Filler Particle Shape Research Articles

Synthesis, structural and mechanical properties of porous polymeric scaffolds for bone tissue regeneration based on neat poly(ε‐caprolactone) and its composites with calcium carbonate

AbstractThe aim of the present study was to develop new materials which could be applicable as bone substitutes or be used in bone tissue engineering. Two types of porous scaffolds based on poly(ε‐caprolactone) (PCL) were investigated. Type 1 scaffolds were prepared by solvent casting/particulate leaching technique, using NaCl with the grain size 250–500 µm as a porogen. In the case of Type 2 scaffolds, the biodegradable polymer was blended with calcium carbonate, which, in contrast to NaCl, is not leached out from the product during manufacture, either in the form of calcite powder or aragonite (needle‐like crystals). Influence of manufacturing technique and initial substrate composition on product properties was investigated. The tests involved porosity measurements, structure analysis by optical and scanning electron microscopy and mechanical studies (determination of compression strength and modulus). The results indicate the important role of the phase exchange process in the formation of micropores. In this process PCL precipitated from its acetone solution in the presence of water creating microporous three‐dimensional polymer structures. The Type 1 scaffolds possessed both micropores and macropores. Good interconnectivity between the pores was observed for samples of the initial porogen content higher than 33%. Microporous samples containing inorganic filler have lower porosity and higher compression strength. For Type 2 scaffolds the shape of filler particles has an important influence on mechanical properties—replacing powder with needle‐like crystals (in the same weight amount) results in a three‐ to five‐fold increase in compression modulus. Copyright © 2006 John Wiley & Sons, Ltd.

Properties of Aluminum Filled Polypropylene Composites

Polymers and metals have a long history of use in diverse applications. Metal filled polymer composites are nothing new, as the first attempt to combine these two classes of materials was made in the earlier years of the 20th century. The composites made by incorporation of powdery metal fillers into thermoplastic polymers combine the advantageous properties of metals and plastics. They offer light weight, resistance to corrosion, rapid fabrication rates and a wide range of moduli etc. In the present study, aluminum filled polypropylene (PP) composites with different filler particle shapes and filler loadings varying from 0% to 55% by volume were prepared. The effect of filler loadings and filler particle shapes on the properties of the composites was identified. The percolation concentrations were between 15% and 30% by volume for flaky aluminium filled PP composites, whereas with spherical aluminium particles the percolation concentrations were between 30% and 45% by volume. A steep decrease in electrical resistivity and a pronounced decrease in tensile strength and elongation at break on addition of the metal filler occurred for all investigated systems. Thermal characterization studies showed that the addition of aluminium reduced the crystallinity of the polypropylene and slightly retarded its thermal degradation. High void levels must be taken into account in evaluating the results.

Influence of CdS-filler on the thermal properties of poly(methyl methacrylate)

