Curing with radiation

Curing with radiation (IR, UV, electron beams, laser beams, plasma arc)... 

Curing with Radiation. See also Section 3.7. Radiation curing methods have become increasingly important in the last few years. Paint curing proceeds more rapidly than in circulating air curing since the whole workpiece does not have to be heated. However, only large flat parts can be satisfactorily treated. 

However, the curiosity-motivated research on fluoro-oleftn polymers was well rewarded and a variety of novel products tumbled out. First came plastic polyvinyl fluoride and polyvinylidene fluoride each of which had remarkable physical properties. Then Tom Ford discovered that flexible but leathery products were produced when he copolymerized vinylidene fluoride with some unsaturated monomers[3]. Hanford and Roland discovered that a copolymer of propylene with tetrafluoroethylene was rubbery and even recommended that it be cured with radiation or peroxide (Figure 2). About the same time 1 found that plastic polyethylene could be changed to a limp rubbery material by attachment of as little as 5 mol percent of trifluoromethylethylene (Figure 3)[5]. However, with the urgent pressures of the war, there wasn t enough manpower to pursue these leads. Then in the press of the post World War II industrial boom these developments were put aside. There were just too many ripe apples on the tree. 

For the EPDM/NR joint, the modification of the EPDM rubber increases its cure compatibility with NR. This, thus, increases with radiation dose up to 50 kGy beyond which a drop in the absorbance values due to predominant chain scission of the rubber also lowers the bond strength. Besides, interdiffusion of the mbber molecules across the interface also contributes to the formation of the bond. 

Poly(aryloxyphosphazene) elastomers can be cured with peroxides, sulfur and radiation. The resulting vulcanizates are resistant to attack by moisture and oils and have been found to have desirable characteristics for electrical insulation applications where fire safety is a concern (Table II) (12). Fire resistant, low smoke, closed cell foams with excellent properties (Table III) have also been developed from poly(aryloxyphosphazene) elastomers (13). Applications for these foams, which can be produced as either slabstock or tube stock, are being developed for military, aerospace and commercial uses. (See Table II and III.)... 

The copolymers can only be cured by peroxides or radiation, whilst the terpolymers can be cured with peroxides, sulphur systems, resin cures and radiation. 

The prevulcanization of natural rubber in latex form has also been a subject of much investigation. The cross-linking mechanism is not yet fully understood, but the water apparently plays a major role in it. Irradiation results in the cross-linking of the rubber molecules and in coarsening of the latex particles. A process of cross-linking of natural rubber latex has been developed to the point that it can be used for an industrial-scale application. The irradiation is performed in aqueous media by electron beam without a prorad (sensitizer) at a dose of 200 kGy (20 Mrad) or in the presence of n-butyl acrylate at considerably lower doses, typically 15 kGy. The cross-linked film exhibits physical properties comparable to those obtained from sulfur cured (vulcanized) film. As an alternative, the addition of a variety of chloroal-kanes makes it possible to achieve a maximum tensile strength with radiation doses of less than 5 Mrad (50 kGy). ... 

Cancer chemotherapy combined with radiation therapy and/or surgery can be effective in restraining or even curing many forms of cancer. As our understanding of cellular mechanics continues to grow, so will our ability to increase the overall survival rates of cancer patients. 

Therapeutic modalities in cancer treatment may involve surgery, radiation, and/or chemotherapy. The objectives of cancer chemotherapy include (1) cure, (2) reduction in tumor size, and (3) prolongation of life. At the present time, approximately 50 percent of patients with cancer can be cured, with drug treatment estimated to contribute in 17 percent of cases. Cancer chemotherapy can be curative in testicular cancer, diffuse large cell lymphoma, Hodgkin s disease, choriocarcinoma, certain childhood tumors (acute lymphoblastic leukemia, Burkitt s lymphoma, Wilms tumor, and embryonal rhabdomyosarcoma). Certain cancers are more resistant to chemotherapy than others (e.g., lung and colon). 

In general, the synthesis of polyphosphazene polymers is unique in that, in theory, an infinite number of polymers with a variety of properties can be derived from the common polymeric intermediate, poly(dichlorophosphazene) (PNCI2), by replacing the chlorines with different nucleophiles. If the polydichlorophosphazene precursor is reacted with the sodium salts of trifluoroethanol and a mixed fluorotelomer alcohol, a poly(fluoroaIkoxyphosphazene) elastomer (FZ elastomer) is obtained. It contains a small amount of an unsaturated substituent as a curing site. The polymer is a soft gum, which can be compounded with carbon blacks and fillers and cured with sulfur or peroxides or by radiation. 

---