Frank Haupert

Epoxy nanocomposites with high mechanical and tribological performance

Abstract Small ceramic particles are known to enhance the mechanical and tribological properties of polymers. Introduced into an epoxy resin, the filler morphology, size, particle amount and the dispersion homogeneity influence extensively the composites performance. In the present study, various amounts of micro- and nano-scale particles (calcium silicate CaSiO3, 4–15 μm, alumina Al2O3, 13 nm) were systematically introduced into an epoxy polymer matrix for reinforcement purposes. The influence of these particles on the impact energy, flexural strength, dynamic mechanical thermal properties and block-on-ring wear behavior was investigated. If the nanoparticles were incorporated only, they yield an effective improvement of the epoxy resin at a nanoparticle content of already 1–2 vol.% Al2O3. Choosing the nanocomposite with the highest performance as a matrix, conventional CaSiO3 microparticles were further added in order to achieve additional enhancements in the mechanical properties. In fact, synergistic effects were found in the form of a further increase in wear resistance and stiffness. Several reasons to explain these effects in terms of reinforcing mechanisms were discussed.

Microhardness studies on functionally graded polymer composites

Functionally graded polymer composites based on an epoxy resin matrix and SiC filler particles were prepared. By controlling the preparation conditions during centrifugation, a high gradient in the particle distribution (from 0 to 45 vol.%) could be achieved. The gradient of the mechanical properties along the centrifugal force axis was mapped by means of microhardness measurements. A continuous increase of the hardness from 210 up to 640 MPa over the length of the samples was observed. An almost linear dependence of the Vickers hardness on the SiC volume content in the broad range from 7 to 45% was found. An attempt was made to explain the deviation of this relationship from the usual microhardness additivity law (rule of mixtures). It was shown that the elastic modulus derived from the universal hardness measurements can be successfully used for studying the trend of the elastic properties in functionally graded materials.

Ultrasonic dispersion of inorganic nanoparticles in epoxy resin

The incorporation of nanoscale fillers into a polymer can lead to a considerable improvement of mechanical properties, i.e. stiffness and toughness of a material can be enhanced simultaneously by the insertion of nanofillers. Thereby, the crucial difference between conventional microscale fillers and nanofillers is the high specific surface of the latter. In order that this surface can interact with the matrix material a good dispersion, i.e. a good separation and a homogeneous distribution of the nanoparticles into the polymer, is required. In the present study ultrasonic waves generated by an ultrasonic horn were used to disperse titanium dioxide nanoparticles into epoxy resin. The process parameters, e.g. the ultrasonic amplitude, the dispersion time and the materials volume, were varied systematically with the aim of achieving an optimum dispersion process. A dispersion model for bead mills was adapted to the ultrasonic process and compared to a second dispersion model in order to find an adequate mathematical expression to correlate the ultrasonic process parameters to the particle sizes in the material and to allow predictions for further experiments.

Preparation of TiO2/epoxy nanocomposites by ultrasonic dispersion and their structure property relationship.

By the insertion of nanoparticles into a polymer matrix a considerable improvement of mechanical properties can be achieved. Therefore, a homogeneous distribution of fillers within the matrix is required. In the present paper the dispersion of TiO(2)-nanoparticles in a DGEBA (diglycidyl ether of bisphenol A) epoxy resin by means of an ultrasonic horn was studied. The systematic examination of process parameters of a previous study was completed in order to determine the optimum processing window leading to a good dispersion result without degrading the molecular structure of the epoxy resin. Therefore, particle sizes were examined using a dynamic light scattering device, and the effect of the ultrasonic treatment on the resin was surveyed by FT-IR spectroscopy (Fourier transform infrared spectroscopy). Furthermore, the mechanical performance of the nanocomposites was examined for various contents of TiO(2)-nanoparticles to show that the materials prepared by ultrasonic dispersion show an improved propertys profile. In order to understand the reinforcing mechanisms of nanoparticles in the polymer matrix providing improved mechanical properties, scanning electron microscope (SEM) pictures of the fracture surfaces of the samples were carried out, which revealed that nanocomposites show a significantly rougher surface than the neat epoxy resin. This indicates a change in the fracture mechanisms.

Current and Future Applications of Polymer Composites in the Field of Tribology

The use of polymers and polymer composites in various tribological situations has become state of the art. Nevertheless, further developments are still under way to explore new fields of application for these materials and to tailor their properties for more extreme loading conditions. This overview describes how to design polymeric composites in order to operate under low friction and low wear against various counterparts. Particular emphasis is focused on special fillers (including spherical nano-particles), often in combination with classical tribo-fillers (such as carbon fibers, graphite flakes, polytetrafluoroethylene particles), for the tribological improvement of thermoplastics and thermosets. An attempt is made to do systematic parameter studies by the use of artificial neural networks. The principle effects are demonstrated by describing practical examples in various fields of application. These include (a) high temperature polymer composites for sliding elements in textile drying machines, (b) friction torque limiters for damped flywheel clutches in modern automotives, (c) epoxy-based particle-filled composites for thick covers of calender rollers in the paper making industry, and (d) thermoplastic nanocomposite coatings for hybrid bushings used in automotive components under the hood, to mention only a few.

