Volker Altstädt

University of Bayreuth · Department of Polymer Engineering

Polystyrene-based bead foams are used in various applications under non-steady loading conditions, ranging from sports protectors to automobiles. However, the cyclic dynamic behaviour of bead foams and the influence of density on flexural fatigue behaviour have not yet been investigated. In this context, an analysis is conducted on both the morphol...

Bead foams made from standard polymers such as expanded polystyrene (EPS) or expanded polypropylene (EPP) are widely used in everyday products. In order to expand the application window of bead foams, the industry, such as the automotive industry among others, is striving for higher‐performance materials to create a lightweight material for high‐te...

The use of carbamate to foam epoxy depends significantly on the precured modulus to stabilize the cellular structure. The optimum precured modulus is developed from the reaction of epoxy resin and the neat amine. The selection of the neat amine relies on its reaction temperature with epoxy, which is required to be below the decomposition temperatur...

Polymer foams offer high sustainable performance in terms of their lightweight potential, insulation and high specific mechanical properties. The foaming of polymers depends on the properties of gas-laden solids or liquids. For foaming in the solid state, the foaming temperature must be higher than the glass transition temperature of the saturated...

Currently, the application of composites in aerospace parts exposed to higher temperatures and in aggressive media is still severely limited. To replace metal alloys, alternative resins systems with suitable long‐term heat resistance are needed. In this study, the effect of the aviation hydraulic fluid Skydrol on the thermal and mechanical properti...

Thermoplastic composites offer short cycle times and high automation with good recyclability. Function integration through overmolding can drastically reduce the following assembly steps compared to state-of-the-art aluminum differential design. This study shows in detail the upscaling and process control for thermoforming and overmolding the outer...

Polymers are omnipresent in our everyday lives. For specific applications, their properties can be extensively modified by various types of additives, e.g., processing stabilizers, antioxidants, UV-stabilizers, flame retardants, and plasticizers. While several additives are nowadays considered to be toxic or persistent in the environment, quantitat...

Poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)), as one of the best known piezoelectric polymers, offers unique properties which makes it material of choice for many cutting-edge technologies such as sensors, actuators, and generators. However, the dielectric constant of the polymer in the pure form does not meet the requirements of most...

To develop eco-friendly elastomeric nanocomposites with high dielectric response, poly(lactic acid) (PLA) was melt compounded with varying amounts of thermoplastic polyurethane(TPU) and a fixed loading of (3 wt.%) graphene oxide(GO). The electrical and dielectric properties of the nanocomposites, in terms of TPU and GO loadings and selective locali...

Additive manufacturing is on the verge of replacing established processes in dentistry, as it offers the possibility of manufacturing individual parts simply and cost‐effectively. Due to its suitability for a wide variety of materials and, above all, its high precision, the focus is currently on stereolithographic processes. Intrinsic brittleness o...

Polymers are omnipresent in our everyday lives. For specific applications, their properties can be extensively modified by various types of additives, e.g., processing stabilizers, antioxidants, UV-stabilizers, flame retardants, and plasticizers. While several additives are nowadays considered to be toxic or persistent in the environment, quantitat...

Expanded polymeric beads offer the advantage of being able to produce parts with complex geometries through a consolidation process. However, established polymeric beads are made of thermoplastics, deform and melt beyond their temperature services. In this manuscript, a new technique is proposed to fabricate expandable epoxy beads (EEBs), then expa...

Environmental stress cracking (ESC) is one of the most prominent failure mechanisms for polymer components. The high sensitivity of plastics in regard to environmental influences has always meant that plastics as materials have been viewed very critically in outdoor applications. Recently, the massive occurrence of microplastics in the environment...

The foaming of epoxy resin is a challenge process in optimizing the flow foaming and curing to obtain a homogeneous cellular structure. This study presents a new method for preparing of epoxy foams, which is called solid-state carbamate foaming technique. The epoxy resin was formulated based on epoxy, hardener (amine or polyamide) and carbamate. Th...

Poly(butylene terephthalate) (PBT) is difficult to foam due to its unfavorable rheological behavior (low melt strength, no strain hardening). In particular, a high expansion as well as a homogeneous cell morphology are difficult to achieve. This can be altered successfully by addition of multifunctional chain extenders. Chain extenders cause non‐de...

