Room Temperature Composition Research Articles

Prewarming effect on adaptation, porosities, and strength of a composite resin

Warming composite resin before insertion to reduce viscosity is advocated for improving adaptation and reducing voids. This study evaluated how prewarming altered porosities, adaptation, and strength.Twenty composite restorations were placed in 2 increments in typodont teeth with a large Class II preparation. The composite was either at room temperature (control) or prewarmed to 68 °C (n = 10/group). Each increment was light-cured for 20s. After 24h, the restored teeth were sectioned and imaged under a stereomicroscope. Examiners ranked the quality of adaptation to walls and between increments, and the presence of voids on a 0–3 scale. Results were statistically analyzed using Mann-Whitney U Test. Diametral tensile strength of monolithic or incrementally-filled composite cylinders (6 mm diameter × 4 mm height; n = 10/group) made with room temperature or prewarmed composite were tested at 0.5 mm/min. Strength results were analyzed using ANOVA statistics followed by pairwise comparisons.Restorations made with prewarmed composite had significantly fewer large voids and better adaptation to cavity walls and between layers (P < 0.05). Strength of prewarmed composite was higher than room temperature composite, and was significantly higher in monolithic specimens (P < 0.05).It was concluded that prewarming conventional composite can improve its handling, making it handle more like a flowable composite without jeopardizing physical properties. The prewarmed composite was found to have better adaptation and fewer voids, and attained higher strength than composite that was not prewarmed.

Selective catalytic oxidation of pollutant H2S over Co-decorated hollow N-doped carbon nanofibers for high-performance Li-S batteries

Hydrogen sulfide (H2S) is one of the most harmful pollutants to human health and the environment. Using carbon-based catalysts, H2S can be selectively oxidized to elemental sulfur (S) at room temperature and carbon-sulfur composites are produced, which enlightens a facile solution combining desulfurization with cathode preparation for high-performance lithium-sulfur batteries (LSBs). Herein, a heterogeneous catalyst of cobalt decorated N-doped hollow carbon nanofibers (Co-NHCFs) is designed for realizing the integrated application, in which the electron redistribution arising from long-range interactions of Co/N-doped carbon significantly promotes the oxygen radical generation and H2S dissociation, leading to its robust catalytic activity for H2S oxidation. Benefiting from the hollow framework with capacious storage space for rapid gas diffusion, the in-situ fabrication of high S-loading carbon-based cathodes (S@Co-NHCFs) used for LSBs is achieved during the H2S oxidation processing. Due to the more favorable diffusion of H2S gas than liquid S, this kind of chemical reaction-induced deposition can realize a more uniform distribution of solid S upon carbon than the traditional method by molten infusion, which, coupled with the catalysis of heterogeneous effect on the reversible sulfur-redox reaction, results in superior electrochemical performance of S@Co-NHCFs in LSBs.

Nanomodification, Hybridization and Temperature Impact on Shear Strength of Basalt Fiber-Reinforced Polymer Bars.

This paper presents fiber-reinforced polymer composites which were modified by fibers hybridization as well as matrix nanomodifiaction with nanosilica. The article analyzed the nanosilica matrix modification and basalt-carbon hybridization’s effect on key properties of composites use as the main reinforcement in concrete structures. The comparative analysis was based on results of bars strength parameters determined in a shear test with the ASTM standard. The tests were performed for three bar diameters at room temperature and pre-heated FRP composites at 80 °C and 200 °C for 2 h with the aim of verifying the influence of the fiber hybridization-basalt-carbon fiber-reinforced polymer (HFRP) bars and the effect of nanosilica modification of the epoxy matrix (nHFRP). The test results were also compared with results of the shear test carried out after the bars were heated to 80 °C for 30 min in order to verify and evaluate the effect of the heating time. These types of tests are relevant to the conditions that occur in FRP composites when exposed to elevated temperatures.

