, notched Izod impact strength, glass transition temperature (T_g), dynamic shear storage modulus (E'), shrinkage ratio, and roughness) investigated including die temperature, pulling rate, postcure temperature and time, and filler type and content. Results show that the pultruded composites possessed various optimum pulling rates at different die temperatures. On the basis of the DSC diagram, the swelling ratio and the mechanical properties of pultruded composites, the optimum die temperature can be determined. The mechanical properties and T_g increase at a suitable postcure temperature and time. Furthermore, the properties which decrease due to the degradation of pultruded composites for a long postcure time will be discussed. The mechanical properties of pultruded composites reach a maximum value at various filler content corresponding to the talc and calcium carbonate, respectively, and then decreased. When the fillers are added to the pultruded glass fiber reinforced FA composites, the shrinkage ratio of composites become smaller, and the surface of composites became smooth. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Water absorption,residual mechanical and thermal properties of hydrothermally conditioned nano-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> enhanced glass fiber reinforced polymer composites

The durability of the nano-Al₂O₃ enhanced glass fiber reinforced polymer (GFRP) composites in hydrothermal environment is necessary for hydro/hygro thermal applications. The present investigation emphasizes the effect of nano-Al₂O₃ filler concentration on moisture absorption kinetics, residual mechanical and thermal properties of hydrothermally treated GFRP nano-composites. Nano-Al₂O₃ particles were mixed with epoxy matrix through temperature assisted magnetic stirrer and followed by ultrasonic treatment. It has been observed that, the addition of 0.1 wt% of nano-Al₂O₃ into the GFRP nano-composites reduces the moisture diffusion coefficient by 10%, as well as improves the flexural residual strength by 16% and interlaminar residual shear strength by 17% as compared to the neat epoxy GFRP composites. However, the glass transition temperature has not been improved by the addition of nano-Al₂O₃ filler. Weibull design parameters have been determined for dry and hydrothermally conditioned nano-composites. A good agreement between the experimental and the simulated stress–strain results has been observed. The interface failure mechanism has been evaluated by field emission scanning electron microscope to support the new findings.     

Dynamic mechanical properties of polypropylene composites filled with ultrafine particles

The dynamic moduli of isotactic polypropylene (PP) filled with ultrafine SiO₂ and micron sized glass particles are measured in the temperature range 30–130°C at frequency 10 Hz. The storage moduli of PP composites, E′_c, increase with filler content and decreasing filler size in the whole range of temperature. The loss moduli of PP composites, E″_c, increase with filler content and decreasing filler size above 40°C. The intensity of the broad despersion which appears at ca. 60°C increases with filler content and decreasing filler size. By assuming that the energy is not dissipated in the effective volume, namely, filler volume plus that of immobilized interfacial region, the effective volume fraction is evaluated from the relative loss modulus, E″_cE″₀ at 60°C. The effective volume fraction increases with filler content and decreasing filler size. The effect of addition of ultrafine particles on the broad dispersion at ca. 60°C resembles the effect of increasing crystallinity of pure PP. It is concluded that the broad dispersion which appeared at ca. 60°C seemed to be assigned to the grain boundary of PP composities or crystalline boundary of pure PP.     

The effect of time and temperature on the mechanical behavior of epoxy composites

A crosslinked epoxy resin consisting of a 60/40 weight ratio of Epon 815 and Versamid 140 and composites of this material with glass beads, unidirectional glass fibers and air (foams) were tested in tension, compression and flexure to determine the effect of time and temperature on the elastic properties, yield properties and modes of failure. Unidirectional continuous fiber-filled samples were tested at different fiber orientation angles with respect to the stress axis. Strain rates ranged from 10^?4 to 10 in./in.-min and the temperature from ?1 to 107°C. Isotherms of tangent modulus versus strain rate were shifted to form master modulus curves. The moduli of the filled composites and the foams were predictable over the entire strain rate range. It was concluded that the time-temperature shift factors for tangent moduli and the time-temperature shift factors for stress relaxation were identical and were independent of the type and concentration of filler as well as the mode of loading. The material was found to change from a brittle-to-ductile-to-rubbery failure mode with the transition temperatures being a function of strain rate, filler content, filler type and fiber orientation angle, indicating that the transition is perhaps dependent on the state of stress. In the ductile region, an approximately linear relationship between yield stress and log strain is evident in all cases. The isotherms of yield stress versus log strain rate were shifted to form a practically linear master plot that can be used to predict the yield stress of the composites at any temperature and strain rate in the ductile region. The time-temperature shift factors for yielding were found to be independent of the type, concentration and orientation of filler and the mode of loading. Thus, the composite shift factors seem to be a property of the matrix and not dependent on the state of stress. The compressive-to-tensile yield stress ratio was practically invariant with strain rate for the unfilled matrix, while fillers and voids raised this ratio and caused it to increase with a decrease in strain rate. The yield strain of the composites is less than the unfilled matrix and is a function of fiber orientation and strain rate.     

