Mixed Fillers Research Articles

Multiwalled carbon nanotubes–BaTiO3/silica composites with high complex permittivity and improved electromagnetic interference shielding at elevated temperature

Abstract Composites with silica matrix and mixed filler of multiwalled carbon nanotubes (MWCNTs) and BaTiO3 powder were fabricated. Excellent uniform dispersion of MWCNTs can be obtained using a two-step mixing method. Both of the real and imaginary parts of complex permittivity increased with increasing MWCNT content and measured temperature. The electromagnetic interference (EMI) shielding results showed that the absorption mechanism is the main contribution to the total EMI shielding effectiveness (SE). Compared with the EMI SE resulting from reflection, the absorption showed more dependence on the MWCNT content, measured temperature and frequency. The total EMI SE is greater than 20 dB at 25 °C and 50 dB at 600 °C in the whole frequency range of 12.4–18 GHz with a 1.5 mm composite thickness, which suggests that the MWCNT–BaTiO3/silica composites could be good candidates for the EMI shielding materials in the measured frequency and temperature region.

The Impact of Mineral Fillers on the Mechanical and the Thermal Properties of Polyester

Polyester resins has found a wide spread in many applications. Filler materials are used extensively with polyester resin for a variety of reasons like cost reduction, and more importantly to enhance some physical and/or mechanical properties. Through the present work several types of inorganic fillers (cement, silica fume, and sand) were incorporated into the polyester resin. Their effects on the mechanical and the thermal properties were investigated. Quantitative measurements and qualitative observations were made to recognize the different aspects related to their employment in attempt to find an appropriate means to enhance a prescribed property. Test results revealed that although a pronounced enhancement of the mechanical properties was achieved, but a specific filler type may not has the same effect on each mechanical property. Therefore, in real applications where only some of the properties are of concern, the proper filler type and content should be specified accordingly. Anyhow, employing a combination of filler types (mixed fillers) is an efficient way to utilize the benefits of each of the employed fillers.

OPTICAL PROPERTIES AND STRUCTURE OF COBALT CHLORIDE DOPED PVA AND ITS BLEND WITH PVP

Solution cast technique has been used to prepare films of PVA and its blend with PVP. Moreover, cobalt chloride ( CoCl 2) has been doped in PVA and also PVA/PVP 90/10 as a host matrix for it. Also, UV/VIS optical analysis has been used to drop more light on the structural modification that occurs due to doping CoCl 2 with different levels in different polymeric matrixes. Indeed, UV–Vis spectra is a useful tool for studying the absorption spectra and estimating the values of absorption edge, Eg, and band tail, Eu, for all samples. The optical absorption measurements have been carried out in the wavelength region from 200 nm to 900 nm. In addition, the ligand field parameters and optical energy gaps have been calculated and discussed. X-ray diffraction (XRD) and fourier transform infrared (FTIR) spectroscopy have been used to characterize the studied samples which illustrates that PVA is strongly affected by mixed fillers.

Modeling the electrical percolation of mixed carbon fillers in polymer blends

A model based on excluded volume theory is proposed for describing the electrical percolation of mixed carbon fillers in polymer blends by adjusting the unit volume of the previous model concerning mixed carbon-filler-filled single polymer systems. An equation capable of predicting the percolation threshold from those of individual carbon fillers in the single matrix polymer is developed from the model and further corrected to suit the actual situation. The corrected equation fits the experimental results obtained from multi-walled carbon nanotubes/carbon black-filled polybutylene terephthalate/styrene–acrylonitrile (SAN), polycarbonate (PC)/SAN and PC/acrylonitrile–butadiene–styrene blends well. The model and equation show clearly the advantages of using both mixed fillers and polymer blends, and can provide an important theoretical basis for designing the structures and predicting the electrical properties of conductive polymer composites.

