Papers by Volker Altstädt
Der vorliegenden Erfindung liegt die Aufgabe zugrunde, ein Verfahren zur Exfolierung von organisc... more Der vorliegenden Erfindung liegt die Aufgabe zugrunde, ein Verfahren zur Exfolierung von organisch modifizierten Schichtsilikaten anzugeben, bei denen es zu einer zumindest annahernd vollstandigen Separierung der einzelnen das Schichtsilikat aufbauenden Schichtsilikatlamellen kommt. Diese Aufgabe wird erfindungsgemass durch ein Verfahren zur Exfolierung von organisch modifizierten Schichtsilikaten gelost, bei dem: eine Harzkomponente und das Schichtsilikat zu einem fliessfahigen Gemisch vermischt werden; das Gemisch bei einem Druck von uber 50 bar und einer Temperatur von uber 0°C hochdruckdispergiert wird. Auf diese Weise gelingt es mit der Hochdruckdispergierung aufgrund der so erzeugbaren Scherkrafte an der Grenzflache Harz - Schichtsilikat bei der Entspannung des dispergierten Gemisches von dem hohen Druck auf einen deutlich tiefer liegenden Druck, z.B. Atmospharendruck, die einzelnen Schichtsilikatlamellen voneinander abzulosen und diese dann als stabile Suspension vorliegen zu...
Composite Materials
Abstract Fiber-reinforced polymers (FRPs) are currently used in a variety of industry sectors to ... more Abstract Fiber-reinforced polymers (FRPs) are currently used in a variety of industry sectors to reduce the overall mass of vehicles, trains, or airplanes and increase energy efficiency. As far as passenger transport is concerned, the fire behavior of FRPs is an important material property in addition to mechanical strength and stiffness. Certain classes of polymeric material systems have already shown intrinsically good fire performance while others require additives to obtain excellent flame-retardant properties. To achieve improved flame-retardant properties of these materials, a great variety of additives are available, which are classified by their chemical nature (i.e., metal complexes, halogenated, phosphorous, silicone-based, or nitrogen-based additives) and their mode of action using either gas or condensed phase active systems. This chapter aims to give a detailed overview of flame-retardant additives for FRPs used in different applications from aircraft industries to the railways, automotive, civil engineering, and electronics, along with their flame-retardant mechanisms at nanoscale, microscopic, and macroscopic levels. Besides the flame-retardant properties, the effect of the additives on other material properties like mechanical performance, glass transition temperature, or processability to FRPs is presented as well. According to the market size of matrix materials for FRPs, the focus is particularly on thermosetting matrix systems with a brief coverage of thermoplastics.
Advanced Science, 2022
Due to their lightweight and cost-effectiveness, cellular thermoplastic foams are considered as i... more Due to their lightweight and cost-effectiveness, cellular thermoplastic foams are considered as important engineering materials. On the other hand, additive manufacturing or 3D printing is one of the emerging and fastest growing manufacturing technologies due to its advantages such as design freedom and tool-less production. Nowadays, 3D printing of polymer compounds is mostly limited to manufacturing of solid parts. In this context, a merged foaming and printing technology can introduce a great alternative for the currently used foam manufacturing technologies such as foam injection molding. This perspective review article tackles the attempts taken toward initiating this novel technology to simultaneously foam and print thermoplastics. After explaining the basics of polymer foaming and additive manufacturing, this article classifies different attempts that have been made toward generating foamed printed structures while highlighting their challenges. These attempts are clustered into 1) architected porous structures, 2) syntactic foaming, 3) post-foaming of printed parts, and eventually 4) printing of blowing agents saturated filaments. Among these, the latest approach is the most practical route although it has not been thoroughly studied yet. A filament free approach that can be introduced as a potential strategy to unlock the difficulties to produce printed foam structures is also proposed.
Polymers, 2021
Polylactide (PLA) is one of the most important bioplastics worldwide and thus represents a good p... more Polylactide (PLA) is one of the most important bioplastics worldwide and thus represents a good potential substitute for bead foams made of the fossil-based Polystyrene (PS). However, foaming of PLA comes with a few challenges. One disadvantage of commercially available PLA is its low melt strength and elongation properties, which play an important role in foaming. As a polyester, PLA is also very sensitive to thermal and hydrolytic degradation. Possibilities to overcome these disadvantages can be found in literature, but improving the properties for foaming of PLA as well as the degradation behavior during foaming have not been investigated yet. In this study, reactive extrusion on a twin-screw extruder is used to modify PLA in order to increase the melt strength and to protect it against thermal degradation and hydrolysis. PLA foams are produced in an already known process from the literature and the influence of the modifiers on the properties is estimated. The results show that ...