Impact fracture behavior of PP/EPDM/glass bead ternary composites

The effects of glass bead filler content and surface treatment of the glass with a silane coupling agent on the room temperature impact fracture behavior of polypropylene (PP)/ethylene‐propylene‐diene monomer copolymer (EPDM)/glass bead(GB) ternary composites were determined. The volume fraction of EPDM was kept constant at 10%. The impact fracture energy and impact strength of the composites increased with increasing volume fraction of glass beads (?_g). Surface pretreatment of the glass beads had an insignificant effect on the impact behavior. For a fixed filler content, the best impact strength was achieved when untreated glass beads and a maleic anhydride modified EPDM were used. The impact strength exhibited a maximum value at ?_g=15%. Morphology/impact property relationships and an explanation of the toughening mechanisms were developed by comparing the impact properties with scanning electron micrographs of fracture surfaces.     

Fracture and impact properties of polycarbonates and MBS elastomer-modified polycarbonates

Mechanical properties of polycarbonates (PCs) and elastomer-modified polycarbonates with various molecular weights (MW) are investigated. Higher MW PCs show slightly lower density, yield stress, and modulus. The ductile–brittle transition temperature (DBTT) of the notched impact strength decreases with the increase of PC MW and with the increase of elastomer content. The elastomer-modified PC has higher impact strength than does the unmodified counterpart if the failure is in the brittle mode, but has lower impact strength if the failure is in the ductile mode. The critical strain energy release rate (G_c) measured at ?30°C decreases with the decrease of PC MW. The extrapolated zero fracture energy was found at M_n = 6800 or MFR = 135. The G_c of the elastomer-modified PC (MFR = 15, 5% elastomer) is about twice that of thee unmodified one. The presence of elastomer in the PC matrix promotes the plane–strain localized shear yielding to greater extents and thus increases the impact strength and G_c in a typically brittle fracture. Two separate modes, localized and mass shear yielding, work simultaneously in the elastomer-toughening mechanism. The plane–strain localized shear yielding dominates the toughening mechanism at lower temperatures and brittle failure, while the plane–stress mass shear yielding dominates at higher temperatures and ductile failure. For the elastomer-modified PC (10% elastomer), the estimated extension ratio of the yielding zone of the fractured surface is 2 for the ductile failure and 5 for the brittle crack. A criterion for shifting from brittle to ductile failure based on precrack critical plastic-zone volume is proposed.     

Effect of filler content and surface treatment on the tensile properties of glass‐bead‐filled polypropylene composites

The tensile properties of polypropylene (PP) filled with two A‐glass beads with the same size, PP/3000 (glass bead surface pretreated with a silane coupling agent) and PP/3000U (no surface pretreatment), have been measured by using an Instron materials testing machine at room temperature, to identify the effects of the filler surface pretreatment and its content on the tensile properties of these composites. The results show that the Young's modulus E_c of the composites increases non‐linearly with increasing volume fraction of glass beads ϕ_f, while the tensile yield strength σ_yc and tensile stress at break σ_bc of the composites decrease with an increase of ϕ_f, in the ϕ_f range 0–30%. Furthermore, the values of E_c and σ_bc of the PP/3000 system are somewhat higher than those of the PP/3000U system under the same test conditions, but this is in contrast to the tensile strain at break ε_bc and tensile fracture energy E_bc, especially at higher ϕ_f values. Good agreement is shown between the measured tensile strength and the predicted value by using an equation proposed in previous work. In addition, ε_bc and E_bc reach maximum values at ϕ_f = 25% for both systems. This indicates that there is a brittle–ductile transition for the composites in tension. © 2000 Society of Chemical Industry     

