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Modern and energy-efficient materials are essential for innovative designs for aerospace and automotive industries. Current technologies for rapid manufacturing such as additive manufacturing and liquid composite moulding by polymer Extrusion allow innovative ways of creating robust and lightweight constructions. Commercially available printing devices often use polylactide (PLA) or acrylonitrile butadiene styrene (ABS) as raw material. Therefore, parameters like the infill ratio, influencing the ability to resist mechanical stress, may have a beneficial impact on the lifetime of components.
These manufacturing technologies require a good knowledge about materials and even adapted non-destructive testing technologies and methods. Airborne ultrasonic testing has beneficial advantages for testing those lightweight constructions. It is a contact-free testing method, which does not require a liquid couplant. Therefore, it allows fast test cycles without any unwanted alternations of the material properties due to interactions with any coupling liquid. This contribution deals with the characterisation of printed specimens based on PLA by using airborne ultrasound and presents the current edge of non-destructive testing and evaluation using airborne ultrasonic transducers. The specimens, manufactured by polymer extrusion, are printed as thin plates. The infill ratio, as well as the material thickness, were varied to model density imperfections with different geometric shapes and properties. For better understanding of the limits of airborne ultrasonic testing in transmission, we compared own-developed transducers based on different physical principles: on ferroelectrets, on the thermoacoustic effect, as well as a new type of transducers based on gas discharges.
The influence of material properties on bacterial attachment to surfaces needs to be understood when applying polymer-based biomaterials. Positively charged materials can kill adhered bacteria when the charge density is sufficiently high but such materials initially increase the adherence of some bacteria such as Escherichia coli. On the other hand, negatively charged materials have been shown to inhibit initial bacterial adhesion, but this effect has only been demonstrated in relatively few biomaterial classes and needs to be evaluated using additional systems. Gradients in surface charge can impact bacterial adhesion and this was tested in our experimental setup.
Moreover, the evaluation of bacterial adhesion to biomaterials is required to assess their potential for biological applications. Here, we studied the bacterial adhesion of E. coli and Bacillus subtilis on the surfaces of acrylonitrile-based copolymer samples with different amounts of 2-methyl-2-propene-1-sulfonic acid sodium salt (NaMAS) comonomer. The content related to NaMAS based repeating units nNaMAS varied in the range from 0.9 to 1.5 mol%.
We found a reduced colonized area of E. coli for NaMAS containing copolymers in comparison to pure PAN materials, whereby the bacterial colonization was similar for copolymers with different nNaMAS amounts. A different adhesion behavior was obtained for the second tested organism B. subtilis, where the implementation of negative charges into PAN did not change the overall adhesion pattern. Furthermore, it was observed that B. subtilis adhesion was significantly increased on copolymer samples that exhibited a more irregular surface roughness.
Mixtures of hexamethyldisiloxane (HMDSO) and oxygen have been used for deposition of SiO2-like layers by plasma polymerization under low-pressure conditions onto polyethylene and polystyrene used as basecoat. Water glass was cast onto these 0.5 pm plasma thick siloxane-like layers with a thickness of 5 to 40 mu m. The adhesion of these bilayer systems and their flame resistance were tested. The effect of different plasma parameters such as monomer/gas ratio, pressure and power input into the discharge on the deposition rate and the composition of the formed layers was studied. Characterization and chemical composition of the formed films were performed using infrared, X-ray photoelectron and solid state nuclear magnetic resonance spectroscopy. Peel strengths of composites were measured and the locus of peel front propagation was detected. Thermal properties of composites were analyzed by thermo-gravimetric analysis. Finally, the fire-retardant properties of thick coated polymers were determined by exposure to flames and the behavior of coatings on the polymers during flaming was observed visually.
This contribution investigates laser-induced damage of thin film and bulk polymer
samples, with the focus on physical processes occurring close to the damage threshold. In-situ
real-time reflectivity (RTR) measurements with picosecond (ps) and nanosecond (ns) temporal
resolution were performed on thin polymer films on a timescale up to a few microseconds (µs).
A model for polymer thin film damage is presented, indicating that irreversible chemical
modification processes take place already below the fluence threshold for macroscopic damage.
On dye-doped bulk polymer filters (as used for laser goggles), transmission studies using fs-and
ps-laser pulses reveal the optical saturation behavior of the material and its relation to the
threshold of permanent damage. Implications of the sub-threshold processes for laser safety
applications will be discussed for thin film and bulk polymer damage.