Hybrid materials based on polyethylene and MCM-41 microparticles functionalized with silanes: catalytic aspects of in situ polymerization, crystalline features and mechanical properties

New nanocomposites based on polyethylene have been prepared by in situ polymerization of ethylene in presence of mesoporous MCM-41. The polymerization reactions were performed using a zirconocene catalyst either under homogenous conditions or supported onto mesoporous MCM-41 particles, which are synthesized and decorated post-synthesis with two silanes before polymerization in order to promote an enhanced interfacial adhesion. The existence of polyethylene chains able to crystallize within the mesoporous channels in the resulting nanocomposites is figured out from the small endothermic process, located at around 80 C, on heating calorimetric experiments, in addition to the main melting endotherm. These results indicate that polyethylene macrochains can grow up during polymerization either outside or inside the MCM-41 channels, these keeping their regular hexagonal arrangements. Mechanical response is observed to be dependent on the content in mesoporous MCM-41 and on the crystalline features of polyethylene. Accordingly, stiffness increases and deformability decreases in the nanocomposites as much as MCM-41 content is enlarged and polyethylene amount within channels is raised. Ultimate mechanical performance improves with MCM-41 incorporation without varying the final processing temperature.

Effects of infiltration pressure on mechanical properties of Al–12Si/graphite composites for piston engines

In this work results for the flexural strength and the thermal properties of interpenetrated graphite preforms infiltrated with Al-12wt%Si are discussed and compared to those for packed graphite particles. To make this comparison relevant, graphite particles of four sizes in the range 15–124 μm, were obtained by grinding the graphite preform. Effects of the pressure applied to infiltrate the liquid alloy on composite properties were investigated. In spite of the largely different reinforcement volume fractions (90% in volume in the preform and around 50% in particle compacts) most properties are similar. Only the Coefficient of Thermal Expansion is 50% smaller in the preform composites. Thermal conductivity of the preform composites (slightly below 100 W/m K), may be increased by reducing the graphite content, alloying, or increasing the infiltration pressure. The strength of particle composites follows Griffith criterion if the defect size is identified with the particle diameter. On the other hand, the composites strength remains increasing up to unusually high values of the infiltration pressure. This is consistent with the drainage curves measured in this work. Mg and Ti additions are those that produce the most significant improvements in performance. Although extensive development work remains to be done, it may be concluded that both mechanical and thermal properties make these materials suitable for the fabrication of piston engines.

The effect of polypropylene-graft-maleic anhydride on the morphology and dynamic mechanical properties of polypropylene/polystyrene blends

Polypropylene (PP) and polystyrene (PS) blends were prepared by melt processing in a haake at 180 °C. PP/PS blends are immiscible and the blend morphologies were characterized by scanning electron microscopy. The viscoelastic properties were characterized using dynamic mechanical analysis (DMA) with reference to blend ratio. The blend morphologies such as matrix droplet and phase inverted morphologies were observed. The storage modulus of the blends increased with increase in PS content and the value was maximum for neat PS. DMA showed changes in the polystyrene glass transition temperatures (Tg) over the entire composition range. There was a sharp increase in the Tg of PS with increasing PP content in the blend and a 12 °C elevation in Tg was observed. The increase in Tg was explained by proposing a new model based on the physical interaction between the blend components. It is assumed that the different effects by the PP phase resulted in the formation of constrained PS chains leading to high Tg values. The addition of PP-g-MAH has a positive effect on the morphology, increases the storage modulus, and decreases the Tg till 80/20 blends. However, for PP/PS blends with higher concentrations of PS, the PP-g-MAH has little effect or adverse effect on the morphology, and storage modulus, but decreases the Tg.

Mechanical properties and microstructure of powder metallurgy Ti-xNb-yMo alloys for implant materials

In this study, a series of Ti-xNb-yMo (x = 5-40 wt.% in 5 wt.% increments; and y = 3, 5, 10 wt%) alloys were fabricated by powder metallurgy and studied with respect to their microstructures, compressive mechanical properties and hardness. Increases in Nb and Mo content led to decreases in compressive and yield strengths, elastic modulus and hardness of the sintered alloys. Among the studied alloys, Ti-10Nb-3Mo alloy exhibited the optimum combination of strength and ductility. Alloys with a lower amount of Nb (≤ 25 wt.%) and Mo (≤ 5 wt.%) developed Widmanstätten structure, while further increase in Nb and Mo additions led to the microstructure predominantly consisting of β phase with varying regions of α + β phase. The effects of sintering temperature on elastic modulus and hardness were also investigated for Ti-xNb-3Mo alloys.

