Characterization and in vitro application of nano-crystalline calcia stabilized zirconia (CSZ)/copolymer composites

The ideal implant should have long stable life in the physiological environment and induce natural bone growth around implants. In this study, nano-sized particles of calcia stabilized zirconia (CSZ) was used as a filler in poly(hydroxyethylmethacrylate–methylmethacrylate) p(HEMA–MMA) grafted onto chitosan copolymer to produce a bioactive composites analogous to bone. Results coming from this study confirmed that the grafting percentage of CSZ–copolymer composite was enhanced compared to the copolymer as a result of nano-sized filler. Thermo-gravimetric analysis (TGA) proved the presence of attached copolymer layer onto the filler particles for CSZ–copolymer composite. Swelling properties was reduced for CSZ–copolymer composite proving the stability and lower affinity of this composite to water molecules. In vitro tests indicate that the adsorption of calcium ions (Ca²⁺) and phosphate ions (PO₄³⁻) on the surface of the composites are enhanced. That was confirmed by the formation of a bone-like apatite layer. Fourier transformer infrared spectrophotometer (FT-IR) post-immersion confirmed the formation of carbonate-apatite layer onto the surface of the copolymer and CSZ–copolymer composite at 3 and 21 days, respectively. SEM post-immersion showed enhanced bone-like apatite layer (calcium-phosphate layer) onto the CSZ–polymer composite compared to the copolymer. Subsequently, the formation of a bone-like apatite layer is found to be controlled by the change in content of CSZ filler.     

Structural,dielectric and mechanical behaviors of (La,Nb) Co-doped TiO2/Silicone rubber composites

Ceramic/polymer composites have great potential to achieve the concomitant enhancement of both dielectric constant and breakdown field while maintaining other superior properties of the polymer matrix, ideal for elastomer sensors, actuators, capacitive energy storage, and many other applications. However, material incompatibility between the ceramic filler and the polymer matrix often leads to void formation, particle aggregation and phase separation, with significantly degraded performance. Herein, through surface modification, co-doped TiO₂ particles were uniformly dispersed and bridged onto the silicone rubber matrix via a silane coupling agent for fabricating composites via mechanical mixing and hot-pressing. The synthesized composites exhibit enhanced dielectric constant, increased from 2.78 to 5.06 when 50 wt% co-doped TiO₂ particles are incorporated. Their dielectric loss is less than 0.001 in a broad frequency range. Theoretical modelling and experimental results reveal that the morphology and dispersion state of co-doped TiO₂ particles were crucial to the dielectric properties of the silicone rubber-based composites. Besides, the composites are thermally stable up to 400 °C. Significantly increased tensile strength (612 kPa) and elongation at break (330%) were obtained for the composite incorporated with 30 wt% co-doped TiO₂ particles, accompanied by a moderate increased elastic module (540 kPa). Such composites have the potential for different applications.     

Comparative performance analysis of electrospun TiO2 embedded poly(vinylidene fluoride) nanocomposite membrane for supercapacitors

For an efficient energy storage system, effective material is to be used. In the present work, novel poly(vinylidene fluoride)/titanium oxide (PVdF/TiO₂) composite membranes were developed using electrospinning technique, as separator for supercapacitors. Different weight percentages of TiO₂ nanoparticle (0, 5, 10, 15, and 20 wt%) were mixed with 20 wt% of PVdF in a 50:50 wt% of tetrahydrofuran and dimethylacetamide solvent. Various physical and electrochemical properties including fiber diameter, thermal stability, crystallinity, porosity, and electrolytic uptake were studied to identify the best membrane with optimum TiO₂ wt% exhibiting superior characteristics. SEM and TGA studies revealed that the developed PVdF/TiO₂ composite membrane with 10 wt% showed improved properties with a lower average diameter of about 66 ± 8 nm, enhanced thermal stability up to 513.15°C and higher porosity of 89%, respectively compared to other membranes. The crystallinity, ionic conductivity, and specific capacitance of the nonwoven separator membranes were determined using X-ray diffraction technique, electrolytic uptake, and charge–discharge studies, respectively. The present study revealed that the addition of TiO₂ nanoparticles improved the physical and thermochemical properties of the separator membrane substantially and PVdF/TiO₂ composite membrane with 10 wt% displayed superior performance compared to other membranes.     