Research on electrical conductive adhesives filled with mixed filler

A new type of electrical conductive adhesives (ECAs) with flaky and spherical silver powder as mixed conductive filler is investigated in this paper. And the mixed filler could achieve the dense packing structure after ultrasonic treatment. According to scanning electron microscope (SEM) images, it can be proved that flaky and spherical silver powder is well dispersed in the epoxy matrix without obvious agglomeration after ultrasonic treatment. The thermal, electrical and mechanical properties of ECAs were characterized. The thermal conductivity of ECAs increases with the raise of silver content. However, the bulk resistivity and tensile–shear strength decreases with the increase of silver content. In addition, small agglomeration and free dispersed spherical silver can improve thermal conductivity of ECAs. The thermal conductivity model is explored in this paper.

Synergistic effects of functionalized graphene and functionalized multi-walled carbon nanotubes on the electrical and mechanical properties of poly(ether sulfone) composites

Mixed fillers composed of functionalized graphene (f-G) and functionalized multi-walled carbon nanotubes (f-CNTs) (f-G-f-CNTs) were prepared and their synergistic effects in terms of enhancing the electrical conductivity and tensile modulus of poly(ether sulfone) (PES) composites were investigated. The results indicate that the electrical conductivity of the 5wt% f-G-f-CNTs(Wf-G/Wf-CNTs=1:1)/PES composite was 2.2 times higher than that of the 5wt% f-G/PES composite and 8.9 times higher than that of the 5wt% f-CNTs/PES composite. Moreover, the tensile modulus of the 5wt% f-G-f-CNTs(Wf-G/Wf-CNTs=1:1)/PES composite relative to that of the 5wt% f-G/PES composite and 5wt% f-CNTs/PES composite increased by 16.5% and 50.6%, respectively. Additionally, enhancements in the electrical conductivity and tensile modulus of the PES composite depended on the weight ratio of f-G and f-CNTs in the mixed fillers. The electrical conductivity and tensile modulus exhibited maximum values when the weight ratios of f-G and f-CNTs were 1:3 and 1:1, respectively. When the weight ratio of f-G and f-CNTs was fixed at 1:1, the f-G-f-CNTs(Wf-G/Wf-CNTs=1:1)/PES composite showed a percolation threshold of 0.22vol%, much lower than that of the f-G/PES composite.

Surface and mechanical properties of graphene–clay/polyimide composites and thin films

Nano-graphene sheets (NGS) and clay mixed fillers were dispersed in a high performance polyimide (PI) matrix by in situ condensation polymerization. The dispersive (γsd) and polar (γsp) surface energy components of NGS/PI, clay/PI and NGS–clay/PI composite films were studied by using dynamic contact angle analyzer with water and diiodomethane as wetting liquids. The total surface energy (γs) of NGS/PI composites increases with increasing NGS concentration while that of clay/PI composites decreases with increasing clay concentration. Addition of clay into NGS/PI composites decreases the surface energy of the resulting composites due to the presence of long chain organic modifiers and decreased external composite surface roughness. Investigating the influence of clay on the surface properties of graphene/polyimide composite provides a useful insight into a relatively cheaper surface modification methodology for graphene-based composite materials. The viscoelastic behavior of the NGS–clay/PI composites, investigated using dynamic mechanical spectrometry (DMS), showed significant improvement in storage modulus of the composite over that of the matrix (EC/EM∼1835) at 4.5vol.% clay concentration. Damping ability of the NGS–clay/PI composite, which is correlated with the area under the alpha (α) transition peak, was significantly improved in the presence of clay. X-ray diffraction showed the graphitic and clay diffraction peak at 26.5° and 4.76°, respectively.

