Search results for "Curing"
showing 10 items of 102 documents
In vitro evaluation of shear bond strength of orthodontic stainless steel brackets using transillumination
2018
Background The objective of this study was to compare the effect of transillumination techniques to conventional light curing on shear bond strength (SBS) and adhesive remnant index (ARI) of orthodontic stainless steel brackets. Material and Methods 240 extracted human maxillary incisors, canines and premolars were randomly separated into four control and four experimental groups, based on tooth type. Labio-lingual thickness was measured. Control groups were light cured from buccal surface and experimental groups from lingual surface (transillumination) from four directions (mesial-distal, incisal-direct, direct, mesial-distal-incisal). SBS was measured using an Instron machine and ARI eval…
Noninvasive monitoring of polymer curing reactions by dielectrometry
2011
A microwave sensor system for the noninvasive monitoring of the curing process of a thermoset material placed inside a metallic mold is described. The microwave sensor is designed as an open-ended coaxial resonator with a curved surface adapted to the mold inner shape. The analysis of the microwave resonator comprises a recently developed method for deembedding the effect of coupling network in overcoupled resonators, so the range of permitted measurements encompass both low and high dielectric losses of polymeric materials. Results show that noninvasive, continuous monitoring of the microwave dielectric properties of the thermoset material can be performed in real time, allowing one to che…
Study of the influencing effect of pigments on the photoageing of terpenoid resins used as pictorial media
2006
Abstract Terpenoid resins have been mainly used as components of pictorial varnishes and binding media from ancient times. In such latest instances, the resin is mixed with pigments affecting its physical and chemical properties. A new procedure based on gas chromatography–mass spectrometry (GC/MS) has been applied, in this work, in combination with Fourier transform infrared spectroscopy (FTIR), with the aim of determining the changes undergone by di- and triterpenoid resins employed as components of binding media. The GC/MS method is based on the derivatisation of these resins using trimethylsilylimidazol. Characterization of the main components of the di- and triterpenoid fractions and t…
Leach-Proof Sol–Gel Microcapsules as Curing Agents for One-Pot Thermosetting Resins
2013
The sol-gel microencapsulation of free-radical initiator benzoyl peroxide in sol-gel methyl-modified silica microcapsules of core/shell geometry allows curing of acrylate-based polyurethane and polyester resin formulations sprayed from a pressurized can without the need to compartmentalize reactants from the initiator to cross-link. These results open the route to widespread application of sol-gel microcapsules to efficiently cure polymer and composite mixtures that are widely used as functional coatings, molding compounds, adhesives, and sealants.
FTIR isothermal cure kinetics and morphology of dicyanate ester resin/polysulfone blends
2005
Abstract The isothermal cure of a dicyanate ester monomer by “in situ” Fourier transform infrared spectroscopy (FTIR) has been investigated. The degree of cyanate conversion and the kinetic parameters have been determined for cobalt catalyzed and uncatalyzed resin as well as for polysulfone (PSF) modified systems at different curing temperatures. The cyanate conversion increases with the increment of temperature and with the addition of a catalyst, but it does not vary with the addition of PSF. In all the systems studied, the rate of reaction showed a second-order dependence on the cyanate concentration in the kinetically controlled stage. Moreover, the addition of PSF generates a matrix wi…
Cure monitoring of catalysed cyanate ester resins
2000
The cure behaviour of two bisphenol A-based cyanate ester resins, AroCy B10 and B30, catalysed by copper acetylacetonate and nonylphenol was studied. For this purpose, differential scanning calorimetric (DSC) and rheological measurements were carried out at temperatures between 130 and 170 °C. The cyanate conversion profiles are fitted with a second-order rate law in the kinetically controlled regime where a good time–temperature superposition is attained. However, it is necessary to add an empirical kinetic term to give a good description of the entire range of curing. Simultaneously, times to gelation and vitrification have been determined by dynamic rheological measurements over the same…
Morphology and thermal behavior of dicyanate ester-polyetherimide semi-IPNS cured at different conditions
2000
A high-temperature thermosetting bisphenol-A dicyanate, BADCy was modified with polyetherimide, PEI, at various compositions. Phase separation and rheokinetics through curing were studied by optical microscopy, dynamic and isothermal differential scanning calorimetry, and rheological measurements. The PEI phase separated at the early stages of curing, well before gelation, and did not affect the polycyclotrimerization kinetics. The phase structure and thermal properties of the final network were investigated as a function of the PEI content and cure temperature. For this purpose, dynamic mechanical analysis, scanning electron microscopy studies, and thermogravimetrical analysis were carried…
Optimal manufacturing and mechanical characterization of high performance biocomposites reinforced by sisal fibers
2018
Abstract The increasing interest about eco-sustainable materials in the industrial production (automotive, civil construction, packaging), has led to the increase of the research works dealing with biocomposites. However, until now the most attention has been devoted to the development of short fiber biocomposites for non-structural applications, whereas only a few works have considered high performance biocomposites for structural applications. Consequently, the development of structural biocomposites from robust natural fibers, as sisal fibers, is a result expected from the scientific community, but not yet achieved. In order to give a contribution to the implementation of high performanc…