Interlayer adhesion and mechanical properties of wood-based multilayer composites fabricated by fused deposition modeling

Polyetherimide (PEI) possesses remarkable mechanical and thermal properties that make it a promising high-performance material for a wide range of applications. In addition to its simple processability, adhesive properties, and minimal smoke emission when heated, PEI is a suitable material for additive manufacturing. Because of its low cost and straightforward method, fused deposition modeling, or FDM, is a popular additive manufacturing technique for extruding thermoplastic filaments. Parts printed with the FDM approach, on the other hand, have common drawbacks such as low mechanical strength, shape inaccuracy, high porosity, void formation, interlayer adhesion problems, and anisotropic properties. The purpose of this study was to evaluate the effect of the thermal process during printing on the interlayer adhesion strength and the mechanical performances of PEI. The thermal treatment was done on a radiant heating system at 390 °C with a printing speed of 35 mm/s. In this study, parts printed with and without radiant heating system were characterized and analyzed with scanning electron microscopy (SEM), optical microscopy (OM), X-ray microtomography (µ-CT), optical profilometry (OP), atomic force microscopy (AFM), dynamic mechanical analysis (DMA), and tensile tests. The results revealed that the treated specimen exhibited better interlayer adhesion between printed layers. The interfacial voids were less visible in treated specimens. Furthermore, the treated specimen had lower porosity (5%) than the untreated one (8%). Moreover, increases of 183% in tensile strength, 22% in elastic modulus, and 190% in elongation at break were observed for treated specimens when compared to untreated ones.

Developing 3D printing high‐performance biodegradable materials is important to protect the environment and deal with emergencies such as COVID‐19. Fused deposition modeling (FDM), one of the 3D printing methods, has many advantages, such as low cost and wide range of materials. However, the weak interlayer adhesion is an important factor restricting the development of FDM. In addition to the influence of material properties, the optimization of 3D printing parameters is also an important means to give full play to the inherent properties of materials. The optimal 3D printing parameters are conducive to the diffusion and entanglement of molecular chains between adjacent layers. PLA/PBAT/PLA‐g‐GMA (70/30/10 wt%, PLA‐g‐GMA was a compatibilizer synthesized in our lab) was used as the research object. This work aims to analyze the mechanical properties response of biodegradable polymers products manufactured through FDM. Herein, the effect of 3D printing parameters including layer thickness, nozzle temperature, printing speed and platform temperature have been systematically investigated by orthogonal experimental design. The result showed that the excellent performance of 3D printing specimen was obtained when the layer thickness was 0.15 mm, the printing speed was 50 mm·s−1, the nozzle temperature was 200°C and the platform temperature was 50°C. The SEM images showed that the optimal 3D printing products had the best interlayer adhesion and the lowest porosity. Undergoing optimization of 3D printing processing, the yield strength and elongation at break of specimen increased by 115% and 229%, respectively. In this paper, the interlayer adhesion and mechanical properties of 3D printing products can be significantly improved by simply optimizing the 3D printing parameters without complex material modification. This work provided a new method for improving the interlayer adhesion of FDM and the mechanical properties of FDM products.

Investigation of in-situ chemical cross-linking during fused filament fabrication process on parts shrinkage reduction and interlayer adhesion

Investigation of processing parameters on tensile performance for FDM-printed carbon fiber reinforced polyamide 6 composites

Additive manufacturing via fused deposition modeling (FDM) has become one of the most widely used technologies owing to its ease of operation and effective cost. However, the disappointing interlayer adhesion produced by FDM often results in inferior mechanical properties, which has become a technical bottleneck for industrial production. Herein, we demonstrate a facile and efficient printing strategy to enhance interlayer adhesion by introducing a self-healing mechanism into the printing material, thereby concurrently enhancing the mechanical properties and isotropy of the printed products. This strategy relies on the self-healing property of three-dimensional-printing materials. This self-healing property is endowed by introducing dynamic urea bonds on the thermoplastic polyurethane (TPU) molecular chains, and then, such dynamic bonds can be activated through thermal heating. Accordingly, the synthesized TPU reveals an efficient self-healing property and excellent printability owing to the existence of dynamic reversible covalent bonds. Moreover, objects with complex structures can be split and printed and then assembled using this strategy, avoiding the need for supporting structures and realizing the rapid prototyping of large-sized objects. The printing strategy proposed paves a candidate way to overcome the current challenges in obtaining high-quality products via FDM.

