Effect of shade and thermo-mechanical viscosity stimulation methods on the rheological properties of nanohybrid resin composite

The aim of the present study is to measure the rheological properties of nanohybrid resin composite of three shades in pre-polymerized phase using different thermomechanical stimulations. Nanohybrid composite (Kerr Herculite XRV Ultra) in enamel, dentin, and incisal shades was included. Rheological measurements were made with a rotational rheometer in dynamic oscillation mode using three methods: (a) Strain Sweep test explored a range of deformation γ₀ from 0.025 to 3% with a frequency ω = 1 Hz (temperature set at 25 and 65?°C), (b) Frequency Sweep test explored frequencies between 1 and 100 rad/s applying a deformation γ₀ = 0.5% (temperature set at 25; 45; 65?°C), and (c) Ramp Temperature test explored a heating phase from 25 to 75?°C then a cooling phase back to 25?°C applying a γ₀ = 0.5% and a ω = 10 rad/s. Data were analyzed using a three-way ANOVA and Tukey’s test (α = 0.05). Viscosity measurement (p < 0.05) and shade of the composites (p < 0.05) significantly affected the results. Viscosity turned out to be subordinate to strain amplitude, frequency, temperature, and axial force applied during each test. Enamel shade was the most viscous whereas dentin shade was 8% less viscous (p < 0.05). The incisal shade was significantly less viscous (70%) than enamel (p < 0.05). Pre-heating decreased viscosity of incisal shade (30%) above 50?°C but this value was 90 and 98%, respectively, for strain and frequency sweep test. Preheating had a side effect as in the cooling phase, viscosity increased from 66 to 450% exceeding the value recorded at the beginning of the test. Preheating was not effective to reduce viscosity, and may reveal some side effects. The composite tested might not be pre-heated above 45?°C.     

Recycling of Waste PET: Usage as Secondary Plasticizer for PVC

Postconsumer water bottle poly(ethylene terephthalate) (PET) flakes were depolymerized with ethylene glycol (EG) by the glycolysis reaction in the presence of zinc acetate as the catalyst. In the depolymerization reactions, different weight ratios of PET/EG were used. In order to obtain polyesters used as PVC plasticizers, these glycolysis products containing hydroxyl end groups were reacted with an adipic acid (AA)–containing diacid group at equivalent amounts. In order to obtain PVC plastisols, PVC was dispersed into a plasticizers' mixture composed of di-isooctyl phthalate (DOP) and polyester products by using a high-speed mixer (PVC/plasticizers, 65/35 w/w). For the preparation of plasticizer mixture polyester products were used at a weight ratio of 20%, 40%, 60% of DOP. Plasticized PVC sheets were prepared from plastisols and their glass transition temperatures (T_g), migration, and mechanical properties were determined. The results show that the polyester products obtained from glycolysis products of waste PET can be used as secondary plasticizers, with DOP for PVC.     

Equilibrium Swelling Studies of Chemically Cross-Linked Highly Swollen Acrylamide-Sodium Acrylate Hydrogels in Various Water-Solvent Mixtures

Swelling behavior of acrylamide (AAm)/sodium acrylate (SA) hydrogels was investigated in water-solvent (methanol, ethanol, t-butanol and acetone) mixtures of various compositions. AAm/SA hydrogels were prepared by free radical solution polymerization in aqueous solutions of AAm with SA as comonomers and a multifunctional cross-linker such as trimethylolpropane triacrylate (TMPTA). Swelling experiments were performed in water and water-organic solvent mixtures of various compositions at 25°C, gravimetrically. The value of S_eq% of AAm/SA hydrogels are 64–152% for 60% of metanol, 84–102% for 60% of ethanol, 127–176% for 60% of t-butanol, 131–585% for 60% of acetone, while the value of S_eq% of AAm/SA hydrogels are 780–4510% for water and water-solvent mixtures. Some swelling kinetic parameters were found. Diffusion behavior of water and water-solvent mixtures was investigated. Diffusion of water and water-solvent mixtures into the hydrogels was found to be non-Fickian in character.     

Effect of Physicochemical Surface Treatments on the Bond Strength and Adhesion of Porcelain Denture Teeth to Heat-Polymerized Acrylic Resin Denture Base Material

