Crosslinking electron beam

Sulfur chemistry [29] has also been used to crosslink rubber/resin PSAs, although the use of elemental sulfur itself yields tapes that can stain substrates. Other patents exemplify the use of typical rubber vulcanizing chemistry such as Tetrone A , dipentamethylenethiuramtetrasulfide, and Tuads , tetramethylthiu-ram disulfide [30], or zinc butyl xanthate [31] for this purpose. Early art [32] also claimed electron beam curing of both natural rubber and other adhesives that were solvent coated on tape backings. Later references to electron beam curing... 

Unsaturated polyester finishes of this type do not need to be stoved to effect crosslinking, but will cure at room temperature once a suitable peroxide initiator cobalt salt activator are added. The system then has a finite pot life and needs to be applied soon after mixing. Such a system is an example of a two-pack system. That is the finish is supplied in two packages to be mixed shortly before use, with obvious limitations. However, polymerisation can also be induced by ultra violet radiation or electron beam exposure when polymerisation occurs almost instantaneously. These techniques are used widely in packaging, particularly cans, for which many other unsaturated polymers, such as unsaturated acrylic resins have been devised. 

Chattopadhyay, S., Chaki, T.K., Bhowmick, A.K., Gao, G.J.P., and Bandyopadhyay, S., Structural characterization of electron-beam crosslinked thermoplastic elastomeric films from blends of polyethylene and ethylene-vinyl acetate copolymers, J. Appl. Polym. Sci., 81, 1936, 2001. 

Much research into radiation effects on polymers is done with samples sealed under vacuum. However, polymer materials may, in practical applications, be subjected to irradiation in air. The effect of irradiation is usually substantially different in air, with increased scission at the expense of crosslinking, and the formation of peroxides and other oxygen-containing structures. Diffusion rates control the access of oxygen to radicals produced by the radiation, and at high dose rates, as in electron beams, and with thick samples, the behaviour may be similar to irradiation in vacuum. Surface changes may be quite different from bulk due to the relative availability of oxygen. 

The increase in the modulus for Bis A PSF and Hq/Bp PSF with irradiation indicated that crosslinking predominated for both polymers and that the crosslink structures were probably basically similar. Hq/Bp(50) PSF was considerably more radiation resistant than Bis-A PSF, as shown by the rate of decrease in the elongation at failure. For both polymers, there was an initial rapid decrease in the elongation at failure followed by a slower decrease. This effect was also demonstrated by the variation in the fracture toughness (KI(.) with irradiation for Bis-A PSF. This work with cobalt-60 gamma radiation complements earlier studies of these materials using high dose rate electron beam irradiation (6). 

To avoid all these drawbacks new wound dressing materials have been tested. So, PEO/PVA hydrogel, crosslinked by electron beams, has been synthesized and tested as dressing on animals wounds. Wounds dressed with a hydrogel healed almost completely within 14 days, while those using gauze were only half-healed within that time. Clinical tests confirmed the safety and effects of this product [234],... 

This problem leads to two undesirable phenomena first, since an electron beam exposure system requires 10 to 60 minutes in order to serially expose a wafer or mask, sections of the surface exposed last will show a degree of crosslinking less than sections exposed earlier. Since the linewidth of an image is proportional to the exposure dose, it is imperative that we allow the reaction to proceed to the same extent across the entire wafer if we are to control the linewidth across a wafer or mask. 

LDPE and EVA were blended in a 80/20 ratio and the non-crosslinked foam thereof was exposed to various doses of electron beam irradiation in air. The foam was made using isobutane as blowing agent. It was found that foam with uniform cell structure was not achieved in the case of pre-crosslinked foam with more than 40% gel fraction. Non-crosslinked foams were, however, easily crosslinked to a gel content of about 57% with electron beam irradiation under optimum conditions. The gel... 

Of technical importance are radically crosslinking reactions on finished articles of polyolefins by means of electron beams in order to increase, for example, the thermostability. The technical importance of networks consisting of polydienes and other rubbers, polyurethanes, formaldehyde resins, alkyd resins, and silicones has already been explained in Sects. 1.3.3.3,4.1 and 4.2. 

Polyethylene may be crosslinked by electron beams or by free-radical initiators. These polymers have elastic memory, i.e., stretched crosslinked Aims or tubing shrinks to the original dimensions when heated. 

Cross-Knking AB www.crosslinking.com Electron beam equipment, dose measuring equipment... 

Electron beam crosslinking, which produces less free radicals (33), and... 

Highly crosslinked UHMWPE can be produced by irradiation of a blank UHMWPE with ionizing radiation, in particular by X-rays, y-rays or electron beams, in order to produce radicals. The subsequent treatment of the irradiated material consists in exciting free radicals, which have not recombined, by means of microwave radiation or ultrasound. The process is claimed to ensure a substantially complete recombination of the free radicals. In addition, the crosslinking of the UHMWPE is also further optimized (30). 

---