Aluminum oxide particles/silicon carbide whiskers’ synergistic effect on thermal conductivity of high-density polyethylene composites

Aluminum oxide (Al₂O₃) particles and silicon carbide (SiC) whiskers improved the thermal conductivity of high-density polyethylene (HDPE). To improve the dispersion of inorganic fillers in the matrix, 5 wt% of maleic anhydride-modified polyethylene was added into HDPE as a compatibilizer, and the hybrid matrix was denoted as mHDPE. The thermal conductivity, heat resistance, and tensile properties of resulting HDPE composites were characterized. The results showed that the thermal conductivity reached its maximum value of 0.8876 W/(m K) at 1/4 weight ratio of Al₂O₃/SiC, which was 110.3, 54.8, and 8.8% higher than that of pure HDPE, mHDPE/Al₂O₃, and mHDPE/SiC composites, in the order given, indicating that hybrid fillers have synergistic effect on the thermal conductivity of HDPE composites. Moreover, they also have a synergistic effect on the heat resistance and Young’s modulus. As the SiC content increases, the heat resistance of the composites increases at first and then falls, and the maximum VST is reached at an Al₂O₃/SiC weight ratio of 3/2, which is 5.4 °C higher than that of HDPE. The maximum Young’s modulus of the composites (1160 MPa) is obtained at an Al₂O₃/SiC weight ratio of 1/4, and the yield strength increases gradually as the SiC whiskers’ content increases.     

Synthesis and characterization of soybean‐oil‐based polyurethane composites containing industrial and agricultural residual wastes as fillers

Thermosetting composites were prepared from soybean‐oil‐based polyols (hydroxyl number = 190 mg of KOH/g, [OH]/[NCO] for 2,4‐toluene diisocyanate = 0.9) and fillers (10 wt %) from industrial and agricultural residual wastes. Different types of inexpensive residual wastes were used: black rice husk ash, coconut husk ash, calcined retorted oil shale, and retorted oil shale. The fillers were characterized by thermogravimetric analysis and measurements of particle size distribution, specific surface area, and pore size distribution. The fillers were microporous materials with different chemical compositions, with average particle diameters varying from 5.6 to 76.6 μm, specific surface areas varying between 6 and 165 m²/g, and thermal stability at the polyurethane cure temperature (65°C). All composites were characterized by dynamic mechanical analysis, flexural tests, Shore A hardness tests, thermogravimetric analysis, and scanning electron microscopy analysis. Coconut husk ash, rice husk ash, and retorted oil shale presented better mechanical properties; nevertheless, coconut husk ash and rice husk ash had higher particle sizes, which caused bad dispersion of the filler in the matrix and resulted in nonhomogeneous composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Studies on γ‐Fe2O3–high‐density polyethylene composites and their additives

γ‐Fe₂O₃–high‐density polyethylene (HDPE) composite films are prepared by a gel‐casting technique. To understand the effect of additives, rice husk ash and thiourea are made to disperse in the HDPE matrix to obtain the composite films with additives. The as‐prepared γ‐Fe₂O₃–HDPE composite films with their additives are subjected to characterization and study through X‐ray diffraction, thermal, scanning electron microscopy, and dielectric measurements. The results are qualitatively treated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1527–1533, 2004     

Static and Dynamic Mechanical Properties of Poly (vinyl chloride) and Waste Rice Husk Ash Composites Compatibilized with <Emphasis Type="Italic">γ</Emphasis>-aminopropyltrimethoxysilane

In this paper, γ-aminopropyltrimethoxysilane treated poly(vinyl chloride) (PVC)/rice husk ash (RHA) composites were successfully prepared by a reactive extrusion process. Experimental results revealed that both the tensile modulus and tensile strength increased at all silane coupling agent concentrations. The composites with 1 wt% silane exhibited the highest impact strength with 44 % increment. For the untreated composites, poor interfacial adhesion between PVC and RHA was clearly observed. Below the glass transition temperature (T_g), the silane induced higher storage modulus (E ^′) but it seemed to be independent of E^′ above T_g. Total water absorption at 90 days reduced by 38 % when the silane was added at 1 wt%, which confirmed that some voids were eliminated.     

