How Does The Electron Beam Crosslinking Process... ##BEST##
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.
How Does The Electron Beam Crosslinking Process...
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]
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.
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]
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]
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]
Polymers commonly crosslinked using the electron-beam irradiation process include polyvinyl chloride (PVC), thermoplastic polyurethanes and elastomers (TPUs), polybutylene terephthalate (PBT), polyamides / nylon (PA66, PA6, PA11, PA12), polyvinylidene fluoride (PVDF), polymethylpentene (PMP), polyethylenes (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.[9]
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]
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 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]
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]
Ethylene vinyl alcohol (EVOH) provides the required oxygen barrier typically of 2/24 hrs to provide shelf stability and avoid meat rancidity from oxygen contamination. Low-voltage electron beam cross-linking of the outer ionomer layer provides the required temperature resistance of > 200 C to the ionomer. This layer is in direct contact with the heating surface, while the inside sealant layer is not EB-treated and hermetically seals to the tray at a lower temperature. Low-voltage 125 kV operation of the EB unit restricts penetration to the inside sealant layer (DD125kV), providing essentially no dose to the sealant layer, as shown in Figure 6.
Use is increasing for low-voltage electron beam processes (less than 125 kV operating range) to cross-link polyethylene-based films for packaging applications. When high-barrier packaging is required for shrink bags or skin packaging, electron beam cross-linking provides advantages, including longer shelf life to reduce waste. Sustainable packaging, with a mandate for lower energy consumption, is paving the path for use of these smaller, energy-efficient electron beam accelerators. Moving forward, use of EB technology either to cross-link film or initiate in situ polymerization for packaging will grow.
The electron beam sterilization process begins with an electron beam accelerator. E-BEAM Services uses high power state of the art accelerators to create a powerful beam of electrons. The beam is scanned back and forth to create a curtain of fast electrons, which shower and safely ionize the materials that they strike. There is no radioactivity involved.
In electron beam sterilization, boxes of medical devices are put on a conveyor in a single layer. As they pass through the beam, electrons penetrate the cardboard box and all the medical devices in their individual packages inside the carton. Harmful microorganisms are completely inactivated with minimal effect on the medical devices. As the electrons penetrate the products, the radiation dose diminishes so less radiation leaves the box then entered. Medical devices are usually turned over and irradiated from the opposite side in order to get a relatively uniform dose. Electron-beam machines are highly reliable and provide consistent radiation sterilization, because the dosing they provide is precisely repeatable.
We here at E-BEAM Services understand that the conversion from your current sterilization method to electron beam takes effort and will involve upfront costs. However, we can also help you determine your eventual cost savings and how quickly you will recoup your costs when you convert to high-quality, reliable, cost effective electron beam sterilization.
At LOROM we offer all crosslinking technologies available, such as chemical crosslinking, which is commonly used in the industry, as well as our radiation e-beam crosslinking. Comparing the two different crosslinking technologies eBeam crosslinking enables us to crosslink a large variety of plastic materials at higher line speeds, driving overall cost down, which can meet the critical economical price points of our diverse customer base.
eBeam crosslinking, the energy to modify the polymer is delivered directly by the electrons with precision and control. The crosslinking happens instantaneously as the material meets the electron-beam and the enhanced properties have been achieved.
In short positive effects of electron-beam crosslinking. After insulation systems and materials have been exposed to the eBeam. The polymer chains are linked to each other and the polymer can no longer melt and flow. These unique characteristics improve the temperature resistance, as well as improved resistance to solvents, oils and not least abrasions.
Electron beams are an exceptional source of energy that are capable of initiating chemical reactions without the need for catalysts, high temperature or high pressure. The high kinetic energy and penetrating nature of the electrons provide significant benefits over typical chemical methods.
Electron beam processing involves the absorption of large doses of energy from accelerated electrons in materials in order to modify them in some beneficial manner. The main processes initiated by electron beam are polymer modification by crosslinking or scission, curing of coatings, decomposition of industrial effluents or synthesis of a new substance. Some materials that have been successfully processed via electron beam include plastics and rubber, wire and cable insulation, crosslinking of ultra-high molecular weight polyethylene for hip and joint replacement in the medical industry and many more. Beneficial changes produced in treated materials are improved thermal and chemical resistance, stability at elevated temperatures, improved tensile strength and other mechanical properties. Electron beam technology provides an efficient, safe and environmentally friendly way to drive chemical reactions. 041b061a72