Evaluation of the shear bond strength of two resin cements on different CAD/CAM materials

Objective: This study investigated the bond strength of two resin cements (Panavia F 2.0 and Multilink N) to different CAD/CAM materials: resin nanoceramic (RNC; Lava Ultimate), hybrid ceramic (HC; Vita Enamic), zirconia-reinforced lithium silicate ceramic (ZLDC; Vita Suprinity), and lithium disilicate glass-ceramic (LDG; IPS e.max CAD HT).

Material and methods: CAD/CAM blocks of 2-mm thickness were sectioned with a slow-speed diamond-saw sectioning machine. The slabs were then embedded in autopolymerizing acrylic resin (n = 12), and resin cements were applied to the surface of the specimens. All specimens were stored in water for 24 h and subjected to 5000 thermal cycles. Bond strength was measured by means of the shear bond strength test. The data were statistically analyzed by two-way ANOVA and Tukey LSD post hoc tests.

Results: The results of the two-way ANOVA test indicated that the bond strength values varied significantly depending on the CAD/CAM restorative materials, resin cements, and interaction of these variables (p < 0.05). The RNC group showed the highest bond strength for Panavia F 2.0 (p < 0.05); there were no significant differences among other CAD/CAM materials for Panavia F 2.0 (p > 0.05). The LDG group showed the highest bond strength for Multilink N, it was followed by the ZLDC group (p < 0.05); there were no significant differences between RNC and HC groups (p > 0.05).

Conclusions: Choosing resin cements for restorations should be done carefully because bond strength values vary significantly depending on the resin cement and CAD/CAM restorative material.     

Zinc and tin xanthates in the coordination polymerization of propylene oxide

The polymerization of propylene oxide with zinc and tin xanthates was studied. Polymerization with both systems was found to be a zeroth‐order, nonterminating process, where the molecular weight was controlled by transfer reactions. It is discussed that these observations were consistent with a mechanism in which the rate‐determining step was the addition of monomer on the growing chain rather than the coordination of the monomer to active sites. These catalysts turned out to be quite stable, even under semiclosed conditions. With zinc isopropyl xanthate, high conversions in short polymerization times could be obtained. The product had a very broad molecular weight distribution and could be split into crystallizable and amorphous fractions. The crystallizable fractions consisted of stereoregular segments separated from each other by stereoirregularities or regioirregularities. The degrees of polymerization of stereoregular segments (S₁'s) were estimated from melting point measurements. It was found that the melting points and, hence, average S₁ values changed in different fractions. It was concluded that there was only one type of active center; however, the rates of wrong additions (e.g., head‐to‐head addition) of incoming monomer controlled the average S₁ value of the chain. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Polythiophene/borax conducting composite II: Electrorheology and industrial applications

In this study, polythiophene (PT) and polythiophene/ borax conducting composite (PT/borax) were in‐situ synthesized using FeCl₃ as oxidizing agent containing 89.2% PT and 10.8% borax. The electrorheological (ER), creep‐recovery, and vibration damping characteristics of the PT/borax composite were investigated. A volume fraction series (φ = 5–25%) of the PT/borax/silicone oil dispersions were prepared and sedimentation stabilities were determined. An ER activity was observed from the samples, when subjected to external electric field strength thus, they were classified as smart materials. Some parameters affecting the ER properties of the dispersions such as volume fraction, shear rate, electric field strength, frequency and temperature were investigated. Creep tests were applied to the suspensions to investigate the viscoelastic behaviors and recoverable viscoelastic deformations observed. Finally, real time vibration damping experiment was carried out on a modified automobile shock absorber and a 68% vibration damping capacity determined for borax/SO suspension system under E = 0.3kV/mm condition. POLYM. COMPOS., 2011.© 2011 Society of Plastics Engineers     

Fluorescence study on drying of ι-carrageenan gels at different temperatures prepared with various CaCl<Subscript>2</Subscript> content

