Radiation Processing Basics
Electrons & X-rays
Energy,power,dose
Accelerators
Radiation effects
Crosslinking
The Industry
Food Irradiation
Online Sterilization

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Crosslinking

The production of free radicals by radiation leads to cross linking which creates longer molecular chains. It may also cause degradation due to oxidation by peroxide radicals. Polymerization and degradation (scission) occur simultaneously but the crosslinking is most important at moderate doses and degradation dominates when the total absorbed dose is very high.

Curing and cross-linking of plastics are the largest existing industrial applications of radiation processing as there are more than 500 low-energy accelerators currently in use for these purposes. Manufacturing companies use accelerators to cross-link polymers to enhance their physical properties in producing a wide range of industrial and consumer products.

The market for high-power electron beam treatment includes the molecular weight tailoring of plastics in pellet form and the cross-linking of post formed products such as cables and pipes. Post-formed cross-linking improves the performance of traditionally made plastics by changing its properties to provide scuff resistance, fire retardance, and other benefits. Because volumes have not yet justified dedicated plants, polymer cross-linking is primarily a service centre business except for wire and cable manufacturing.

Composites

The curing of advanced composites represents a substantial market yet to be exploited. The opportunity is to greatly reduce the cost to produce complex advanced composite components used in the aerospace industry (such as wing components) by curing them with electron beams. These benefits could also be important to other transportation products and to structural components. Successful application of accelerator technology would effectively revolutionize the way in which large composite structures are made.

Cellulose/Viscose

Industries making products from cellulose could use electron beams but have as yet not put the technology into commercial production. Viscose producers transform cellulose pulp into a syrupy liquid called viscose through a reaction with carbon disulphide followed by dissolution in alkali. The viscose is then extruded and spun to produce filaments and fibres for textiles, diapers, cellophane, tapes etc. The use of electron-treated cellulose in the viscose process offers significant advantages. Electron processing renders the cellulose more accessible to chemicals and reduces the amount of alkali, carbon disulphide, and acid used in the process. In addition to potential savings of about U.S. $3 million per annum for a typical plant (a short pay-back period of 2 to 3 years on the initial investment), the lower chemical demand translates into reduced emissions of polluting chemicals, a key factor as viscose producers are facing increasingly strict environmental regulations. Electron processing may allow a plant to stay in operation under current emission standards, or expand its operation without the need for further pollution control. The economic and environmental benefits offered by electron processing present a very attractive opportunity in this industry.

The electron beam accelerator can also be applied to thermomechanical pulp production. Pre irradiating the chips leads to reduces the energy needed for pulping, however at the cost of some paper strength. The principles have been demonstrated but never implemented commercially.

Quarantine

Quarantine treatments are differentiated from food irradiation treatments for two reasons. Some quarantine treatments are used on non-food items. These include tatami mats, bark products, bird seed, talcum powder &c. . There is no limit to the dose that can be applied for these products. For food items (e.g. lettuce exported from Mexico to the USA) the need is to eliminate insects. It is necessary to select a dose high enough to kill or prevent the target insect from reproducing while sufficiently low that it does not damage the food.

Opportunities for electron processing exist in the agricultural sector in the treatment of grain and specialized seed, high grade hay, lumber and wood chips, to eliminate insects and open new export markets. Animal feed and fish meal are also products that would benefit directly from bulk low cost sterilization.

Food

Given the heightened concerns in the U.S. over bacteria in meat and poultry products and the large volume of hamburger and chicken consumed, the food irradiation market has tremendous potential. There are a number of applications within the food area where irradiation offers important benefits, the most important being the elimination of pests and microbes in agricultural commodities and the elimination of food borne disease in meat and poultry. The market for eliminating pests and microbes in agricultural commodities as a quarantine measure has been small historically because of the use of methyl bromide fumigation which is a very low cost treatment. However, the reduction in use or outright ban is currently being considered.

Environmental

Treatment of waste and toxic materials through electron beam processing has long term potential. The primary obstacle to the development of these markets is cheaper alternative disposal methods such as dumping. There have been demonstrations of sewage sludge processing, in Germany, Japan and Florida. None has moved from the demonstration phase to commercial use. For example, a major US civil engineering firm submitted a proposal to a mid sized city several years ago for dewatering and disinfecting sewage sludge. The city's independent review showed that irradiation was equal to the lowest cost biological technique and only marginally more expensive than the cost to spread non-sterile sewage on farmland. Despite this, a decision was made to continue to spread the sewage on farmland.

Degradation

All polymers degrade if irradiated to a high enough dose. The level at which the polymer loses its function differs greatly between polymers. An important material that loses function at relatively low doses is PTFE (Teflon).

Electron accelerators are used to degrade materials which are not readily broken down by other means. The most widespread use is in the degradation of both scrap and virgin Teflon® to enable it to be ground to a fine powder for lubricants. The opportunity is also available to degrade toxic chemicals and some of these applications have been demonstrated in laboratory tests and in plants. For example, pollutants from ground water near a synthetic rubber plant in Russia were removed using electron irradiation.

Gemstones

At high doses, certain gemstones change colors when irradiated. This is widely used in the production of topaz for jewellery.

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