Higher Degree Of Conversion Research Articles

Unveiling the Role of Key Parameters during Molecular Growth for Optimal Poly(glycerol sebacate) Synthesis

AbstractPoly(glycerol sebacate) (PGS) belongs to the hyperbranched polyesters family (HBP), which possesses an extensive variety of applications due to its tunable chemical and mechanical properties, together with its biocompatibility and biodegradability. However, the understanding of PGS synthesis becomes a challenge due to the lack of consistency when determining its synthesis parameters. Understanding these parameters is fundamental to control PGS synthesis and obtain a scalable and reproducible final product for biomedical applications. To unveil their effect on diverging PGS properties, diols are used as glycerol analogs and the reaction is chemically and thermally monitored, suggesting a heterogeneous reactivity of the exposed hydroxyl groups. Also, confinement of the prepolymerization is proven to be fundamental In order to maintain the equimolar ratio of initial monomers during synthesis. Early stages of the polycondensation (first 4 h) tend to linear and less branched oligomers by consuming primary hydroxyls rather than secondary hydroxyls. However, physicochemical characterization determines that a high degree of conversion (40%) is reached during these early stages. Afterward, the oligomers tend to condense through the secondary hydroxyls into a more crosslinked elastomer. This study demonstrates how hydroxyl affinity, water presence, and glycerol loss are crucial for the scalability and reproducibility of its final product.

Исследование активности бифункциональных катализаторов на превращение н-гексана

The production of various motor fuels is carried out by processing light fractions of oil with an initial temperature of boiling to 350°С. The current trend shows that oil in new fields has more weight than before. New oil reservoirs are deeper with a greater proportion of dark fraction with a boiling point of 350°С. This situation stimulates to find new ways of increasing the processing depth light fractions for synthesis target product. One of the main solution path for the problem is creation of new catalytic systems or modernization of existing ones. Motor fuels must meet the necessary operational and environmental characteristics, which is determined by their chemical composition. This article is devoted to the study of bifunctional catalyzers for the conversion of n-hexane. High molecular zeolite CVM (ZSM-5) was used as a carrier, which has functionality due to the presence of various active centers. Platinum (Pt/CVM), praseodymium (Pr/CVM) were also applied to the carrier, and praseodymium and platinum (Pt,Pr/CVM) were successively applied by impregnation. Normal hexane was used as a raw material. The choice of this raw material is associated with the ability to aromatization reaction, as well as the presence of n-hexane in the raw materials of the process of obtaining motor fuels-catalytic reforming. As a result of the transformation of raw materials, liquid fuel of multicomponent composition with the number of carbon atoms in the chain from 3 to 14, as well as gases containing C1 – C5 hydrocarbons, was obtained. When n-hexane is converted on the catalyzers under study, both the octane number and the content of aromatic hydrocarbons increase with increasing temperature. It has been found that when the process is carried out at a temperature of 450°C, the highest yield of the catalysate is (33.8% by weight.) on a Pt,Pr/CVM catalyzer. With an increase in temperature, the yield of benzene increases. Minimum benzene yield (0.6 wt. %) is achieved at 450°C marked by a bimetallic catalyzer, which corresponds to the EURO-5 gasoline standard. The highest degree of conversion was observed during the conversion of n-hexane on the Pt,Pr/CMC catalytic system at a temperature of 450° C, which was (97%).

SYNERGETIC EFFECTS OF PALLADIUM(II) AND COPPER(II) COMPOUNDS FIXED ON MODIFIED PHLOGOPITE IN THE REACTION WITH SULFUR DIOXIDE

