Small Filler Research Articles

Enhanced thermal conductivity of epoxy composites by constructing thermal conduction networks via adding hybrid alumina filler

AbstractHigh thermal conductivity of polymer composites could be achieved through constructing 3D continuous thermally conductive networks into polymer composites. Herein, we demonstrate a simple, effective method to optimize the segregated alumina networks by using ternary mixture of alumina particles with different diameter ratios (5.8 μm + 2.6 μm + 0.5 μm) at the fixed total content of 60 wt% via conventional melt blending method. The thermal properties of epoxy composites were investigated as a function of the weight fraction and particle size of alumina particles. The thermal conductivity (TC) values of composites with coarse fillers (13.2 μm) are in agreement with Agari model at high filler loading (57 ~ 67 wt%). And the value of C2 was ~0.949 (close to 1), indicating that the formation of heat conduction paths in the composites. The addition of 60 wt% smaller fillers (2.6 μm) facilitates a higher interaction degree between the polymer/fillers, consequently, leads to a higher Tg of 147.8°C. A high TC of 1.109 W m−1 K−1 is achieved as the ratio of alumina filler with different particle sizes is 7/2/1, corresponding to a TC enhancement of 23%–32% compared to the composites with a single particle size filler. A suitable proportion of hybrid fillers is crucial for constructing three‐dimension continuous network, in which nano‐particles filled between the micro‐particles could increase the particle‐to‐particle connectivity.

Rheology of Polytriazole/ZIF-8 Solutions and Dynamics of Mixed-Matrix Composite Films

Adhesion between fillers and a polymeric matrix is an essential characteristic for mixed-matrix membranes for molecular separation to avoid defects and cavities that would decrease selectivity. We demonstrate here how solution rheology can be an excellent tool to identity polymer–filler pairs with strong interaction. The investigated system was polytriazole with and without hydroxyl functionalization (PTA-OH and PTA) and ZIF-8. ZIF-8/PTA-OH forms stable gels even with a small filler content, which was investigated under increasing shear rates and different temperatures, while analogous systems without OH functionalization do not gel. The investigations were supported by spectroscopic methods, electron microscopy, and dynamic mechanical analysis of the final solid film. While small ZIF contents lead to sensitive changes in the solution viscosity, only minor changes in the Fourier transform infrared and NMR spectra were detected for the same system. The good adhesion between PTA-OH and ZIF-8 could be seen by electron microscopy, while the analogous PTA/ZIF-8 composites provided films with poor matrix–filler adhesion and undesired cavities. The methods described in this work can be extended as useful tools in the development of composites such as mixed-matrix membranes applied to a large variety of currently available metal–organic frameworks and polymers.

Efficient prediction of the packing density of inorganic fillers in dental resin composites for excellent properties

ObjectiveThe purpose of this study is to develop a mathematical model for efficient prediction of the packing density of different filler formulations in dental resin composites (DRCs), and to study properties of DRCs at the maximum filler loading (MFL), thereby providing an effective guidance for the design of filler formulations in DRCs to obtain excellent properties. MethodsThe packing density data generated by discrete element model (DEM) simulation were used to re-derive the parameters of 3-parameter model. The modifier effect was also induced to modify the 3-parameter model. DRCs with 10 filler formulations were selected to test properties at the MFL. The packing densities of binary and ternary mixes in DRCs were calculated by 3-parameter model to explore the regularity of composite packing. ResultsThe predicted packing density was validated by simulation and experimental results, and the prediction error is within 1.40 vol%. The optimization of filler compositions to obtain a higher packing density is beneficial to enhancing the mechanical properties and reducing the polymerization shrinkage of DRCs. In binary mixes, the maximum packing density occurs when the volume fraction of small fillers is 0.35−0.45, and becomes higher with the reduction of particle size ratio. In ternary mixes, the packing density can reach the maximum value when the volume fractions of large and small fillers are in the 0.5−0.75 and 0.15−0.4 ranges, respectively. SignificanceThe modified 3-parameter model can provide an effective method to design the multi-level filler formulations of DRCs, thereby improving the performance of the materials.