Fused deposition modeling (FDM) 3D printing has printed thermoplastic materials layer-by-layer to form three dimensional products whereby interlayer adhesion must be well controlled to obtain high mechanical performance and product integrity. This research studied the effects of ambient temperatures and crystalline structure on the interlayer adhesion and properties of thermoplastic FDM 3D printing. Five kinds of poly(lactic acid) (PLA) filaments, both commercially available and the laboratory-made, were printed using the enclosure FDM 3D printer. The ambient temperatures were set by the temperature-controlled chamber from room temperature to 75 °C with and without a cooling fan. The interlayer adhesion was characterized by the degree of entanglement density, morphology, and fracture toughness. In addition, PLA filament with high crystallinity has induced heat resistance, which could prevent filament clogging and successfully print at higher chamber temperatures. The ambient temperature increased with increased chamber temperature and significantly increased when printed without a cooling fan, resulting in improved interlayer bonding. The crystalline structure and dynamic mechanical properties of the 3D printed products were promoted when the chamber temperature was increased without a cooling fan, especially in PLA composites and PLA containing a high content of L-isomer. However, although the additives in the PLA composite improved crystallinity and the degree of entanglement density in the 3D-printed products, they induced an anisotropic characteristic that resulted in the declination of the interlayer bonding in the transverse orientation products. The increasing of chamber temperatures over 40 °C improved the interlayer bonding in pristine PLA products, which was informed by the increased fracture toughness. Further, it can be noted that the amorphous nature of PLA promotes molecular entanglement, especially when printed at higher chamber temperatures with and without a cooling fan.

Additive manufacturing (AM) is a class of manufacturing processes where material is deposited in a layer-by-layer fashion to fabricate a three-dimensional part directly from a computer-aided design model. With a current market share of 44%, thermoplastic-based additive manufacturing such as fused deposition modeling (FDM) is a prevailing technology. A key challenge for AM parts (especially for parts made by FDM) in engineering applications is the weak inter-layer adhesion. The lack of bonding between filaments usually results in delamination and mechanical failure. To address this challenge, this study embedded carbon nanotubes into acrylonitrile butadiene styrene (ABS) thermoplastics via a filament extrusion process. The vigorous response of carbon nanotubes to microwave irradiation, leading to the release of a large amount of heat, is used to melt the ABS thermoplastic matrix adjacent to carbon nanotubes within a very short time period. This treatment is found to enhance the inter-layer adhesion without bulk heating to deform the 3D printed parts. Tensile and flexural tests were performed to evaluation the effects of microwave irradiation on mechanical properties of the specimens made by FDM. Scanning electron microscopic (SEM) images were taken to characterize the fracture surfaces of tensile test specimens. The actual carbon nanotube contents in the filaments were measured by conducting thermogravimetric analysis (TGA). The effects of microwave irradiation on the electrical resistivity of the filament were also reported.

Poly(lactic acid) (PLA) filaments have been the most used in fused deposition modeling (FDM) 3D printing. The filaments, based on PLA, are continuing to be developed to overcome brittleness, low heat resistance, and obtain superior mechanical performance in 3D printing. From our previous study, the binary blend composites from PLA and poly(butylene adipate-co-terephthalate) (PBAT) with nano talc (PLA/PBAT/nano talc) at 70/30/10 showed an improvement in toughness and printability in FDM 3D printing. Nevertheless, interlayer adhesion, anisotropic characteristics, and heat resistance have been promoted for further application in FDM 3D printing. In this study, binary and ternary blend composites from PLA/PBAT and poly(butylene succinate) (PBS) with nano talc were prepared at a ratio of PLA 70 wt. % and blending with PBAT or PBS at 30 wt. % and nano talc at 10 wt. %. The materials were compounded via a twin-screw extruder and applied to the filament using a capillary rheometer. PLA/PBAT/PBS/nano talc blend composites were printed using FDM 3D printing. Thermal analysis, viscosity, interlayer adhesion, mechanical properties, and dimensional accuracy of binary and ternary blend composite 3D prints were investigated. The incorporation of PBS-enhanced crystallinity of the blend composite 3D prints resulted in an improvement to mechanical properties, heat resistance, and anisotropic characteristics. Flexibility of the blend composites was obtained by presentation of PBAT. It should be noted that the core–shell morphology of the ternary blend influenced the reduction of volume shrinkage, which obtained good surface roughness and dimensional accuracy in the ternary blend composite 3D printing.

