Additive manufacturing, especially material extrusion (MEX), has received a lot of attention recently. The reasons for this are the numerous advantages compared to conventional manufacturing processes, which result in various new possibilities for product development and -design. By applying material layer by layer, parts with complex, load-path optimized geometries can be manufactured at neutral costs. To expand the application fields of MEX, high-strength and simultaneously lightweight materials are required which fulfill the requirements of highly resilient technical parts. For instance, the embedding of continuous carbon and flax fibers in a polymer matrix offers great potential for this. To achieve the highest possible variability with regard to the material combinations while ensuring simple and economical production, the fiber–matrix bonding should be carried out in one process step together with the actual parts manufacture. This paper deals with the adaptation and improvement of the 3D printer on the one hand and the characterization of 3D printed test specimens based on carbon and flax fibers on the other hand. For this purpose, the print head development for in-situ processing of contin uous fiber-reinforced parts with improved mechanical properties is described. It was determined that compared to neat polylactic acid (PLA), the continuous fiber-reinforced test specimens achieve up to 430% higher tensile strength and 890% higher tensile modulus for the carbon fiber reinforcement and an increase of up to 325% in tensile strength and 570% in tensile modulus for the flax fibers. Similar improvements in performance were achieved in the bending tests.

Sugar beet residues (SBR) were converted into thermomechanical pulp (sugar beet pulp, SBP) and compounded with either polylactic acid (PLA) or high‐density polyethylene (HDPE) as matrix. Pressed, thin sheets made with the compounds were placed on soil for 16 weeks outdoors and changes in material properties, including weight losses, monitored. Chloroform extraction showed that proportionally more SBP than PLA was degraded after biodegradation. A reduction in molecular weight of the PLA in composites during processing was determined, which was attributed to moisture in SBP and led to PLA hydrolysis. No further significant reduction in molecular weight of the PLA in composites occurred during outdoor exposure. In case of the HDPE‐SBP composites, results of acid hydrolysis indicated that primarily, the SBP component was degraded. Tensile strength tests, microscopy, FT‐IR spectroscopy and thermal analyses were also performed with the composites. Under the conditions of this study, it was shown that PLA composites with 70% (wt.) of SBP were completely disintegrated before completion of 12 weeks exposure. The addition of SBP to PLA accelerates biodegradation significantly which is an asset for agricultural (mulch films), forestry, horticulture and packaging applications. Highlights: Degradation of composites based on SBP with PLA or HDPE matrix was evaluated on soil Addition of SBP increased weight loss, irrespective of the matrix type during the degradation tests Differences in material composition over exposure time were analyzed Combination of SBP with PLA enhances biodegradability of composites SBP offers huge potential as filler in biodegradable polymer composites

Various fire-retardants (FR) for the pre-treatment of wood flour, for example, ammonium polyphosphate and different formulations based on phosphorus- and nitrogen-compounds, as well as for application during compounding were tested for their effectiveness in injection-molded and extruded composites based on high-density polyethylene and polypropylene. Small-scale tests for flammability of polymeric materials and for determination of the limiting oxygen index were used to characterize the composite materials. Differences pertaining to the applied compounding conditions, i.e., underwater granulation versus air granulation, were determined. The amount of phosphorus leached from FR during underwater granulation was analyzed. Artificial weathering trials were performed and reaction-to-fire performance and color changes of FR-composites were evaluated. Tensile strength properties of the composites and results for cold water immersion tests are also reported. An optimized formulation based on pre-treated wood flour was developed and extruded into façade profiles for the single burning item test according to DIN EN 13823. The test showed that classification C-s3, d0 according to DIN EN 13501-1 can be achieved if pre-treated wood flour is used. The use of untreated wood flour leads to a lower classification (D-s2, d0). Fire performance of extruded façade profiles can be improved by the use of pre-treated wood flour and enables new applications in the building sector.