Elmo Silvano de Araujo

Effects of gamma-irradiation on some properties of durolon polycarbonate

Abstract Amorphous Brazilian bisphenol-A polycarbonate (Durolon) is used in medical supplies. Upon gamma-irradiation it undergoes main chain scissions. The major consequences are a decrease in the molecular weight and a yellowness of the polymer. The G (main chain scissions/100 eV)=1.49, calculated for the dose range of 10–200 kGy through the viscometry method, is not sufficient to promote significant changes in the mechanical properties. The FTIR spectra of irradiated samples show a decrease in carbonyl groups with increase of radiation dose, evidence of scissions in this groups. On the other hand, oxygenated products are not produced in the radiolysis of Durolon. The mechanical properties are not affected significantly up to a dose of 100 kGy, indicating that medical supplies made of Durolon can withstand four sterilization irradiations.

Diamondoids: occurrence in fossil fuels, applications in petroleum exploration and fouling in petroleum production. A review paper

In this review paper, we report the molecular structure, origin, natural occurrence and variety of diamondoid hydrocarbons in petroleum fluids and other fossil fuels. In addition, we present the role of diamondoids as geochemical tools for petroleum characterisation, ways diamondoid molecules are used to play an important role in petroleum evaluation, and may be used to assess origin, extend of biodegradation and thermal maturity, as well as to identify the occurrence of petroleum. The diamondoid-based diagnostic ratios in environment science as well as diamondoid-based diagnostic ratios for petroleum maturity parameters are also presented and discussed. Such diamondoid-based parameters may be used to assess oil source, maturity and biodegradability, providing supporting information, especially when traditional evaluation data are not available or are difficult to interpret. We also report applications and problems associated with diamondoids in petroleum exploration and production. That is the role of diamondoids in petroleum and natural gas production fouling as well as separation, detection and measurements of petroleum diamondoids. We realise that the presence of diamondoids in petroleum has become much more than a chemical curiosity since it has advanced to be a resourceful instrument in petroleum science, biomedicine, materials science and an important family of molecular building blocks in nanotechnology. (Received: August 9, 2011; Accepted: November 23, 2011)

The effect of gamma radiation on mechanical properties of biodegradable polymers poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Brazilian poly(3-hydroxybutyrate), P(3-HB), and its copolymer, poly (3-hydroxybutyrate-co-3-hydroxyvalerate), P(3-HB-co-3-HV) were irradiated with gamma radiation (60Co) at room temperature and in the presence of oxygen. The viscosity-average molar mass (Mv) was analyzed by viscometry using an Ostwald-type capillary viscometer. Both polymers showed a decrease in molar mass with the increase in dose, reflecting that random main chain scissions occurred. The value G (scissions/100 eV of energy transferred to the system) and the parameter α (scissions per original molecule) were also determined. Mechanical properties decrease with the increase in dose, revealing that P(3-HB) underwent significant changes, especially at doses higher than 50 kGy. Tensile at break and impact resistance properties were the most affected by radiation, while the elastic modulus remained virtually unaltered up to 100 kGy dose.

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.