Effect of nanoclay on positive temperature coefficient to resistivity characteristics of high density polyethylene/silver‐coated glass bead composites

Positive temperature coefficient to resistivity characteristics of high density polyethylene (HDPE)/silver (Ag)‐coated glass bead (45 wt%) composites, without and with nanoclay, has been investigated with reference to HDPE/carbon black (CB) (10 wt%) composites. Plot of resistivity versus temperature of HDPE/CB (10 wt%) composites showed a sudden rise in resistivity (PTC trip) at ≈128°C, close to the melting temperature (T_m) of HDPE. However, for HDPE/Ag coated glass bead (45 wt%) composites, the PTC trip temperature (≈88°C) appeared well below the T_m of HDPE. Addition of 1 phr clay in the composites resulted in an increase in PTC trip temperature of HDPE/Ag‐coated glass bead (45 wt%) composites, whereas no significant effect of clay on PTC trip temperature was evident in HDPE/CB/clay composites. We proposed that the PTC trip temperature in HDPE/Ag‐coated glass bead composites was governed by the difference in coefficient of thermal expansion of HDPE and Ag‐coated glass beads. The room temperature resistivity and PTC trip temperature of HDPE/Ag‐coated glass bead (45 wt%) composites were found to be very stable on thermal cycling. Dynamic mechanical analyzer results showed higher storage modulus of HDPE/Ag‐coated glass bead (45 wt%) composites compared with the HDPE/CB (10 wt%) composites. Thermal stability of HDPE/Ag‐coated glass bead (45 wt%) composites was also improved compared with that of HDPE/CB (10 wt%) composites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Study of the morphology and mechanical properties of polypropylene composites with silica or rice‐husk

The mechanical, morphological behavior and water absorption characteristics of polypropylene (PP) and silica, or PP and rice‐husk, composites have been studied. The silica used in this study as filler was a commercial type produced from soluble glass or rice husks. The compatibilizing effect of PP grafted with monomethyl itaconate (PP‐g‐MMI) and/or with vinyltriethoxysilane (PP‐g‐VTES) as polar monomers on the mechanical properties and water absorption was also investigated. In general, a high loading of the studied fillers in the polymer matrix increases the stiffness and the water absorption capacity. This effect is more noticeable in the tensile modulus of the PP/silica composite with PP‐g‐VTES as compatibilizer. However, the increase of the rice‐husk charge as a natural filler in the PP matrix decreases the stiffness, and in the presence of PP‐g‐MMI as compatibilizer in PP/rice‐husk, the tensile modulus and water absorption of the composite were improved. The better adhesion and phase continuity in the PP/silica and PP/rice‐husk composites with different compatibilizers was confirmed by the morphological study. Copyright © 2004 Society of Chemical Industry     

Injection‐molded high‐density polyethylene–hydroxyapatite–aluminum oxide hybrid composites for hard‐tissue replacement: Mechanical,biological, and protein adsorption behavior

In this article, we report the mechanical and biocompatibility properties of injection‐molded high‐density polyethylene (HDPE) composites reinforced with 40 wt % ceramic filler [hydroxyapatite (HA) and/or Al₂O₃] and 2 wt % titanate as a coupling agent. The mechanical property measurements revealed that a combination of a maximum tensile strength of 18.7 MPa and a maximum tensile modulus of about 855 MPa could be achieved with the injection‐molded HDPE–20 wt % HA–20 wt % Al₂O₃ composites. For the same composite composition, the maximum compression strength was determined to be 71.6 MPa and the compression modulus was about 660 MPa. The fractrography study revealed the uniform distribution of ceramic fillers in the semicrystalline HDPE matrix. The cytocompatibility study with osteoblast‐like SaOS2 cells confirmed extensive cell adhesion and proliferation on the injection‐molded HDPE–20 wt % HA–20 wt % Al₂O₃ composites. The cell viability analysis with the 3(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay revealed a statistically significant difference between the injection‐molded HDPE–20 wt % HA–20 wt % Al₂O₃ composites and sintered HA for various culture durations of upto 7 days. The difference in cytocompatibility properties among the biocomposites is explained in terms of the difference in the protein absorption behavior. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Interfacial strengthening of polypropylene composites via bimodal porosity in Rice husk ash: Comparison with calcium carbonate reinforcement