Study of morphology and gas separation properties of polysulfone/titanium dioxide mixed matrix membranes

Polysulfone (PSf)‐based mixed matrix membranes (MMMs) with the incorporation of titanium dioxide (TiO₂) nanoparticles were prepared. Distribution and agglomeration of TiO₂ in polymer matrix and also surface of membranes were observed by scanning electron microscopy, transmission electron microscopy, and energy dispersive X‐ray. Variation in surface roughness of MMMs with different TiO₂ loadings was analyzed by atomic force microscopy. Physical properties of membranes before and after cross‐linking were identified through thermal gravimetric analysis. At low TiO₂ loadings (≤3 wt%), both CO₂ and CH₄ permeabilities decreased and consequently gas selectivity improved and reached to 36.5 at 3 bar pressure. Interestingly, PSf/TiO₂ 3 wt% membrane did not allow to CH₄ molecules to pass through the membrane and this sample just had CO₂ permeability at 1 bar pressure. Gas permeability increased considerably at high filler contents (≥5 wt%) and CO₂ permeance reached to 37.7 GPU for PSf/TiO₂ 7 wt% at 7 bar pressure. It was detected that, critical nanoparticle aggregation has occurred at higher filler loadings (≥5 wt%), which contributed to formation of macrovoids and defects in MMMs. Accordingly, MMMs with higher gas permeance and lower gas selectivity were prepared in higher TiO₂ contents (≥5 wt%). POLYM. ENG. SCI., 55:367–374, 2015. © 2014 Society of Plastics Engineers     

Synthesis and electrochemical properties of monoclinic Li3V2(PO4)3/C composite cathode material prepared from a sucrose-containing precursor

Monoclinic structure Li₃V₂(PO₄)₃/C composite powders are synthesized via a novel homogeneous mixing route followed by a one-step heat treatment. The composites were characterized by X-ray diffraction (XRD) and galvanostatic charge/discharge, CV measurements. The influence of the heat treatment on the electrochemical properties of Li₃V₂(PO₄)₃/C composites was investigated. To examine the effect of residual carbon content on the properties of the composites, six samples with 1.2, 2.3, 3.4, 4.4, 5.8, and 7.0 wt% carbon were prepared. The sample with 4.4 wt% carbon exhibited good cycling performance and rate capability in the range of 3.0–4.8 V.     

Effect of zircon and anatase titanium dioxide nanoparticles on glass fibre reinforced epoxy with mechanical and morphological studies

In recent years, researchers have been interested in incorporating inorganic nanoparticles into thermosetting epoxy composites to improve their mechanical properties. This research explores the diffusion of ball milled zircon (ZrSiO₄) and anatase TiO₂ nanoparticles with glass fibre reinforced epoxy polymer (GFRP) composites at the same weight percentages (0:0, 2.5:2.5, 5:5, and 7.5:7.5) to improve mechanical properties. The ZrSiO₄ and TiO₂ nanoparticles were prepared by an ultrasonic liquid processor, and composites were fabricated using the compression molding technique. The void percentage was calculated from the theoretical and measured densities of composites. Mechanical tests were conducted in accordance with ASTM standards. The particle sizes of zircon and titanium dioxide were calculated as 70.5 nm and 64.5 nm, respectively, using field emission scanning electron microscopy (FESEM), which reveals the fibre pullout, damaged interfaces, filler dispersion, and voids in specimens. The chemical composition, crystalline structure, and size were determined using X-ray diffraction (XRD). It was found that the GFRP composite with Zircon and TiO₂ incorporated at a concentration of 5:5 wt% has a greater tensile strength of 74.34%, a tensile modulus of 18.14%, a flexural strength of 33.55%, a flexural modulus of 33.61%, a shore "D" hardness of 4.66%, and a capacity to absorb energy of 61.14% in notched specimens with neat GFRP. With filler addition, the percentage of elongation at failure in the 5:5 wt percent for the tensile test is 44.36%, and the flexural test is 24.38% higher than the neat sample. Hence, this work improves the GFRP composites' mechanical and structural properties.     

