Uncured Composite Research Articles

Experimental and Simulative Analysis of the Pressure Development in a Closed Injection Pultrusion Process with Multiple Chamber Geometries

The use of innovative higher-performance highly reactive resin systems requires an enhancement of the established method of fiber impregnation (open bath) towards closed resin-injection pultrusion (CIP), due to the short pot life of the resin systems. The result is that the open bath is developed into a closed injection and impregnation chamber ("ii-chamber"). In this study, three parameters-resin viscosity, opening angle and opening factor at the injection point on the ii-chamber-are varied, each in three stages. For each set of parameters, a pultrusion trial is conducted and the process pressures in the ii-chamber and pultrusion die measured. This enables direct feedback via the process conditions of the as yet uncured composite. The data obtained are used to validate a newly developed simulation model. The model is based on Darcy's law, which has been extended to take fiber movement into account and thus represent the resulting pressure increase in the die. The flexible ii-chamber and die concept enhance our understanding of the processes taking place in the die system. The sensitivity of the process pressures can be shown for the three influencing variables. The experiment shows that of the three influencing variables investigated, viscosity has the greatest sensitivity to pressure development. In general, it can be said that over the length of the pultrusion die system, the pressure level increases across the three measuring points.

Analytical model for the transient permittivity of uncured TiO 2 whisker/liquid silicone rubber composites under an AC electric field

The electric field grading of dielectric permittivity gradient devices is an effective way of enhancing their insulation properties. The in-situ electric field-driven assembly is an advanced method for the fabrication of insulation devices with adaptive permittivity gradients, however, there is no theoretical guidance for design. In this work, an analytical model with a time constant is developed to determine the transient permittivity of uncured composites under an applied AC electric field. This model is based on optical image and dielectric permittivity monitoring, which avoids the direct processing of complex electrodynamics. For a composite with given components, the increased filler content and electric field strength can accelerate the transient process. Compared with the finite element method (FEM) based on differential equations, this statistical model is simple but efficient, and can be applied to any low-viscosity uncured composites, which may contain multiple fillers. More importantly, when a voltage is applied to an uncured composite insulating device, the proposed model can be used to analyse the spatiotemporal permittivity characteristics of this device and optimise its permittivity gradient for electric field grading.

In Situ Alloying of Thermally Conductive Polymer Composites by Combining Liquid and Solid Metal Microadditives.

Room-temperature liquid metals (LMs) are attractive candidates for thermal interface materials (TIMs) because of their moderately high thermal conductivity and liquid nature, which allow them to conform well to mating surfaces with little thermal resistance. However, gallium-based LMs may be of concern due to the gallium-driven degradation of many metal microelectronic components. We present a three-component composite with LM, copper (Cu) microparticles, and a polymer matrix, as a cheaper, noncorrosive solution. The solid copper particles alloy with the gallium in the LM, in situ and at room temperature, immobilizing the LM and eliminating any corrosion issues of nearby components. Investigation of the structure-property-process relationship of the three-component composites reveals that the method and degree of additive blending dramatically alter the resulting thermal transport properties. In particular, microdispersion of any combination of the LM and Cu additives results in a large number of interfaces and a thermal conductivity below 2 W m-1 K-1. In contrast, a shorter blending procedure of premixed LM and Cu particle colloid into the polymer matrix yields a composite with polydispersed filler and effective intrinsic thermal conductivities of up to 17 W m-1 K-1 (effective thermal conductivity of up to 10 W m-1 K-1). The LM-Cu colloid alloying into CuGa2 provides a limited, but practical, time frame to cast the uncured composite into the desired shape, space, or void before the composite stiffens and cures with permanent characteristics.

Определение параметров формования отверстий в неотвержденном тканом композите методом прокалывания заостренным индентором

Определение параметров формования отверстий в неотвержденном тканом композите методом прокалывания заостренным индентором

Case Report: A Predictable Technique to Establish Occlusal Contact in Extensive Direct Composite Resin Restorations: The DSO-Technique.