Ab-Initio Molecular Dynamics investigation of gas adsorption on α-quartz (001) for CO2 enhanced natural gas recovery

In this work, the interaction of methane and carbon dioxide on α-quartz with surface 001, with a siloxane termination (dense) surface was investigated by means of Ab-Initio Molecular Dynamics. Different temperatures were addressed, ranging from 298 to 423 K. For completeness, pure and mixed compositions were considered, to replicate the conditions present during Enhanced Gas Recovery processes by CO 2 injection. When considering pure compositions, both gases stick to the surface, except for the highest temperature (423 K), where most of CH 4 tend to desorb. When mixed compositions are addressed, carbon dioxide generally hinders the interaction of methane, except for high temperature, where both gases are equally distributed both close and far from the surface. To the goal of improving EGR processes on sandstone reservoirs, this work shows that a temperature of 323 K offers the best efficiency by increasing the interaction of carbon dioxide and pushing methane out of the surface. At the same time, this study would not recommend the use of very high temperatures (T > 373 K) and excessive concentration of CO 2 , as the majority of this gas would desorb, without improving methane extraction in a meaningful way. • With pure compositions, CH 4 possesses high mobility on α-quartz compared to CO 2 , though both gases are characterized by the same interaction. • At room temperature and mixed composition, both gases interact strongly with the surface, so the extraction of methane is usually inefficient. • A temperature of 323 K offers the best EGR efficiency, improving carbon dioxide interaction with the surface and pushing methane out. • Very high temperatures and excessive concentration of CO 2 could reduce gas recovery and sequestration.

РЕГУЛИРОВАНИЕ СВОЙСТВ ЭПОКСИДНЫХ ПОЛИМЕРОВ НА ОСНОВЕ ДИФЕНИЛОЛМЕТАНА С ПОМОЩЬЮ ОЛИГОБУТАДИЕНОВОГО КАУЧУКА С КОНЦЕВЫМИ КАРБОКСИЛЬНЫМИ ГРУППАМИ

The influence of modifying additives of oligobutadiene rubber with terminal carboxyl groups of the SKD-KTR brand on the deformation-strength and adhesive properties of epoxy polymers based on the EDFM-19 product, which is a diglycidyl ether of diphenylolmethane, is studied in a wide range of concentrations. The compositions are cured with triethylentetramine methylphenol UP-583T and triethylentetramine THETA without heat supply from the outside and when heated to a temperature of 120°C. It is found that with increasing rubber concentration, the tensile strength and elastic modulus indicators monotonously decrease, especially intensively when the modifier content is up to 15 mass parts. The dependence of the glass transition temperature and adhesion strength on the amount of introduced rubber is extreme. In the range of modifier concentrations from 5 to 15 parts by weight peaks are observed, the position of which depends on the chemical nature of the hardener of the epoxy resin and the curing mode of the composition. The deformation at break increases monotonously with the increase in the elastomer content, most rapidly in the range of modifier concentrations of 5-25 mass parts. The effect is shown both for samples cured at room temperature and heat-treated compositions. Due to a significant increase in the ability of the sample to develop deformation, despite the decrease in the strength parameter, the work of destruction of modified samples increases significantly. It contributes to improving the performance of composites modified by SKD-KTR rubber under the action of shock and vibration loads.

COMPARATIVE EVALUATION OF THE MARGINAL ADAPTATION OF FOUR DIFFERENT COMPOSITE RESINS WITH OR WITHOUT PREHEATING – AN IN VITRO STUDY

