Additive Manufacturing and Vulcanization of Carbon Black Filled Natural Rubber Based Components

Additive manufacturing of thermoplastics or metals is a well-approved sustainable process for obtaining rapidly precise and individual technical components. Except for crosslinked silicone rubber or thermoplastic elastomers, there is no method of additive manufacturing of elastomers. Based on the development of the additive manufacturing of elastomers (AME) process, the material group of rubber-based cured elastomers may gain first access to the process field of three-dimensional (3D) printing. Printing and crosslinking of rubber is separated into two steps. In the first step, printing is realized by extrusion of the rubber by using a twin-screw extruder, which works according to the derived fused-filament-fabrication principle. In the second step, the component is vulcanized in a high-pressure hot-air autoclave. Because of the plastic flow behavior of non–crosslinked rubber materials, a thermoplastic shell is probably needed to maintain the geometry and position of the additively manufactured rubber. In this way, one layer of thermoplastic and one layer of rubber are printed alternatingly until the component is finished. Afterward, the manufactured binary component is placed in an autoclave to obtain the elastomer after vulcanization under a hot-air and high-pressure atmosphere. Then, the thermoplastic shell is removed from the elastomer and can subsequently be recycled. As compared with conventional thermoplastics, the high viscosity of rubber during processing and its instable shape after extrusion are challenging factors in the development of the AME. This contribution will show a modified 3D printer; explain the printing process from the designed component, via shell generation, to the vulcanized component; and show first printed components

Tailoring the Curing Kinetics of NBR-Based Rubber Compounds for Additive Manufacturing of Rod Seals

The additive manufacturing (AM) of elastomeric parts based on high-viscosity reinforced rubbers has increasingly become a topic of scientific research in recent years. In addition to the viscosity, which is several decades higher during processing than the viscosities of thermoplastics, the flowability of the compound after the printing process and the necessary chemical crosslinking of the printed component play a decisive role in producing an elastic, high-quality, and geometrically stable part. After the first technological achievements using the so-called additive manufacturing of elastomers (AME) process, the knowledge gained has to be transferred first to concrete industrial parts. Therefore, in this study, the cure kinetics of a conventional rubber compound are tailored to match the specific requirements for scorch safety in the additive manufacturing of an industrial 2-component rod seal based on an acrylonitrile butadiene rubber O-ring in combination with a thermoplastic polyurethane as the base body. Experimental tests on a test rig for rod seals demonstrate the functionality of this additively manufactured 2-component rod seal

Hybrid organic-inorganic two-dimensional metal carbide MXenes with amido- and imido-terminated surfaces

Two-dimensional (2D) transition-metal carbides and nitrides (MXenes) show impressive performance in applications, such as supercapacitors, batteries, electromagnetic interference shielding, or electrocatalysis. These materials combine the electronic and mechanical properties of 2D inorganic crystals with chemically modifiable surfaces, and surface-engineered MXenes represent an ideal platform for fundamental and applied studies of interfaces in 2D functional materials. A natural step in structural engineering of MXene compounds is the development and understanding of MXenes with various organic functional groups covalently bound to inorganic 2D sheets. Such hybrid structures have the potential to unite the tailorability of organic molecules with the unique electronic properties of inorganic 2D solids. Here, we introduce a new family of hybrid MXenes (h-MXenes) with amido- and imido-bonding between organic and inorganic parts. The description of h-MXene structure requires an intricate mix of concepts from the fields of coordination chemistry, self-assembled monolayers (SAMs) and surface science. The optical properties of h-MXenes reveal coherent coupling between the organic and inorganic components. h-MXenes also show superior stability against hydrolysis in aqueous solutions.Comment: 10 pages, 4 figure

Bewertung der stofflichen Homogenität von Kautschukmischungen durch Einsatz der Laser Induced Breakdown Spectroscopy (LIBS)

