All issues / Volume 5 (2011) / Issue 12 (December)
This is an editorial article. It has no abstract.
This study aims to investigate the limitations and applicability of different ion exchanged zeolites as antimicrobial additive in thermoplastic polyether type polyurethanes. These composites were designed to improve the health quality of hospitalized patients by expressing both biocompatibility and relevant antimicrobial activity. The zeolites were exchanged with silver, copper and zinc ions and single, binary and ternary ion-exchanged zeolite-polyurethane composites were prepared. The antimicrobial activity and the resistance of the composites against the human environment play vital role in the applicability of the materials as a medical device therefore these properties were investigated. The antimicrobial test were performed on Methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa and Candida tropicalis. The tests showed that the efficiency of the silver ions is superior to the other single ionic systems. Besides, the binary and ternary ion-exchanged samples had similar antimicrobial efficiency regardless the type of the ions in the zeolite. The biocompatibility tests were carried out in-vitro in artificial body fluids for a period of 12 weeks. As a result of the invitro test, degradation of the composites were observed and the structural changes of the materials were detected and described by Scanning Electron Microscopy, Contact Angle measurements and Attenuated Total Reflection Fourier Transform Infrared Spectroscopy.
Microstructure and magneto-dielectric properties of the chitosan/gelatin-YIG biocomposites
E. J. J. Mallmann, J. C. Goes, S. D. Figueiro, N. M. P. S. Ricardo, J. C. Denardin, A. S. B. Sombra, F. J. N. Maia, S. E. Mazzeto, P. B. A. Fechine
Vol. 5., No.12., Pages 1041-1049, 2011
Vol. 5., No.12., Pages 1041-1049, 2011
This work is devoted to the preparation of yttrium iron garnet (YIG) ferrimagnetic biocomposites based in biodegradable chitosan and gelatin. The aim was to produce composite films containing controlled amounts of YIG to obtain a new biological material with magneto-dielectric features. Structural characterization of the biocomposites was made by scanning electron microscopy, X-ray diffraction, infrared absorption spectroscopy and thermal analysis, while the dielectric and magnetic properties were obtained from dielectric spectroscopy and magnetic hysteresis loops, respectively. The versatility of the films obtained makes them possible candidates for use as biomaterials or electronic device.
Perkalite is an unusual clay in the domain of polymer-based nanocomposites. In this paper, the use of perkalite as a filler for poly(1-butene) was investigated. Particular attention was posed on the study of the effect of this particular kind of clay on the rate of II→I phase transition of the matrix. Wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) were used to determine the structure and morphology of the samples, the degree of dispersion of the filler and to follow the kinetics of the phase transition of poly(1-butene). Mechanical properties were moreover measured. Perkalite was found to increase the rate of II→I phase transition with respect to the neat matrix, because it affected the free energy of the crystalline phase, by decreasing the perfection of the crystals. Rather than the disruption of the regular ordering at a crystalline cell level, the effect on the lamellar morphology seems to be preponderant. The fragility of perkalite layers and the substantial reduction of the tactoids did not allow to influence the entropic factor to the phase diagram of poly(1-butene), because the filler was not able to locally increase the pressure on the nascent crystalline domains. Perkalite was therefore not able to achieve a direct formation of the phase I of poly(1-butene) directly from the melt. The reduction of the size of perkalite tactoids confirmed that poly(1-butene) is very efficient in homogeneously dispersing the filler, thereby justifying the use of the materials produced in the present study as viable masterbatches for the production of polyolefin-based nanocomposites.
With the advancement of interdisciplinary approaches in today’s modern engineering, current efforts in optimal design of composites include seeking material selection protocols that can (1) simultaneously consider a series of mechanical/electrical/chemical cost criteria over a set of alternative material options, and (2) closely take into account environmental aspects of final products including recycling and end-of-life disposal options. In this paper, in addition to a review of some recent experimental and methodological advances in the above areas, a new application of multiple criteria decision making (MCDM) is presented to deal with decision conflicts often seen among design criteria in composite material selection with the help of life cycle assessment (LCA). To show the application, an illustrative case study on a plastic gear material selection is conducted where the cost, mechanical and thermal properties along with environmental impact criteria are to be satisfied simultaneously. A pure plastic gear is compared to a Polyethylene terephthalate (PET)/aluminum-powder composite alternative. Results suggest that simple MCDM models, including a signal-to-noise measure adapted to MCDM in the same case study, can be used to explore both trade-offs and design break-even points in large decision spaces as the decision maker’s perspective over environmental, material performance and cost attributes change during the design process. More advanced topics including the account of material data uncertainties are addressed.
