Melt compounded polylactic acid-hexagonal boron nitride-aluminum oxide hybrid composites for electronic applications: impact of hybrid fillers on thermophysical,dielectric, optical,and hardness properties

ABSTRACT

The dielectric, thermophysical, optical, and hardness of pure polylactic acid (PLA) and hBN micropowder and Al₂O₃ nanopowder (1% to 30%) reinforced PLA hybrid composites were investigated. Hybrid composites exhibit improved thermal conductivity (k – 0.54 W/mK), permittivity (?? – 4.6720 @ 1 MHz to 1 GHz) with very low loss tangent (tan δ < 0.02). High absorption in UV region was observed for all hybrid composites. Overall, the prepared hybrid composites can be used as a bio-based dielectric substrates, enclosures, thermal interface material for low temperature applications and UV-absorbable coating materials for fabric, packaging, and storage applications.     

Enhancement of electrical and thermal conductivities of a polysiloxane/metal complex with metal oxides

Block copolymer‐type polysiloxane was synthesized to investigate the influence of metal oxide addition on the dispersity of metal particles in a polysiloxane/metal composite. The metal oxide was introduced in a newly synthesized polysiloxane to improve the electrical and thermal conductivities of the polysiloxane/metal composite. The composite containing the metal oxide showed better dispersion than the composite without the metal oxide. The electrical conductivity displayed a typical percolation threshold behavior. The composite containing the metal oxide showed a slightly lower critical concentration (φ_c) than the composite without. The thermal conductivity of the composite increased considerably with the concentration of the filler. Thermal conductivity was used to calculate thermal interconnectivity, and the composite containing metal oxide showed an enhanced thermal interconnectivity. POLYM. COMPOS., 31:1669–1677, 2010. © 2010 Society of Plastics Engineers.     

Fabrication of insulated metal substrates with organic ceramic composite films for high thermal conductivity

Insulated metal substrates (IMSs) were fabricated and characterized using an organic ceramic composite as a coating mixture. Organic‐inorganic sol solutions were prepared by a sol‐gel process using TEOS (tetraethylorthosilicate), MTMS (methyltrimethoxysilane) and PhTMS (phenyltrimethoxysilane). Ceramic fillers were composed of aluminum oxide (1 and 4 µm) and silicon nitride. The optimal ratio of ceramic filler in the coating mixture was found to be 70 wt%. A thermal conductivity of 3.16 W/mK and a breakdown voltage of 4 kV with a leakage current of 0.17 mA/cm² were obtained for the 122 µm-thick film. A well-networked microstructure between the sol resin and filler in the organic ceramic composite films enhanced the properties of the IMS, such as thermal conductivity and electric insulation.     

Investigation of thermal behaviour and mechanical property of the functionalised graphene oxide/epoxy resin nanocomposites

ABSTRACT

Graphite oxide (GO) and functionalised graphite oxide (FGO) were successfully prepared with -NH₂-terminated GO in the paper, and their chemical structures were characterised with Fourier transform infrared (FTIR), Energy-Dispersive X-ray Spectroscopy (EDS), UV spectrum analysis and XRD, their microstructures were researched by a scanning electron microscope (SEM) and a transmission electron microscope (TEM), and their thermal properties were characterised by TG. The result showed the carbon residue of FGO was 82.1% and the residual char of GO was 48%, the composite materials were prepared with curing for epoxy resin. The thermal stability, mechanical properties, and morphology after impacting tests of composite materials were investigated using thermogravimetric analysis, tensile and charpy impact tests and SEM. The result showed when the 0.2% FGO was filled into the epoxy, the tensile strength was 55.4?MPa, the impact strength was 17.3?KJ/m², the flexural strength was 82?MPa, and the flexural modulus was 2760?MPa. The mechanical properties of composite materials were higher than those of pure epoxy and improved the strength and toughness of epoxy nanocomposites.     

