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Paper des Monats
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In welding experiments conducted on heavy wall pipes, the penetration mode (full or partial penetration) occurred to be a significant factor influencing appearance of solidification cracks. To explain the observed phenomena and support further optimization of manufacturing processes, a computational model was developed, which used a sophisticated strategy to model the material. High stresses emerged in the models in regions which showed cracking during experiments. In partial penetration welding, they were caused by the prevention of weld shrinkage due to the cold and strong material below the joint. Another identified factor having an influence on high stress localization is bulging of the weld.
In den letzten Jahren hat die Verwendung von Kunststoffen im Bauwesen einen erheblichen Aufschwung genommen. Hierbei hat nicht nur der Umsatz, sondern auch der Verwendungsumfang von Jahr zu Jahr zugenommen, was nicht zuletzt seine Ursache in den Variationsmöglichkeiten der Eigenschaften von Kunststoffen hat. So befindet sich eine Vielzahl von Kunststoff-Erzeugnissen für das Bauwesen mit unterschiedlichen Eigenschaften auf dem Markt. Um Bauherren, Bauträgern und Architekten eine Übersicht über geeignete Kunststoff-Erzeugnisse und ihre technischen Anwendungsmöglichkeiten im Bauwesen zu geben, ist vom Bundesministerium für Wohnungswesen, Städtebau und Raumordnung die Aufstellung eines Verzeichnisses „Kunststoffe im Bauwesen“ angeregt worden. Dieses Verzeichnis soll die Anwendung von solchen Kunststoff-Erzeugnissen erleichtern, die sich als geeignet und bewährt herausgestellt haben. Dadurch wird indirekt eine Steigerung der Güte, der baulichen Ausführung und Wohnungsausstattung ermöglicht, überdies wird das Kunststoff-Verzeichnis dazu beitragen, Vorurteile gegen die Verwendung von Kunststoffen zu beseitigen. Das Verzeichnis hat keinerlei amtlichen Charakter, wobei jedoch angenommen wird, das sich auch amtliche Stellen des Verzeichnisses bedienen werden. Es enthält keine Preisangaben.
A method for the determination of very volatile organic compounds (VVOC) in air was developed and successfully tested for methanol and ethanol. Carbotrap300® (a multi-bed tube using Carbopack C®, Carbopack B® and Carbosive SIII®) was selected as sorption material for thermal desorption and tested for its suitability for emission test chamber measurements. The adsorption behaviour and the chromatographic results are influenced negatively by spiking aqueous solutions on the adsorption medium for calibration purposes. The latter effect can be reduced by blowing dry air across the adsorbent to remove the adsorbed water. Detection and quantification limits were determined for a GC-FID system and compared to GC-MS. The applicability of the method was tested with a methanol eliminating silane modified polymeric adhesive (SMP-adhesive for parquet) in an emission test chamber
Odour measurements become increasingly important in view of the assessment of indoor air quality and the emissions of building products. Hence they need to be implemented into evaluation schemes such as the AgBB scheme. While there are already standards like DIN ISO 16000-28 and VDI 4302 Part 1 specifying the procedure of odour measurements using a comparison scale, no final validation of the method has been carried out so far. Therefore, a round robin test was conducted in 2012 with 12 participating laboratories that mainly consisted of the following two parts: 1) testing of the available comparison scales with respect to their operational performance and 2) execution of an odour assessment of an acrylic sealant using emission test chambers. Part one included the measurement of the air flow rates and the provided concentrations of the reference substance (acetone). Part two was conducted to test the performance of the laboratories and the applicability of DIN ISO 16000-28 and supplementary VDI 4302 Part 1 by assessing the perceived intensity and the hedonic tone of the air samples. Moreover, samples for VOC analysis were taken from the air in the emission test chamber on the 7th day of testing to allow for quality control. Resulting from this round robin test main deficits were detected and suggestions for the improvement of the odour measurement procedure were made.
