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Increasing demand for energy-efficient means of transport has steadily intensified the trend towards lightweight components. Thermoplastic glass fiber composites (organo sheets) play a major role in the production of functional automotive components. Organo sheets are cut, shaped and functionalized by injection molding to produce hybrid components, such as those used in car door modules. The cutting process produces a considerable amount of production waste, which has thus far been thermally recycled. This study develops a closed mechanical recycling process and analyzes the different steps of the process. The offcuts were shredded using two shredding methods and implemented directly in the injection-molding process. Using tensile tests and impact bending tests, the material properties of the recycled materials were compared with the virgin material. In addition, fiber length degradation via the injection-molding process and the influence of the waterjet-cutting process on the mechanical properties are investigated. Recycled offcuts are both comparable to new material in terms of mechanical properties and usability, and are also economically and ecologically advantageous. Recycling polypropylene waste with glass fiber reinforcement in a closed loop is an effective way to reduce industrial waste in a sustainable and economical production process.
In this contribution the frequency domain fluorescence lifetime imaging microscopy (FD-FLIM) technique is evaluated for post-consumer wood sorting. The fluorescence characteristics of several wood samples were determined, whereby two excitation wavelengths (405 and 488 nm) were used. The measured data were processed using algorithmic methods to identify the wood species and post-consumer wood category. With the excitation wavelength of 405 nm, 16 out of 19 samples could be correctly assigned to the corresponding post-consumer wood category by means of the fluorescence lifetimes. Thus, the experimental results revealed the high potential of the FD-FLIM technique for automated post-consumer wood sorting.
Due to their lightweight potential and good eco-balance, thermoplastic hybrid composites with natural fiber reinforcement have long been used in the automotive industry. A good alternative to natural fibers is wood fibers, which have similar properties but are also a single-material solution using domestic raw materials. However, there has been hardly any research into wood fibers in thermoplastic back-injected hybrid composites. This article compares the bond strength of an injection molded rib from polypropylene (PP) and wood fibers to different non-wovens. The non-wovens consisted of wood fibers (spruce) or alternatively natural fibers (kenaf, hemp), both with a polypropylene matrix. Pull-off and instrumented puncture impact tests show that, given similar parameters, the natural and wood-fiber-hybrid composites exhibit very similar trends in bond strength. Further tests using viscosity measurements, microscopy, and computed tomography confirm the results. Wood-fiber-reinforced thermoplastic hybrid composites can thus compete with the natural fiber composites in terms of their mechanical behavior and therefore present a good alternative in technical semi-structural applications.
A new approach for the friction and wear characterisation of polymer fibres under dry, mixed, and hydrodynamic sliding conditions is developed. The production process of the tested polymer fibres is described and an introduction in fibre-reinforced concrete is given. Tribotesting is done on an optimised tribometer capable of measuring the friction and wear behaviour of polymer fibres with diameters of a few 100 µm under lubricated conditions. Three extruded polypropylene macro fibres with varying diameters are characterised under tribological conditions found in an industrial concrete mixing process. It is shown that detailed friction and wear data of polymer fibres can be gathered.
We present a novel differential relaxation oscillator for inductive power transfer. The proposed oscillator offers an automatic adaption of the oscillation period to a change in the power link impedance, which ensures a high efficient operation for variable loads and coupling factors. A detailed circuit model of the self-oscillation system is provided with analytical design equations. We find a large self-oscillation range for variable coupling factors and loads. The theoretical results are confirmed by circuit simulation and measurements carried out on a low-power demonstrator system. We demonstrate non-resonant and robust self-adaption of the relaxation oscillator to coupling factors ranging from k=0.6-0.9.