SC–CO<Subscript>2</Subscript>-assisted rubber dispersion and dynamic vulcanization in blending of PP/EPDM thermoplastic olefin

Supercritical CO₂ (SC–CO₂), as a green medium, was induced in the traditional way of preparing polypropylene/ethylene–propylene–diene terpolymer (EPDM) thermoplastic olefin (TPO) by dynamic vulcanization using a twin-screw extruder. The morphology observation suggested that the SC–CO₂ not only promoted the rubber dispersion, but also facilitated the rubber dynamic vulcanization; therefore, the crosslinked EPDM particles were more densely distributed in the TPOs prepared with SC–CO₂, and existed as a stronger viscoelastic phase restricting the mobility of polymer chains, increasing the complex viscosity and storage modulus and promoting the mechanical properties.     

Aluminium foam–polymer composites: processing and characteristics

Dissemination of closed cell metal foam unique properties (low density, efficient energy absorption, high vibration/sound attenuation) in real life products has often been difficult to realise. With advanced pore morphology (APM) aluminium foam–polymer hybrids a new and simplified process route targeted at application in foam-filled structures (e.g. automotive A-pillar) has been introduced. APM foams are made from spherical, small volume foam elements joined to each other in a separate process step. Joining the aluminium foam elements by adhesive bonding delivers composite foam with approximately 80–95 wt.% aluminium foam and 5–20 wt.% adhesive (polymer). Setting up cellular structures from spherical foam elements allows for automatic part production, good pore morphology control and cost effective aluminium foam application. An automated production line is displayed and discussed. Mechanical properties of APM aluminium foam–polymer hybrids are similar to other closed cell aluminium foams. Integration of APM foams in profiles resulted in significantly improved properties as observed for conventional closed cell aluminium foam fillings. The unique properties of APM composite foams make them an attractive alternative as a cost effective and easily applicable material of construction with targeted uses such as energy absorbing reinforcement of composite structures.     

Solid emulsion gel as a novel construct for topical applications: synthesis, morphology and mechanical properties

A series of the solid emulsion gels with the oil volume fraction in the range of 0–50% were synthesized through a polycondensation reaction between activated p-nitrophenyl carbonate poly(ethylene glycol) and protein-stabilized oil-in-water emulsions. The resultant structures were investigated in terms of swelling behavior, composition, morphology, mechanical and skin hydration properties. Solid emulsions gels share the properties of both hydrogel and emulsion. Similar to the classical hydrogel, the SEG swells in water up to equilibrium swelling degree, which decreases as the oil volume fraction increases, and comprises immobilized drops of protein-stabilized oil. The impregnation of the oil phase is found to reduce tensile stiffness of the material, but improves material’s extensibility. The mechanical properties of the constructs (Young moduli in the range of 9–15 kPa and the elongation at break of 120–220%) are interpreted according to the “rule of elasticity mixture” that considers the elasticity of the composite material to be a sum of the contributions from individual components, i.e. hydrogel and dispersed oil drops. An idealized model that takes into account the history of the material preparation has been proposed to explain the improved extensibility of the constructs. The results of the mechanical tests, equilibrium swelling, and the skin hydration effect of the solid emulsion gels in vivo are discussed from the perspective of the biomedical applications of the solid emulsion gels, in particular, for the transdermal delivery of hydrophilic and lipophilic drugs.     

Influence of the mechanism and parameters of hardening of modified novolac phenol-formaldehyde resins on the physicomechanical properties of the composite

We study the influence of concentrations of the components of reactive compositions and the conditions of production and hardening of phenol-formaldehyde resins with the help of epoxy resins in the presence of polyvinylpyrrolidone on the physicomechanical, thermal, adhesion, insulation, and anticorrosion properties of the composites. The positive effect of modifications with polyvinylpyrrolidone and epoxy resin manifests itself within the following ranges of concentrations: 0.5–1 wt.% of polyvinylpyrrolidone and 25–30 wt.% of ED-20 in the presence of 1 wt.% of N, N-dimethylaniline. Thus, the adhesion strength of a glue based on the developed composition becomes four times higher and constitutes 5–6 MPa; the impact strength, static strength in bending, surface hardness, and the specific bulk electric resistance of the specimens hardened at 150–160°C for 25–30 min become 1.5–2.5 times higher and are equal to 5–6J/m², 15–17 MPa, 350–420 MPa, and (5.5–6.5)⋅10¹⁰ Ω⋅m, respectively. The behavior of these characteristics strongly depends on the conditions of hardening. We optimized the composition of modified phenol-formaldehyde resins, which made it possible to produce materials with predicted properties.     

