Electron-beam processing or electron irradiation (EBI) is a process that involves using electrons, usually of high energy, to treat an object for a variety of purposes. This may take place under elevated temperatures and nitrogen atmosphere. Possible uses for electron irradiation include sterilization, alteration of gemstone colors, and cross-linking of polymers.
Electron energies typically vary from the keV to MeV range, depending on the depth of penetration required. The irradiation dose is usually measured in grays but also in Mrads (1 Gy is equivalent to 100 rad).
The basic components of a typical electron-beam processing device include:[1] an electron gun (consisting of a cathode, grid, and anode), used to generate and accelerate the primary beam; and, a magnetic optical (focusing and deflection) system, used for controlling the way in which the electron beam impinges on the material being processed (the "workpiece"). In operation, the gun cathode is the source of thermally emitted electrons that are both accelerated and shaped into a collimated beam by the electrostatic field geometry established by the gun electrode (grid and anode) configuration used. The electron beam then emerges from the gun assembly through an exit hole in the ground-plane anode with an energy equal to the value of the negative high voltage (gun operating voltage) being applied to the cathode. This use of a direct high voltage to produce a high-energy electron beam allows the conversion of input electrical power to beam power at greater than 95% efficiency, making electron-beam material processing a highly energy-efficient technique. After exiting the gun, the beam passes through an electromagnetic lens and deflection coil system. The lens is used for producing either a focused or defocused beam spot on the workpiece, while the deflection coil is used to either position the beam spot on a stationary location or provide some form of oscillatory motion.
In polymers, an electron beam may be used on the material to induce effects such as chain scission (which makes the polymer chain shorter) and cross-linking. The result is a change in the properties of the polymer, which is intended to extend the range of applications for the material. The effects of irradiation may also include changes in crystallinity, as well as microstructure. Usually, the irradiation process degrades the polymer. The irradiated polymers may sometimes be characterized using DSC, XRD, FTIR, or SEM.[2]
In poly(vinylidene fluoride-trifluoroethylene) copolymers, high-energy electron irradiation lowers the energy barrier for the ferroelectric-paraelectric phase transition and reduces polarization hysteresis losses in the material.[3]
Electron-beam processing involves irradiation (treatment) of products using a high-energy electron-beam accelerator. Electron-beam accelerators utilize an on-off technology, with a common design being similar to that of a cathode ray television.
Electron-beam processing is used in industry primarily for three product modifications:
Crosslinking of polymer-based products to improve mechanical, thermal, chemical and other properties,
Material degradation often used in the recycling of materials,
Sterilization of medical and pharmaceutical goods.[4]
Nanotechnology is one of the fastest-growing new areas in science and engineering. Radiation is early applied tool in this area; arrangement of atoms and ions has been performed using ion or electron beams for many years. New applications concern nanocluster and nanocomposites synthesis.[5]
Crosslinking
The cross-linking of polymers through electron-beam processing changes a thermoplastic material into a thermoset.[2][6] When polymers are crosslinked, the molecular movement is severely impeded, making the polymer stable against heat. This locking together of molecules is the origin of all of the benefits of crosslinking, including the improvement of the following properties:[7]
Thermal: resistance to temperature, aging, low-temperature impact, etc.
Cross-linking is the interconnection of adjacent long molecules with networks of bonds induced by chemical treatment or electron-beam treatment. Electron-beam processing of thermoplastic material results in an array of enhancements, such as an increase in tensile strength and resistance to abrasions, stress cracking and solvents. Joint replacements such as knees and hips are being manufactured from cross-linked ultra-high-molecular-weight polyethylene because of the excellent wear characteristics due to extensive research.[8]
An example of an electron-beam crosslinked part is connector made from polyamide, designed to withstand the higher temperatures needed for soldering with the lead-free solder required by the RoHS initiative.[10]
Cross-linked polyethylene piping called PEX is commonly used as an alternative to copper piping for water lines in newer home construction. PEX piping will outlast copper and has performance characteristics that are superior to copper in many ways.[11]
Foam is also produced using electron-beam processing to produce high-quality, fine-celled, aesthetically pleasing product.[12][13]
Long-chain branching
The resin pellets used to produce the foam and thermoformed parts can be electron-beam-processed to a lower dose level than when crosslinking and gels occur. These resin pellets, such as polypropylene and polyethylene can be used to create lower-density foams and other parts, as the "melt strength" of the polymer is increased.[14]
Chain scissioning
Chain scissioning or polymer degradation can also be achieved through electron-beam processing. The effect of the electron beam can cause the degradation of polymers, breaking chains and therefore reducing the molecular weight. The chain scissioning effects observed in polytetrafluoroethylene (PTFE) have been used to create fine micropowders from scrap or off-grade materials.[4]
Chain scission is the breaking apart of molecular chains to produce required molecular sub-units from the chain. Electron-beam processing provides Chain scission without the use of harsh chemicals usually utilized to initiate chain scission.