This paper describes the application technique of direct shaping by occlusion (DSO) for large composite restorations including the entire occlusal surface. For this technique, matrix bands and wedges are inserted without interference with antagonists in the desired occlusion. The final increment of soft-composite resin is shaped by letting the patient occlude on the uncured composite. Due to the nature of the technique, special care has to be taken for moisture control and handling of contamination. The procedure, advantages, and limitations of the technique are discussed.

Simple optical method for measuring free shrinkage

ObjectivesA simple optical method for measuring polymerization shrinkage of dental composites is compared with an established dilatometer. MethodsFive restorative composites were used to test the methods: Filtek Supreme Ultra (3M ESPE), Filtek LS (3M ESPE), Premise (Kerr), Gradia Direct (GC), and GC Kalore (GC). Uncured composites were attached to sandblasted silane-treated glass slides. The slides were placed sample side inside a mercury-filled dilatometer (ADAF). The mercury levels were recorded as the materials were light-cured through the glass-slides (40s). Mercury levels, which correlated with volumetric shrinkage, were recorded for 60min (N=6). For the optical method, uncured composite was placed on a smooth silicone platform. A pre-polymerization image was captured under a stereomicroscope, and the specimen was light-cured (40s). Post-polymerization images were captured at 2, 10, 60, and 90min (N=10). Composite outlines were traced to obtain projected surface areas (ImageJ) and volumetric shrinkage was calculated. Results were analyzed using two-way ANOVA (α=0.05) and Pearson Correlation tests. Shrinkage deformation for both methods was modeled using finite element analysis. ResultsVolumetric shrinkage at 60min ranged between 1.24% and 2.24% for dilatometer and 1.35–2.68% for optical methods. Optical method shrinkage was consistently higher than the dilatometer (P=.0001), but the ranking of the composites was the same (Pearson Correlation Coefficient 0.9997). Finite element analysis showed that lower shrinkage values of the dilatometer method could be attributed to bonding of its samples. SignificanceThe optical method using a general-purpose stereomicroscope and public-domain software is a simple and accurate alternative to measure free shrinkage.

Realization of embedded capacitors using polymer matrix composites with barium titanate as high-k-active filler

Polymer matrix composites (PMC) with barium titanate as high-k-active filler have high potential in embedded capacitors within a printing circuit board (PCB) enabling high permittivity values and low loss factors. These PMCs allows for the use of established polymer processing techniques like screen printing and curing, which are compatible to the established PCB-materials and shaping processes. In this work a process chain, starting with a material optimization of the nano-sized barium titanate, dispersed in an unsaturated polyester-styrene reactive resin, and a further specific process development, will be presented. With respect to the optimization of the individual process steps the flow behaviour of the uncured composite, the polymerization process and the dielectric properties were characterized comprehensively. Using a composite with a barium titanate filler load of 74 wt% allows for a dielectric layer formation by a modified screen printing technique. After capacitor mounting and composite curing an initial capacity density of 13.3 pF/mm² could be achieved.

Measurement of shrinkage of composite resin by laser speckle contrast analysis

The aim of this study was to evaluate the shrinkage of a microhybrid dental composite resin photo-activated by one LED with different power densities by means of speckle technique. The dental composite resin Filtek™ Z-250 (3M/ESPE) at color A2 was used for the samples preparation. Uncured composite was packed in a metallic mold and irradiated during 20 s from 100 to 1000 mW cm−2. For the photo-activation of the samples, it was used a LED prototype (Light Emission Diode) with wavelength centered at 470 nm and adjustable power density until 1 W cm−2. The speckle patterns obtained from the bottom composite surfaces were monitored using a CCD camera without lens. The speckle field is recorded in a digital picture and stored by CCD camera as the carrier of information on the displacement of the tested surface. The calculated values were obtained for each pair of adjacent patterns and the changes in speckle contrast as a function of time were obtained from six repeated measurements. The speckle contrasts obtained from the bottom surface with 100 mW cm−1 were smaller than those than the other power densities. The higher power densities provided the higher shrinkage.

