Volker Wachtendorf

The influence of weathering on scratches and on scratch and mar resistance of automotive coatings

Automotive coatings are expected to retain a good scratch resistance over years of service. On the other hand, scratches once arisen should disappear by reflow or should not become more visible during further use of the car. These expectations are a challenge to the paint manufacturer and are not easy to fulfil as our work will show. Seven car coatings were examined, each with different PU clearcoats. The coatings were treated under artificial weathering conditions before and after the scratch test. Scratching was carried out using laboratory car wash and Nano Scratch techniques. In comparison to other essential coating properties measured, the scratch and mar resistance was mainly affected by pre-weathering. Alterations in reflow behaviour, shape and size of single scratches were observed during post-weathering which included partly acid precipitation.

Enhanced flame-retardant effect of a montmorillonite/phosphaphenanthrene compound in an epoxy thermoset

A phosphaphenanthrene and triazinetrione group containing flame retardant (TAD) is combined with organically modified montmorillonite (OMMT) in epoxy resin thermosets (EP) to improve the performance of the flame-retardant system. When only 1 wt% OMMT/4 wt% TAD is introduced into the EP, the limited oxygen index (LOI) rises from 26% to 36.9% and a V-0 rating is achieved in a UL 94 test. The decomposition and pyrolysis products in the gas phase and condensed phase were characterized using thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR). The influence on the decomposition of EP, such as the increase in char yield, is limited with the incorporation of OMMT; a large amount of the phosphorus is released into the gas phase. The flame-retardant effect evaluation based on cone calorimeter data testified that OMMT improves the protective-barrier effect of the fire residue of OMMT/TAD/EP on the macroscopic scale, while TAD mainly causes flame inhibition. The fire residues showed a corresponding macroscopic appearance (digital photo) and microstructure (scanning electron microscope [SEM] results). The protective barrier effect of OMMT and the flame-inhibition effect of TAD combined to exert a superior flame-retardant effect, resulting in sufficient flame-retardant performance of OMMT/TAD/EP.

Multilayer Graphene/Carbon Black/Chlorine Isobutyl Isoprene Rubber Nanocomposites

High loadings of carbon black (CB) are usually used to achieve the properties demanded of rubber compounds. In recent years, distinct nanoparticles have been investigated to replace CB in whole or in part, in order to reduce the necessary filler content or to improve performance. Multilayer graphene (MLG) is a nanoparticle made of just 10 graphene sheets and has recently become commercially available for mass-product nanocomposites. Three phr (part for hundred rubbers) of MLG are added to chlorine isobutyl isoprene rubber (CIIR)/CB composites in order to replace part of the CB. The incorporation of just 3 phr MLG triples the Young’s modulus of CIIR; the same effect is obtained with 20 phr CB. The simultaneous presence of three MLG and CB also delivers remarkable properties, e.g. adding three MLG and 20 phr CB increased the hardness as much as adding 40 phr CB. A comprehensive study is presented, showing the influence on a variety of mechanical properties. The potential of the MLG/CB combination is illustrated to reduce the filler content or to boost performance, respectively. Apart from the remarkable mechanical properties, the CIIR/CB/MLG nanocomposites showed an increase in weathering resistance.

Polypropylene Numerical Photoageing Simulation by Dose–Response Functions with Respect to Irradiation and Temperature: ViPQuali Project

The aim of the joint project ViPQuali (Virtual Product Qualification) was to describe a component’s ageing behaviour in a given environment, by numerical simulation.

Excitation energy transfer of a bichromophoric cross-shaped molecule investigated by polarized fluorescence spectroscopy

The excitation energy transfer (EET) of a bichromophoric cross-shaped molecule was investigated by stationary polarized fluorescence spectroscopy in the solid state. For this purpose 2,2′,7,7′-tetrakis(biphenyl-4-yl)-9,9′-spirobifluorene was embedded in a polymeric bisphenol-A-polycarbonate (PC) matrix. The dependence of the fluorescence on concentration and wavelength was determined. The role of the intermolecular and intramolecular EET is dealt with separately and discussed by means of the degree of polarization. The intermolecular excitation energy transfer is described in terms of a Forster transfer mechanism. The intramolecular transfer is prevented for the zero-point vibrational levels by the molecular cross-shaped structure, but is found for a wide range of wavelength, presumably based on vibrationally excited states.

