Particulate-filled Polymer Composites Research Articles

Solid particle erosion wear characteristics of fiber and particulate filled polymer composites: A review

The solid particle erosion behaviour of fiber and particulate filled polymer composites has been reviewed. An overview of the problem of solid particle erosion was given with respect to the processes and modes during erosion with focus on polymer matrix composites. The new aspects in the experimental studies of erosion of fiber and particulate filled polymer composites were emphasised in this paper. Various predictions and models proposed to describe the erosion rate were listed and their suitability was mentioned. Implementation of design of experiments and statistical techniques in analyzing the erosion behaviour of composites was discussed. Recent findings on erosion response of multi-component hybrid composites were also presented. Recommendations were given on how to solve some open questions related to the structure-erosion resistance relationships for polymers and polymer based hybrid composites.

A study on a possible correlation between thermal conductivity and wear resistance of particulate filled polymer composites

In this study, thermal conductivity of particulate filled polymer composites is investigated experimentally by guarded heat flow meter method in accordance with ASTM E 1530. The objective of this research is to attain a better understanding of global and local thermal behavior of a composite system through basics of thermal properties. The results obtained from this study are compared with an existing theoretical model for validation purposes of pine bark reinforced epoxy based resin composites with and with out particulate filler content. To this end, a correlation has been made between the thermal conductivity and specific wear resistance of the tested samples, highlighting the importance of the insulating material. The relationship between control factors and performance outputs are established by means of non-linear regression analysis resulting in a valid mathematical model. Finally, a popular evolutionary approach known as genetic algorithm (GA) is used to generalize the method of finding out optimal factor settings for minimization of thermal conductivity and specific wear rate.

Effects of Particle Size and Coupling Agent Concentration on Mechanical Properties of Particulate-filled Polymer Composites

In this study the influence of filler particle size (40, 50, and 60 meshes) and coupling agent concentration (0 and 2 wt%) on the composite mechanical properties were studied. Specimens having 30 wt% wood flour of poplar were mixed with polypropylene and polypropylene grafted maleic anhydride (PP-g-MA) as coupling agent. It was found that strength properties of the composites can be improved moderately by adding 2 wt% PP-g-MA. It was also observed that smaller filler particles provide higher tensile modulus than the larger sized filler. Moreover, increase in aspect ratio of the wood particles contributed to the enhancement in the mechanical properties of the composites. The elongation value was not found to have any considerable variation with particle size. The PP-wood flour composites exhibited low impact strength compared to pure PP. In general, Wood flour could be considered as a potential source of low cost, natural fibers for composites.

Effect of Particle Size and Concentration of Flyash on Properties of Polyester Thermoplastic Elastomer Composites

The performance of filled polymers is generally determined on the basis of the interface attraction of filler and polymers. Particulate filled polymer composites are becoming attractive because of their wide applications and low cost. In this study the effects of flyash with three varying particle size and filler concentrations (viz. 5 to 40 weight %) on the mechanical, thermal, electrical, rheological and morphological properties of polyester thermoplastic elastomer (Hytrel®) was investigated. Composites of polyester thermoplastic elastomer with varying concentrations of flyash were prepared by twin screw extrusion. Mechanical properties such as flexural strength and modulus increases with filler loading, where as tensile strength is found to be decrease with increase in flyash loading. Dielectric strength of composites also increases with flyash loading. Morphological studies revealed that there is good dispersion of filler in the polymer matrix. Thermal properties were found to be improved with flyash addition. Further, it was observed that the mechanical (flexural), thermal as well as electrical properties of composites improved with decrease in particle size of filler.

Effect of Concentration of Mica on Properties of Polyester Thermoplastic Elastomer Composites

Particulate filled polymer composites are becoming attractive because of their wide applications and low cost. In this study the effects of mica with varying concentration on the mechanical, thermal, electrical, rheological and morphological properties of polyester thermoplastic elastomer (Hytrel ® ) was investigated. Composites of Hytrel ® with varying concentrations (viz. 5 to 40 weight %) of mica were prepared by twin screw extrusion. Mechanical properties such as flexural strength and modulus were found to increase with mica concentration, whereas tensile strength was found to decrease at higher concentrations. Electrical and thermal properties of composite were found to increase with filler concentration. Morphological studies revealed that there is a good dispersion of filler in the polymer matrix at lower concentrations.