Influence of in-situ reaction on luminescent properties of samarium-complex/hydrogenated acrylonitrile-butadiene composites

In this work, acrylato(1,10-phenanthroline)bis(2-thenoytrifluoroacetonato) samarium(III) [Sm(TTA)2(AA)(Phen)] [Sm-AAPhen; TTA=4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione, AA=acrylic acid, Phen=1,10-phenanthroline] has been synthesized for the first time, which combines the good fluorescence property of Sm(TTA)3(Phen) and the reactivity of acrylic acid with radicals. The uncured composites were prepared by adding different amounts of the Sm(TTA)3(Phen) complex and a certain amount of peroxide into hydrogenated acrylonitrile-butadiene rubber (HNBR). The cured composites were prepared by vulcanizing the uncured composites at 160°C under a pressure of 15MPa for 20min. Fourier Transform Infrared (FTIR) spectra show that the intensity of peaks assigned to reactive CC bond decreases after the curing process, verifying that the in-situ reaction (including polymerization and grafting) of Sm-AAPhen initiated by peroxide radicals took place during the cross-linking of the HNBR matrix. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) observations show that the dispersion dimension of the cured composite is far finer than that of the uncured composite. Wide-angle X-ray diffraction (WAXD) testing shows that the crystallinity of Sm-AAPhen in the composites was absent dramatically after the curing process, implying that most of crystalline Sm-AAPhen complex took part in the in-situ reaction and formed the non-crystalline poly(Sm-AAPhen). The dispersion phase of cured Sm-AAPhen/HNBR composites is composed of completely almost nanometer-sized poly(Sm-AAPhen) and few residual Sm-AAPhen particles with significantly reduced dimensions. The fluorescent intensity, lifetime and quantum yields of the cured composite are much higher than that of the uncured one with the same Sm-AAPhen content due to the in-situ reaction.

A pilot study of a simple photon migration model for predicting depth of cure in dental composite

Objectives The purpose of this study was to build a photo migration model to calculate the radiant exposure (irradiance×time) in dental composite and to relate the radiant exposure with extent of cure using polymer kinetics models. Methods A composite (Z100, Shade A2) cylinder (21 mm diameter by 15 mm deep) was cured with a tungsten–halogen lamp emitting 600 mW/cm 2, 1 mm above the composite for 60 s. For each of the 2×1 mm grids along the longitudinal cross section (diameter versus depth), the degree of conversion (DC) and hardness (KHN) were measured to construct the curing extent distribution. The inverse adding-doubling method was used to characterize the optical properties of the composite for the Monte Carlo model simulating the photon propagation within the composite cylinder. The calculated radiant exposure ( H) distribution along the cross section was related to the curing extent DC/ DC max distribution and fitted with two polymer curing kinetics models, the exponential model DC = DC max [ 1 − exp ( ( ln 0.5 ) H / H dc 50 % ) ] and Racz's model DC = DC max / [ 1 + ( H / H dc 50 % ) − 2 ] , where H dc 50 % is a fitting parameter representing the threshold for 50% of the maximum curing level. Results and Significance The absorption and scattering coefficients of uncured composite were higher than that of cured composite at wavelengths between 420 and 520 nm. A roughly hemi-spheric distribution of radiant exposure in the Monte Carlo simulation result was comparable with the curing profiles determined by both DC and KHN. The relationship between DC (or KHN) and H agreed with the Racz model ( r 2=0.95) and the exponential model ( r 2=0.93). The H dc 50 % was 1.5(0.1), equal for the two models ( P<0.05). The estimated radiant exposure threshold for 80% of the maximum curing level was between 3.8 and 8.8 J/cm 2. The simulation results verify that the radiant exposure extends to a greater depth and width for composite with lower absorption and scattering coefficients. Given the optical properties and the geometry of the composite, and the spectrum and the geometry of the light source, the Monte Carlo simulation can accurately describe the radiant exposure distribution in a composite material to predict the extent of cure.

