The effects of multiple recycling cycles on bamboo flour-thermoplastic polyurethane filaments and their properties in fused filament fabrication were investigated. Successive recycling induced progressive thermomechanical degradation of the thermoplastic polyurethane matrix, decreasing the average number and average molecular weight, while increasing polydispersity as shown by chain scission. Scanning electron microscopy images revealed increasingly rough and irregular filament surfaces with recycling, whereas gel permeation chromatography and differential scanning calorimetry confirmed reduced chain length and crystallinity, followed by partial recrystallization after three recycling cycles due to increased chain mobility. Mechanical testing indicated significant property deterioration, with the tensile strength, modulus and elongation at break decreasing by more than 50% after three recycling cycles. The decline in tensile properties was attributed to reduced thermoplastic polyurethane molecular weight, thermal degradation of bamboo flour, and persistent porosity, despite some compensatory effects from improved the adhesion between bamboo flour and matrix. With respect to printing by fused filament fabrication with bamboo flour-thermoplastic polyurethane parts from recycled filaments, additional property losses occurred because of weakened layer bonding, although the change in tensile modulus was not influenced significantly. Additionally, correlations between weight-average molecular weight and tensile properties highlighted molecular weight as a reliable processing-structure-property indicator. Despite property reductions, the recycled parts maintained mechanical properties comparable to those of elastomers and leather, underscoring their potential for applications in additive manufacturing and footwear applications.

In this study, bamboo flour (BF)-reinforced thermoplastic polyurethane composite (BTC) filaments and their 3D-printed parts were prepared through fused filament fabrication (FFF) and evaluated. Bamboo flour addition (0-15 wt%) significantly altered the aesthetic and physical properties: The filaments and 3D-printed parts exhibited darker coloration and rougher surfaces with increased BF content, which was attributed to thermal degradation and layer porosity. Thermal analyses indicated that bamboo flour induced TPU recrystallization, acting as a nucleating agent, but reduced the overall thermal stability because of the nature of the lignocellulosic flours. Mechanically, the BTC filaments and printed parts demonstrated a significant stiffness-ductility tradeoff. Although the tensile modulus and rigidity substantially improved with increasing BF content, increasing BF content also led to decreased tensile strength, elongation at break, and toughness, which were largely influenced by interfacial incompatibility and increased porosity. Additionally, dynamic mechanical analysis highlighted enhanced energy dissipation and damping properties in BTC parts with moderate bamboo flour content (10 wt%), suggesting targeted applications in vibration-sensitive environments. Therefore, the integration of bamboo flour into TPU enables the creation of stiff and lightweight composites but requires optimization of the filler content and interfacial interactions to achieve balanced mechanical properties suitable for practical FFF applications.

In this study, spent coffee grounds (SCGs) were incorporated into polylactic acid (PLA) filaments and 3D-printed parts to investigate their effects on thermal, physical, and mechanical properties. Differential scanning calorimetry showed that SCG addition slightly reduced the glass transition temperature of PLA while markedly increasing its crystallinity, whereas thermogravimetric analysis revealed a moderate decrease in degradation onset temperature that remained well above the processing and printing temperatures, ensuring safe fabrication. Tensile testing indicated that SCG incorporation led to noticeable reductions in filament strength and stiffness, whereas the elongation at break was only weakly affected because of counteracting plasticization effects. For the printed parts, SCGs imparted a dark brown coloration, decreased density, and increased moisture uptake due to their porous and hydrophilic nature, while tensile, flexural, and impact strengths were reduced and the tensile modulus and elongation at break remained statistically similar across the 0-20 wt% range. These findings indicate that SCGs can be effectively incorporated to tailor the crystallinity, color, and density of PLA-based 3D-printed composites, albeit with trade-offs in strength and impact performance.

Wood fibers (WFs) were treated at a fixed heat temperature (180 °C) for 2−6 h and added to a polylactic acid (PLA) matrix to produce wood−PLA composite (WPC) filaments. Additionally, the effects of the heat-treated WFs on the physicomechanical properties and impact strength of the WPC filaments and 3D-printed WPC parts using fused filament fabrication (FFF) were examined. The results revealed that heat-treated WFs caused an increase in crystallinity and a significant reduction in the number of pores on the failure cross section of the WPC filament, resulting in a higher tensile modulus and lower elongation at break. Additionally, the printed WPC parts with heat-treated WFs had higher tensile strength and lower water absorption compared to untreated WPC parts. However, most of the mechanical properties and impact strength of 3D-printed WPC parts were not significantly influenced by adding heat-treated WFs. As described above, at the fixed fiber addition amount, adding heat-treated WFs improved the dimensional stability of the WPC parts and it enabled a high retention ratio of mechanical properties and impact strength of the WPC parts.

