Agro-materials : a bibliographic review

Facing the problems of plastic recycling and fossil resources exhaustion, the use of biomass to conceive new materials appears like a reasonable solution. Two axes of research are nowadays developed : on the one hand the synthesis of biodegradable plastics, whichever the methods may be, on the other hand the utilization of raw biopolymers, which is the object of this paper. From this perspective, the “plastic” properties of natural polymers, the caracteristics of the different classes of polymers, the use of charge in vegetable matrix and the possible means of improving the durability of these agro-materials are reviewed

The pressure-volume-temperature relationship of cellulose

Pressure–volume–temperature (PVT) mea- surements of a-cellulose with different water contents, were performed at temperatures from 25 to 180 °C and pressures from 19.6 to 196 MPa. PVT measurements allowed observation of the combined effects of pressure and temperature on the specific volume during cellulose thermo-compression. All isobars showed a decrease in cellulose specific volume with temperature. This densification is associated with a transition process of the cellulose, occurring at a temperature defined by the inflection point Tt of the isobar curve. Tt decreases from 110 to 40 °C with pressure and is lower as moisture content increases. For isobars obtained at high pressures and high moisture contents, after attaining a minimum, an increase in volume is observed with temperature that may be related to free water evaporation. PVT a-cellulose experimental data was compared with predicted values from a regression analysis of the Tait equations of state, usually applied to synthetic polymers. Good correla- tions were observed at low temperatures and low pressures. The densification observed from the PVT experimental data, at a temperature that decreases with pressure, could result from a sintering phenomenon, but more research is needed to actually understand the cohesion mechanism under these conditions

Aggregation of Synthetic Chrysotile Nanotubes In the Bulk and In Solution Probed By Nitrogen Adsorption and Viscosity Measurements

Chrysotile nanotubes (ChNTs) were synthesized under hydrothermal conditions. The shape and size of individual ChNTs were examined by transmission electron microscopy (TEM). Specific surface area (SSA) of nanotubes surface treated with a silane coupling agent and of pristine nanotubes in the bulk was determined by BET analysis of N-2 adsorption at 77 K. The theoretical SSA of a single nanotube and of nanotubes organized in a bundle was calculated as a function of nanotube geometrical parameters and the bundle size, that is, number of nanotubes in the bundle. A comparison of experimental and theoretically calculated SSA values indicated that nanotubes form bundles in the bulk. The characteristic bundle size in the bulk was estimated. The tendency of ChNTs to form bundles was also investigated in polar (ethanol) and nonpolar (xylene) solvents by measuring the complex viscosity behavior of the corresponding colloidal solutions. Viscosity measurements showed that nanotubes form bundles and that they are larger, consisting of more nanotubes, in nonpolar xylene than in polar ethanol. The tendency of ChNTs to aggregate in the bulk and in the solution was reduced by surface treatment of nanotubes with a silane coupling agent