Real‐time dimensional change in light‐cured composites at various depths using laser speckle contrast analysis

Laser speckle contrast analysis is an interferometric technique that is used to measure the displacement of the rough surface of a specimen. The purpose of this study was to present a laser speckle correlation method for monitoring real-time dimensional changes of light-cured composites. Uncured composite was condensed into a glass tube and irradiated for 30 s with 600 or 200 mW cm(-2). The speckle patterns obtained from lateral and bottom composite surfaces were monitored using a speckle analyser. The speckle field is recorded in a digital frame and stored by image processing system as the carrier of information on the displacement of the tested surface. The calculated values were obtained for each pair of adjacent patterns and the changes in speckle contrast as a function time were obtained from five repeated measurements. The overall magnitude of the speckle contrasts decreased soon after the initial light exposure and gradually increased thereafter. The speckle contrasts obtained from the bottom surface were smaller than those obtained from the lateral surface. This tendency was more pronounced when the specimen was irradiated with lower power density. It can be concluded that monitoring differential shrinkage at various levels of depth can be achieved with this new technique.

Single-step adhesives are permeable membranes

Objectives. This study tested the hypotheses that micro-tensile bond strengths of all currently available single-step adhesives to dentine are adversely affected by delayed activation of a light-cured composite, and that such a phenomenon only occurs in the presence of water from the substrate side of the bonded interface. Methods. In experiment I, a control three-step adhesive (All-Bond 2, Bisco) and six single-step adhesives (One-Up Bond F, Tokuyama; Etch&Prime 3.0, Degussa; Xeno CF Bond, Sankin; AQ Bond, Sun Medical; Reactmer Bond, Shofu and Prompt L-Pop, 3M ESPE) were bonded to sound, hydrated dentine. A microfilled composite was placed over the cured adhesive and was either light-activated immediately, or after leaving the composite in the dark for 20 min. In experiment II, three single-step adhesives (Etch&Prime 3.0, Xeno CF Bond and AQ Bond) were similarly bonded to completely dehydrated dentine using the same delayed light-activation protocol. In experiment III, a piece of processed composite was used as the bonding substrate for the same three single-step adhesives. The microfilled composite was applied to the cured adhesives using the same immediate and delayed light-activation protocols. Bonded specimens were sectioned for micro-tensile bond strength evaluation. Fractographic analysis of the specimens was performed using SEM. Stained, undemineralised sections of unstressed, bonded specimens were also examined by TEM. Results. When bonded to hydrated dentine, delayed light-activation had no effect on the control three-step adhesive, but significantly lowered the bond strengths of all the single-step adhesives ( p<0.05). This adverse effect of delayed light-activation was not observed in the three single-step adhesives that were bonded to either dehydrated dentine or processed composite. Morphological manifestations of delayed light-activation of composite in the hydrated dentine bonding substrate were exclusively located along the composite–adhesive interface, and were present as large voids, resin globules and honeycomb structures that formed partitions around a myriad of small blisters along the fractured interfaces. Conclusion. These features resembled the ‘overwet phenomenon’ that was previously reported along the dentine–adhesive interfaces of some acetone-based three-step adhesives. The cured adhesive layer in single-step adhesives may act as semi-permeable membranes that allow water diffusion from the bonded hydrated dentine to the intermixed zone between the adhesive and the uncured composite. Osmotic blistering of water droplets along the surface of the cured adhesive layer and emulsion polymerisation of immiscible resin components probably account for the compromised bond strength in single-step adhesives after delayed activation of light-cured composites.

Novel approach to measure composite conversion kinetics during exposure with stepped or continuous light-curing.

