Salvatore Ipsale

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.

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.

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.

Natural weathering of some new ethylene copolymers

The outdoor ageing of three ethylene-octene copolymer films having different values concerning crystallinity and thermal characteristics has been studied. The thermal oxidation strength of these films diminishes to only 3 min after 500 exposure hours. After 1000 exposure hours the concentration of the carbonyl groups increases and the mechanical properties undergo a meaningful diminution. The materials under study have a behaviour very close to that of an isotactic polypropylene film previously examined under similar conditions. Unlike polypropylene and polyethylene these copolimers give rise to a lot of peroxide derivatives after about 3000 exposure h.

Degradation of outdoor exposed poly (1-trimethylsilyl)-1-propyne

Abstract The outdoor ageing of poly(1-trimethylsilyl)-1-propyne (PTMSP) membranes has been studied mainly by means of differential scanning calorimetry (DSC), thermogravimetry, viscosimetry and infra-red spectroscopy. Membranes lose their integrity within 288 h of exposure. After exposure for 192 h the oxidation time at 523 K decreases from 25 to 0.5 min, while the starting temperature of degradation, as measured by DSC, changes from 543 K to 393 K and the viscosimetric molecular weight decreases five times. The high speed of the photodegradation process can be accounted for by the high oxygen solubility of this polymer.

Environmental degradation of LDPE observed by UV spectroscopy

Abstract LDPE films exposed outdoors have been examined by UV spectroscopy. After the first 2500 h, the spectra show absorptions at 204 and 220 nm attributable to conjugated structures of the type which disappear after about 3000 h. After 9000 hours exposure these signals are observed again. The signal at 220 nm continues to grow throughout the experiment. Increases in the absorbances at 204 and 220 nm have been observed, even when the exposed samples were kept in the dark.

Outdoor ageing of ethylene–carbon monoxide alternating copolymer

Abstract The outdoor ageing of ethylene–carbon monoxide alternating copolymer films, has been investigated by thermal analysis, infrared spectroscopy and scanning electron microscopy (SEM). Samples exposed to the sun light, in open air, for times ranging from 0 to 480 h have been investigated. After 480 h of exposure polymer films break spontaneously. Infrared spectroscopy indicates that the degradation takes place with formation of new chemical species that contain ether linkages. Moreover thermal measurements clearly indicate that an etherogeneous system is formed as a consequence of degradation. Both infrared and SEM evidence indicates that the photodegradation process is confined to a thin layer near the exposed surface of the samples.

Selective synthesis of alkynes by catalytic dehydrogenation of alkenes over polymer-supported palladium acetate in the liquid phase

A heterogenized palladium acetate catalyst, in the presence of oxygen and perchloric acid in theanol–water caused the direct conversion of terminal and internal monoalkenes into the corresponding alkynes, under mild conditions and in high yields; Wacker-type ketonization occurs with the same reagents in dioxane–water.