Preparation,characterization, and properties of TiO2/PLA nanocomposites by in situ polymerization

In situ polymerization method was used to prepare TiO₂/polylactide (PLA) nanocomposites with different contents of TiO₂ in this work. The size of the organically modified TiO₂ particles was investigated by X‐ray diffraction (XRD) analysis. Scanning electron microscope (SEM) shows that nano‐TiO₂ particles disperse in the PLA evenly when the content of TiO₂ is low (less than 3 wt%). The differential scanning calorimeter (DSC), thermogravimetry analysis (TGA), and tensile test were used to study the thermal and mechanical properties of the composites. Results show that both the thermal and mechanical properties are markedly improved when the content of TiO₂ is 3 wt%. UV light irradiation and solution degradation experiment show that degradation of the composites is higher when the content of TiO₂ increases and due to the introduction of TiO₂ particles in the nanocomposites, the TiO₂/PLA nanocomposites exhibit remarkable bacteriostasic activity. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Application of poly (amide-<Emphasis Type="Italic">b</Emphasis>-ethylene oxide)/zeolitic imidazolate framework nanocomposite membrane in gas separation

Mixed matrix membranes (MMMs) are gaining increasing interest in academic and industrial research due to their combined, desirable properties of both polymers and organic/inorganic filler as important materials. In this work, synthesized zeolitic imidazolate framework (ZIF-8) suspension (10–50 wt%) was directly incorporated into a [poly (amide-b-ethylene oxide) Pebax^® 1657] matrix in order to improve the gas separation performance of the membrane. Dynamic light scattering (DLS) analysis showed an average diameter of 77.4 nm for the prepared nanoparticles. The transparent membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffractometry (XRD). These indicated excellent dispersion of nanoparticles, which was achieved by ultrasonication before casting the solution. Incorporation of ZIF-8 as filler in the polymer matrix led to improved thermal and mechanical stability of the membranes. This was confirmed by TGA and tensile analyses, indicating good contacts provided at the polymer/filler interfaces. The effect of ZIF-8 loading (up to 50 wt%) on membrane performance was investigated and it showed an optimum loading of 30 %. Single gas (CO₂, N₂ and CH₄) permeation tests revealed rapid, enhanced permeability of the nanocomposite membranes without significant changes in selectivity (compared to those of the pristine polymeric membrane). The permeability increases for CO₂, CH₄ and N₂ in the optimum Pebax^® 1657/ZIF-8 (30 wt%) membrane were found in the stated order as 111, 88 and 99 %. The study revealed that Pebax^® 1657/ZIF-8 membranes displayed better gas permeation properties compared to those of Pebax^® 1657.     

Hollow polyaniline/Fe3O4 microsphere composites: Preparation,characterization, and applications in microwave absorption

Hollow polyaniline/Fe₃O₄ microsphere composites with electromagnetic properties were successfully prepared by decorating the surface of hollow polyaniline/sulfonated polystyrene microspheres with various amounts of Fe₃O₄ magnetic nanoparticles using sulfonated polystyrene (SPS) as hard templates and then removing the templates with tetrahydrofuran (THF). The synthesized hollow microsphere composites were characterized by FT-IR, UV/Vis spectrophotometry, SEM, XRD, elemental analysis, TGA, and measurement of their magnetic parameters. Experimental results indicated that the microspheres were well-defined in size (1.50–1.80 μm) and shape, and that they were superparamagnetic with maximum saturation magnetization values of 3.88 emu/g with a 12.37 wt% content of Fe₃O₄ magnetic nanoparticles. Measurements of the electromagnetic parameters of the samples showed that the maximum bandwidth was 8.0 GHz over ?10 dB of reflection loss in the 2–18 GHz range when the Fe₃O₄ content in the hollow polyaniline/Fe₃O₄ microsphere composites was 7.33 wt%.     

