Curing Procedure Research Articles

Optical bonding with fast sol-gel

We investigate here the properties of fast sol-gel for optical bonding. The precursors of the fast sol-gel material are organically modified alkoxides generating a transparent hybrid (organic-inorganic) substance with silica glass-like properties whose index of refraction can be modified by the addition of various metal-oxides. The fast sol-gel method consists of rapid fabrication of a viscous resin and its subsequent dilution for long shelf life use. This material, when used as an adhesive offers the option of either a thermal or UV curing procedure. We demonstrate a bonding strength of ~ 10 MPa when a 15 µm layer is applied between two glass elements. The bonding remained stable after an extensive -40ºC – 120ºC temperature cycling with minimal residual solvent evaporation at 150ºC. The fast sol-gel material was tested for optical bonding between silica bulks, between silica bulk and silicon wafers and as an adhesive in silica fibre couplers.

Investigation of the Curing Mechanism of Foamed Asphalt Mixes Based on Micromechanics Principles

This study investigated the curing mechanism of foamed asphalt mixes. Various laboratory strength and stiffness tests were performed on mixes with various asphalt and portland cement contents, and the specimens were subjected to two relatively extreme curing conditions. It was found that portland cement enhances certain properties of foamed asphalt mixes by strengthening the mineral filler phase, with the curing mechanism similar to that of typical cement treated materials. The curing mechanism of foamed asphalt mastic is primarily related to water evaporation. The bonding between asphalt mastic and aggregate particles cannot fully develop until most of the water retained at the interface evaporates. This bonding, once formed, is only partially damaged by reintroduced water. This proposed mechanism was supported by observations of fracture faces on tested specimens. A long-term curing study confirmed the validity of this mechanism regardless of the curing duration. Standard curing procedures are proposed for use in project level mix design and evaluation based on the findings.

Effect of tree types of light-curing units on 5-year colour changes of light-cured composite

The purpose of this study was to determine colour changes in a composite cured with tungsten-halogen, light-emitting diode (LED) or a plasma arc after 5 years. Five specimens 10 mm in diameter and 2 mm in height were prepared using Hybrid (Clearfil AP-X) composite for each test group. The corresponding specimens were cured with a tungsten-halogen curing light, a LED unit or with a plasma arc. Specimens were stored in light-proof boxes for 5 years after the curing procedure to avoid further exposure to light and stored in 37 degrees C in 100% humidity. Colorimetric values of the specimens immediately after curing and after 5 years were measured using colorimeter. The DeltaE*( ab ) values varied significantly depending on the curing unit used (p < 0.001). Curing time did not affect the colour changes of the specimens (p = 0.4). The results of this study suggest that composite materials undergo measurable changes due to the curing unit exposure.

Development of a photocurable gelatin-based gelation material for application to periodontal regeneration

Novel photocurable materials, comprised mixed aqueous solutions of photoreactive gelatin – gelatin partially derivatized with eosin – and polyamine, which is a polymer of N, N-dimethylaminopropylacrylamide, were designed. The materials had appropriate viscosity for shape formation at 37 °C. When photoirradiated with a clinically used visible light source, the materials were almost completely converted to hydrogels to fix their shape in the desired form within several tenths of a second. Cells that were seeded on the eosin–gelatin-coated surface showed good proliferation. Negligible cytotoxicity of eosin–gelatin was confirmed when culturing was performed in the presence of a large amount of eosin–gelatin. The developed photocurable materials could be converted to a hydrogel with desired physical property change by using a convenient curing procedure of photoirradiation at any desired time and in any shape with minimal cytotoxicity, which was appropriate for the application in periodontal tissue regeneration.

On the Nature of the Multi-Zone Interphase of a Thermoset/Thermoplastic Composite–An Analysis Employing Dynamic-Mechanical Thermal Analysis and Nanoindentation

As a model system for a thermoplastic/thermosetting composite material, a stoichiometric amine-epoxy formulation was cured in the presence of the thermoplastic poly(vinylpyrrolidone) (PVP). The epoxy system consisted of the resin diglycidyl ether of bisphenol A (DGEBA) and the aromatic curing agent 4,4′-diaminodiphenylsulfone (DDS). Using nanoindentation, profiles of the sample Young's modulus, E s , the hardness, H, as well as the plasticity index, ψ, were measured and found to show significant variations. From the hardness profile three different interphase (IP) zones can be identified. They add up to a total interphase width of ∼ 230 microns. Further information on the nature of the interphasial zones was deduced from temperature-dependent dynamic mechanical thermal analysis (DMTA) and energy-dispersive analysis of X-rays (EDX). In particular, the outer edge of zone Z2 is consistent with the width of the amine depletion zone. Finally, the different IP zones are discussed in terms of the diffusion processes taking place during the epoxy curing procedure.