M. Sc. Michaela Kersch1, Dr.-Ing. Felipe Wolff Fabris1, Dipl.-Chem. Marieluise Stumpf1, Dipl.-Che... more M. Sc. Michaela Kersch1, Dr.-Ing. Felipe Wolff Fabris1, Dipl.-Chem. Marieluise Stumpf1, Dipl.-Chem. Florian Richter2, Prof. Dr. Hans-Werner Schmidt2,3, Prof. Dr.-Ing. Volker Altstadt1,3 aPolymer Engineering, University of Bayreuth, Universitatsstrase 30, 95447 Bayreuth, Germany bMacromolecular Science I, University of Bayreuth, Universitatsstrase 30, 95447 Bayreuth, Germany cBayreuther Institut fur Makromolekulforschung (BIMF)
Verfahren zur Herstellung eines offenzelligen Polymerschaums mit folgenden Schritten: Herstellen ... more Verfahren zur Herstellung eines offenzelligen Polymerschaums mit folgenden Schritten: Herstellen einer aus einem thermoplastischen Polymer gebildeten Schmelze, Losen eines organischen Nukleierungsmittels in der Schmelze, Versetzen der Schmelze mit einem Treibmittel und Extrudieren der Schmelze.
The present invention relates to a process for producing a fibrous composite material using at le... more The present invention relates to a process for producing a fibrous composite material using at least one epoxy resin and at least one initiator, which contains one or more cationic Metallolefinkomplexe. The invention further relates to a fiber-containing agent and a fibrous composite material as such.
Journal of Cellular Plastics, 2019
Polystyrene is a low-priced, amorphous polymer, showing excellent foaming behavior. Polystyrene f... more Polystyrene is a low-priced, amorphous polymer, showing excellent foaming behavior. Polystyrene foams are widely used in a variety of applications including insulation panels for building and construction. In this context, foam morphology plays a significant role to tune the macroscopic properties of the foams and research focusses on the fabrication of foams with homogenous morphology and an average cell size distinctly below 100 µm at densities lower than 100 kg/m³. Here, we demonstrate how 1,3,5-benzene-trisamides can be used as supramolecular foam nucleating agents to control the morphology of extruded amorphous polystyrene foams. Depending on the concentration and the processing temperature, benzene-trisamides can be homogeneously dissolved in the polystyrene melt. Upon cooling, the benzene-trisamides self-assemble into finely dispersed, solid supramolecular nano-objects, which subsequently act as nucleating sites for foam cell formation. Various concentrations of the benzene-t...
AIP Conference Proceedings, 2019
In this work bead foams from a thermoplastic engineering polymer, exhibiting a higher service tem... more In this work bead foams from a thermoplastic engineering polymer, exhibiting a higher service temperature than the established bead foam polymers polystyrene and polypropylene, were developed. For the first time bead foams from polybutylene terephthalate (PBT) with a density below 160 kg/m 3 were produced and welded. In particular, the influence of a multifunctional epoxy chain extender on the rheological behavior, the foam morphology as well as the weldability was investigated. Due to the reaction of the chain extender during the processing the viscosity could be increased and strain hardening was observed, leading to improved foaming behavior. An optimum chain extender concentration regarding density reduction and cell morphology was determined as 1 wt.-%.
Rheologica Acta, 2016
The rheological properties of a long chain branched polypropylene (LCB-PP) were investigated at t... more The rheological properties of a long chain branched polypropylene (LCB-PP) were investigated at the processing conditions of foam extrusion, namely high pressure, gas loading and high shear rates, as well as in elongational deformation. For measuring the rheological properties of PP at moderate and high deformation rates, an in-line rheometer was used. Comparison of the results to standard rotational rheometry showed good agreement. The effect of the processing parameters was quantified using shift factors for temperature, pressure and gas concentration. The influence of pressure on the shear viscosity was found to be of minor importance. In contrast, the shear viscosity was distinctly affected by CO 2 concentration, reducing it to one third of its gas-free value at a concentration of 6 wt% at a specific shear rate. The change of viscosity by a variation of temperature is similar in magnitude compared to the variation due to dissolved blowing agent. Furthermore, thermo-rheological complex behaviour was observed. In the foaming process, thermo-rheological complexity could contribute to a better morphology control of long chain branched polymers compared to linear ones. The elongational viscosity was measured using both a hyperbolic die and a film stretching tool (UXF) for comparison. It is almost three decades higher than the shear viscosity in the non-linear region, due to pronounced strain hardening of the melt.
Solid State Phenomena, 2007
There is enormous scientific and economic interest in the development and evaluation of polymer n... more There is enormous scientific and economic interest in the development and evaluation of polymer nanocomposites due to the fact that the properties of a material become increasingly insensitive to flaws at the nanoscale, enabling the exploitation of the unique physical and mechanical properties of very small objects in large-scale components. However, the successful industrial implementation of such novel materials poses unique challenges which are not only related to the small size of the reinforcements. Decades of intensive research have shown that polymer nanocomposites differ from their counterparts based on traditional reinforcements in many ways and a fundamental understanding of the structure-propertyrelationships of such novel materials is only slowly emerging. Although issues such as the intrinsic properties of the nanoscale constituent as well as the degree of dispersion and orientation of individual filler particles clearly appear to be important factors, molecular interac...
