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Polymer engineering & science 63(5), 1598-1612 (2023). doi:10.1002/pen.26309, Published by Wiley, Hoboken, NJ

92. Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM), GAMM, Aachen, Germany, 15 Aug 2022 - 19 Aug 2022; Proceedings in applied mathematics and mechanics : PAMM 23(1), e202200069 (2023). doi:10.1002/pamm.202200069 special issue: "Special Issue: 92. Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM) / Issue Edited by: Ch. Böhm, K. Mang, B. Markert, S. Reese, M. Schmidtchen, J. Waimann, M. Kaliske", Published by Wiley-VCH, Weinheim

Polymer composites (2022). doi:10.1002/pc.26479, Published by Society of Plastic Engineers, Brookfield, Conn.

Polymer engineering & science (2021). doi:10.1002/pen.25800, Published by Wiley, Hoboken, NJ

Materials science and engineering technology = Materialwissenschaft und Werkstofftechnik 52(4), 367-378 (2021). doi:10.1002/mawe.202000158, Published by Wiley-VCH, Weinheim

Missing Journal / Fehlende Zeitschrift 2021, 1-5 (2021).

Polymer engineering & science (2020). doi:10.1002/pen.25383, Published by Wiley, Hoboken, NJ

Journal of applied polymer science (2019). doi:10.1002/app.48863, Published by Wiley, New York, NY [u.a.]

Cellulose acetate (CA) is a bio-based polymer suitable to replace foamed polystyrene (PS) in packaging applications. Foam trays can be produced by thermoforming of extruded sheets foamed with physical blowing agents. In this paper, the effects of various process settings and the calibration of the sheet on foam morphology and surface quality of extruded CA sheets are presented. Different contact cooling options were applied in order to investigate their influence on surface roughness, density, and morphology of the sheets. By adjusting cooling parameters, blowing agent formulation, and process settings, smooth foam sheets with a surface roughness below 10 µm and a density in the range of 150 kg m−3 were produced.

Insbesondere die optische Transparenz und die hervorragende Sperrwirkung siliziumoxidischer Beschichtungen gegenuber Gasen und Aromen sichern den PECVD-Schichten in der Barriereausrustung von Kunststoffen ihre Bedeutung. Wahrend fur Kunststoffe die Transportvorgange von Gasen und Aromen durch das Arrhenius-Modell als Permeation durch einen Festkorper beschrieben werden kann, sind fur die PECVD-Schichten und insbesondere mehrschichtige Verbunde aus PECVD-Schichten nur wenige Modelle in der Literatur beschrieben. Es existieren Modelle, die auf der Diffusion durch Defekte innerhalb der PECVD-Beschichtungen basieren und annehmen, dass auserhalb der Defekte keine Permeation stattfindet. Gegenstand der Forschung ist die Uberprufung der Gultigkeit der verschiedenen Modelle vor dem Hintergrund experimenteller Daten zu Sauerstoff- und Wasserdampftransmission. Um die Gultigkeit der verschiedenen Modelle abzuleiten, werden ein- und beidseitige Beschichtungen aus variierenden Schichtarchitekturen miteinander verglichen.

Physical foaming usually requires special metering equipment to inject the blowing agent at high pressures. In this study, low density polyethylene (LDPE) was foamed in the extrusion process using dry ice as physical blowing agent. The blowing agent was metered in form of pellets over the hopper. To determine relevant process parameters and improve the understanding of the process a melting model is applied. The influence of the formation of a melt film and melt pool on the dissolution of the blowing agent is discussed. The theoretical considerations are validated in a design of experiment study. As a result, the efficiency of the process is especially affected by the throughput rate, granules temperature, and blowing agent concentration. Further varied parameters are the barrel temperature in the melting zone and diameter of the dry ice pellets. Fast melting and pressure build-up were shown to reduce blowing agent losses. POLYM. ENG. SCI., 55:2821–2828, 2015. © 2015 Society of Plastics Engineers

Amorphous hydrogenated carbon (a-C:H) deposited on steel with plasma enhanced chemical vapor deposition can be used as elongation tolerant oxygen barrier. However, the elongation tolerance of the a-C:H film is lost if deposited on a poly(ethylene terephthalate) (PET) for reasons unknown. To assess this phenomenon, a-C:H was deposited on PET, silicon substrates, and silicon micro-cantilevers, and the stress was determined by measuring the radius of curvature. a-C:H deposited on PET showed lower compressive stress than on silicon. This difference is not due to the formation of a gradient layer or plastic deformation of PET. Instead, the most probable explanation is that energetic ions cause a partial release of biaxial orientation within the PET, thereby reducing the compressive stress.