Inkjet single pass color printing with UV curable ink.

Studies on an inkjet printhead, capable of 847 mm/s printing rate with 600 dpi single pass resolution for 108 mm print swath, were reported by one of the authors. In this study, the printhead is applied to UV curable inks for color prints on non absorbable media. Four of the printheads are arranged for a color printing system using Y, M, C and K UV curable inks accompanied with a UV lamp. Studies are made on effects of printing and curing procedure for image quality achieved by the printer. As a general tendency, it is confirmed that the faster a print speed becomes, the image quality got improved in terms of sharpness. The results reveal dependency of image quality upon a time that allows drops to be driven on a media by surface tension before the curing. Also, the images obtained by the single pass printing with a certain pass speed shows potential for practical applications in terms of image quality as well as productivity although it is limited in a certain application area that uses relatively simple images.

Curing Behaviour of Epoxy Resin with a Diamine Containing Heterocyclic Rings

The curing behaviour of a new epoxy curing agent, 2, 6-di (p-aminophenyl) benzo[1.2.5.4] bisoxazole (DIABO) was discussed. Diglycidyl-4, 5-epoxycyclohexane -1,2-dicarboxylate (TDE) was cured with a mixture of DIABO and diaminodiphenylsulfone (DDS). The aspects investigated including the curing procedure, reaction kinetics parameters and the heat resistance of the product. Average apparent activation energy of the resin's curing reaction was 63.55 kJ/mol, calculated according to the Kissinger and the Ozawa methods. The glass transition temperature was 261 °C and 257 °C determined by torsional braid analysis (TBA) and differential scanning calorimetry (DSC) respectively. The integral procedural decomposition temperature (IPDT) was 814 °C, respectively. Char residue was 44.58% at 572 °C. Compared to cure with TDE/DDS, these properties were improved by 18%, 8%, 30% and 50%, respectively.

The resistance of compressed spun concrete members reinforced by high-strength steel bars

The expediency of using precast spun concrete columns and other members of annular cross sections reinforced by high-strength steel bars is discussed. Test material properties and production, curing and testing procedures, response factors and ultimate compressive stresses of plain and reinforced spun concrete specimens are presented. The strength and strain features of compressed tubular reinforced concrete members are considered. Modeling of a bearing capacity of eccentrically loaded members of annular cross sections is based on the concepts of bending with an concentrical force and compression with a bending moment. The comparison of modeling and test data of concentrically and eccentrically loaded members is analysed.

The effect of the heat-treatment regime on the properties of reactive powder concrete

The influence of the curing regime on the mechanical properties and microstructure of ultra-high-strength mortar was studied. Nine different curing procedures were applied in which the start and duration of the heat treatment were varied. The studied mortars had a water-to-binder ratio of 0.17 and additions of amorphous silica fume and fine quartz filler. The microstructure and microchemistry were investigated by electron scanning microscopy and mercury intrusion porosimetry. The results revealed that longer heating times increased the degree of hydration, refined the microstructure and resulted in higher ultimate compressive strength. Very late and very early application of the heat treatment caused a lower degree of hydration and a smaller long-term increase of compressive strength. The scanning electron microscopy investigation revealed the formation of one hydration rim around anhydrous cement particles and the presence of a hollow shell in all investigated specimens.