Fabrication of polymethyl methacrylate/polysulfone/nanoceramic composites for orthopedic applications

We report the fabrication of polymethyl methacrylate/polysulfone/nanohydroxyapatite (PMMA/PSu/nHA) and PMMA/PSu/nanotitania (PMMA/PSu/nTiO₂) composites using N′N′‐methylene‐bis‐acrylamide (MBA) to crosslink PMMA and act as a blending agent. The composite was made porous by incorporating polyethylene glycol as the pore‐forming agent. The blend between PMMA and PSu was confirmed using Fourier transform infrared spectroscopy and thermogravimetric analysis (TGA). The surface morphology of the composites analyzed using scanning electronic microscopy (SEM) revealed the porous structure and the wide distribution of the fillers that were found to aggregate at higher concentrations. The maximum tensile strength observed for composites was with 5% nHA (23 MPa) and 7.5% TiO₂ (30 MPa). The TGA of the composites showed better thermal stability with increase in the filler concentrations. The X‐ray diffraction analysis showed that appearance of new peaks in the blend polymers indicating a strong interaction between PMMA and PSu. The surface of the composites was coated with amoxicillin and its efficiency was examined by the Zone of Inhibition test using Streptococcus mutans. The bioactivity of the composites was evaluated by immersing them in simulated body fluid and examining their surface for the formation of calcium‐phosphate layer using SEM and EDAX. Bioactivity was found to increase with increase in filler content. The in vitro biocompatibility of the composites, evaluated using monkey kidney epithelial cells by MTT assay showed that the composites containing nHA showed better cell viability than the composites with nTiO₂. The study showed that the composites with nTiO₂ exhibited better strength when compared with nHA composites while the later exhibited better biocompatibility. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Structural investigations on P2O5-CaO-Na2O-K2O: SrO bioactive glass ceramics

In the present work, glasses of a particular composition (60-x) P₂O₅-20CaO-17Na₂O-3K₂O: xSrO (0.5≤x≤1.5) mol% were synthesized using conventional melt quenching technique. Further, samples were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Differential Thermal Analyses (DTA) techniques and Fourier Transform Infrared (FT-IR) spectra. In vitro bioactivity was evaluated by soaking glass ceramic powders in SBF solution for 7 and 15 days. XRD patterns of glass ceramics have clearly confirmed the formation of various crystalline phases K₂Sr(PO₃)₄, α-Ca₂P₂O₇, Ca₂Sr(PO₄)₂, Ca₅(PO₄)₃(OH) and Ca₃(PO₄)₂. Random spreading of uneven sized micro crystals with distinct boundaries in the glass matrix have been observed from SEM pictures. DTA scans revealed an increase in the content of SrO with heating rate causes the glass transition (T_g) and crystallization temperatures (T_c) towards lower side, that confirms the decrease in rigidity of glass network. FT-IR spectra showed that there is an increase in the degree of structural disorder and the formation of a crystalline hydroxyapatite layer with soaking time. From the analyses of all the above results, it can be concluded that the sample doped with 1.5 mol% of strontium is found to exhibit high bioactivity.     