Combined impact of UV radiation and nitric acid on HDPE containers during outdoor exposure

Abstract Unpigmented HDPE jerrycans filled with nitric acid (55 wt.-%) and water respectively had been exposed to outdoor conditions for one Berlin summer season. As both liquids underwent equal temperature progression, exposure effects of UV radiation and nitric acid as well as of the combination of both can be separated and compared. On the basis of various property changes after these exposures, synergistic action is evaluated and compared to a damaged Intermediate Bulk Container (IBC) from a transport accident. It is found that carbonyl formation accompanies lightness increase in color measurement due to microcracking and with a worsening in mechanical behavior, all of them showing the synergistic effects of UV and nitric acid exposure. By contrast, embedding nitrogen compounds accompanies yellowing of the material but cannot be correlated to oxidation. The reason for intensified damaging is the decomposition of the 55-percent nitric acid and the formation of nitrogen oxides even at ambient temperatures, caused by UV radiation. Thus, damaging effects become similar to those caused by fuming nitric acid exposure at temperatures above 60 °C, resulting in strong oxidative degradation of the polyethylene. By contrast, exclusive exposure to the 55 wt.-% nitric acid at 40 °C does not cause any failure. It can therefore be assumed that the damaged IBC too had been exposed to both UV radiation and nitric acid, probably outdoors.

Contaminant release from aged microplastic

Environmental context Increasing global plastic production adds plastic debris to the environment. We show that potentially harmful additives present in plastic particles are released to water at an increased rate when material properties change by aging due to exposure to high temperature and especially to UV radiation. For risk assessment of such plastic additives, more information on their degradation products and their toxicity is needed. Abstract Recycled plastic granules of high-density polyethylene, polyvinyl chloride and polystyrene the size of microplastics were exposed to artificial aging conditions (2000h; photooxidative and thermo-oxidative) to simulate their fate outdoors. Their potential to leach into water during the aging process was investigated using column percolation tests. Aging-related changes on the surface of the material were characterised by IR measurements indicating oxidation reactions with the formation of new adsorption bands (C=O, C–O and OH), especially in the case of photooxidative aging. These findings were confirmed by the identification of leachable organic compounds. Leaching of total organic carbon, Cl, Ca, Cu and Zn is clearly affected by changes due to aging, and their release is increased after photooxidative aging. In general, exposure to photooxidative conditions shows a greater influence on aging and thus on leaching and seems to be the more important mechanism for the aging of microplastic in the environment. Comparison with the total content of inorganic species revealed that, for most elements, less than 3% of the total content is released after 2000h of photooxidative aging.

Multilayer graphene rubber nanocomposites

Multilayer Graphene (MLG), a nanoparticle with a specific surface of BET = 250 m2/g and thus made of only approximately 10 graphene sheets, is proposed as a nanofiller for rubbers. When homogenously dispersed, it works at low loadings enabling the replacement of carbon black (CB), increase in efficiency, or reduction in filler concentration. Actually the appropriate preparation yielded nanocomposites in which just 3 phr are sufficient to significantly improve the rheological, curing and mechanical properties of different rubbers, as shown for Chlorine-Isobutylene-Isoprene Rubber (CIIR), Nitrile-Butadiene Rubber (NBR), Natural Rubber (NR), and Styrene-Butadiene Rubber (SBR). A mere 3 phr of MLG tripled the Young’s modulus of CIIR, an effect equivalent to 20 phr of carbon black. Similar equivalents are observed for MLG/CB mixtures. MLG reduces gas permeability, increases thermal and electrical conductivities, and retards fire behavior. The later shown by the reduction in heat release rate in the cone calorimeter. The higher the nanofiller concentration is (3 phr, 5 phr, and 10 phr was investigated), the greater the improvement in the properties of the nanocomposites. Moreover, the MLG nanocomposites improve stability of mechanical properties against weathering. An increase in UV-absorption as well as a pronounced radical scavenging are proposed and were proved experimentally. To sum up, MLG is interesting as a multifunctional nanofiller and seems to be quite ready for rubber development.

Chemiluminescence Detection: Principles, Chances and Limitations for the Shortening of Weathering Tests

Improvements in the stabilization of polymeric materials mean that the duration of weathering tests increases. At the same time, however, an increasing number of new developments in ever-shorter development cycles brings about greater demands to shorten the test duration. Apart from accelerating the degradation rate by enhancing exposure parameters, another approach to increasing the test throughput consists in using more sensitive means of detecting degradation effects in earlier stages of the degradation process. The degradation process begins on a molecular level before it starts to spread over higher proportions of the polymer. The effect of degradation on the material builds up until macroscopic properties begin to change, either showing an abrupt threshold behavior or a more gradual response to increasing degradation on a molecular level. From a theoretical point of view, a detection of the earlier stages of the degradation process can be expected by switching from the established, more macroscopic properties in the evaluation of effects to more microscopic ones. While both physical processes and chemical reactions contribute to the degradation of materials, chemical reactions usually are more dominant since their effects tend to be irreversible. Within these chemical reactions, oxidation reactions with oxygen usually are of Chapter 21