Reducing weight not only consumes fewer resources for manufacturing but also requires less energy for transportation, thus preserving resources and reducing CO₂ emissions. The latter part is of utmost importance in mobility applications. For example, in the automotive industry, the large-scale production of lightweight structural parts is becoming a main issue. An effective method to meet these requirements is foam injection moulding. In this study, physical (MuCell technology) and chemical foam injection moulding was used to produce plates made from wood-fibre- and cellulose-fibre-reinforced polypropylene, respectively. For both technologies, the used core-back method enabled precise mould opening during injection and thus allowed for variation in the plate thickness and density. The simpler short-shot technology, used only for the chemical foaming trials with differing shot volumes, provided plates with constant thicknesses. The foam structure and finally the mechanical properties of the plates depended on the filler type, the foaming method and the density. The latter was directly linked to either the plate thickness or the shot volume. Physical foaming appeared to be slightly more effective regarding the achievable density reduction (up to 37% reduction), but the physically foamed parts had worse mechanical properties at equal density than their chemically foamed counterparts. Besides the comparison of different foaming methods, this study provides the tensile, flexural and impact properties of natural-fibre-reinforced polypropylene composites over a wide density range, thus offering a good basis for evaluating weight-saving potential for various applications.

The use of cellulose fiber-filled polypropylene (PP) composites in combination with foam injection molding has enabled the lightweight design of injection-molded parts. The study provides achievements for the physical foam injection molding (MuCell^®) process of PP–cellulose fiber compounds by using CO₂ as the direct foaming agent, including a comparison of MuCell^® foaming with N₂ and a comparison to a chemical foaming process. Weight and density reductions, foam structure and specific mechanical properties are highly dependent on the applied processing parameters. The maximum weight reduction reached values of up to 16%, and density reduction even reached 33% in relation to the compact plates. The extent of weight and density reduction could be adjusted, among other factors, by a reduction in the shot volume. Setting the density reduction to 22% allowed for simultaneously decreasing weight while sustaining the specific flexural properties and limiting the loss of specific impact strength. By using optimized FIM parameters, the mechanical performance could be improved, with specific modulus values even outperforming the compact reference sample. This presents a significant benefit for the preparation of lightweight products and sets the basis for further optimization and modeling studies.

This study investigates the development of electrically conductive panels for application as emergency detection sensors in smart house systems. These panels, composed of wood chips coated with polymeric methylene diphenyl isocyanate, were modified with carbon black and carbon fibers to enable detection of moisture, temperature, and pressure variations. Manufactured via hot pressing, the panels retained standard mechanical properties and exhibited stable performance under diverse environmental conditions. Carbon black-filled panels achieved electrical percolation at a lower filler concentration (5%) compared to carbon fiber-filled panels. The incorporation of carbon black reduced the electrical resistivity to 8.6 ohm·cm, while the addition of carbon fibers further decreased it to 7.7 ohm·cm. In terms of sensor capabilities, panels containing carbon fibers demonstrated superior sensitivity to moisture and pressure changes. However, carbon black was ineffective for temperature sensing. Among the carbon fiber-filled panels, those with 20 wt.% concentration exhibited the best performance for moisture and pressure detection, whereas panels with 40 wt.% carbon fiber content displayed the most reliable and consistent temperature-sensing properties.