Modeling the effect of asymmetric rolling on mechanical properties of Al-Mg alloys

The mechanical behavior under uniaxial tension of Al-Mg alloy 5182 pre-deformed in conventional rolling (CR), asymmetric rolling-continuous (ASRC), and asymmetric rolling-reversed (ASRR) was investigated and modeled with a rate dependent crystal plasticity finite element method and VPSC (Visco-Plastic Self Consistent) model. M-K theory combined with Yld2000 model by Barlat et al. (Int. J. Plasticity 2003, 19, 1297) was used to predict the strain-based and stress-based formability for AA 5182 material. It was concluded that the new ASRR process has very compatible formability with improved strength compared to CR process. These merits can be directly applied for clam-shell resistant design in rigid-packaging industry.

Effects of Nd on the microstructures, mechanical properties and in vitro corrosion behavior of cast Mg-1Mn-2Zn-xNd alloys

Effects of neodymium (Nd) on the microstructures, mechanical properties, in vitro corrosion behavior, and cytotoxicity of as-cast Mg- 1Mn-2Zn-xNd alloys (x = 0.5, 1.0, 1.5, mass%) have been investigated to assess whether Nd is an effective element to increase the strength and corrosion resistance of Mg alloys, and to evaluate whether those alloys are suitable for biomedical applications. The microstructures were examined by X-ray diffraction analysis and optical microscopy. The mechanical properties were determined from uniaxial tensile and compressive tests. The corrosion behavior was studied using electrochemical measurement and cytotoxicity was evaluated using osteoblast-like SaOS2 cell. The results indicate that all the cast Mg-1Mn-2Zn-xNd alloys are composed of both alpha phase of magnesium (Mg) and a compound of Mg7Zn3, and their grain sizes decrease with Nd content. Nd is not an effective element to improve the strength and corrosion resistance of cast Mg-Mn-Zn alloys. Increase of Nd content from 0.5 to 1.5 does not significantly change biocompatibility of alloys. The cast alloys exhibit much better corrosion resistance than pure Mg and good biocompatibility.

Transesterification induced mechanical properties enhancement of PLLA/PHBV bio-alloy

In order to improve the miscibility and mechanical properties of poly(l-lactic acid) (PLLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) bio-alloy, small amount of transesterification catalyst, zinc acetate was added in the melt blending process. We show that the PLLA-PHBV copolymer generated during the melt blending significantly improves the miscibility and therefore enhances the mechanical properties of the product. Dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), and tensile tests were performed to study the miscibility and mechanical properties of the blends. Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) were used to reveal the molecular structural, and molecular weight changes of PLLA and PHBV after melt mixing with zinc acetate. SEM and FTIR results have clearly shown that the PLLA-PHBV copolymer generated from transesterification reaction acted as a compatibilizer and therefore resulted in an improved interfacial miscibility and ductility of PLLA/PHBV blend. In our mechanistic study, a competition between the PLLA/PHBV transesterification reaction and the thermal decomposition of PHBV was identified for the first time. On the basis of these observations, a new mechanism of transesterification reaction was proposed.

Equal-channel angular pressing and annealing of a twinning-induced plasticity steel : microstructure, texture, and mechanical properties

In this work, a high-manganese Fe-23Mn-1.5Al-0.3C Twinning-Induced Plasticity (TWIP) steel was subjected to plastic shear deformation using Equal-Channel Angular Pressing (ECAP) at 300 °C following route BC and additional annealing. The microstructure evolution during both deformation by ECAP and subsequent annealing was investigated and correlated with the mechanical properties. The successive grain refinement during ECAP was promoted by two parallel mechanisms, namely dislocation driven grain fragmentation and twin fragmentation, and accounted for the ultra-high strength. In addition, due to the relatively low volume fraction of deformation twins after ECAP at 300 °C, further contribution of deformation twinning during room temperature deformation allowed additional work-hardening capacity and elongation. During subsequent recovery annealing the ultra-fine grains and deformation twins were thermally stable, which supported retainment of the high yield strength along with regained uniform elongation. For the first time, the texture evolution during ECAP and during the following heat treatment was analyzed. After 1, 2, and 4 ECAP passes a transition texture with the characteristic texture components of both high- and low-SFE materials developed. During the following heat treatment the texture evolution proceeded similar to that observed in the same material after cold rolling. Retaining of the ECAP texture components due to oriented nucleation at grain boundaries and triple junctions as well as annealing twinning accounted for the formation of a weak, retained ECAP texture after recrystallization.