An example of this process is the breaking down of cellulose fibers extracted from wood in order to shorten the molecules, thereby producing a raw material that can then be used to produce biodegradable detergents and diet-food substitutes.
"Teflon" (PTFE) is also electron-beam-processed, allowing it to be ground to a fine powder for use in inks and as coatings for the automotive industry.[15]
Microbiological sterilization
Electron-beam processing has the ability to break the chains of DNA in living organisms, such as bacteria, resulting in microbial death and rendering the space they inhabit sterile. E-beam processing has been used for the sterilization of medical products and aseptic packaging materials for foods, as well as disinfestation, the elimination of live insects from grain, tobacco, and other unprocessed bulk crops.[16]
Sterilization with electrons has significant advantages over other methods of sterilization currently in use. The process is quick, reliable, and compatible with most materials, and does not require any quarantine following the processing.[17] For some materials and products that are sensitive to oxidative effects, radiation tolerance levels for electron-beam irradiation may be slightly higher than for gamma exposure. This is due to the higher dose rates and shorter exposure times of e-beam irradiation, which have been shown to reduce the degradative effects of oxygen.[18]
Notes
↑ Hamm, Robert W.; Hamm, Marianne E. (2012). Industrial Accelerators and Their Applications. World Scientific. ISBN978-981-4307-04-8.
1 2 Imam, Muhammad A; JEELANI, SHAIK; RANGARI, VIJAYA K. (Oct 2015). "Electron-Beam Irradiation Effect on Thermal and Mechanical Properties of Nylon-6 Nanocompoiste Fibers Infused with Diamond and Diamond Coated Carbon Nanotubes". International Journal of Nanoscience. World Scientific. 15 (1n02). doi:10.1142/S0219581X15500313.
↑ Cheng, Zhoung-Yang; Bharti, V.; Mai, Tian; Xu, Tian-Bing; Zhang, Q. M.; Ramotowski, T.; Wright, K. A.; Ting, Robert (Nov 2000). "Effect of High Energy Electron Irradiation on the Electromechanical Properties of Poly(vinylidene Fluoride-Trifluoroethylene) 50/50 and 65/35 Copolymers". IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society. 47 (6): 1296–1307. doi:10.1109/58.883518. PMID18238675. S2CID22081881.
1 2 Bly, J. H.; Electron Beam Processing. Yardley, PA: International Information Associates, 1988.
↑ Berejka, Anthony J.; Daniel Montoney; Marshall R. Cleland; Loïc Loiseau (2010). "Radiation curing: coatings and composites"(PDF). Nukleonika. Institute of Nuclear Chemistry and Technology. 55 (1): 97–106.
↑ "Chain Scission". Iotron Industries: Electron Beam Sterilization Processing Services. Archived from the original on 2012-12-25. Retrieved 2013-02-11.
↑ Singh, A., Silverman, J., eds. Radiation Processing of Polymers. New York, NY: Oxford University Press, 1992.
A polymer is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and natural polymers play essential and ubiquitous roles in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. Their consequently large molecular mass, relative to small molecule compounds, produces unique physical properties including toughness, high elasticity, viscoelasticity, and a tendency to form amorphous and semicrystalline structures rather than crystals.
A photoresist is a light-sensitive material used in several processes, such as photolithography and photoengraving, to form a patterned coating on a surface. This process is crucial in the electronics industry.
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bottles, etc.). As of 2017, over 100 million tonnes of polyethylene resins are being produced annually, accounting for 34% of the total plastics market.
A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening ("curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and may be promoted by high pressure, or mixing with a catalyst. Heat is not necessarily applied externally, but is often generated by the reaction of the resin with a curing agent. Curing results in chemical reactions that create extensive cross-linking between polymer chains to produce an infusible and insoluble polymer network.
