Thermal oxydation during extrusion of polyolefins

International audienceThe thermal oxidation during extrusion of polyethylene was studied under inert gas (nitrogen and CO2) and compared with extrusion under air atmosphere. A strong reduction of degradation rate was found by optical observation and by infrared analyses. A mechanism for the change of color is proposed

Effects of nitrogen and carbon dioxide gases on the degradation of low-density polyethylene during extrusion and origin of the color

International audienceThe effect of inert gases, nitrogen and carbon dioxide, on the oxidative degradation of low-density polyethylene appearing as colored spots has been studied during an extrusion process in competition with an antioxidant. Extrusion under inert gases significantly decreases the degradation level in the critical region of the process in comparison with classical extrusion under air. The effect of antioxidants on degradation during extrusion at a high temperature is weak. The main processes acting on this reduction of polymer oxidation and the origin of the color of degraded domains have been investigated. Energy-dispersive spectra of particles have confirmed that degradation is caused by thermooxidation. The nature of chromophore groups in degraded areas has been identified by IR microscopy. We found that β-conjugated ketoenols are present inside colored spots and seem to be responsible for the color of degraded parts. Quantum calculations have confirmed that such chemical structures absorb visible light and create reddish and brown colors

Negative-type soluble photosensitive polyimides derived from benzhroltetracarboxylic dianhydride: synthesis and characterization

International audienceThe present paper deals with the synthesis and the characterization of negative-type soluble photosensitive polyimides based on benzhydroltetracarboxylic dianhydride. These polymers were prepared either by a thermal or chemical imidization, and the photoreactive methacryloyl group was introduced through the reaction between the hydroxyl group and the isocyanate group of methacryloyl isocyanate to yield a carbamate linkage. Bis(4-aminophenyl)methane, bis(3,5-dimethyl-4-aminophenyl)methane and bis(3-methyl-5-isopropyl-4-aminophenyl)methane were used as aromatic diamines, and 1,1,1,3,3,3-hexafluoropropane-2,2-di(4′-phthalic anhydride) as aromatic dianhydride, 4-N,N-Dimethylamino-3′,5′-diaminobenzophenone was also used in order to produce an autophotosensitive polymer. The resulting methacryloyl carbamate-modified polyimides were found to be soluble in polar solvents and they were characterized by infrared and 1H and 13C nuclear magnetic resonance spectroscopies. Inherent viscosities, glass transition temperatures, thermal behaviour and dielectric constants were also determine