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Curing Time (curing + time)
Selected AbstractsAdhesion Characteristics of PDMS Surfaces During Repeated Pull-Off Force Measurements,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Elmar Kroner Abstract To mimic the adhesive effects of gecko toes, artificial surfaces have been manufactured recently using polydimethylsiloxanes (PDMS). However, the effects of repeated contacts on the adhesive properties remain largely unexplored. In this paper we report on the effect of repeated pull-off force measurements on the adhesion behavior of PDMS (polymer kit Sylgard 184, Dow Corning) tested with a borosilicate glass probe. A decrease in pull-off force with increase in number of test cycles is found until a plateau is reached. The initial value and the rate of change in pull-off force strongly depend on the sample preparation procedure, including curing time and cross-linking. It is proposed that the behavior is due to steady coverage of the probe with free oligomers. The results are crucial for developing reusable, durable, and residue-free bioinspired adhesives. [source] Effects of curing systems and polysulfonamide pulp on the curing characteristics, mechanical properties, and swelling behavior of ethylene,propylene,diene elastomer compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2010Xiaolong Jia Abstract The effects of three curing systems and polysulfonamide (PSA) pulp on the curing characteristics, mechanical properties, and swelling behavior of ethylene,propylene,diene elastomer (EPDM) composites were investigated. The maximum torque value and the optimum curing time were highest for EPDM composites cured with a peroxide system, and they were closely followed by those cured with a sulfur system. In comparison with those cured with peroxide and phenolic resin systems, EPDM composites cured with the sulfur system showed higher mechanical properties and dimensional stability. With increasing PSA pulp content, the maximum torque value of the EPDM composites increased, whereas the optimum curing time of the composites decreased. The orientation percentage of the PSA pulp in the EPDM composites was maximum at 30 phr pulp, as determined from green strength measurements. In the longitudinal direction along which the pulp was oriented, the EPDM composites showed higher tensile strength as well as lower elongation and swelling ratios. Also, with increasing PSA pulp content, the tensile strength of the EPDM composites decreased up to 10 phr pulp and subsequently increased, whereas the elongation and swelling ratio of the EPDM composites decreased linearly. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Synthesis and evaluation of novel injectable and biodegradable polyglycolide-based compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2007Dong Xie Abstract Novel 3-arm methacrylate-endcapped biodegradable polyglycolide prepolymer was synthesized and characterized. Injectable and in situ curable composites formulated with the liquid prepolymer and bioabsorbable ,-tricalcium phosphate were prepared. The pastelike composites were cured at room temperature using a redox-initiation system. The initial compressive strengths (CSs), curing time, exotherm, and degree of conversion of the cured composites were determined. The composites showed initial yield CS ranging from 20.1 to 92.3 MPa, modulus from 0.73 to 5.65GPa, ultimate strength from 119.9 to 310.5 MPa, and toughness from 630 to 3930 N mm. Increasing filler content increased yield strength and modulus but decreased ultimate strength and toughness. Diametral tensile strength test showed the same trend as did CS test. Increasing filler content also increased curing time but decreased exotherm and degree of conversion. During the course of degradation, all the materials showed a significant burst degradation behavior within 24 h, followed by a significant increase in strength between Day 1 and Day 3, and then continuous degradation until no strength was detected. The composites with higher filler content retained their strengths longer but those with lower filler contents lost their strengths in 45 or 60 days. The degradation rate is filler-content dependent. