Overcoming interfacial affinity issues in natural fiber reinforced polylactide biocomposites by surface adsorption of amphiphilic block copolymers

This work demonstrates that the interfacial properties in a natural fiber reinforced polylactide biocomposite can be tailored through surface adsorption of amphiphilic and biodegradable poly (ethylene glycol)-b-poly-(L-lactide) (PEG-PLLA) block copolymers. The deposition from solvent solution of PEG-PLLA copolymers onto the fibrous substrate induced distinct mechanisms of molecular organization at the cellulosic interface, which are correlated to the hydrophobic/hydrophilic ratios and the type of solvent used. The findings of the study evidenced that the performance of the corresponding biocomposites with polylactide were effectively enhanced by using these copolymers as interfacial coupling agents. During the fabrication stage, diffusion of the polylactide in the melt induced a change in the environment surrounding block copolymers which became hydrophobic. It is proposed that molecular reorganization of the block copolymers at the interface occurred, which favored the interactions with both the hydrophilic fibers and hydrophobic polylactide matrix. The strong interactions such as intra- and intermolecular hydrogen bonds formed across the fiber−matrix interface can be accounted for the enhancement in properties displayed by the biocomposites. Although the results reported here are confined, this concept is unique as it shows that by tuning the amphiphilicity and the type of building blocks, it is possible to control the surface properties of the substrate by self-assembly and disassembly of the amphiphiles for functional materials.

Digital material representation and testing of metal foams

In recent years, metal foams are becoming more and more popular due to their high energy absorption ability and low density, which are being widely used in automotive engineering and aerospace engineering. As a design guide, foams can be characterised by several main geometric parameters, such as pore size, pore shape, spatial distribution and arrangement and so on. Considering most foam materials have random distributions of cell size and cell shape, the digital material representation and modelling of such materials become more complex. Cell size and shape effects on mechanical behaviours of metal foams have been found and investigated numerically and experimentally in authors' previous studies in which the authors have developed a digital framework for the representation, modelling and evaluation of multi-phase materials including metal foams. In this study, 2-/3-D finite element models are both developed to represent metal foams with random cell distributions and then a series of digital testing are simulated to investigate the mechanical behaviours of such foams. For validation and verification purpose, the results obtained from 2-/3-D models have been compared and good agreement has been found which demonstrated the effectiveness of the digital framework developed for metal forms. © (2014) Trans Tech Publications, Switzerland.

'Laser chemistry' synthesis, physicochemical properties, and chemical processing of nanostructured carbon foams

Laser ablation of selected coordination complexes can lead to the production of metal-carbon hybrid materials, whose composition and structure can be tailored by suitably choosing the chemical composition of the irradiated targets. This 'laser chemistry' approach, initially applied by our group to the synthesis of P-containing nanostructured carbon foams (NCFs) from triphenylphosphine-based Au and Cu compounds, is broadened in this study to the production of other metal-NCFs and P-free NCFs. Thus, our results show that P-free coordination compounds and commercial organic precursors can act as efficient carbon source for the growth of NCFs. Physicochemical characterization reveals that NCFs are low-density mesoporous materials with relatively low specific surface areas and thermally stable in air up to around 600°C. Moreover, NCFs disperse well in a variety of solvents and can be successfully chemically processed to enable their handling and provide NCF-containing biocomposite fibers by a wet-chemical spinning process. These promising results may open new and interesting avenues toward the use of NCFs for technological applications.

