Determination of the true density and the filler content of pinus sylvestris wood particles in polymer-wood-composites

Measuring the natural fiber content in fiber-filled polymers remains challenging. Conventional methods, such as density calculations based on the specific bulk densities of the mixed components or determining the remaining fiber weights after calcination, often yield inaccurate results. Even helium pycnometer measurements tend to overestimate the true density of natural fibers. This study introduces a novel and potentially more cost-effective method to accurately determine the true density of natural filler materials. The approach involves mixing these fillers into plastic melts and injection molding them under pressures up to 1000 bar. Using this method, the true density of Pinus sylvestris heartwood chips combined with a lactic acid polymer was precisely calculated as 1.40092 g/cm3 +/- 0.0102 g/cm3. Knowing the true density of material like Pinus sylvestris heartwood offers an accurate calculation of filler content in unknown recycled mixtures. This method can calculate the amount of wood fillers in polymer compounds, such as those from former decking, fences, privacy screens or soundproof wall claddings.Highlights Precise method to determine specific actual densities of biofillers High-resolution CT measurements of polymers filled with wood fibers Localization of density fluctuations in wood fiber filled polylactide Methodology for measuring the biofiber content of recyclates Verification of the rule of mixture model with the measured means and deviations on the abscissa axis and the calculated means and deviations by a set precision of 99.9 % confidence level on the ordinate axis. The dashed lines limit the one percent deviation from the rule of mixture results. The predicted density of 100 % HWC has no measurement deviation because a direct measurement is not feasible with the given methods. image