Background: Resin composites as direct posterior restorative material was associated with the polymerization contraction and microleakage. Different methods have been introduced to overcome these drawbacks by increasing the degree of monomer conversion and to minimize the polymerization shrinkage. Composite preheating is an innovative method to improve the handling and physical properties. So this study was done to evaluate the effect of prepolymerization warming of different composites on the marginal adaptation. &#x0D; Materials and Methods: This in vitro study was conducted on 80 extracted human maxillary premolars. Class II cavities on the proximal surface were prepared with the dimensions of 4 mm buccolingual width, 2 mm axial depth, and gingival margin at the cementoenamel junction. They were divided into four groups of 20 teeth each and were restored accordingly: Group I – Bulkfill nanohybrid; Group II – Nanofill; Group III – Ormocer; Group IV – microhybrid composites. Each group was further sub - divided into subgroups of 10 teeth, according to the preheated composites and room temperature composites used. After restorative procedures, samples were sectioned in the mesiodistal direction through the centre of the restoration and analysed using Scanning Electron Microscope at 200x magnification and marginal gap width was measured in three areas at the axial wall using Image Processing and Analysis in Java (ImageJ 1.5 2a) software.&#x0D; Statistical Analysis: Data was entered in Statistical Package for Social Sciences version 21 Software for Windows. The comparisons of four different composite materials with two subgroups were analyzed using Kruskal Wallis test. The level of significance was kept at p &lt; 0.05.&#x0D; Results: Preheating results in more gap formation with the bulk fill nanohybrid and Ormocer showed higher MQ4 scores than the room temperature composites. No statistically significant results were found. But the percentage of gap formation was comparatively higher in preheated composite group.&#x0D; Conclusion: Within the limitations of the present study, it could be concluded that preheated composites showed poor internal marginal adaptation with increased frequency of gap formation.&#x0D; Key words: Internal marginal adaptation, Ormocer, Filtek nanofill, Microhybrid, Tetric bulk fill

Temporal and spatial variations in characteristics of fluid inclusions in epizonal magmatic-hydrothermal systems: Applications in exploration for porphyry copper deposits

Temporal and spatial variations in the room temperature phase relations of fluid inclusions serve as a proxy for the PTX properties of fluids associated with emplacement and crystallization of a shallow epizonal intrusion following the “Burnham Model”. Accordingly, during magma ascent, hydrous magmas approach and achieve volatile saturation in response to decreasing pressure (“first boiling”) and/or as a result of cooling and crystallization of anhydrous mineral phases (“second boiling”). In both cases, a magmatic aqueous fluid phase will exsolve from the volatile-saturated silicate melt. Fluid inclusions that trap the exsolved magmatic fluid show predictable room temperature phase relations, compositions, and microthermometric characteristics indicative of the pressure and temperature conditions of the trapping environment.We model aqueous phase equilibria as a function of temperature, pressure, and fluid composition. The composition and phase behavior of the magmatic aqueous fluid phase is adequately approximated by the system H2O-NaCl, and the PVTX characteristics of the magmatic fluids may be determined at any temperature and pressure using phase equilibrium data for this binary system. Then, PVTX data for the system H2O-NaCl are used to predict the room temperature phase relations and homogenization temperatures of fluid inclusions that trap the magmatic fluid at various times and locations in the magmatic-hydrothermal system. The temperature at any position in the system is based on established numerical models of conductive and convective cooling of shallow plutons, and the pressure at any depth is calculated assuming that hydrostatic conditions apply at temperatures <400 °C, and that lithostatic conditions are applicable at higher temperatures.We apply the model to four different stages during the crystallization of a shallow, intermediate composition magma, beginning in the early stages of crystallization and immediately following initial volatile saturation, and ending with complete crystallization of the melt. Mapping the stable fluid phase fields onto a cross-section of the pluton allows us to predict the characteristics of fluid inclusions trapped at various times and locations in the overall system. The fluid inclusion characteristics are predicted along five depth profiles that extend from the center of the pluton to the periphery. The results show good agreement with numerous studies that describe the distribution of halite-bearing, vapor-rich, and two-phase, liquid-rich inclusions in porphyry copper deposits.The results of this study may be applied in exploration for porphyry copper mineralization, as well as other magmatic-hydrothermal porphyry deposits in which the magmatic fluids can be approximated by the system H2O-NaCl. Importantly, halite-bearing fluid inclusions occur only within the pluton and in the immediately surrounding wallrocks, which represents the part of the system that often hosts mineralization. Similarly, fluid inclusion assemblages comprised of only vapor-rich inclusions occur in the near-surface, sub-volcanic part of the system, whereas coexisting halite-bearing and vapor-rich inclusions characterize the deeper parts of the system. The distribution of fluid inclusion types constrains the vertical and lateral position within the overall magmatic-hydrothermal system and, thus, develops vectors towards the magmatic center of the system that is most likely to host economic mineralization.