Effect of filler dispersion on the electrical conductivity and mechanical properties of carbon/polypropylene composites

Conducting carbon/polypropylene composites containing a mixed filler of crystalline natural graphite powder, carbon black, and multiwalled carbon nanotubes have been prepared. The effect of the filler dispersion on the electrical conductivity and mechanical properties has been studied. Keeping the graphite content constant and increasing the ratio of carbon black to nanotubes, the conductivity and the flexural modulus increased linearly at different graphite contents. Graphite aggregates on the cross sections were analyzed by optical microscopy to characterize the dispersion of graphite. The results of the optical microscopy studies showed that the dispersion of graphite is affected by the composition and amount of the nanofiller system. Based on the observations simplified morphological models were set up, that allowed to explain the change in the electrical and mechanical properties of the composites of different compositions. POLYM. COMPOS., 34:1195–1203, 2013. © 2013 Society of Plastics Engineers

Rare Earth Oxide Containing Filler for Dental Composite Resin

A composite resin (CR) with photo-polymerization is widely used for dental filling material. Because of their good esthetics, the visual inspection of restored teeth becomes difficult. In this study, the fluorescent glass/ceramics fillers containing rare earth oxides — which are well-known fluorescent materials — was prepared and applied in CR to enhance visual inspection capability with small influence in color. Eu2O3-containing Y2O3 filler (Y2O3:Eu) prepared with homogeneous coprecipitaion method showed clear fluorescence at 614nm with near ultraviolet light (385nm) excitation. The fluorescence intensity of the prepared Y2O3:Eu filler increased with increase of Eu content in the Y2O3 filler upto 15mol% of Eu content. The composite resin was prepared with the mixed filler of Y2O3:Eu filler and the conventional glass filler. The content of Y2O3:Eu was varied between 0 to 40wt% of mixed filler. The prepared composite resin also showed clear fluorescence with quite small affect to the color change and the Vickers hardness of composite resin. Therefore, the prepared rare earth oxide containing Y2O3 filler was applicable as the filler of dental composite resin.

Rubber composites based on graphene nanoplatelets, expanded graphite, carbon nanotubes and their combination: A comparative study

Abstract Solution styrene butadiene rubber (S-SBR) composites reinforced with graphene nanoplatelets (GnPs), expanded graphite (EG), and multiwalled carbon nanotubes (MWCNTs) were prepared and the electrical and various mechanical properties were compared to understand the specific dispersion and reinforcement behaviours of these nanostructured fillers. The electrical resistivity of the rubber composite gradually decreased with the increase of filler amount in the composite. The electrical percolation behaviour was found to be started at 15 phr (parts per hundred rubber) for GnP and 20 phr for EG filled systems, whereas a sharp drop was found at 5 phr for MWCNT based composites. At a particular filler loading, dynamic mechanical analysis and tensile test showed a significant improvement of the mechanical properties of the composites comprised of MWCNT followed by GnP and then EG. The high aspect ratio of MWCNT enabled to form a network at low filler loading and, consequently, a good reinforcement effect was observed. To investigate the effect of hybrid fillers, MWCNT (up to 5 phr) were added in a selected composition of EG based compounds. The formation of a mixed filler network showed a synergistic effect on the improvement of electrical as well as various mechanical properties.

Analysis of Characteristics of Electrically Conductive Asphalt Concrete Prepared by Multiplex Conductive Materials

The main objective of this paper is to analyze the characteristics of electrically conductive asphalt concrete (ECAC) by adding multiplex electrically conductive materials. First, it is proved that all the mechanical properties of ECAC meet the design requisition in this study. The effects of filler type, filler content, and mixed fillers on the resistivity of asphalt concrete were then systematically investigated. Experimental results showed that the combination function of mixed fillers has appreciable advantages over single powder in electrical conductivity. Both laboratory and field tests were conducted to prove that the ECAC provides an efficient method for snow melting through direct current. In addition, an infrared imaging technology was used to assess the temperature field distribution. Furthermore, the effects of temperature, voltage, and temperature circulation on the resistance of ECAC were explained by the break and rebuild of conductive pathways. Finally, X-ray computed tomography provides insight into the mechanisms of conductivity enhancement for mixed fillers. It is shown that the conductive chain formed in ECAC largely depends on the conductive filler’s distribution in asphalt mortar.