Nanocomposite hybrid membranes containing polyvinyl alcohol or poly(tetramethylene oxide) for fuel cell applications

New hybrid membranes containing polyvinyl alcohol (PVA) and poly(tetramethylene oxide) (PTMO) with heteropolyacid (HPA) as a hydrophilic inorganic modifier in an organic/inorganic matrix were developed for low-temperature proton exchange membrane fuel cells (PEMFCs). A maximum conductivity of 4.8 × 10⁻³ S cm⁻¹ was obtained at 80 °C and 75% RH for PVA/PWA/PTMO/H₃PO₄ (10/15/70/5 wt%), whereas the PVA/SiWA/MPTS/H₃PO₄ (50/10/10/30 wt%) membrane demonstrated a maximum conductivity of 8.5 × 10⁻³ S cm⁻¹ under identical conditions. These hybrid composite membranes were subsequently tested in a fuel cell. A maximum current density of 240 mA cm⁻² was produced at 70 °C for the PVA/PWA/PTMO/H₃PO₄ membrane, and the corresponding value for the PVA/SiWA/MPTS/H₃PO₄ membrane under identical conditions was 230 mA cm⁻². The small deviations in cell performance can be explained in terms of the variations in thickness of the membranes as well as differences in their conductivities. The fuel cell performances of these membranes decreased drastically when the temperature was increased to 100 °C.     

Preparation and properties of TiO2‐filled poly(acrylonitrile‐butadiene‐styrene)/epoxy hybrid composites

Poly (acrylonitrile‐butadiene‐styrene) (ABS) was used to modify diglycidyl ether of bisphenol‐A type of epoxy resin, and the modified epoxy resin was used as the matrix for making TiO₂ reinforced nanocomposites and were cured with diaminodiphenyl sulfone for superior mechanical and thermal properties. The hybrid nanocomposites were characterized by using thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), universal testing machine (UTM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The bulk morphology was carefully analyzed by SEM and TEM and was supported by other techniques. DMA studies revealed that the DDS‐cured epoxy/ABS/TiO₂ hybrid composites systems have two T_gs corresponding to epoxy and ABS rich phases and have better load bearing capacity with the addition of TiO₂ particles. The addition of TiO₂ induces a significant increase in tensile properties, impact strength, and fracture toughness with respect to neat blend matrix. Tensile toughness reveals a twofold increase with the addition of 0.7 wt % TiO₂ filler in the blend matrix with respect to neat blend. SEM micrographs of fractured surfaces establish a synergetic effect of both ABS and TiO₂ components in the epoxy matrix. The phenomenon such us cavitation, crack path deflection, crack pinning, ductile tearing of the thermoplastic, and local plastic deformation of the matrix with some minor agglomerates of TiO₂ are observed. However, between these agglomerates, the particles are separated well and are distributed homogeneously within the polymer matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Microstructure and mechanical properties of (Zr,Ti)B2–SiC composites obtained by pressureless sintering of ZrB2–SiC–TiO2 powder mixtures

Multiphase ceramics have been highlighted due to the combination of different properties. This work proposes to obtain the multiphase composite of (Zr,Ti)B₂–SiC based on the mixture of ZrB₂, SiC, and TiO₂ sintered without pressure. The effect of TiO₂ addition on solid solution formation with ZrB₂, densification, microstructure, and mechanical properties was investigated. For this, 2.0 wt% TiO₂ was added to ZrB₂–SiC composites with 10–30 vol% SiC and processed by reactive pressureless sintering at 2050 °C with a 2 h holding time. Sinterability, crystalline phases, microstructure, Vickers hardness, and indentation fracture toughness of these composites were analyzed and compared to the non-doped ZrB₂–SiC samples. The XRD analysis and EDS elemental map images indicated the incorporation of Ti atoms into the ZrB₂ crystalline structure with solid solution generation of (Zr,Ti)B₂. The addition of TiO₂ resulted in matrix grain size refinement and a predominant intergranular fracture mode. The relative densities were not significantly modified with the TiO₂ addition, though a higher weight loss was detected after the sample sintering process. The composites doped with TiO₂ showed an increase in fracture toughness but exhibited a slightly lower Vickers hardness compared to composites without TiO₂ addition.     

