Polymer modification radiation effect

Recently the number of papers about radiation effects of ion beams on polymers has been increasing very rapidly both in the fundamental and applied fields. A fairly large number of papers have been published on the fundamental aspects of radiation effects of ion beams on polymers, including high density electronic excitation effects [1, 2]. A number of papers have been published on the more applied aspects of the ion beam assisted advanced science and technology of polymers examples of these are ion beam modification [1. 2] and lithography [3],... 

Marietta, G., Chemical reactions and physical property modifications induced by keV ion beams in polymers, Nucl. Instrum. Methods Phys. Res., B46, 295-305 (1990). Dienes, G. J., and Vineyard, G. H., Radiation Effects in Solids, Interscience, New York, 1957. 

An effective method of NVF chemical modification is graft copolymerization [34,35]. This reaction is initiated by free radicals of the cellulose molecule. The cellulose is treated with an aqueous solution with selected ions and is exposed to a high-energy radiation. Then, the cellulose molecule cracks and radicals are formed. Afterwards, the radical sites of the cellulose are treated with a suitable solution (compatible with the polymer matrix), for example vinyl monomer [35] acrylonitrile [34], methyl methacrylate [47], polystyrene [41]. The resulting copolymer possesses properties characteristic of both fibrous cellulose and grafted polymer. 

EB irradiation of polymeric materials leads to superior properties than the 7-ray-induced modification due to the latter having lower achievable dose rate than the former. Because of the lower dose rate, oxygen has an opportunity to diffuse into the polymer and react with the free radicals generated thus causing the greater amount of chain scissions. EB radiation is so rapid that there is insufficient time for any significant amount of oxygen to diffuse into the polymer. Stabilizers (antirads) reduce the dose-rate effect [74]. Their effectiveness depends on the abUity to survive irradiation and then to act as an antioxidant in the absence of radiation. 

For the last 50 years, radiation processing by gamma rays, electron beams (E-beams) or X-rays has been an effective technique for improving the end-use properties of various kinds of polymers. The main applications for modification of... 

Another major effect, found in PGA, is optical inversion of L-glutamate to D-glutamate residues. One implication of the radiation-induced optical inversion in proteins is that some modification of amino acids may pass undetected by the usual chemical analyses which do not distinguish between l- and D-isomers. Furthermore, introducing a D-amino acid residue into a protein could have a far-reaching effect on the secondary and tertiary structures, and this could have a more serious effect on the functional properties of the molecule than changes in the side chains. One biological property of PGA which is affected by irradiation in solution is its hydrolysis by proteolytic enzymes. The conformation of the polymer has a marked effect on its susceptibility to hydrolysis by certain enzymes 27), and we have... 

IR spectroscopy can be used to characterise not only different rubbers, but also to understand the structural changes due to the chemical modification of the rubbers. The chemical methods normally used to modify rubbers include hydrogenation, halogenation, hydrosilylation, phosphonylation and sulfonation. The effects of oxidation, weathering and radiation on the polymer structure can be studied with the help of infrared spectroscopy. Formation of ionic polymers and ionomeric polyblends behaving as thermoplastic elastomers can be followed by this method. Infrared spectroscopy in conjunction with other techniques is an important tool to characterise polymeric materials. 

It is now well established that organic polymers are rather more sensitive to various ionizing radiations. In a recent study (23) it has been shown that the irradiation of polystyrene films by 20 MeV 28gi beam results in ion-induced modifications of the sample because a significant quantity of H and C nuclei is released when the beam dose is increased above 1012 ions cm 2. Similar effects of erosion of H and C profiles of plasma-polymerized hexamethydisilasene (HMDSN) thin... 

During the last decade, there has been considerable interest in studying the interaction between ultraviolet radiation and polymers by the use of pulsed excimer laser (1-41. In fact, some attractive applications in microelectronics and surgery have been successfully implemented (5.), and further informations about the different mechanisms (photochemistry, thermal effect...) involved at the polymer surface have been invoked in order to elucidate their relative contributions. More recently, the attention has been focused on this type of polymer surface modifications to improve some surface properties like the adhesion in metallized polymer structures. 

In this work, we present the effect of 193 nm pulsed UV high intensity radiation on polyimide, a polymer well known for its applications in solid-state technology (thermal stability and dielectric properties). We have used XPS in order to determine the evolution of chemical surface composition versus laser fluence and have obtained some attractive informations about these modifications induced by UV laser radiation. 

A product of given characteristics can be obtained by mixing pellets of different polymers, additives such as colorants, stabilizers, antioxidants, flame-retardants, and so forth. Thermomechanical modifications can be brought about either by silanes or peroxides or by exposure to ionizing radiation. A product of good quality is certainly the result of experience, ability, and good knowledge of the interactions between the different substances, and also characterization of final products with the most effective techniques is of vital importance. Many techniques, collected in Table 1, are available for the characterization of PEX. ... 

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