The statistical two-order and two-scale method for predicting the mechanics parameters of core-shell particle-filled polymer composites

The statistical two-order and two-scale method is developed for predicting the mechanics parameters, such as stiffness and strength of core-shell particle-filled polymer composites. The representation and simulation on meso-configuration of random particle-filled polymers are stated. And the major statistical two-order and two-scale analysis formulation is briefly given. The two-order and two-scale expressions for the strains and stresses of conventionally strength experimental components, including the tensional or compressive column, the twist bar and the bending beam, are developed by means of their classical solutions with orthogonal-anisotropic coefficients. Then a new effective mesh generation algorithm is presented. The mechanics parameters of core-shell particle-filled polymer composites, including the expected stiffness parameters, minimum stiffness parameters, and the expected elasticity limit strength and the minimum elasticity limit strength, are defined by means of the stiffness coefficients and elasticity strength criterions for core, shell and matrix. Finally, the numerical results for predicting both stiffness and elasticity limit strength parameters are compared with the experimental data.

Effective Thermal Conductivity of Polymer Composites

A theoretical model for predicting effective thermal conductivity (ETC) of particle filled polymer composites is developed assuming spherical inclusions arranged in a three dimensional cylindrical array. The arrangement has been divided into unit cylinders each of that contains a sphere. Green's function technique has been applied to determine the value of effective thermal conductivity. To incorporate random packing and non uniform shape of particles, a correlation term is included. It is found to dependent on volume fractions and the ratio of thermal conductivities of the constituent phases. The theoretical expression so obtained predicts values of effective thermal conductivity that are quite close to the experimental results.

Investigation of the thermal, mechanical, and fracture properties of alumina–epoxy composites

A combination of dynamic shear rheology, thermomechanical analysis (TMA), scanning electron microscopy (SEM), Near-Edge X-ray Absorption Fine Structure (NEXAFS), and fracture toughness testing was utilized to characterize the thermal, mechanical, chemical, and fracture properties of alumina (α-Al2O3)-filled epoxy resins as a function of average filler size, size distribution, particle shape, loading, and epoxy crosslink density. In general the cured properties of the filled composites were robust. Small changes in particle size, shape, and size distribution had little impact on the final properties. Resin crosslink density and filler loading were the most critical variables, causing changes in all properties. However, most applications could likely tolerate small changes in these variables also. SEM and NEXAFS characterization of the fracture surfaces revealed that the fracture occurs at the filler interface and the interfacial epoxy composition is similar to the bulk resin, indicating a weak epoxy–alumina interaction. These results are critical for implementation of particulate-filled polymer composites in practical applications because relaxed material specifications and handling procedures can be incorporated in production environments to improve efficiency.

Strain effects on percolation conduction in conductive particle filled composites

The effect of uniaxial and multiaxial mechanical strain on the electrical conductivity of particle filled polymer composites is investigated in the framework of concentration-driven percolation. For composites consisting of low aspect ratio, rigid conductive particles in a compliant polymer matrix, a simple argument leads to the conclusion that the effective volume fraction of conductive particles (the ratio of total particle volume to the total volume of the deformed composite) plays a dominant role, with conductivity remaining isotropic despite the directional bias of the strain state. As such, conductivity is expected to exhibit classical power, law-dependence on concentration, which in this case takes the form of a strain-dependent effective volume fraction. Consideration of deformation effects on particle agglomerates suggest, however, that particle-to-particle network connections are likely to be affected most significantly along directions experiencing the most severe strains, introducing a directional bias in network connectivity at a higher length scale. To assess the importance of this possible directional bias, random resistor network models are used to study the conductivity of uniaxially strained composites. For conservative assumptions on the severity of the bias in bond probabilities, network conductivities exhibit approximately isotropic, concentration-driven behavior for moderate strains, supporting the predictive utility of the simple percolation conduction-effective volume fraction approach. Further corroboration is provided by experiments in the literature on silicone-graphite composites subjected to uniaxial compressive strain, where good agreement is obtained through moderate strains for the theoretically correct value of the conduction exponent in concentration-driven percolation.