Enhanced CO2 selectivity of polyimide membranes through dispersion of polyethyleneimine decorated UiO-66 particles

Branched polyethyleneimine (PEI) functionalized UiO-66 were synthesized and used as fillers to fabricated mixed-matrix membranes (MMMs) for CO₂/CH₄ separation. The purpose of introducing amino-functional groups in the filler is to improve the interfacial compatibility of the filler with the polymer through the formation of hydrogen bonds with the carbonyl group of 6FDA-ODA. Additionally, the amino group can facilitate CO₂ transport through a reversible reaction, enhancing the CO₂/CH₄ separation properties of MMM. The chemical structure and morphology of fillers and membranes were characterized by employing X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), thermogravimetric (TGA), Derivative thermogravimetry (DTG) and scanning electron microscope (SEM). Furthermore, the effects of filler loading and feed pressure on CO₂ permeability and CO₂/CH₄ selectivity have been investigated. MMMs present higher gas separation performance than pure 6FDA-ODA due to the presence of amino groups and the improvement of interface morphology. In particular, the MMM with 15 wt% loading of UiO-66-PEI shows optimum CO₂ permeability of 28.23 Barrer and CO₂/CH₄ selectivity of 56.49. Therefore, post-synthetic modification of UiO-66 particle with PEI is a promising alternative to improved membrane performance.     

Preparation and characterization of wollastonite/titanium oxide nanofiber bioceramic composite as a future implant material

In this study, novel composites consisting of electrospun titanium dioxide (TiO₂) nanofibers incorporated into high-purity wollastonite glass ceramics were prepared as materials for use in hard tissue engineering applications. These materials were characterized and investigated by means of physical, mechanical and in vitro studies. The proposed composite showed greater densification and better mechanical characteristics compared to pure wollastonite. The influence of densification temperature and TiO₂ content was investigated. Typically, TiO₂/wollastonite composites having 0, 10, 20 and 30 wt% metal oxide nanofibers were sintered at 900, 1100 and 1250 °C. The results indicated that increasing TiO₂ nanofibers content leads to increase the bulk density, compressive strength and microhardness with negligible, high and moderate influence for the densification temperature, respectively. While porosity and water adsorption capacity decreased with increasing the metal oxide nanofibers with a considerable impact for the sintering temperature in both properties. Moreover, bone-like apatite formed on the surface of wollastonite and wollastonite/TiO₂ nanofibers soaked in simulated body fluid (SBF). All these results show that the inclusion of TiO₂ nanofibers improved the characteristics of wollastonite while preserving its in vitro bioactivity; hence, the proposed composite may be used as a bone substitute in high load bearing sites.     

Effect of Sizes of Nano Ca3(PO4)2 on Mechanical and Thermal Properties of Polyurethane Foam Composites

Particular sizes of nano inorganic filler, Ca₃(PO₄)₂ were prepared by following the matrix mediated growth technique. Composite foams were prepared on addition of different concentration (0.5–2.5 wt.%) of nano size filler in a single–phase polyurethane matrix. The differential Scanning Calorimetry (DSC) for composite as well as pure polyurethane was done to ascertain the degree of interaction of filler with the structure of the matrix as active sites. The degree of cell formation increases on increase in amount of reduced size nano filler in the composites where as decrease in case of larger size filler in composites. The increment in specific gravity from 0.17–0.25 for reduced nano size filler and 0.17–0.18 in case of larger size filler makes a strong support for the increment of cell numbers. The significant enhancement 250% in compressive strength, and the reduction of cell sizes shown in optical photographs satisfies the reasons of increment in heat of fusion (ΔH) in DSC. The decrement in (ΔH) cal/g in case of larger size filler for curing shows the conduction of heat is more due formation of cells less in numbers results in reduction of rate of heating more. Thermal gravimetric analysis (TGA) was done to know the degradation behavior. The TGA results, shows increment in onset temperature and mid temperature of the first step degradation in case of larger size nano filler. Decrement of flammability from 0.47–13.14 sec/mm for reduced nano size filler and 0.47–8.23 sec/mm in case of larger size filler, show that the incorporation of nano particles not only improves the mechanical properties but also retards the flammability.     