Mechanical properties of particulate‐filler/woven‐glass‐fabric‐filled vinyl ester composites

Studies of the effect of particulate fillers on specific mechanical properties of vinyl ester epoxy (VE) reinforced with woven glass fiber composites were carried out with different filler types and particulate filler contents (1%, 3%, and 5% by weight). Two types of particulate filler were used, i.e., calcium carbonate (CC) and phenolic hollow microspheres (PHMS). The composites were prepared by using a hand lay‐up and vacuum bagging method. Woven glass fabric composites filled with particulate PHMS were observed to have better specific flexural strength and specific impact strength, as well as lower density, than those filled with particulate CC. Morphological features determined by scanning electron microscope (SEM) proved that the PHMS filler experienced good bonding in the VE matrix, a feature which contributed to the improvement in the properties of the composites. The incorporation of particulate fillers into the composites also influenced the storage modulus with a minimal effect on T_g. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers     

Mechanical properties and fracture behaviors of epoxy composites with phase‐separation formed liquid rubber and preformed powdered rubber nanoparticles: A comparative study

Epoxy composites filled with phase‐separation formed submicron liquid rubber (LR) and preformed nanoscale powdered rubber (PR) particles were prepared at different filler loading levels. The effect of filler loading and type on the rheological properties of liquid epoxy resin suspensions and the thermal and mechanical properties of the cured composites as well as the relative fracture behaviors are systematically investigated. Almost unchanged tensile yield strength of the cured epoxy/PR composites is observed in the tensile test compared with that of the neat epoxy; while the strength of the cured epoxy/LR composites shows a maximum value at ∼4.5 wt% and significantly decreases with increasing LR content. The glass transition temperature (T_g) of the cured PR/epoxy has shifted to the higher temperature in the dynamic mechanical thermal analysis compared with that of the cured pure epoxy and epoxy/LR composites. Furthermore, the presence of LR results in highly improved critical stress intensity factor (K_IC) of epoxy resin compared with the corresponding PR nanoparticles. In particular, the PR and LR particles at 9.2 wt% loading produce about 69 and 118% improvement in K_IC of the epoxy composites, respectively. The fracture surface and damage zone analysis demonstrate that these two types of rubber particles induce different degrees of local plastic deformation of matrix initiated by their debonding/cavitation, which was also quantified and correlated with the fracture toughness of the two epoxy/rubber systems. POLYM. COMPOS., 36:785–799, 2015. © 2014 Society of Plastics Engineers     

The yield strength of particulate reinforced thermoplastic composites

The effects of the filler volume fraction and strength of adhesion on the mode of tensile failure of a particulate reinforced polypropylene (PP) are investigated using finite element simulation (FES). When there is perfect adhesion between constituents, an upper bound for tensile yield strength is found to be 1.33 times the matrix yield strength above a critical volume of particulate concentration. Utilizing Sjoerdsma's model for interacting stress concentration fields, one can determine the concentration dependence of the yield strength below the critical filler volume fraction. When there is no adhesion between constituents, a modified version of an equation by Nicolais and Narkis adequately describes a lower bound for the tensile yield strength. The particulate concentration and the matrix ductility are the prime factors in controlling the brittle failure of the composite. Upper and lower bounds for brittle failure strength are characterized using a strength-of-materials approach and stress concentration factors for both “perfect” and “zero” adhesion. The properties of calcium carbonate filled PP homopolymer were measured over a wide range of filler volume fractions. CaCO₃ was either treated with stearic acid to prevent adhesion between constituents or used as received. Maleic anhydride grafted PP (MPP) was used to promote adhesion. For filler volume fractions below 0.2, yielding of the composite by combined microcavitation and shear deformation was the principal failure mechanism. At v_f above 0.35, a brittle failure mechanism dominated. In the range between 0.2 and 0.35, both failure modes were observed in the populations tested. Good agreement was found between the experimental results and the proposed model.     