Effect of the additional application of a resin layer on dentin bonding using single-step adhesives

The purpose of this study was to prove that an intermediate resin layer (IRL) can increase the bond strength to dentin by reducing the permeability of single-step adhesives. Flat dentin surfaces were created on buccal and lingual side of freshly extracted third molar using a low-speed diamond saw under copious water flow. Approximately 2.0 ㎜ thick axially sectioned dentin slice was abraded with wet #600 SiC paper. Three single-step self-etch adhesives; Adper Prompt L-Pop (3M ESPE, St Paul, MN, USA), One-Up Bond F (Tokuyama Corp, Tokyo, Japan) and Xeno III (Dentsply, Konstanz, Germany) were used in this study. Each adhesive groups were again subdivided into ten groups by; whether IRL was used or not; whether adhesives were cured with light before application of IRL or not; the mode of composite application. The results of this study were as follows; 1. Bond strength of single-step adhesives increased by an additional coating of intermediate resin layer, and this increasement was statistically signigicant when self-cured composite was used (p < 0.001). 2. When using IRL, there were no difference on bond strengths regardless the curing procedure of single-step adhesives. 3. There were no significant difference on bond strengths between usage of AB2 or SM as an IRL. 4. The thickness of hybrid layer was correlated with the acidity of adhesive used, and the nanoleakage represented by silver deposits and grains was examined within hybrid and adhesive layer in most of single-step adhesives. 5. Neither thickness of hybrid layer nor nanoleakage were related to bond strength.

The Effect of Curing Conditions on the Properties of Silica Modified Glass Fiber Reinforced Epoxy Composite

The effects of curing conditions on the mechanical properties of glass fiber reinforced epoxy composites under different fiber prestressing levels were quantitatively studied. The composite samples were prepared with silica particle modified continuous E-glass fibers, epoxy resin matrix, fiber prestressing and step curing processing. Room temperature cured and isothermal high temperature cured composite samples, with the same content and structure, were made to study the difference of three curing conditions on a quantitative level. Based on the test results of flexural, shear, and impact properties of the composite samples, it was found that the step curing procedure generates composite samples with up to 47% and 14% increased properties than room temperature cured and isothermal high temperature cured samples, respectively, when manufactured under the same fiber prestressing level. The possibility of generating an optimum residual stress within the samples during processing is proposed and discussed to explain the contribution of the step curing process to the composite properties.

Evidence for a three-zone interphase with complex elastic–plastic behaviour: nanoindentation study of an epoxy/thermoplastic composite

A detailed study of the mechanical interphase (IP) between an amine-cured epoxy and the amorphous thermoplastic polyvinylpyrrolidone (PVP) was performed. The amine curing agent was diaminodiphenylsulphone (DDS). With 170 °C, the curing temperature was close to the glass transition temperature of PVP. Using a depth-sensing indentation setup equipped with a Berkovich indenter, force penetration curves were measured at different positions on the cross-section of an epoxy/PVP/epoxy sandwich specimen. Profiles of the sample Young's modulus, Es, the hardness, H, and the plasticity index, ψ, were analysed as a function of the distance from the epoxy/PVP interface. Each of these quantities showed significant variations. Furthermore, the profile of the ratio between the reduced modulus of the tip–sample contact, Er, and the hardness is shown to reflect the profile of the plasticity index, that is the relative amount of plastic indentation work. A relationship is presented that allows the calculation of the plasticity index from the ratios Er/H and hf/hc, where hf and hc denote the final depth and the contact depth, respectively. Although the Young's modulus shows strong variations, the hardness appears to be the most sensitive parameter for IP property variations. Three different zones can be identified from the hardness profile, with respective widths of ∼21.3, 52.5 and 160.9 µm, which add up to a total IP width of ∼234.7 µm. Zone Z1 is located next to the PVP layer. The outer edge of zone Z2 is located at a position similar to the one of the amine depletion zone. The latter was detected by means of energy-dispersive analysis of x-rays and its width is ∼71 µm. Inspection of the residual imprints shows a larger plastic deformation for zone Z1, in agreement with the high values of the plasticity index and of the creep deformations. From these grounds, the different IP zones are discussed in terms of the diffusion processes taking place during the epoxy curing procedure. Zone Z1 is associated with bi-directional interdiffusion across the initial interface. Zone Z3 can be attributed to long-ranging effects reaching far beyond the amine depletion zone.

