This paper describes the development and characterisation of wood-filled polylactic acid (PLA) composite filaments for application in fused filament fabrication three-dimensional (3D) printing. Four different wood-polymer composite filaments for 3D printing were prepared, and specimens were 3D-printed with the obtained materials. The composite filaments consisted of wood particles (10% or 20% mass ratio) and a PLA polymer matrix. Wood particles were prepared by grinding and sieving non-modified beech wood and thermally modified (TM) (at 200 °C) beech wood. Thermal modification of wood affected particle preparation and smaller particles with lower aspect ratios were obtained. Filaments with TM wood particles were extruded better than with non-modified wood particles, with lower surface roughness and lower porosity. With a higher wood ratio, the surface roughness and porosity of the filament increased. Non-homogenous filaments also affected extrusion in 3D printing and reduced the properties of 3D-printed parts. Parts 3D-printed from filaments with TM particles had better tensile strength than from filaments with non-modified particles, but were lower than from pure PLA filaments. The tensile strength of the injection-moulded specimens was 18–69% higher than that of the 3D-printed specimens, depending on the filament composition. The results indicate some positive effects of thermal modification of wood particles on the properties of filaments and 3D-printed parts. Nevertheless, further optimisation of particle preparation and extrusion parameters is needed to obtain quality filaments with this size of wood particles.

The importance of thermal modification is increasing worldwide. Increased use of thermally modified timber (TMT) has resulted in a need for reliable quality control, comprising control of variation of the production within defined limits, allowing third-party control in the case of certification and the regulation of customer complaints and claims. Techniques are thus needed to characterise the modification of quality in terms of improved target properties of TMT during industrial production, and of TMT products that have been in service for an arbitrary time. In this study, we aimed to utilise dynamic vapor sorption (DVS) for this purpose. Norway spruce (Picea abies) and European beech (Fagus sylvatica) samples were thermally modified at different temperatures according to different heat treatment techniques: (1) the Silvapro process based on an initial vacuum; (2) an air heat treatment, whereby samples were wrapped in aluminium foil; (3) thermal modification of wood samples in the ambient atmosphere in a laboratory oven. Wood samples from closed processes were analysed for validation. TMT was characterised with respect to mass loss, colour and density. Mass loss of wood due to modification (ML_TM) was correlated with factors derived from DVS analysis. The present DVS measurements suggest that the equilibrium wood moisture content (EMC_{95% RH}), the time to reach 10% wood moisture content (t_{10% MC}), and the elongation factor, c, derived from a logarithmic function, can serve as alternative parameters to characterise the quality of several thermal modification processes. Further studies are recommended using other wood species, different modification processes and further parameters gained from DVS measurements to understand the robustness and the predictive power of the applied technique.

Fungal growth and degradation of wood may be caused by damage in the surface coating. The larger the cracks, the greater in principle the possibility of moisture-induced problems. Measuring basic unknown material parameters and employing hygrothermal simulations, the suitability and the maximum acceptable vertical crack size in the surface coating for a given bottom window profile made of thermally modified (TM) spruce(wood) with that made of native spruce were compared for location Ljubljana. Validation with the field test data was the second objective of the respective research. The average calculated maximum moisture content in TM spruce is about 4% (kg/kg) lower than that of native spruce. The 3 mm wide crack in the surface coating of a window frame made of native spruce is of the highest concern, whereas a 9 mm wide crack in the coating of a TM spruce profile is still acceptable. As far as moisture content is concerned in our study the TM spruce window frames were proved to be significantly more suitable for installation than the corresponding frames made of native Norway spruce. It was shown that isopleth, VTT and biohygrothermal models for mould growth do not properly capture the comparison between both materials, mainly because they classify both in the same material class/substrate category and they do not consider the material moisture content.

Highly filled magnetic filaments require binder systems that balance powder loading, melt flow, filament strength, and strand stability during material extrusion (MEX). Here, a polyolefin-based binder composed of a thermoplastic elastomer and grafted polyolefin (TPE + gPO) was used to prepare Sm₂Fe₁₇N₃- and SrFe₁₂O₁₉-based magnetic filaments. The feedstocks were compounded, extruded into 2.85 mm filaments using a single-screw extrusion line with automatic spooling, and printed by MEX into ring-shaped specimens. Thermogravimetric analysis confirmed high powder contents, with residual masses of approximately 89 wt.% for Sm₂Fe₁₇N₃ and 85 wt.% for SrFe₁₂O₁₉. The filaments showed good dimensional control, with a diameter of 2.85 ± 0.07 mm and ovality ≤ 0.017 mm. Small-amplitude oscillatory rheology at 200–240 °C showed pronounced shear-thinning behavior and an elastic-dominant response (G′ > G″) over 0.01–100 Hz, supporting flow through the nozzle and shape retention after deposition. Mechanical testing confirmed sufficient handling performance, with a maximum flexural stress of 36.1 ± 0.1 MPa for SrFe₁₂O₁₉ and a flexural modulus up to 5.5 ± 0.2 GPa for Sm₂Fe₁₇N₃. The results demonstrate that the TPE + gPO binder provides a suitable processing window for highly filled magnetic filaments for MEX-printed bonded magnets.