Elmar Moritzer

Effect of atmospheric pressure plasma pre-treatment and aging conditions on the surface of thermoplastics

The application of atmospheric pressure plasma is a popular pre-treatment method in the field of joining technology. Its purpose is the improvement of adhesion between different materials, e.g., for adhesive bonding, painting, or injection molding. Especially, while bonding parts with lower surface energies, efficient surface activation can be achieved via this treatment method. The surface is specifically modified in its chemical, physical, and topographical properties. However, after surface treatment, it is possible that these new surfaces progressively change by aging and compensation processes. Knowing the time-variant surface state after pre-treatment is extremely important for interpreting the entire process chain. Additionally, the effect of the pre-treatment on other properties—such as the bonding strength of an adhesive bond—must be known. The aging behavior of an atmospheric pressure plasma-treated plastic surface has been demonstrated in several studies based on the surface properties (chemical composition, surface energy, etc.). Whether these property changes also significantly affect the bond strength of structural adhesive joints is to be clarified in the present analysis. In this study, the aging behavior of three typical thermoplastics (polyethylene, polypropylene, and polystyrene) is examined after a treatment with an atmospheric plasma jet. The aging is taken into account by two factors: ambient temperature and time. Kinematic parameters (distance and velocity) of the pre-treatment are integrated in the experimental design to include the effects of the pre-treatment method in the investigation. The dependence of these influencing effects on bond strength and surface energy is analyzed with the help of central composite experimental designs. The results show a change in surface properties over time and ambient temperature. An increase of temperature and time leads to a reduction of surface energy. Furthermore, the kinematic factors of the plasma treatment determine aging. However, a mathematical correlation between bond strength and aging parameters could not be detected in this study. The bond strength is time-invariant but significantly dependent on the parameters distance and speed. Additionally, a dimensional analysis was conducted in order to describe the dependency of surface energy and load factor on the investigated parameters. Therefore, several dimensionless parameters were developed. Regarding the load factor, it was possible to describe the ongoing processes based on the correlations discovered by dimensional analysis. This allows the prediction of the load factor based on process and storage parameters. A relationship between the investigated Π-numbers could not be detected for the surface energy, which means a functional relationship to describe the surface energy could not be found.

Examination of Interpenetrating Polymer Networks of Polyurea in Silicone Molds Arising during Vacuum Casting Processes

ABSTRACT We present an in-depth investigation of the aging effects in silicone molds for vacuum casting processes. Their lifetime is limited to a few production cycles due to contamination with the diisocyanate component of polyurethane casting materials. Using thermogravimetric analysis measurements, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and helium-ion-microscopy the chemical and physical mechanisms of the aging process have been identified. It has been shown that a diffusion process of diisocyanate into the cavity surface leads to the formation of interpenetrating polymer networks of polyurea derivatives in silicone rubber. This has been proven by extracting and analyzing polyurea of low molecular weights from the silicone. GRAPHICAL ABSTRACT

Vorbehandlung von Kunststoffen

Kunststoffoberflachen konnen mithilfe unterschiedlicher Verfahren gezielt aufs anschliesende Kleben vorbereitet werden. Die jeweils richtige Vorbehandlung soll die Substratoberflache sowohl auf den einzusetzenden Klebstoff einstellen als auch durch die damit erfolgte Konditionierung zur Prozesssicherheit der Klebung beitragen. Alle vorgestellten Vorbehandlungstechniken haben ihre Vor- und Nachteile. Welche Oberflachenvorbehandlung gewahlt werden sollte, hangt von folgenden Faktoren ab: Art und Menge der auftretenden Kontaminationen bzw. Randschichten, Art des Kunststoffs (Polaritat des Materials, Bestandigkeit des Materials gegenuber Losungsmittel, Warme etc.), Grose der zu klebenden Kunststoffbauteile bzw. Halbzeuge, Geometrie der Klebflachen (flach, komplex 3D geformt bzw. flachige Klebung, Stuckzahl der zu klebenden Bauteile (manuell, automatisiert), Taktzeit und Grose der Klebflache (Flachenleistung), HSE-Aspekte (Health, Safety and Environment Protection) und Fertigungsumgebung, Investitions- und Betriebskosten. Somit muss die gewahlte Vorbehandlungstechnik ein recht umfangreiches und individuelles Anforderungsprofil erfullen. Fur besonders hochwertige Klebungen mit extremen Anforderungen an deren Langzeitstabilitat werden zum Teil auch hybride Vorbehandlungsmethoden eingesetzt.

