View source for Electron-beam processing

{{Short description|Use of high-energy electrons to treat an object}}
{{for|Electron beam|Cathode ray}}

'''Electron-beam processing''' or '''electron irradiation''' ('''EBI''') is a process that involves using [[electron]]s, 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 (microbiology)|sterilization]], [[Gemstone irradiation|alteration of gemstone colors]], and [[cross-link]]ing of [[polymer]]s.

Electron energies typically vary from the [[keV]] to [[MeV]] range, depending on the depth of penetration required. The irradiation dose is usually measured in [[Gray (unit)|gray]]s but also in [[Rad (unit)|Mrads]] ({{nowrap|1 Gy}} is equivalent to {{nowrap|100 rad}}).

The basic components of a typical electron-beam processing device include:<ref>{{cite book | first1=Robert W. | last1=Hamm | first2=Marianne E. | last2=Hamm | title=Industrial Accelerators and Their Applications | publisher=World Scientific | year=2012 | isbn=978-981-4307-04-8}}</ref> 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 [[cathode ray|electron beam]] may be used on the material to induce effects such as chain scission (which makes the polymer chain shorter) and [[cross-link]]ing. 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 [[polymer degradation|degrades the polymer]]. The irradiated polymers may sometimes be characterized using [[Differential scanning calorimetry|DSC]], [[X-ray crystallography|XRD]], [[Fourier-transform spectroscopy|FTIR]], or [[Scanning electron microscopy|SEM]].<ref name="World Scientific">{{cite journal |last1= Imam |first1= Muhammad A |title= Electron-Beam Irradiation Effect on Thermal and Mechanical Properties of Nylon-6 Nanocompoiste Fibers Infused with Diamond and Diamond Coated Carbon Nanotubes |first2=SHAIK|last2=JEELANI|first3=VIJAYA K.|last3=RANGARI|journal= International Journal of Nanoscience |publisher= World Scientific |date= Oct 2015 |volume= 15 |issue= 1n02 |doi=10.1142/S0219581X15500313}}</ref>

In poly(vinylidene fluoride-trifluoroethylene) copolymers, high-energy electron irradiation lowers the [[activation energy|energy barrier]] for the ferroelectric-paraelectric phase transition and reduces polarization hysteresis losses in the material.<ref>{{cite journal |last1= Cheng |first1= Zhoung-Yang |first2=V.|last2=Bharti|first3=Tian|last3=Mai|first4=Tian-Bing|last4=Xu|first5=Q. M.|last5=Zhang|first6=T.|last6=Ramotowski|first7=K. A.|last7=Wright|first8=Robert|last8=Ting|title= Effect of High Energy Electron Irradiation on the Electromechanical Properties of Poly(vinylidene Fluoride-Trifluoroethylene) 50/50 and 65/35 Copolymers |journal= IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control |volume= 47 |issue= 6 |pages= 1296–1307 |publisher= IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society |date= Nov 2000 |doi= 10.1109/58.883518|pmid= 18238675 |s2cid= 22081881 }}</ref>

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.<ref name="Bly">Bly, J. H.; Electron Beam Processing. Yardley, PA: International Information Associates, 1988.</ref>

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.<ref>{{cite journal |last= Chmielewski |first= Andrzej G. |title= Worldwide developments in the field of radiation processing of materials in the down of 21st century |journal= Nukleonika |volume= 51 |issue= Supplement 1 |pages= S3–S9 |publisher=Institute of Nuclear Chemistry and Technology |year= 2006 |url= http://www.ichtj.waw.pl/ichtj/nukleon/back/full/vol51_2006/v51s1p003f.pdf }}</ref>

== Crosslinking ==
The [[cross-link]]ing of polymers through electron-beam processing changes a thermoplastic material into a [[thermoset]].<ref name="World Scientific"/><ref>{{cite journal |last= Berejka |first= Anthony J. |author2=Daniel Montoney |author3=Marshall R. Cleland |author4=Loïc Loiseau  |title= Radiation curing: coatings and composites |journal= Nukleonika |volume= 55 |issue= 1 |pages= 97–106 |publisher= Institute of Nuclear Chemistry and Technology |year= 2010 |url= http://www.nukleonika.pl/www/back/full/vol55_2010/v55n1p097f.pdf}}</ref> 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:<ref>{{cite web |title= Technology |publisher= E-BEAM |url= http://www.ebeamservices.com/technology.htm }}{{better source needed|date=February 2013}}</ref> 
* Thermal: resistance to temperature, aging, low-temperature impact, etc.
* Mechanical: [[tensile strength]], modulus, abrasion resistance, pressure rating, creep resistance, etc.
* Chemical: stress crack resistance, etc.
* Other: [[heat shrink]] memory properties, [[positive temperature coefficient]], 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.<ref>{{Cite web |url=http://www.massgeneral.org/research/researchlab.aspx?id=1018 |title=Harris Orthopaedics Lab (HOL) - Massachusetts General Hospital, Boston, MA |access-date=2014-08-21 |archive-date=2014-08-26 |archive-url=https://web.archive.org/web/20140826160900/http://www.massgeneral.org/research/researchlab.aspx?id=1018 |url-status=dead }}</ref>

