E-beam curing

Polyisoprene can be UV or e-beam cured [43,44]. The 3,4 units are particularly prone to crosslinking at low dose [45]. SIS and SBS are also crosslinkable, even conventional linear materials with low vinyl content however, small amounts of liquid trithiol or triacrylate compounds speed cure dramatically [44]. Like UV, e-beam cure is strongly affected by tackifier choice. Hydrogenated, non-aromatic resins provide much less interference with cure [36,37]. 

Kraton Polymers has developed a multiarm SIS (Kraton 1320X [37,46,47,50]) and SBS (Kraton KX-222C, [48,49]) for rapid UV/e-beam cure. Besides heat resistance improvements, plasticizer resistance is also improved in cured rubber-based systems. The dioctyl phthlate plasticizer common in PVC backing films is soluble in the styrenic domains of SBCs. Crosslinking of the mid-block provides cohesion even after plasticizer attack [51]. 

The combination of processability and performance has driven significant growth in thermoset applications where dimensional stability and accuracy are critical. For example, thermosets (usually UV or e-beam cured) are the materials of choice as the medium for rapid prototyping. Similarly, the combination of processability, dimensional stability, and strength have driven the use of thermosets for automotive components, structural members in aircraft, and braking systems in both automotive and aircraft applications. 

H. Ichikawa, K. Okamura, and T. Seguchi, Oxygen-fiee Ceramic Fibers From Organo-silicon Precursors and E-beam Curing, Proc. Second International Conference on High-temperature Ceramic Matrix Composites, Santa Barbara, CA, USA, 65-74 (1995). 

One of the newer developments in adhesives is the growing use of ultraviolet light or electron beam radiation to cure adhesives. Adhesives designed for UV- or E-beam curing are usually pressure sensitive or hot-melt systems based on acrylates, functional rubbers, or epoxidized rubbers, and use special UV or EB lamps to provide the cure. These systems can provide greatiy improved heat resistance compared to hot melts, and avoid the soivent emission problems of some of the solvent-based systems with which they compete. 

Alessi, S., Dispenza, C., Puochi, P, Gorda, U., Lavalle, M., Spadaro, G., E-beam curing of epoxy-based blends in order to produce high-performance composites. Radiation Physics and Chemistry 2007, 76,1308-1311. 

Reasonably early however in the development of telechelic polybutadiene/acrylonitrile, Brenner and Drake (22) showed that mercaptan- and carboxyl-terminated liquid polybutadiene/acrylonitrile did respond to electron-beam (1-5 megarads) and cure (2-3 seconds/pass) from the liquid to the solid state. The mercaptan polymer (3.1% RSH, 23% bound acrylonitrile, Mn 1700) cured more readily. CTBN as expected required 50-100% higher irradiation dosage levels. With both MTBN and CTBN-type products of higher acid content (6% vs 3%), gum rubber properties of 13.8-34.5 mPa were obtained with 60-100% elongation. The E-beam cures were carried out in air at ambient temperature. Thus, unformulated telechelic polybutadienes were shown to be substantive to cure in the presence of ionizing radiation. 

Glennon (26) has been able to modify a resin-tackified linear block copolymer of butadiene/styrene dissolved in n-butyl acrylate monomer with a CTBN-type polymer. This easily E-beam cures on Mylar at 3 megarads irradiation dosage to obtain 700 N/m Mylar to painted steel adhesion... 

Figure 5. Variations of the entrapped radicai concentration at room temperature as a function of the pyroiysis temperature in E-beam cured PCS fibers (1,1 wt.% 0), from [47] reproduced with permission from tfie American Ceramic Society, Westenriiie, Ohio 43086.

The change in free radical concentration as a function of the pyrolysis temperature (Figure 5) shows that free radicals are formed and remain entrapped in the fibers [47]. The curve for the E-beam cured fibers can be decomposed into two peaks at 625"C and 1025 C, the former being more intense than the latter (whereas it is the reverse for the oxygen cured fibers). There is a correlation between the gas evolution (Figure 3) and the entrapped radical concentration (Figure 5), suggesting a two step pyrolysis process. 

E-beam curing A process whereby green fibers are rendered infusible through irradiation with an electron beam. 

E-beam curing Electron beam curing for composites. 

Another interesting approach to avoid autoclave curing is electron-beam (EB) or E-beam curing, often combined with automated fiber placement (AFP). EB curing activates the cross-linking process of the resin system by... 

E-beam cured composite laminate. (From reference 27.)... 

Dayton Research Institute in cooperation with the Air Force Research Laboratory (120,121). These sensors, which include thermal, spectroscopic, and other techniques, are enabling the generation of new knowledge, understanding, and optimization of the e-beam curing process for composite materials. 

Chen, C. and Anderson, D.P. (2007) E-beam-cured layered-silicate and spherical silica epoxy nanocomposites. Journal of Applied Polymer Science, 106, 2132—2139. 

Ichikawa, H., Okamura, K., Seguchi, T. (1995). Oxygen-free ceramic fibers from organosilicon precursors and e-beam curing. Ceramic Engineering and Science Proceedings, 58, 65-74. 

---