Effects of Al2O3 on Thermal Conductivity of Silicone Rubber

Thermal conductivities of silicone rubber filled with Al2O3 were prepared. Thermal conductivity experimental results obtained were analyzed using the Nielsen and Agari models to explain the effect of Al2O3 filler on the formation of thermal conductive networks. Thermal conductivities increased with the adding of mixed Al2O3 of large and small sizes fillers. The scanning electron microscopy (SEM) showed that it is the optimum particle sizes and quantities that made the filler packing closer, which thus leads to formation of more thermal conductive chains.

Force-displacement analysis of PMMA/zircon composites using dynamic mechanical analyzer (DMA)

In the study, poly(methyl methacrylate) (PMMA)/zircon (ZrSiO4) composites were successfully prepared using the liquid method at different compositions of 1, 2.5, and 5 wt% of zircon. The zircon filler was processed from a natural, local zircon sand and was processed via a top-down method using wet ball-milling for 5 and 15 h as well as annealing at temperature of 200 °C for 1 h. The force-displacement curves of the composites have been acquired using a DMA (dynamic mechanical analyzer) technique in tensile mode. XRD (x-ray diffraction) data of the composites were collected and analyzed in order to examine the present phases and used as the evidence of the formation of the composites. Furthermore, MAUD software was used to estimate the crystallite size of the filler. Results indicated that zircon crystallite size for 15 h wet ball-milling was smaller than that of 5 h. Furthermore, the maximum DMA force (also representing stress) for the composite with smaller filler was generally higher than that of 5 h, ca. by 2.5 times. In addition, in general, the composites exhibited an increasing slope of force-displacement curve with increasing amount of filler.

Coarse-grained molecular dynamics simulation of wettability and bleed out of capillary underfill

Coarse-grained molecular dynamics simulations were performed to elucidate the capillary flow process of liquid state capillary underfill (CUF), a sealing resin material. First, we ran a wettability simulation with the CUF consisting of a monomer with small and large fillers. We observed that a certain amount of the monomer spreads ahead on the substrate, while many fillers are left inside the droplet. This was confirmed by subsequent mean square deviation (MSD), which showed that the monomer had a higher MSD, 25–45 σ2, than the small and large fillers, which were 0.4–1.4 σ2 and 0.02–0.2 σ2, respectively. When one part of large fillers was replaced with small fillers, small fillers helped accelerate the wetting dynamics because they could move fast. However, when the small filler ratio was high (20%), the MSD of small fillers decreased. Next, we performed a capillary flow simulation in which the CUF flowed between parallel walls and observed that it formed a ridgeline at the upper wall edge. Small fillers contributed to a decreased flow time. However, when the small filler ratio was even higher, the flow time increased. Then, the small fillers slowed themselves down, as shown in the MSD. This is due to an increase in monomer interactions and less space to move. We also found that the bleed length decreased with an increase in the small filler ratio. This study clarified the effects of filler usage on the flow time and bleed length and contributed to new insight into the capillary actions and material design relevant to CUF.

Research of the structure and dynamic interactions of particles in the Li0.42K0.58NO3– R (R = α-Al2O3, γ-Al2O3, SiO2) and (LiNO3–LiClO4) – γ-Al2O3 composites in various temperature conditions and phase states

The paper presents a comprehensive study of the Li0.42K0.58NO3– R (R = α-Al2O3, γ-Al2O3, SiO2) and (LiNO3 – LiClO4) - γ- Al2O3 composite salt systems by vibrational spectroscopy, X-ray diffractometry, and differential scanning calorimetry. According to the results of Raman spectra and XRD analysis, it has been found that in the case of a sufficiently small filler (15 nm-γ-Al2O3 and SiO2), an amorphous phase appears, both for systems based on Li0.42K0.58NO3 and for the nanocomposite based on (LiNO3)0.5-(LiClO4)0.5. In the case of nanocomposites based on the Li0.42K0.58NO3 system, this additionally leads to the formation of the metastable KNO3 (R3m) phase. The temperature changes in the half-widths of the corresponding bands of the Raman spectrum during the transition from a solid-phase to a molten state become less significant as the concentration of the oxide filler increases. At x ≥ 0.7, on the temperature dependences of the half-width of the ν1 (A) band in the vicinity of the melting point, only a small kink characteristic of amorphous systems is noticed. This is confirmed by the results of thermal analysis. It has been found that the solid filler has a different effect on the processes of orientational and vibrational relaxation in the molten phases of the studied NIS, namely, the orientational mobility of NO3– decreases, while the relaxation rate of its vibrational excitation increases.