MS2 bacteriophage capsid studied using all-atom molecular dynamics.

The all-atom model of an MS2 bacteriophage particle without its genome (the capsid) was built using high-resolution cryo-electron microscopy (EM) measurements for initial conformation. The structural characteristics of the capsid and the dynamics of the surrounding solution were examined using molecular dynamics simulation. The model demonstrates the overall preservation of the cryo-EM structure of the capsid at physiological conditions (room temperature and ions composition). The formation of a dense anion layer near the inner surface and a diffuse cation layer near the outer surface of the capsid was detected. The flow of water molecules and ions across the capsid through its pores were quantified, which was considerable for water and substantial for ions.

The effect of preheating of composite resin on its color stability after immersion in tea and coffee solutions: An in-vitro study.

BackgroundOne of the concerns in using composite resins is color change. The aim of this study was to investigate the effect of preheating on color stability of composite resins when immersed in coffee and tea.Material and MethodsThis experimental study included 60 composite disks. The samples were divided into 2 groups, one group prepared at room temperature and the other prepared at 68 °C. After curing, the samples were placed in 37 °C distilled water for 24 hours. The color of the samples was measured (t0) using spectrophotometer according to CIE-L*a*b* system. The samples of each group were then divided into 3 subgroups and respectively immersed in distillated water, coffee and tea for 30 days and the final color (t1) was measured. The difference between the measured colors was calculated (∆E) and the results were analyzed using version 21.0 of SPSS software, Paired t-test, ANOVA, Tukey’s test, and Dunnett t-test.ResultsThe preheated composites showed significantly lower staining in the coffee solution than the room temperature composites (p<0.0001). In contrast, no statistically significant difference was observed for the tea solution (p =0.317). The staining of the preheated composites in distillated water was higher than those in the room temperature, however, the difference was not significant (p =0.99).ConclusionsWithin the limits of this study, preheating was effective to improve color stability of composite resin after long time immersion in coffee solution. Key words:Composite resin, color stability, preheating.

Mesoporous silica based composite membrane formation by in-situ cross-linking of phenol and formaldehyde at room temperature for enhanced CO2 separation

In the present report, composite membranes (CM) were prepared from a resin, derived from phenol and formaldehyde as matrix and mesoporous silica SBA-15 as filler on the clay-alumina tubular support. Membrane matrix was formed by in-situ cross-linking of phenol (P) and formaldehyde (F) at room temperature. The structural changes of membrane matrix with curing time influence the final properties of the membranes. The surface morphology and the filler-polymer interaction i.e. surface silanol group of SBA-15 and –CH2OH/–OH group of P–F resin of composite membrane were established by FESEM and Fourier transformation of infrared spectroscopy (FT-IR) and X-ray Photoelectron Spectroscopy (XPS) respectively. Thermal stability of the membranes was characterized by Thermogravimetric analysis (TGA) and Differential Thermal Analysis (DTA). Finally, the permeability and the separation efficiencies of the developed composite membranes were studied in details with varying curing time of resin at room temperature, feed pressure and different gas compositions for CO2/H2 and CO2/CH4 mixture gases. For CO2/H2 ‘reverse selectivity’ was observed with the membrane. The highest separation factor of CO2/H2 and CO2/CH4 were achieved upto 16.6 and 62.4 for 67:33 (CO2/H2) and 45:55 (CO2/CH4) feed composition respectively. The room temperature cross-linking of P–F resin modified the interfacial defect of membrane and its effect on the CO2 separation efficiencies is the unique observation of the present work. The obtained permeability and selectivity values of different gases were surpassing the 2008 Robeson upper bound line.