Particle fracture in metal-matrix composite friction joints

The influence of welding parameters, reinforcing particle chemistry and shape, matrix condition and silver interlayers on particle fracture during similar and dissimilar friction welding of aluminium-based metal-matrix composite (MMC) base material was investigated. Two composite base materials were examined, one containing Al₂O₃ particles and the other containing 72 wt% Al₂O₃–7 wt % Fe₂O₃–17 wt % SiO₂–3 wt % TiO₂ particles. The different material combinations comprised MMC/MMC, MMC/alloy 6061, MMC/AISI 304 stainless steel and MMC/1020 mild steel joints. Particle fracture was confined to a narrow region immediately adjacent to the dissimilar joint interface. The calculated normal pressure for fracture of Al₂O₃ particles ranges from 0.56–17.58 MPa and is in agreement with an experimentally measured pressure of 1.06 MPa found during sliding wear testing of aluminium-based composite base material. Because the lowest normal pressure applied during friction joining was 30 MPa, particle fracture occurs very early in the joining operation (immediately following contact between the two substrates). The application of a silver interlayer during dissimilar MMC/AISI 304 stainless steel joining decreased the particle fracture tendency. It is suggested that the presence of a silver interlayer decreased the coefficient of friction and lowered the stresses applied at the contact region. The particle fracture tendency was markedly increased when the MMC material contained blocky alumina particles. However, there was negligible particle fracture when the MMC base material contained spherical 72 wt % Al₂O₃–7 wt % Fe₂O₃–17 wt % SiO₂–3 wt % TiO₂ particles. This revised version was published online in November 2006 with corrections to the Cover Date.     

Room-temperature indentation creep of lead-free Sn–Bi solder alloys

Creep behavior of the lead-free Sn–Bi alloys with bismuth contents in the range of 1–5 wt.% was studied by long time Vickers indentation testing at room temperature. The materials were examined in the homogenized cast and wrought conditions. The stress exponents, determined through different indentation methods, were in good agreement. The exponents of 13.4–15.3 and 9.2–10.0, found respectively for the cast and wrought conditions, are close to those determined by room-temperature conventional creep testing of the same material reported in the literature. Due to the solid solution hardening effects of Bi in Sn, creep rate decreased and creep resistance increased with increasing Bi content of the materials. Cast alloys, with a rather coarser grain structure and some Bi particles at the grain boundaries, showed typically higher resistance to indentation creep compared to the wrought materials. These two factors have apparently resulted in a less tendency of the material for grain boundary accommodated deformation, which is considered as a process to decrease the creep resistance of soft materials.     

Investigation on properties of Ga to Sn–9Zn lead-free solder

The influences of different Ga content on the properties of Sn–9Zn lead-free solder were investigated. The results indicate that Ga plays an important role not only in the structure and melting behavior, but also in the solderability and mechanical property. Sn–9Zn–0.5Ga shows finer and more uniform microstructure than Sn–9Zn. With the addition of low-melting-point Ga, TL (liquidus temperature) and TS (solidus temperature) of the alloys decreases with increasing of Ga content while △T (liquidus temperature minus solidus temperature) increases. Ga can improve the oxidation resistance and reduce the surface tension of solder, so the solderability of Sn–9Zn–xGa lead-free solder is significantly improved. When the content of Ga is 0.5 wt.%, the pull force of soldered joint is 16.1 N, enhanced by 11% compared to that of Sn–9Zn, and the fracture micrographs show that the joint failed in a ductile manner. The addition of 3 wt.%Ga resulted in a brittle failure. The introduction of 0.5 wt.% Ga into Sn–9Zn alloy improves creep resistance of the solder.     

