Summary: The paper presents an experimental study of L‐lactide polymerization in molten state using as initiator the Stannous Octoate. The experiments were performed in a Haake mixer. The operating temperatures were between 170 and 195°C, the reaction time up to 60 min and monomer to initiator initial molecular ratio between 102 and 5 · 103. The conversion was determined by using 1H NMR and the molecular weights distributions by SEC. A preliminary mathematical modeling study was also performed, based on experimental data and a previously published reaction scheme.

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The kinetics of L‐lactide ring‐opening polymerization initiated by stannous octoate and triphenylphosphine was investigated in a batch apparatus (Haake Rheocord Mixer). Based on the experimental data, a kinetic model is developed, considering a coordination‐insertion mechanism. Reactive extrusion experiments were further conducted for the same polymerization process, on a co‐rotating twin screw extruder. The melted material flow and mixing was described by using the Ludovic® commercial simulator. Based on the developed kinetic model and simulated flow of L‐lactide polymerization mixture, a mathematical model of reactive extrusion process is formulated, describing the evolutions of monomer conversion and average molecular weight along the extruder. The model is predicting with a reasonable good accuracy the experimental data.

We studied the microstructure of physical chitosan hydrogels formed by the neutralization of chitosan aqueous solutions highlighting the structural gradients within thick gels (up to a thickness of 16 mm). We explored a high polymer concentrations range (C ≥ 1.0% w/w) with different molar masses of chitosan and different concentrations of the coagulation agent. The effect of these processing parameters on the morphology was evaluated mainly through small-angle light scattering (SALS) measurements and confocal laser scanning microscopy (CLSM) observations. As a result, we reported that the microstructure is continuously evolving from the surface to the bulk, with mainly two structural transitions zones separating three types of hydrogels. The first zone (zone I) is located close to the surface of the hydrogel and constitutes a hard (entangled) layer formed under fast neutralization conditions. It is followed by a second zone (zone II) with a larger thickness (∼3-4 mm), where in some cases large pores or capillaries (diameter ∼10 μm) oriented parallel to the direction of the gel front are present. Deeper in the hydrogel (zone III), a finer oriented microstructure, with characteristic sizes lower than 2-3 μm, gradually replace the capillary morphology. However, this last bulk morphology cannot be regarded as structurally uniform because the size of small micrometer-range-oriented pores continuously increases as the distance to the surface of the hydrogel increases. These results could be rationalized through the effect of coagulation kinetics impacting the morphology obtained during neutralization.

The process of methanol conversion to dimethyl ether over an H-SAPO-34 molecular sieve was studied, using the catalyst as synthesized or formulated in an alumina matrix. The experiments were performed on the temperature interval 100−250 °C, liquid space velocities of 1−5 h−1, and pressures between 1 and 10 bar. The results evidenced a high catalytic activity of the H-SAPO-34 molecular sieve, providing in these conditions a practically total methanol transformation to dimethyl ether. Also, a special run, performed at 180 °C, with an output composition close to chemical equilibrium, showed no significant change of catalyst activity during an on-stream time of 50 h, this proving a good stability and resistance to deactivation. A published rate expression for the methanol dehydration reaction was selected and adapted to describe the experimentally observed process kinetics.