Polypropylene is used in the textile industry in the manufacturing of plastic yarns, tapes, etc., but its low tensile strength and Young's modulus limits its associated applications. Composites of polypropylene with reinforcement of CaCO₃ and rice husk ash were processed by compression molding. Bimodal porosity in rice husk ash particles has shown an improved interfacial anchoring effect via capillary effect resulting in enhanced mechanical properties, whereas such an effect is not observed with CaCO₃ reinforcement in polypropylene matrix. On reinforcement with 10 wt % of each of rice husk ash and CaCO₃, thermal decomposition temperature of polypropylene (333.3 °C) shifted to higher value of 415.9 °C and polypropylene Young's modulus (749.5 MPa) increased to 789.5 MPa (by 5.3%), but tensile strength decreased from 23.5 to 21.2 MPa (by 2.3 MPa only). The isolated contribution of CaCO₃ and rice husk ash has been delineated, and resulting interfacial strengths have been quantified using analytical models. Rice husk ash has shown a stronger interfacial anchoring and can effectively replace CaCO₃ as reinforcement for achieving improved mechanical and thermal properties of polypropylene composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46989.     

Dry Sliding Friction and Wear Behavior of AA7075-Si<Subscript>3</Subscript>N<Subscript>4</Subscript> Composite

The present investigation is aimed at identifying the influence of Si₃N₄ reinforcement on the mechanical and tribological behavior of AA7075-Si₃N₄ composite. Five different composites of AA7075 aluminum alloy reinforced by silicon nitride particles have been fabricated by the stir casting route. The percentage of silicon nitride was varied from 0-8 wt%. The cast composites were tested for hardness, density and compression strength. Unidirectional friction and wear testing was carried out for all compositions under five different loading conditions (10 N, 20 N, 30 N, 40 N and 50 N) at a constant sliding speed of 1 m/s. SEM and EDS analysis was also carried out for worn surface analysis and elemental analysis of the composites. The hardness and compression strength of the composites exhibited an increasing trend with an increase in wt% of reinforcement in the base alloy, showing 20% improvement in hardness and around 50% improvement in compression strength for 8 wt% Si₃N₄ addition. The addition of Si₃N₄ particles led to an improvement in the wear resistance by 37% at low loads (10 N) and 61% at higher loads (50 N). The COF for all varied compositions at low load (10 N) and high load (50 N) ranges from 0.10 to 0.20 and 0.25 to 0.30 respectively. Moreover, the COF is observed to increase until 4 wt% and beyond it decreases. Microscopic studies of worn surfaces revealed a dominance of delamination wear at lower concentrations (0 wt% and 2 wt%) and ploughing at higher concentrations (6 wt% and 8 wt%). The developed composites exhibited better mechanical and anti-wear properties and could serve as potential candidates in sliding applications such as bearings, brake drums, gears, sprockets and brake rotors.     

Processing–Nanostructure–Property Relationships of All‐Polyethylene Composites Reinforced by Flow‐Induced Oriented Crystallization of UHMWPE

All‐polyethylene composites exhibiting substantially improved toughness/stiffness balance are readily produced during conventional injection molding of high density polyethylene (HDPE) in the presence of bimodal polyethylene reactor blends (RB40) containing 40 wt% ultrahigh molar mass polyethylene (UHMWPE) dispersed in HDPE wax. Scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) analyses shows that flow‐induced crystallization affords extended‐chain UHMWPE nanofibers forming shish which nucleates HDPE crystallization producing shish‐kebab structures as reinforcing phases. This is unparalleled by melt compounding micron‐sized UHMWPE. Injection molding of HDPE with 30 wt% RB40 at 165 °C affords thermoplastic all‐PE composites (12 wt% UHMWPE), improved Young's modulus of 3400 MPa, tensile strength of 140 MPa, and impact resistance of 22.0 kJ/m². According to fracture surface analysis, the formation of skin‐intermediate‐core structures accounts for significantly improved impact resistance. At constant RB40 content both morphology and mechanical properties strongly depend upon processing temperature. Upon increasing processing temperature from 165 °C to 250 °C the average shish‐kebab diameter increases from the nanometer to micron range, paralleled by massive loss of self‐reinforcement above 200 °C. The absence of shish‐kebab structure at 250 °C is attributed to relaxation of polymer chains and stretch‐coil transition impairing shish formation.     

