Ionizing radiation cross-linking

Polybutene can be cross-linked by irradiation at ambient temperature with y-rays or high energy electrons in the absence of air. The performance of articles manufactured from polybutene is only slightly affected by ionizing radiation at doses below 30 kGy (3 Mrad) (26). PMP is also relatively stable to P-and y-radiation employed in the sterilization of medical suppHes (27). 

Mechanical properties, such as elastic modulus and yield point, that depend on crystallinity per se are not seriously affected by low to moderate doses of ionizing radiation. On the other hand, those mechanical properties that are sensitive to interlamellar activity are most dramatically affected by the low to moderate radiation doses. This is seen in the ultimate tensile strength and elongation at failure of the polyolefins. It is also reflected in the large change in melt index between 0 and 18 Mrad, which indicates formation of cross-links that increase with increasing... 

By using ionizing radiation to generate main-chain free radicals which can recombine as cross-link junctions... 

The use of ionizing radiation to induce cross-linking is another important technique for producing hydrogels from linear water-soluble polymers. When such polymers are bombarded by ionizing radiation, either in the bulk state or in solu-... 

Polyethylene Is well known to be cross-linked by ionizing radiation through the recombination of polyethylene radicals produced by the irradiation (1). The efficiency of the reaction is not so high and the G-value has been reported to be 1-5 (2, 3). 

Ionizing radiation, such as gamma rays and x-rays, causes complex types of DNA damage that are difficult to repair. Including double-strand and single-strand breaks and cross-links that may lead to leukemia and cancers of many organs. 

The primary effect of any ionizing radiation is based on its ability to excite and ionize molecules, and this leads to the formation of free radicals, which fhen initiate reactions such as polymerization and cross-linking or degradation. Accelerated electron beams have energy sufficient to affect the electrons in the atom shell, but not its nucleus, and can therefore only initiate chemical reactions. Typically, the reactions initiated by electron beam are extremely fast and are completed in fractions of a second. 

For an un-cross-linked material that undergoes predominantly cross-linking when exposed to ionizing radiation, solvent extraction experiments reveal that at certain absorbed dose (the critical dose), a percentage of the material, is converted into insoluble gel. Beyond that point, the percentage of gel increases as a function of irradiation dose. In general, both the degrees of... 

Polymers can be classified into two groups according to their response to ionizing radiation. One group exhibits predominant cross-linking, the other predominant chain scission (see Table 5.1). ... 

Normally, TPEs are not cross-linked because the thermoplastic nature is their desired property in most cases. However, in some cases cross-linking is used to improve mechanical properties, influence flow to reduce swelling in oils and solvents, eliminate dissolution of fhe polymer in oils and solvenfs, increase heat resistance, and influence ofher performance characteristics. Examples where cross-linking by ionizing radiation is necessary for fhe given processes are ... 

Polystyrene is a clear, amorphous polymer with a high stiffness and good dielectric properties. It is easily cross-linked by ionizing radiation. Often small amounts of divinyl benzene may enhance the degree of cross-linking.98... 

Ionizing radiation on poly(alkyl acrylates) results in cross-linking efficiencies, which are sensitive to the structure of the alkyl ester group."... 

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