Palladium(II) and cuprum(II) compounds are the basic components of the Wacker-type heterogeneous catalyst for the low-temperature oxidation of carbon monoxide with oxygen. Al2O3, activated carbon and carbon fiber materials are most commonly used as a carrier. In search of new potential natural media, layered aluminosilicate – phlogopite as part of natural phlogopite concentrate was investigated and it was proved that copper-palladium catalysts are formed on acid-modified samples of phlogopite, which provide a high degree of conversion of carbon monoxide, which meets the sanitary and chemical norm of CO in the working area, namely CKCO ≤ 20 mg/m3. Regardless of the nature of the carrier, it was found that the catalytic effect is achieved due to the synergism of palladium(II) and copper(II). A typical situation is when carbon monoxide and sulfur dioxide are simultaneously present in the waste gases of industrial enterprises. In this regard, research on the polyfunctionality of the Pd(II)-Cu(II)/S̅ nanocatalyst is relevant. The kinetics of the interaction of sulfur dioxide with mono- and bimetallic compositions based on compounds of palladium(II), copper(II) and acid-modified natural (Phl) and thermally swollen (TS-Phl) phlogopite were studied. It was established that monometallic compositions М(ІІ)-KBr/X̅Н-TC-Phl-1, М(ІІ) = Cu(ІІ), Pd(ІІ) fixed on acid-modified samples of swollen phlogopite, except for 6Н-TS-Phl-1, do not show protective properties against sulfur dioxide. It has been proven that the bimetallic compositions Pd(II)-Cu(II)-KBr/S̅ (S̅ = 6H-Phl-1; X̅H-TS-Phl-1, X̅ = 1, 2, 3, 6 M HNO3) in the reaction with SO2 reveal a synergistic effect with a coefficient of КS >> 1, which leads to an increase in the time of the protective action of the samples and the amount of absorbed sulfur dioxide. The synergism constant depends on the conditions of acid modification of the carrier and has a maximum value in the case of the bimetallic composition fixed on the carrier 2Н-ТS-Phl-1.

Direct grafting of microwrinkled hydrogels by atmospheric-pressure plasma polymerization: Going simple and environmentally friendly

The simple, direct fabrication of pH-responsive hydrogel coatings with microstructured wrinkles from a monomer mixture containing 2-hydroxyethyl methacrylate and 2-(diethylamino)ethyl methacrylate, grafted on silicon substrates via atmospheric-pressure plasma polymerization is reported. The process allows the synthesis of hydrogels with high conversion degree, which preserve the functionalities of both monomers as proven by XPS and FT IR analysis. Atomic force microscopy was conducted to characterize the wrinkle dimension, which revealed an increase of the wrinkle wavelength λ and amplitude A with the film’s thickness. The chemical and morphological properties of the hydrogel films are preserved, even after immersion in deionized water for several days, indicating the high stability of the plasma-polymerized hydrogels. The simplicity of atmospheric-pressure plasma polymerization to deposit responsive hydrogels which are highly stable and having tunable properties as “materials on demand”, will certainly extend the applications of plasma-based hydrogels especially for biomedical applications.

Cytocompatibility Evaluation of PEG-Methylsulfone Hydrogels.

Methylsulfone derivatized poly(ethylene) glycol (PEG) macromers can be biofunctionalized with thiolated ligands and cross-linked with thiol-based cross-linkers to obtain bioactive PEG hydrogels for in situ cell encapsulation. Methylsulfonyl-thiol (MS-SH) reactions present several advantages for this purpose when compared to other thiol-based cross-linking systems. They proceed with adequate and tunable kinetics for encapsulation, they reach a high conversion degree with good selectivity, and they generate stable reaction products. Our previous work demonstrated the cytocompatibility of cross-linked PEG-MS/thiol hydrogels in contact with fibroblasts. However, the cytocompatibility of the in situ MS-SH cross-linking reaction itself, which generates methylsulfinic acid as byproduct at the cross-linked site, remains to be evaluated. These studies are necessary to evaluate the potential of these systems for in vivo applications. Here we perform an extensive cytocompatibility study of PEG hydrogels during in situ cross-linking by the methylsulfonyl-thiol reaction. We compare these results with maleimide-thiol cross-linked PEGs which are well established for cell culture and in vivo experiments and do not involve the release of a byproduct. We show that fibroblasts and endothelial cells remain viable after in situ polymerization of methylsulfonyl-thiol gels on the top of the cell layers. Cell viability seems better than after in situ cross-linking hydrogels with maleimide-thiol chemistry. The endothelial cell proinflammatory phenotype is low and similar to the one obtained by the maleimide-thiol reaction. Finally, no activation of monocytes is observed. All in all, these results demonstrate that the methylsulfonyl-thiol chemistry is cytocompatible and does not trigger high pro-inflammatory responses in endothelial cells and monocytes. These results make methylsulfonyl-thiol chemistries eligible for in vivo testing and eventually clinical application in the future.