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2977,2984, 2007 [source] The Dynamic Interaction of Water with Four Dental Impression Materials During CureJOURNAL OF PROSTHODONTICS, Issue 4 2009Dariush Hosseinpour PhD Abstract Purpose: The purpose of this work was to investigate the interaction of water with four different dental impression materials: Aquasil (Ultra XLV Type 3), Take 1 (Wash Regular Set), Genie (Light Body, Standard Set), and Impregum Garant (Soft Light Bodied Consistency). Materials and Methods: Apparent contact angles of de-ionized water made against thin horizontal sample films of the different materials under different conditions were measured from analysis of profile images of symmetrical sessile drops of water placed on the sample films using a Model FTÅ200 dynamic drop shape analysis system, which included a JAI M30 high speed CCD camera combined with a zoom microscope. Data were taken for specimens of dry ages (times following mixing) from a minimum of 20 seconds up to 1220 seconds. Imaging was started before the initial water/impression material contact, and lasted for at least 420 seconds in each case. The interval at the beginning of each run was 0.033 second, and then increased by a factor of 1.012 to the end. During the initial 3 seconds following the drop deposition, the drop's shape oscillated due to inertial effects, so apparent contact angle data during this period were neglected in all cases. All measurements were made at room temperature. The drops were enclosed in a humidified chamber that suppressed evaporation. All data were repeated at least five times, and results were analyzed where appropriate using one-way ANOVA. Microscopic images of the water/impression material interactions for fresh (uncured) materials were acquired to reveal the destructive interactions that resulted from such contact. Finally, surface tension measurements were made of water that had been contacted with material of varying dry age using the pendant drop method capability of the drop shape analysis system. These helped to assess the origin of hydrophilicity development for the different materials. Results: For short curing times (dry ages), water showed a destructive effect on the integrity of all of the impression materials, as evidenced by the formation of a crater beneath the water drop and a scum of material at its surface. These effects diminished with dry age until a critical curing time was reached, beyond which such destructive interactions were no longer detectable. These critical curing times were determined to be 80, 140, 110, and 185 seconds for Aquasil, Take 1, Genie, and Impregum, respectively. The initial contact angle following the respective critical curing time was lowest for Impregum, at 66°; while values for Aquasil, Genie, and Take 1 were 93°, 104°, and 110°, respectively. Beyond the critical curing times for the different materials, different degrees of hydrophilicity were observed. Aquasil showed the lowest final contact angle (<10°), with Impregum, Take 1, and Genie showing 31°, 34°, and 40°, respectively. Measurements of the surface tension of water after contact with the different materials suggested that for Aquasil, hydrophilicity appears to be developed through the leaching of surfactant from the material, whereas for Impregum, Take 1, and Genie, hydrophilicity is developed at least in part through a change in surface structure in contact with water. Impregum and Aquasil materials of dry ages well beyond the critical curing time exhibited a stick-slip behavior in their interline movement or contact angle evolution. This was believed to be due to the slowness in the leaching of surfactant (in the case of Aquasil) or the re-orientation of unleachable surface groups (in the case of the other materials) in comparison to the inherent kinetics of water drop spreading. Conclusions: All materials investigated in the fresh, uncured state showed qualitative decomposition when put in contact with water through the formation of a crater beneath the water drop and a scum of material at its surface. These effects diminished with curing time until beyond a critical value, no such effects were evident. The initial hydrophilicity of the materials as determined by the contact angles obtained at their respective critical dry ages was greatest for Impregum. Beyond the critical curing time, different degrees of hydrophilicity were observed, with Aquasil showing the lowest final contact angle. [source] Statistical Analysis of Strength Development as a Function of Various Parameters on Activated Metakaolin/Slag CementsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2010Oswaldo Burciaga-Díaz This investigation statistically examines the strength development on alkaline activation of metakaolin (Mk)/blast furnace slag (BFS) pastes. The main parameters studied are: BFS/Mk weight ratio (100/0, 80/20, 50/50, 20/80, and 0/100), modulus of the alkaline solutions of sodium silicate (M=SiO2/NaO2 at 0, 1, 1.5, 2), %Na2O (5%, 10%, and 15%), and curing time. Cubes were cured at 20°C for up to 360 days; the compressive strength and other characteristics were investigated. A fully factorial experimental design was used to determine the influence of each variable. The curing time and the interaction of the factors BFS/Mk ratio-%Na2O were the most