Synergistic effect of boron nitride and tetrapod‐shaped zinc oxide whisker hybrid fillers on filler networks in thermal conductive HDPE composites

In this paper, in order to investigate and predict the synergistic effect of the tetra‐needle‐shaped zinc oxide whisker (T‐ZnO) and boron nitride (BN) hybrid fillers in the thermal conductive high‐density polyethylene (HDPE) composites, the filler networks were studied through dynamic rheological measurement. Moreover, the crystallinity of the HDPE in the composites, and the thermal and electrical conductivity of the composites were also investigated. It was found that when the ratio of the BN and T‐ZnO in hybrid fillers was 20:10, the HDPE/hybrid fillers composite not only had the highest thermal conductivity but also can maintain the electrically insulating. Furthermore, the gel point of the HDPE/hybrid fillers composites was 11.2 wt%, and it was close to the 10 wt%. Therefore, the synergistic effect of the T‐ZnO and BN hybrid fillers in the HDPE/hybrid fillers composites can be successfully predicted through dynamic rheology date. Simultaneously, the Scanning electron microscope results showed that the T‐ZnO and BN particles can contact each other to form the thermal conductive paths so that the thermal conductivity of the HDPE can be enhanced through addition of the hybrid fillers. In addition, it was also found that the improved thermal conductivity of the HDPE/hybrid fillers composites was not because of a change in the crystallinity of the HDPE in the HDPE/hybrid fillers composites. POLYM. COMPOS., 38:1902–1909, 2017. © 2015 Society of Plastics Engineers     

Use of rice husk ash as filler in natural rubber vulcanizates: In comparison with other commercial fillers

Rice husk ash is mainly composed of silica and carbon black remaining from incomplete combustion. Both silica and carbon black have long been recognized as the main reinforcing fillers used in the rubber industry to enhance certain properties of rubber vulcanizates, such as modulus and tensile strength. In this study, two grades of rice husk ash (low‐ and high‐carbon contents) were used as filler in natural rubber. Comparison was made of the reinforcing effect between rice husk ashes and other commercial fillers such as talcum, china clay, calcium carbonate, silica, and carbon black. Fourier transform infrared spectroscopy (FTIR) analysis was employed to study the presence of functional groups on the ash surface. The effect of silane coupling agent, bis(3‐triethoxysilylpropyl)tetrasulfane (Si‐69), on the properties of ash‐filled vulcanizates was also investigated. It was found that both grades of rice husk ash provide inferior mechanical properties (tensile strength, modulus, hardness, abrasion resistance, and tear strength) in comparison with reinforcing fillers such as silica and carbon black. However, the mechanical properties of the vulcanizates filled with rice husk ash are comparable to those filled with inert fillers. The addition of silane‐coupling agent has little effect on the properties of the ash‐filled vulcanizates. This is simply due to the lack of silanol groups on the ash surface. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2485–2493, 2002     

Wear behavior of Al(OH)<Subscript>3</Subscript>-GF/epoxy composites in low velocity

Effects of fiber content, size, and weave form, and addition of particles on wear behaviors of epoxy composites are studied widely, while little investigation is paid on thermal effect in friction. In this study, effects of Al(OH)₃ powder on wear behavior of glass fiber reinforced epoxy composites are investigated. The experimental results show that within 6 wt%, the addition of Al(OH)₃ powder could decrease the friction surface temperature, friction coefficient, and wear mass loss of the composites. The decrease is attributed to the heat absorption when Al(OH)₃ powder decomposes. However, when the content of Al(OH)₃ powder increases to 9 wt%, the temperature, the friction coefficient, and the wear mass loss increase to nearly equal to those of pure epoxy resin-based composites. It is considered resulting from the decrease in mechanical property, which could lead to more serious fatigue wear. In a word, within a proper content, the addition of Al(OH)₃ powder in epoxy could increase the resistance to wear and friction.     