Novel core–shell-structured ironbark-like TiO2 as fillers for excellent discharged energy density of nanocomposites

The perpendicular orientation of nanowires to electric fields would greatly improve the breakdown strengths (Eb) of polymer-based nanocomposites; however, the relatively small polarization at small filler fraction, and thus the unsatisfactory discharged energy density (Ud), greatly restrict their further application. In this study, x vol.% TO@TO/PVDF nanocomposites with superior energy storage performances have been fabricated, where the ironbark-like TiO2 fillers (TO@TO) with core–shell structures lead to greatly enhanced polarization and Eb simultaneously. The former is due to the coupling effects of the increased interfacial polarization, while the latter is due to the enhanced path tortuosity of electric tree growing at small TO@TO fraction. Strikingly, an excellent Ud of 13.1 J/cm3 was achieved in the 1.5 vol.% TO@TO/PVDF nanocomposite at 383 MV/m, which is greatly increased by 220% compared with that of pure PVDF (5.98 J/cm3). The primary results might provide a strategy to design and fabricate nanocomposites with satisfactory energy storage performances as well as the flexible and easy processing ability at small filler fraction.

Preparation of PP/2D-Nanosheet Composites Using MoS2/MgCl2- and BN/MgCl2-Bisupported Ziegler–Natta Catalysts

Polypropylene/molybdenum disulfied (PP/MoS2) and Polypropylene/hexagonal boron nitride (PP/hBN) nanocomposites with varying concentration (0–6 wt %) were fabricated via in situ polymerization using two-dimensional (2D)-nanosheet/MgCl2-supported Ti-based Ziegler–Natta catalysts, which was prepared through a novel coagglomeration method. For catalyst preparation and interfacial interaction, MoS2 and hBN were modified with octadecylamine (ODA) and octyltriethoxysilane (OTES), respectively. Compared with those of pristine PP, thermal stability of composites was 70 °C higher and also tensile strength and Young’s modulus of the composites were up to 35% and 60% higher (even at small filler contents), respectively. The alkyl-modified 2D nanofillers were characterized by strong interfacial interactions between the nanofiller and the polymer matrix. The coagglomeration method employed in this work allows easy introduction and content manipulation of various 2D-nanosheets for the preparation of 2D-nanosheet/MgCl2-supported Ti-based Ziegler–Natta catalysts.

Tensile and Compressive Properties of Glass Fiber-Reinforced Polymer Hybrid Composite with Eggshell Powder

This paper explores the utilization of chicken eggshell powder (ESP) as a biofiller material in glass fiber-reinforced polymer (GFRP) composites. ESP has a very low density, is highly abundant, and is frequently disposed of as agriculture waste. This paper investigates the mechanical strength of the GFRP composites filled with 10 wt% to 40 wt% of ESP filler loading. The size of the ESP is 100 and 150 microns. The collected chicken eggshells were cleaned with clear water. The membrane of the eggshells was removed, dried, crushed, pulverized, and sieved to obtain the desired particle size. The GFRP laminates were manufactured using wet hand layup and resulted in a fiber volume fraction of 0.34. Findings reveal that the composite with a small ESP filler size shows superior strength in both tension and compression properties. The tensile strength and compressive strength increased by 18% and 30%, respectively, with the addition of 10 wt% of 100 µm ESP. The findings reveal the potential of eggshell wastes to be channeled toward the production of value-added composite materials for sustainable development.

