Effect of Surface Modification on Structural and Thermal Properties of Nanocarbons of Different Dimensionalities

Multi-walled carbon nanotubes and graphite nanoplatelets were functionalized via acid treatment to overcome the problem of agglomeration. Fourier transform infrared spectroscopy showed the chemical modification of the nanocarbons while the general relationship between the chemical treatment and the defects population was analyzed by Raman spectroscopy. The information regarding the mass loss and impurities is obtained from the thermogravimetric analysis. X-ray diffraction showed the effect of acid treatment on the physical states of the nanocarbons including the crystalline texture. The comparative high interlayer distance in graphite suggested that graphite particles are exfoliated into sheets of graphene by this technique with smaller particle sizes. The thermogravimetric analysis confirmed the complete removal of impurities in the case of multi-walled carbon nanotubes (MWCNTs) and about 20 % of impurities as seen in oxidized graphite attributable to the presence of residual manganese that might have been introduced during the functionalization process. Moreover, the thermal stability was also observed well in the case of MWCNTs with lesser impurities left. Overall, two different nanocarbons with well-structured chemical modifications were obtained with a variation in the feasibility of functionalization.

Aspects of the Ageing of Elastomeric Materials

Rising raw materials prices and increasing customer demands for reliability and durability mean that there is huge interest in finding more and more ways of improving the service life of elastomeric products, for economic and environmental reasons, by boosting their resistance under the relevant operating conditions. The material-dependent oxygen absorption capacity and oxygen permeability play an important role in oxidative ageing processes and their modelling. Thus, ageing resistance is substantially dependent on the rate of oxygen diffusion into the bulk of the material in the case of thermo-oxidative attack. To evaluate the resistance of materials to external influences, artificial ageing methods are used in practice. The advantage of these methods is that, as a result of intensifying the test parameters, e.g. temperature and humidity, the ageing processes in the vulcanisate are accelerated. Within the scope of this study, the influence of accelerated ageing on the mechanical and viscoelastic properties of mainly carbon-black-filled natural rubber (NR) vulcanisates was studied in an oxygen atmosphere at elevated temperature and in oxygen with solar radiation. The filler content was varied and the antioxidant IPPD was used. The analyses showed that, as well as mechanical properties such as hardness and tensile strength, the viscoelastic properties are also affected, depending on the ageing time and the type of ageing. In addition to the investigation of mechanical properties, a direct evaluation of the material change was carried out for selected samples by means of analytical tests. The investigations showed the deterioration of the antioxidant activity.

Synthesis and Characterization of Nanostructured Blends of Epoxy Resin and Block Copolymers

Polystyrene–polybutadiene block copolymers having different molecular architectures were epoxidized by using meta-chloroperoxybenzoic acid (MCPBA). Then, the blends with epoxy resin (diglycidyl ether of bisphenol-A; DGEBA) and their nanocomposites with boehmite and layered silicate nanofiller in presence of methylene dianiline (MDA) as a hardener were prepared. The epoxidized copolymers and the composites were characterized by Fourier transform infrared (FTIR) spectroscopy and microindentation technique. In this way, it was possible to tune the morphology of the nanostructured blends of the epoxy resin using the functionalized block copolymer as the template. The presence of nanostructured morphology was attested by the optical transparency of the blends as well as of the composites with nanofiller. The microhardness properties were improved by the incorporation of the nanoparticles, viz. boehmite and layered silicate. Nepal Journal of Science and Technology Vol. 13, No. 1 (2012) 81-88 DOI: http://dx.doi.org/10.3126/njst.v13i1.7445

Fracture surface statistics of filled elastomers

Roughness profiles of fracture surfaces formed as a result of the fast crack propagation through a filled rubber were analyzed by means of the height-height correlation functions. The fracture surface was found to be anisotropic in a certain domain of values of length scales; i.e., different values of roughness exponents are observed across and along the crack propagation direction. A two-dimensional analysis reveals a Family-Vicsek scaling in this domain characterized as well by two exponents. These characteristic values of the roughness exponents are found to be close to those observed for fracture surfaces of certain nonrubber materials at length scales smaller than the size of the fracture process zone. Hence, a ductile fracture process can be surmised to occur within the domain of the corresponding length scales.