Study on the properties of crosslinking of poly(ethylene oxide) and hydroxyapatite–poly(ethylene oxide) composite

This study covers the crosslinking of poly(ethylene oxide) (PEO) and its composite with calcium hydroxyapatite (HA), their mechanical and swelling properties, and morphology. Sheets of the composites of PEO (two different grades with M_v: 5 × 10⁶ and 2 × 10⁵) and HA and neat PEO were prepared by compression molding. The prepared composite and PEO (0.1‐mm‐thick) sheets were crosslinked with exposure of UV‐irradiation in the presence of a photoinitiator, acetophenone (AP). This simple method for crosslinking, induced by UV‐irradiation in the presence of AP, yielded PEO with gel content up to 90%. Gel content, equilibrium swelling ratio, and mechanical and morphological properties of the low molecular weight polyethylene oxide (LMPEO)–HA crosslinked and uncrosslinked composites were evaluated. Although the inclusion of HA into LMPEO inhibits the extent of crosslinking, the LMPEO–HA composite with 20% HA by weight shows the highest gel content, with appreciable equilibrium swelling and mechanical strength. The growth of HA in simulated body fluid solutions on fractured surfaces of LMPEO and also LMPEO–HA was found to be very favorable within short times. The dimensional stability of these samples was found to be satisfactory after swelling and deposition experiments. The good compatibility between the filler hydroxyapatite and poly(ethylene oxide) makes this composite a useful tissue‐adhesive material. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 488–496, 2003     

Barrier,rheological, and antimicrobial properties of sustainable nanocomposites based on gellan gum/polyacrylamide/zinc oxide

In this study, we used a solution casting method to prepare gellan gum (G)-based ternary nanocomposite films containing polyacrylamide (P) and zinc oxide (ZnO) nanoparticles. All composites were prepared using the chemical cross-linker N,N-methylenebisacrylamide. The nanocomposites were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction, and scanning electron microscopy. Attenuated total reflectance FTIR revealed strong hydrogen bonding interactions among gellan gum, polyacrylamide, and ZnO, which enhanced the physiochemical, thermal, and mechanical properties of the GPZnO nanocomposites. The addition of ZnO nanoparticles increased the glass transition temperature (T_g: 181.8–196.3°C), thermal stability (T_5%: 87.8–96.5°C), and char yield (23.9–29.1%) of the GP composite films, as well as their the tensile strength (from 33.5 to 43.8 MPa) and ultraviolet (UV) blocking properties (~99.2% protection against UVB [280–320 nm]). ZnO significantly influenced the rheological properties of the GP composite. The prepared GP and GPZnO nanocomposites exhibited shear thinning behavior and their viscosities decreased when there is an increase in shear rate. Storage and loss modulus increased with frequency with the addition of ZnO nanoparticles. The GPZnO films exhibited reduced hydrophilicity, moisture content, and water barrier properties compared with the GP film. The GPZnO nanocomposites exhibited effective antimicrobial activity against six different pathogens. The prepared GPZnO films could be useful in biodegradable packaging applications.     

Effect of different size complex fillers on thermal conductivity of PA6 thermal composites

ABSTRACT

Nylon 6 (PA6) thermal conductive composites were prepared by melt blending with different sizes of spherical Al₂O₃ and AlN and the filling amount was 60 wt%. This paper explored the effects of different particle sizes and filler kinds on the thermal conductivity and mechanical properties of the composites. The results showed that the composites filled with AlN and spherical Al₂O₃ had higher thermal conductivity than the composites filled with single filler under the same filling amount. When the mass ratio of 48 μm spherical Al₂O₃ and 14 μm AlN was 1:2, the thermal conductivity and thermal diffusivity was 2.44 W/(m·K) and 0.72 mm²/s, respectively. In addition,the tensile strength was 57.50 MPa and the impact strength was 6.13 KJ/m². By comparing actual thermal conductivity value with the theoretical value calculated by Agari model, we found that actual value of alumina filling was close to the theoretical value.     