Dynamic percolation in highly oriented conductive networks formed with different carbon nanofillers

Dynamic percolation in highly oriented conductive networks formed with different carbon nanofillers is investigated during disorientation upon annealing. Conductive networks are constructed by solid-state drawing, subsequent annealing, and using fillers with different dimensions (multiwalled carbon nanotubes (MWCNTs) and carbon black (CB)) in a bicomponent tape. Interestingly, it is observed that a less entangled network work is formed by mixed filler containing CB; consequently, this result in an accelerated dynamic percolation process and reduced activation energy of such process. Three different analytical approaches have been utilized to analyze this interesting behavior. It is concluded that the dynamic percolation process in highly oriented conductive polymer composites filled with MWCNTs can indeed be accelerated by the addition of CB, since less entangled networks are formed in a hybrid filler system compared with MWCNTs alone.

Study on Stirring Brazing of SiCp/A356 Composites with the Zn27Al Filler Alloy in Air

The joining process of SiCp/A356 composites is investigated. The two substrates are heated up to the melt temperature of Zn27Al filler metal by a resistance heating plate. At the time, a stirrer is introduced into the liquid weld seam in order to mix filler metal and two sides of substrates into a single uniform joint. After stirring, specimens are sectioned for the analysis of macro- and micro-structures along the weld region. The research shows that two typical joint interfaces with oxide film and without one were found. So, oxide film on the substrate wasn’t completely disrupted during stirring brazing at 500°C.And, the tensile strength of joint is only 50MPa.

Research on Decomposition of Toluene Using Adsorption Combined with Non-Thermal Plasma

The paper made a research on synergetic effect of gaseous toluene decomposition using dielectric barrier discharge plasma and adsorption. A systematic investigation on toluene removal efficiency and ozone byproduct generation was done using different types of fillers. The mixed fillers were found to be promising as ideal fillers. In terms of toluene removal efficiency, mixed fillers of zeolite and ceramic rings was the highest, around 97%, next is zeolite, then followed by ceramic rings and no filler-packed. Among the tested fillers, mixed fillers showed the least amount of ozone generation. For practical use of mixed fillers, it’s preferable to operate at 18kV than 20 kV, avoiding forming more undesirable O3byproduct on achieving the same toluene removal effect.

Strength and microstructure of semi-solid stirring brazing of SiCp/A356 composites and aluminum alloy in air

The semi-solid stirring brazing process of SiCp < /sub>/A356 composites and 2024 aluminum alloy was investigated. The two substrates were heated up to the semisolid temperature range of Zn27Al filler metal in the joint region by a resistance heating plate in air. At this point a stirrer was penetrated into the semi-solid weld seam in order to mix filler metal and the two sides of substrates into a single uniform joint. After stirring, specimens were sectioned for analysis of macro- and micro-structures along the weld region. The research shows that SiCp < /sub>/A356 composites and aluminum alloy can be successfully joined with semi-solid filler metal by optimizing stirring temperature. It can be found that most of the oxide film on the surface of the base metal was disrupted and removed through the observation by SEM. The metallurgical bonds formed between the filler metal and the base materials. Since the semisolid temperature range of filler metal is narrow, the accurate controlling of weld pool temperature must be considered.

Cooperative performance of chitin whisker and rectorite fillers on chitosan films

We prepared chitosan/chitin whisker/rectorite ternary films and studied the cooperative effects of nanofibril whisker and layered organic rectorite on the properties of chitosan matrix. The ternary film exhibited higher thermal stability and smoother surface than the whisker or rectorite reinforced binary films due to the intercalation of chitosan chains into the layered rectorite and the impregnation between the clay and rod-like whisker. With increasing the ratio of mixed fillers from 0 to 229mg/g, the break elongation first increased to a maximum value (144%) with the mixed fillers of 114.5mg/g and then decreased. Antimicrobial assay against Escherichia coli and Staphylococcus aureus showed that the ternary films had higher antimicrobial effect than the pure or binary films because of the significant adsorption capacities of the enlarged interlayer of rectorite. Overall, the chitosan-based ternary film with chitin whisker and rectorite proves to be a suitable material for food-packaging applications.