A key sector of the rubber processing industry deals with improving mixing processes in silica/silane technology and with the discontinuous batch production of the corresponding rubber compounds in the rubber internal mixer compounding process. To achieve the desired material properties in the respective end product, both producers of technical rubber products and tire makers are in need of a mixing process that is effective (in terms of both dispersion and distributive mixing efficiency). Major differences in polarity between nonpolar rubber and highly polar silica impede the incorporation and dispersion of silica, the active filler. This effect also influences the quality of distributive mixing of other compound ingredients and thus the compound homogeneity that is to be attained.Whereas the reflected-light microscopy method, with image processing, has been tested and fully developed for industrial grade use in analyzing filler particle macrodispersion, employment of Laser Induced Breakdown Spectroscopy (LIBS) remains relatively unknown in rubber processing as a means of analyzing distributive mixing efficiency via determination of the homogeneous distribution of a specific marker across a batch volume.The results of this research activity have shown that under atmospheric conditions (with no vacuum), LIBS is a suitable method for analyzing the distributive mixing quality of components within a rubber compound batch. The method can be applied both in compounds free of carbon black fillers and in those containing carbon black fillers. Thanks to its very short measurement time (here: approx. 40 s for analysis of a roughly postage-stamp-sized specimen surface), it yields a statistically representative statement as to the distributive quality of a marker (like zinc) in the used compound

Additive Fertigung und Vulkanisation von Natur- und Synthesekautschuken

Additive manufacturing of thermoplastics and metals is a sustainable and established process in industry for the rapid production of individual technical components. For a long time, this technology was not accessible for the group of elastomers, or only to a limited extent in the form of thermoplastic elastomers or silicone rubbers. The development of the Additive Manufacturing of Elastomers (AME)-process has enabled the additive manufacturing of high viscosity rubbers. In future, additively manufactured rubber components may be used in technical logistics in particular. On the one hand, the supply of spare parts such as sealing and damping elements is possible, and on the other hand, the production of individual geometries for grippers in handling technology. For the additive manufacturing of rubber, an industrial 3D-printer was modified by a twin screw extruder, which can process rubber filament and deposit it on a printing plate in strand form, similar to the thermoplastic Fused Filament Fabrication (FFF)-process. The use of a screw extruder is necessary because the viscosity of the rubber does not decrease sufficiently with heating, making it impossible to guide the filament through conventional print heads for thermoplastic filaments. The AME-process is a two-step manufacturing process. First, the components are additively manufactured, followed by vulcanization in a high-pressure autoclave or heating oven. Single-part production is a particular challenge in this case, as the vulcanization time depends on the rubber compound and the component geometry. In order to avoid waste, it is therefore necessary to know the optimum vulcanization time before vulcanization. For this purpose, a simulation was developed and validated that outputs the degree of crosslinking in the component as a function of the vulcanization temperature and time.Die additive Fertigung von Thermoplasten und Metallen ist ein nachhaltiges und in der Industrie zur schnellen Herstellung von individuellen technischen Bauteilen bewährtes Verfahren. Lange Zeit war diese Technologie für die Werkstoffgruppe der Elastomere nicht oder nur eingeschränkt in Form von Thermoplastischen Elastomeren oder Silikonkautschuken zugänglich. Durch die Entwicklung des Additive Manufacturing of Elastomers (AME)-Verfahrens ist nun auch die additive Fertigung von hochviskosen Kautschuken möglich. Besonders in der technischen Logistik können zukünftig additiv gefertigte Kautschukbauteile Einsatz finden. Einerseits ist die Bereitstellung von Ersatzteilen wie Dichtungs- und Dämpferelementen möglich, aber auch die Fertigung individueller Geometrien für Greifer in der Handhabungstechnik. Zur additiven Fertigung von Kautschuk wurde ein industrieller 3D-Drucker um einen Zweischneckenextruder erweitert, der Kautschukfilament verarbeiten und ähnlich zum thermoplastischen Fused Filament Fabrication (FFF)-Verfahren strangförmig auf eine Druckplatte auftragen kann. Der Einsatz eines Schneckenextruders ist notwendig, da die Viskosität des Kautschuks nicht ausreichend durch Erwärmung abnimmt und somit eine Führung des Filaments durch konventionelle Druckköpfe für thermoplastische Filamente nicht möglich ist. Das AME-Verfahren ist ein zweistufiges Fertigungsverfahren. Zuerst werden die Bauteile additiv gefertigt, anschließend folgt die Vulkanisation in einem Hochdruckautoklav oder Wärmeschrank. Hierbei ist besonders die Einzelteilfertigung eine Herausforderung, da die Vulkanisationszeit abhängig von der Kautschukmischung und der Bauteilgeometrie ist. Um keinen Ausschuss zu produzieren ist es daher notwendig die optimale Vulkanisationszeit vor der Vulkanisation zu kennen. Hierfür wurde eine Simulation, die den Vernetzungsgrad im Bauteil in Abhängigkeit von der Vulkanisationstemperatur und -zeit ausgibt, entwickelt und validiert