Facile synthesis and thermal properties of waterglass-based silica xerogel nanocomposites containing reduced graphene oxide

In this study, new rGO-silica xerogel nanocomposites (SX-rGO) and its glass fiber reinforced composites (GFR-SX-rGO) were prepared, and its microstructure and thermal properties were evaluated. The raw material was a mixed dispersion prepared by adding 0.01–2.5?wt% of reduced graphene oxide (rGO) to waterglass (6% SiO₂). A hydrogel was prepared via sol-gel reaction of this raw material, which was then immersed in hydrochloric acid, hydrophobized in a siloxane/2-propanol reaction system, and then dried at ambient pressure to obtain a hydrophobic carbon-silica xerogel composite. The obtained samples were characterized by N₂ physisorption (at 77?K), solid ²⁹Si Magic angle spinning nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, differential scanning calorimetry, thermogravimetric analysis, hydrophobicity, and thermal conductivity. It was found that as the amount of rGO was increased, the specific surface area of the nanocomposite decreased by ~25% from 535 to 403?cm²/g, and the average pore size and pore volume were almost halved. The thermal decomposition temperature of the SX-rGO was increased markedly by the addition of rGO. Moreover, the GFR-SX-rGO-0.5 showed low density (0.208?g/cm³), high contact angle (146°) and low thermal conductivity (0.0199?W/mK).     

Effect of copper sulfate pentahydrate on the structure and properties of poly(vinyl alcohol)/graphene oxide composite films

Poly(vinyl alcohol) (PVA)/graphene oxide (GO)/copper sulfate pentahydrate (CuSO₄·5H₂O) composite films were prepared by the solution casting method, and the effect of CuSO₄·5H₂O on the structure and properties of the PVA/GO composites was investigated. Fourier transform infrared (FTIR) analysis proved the crosslinking interaction between CuSO₄·5H₂O and the ? OH group of PVA. The crystallinity of the composite films increased first and then decreased. For the composite films, the tensile strength, Young's modulus, and yield stress values improved with increasing CuSO₄·5H₂O, whereas the elongation at break decreased compared with that of the neat PVA/GO composite film. The thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) patterns of the PVA/GO/CuSO₄·5H₂O composite films showed that the thermal stability decreased; this was consistent with the TGA–FTIR analysis. A remarkable improvement in the oxygen‐barrier properties was achieved. The oxygen permeability coefficient was reduced by 60% compared to that of the neat PVA/GO composite film. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44135.     

Influence of alumina content and thermal treatment on the thermal conductivity of UPE/Al2O3 composite

Ultra high molecular weight polyethylene/alumina (UPE/Al₂O₃) microcomposites with high loading micro alumina (Al₂O₃, 20 to 100 phr) were prepared by casting method. The composites were thermal treated (cooled slowly) and then the thermal properties were studied at temperatures from 25 to 125°C. Thermogravimetric analysis (TGA) and scanning electron microscopic (SEM) proves the homodispersion of Al₂O₃ microparticles in UPE. TGA indicates that the temperature of 5% weight loss of UPE/Al₂O₃ (100 phr) composite is 467.0°C, 10.5°C higher than that of pure UPE. Differential scanning calorimetry (DSC) shows that the melting point and the real degree of crystal (X_rc) of treated UPE/Al₂O₃ composite (100 phr) are 141.4°C and 65.7%, respectively, all higher than that of untreated composite, which can be described by crystal bridge mechanism. The density of the composite is also be enhanced because of crystal volume shrinkage induced by thermal treatment. The thermal conductivity of the treated UPE/Al₂O₃ composite (100 phr) is 1.920 W (m K)^?1 at 25°C, 23.6% higher than that of the untreated composite. Crystal bridge thermal conduction mechanism is proposed. The thermal conductivity of UPE/Al₂O₃ composite has some dependency on the increasing Al₂O₃ content and also thermal treatment. These results can give some advice to design formulations for practical applications in pipe area and other wear area. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40528.     