Determination of strength and deformation behavior of human cartilage for the definition of significant parameters

In reconstructive surgery, an artificial supporting scaffold made from autogenous cartilage from the rib, the ear concha, or the nasal septum is used as a substitute for the destroyed endogenous tissue in the ear concha, the nose, the trachea, and in parts of the facial skeleton. For the successful use of polymer materials in reconstructive surgery, an exact knowledge of the material properties of the natural tissues is required. The applicability of conventional material test methods was examined with regard to the suitability of the test methodology. Materials properties are to be assessed for different specimen sizes and geometries. Human cartilage specimens from the septum, rib, and ear were subsected to the following test methods: (1) tension, (2) bending, (3) compression, and (4) micro-hardness measuring. Specimen geometry was evaluated for each experimental method by taking into account the dimensions of samples used in plastics testing as well as the appropriate model of miniaturization. Elastic properties determined using test methods (1), (2), and (3) are Et-sep=(7.2+/-3.4) MPa, Ef-rib=(8.8+/-2.9) MPa, and Ec-rib=(103+/-30) MPa. The micro-hardness values hpl fluctuate for septum from 1 to 4 N/mm2 and for the rib from 0.5 to 1.3 N/mm2. The experiments have shown that, beside the sex- and age-specific values recorded, the standard values and their variation are particularly influenced by preparation technique and by the conditions of storage. As a result of these first investigations, characteristic values for strength and deformation were determined under quasistatic and dynamic load conditions. The aim of this study was not the determination of statistically firmed properties, but the examination of the applicability of mechanical test methods of the polymer testing for these materials.

Erweiterter push out-Test zur Schädigungscharakterisierung der Implantat-Knochen-Grenzfläche / Extended push-out test to characterize the failure of bone-implant interface

To study the mechanical behaviour of the implant-bone interface the push- or pull-out test was overtaken from material science. Most authors equate the maximum load (break point) with the failure of the implant integration. Extending the test procedure by acoustic emission analysis reveals the possibility to detect the failure of the interface more in detail and from its earliest beginning. The development of disconnection between host and implant was found to start long before the ultimate load is reached and can be monitored and quantified during this period. The active interface mechanisms are characterized by the distribution function of acoustic emissions and the number of hits per time defines the kinetics of the failure. From clinical studies a gradual subsidence of loaded implants is known starting long time before the definite implant failure. The presented extension of the push-out test with acoustic emission analysis allows the detection of a critical shear stress tc which demarks the onset of the gradual interface failure. We believe this value to represent the real critical load which should not be exceeded in the clinical application of intraosseous implants.

Investigation of Mechanical and Fracture Mechanical Properties of Elastomers Filled with Precipitated Silica and Nanofillers Based upon Layered Silicates

The aim of this paper is to show possibilities of experimental methods of polymer diagnostics and fracture mechanics for quantitative characterization of crack initiation and propagation properties of elastomeric materials. At first, a general overview of methods of technical fracture mechanics is given. This is followed by a short discussion of some possibilities for determination of tearing energy T for elastomers. In the main part, results of various mechanical and fracture mechanics experiments on filled natural rubber vulcanizates are shown. The vulcanizates were filled with different contents (5–70 phr) of two filler types. The fillers were precipitated silica and an organic-modified nano-disperse layered silicate. Th aim of the experiments was to prove possibilities of several fracture mechanics testing methods for quantifying the influence of the filler content, filler type and additionally the specimen direction on the deformation and fracture behavior. Tear-analyzer results were used to assess the crack propagation behavior under fatigue-like loading conditions. Furthermore, instrumented tensile-impact tests were performed for the characterization of the crack resistance of the materials under impact-like loading conditions. To obtain information about the initiation and propagation of a stable crack, a quasi-static fracture mechanics test was applied, and crack resistance curves were recorded. Here, specimens with various thicknesses were investigated. Additionally, conventional tear tests were done and the results were compared to that of the fracture mechanics test. Generally, it was found that all methods are useful for the description of the fracture properties. Furthermore, the fracture behavior is influenced positively especially by high filler contents. Strong differences of several parameters were found depending on the filler type. Another important result is that again differences were found between the crack initiation and propagation behavior.

How do roll compaction/dry granulation affect the tableting behaviour of inorganic materials?

The effect of roll compaction/dry granulation on the ribbon and tablet properties produced using different magnesium carbonates was evaluated. The ribbon microhardness and the pore size distribution of tablets were used as evaluation factors. Increasing the specific compaction force resulted in higher microhardness for ribbons prepared with all four magnesium carbonates accompanied with decreased part of fine. Consequently, the corresponding produced tablets displayed a lower tensile strength. A possible correlation between the particle shape, surface area and the resulting pore structure of tablets produced with the four different types of magnesium carbonate was observed. The tensile strength of tablets prepared using granules was lower than tensile strength of tablets produced using starting materials. The partial loss of compactibility resulted in a demand of low loads during roll compaction. However, the impact of changes in the material properties during the roll compaction depended greatly on the type of magnesium carbonate, the specific compaction force and the tableting pressure applied.