Search results for "engineering.material"
showing 10 items of 2352 documents
Buckling of a coating strip of finite width bonded to elastic half-space
2008
AbstractA solution for buckling of a stiff strip of finite width bonded to a compliant elastic half-space and subjected to uniform axial compression is presented. Approximate semi-analytical and finite element solutions are obtained and compared with a two-dimensional case of a plate on elastic foundation. The comparison demonstrates that the two-dimensional solution can be applied to predict the buckling wavelength and critical compressive strain when the width of the strip is equal to or larger than the buckling wavelength. For narrow strips, the wavelength is smaller and critical strain is higher than that of a plate on foundation.
Continuously tunable diamond Raman laser for resonance laser ionization.
2019
We demonstrate a highly efficient, tunable, ∼5 GHz line- width diamond Raman laser operating at 479 nm. The diamond laser was pumped by a wavelength-tunable intra- cavity frequency-doubled titanium sapphire (Ti:Sapphire) laser operating at around 450 nm, at a repetition rate of 10 kHz with a pulse duration of 50 ns. The Raman reso- nator produced a continuously tunable output with high stability, high conversion efficiency (28%), and beam quality (M$^{2}$ <1.2). We also demonstrate that the linewidth and tunability of the pump laser is directly transferred to the Stokes output. Our results show that diamond Raman lasers offer great potential for spectroscopic applications, such as resonance…
Core-shell PLA/Kef hybrid scaffolds for skin tissue engineering applications prepared by direct kefiran coating on PLA electrospun fibers optimized v…
2021
Abstract Over the recent years, there is a growing interest in electrospun hybrid scaffolds composed of synthetic and natural polymers that can support cell attachment and proliferation. In this work, the physical and biological properties of polylactic acid (PLA) electrospun mats coated with kefiran (Kef) were evaluated. Gravimetric, spectroscopic (FTIR-ATR) and morphological investigations via scanning electron microscopy confirmed the effective formation of a thin kefiran layer wrapped on the PLA fibers with an easy-tunable thickness. Air plasma pre-treatment carried out on PLA (P-PLA) affected both the morphology and the crystallinity of Kef coating as confirmed by differential scanning…
Synthesis of novel reactive coalescing agents and their application in a latex coating
2002
The syntheses and the performance of five glycidyl compounds as novel reactive coalescing agents are presented. The reactive coalescing agents were synthesized with moderate yields, structures were verified using spectroscopic methods, and the properties of glycidyl compounds such as boiling points and evaporation rates were measured. The applicability of five glycidyl compounds as reactive coalescing agents was tested in characterized carboxyl functional latex. Properties like pendulum hardness, gloss, and efficiency of the glycidyl compound to reduce the minimum film-formation temperature (MFFT) of the latex were measured from the cured latex films. The application test results were compa…
Comparison of cellulose nanocrystals obtained by sulfuric acid hydrolysis and ammonium persulfate, to be used as coating on flexible food-packaging m…
2016
Cellulose nanocrystals (CNCs), extracted from trees, plants, or similar cellulose-containing materials, can be used in combination with other materials to improve their performance or introduce new applications. The main purpose of this study was to compare and understand the potentialities, as coatings for Poly(ethylene terephthalate) films, of CNCs obtained starting from the same cotton linters by two different processes: sulfuric acid hydrolysis and a less common treatment with ammonium persulfate (APS), able to provide also a cellulose oxidation. The results showed that CNCs produced through the APS treatment showed higher charge densities, due to the carboxylic groups formed during the…
Rheological Response of Polyethylene/Clay Nanocomposites to Annealing Treatment
2007
The rheological response of a polyethylene/clay nanocomposite to annealing treatment under air and nitrogen atmospheres was studied. The treatment influences the rheology of the nanocomposite significantly. In particular, the viscosity and the non-Newtonian behavior dramatically increase with annealing time, and a liquid-like/solid-like transition is observed. The annealed samples were characterized by ATR-FT-IR spectrometry and it was shown that a silicate-rich layer is formed on the surface of the nanocomposite. This result was confirmed by TEM images of bulk and surface of annealed samples. It was demonstrated that the formation of this coating is the main cause of the change of rheologi…
The effect of prepolymerization of a titanium catalyst on its deactivation in propylene polymerization
1997
Propylene polymerization rate was investigated in the presence of anunsupported titanium catalyst (TiCl3) that had been modified with a Lewis base (di-n-butyl ether) and activated (precat), or not activated (cat), by being used in a suspension prepolymerization (70°C, 0.6 MPa) of an identical monomer. The initial polymerization rate was higher with the precat than with the cat catalyst. Prepolymerization was also found to enhance the kinetic stability of catalyst's active sites, presumably by reason of the prepolymerization-induced modification of catalyst's morphology. Deactivation rate constants were evaluated for the active sites of either catalyst examined.
Studies of alumina as a support of titanium catalyst for low-pressure ethylene polymerization
1986
The effect of alumina treatment with aqueous solutions of hydrochloric acid and ammonium fluoride as well as temperature of its calcination on the activity of Al-Ti/Al2O3 supported organometallic catalyst for ethylene polymerization has been studied. The dependence between the specific surface area of the support and both the kind and concentration of the modifying agent, concentration of OH-groups on Its surface and concentration of active centres with various activities is discussed with reference to the activity of the supported Al-Ti/Al2O3 catalyst. It was demonstrated that there is no simple relationship between the concentration of OH-groups on the support and the activity of the Ti-…
New concept in bioderived composites: Biochar as toughening agent for improving performances and durability of agave-based epoxy biocomposites
2021
Biocomposites are increasingly used in the industry for the replacement of synthetic materials, thanks to their good mechanical properties, being lightweight, and having low cost. Unfortunately, in several potential fields of structural application their static strength and fatigue life are not high enough. For this reason, several chemical treatments on the fibers have been proposed in literature, although still without fully satisfactory results. To overcome this drawback, in this study we present a procedure based on the addition of a carbonaceous filler to a green epoxy matrix reinforced by Agave sisalana fibers. Among all carbon-based materials, biochar was selected for its environment…
Self-Assembly of 1D/2D Hybrid Nanostructures Consisting of a Cd(II) Coordination Polymer and NiAl-Layered Double Hydroxides
2015
The preparation and characterization of a novel hybrid material based on the combination of a 2D-layered double hydroxide (LDH) nanosheets and a 1D-coordination polymer (1D-CP) has been achieved through a simple mixture of suspensions of both building blocks via an exfoliation/restacking approach. The hybrid material has been thoroughly characterized demonstrating that the 1D-CP moieties are intercalated as well as adsorbed on the surface of the LDH, giving rise to a layered assembly with the coexistence of the functionalities of their initial constituents. This hybrid represents the first example of the assembly of 1D/2D nanomaterials combining LDH with CP and opens the door for a plethora…