Protective coating for magnesium alloy

A phosphate–permanganate conversion coating was applied as the pretreatment process for AZ91D magnesium alloy substrate. Zn–Ni alloys were electrodeposited onto the treated AZ91D magnesium alloy from sulfate bath. The morphology and phase composition of the coatings were determined with X-ray diffraction (XRD) and Scanning Electron Microscope (SEM). The results reveal that the conversion rate depends on pH of solution and treatment time. Salt spray and the electrochemical polarization testing were applied to evaluate the corrosion performance of phosphate–permanganate and Zn–Ni coated alloys. It was found that Ni content in deposit is a function of current density and bath composition. Zn–13 wt.% Ni coating provides very good corrosion protective function to inner AZ91D magnesium alloy. Phosphate–permanganate treatment enhances the corrosion resistance of Zn–Ni coatings.     

Electromagnetic interference shielding of carbon nanotube/ethylene vinyl acetate composites

Single-walled carbon nanotube (SWCNT) and ethylene vinyl acetate (EVA) composites were synthesized in an internal mixer by melt mixing. The electrical conductivity as well as electromagnetic interference (EMI) shielding effectiveness (SE) over the X-band (8–12 GHz) and microwave (200–2,000 MHz) frequency ranges of these composites were investigated. It was observed that the electrical conductivity of composites increases with increasing SWCNT loading. A percolation threshold of about 3.5 wt.% was obtained and the electrical conductivity of EVA was increased by ten orders of magnitude, from 10⁻¹⁴ to 10⁻⁴ Ω⁻¹ cm⁻¹. The effect of sample thickness on SE was investigated. The correlation between SE and conductivity of the composites is discussed. The experimental data showed that the SE of the composites containing higher carbon nanotube loadings (above 10 wt.%) could be used as an EMI shielding material and lower SWCNT loadings could be used for the dissipation of electrostatic charge.     

Rheology and microstructure of MDI–PEG reactive prepolymer-modified bitumen

This paper deals with the use of a new bitumen modifier, a reactive prepolymer, based on the reaction of 4,4^′-diphenylmethane diisocyanate (MDI) and a low molecular weight polyethylene glycol (PEG). The rheological and thermal behaviours of modified bitumen containing a low MDI–PEG concentration, as well as its morphology, have been studied. A relatively low amount of MDI–PEG (0.5 to 1.5% wt.) yields a significant improvement in the modified bitumen rheological properties, mainly in the high in-service temperature region. In this range of temperature, the rheological properties are clearly affected by curing time at room temperature. These results indicate that chemical changes, due to the reaction of MDI isocyanate groups with the most polar groups (–OH; –NH) of asphaltenes and resins, are produced. Thus, new chemical structures, non-visible by optical microscopy, slowly develop in MDI–PEG modified bitumen when samples are cured at room temperature.     

Deposition of TiN films on Co–Cr for improving mechanical properties and biocompatibility using reactive DC sputtering

This study reports the deposition of TiN films on Co–Cr substrates to improve the substrates’ mechanical properties and biological properties. In particular, the argon to nitrogen (Ar:N₂) gas flow ratio was adjusted to control the microstructure of the TiN films. A Ti interlayer was also used to enhance the adhesion strength between the Co–Cr substrate and TiN films. A series of TiN films, which are denoted as TiN-(Ar/N₂)1:1, Ti/TiN-(Ar/N₂)1:1, and Ti/TiN-(Ar:N₂)1:3, were deposited by reactive DC sputtering. All the deposited TiN films showed a dense, columnar structure with a preferential orientation of the (200) plane. These TiN films increased the mechanical properties of Co–Cr, such as the critical load during scratch testing, hardness, elastic modulus and plastic resistance. In addition, the biological properties of the Co–Cr substrates, i.e. initial attachment, proliferation, and cellular differentiation of the MC3T3-E1 cells, were improved considerably by deposition of the TiN films. These results suggest that TiN films would effectively enhance both the mechanical properties and biocompatibility of biomedical Co–Cr alloys.     