Nowadays, polymer composites are widely used in many fields of technology. Among them a significant roles play polymers containing semiconductor particles, especially for the manufacturing of electronic devices [1]. Therefore, it is important to understand the effects of these fillers on the properties of composites. The properties of composites mostly depend on size and shape of filler particles, their concentration as well as the type of interaction with polymer matrix. Poly(methyl methacrylate) (PMMA) is an important thermoplastic material with excellent transparency. However, its lower thermal stability restrains it from applications in higher temperature region. To improve the thermal properties of PMMA, fillers such as silica, titania, zirconia and alumina [2–8], as well as clay [9] were introduced into the PMMA. Recently, we showed significant improvement of the thermal stability of the polystyrene matrix filled up to a few mass% with the CdS nanoparticles (the mean particle diameter was 50 A) [10]. This effect is a consequence of high surface to bulk ratio of the CdS nanofiller and the presence of large number of dangling bonds that lead to the formation of chemical bonds between surface atoms of the CdS nanoparticles and the polymer chains. However, the synthetic route for preparation of nanocomposites is quite complex involving transfer of nanoparticles from water to organic phase. Because of that, simplified synthetic route for preparation of the polystyrene–CdS composite was developed based on mixing the CdS-filler in micrometer size range with the polymer melt [11]. In the present study, we synthesized new composite using PMMA as a matrix and submicronic CdS particles as a filler. The composite was characterized using structural techniques and the influence of the CdS-filler on the thermal properties of the PMMA–CdS composite was discussed in detail. The CdS-filler particles were prepared by mixing 500 mL of aqueous solutions containing 7.0 · 10 M Cd(NO3)2 (Merck) and 1.0 · 10 M Na2S (Fluka) at 90 C. Precipitate was washed out several times with water. In order to make surface of CdS-filler particles hydrophobic 150 (L of castor oil (Akzo Chemie) was added. Finally, colloidal dispersion was filtered, and precipitate was dried. The PMMA–CdS composite was prepared by dissolving appropriate amount of CdS in solution of PMMA (Diakon CMG314V)) in xylene, and consequent evaporation of solvent. The contents of inorganic phase were chosen to be 1.5, 3.0 and 6.0 wt%. In order to characterize morphology of the PMMA–CdS composite atomic force microscopy (AFM) was performed using Quesant Universal SPM instrument operating in noncontact (intermittent) mode. Measurements were performed in air using Si probes. Typical AFM image of the PMMA–CdS composite is shown in Fig. 1. Non-agglomerated spherical CdS particles in the size range from 0.2 to 0.35 lm in the PMMA matrix can be noticed. The X-ray diffraction (XRD) spectra of the PMMA–CdS composites were obtained by using Philips PW 1710 diffractometer. A typical XRD spectrum of the PMMA–CdS composite is shown in Fig. 2. The XRD peaks corresponding to 1 1 1, 2 2 0 and 3 1 1 crystallographic planes indicate that CdS is in a cubic phase (12] The CdS XRD peaks are very broad due to the small crystalline domains in the particles. The Scherrer diffraction formula was used to estimate the crystalline domain size (D) J. Kuljanin-Jakovljevic AE Z. Stojanovic AE J. M. Nedeljkovic (&) Vinca Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade, Serbia and Montenegro e-mail: jovned@vin.bg.ac.yu J Mater Sci (2006) 41:5014–5016 DOI 10.1007/s10853-006-0111-y

Complex permittivity of composite systems: a comprehensive interphase approach

The present paper reports the development of a unique model to provide physical insights to the complex permittivity of composite systems. The model takes into account interactions between the components of the composite system in the form of interphase regions. The resultant model, termed the interphase power-law (IPL) model, relies on the permittivities of the filler component, the matrix component and the interphase region as well as the volume fractions of each. The model is applicable to any uniform composite system of discrete particles dispersed within a matrix. Trends in the composite material's effective permittivity as a function of filler volume fraction, interphase permittivity, filler surface area and filler particle shapes are explored.

Multiple Threshold Percolation in Polymer/Filler Composites

AbstractLocal variations in filler particle concentration and/or shape and orientation in static filler/polymer composites are modelled as distributions of percolation thresholds. The concentration variations can be due to insufficient mixing, formation of semicrystalline voids during cooling from the melt, shrinkage during polymer curing, flow during physical compression or the like. Irregular filler shapes, especially elongated shapes, reduce the percolation threshold; thus natural variations in the shapes and orientations of filler particle aggregates lead to locally varying percolation thresholds. A distribution of percolation thresholds leads to an apparent percolation threshold based on the conductivity below the mean percolation threshold. For filler concentrations above the apparent percolation threshold the dielectric constant continues to increase before reaching a lowered peak value at the mean percolation threshold and then decreasing. Own experimental results on EBA /carbon black composites support the theory.

Multiple threshold percolation in polymer/filler composites

Local variations in filler particle concentration and/or shape and orientation in static filler/polymer composites are modelled as distributions of percolation thresholds. The concentration variations can be due to insufficient mixing, formation of semicrystalline voids during cooling from the melt, shrinkage during polymer curing, flow during physical compression or the like. Irregular filler shapes, especially elongated shapes, reduce the percolation threshold; thus, natural variations in the shapes and orientations of filler particle aggregates lead to locally varying percolation thresholds. A distribution of percolation thresholds leads to an apparent average percolation threshold based on the conductivity below the mean percolation threshold. For filler concentrations above the apparent percolation threshold, the dielectric constant continues to increase before reaching a lowered peak value at the mean percolation threshold and then decreasing. This can explain some ‘anomalous’ published experimental results concerning the dielectric constant just above the percolation threshold. In the frequency plane, the percolation threshold distribution can lead to a slight reduction of the apparent critical exponents x and y of the frequency dependencies of the conductivity and relative dielectric constant, respectively. Our experimental results on ethylene butylacrylate copolymer/carbon black composites support the theory.