Sodium alginate/bismuth (III) oxide composites for γ-ray shielding applications

In the present work, we have explored the efficacy of bismuth (III) oxide (Bi₂O₃) loaded, calcium ion cross-linked solution cast sodium alginate composite films for radioprotective applications. Calcium ion cross-linking increased the water and chemical resistance, which further improved on introduction of Bi₂O₃ into the composites. The 40 wt% Bi₂O₃ loaded films showed good heat resistance with the peak degradation temperature reaching as high as 251°C. The Bi₂O₃ loaded composites showed enhanced tensile strength (TS) and Youngs modulus (YM). Compared to high-modulus polymers like epoxy, high-density polyethylene (HDPE) and poly (vinyl chloride) (PVC), these exhibit relatively greater extent of stretching before breaking. The γ-ray attenuation experiments showed that mass attenuation coefficients of the composites at various γ-ray energies increased with filler loading. These composites are effective in shielding γ-rays from radioactive sources like ¹³⁷Cs, ²²Na, ¹³³Ba, and ⁶⁰Co that are widely employed in several medical and industrial applications. The overall enhancement in thermal, mechanical, and radiation shielding characteristics of the composites may be attributed to the uniform distribution of the fillers in alginate matrix. These nontoxic sodium alginate/Bi₂O₃ composites can be used as soft and biodegradable radiation shields, which may be processed to wearable forms.     

Propylene-ethylene Copolymer Filled Nanocomposites: Influence of Zn-ion Coating upon Nano-SiO2 on Structural,Thermal, and Dynamic Mechanical Properties

Propylene-ethylene copolymer (EP) nanocomposites based on nano-SiO₂ with and without Zn-ion coating were developed by conventional melt blending technique in a sigma internal mixer. Two composites each with 2.5 wt% filler were developed. The first composite was made by melt blending EP with nano-SiO₂ in a co-rotating sigma internal mixer. The second one was obtained by melt blending the same EP, but with Zn-ion coated nano-SiO₂. In case of Zn-ion coated nano-SiO₂ filled EP, wide-angle X-ray diffraction study (WAXD) showed a decrease in interplanar distance and lamellar polymer crystal size when compared to nano-SiO₂ filled EP. Differential scanning calorimetric (DSC) results showed Zn-ion coated nano-SiO₂ acting more as an effective nucleating agent than that of the nano-SiO₂. Thermogravimetric analysis (TGA) results showed improved thermal stability for EP in the presence of both the nanofillers. However, the thermal stability of Zn-ion coated nano-SiO₂ filled EP is higher than that of the nano-SiO₂ filled EP. Scanning electron microscope (SEM) study reveals that the Zn-ion coated nano-SiO₂ homogeneously distributed in the matrix, whereas nano-SiO₂ forms chainlike aggregates in the matrix phase. Dynamic mechanical analysis (DMA) study indicates that both the fillers increase storage modulus, E′; this increment is more prominent in nano-SiO₂ filled EP due to the formation of chain-type aggregates of nano-SiO₂.     

Insights into the synergistic mechanism of reactive aliphatic soft chains and nano-silica on toughening epoxy resins with improved mechanical properties and low viscosity

Toughening epoxy resin (EP) without sacrificing strength, modulus, and processing performance is always a harsh task. Here, a series of epoxy systems containing soft butyl glycidyl ether (BGE) and rigid nano-silica (nano-SiO₂) were prepared. Micro-phase separation structures derived from the self-assembly effect of BGE can be observed in atomic force microscopy images by controlling the total amount of BGE and nano-SiO₂ at 2 wt% for the EP_C:Si-m:n (m + n = 4) systems. Due to the synergistic effect of self-assembly effect of BGE and the rigid effect of well dispersed nano-SiO₂, EP_C:Si-2:2 system exhibited improvement of tensile strength of 59.3% (92.63 MPa), tensile modulus of 24.8% (3.52 GPa), elongation at break of 78.6% (4.84%), and glass transition temperature of 2.4% (138.4°C) compared with Pure EP system. Besides, due to the low loading of nano-SiO₂ (≤2 wt%) and the dilution effect of BGE, the viscosity of all the toughening systems is lower than 600 mPa·s, which can provide this toughening system with superior processing performance for large production of composites by automotive manufacturing methods such as vacuum assistant resin infusion technology.     