Complete virus capsid at all-atom resolution: Simulations using molecular dynamics and hybrid molecular dynamics/hydrodynamics methods reveal semipermeable membrane function

Simulations of complete virus capsid at atomistic details have been performed using standard molecular dynamics as well as original hybrid molecular dynamics/hydrodynamics methodologies. The results show that the capsid is stable in water solution at room temperature and ions composition similar to physiological conditions. Detailed analysis of the flow of water molecules and ions through the capsid's wall is performed. It demonstrates that ions do not cross the capsid shell, while water exhibits substantial flows in both directions. This behaviour can be classified as a semipermeable membrane and may play a role in mechanical properties of the virus particle.

Randomized Controlled Trial of Postoperative Sensitivity with Warm and Room Temperature Composite.

Physical properties of composite improve when it is preheated prior to polymerization. However, postoperative sensitivity may be considered a potential complication. A review of the literature revealed no reported randomized controlled trials (RCTs) of postoperative sensitivity when using preheated composite resin. The objective of the study was to determine if preheating composite leads to changes in postoperative sensitivity in a parallel RCT. In total, 120 eligible, consenting adults were recruited in private dental practice and randomized into 2 groups of 60 patients. One group had room temperature composite restorations placed and the second had composite preheated to 39°C. The primary outcome was sensitivity after 24 h by the visual analog scale (VAS), recorded blind by patients. Secondary outcomes were VAS scores recorded over a month. Blind statistical analysis used the Mann-Whitney U test to compare the 24-h VAS score between groups and repeated-measures analysis of variance to assess the change over time. Potential confounders were tested using regression models. A total of 115 patients completed the trial: 57 in the heated composite group and 58 in the room temperature group. Analysis of 24-h VAS scores found no statistically significant difference between the 2 groups ( P = 0.162). Examining the potential confounders confirmed the nonsignificant difference between heated and room temperature groups on the 24-h VAS score, after controlling teeth type and preoperative pulp test (effect size = 0.173, P = 0.317). Analysis of the secondary outcomes found significant changes (within-subject effect) in VAS scores over the review period ( F statistic = 4.7, P = 0.002) but not a significant (between-subject effect) difference between heated and room temperature groups over time (effect size = 0.102, P = 0.197). There was a significant correlation between preoperative VAS score and postoperative VAS score ( P < 0.001). For the restorations in this study, there was no detectable difference in postoperative VAS score between preheated and room temperature composite. Postoperative sensitivity decreased throughout the first month. Postoperative sensitivity was correlated to preoperative sensitivity (ISRCTN 76727312). Knowledge Transfer Statement: The results of this study can be used by clinicians when considering the advantages and disadvantages of preheated composite. The study found no evidence of any change in postoperative sensitivity when using preheated composite. Since preheated composite has superior physical properties, its use for routine care can be considered good practice.

Pre-heating of high-viscosity bulk-fill resin composites: Effects on shrinkage force and monomer conversion