Influence of Fe2O3-filler on the thermal properties of polystyrene

Nowadays, filled polymers are widely used in many fields of technology. Among them, polymers containing semiconductor particles play significant roles, especially for the manufacturing of electronic devices [1]. Therefore it is important to understand the effects of these fillers on the properties of filled polymers in order to design materials with desired properties. The properties of filled polymers mostly depend on the type of materials used, of size and shape of filler particles, their concentration as well as the type of interaction between filler particles and polymer matrix. In our previous studies [2, 3] significant improvement of the thermal stability of the polystyrene (PS) matrix filled up with the hematite (Fe2O3) nanoparticles (the mean particle diameter was 5 nm) was found. This effect is consequence of high surface to bulk ratio of the Fe2O3 nanofiller. However, the synthesis route for preparation of nanocomposites is quite complex involving transfer of nanoparticles from water to organic phase. In the present study simple synthesis route for preparation of the PS-Fe2O3 filled polymer was developed based on mixing the Fe2O3-filler in sub-micrometer size range with the polymer melt. The influence of particle size of the Fe2O3-filler on the thermal properties of the PS-Fe2O3 filled polymer was discussed. Also, our goal was to examine influence of the content of inorganic phase on the thermal stability of the PS-Fe2O3 filled polymer. We synthesized the Fe2O3-filler particles by using the method of Matijevic et al. [4]. Briefly, 100 ml of 0.02 M FeCl3 was mixed with 1000 ml of 0.01 M HCl at elevated temperature (353 K). The solution was kept at elevated temperature for 24 h, and then precipitate was washed out several times with water, filtered and finally dried. In order to determine morphology and size of Fe2O3-filler particles scanning electron microscopy (SEM; Jeol JSM-3T) was used. The micrographs were taken at 0◦ tilt angle, thus making the topography contrast and shape of the particles irrelevant. Spherical Fe2O3 particles in the size range from 0.2 to 0.5 μm were observed, Fig. 1. This observation is in agreement with the results obtained by Matijevic et al. [4]. The PS-Fe2O3 filled polymers were prepared by mixing, in appropriate ratio, the Glaskar PS (PS 143 E) and the Fe2O3-filler in Haake rheometer at 473 K. The contents of inorganic phase were chosen to be 5, 10 and 17 wt%. Mixing was carried out at 32 rpm rotor speed

Influence of Filler on the Pore Structure of Films of Ultra-High-Molecular-Weight Polyethylene Xerogels

The pore structure of filled films of xerogels of ultra-high-molecular-weight polyethylene prepared by gel-casting technique was studied by Fourier IR spectroscopy, attenuated total internal reflection spectroscopy, and optical microscopy. The influence of the filler nature, particle shape, and concentration on the pore structure formation of filled xerogels of ultra-high-molecular-weight polyethylene was examined.

Control of percolation curve by filler particle shape in Cu-SBR composites

Control of percolation curve by filler particle shape in Cu-SBR composites

Failure mechanics in ternary composites of polypropylene with inorganic fillers and elastomer inclusions

The effects of phase morphology, interfacial adhesion and filler particle shape and volume fraction on the fracture toughness of polypropylene (PP) filled with CaCO3 or Mg(OH)2 and ethylene-propylene elastomer (EPR) were investigated. Separation of the inorganic filler and elastomer particles was achieved using maleic-anhydride-grafted PP (MPP) to enhance the inorganic filler-matrix adhesion. Encapsulation of the rigid filler by the elastomer was achieved by using maleic-anhydride-grafted EPR (MEPR) to increase the inorganic filler-elastomer adhesion. The two limiting morphologies differed significantly in fracture toughness under impact loading at the same material composition. A model for a mixed mode of failure, accounting for the plane strain and plane stress contributions to the strain energy release rate,G c, was used to predict the upper and lower limits forG c for the two limiting morphologies over an interval of elastomer volume fractions,v e, from 0–0.2 at a constant filler volume fraction,V f = 0.3, and over the filler volume fraction from 0–0.4 at constant EPR content. The role of material yield strength in controlling fracture toughness has been described successfully using Irwin's analysis of plastic zone size. The presence of elastomer enhances both the critical strain energy release rate for crack initiation,G c, and the resistance to crack propagation as expressed by Charpy notched impact strength for the two limiting morphologies. Satisfactory agreement was found between the experimental data and predictions of upper and lowerG c limits.