Printed 3D objects built by fused deposition modeling (FDM) are well-known to exhibit large anisotropic mechanical properties. This anisotropy is due to poor diffusion and entanglement of chains between filaments during the deposition process. A weak interlayer bond is thus formed. To combat anisotropy in FDM printed parts, our group has utilized bimodal blends of a chemically identical low molecular weight surface segregating additive (LMW-SuSA) blended with a bulk, commercially available poly(lactide) (PLA). Drastic improvements to the interlayer adhesion and a reduction in the anisotropic character are realized with the introduction of the LMW-SuSA. To expand our understanding of the mechanism responsible for this improvement, we report the introduction of LMW-SuSAs of miscible styrene-co-acrylonitrile (SAN), poly(methyl methacrylate) (PMMA), and immiscible PLA to ABS and their impact on the mechanical properties of printed FDM parts. Decreases in the anisotropy of mechanical properties of ABS blends containing SAN (8.5k, 33k, and 75k), PMMA (33k, 67k, and 100k), and PLA (33k-3 arm and 220k) are tested. With the addition of 33k PMMA and 33k-3 arm PLA to ABS, the transversely oriented parts maximum stress increases by 40 and 25%, respectively. A significant improvement in isotropy in the modulus is also observed. Interestingly, LMW-SuSAs of SAN do not improve the isotropy of the part. More importantly, experiments utilizing energy dispersive X-ray spectroscopy (EDS) confirm the surface segregation of LMW PMMA and PLA to the interfilament interface, indicating that improvements in layer adhesion are a result of increased diffusion and entanglement of chains across the interlayer interface.

Hybrid material extrusion 3D printing to strengthen interlayer adhesion through hot rolling

Thermoreversible gels – Optimisation of processing parameters in fused Deposition Modelling

Additive Manufacturing (AM) has revolutionized the production of three-dimensional objects by utilizing a layer-by-layer approach. Among the materials used, carbon fiber-reinforced polymer (CFRP) composites have gained significant attention. The integration of carbon fibers and a polymer matrix offers enhanced structural integrity, thermal stability, and corrosion resistance, making these composites appealing for aerospace, automotive, and a broad range of other engineering applications. AM of CFRP composites allows the precise alignment of carbon fibers during fabrication for the optimization of mechanical performance. Multiple AM methods have been developed for AM of CFRP, including fused deposition modeling (FDM), stereolithography (SLA), and continuous fiber printing. Challenges associated with the AM of CFRP include interfacial bonding, resin impregnation, printability and process control, and post-processing. This presentation reported an investigation of the printability, material property, and geometrical accuracy of CFRP composites using the FDM method. Short carbon fiber and polylactic acid (PLA) are selected and prepared as the filament for 3D printing. The 3D printing capability of short carbon fiber reinforced composites is investigated using different layer heights, printing speeds, and nozzle and build-bed temperatures to determine the optimal printing parameters. Critical mechanical properties of the 3D printed composites, including tensile and flexural moduli and strengths, are characterized following ASTM standards. The interlayer adhesion within composites is studied by scanning electron microscopy, optical microscopy, and porosity tests. The microstructures, particularly porous size and shape can be visualized using microscopy technologies. The average porosity of 3D printed composites can be calculated by comparing the design of 3D printed composites and the original filament. This study can lead to an improved understanding of AM-processed structural composites for broad aerospace, automotive, and mechanical applications.

