PLA-based nanocomposites filled with the commercial organomodified montmorillonite Dellite 43B (D43B) and containing acetyl tri-n-butyl citrate (ATBC) as plasticizer were prepared by extrusion in a pilot-scale twin-screw extruder and melt casted into flexible films. A preliminary investigation was carried out in a laboratory batch mixer by varying blending conditions and addition procedures of the components. Indeed, the method of addition of ATBC and D43B considerably affected thermo-mechanical properties and morphology of the resultant nanocomposites. The simultaneous introduction of both ATBC and D43B during the extrusion process allowed producing clearly exfoliated nanocomposite materials with modulated mechanical and thermal properties. Moreover, rheological results, obtained during melt extrusion, assessed the processability of nanofilled-plasticized PLA, making this simple procedure interesting in view of the industrial production of nanostructured biomaterials based on plasticized PLA. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013

Low-density polyethylene/layered double hydroxide (LDPE/LDH) nanocomposites were prepared via melt extrusion using organo-LDH particles and maleic anhydride functionalized polyethylene as compatibilizer. Processing parameters, preparation method, and feed composition were properly modulated until obtaining nanocomposites with intercalated/exfoliated morphologies, and an uniform distribution of nanolayers, as evidenced by X-ray diffraction and transmission electron microscopy analysis. These materials showed a significant improvement of the thermal-oxidative stability, which increased of about 50 degrees C during the first step of the degradation process. Moreover, a remarkable reduction of the oxygen permeability, proportional to the aspect ratio of LDH stacks dispersed in the polyolefin matrix was evidenced, indicating the possible application of nanocomposite films as food packaging materials. As highlighted by dynamic mechanical thermal analysis, interactions at the interface between LDH layers and polymer chains caused a shift of the LDPE beta-relaxation toward higher temperatures and a reduction of the peak intensity with respect to the matrix. It was also found that the storage modulus of the nanocomposites was lower in all the temperature range with respect to the reference samples. Finally, on-line capillary rheometer measurements evidenced that the shear thinning behavior of the nanocomposites was dominated by the matrix so that the melt processability was not compromised by the presence of the filler. Copyright (C) 2010 John Wiley & Sons, Ltd.

The flow induced crystallization behaviour of a LDPE:PE-g-MA:D72T 90:9:1 nanocomposite has been investigated by in-situ Rheo-SALS technique and data have been compared with those obtained from a reference LDPE:PE-g-MA 90:9 sample. Rheo SALS results, confirming thermal analysis findings, indicate that under mild shear flow fields the organoclay exhibits a negligible nucleating effect. Both nucleation density and, as a consequence, crystallization rate, are not appreciably affected by the application of external flow field for both the examined systems, revealing that no evident synergic effects between the organoclay and the shear flow are present. On the other hand, Rheo SALS analysis indicates that the nanocomposite submitted to flow exhibits a higher level of crystal orientation. TEM morphological analyses support this observation suggesting that the orientation of the nanofiller along the flow direction templates the growth of oriented crystals.

A careful insight into melt compounding procedure is proposed in order to achieve a better understanding and control of the dispersion and orientation mechanisms of organo-clay platelets into LDPE nanocomposites. The method involved is the preparation of a maleic anhydride grafted polyethylene master-batch containing 10 wt% organo-clay via twin-screw extrusion. A substantial nano-dispersion and orientation of clay platelets was obtained as observed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. Moreover, the nanocomposites prepared by diluting the master-batch through the blend mixing with additional LDPE preserved or improved the exfoliation and lamellae orientation. Finally, the thermo-gravimetric analysis (TGA) showed a significant improvement of the thermal stability while both differential scanning calorimetry (DSC) and XRD evidenced a slight increase of the LDPE crystallinity degree with respect to neat polymer matrices thus suggesting the occurrence of orientation also for the polymer.

A methodology, which combines experimental evidence and theoretical calculations, able to give a molecular interpretation and a quantification of the photooxidation of polyolefins is here derived. The methodology involves the analysis of experimentally recorded infrared spectra in combination with density functional theory calculations. Environmental effects are taken into account by exploiting the polarizable continuum model. A test against polyethylene and polypropylene samples UV-irradiated under the conditions used for the photocoating is reported. The results obtained with the combined theoretical/experimental methodology are in good agreement with previous findings obtained by exploiting more complex purely experimental approaches.

Catalytic amounts of glucose oxidase from Aspergillus niger (GO) are active in the reduction of O_2 to H_2O_2 in the presence of irradiated suspensions of TiO_2 and isopropyl alcohol as electron donor. An explanation of this behaviour is given on the basis of the ability of the enzyme to capture electrons from the photoexcited TiO_2 instead of its natural substrate, glucose. This process has a marked positive effect on both the oxidation of isopropyl alcohol to acetone and the formation of radical intermediates, which have been detected, for the first time, by EPR—spin trapping investigation.

Catalytic amounts of glucose oxidase from Aspergillus niger (GO) are active in the reduction of O 2 to H 2 O 2 in the presence of irradiated suspensions of TiO 2 and isopropyl alcohol as electron donor. An explanation of this behaviour is given on the basis of the ability of the enzyme to capture electrons from the photoexcited TiO 2 instead of its natural substrate, glucose. This process has a marked positive effect on both the oxidation of isopropyl alcohol to acetone and the formation of radical intermediates, which have been detected, for the first time, by EPR—spin trapping investigation.

Photoexcited iron porphyrins can be used to mimic the catalytic activity of cytochrome P-450 oxygenases both in the reduction of halogenated alkanes and in the oxidation of hydrocarbons by O2 itself at room temperature and atmospheric pressure. The results reported indicate that there is a similarity and a complementarity of photonic activation with other more conventional methods of activation of model systems of oxygenases. In fact, by irradiating at suitable wavelengths, it is possible to induce redox reactions which mimic those of natural oxygenases, avoiding the difficulties caused by parallel processes which could be expected when chemical reagents are used. These processes occur with good turnover values of the photocatalyst and in mild temperature and pressure conditions. By controlling the reaction environment, it is possible to address the selectivity of the process. In this regard, the very recent results obtained after heterogenization of the photocatalysts inside membranes of Nafion® are particularly promising for the development of new biomimetic photocatalysts in heterogeneous or organized systems.

Heterogenization of iron porphyrins inside Nafion creates new photocatalytic systems which can be used to oxidize cyclohexene and cyclohexane with sunlight and O-2 under mild conditions (room temperature, atmospheric pressure); the polymeric matrix makes the iron porphyrin a good photocatalyst for the monooxygenation of the substrate and increases both its photocatalytic efficiency (about ten times) and its stability (turnover values > 1000).