Effect of morphology on the behaviour of ternary composites of polypropylene with inorganic fillers and elastomer inclusions

The effects of phase morphology, interfacial adhesion, rigid filler particle shape and elastomer volume fraction on the tensile yield strength of polypropylene (PP) filled with inorganic filler (CaCO3 or Mg(OH)2) and ethylene-propylene elastomer (EPR) were investigated. Separation of the filler and elastomer particles was achieved using maleic-anhydride-grafted PP (MPP) to enhance the filler-matrix adhesion. Encapsulation of the rigid filler by the elastomer was achieved using maleic-anhydride-grafted EPR (MEPR) to increase the filler-elastomer adhesion. The two limiting morphologies differ significantly in mechanical properties under tensile loading at the same material composition. Elastomer particles separately dispersed in the matrix enhance the shear banding in the bulk matrix which prevents the crazes growing from the filler surface from becoming unstable and, thus, increases the ductility of the material. Encapsulation by an elastomer layer on the filler surface relieves triaxial stresses at the filler surface, changing the major local failure mechanism from crazing to shear yielding and, hence, increasing the ductility of the material. Increase of the elastomer volume fraction also causes, in both cases, an increase in matrix ductility. Composite models are used to predict upper and lower limits of yield strength (σy) for the two limiting morphologies over an interval of elastomer volume fractions (V e) from 0 to 0.2 at a constant filler loading of 30 vol.% and over a filler volume fraction from 0 to 0.4 at a constant EPR content in the matrix. Satisfactory agreement was found between the experimental data and theoretical predictions.

The effect of filler particle shape on the viscosity of molten polyethylene and polystyrene

The effect of filler particle shape on the viscosity of molten polyethylene and polystyrene

Dual‐cure luting composites. Part I: filler particle distribution

Fourteen dual-cure luting composites were analyzed for their filler particle shape, predominant and maximum filler size, and filler weight in function of their clinical use. Polished surfaces were etched with an argon ion beam and studied by means of scanning electron microscopy. The type of filler particles, either inorganic or prepolymerized, could clearly be recognized. Their shapes were angular, rounded or spherical, depending on the product. The maximum filler size varied extremely from less than 1 micron to 250 microns. A particle-size distribution analyser disclosed a bell-shaped filler-size distribution. The predominant filler size for all the products was much smaller than the maximum filler size. The filler weight varied from 36 to 77%. After ion etching, some products showed small areas with a low degree of filler loading. A classification of the luting composites based on the maximum filler size is proposed. Since the particle size varies widely within the group of products analyzed, a standard specification for luting composites is urgently needed.

シリカ粒子高充てんエポキシ樹脂の強度特性に及ぼす粒子形状と粒度の影響

Epoxy resins for encapsulating integrated circuit (IC) devices are filled with silica particles to reduce thermal expansion coefficient and to improve thermal conductivity. Since these particles occupy roughly 60-70% of the total volume, they have a significant effect on the fracture properties of the resins. This study reports the effects of filler particle shape and size on the static strength of smooth specimens and crack propagation of highly silica particulate-filled epoxy resins for IC encapsulation. The smooth specimen strength, fracture toughness and fatigue crack propagation rate were measured, respectively, by the three-point bending test, the double torsion test and the cyclic tensile test of singleedge notched specimens. The effect of particle shape was examined using one type of irregularly shaped and two types of spherical particles.It was found that large particles lower the static strength, while large and also irregularly shaped particles improve resistance to crack propagation. Although large filler particles cause cracks to originate at the smooth specimen surface, they help to resist crack propagation.