Atomic layer deposition (ALD) is increasingly becoming commonplace to deposit high density, conformal films, as novel deposition techniques allow improved deposition rates on various substrates. Diffusion and miscibility of ALD precursors with polymers are known to affect film nucleation. To assess the influence of polymeric underlayer on the growth and mechanical behavior of ALD films, we deposited aluminum oxide (Al2O3) and titanium dioxide (TiO2) films on three different polymers with known reactivity to the ALD precursors and compared them to films on polyethylene terephthalate (PET). We present the trends in nucleation and penetration of the ALD films on the various polymers as well as the in situ mechanical behavior under tensile strain. X-ray photoelectron spectroscopy (XPS) revealed that Cytop, a fluorinated polymer and polyethyleneimine ethoxylated (PEIE) delay the nucleation of Al2O3 and TiO2 films. Time-of-flight mass spectrometry (ToFSIMS) shows the extent of diffusion of the ALD precursors into the polymer underlayer, delaying nucleation. Tensile tests show that while the crack onset strain remained unchanged despite the various polymer underlayers, the crack saturation density decreased for ALD films on PEIE and polyhydroxystyrene (PHOST). Films on Cytop showed no crack saturation limit until the nucleation delay was overcome indicating that judicious choice of the ALD film and polymer underlayer will allow tailoring of the length of the diffusion zone and crack saturation, but not the crack onset strain, which will be addressed in future studies.

Environmental stress cracking (ESC) is a premature failure of a polymer exposed to a fluid, under stress which is much less than its yield stress. Many experimental works were done before in an effort to predict experimentally the ESC potential of a fluid in different polymers. None of the previous works applied molecular modeling techniques to predict this potential so this work is a pioneering work. This study's goal was to apply atomistic molecular modeling techniques to gain a better understanding of the ESC mechanism and to predict the ESC potential of different fluids in polymers. Our model experimental system was amorphous polycarbonate (PC) with water as an ESC fluid. The computational study was expanded to include a high level ESC fluid for PC–toluene and a non ESC fluid–BD, together with the moderate ESC fluid–water. A clear distinction between ESC fluids and non ESC fluids for PC was achieved by means of molecular modeling. The experimental work approved that water is an ESC fluid for PC as predicted in the computational part. Copyright © 2014 John Wiley & Sons, Ltd.

Polypropylene (PP) composites containing 20 wt% short flax fibers are prepared, and the process parameters such as throughput, rotational speed, and screw configuration are varied during melt compounding with a corotating intermeshing twin-screw extruder. The investigations reveal that low rotational speeds, high throughputs, and moderate shear energy inputs by the screw configuration led to an optimum set of mechanical properties. To investigate the influence of different composite compositions on the mechanical properties, composites with fiber contents between 0 and 40 wt% and maleic anhydride-grafted PP (PP-g-MA) contents between 0 and 7 wt% are prepared. Increasing fiber contents enhance the Young's modulus and decrease the elongation at break and the notched impact strength. The tensile strength is barely affected. The addition of PP-g-MA increases the tensile strength as well as the elongation at break, whereas the Young's modulus is not influenced. Thus, PP-g-MA enhances the adhesion between PP and flax fibers significantly. POLYM. COMPOS., 2014. © 2014 Society of Plastics Engineers