ObjectivesTo investigate the influence of pre-heating of high-viscosity bulk-fill composite materials on their degree of conversion and shrinkage force formation. MethodsFour bulk-fill composite materials (Tetric EvoCeram Bulk Fill—TECBF, x-tra fil—XF, QuixFil—QF, SonicFill—SF) and one conventional nano-hybrid resin composite (Tetric EvoCeram—TEC) were used. The test materials were either kept at room temperature or pre-heated to 68°C by means of a commercial heating device, before being photoactivated with a LED curing unit for 20s at 1170mW/cm2. Shrinkage forces (n=5) of 1.5-mm-thick specimens were recorded in real-time for 15min inside a temperature-controlled chamber at 25°C (simulating intraoral temperature after rubber dam application) with a custom-made stress analyzer. Degree of conversion (n=5) was determined at the bottom of equally thick (1.5mm) specimens using Fourier transform infrared spectroscopy. Data were analyzed with Student’s t-test, ANOVA and Tukey’s HSD post-hoc test (α=0.05). ResultsComposite pre-heating significantly increased the degree of conversion of TECBF, but had no effect on monomer conversion of the other materials investigated. For each of the test materials, pre-heated composite generated significantly lower shrinkage forces than room-temperature composite. At both temperature levels, TECBF created the significantly highest shrinkage forces, and QF caused significantly higher shrinkage forces than both XF and TEC. ConclusionsBoth the composite material and the pre-cure temperature affect shrinkage force formation. Pre-heating of bulk-fill and conventional restorative composites prior to photoactivation decreases polymerization-induced shrinkage forces without compromising the degree of conversion. Clinical significanceComposite pre-heating significantly reduces shrinkage force formation of high-viscosity bulk-fill and conventional resin composites, while maintaining or increasing the degree of monomer conversion, dependent upon the specific composite material used.

Effect of preheating on the viscoelastic properties of dental composite under different deformation conditions.

Preheating of dental composites improves their flowability, facilitating successful restorations. However, the flowability of dental composites is affected not only by temperature but also by the deformation conditions. In the present work, the effects of various deformation conditions upon the viscoelastic properties of a preheated dental composite were studied. The rheological properties of Z350 dental composites at 25, 45, and 60°C were measured by a strain-controlled rheometer. When a low strain (0.03%) was applied, the preheated composite exhibited greater shear storage modulus (G') and complex viscosity (η*) than a room-temperature composite. Oppositely, when a high strain (50%) was applied, G' and η* of a preheated composite were lower than those of a room-temperature composite. Preheating of dental composites might be helpful in clinical practice both to increase the slumping resistance when minimal manipulation is used (e.g., during the build-up of a missing cusp tip) and to increase flowability when manipulation entailing high shear strain is applied (e.g., when uncured composite resin is spread on a dentin surface).

Metastability in pixelation patterns of coexisting fluid lipid bilayer phases imposed by e-beam patterned substrates.

We study the dynamic evolution of pixilation patterns of the liquid-ordered (Lo) phase in coexistence with the liquid-disordered phase in lipid multibilayers. The pixilation patterns were formed by imposing lattice patterns of localized high curvature on phase-separating multibilayers using curvature-patterned regions of an underlying support. The projected radius of underlying hemisphere-like features, that provided the local curvature, was varied from 60 nm to 100 nm and the square lattice spacing between the features was varied between 200 nm and 400 nm using standard electron (e) -beam lithography. Over time, the area fraction of the Lo phase on the patterned regions of the substrate decreased toward zero at room temperature. This apparent metastability of the pattern derives from the high line energy of a pixelation pattern where a Boltzmann distribution shows near zero equilibrium partitioning of the Lo phase in the patterned regions. Kinetic rate analysis identifies two pattern-dependent mechanisms that dominate the transition to zero Lo area fraction; diffusion limited dissolution of the Lo phase driven by an Ostwald ripening-type process or the cooperative formation of vesicles containing Lo phase lipids. Interestingly, we observed the spontaneous formation of tubules in the corners of the array due to the high local curvature applied to the membrane. Furthermore we show that it is possible to regenerate pixilation patterns on the curvature-patterned regions by cooling below room temperature. Regenerated area fractions are in agreement with a room-temperature composition of primarily Ld phase and the high degree of overlap with the original patterns is suggestive of fixed nucleation sites.

Ferroelectricity in the xAg2Nb4O11–(1−x)Na2Nb4O11 solid solution

Compositions in the (AgxNa1−x)2Nb4O11 solid solution have been prepared by a conventional solid state method. Composites containing Ag2Nb4O11 have been shown to be ferroelectric and the Curie temperature shown to decrease from 149 °C at x=1 to 62 °C at x=0.7. Room-temperature compositions with x≤0.7 are monoclinic, while those with x≥0.8 are rhombohedral with structures consistent with the relevant end members. At x=0.75, the structure was mainly rhombohedral but with coexistence of the monoclinic structure, indicating the proximity of a phase boundary.

