High Volume Fraction Of Filler Research Articles

Synergistic enhancement of thermal and dielectric properties in PVDF films with Au-BaTiO3 hybrid nanoparticles

In our investigation of poly(vinylidene fluoride) (PVDF) films embedded with Au-BaTiO3 (AuBT) nanoparticles, we noted a synergistic improvement in both thermal stability and dielectric properties. PVDF films with varying concentrations of AuBT were expertly fabricated. Remarkably, the films retained their flexibility even at a high volume fraction of filler (f AuBT = 0.5). The predominant phases of PVDF (α, β, and γ) were observed. An increase in f AuBT resulted in a modest decrease in the melting temperature, while simultaneously causing a significant 40% increase in thermal conductivity compared to pure PVDF. The dielectric permittivity reached ∼160 at 1 kHz, while maintaining a loss tangent of ∼0.05. These improvements were attributed to discrete Au growth on BT particles, hindering conduction in PVDF. The rise in dielectric response resulted from interfacial polarization and inherent high dielectric permittivity of BT.

Nature inspired hierarchical structures in nano-cellular epoxy/graphene-Fe3O4 nanocomposites with ultra-efficient EMI and robust mechanical strength

• Nacre/bone like hierarchical structures in epoxy-based nanocomposites. • Simple compression molding with eco-friendly supercritical CO 2 foaming process to achieve porous layered nanocomposites. • Lightweight nano-cellular (52.6 nm) nanocomposite with 75 wt.% rGO-Fe 3 O 4 loading. • Low density (1.26 g/cm 3 ) and high specific EMI SE >5200 dB/cm 2 /g, with preserved tensile strength of 67 MPa achieved. Hierarchical layered structures, whether in a compact form like nacre or a porous manner like bone, are well known for their combined features of high stiffness, strength, and lightweight, inspiring many man-made materials and structures for high performance applications. The use of nacre/bone like hierarchical structures in polymer nanocomposites can achieve excellent mechanical and functional properties with high filler volume fractions after carefully aligning functional nanofillers, although the fabrication and processing remain a great challenge. In this work, a bio-inspired lightweight nano-cellular epoxy/graphene-Fe 3 O 4 nanocomposite with high nanofiller loading of 75 wt.% was successfully fabricated by combining features from both nacre and bone structures, via a simple compression molding process together with an eco-friendly supercritical CO 2 foaming process to achieve robust mechanical strength and excellent electromagnetic interference (EMI) shielding effectiveness (SE) simultaneously. Highly aligned graphene-Fe 3 O 4 nanoplatelets with well controlled nanoscale porous structures (52.6 nm) enabled both low density (1.26 g/cm 3 ) and high specific EMI SE >5200 dB/cm 2 /g, as well as preserved tensile strength of 67 MPa. This study provides a sustainable route to fabricate nature mimicked structures with high performance and high flexibility for a wide range of applications, from portable electronics to healthcare devices.

Assessment of existing micro-mechanical models for asphalt mastic considering inter-particle and physico-chemical interaction

Micromechanical models have been used since the 1990s to predict the properties of asphalt mastic. However, most of these models are found to be unsatisfactory in predicting the mastic’s properties because the models were derived from the research of particle-filled composites that did not take into account the asphalt-filler physico-chemical interactions and particle interactions. In this paper, three micro-mechanical models for predicting the complex shear modulus master curve of asphalt mastic are evaluated: the generalized self-consistent scheme model, the four-phase micro-mechanical model, and the particle interaction model. All three micro-mechanical models are based on the mechanical properties of their constituent materials as well as the filler-asphalt physiochemical interactions and the particle interactions. Two virgin asphalt binders and two polymer modified asphalt binders were selected to fabricate 16 mastics of four different filler volume fractions. The accuracy of prediction was evaluated by comparing the relative differences between the experimental complex shear modulus master curves and that predicted by the models. The results suggest that (1) the generalized self-consistent scheme model have a satisfactory prediction at a low filler volume fraction, but their accuracy is significantly affected by frequency; (2) the particle interaction model cannot calculate the complex shear modulus of mastic with a filler volume fraction of more than 0.53; (3) the four-phase model shows a precise forecast of complex shear modulus for mastic with moderate and high filler volume fractions; and (4) for all of the three models, the deviations increase severely with the increase of the filler volume fraction.

Heat conduction model based on percolation theory for thermal conductivity of composites with high volume fraction of filler in base matrix

In this article, we propose a computational heat conduction model to estimate the thermal conductivity of composites with high volume fraction of filler particles distributed randomly in the base matrix. Most of the presently available models used for estimating the thermal conductivity of the composite materials fail after a certain volume fraction of the filler due to the effect of percolation i.e. the formation of ‘heat transfer paths’ formed by the filler particles within the composite. The proposed model accounts for this percolation effect and estimates the thermal conductivity of a composite material with Aluminium as the filler in the Epoxy matrix. The algorithm for the proposed model is developed using MATLAB program and is used to obtain the thermal conductivity of the composite by entering the specifications of the parent components of the composite. The proposed model is able to predict the thermal conductivity of composites of high volume fraction of filler over the temperature range of 50 K–300 K and the results obtained are in good agreement with the experimental data.

