Porous PLAs with Controllable Density by FDM 3D Printing and Chemical Foaming Agent

Characterization of PLA/LW-PLA Composite Materials Manufactured by Dual-Nozzle FDM 3D-Printing Processes

This study investigates the properties of 3D-printed composite structures made from polylactic acid (PLA) and lightweight-polylactic acid (LW-PLA) filaments using dual-nozzle fused-deposition modeling (FDM) 3D printing. Composite structures were modeled by creating three types of cubes: (i) ST4-built with a total of four alternating layers of the two filaments in the z-axis, (ii) ST8-eight alternating layers of the two filaments, and (iii) CH4-a checkered pattern with four alternating divisions along the x, y, and z axes. Each composite structure was analyzed for printing time and weight, morphology, and compressive properties under varying nozzle temperatures and infill densities. Results indicated that higher nozzle temperatures (230 °C and 240 °C) activate foaming, particularly in ST4 and ST8 at 100% infill density. These structures were 103.5% larger on one side than the modeled dimensions and up to 9.25% lighter. The 100% infill density of ST4-Com-PLA/LW-PLA-240 improved toughness by 246.5% due to better pore compression. The ST4 and ST8 cubes exhibited decreased stiffness with increasing temperatures, while CH4 maintained consistent compressive properties across different conditions. This study confirmed that the characteristics of LW-PLA become more pronounced as the material is printed continuously, with ST4 showing the strongest effect, followed by ST8 and CH4. It highlights the importance of adjusting nozzle temperature and infill density to control foaming, density, and mechanical properties. Overall optimal conditions are 230 °C and 50% infill density, which provide a balance of strength and toughness for applications.

Forefront Research of Foaming Strategies on Biodegradable Polymers and Their Composites by Thermal or Melt-Based Processing Technologies: Advances and Perspectives

The last few decades have witnessed significant advances in the development of polymeric-based foam materials. These materials find several practical applications in our daily lives due to their characteristic properties such as low density, thermal insulation, and porosity, which are important in packaging, in building construction, and in biomedical applications, respectively. The first foams with practical applications used polymeric materials of petrochemical origin. However, due to growing environmental concerns, considerable efforts have been made to replace some of these materials with biodegradable polymers. Foam processing has evolved greatly in recent years due to improvements in existing techniques, such as the use of supercritical fluids in extrusion foaming and foam injection moulding, as well as the advent or adaptation of existing techniques to produce foams, as in the case of the combination between additive manufacturing and foam technology. The use of supercritical CO2 is especially advantageous in the production of porous structures for biomedical applications, as CO2 is chemically inert and non-toxic; in addition, it allows for an easy tailoring of the pore structure through processing conditions. Biodegradable polymeric materials, despite their enormous advantages over petroleum-based materials, present some difficulties regarding their potential use in foaming, such as poor melt strength, slow crystallization rate, poor processability, low service temperature, low toughness, and high brittleness, which limits their field of application. Several strategies were developed to improve the melt strength, including the change in monomer composition and the use of chemical modifiers and chain extenders to extend the chain length or create a branched molecular structure, to increase the molecular weight and the viscosity of the polymer. The use of additives or fillers is also commonly used, as fillers can improve crystallization kinetics by acting as crystal-nucleating agents. Alternatively, biodegradable polymers can be blended with other biodegradable polymers to combine certain properties and to counteract certain limitations. This work therefore aims to provide the latest advances regarding the foaming of biodegradable polymers. It covers the main foaming techniques and their advances and reviews the uses of biodegradable polymers in foaming, focusing on the chemical changes of polymers that improve their foaming ability. Finally, the challenges as well as the main opportunities presented reinforce the market potential of the biodegradable polymer foam materials.

