The investigation of mica and mica/epoxy-composites has always been of high importance and has gained increased attention in recent years due to their significant role as insulation material in the electrical industry. Electrical insulation represents a key factor regarding the reliability and lifespan of high voltage rotating machines. As the demand for generating power plants is increasing, rotating machines are of intrinsic importance to the electrical energy supply. Therefore, impeccable functioning is of immense importance for both the producers of high voltage machines as well as the energy suppliers. Thus, cost reduction caused by shorter maintenance times and higher operational lifespan has become the focus of attention. Besides the electrical properties, composites should offer compatible chemical and mechanical, as well as thermal characteristics for their usage in insulating systems. Furthermore, knowledge of several occurring stresses leading to the final breakdown of the whole insulation is required. This review aims to give an overview of the properties of pure components, the composite, and the possible occurring failure mechanisms which can lead to a full understanding of insulation materials for high voltage rotating machines and therefore establish a basis for prospective optimizations.

Printed circuit boards (PCBs) have a wide range of applications in electronics where they are used for electric signal transfer. For a multilayer build-up, thin copper foils are alternated with epoxy-based prepregs and laminated to each other. Adhesion between copper and epoxy composites is achieved by technologies based on mechanical interlocking or chemical bonding, however for future development, the understanding of failure mechanisms between these materials is of high importance. In literature, various interfacial failures are reported which lead to adhesion loss between copper and epoxy resins. This review aims to give an overview on common coupling technologies and possible failure mechanisms. The information reviewed can in turn lead to the development of new strategies, enhancing the adhesion strength of copper/epoxy joints and, therefore, establishing a basis for future PCB manufacturing.

Photopolymerization offers substantial advantages in terms of time, temperature, energy consumption, and spatial control of the initiation. The application however is strongly limited due to the constrained penetration of light into thick films. Strategies to overcome the problem of limited curing depth, as well as to improve the curing of shadow areas, involve dual curing, frontal polymerization, and upconversion of particles. Whereas excellent results have been accomplished applying photofrontal polymerization on a theoretical level, few studies report on practical applications achieving high curing depth within short time. This study aims to investigate the potential of photofrontal polymerization, performed only with photoinitiator and light, for the fast and easy production of several-centimeter-thick (meth)acrylic layers. Monomer/ initiator systems were evaluated with respect to their optical density as well as photobleaching behavior. Moreover, depth-dependent polymerization was studied in specimens of varying monomer ratio and photoinitiator concentration. When an ideal photoinitiator concentration was selected, curing up to 52 mm in depth was accomplished within minutes.

The adhesion of the polymer to ceramic nanoparticles is a key aspect in the manufacturing of ceramic parts by additive manufacturing and injection molding, due to poor separation results in separation during processing. The purpose of this research is to investigate, by means of molecular dynamics simulations and experimental methods, the role of improved interfacial interactions by acrylic acid grafting-high density polyethylene on the adhesion to zirconia nanoparticles and on the composite properties. The polymer grafting results in high adhesion to the nanoparticles, increases the nanoparticles dispersion and improves the viscoelastic and mechanical properties required for additive manufacturing and injection molding.

The aim of this study was the investigation of the use of modified talcum for supporting crosslinking and as novel nucleating agent for physical foaming of polyethylene. For the modification of the talcum, a thermal initiator was linked to the talcum surface. During the extrusion process, the initiator decomposes, and gas and radicals are formed. The gas generates the nucleation of cells and the radicals support the crosslinking process between the polymer chains. The modification of the talcum was performed in three steps: The first step was the grafting of alkoxysilanes onto the talcum surface. The second step was the chlorination of the thermal initiator for an easier linkage, and the last step was the linking between the initiator and the silanes grafted onto the talcum surface. For this study, two investigations were carried out. One investigation was the analysis of the crosslinking effect with the modified talcum. For this purpose, polyethylene plates were compression molded and the viscoelastic properties were measured with a parallel plate rheometer. The use of the modified talcum led to a higher crosslinking density. The second investigation was the physical foaming experiment in an extrusion process with nitrogen as blowing agent using both a pure and the modified talcum as nucleating agents. The foamed samples were characterized in terms of density, cell size and cell density, and compared with each other. The blend with the modified nucleating agent indicated a foam structure with a smaller mean cell size and a lower density compared to the use of the pristine nucleating agent.