Cationic UV curing behavior and thermal properties of oxetane‐modified polysiloxane prepared from tetraethyl orthosilicate

The oxetane‐modified polysiloxane (Oxe‐PSiO) was synthesized via the partial hydrolysis/condensation of tetraethyl orthosilicate (TEOS) and then transesterification reaction with 3‐ethyl‐3‐(hydroxymethyl)oxetane (EHO), and characterized by FT‐IR, ¹H NMR, ¹³C NMR, and ²⁹Si NMR spectroscopy. Using the water/TEOS molar ratios of 0.8–1.2, the number‐average molecular weights and polydispersity indices were obtained by GPC to range from 1.013 to 2.716 g mol^?1 and around 2.0, respectively. The viscosity of Oxe‐PSiO prepared from the water/TEOS molar ratio of 1.2 sharply increased to 177,545 cps from 438 cps of that from the molar ratio of 0.8. A series of cationic UV‐curable formulations were prepared by blending the Oxe‐PSiO synthesized with the water/TEOS molar ratio of 1.0 into an commercial oxetane‐based resin, 3,3′‐[oxydi(methylene)]bis(3‐ethyloxetane), in different weight ratios. The photopolymerization kinetics studied by photo‐DSC in the presence of triphenylsulphonium hexafluoroantimonate as a cationic photoinitiator showed that both the maximum photopolymerization rate and final oxetane conversion in the cured film decreased with increasing Oxe‐PSiO loading mainly due to the sharp increase in viscosity. The DMTA and DSC results both indicated the improvement in thermal stability, showing 12 and 13.4°C, respectively, higher T_g for the cured film with 50 wt % Oxe‐PSiO loading compared with the pure polymer. Moreover, the temperatures (T_10% and T_50%) at the weight loss of 10 and 50% and final char yields measured by TGA increased with increasing Oxe‐PSiO content. After adding 50 wt % Oxe‐PSiO, compared with the pure polymer the T_10% increased from 349 to 361°C, while the T_50% increased from 409 to 424°C, and with a char yield increase of 8.2% at 800°C. In addition, its greatly increased crosslinking density due to the formation of silica network resulted in the enhancement in pencil hardness from B of the pure polymer to 2H grade. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Morphological and thermal properties of photodegradable biocomposite films

Biocomposites containing ultraviolet (UV) radiation absorbing inorganic nanofillers are of great interest in food packaging applications. The biodegradable polylactide (PLA) composite films were prepared by solvent casting method by incorporating 1 wt % of titanium dioxide (TiO₂) and Ag‐TiO₂ (silver nanoparticles decorated TiO₂) nanoparticles to impart the photodegradable properties. The films were exposed to UV radiation for different time periods and morphology of the composite films before and after UV exposure were investigated. The results showed that homogenous filler distribution was achieved in the case of Ag‐TiO₂ nanoparticles. The thermal properties and thermomechanical stability of the composite film containing Ag‐TiO₂ nanoparticles were found to be much higher than those of neat PLA and PLA/TiO₂ composite films. The scanning electron microscopy and X‐ray diffraction studies revealed that the photodegradability of PLA matrix was significantly improved in the presence of Ag‐TiO₂ nanoparticles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Influence of MWCTs and nanometal oxide/MWCTs hybrids on the thermal conduction of their acrylic-based nanocomposites

In this study, acrylic-based nanocomposites containing different contents of multi-walled carbon nanotubes (MWCNTs) and metal oxide nanoparticles (i.e., TiO₂, CuO and Fe₂O₃) were fabricated by solvent mixing method. The thermal conductivity of these samples was evaluated. The results indicated that the thermal conductivity of all fabricated samples was significantly improved even at small loading of MWCNTs. It was found that the thermal conductivity was enhanced by increase in MWCNTs content up to 5 wt%. Similarly, the metal oxide nanoparticles caused up to 75 % increment in thermal conductivity at 1.5 wt% of their loading in acrylic film. Contrary to expectations, the thermal conductivity of acrylic film was more increased by nanometal oxides (i.e., TiO₂, CuO and Fe₂O₃) than MWCNTs. The effect of hybridizing of nanometal oxide particles (1.5 wt%) and MWCNTs (1.5 wt%) on thermal conduction was investigated as well. It was found that hybridizing improved thermal conductivities by about 85, 94 and 97 % for Fe₂O₃, TiO₂ and CuO, respectively. Finally, the effects of TiO₂ pigment and CaCO₃ extender on the thermal conductivity of acrylic polymer and nano-TiO₂ acrylic composites were studied. It was found that TiO₂ could increase considerably thermal conduction of its acrylic films and acrylic nanocomposites.     