Additive manufacturing refers to a new technology in which physical parts are directly produced from a computer model by incremental addition of the constituent materials. Fused deposition modeling (FDM) is one of the most common types of additive manufacture processes. The ultimate mechanical performance of FDM printed parts is a function of the interlayer bond quality. Current literature however focuses only on the phenomenological evolution of standard mechanical properties (such as tensile and bending) as a function of printing conditions. Such studies do not provide direct information about the interlayer adhesion and in-practice failure characteristics. In this work, a fracturemechanics- based methodology was used to characterize the fracture resistance of FDM 3D printed Acrylonitrile Butadiene Styrene (ABS) samples as a function of nozzle and bed temperatures. Double cantilever beam (DCB) specimens was printed in such pattern that the applied load exerted only tensile opening stresses at the crack front. This facilitated the measurement of crack growth under pure mode-I condition. A finite element model was then used to obtain the J-integral strain energy release rate values, as a measure of the fracture resistance. Since the crack propagated at the interlayer in all the cases, the fracture resistance was a direct indication of the interlayer adhesion. The results revealed that the critical crack growth load, the actual fracture surface area (governed by printed mesostructure) and the apparent fracture resistance all increased when the nozzle or bed temperature was increased; the nozzle temperature showed a much stronger effect. The layer-to-layer adhesion, as reflected by the interlayer fracture resistance, did not show monotonous increase with the temperatures and appeared to level off at higher temperatures, indicating that complete interlayer fusion was achieved. This work provides insight into and characterizes the relationships between the 3D printing conditions, the resultant mesostructure, the apparent fracture resistance and the interlayer adhesion in FDM 3D printed materials.

3D printing has been steering the manufacturing market since its birth in 1984 by Charles Hulls and is predicted to share US $32.78 billion global economy before celebrating its four decades of discovery (2023). The printing has subdued the conventional systems with its bottom-up layered additive engineering, intricate three axial build-ups, energy efficiency, economical processing, and time efficiency. Layer building can be accomplished by powders or liquid effused from a nozzle or bedded on the platform from separate reservoir. This printing mechanism traverses across different classes of materials, e.g., polymers, ceramics, metal, hydrogels, alloys, and composites for numerous domain applications. Material categories assisted with other requisite variations engender different setup design, chiefly classified as stereolithography (acronym as SLA), selective laser melting (SLM), fused deposition modeling (FDM), selective laser sintering (SLS), and polyjet or multimaterial printing. Fabrication of constructs entails software modeling as a blueprint for designing and optimization of processing parameters (printing speed, layer thickness, hatch distance, infill density, rheology (viscosity), nozzle diameter, nozzle temperature, platform temperature, dispensing orientation, etc.) for coordinating precursors with anticipated properties. Amid all these parametric constraints, temperature is one at the core of printing which monitors the rheology (flowability and printability), interlayer adhesion, and structural deviations of the prototype. The aftereffect of opted variables can be evidenced with the physical, mechanical, and biological characteristics, i.e., temperature manifests direct parametric relationship with interlayer adhesion, dwindling of which accoutered delamination, shrinkage, impaired tensile strength, increased porosity, and the pivotal residual stress. The aforesaid stress (fostered during solidification mechanism in an inapt temperature range) is counterproductive to printing as it bestows the structure with instability, warping or dimensional fluctuations, crack initiation, and fracture propagation ease. The above-said challenges can be trounced by modulating the thermal ranges, i.e., apposite platform temperature to avert ample gradient, nozzle temperature to obviate degradation meanwhile retaining the requisite viscosity, etc. Following the optimization, modeled structure is printed targeting multifarious domains, i.e., food industry, space, defense, automobiles, biomedical, electronics, bio-mimetic, and counting. This chapter appraises the temperature factor and its cautious implementation in printing with above-mentioned techniques for the smooth and impeccable output.

3D-printed multi-materials are widely used in structural applications. However, variations in material properties can cause interlayer residual stresses, reducing overall part performance and often leading to defects such as warping, cracking, and delamination. In this study, the interlayer adhesion behavior of 3D-printed pure polyethylene terephthalate glycol (PETG) and 10wt% carbon fiber-reinforced PETG (PETG-CF) composites, fabricated via Fused Deposition Modelling (FDM), was investigated. Lap shear, flexural, and tensile tests were conducted to evaluate adhesion strength and stress distribution across the interfaces of PETG and PETG-CF layers for both annealed and unannealed specimens. The results indicate that annealing at elevated temperatures and longer durations significantly enhanced interlayer adhesion and mechanical strength. Microscopic analysis confirmed improved layer fusion in annealed specimens, characterized by reduced voids and delamination, indicating enhanced interlayer bonding. By optimizing annealing conditions, this study provides clear insights and suggests a pathway to improve the mechanical performance of multi-material 3D-printed components and reducing interlayer failures.