Nano-scratch as a new tool for assessing the nano-tribological behavior of cement composite

This paper presents a preliminary exploration on tribological properties of cement composite material at micro- and nano-scales by means of the nano-scratch technique, which is a new instrument overcoming the limitations of both the classical stylus scratch test and the atomic force microscope. Measurements were conducted on two very different types of material: cement clinker paste and polymer-based cement clinker. Mechanical parameters related to the nano-tribological performance, i.e. penetration depth, coefficient of friction, and elastic deformation ratio, were obtained from the scratching processes. By statistical deconvolution analysis, microstructure constituents with a large discrepancy in elastic modulus and hardness values can be captured as single peaks, but not for the mixture of C–S–H and Ca(OH)₂ phases. A reverse tendency was observed between penetration depth and coefficient of friction of both the substrate and hard particle phase embedded in. An H/E ratio dependent elasto–plastic behavior was identified, with the elastic deformation to be dominant in high H/E ratio phases. The results confirm this new technique as a promising method for quantitative characterization of elasticity, hardness and mar resistance of heterogonous phases in cement composite.     

Effects of introducing silica particles on the rheological properties and crystallization behavior of poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET)/silica composites were prepared by melt compounding, and their rheological properties and isothermal crystallization were discussed. Introduction of silica particles (0.5–2 wt.%) increased the storage modulus (G′) and decreased loss tangent (tanδ). However, the effect of the particles on rheological properties became negligible at a high frequency more than ca. 70 rad/s. In the Cole–Cole plot, the PET/silica composites showed little deviation from the master curve regardless of the presence of silica particles. The particles increased the relaxation time of PET at particularly low frequency. The isothermal crystallization kinetics of PET/silica was examined using a differential scanning calorimeter (DSC). The half-time of crystallization was decreased with increasing the silica content. The incorporation of silica particles decreased the equilibrium melting temperature by ca. 5.5 °C. In addition, the composites exhibited higher average value of Avrami exponent (2.7–2.9) in comparison with that of pure PET (2.2).     

Hot-pressed phosphate glass–ceramic matrix composites containing calcium phosphate particles for nuclear waste encapsulation

Sodium aluminium phosphate (NaAlP) glass–ceramic composites were produced as potential wasteforms for the immobilization of special categories of halide-containing radioactive waste. Sintering conditions for encapsulating a simulated waste (a calcinated mixture of calcium phosphate host and various oxides) in the cold-pressed NaAlP glass–ceramic were first determined and the results were compared with similar samples prepared by hot pressing. In both cases, the conditions aimed to provide a very high-density material, via as low production temperatures as possible, in conjunction with a high waste loading (75 wt.% simulated waste to 25 wt.% glass). It was found that by hot pressing and using a NaAlP glass–ceramic containing 2 mol% B₂O₃, significantly lower temperatures could be employed compared to the cold pressing and sintering route. The lowest temperature at which a sufficiently dense hot-pressed product was achieved (86% theoretical density), that exhibited mechanical properties similar to those of borosilicate glass (e.g. Young’s modulus 67 ± 2 GPa), was 550 °C. This processing temperature is considerably lower than values reported in the literature for similar systems. As such, hot pressing can be considered as a convenient technique for the fabrication of this type of composite for waste encapsulation.     

Dielectric properties and structural dynamics of melt compounded hot-pressed poly(ethylene oxide)–organophilic montmorillonite clay nanocomposite films

The dielectric properties of melt compounded hot-pressed nanocomposite films consisting of a poly(ethylene oxide) (PEO) and organophilic montmorillonite (OMMT) clay surface modified with trimethyl stearyl ammonium as filler with increasing amount up to 20 wt.% OMMT were investigated in a frequency range of 20 Hz–1 MHz at 30 °C. The predominance of OMMT exfoliated structures in PEO–OMMT nanocomposites were recognized by a decrease of the real part of complex dielectric function. OMMT concentration dependent dielectric and electric modulus relaxation times have revealed that the interactions compatibility between PEO molecules and dispersed OMMT nano-platelets in PEO matrix governs the PEO segmental dynamics. A.C. conductivity of these nanocomposites increases by two orders of magnitude in the experimental frequency range.     