Mechanical behavior and dilatation of particulate-filled thermosets in the glassy state

Dilatation of specimens is measured during tensile tests to investigate the mechanical response of particulate-filled amorphous networks in the glassy state. The effects of particle size, volume fraction of filler, coupling agents, and crosslink density of the matrix on the mechanical-dilatational behavior are studied on model composites of glass-bead-filled polyurethanes. It is found that the stress-strain response of composites with untreated glass beads shows nonlinearity and subsequent yielding due to dewetting of particles from the matrix. In contrast, composites containing particles coated with a comupling agent fracture in a brittle manner, showing no significant nonlinearity and dewetting. Coated particles provide a higher tensile strength, but a lower strain at fracture, than uncoated particles. The volume fraction of the filler has an effect on Young's modulus, which is independent of the degree of coupling between the matrix and the filler. Tensile strength and strain at break decrease with increasing filler content for coated and uncoated particles. No strong effect of particle size is observed on either the tensile modulus or the dilatational behavior in the 25 μm to 160 μm diameter range. However, strain at break increases with decreasing particle size. When the accompanying yield phenomena shift to smaller strains, and a transition to brittle fracture takes place at high crosslink densities.     

Mechanical properties of drawn poly(methyl methacrylate) filled with ultrafine particles

The elastic and yield properties of drawn poly(methyl methacrylate) (PMMA) filled with ultrafine SiO₂ are described as functions of filler content and size. The drawn PMMA composites were made by uniaxially drawing to x4.0 at 100°C and at a rate of 20 mm/min. Four compliance values, i.e., S₃₃, S₁₁, S₁₃, and S₄₄ were determined. These values decreased with filler content and decreasing filler size. The relative compliance values S^de/S^do(S^de is the compliance of drawn PMMA composites and S^do is that of drawn unfilled PMMA) are almost equivalently changed with changes in filler content. The elastic properties of drawn PMMA composites are thus reinforced isotopically. This is characteristic of PMMA which has a large side group. The yield behavior of drawn PMMA composites have similar filler size and content dependence to those of elastic properties except that the transverse yield stresses become more brittle with filler content. The anisotropy in yield stress is relatively larger than that of elastic properties. This is probably because the anti-reiforcing effect, such as fibrillation becomes prominent with increasing filler content in the perpendicular direction.     

Effect of Crosslinking Density and Dilution during Polymerization on the Stress-Strain and Viscoelastic Behaviour of (2-Hydroxyethyl Methacrylate) Networks in Dry and Swollen States filled with SiO2

Abstract

Linear viscoelastic and stress-strain behaviour of poly(2-hydroxyethyl methacrylate) PHEMA networks filled with SiO₂ and prepared by crosslinking copolymerization has been investigated. The main attention was devoted to the effect of the volume concentration of the filler within the range v _f = 0 –0.194, concentration of the crosslinking agent (ethylene dimethacrylate) within the concentration range c = 0.13 – 7.84 %, and water present during polymerization with the volume fraction of water ranging from 0.0 to 0.75. It was established that an increasing concentration of the filler had as its consequence a rapid increase in the modulus in the rubberlike region; this effect is more pronounced than in the case of natural rubber filled with active fillers. The effect of the filler decreases with swelling, which is in accordance with the assumption that the polymer-water interactions are stronger than the polymer-filler interactions. The presence of water during polymerization also leads to a decrease in the effect of SiO₂ in both dry and swollen systems. With increasing concentration of the filler, the retardation spectra are shifted toward longer times, and their slopes in the main transition region become smaller; this effect, however, is not pronounced on the whole. Whereas the concentration of the crosslinking agent affects the viscoelastic behaviour most, the water content during polymerization has no effect at all.     

Tensile behavior of polyolefin composites: the effect of matrix parameters

Polyolefin composites were prepared from 14 PE matrices and three different mineral fillers (montmorillonite, palygorskite and glass microspheres) via melt compounding in an extruder. Mechanical properties of the obtained systems were analyzed with emphasis on elongation at break and conditions for ductile/brittle failure were determined. When filler content is raised beyond a certain “critical” value, tensile properties are dramatically altered and transition occurs from ductile behavior to brittle fracture. This transition is displayed by a well‐defined “step” on the plot of strain at break versus concentration of particles. The value of “critical filler content” was found to depend mainly on level of crystallinity of a matrix while other parameters (chemical nature of filler particles, their size, shape and surface treatment) are less significant. “Critical filler content” will decrease with growth of crystallinity of a polymer and with highly crystalline HDPEs it is as low as 2–8 vol %. Otherwise, with noncrystallizing and low‐crystalline polymers elongation at break decreases gradually with concentration of mineral particles and ductile type deformation is maintained at fairly large filler fractions. The results presented here will be useful for a proper selection of a matrix polymer in composites with mineral fillers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43819.     