Thermal decomposition kinetic study on one-pack formulations of epoxy resin cured with novel phosphorus-containing flame retardant latent curing agents

Several phosphorous-containing flame retardant latent curing agents newly derived from 4,4-diamino diphenyl sulfone (DDS) and 4,4-diamino diphenyl methane (DDM) were designed to cure epoxy resin alongside dicyandiamide (Dicy). The thermal decomposition and kinetics of cured one-packed systems were investigated in detail. The epoxy systems were studied under a nitrogen atmosphere by using thermal gravimetric analysis at different heating rates. The kinetics of thermal decomposition was evaluated by Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink methods. The correlation coefficient for all systems obtained by the three above methods was almost equal to one, indicating that these three methods were correctly chosen. The results demonstrated that the activation energy of epoxy/Dicy blended with different phosphorous-containing DDS- and DDM-derived curing agents at a lower degree of conversion decreased by incorporation of the agents while increasing at a higher degree of conversion. The thermodynamic parameters (ΔH*, ΔG*, and ΔS*) of the studied systems were calculated by the obtained activation energy via three kinetics methods. It was found that as the conversion degree and the enthalpy increased, the Gibbs free energy decreased, while entropy changed from negative to positive values.

Influence of silane interfacial chemistry on the curing process of anionic Polyamide 6 in glass reinforced composites

The manufacturing of composites based on reactive thermoplastic polyamide 6 (PA6), reinforced with glass particles or fibers for structural applications, is quite sensitive to the state of the interface. Surface hydroxyls present at the glass surface can completely inhibit both the PA6 polymerization and crystallization processes. Care must then be exerted when tuning the interfacial chemistry in this system. This work demonstrates how an adequate choice of silane coupling agent, combined with a precise surface grafting methodology and tight control of hydroxyl groups density on glass particulates, yields kinetics and degrees of polymerization and crystallization comparable to the pure PA6 resin. Various silanes were grafted onto the microparticles and their surfaces were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, confocal laser scanning microscopy and contact angle measurements. The activator was also grafted onto the glass surface to initiate polymerization directly from the surface. The results showed that all treated glass particles surfaces allowed obtaining a high degree of conversion but with varying polymerization and crystallization kinetics. The results provide fundamental information on the role of the surface chemistry of glass reinforcements on the polymerization and crystallization of PA6, which are essential for the proper control of composite manufacturing.

Dielectric and physico-chemical behavior of single thermally thick wood blocks under microwave assisted pyrolysis

Pyrolysis of thermally thick beech wood blocks with a size of around 2.5 × 8 × 6 cm3 (width × length × height) was carried out in a lab scale microwave reactor with a frequency of 2.45 GHz, operated, both, at 300 W and 600 W under inert conditions, using N2 at around 400 mbar absolute pressure. The microwave cavity had a size of 20 × 20 × 20 cm3. The specific energy supply referred to the untreated wood block was 4–8 W/g, with slight variations depending on the initial water content. The mass loss and the reflected microwave power were in-situ monitored during the experiments. The sample surface and chamber temperatures were measured with a pyrometer and a thermocouple, respectively. Physico-chemical and dielectric properties of the produced solids were investigated and compared to those of chars produced under conventional pyrolysis using the same raw materials. It is shown that the complex dielectric permittivity of the solid products changed drastically during the pyrolysis process, with increasing heating properties as the conversion process evolved. This was easily achieved using 600 W without susceptors. However, 300 W was not enough to achieve a high conversion degree, independently of the irradiation time. This, together with the physico-chemical analyses of the solids, hinted to the importance of the transport kinetics in thermally thick materials, although further investigation is still required.