Polyvinylidene fluoride or polyvinylidene difluoride (PVDF) is a highly non-reactive thermoplastic fluoropolymer produced by the polymerization of vinylidene difluoride. Its chemical formula is (C2H2F2)n.
In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural polymers.
Irradiation is the process by which an object is exposed to radiation. An irradiator is a device used to expose an object to radiation, notably gamma radiation, for a variety of purposes. Irradiators may be used for sterilizing medical and pharmaceutical supplies, preserving foodstuffs, alteration of gemstone colors, studying radiation effects, eradicating insects through sterile male release programs, or calibrating thermoluminescent dosimeters (TLDs).
EPDM rubber is a type of synthetic rubber that is used in many applications. Dienes used in the manufacture of EPDM rubbers are ethylidene norbornene (ENB), dicyclopentadiene (DCPD), and vinyl norbornene (VNB). 4-8% of these monomers are typically used.
Ethylene-vinyl acetate (EVA), also known as poly(ethylene-vinyl acetate) (PEVA), is a copolymer of ethylene and vinyl acetate. The weight percent of vinyl acetate usually varies from 10 to 40%, with the remainder being ethylene. There are three different types of EVA copolymer, which differ in the vinyl acetate (VA) content and the way the materials are used.
Ultra-high-molecular-weight polyethylene is a subset of the thermoplastic polyethylene. Also known as high-modulus polyethylene (HMPE), it has extremely long chains, with a molecular mass usually between 3.5 and 7.5 million amu. The longer chain serves to transfer load more effectively to the polymer backbone by strengthening intermolecular interactions. This results in a very tough material, with the highest impact strength of any thermoplastic presently made.
Cross-linked polyethylene, commonly abbreviated PEX, XPE or XLPE, is a form of polyethylene with cross-links. It is used predominantly in building services pipework systems, hydronic radiant heating and cooling systems, domestic water piping, insulation for high tension electrical cables, and baby play mats. It is also used for natural gas and offshore oil applications, chemical transportation, and transportation of sewage and slurries. PEX is an alternative to polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC) or copper tubing for use as residential water pipes.
Radiation chemistry is a subdivision of nuclear chemistry which studies the chemical effects of ionizing radiation on matter. This is quite different from radiochemistry, as no radioactivity needs to be present in the material which is being chemically changed by the radiation. An example is the conversion of water into hydrogen gas and hydrogen peroxide.
Hot-melt adhesive (HMA), also known as hot glue, is a form of thermoplastic adhesive that is commonly sold as solid cylindrical sticks of various diameters designed to be applied using a hot glue gun. The gun uses a continuous-duty heating element to melt the plastic glue, which the user pushes through the gun either with a mechanical trigger mechanism on the gun, or with direct finger pressure. The glue squeezed out of the heated nozzle is initially hot enough to burn and even blister skin. The glue is sticky when hot, and solidifies in a few seconds to one minute. Hot-melt adhesives can also be applied by dipping or spraying, and are popular with hobbyists and crafters both for affixing and as an inexpensive alternative to resin casting.
Polysulfones are a family of high performance thermoplastics. These polymers are known for their toughness and stability at high temperatures. Technically used polysulfones contain an aryl-SO2-aryl subunit. Due to the high cost of raw materials and processing, polysulfones are used in specialty applications and often are a superior replacement for polycarbonates.
Shape-memory polymers (SMPs) are polymeric smart materials that have the ability to return from a deformed state to their original (permanent) shape when induced by an external stimulus (trigger), such as temperature change.
Radiation damage is the effect of ionizing radiation on physical objects including non-living structural materials. It can be either detrimental or beneficial for materials.
In polymer chemistry photo-oxidation is the degradation of a polymer surface due to the combined action of light and oxygen. It is the most significant factor in the weathering of plastics. Photo-oxidation causes the polymer chains to break, resulting in the material becoming increasingly brittle. This leads to mechanical failure and, at an advanced stage, the formation of microplastics. In textiles the process is called phototendering.
Expanded polyethylene refers to foams made from polyethylene. Typically it is made from expanded pellets made with use of a blowing agent, followed by expansion into a mold in a steam chest - the process is similar to that used to make expanded polystyrene foam.
The thermally induced unidirectional shape-shape-memory effect is an effect classified within the new so-called smart materials. Polymers with thermally induced shape-memory effect are new materials, whose applications are recently being studied in different fields of science, communications and entertainment.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