Effect of fiber orientation on the mechanical properties of multi layers laminate nanocomposites

The effect of fiberglass type and adding a very small amount of Nano filler in the resin on mechanical and thermal properties of multilayers laminate composite has been studied. The results show clearly that laminate composites can be achieved by controlling the fiberglass type and by dispersing nanoparticles in the resin. Using continues fiber glass helps to increase the impact strength by 17 %–24% compared with samples with random fiberglass. The barcol hardness of continues fiberglass composite is 7% higher than random fiberglass composite. The results of this study show that using small amount form Nano filler in the resin could produce a laminate composite with excellent thermal and mechanical properties.

Effect of surface characteristic of different restorative materials containing glass ionomer on Streptococcus mutans biofilm.

The aims of this study were to evaluate the surface morphology and surface roughness of restorative materials containing glass ionomer, analyze Streptococcus mutans biofilm formation on the surface of materials, and determine the correlation between surface roughness and biofilm. Four restorative materials: resin-modified glass ionomer; giomer; amalgomer; and glass carbomer were used and for each material, 6 mm in diameter and 2 mm in thickness disc-shaped specimens were prepared to evaluate the surface morphology (n = 3), surface roughness (n = 16), and biofilm (n = 20). Surface morphology was analyzed with a scanning electron microscope. Surface roughness was evaluated via an atomic force microscope. The biofilm was evaluated by counting the colony-forming units. Surface roughness measurements were evaluated using a one-way analysis of variance and Tukey HSD test. Biofilm parameters were analyzed using the Kruskal-Wallis H and Mann-Whitney U test. Pearson's correlation test was used to determine the correlation between surface roughness and biofilm. While the highest roughness values were obtained for amalgomer and glass carbomer, the lowest roughness values belonged to giomer and resin-modified glass ionomer. Statistically significant differences in the number of adherent bacteria were observed between the materials only on day 1. No statistically significant correlation was determined between surface roughness and biofilm. The resin content and small filler particle size of material positively affect surface roughness. However, there is no direct relationship between surface roughness and biofilm.

Design of nano-modified PVDF matrices for lead-free piezocomposites: Graphene vs carbon nanotube nano-additions

Graphene nano-additions to polymer matrices have demonstrated exceedingly better mechanical properties compared to carbon-nanotube modified matrices. Therefore, in the context of mechanically superior high-performance piezo-composites, graphene-modified composite architectures represent an important design direction. In this paper, we first develop an effective property model for graphene-modified piezoelectric matrices, taking into account the mechanical anisotropy of the matrix. We further evaluate the piezoelectric performance of the matrix architecture which incorporates lead-free BaTiO3 polycrystal inclusions. In order to obtain comparisons with well-established composites, we compare the electro-elastic response of two composite architectures in which the matrix is modified by multiwalled CNTs and graphene respectively. It is seen that, near percolation of the nano-additions, graphene-based systems exhibit an order of improvement in the piezoelectric response compared to the composite without nano modification. This improvement is comparable to CNT-based systems, but the matrix hardening is lesser than half the hardening observed in CNT-modified composites. This feature is due to a considerably smaller percolation threshold of graphene compared to CNTs which brings about percolative conditions at very small filler concentrations. We further investigate the dependence of the electric flux and fields in the graphene-modified piezocomposite on the polycrystallinity of the piezoelectric inclusions to identify the polycrystalline configurations that can lead to improved performance in such nanomodified piezocomposites.

Friction and Wear between Polymer and Metal in the Mixing Process.

In order to obtain a longer mixing chamber life, a layer of hard alloy coating is generally welded on the surface. However, when the mixing chamber is used for a long time, the surface will be worn due to friction with small fillers and rubber. As a result, there will be a large gap between the mixing chamber and the rotor, which will further affect the quality of the mixed rubber. In this paper, the dispersion process of the reinforcing system is simulated at first, and the mixed rubber samples are obtained from different dispersion stages in preparation for experiments with the chamber material. On this basis, the friction experiment is carried out with the same material as the mixing chamber on the friction experiment machine employed in the improved test part. The experiment shows that the friction and wear between the mixture and metal produced in each mixing stage are different. The wear in the stage with high friction is not necessarily large. The wear will be intensified in the middle and later mixing periods, while the friction will tend to be stable. In this paper, besides the exploration on the friction of fillers and rubber on the mixing chamber in different mixing stages, the most important thing is to change the mixing process of rubber formula, so as to extend the service life of the mixing chamber without changing the comprehensive physical properties of the mixing rubber.