A New Approach for Synthesizing Fatty Acid Esters from Linoleic-Type Vegetable Oil

Countries around the world recognize the numerous social, economic and environmental advantages of promoting liquid biofuels. They invest in its development and introduce tax incentives for its manufacture and tariffs of production regulation. In most studies, the process of synthesizing fatty acid esters takes a long time from 1 to 8 h. In this work, the synthesis of fatty acid esters was carried out in the range of volumetric ratios of ethanol to linoleic type oil in order to increase the kinetics of the process. The main parameters of the synthesis were studied by use of magnetic stirred tank reactors in a parallel reactor system, H.E.L. The synthesis was carried out in the presence of a homogeneous alkaline catalyst. The volumetric ratio of ethanol to oil was maintained at 1:1, 2:1, 3:1, 4:1 and 5:1. The amount of catalyst added to the reaction mixture ranged from 0.25 to 2.5% by the weight of the reaction alcohol. The dryness of ethanol varied from 91 to 99%. Effective process conditions have been established to reduce the reaction time from 2.5 h to 5 min while maintaining a high degree of conversion. The results obtained during the study suggest the possibility of using a continuous reactor to produce fatty acid esters from linoleic raw materials containing up to 16% of free fatty acids. This also means the possibility of using second generation biofuel feedstock.

Numerical simulation of biogas chemical looping reforming in a dual fluidized bed reactor

Conversion technologies with low environmental impact and high energetic efficiency are needed to ensure clean, efficient, and cost-effective exploitation of renewable carbonaceous fuels like biogas. In the present study, the Chemical Looping Reforming of biogas is proposed and numerically investigated to pursue this goal. Preliminarily, a thermodynamic model was implemented by means of the Aspen Plus® commercial software to identify the conditions where carbon formation and deposition do not occur. A simple hydrodynamic model of a Dual Fluidized Bed reactor coupled with a 1D, static, and isothermal kinetic model was adopted. The effects of variations in biogas composition (namely, CH4:CO2 ratio and water content) and in other relevant process parameters (e.g., the oxygen-to-fuel ratio and FR operating temperature) on the process performances in terms of the reactants conversion degree, syngas yield, and syngas composition were assessed and critically discussed. Very high conversion degree for both CH4 (93%) and CO2 (87%), as well as syngas yield ranging up to 3.74, were evaluated.

Degree of conversion and residual monomer elution of 3D-printed, milled and self-cured resin-based composite materials for temporary dental crowns and bridges

The aim of this work was to investigate the elution of residual monomers as a function of the manufacturing process, which are CAD/CAM manufacturing, self-curing and 3D printing. The experimental materials used consisted of the base monomers TEGDMA, Bis-GMA and Bis-EMA and 50 wt.% fillers. Additionally, a 3D printing resin without fillers was tested. The elution of the base monomers into the different media (water, ethanol and ethanol/water (75/25 vol. %)) at 37 °C over a period of up to 120 d as well as the degree of conversion (DC) by FTIR were investigated. No monomer elution could be detected in water. Most residual monomers in both other media were released from the self-curing material whereas the 3D printing composite released relatively little. The CAD/CAM blanks released hardly any quantitatively detectable amounts of monomers. Relative to the base composition, TEGDMA eluted less than Bis-GMA and Bis-EMA. DC did not correlate with residual monomer release; thus, leaching was determined not only by the amount of residual monomers present but by further factors as possibly network density and structure. The CAD/CAM blanks and the 3D printing composite showed similar high DC but lower residual monomer release from the CAD/CAM blank, likewise the self-curing composite and the 3D printing resin exhibited similar DC but different monomer elution. In terms of residual monomer elution and DC, the 3D printing composite seems promising as a new material class for the use as temporary dental crowns and bridges.Graphical

Selective oxidation of the 4-ethyl-3-methylcinnoline methylene group by al<sub>2</sub>o<sub>3</sub>-supported chromium oxide

The optimal conditions for the oxidation of the methylene group in 4-ethyl-3-methylcinnoline to the corresponding ketone, 3-methyl-4-acetylcinnoline, were selected. It was shown that preliminary deposition of 4-ethyl-3-methylcinnoline on some inorganic substrates has a significant effect both on the selectivity of the oxidation of only the methylene group and on a high degree of conversion to the target product.