Dielectric and dynamic mechanical relaxation behavior of exfoliated nano graphite reinforced flouroelastomer composites

Dynamic mechanical analysis and dielectric relaxation spectra of exfoliated nano graphite reinforced flouroelastomer composites were used to study their relaxation behavior as a function of temperature (−80°C to +40°C) and frequency (0.01 to 10⁵ Hz). The effect of filler loadings on glass transition temperature was marginal for all the composites and T_g value was in the narrow range of 7.8–8.4°C, which has been explained on the basis of relaxation dynamics of polymer chains in the vicinity of fillers. Strain‐dependent dynamical parameters were evaluated at dynamic strain amplitudes of 0.01–10%. The nonlinearity in storage modulus has been explained on the concept of filler‐polymer interaction and filler aggregation of the nano graphite platelets. The variation in real and complex part of impedance with frequency has been studied as a function of filler. The percolation of the nano graphite as studied by conductivity measurements is also reported. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers.     

Poly(lactic acid)/areca fiber laminate composites processed via film stacking technique

Bio‐based laminate composites, consisting of alternatively stacked poly(lactic acid) (PLA) sheet and randomly oriented areca fiber mat, were processed via film stacking technique (FST). FST was chosen as it is a commercially viable, low energy‐intensive process for fabricating fiber‐reinforced composite, thereby advocating environmental sustainability. Laminate composites exhibited mechanical strength of 6.5 MPa at 16 wt % fiber loading. Crystallinity of as‐received PLA sheets was found to be 26% due to the presence of ～30 wt % inorganic filler, and showed further enhancement to 50% upon the addition of 22 wt % areca fiber. Dynamic mechanical analysis showed higher glass transition temperature (83 °C) for PLA sheets, mainly due to the presence of higher filler content. This work demonstrates the use of bio‐based laminate composite processed at the lowest possible temperatures as viable alternatives to thermoplastic polyolefins in automobiles. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45795.     

Mechanical properties and morphology of glass bead–filled polypropylene composites

The effects of the filler content and size on the mechanical properties such as tensile modulus, E_c, yield strength, σ_yc, and impact strength, S_IC, of glass bead–filled polypropylene (PP) composites have been investigated employing an Instron materials tester and a Ceast impact tester at room temperature. With increasing concentration of glass beads, E_c and S_IC increase, but σ_yc decreases non–linearly, within a filler volume fraction range of 0%−20%; under the same test conditions, the values of E_C and σ_yc for PP with bigger beads are somewhat lower than those of PP with smaller ones; the maximum values of S_IC for the composites are about 1.4 times as high as the unfilled PP; the interface between the matrix and the beads is a weak bond. The results indicate that the stiffness and the toughness of the PP composites are effectively improved by addition of glass beads.     

Polypropylene (PP)–Acacia mangiumcomposites: the effect of acetylation on mechanical and water absorption properties

Acacia mangiumwood flour (AMWF)–polypropylene (PP) composites were produced at different filler loading (20, 30, 40, and 50 w/w) and mesh no. (35, 60, 80, and 100 mesh). The AMWF–PP composites (using unmodified or modified wood flour) were compounded using a Haake Rheodrive 500 twin screw compounder. The mechanical and water absorption (WA) properties of modified (only at mesh no. 100) and unmodified AMWF–PP composites were investigated. Increase in the mesh number (35–100) of the unmodified AMWF showed increased flexural and impact properties. Flexural modulus exhibited higher properties as the filler loading increased (20–50). However, flexural and impact strength showed the opposite phenomenon. Water absorption and thickness swelling increased as the mesh number and filler loading increased. This has been attributed to the presence of hydrophilic hydroxyl groups of the filler. Modified AMWF–PP composites exhibited higher mechanical properties and good water resistance when compared to unmodified AMWF–PP composites at all values of filler loading. The evidence of the failure mechanism (from impact strength) of the filler–matrix interface was analyzed using scanning electron microscope.