Thermal conductivity of ceramic particle filled polymer composites and theoretical predictions

Models and theories for predicting the thermal conductivity of polymer composites were discussed. Effective Medium Theory (EMT), Agari model and Nielsen model respectively are introduced and are applied as predictions for the thermal conductivity of ceramic particle filled polymer composites. Thermal conductivity of experimentally prepared Si3N4/epoxy composite and some data cited from the literature are discussed using the above theories. Feasibility of the three methods as a prediction in the whole volume fraction region of the filler from 0 to 1 was evaluated for a comparison. As a conclusion: both EMT and Nielsen model can give a well prediction for the thermal conductivity at a low volume fraction of the filler; Agari model give a better prediction in the whole range, but with larger error percentage.

Processing and properties of glass bead particulate-filled functionally graded Nylon-11 composites produced by selective laser sintering

This article investigates the fabrication of functionally graded materials (FGMs) by selective laser sintering (SLS) of Nylon-11 composites filled with different volume fractions of glass beads (0–30%). The investigation involved a combination of experimental studies, theoretical modeling and numerical analysis. Optimal processing parameters for each composition were developed by design of experiments (DOE). These parameters were then compared with parameters predicted by numerical modeling. Specimens for tensile and compressive testing for each composition and for a 1D FGM composition were fabricated and tested. The experimentally measured tensile and compressive moduli were compared with moduli predicted by Halpin's theoretical model and were found to be in excellent agreement. The results showed that the tensile and compressive modulus increases while strain at break and strain at yield decreases as a function of glass bead volume fraction. A finite element model for the compressive properties of the 1D FGM specimen showed good agreement with experimentally measured values. Finally, to demonstrate the SLS-based FGM approach, two components exhibiting a one-dimensional functional gradient of particulate-filled polymer composites were fabricated.

A Numerical and Experimental Study on Thermal Conductivity of Particle Filled Polymer Composites

In this study, thermal conductivity of particle filled polymer composites is investigated numerically and experimentally. In the numerical study, the finite-element program ANSYS is used to calculate the thermal conductivity of the composite by using the results of the thermal analysis. Three-dimensional models are used to simulate the microstructure of composite materials for various filler concentrations at various ratios of thermal conductivities of filler to matrix material. The models used to simulate particle filled composite materials are cubes in a cube lattice array and spheres in a cube lattice array. A modified hot wire method is used to measure the thermal conductivity of the composites consisting of a high-density polyethylene (HDPE) matrix filled with tin particles up to 16% by volume. The experimentally measured thermal conductivities are compared with numerically calculated ones by using the spheres in cube model and also with the already existing theoretical and empirical models. At low particle content, up to 10% of volume content of tin filler, numerical estimation and all other models except for the Cheng and Vachon model, predict well the thermal conductivity of the composite. For more heavily filled composites there is an exponential increase in thermal conductivity and most of the models fail to predict thermal conductivity in this region.

The Influence of Interfacial Adhesion on the Predicted Young's Modulus of Mica-Reinforced Nylon-6

ABSTRACT Particle-filled polymer composites have become attractive because of their wide applications and low cost. Various factors influence the mechanical properties of thermoplastic composites. Of these, the aspect ratio of the reinforcement, interfacial adhesion, and binder content are the most important. Other than these, the particle size and particle size distribution of the reinforcement also influence the mechanical properties. In this paper, injection molded mica composites were investigated, using nylon-6 as a binder. Many models are available to predict the Young's modulus of the composites. A theoretical model for Young's modulus by Lewis and Nielsen was used to predict the Young's modulus of the composites. Tetra isopropyl titanate (TYZOR® TPT) was used to modify the adhesion between the reinforcement and the binder by mixing it with the reinforcement prior to compounding. It was found that Young's modulus was greater than the predicted values.

