Irradiation curing

The resins are commonly cured by the use of peroxide with or without cobalt accelerators, depending on whether the hardening is to be carried out at room temperature or at some elevated temperature. Electron irradiation curing, which can be completed within a few seconds, has, however, been introduced for coatings on large flat surfaces such as plywood, chipboard and metal panels. 

This paper describes an irradiation curing method which improves the mechanical, chemical, and thermal properties of multilayered flexible materials, increases the bond strength among the adhesively bonded layers, and provides flexible packages that can withstand the thermo-... 

Makhlis et al. [66] proved that more than one degradative processes are operative in thermal-oxidative dagradation of EPR. The low activation energy also indicates the existence of weak bonds. The rate of thermal degradation of y-irradiation cured vulcanizates can be effectively reduced by vacuum heat treatment at 200-250 °C. During thermal degradation [67] at 65° and > 350 °C in vacuum. EPR exhibited an... 

Palmas et al. (2001) highlighted the y-irradiation curing and thermal ageing of EPDM synthetic elastomers studied by both C high-resolution and H wideline solid-state NMR. 

Gamma irradiation curing of epoxy resins for structural adhesives — Radiation cure polymerization of commercial diglycidyl ether of bisphenol F epoxy resin has been achieved using Co-60 irradiation source, compounding the monomer with and onium salt catalyst [9],... 

Silicone resins (at room temperature or by heating and by UV-irradiation curing products) mainly for sealings and coverings [4]... 

Included in the table, properties are achieved after thermal fusion at 200"C for 2 min and UV irradiation curing (5 sec under medium power mercury lamp of 150 W/sq. foot). 

Figure 4. Irradiation curing of green PCS fibers gel fraction in irradiated PCS [26] reproduced with permission from the American Ceramic Society, Westerville, Ohio.

Manshaie et studied the physico-mechanical properties of NR/SBR blends cured by electron beam irradiation and sulphur. They showed that the irradiated blends have better mechanical properties than those cured by sulphur system. They also showed that the irradiation cured samples exhibited better heat stability than the sulphur cured samples. 

Zanardi E., Battaglia A., Ghidini S., Conter M., Badiani A., lanieri A. Evaluation of 2-alkylcydobutanones in irradiated cured pork products during vacuum-packed storage. Journal of Agricultural and Food Chemistry, 55 4264-4270 (2007). 

The DADC monomer has been copolymerized with small amounts of polyfunctional methacryflc or acryflc monomers. For example, 3% triethylene glycol dimethacrylate was used as a flexibiflzing, cross-linking agent with a percarbonate as initiator (26). CR-39 and diethylene glycol diacrylate containing isopropyl percarbonate were irradiated with a mercury lamp to a 92% conversion and then cured at 150°C (27). By a similar two-step process DADC was copolymerized with methyl methacrylate and tetraethylene glycol dimethacrylate (28). 

Among the preformed polymers cured by minor additions of aHyl ester monomers and catalysts followed by heat or irradiation are PVC cured by diallyl fumarate (82), PVC cured by diallyl sebacate (83), fluoropolymers cured by triaHyl trimeUitate (84), and ABS copolymers cured by triaUyl trimeUitate (85). 

Fig. 3. Polymerization initiation and propagation by radiation-generated free radicals. A is the initiating radical produced by irradiating the Hquid coating. (1) represents the Hquid monomer—unsaturated polymer reactive coating system. R is functional. (2) is the growing polymer chain (free radical). The cured...

Fig. 9. Initiation of epoxy cure. Irradiation of a triaryl sulfonium salt produces a radical cation that reacts with an organic substrate RH to produce a cation capable of releasing a proton. The proton initiates ring-opening polymerization. X = BF , PFg, AsFg, and SgFg. ...

Clinically, GM-CSF or G-CSF have been used to accelerate recovery after chemotherapy and total body or extended field irradiation, situations that cause neutropenia and decreased platelets, and possibly lead to fatal septic infection or diffuse hemorrhage, respectively. G-CSF and GM-CSF reproducibly decrease the period of granulocytopenia, the number of infectious episodes, and the length of hospitalization in such patients (152), although it is not clear that dose escalation of the cytotoxic agent and increased cure rate can be rehably achieved. One aspect of the effects of G-CSF and GM-CSF is that these agents can activate mature cells to function more efficiently. This may, however, also lead to the production of cytokines, such as TNF- a, that have some toxic side effects. In general, both cytokines are reasonably well tolerated. The side effect profile of G-CSF is more favorable than that of GM-CSF. Medullary bone pain is the only common toxicity. 

In 1919, Huldschinski (8) realized that uv light cured rickets and impacted on its etiology. The uv light and codHver oil were found to be usehil in the treatment of the disease, and irradiation of food produced the same effect as irradiation of the animal. The link between irradiation and plant materials led to the conclusion that ergosterol was an antirachitic substance, and an extensive effort was made to characterize the chemistry of irradiated ergosterol. 

The use of nylon-11 for powder coatings or dry coatings (qv) has been developed in response to a growing concern for the environment (44) (see Coating PROCESSES, powder technology). Electrostatic deposition allows thin films to be appHed to metal substrates. Once the powder is appHed, it must be melted and coalesced into a continuous plastic film. Eorced draft or irradiant ovens are used for fusion, and because no polymerization or cross-linkage are required for curing, coated objects can be processed quickly and air-cooled (45). 

Silicone acrylates (Fig. 5) are again lower molecular weight base polymers that contain multiple functional groups. As in epoxy systems, the ratio of PDMS to functional material governs properties of release, anchorage, transfer, cure speed, etc. Radiation induced radical cure can be initiated with either exposure of photo initiators and sensitizers to UV light [22,46,71 ] or by electron beam irradiation of the sample. 

An analogous mechanism should also produce polymers on irradiation of epoxies. Crivello s recent mechanistic suggestions [29] are consistent with the mechanisms given above. One can conclude that radiation-induced polymerization of epoxies can proceed via several mechanisms. However, further work is needed to determine the relative contributions of the different mechanisms, which might vary from one epoxy to another. As part of the Interfacial Properties of Electron Beam Cured Composites CRADA [37], an in-depth study of the curing mechanism for the cationic-initiated epoxy polymerization is being undertaken. 

If infra-red heating or any other radiation curing method is employed, areas which are shaded from the rays or are outside the area of greatest flux density, cannot dry as hard as the fully irradiated surfaces, and may form weak spots susceptible to mechanical damage and consequent corrosion. 

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