Francisco Comino

Purpose: This study aims to investigate polylactic acid (PLA)/olive wood (PLA/OW) composites for material extrusion (MEX) and frames 3D pyrography as a process-tunable surface appearance feature, linking printing conditions to surface texture and colour. Design/methodology/approach: PLA/OW filaments (0–20 Wt.% OW) were compounded and printed while varying extrusion temperature and printing speed. FTIR, differential scanning calorimeter and thermogravimetric analysis supported thermo-chemical assessment and oscillatory rheology aided printability evaluation. Surface texture was quantified by confocal areal roughness, and colour was measured in CIELAB and expressed as ΔE00. Multifactor analysis of variance and second-order response surfaces were used to map process–appearance relationships within the tested range. Findings: Increasing OW reduced crystallinity and thermal stability and increased melt viscoelasticity, narrowing the practical processing window. Roughness rose with OW content and was further governed by printing conditions. Temperature dominated chromatic change, promoting darkening (lower L*) and higher ΔE00, whereas higher printing speeds reduced thermal exposure and helped preserve lighter shades. The response surfaces provide consistent maps for combined texture–colour tuning. Practical implications: The approach can support aesthetic tuning using a single biofilled filament, potentially reducing the need for multiple coloured materials, filament changeovers and purge-related waste in design-oriented MEX applications. Originality/value: This work provides a quantitative framework that treats 3D pyrography in PLA/OW as a controllable process feature, jointly mapping colour (CIELAB/ΔE00) and surface texture as outcomes of MEX parameters, enabling reproducible tone modulation without post-processing.

Wood-filled PLA filaments enable 3D pyrography in material-extrusion (MEX) printing, in which tonal gradients and surface shading are generated in situ by controlling the thermal history during deposition, thereby avoiding post-processing or multi-material strategies. This enables the direct embedding of motifs and graded shading for customized product design, while also allowing appearance stabilization for repeatable manufacturing of wood-filled PLA parts. In this work, PLA/olive-wood (OW) composite filaments containing 0-20 wt.% OW (particle size < 180 µm) were manufactured and printed into 20 mm discs using MEX. The extrusion (nozzle) temperature was varied from 180 to 280 °C, and the printing speed was set to 20 and 200 mm/s to modulate thermal exposure. Surface color was quantified as L ^* , a ^* , b ^* from visible absorbance measurements (400-700 nm) converted into CIELAB coordinates. Percentual differences were assessed using the CIEDE2000 metric ΔE ₀₀ . The results demonstrated that increasing nozzle temperature progressively reduced lightness L ^* , and under severe conditions, a marked loss of chroma ( a ^* and b ^* ), particularly for higher OW contents. Low-speed printing (20 mm/s) amplified the pyrographic effect, reaching strong perceptual contrasts (maximum ΔE ₀₀ ≈ 9 at 280 °C for 20 wt.% OW), whereas high-speed printing (200 mm/s) mitigated extreme darkening and maintained more moderate, controlled color differences (typically ΔE ₀₀ < 3). Accordingly, ΔE00< 3 can be used as a practical “color-stable” target for uniform-looking parts, whereas ΔE00= 3-9 provides clearly distinguishable shades for pyrographic marking/shading. These findings defined practical process windows to either maximize tonal contrast for 3D pyrography or stabilize the appearance for consistent manufacturing of PLA/OW parts.

The objective of the present research was to identify the mechanical properties of 3D-printed biocomposite parts and their variation with different natural fillers (olive wood and almond shell). The materials were produced by filament extrusion with 5% fiber content in the polylactic acid matrix, and the samples were fabricated using the Material Extrusion Additive Manufacturing process. 3D printed specimens underwent tensile and flexural tests to assess their mechanical properties. The results showed reductions of 5%-18% in the tensile modulus and 10%-38% in the tensile strength for olive wood-and almond shell-based PLA, respectively. The same trend was detected for the flexural properties, with a slight reduction of 2%-3% in the flexural modulus and 3%-5% in flexural strength.

This study explored developing and characterizing sustainable composite materials based on polylactic acid (PLA) and olive wood particles. The composites were produced with varying wood contents (5–20 wt.%) and analyzed for their microstructural, thermal, and mechanical properties. Scanning Electron Microscopy (SEM) revealed a homogeneous dispersion of wood particles at lower concentrations, while higher wood contents led to agglomeration and interfacial defects. Differential Scanning Calorimetry (DSC) indicated that incorporating wood particles slightly reduced the matrix crystallinity, though the melting temperature remained unaffected. Tensile tests showed that small additions of wood particles (≤10 wt.%) maintained reasonable mechanical properties, slightly increasing Young's modulus at 10 wt.%. However, higher filler concentrations (>10 wt.%) significantly reduced tensile strength and ductility due to poor interfacial adhesion and particle agglomeration. These findings contribute to developing sustainable materials for applications that balance mechanical performance and eco-friendliness. Further optimization of processing conditions and interfacial compatibility is necessary to maximize performance in industrial applications, particularly in biodegradable and renewable material solutions.