The Surface Modification of ZnOw and its Effect on the Mechanical Properties of Filled Polypropylene Composites

Compared with the conventional particle-filled or fiber-filled polymer composites, the use of tetrapod-like zinc oxide whiskers (T-ZnOw) as inorganic functional fillers offers a possibility to manufacture polymer composites with isotropic property using simple processing techniques. In this article, T-ZnOw has first been modified with several coupling agents. Active index test and FTIR are performed to evaluate the effects of the surface treatment of the whiskers. Polypropylene composites filled with as-treated T-ZnOw are prepared by hot-press method and the mechanical properties of the composites are investigated. The experimental results show that different coupling agents have different effects on the surface modification of the whiskers. The data of the mechanical properties of the composites show that the tensile strength and impact strength increase with an increasing content of T-ZnOw in the range of 0-4 vol%. At a T-ZnOw loading of 4 vol%, they reach the highest value, 28.7 MPa and 23.3 kJ/m2, respectively. Furthermore, different coupling agents have different reinforcing effects on the as-prepared polypropylene composites.

Description of the Structure of the Polymer Matrix of Particulate-Filled Polymer Composites as a Thermal Cluster: the Critical Indices

The adequacy of the model of a thermal cluster for describing the structure of the polymer matrix of particulate-filled composites is shown. The equality of the critical indices βT = β of thermal and percolation clusters is realized in the composites at a nonzero molecular mobility, which is characterized by the fractal dimension D of the chain fragment between entanglements. The variation interval of D for the polymer matrix of a composite is smaller than for the initial polymer because of the influence of the filler on its structure.

Fractal and structural aspects of adhesion in particulate-filled polymer composites

Two types of composites based on poly(hydroxy ether) and graphite with various amounts of a filler have been investigated by various methods. The methods have been used to estimate the characteristics of adhesion and interfacial layer, including its thickness and tensile strength and interdependence between these values and adhesion. The results are treated on the basis of the theory of irreversible aggregation, cluster theory of the polymer structure and fractal analysis. It is established that all important characteristics of adhesion, interfacial layer and mechanical properties are interconnected with the difference between fractal dimensions of the surface of the aggregates of filler particles and of a polymer matrix, whose structure is distorted under the influence of the filler surface.

Prediction of failure and fracture mechanisms of polymeric composites using finite element analysis. Part 1: Particulate filled composites

AbstractMicro‐mechanical analysis of polymeric composites proves a powerful means for the quantitative assessment of their bulk behavior. In this paper we describe a robust finite element model (FEM) for the micro‐structural modeling of the behavior of particulate filled polymer composites under external loads. The developed model is applied to simulate stress distribution in polymer composites containing particulate fillers. Quantitative information about the magnitude and location of maximum stress concentrations obtained from these simulations is used to predict the dominant failure and crack growth mechanisms in these composites. The model predictions are compared with the available experimental data and also with the values found using other methods reported in the literature. These comparisons show the range of the validity of the developed model and its predictive potential.

The strength of the tailored polymer/inclusion interface in polymer composites evaluated in situ by acoustic emission

A correlation between interface strength and data of acoustic emission measurements in particle filled polymer composites was found. The method allows the evaluation of the interface strength in situ in polymer composite specimens at uniaxial loading. The measurements have shown that the tailored interface with the monomolecular tethered polymer layers of various grafting density change the mechanism of microdefect formation.

Equations for Time-Dependent Wear and Induced Concentration Profiles in Particle-Filled Polymer Composites

A time-dependent description of the sliding wear behavior of hard particle-filled polymer composites is developed. The description is based upon the accumulation of wear-resistant filler particles in the surface region, and development of wear-induced subsurface concentration profiles. Descriptive expressions for wear volume and induced filler volume fraction profile are functions of sliding distance as well as composite characteristics such as filler and matrix bulk volume fractions and specific wear rates. An experimental demonstration validates filler surface accumulation phenomenon as a basis for this model of time-dependent polymer composite wear. The demonstration also supports the feasibility of engineering composite materials with near-surface graded volume fraction profiles, resisting run-in wear contributions at the onset of sliding. Model predictions of steady-state volume fraction profile may guide design of such graded composite bearing surfaces.

Self-similarity and range of measurement scales for the network of filler particles in polymer composites

Fractal conceptions are used for the description of particulate-filled polymer composites. A network of filler particles is a fractal in the finite interval of self-similarity. This interval is evaluated for several polymer composites. It is also shown that the minimum interval covers at least one iteration of self-similarity.