Effect of the Material Extrusion Process Parameters on the Compressive Properties of Additively Manufactured Foamed and Nonfoamed Polylactic Acid Structures

This work evaluates the potential for foamable polymer filaments to be used to make lightweight, energy-absorbing structures using additive manufacturing. To achieve this, a commercial, foamable polylactic acid filament was extruded using a material extrusion process to make parts for compression testing. It was found that a maximum foam expansion could be achieved at an extrusion nozzle temperature of 220°C, but that to achieve dimensional accuracy, the material flow rate through the nozzle had to be adjusted by decreasing the extrusion multiplier value. In a novel approach, accurate and faster builds could be achieved by decreasing the infill instead. When compared with porous structures achieved by using partial infilling instead or as well as foaming, all materials were found to follow the same power-law function of the solid fraction. These trends indicated that the mechanical response was, within experimental scatter, a function of the overall solid fraction and not influenced by whether the porosity was within or between the raster lines. Although there was no apparent benefit to the mechanical performance in introducing porosity into a polymer by foaming, foamable filaments are desirable if stiff, lightweight structures with low fractions of interconnected porosity are required and can be used in combination with infilling to produce low-density structures that would be highly suitable for cores in novel lightweight sandwich structures.

PLA-Based Composite Panels Prepared via Multi-Material Fused Filament Fabrication and Associated Investigation of Process Parameters on Flexural Properties of the Fabricated Composite

This study prepares composite panels with three Polylactic acid (PLA)-based materials via the multi-material fused filament fabrication method. The influences of four processing parameters on the mechanical properties of 3D-printed samples are investigated employing the Taguchi method. These parameters include the relative volume ratio, material printing order, filling pattern, and filling density. A "larger is better" signal-to-noise analysis is performed to identify the optimal combination of printing parameters that yield maximum bending strength and bending modulus of elasticity. The results reveal that the optimal combination of printing parameters that maximizes the bending strength involves a volume ratio of 1:1:2, a material sequence of PLA/foam-agent-modified eco-friendly PLA (ePLA-LW)/glass fiber-reinforced eco-friendly PLA (ePLA-GF), a Gyroid filling pattern, and a filling density of 80%, and the optimal combination of printing parameters for maximum bending modulus involves a volume ratio of 1:2:1 with a material sequence of PLA/ePLA-LW/ePLA-GF, a Grid filling pattern, and 80% filling density. The Taguchi prediction method is utilized to determine an optimal combination of processing parameters for achieving optimal flexural performances, and predicted outcomes are validated through related experiments. The experimental values of strength and modulus are 43.91 MPa and 1.23 GPa, respectively, both very close to the predicted values of 46.87 MPa and 1.2 GPa for strength and modulus. The Taguchi experiments indicate that the material sequence is the most crucial factor influencing the flexural strength of the composite panels. The experiment result demonstrates that the flexural strength and modulus of the first material sequence are 67.72 MPa and 1.53 GPa, while the flexural strength and modulus of the third material sequence are reduced to 27.09 MPa and 0.72 GPa, respectively, only 42% and 47% of the first material sequence. The above findings provide an important reference for improving the performance of multi-material 3D-printed products.

A Review of the Preparation of Porous Fibers and Porous Parts by a Novel Micro-Extrusion Foaming Technique

This review introduces an innovative technology termed "Micro-Extrusion Foaming (MEF)", which amalgamates the merits of physical foaming and 3D printing. It presents a groundbreaking approach to producing porous polymer fibers and parts. Conventional methods for creating porous materials often encounter obstacles such as the extensive use of organic solvents, intricate processing, and suboptimal production efficiency. The MEF technique surmounts these challenges by initially saturating a polymer filament with compressed CO2 or N2, followed by cell nucleation and growth during the molten extrusion process. This technology offers manifold advantages, encompassing an adjustable pore size and porosity, environmental friendliness, high processing efficiency, and compatibility with diverse polymer materials. The review meticulously elucidates the principles and fabrication process integral to MEF, encompassing the creation of porous fibers through the elongational behavior of foamed melts and the generation of porous parts through the stacking of foamed melts. Furthermore, the review explores the varied applications of this technology across diverse fields and imparts insights for future directions and challenges. These include augmenting material performance, refining fabrication processes, and broadening the scope of applications. MEF technology holds immense potential in the realm of porous material preparation, heralding noteworthy advancements and innovations in manufacturing and materials science.