In the original publication [...]

For a long time, the number of available bead foam variants limited to standard polymers which restricted their functionality mainly to packaging, thermal insulation (e.g. in construction) and shock absorption (e.g. in transportation). In particular, standard polymers such as expanded polystyrene, expanded polyethylene and expanded polypropylene we...

Due to their lightweight potential and good eco-balance, thermoplastic hybrid composites with natural fiber reinforcement have long been used in the automotive industry. A good alternative to natural fibers is wood fibers, which have similar properties but are also a single-material solution using domestic raw materials. However, there has been har...

Irradiation process is an effective technique to modify the molecular architecture, and therefore, the processability and thermo-mechanical properties of polyolefins. In this study, the utility of irradiation dose and atmosphere, heat treatment of the raw material prior to irradiation and the polymer grade, as the most important parameters to influ...

Lightweight design with fiber-reinforced plastics saves energy resources in the use phase of automobiles and aircraft. However, the savings are often offset by higher consumption in production. Therefore, the focus is increasingly shifting to sustainability in manufacturing. The Research Institute Neue Materialien Bayreuth has conducted a correspon...

Due to their light‐weight 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...

Nowadays, numerous techniques are used to quantify the resistance of cellular polymers against a thermal load. These techniques differ in significance and reproducibility and are all dependent on foam density, structure (i.e., cell size and -distribution) and sample geometry. Very different behaviors are expected for extrusion- and bead foams, as w...

When plastics enter the environment, they are exposed to abiotic and biotic impacts, resulting in degradation and the formation of micro- and nanoplastic. Microplastic is ubiquitous in every environmental compartment. Nevertheless, the underlying degradation processes are not fully understood. Here, we studied the abiotic degradation of commonly us...

The current research focuses on suggesting a new potential application of polymeric materials for capacitor applications by focusing on polystyrene (PS)/ethylene-α-octene copolymer (EOC) blends. Polymeric materials have high dielectric strength (≈ 200 for PS), good processability, and flexibility. However, their low dielectric constants make them n...

Reactive compounding of terminally phenolic OH-functionalized polycarbonate (PC) with epoxy-functionalized polymethylmethacrylate (PMMA) prepared by copolymerization with glycidyl methacrylate was investigated. It was spectroscopically demonstrated that a PC/PMMA copolymer was formed during the melt reaction of the functional groups. Zirconium acet...

In this study, an empirical correlation between the tack of phenolic prepregs and the rheological state of the base resin was established. Multivariable analyses were carried out to investigate the determining mechanisms of the prepreg tack along with the temperature- and time-dependent state of the resin. The material storage stability in terms of...

Objective of this work was to deeper understand the influence of a grafted coupling agent in EVA/LLDPE based blends containing mineral filler acting as a flame‐retardant. EVA/LLDPE blends (50:50 phr) containing magnesium‐di‐hydroxide (MDH) were compounded. For comparison, parts (4%–5%) of LLDPE were substituted with MAA‐g‐LLDPE copolymer as a coupl...

In transport sectors such as aviation, automotive and railway, materials combining a high lightweight potential with high flame retardant properties are in demand. Polymeric foams are suitable materials as they are lightweight, but often have high flammability. This study focuses on the influence of different flame retardants on the burning behavio...

With macroscopic litter and its degradation into secondary microplastic as a major source of environmental pollution, one key challenge is understanding the pathways from macro- to microplastic by abiotic and biotic environmental impact. So far, little is known about the impact of biota on material properties. This study focuses on recycled, bottle...

Additive manufacturing processes are still on the way from a prototyping process to an established serial production process. Often the limiting factors are the variety and costs of materials compared with standard materials. Polypropylene is a commonly used material in series production. The processing of polypropylene in additive- and extrusion-b...

This study focuses on the effect of part geometry and infill degrees on effective mechanical properties of extrusion additively manufactured stainless steel 316L parts produced with BASF’s Ultrafuse 316LX filament. Knowledge about correlations between infill degrees, mechanical properties and dimensional deviations are essential to enhance the part...

Foamed plastics are increasingly employed due to the high demand in functional materials with reduced weight. Bead foams in general offer low weight and excellent thermal insulation properties combined with extremely high freedom in design. Though foams show increased risk of ignition and heightened heat release, literature on burning behavior is r...