The objective of this research was to evaluate a novel approach to monitor the polymerization reaction during a light-curing exposure by using infrared (IR) spectroscopy. An IR spectrometer was equipped to use an attenuated total reflectance (ATR) element as an IR-active substrate. The uncured composite (Herculite XRV, Shade A2, Kerr, Orange, California) was placed against the crystal, and the IR spectrum was continuously obtained during various exposure scenarios. The degree of conversion and the maximum rate of reaction were monitored at 0 mm (top surface), 1 mm, 2 mm, and 3 mm beneath the surface. The exposure conditions included continuous 40-second or 60-second exposures at 100% intensity (800 mW/cm2) or a stepped output of 10 seconds at 17% maximal output (133 mW/cm2) followed by full output for the remainder of the 40-second or 60-second exposure (Elipar Highlight, ESPE, Norristown Pennsylvania). The results were analyzed using MANOVA with appropriate post hoc tests (p < or = .05). For 40-second exposures, the peak conversion rates were significantly reduced (p < .05) when using the stepped exposure mode compared to the continuous exposure: 40-second top surface: stepped = 5.5%/s +/- 0.4, continuous = 10.5%/s +/- 1.0; 1 mm step = 3.6%/s +/- 0.4, continuous mode = 4.8%/s +/- 0.2. The same trend was noted when using the 60-second exposure. Equivalent conversion values (p > .05) beneath the surface between stepped and continuous exposure modes at similar depths 60 seconds after light initiation were only attained at 3 mm 4 for the 40-second exposure. However, using the 60-second exposure, equivalent conversion values between step and continuous exposure modes at similar depths were obtained. Even with a reduced conversion rate at the surface using the stepped cure mode, polymerization shrinkage forces were sufficient to debond the specimens from the test crystal after only 20 seconds into the exposure. This result indicated that stress development in the curing composite was non-uniform, and stress values developed at the surface of the restoration were the greatest. Stepped intensity curing for the ESPE Highlight unit was shown to produce significantly lower conversion rates at the surface and at 1-mm depths, but longer exposure times were still required to provide conversion values equivalent to continuous exposure.

Dimensional stability of record bases fabricated from light-polymerized composite using two methods

Statement of problem. Record bases fabricated from resin-based composite, which undergoes polymerization shrinkage during curing, can distort during curing to produce significant gaps along the posterior border. Purpose. This study evaluated the pattern of gap formation that occurs over the palatal area of a maxillary record base fabricated from light-cured composite (Triad), and determined whether changes in the fabrication method affects the size and pattern of gap formation. Effects of composite width and passage of time on gap formation were also analyzed. Material and methods. Twenty record bases were fabricated with two methods: (1) according to the manufacturer's directions, the entire surface of the record base was exposed to the curing light; and (2) the palatal area of the record base was covered with foil to prevent light penetration, and the base was light cured in three stages with readaptation of the uncured composite between stages. Ten record bases from each group were tested 1 hour after fabrication; the remaining 10 from each group were tested 7 days after fabrication. Measurements of adaptation were made at three points representing the right and left ridge crests and midpalatal areas. The first measurement was taken at the posterior border and subsequent measurements were made at 5 mm increments after reduction of the posterior border of the cast and record base with a model trimmer. Results. Dimensional changes were observed in both procedures. The largest discrepancy occurred at the posterior border of record bases fabricated using method 1. Mean gap formation at the posterior border in this group after 1 hour was 454, 729, and 334 μm and 483, 841, and 330 μm after 7 days at points A, B, and C, respectively. Record bases fabricated with procedure 2 demonstrated mean gap sizes at the posterior border after 1 hour of 219, 421, and 208 μm and 267, 403, and 192 μm after 7 days at points A, B, and C, respectively. No significant influence of composite width on gap size was found. Conclusion. The average gap size due to stage curing (method 2) was never greater than the corresponding gap that arose from the use of the manufacturer's recommendations (method 1). Limiting the amount of surface area exposed to the curing light and readapting the uncured composite to the cast between curing episodes can significantly reduce the mean gap size occurring at the posterior border. (J Prosthet Dent 1998;79:399-403.)

Short Fibers Rubber Composites: the Comparative Properties of Treated and Discontinuous Cellulose Fibers

Composites produced by dispersion of selected short cellu lose fibers in elastomeric matrices are useful engineering materials. These fibers are pre-treated to provide dispersion in conventional mixing equip ment while minimizing fiber damage, and to give bonding to utilize the rubber reinforcing ability of the fiber. In the uncured composite, the fibers contribute higher green tensile strength, and almost no die swell on extru sion. The vulcanized composites show a monotonic increase in Young's Modulus and a decrease in ultimate elongation with increasing fiber load ing. As with many composites, the tensile strength is less than the matrix strength at very low fiber loading, but at higher fiber levels the matrix is reinforced and the composite tensile strength exceeds the matrix strength. The stiffening action of the fibers provides a harder material with greatly reduced solvent swelling characteristics compared to the matrix rubber. Finally, the tensile properties of the composite are precisely related to the orientation of the fibers in the matrix which can vary from uniaxial to random.