Rheology, dispersion, and cure kinetics of epoxy filled with amine‐ and non‐functionalized reduced graphene oxide for composite manufacturing

This study evaluates the effect of plasma surface functionalization of reduced graphene oxide particles on the processing characteristics and homogeneity of dispersion of a bisphenol A‐(epichlorhydrin) epoxy matrix and amine‐based hardener with varying weight fractions from 0.00 to 1.50 wt%. It was observed that amine‐functionalized reduced graphene oxide leads to a more drastic viscosity increase of up to 18‐fold of the uncured suspensions and that its presence influences the conversion rates of the curing reaction. Optical microscopy of thin sections and transmission electron microscopy analysis showed that a more homogeneous dispersion of the particles could be achieved especially at higher weight fractions by using an appropriate surface functionalization. This knowledge can be used to define suitable processing conditions for epoxies with amine‐based hardeners depending on the loading and functionalization of graphene‐related particles

Fabrication of chitosan-flax composites with differing molecular weights and its effect on mechanical properties

An aqueous fabrication method is investigated for a composite reinforced with chitosan and flax fibers. The composite is characterized structurally, mechanically and chemically. A strong influence of molecular weight (MW) is identified on the composite properties. A strong fiber-matrix interface, which is associated with porosity and effective fiber impregnation, is achieved by applying low molecular weight (LMW) solution followed by casting using LMW or medium molecular weight (MMW) solution. Porosity is analyzed using μ-CT analysis. Increasing porosity with increasing molecular weight results in a decline of the tensile and flexural properties of the composites. The chitosan-flax composites have a low density compared to synthetic and natural fiber composites, which is a competitive advantage as a replacement material for particle board or plyboard in suspended ceilings, furniture compartments, sports or leisure equipment. A multiscale simulation is carried out to compute the directional effective elastic properties and predicts a potential 21% improvement of the tensile modulus if the process is optimized. This work shows the potential of chitosan-flax composites as a sustainable green material with an aqueous fabrication procedure and useful mechanical properties

Zeit- und kosteneffiziente Prozess- und Produktentwicklung für den Hochleistungs-Faserverbundleichtbau mittels Nasspresstechnologie

Großserientaugliche Produktionsprozesse von Hochleistungs-Faserverbundkunststoffen stellen aufgrund der gewünschten Prozesseffizienz bei gleichzeitiger Realisierung herausragender gewichtsspezifischer Materialeigenschaften ein wichtiges, zukunftsträchtiges Themenfeld dar. Im Automotive-Bereich kommen diese Prozesse verstärkt zur Anwendung, insbesondere bei Premiumfahrzeugen und im Rahmen der E Mobilität. Der erheblichen Gewichtseinsparung und hohen Energieeffizienz von Leichtbaustrukturen stehen bisher jedoch noch hohe Entwicklungs- und Stückkosten (Material, Prozessaufwand) gegenüber. Neben den verschiedenen Varianten der Resin Transfer Moulding (RTM) Technologie bietet sich zur Herstellung leichter, komplex geformter Strukturbauteile das Nasspressverfahren als Großserienanwendung an. Durch Parallelisierung von Prozessschritten in Verbindung mit hochreaktiven Harzsystemen können niedrigere Zykluszeiten erreicht werden als beim RTM-Verfahren. Da für den Nasspressprozess bisher weder ein umfassendes physikalisch-basiertes Prozessverständnis, noch Methoden zur virtuellen Prozesssimulation und -optimierung existieren, besteht ein erheblicher Forschungsbedarf für eine ressourceneffiziente Prozess- und Bauteilentwicklung [1]. Die Forschungsbrücke „KIT – Uni Stuttgart“ baut auf der langjährigen wissenschaftlichen und strategischen Zusammenarbeit der Leichtbau-Institute des Karlsruher Instituts für Technologie (KIT-FAST) und der Universität Stuttgart (IFB Stuttgart) auf und widmet sich der Erforschung und Weiterentwicklung des Nasspressprozesses (vgl. Abbildung 1). Dabei werden zwei unterschiedliche Prozessrouten grundlegend untersucht, modelliert, optimiert und bewertet. Besondere Herausforderungen sind die fundierte Material- und Prozessanalyse der Nasspresstechnologie sowie die Methodenentwicklung zur effizienten, virtuellen Prozess- und Bauteilentwicklung und die ganzheitliche Optimierung