Epoxidharzklebstoffe zum Kleben von Kunststoffen

Das Kleben mittels elektromagnetischer Induktion ermoglicht schnelle Prozesse und eine Aushartung auch dicker oder schwer zuganglicher Klebspalte. Fur die Formulierung induktiv hartender Klebstoffe sind Epoxidharze gut geeignet. Zur Verfugung stehen 1K- und 2K-Systeme, mit denen sowohl metallische Werkstoffe als auch Kunststoffe geklebt bzw. vergossen werden konnen.

Improved abrasion resistance of textile fabrics due to polymer coatings

Textile fabrics are often subject to abrasion, starting from exposed parts of garments to a variety of technical textiles. Abrasion protection by usual coatings, however, can significantly decrease the water vapor transport through a fabric which is often not desired, especially in the case of garments. In our paper, we report on an approach to combine increased abrasion resistance with sufficient water vapor transport properties. For this, different polymers (poly(methyl methacrylate), acrylonitrile butadiene styrene, or amorphous polyamides) were coated on cotton and polyester woven fabrics. The results of abrasion tests against sandpaper show significantly increased abrasion resistance. The absolute evaporation resistance, measured by a Permetest testing device, was only slightly increased up to values still acceptable for typical garments. Images of all coatings by helium ion microscopy deliver an explanation for the measuring results. Polymer coatings on the polyester fabric resulted in a slight reduction of the hydrophobicity, while coating the cotton fabric severely increased the contact angles of the originally superhydrophilic material.

Inline-Oberflächenaktivierung im Spritzgießprozess für hohe Klebfestigkeiten

Der Einsatz von Kunststoffen wird unter dem Gesichtspunkt des Leichtbaus mehr und mehr forciert. Ein sehr wichtiges Fügeverfahren stellt in diesem Kontext das Kleben von Kunststoffen dar. Aufgrund ihrer niedrigen Oberflächenenergie ist für viele Anwendungen eine Oberflächenaktivierung notwendig, damit eine Haftung zwischen Klebstoff und Fügeteil entstehen kann. Dabei können verschiedene Methoden zur Oberflächenvorbehandlung zum Einsatz kommen. Ein vielversprechendes Verfahren stellt die Oberflächenaktivierung mittels Plasma dar, die zu einer Erhöhung der Oberflächenenergie des Kunststoffes durch den Einbau polarer funktioneller Gruppen führt /1/. Aufgrund der großen Anwendungsvielfalt ist das Atmosphärendruck (AD)Plasmaverfahren ein gängiges Verfahren zur Oberflächenfunktionalisierung von Kunststoffen. Wie bei allen anderen möglichen Behandlungsverfahren ist jedoch auch für dieses Verfahren ein separater Prozessschritt notwendig, der die Wirtschaftlichkeit des Produktes beeinträchtigt. Das Direktinjektion-Plasma (DIP)-Verfahren (siehe Infobox) führt zu einer Integration der Oberflächenaktivierung in den Spritzgießprozess. Aufgrund des neuartigen Verfahrensprinzips sind bisherige Erkenntnisse aus der Forschung für AD-Plasmaverfahren nicht direkt übertragbar. Das Ziel der nachfolgend beschriebenen Untersuchung war daher die Analyse der Behandlungswirkung des DIP-Verfahrens unter Betrachtung der Oberflächenaktivierung und der erzielbaren Klebfestigkeiten. Untersuchungsaufbau