Study on Steam Co-Gasification of Waste Tire Char and Sewage Sludge

The large and growing volume of tire waste and sewage sludge requires disposal, for which thermochemical processes such as gasification can be used. Co-gasification of these two waste products allows the tire char to be used as a charge stabilizer and the sewage sludge to improve reactivity and efficiency. The purpose of this study was to evaluate the effect of the composition of a waste tire char and sewage sludge fuel blend on the gasification process, using steam as the gasification agent. Tests were carried out for tire char, municipal sewage sludge, and blends of the two in ratios of 90:10 and 67:33. An analysis of the materials used was carried out (ultimate and proximate analysis as well as ash composition), and isothermal measurements of steam gasification were taken using the thermal volumetric method for temperatures of 800, 850, and 900 °C at an elevated pressure of 1 MPa. On the basis of the results, the formation curves of the main gasification products (H2, CO, CO2, and CH4) were created, the curves for the degree of carbon conversion were plotted, the reactivity indexes were determined for different degrees of conversion (0.25, 0.5, and 0.75), and the quantity and composition of the resulting gas were analyzed. Using the grain model, the kinetic parameters (activation energy and pre-exponential factor) of the gasification reaction were calculated. The addition of municipal sewage sludge had a positive effect on the reactivity of tire char and increased the efficiency of gasification, because it contained components that act as catalysts in the gasification process. There was a favorable effect from the addition and higher amount of sewage sludge on lowering both the activation energy (49.5 kJ/mol and 89.2 kJ/mol for 90:10 and 67:33 blends, respectively) and the pre-exponential factor. A significant improvement in reactivity, with a high degree of conversion and the best gas composition, was obtained for a 90:10 blend at 900 °C.

Enzyme Conditioning of Chicken Collagen and Taguchi Design of Experiments Enhancing the Yield and Quality of Prepared Gelatins.

During the production of mechanically deboned chicken meat (MDCM), a by-product is created that has no adequate use and is mostly disposed of in rendering plants. Due to the high content of collagen, it is a suitable raw material for the production of gelatin and hydrolysates. The purpose of the paper was to process the MDCM by-product into gelatin by 3-step extraction. An innovative method was used to prepare the starting raw material for gelatin extraction, demineralization in HCl, and conditioning with a proteolytic enzyme. A Taguchi design with two process factors (extraction temperature and extraction time) was used at three levels (42, 46, and 50 °C; 20, 40, and 60 min) to optimize the processing of the MDCM by-product into gelatins. The gel-forming and surface properties of the prepared gelatins were analyzed in detail. Depending on the processing conditions, gelatins are prepared with a gel strength of up to 390 Bloom, a viscosity of 0.9-6.8 mPa·s, a melting point of 29.9-38.4 °C, a gelling point of 14.9-17.6 °C, excellent water- and fat-holding capacity, and good foaming and emulsifying capacity and stability. The advantage of MDCM by-product processing technology is a very high degree of conversion (up to 77%) of the starting collagen raw material to gelatins and the preparation of 3 qualitatively different gelatin fractions suitable for a wide range of food, pharmaceutical, and cosmetic applications. Gelatins prepared from MDCM by-product can expand the offer of gelatins from other than beef and pork tissues.

Degree of conversion of 3D printing resins used for splints and orthodontic appliances under different postpolymerization conditions.

To measure the degree of conversion (DC) of different 3D printing resins used for splints or orthodontic appliances under different postpolymerization conditions. Five 3D-printed photopolymer resins were studied. Each resin was analyzed in liquid form (n = 15), and then cylindrical specimens (n = 135) were additively manufactured and postcured with Form Cure (Formlabs) at different times (10, 60, and 90min) and temperatures (20°C, 60°C, and 80°C). The DC of each specimen was measured with Fourier transform infrared spectroscopy (FTIR). The data were statistically analyzed using a 3-way ANOVA followed by Tukey's post hoc test. The time and temperature of postpolymerization significantly influenced the DC of each resin: when time and/or temperature increased, the DC increased. For all resins tested, the lowest DC was obtained with a postcuring protocol at 10min and 20°C, and the highest DC was obtained at 90min and 80°C. However, at 80°C, the samples showed a yellowish color. With the Form Cure device, the time and temperature of postcuring could have an impact on the DC of the 3D printing resins studied. The DC of the 3D printing resins could be optimized by adjusting the postpolymerization protocol. Regardless of the resin used, when using the Form Cure device, postcuring at 60min and 60°C would be the minimal time and temperature conditions for achieving proper polymerization. Beyond that, it would be preferable to increase the postcuring time to boost the DC.