Effects of Reactive and Non-Reactive Tackifying Agents on Mechanical Neat Resin and Composite Performance for Preforming Processes and Liquid Resin Infusion (LRI) Techniques

AbstractPreforming processes can be used for automated manufacturing of fiber reinforced polymers . Different technologies are used for processing of dry textile fabrics into 2D or 3D preforms. Due to missing tack of dry fabrics, auxiliary binder systems are used for fixation of the fabrics onto a substrate material and in order to achieve sufficient adhesion between layers. In this study, seven reactive and non-reactive tackifying agents have been dissolved in neat resin samples of three epoxy resin systems, showing different degrees of solubility and a variation on neat resin tensile properties (ΔσAVG = 20%) as well as a reduction on thermal properties (up to ΔTg = - 18 °C). Subsequently, fiber reinforced polymers were manufactured using Liquid Resin Infusion techniques in order to characterize the influence of binder systems on water absorption (cs,max = 1.38 wt%) and Interlaminar Shear Strength (ILSS). It was shown that ILSS properties are negatively affected by non-reactive tackifying agents (up to - 27%)

The advanced ply placement process – an innovative direct 3D placement technology for plies and tapes

Breaking down the cost structure of state-of-the-art CFRP part shows that a major share of the costs is caused by labor and equipment as well as process energy consumption. Therefore, the main goal of the EU funded FP7 project LOWFLIP (Low Cost Flexible Integrated Composite Process) has been the reduction of these costs by introducing new technologies into CFRP production processes. The LOWFLIP concept focuses on three main aspects:• Development of a new out-of-autoclave (OOA) prepreg system with snap cure capabilities. • Development of a direct 3D placement technology for plies and tapes. • Development of energy efficient and fast heating toolings. The main content of this paper is detailed information on a novel direct 3D prepreg layup process for automated production of large-scale fiber reinforced parts of small and medium lot sizes. The advanced ply placement process, which is able to drape and compact unidirectional prepreg tapes with currently up to 300 mm ply width directly into a double curved tooling, is being introduced. Two large-scale demonstrator parts from the transport and aerospace sector will be presented. Experiences gained during prototype manufacturing will be reflected and benchmarks of the equipment are presented

Structural optimization through biomimetic-inspired material-specific application of plant-based natural fiber-reinforced polymer composites (Nfrp) for future sustainable lightweight architecture

Under normal conditions, the cross-sections of reinforced concrete in classic skeleton construction systems are often only partially loaded. This contributes to non-sustainable construction solutions due to an excess of material use. Novel cross-disciplinary workflows linking architects, engineers, material scientists and manufacturers could offer alternative means for more sustainable architectural applications with extra lightweight solutions. Through material-specific use of plant-based Natural Fiber-Reinforced Polymer Composites (NFRP), also named Biocomposites, a high-performance lightweight structure with topology optimized cross-sections has been here developed. The closed life cycle of NFRPs promotes sustainability in construction through energy recovery of the quickly generative biomass-based materials. The cooperative design resulted in a development that were verified through a 1:10 demonstrator, whose fibrous morphology was defined by biomimetically-inspired orthotropic tectonics, generated with by the fiber path optimization software tools, namely EdoStructure and EdoPath in combination with the appliance of the digital additive manufacturing technique: Tailored Fiber Placement (TFP)

Mechanical, Thermal and Electrical Properties of Epoxy Nanocomposites with Amine-Functionalized Reduced Graphene Oxide via Plasma Treatment

A suitable functionalization of graphene and its derivatives can further enhance the material properties of nanocomposites. In contrast to chemical functionalization methods that have been extensively researched, functionalization by plasma treatment is relatively unexplored. In this work, we compare the mechanical, thermal and electrical characteristics of an epoxy matrix incorporating loadings from 0.00 to 1.50 wt% of non-functionalized (rGO) and amine-functionalized reduced graphene oxide (frGO) for which the functionalization is realized by plasma processing. No significant difference between the rGO- and frGO-including nanocomposites was observed with respect to the stiffness, strength, specific heat capacity, coefficient of thermal expansion and electrical conductivity. Yet, the composites with 1.50 wt% frGO (rGO) exhibited a thermal conductivity that was 27% (20%) higher than the neat polymer due to the enhanced interface, which enabled a better transfer of heat. In addition, a considerable increase in the specific heat capacity and thermal conductivity was established with rising temperatures. This information will facilitate the choice of materials depending on the loading and functionalization of graphene materials for composite applications with an epoxy matrix