Study of the mechanical, dielectric, and thermal properties of annealed modified nanodiamond/epoxy composites

Electrical properties of Nanodiamond (NDs) with individual diameters of ∼5 nm are important for many engineering applications and drawing significant attention of the current research community. In this paper, we reported a systematic approach to remove sp2 carbon content from NDs particles by annealing method to enhance the interfacial molecular bonding between reinforcement and matrix. X-ray Diffraction (XRD) and Fourier Transform Infra-Red Spectrophotometer (FTIR) studies revealed that annealing of NDs occurs at 450 °C, indicating that the decrease in resistivity is based on the sp2/sp3 carbon ratio of NDs. Thus, it is interesting to study the properties of annealed NDs/epoxy nanocomposites with small filler concentrations varying from 0.1 wt% to 0.5 wt%. In this paper, the Dielectric properties (dielectric constant and dielectric strength), thermal conductivity, impact strength, micro-hardness, and compressive behaviour of NDs/epoxy nanocomposites were investigated. Dispersion of NDs at very low concentration was ensured with the help of UV–vis–NIR absorbance spectra analysis. It was observed that the dielectric constant (ε′) was enhanced with NDs loading and reached an optimum value at 0.3 wt% of the loading of NDs whereas the dielectric strength showed a reverse pattern. The thermal conductivity and Izod impact strength showed maximum improvement of 21% and 104.0% respectively at 0.3 wt% NDs loading.

Massive and sustained enhancement of the electrical conductivity of polystyrene using multilayer graphene at Low loadings, and carbon black as a dispersion aid

The high electrical conductivity of multilayer graphene (MLG) and their sheet like morphology results in a low percolation threshold, and makes it an attractive filler for inducing electrical conductivity in an insulating polymer at small filler loadings. However, strong van der Waals forces between the flat faces of multilayer graphene cause agglomeration, making it difficult to disperse them in a polymer. The loading required for forming a percolating network of these MLGs then increases dramatically, and the advantage of their sheet-like morphology is lost. To enhance the dispersion of MLGs, carbon black nanoparticles (CB) were added as secondary fillers to a polystyrene (PS) matrix containing 2.5 vol% MLG. The electrical conductivity of the composite increased from 10−9 S/m with no CB to 10-4 S/m with 1.5 vol% CB, asymptoting to 103 S/m at ∼12 vol% CB. Using Raman spectroscopy and wide-angle X-ray diffraction, we confirmed that the CB particles act as dispersion aids and prevent MLG restacking, reducing agglomeration and enhancing dispersion of the MLG sheets in PS. This leads to an increase of several orders of magnitude in electrical conductivity.

Compressive characteristics of bimodal aluminium matrix syntactic foams

High performance metal matrix syntactic foams (MMSFs) have been produced by liquid state infiltration of AlSi12 alloy into two loosely packed sets of different nominal diameter (150 μm and 1500 μm) oxide hollow spheres (CHSs) and their mixed packs. The structure of the MMSFs has been studied by X-ray computer tomography and microscopy. The mechanical properties were mapped by compressive tests. The structural investigations showed proper infiltration. In the case of pure small and large CHS filler, the compressive tests revealed high strength levels all over the deformation of the materials up to 50% compressive strain, with the dominance (higher strength values) of the smaller CHSs filled MMSFs. In the case of bimodal CHS filling, the compressive features of the MMSFs have been mixed with two local peaks corresponding to the failure of the smaller and larger CHS filled MMSFs. Rule of mixtures is applicable to estimate the compressive strength.