Room-Temperature Synthesis Leading to Nanocrystalline Ag2V4O11

This work highlights a room-temperature composition study of the Ag(2)O/V(2)O(5)/HF((aq)) ternary system, leading to the precipitation of either various silver vanadates having Ag/V ratios from 1/2 to 3/1 or the new silver vanadium oxyfluoride compounds Ag(4)V(2)O(6)F(2) and Ag(3)VO(2)F(4), and a synthetic procedure that affords nanocrystalline Ag(2)V(4)O(11) (SVO) at room temperature. The as-precipitated SVO particles exhibit an acicular morphology, 10-15 x 50-200 nm in size, and present a peculiar reactivity vs lithium notably through a Ag(+)/Li(+) displacement reaction that progresses in a reversible fashion. This step forward thus enables the reversible and simultaneous combination of two active redox processes (silver and vanadium), providing a significant enhancement in the cathode gravimetric capacity of 320 mAh/g at C rate and more than 250 mAh/g at 5C.

Vibrational spectrum, ab initio calculations, conformational stabilities and assignment of fundamentals of 1,2-dibromopropane

The mid and far infrared and the Raman spectrum of 1,2-dibromopropane is reported in solid, liquid and gas. Several bands reported by earlier workers are not present in the spectrum of the purified material. Ab initio calculations of optimized geometry, energy, dipole moment, molar volume, vibrational spectrum and normal coordinate calculation were performed using the density functional B3LYP/6-311++g(3df,2pd), and the results used to assist a complete assignment of the 81 fundamental modes of vibrations of the three conformers of 1,2-dibromopropane. Relative energies found conformer A the lowest with G and G′ at 815.6 and 871.4 cm −1 higher. The temperature dependence of the Raman spectrum of the liquid was investigated in the CCC bending region and the relative energies determined. It was found that the G′ and G conformers lie 236 ± 11 and 327 ±11 cm −1, respectively above the A conformer, leading to the room temperature composition of the liquid as A, 65 ± 1; G′, 21 ± 1; G, 14 ± 1%. It is apparent that the calculated highest energy conformer G′ is stabilized more than the G conformer in the liquid. The G′ conformer has the lowest molar volume effectively changing the interaction distance between conformers in the liquid, and enhancing the effect of its dipole moment.

Mechanical properties and styrene emission levels of a UV-cured glass-fibre/vinylester composite

The mechanical performance of a UV-cured glass-fibre/vinylester composite was compared with conventional room temperature cured and thermally post-cured counterparts. The UV-cured composite was exposed to UV light for 10 min, whereas the room temperature and post-cured composites required several hours of processing. The fibre-dominated tensile and flexural properties were comparable for each composite. The resin-sensitive interlaminar shear strength was highest for the UV-cured and post-cured composites and, within scatter, the performance of the UV-cured composite was comparable to its post-cured counterpart. In addition, the UV-cured composite emitted approximately four times less styrene during lamination and cure in an open mould than the conventional room temperature cured composite. The results highlight the potential for UV-curing composites to provide excellent mechanical performance while reducing manufacturing times and improving the manufacturing environment.

Degree of conversion and residual stress of preheated and room-temperature composites

The aim of this study was to determine the degree of conversion and residual stress of resin composite preheated to different temperatures and to compare it to room-temperature composite. The composite resin was preheated to 40 degrees C, 50 degrees C, and 60 degrees C and packed into brass rings and light-cured. The degree of conversion and residual stress were analysed using Fourier transform infra-red spectroscopy and X-ray diffraction, respectively. The results obtained were tabulated and statistically analyzed using Kruskal-Wallis test and Tukey's honestly significantly different test. The results showed significant increase in the degree of conversion and residual stress with increase in preheating temperature.