Electron beam processing
Encyclopedia
Electron beam processing or electron irradiation
is a process which 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
and to cross-link
polymers.
Electron energies typically varies from the keV to MeV range, depending on the depth of penetration required. The irradiation dose is usually measured in Gray
but also in Mrads
. Where is equivalent to .
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.
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 .
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:
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 http://www.ichtj.waw.pl/ichtj/.../full/.../v51s1p003f.pdf.
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 Polyethylene because of the excellent wear characteristics.
Polymers which are commonly crosslinked using the electron beam irradiation process include polyvinyl chloride (PVC
), thermoplastic polyurethanes
and elastomers (TPUs), polybutylene terephthalate
(PBT), polyamide
s / nylon
(PA66, PA6, PA11, PA12), polyvinylidene fluoride
(PVDF), polymethylpentene
(PMP), polyethylene
s (LLDPE, LDPE, MDPE, HDPE, UHMWPE), 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.
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.
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 created fine micropowders from scrap or off-grade materials.
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.
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.
Sterilization with electrons has significant advantages over other methods of sterilization currently in use. The process is quick, reliable, and compatible with most materials. Does not require any quarantine following the processing. 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.
Fruits, vegetables, grains and other food items can be processed by Electron Beam to control fruit flies and other insects that use these commodities as a host for propagation. Suitable as a quarantine measure, several countries rely on this technology to treat food commodities prior to exporting.
Irradiation
Irradiation is the process by which an object is exposed to radiation. The exposure can originate from various sources, including natural sources. Most frequently the term refers to ionizing radiation, and to a level of radiation that will serve a specific purpose, rather than radiation exposure to...
is a process which 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
Sterilization (microbiology)
Sterilization is a term referring to any process that eliminates or kills all forms of microbial life, including transmissible agents present on a surface, contained in a fluid, in medication, or in a compound such as biological culture media...
and to cross-link
Cross-link
Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of...
polymers.
Electron energies typically varies from the keV to MeV range, depending on the depth of penetration required. The irradiation dose is usually measured in Gray
Gray (unit)
The gray is the SI unit of absorbed radiation dose of ionizing radiation , and is defined as the absorption of one joule of ionizing radiation by one kilogram of matter ....
but also in Mrads
Rad (unit)
The rad is a unit of absorbed radiation dose. The rad was first proposed in 1918 as "that quantity of X rays which when absorbed will cause the destruction of the malignant mammalian cells in question..." It was defined in CGS units in 1953 as the dose causing 100 ergs of energy to be absorbed by...
. Where is equivalent to .
In polymers, an electron beam
Cathode ray
Cathode rays are streams of electrons observed in vacuum tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, the glass opposite of the negative electrode is observed to glow, due to electrons emitted from and travelling perpendicular to the cathode Cathode...
may be used on the material to induce effects such as chain scission (which makes the polymer chain shorter) and cross linking
Cross-link
Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of...
. 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
Crystallinity
Crystallinity refers to the degree of structural order in a solid. In a crystal, the atoms or molecules are arranged in a regular, periodic manner. The degree of crystallinity has a big influence on hardness, density, transparency and diffusion. In a gas, the relative positions of the atoms or...
as well as microstructure
Microstructure
Microstructure is defined as the structure of a prepared surface or thin foil of material as revealed by a microscope above 25× magnification...
. Usually, the irradiation process degrades the polymer
Polymer degradation
Polymer degradation is a change in the properties—tensile strength, colour, shape, etc.—of a polymer or polymer-based product under the influence of one or more environmental factors such as heat, light or chemicals such as acids, alkalis and some salts...
. The irradiated polymers may sometimes be characterized using DSC
Differential scanning calorimetry
Differential scanning calorimetry or DSC is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature. Both the sample and reference are maintained at nearly the same temperature...
, XRD
X-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...
, FTIR
Fourier transform spectroscopy
Fourier transform spectroscopy is a measurement technique whereby spectra are collected based on measurements of the coherence of a radiative source, using time-domain or space-domain measurements of the electromagnetic radiation or other type of radiation....
, or SEM.
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 .
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
Cathode ray
Cathode rays are streams of electrons observed in vacuum tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, the glass opposite of the negative electrode is observed to glow, due to electrons emitted from and travelling perpendicular to the cathode Cathode...
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, and
- terilization of medical and pharmaceutical goods.
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 http://www.ichtj.waw.pl/ichtj/.../full/.../v51s1p003f.pdf.
