Acoustic emission (AE) was applied for detection of microcrack initiation in carbon fiber reinforced polymer composites subjected to shear stresses. Experimental materials were prepared from polyester bonded unidirectional (1D) non-crimp fabric and 2D plain-weave carbon fiber fabrics, using the resin transfer moulding technology. Control of epoxy resin/carbon textile proportions enabled variation of fiber volume content from small (34/35% for 2D/1D), through medium (51%) to high (68%). Rectangular samples (45×4×2 mm) were cut from 1D plates along  and across  fibers. Similar size samples from 2D plates were cut along warp/weft axes as well as in two orthogonal bias directions. Selected side surfaces were polished for microscopic (SEM) observations. Short-beam-strength tests were performed in 3-point bending (l/h=4), with two AE sensors attached for damage monitoring, which allowed to interrupt loading sequence before final failure. The acoustic emission historic index was the most effective AE parameter in damage initiation control. Microcracks developing on polished composite side-surfaces were observed under the SEM and direct microscopic evidence confirmed fiber debonding to be the principal mechanism of crack initiation in these materials and testing conditions before any further damage.
The goal of this study was to investigate the influence of multi-walled carbon nanotubes (MWCNTs) before and after chemical functionalisation, graphene oxide (GO), and hybrid coating deposited on a titanium (Ti) surface on the nerve cell response in vitro. The physicochemical properties of the surface of the carbon nanomaterial coatings deposited on the Ti substrate using electrophoretic deposition were investigated, followed by biological tests. Scanning and transmission electron microscopy and X-ray photoelectron spectroscopy were used to evaluate the microstructure and chemistry of the carbon nanomaterial coatings. Electrochemical characterisation of the carbon nanomaterial coatings on metal substrates was investigated using cyclic voltammetry and cathodic charge storage capacity. During in vitro analysis, all samples were placed in direct contact with human neuroblastoma SH-SY5Y cells. The viability were analysed after 48 and 72 h of culture. Moreover, the cell morphology in contact with the carbon nanomaterial coatings was observed using fluorescence microscopy. Additionally, the neurite outgrowth and number of pyknotic nuclei were examined using cell microphotographs. GO exhibited the best biological results among all analysed samples, with a positive effect on cell viability, neural cell morphology, and especially neurite outgrowth, and significantly improved the biological properties of the other hybrid (nanocomposite) coatings. GO coating is not an electrochemically active material, thus its applicability for the production of electrodes for nerve stimulation is limited. However, it may be useful as a scaffold for nerve cell stimulation and regeneration. The advantageous electrochemical activity of MWCNT coatings and a satisfactory cell response greater than the Ti surface alone will pave the way for further research on electrodes for nerve cell stimulation
In this paper we have presented results of our studies on chitosan/graphene oxide (CS/GO) and chitosan/re-duced graphene oxide (CS/rGO) hybrid nanocomposites. First, L-ascorbic acid (L-AA), grape extract (GE), and green tea extract (GT) were tested as green reducing agents for reduced graphene oxide synthesis. Structural and chemical properties of the obtained rGOs were examined by X-ray diffraction (XRD), attenuated total re flection Fourier-transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS). Next, GO and rGOs were introduced into the chitosan matrix to prepare a series of hybrid nanocomposites. Their physico-chemical properties were evaluated by XRD, ATR-FTIR, DSC (differential scanning calorimetry), SEM (scanning electron microscopy), wettability and mechanical testing. It was found that all of the introduced nanofillers affected the structural, thermal, microstructural, mechanical, and surface properties of the nanocomposites. Addition of GO resulted in the increase of Young's modulus by 35%, while the composites reinforced with rGO_L-AA were soft and easy to bend in hand without cracking. We showed that simultaneous synthesis of rGO-L-AA and fabrication of the CS/rGO_L-AA hybrid nanocomposite allowed to fully exploit the potential of the chitosan/rGO system. The developed materials, after detailed biological characterization, may be potentially applicable in bone and cartilage tissue engineering.
Increased application of organic compounds, mainly in form of synthetic resins, used as binders for moulding and core sands in metal casting, may have an adverse effect on the environment and work conditions in foundry plants. In this article we focused on the identification of the degradation products formed during laboratory scale simulation of complex thermal degradation of commercial binder. For our investigation we have chosen the phenol-formaldehyde based resin hardened by a mixture of organic esters (PFRE) as it is widely used in the core and mould sand technology. The identified degradation products obtained during the experiments varied depending on mechanism used for pyrolysis. In the “slow” evaluation, simple compounds such as: CO, CO2,NH3,H2O, phenol and CH4 were generated. Meanwhile, during the “fl” pyrolysis (500, 700, 900 and 1100 °C), mainly phenol and its methyl and ethyl derivatives as well as benzene were released. It was determined that the pyrolysis products and their ratio depended on the temperature during the degradation process.