Febo Severini

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.

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.

Enthalpy of maleic anhydride polymerization in the presence of pyridine

Abstract The polymerization of maleic anhydride in the presence of pyridine was studied by means of differential scanning calorimetry with isothermal tests at 328 K. The ΔH value increases with the percentage of the base. The enthalpy of the polymerization reaction of maleic anhydride in the presence of a large excess of pyridine (93.6 kJ per mol MA) was obtained by extrapolation.

Enthalpy of free radical polymerization of maleic anhydride

Abstract The polymerization of maleic anhydride in the presence of benzoyl peroxide or 2,2-azobisisobutyronitrile was studied by means of differential scanning calorimetry with dynamic and isothermal tests. The absolute ΔH values increase with the percentage of the initiators. The enthalpies of the polymerization reaction in the presence of a large excess of benzoyl peroxide (−85.3 kJ (mol MA)−1) or 2,2-azobisisobutyronitrile (−95.1 kJ (mol MA)−1) were obtained by extrapolation.

Thermal behaviour of fulvic and humic acids in comparison with a maleic anhydride oligomer

Abstract The thermal behaviour of samples of maleic anhydride oligomer (MAO), fulvic acid (FA) and humic acid (HA) of well-known origins has been studied. FA crystallizes very easily: m.p. = 441 K, melting Δ H = 230.5 J g −1 . The thermogravimetric analysis revealed similar behaviour for FA and MAO, which decompose with comparable rates. In contrast, the decomposition of HA proceeds more slowly and with formation of a 10–20% residue.

A 1H NMR Study of the Kinetics of the Reaction of Diisocyanates with Ethlene Oxide-Dimethylsiloxane-Ethylene Oxide Block Copolymer

Abstract The reaction of pure 2–4 and 2–6 tolylene diisocyanate with an OH terminated ethylene oxide-dimethylsiloxane-ethylene oxide ABA block copolymer was carried out directly in a n.m.r. tube. The kinetic of the reaction was studied by 1H nmr spectroscopy.