Crosslinking
The cross-linking of polymers through electron beam processing changes a thermoplastic material into a hermoset]http://www.ichtj.waw.pl/nukleonika/.../v55n1p097f.pdf. 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:- Thermal: resistance to temperature, aging, low temperature impact, etc.
- Mechanical: tensile strengthTensile strengthUltimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...
, 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 Polyethylene because of the excellent wear characteristics.
Polymers which are commonly crosslinked using the electron beam irradiation process include polyvinyl chloride (PVC
PVC
Polyvinyl chloride is a plastic.PVC may also refer to:*Param Vir Chakra, India's highest military honor*Peripheral venous catheter, a small, flexible tube placed into a peripheral vein in order to administer medication or fluids...
), thermoplastic polyurethanes
Thermoplastic polyurethanes
Thermoplastic polyurethanes are a class of polyurethane plastics with many useful properties, including elasticity, transparency, and resistance to oil, grease and abrasion...
and elastomers (TPUs), polybutylene terephthalate
Polybutylene terephthalate
Polybutylene terephthalate is a thermoplastic engineering polymer, that is used as an insulator in the electrical and electronics industries. It is a thermoplastic crystalline polymer, and a type of polyester...
(PBT), polyamide
Polyamide
A polyamide is a polymer containing monomers of amides joined by peptide bonds. They can occur both naturally and artificially, examples being proteins, such as wool and silk, and can be made artificially through step-growth polymerization or solid-phase synthesis, examples being nylons, aramids,...
s / nylon
Nylon
Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...
(PA66, PA6, PA11, PA12), polyvinylidene fluoride
Polyvinylidene fluoride
Polyvinylidene fluoride, or PVDF is a highly non-reactive and pure thermoplastic fluoropolymer.PVDF is a specialty plastic material in the fluoropolymer family; it is used generally in applications requiring the highest purity, strength, and resistance to solvents, acids, bases and heat and low...
(PVDF), polymethylpentene
Polymethylpentene
Polymethylpentene is a thermoplastic polymer of methylpentene monomer units. It is used for gas permeable packaging, autoclavable medical and laboratory equipment, microwave components, and cookware...
(PMP), polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
s (LLDPE, LDPE, MDPE, HDPE, UHMWPE), and ethylene copolymers such as ethylene-vinyl acetate
Ethylene-vinyl acetate
Ethylene vinyl acetate is the copolymer of ethylene and vinyl acetate. The weight percent vinyl acetate usually varies from 10 to 40%, with the remainder being ethylene....
(EVA) and ethylene tetrafluoroethylene (ETFE
ETFE
Ethylene tetrafluoroethylene, ETFE, a fluorine based plastic, was designed to have high corrosion resistance and strength over a wide temperature range. ETFE is a polymer, and its systematic name is poly. ETFE has a very high melting temperature, excellent chemical, electrical and high energy...
). Some of the polymers utilize additives to make the polymer more readily irradiation crosslinkable.
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.
Chain-scissioning
Chain scissioning or polymer degradationPolymer degradation
Polymer degradation is a change in the properties—tensile strength, colour, shape, etc.—of a polymer or polymer-based product under the influence of one or more environmental factors such as heat, light or chemicals such as acids, alkalis and some salts...
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
Polytetrafluoroethylene
Polytetrafluoroethylene is a synthetic fluoropolymer of tetrafluoroethylene that finds numerous applications. PTFE is most well known by the DuPont brand name Teflon....
(PTFE) have been used to created fine micropowders from scrap or off-grade materials.
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.
Microbiologal 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 sterilizationSterilization (microbiology)
Sterilization is a term referring to any process that eliminates or kills all forms of microbial life, including transmissible agents present on a surface, contained in a fluid, in medication, or in a compound such as biological culture media...
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.
Sterilization with electrons has significant advantages over other methods of sterilization currently in use. The process is quick, reliable, and compatible with most materials. Does not require any quarantine following the processing. 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.
Pest & Pathogen Control
Electron Beam processing as a disinfestation method replaces antiquated environmentally unfriendly methods such as fumigation and chemical dipping. A significant area for this technology is the herb and spice industry. These commodities are valued for their distinctive flavors, aromas and colors. They can be processed by this technology to reduce bacterial contamination without compromise to their sensory properties.Fruits, vegetables, grains and other food items can be processed by Electron Beam to control fruit flies and other insects that use these commodities as a host for propagation. Suitable as a quarantine measure, several countries rely on this technology to treat food commodities prior to exporting.