Raffaele Gallo

Environmental degradation of polypropylene

Abstract The environmental degradation of a polypropylene film was studied up to 2424 h of exposure. A continuous reduction of the mechanical properties studied begins after about 700 h. The crystallinity changes irregularly and the thermal oxidation strength decays in the initial stages. Data are reported on the absorbance of the carbonyl groups, molecular weight and quantum yield. The proposed degradation mechanism is based mainly on the β-scission reaction.

Environmental degradation of stabilized LDPE. Later stages

The environmental degradation of a stabilized low density polyethylene film was studied up to 12 480 h of exposure. The highest concentrations of carbonyl and vinyl groups are observed between 8000 and 10 500 h of exposure. In the same time range the mechanical properties undergo the most meaningful diminution, while Mw and the thermal oxidation strength reach the lowest values. A spontaneous tearing of the film starts after about 10 000 h of exposure. The areas close to the tearing lines show the highest values of the relative optical densities of the carbonyl and vinyl groups. The crystallinity remains steady. The proposed degradation mechanism is based mainly on reactions of the Norrish I type.

Structural investigations of humic acid from leonardite by spectroscopic methods and thermal analysis

Abstract Humic acid from leonardite, an immature coal, has been examined by spectroscopic methods (UV-VIS, IR-FT, 1 H, 31 P, 13 C-NMR), mass spectrometry (FAB-MS) and thermal analysis. These techniques provided complementary informations. A quantitative 13 C-NMR technique was applied to this humic acid: the aromaticity calculated from the NMR data is high, about 76%, in agreement with mass spectrometric and thermal analysis data.

Environmental degradation of stabilized LDPE. Initial step

Abstract The environmental degradation of a stabilized low density polyethylene film was studied. The polymer degradation has started in the first 2400 h of exposure. Irregular changes in tensile strength and elongation at break up to exposure times of 7080 h are observed. A constant reduction of the mechanical properties studied begins at 7080 h of exposure. The relative optical density of the carbonyl and vinyl groups increases regularly during the whole exposure time, while a small change in the relative optical density of the vinylidene groups is observed. The thermal oxidation strength decreases after 7080 h of exposure. The crystallinity remains steady. Reflection infra-red-Fourier Transform measurements indicate that the oxidation reaction proceeds at the same rate on both sides of the film.

Environmental degradation of isotactic polypropylene plates as studied by positron annihilation lifetime spectroscopy

Outdoor degradation of isotactic polypropylene (PPI) plates was studied by means of positron annihilation lifetime spectroscopy (PALS), absorption infrared spectroscopy, differential scanning calorimetry (DSC) and density measurements. Infrared spectra reveal the presence of oxygenated species into the exposed polymer induced by external agents. Results from thermal and density analysis suggest an increase of crystallinity of the sample with exposure time. Positron data strengthen such a conclusion, showing a reduction of the amorphous zones as monitored by the corresponding decrease of positronium (Ps) formation. Furthermore, an estimation of the average sizes of the free volume holes and of the defects in the crystalline regions was obtained.

Palladium catalysts supported on oligomeric aramides in the liquid-phase hydrogenation of phenylacetylene

Abstract The catalytic behaviour of palladium supported on oligomeric aramides has been investigated in the liquid phase selective hydrogenation of phenylacetylene to styrene, by comparison with conventional Pd-supported systems, such as Pd/carbon. Pd/Al 2 O 3 and Pd/SiO 2 . The influences of the reduction temperature and metal loading on the activity/selectivity behaviour of the title reaction are explained in terms of different reducibility patterns of the catalysts, as well as in the light of a peculiar support effect of the organic matrix on Pd particles.

Induction time and later degradation of outdoor exposed polypropylene cast film studied by differential scanning calorimetry

The outdoor ageing of a polypropylene (PP) cast film, free of stabilisers and exposed directly or covered by glass, has been studied mainly by means of differential scanning calorimetry (DSC) measurements. Time dependences of the enthalpies and the peak temperatures of all the samples are not straight lines. The recurrence of high and low values of these quantities has been related to the organization of the system from the starting polypropylene matrix and from the occurring oxygenated fragments. In fact, meaningful changes in these thermal parameters take place even during the first 800 exposure hours, in the absence of oxidation. This shows that the oxidation reaction of the system is preceded by considerable morphological changes in the material.

Some aspects of the environmental photo-degradation of LDPE

Apparent quantum yield values for random chain scission during environmental photo-degradation of a stabilised low density polyethylene film were calculated on the basis of the reduction of Mw during exposure. Quantum yields are in the range 3 × 10−6 to 3 × 10−5 and change with exposure energy and concentration of carbonyl groups.

Thermal isomerization of photochemically synthesized (Z)-9-styrylacridines. An unusually high enthalpy of Z→E conversion for stilbene-like compounds

Eight stable (Z)-9-styrylacridines, have been photochemically synthesized and their enthalpies of thermal isomerization (ΔHZ→E) determined by means of thermal analysis. The enthalpy values were found to be influenced by both electronic and steric effects. The title compounds were used as models in order to gain insight into the energetic implications involved in the Z→E isomerization process and its applicability to photochemical energy conversion by irradiation in the visible wavelength region.

A high enthalpy value in thermal isomerization of photosynthesized cis-9-styrylacridines

Four stable stilbene-like cis-isomers - i.e. 9-styrylacridines - were photosynthesized and their ΔH cis → trans thermal isomerization determined.