Alkali-treated bamboo fibers (AFs) treated with different NaOH concentrations (5 and 10%) and treatment times (1, 12, and 24 h) were used as fillers to fabricate cementitious composites with AFs (CAFs) in the present study. The results demonstrated that alkali treatment caused the partial decomposition of hemicellulose and lignin and an increase in the surface roughness of bamboo fibers. Additionally, the amounts of calcium hydroxide in alkali-treated CAFs were higher than in untreated CAFs, and they increased with increasing NaOH concentration and treatment time. For drying shrinkage (DS) under 75% relative humidity (RH), the DS values of the CAFs significantly decreased after adding AFs compared to the DS values of untreated CAFs. Compared to untreated CAFs, the density of the 5% and 10% NaOH-treated CAFs with longer treatment times decreased by 2.9% and 5.1%, respectively. Furthermore, the tensile strength of all alkali-treated CAFs exhibited no significant differences when compared with that of untreated CAFs, while the modulus of rupture and compressive strength were significantly decreased by NaOH treatment. These results indicated that the AFs significantly improved the drying shrinkage of the CAFs and hydration retardation effect of cement pastes, while the density and mechanical strength of the CAFs decreased.

This study investigated the closed-loop recycling of 3D-printed wood fiber (WF)-filled polylactic acid (PLA) composites via fused filament fabrication (FFF). The WF–PLA composites (WPCs) were extruded into WPC filaments (WPCfs) to produce FFF-printed WPC parts (WPCps). The printed WPCps were reprocessed three times via extrusion and 3D-printing processes. The tensile properties and impact strengths of the WPCfs and WPCps were determined. To further investigate the impact of closed-loop recycling on the surface morphology, crystallinity, and molecular weight of WPCfs, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC), respectively, were used. After closed-loop recycling, the surface morphology of the WPCfs became smoother, and a decrease in the pore sizes was observed; however, the tensile properties (tensile strength and elongation at break) deteriorated. With increasing numbers of recycling iterations, the molecular weight of the PLA matrix decreased, while an increase in crystallinity was observed due to the recrystallization of the low-molecular-weight PLA molecules after recycling. According to the SEM images of the recycled WPCps, their layer heights were inconsistent, and the layers were rough and discontinuous. Additionally, the color difference (ΔE*) of the recycled WPCps significantly increased. Compared with those of the WPCps after recycling them only once, the tensile strength, elongation at break, and impact strength of the WPCps noticeably decreased after recycling them twice. Considering the changes in various properties of the WPCfs and WPCps, the FFF-printed WPC parts can be reprocessed only once through 3D printing.

The effects of thermal modification and flexural configuration on the physical and flexural properties of makino bamboo (Phyllostachys makinoi) with various density ranges were investigated. The density and equilibrium moisture content (EMC) of bamboo significantly decreased with increasing treatment temperature from 140 degrees C to 220 degrees C. Simultaneously, the modulus of rupture (MOR) and ductility factor (DF) of thermally modified bamboo showed a declining trend. In the flexural test, loading on the outer side in tension (OT) and loading on the outer side in compression (OC) of the bamboo specimens were applied using different flexural configurations. The MOR of the nontreated OC specimen (MOROC) was higher than that of the nontreated OT specimen (MOROT), while the MOROC of the 220 degrees C-treated specimen was lower than the MOROT. Additionally, the nontreated OT specimen showed a higher DF than the nontreated OC specimen. Despite the density range and flexural configuration, the DF of the thermally modified specimen decreased when the treatment temperature increased above 140 degrees C. However, the modulus of elasticity exhibited no significant differences among all the specimens under different treatment temperatures and flexural configurations.

Vacuum heat-treated bamboo fibers (HFs) with different treatment temperatures (160–200 °C) and times (2–4 h) were used as fillers, and they were added to cement paste to fabricate cementitious composites with HFs (HFCs). The results showed that a high intensity of heat treatment could not only lead to the decomposition of hemicellulose and cellulose in the chemical composition but also to an increase in the mass loss of a bamboo fiber. Adding fibers treated at relatively high treatment temperatures (> 180 °C) for a long duration (> 2 h) significantly decreased the densities of HFCs. Additionally, the HFs improved the drying shrinkage of HFCs at a 75% relative humidity in an early drying period. Furthermore, the tensile strength and compressive strength of HFCs with 2 h-treated fibers increased with increasing treatment temperature. However, the mechanical strengths of HFCs were not influenced by adding fibers treated for more than 2 h.