Bonding of wood-plastic composites (WPC)—material and surface modification for special applications

As part of the current research at the Kunststofftechnik Paderborn (KTP), foundational experiments are being conducted on adhesive bonding of wood-plastic composites (WPC) with dispersion adhesives. The setting mechanism of this type of adhesive is characterized by the evaporation of the dispersion medium (water). The challenge is therefore to remove the water in the adhesive fluid from the joining plane. In conventional applications, dispersion adhesives are used to bond wood, paper, or other porous materials. Wood-plastic composites, however, which consist of wood particles in a polymer matrix, cannot absorb the necessary amount of water within the required time period, as they do not possess a similarly porous structure. Part surfaces are treated in various processes in order to expose the wood fibers. This is intended to improve the material’s capacity to absorb water, which should lead to more rapid setting. In addition to surface treatments, the WPC formula is modified by the addition of hygroscopic additives. A further approach is to drill holes at regular intervals into the joining plane as additional points where evaporation can occur. The water in the adhesive layer migrates towards these holes through diffusion processes and then evaporates into the ambient atmosphere.

Fiber length reduction during shearing in polymer processing

In recent years a continuously rising demand of short-fiber-reinforced thermoplastics has been noted. The reason for the rising demand are the excellent weight specific mechanical properties compared to non-reinforced thermoplastics. The mechanical properties of the compound of high-strength fibers and the ductile matrix polymer is based on complex physical relations in which the fiber length is a major influencing factor. When processing short fiber-reinforced thermoplastics with screw machines (injection molding, extrusion) the fiber length is a resulting material property that is, to some extent, influenced by the process parameters. The extent of the influence and the effects of the process parameters have been carried out in many different studies, mainly with parameter variations. Nevertheless, the influence of the shearing stress on the fiber breaking is also physically modelled. However, the influences of different fiber contents are not taken into account.To investigate the correlation between th...

Universal Micromachining Platform and Basic Technologies for the Manufacture and Marking of Microphysiological Systems

Micro Physiological Systems (MPS), also known as Multi-Organ-Chip, Organ-on-a-Chip, or Body-on-a-Chip, are advanced microfluidic systems that allow the cultivation of different types of cells and tissue in just one common circuit. Furthermore, they thus can also adjust the interaction of these different tissues. Perspectival MPS will replace animal testing. For fast and flexible manufacturing and marking of MPS, a concept for a universal micromachining platform has been developed which provides the following latest key technologies: laser micro cutting of polymer foils, laser micro- and sub-micro-structuring of polymer foils, 3D printing of polymer components as well as optical inspection and online process control. The combination of different laser sources, processing optics, inspection systems, and print heads on multiple axes allows the change and exactly positioning to the workpiece during the process. Therewith, the realization of MPS including 3D printed components as well as direct laser interference patterned surfaces for well-defined cell adhesion and product protection is possible. Additional basic technologies for the generation of periodical line-like structures at polycarbonate foils using special Direct Laser Interference Patterning (DLIP) optics as well as for the 3D printing of fluid-tight cell culture reservoirs made of Acrylonitrile Butadiene Styrene directly onto polycarbonate microfluidics were established. A first prototype of the universal micromachining platform combining different lasers with Direct Laser Writing and DLIP is shown. With this laser micro cutting as well as laser micro-structuring of polycarbonate (PC) foils and therewith functionalization for MPS application could be successfully demonstrated.

Mechanical recycling of continuous fiber-reinforced thermoplastic sheets

This contribution examines possible material recycling of offcuts generated during the production of continuous-fiber-reinforced composite sheets. These sheets consist of a polyamide 6 matrix and glass fiber fabric. In the initial step, the offcut is shredded to obtain particles; following that, the particles are processed in a twin-screw process to produce fiber-reinforced plastic pellets with varying fiber contents. These pellets are intended for use in injection molding processes as a substitution for new raw materials. This investigation centers on the mechanical properties which can be achieved with the recycled material after both the twin-screw process and injection molding.