The Effects of Filler Content and Size on the Properties of PTFE/SiO2 Composites

A study on PTFE reinforced with SiO₂ was described. It included the manufacturing process of SiO₂-reinforced PTFE and the effects of the SiO₂ content and size on the properties of the composite material, such as thermal, dielectric, tensile strength and morphology, etc. PTFE/SiO₂ composites loaded with two sizes (5 μm or 25 μm SiO₂) of filler contents varied from 0–60 wt% were mixed by a high-speed dispersion mixer and made via a two-roll milling machine. Our results showed that the composite filled with 25 μm SiO₂ at 60 wt% filler content had the highest modulus, lowest CTE _z and acceptable dielectric properties. Composites with different sizes of filler showed a similar trend of decreasing tensile strength and coefficient of thermal expansion (CTE _z ), and increasing tensile modulus, water absorption and dielectric properties as the filler content increased. Furthermore, the composites filled with small-size filler showed higher water absorption and dielectric loss properties due to the presence of higher SiO₂ surface area. Poor adhesion between filler and matrix is a primary cause of low tensile properties and lack of increase in thermal stability. Such phenomenon was also confirmed by fracture surface analysis of scanning electron microscope (SEM). Experimental data were compared with theoretical models from the literatures, which are used to predict the properties of two component mixtures. The results revealed that experimental values of dielectric constant and CTE _z agreed with the theoretical calculated values. It was also found that the modified Nicolais-Narkis equation provided a good estimation for the tensile strength of composite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Simultaneous enhancement of mechanical and microwave absorption properties with a novel in-situ synthesis α-Al2O3 fillers for SiCf/SiC composites

The Al and H₃BO₃ mixed powder was introduced into the PCS/Xylene precursor solution as in-situ synthesis α-Al₂O₃ filler by precursor infiltration and pyrolysis (PIP) method. The in-situ synthesis filler can effectively decrease the open porosity of SiC_f/SiC composites and give rise to multiple scattering of microwave and dipolar polarization. Therefore, the mechanical and microwave absorption properties of SiC_f/SiC composites can be simultaneously enhanced. The effects of in-situ synthesis filler on the morphologies, flexure strength and reflection loss values of SiC_f/SiC composites were investigated. With 2 wt% in-situ synthesis filler, the flexure strength of SiC_f/SiC composite was 305 MPa and the maximum reflection loss (RL_m) can reach ? 54.68 dB with the effective absorption band (EAB) of 3.51 GHz in the X band. With 5 wt% in-situ synthesis filler, the flexure strength of SiC_f/SiC composite was 207 MPa and the RL_m was ? 30.91 dB. Due to the inefficient infiltration process, the RL_m of SiC_f/SiC composites with 10 wt% in-situ synthesis filler was only ? 27.36 dB. Nevertheless, the flexure strength of that composite was 259 MPa, owing to the dense matrix. Additionally, the flexure strength of SiC_f/SiC composite without filler was 148 MPa and the RL_m was ? 26.40 dB.     

Dynamic mechanical, thermal, and morphological study of ABS/textile fiber composites

In this work, acrylonitrile–butadiene–styrene ABS terpolymer was mixed with acrylic fiber, cotton fiber, and waste textile fiber (WTF) (50/50 wt% cotton/acrylic fiber) with 10 and 30 wt% of fiber content in a batch mixer. The composites with 30 wt% of acrylic fiber showed the highest stabilized torque, while the compositions with 30 wt% of cotton were situated at the lowest values in torque rheometry. The fiber addition up to 30 wt% did not have effect on the degradation behavior of ABS matrix. The composites with 30% textile fiber showed a higher degradation step, which is related to fiber degradation. The fiber content resulted in a considerable increase in stiffness at all temperatures as can be observed on the dynamic mechanical thermal properties (DMTA). The reinforcing effect was higher in the region above the glass transition temperature, T _g, of the matrix, this is primarily due to the larger difference in mechanical properties between the filler and the matrix as it goes from the glassy to the rubbery state.