important, followed by the modulus and then the %Na2O; others such as the interaction BFS/Mk ratio modulus were less important. The results indicated that the addition of Mk to BFS reduced the strength, more notably at contents above 50%. For strength development, the most effective modulus was Ms=1 and higher %Na2O were required with higher Mk loads. [source] A Numerical Model for the Optimal Vulcanization of 2D Polar Rubber Compounds Using MicrowavesMACROMOLECULAR THEORY AND SIMULATIONS, Issue 6 2009Gabriele Milani Abstract A numerical model is presented for the optimal vulcanization of 2D extruded polar rubber with microwaves and peroxides. Magnetron power and curing time are used as the input production parameters, and the output mechanical property selected for optimization is the average tensile strength of the item. A 2D thick weather strip is analyzed to validate the model. The electric field is evaluated by means of Yee cells (FDTD approach) and suitably inserted in Fourier's heat transmission law, thus allowing point-by-point temperature profiles to be determined. The temperature is then used to evaluate the degree of peroxidic reticulation, and thus the final tensile strength. A so-called alternating tangent approach based on the bisection method is finally proposed to estimate the optimal magnetron power and curing time. [source] Spectroscopic ellipsometry and ellipsometric porosimetry studies of CVD low-k dielectric filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2008P. Marsik Abstract Aurora® ELK, a porous low-k SiCOH film deposited by CVD, was used to study the effect of UV curing. Samples were cured for various curing times and the purpose of this work is to observe the effects of UV curing on optical, mechanical and structural properties of the low-k film. We have used 1) ellipsometric porosimetry to determine the porosity and the pore-size distribution and 2) nitrogen purged UV ellipsometry in a range from 2 to 9 eV to observe the changes of the dielectric function of the cured material. Additional FTIR and laser-induced surface acoustic wave measurements were performed. The porogen removal and the increase of porosity were observed, and a k-value of 2.3 was reached for the optimum curing time. However for longer curing times, densification and reduction of the porosity occurs. The growth of the hydrogen incorporation has been observed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of resin compositions on microwave processing and thermophysical properties of benzoxazine-epoxy-phenolic ternary systems filled with silicon carbide (SiC) whiskerPOLYMER ENGINEERING & SCIENCE, Issue 5 2009Chanchira Jubsilp Microwave processing of silicon carbide (SiC) whisker filled ternary systems based on benzoxazine, epoxy, and phenolic resins has been investigated using an industrial microwave apparatus at a fixed frequency of 2.45 GHz. The low viscosity molding compound and void-free cured specimens can easily be obtained from the resin mixtures. Increasing of epoxy mass fraction in the ternary systems provided a better microwave coupling, therefore, a faster curing time and higher conversion under microwave irradiation. However, the greater amount of epoxy resin in the mixture was observed to retard the traditional thermal cure process as seen in the shifting of the exothermic curing peaks to higher temperature. The higher dielectric constant of epoxy resin comparing with the benzoxazine resin can be attributed to the observed phenomenon. Additionally, benzoxazine fraction was found to render a reduction in linear thermal expansion coefficient of the ternary systems. The development of ternary systems yields the polymer systems with high flexibility in resin-curing agent mixing ratios with relatively high Tg in the broader range of mixing ratios i.e., BEP451-BEP811. Synergism in glass transition temperature of the ternary systems is also observed with the maximum Tg up to 160°C in BEP721. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] Correlating the surface area and synthesis conditions of block co-polymer templated mesoporous silicaASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010A. T. Harris Abstract In this work we investigate the influence of (1) temperature, (2) curing (post reaction ageing) technique, (3) curing time, (4) surfactant (block co-polymer) concentration, and (5) the addition of secondary (pore swelling) reagents on the surface area and structure of ordered hexagonal mesoporous silica (SBA-15). We also investigate the use of microwave preparation and curing techniques, as a precursor to the development of large-scale synthesis processes for mesoporous silica. Samples were analyzed using transmission electron microscopy and nitrogen pore size analysis. The results of the study show that it is possible to optimize the surface area of the final material in a reproducible way, by using higher hydrolysis temperatures or lower surfactant concentrations. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Degree of conversion and permeability of dental adhesivesEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 6 2005Milena Cadenaro The aim of this study was to analyse the extent of polymerization of different adhesive films in relation to their permeability. One adhesive of each class was investigated: OptiBond FL; One-Step; Clearfil Protect Bond; and Xeno III. Adhesive films were prepared and cured with XL-2500 (3M ESPE) for 20, 40 or 60 s. Polymerization kinetic curves of the adhesives tested were obtained with differential scanning calorimetry (DSC) and data were correlated with microhardness. The permeability of the adhesives under the same experimental conditions was evaluated on human extracted teeth connected to a permeability device and analysed statistically. The results showed that the extent of polymerization obtained from DSC exotherms was directly correlated with microhardness. An increased level of polymerization after prolonged light-curing was confirmed for all adhesives. Simplified adhesives exhibited a lower extent of polymerization and showed incomplete polymerization, even after 60 s. An inverse correlation was found between the degree of cure and the permeability. This study supports the hypothesis that the permeability of simplified adhesives is correlated with incomplete polymerization of resin monomers and the extent of light exposure. These adhesives may be rendered less permeable by using longer curing times than those recommended by the respective manufacturer. [source] Color stability of resin matrix restorative materials as a function of the method of light activationEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 3 2004Ralf Janda The purpose was to investigate the influence of curing devices and curing times on the yellow value (b-value) of composites, ormocers and compomers after performing a suntest (EN ISO 7491). Eight samples of Charisma (CH), Durafill (DU), Definite (DE), and Dyract AP (DY) each were light cured with Translux Energy (tungsten halogen light) for 20, 40 or 60 s and with Apollo 95-E (plasma light) for 3, 10 or 20 s. All samples were subjected to a suntest. Before and after the suntest the yellow values (b-values) were determined and the change (,b) was calculated. When cured with Translux Energy for 20 and 40 s DU, CH, and DY revealed significantly negative ,b-values. The b-value of DE remained nearly constant. When cured for 60 s, DU and DE shifted to more yellow while CH and DY still bleached a little. When cured with Apollo 95-E, a dramatic bleaching process of all materials investigated occurred after the suntest (significant negative ,b). It may be concluded that the bleaching of composites, ormocers and compomers depends on (i) the used light curing device and (ii) the chosen curing times. The tungsten halogen light provided highly significantly superior results. [source] Instrumental and Expert Assessment of Mahon Cheese TextureJOURNAL OF FOOD SCIENCE, Issue 7 2000J. Benedito ABSTRACT: To improve Mahon cheese texture assessment, the relationship between instrumental and sensory measurements was sought. For that purpose 30 pieces of Mahon cheese from different batches and 2 different manufacturers were examined. Textural characteristics at different curing times were evaluated by uniaxial compression, puncture, and sensory analysis. Significant linear correlations were found between instrumental and sensory measurements. A logarithmic model (Weber-Fechner) fitted data better than a linear one. Only 1 factor was extracted when considering all the instrumental and sensory variables, thus indicating that both sets of measurements are related to the same phenomenon. The best predictors for Mahon cheese sensory attributes were found to be cheese moisture, deformability modulus, and slope in puncture. [source] The Dynamic Interaction of Water with Four Dental Impression Materials During CureJOURNAL OF PROSTHODONTICS, Issue 4 2009Dariush Hosseinpour PhD Abstract Purpose: The purpose of this work was to investigate the interaction of water with four different dental impression materials: Aquasil (Ultra XLV Type 3), Take 1 (Wash Regular Set), Genie (Light Body, Standard Set), and Impregum Garant (Soft Light Bodied Consistency). Materials and Methods: Apparent contact angles of de-ionized water made against thin horizontal sample films of the different materials under different conditions were measured from analysis of profile images of symmetrical sessile drops of water placed on the sample films using a Model FTÅ200 dynamic