Mechanical ageing performance of minimalist and traditional footwear foams

The aim of this study was to obtain a fundamental understanding of how running shoe midsole foam thickness contributes to footwear degradation using the heel and forefoot regions of traditional (TS) and minimalist (MS) running shoes. We hypothesized that ethylene vinyl acetate (EVA) foam midsole material properties and footwear degradation performance under a biofidelic mechanical ageing protocol would differ as a function of shoe type and thickness. Attenuated totalreflectance Fourier transform infrared spectra indicated that the foam chemical compositions were similar and confirmed that all midsoles were composed of EVA copolymer. Differences in density and cell size were detected between shoes and thicknesses. MS foam was uniformly high density (rMS D 240 kg/m3), while TS foam consisted of two co-molded layers with forefoot density (rTS-FF D 250 kg/m3) greater than heel (rTS-H D 160 kg/m3). Relative density and cell size values were generally proportional and inversely proportional to density, respectively. Degradation from mechanical ageing was greatest in the first 2 km of ageing, with the full ageing (21 km) resulting in an average 54% loss of energy absorption. Regardless of shoe type or foam microstructure, thicker and softer heel foams absorbed 83% more energy but degraded ata 49% faster rate. The fact that the heel degraded more rapidly than forefoot caused the drop to decrease at an equivalent rate for both shoe types. Overall, thickness was a greater predictor of average performance than microstructure variables for the present footwear conditions. However, the apparent drawback of thicker foam was exemplified by heel samples, which underwent a 1.4 mm greater loss of thickness and lost 550 mJ more energy absorption than forefoot samples.

Stabilizing and destabilizing protein surfactant-based foams in the presence of a chemical surfactant: Effect of adsorption kinetics.

Stimuli-responsive protein surfactants promise alternative foaming materials that can be made from renewable sources. However, the cost of protein surfactants is still higher than their chemical counterparts. In order to reduce the required amount of protein surfactant for foaming, we investigated the foaming and adsorption properties of the protein surfactant, DAMP4, with addition of low concentrations of the chemical surfactant sodium dodecylsulfate (SDS). The results show that the small addition of SDS can enhance foaming functions of DAMP4 at a lowered protein concentration. Dynamic surface tension measurements suggest that there is a synergy between DAMP4 and SDS which enhances adsorption kinetics of DAMP4 at the initial stage of adsorption (first 60s), which in turn stabilizes protein foams. Further interfacial properties were revealed by X-ray reflectometry measurements, showing that there is a re-arrangement of adsorbed protein-surfactant layer over a long period of 1h. Importantly, the foaming switchability of DAMP4 by metal ions is not affected by the presence of SDS, and foams can be switched off by the addition of zinc ions at permissive pH. This work provides fundamental knowledge to guide formulation using a mixture of protein and chemical surfactants towards a high performance of foaming at a low cost.

Does firefighting foam affect the growth of some Australian native plants?

Firefighting foams (Class A foams) are an effective and widespread firefighting tool, and are frequently used in environmentally sensitive areas. They are known to be ecologically damaging in aquatic environments; however, their impacts at the plant species or ecosystem level are relatively unknown. Reports of shoot damage to plants, suppressed flowering and changes in plant community composition suggest that the environmental damage caused by their use may be unacceptable. Applications of four levels of foam to seedlings of seven Australian plant species, from five representative and widespread families, showed no detectable impacts on a range of vegetative growth characteristics. The results are encouraging for continued use of firefighting foam in sensitive natural habitats.

Novel titanium foam for bone tissue engineering

Titanium foams fabricated by a new powder metallurgical process have bimodal pore distribution architecture (i.e., macropores and micropores), mimicking natural bone. The mechanical properties of the titanium foam with low relative densities of approximately 0.20-0.30 are close to those of human cancellous bone. Also, mechanical properties of the titanium foams with high relative densities of approximately 0.50-0.65 are close to those of human cortical bone. Furthermore, titanium foams exhibit good ability to form a bonelike apatite layer throughout the foams after pretreatment with a simple thermochemical process and then immersion in a simulated body fluid. The present study illustrates the feasibility of using the titanium foams as implant materials in bone tissue engineering applications, highlighting their excellent biomechanical properties and bioactivity.

Processing of biocompatible porous Ti and Mg

A new powder manufacturing process for Ti and Mg metallic foams designs porosity, pore size and morphology. These open-cellular foams (pores: 200–500 μm) have exceptional characteristics (e.g., Ti foam porosity 78%, compressive strength 35 MPa, Young's modulus 5.3 GPa). Anticipated applications include biocompatible implant materials.