Continuous aluminum oxide-mullite-hafnium oxide composite ceramic fibers with high strength and thermal stability by melt-spinning from polymer precursor

Continuous aluminum oxide-mullite-hafnium oxide (AMH) composite ceramic fibers were obtained by melt-spinning and calcination from polymer precursor that synthesized by hydrolysis of the aluminum isopropoxide, dimethoxydimethylsilane and hafnium alkoxide. Due to the fine diameter of 8–9 µm, small grain size of less than 50 nm and the composite crystal texture, the highest tensile strength of AMH ceramic fibers was 2.01 GPa. And the AMH ceramic fibers presented good thermal stability. The tensile strength retention was 75.48% and 71.49% after heat treatment at 1100 °C and 1200 °C for 0.5 h respectively, and was 61.57% after heat treatment at 1100 °C for 5 h. And the grain size of AMH ceramic fibers after heat treatment was much smaller than that of commercial alumina fibers even when the heat treatment temperature was elevated to 1500 °C, benefited by the grain size inhibition of monoclinic-HfO₂ (m-HfO₂) grains distributed on the boundary of alumina and mullite grains.     

Low thermal conductivity in porous SiC–SiO2–Al2O3–TiO2 ceramics induced by multiphase thermal resistance

The introduction of multiple heterogeneous interfaces in a ceramic is an efficient way to increase its thermal resistance. Novel porous SiC–SiO₂–Al₂O₃–TiO₂ (SSAT) ceramics were fabricated to achieve multiple heterogeneous interfaces by sintering equal volumes of SiC, SiO₂, Al₂O₃, and TiO₂ compacted powders with polysiloxane as a bonding phase and carbon as a template at 600 °C in air. The porosity could be controlled between 66% and 74% by adjusting the amounts of polysiloxane and the carbon template. The lowest thermal conductivity (0.059 W/(m·K) at 74% porosity) obtained in this study is an order of magnitude lower than those (0.2–1.3 W/(m·K)) of porous monolithic SiC, SiO₂, Al₂O₃, and TiO₂ ceramics at an equivalent porosity. The typical specific compressive strength value of the porous SSAT ceramics at 74% porosity was 3.2 MPa cm³/g.     

Optimisation and Evaluation of La0.6Sr0.4CoO3 – δ Cathode for Intermediate Temperature Solid Oxide Fuel Cells

In this work, La_0.6Sr_0.4CoO_{3 – δ}/Ce_{1 – x}Gd_xO_{2 – δ} (LSC/GDC) composite cathodes are investigated for SOFC application at intermediate temperatures, especially below 700 °C. The symmetrical cells are prepared by spraying LSC/GDC composite cathodes on a GDC tape, and the lowest polarisation resistance (R_p) of 0.11 Ω cm² at 700 °C is obtained for the cathode containing 30 wt.‐% GDC. For the application on YSZ electrolyte, symmetrical LSC cathodes are fabricated on a YSZ tape coated on a GDC interlayer. The impact of the sintering temperature on the microstructure and electrochemical properties is investigated. The optimum temperature is determined to be 950 °C; the corresponding R_p of 0.24 Ω cm² at 600 °C and 0.06 Ω cm² at 700 °C are achieved, respectively. An YSZ‐based anode‐supported solid oxide fuel cell is fabricated by employing LSC/GDC composite cathode sintered at 950 °C. The cell with an active electrode area of 4 × 4 cm² exhibits the maximum power density of 0.42 W cm^–2 at 650 °C and 0.54 W cm^–2 at 700 °C. More than 300 h operating at 650 °C is carried out for an estimate of performance and degradation of a single cell. Despite a decline at the beginning, the stable performance during the later term suggests a potential application.     

Swelling,thermal stability,antibacterial properties enhancement on composite hydrogel synthesized by chitosan-acrylic acid and ZnO nanowires

ABSTRACT

A series of antibacterial superabsorbents containing zinc oxide nanowires (ZnO NWs) based on chitosan (CS) and acrylic acid (AA) were prepared by one-step synthesis. Antibacterial influence of the content with ZnO NWs complex in superabsorbents on Escherichia coli and Staphylococcus aureus was studied, as well as water absorbency, swelling behavior, and thermal stability. Results showed that water absorbency for CS-co-AA composite hydrogel in water was 1000 g/g, because of the presence of ZnO NWs within CS-co-AA hydrogel facilitated the water absorbency ability. Furthermore, results also showed that the antibacterial effect of CS-co-AA composite hydrogels increased with an increase of ZnO NWs content.     