drop shape analysis system, which included a JAI M30 high speed CCD camera combined with a zoom microscope. Data were taken for specimens of dry ages (times following mixing) from a minimum of 20 seconds up to 1220 seconds. Imaging was started before the initial water/impression material contact, and lasted for at least 420 seconds in each case. The interval at the beginning of each run was 0.033 second, and then increased by a factor of 1.012 to the end. During the initial 3 seconds following the drop deposition, the drop's shape oscillated due to inertial effects, so apparent contact angle data during this period were neglected in all cases. All measurements were made at room temperature. The drops were enclosed in a humidified chamber that suppressed evaporation. All data were repeated at least five times, and results were analyzed where appropriate using one-way ANOVA. Microscopic images of the water/impression material interactions for fresh (uncured) materials were acquired to reveal the destructive interactions that resulted from such contact. Finally, surface tension measurements were made of water that had been contacted with material of varying dry age using the pendant drop method capability of the drop shape analysis system. These helped to assess the origin of hydrophilicity development for the different materials. Results: For short curing times (dry ages), water showed a destructive effect on the integrity of all of the impression materials, as evidenced by the formation of a crater beneath the water drop and a scum of material at its surface. These effects diminished with dry age until a critical curing time was reached, beyond which such destructive interactions were no longer detectable. These critical curing times were determined to be 80, 140, 110, and 185 seconds for Aquasil, Take 1, Genie, and Impregum, respectively. The initial contact angle following the respective critical curing time was lowest for Impregum, at 66°; while values for Aquasil, Genie, and Take 1 were 93°, 104°, and 110°, respectively. Beyond the critical curing times for the different materials, different degrees of hydrophilicity were observed. Aquasil showed the lowest final contact angle (<10°), with Impregum, Take 1, and Genie showing 31°, 34°, and 40°, respectively. Measurements of the surface tension of water after contact with the different materials suggested that for Aquasil, hydrophilicity appears to be developed through the leaching of surfactant from the material, whereas for Impregum, Take 1, and Genie, hydrophilicity is developed at least in part through a change in surface structure in contact with water. Impregum and Aquasil materials of dry ages well beyond the critical curing time exhibited a stick-slip behavior in their interline movement or contact angle evolution. This was believed to be due to the slowness in the leaching of surfactant (in the case of Aquasil) or the re-orientation of unleachable surface groups (in the case of the other materials) in comparison to the inherent kinetics of water drop spreading. Conclusions: All materials investigated in the fresh, uncured state showed qualitative decomposition when put in contact with water through the formation of a crater beneath the water drop and a scum of material at its surface. These effects diminished with curing time until beyond a critical value, no such effects were evident. The initial hydrophilicity of the materials as determined by the contact angles obtained at their respective critical dry ages was greatest for Impregum. Beyond the critical curing time, different degrees of hydrophilicity were observed, with Aquasil showing the lowest final contact angle. [source] Spectroscopic ellipsometry and ellipsometric porosimetry studies of CVD low-k dielectric filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2008P. Marsik Abstract Aurora® ELK, a porous low-k SiCOH film deposited by CVD, was used to study the effect of UV curing. Samples were cured for various curing times and the purpose of this work is to observe the effects of UV curing on optical, mechanical and structural properties of the low-k film. We have used 1) ellipsometric porosimetry to determine the porosity and the pore-size distribution and 2) nitrogen purged UV ellipsometry in a range from 2 to 9 eV to observe the changes of the dielectric function of the cured material. Additional FTIR and laser-induced surface acoustic wave measurements were performed. The porogen removal and the increase of porosity were observed, and a k-value of 2.3 was reached for the optimum curing time. However for longer curing times, densification and reduction of the porosity occurs. The growth of the hydrogen incorporation has been observed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||