The influence of temperature and salt content on drying was investigated by using steady-state fluorescence (SSF) technique. Supporting gravimetric and volumetric measurements were also carried out during drying of gels at various temperatures. ι-Carrageenan gels were prepared with various CaCl₂ content. Pyranine was introduced as a fluorescence probe during gel preparation. Apparent fluorescence intensity, I, was measured during in situ drying process at each temperature and it was observed that fluorescence intensity values decreased for all gel samples. A simple model consisting of Case II diffusion was used to produce the packing constants, k ₀, for helixes. It was observed that k ₀ increased as the drying temperature was increased. On the other hand at each temperature, it was seen that k ₀ decreased as CaCl₂ content was increased. Packing energies for drying processes were obtained from fluorescence, volumetric, and gravimetric measurements separately.     

Saponins: properties, applications and processing

Saponins are a diverse group of compounds widely distributed in the plant kingdom, which are characterized by their structure containing a triterpene or steroid aglycone and one or more sugar chains. Consumer demand for natural products coupled with their physicochemical (surfactant) properties and mounting evidence on their biological activity (such as anticancer and anticholesterol activity) has led to the emergence of saponins as commercially significant compounds with expanding applications in food, cosmetics, and pharmaceutical sectors. The realization of their full commercial potential requires development of new processes/processing strategies to address the processing challenges posed by their complex nature. This review provides an update on the sources, properties, and applications of saponins with special focus on their extraction and purification. Also reviewed is the recent literature on the effect of processing on saponin structure/properties and the extraction and purification of sapogenins.     

Nail penetration test for determining the uniaxial compressive strength of rock

We offer a new and practical index test method, the nail penetration test (NPT), to estimate the UCS of intact rocks, to be used as alternative to the point load test (PLT) or Schmidt rebound hammer test (SRH). The major tools used in the investigation include a gasnailer with 130 J power and its nails ranging from 25 to 60 mm in length. The study material covers 65 rock blocks of gypsum, tuff, ignimbrite, andesite, sandstone, limestone, and marble. For the NPT, five nail shots were performed on each block sample and the average value was obtained. Two to three uniaxial compression tests were carried out on each specimen. Ten impacts were applied on rock blocks by using both the L- and N-types of SRH. Regarding the PLT, either 10 axial or 10 block tests was applied on each rock type.The average nail penetration depths were correlated with the UCS, I_S(50) and rebound number for both types of the SRH. Also, the measured UCS values were compared with those obtained from the empirical relationships using the data from the NPT, PLT, and SRH. It was found that the NPT provides better estimates for UCS than the PLT or SRH. Particularly applicable to weak to very weak rocks, the NPT is capable of indirectly estimating the UCS of intact rocks up to 100 MPa. The test is proposed for use in mainly in situ applications.     

Determination of secondary transitions and thermodynamic interaction parameters of poly (ether imide) by inverse gas chromatography

Summary The retention diagrams of poly(ether imide) for ethyl benzene, n-propyl benzene, isopropyl benzene, chloro benzene, n-butyl acetate, tert-butyl acetate, isoamyl acetate, n-nonane, n-decane, n-undecane, n-dodecane and n-tridecane were obtained by inverse gas chromatography technique. In this work, the slope changes on the diagram were assigned as secondary transitions. The secondary transition temperatures obtained by inverse gas chromatography technique are in good agreement with the ones obtained by thermally stimulated depolarization current in the literature. Specific retention volume, V_g⁰, the weight fraction activity coefficients of the solvents at infinite solution, Ω₁^∞, Flory-Huggins polymer-solvent interaction parameters,χ₁₂^∞, equation-of-state polymer-solvent interaction parameters,χ₁₂^*, effective exchange energy parameters, X_eff were determined. Later, the partial molar heat of sorption, and the partial molar heat of mixing, were obtained. The solubility parameter of poly(ether imide), δ₂ was determined as 10.7 (cal/cm³)^1/2 by extrapolation of the δ₂ values obtained by considering the free volume effects from studied temperature range to room temperature.