Polymer Based Filler Materials as Infill for GFRP Pile Connector

Recently glass fibre reinforced polymer (GFRP) tubular piles have been developed for civil engineering applications instead of conventional concrete piles. Considering their suitable applications, the new polymer based filling materials are being developed at the University of Southern Queensland as a part of work done for timber pile rehabilitation. This ongoing project aims to replace portion of the deteriorated timber pile by using GFRP piles. Due to good compressive strength, pumpability and workability, the new polymer base materials are to be filled in between GFRP pile and existing timber pile base. An ongoing research program has been initiated to improve fundamental understanding of these materials and to provide the knowledge required for their broad utilization. In this development, sample trial mixes were considered based on several weight percentages of polymer resin, fly ash and sand. Material parameters such as compressive strength, stiffness, shrinkage and gel time were achieved from the experimental investigation. It has been found that most polymer based trial mixed fillers have high compressive strength and considerable plastic region with more than 10% strain. These results imply that the polymer based filling materials are suitable for both compression and tensile loading situations. However, the behaviour of fillers with GFRP pile connector under different loading conditions is yet to be fully understood.

Semi-Solid Stirring Brazing of SiCp/A356 Composites and Aluminum Alloy in Air

The semi-solid brazing process of SiCp/A356 composites and aluminum alloy was investigated. The two substrates were heated up to the semisolid temperature range of Zn-Al filler metal in the joint region by a resistance heating plate. At this point a stirrer was introduced into the weld seam in order to mix filler metal and the two sides of substrates into a single uniform joint. After stirring, specimens were sectioned for analysis of macro- and micro-structures along the weld region. The research shows that SiCp/A356 composites and aluminum can be successfully joining with semi-solid filler metal. It can be found that most of the oxide film on the surface of the base metal was disrupted and removed through the observation by SEM. The metallurgical bonds formed between the filler metal and the base materials. Moreover, the oxide film of surface of aluminum alloy was more thoroughly disrupted and removed than that of surface of composites with existing of Sic particle. The joint microstructure with globular α-Al grain enclosed by rich-Zn phase can be obtained after stirring brazing.

Elastomer composites based on improved fumed silica and carbon black. Advantages of mixed reinforcing systems

The combination of reinforcing fillers is one of the most promising tendencies in elastomer reinforcement, where a synergic effect between them is desired. Up to now, the use of mixed fillers has been focused on the preparation of dual fillers based on a complex synthesis process where silica particles are in situ generated in a carbon black matrix. In this paper, mixed filler systems are prepared following a straightforward methodology, where carbon black is gradually and partially substituted by modified fumed silica. The presence of reinforcing fillers with different surface energies significantly decreases filler networking, reducing the non-linear viscoelastic response of the composites. The hybrid reinforcing systems prepared were easily incorporated into the elastomer matrix by conventional methods in rubber technology. Physical and dynamic responses of the elastomeric composites were characterized in order to find the optimum mixed system combination. Filler–rubber interface was characterized combining 1H low field DQ (Double Quantum) NMR spectroscopy and equilibrium swelling experiments.

Structural, optical and some physical properties of PVDF films filled with LiBr/MnCl 2 mixed fillers

Films of polyvinylidene fluoride (PVDF) filled with ( X)LiBr(20 −X)MnCl 2 mixture, where X=0, 1, 2, 8, 16 and 20 wt%, were prepared by casting method and studied by ultraviolet/visible optical absorption (UV), differential scanning calorimetry (DSC), X-ray diffraction (XRD), infrared transmission (IR) and electron spin resonance (ESR). The optical absorption spectra suggested the presence of an optical gap ( E g) which depends on filler concentration ( W) and arises due to the variation in crystallinity within the polymer matrix. Melting and degradation temperatures were identified using DSC. XRD implied a semicrystalline structure (containing α- and β-PVDF phases for all films). Conjugated double bonds and the role of dimethylformamide with a PVDF chain were detected by IR spectra. The ESR analysis revealed the existence of both isolated and aggregated Mn 2+ ions within the PVDF matrix.