In this study, disintegrated bamboo fibers (DBFs) were extracted from alkali-treated makino bamboo sticks (BSs). The chemical compositions and tensile properties of DBFs were investigated using Fourier transform infrared (FTIR), X-ray diffraction (XRD), thermogravimetric (TG) analysis, and tensile tests. The results indicated that a change in functional groups, a reduction in the crystallinity index, and better thermal stability were observed for DBFs than for BSs. Regardless of the collapse of parenchyma cells and separation and twist of the fibers on the surface of the DBF, its average tensile strength and tensile modulus were 204 MPa, and 13 GPa, respectively. Additionally, DBFs were added into a cement matrix to fabricate bamboo fiber/cementitious composites (BCCs).The apparent density and most of the mechanical properties of BCCs decreased when the addition of the DBFs increased above 1 wt%. However, the BCC with 1 wt% of DBFs showed the lowest drying shrinkage and a slight increase in the specific energy under tensile testing. Accordingly, the results showed that 1 wt% DBFs as an adequate content is proposed to be added into the cement.

In this study, a bamboo stick board with rotary-cut bamboo veneers was successfully fabricated. Additionally, vacuum heat (VH) treatment, which is a popular thermal modification method, was used to modify bamboo sticks. Therefore, the effects of different VH treatment temperatures on the dimensional stability and flexural properties of bamboo stick boards with and without bamboo veneers were investigated. For all boards, as the temperature increased to 220 °C, the thickness change rate and equilibrium moisture content decreased, and the flexural properties increased. The results exhibited that VH treatment improved the dimensional stability and flexural properties of the boards. Furthermore, the board with veneers had lower flexural properties and higher thickness swelling after water absorption than the board without veneers (BSB). The results indicated that bamboo veneer caused low flexural properties and high thickness swelling of the board compared to the BSB. However, the bamboo veneer played an aesthetic role in the appearance of the bamboo stick board.

The effects of treatment temperature on the physicomechanical properties and dimensional stability during water immersion of moso bamboo were investigated as a function of density. The results indicated that most of the physical and flexural properties and dimensional instability significantly decreased when the temperature increased to 220 degrees C. Additionally, the flexural properties of untreated and heat-treated bamboo showed a positive relationship with the apparent density, while their water absorption (WA) increased with decreasing apparent density. Furthermore, despite the treatment temperatures, the modulus of elasticity and WA for all the bamboo samples were better described using linear relationships and exponential decay equations, respectively.

The influence of heat treatment on the physico-mechanical properties, water resistance, and creep behavior of moso bamboo (Phyllostachys pubescens) was determined in this study. The results revealed that the density, moisture content, and flexural properties showed negative relationships with the heat treatment temperature, while an improvement in the dimensional stability (anti-swelling efficiency and anti-water absorption efficiency) of heat-treated samples was observed during water absorption tests. Additionally, the creep master curves of the untreated and heat-treated samples were successfully constructed using the stepped isostress method (SSM) at a series of elevated stresses. Furthermore, the SSM-predicted creep compliance curves fit well with the 90-day full-scale experimental data. When the heat treatment temperature increased to 180 °C, the degradation ratio of the creep resistance (rd) significantly increased over all periods. However, the rd of the tested bamboo decreased as the heat treatment temperature increased up to 220 °C.

This study used digital image correlation (DIC) to perform a strain analysis of Moso bamboo (Phyllostachys pubescens) in the tangential section subjected to longitudinal tensile force to compare samples from outer/inner position of the culm wall. Simultaneously, an electrical resistance strain gauge (SG) was used to measure the strain profile for comparison with the strain analysis using DIC. During loading, the rate of the longitudinal strain between different positions was significantly different. As the load time increased, there was no difference in the rate of the transverse strain between the outer and inner samples, while the rate of the longitudinal strain for the inner sample was higher than that for the outer sample. Additionally, DIC showed that the longitudinal direction showed a relatively homogeneous strain contour compared to the transverse direction. Furthermore, the result indicated that the Poisson’s ratio was dependent on the positions of the bamboo in the radial direction of the culm wall. Using SG recording as a reference, the DIC revealed appropriate strain behavior of bamboo in terms of longitudinal and transverse strains within full-field area. Therefore, the DIC recording may help to characterize strain deformation on the bamboo during the application of a tensile force.

The present study investigated the effects of heat treatment on the thermal decomposition behavior (changes in the chemical composition and color, strain variation, and tensile properties) of a thin Makino bamboo (Phyllostachys makinoi) sliver. The performances, reactions, and formations in heat treated bamboo slivers were measured by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD). The results indicated that a high thermal stability, cross-linking of lignin condensation, hemicellulose deacetylation, and an increase in cellulose crystallinity were observed. In addition, the bamboo slivers after heat treatment had a higher Poisson's ratio due to a decrease in the ductility in the loading direction and an increase in the transverse shrinkage. Furthermore, using isothermal dynamic mechanical analysis (DMA), the normalized storage modulus of the bamboo slivers rapidly decreased when the treatment temperature exceeded 220 degrees C. According to first-order thermal decomposition kinetics by Arrhenius activation theory, the activation energy for thermal decomposition of the bamboo slivers was calculated to be 142.2 kJ/mol.