Preparation and characterisation of open-cell microporous nickel

In the present study, nickel foams with an open cell microporous structure were fabricated by the so-called space-holding particle sintering method, which included the adding of a particulate polymeric material (PMMA). The average pore size of the nickel foams approximated 10.5 μm; and the porosity ranged from 70 % to 80 %. The porous characteristics of the nickel foams were observed using scanning electron microscopy and the mechanical properties were evaluated using compressive tests. For comparison, nickel foams with an open-cell macroporous structure (pore size approximately 1.3 mm) were also presented. Results indicated that the nickel foams with a microporous structure possess enhanced mechanical properties than those with a macroporous structure.

Preparation and characterisation of new titanium based alloys for orthopaedic and dental applications

Various types of titanium alloys with high strength and low elastic modulus and, at the same time, vanadium and aluminium free have been developed as surgical biomaterials in recent years. Moreover, porous metals are promising hard tissue implants in orthopaedic and dentistry, where they mimic the porous structure and the low elastic modulus of natural bone. In the present study, new biocompatible Ti-based alloy foams with approximate relative densities of 0.4, in which Sn and Nb were added as alloying metals, were synthesised through powder metallurgy method.
The new alloys were prepared by mechanical alloying and subsequently sintered at high temperature using a vacuum furnace. The characteristics and the processability of the ball milled powders and the new porous titanium-based alloys were characterised by X-ray diffraction, optical
microscopy and scanning electron microscopy .The mechanical properties of the new titanium alloys were examined by Vickers microhardness measurements and compression testing.

Processing and mechanical properties of porous titanium-niobium shape memory alloy for biomedical applications

Ti-26 at.%Nb (hereafter Ti-26Nb) alloy foams were fabricated by space-holder sintering process. The porous structures of the foams were characterized by scanning electron microscopy (SEM). The mechanical properties of the Ti-26Nb foam samples were investigated using compressive test. Results indicate that mechanical properties of Ti-26Nb foam samples are influenced by foam porosity. The plateau stresses and elastic moduli of the foams under compression decrease with the increase of their porosities. The plateau stresses and elastic moduli are measured to be from 10~200 MPa and 0.4~5.0 GPa for the Ti-26Nb foam samples with porosities ranged from 80~50 %, respectively.

Mechanical properties of micro-porous metals produced by space-holding sintering

Micro-porous nickel foams with an open cell structure were fabricated by the space-holding sintering. The average pore size of the micro-porous nickel specimens ranged from 30 μm to 150 μm, and the porosity ranged from 60 % to 80 %. The porous characteristics of the nickel specimens were observed using scanning electron microscopy (SEM). The mechanical properties were studied using compressive tests. For comparison, macro-porous nickel foams prepared by the chemical vapour deposition method with pore sizes of 800 μm and 1300 μm and porosity of 95 % were also presented. Results indicated that the ratio value of 6 and higher for the specimen length to cell size (L/d) is satisfying for obtaining stable compressive properties. The micro-porous nickel specimens exhibited different deformation behaviour and dramatically increased mechanical properties, compared to those of the macro-porous nickel specimens.

Compressive deformation behaviour of a closed-cell aluminum

The mechanical properties of a closed-cell aluminium foam were investigated by compressive tests, and the deformation behaviours of the aluminium foams were studied using Xray microtomography. The results indicate that the deformation of the aluminium foams under compressive loading was localized in narrow continuous deformation bands having widths of order of a cell diameter. The cells in the deformation bands collapsed by a mixed deformation mechanism, which includes mainly bending and minor buckling and yielding. Different fractions of the three deformation modes led to variations in the peak stress and energy absorption for different foam samples with the same density. It was also found that the cell morphology affects the deformation mechanism significantly, whilst the cell size shows little influence.