Mechanical and electrical properties of polyamide‐6‐based nanocomposites reinforced by fulleroid fillers

The effect of the fulleroid fillers (fullerene C₆₀, mixture of C₆₀/C₇₀ and fulleroids soot) on mechanical, tribological, and electrical properties of the nanocomposites based on polyamide‐6 (PA6) was investigated. The nanocomposites were prepared by in situ polymerization. Both the tensile modulus and tensile strength of polymer composites were improved up to 15% with loading of 0.001–0.1 wt% of fulleroids materials. For nanocomposites with fulleroid fillers, the friction coefficients were practically two times as lower that of neat PA6. Electrical volume resistivity of composites decreases at loading of fulleroid fillers. The minimal electrical volume resistance was about 10⁷ Ω cm at 0.1 wt% loading of fullerene soot. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Viscoelastic,thermal, and morphological analysis of HDPE/EVA/CaCO<Subscript>3</Subscript> ternary blends

High density polyethylene (HDPE), calcium carbonate (CaCO₃), and ethylene vinyl acetate (EVA) ternary reinforced blends were prepared by melt blend technique using a twin screw extruder. The thermal properties of these prepared ternary blends were investigated by differential scanning calorimetry. The effect of EVA loading on the melting temperature (T _m) and the crystallization temperature (T _C) was evaluated. It was found that the expected heterogeneous nucleating effect of CaCO₃ was hindered due to the presence of EVA. The melt viscosities of the ternary reinforced blends were affected by the % loading of CaCO₃, EVA, and vinyl acetate content. Viscoelastic analysis showed that there is a reduction of the storage modulus (G′) with increasing of EVA loading as compared to neat HDPE resin or to HDPE/CACO₃ blends only. The morphology of the composites was characterized by scanning electron microscopy (SEM). The dispersion and interfacial interaction between CaCO₃ with EVA and HDPE matrix were also investigated by SEM. We observed two main types of phase structures; encapsulation of the CaCO₃ by EVA and separate dispersion of the phases. Other properties of ternary HDPE/CaCO₃/EVA reinforced blends were investigated as well using thermal, rheological, and viscoelastic techniques.     

Rice‐husk‐ash‐filled natural rubber. II. Partial replacement of commercial fillers and the effect on the vulcanization process

In a previous investigation, we observed that in the presence of a conventional vulcanization system, the addition of white rice husk ash (WRHA) to natural rubber (NR) compounds increased the rate of crosslinking and lowered the apparent activation energy (E_a) of the vulcanization reaction more strongly than the other fillers used. In this work, commercial fillers, such as precipitated silica (Zeosil‐175) and carbon black (N762), were partially replaced by black rice husk ash and WRHA. Cure studies were carried out on a TI‐100 curometer at 150, 160, 170, and 180°C, and the overall rates and the E_a's for the vulcanization process were calculated for each compound, with the assumption that vulcanization followed first‐order kinetics. Again, WRHA showed some catalytic effect on the NR vulcanization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1405–1413, 2003     

Processing and properties of MWNT/HDPE composites

Multi-walled carbon nanotube (MWNT) composites were fabricated using the screw extrusion and injection technique. The polymer-wrapped MWNTs were dispersed in fumed silicon dioxide with the help of ultrasonic stirring, and then further dispersed in a high density polyethylene (HDPE) matrix by a twin-screw extruder. It was found that there was a critical MWNT concentration around 1.0 wt% where a fine network of MWNT/SiO₂ was formed. This gives the MWNT/HDPE composites much improved mechanical properties. From the mechanical property, it was found that the surface treatment of MWNT/SiO₂ had a large effect on the performance of the composites. Thermogravimetric analysis (TGA) measurement showed that MWNT could stabilize HDPE when its weight content was greater than 2.0 wt%, whereas silicon dioxide accelerated thermo-oxidation of the composites.