Use of light-weight foaming polylactic acid as a lung-equivalent material in 3D printed phantoms

The 3D printing of lung-equivalent phantoms using conventional polylactic acid (PLA) filaments requires the use of low in-fill printing densities, which can produce substantial density heterogeneities from the air gaps within the resulting prints. Light-weight foaming PLA filaments produce microscopic air bubbles when heated to 3D printing temperatures. In this study, the expansion of foaming PLA filament was characterised for two 3D printers with different nozzle diameters, in order to optimise the printing flow rates required to achieve a low density print when printed at 100% in-fill printing density, without noticeable internal air gaps. Effective densities as low as 0.28 g cm- 3 were shown to be achievable with only microscopic air gaps. Light-weight foaming PLA filaments are a cost-effective method for achieving homogeneous lung-equivalency in 3D printed phantoms for use in radiotherapy imaging and dosimetry, featuring smaller air gaps than required to achieve low densities with conventional PLA filaments.

On the Creation and Optical Microstructure Characterisation of Additively Manufactured Foam Structures (AMF)

Plastic-based additive manufacturing processes are becoming increasingly popular in the production of structural parts. Based on the idea of lightweight design and the aim of extending the functionality of additive structures, the production of additively manufactured foam structures has emerged as a new field of application. The optical characterisation of these structures is of particular importance for process adjustments and the identification of (unwanted) changes in the foam structure. The degree of foaming and the fineness of a foam structure are of interest at this point. In this context, only the part of a structure dominated by foam pores is considered a foam structure. So far, there are no sophisticated methods for such an optical characterisation. Therefore, in this work, microscope images of manufactured as well as artificially created additively manufactured foam structures were evaluated. On these images, the features porosity, pore size, pore amount and a measure for the textural change were determined in order to obtain information about changes within an additively manufactured foam structure. It is shown that additive structures show changing pore shapes depending on the orientation of the cutting plane, although there are no changes in the foaming behaviour. Therefore, caution is required when identifying changes within the foam structure. It was also found that, owing to the additive process, the total porosity is already set in the slicing process and remains constant even if the degree of foaming of individual tracks is changed. Therefore, the degree of foaming cannot be determined on the basis of the total porosity, but it can be assessed on the basis of the formation of large networks of process-related pores.

Additively manufactured foamed polylactic acid for lightweight structures

Purpose

This study aims to make foamed polylactic acid (PLA) structures with different densities by varying deposition temperatures using the material extrusion (MEX) additive manufacturing process.

Design/methodology/approach

The extrusion multiplier (EM) was calibrated for each deposition temperature to control foaming expansion. Material density was determined using extruded cubes with the optimal EM value for each deposition temperature. The influence of deposition temperature on the tensile, compression and flexure characteristics of the foamable filament was studied experimentally.

Findings

The foaming expansion ratio, the consistency of the raster width and the raster gap significantly affect the surface roughness of the printed samples. Regardless of the loading conditions, the maximum stiffness and yield strength were achieved at a deposition temperature of 200°C when the PLA specimens had no foam. When the maximum foaming occurred (220°C deposition temperature), the stiffness and yield strength of the PLA specimens were significantly reduced.

Practical implications

The obvious benefit of using foamed materials is that they are lighter and consume less material than bulky polymers. Injection or compression moulding is the most commonly used method for creating foamed products. However, these technologies require tooling to fabricate complicated parts, which may be costly and time-consuming. Conversely, the MEX process can produce extremely complex parts with less tooling expense, reduction in energy use and optimised material consumption.

Originality/value

This study investigates the possibility of stiff, lightweight structures with low fractions of interconnected porosity using foamable filament.