Effect of curing order on the curing kinetics and morphology of bisGMA/DGEBA interpenetrating polymer networks

AbstractThe curing kinetics and morphology of an interpenetrating polymer network (IPN) formed from an epoxy resin (DGEBA) cured by an imidazole (1‐MeI) and a dimethacrylate resin (bisGMA), cured by low‐ and high‐temperature peroxide initiators (TBPEH and DHPB, respectively) have been studied by temperature‐ramping DSC, isothermal near‐infrared (NIR), DMTA and small‐angle neutron scattering (SANS). bisGMA and DGEBA are polar and chemically similar thermosetting resins which should enhance the miscibility of their IPNs. The phase structure was controlled by varying the curing procedure: the order of gelation of the components is dependent on the choice of low‐ and high‐temperature initiators for bisGMA and this affects the morphology formation. In the cure of the bisGMA/TBPEH:DGEBA/1‐MeI system, the dimethacrylate cures first. For isothermal cure studies at 80 °C, the final conversion of the epoxy is reduced by high crosslinking of the methacrylate groups in the IPN causing vitrification before full cure. The dimethacrylate conversion is enhanced due to plasticisation with unreacted DGEBA, and its cure rate is increased due to accelerated decomposition of TBPEH initiator by 1‐MeI. SANS revealed that phase separation occurs in these IPNs with domains on the scale of 6–7 nm. In the cure of the bisGMA/DHBP:DGEBA/1‐MeI system, the epoxy cures at a similar rate to that of the methacrylate groups. For isothermal cure studies at 80 °C, similar final conversions of the epoxy have been observed except for the 75:25 IPN. The cure rate of the methacrylate groups in the IPN is increased also due to accelerated decomposition of DHBP initiator by 1‐MeI, and the extent of accelerated decomposition for DHBP is stronger than that in the TBPEH‐based systems. SANS studies revealed that this system is more homogeneous due to the rapid formation of the dimethacrylate gel in the presence of the preformed epoxy network which interlocks the networks at low degrees of methacrylate conversion. Copyright © 2006 Society of Chemical Industry

Imprecise excision of insertion element IS5 from the fliC gene contributes to flagellar diversity in Escherichia coli

Motile strains of Escherichia coli K12 carrying both a chromosomal fliC-H48 gene and a plasmid encoded fliC-H4 gene express both types of flagellins, which are coassembled into functional flagella. By using flagellar-H48-specific antiserum and a plasmid curing procedure, nonmotile mutants were found that carried an IS5 insertion in the chromosomal fliC-H48 gene. Motile revertants were isolated that showed deletions of the IS5 element together with sections of the fliC-H48 gene resulting in an altered flagellar serotype in these strains. As IS5 elements were found associated with 35 of 53 known H-types in wildtype E. coli strains, this insertion element might play a major role in serotype diversity.

Synthesis and characterization of oligosalicylaldehyde-based epoxy resins

AbstractThe synthesis of a new epoxy resin of oligosalicylaldehyde by the reaction with epichlorohydrin is reported. New resin’s epoxy value and chlorine content were determined and found to be 25% and 1%, respectively. The characterization of the new resin was instrumented by FTIR, 1H NMR, scanning electron microscopy, and thermal gravimetric analyses. TGA results showed that the cured epoxy resin has a good resistance to thermal decomposition. The mass losses of cured epoxy resin were found to be 5%, 10%, 50% at 175°C, 240°C, and 400°C, respectively. On the curing procedure the resin was cured with polyethylenepolyamine at 25 °C for 8 h and 100°C for 1.5 h. The FTIR spectrum of new epoxy resin gave the peak of oxirane ring at ṽ = 918 cm−1.

Resin composite shrinkage and marginal adaptation with different pulse‐delay light curing protocols

The aims of this study were, first, to measure shrinkage induced by different methods of pulse-delay light curing and, second, to verify their influence on the marginal adaptation of class V restorations in enamel and dentin. Eight groups, comprising seven groups (n = 6) with different pulse-delay parameters and a control group, were compared for dynamic linear displacement and force by using a fine hybrid composite. Based on these results, the pulse-delay curing procedure with the lowest shrinkage force was chosen and tested against the control group with respect to marginal adaptation in class V restorations (n = 8) before and after simultaneous thermal and mechanical loading. Statistically significant differences between groups were found for both shrinkage properties tested, with one pulse-delay group giving the lowest overall shrinkage values. However, the percentages of 'continuous margin' of this group, and of the control before and after loading, were not significantly different in dentin, whereas a significantly lower percentage of 'continuous margin' was detected in the pulse-delay group in enamel after loading.

