Materials Modification

Apart from the principally high spatial resolution electron-beam processing generates, electron beam processing opens up further possibilities in materials processing due to its high energy and particle character. At Fraunhofer FEP, the electron beam has been used for many years to achieve controlled chemical and biological effects on material surfaces. For seed dressing – a method already established on the market – low-energy accelerated electrons are used to destroy the DNA of harmful pests.

By means of low-energy accelerated electrons, surfaces of medical products (implants, devices), packaging or food- and feedstuffs can also be sterilized or disinfected. Even sensitive materials and products can be efficiently disinfected or sterilized within milliseconds to seconds with the technology under environmentally friendly conditions. The samples can be processed under atmospheric pressure and retain their shape stability as well as their product-specific properties. In this case, the electron beam can also sterilize the product surface while even passing through packaging, which considerably simplifies sterilization processes.

In contrast to other sterilization processes that work with irradiation, sterilization/disinfection with low-energy electrons (up to a maximum of 300 keV) only requires simple, local radiation shielding. This makes this technology compact and easy to integrate into existing process chains in-line. A mobile application can also be considered here and has already been carried out successfully with the example of seed dressing.

In addition, surface morphological as well as energetic characteristics counteract bacterial adhesion, which means that germs cannot accumulate on the surface. This strategy is also used to modify the surface of coatings by means of non-thermal electron beam technology, whereby the adhesion properties of surfaces can be specifically adapted.

In addition, the electron beam is a very flexible tool that provides a wealth of possibilities for modification and variation, especially in the treatment of plastics. At Fraunhofer FEP, surfaces can be sterilized, cross-linked or otherwise modified (functionalized) by low-energy electron beams. This is made possible by changing the process parameters. Thus, a change in the acceleration energy leads to different penetration depths of the electron beam into the material, whereas a differentiation of the irradiated energy dose in time and quantity leads to different processes in the substrate. When reactive gases or reactive precursors are added or coupled with other coating methods, such as physical gas phase deposition (PVD), cover layers can be deposited and the surface chemically modified. Modifying plastics with electron beams is mainly used to improve adhesion to surfaces. Particularly in the printing industry, optimum adhesion is of decisive importance when inks are applied, polymer granules compounded or barrier coatings applied for various uses on plastic films.

The properties of synthetic or biopolymeric plastics can be selectively modified on surfaces and edge layers. Fraunhofer FEP can modify the following material properties:

• Mechanical strength values (hardness, elongation, modulus of elasticity, bending stiffness, impact strength, melt index)
• Swelling and dissolution behavior
• Surface topography (smooth, rough)
• Wetting behavior
• Surface reactivity by incorporating chemically reactive groups or grafting reactive components
  
• Adhesion of organic coatings by co-crosslinking of layer and substrates