Investigation of debonding propagation in aluminum/composite joints under fatigue loading

In this paper, Fracture Mechanics is used to predict debonding propagation in adhesive joint between aluminum and composite plates. Three types of loadings (λ = 0, λ = 0.5, and λ = 1 when λ is the ratio of lateral to in-plane loading) and two types of glass–epoxy composite sequences: [0/90]_2s and [0/45/?45/90]_s are considered for the composite plate and their results are compared. It was seen that generally the cases with stacking sequence of [0/45/?45/90]_s have much shorter lives than cases with [0/90]_2s. It was also seen that in cases with λ = 0, the ends of the debonding front propagates forward more than its middle, while in cases with λ = 0.5 or λ = 1 it is vice versa. Moreover, regardless of value of λ, the difference between the debonding propagations of the ends and the middle of the debonding front is very close in cases λ = 0.5 and λ = 1. Another main conclusion was that the non-dimensionalized debonding front profile is almost independent of sequence type or the applied load value.     

High‐performance varistors prepared by hot‐dipping tin oxide thin films in Sb2O3 powder: Influence of temperature

A series of SnO_x–Sb₂O₃ thin film varistors were fabricated through hot‐dipping tin oxide films deposited by radio‐frequency magnetron sputtering in Sb₂O₃ powder at varied temperatures in air. With the increase in hot‐dipping temperature (HDT) from 200°C to 600°C, the nonlinear coefficient (α) of the samples increased first and then decreased, reaching the maximum at 500°C, which was mainly determined by the completeness of high‐resistant Sb₂O₃ layer at tin oxide grain boundary and the chemical composition of tin oxide films. Correspondingly, the leakage current (I_L) decreased first and increased later. The breakdown electric field (E_100 mA) decreased constantly with increasing HDT. The SnO_x–Sb₂O₃ film varistors prepared at 500°C exhibited the optimum nonlinear properties with the maximum α of 10.88, the minimum I_L of 36.3 mA/cm², and an E_100mA of 0.0188 V/nm. The obtained nanoscaled film varistors would be promising in electrical/electronic devices working in low voltage.     

Bond strengths of bulk-fill resin composite repairs: effect of different surface treatment protocols in vitro

To evaluate the effect of different surface treatment protocols on the microtensile bond strength (μTBS) of bulk-fill resin composite repairs. Thirty-five bulk-fill resin composite samples (Filtek Bulk Fill) were prepared (5 × 5 × 5 mm) and aged by thermocycling (X5000). Samples were randomly divided into five groups (n = 7): a control (no treatment) and four surface treatment groups (Single Bond Universal [SBU]; phosphoric acid (37%) + SBU; Er,Cr:YSGG laser + SBU; aluminum oxide sandblasting + SBU). Filtek Ultimate Universal composite was used as a repair material. After storage for 24 h in distilled water (37 °C), sticks were obtained and subjected to a μTBS test. The data (MPa) were analyzed by one-way ANOVA with a post hoc test (α = 0.05). Failure mode was evaluated using a light microscope (10×). There were significant differences between the groups (p < 0.05). The lowest bond strength values were obtained in the control group (p < 0.05). No significant difference was observed between Group II (universal adhesive) and Group III (acid etch + universal adhesive) (p > 0.05). The bond strength of Group II was significantly lower than that of the other surface treatment groups (p < 0.05). While Group III showed significantly lower values than those of the laser treatment group (Group IV), similar values were obtained with Al₂O₃ sandblasting group (Group V). The highest repair bond strength was obtained in Group IV (p < 0.05) which was not significantly different from the Al₂O₃ sandblasting group (p > 0.05). The predominant failure mode was adhesive. Treatment of aged bulk-fill resin composite surfaces with laser and Al₂O₃ sandblasting provided higher repair bond strength values.