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Due to the significantly different processing ranges of polyhydroxybutyrate (PHB) and polyamide 6 (PA 6), processing the two polymers together is a challenge in terms of process engineering. In order to assess the compatibility and processability of the PA 6-PHB blends, a suitable preparation process was first developed on a twin-screw extruder. In addition, the production of painted PHB (C) was carried out as a compatibilizer. Using two- and three-component blends, it was shown that it is possible to produce the blends, but that they tend to coalesce. Although the C-types partially refine the morphology, they do not effectively prevent coalescence. However, atomic force microscopic images and mechanical examinations can demonstrate a limited compatibilizing effect. It is also clear that a synergistic stiffening effect leads to increased tensile moduli of the blends. As a result, up to 131% of the pure PA 6 value is achieved in the spray-dry state and 151% after conditioning. Using dynamic differential calorimetry and Fourier transform infrared spectroscopy, the effect could be attributed to the increase in crystallinity.

Doctoral committee

Chairman: Prof. Dr. rer. nat. W. Reimers, Technische Universität Berlin
Reviewer: Prof. Dr.-Ing. D. W. Auhl, Technische Universität Berlin
Reviewer: Prof. Dr.-Ing. R. Weinlein, ikd, Darmstadt University of Applied Sciences

Day of the scientific debate: 17.12.2019, Technical University of Berlin

Generative manufacturing processes have been a widely used tool for the production of prototypes in the industrial environment for more than 30 years. Fused layer manufacturing (FLM) generates visual samples from thermoplastic filaments using the 2½-dimensional strand deposition process. The fact that this process is only suitable for the production of functional samples to a very limited extent is due to the strong anisotropy of the layered components. The weak point of components with a mesostructure is the adhesion of the individual component layers to each other. Reduced adhesive properties in the joining seams are additionally superimposed in the edge zones by continuously introduced stress concentrations.

A low-cost FLM system that is open in terms of both space and software, with investment costs of around €1000, is extended to include in-line surface activation. This extension, which costs less than €250, has made it possible to significantly improve coating adhesion. If a component layer is activated with infrared radiation or hot air before the next layer is applied, thus increasing the temperature at the moment of joining, the cohesive proportion in the joining zone is also increased. These interlaminar, molecular entanglements must be loosened during the destructive impact test according to Charpy, which is evidently indicated by the formation of white fractures. The increase in the impact energy to destroy the test specimens with an activated surface is representative of the increase in coating adhesion. A microscopic fracture surface analysis shows that the cohesive proportion of the total surface is increased by the surface activation.

The production and testing of the investigated test specimen geometries on a high-end FLM system with a closed installation space tempered to 75 °C and investment costs of around € 15,000 leads to coating adhesion values similar to those of the low-cost FLM system and validates the functionality of the further developed process.

Day of the scientific debate: 03.09.2018, Technical University of Berlin

The initial melting of thermoplastic polymers by plastic energy dissipation is not sufficiently understood and is still a crucial knowledge gap in the process description of the co-rotating twin-screw extruder.

A test setup is presented in which the conveying, compression and deformation of plastic pellets in the cross-section of the plasticizing zone of a twin-screw extruder can be observed and recorded. Systematic investigations were carried out with different speeds, temperatures, thermoplastic polymers, pellet geometries and filling levels in order to demonstrate their influence on the initial melting due to plastic energy dissipation. The evaluation was carried out using high-speed recordings and torque measurements. This setup made it possible for the first time to gain insights into the significant influencing parameters of the initial melting by plastic energy dissipation of thermoplastics during processing on co-rotating twin-screw extruders.

The investigations have shown that a lot of energy is supplied to the material in a very short time during plastic energy dissipation. This leads to a local temperature increase of approx. 21K in a few hundredths of a second. The polymer with its mechanical and thermodynamic properties has a decisive influence on the energy input. The amount of material that is deformed in the gusset area depends primarily on the size of the pellets. As the speed and pressure increase, more energy is supplied to the material.

Day of the scientific debate: 20.07.2018, Technical University of Berlin

In this work, it was shown that it is possible to process a high-temperature thermoplastic (PPS) using laser sintering with a modified system.

By analysing and optimizing PPS, it was possible to evaluate characterization methods. Polyamide 12 was used as a reference. It was shown that individual measurement methods for determining the flowability and flowability show the same tendency, but are not directly comparable with each other. Each measuring method is meaningful in itself, but cannot be transferred. The tests show that the flowability is highly dependent on the particle shape and size. In particular, the particle size distribution has a significant influence. The interparticle adhesion forces in the powder also play a major role.

The process control has the most significant influence on the component quality. The available and used plant technology therefore plays a decisive role. There is generally a great need for improvement here, especially when processing alternative polymers. This is due to the need for more precise process control close to the polymer characteristic curve.

Day of the scientific debate: 14.07.2016, Technical University of Berlin

Day of the scientific debate: 07.07.2015, Technical University of Berlin

In order to make plastics electrically conductive, fillers are mixed into the polymer matrix during compounding. If you accept the black color, carbon black is the material of choice because it is the easiest to process and the most economical. The mixing process is the biggest challenge for the compounder. For a good compound, the carbon black should be homogeneously distributed in the polymer matrix while retaining its - shear-sensitive - structure. If it is possible to retain the structure of the carbon black, a continuous, electrically conductive network of carbon black with a low filler content can be achieved. This work investigates the influence of the process technology of a planetary roller extruder (PWE) on the electrical conductivity of carbon black-filled polyolefins. Compounds based on semi-crystalline plastics are produced under different processing conditions and with different carbon black contents. The electrical conductivity is determined on injection-molded and pressed test specimens. In addition to the electrical properties, morphological and mechanical properties are also investigated. In the injection molding process, dosing directly into the melt leads to the highest electrical conductivity, while the plate pressing process leads to the lowest. Another finding of this work is that the electrical conductivity is less influenced by the process technology of the planetary roller extruder than by the type of carbon black, the carbon black content and the processing method. When looking at the mechanical properties of the test specimens, it was found, as expected, that the notched impact strength and elongation values decrease with increasing carbon black content, while the characteristic values relevant to strength, such as tensile modulus and breaking stress, are improved.

Day of the scientific debate: 10.12.2013, Technical University of Berlin

Day of the scientific debate: 01.11.2011, Technical University of Berlin