AIP Conference Proceedings, 2015
Thermoplastic vulcanizates (TPVs) combine the elastic properties of thermoset cross-linked rubber... more Thermoplastic vulcanizates (TPVs) combine the elastic properties of thermoset cross-linked rubbers with the melt processability of thermoplastics. The most representative examples of this class are the TPVs based on polypropylene (PP) and ethylene-propylene-diene terpolymer rubber (EPDM). The PP/EPDM blends were produced by dynamic vulcanization in a continuous extrusion process. The influence of different crosslinking systems was studied with regard to cross-link density, compression set, tensile strength/elongation at break and morphology. With increasing peroxide concentration, the cross-link density increases, leading to a reduction of the compression set by 50 %. The same improvement is only reachable with twice the concentration of phenolic resin. Only the peroxide cross-linked blends show smaller dispersed EPDM particles with increasing peroxide concentration. With a peroxide concentration between 0.2 and 0.5 wt. %, a maximum in tensile strength and elongation at break was found. For the phenolic r...
Electron Beam Curing of Composites, 2010
Journal of the mechanical behavior of biomedical materials, 2014
This paper investigates the structure-property relationship of a new generation of poly(styrene-b... more This paper investigates the structure-property relationship of a new generation of poly(styrene-b-isobutylene-b-styrene) (SIBS) block copolymers with a branched (dendritic) polyisobutylene core with poly(isobutylene-b-para-methylstyrene) end blocks (D_IBS), and their carbon black (CB) composites. These materials display thermoplastic elastomeric (TPE) properties, and are promising new biomaterials. It is shown that CB reinforced the block copolymer TPEs, effectively delayed the oxidative thermal degradation of the D_IBS materials, and greatly improved their dynamic fatigue performance. Specifically, the dynamic creep of a CB composite was comparable to that of chemically crosslinked and silica-reinforced medical grade silicone rubber, used as a benchmark biomaterial.
Polymer, 2004
The fatigue behaviour of poly(aliphatic/aromatic-ester) (PED) multiblock copolymers has been eval... more The fatigue behaviour of poly(aliphatic/aromatic-ester) (PED) multiblock copolymers has been evaluated using the hysteresis loop method. Stepwise increasing strain test (SIST) was performed at a frequency of 1 Hz. The strain levels were varied with increasing extension steps: 3, 5, 10, 15, 20, 25 and 30% of the initial strain, while minimum stress has been set at a constant value of 0.1 MPa. It has been found that soft PEDs show a very good stress relaxation due to the fact that they contain high amounts of the amorphous phase and their soft segments do not crystallize. PED copolymers, especially those containing low amounts of crystalline hard domains showed very good damping properties at small strain levels. It has also been found that PED's ability to store and dissipate energy is a function of the hard segment concentration. This method proved to be a useful tool for determining the changes in the material properties of PEDs and other thermoplastic elastomers during deformation.
High Performance Polymers, 2007
As a method of compatibilization of immiscible polyether ether ketone (PEEK)/polysulfone (PSU) bl... more As a method of compatibilization of immiscible polyether ether ketone (PEEK)/polysulfone (PSU) blends, the addition of segmented PEEK/PSU block copolymers based on amorphous bisphenol A-containing PEEK was studied. This approach was evaluated for blends consisting of PEEK and PSU homopolymers with different molecular weights and different amounts of compatibilizers (segmented PEEK/PSU block copolymers and reactive end-functionalized PEEK and PSU oligomers). The compatibilizers were added under varying melt-processing conditions and effectively allowed the homopolymers to interact with the segmented block copolymers in the blend. The influence of the compatibilizers on the phase behavior was examined in both binary and ternary blends. Interactions in the amorphous phase, which effectively induce an enhancement of the toughness properties of the final product, could be detected.
European Polymer Journal, 2003
This paper reports the effects of hard (polystyrene, PS) and soft (polyisobutylene, PIB) segment ... more This paper reports the effects of hard (polystyrene, PS) and soft (polyisobutylene, PIB) segment composition and the molecular architecture (linear versus star, PS and PIB block length) on the morphology and mechanical properties of polystyrene/polyisobutylene (SIBS) block copolymers synthesized by living carbocationic polymerization. Atomic force microscopy, dynamic mechanical thermal analysis and tensile testing verified the phase-separated nature of the block
Polymers, 2021
The use of amine-based carbamates with their dual function, acting as amine curing agents and CO2... more The use of amine-based carbamates with their dual function, acting as amine curing agents and CO2 blowing agents after their decomposition without by-products, are promising for ecofriendly epoxy foams as high-performance materials. However, controlling cell morphology requires a proper adjustment of the viscosity at the foaming step. The viscosity is altered not only by blending neat amine and its derived carbamate at a fixed pre-curing time, but also by changing the pre-curing time at a fixed blend ratio. Within this study, diglycidylether of bisphenol A (DGEBA) epoxy resin is mixed with different blend ratios of isophorone diamine (IPDA) and its derived carbamate (B-IPDA). The systems are characterized by DSC and rheology experiments to identify the pre-curing effects on the derived epoxy foams. Epoxy foams at a blend ratio of 30/70w IPDA/B-IPDA showed the best foam morphology and an optimum Tg compared to other blend ratios. Furthermore, it was found that both pre-curing times, ...
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Papers by Volker Altstädt