Polymers commonly crosslinked using the electron-beam irradiation process include polyvinyl chloride ([[PVC]]), [[thermoplastic polyurethanes]] and elastomers (TPUs), [[polybutylene terephthalate]] (PBT), [[polyamide]]s / [[nylon]] (PA66, [[Nylon 6|PA6]], PA11, PA12), [[polyvinylidene fluoride]] ([[PVDF]]), [[polymethylpentene]] (PMP), [[polyethylene]]s ([[LLDPE]], [[LDPE]], MDPE, HDPE, [[UHMW]]PE), and ethylene copolymers such as [[ethylene-vinyl acetate]] (EVA) and [[ethylene tetrafluoroethylene]] (ETFE). Some of the polymers utilize additives to make the polymer more readily irradiation-crosslinkable.<ref>{{cite web |title= Fluorinated Polymers |publisher= BGS |url= http://www.bgs.eu/fluorierte_kunststoffe.html?&L=1 }}</ref>

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.<ref>{{Cite web |url=http://www.ebeamservices.com/pdf/xl-pa6-study.pdf |title=Archived copy |access-date=2014-08-21 |archive-url=https://web.archive.org/web/20140826114821/http://www.ebeamservices.com/pdf/xl-pa6-study.pdf |archive-date=2014-08-26 |url-status=dead }}</ref>

[[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.<ref>{{cite web |title= Cross-Linking |publisher= Iotron Industries: Electron Beam Sterilization Processing Services |url= http://www.iotron.com/services/cross-linking/ |access-date= 2013-02-11 |archive-url= https://web.archive.org/web/20121225011018/http://www.iotron.com/services/cross-linking/ |archive-date= 2012-12-25 |url-status= dead }}</ref>

Foam is also produced using electron-beam processing to produce high-quality, fine-celled, aesthetically pleasing product.<ref>{{Cite web |url=http://www.toraytpa.com/polyolefin-foams/technology |title=Technology &#124; Toray Plastics (America), Inc |access-date=2014-08-21 |archive-url=https://web.archive.org/web/20140826114759/http://www.toraytpa.com/polyolefin-foams/technology |archive-date=2014-08-26 |url-status=dead }}</ref><ref>{{Cite web |url=http://www.ebeamservices.com/release0407_c.htm |title=Electron beam processing, e-beam processing, plastics crosslinking, medical device sterilization - E-BEAM News |access-date=2014-08-21 |archive-url=https://web.archive.org/web/20140826120756/http://www.ebeamservices.com/release0407_c.htm |archive-date=2014-08-26 |url-status=dead }}</ref>

== 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.<ref>http://www.ebeamservices.com/pdf/E-BEAM-Foam-Applications.pdf {{Bare URL PDF|date=March 2022}}</ref>

== 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.<ref name="Bly"/>

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.<ref>{{cite web |title= Chain Scission |publisher= Iotron Industries: Electron Beam Sterilization Processing Services |url= http://www.iotron.com/services/chain-scission/ |access-date= 2013-02-11 |archive-url= https://web.archive.org/web/20121225005406/http://www.iotron.com/services/chain-scission/ |archive-date= 2012-12-25 |url-status= dead }}</ref>

== 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 (microbiology)|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.<ref>Singh, A., Silverman, J., eds. ''Radiation Processing of Polymers''. New York, NY: Oxford University Press, 1992.</ref>

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.<ref name="I">{{cite web |title= Iotron Industries |publisher= Iotron Industries: Electron Beam Sterilization Processing Services |url= http://www.iotron.com }}{{better source needed|date=February 2013}}</ref> 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.<ref>{{cite web |title= Material Considerations: Irradiation Processing |publisher= Sterigenics |url= http://www.sterigenics.com/services/medical_sterilization/contract_sterilization/material_consideration__irradiation_processing.pdf |access-date= 2010-11-29 |archive-date= 2016-06-21 |archive-url= https://web.archive.org/web/20160621144658/http://www.sterigenics.com/services/medical_sterilization/contract_sterilization/material_consideration__irradiation_processing.pdf |url-status= dead }}</ref>

== Notes ==
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[[Category:Electromagnetism]]
[[Category:Electron beams in manufacturing]]
[[Category:Industrial processes]]
[[Category:Plastics industry]]