No abstract

The influence of the plasticizer content and film preparation procedure on the morphology, density, thermal and mechanical properties of cellulose acetate (CA) films plasticized with poly-(caprolactone triol) (PCL-T), were studied. Differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD) and infrared spectroscopy (FT-IR) techniques were used. The films were prepared by dry-casting CA and CA/PCL-T in acetone or acetone/water solutions, which produced transparent and opaque films, respectively. In contrast to the transparent films, which were dense, the opaque films presented a porous morphology. However, the presence of PCL-T reduced the opaque film porosity, increasing, in consequence, its bulk density. The TMA results revealed that PCL-T reduced the glass transition temperature more significantly in the transparent than in opaque films. Only the transparent CA/PCL-T films presented a melting temperature, that reduced with higher concentrations of PCL-T, suggesting a higher ordering (crystallinity) when the films were prepared in the absence of water, as observed from WAXD curves. The mechanical properties also showed that the transparent films were more soft and tough than the opaque films. In summary, PCL-T was a good plasticizer agent for CA films due to the presence of hydrogen bonds between the components (FT-IR spectra). The presence of water in the dry casting process has a significant effect mainly on film morphology and mechanical properties.

In this investigation, our aim was to evaluate the performance of a controlled release of malathion pesticide loaded in microspheres of pure polymers of poly(3-hydroxybutyrate) and poly(e-caprolactone) (PCL) and of blends of these polymers with compositions of 70/30, 80/20, 90/10, 95/5, and 97/3 w/w. Microspheres were obtained by an emulsion-evaporation method to load a model pesticide. Scanning electron microscopy and differential scanning calorimetry were used to characterize the effect of the pesticide on the morphology and particles size of the biodegradable microspheres. The interaction between the matrix and pesticide was determined by Fourier transform infrared spectroscopy. The test for controlled release was performed in an aqueous medium, and malathion was quantified by ultraviolet spectroscopy. The results show that the release of malathion was improved with the PCL content in the blends; this indicated the possibility of modulating the release of the pesticide in these biodegradable blends.

One of the reasons for resin-dentin degradation is poor polymerization of the adhesive layer. This study evaluated the effect of prolonged polymerization times on the immediate and 6-month resin-dentin bond strengths, silver nitrate uptake, and polymer quality of etch-and-rinse adhesives. Thirty extracted teeth were obtained, and a flat dentin surface was exposed on each tooth. Adhesives (Adper Single Bond 2 and One Step Plus) were applied to the dentin surface of these teeth and light-cured for 10, 20, or 40 s at 600 mW cm(-2) . Bonded sticks (0.6 mm(2) ) were tested in tension (0.5 mm min(-1) ) and analyzed, after immersion in 50% silver nitrate, using scanning electron microscopy. The polymer quality of adhesive films was evaluated using thermogravimetric analysis. Statistically higher bond strengths were observed for both adhesives when light-cured for 40 s. Degradation of dentin bonds occurred under all experimental conditions but it was less pronounced for adhesives light-cured for 40 s. Longer exposure times reduced silver nitrate uptake for Adper Single Bond 2. Solvent retention and the amount of residual monomer were statistically lower when both adhesives were light-cured for 40 s. Although longer exposure times than those recommended cannot prevent degradation of the dentin bonds, they can increase bond strength, probably because of the removal of an increased amount of solvent and the presence of a lower amount of residual monomer.

No abstract

No abstract

This study evaluated the immediate and long-term bond strength to dentin (microtensile bond strength, μTBS) and silver nitrate uptake (SNU) of a three- and two-step etch-and-rinse adhesive under different water immersion times and frequency of water exchange. The adhesives and composite resin were applied according to the manufacturer's instructions in a flat occlusal demineralized dentin of 48 molars. Teeth were assigned to four groups of immersion time (immediate and 1, 3, and 6 months), sectioned to obtain resin-dentin beams, and then subdivided into three groups of water exchange (daily, weekly, and monthly) before being tested in tension. Two resin-dentin beams from each tooth were immersed in silver nitrate and analyzed by SEM. Significant difference in μTBS and SNU was detected for both adhesives (p ≤ 0.0001 for the cross-product interaction). For Adper Single Bond 2, the most pronounced reductions of μTBS were observed for the daily exchange groups in all times. For Adper Scotchbond Multi Purpose, 1-month immersion period was not capable to induce degradation of the dentin bonds, except when the water was exchanged daily. For both adhesives, all storage regimens showed increased SNU results only after 6-month water storage; this being more pronounced for daily water exchange groups. For both adhesives, the highest SNU was observed in the daily water exchange group. The daily water exchange is a fast and reliable in vitro aging method for testing the durability of the adhesive interface produced by adhesive systems.

No abstract