An interlayer model for the complex dielectric constant of composites: An extension to ellipsoidally shaped particles

A theoretical interlayer model (IL) has been developed for the complex dielectric constant of a composite in which the filler particles are enveloped with a layer of interfacial material. The filler particles can be of any ellipsoidal shape. Special cases such as spherical particles, needles, and fabrics are shown to be covered by the model. The analytical formula as derived describes the composite properties as a function of the volume fractions of the filler, the layer and the matrix material, their dielectric properties and the filler particle shape factor. In the case of a two-phase composite the model reduces to the well-known Sillars relation for the complex dielectric constant of composite which contains filler particles of ellipsoidal shape. The effect of an interfacial layer on the static dielectric constant of the composite is discussed using the model. Next, the special case of a conductive interfacial layer in an otherwise non-conductive composite is discussed; it illustrates the effect of interfacially adsorbed water on the electrical properties of composites. Some practical examples are shown.

Peculiarities of mechanical response of heavily filled polypropylene composites

Temperature dependences of dynamic moduli of polypropylene filled with flame retardant Mg(OH)2 or with CaCO3 were investigated. The filler content varied from O to 50 vol% and both storage (G′) and loss (G″) shear moduli were measured from + 50 to + 300 °C at frequencies 1 and 90 Hz. The influence of the filler particle shape was dominant for the origin of the physical network. Chemical adhesion aid was superfluous in composites with subcritical particle size. Two step decrease of G′ and two peaks on G″ temperature dependences were observed above the critical filler concentration. The explanation of this phenomenon was based on the proposal that polypropylene immobilized on the filler surface creates a new continuous phase, while primary polypropylene exists only in separated domains. Destruction of the physical network was explained using results of thermoanalysis, providing the catalytic effect of Mg(OH)2 on the thermal oxidation of polypropylene in the interlayer above 240 °C.

Yield behavior of polypropylene filled with CaC03 and Mg(OH)2. I: “Zero” interfacial adhesion

AbstractThe composition dependence of tensile yield stress (σyc), and the effects of filler particle shape and surface treatment were investigated for polypropylene (PP) filled with CaCO3 or with Mg(OH)2. Poor adhesion between PP and CaCO3 accounted for a decrease of σyc with increasing σf. In spite of the poor adhesion between PP and Mg(OH)2, σyc either slowly decreased with increasing Vf or remained constant up to Vf = 0.25. Surface treatment of the fillers facilitated better dispersion in PP. On the other hand, σyc was reduced due to the lower thermodynamic work of adhesion (WA). The semiempirical one‐parameter equation proposed by Turczanyi, Pukanszky, and Tüdüs (TPT) was considered plausible and was employed in the study of the effects of matrix‐filler interaction.

Influence of the filler particle shape on the elastic moduli of PP/CaCO3 and PP/Mg(OH)2 composites

On etablit l'influence de l'adhesion interfaciale sur la reponse viscoelastique des composites du titre et on etudie l'applicabilite de modeles classiques existants pour ces melanges

Influence of filler particle shape on elastic moduli of PP/CaCO3 and PP/Mg(OH)2 composites

The effects of filler particle shape on the Young's and shear moduli of PP/CaCO3 and PP/Mg(OH)2 composites were studied in the concentration interval up to 50 vol/vol % filler. Calcium carbonate had irregular, approximately spherical particles and magnesium hydroxide had particles either in the form of hexagonal plates or micro-needles. The analysis based on the classical models together with structural observations enabled explanation of the composition dependences of elastic moduli of the blends studied. It was found that immobilization of PP matrix on the filler surface prominently influenced the values ofG′ andE′ moduli of PP/CaCO3 and PP/Mg(OH)2 composites. The presence of the strongly immobilized PP with increasing geometrical anisotropy of the filler particles enabled a hyperstructure creation in the composites PP/Mg(OH)2.

Materials Science

The wear behavior of 12 commercial restorative composites (conventional and microfilled) and an unfilled restorative material was evaluated using an in vitro wear test referred to as an oscillatory wear test. The effect of varying test conditions was evaluated in a series of preliminary experiments in order to define test conditions for material evaluation. The materials were tested after being aged in water at 37 degrees C for periods of from seven days to one year. The results indicated consistently lower wear rates for the microfilled materials as compared with those of the conventional composites. Aging did not result in significant differences in wear rates measured by this method. Scanning electron micrography of worn surfaces suggested a possible effect of filler particle shape and bonding to the matrix to explain this difference. Although the relevance of the results to clinical behavior is not yet known, the study indicated the importance of material variables on wear.