A comparison of continuous SPD processes for improving the mechanical properties of aluminum alloy 6111

Microstructure evolution, mechanical properties, formability, and texture development were determined for AA6111 samples processed by asymmetric rolling (ASR) with different roll friction, velocity, or diameters, conventional rolling (CR), and equal-channel-angular pressing (ECAP). Highly elongated or sheared grain structures were developed during ASR/CR and ECAP, respectively. ASR led to improved r-values and formability compared with CR primarily as a result of the development of moderate shear-texture components analogous to those developed during ECAP of billet material. ASR based on different roll diameters gave the best combination of strength, ductility, and formability.

Miscibility, UV resistance, thermal degradation, and mechanical properties of PMMA/SAN blends and their composites with MWCNTs

Poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) (PMMA/SAN) blends, with varying concentrations, were prepared by melt-mixing technique. The miscibility is ensured by fixing the acrylonitrile (AN) content of styrene acrylonitrile (SAN) as 25% by weight. The blends were transparent as well. The Fourier transform infrared spectroscopic (FTIR) studies did not reveal any specific interactions, supporting the well accepted 'copolymer repulsion effect' as the driving mechanism for miscibility. Addition of SAN increased the stability of PMMA towards ultraviolet (UV) radiations and thermal degradation. Incorporation of even 0.05% by weight of multi-walled carbon nanotubes (MWCNTs) significantly improved the UV absorbance and thermal stability. Moreover, the composites exhibited good strength and modulus. However, at higher concentrations of MWCNTs (0.5 and 1% by weight) the thermo-mechanical properties experienced deterioration, mainly due to the agglomeration of MWCNTs. It was observed that composites with 0.05% by weight of finely dispersed and well distributed MWCNTs provided excellent protection in most extreme climatic conditions. Thus, PMMA/SAN/MWCNTs composites can act as excellent light screens and may be useful, as cost-effective UV absorbers, in the outdoor applications.

Comparative acoustic performance and mechanical properties of silk membranes for the repair of chronic tympanic membrane perforations

The acoustic and mechanical properties of silk membranes of different thicknesses were tested to determine their suitability as a repair material for tympanic membrane perforations. Membranes of different thickness (10-100μm) were tested to determine their frequency response and their resistance to pressure loads in a simulated ear canal model. Their mechanical rigidity to pressure loads was confirmed by tensile testing. These membranes were tested alongside animal cartilage, currently the strongest available myringoplasty graft as well as paper, which is commonly used for simpler procedures. Silk membranes showed resonant frequencies within the human hearing range and a higher vibrational amplitude than cartilage, suggesting that silk may offer good acoustic energy transfer characteristics. Silk membranes were also highly resistant to simulated pressure changes in the middle ear, suggesting they can resist retraction, a common cause of graft failure resulting from chronic negative pressures in the middle ear. Part of this strength can be explained by the substantially higher modulus of silk films compared with cartilage. This allows for the production of films that are much thinner than cartilage, with superior acoustic properties, but that still provide the same level of mechanical support as thicker cartilage. Together, these in vitro results suggest that silk membranes may provide good hearing outcomes while offering similar levels of mechanical support to the reconstructed middle ear.

Mechanical properties, in vitro corrosion and biocompatibility of newly developed biodegradable Mg-Zr-Sr-Ho alloys for biomedical applications

Our previous studies have demonstrated that Mg-Zr-Sr alloys can be anticipated as excellent biodegradable implant materials for load-bearing applications. In general, rare earth elements (REEs) are widely used in magnesium (Mg) alloys with the aim of enhancing the mechanical properties of Mg-based alloys. In this study, the REE holmium (Ho) was added to an Mg-1Zr-2Sr alloy at different concentrations of Mg1Zr2SrxHo alloys (x = 0, 1, 3, 5 wt. %) and the microstructure, mechanical properties, degradation behaviour and biocompatibility of the alloys were systematically investigated. The results indicate that the addition of Ho to Mg1Zr2Sr led to the formation of the intermetallic phases MgHo3, Mg2Ho and Mg17Sr2 which resulted in enhanced mechanical strength and decreased degradation rates of the Mg-Zr-Sr-Ho alloys. Furthermore, Ho addition (≤5 wt. %) to Mg-Zr-Sr alloys led to enhancement of cell adhesion and proliferation of osteoblast cells on the Mg-Zr-Sr-Ho alloys. The in vitro biodegradation and the biocompatibility of the Mg-Zr-Sr-Ho alloys were both influenced by the Ho concentration in the Mg alloys; Mg1Zr2Sr3Ho exhibited lower degradation rates than Mg1Zr2Sr and displayed the best biocompatibility compared with the other alloys.