The aim of this study was to compare the effect of physicochemical surface treatments on the adhesive bond strength of porcelain denture teeth (PDT) to acrylic resin denture base material (PMMA). Totally, 100 PDT specimens, 50 with retentive palatal pins (+P) and 50 without pins (?P), were selected and assigned to 10 experimental groups (n = 10). Control groups CON-P and CON + P, did not receive any treatment. Groups SB + P and SB-P were sandblasted, groups SB/AE + P and SB/AE-P were sandblasted and acid-etched, groups TSC + P and TSC-P were tribochemically silica-coated, and groups FB + P and FB-P were covered with fibers. Cylindrical PMMA rods were polymerized onto treated palatal PDT surfaces. Force (N) was applied on palatal incisal edges of PDT specimens until debonding of PMMA. Obtained data were statistically analyzed with Kruskal-Wallis and Bonferroni corrected Mann Whitney U tests. The significance level was set at (p < .05). Mean force values of test groups ranged in descending order as follows: TSC+P (132.5 N ± 26.5), SB+P (113.5 N ± 47.5), SB/AE+P (112.2 N ± 26.1), CON+P (103.1 N ± 39.6), TSC-P (90.6 N ± 22.2), FB+P (77.7 N ± 18.3), SB/AE-P (47.6 N ± 10.5), SB-P (18.1 N ± 4.0), CON-P (4.6 N ± 5.4), and FB-P (0.0 N ± 0.0). No significant difference was found between groups with pins (+P) except group FB+P which displayed lower values than CON+P (p < .024), and TSC+P (p < 045). Groups (+P) showed significantly higher bond strength values than groups (?P) except for group TSC-P (p < .09 and p < 1). In groups without pins (P?), differences between groups were significant and ranged as follows: TSC-P>SB/AE-P (p < .0094), SB/AE-P > SB-P (p < .007), and SB-P > CON-P (p < .0013). Groups CON-P and FB-P did not show differences (p ≤ 1). Groups (+P) displayed higher bond strength values than groups (?P). SB-P, SB/AE-P, and TSC-P increased the adhesive bond between PDT and PMMA, respectively. Fiber coating negatively affected the bond.     

Photodegradation of Methylene Blue with Ag2O/TiO2 under Visible Light: Operational Parameters

Ag₂O modified TiO₂ nanoparticles were synthesized by precipitation and wet impregnation method. They were characterized by X-ray diffraction technique, UV-vis diffuse reflectance spectrophotometry and Fourier transform infrared spectroscopy. Inductively coupled plasma mass spectrometry was performed to quantify Ag amount in the photocatalysts. The photocatalysts occurred in the concentration range of 0.05%–2% in the Ag/Ti molar ratio. The photocatalytic activity was investigated for the degradation of methylene blue as a model organic dye. Optimum reaction conditions were determined to provide maximum dye degradation efficiencies under visible light. Under visible light illumination, C2-Ag₂O/TiO₂ (Ag/Ti = 0.1/100) showed the highest activity. Reaction rate constants were calculated and compared for various reaction conditions.     

DEVELOPMENT AND DESIGN OF A LIQUID MEMBRANE ENZYME REACTOR FOR THE DETOXIFICATION OF BLOOD

Liver failure causes the enrichment of different lipophilic metabolites: phenol derivatives, mercaptans and short-chain fatty acids in blood. The removal of these toxines from blood is necessary to avoid death and to support the liver's self-regeneration. The liquid surfactant membrane technique with consecutive chemical reaction is used for this purpose.

Liquid membranes were developed for the extraction of fatty acids. Enhancement of mass transfer is achieved by an instantaneous chemical reaction inside the emulsion globules, selectivity is obtained by using a suitable carrier. Essential fatty acids are not affected. Phenolic compounds are removed by extraction and consecutive enzymatic reaction inside the liquid membrane globules. This way of detoxification is identical with elimination in the living organism. Furthermore, a new model is being developed to describe the results of phenol extraction. This model makes possible the simulation of the detoxification process in the human organism. A flow sheet is proposed showing how to apply the liquid surfactant membrane technique to artificial liver support and the detoxification rate is calculated. Artificial liver Liquid membrane Blood detoxification     

Development and Thermal Modeling of a New Construction Biomass Dryer

A new dryer construction has been developed for drying biomass basic materials for energy purposes (straw, sawdust, and other light granular materials). As a result of its simple design, the machine is perfectly suitable for reducing moisture by heat transfer. Compared to the machine types applied thus far, this new construction provides a better ratio of dryer floor space and drying distance and, as a result, a longer drying time. A differential equation system for convection drying was applied for the thermal modeling of the equipment; the mathematical model produced on the basis there of is suitable for examining the heat and mass transfer processes within the dryer. In the course of experimental measurements performed in an industrial size apparatus, the temperature and moisture content of the drying gas were recorded with the initial and final moisture content and surface temperature of the product. The measured values were compared to the results of calculations using the mathematical model.     

The effects of incorporating wild‐type strains of Lactococcus lactis into Turkish white‐brined cheese (Beyaz peynir) on the fatty acid and volatile content

The development of free fatty acids (FFA) and volatile flavour compounds in the Turkish white‐brined cheese Beyaz peynir made by using three wild strains of Lactococcus lactis subsp. lactis was investigated over 90 days. Results showed that production of both FFA and flavour compounds in the control (PK1) and experimental cheeses (MBLL9, MBLL23 and MBL27) was strain dependent. The hydrolysis of milk fat was more evident in the cheese made using Lc. lactis subsp. lactis MBL27. Considering the production of fat breakdown compounds and acidification activities of the strains MBLL23 and MBL27, the combination of these strains could be proposed for the production of white‐brined cheese.