The use of coconut fiber (CF) agricultural waste was considered as an environmentally friendly and inexpensive alternative in flame retarded biocomposites. To decrease the high content of aluminum trihydrate (ATH) required, the thermal decomposition (thermogravimetry), flammability [oxygen index (LOI) and UL 94 test] and fire behavior (cone calorimeter) of a combination of CF and ATH were investigated in a commercial blend of thermoplastic starch (TPS) and cellulose derivatives. CF induced some charring activity, slightly decreasing the fire load and burning propensity in cone calorimeter test. ATH decomposes endothermically into water and inorganic residue. Significant fuel dilution as well as a pronounced residual protection layer reduces the fire hazards. Replacing a part of ATH with coconut fibers resulted in improved flame retardancy in terms of ignition, reaction to small flame, and flame-spread characteristics [heat release rate (HRR), fire growth rate (FIGRA), etc.]. The observed ATH and CF synergy opens the door to significant reduction of the ATH contents and thus to interesting flame retarded biocomposites.
A fiber Bragg grating (FBG) strain patch specially adapted for long-term and high-strain applications has been developed and characterized. The design concept for the patch is based on a glass-fiber reinforced plastic (gfrp) carrier material. The developed concept for the FBG integration into the carrier material was derived from reliable integration procedure of FBG sensors into composite structures. The patches' temperature sensitivity, strain gauge factor, fiber–matrix interface adhesion and fatigue behavior were characterized. As a result, FBG strain patches with linear temperature and strain behavior, as well as excellent fatigue resistance, were developed and can be used as part of a monitoring system for advanced composite materials in aerospace structures or wind turbine power plants.
Effect of well dispersed amorphous silicon dioxide in flame retarded styrene butadiene rubber
(2013)
Spherically shaped amorphous silicon dioxide with broad size particle distribution was used in combination with aluminium trihydroxide (ATH) in styrene butadiene rubber composites. The pyrolysis, flammability, fire properties, flame spread and gas diffusion were investigated. The kind and amount of ATH, but in particular the fine silicon dioxide chosen as an additive, influenced the thermal decomposition and fire behaviour of styrene butadiene rubber composites. Gravimetric gas sorption measurements showed that the gas diffusion was systematically lower with silicon dioxide. The initial pyrolysis gas release was hindered, increasing the temperature at which decomposition begins as well as the ignition time in fire tests. During combustion, ATH and silicon dioxide accumulate on the surface of the specimen, forming a residual protective layer. A reduced peak heat release rate and fire spread were observed. The addition of a special kind of silicon dioxide is proposed to play a key role in optimising fire retardancy.
Several construction and building materials, including wood, glue and coatings, are possible sources of very volatile organic compounds (VVOCs) and volatile organic compounds (VOCs) like formic and acetic acid. Due to very high air tightness and very low air exchange rates in new buildings concentrations of these harmful substances can increase considerably. To minimize the risk, emissions from building products should be identified and quantified. With the common standard method, this means Tenax® sampling followed by thermal desorption and GC-MS analysis, these acids could not be detected sufficiently. The aim oft this study is the comparison of two different methods for the determination of acetic and formic acid. The sampling of method one, which is usually used for identification and quantification of VOCs, is done in accordance with ISO 16000-6 and ISO 16017-1 on Carbotrap® 202 multi-bed thermal desorption tube by subsequent identification and quantification with GC-MS. Method two is based on sampling on 2,4-dinitrophenylhydrazine (DNPH) cartridges, derivatisation, elution, identification and quantification of the derivatives with LC-MS/MS (liquid chromatography mass spectrometry/mass spectrometry).
The pyrolysis and fire behavior of halogen-free flame-retarded DGEBA/DMC, RTM6 and their corresponding 60 vol.-% carbon fibers (CF) composites were investigated. A novel phosphorous compound (DOPI) was used. Its action is dependent on the epoxy matrix. DGEBA/DMC and DOPI decompose independently of each other. Only flame inhibition occurs in the gas phase. RTM6 shows flame inhibition and a condensed phase interaction increasing charring. Both mechanisms decrease with increasing irradiance, whereas in RTM6-CF charring is suppressed at low ones. RTM6+DOPI shows a higher LOI (34.2%) than DGEBA/DMC+DOPI and a V-0 classification in UL 94. Adding CF only enhances the LOI, DOPI+CF leads to a superposition in LOI for DGEBA/DMC-CF+DOPI (31.8%, V-0) and a synergism for RTM6-CF+DOPI (47.7%, V-0).