Li2.6V6O16±y, K’-bronze: Synthesis by the alkoxide process, conductivity, and electrochemical performance

The K’-bronze Li_2.6V₆O_16+-y was prepared from VO(OPrⁱ)₂, VO(OBuⁱ)₃, and LiOR (R = Et, Pr). As determined by x-ray diffraction and electron scanning microscopy, the bronze had a highly textured microstructure. The vanadium(IV) and vanadium(V) contents of the bronze were determined by cyclic voltammetry, and the electrical conductivity was measured in the temperature range 20–400°C. The alkoxide process was shown to ensure good reproducibility of the electrical properties of the material. The electrochemical behavior of the bronze was studied in a 1 M solution of LiClO₄ in a propylene carbonate (70 wt %) + dimethoxyethane (30 wt %) mixture in a galvanostatic cycling regime using Li metal counter and reference electrodes     

Compressive properties of a new metal–polymer hybrid material

Compressive properties of a new hybrid material, fabricated through filling of an aluminum foam with a thermoplastic polymer, are investigated. Static (0.01 s⁻¹) and dynamic (100 s⁻¹) compression testing has been carried out to study the behavior of the hybrid material in comparison with its parent foam and polymer materials. Considering the behavior of metal foams, the point on a compressive stress–strain curve corresponding to the minimum cushion factor is defined as the “densification” point. The analysis of the stress–strain curves provides insight into the load carrying and energy absorption characteristics of the hybrid material. At both strain rates, the hybrid is found to carry higher stresses and absorb more energy at “densification” than the foam or polymer.     

The effect of manganese on the microstructure and mechanical properties of zinc–aluminium based ZA-8 alloy

In this investigation, the effect of manganese as an alloying element in the range 0.01%–0.53 wt.%, on the hardness, 0.2% yield, tensile and impact strength, and creep properties of a gravity cast Zn–Al based ZA-8 alloy has been investigated. It was found that addition of Mn over the entire range of concentrations has a useful effect on the hardness of the alloy. Also, the 0.2% yield and ultimate tensile strength (UTS) of the samples did not change significantly with Mn additions up to 0.045 wt.% but decreased with a further increase in Mn content. Furthermore, the impact strength of the alloy improved with increasing Mn up to 0.045 wt.% and then decreased gradually with a further increase in Mn content. On the other hand, the creep resistance of the alloy increased continuously with increasing Mn content up to 0.53 wt.% Mn. Metallographic studies showed that addition of Mn resulted in microstructural modifications of the alloy involving the formation of complex intermetallic compound identified as MnAl₆. The increase in creep resistance and decrease in tensile and impact strength were thought to have been caused by the changing morphology and amount of the intermetallic.     

ABS-maleated SEBS blend as a 3D printable material

A key enabler for the advancement of material extrusion 3D printing is the implementation of new printable materials with a wide variety of physical properties. The focus of this study is the development of 3D printable polymer blends based on compounding acrylonitrile butadiene styrene (ABS) with styrene ethylene butylene styrene. Here the mechanical properties of the resulting novel material systems were manipulated through the change of mixture composition. The novel blends were evaluated based on mechanical testing and fracture surface analysis. Additionally, the rheological characteristics were determined based on melt flow index values. Key results were the significant increase in elongation at break values from 8.53% (ABS baseline) to 1506.57% (rubberised ABS) and the drastic difference in fracture surface morphology when comparing the various blends to ABS.     

Capacitive characteristics of Ni–Co oxide nano-composite via coordination homogeneous co-precipitation method

A series of Ni–Co oxide nano-composites were prepared by thermal decomposition of the precursors obtained via coordination homogeneous co-precipitation method. Thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), and transition electron microscopy (TEM) tests were applied to investigate the thermal behavior, crystalline. and morphology of the Ni–Co oxide composites. The electrochemical properties of Ni–Co oxide electrodes were evaluated by cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance measurements. Results showed that the calcination temperature had great effect on morphology and specific capacitance of product. The effect of the molar ratios of Ni²⁺/Co²⁺ in the reaction system on the electrochemical properties of Ni–Co oxide electrodes was also discussed.