Rutile Titania-Filled Polyethylene Composites: Microstructural Evolution, Empirical Modeling of the Mechanical Properties and Comparative Validation of the Quasi-Elastic Modulus Using Micromechanical Models

The effect of filling Low Density Polyethylene with mesoparticles of Rutile Titania for mechanical properties’ improvement was experimentally and numerically studied. Experimental techniques used were scanning electron microscopy, bi-axial tensile and three-point bending tests. Modeling techniques used were Least Square Polynomial Regressions, “Guth’s, Kerner’s, Hirsch’s, Halpin-Tsai’s, Halpin-Tsai-Nielsen’s and Modified Halpin-Tsai-Nielsen’s Models” encoded in Python-Shell. The prediction accuracy of the regression models was computationally validated with various statistical tests in Originlab Pro software package. The results showed micromechanics of deformation of the composites to be pronounced with craze-induced interconnected microvoids’ coalescence and dewetting-induced particle debonding at high volume fraction of filler. The composites delivered superlative enhancements of 309.85, 48.10, 12.28 and 15.12 % in tensile strength, tensile modulus, flexural strength and flexural modulus, respectively. Correspondingly, from least square regression models, specific polynomial orders showed correlations with experimental data at 0.05 null hypothesis rejection. The trend of regression model’s prediction for the quasi-elastic modulus agrees with that of the micromechanical models. However, underpredictions by most micromechanical models were attributed to the influence of unconsidered processing parameters on the models. Overall, the modified Halpin-Tsai-Nielsen evinced the greatest correlation.

Thermoelectric Properties of ZnO-P<sub>2</sub>O<sub>5</sub>/(Ni) Composites

The overall purpose of the present study is basically to understand the manifestation of the thermo-electrical properties of the matrix ZnO-P2O5 first, and of the ZnO-P2O5 composites loaded with different volume fractions of nickel (Ni) as conductive fillers. In the matrix ZnO-P2O5, the values of electrical conductivity varied between 1.14 × 10-8 and 7.8 × 10-7 (S/cm), and the Seebeck coefficient value varied between minimal value 265 and maximal value 670 (μV/K) in the studied temperature. In composite ZnO-P2O5/Ni, it was shown that the Seebeck coefficient changed from high positive to negative values when the filler amount was increased, indicating a non-conducting to conducting phase transition. Such behavior exhibits that this transition is accompanied by the passing of carrier charge from p to n type. The study of thermoelectrically transport for high volume fraction of filler enabled the achievement, for the first time on this kind of composites, of an original transition called PTC transition. Thus, highest values of power factor (PF = S2 ≈ 2 × 10-3 W·m-1·K-2 at 407 K) were obtained, giving a possibility of industrial applications.

Elaboration and relationships between structure and rheological properties of microtalc or nanotalc/polyamide composites

ABSTRACTThis study focuses on the elaboration of nanocomposites processed by melt mixing of a polyamide 12 matrix and a hydrogel filled with synthetic talc particles. The systems are obtained by simultaneous mixing using either an internal mixer or a lab twin‐screw extruder. The structure and rheological properties of synthetic talc/polyamide composites are compared with those of natural talc/polyamide microcomposites and modified montmorillonite/polyamide nanocomposites. A multiscale structure, composed of numerous nanometric particles but also few micrometric aggregates, is obtained for synthetic talc/polyamide composites. In terms of processability, the lab twin‐screw extruder is more adequate than the internal mixer for the elaboration of synthetic talc/polyamide composites with relatively high filler volume fractions. For composites elaborated with the extruder, the percolation threshold, estimated from linear viscoelastic measurements, is close to 1, 6, and 11%, respectively, with modified montmorillonite, synthetic talc, and natural talc particles, in agreement with structural results. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42299.

In vitro bioactivity and degradation of polycaprolactone composites containing silicate fillers