Mechanical and Thermal Properties of Nano-Titanium Dioxide-Reinforced Polyetheretherketone Produced by Optimized Twin Screw Extrusion:

Polyetheretherketone (PEEK), an attractive matrix for highly loaded parts in terms of temperature and mechanical performance, is applied in many engineering applications. However, its improvement in the mechanical properties by, for example, nanoparticles is sometimes necessary to fulfill actual requirements. In this case, the nanoparticles need to be deagglomerated, wetted by the polymer matrix, and equally distributed. Excellent results can be achieved by a second extrusion step applied on the masterbatch. Theoretical calculations of processing parameters (e.g., shear energy) explain the reason for a better dispersion and distribution of nanoparticles inside the matrix for the multipass extrusion process. PEEK compounds reinforced with 15 nm titanium dioxide (TiO2) nanoparticles are compared with PEEK reinforced with 300 nm particles. The incorporation of the nanoparticles into the PEEK matrix was realized by a corotating twin screw extruder (ZE25x44, Berstorff GmbH) with 10 heating barrels. The mechanical and thermal properties of the materials were characterized at room temperatures by tensile and impact testing, differential scanning calorimetry, and dynamic mechanical thermoanalysis. The important distribution quality of the nano-sized particles and corresponding fracture surfaces are shown in high-resolution scanning and transmission electron microscopy micrographs. It becomes visible that the 15 nm particles enhance the polymer properties much better than the 300 nm particles. The 15 nm particles improve the stiffness and the strength as a function of filler content. Highest values of impact energy can be achieved at a filler content of 2.2 vol. %.

Influence of Aggregate Structure on Mode-III Interfacial Fracture between Concrete and CFRP

One of the crucial issues in the use of fiber reinforced polymers for civil engineering applications is the interfacial bonding between the different materials used. As a load transfer from the concrete to the composite components occurs via shear stresses in the interfacial region, studies of the interfacial bond quality should concentrate on load situations in which primarily shear stresses are induced. In this study, a 3-Point Bending Test was modified to initiate shear failure under Mode-III conditions in the interface between a composite and a concrete component. In particular it was the objective to study the interfacial shear strength between three different concretes and an unidirectional carbon fiber reinforced epoxy matrix system. The three concretes had the same compressive strength (B35 KP, German Standard), but differed in the type of filler material: (a) “heavy” concrete, filled with granite (Diorit) particles, (b) “normal” concrete, filled with gravel grains (Pyrite), and (c) “light weight” concrete, filled with vopourtone (Liapur). The mechanical test results showed that both the type of filler exposed to the joint surface as well as the type of adhesive used clearly influence the interfacial shear strength. Best values were achieved with Diorit-fillers, and the Sikadur-adhesive was in all cases superior to the Dywipox-adhesive. Reasons for these differences were demonstrated by light optical and scanning electron micrographs of the fractured surfaces.

Development of nanostructured slide coatings for automotive components

Abstract Polymer based slide coatings have become indispensable as tribological layers of slide bearings. In modern automobiles they are used as tribological coatings for high-temperature applications in the engine compartment such as anti-friction coatings for piston skirts or in low-lubricant applications like journal bearings of diesel fuel injection pumps which often operate under boundary lubrication. Important structure–property relationships for the achievement of a high operating temperature and a high-compression loading capability are discussed in detail for two of the most important polymeric matrices: epoxy resins (EPs) and polyamide imide (PAI). The beneficial effect of nanoparticulate fillers on the tribology of slide coatings is demonstrated on the basis of three current applications from the automotive industry: slide coatings for piston skirts, polymer/metal-slide bearings for high-temperature bearing applications and for use under boundary lubrication.

Verification of a Dispersion Model to Describe the Dispersion of Nanoparticle Agglomerates in Epoxy Resin with a Stirred Bead Mill

In the presented study, the dispersion of titanium dioxide (TiO2) nanoparticle agglomerates in an epoxy resin by the use of a stirred bead mill was investigated. Therefore, systematic dispersion experiments were carried out and the achieved particle sizes were determinated according to the principle of dynamic light scattering. Based on these dispersion experiments a grinding model by Becker[ 1 ] for the description of the milling process in stirred bead mills was constructed and transferred to the dispersion of nanoparticle agglomerates. Afterward, the dispersion model was applied to simulate the particle size distributions of TiO2 nanoparticles for dispersion in the stirred bead mill and, in addition, checked experimentally.

Chapter 18 – Development of nanostructured slide coatings for automotive components

: Tribological layers of polymer/metal-slide bearings slide coatings have become indispensable in the manufacturing of modern automobiles. Furthermore slide coatings are used as tribological coatings for high-temperature and low-lubricant applications in the engine compartment like antifriction coatings for piston skirts or in boundary lubricated journal bearings of diesel fuel injection pumps. Important structure–property relationships for the achievement of a high operating temperature and a high compression loading capability are discussed in detail for two of the most important polymeric matrices: Epoxy Resins and Polyamide–Imide. Other bulk polymers under consideration were Poly-Para-Phenylene and Polyetheretherketone. The beneficial effect of nanoparticulate fillers on the tribology of slide coating is demonstrated on the basis of three current applications from the automotive industry: slide coatings for piston skirts, polymer/metal-slide bearings for high-temperature bearing applications and for use under boundary lubrication.