Due to their good insulating properties and almost unlimited shaping possibilities, plastics have long been an important basic material in both mechanical engineering and automotive construction. However, constantly increasing demands on the heat resistance and chemical resistance, mechanical strength, flammability, and wear behavior of the plastics used require ever new solutions. High-performance plastics such as LCP, PEEK, PES, and PEI can be used in numerous applications. However, they are cost-intensive and, in some cases, very difficult to metallize. When mass-produced or technical plastics are crosslinked using ionizing radiation, they exhibit significantly improved properties in terms of heat resistance, chemical resistance, creep behavior, and abrasion resistance. The service life of the component can be significantly increased, so that in addition to high-priced high-performance plastics, metals in many functional components can also be replaced by radiation crosslinked, injection-molded plastic components.
The technology of radiation crosslinking
Beta rays from electron accelerators with a maximum energy of 10 megaelectron volts (MeV) are generally used for the irradiation of plastic materials. During irradiation, the electrons are slowed down by the material and their energy is absorbed. In a cascade of secondary electrons, the macromolecules of the polymer statistically break down into radicals, which repeatedly combine to form new molecules, thereby crosslinking the material. The result: the properties of the materials refined in this way are sustainably improved. The products can then be used under more demanding conditions. Radiation crosslinking is a precisely controllable process. The desired material quality can be set and exactly reproduced via the radiation dosage.
Crosslinked plastics in use:
Mechanical engineering and e-mobility
The modified material profile and longer service life of radiation crosslinked components also expand their potential fields of application in mechanical engineering. The requirements for materials used in gearboxes and sliding components, such as gears, roller bearings, and slide bushings, are constantly increasing. Radiation crosslinked components with improved tribological properties, such as reduced abrasion and wear as well as reduced creep tendency, can be an economical alternative to metallic materials or cost-intensive high-performance polymers (PEEK, PAI, etc.). For example, metals can be replaced by radiation crosslinked, injection-molded plastic components (e.g., PA or PBT) in numerous applications. Fasteners such as screws and nuts, brackets, or clips can be made from radiation crosslinked polyamide instead of metal. The advantage: reduced weight and lower manufacturing costs due to the elimination of complex metalworking steps.
In the context of growing e-mobility, radiation crosslinking makes the plastics used in electronic components, connectors, and cables competitive for the new requirements. It enables a high degree of flexibility in the selection of raw materials as well as in cable design and construction. Not only individually insulated wires, but also multiple stranded wires or completely assembled cables can be cross linked in a single step. If the use of radiation-sensitive wire insulation or separating and insulating films is required, it is even possible to crosslink only the outer sheath. In addition, lightweight construction is playing an increasingly important role in electric cars to compensate for the additional weight of the battery and associated components, making plastics a key material both now and in the future. Radiation crosslinking enables them to meet the significantly more complex requirements in this environment in a cost-effective manner.
Radiation crosslinking in the logistics chain
In the processing chain, radiation crosslinking is the final step after the components have been shaped by injection molding, extrusion, or blow molding—usually during a short stop at a radiation service provider. It is therefore usually an outsourced process step prior to further processing or final delivery to the end user. Many of the irradiated products are part of series production, which is subject to a fixed schedule in the supply chain. For manufacturers and suppliers, these conditions mean that the irradiation production step must follow seamlessly and quickly after manufacturing. The major advantage of treatment with ionizing radiation is that the products can be used or further processed immediately after a simple release step – without further testing or storage and waiting times.
Radiation crosslinked components and recycling
In the interests of environmental protection, regulatory requirements for plastics are becoming increasingly stringent. The focus is currently on recyclability in particular. Radiation crosslinked components are extremely durable and can therefore be used for very long periods of time. At the end of their service life, there are three processing options: material (physical), raw material (chemical), or energy (thermal) recovery. Material recycling involves using secondary raw materials to produce new plastic components. If the production residues are sorted by type and grade before crosslinking, they can be reused in their original application. Material recycling also works in the presence of crosslinking additives (as regranulate). Crosslinked plastics can be shredded in a pure form and, within certain limits, mixed back into the primary raw materials as regranulate. These limits depend on the material and degree of crosslinking and must be checked on a case-by-case basis. If material recycling is not feasible or possible, radiation crosslinked components can be easily recycled as raw materials or for energy recovery.
Conclusion
Electron beam crosslinking improves the material properties of engineering plastics and enables their use in products that were previously designed with high-performance polymers or even metals. Whether through the optimization of existing applications or the targeted integration of radiation crosslinking at the beginning of the design phase, the possibilities are diverse and offer designers the opportunity to develop innovative and high-performance solutions that meet the requirements of the product and the market.