Summary Electric/electronic devices become increasingly more complex and are used in highly integrated assembly groups. Soft magnets generally show only “moderate” magnetic properties; however, they exhibit a comparably high permeability which allows the material for being used in conjunction with hard magnets as a “magnetic conductor”. Thus, the magnetic flux density of such parts can be improved leading to a better accuracy and functionality of switches, valves or pumps. In particular for micro applications the use of plastics-bonded soft magnets in combination with hard magnets integrated in one injection moulded part provides new opportunities for electric/electronic devices. The Institute of Plastics Processing (IKV) at the RWTH Aachen further develops in cooperation with Siemens, Oechsler, and Arburg soft magnetic compounds focusing on micro applications. The magnetic properties of plastics-bonded soft magnets are significantly reduced compared to pressed or sintered materials. Compounds filled with spherically shaped fillers as iron-silicon show better flow and processing properties compared to irregular- or flaky-shaped fillers. Due to the specific flow conditions the magnetic properties are not homogeneous throughout the part. At the end of the flow path the filler content is considerably increased leading to higher soft magnetic properties. This can be well correlated by means of microscopic analyses.

Summary Polyamide 6-compounds containing carbon nano tubes and carbon fibres are prepared by melt compounding. To investigate the influence of the processing conditions on the mechanical properties and the morphology of carbon fibre reinforced polyamide 6-nanocomposites the process parameters are varied while preparing the compounds. The processing conditions affect the mechanical properties and the morphology. The investigations reveal, that a micro-nano-compound with a PA6-matrix should be compounded at a maximum barrel temperature of 260 °C, a throughput of 15 kg/h at a screw speed of 500 min−1 and a screw configuration, which introduces a low amount of shear energy into the compound. These processing conditions lead to a comparatively high specific mechanical energy input of 334 Wh/kg and to the best set of mechanical properties of the investigated materials. However, the morphology of the investigated carbon fibre reinforced nanocomposites does not show significant differences and has to be further investigated.

The adhesion of thin CVD films on polyolefins is often critical due to the low surface free energy of the polymers. In this study, injection moulded PP samples are produced and investigated. The samples are treated in very well-characterized pulsed plasmas before a HMDSO-based coating is applied. The resulting bond strength is analyzed using pull-off tests. The fractured interfaces are characterized with XPS. Oxygen and argon plasma pre-treatments of the PP samples result in a bond strength improvement by a factor of about 2. Comparing oxygen and argon pre-treatments at equal ion fluences to the surface, it can be shown that the bond strength between CVD-coating and polymer is similar.

In this paper, we present the results of mechanical testing that reveals the onset crack strain and fatigue crack growth of TiO2 and Al2O3 films deposited by atomic layer deposition. Data show that both films have a strong thickness dependence of the onset crack strain, with the strain reducing with increasing film thickness. Additionally, TiO2 films have a lower onset crack strain and strain for fatigue damage than Al2O3. However, TiO2 films are more resilient in harsh environments where fatigue damage in Al2O3 films grows faster.

Polypropylene composites containing 0–5 wt% layered silicate and 0–30 wt% short glass fibers are prepared by melt compounding. To investigate the influence of different compositions on the mechanical properties of short glass fiber-reinforced polypropylene nanocomposites, materials with various filler contents are prepared. At a glass fiber content of 10 wt% Young's modulus of the layered silicate-containing composites decreases by around 30% compared to conventional glass fiber-reinforced polypropylene. But at higher glass fiber loadings, an increasing modulus of up to 10% is observed. However, the addition of layered silicate results in large decreases of the tensile and the notched impact strength. A maleic anhydride-grafted polypropylene enhances Young's modulus and the tensile strength. © 2012 Society of Plastics Engineers

The effect of the melt-compounding conditions with the use of a corotating intermeshing twin-screw extruder and of the nanotube content on the morphology and the mechanical and rheological properties of nylon 6/multiwalled carbon nanotube (MWCNT) composites was investigated. The melt-compounding conditions affected the morphology, but the variations in the morphology did not necessarily result in substantial variations in the mechanical and rheological properties. The mass throughput had the strongest influence on the mechanical properties, whereas the MWCNT feeding substantially affected the rheology. The increase in the MWCNT volume content from 0.0 to 3.5 vol % led to an increase in the Young's modulus, whereas the tensile strength, elongation at break, and notched impact strength exhibited maximum values around 0.5 to 1.0 vol %. With increasing MWCNT volume contents, higher complex viscosities and storage and loss moduli and a lower loss factor compared to neat nylon 6 were observed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40893.