Structural and Mechanical Behavior of Boron Nitride Fibers Derived from Poly[(Methylamino)Borazine] Precursors: Optimization of the Curing and Pyrolysis Procedures

A series of boron nitride fibers were prepared by varying the tension applied on a same lot of poly(methylamino)borazine fibers during their pyrolytic conversion at 1800°C. Their microstructure/microtexture was studied by X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy investigations. Such analyses showed that ceramic fibers presented good crystallinity, but crystallites oriented along the fiber axis with fiber stress. It is most interesting that stretching was essentially effective during the pyrolysis to 1000°C, preventing fiber crimping, and decreasing the fiber diameter. Therefore, the fiber strength increased, while the fiber modulus also increased because of an improvement of the basal layer orientation along the fiber axis.

Effects of bacterial strains on the development of the ripening flavor of cured pork loins

ABSTRACTTo determine the effect of bacteria on the development of the ripening flavor of cured meat, pork loins were cured with pickles containing 8 or 16% sodium chloride at 0 and 8°C. The bacterial flora, total free amino acid content and total free fatty acid content in the cured loins, sensory properties of cooked pork loins and the relationships between the proteolytic and lipolytic activities of isolates and curing conditions were investigated. Desirable bacteria, including salt‐tolerant bacteria and lactic acid bacteria, were predominant under the condition of 8% sodium chloride in the pickles and a curing temperature of 8°C. The total free amino acid content and total free fatty acid content at a curing temperature of 8°C were higher than those at 0°C. Cooked pork loins cured in pickles containing 8% sodium chloride at a temperature of 8°C for more than 7 days were preferred in terms of color, flavor and taste. Before the curing procedure, gram‐negative bacteria (Vibrio, Acinetobacter, Pseudomonas and Enterobacteriaceae) were predominant in the pork loins. During the curing period, the numbers of viable gram‐positive bacteria (Micrococcus, Staphylococcus and Pediococcus) increased and the numbers of viable gram‐negative bacteria decreased. Strains of Micrococcus and Staphylococcus with proteolytic and/or lipolytic activities in cured meat also increased during the curing period and were more predominant in the pork loins cured in pickles containing 8% sodium chloride and at a curing temperature of 8°C than in pork loins cured in pickles containing 16% sodium chloride and at a curing temperature of 0°C. The actions of these bacteria were thought to be important factors affecting the flavor of the cured pork. Micrococcus and Staphylococcus with proteolytic activity might contribute to the development of the ripening flavor of ham. The results of the present study together with the results of further investigations on the relationships of the enzyme activities of Micrococcus and Staphylococcus in cured meat with a preferable flavor would be useful for establishing a novel effective method for using bacteria to produce ham of a high quality.

Flexural and Shear Properties of Silica Particle Modified Glass Fiber Reinforced Epoxy Composite

The objective of this study is to develop a new method of manufacturing glass fiber reinforced epoxy composites and to quantitatively show that the properties of such a new material are superior to that of a conventional fiber reinforced polymer composite of the same material base composition. To achieve this objective, the glass fiber (GF) reinforced epoxy composite samples are prepared in four different ways: Method A, using ‘clean’ GF as the reinforcement (i.e., with no modification or additional treatment to the as-received fiber); Method B, modifying the surface of the GF with silica particles before applying in the composite system; Method C, prestressing the clean GF during the curing procedure of the composite; and Method D, prestressing the silica modified GF during the curing procedure of the composite. Preparation by Method D is the newly developed method. The finished composite samples are tested by the three-point bend test and the short-beam shear test under ASTM standard conditions. The results indicate that the composites prepared by the new method, which include the GF surface modification and the GF prestressing preparation conditions, have an excellent combination of properties when compared to the specimens made by the other three methods.

Testing and Analysis of the Inner Stress in Adhesive Coating Layer Using Strain Gauges and Finite Element Method

The residual stress in epoxy adhesive layer deposited on metal and other substrate at room temperature is studied. With embedded strain gauges in arranged depth of epoxy layer, the strain changes in the adhesive layer induced by the curing procedure and the changes of ambient temperature were measured to evaluate the changes of residual stress in place during a period after the curing procedure finished. The actual strain in epoxy adhesive layer from curing is used to estimate the residual stresses in it. While taking the strain obtained from the surface of the adhesive layer as free strain, the residual stress can be calculated and presented a strongly cyclic variation with a period of 24 h. The inner stress is also analyzed using the finite element method.