THE EFFECT OF PRELIMINARY ELECTRIC RADIO HEATING ON THE PHYSICAL AND THERMAL CHARACTERISTICS OF THE HEAT-RESISTANT CERAMZITONE-CONCRETE BASED ON COMPOSITIVE BINDER OF LOCAL MINERAL RAW MATERIALS

Objectives. The aim of the study is to increase the physico-thermal and operational characteristics of heat-resistant ceramsite concrete with an activated binder by pre-heating the mixture.Method. To conduct the study, a technique was developed by the Research Institute of Concrete and Reinforced Concrete named after A.A. Gvozdev.Results. An analysis of the study results of the effect of preliminary electric heating on the physico-thermal characteristics of heat-resistant ceramsite concrete on the basis of a composite binder showed that, in comparison with drying at a temperature of 105º, the operational properties of heat-resistant ceramsite concrete are enhanced by uniform heating of the samples along the concrete body. This isdue to the pore pressure in the concrete structure being reduced by removing physically bound water. Ceramsite is used as large filler while ceramsite sand is used as small filler; activated composite combination of local mineral raw materials consisting of Portland cement and calcined argillic clay is used as a binder. In the concrete body, due to the removal of physically bound water caused by the decrease in pore pressure, the formation of cracks in the interporal partitions decreases, preventing the explosive destruction of heat-resistant ceramsite concrete and improves its physico-mechanical, thermal and operational characteristics. Activated composite binder based on the combination of Portland cement and fine ground argillite clay reduces shrinkage deformations and increases the concrete strength as well as its heat resistance. Concretes with activated composite binder are less susceptible to volume change during the heating process,contributing to greater preservation of concrete strength and structure due to lower stress levels caused by the temperature deformations.Conclusion. The composition of the developed heat-resistant ceramsite concrete allows its use for monolithic lining of the walls of a tunnel kiln for burning ceramic bricks, as well as various concreting furnaces for the construction industry. The conducted research demonstrates the possibility and expediency of using electric heating for the hardening of heat-resistant ceramsite concrete with a composite binder. The use of electric heating increases the strength of heat-resistant ceramsite concrete both before and after heating to high temperatures. Optimised modes of electric heating of heat-resistant ceramsite concrete with a composite binder are established.

Effect of Alternative Fillers on the Properties of Rubber Compounds

The paper is focused on the influence of alternative fillers on rubber compounds properties. Three different types of powder fillers, drinking water treatment sludge (DWTS), perlite and calcium carbonate, were mixed into rubber compound mixtures. The mixtures were composed of STR20, EPDM, zinc oxide, steric acid, paraffin wax, 2-mercaptobenzothiazole (MBT), sulphur, Wingstay L, and filler. The mixtures were mixed in a Kneader type mixer at temperature of 70°C and then continuously mixed using a two-roll mill at temperature of 70°C. The relationships between type and the amount of filler versus properties of rubber compounds were demonstrated. The results showed that tensile and elongation at break of rubber compounds gradually decreased with increasing the amount of filler. Rubber compounds filled with small particle size filler possessed higher tensile strength and elongation at break than those filled with large particle size filler. Values of DIN abrasion loss of rubber compounds prepared under proper mixing condition were not more than 300 mm3. Under appropriate condition, the rubber compounds with DWTS, perlite and calcium carbonate provided sufficiently high shore A hardness (not less than 50 Shore A hardness). Finally, alternative fillers such as DWTS and perlite were expected to replace calcium carbonate in normal formula.

Influences of morphology and floating rate of CeO2 fillers on controlling infrared emissivity of the epoxy-silicone resin based coatings

Abstract CeO2 powders with flaky morphology and high floating rate are fabricated successfully by ball-milling and stearic acid modification. The influences of ball-milling time and surfactant stearic acid content on the morphology, floating rate, infrared emissivity of CeO2 powders as well as the CeO2/epoxy-silicone coatings have been investigated systematically. The results show that the CeO2 powders transform from irregular grains with larger size to flake grains with smaller size by ball-milling for 4 h. The floating rate of CeO2 enhances from 0 cm2/g to 89.06 cm2/g by increasing stearic acid content from 0 wt% to 1 wt% while diminishes to 60.477 cm2/g with stearic acid content of 3 wt%. Ultimately, the coating with CeO2 fillers ball-milled by 4 h and modified by 1 wt% of stearic acid exhibits the lowest emissivity value of 0.831 in the 8–14 μm waveband. The mechanisms for small and flaky fillers as well as high floating fillers to achieve low emissivity coatings are also fully revealed.