Biomedical subjects

David Chelazzi

Publications and source records attributed to David Chelazzi.

3 recordsLinked to original sources

PubMed2005

Pressure-induced polymerization in solid ethylene.

Ethylene is the simplest organic molecule containing a double bond and is the starting monomeric unit in the synthesis of polyethylene, one of the most largely produced polymers. Here we report a high pressure infrared study of ethylene at room temperature. A polymerization reaction is observed when the crystalline phase I is compressed above 3.0 GPa. The reaction kinetics was investigated at two different pressures, 3.6 and 5.4 GPa. The recovered product was identified in both cases as polyethylene, but while a conformationally disordered and branched low-density polymer is obtained at the highest pressure, a high-density crystalline polymer is obtained at 3.6 GPa. A reaction mechanism was proposed on the basis of the kinetic data and the structural information.

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PubMed2005

Nanoparticles of calcium hydroxide for wood conservation. The deacidification of the Vasa warship.

The seventeenth century Swedish warship Vasa represents a unique case in the study of ancient wrecks and a challenge for finding new methods for artifacts conservation. The presence of sulfuric acid inside the wooden structure of Vasa is one of the possible causes of chemical damage of the wood. During recent investigations, pH values below 2 were observed inside the wreck in several places. Neutralization treatments temporarily raised the surface pH about 6 units, but after a few months the pH reverted back to original values. In this study we show that wood from the Vasa warship can be deacidified by using a dispersion in 2-propanol of calcium hydroxide nanoparticles. These particles can penetrate into the wood allowing a very efficient deacidification. Alkaline nanoparticles are converted into calcium sulfate without mechanical stress to the wood's lumens. Additional applications produce an excess of alkaline nanoparticles that are converted into carbonate, an alkaline reservoir to protect the wood from further acid attack. Artificial aging of Vasa wood demonstrates that nanoparticles facilitate protection of wood toward further acid degradation.

Journal Article↗

PubMed2004

High-pressure synthesis of crystalline polyethylene using optical catalysis.

Polymerization processes are probably the most relevant example of a chemical reaction activated by catalysts or radical initiators. Among polymers, polyethylene is by far the most common and largely produced. Here we present a high-pressure synthesis of high-density crystalline polyethylene by using only physical tools such as pressure and light. Low-density polyethylene is obtained by compressing ethylene at room temperature above 3 GPa in the ordered crystal phase, and a highly crystalline polymer is produced in the fluid phase at pressures lower than 1 GPa by using continuous-wave laser lines (lambda < or = 460 nm) as an optical catalyst. The photo-activation is based on a two-photon absorption process to pi* antibonding states, where the change in molecular geometry favours the polymeric chain formation. The high yield and crystallinity of the polymer recovered by the photoinduced reaction and the simplicity of the synthesis make this process appealing for large-scale applications.

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