This is an editorial article. It has no abstract.
ESR investigation of NR and IR rubber vulcanized with different cross-link agents
P. Posadas, M. A. Malmierca, A. Gonzalez-Jimenez, L. Ibarra, A. Rodriguez, J. L. Valentin, T. Nagaoka, H. Yajima, S. Toki, J. Che, L. Rong, B. S. Hsiao
Vol. 10., No.1., Pages 2-14, 2016
Vol. 10., No.1., Pages 2-14, 2016
This study evaluates the formation of radical species in natural rubber (NR) and poly-isoprene rubber (IR) during the vulcanization process and the uniaxial deformation of the formed networks by means of Electron Spin Resonance (ESR). Vulcanization of NR and IR always shows a radical pathway, where the different vulcanization systems dictate the concentration of radical species in the course of this complex process. The greatest concentration of radicals were detected during the vulcanization with sulfur/accelerator based on efficient systems (EV), followed by conventional (CV) and sulfur donor systems, whereas azide and organic peroxide agents showed smaller concentration of radicals. Independently of the vulcanization system, certain amount of radicals was detected on the vulcanized samples after the end of the vulcanization process. Comparison between different matrices demonstrates that NR always shows higher concentration of radicals than IR in the vulcanization process as well as during uniaxial deformation, fact that could be associated to the presence of nonrubber components in NR.
To achieve uniform curing of resin, internal heating with the addition of carbon nanotubes (CNTs) has attracted considerable attention. Numerical simulations of the residual stress in CNT-filled resins cured by an electric field were carried out in the present study, taking into account the CNT dispersion within the resins. The simulations were based on an unsteady-heat-transfer equation and the cure reaction; the residual stress due to the thermal expansion and cure shrinkage was calculated using a finite element method. In addition, microscope images of actual CNT-filled resins were used for modeling the inhomogeneous electrical conductivity due to CNT aggregates. The simulation results show that, compared to external heating, Joule heating, or resistive heating, in which a conductive material itself generates heat from the passage of an electric current, enables more uniform curing and generally suppresses the residual stress. However, high local residual stress was observed around the high-electrical conductivity region in the model with inhomogeneous electrical conductivity. The present results thus highlight the need to take into account the inhomogeneity of CNT-filled resins for accurate evaluation of the residual stress.
The present paper investigates how the presence of nanofiber interleaves affects the compressibility of the layup during manufacturing of the composites and hence determining the theoretically attainable fiber volume fraction at the given processing pressure. The results show that up to the interleave areal density of 10 g/m2 per nanofiber layer the decrease of fiber volume fraction does not exceed 3% for a laminate of carbon fiber woven fabric. Interleaves inside a fabric laminate are more compressible than a plain electrospun veil. It can be explained as the nanofibers penetrate between the carbon fibers when applying compression during composite manufacturing. It can be stated that there is a strong interference between the interleaves and the carbon reinforcement, which can lead to effective toughness improvement of the composite without significant alteration of fiber volume content.
Polyhydroxyalkanoates are a family of natural polyesters being produced as intracellular carbon and energy reserves by a wide variety of microorganisms. They have developed rapidly in both research and development efforts globally in the last 15 years. Till now, over 100 different types of PHAs have been successfully biosynthesized using both genetic engineering and fermentation techniques. Their unique biodegradable, biocompatible and thermoplastic characteristics make PHAs promising candidates for the commodity and biomedical applications. This review focused on the chemical synthesis of the derivatives of the biosynthesized PHAs.
A simple and efficient method was presented for chemical functionalization of multi-walled carbon nanotubes (MWCNTs) with vitamin B1. Poly(ester-imide) (PEI) based nanocomposites were prepared by the incorporation of different amounts of modified MWCNTs (5, 10, 15 wt%) into a chiral and biodegradable PEI by solution blending and ultrasonic dispersion methods. The chiral PEI was produced by a step-growth polymerization of chiral diacid with 4,4'-thiobis(2-tertbutyl-5-methylphenol). Spectroscopic and microscopic techniques were used to examine the chemical structure, morphology and thermal stability of the functionalized MWCNTs and the obtained nanocomposites. The microstructure study revealed the homogeneous dispersion of modified MWCNTs throughout the PEI matrix. Thermogravimetric analysis results confirmed that the heat stability of the prepared composites was improved compared to the pure PEI.
Elastomagnetic effect (strain induced by magnetic field application) and piezoresistivity (change of electron conductivity due to an induced strain) are coupled in composite materials constituted by magnetic and conductive microparticles into an elastic matrix. On the basis of these effects, the principle of a new method to read magnetization direction changes, in a random sequence, is proposed and experimentally demonstrated. We have produced new composite magnetopiezoresistive samples, constituted of thin chip shaped Fe microparticles inside a silicone matrix, which under an applied magnetic field along their longitudinal axis, undergo an induced strain depending on the local magnetization direction. The resulting resistivity change can be easily detected and used to deduce the local magnetization direction. The magnetization and strain processes are reversible so that after the removal of external magnetizing field the sample is ready for new measurements. A demonstrator prototype has been conceived, produced and tested. The experimental results provide interesting data encouraging to continue the research towards nano-scale devices in order to pursue the intriguing perspective to achieve a magnetic field gradient sensitivity able to reveal magnetization of semipermanent nanomagnets, polarized ‘up’ and ‘down’.
Pyrolytic carbon black (CBp) and pyrolytic oil (Op) made from used tires were used in natural rubber (NR)/styrene-butadiene rubber (SBR) blends. The effects of CBp and Op on the processing properties, the mechanical properties and the dynamic mechanical properties of the NR/SBR blends were investigated and compared with a control sample that was prepared with N550 and commercial process oil. It was found that the effect of CBp on the processing properties of the NR/SBR blends was similar to that of N550. With the increase of the CBp content, the curing properties of the NR/SBR blends changed little. The reinforcing effect of CBp was inferior to that of N550. With the increase of the CBp content, the tensile strength, tear strength and modulus at 100% elongation of the NR/SBR vulcanizates decreased significantly. Dynamic mechanical properties of the NR/SBR blends were also affected and all samples comprising CBp have a higher tan δ than control sample. It is suggested that the low surface area and high ash content of CBp strongly effects all of these property changes of the NR/SBR blends. The morphology and distribution of the carbon black particles are studied using a scanning electron microscope. It was also found that with the increase of the Op content, the properties of the NR/SBR blends were strongly affected due to the high sulfur content of Op, which produced a high crosslinking density.