Organosilicone Compounds in Supercritical Carbon Dioxide.

This review considers the key advantages of using supercritical carbon dioxide as a solvent for systems with organosilicon compounds. Organosilicon polymeric materials synthesis as well as the creation and modification of composites based on them are discussed. Polydimethylsiloxane and analogues used as polymerization stabilizers and nucleation promoters in pore formation processes are analyzed as well.

Liquid-crystalline ordering in bacterial cellulose produced by Gluconacetobaсter hansenii on glucose-containing media.

This research is dedicated to the studies of the microscale morphology of bacterial cellulose (BC) obtained by means of static cultivation of Gluconacetobacter hansenii GH-1/2008. We found that the microscale morphology depended on the BC production rate that was varied by using different glucose concentrations in the cultivation medium. It was revealed that at higher production rates, BC fibrils were aligned in a liquid-crystalline-like (LC-like) order. The observed helical alignment was always left-handed. The half-periods of the helix varied from 50 µm to 150 µm depending on the cultivation conditions. The mechanical and water absorption properties of the obtained BC pellicles were measured. The former correlated mainly with the density of the samples; the latter were the best for films with layered structure, where the BC had segregated into fleece sheets separated by gaps with low density of fibrils.

A New Look at the Chemical Recycling of Polypropylene: Thermal Oxidative Destruction in Aqueous Oxygen-Enriched Medium.

Recycling of plastic waste, in particular polypropylene, represents one of the most pressing challenges facing humanity. Despite the promise of chemical methods for recycling polypropylene, they usually require a high temperature and are energy-intensive. In this work, we investigated the oxidative thermolysis of polypropylene in aqueous media. This approach rendered it possible to carry out the decomposition of the polymer at a comparatively low temperature (150 °C). It was shown that among the tested, the most promising aqueous medium for the decomposition of polypropylene is water saturated with gaseous oxygen at an elevated pressure (14 bar) and at a temperature of 150 °C. In such an environment, polypropylene was converted mostly to acetic acid (up to 1.3 g/g acetic acid to starting polypropylene mass ratio). Moreover, methanol, formic acid, and propionic acid were also detected as the products. Finally, the applicability of the proposed recycling method to real polypropylene waste was shown.

Chemical Recycling of High-Molecular-Weight Organosilicon Compounds in Supercritical Fluids.

The main known patterns of thermal and/or catalytic destruction of high-molecular-weight organosilicon compounds are considered from the viewpoint of the prospects for processing their wastes. The advantages of using supercritical fluids in plastic recycling are outlined. They are related to a high diffusion rate, efficient extraction of degradation products, the dependence of solvent properties on pressure and temperature, etc. A promising area for further research is described concerning the application of supercritical fluids for processing the wastes of organosilicon macromolecular compounds.