FUNDAMENTAL PRINCIPLES OF MICROGEL SYNTHESIS BY INVERSE EMULSION METHOD

Microgels represent a unique class of compounds that combine the properties of such classes of compounds as colloids, macromolecules and surfactants in a unique way. Microgels are widely used for wastewater treatment, as drug delivery systems, for drying biodiesel, in tissue regeneration and implantation, in chromatography, etc. At this point, such methods of microgel synthesis as the precipitation method, suspension polymerisation and the emulsion method have been developed, which have become traditional in the synthesis of microgels. This publication reviews the inverse emulsion method for microgel synthesis based on polyacrylamide and its derivatives. This method was chosen due to a number of advantages, such as a high degree of monomer conversion, the ability to control the granulometric composition of gel particles during synthesis, a simplified drying procedure for the finished product, etc. The article describes the synthesis features that affect the size and shape of microgels, describes the main factors to consider when planning an inverse emulsion synthesis; shows the difference between macroemulsion, nanoemulsion and microemulsion. The article also presents some aspects of the synthesis of microgel based on acrylamide and its derivatives: the main free-radical initiators are listed; monomers that affect microgel properties are described. This review may be of interest to specialists who are just starting research in this field. Based on this publication, the reader will be able to plan and conduct an experiment on the synthesis of polyacrylamide-based microgels by the inverse emulsion method. For citation: Burin D.A., Rozhkova Yu.A., Kazantsev A.L. Fundamental principles of microgel synthesis by inverse emulsion method. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 3. P. 6-17. DOI: 10.6060/ivkkt.20236603.6732.

Crystallization of SAPO-11 Molecular Sieves Prepared from Silicoaluminophosphate Gels Using Boehmites with Different Properties

In this article, we report the results of research the formation of silicoaluminophosphate gels under changing gel aging conditions and the influence of an aluminum source (boehmite), characterized by different properties. The samples of initial gels were characterized by XRF, X-ray diffraction, MAS NMR 27Al and 31P, and scanning electron microscopy (SEM). Products of crystallization were characterized by XRF, X-ray diffraction, MAS NMR 27Al and 31P, scanning electron microscopy (SEM), N2-physical adsorption, and IR spectroscopy with pyridine adsorption. It has been established that the chemical and phase composition of aging gels and the products of further crystallization is conditioned by the size of the crystals and the porous structure of boehmite. Methods of management the morphology and secondary porous structure of SAPO-11, including the hierarchical porous structure, are proposed based on the use of boehmits characterized by different properties and changing the aging conditions of the initial gels. SAPO-based catalyst with a hierarchical porous structure showed excellent catalytic performance in dimerization of α-methylstyrene with a high degree of conversion and selectivity for linear isomers.

Effect of thickness on the degree of conversion, monomer elution, depth of cure and cytotoxicity of bulk-fill composites

Today, bulk-fill composites are used as a single layer with a thickness of up to 4-5 mm. However, is proper polymerization achieved with this increased thickness? This study was designed to investigate the effect of thickness on the degree of conversion (DC) (n = 6), the elution of monomers (n = 6), depth of cure (DoC) (n = 10) and cytotoxicity (n = 6) of the bulk-fill composites SDR Flow Plus (SDR), SonicFill2 SingleFill (SF) and ACTIVA Bioactive Restorative (ACT) in comparison to the conventional G-aenial Posterior (GC). Two-way analysis of variance (ANOVA) was used to assess the interaction between materials and surfaces, and one-way ANOVA and Tukey tests were used to compare the degree of conversion, monomer elution and cytotoxicity values (P < 0.05). The highest DC was found at the top surface of SDR, while the lowest DC was found at SF. The V2 mm/V0 mm DoC ratios of the composites except ACTs were appropriate according to the threshold. None of the composites were cytotoxic on day 1. In bulk-fill composites, DC decreased and monomer elution increased with increasing depth. The V4 mm/V0 mm ratios of all bulk-fill groups were not appropriate. Additionally, only ACTs had a cell viability of <70% on day 7.