In spite of numerous publications on the potential use of combinations of polycaprolactone (PCL)/bioactive fillers for bone regeneration, little information exists on the assessment of solid, nonporous composites prepared via solventless routes and consisting of unmodified, slowly degrading homopolymer with relatively low amounts of reactive fillers such as bioglass or calcium silicate (CS). Thus, composites of PCL with commercial CS and a bioactive glass (BG45S5) at 30 wt.% were produced by melt mixing in a twin screw extruder. Neat fillers, PCL and their composites were immersed in simulated body fluid (SBF) and phosphate buffer saline and tested for in vitro bioactivity and degradation, respectively, over a 4 month period. Testing methods included scanning electron microscopy with energy dispersive X-ray analysis, X-ray diffraction (XRD), elemental analysis and weight and pH changes before and after immersion. Experiments with neat fillers indicated fast growth of calcium phosphate minerals having different textures; they included clusters and globules of mineral precipitates as well as needle-shaped nanosized crystallites and possibly other calcium phosphate structures with varying Ca/P ratio. The bioactive glass composite initially showed fast growth of the precipitated minerals and partial surface coverage after 1 week, whereas in the CS composite, growth and surface coverage increased as a function of immersion time (over a period of 4 weeks) in the SBF solution. XRD results showed early appearance (1 week) of hydroxyapatite for both types of composites with differences attributed to different dissolution rates and different surface reactions of the fillers. Both fillers appeared to enhance the hydrolytic degradation of the matrix. Overall, the limited observed bioactivity of both composites within the test period may be related to the hydrophobicity of the matrix, insufficient ionic activity since SBF was not replenished and the relatively low content of the low surface areas fillers. Optimization of filler properties, such as surface/volume ratio, surface chemistry and size range, appears as a most important factor that would provide, at the required high filler volume fractions, a balance of melt processability and bioactivity.

The effect of inhomogeneities in particle distribution on the dielectric properties of composite films

A practical approach for the modelling of the dielectric constants of thin composite films is presented. A general distribution function for composition fluctuations in the thin composite films is introduced to describe the transition from a non-percolative to a percolative morphology using physically meaningful parameters and is applied to model a wide range of experimental and simulated polymer–ceramic composite film behaviour from the literature, up to ceramic particle filler volume fractions of 75%. The parameters describing the morphologies of the various composites are used to predict effective dielectric properties with good accuracy. The model is applied further to composites that show early percolation behaviour, and the deviation of their effective dielectric behaviour from the standard effective medium theory at high filler volume fractions is discussed.

Modeling viscoelastic behavior of particulate composites with high volume fraction of filler

The linear viscoelastic behavior of dilute and concentrated particulate composites is investigated. New models for the complex Young modulus are developed for concentrated particulate composites with high volume fraction of filler, using a differential scheme along with the solution of an infinitely dilute system. The dispersed phase and the matrix are treated as incompressible viscoelastic solids in the derivation. The proposed models are evaluated using the available experimental data on pore–solid and particulate composites.

Predictive modeling of elastic properties of particulate-reinforced composites

The Young's modulus and Poisson's ratio of isotropic composites made of particulate glass fillers in a BISGMA/TEGDMA resin matrix are determined using an axisymmetric spherical cell finite-element model developed by Guild and co-authors for modeling the elastic properties of rubber particles/epoxy composites with volume fractions of less than 0.5. Here, we have used this method to calculate the elastic properties of particulate-filled composites with a range of filler volume fractions, including those with filler fractions above 0.5, which are of primary interest for dental clinical applications. We have also conducted modeling studies on the influence of imperfect interfaces and thin interlayers on the elastic properties of composites with low and high filler volume fractions. Finally, we have conducted experimental tensile tests in order to compare theoretical predictions with experimental data. The predictions from the current model agree well with the test results for a range of volume fraction up to 0.53.

Finite Element Analysis of Effective Thermal Conductivity of Filled Polymeric Composites

A novel method to predict the macroscopic effective thermal conductivity of filled composites, based on its microstructural characteristics is developed and validated. A finite element method which incorporates the effect of microstructural characteristics such as filler aspect ratio, interfacial thermal resistance, volume fraction, and filler and fiber dispersion to determine the effective thermal conductivity of a composite with circular and rectangular fillers is presented. Filler interactions and chain formation effects are included in the model. To overcome the laborious task of repeated finite element model generation, an algorithm which generates the positions and orientations of the fillers in the matrix is developed. The automated model development capability is used to create several microstructures for finite element analysis. The trends predicted by the finite element models are compared with existing analytical models and available experimental results. The advantage of this method over existing analytical and semi-empirical models is that it can handle interactive effects, provide a detail heat flux pattern, and also model high filler volume fractions.

Mechanical behaviour and structure of light-cured special tray materials

Objectives: This study relates some structural characteristics of representative special tray visible light cured (VLC) resin composites to their creep-recovery, hardness and flexural strength properties. VLC prosthodontic materials have not yet achieved the same acceptance as the VLC resin composites, perhaps because less is known of their structural and performance characteristics. Methods: The VLC resin composites used were Triad, Convertray and Palatray. The inorganic composition was analysed quantitatively by heating known amounts of resin composite to 800 °C, and weighing the ash. Elemental composition was determined using X-ray microanalysis. Mechanical properties, including hardness, flexural behaviour and creep recovery, were obtained by standard methods. Results: The inorganic filler content for Palatray was higher than that of Convertray or Triad, and the flexural modulus and flexural strength of Palatray were superior to that of Triad or Convertray. The mean maximum creep strain for the Palatray specimens was only 2.45% after 5 h loading under 37 MPa and there was a permanent set of 1.5% after 7 h recovery. Conclusions: Palatray exhibited superior overall properties and this evidently related primarily to the high volume fraction of filler.