In this study, application relevant toughened epoxy-amine formulations were investigated regarding their mechanical behavior at low temperatures and compared to a non-toughened reference. The application-oriented resins are based on reactive diluent-modified diglycidylether of bisphenol A (DGEBA) which were tested at 22 °C and −50 °C in regard to t...

The aging behavior of a fast-curing epoxy resin (EP) was examined over three months in unidirectional carbon fiber prepregs for the first time. The semi-latent, 120 °C curing one-pot formulation was developed based on industry-grade diglycidyl ether of bisphenol A (DGEBA) resins without the necessity of B-staging, to fully monitor the property chan...

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...

Foaming an epoxy is challenging because the process involves the curing reaction of epoxy and hardener (from monomer to oligomer, to a gel and a final three-dimensional crosslinked network) and the loading of gas phase into the epoxy phase to develop the cellular structure. The latter process needs to be carried out at the optimum curing stage of e...

The fragmentation of macro- into microplastics (MP) is the main source of MP in the environment. Nevertheless, knowledge about degradation mechanisms, changes in chemical composition, morphology, and residence times is still limited. Here, we present a long-term accelerated weathering study on polystyrene (PS) tensile bars and MP particles using si...

Reactive additives allow to adapt the properties of thermoplastic polymers during processing and for their later use. The chemical modification using multifunctional epoxide styrene-acrylic chain extenders (CE) in reactive processes is by now an established method to prevent degradation and to improve the process ability as well as the final proper...

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...

The combustion properties of natural DNA mixed with the nature‐derived thermoplastic cellulose acetate (CA) were determined. The flame retarding properties of DNA in mixtures with CA were significant and concentration dependent, the higher the DNA content the better the flame retardation. Ammonia was detected during the heating of CA‐DNA mixtures....

Polystyrene foams have become more and more important owing to their lightweight potential and their insulation properties. Progress in this field is expected to be realized by foams featuring a microcellular morphology. However, large-scale processing of low-density foams with a closed-cell structure and volume expansion ratio of larger than 10, e...

The effect of plasma treatment of the multi-walled carbon nanotube (MWCNT) surface on the fracture toughness of an aerospace grade epoxy resin and its unidirectional (UD) carbon fiber prepreg laminates has attracted scientific interest. A prepreg route eliminates the possible risk of carbon nanotube filtration by unidirectional carbon fibers. X-ray...

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...

The combustion properties of natural DNA mixed with the nature‐derived thermoplastic cellulose acetate (CA) were determined. The flame retarding properties of DNA in mixtures with CA were significant and concentration dependent, the higher the DNA content the better the flame retardation. Ammonia was detected during the heating of CA‐DNA mixtures....

Expandable polystyrene (EPS) and expanded polypropylene (EPP) dominate the bead foam market. As the low thermal performance of EPS and EPP limits application at elevated temperatures novel solutions such as expanded polybutylene terephthalate (E-PBT) are gaining importance. To produce parts, individual beads are typically molded by hot steam. While...

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...

Polystyrene foams have become more and more important owing to their lightweight potential and their insulation properties. Progress in this field is expected to be realized by foams featuring a microcellular morphology. However, large-scale processing of low-density foams with a closed-cell structure and volume expansion ratio of larger than 10, e...

Foaming an epoxy is challenging because the process involves the curing reaction of epoxy and hardener (from monomer to oligomer, to a gel and a final three-dimensional crosslinked network) and the loading of gas phase into the epoxy phase to develop the cellular structure. The latter process needs to be carried out at the optimum curing stage of e...

This study focuses on the effect of part geometry and infill degrees on effective mechanical properties of extrusion additively manufactured stainless steel 316L parts produced with BASF’s Ultrafuse 316LX filament. Knowledge about correlations between infill degrees, mechanical properties and dimensional deviations are essential to enhance the part...

In this study, shape memory is thermally induced in a series of graphene oxide (GO) filled poly(lactic acid)/thermoplastic polyurethane (PLA/TPU) blends, prepared via melt mixing process, and their shape recovery and shape fixity are measured, and the results are correlated with morphology, dynamic mechanical properties, crystallinity and creep rec...