Experimental evaluation of lime spray drying for SO&lt;sub&gt;2&lt;/sub&gt; absorption

&lt;abstract&gt; &lt;p&gt;This paper presents the findings of an experimental investigation on the performance of a laboratory-scale spray dryer involving flue gas desulfurization. Using commercial hydrated lime as a sorbent, a systematic set of experiments were performed to evaluate SO&lt;sub&gt;2&lt;/sub&gt; absorption capacity of the spray dryer. The experimentation involved accurate measurement of the spray drying characteristics, such as temperature and SO&lt;sub&gt;2&lt;/sub&gt; concentration along the spray chamber, by varying the input and output variables. Tests were done to investigate the effects of spray characteristics, i.e., inlet gas phase temperature (120–180 ℃) and calcium-to-sulfur ratio (1–2.5), on SO&lt;sub&gt;2&lt;/sub&gt; removal efficiency. The performance of the spray dryer was further evaluated based on the degree of conversion of calcium (sorbent utilization) after SO&lt;sub&gt;2&lt;/sub&gt; absorption. Results indicated an increase in SO&lt;sub&gt;2&lt;/sub&gt; removal efficiency by increasing the stoichiometric ratio and decreasing the temperature. Absorption efficiency of SO&lt;sub&gt;2&lt;/sub&gt; beyond 90% was achieved at a stoichiometric ratio of 2.5. A high degree of conversion of calcium was realized at low stoichiometric ratios, with a maximum utilization of 94% obtained at a stoichiometric ratio of 1.5. The analysis of the final desulfurization product revealed the presence of sulfite with better conversion achieved at a stoichiometric molar ratio of 1.5. A significant amount of unreacted sorbent (63.43%) was observed at a stoichiometric ratio of 2, while samples collected at a stoichiometric ratio of 1.5 had the lowest concentration of unreacted Ca[OH]&lt;sub&gt;2&lt;/sub&gt; (41.23%).&lt;/p&gt; &lt;/abstract&gt;

Antifungal activity, mechanical properties, and accuracy of three-dimensionally printed denture base with microencapsulated phytochemicals on varying post-polymerization time

BackgroundStudies on the antifungal activity, flexural strength, Vickers hardness, and intaglio surface trueness of three-dimensionally printed (3DP) denture bases with microencapsulated phytochemicals with respect to changes in post-polymerization time (PPT) are lacking.MethodsSpecimens of various shapes and dimensions were fabricated with a 3DP denture base resin mixed with 5 wt% phytoncide-filled microcapsules. Each specimen was subjected to different PPT protocols of 5, 10, 20, and 30 min. Specimens without microcapsules with 5-min PPT were used as the negative control group. Cell colonies were counted to evaluate antifungal activity. Three-point bending and Vickers hardness tests were performed to measure the flexural strengths and hardness of the specimens. Fourier-transform infrared spectrometry was used to inspect the degree of conversion (DC). The intaglio surface trueness was measured using root-mean-square estimates calculated by superimposition analysis. A non-parametric Kruskal–Wallis test or one-way analysis of variance was performed (α = 0.05).ResultsThe specimens with microcapsules and 10-min PPT showed the highest antifungal activity among the tested groups. Compared with the positive control group (5-min PPT), the specimens with PPTs of 10 min or longer showed significantly higher mean flexural strength, higher DC, greater hardness, and better trueness (all, P < 0.05). Except for the difference in antifungal activity, no statistically significant differences were detected between the specimens subjected to 10-, 20-, and 30-min PPT.ConclusionThe 3DP denture base filled with microencapsulated phytoncide showed different antifungal activity and physical properties on changing PPT. The 3DP denture base containing phytoncide-filled microcapsules at 5 wt% concentration and subjected to 10-min PPT exhibited sufficient antifungal activity as well as mechanical properties and accuracy within clinical acceptance.