Kátia Aparecida da Silva Aquino

Use of Lead (II) Sulfide Nanoparticles as Stabilizer for PMMA Exposed to Gamma Irradiation

. Among these materials, lead (II) sulfide (PbS) has attracted much attention for its well-known narrow band gap semiconducting features. PbS is chosen for this work because it is commercially available and can also be synthesized easily. A variety of chemical and physical methods were developed to prepare PbS. Among these methods are: gas-phase synthesis

Stibnite Nanoparticles as a New Stabilizer for Poly (Methyl Methacrylate) Exposed to Gamma Irradiation

Poly (methyl methacrylate), PMMA, may be used in manufacturing of devices, which are exposed to gamma irradiation. However, the polymer undergoes significant changes in its properties during process and the use of additives is a common form to stabilize the PMMA matrix. In this way, stibnite was synthesized by sonochemical method and the amorphous powder constituted of nanospheres was obtained and investigated as additive. Commercial PMMA containing stibnite nanoparticles (ST-NP) was investigated and the samples were irradiated with gamma radiation (60Co). Our results showed that the addition of ST-NP at 0.3 wt% into the PMMA decreased the number of main chain scissions caused by the irradiation process, resulting in radiolytic stabilization of the polymer matrix. Analyses of mechanical properties showed influence of the ST-NP in the physical behavior of PMMA. Our findings suggest that stibnite nanoparticles are an effective additive for PMMA used in application of radiation resistance.

Effect of Pressure, Post-Pressing Time, and Polymerization Cycle on the Degree of Conversion of Thermoactivated Acrylic Resin

Herein, the effect of different post-pressing times and pressure in two cycles of polymerization on the degree of conversion (DC) of thermally activated acrylic resin (TRRA) is analyzed to optimize the polymerization of this material. After post-pressing for 0, 6, or 12 h, polymerization was performed with or without a pressure of 60 psi (0.41 MPa) in a short (4 h) or a long (11 h) cycle, totaling 12 groups. To determine the DC, PMMA specimens were analyzed by Fourier transform infrared spectroscopy. The influence of each factor alone on the DC was studied by experimental planning. The statistical tests used were three-way ANOVA, t-test, Tukeys test, and Levenes test, with a margin of error of 5%. Two groups prepared with post-pressing times of 12 h had the lowest DC (p < 0.001). Post-pressing times of 0 and 6 h did not yield statistically different results. Pressure increased the DC in only one group (long cycle +12 h, p=0.001). The short cycle resulted in a higher DC than the long cycle in 2 groups (with pressure +0 h, p=0.002; without pressure +6 h, p=0.015), while the long cycle yielded a statistically higher DC in only one group (with pressure +12 h, p < 0.001). The polymerization showed satisfactory DC in all 12 groups. Small differences found among the specimens indicate that the pressure, post-pressing time, and polymerization cycles herein were not influential factors for the DC of PMMA.

Agarose-silver particles films: Effect of calcium ascorbate in nanoparticles synthesis and film properties

New nanoparticles containing biomaterials are emerging as versatile active platforms in a great number of applications, for example, as skin substitutes and therapeutic media. The present study describes the preparation of silver nanoparticles (AgNPs) embedded in agarose films and the impact of calcium ascorbate in the formation of ANPs as well as in the final properties of the films. Colloidal AgNPs were synthetized by two chemical reduction routes: (i) applying calcium ascorbate and NaBH4 and (ii) applying only NaBH4. AgNPs synthetized using NaBH4 showed sizes ranging from 5 to 18 nm while AgNPs were calcium ascorbate was used showed micrometer from 164 to 955 nm size. Films were prepared in three formulations: agarose control film (A1); agarose + AgNPs without calcium ascorbate (A2) and agarose + AgNPs with calcium ascorbate (A3). The characterization of films by SEM and EDS showed agarose agglomerates in A2 and unreacted calcium ascorbate crystals on surface of A3. Thus, the presence of calcium ascorbate influenced the properties of A3 film. In addition, the antimicrobial analysis showed a silver particles release dependence on the film composition and only the A3 presented activity against Staphylococcus aureus. The results found in this study open an important way for development of new biomaterials, economically competitive, and with medical application.

The Interaction of Gamma Radiation with the Matter in the Process of Sterilization

The sterilization by gamma radiation is used as an international standard and its use has grown substantially in national processes. In this review, it is treated the interaction of ionizing radiation with matter and its effects, in addition to various applications of gamma irradiation as an effective tool for sterilization and decontamination of polymeric materials or reducing microbial load in food and packaging fields. This is a method that consists of exposing the products to the action of short electromagnetic waves generated from sources of Cobalt 60 and Cesium 137 in a specially prepared environment for this procedure. As electromagnetic waves have great penetrating power, organisms can be reached wherever they are, both in sealed packages as products packaged in the various forms, which ensures the overall effectiveness of the process.