In this study, the effect of layer thickness on the physicomechanical properties of the wood fiber-polylactic acid composite (WPC) part obtained by fused filament fabrication (FFF) was investigated. The results showed that most of the characteristics of the FFF-printed WPC part significantly depended on the printing layer thickness. As the layer thickness increased, the density of the printed WPC part decreased significantly, while the dimensional stability of the water-immersed WPC part decreased. In addition, specific tensile properties increased and the other specific mechanical properties (flexural, compressive, and shear properties) decreased with increasing layer thickness. Furthermore, scanning electronic microscopy micrographs illustrated that the number of voids and defects was more often observed on the surface of the WPC part printed with higher layer thickness. Therefore, these results indicated that the different layer thicknesses in FFF manufacturing have a substantial impact on the dimensional stability and specific mechanical properties of the FFF-printed WPC part.

In this study, a wood fiber/polylactic acid composite (WPC) filament was used as feedstock to print the WPC part by means of fused deposition modeling (FDM). The morphology and mechanical properties of WPC parts printed at different speeds (30, 50, and 70 mm/s) were determined. The results show that the density of the printed WPC part increased as the printing speed decreased, while its surface color became darker than that of parts printed at a high speed. The printing time decreased with an increasing printing speed; however, there was a small difference in the time saving percentage without regard to the dimensions of the printed WPC part at a given printing speed. Additionally, the tensile and flexural properties of the printed WPC part were not significantly influenced by the printing speed, whereas the compressive strength and modulus of the FDM-printed part significantly decreased by 34.3% and 14.6%, respectively, when the printing speed was increased from 30 to 70 mm/s. Furthermore, scanning electronic microscopy (SEM) illustrated that the FDM process at a high printing speed produced an uneven surface of the part with a narrower width of printed layers, and pull-outs of wood fibers were more often observed on the fracture surface of the tensile sample. These results show that FDM manufacturing at different printing speeds has a substantial effect on the surface color, surface roughness, density, and compressive properties of the FDM-printed WPC part.

In this study, four types of waste bamboo fibers (BFs), Makino bamboo (Phyllostachys makinoi), Moso bamboo (Phyllostachys pubescens), Ma bamboo (Dendrocalamus latiflorus), and Thorny bamboo (Bambusa stenostachya), were used as reinforcements and incorporated into polypropylene (PP) to manufacture bamboo–PP composites (BPCs). To investigate the effects of the fibers from these bamboo species on the properties of the BPCs, their chemical compositions were evaluated, and their thermal decomposition kinetics were analyzed by the Flynn–Wall–Ozawa (FWO) method and the Criado method. Thermogravimetric results indicated that the Makino BF was the most thermally stable since it showed the highest activation energy at various conversion rates that were calculated by the FWO method. Furthermore, using the Criado method, the thermal decomposition mechanisms of the BFs were revealed by diffusion when the conversion rates (α) were below 0.5. When the α values were above 0.5, their decomposition mechanisms trended to the random nucleation mechanism. Additionally, the results showed that the BPC with Thorny BFs exhibited the highest moisture content and water absorption rate due to this BF having high hemicellulose content, while the BPC with Makino BFs had high crystallinity and high lignin content, which gave the resulting BPC better tensile properties.

The crystallization behavior of bamboo fiber (BF) reinforced polypropylene (PP) composites (BPCs) was investigated using a differential scanning calorimeter (DSC). The results showed that unmodified BF as a nucleation agent accelerated the crystallization rate of the PP matrix during cooling whereas there is no significant effect on the improved crystallization rate in BPCs with acetylated BFs. Based on the Avrami method, Avrami-Ozawa method, and Friedman method, the corresponding crystallization kinetics of PP reinforced with different acetylation levels of BFs were further analyzed. The results demonstrated that the crystal growth mechanism of the PP matrix for BPCs with unmodified and various acetylated BFs exhibited tabular crystal growth with heterogeneous nucleation. A higher cooling rate is required to achieve a certain relative crystallinity degree at the unit crystallization time for BPCs with a higher weight percent gain (WPG) of acetylated BFs (WPG >13%). Furthermore, based on the Friedman method, the lowest crystallization activation energy was observed for the BPCs with 19% WPG of acetylated BFs.