Radiation crosslinked polyethylene oxide

The very first studies with radiation crosslinked polyethylene oxide (PEO) have shown that SAH is able to substantially reduce the sensitivity of plants to water shortage [7], to promote their growth, particularly, under conditions of water deficiency [8], to improve seedling survival and the final crop [9], These results stimulated a more detailed analysis of the effects of SAH in the water balance of... 

Crosslinked polyethylene. For additional investigations, LDPE samples were crosslinked by e-beam radiation with a dose of 250 kGy. In order to remove residual soluble components from the cross-linked LDPE samples, a suitable extraction process was developed [16], After being clamped in a frame, the polyethylene foils were extracted in m-xylene for 24 hours at a temperature of 80 °C. The addition of a small amount of BHT (2,6-di-tert-butyl-4-methylphenol), an antioxidant, prevented unwanted oxidation of the LDPE foils. Afterwards the samples were dried carefully at room temperature for 20 hours, and then dried in vacuo (20 mbar, 48 hours at 40 °C) to constant weight. 

Polyethylene oxide has been shown to be an excellent mucoadhesive polymer. Low levels of polyethylene oxide are effective thickeners, although alcohol is usually added to water-based formulations to provide improved viscosity stability see Table II. Polyethylene oxide films demonstrate good lubricity when wet. This property has been utilized in the development of coatings for medical devices. Polyethylene oxide can be radiation crosslinked in solution to produce a hydrogel that can be used in wound care applications. 

Crosslinked polyethylene by gamma-radiation Polyethylene with carbonyl group introduced by oxidation... 

Enzyme drugs have been coated with polyethylene glycols to mask the enzyme and prevent white blood cells from rapidly destroying the foreign material (16). Such masked drugs last longer and have increased effectiveness. Chapter 5, Section V, also contains a discussion about the use of radiation-crosslinked poly (ethylene oxide) for controlled drug-delivery systems as well as for blood filtration. 

The oxidation levels in the sterilized components were quantified using the ASTM oxidation index and found to vary considerably among radiation-sterilized polyethylene inserts, but not the gas sterilized inserts. None of the gas-sterilized components were found to contain detectable macroradicals, hydroperoxide content, or oxidation, regardless of whether or not they were highly crosslinked. 

In spite of the numerous studies reported on photooxidation of polyolefins, the detailed mechanism of the complete process remains unresolved. The relative contribution by species involved in photoinitiation, the origins of the oxidative scission reaction, and the role played by morphology in the case of photoreactions in solid state are not completely understood. Primary initiator species in polyethylenes [123] and polypropylenes [124] are believed to be mainly ketones and hydroperoxides. During early oxidation hydroperoxides are the dominant initiator, particularly in polypropylene, and can be photolyzed by wavelengths in solar radiation [125]. Macro-oxy radicals from photolysis of polyethylene hydroperoxides undergo rapid conversion to nonradical oxy products as evidenced by ESR studies [126]. Some of the products formed are ketones susceptible to Norrish I and II reactions leading to chain scission [127,128]. Norrish II reactions predominate under ambient conditions [129]. Concurrent with chain scission, crosslinking, for instance via alkoxy macroradical combination [126], can take place with consequent gel formation [130,131]. 

In many cases, plastics degrade in the presence of oxygen at irradiation doses that are without influence or result in crosslinking in vacuum. Because of oxidation, ultimate tensile strength and strain at break in polyethylene, polypropylene, polyvinyl chloride, polystyrene and in styrene-copolymers decrease faster with increasing doses when irradiated in air than when irradiated in a vacuum, whereas this is not the case for polyethylene terephthalate, polyvinyl alcohol, and acetyl cellulose. Oxidative degradation is also the reason for radiation damage doses that are notably smaller when irradiated in air than when irradiated in a vacuum [711],... 

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