The in-plane and through thickness permeability of unidirectional stitched carbon fiber preforms have been determined through vacuum infusion tests. The impregnation of various dry preforms with different stitching characteristics has been monitored by fiber optic sensors that have been stitched together with the dry tow to manufacture the dry preform. The experimental infusion times have been fitted by a numerical procedure based on Finite Element (FE) processing simulations. A good agreement between the numerical and experimental infusion times has been found demonstrating the potentiality of the fiber sensor system as suitable tool to evaluate impregnation times and permeability characteristics.
Efficient one-step melt-compounding of copolyetheramide/pristine clay nanocomposites using water-injection as intercalating/exfoliating aid
F. Touchaleaume, J. Soulestin, M. Sclavons, J. Devaux, F. Cordenier, P. Van Velthem, J. J. Flat, M. F. Lacrampe, P. Krawczak
Vol. 5., No.12., Pages 1085-1101, 2011
Vol. 5., No.12., Pages 1085-1101, 2011
Polyether-block-amide (PEBA) /clay nanocomposites were prepared water-assisted by twin-screw extrusion. Both organomodified and pristine (i.e. purified but non-modified) montmorillonite clays were used. A high-pressure differential scanning calorimetry analysis carried out in the processing conditions demonstrated that PEBA/water blend exhibits some miscibility and that amide blocks and water behave as a single phase. In addition to a significant decrease of the melting temperature, water injected into the melt plays a key role among the filler dispersion and prevents the matrix from degradation during melt-extrusion. This process enables the compounding of pristine clay-based nanocomposites whose dispersion state is high enough for the resulting mechanical performances in tension to be at least equivalent to what is reached with organomodified clay. Effects of the nanofiller dispersion onto the macromolecules’ mobility are detailed and fracture mechanisms are identified for the various structures.
Poly(4-vinylpyridine) (P4VP) is a widely studied polymer for applications in catalysis, humidity sensitive and antimicrobial materials due to its pyridine group exhibiting coordinative reactivity with transition metals. In this work, the non-covalent functionalization of single-walled carbon nanotubes (SWCNTs) with P4VP in CO2-expanded liquids (CXLs) is reported. It is found that P4VP stabilized SWCNTs show good dispersion in both organic solvent and aqueous solution (pH = 2). The ability to manipulate the dispersion state of CNTs in water with P4VP will likely benefit many biological applications, such as drug delivery and optical sensors. Furthermore, the structure and morphology of P4VP/SWCNTs composite are examined, with the focus on molecular weight of P4VP (MW-P4VP), the pressure of CXLs and the concentration of P4VP. It is amazing that the P4VP15470 wrapping patterns undergo a notable morphological evolution from dotlike crystals to bottle brush-like, then to compact kebab-like, and then to widely-spaced dotted kebab patterns by facile pressure tuning in the higher polymer concentration series. In other words, the CXLs method enables superior control of the P4VP crystallization patterns on SWCNTs. Meanwhile, the CXL-assisted P4VP crystal growth mechanism on SWCNT is investigated, and the dominating growth mechanism is attributed to ‘size dependent soft epitaxy’ in P4VP15470/SWCNTs composites. We believe these studies would r
Curing reaction of bisphenol-A based benzoxazine with cyanate ester resin and the properties of the cured thermosetting resin were investigated. The cure behavior of benzoxazine with cyanate ester resin was monitored by model reaction using nuclear magnetic resonance (NMR). As a result of the model reaction, the ring opening reaction of benzoxazine ring and thermal self-cyclotrimerization of cyanate ester group occurred, and then the phenolic hydoroxyl group generated by the ring opening reaction of benzoxazine ring co-reacted with cyanate ester group. The properties of the cured thermosetting resin were estimated by mechanical properties, electrical resistivity, water resistance and heat resistance. The cured thermosetting resin from benzoxazine and cyanate ester resin showed good heat resistance, high electrical resistivity and high water resistance, compared with the cured thermosetting resin from benzoxazine and epoxy resin.