A comprehensive review on fused deposition modelling of polylactic acid

Fused Deposition Modelling (FDM) is one of the additive manufacturing (AM) techniques that have emerged as the most feasible and prevalent approach for generating functional parts due to its ability to produce neat and intricate parts. FDM mainly utilises one of the widely used polymers, polylactic acid, also known as polylactide (PLA). It is an aliphatic polyester material and biocompatible thermoplastic, with the best design prospects due to its eco-friendly properties; when PLA degrades, it breaks down into water and carbon dioxide, neither of which are hazardous to the environment. However, PLA has its limitations of poor mechanical properties. Therefore, a filler reinforcement may enhance the characteristics of PLA and produce higher-quality FDM-printed parts. The processing parameters also play a significant role in the final result of the printed parts. This review aims to study and discover the properties of PLA and the optimum processing parameters. This review covers PLA in FDM, encompassing its mechanical properties, processing parameters, characterisation, and applications. A comprehensive description of FDM processing parameters is outlined as it plays a vital role in determining the quality of a printed product. In addition, PLA polymer is highly desirable for various field industrial applications such as in a medical, automobile, and electronic, given its excellent thermoplastic and biodegradability properties.

Deposition Offset of Printed Foam Strands in Direct Bubble Writing

Direct Bubble Writing is a recent technique to print shape-stable 3-dimensional foams from streams of liquid bubbles. These bubbles are ejected from a core-shell nozzle, deposited on the build platform placed at a distance of approximately 10 cm below the nozzle, and photo-polymerized in situ. The bubbles are ejected diagonally, with a vertical velocity component equal to the ejection velocity and a horizontal velocity component equal to the motion of the printhead. Owing to the horizontal velocity component, a discrepancy exists between the nozzle trajectory and the location of the printed strand. This discrepancy can be substantial, as for high printhead velocities (500 mm/s) an offset of 8 mm (in radius) was measured. Here, we model and measure the deviation in bubble deposition location as a function of printhead velocity. The model is experimentally validated by the printing of foam patterns including a straight line, a circle, and sharp corners. The deposition offset is compensated by tuning the print path, enabling the printing of a circular path to the design specifications and printing of sharp corners with improved accuracy. These results are an essential step towards the Direct Bubble Writing of 3-dimensional polymer foam parts with high dimensional accuracy.

TPU-based porous heterostructures by combined techniques

The production of thermoplastic polyurethane-based porous heterostructures combining physical foaming with fused deposition modeling is detailed in this contribution. The choice of combining these two techniques lies in the possibility of creating objects endowed with a dual-scale structure at millimeter scale by fused deposition modeling and at microscopic scale by gas foaming. Thermal stability and rheological properties of the neat polymer were studied prior to foaming to design a suitable processing protocol and three different combined techniques are proposed: pressure quench, temperature rise and direct 3D foam printing. Foam morphologies were evaluated by SEM and foamed samples were characterized by thermal and mechanical analyses to highlight the differences among the combined processing techniques. Samples foamed via pressure quench exhibit the highest degree of crystallinity and a uniform cell morphology, also resulting in the largest stiffness. The results presented in this contribution open up the possibility of producing objects with complex geometry and porosity architecture at the dual scale.

In Situ Foam 3D Printing of Microcellular Structures Using Material Extrusion Additive Manufacturing

A facile manufacturing method to enable the in situ foam 3D printing of thermoplastic materials is reported. An expandable feedstock filament was first made by incorporation of thermally expandable microspheres (TEMs) in the filament during the extrusion process. The material formulation and extrusion process were designed such that TEM expansion was suppressed during filament fabrication. Polylactic acid (PLA) was used as a model material, and filaments containing 2.0 wt % triethyl citrate and 0.0-5.0 wt % TEM were fabricated. Expandable filaments were then fed into a material extrusion additive manufacturing process to enable the in situ foaming of microcellular structures during layer deposition. The mesostructure, cellular morphology, thermal behavior, and mechanical properties of the printed foams were investigated. Repeatable foam prints with highly uniform cellular structures were successfully achieved. The part density was reduced with an increase in the TEM content, with a maximum reduction of 50% at 5.0 wt % TEM content. It is also remarkable that the interbead gaps of mesostructure vanished due to the local polymer expansion during in situ foaming. The incorporation of TEM and plasticizer only slightly lowered the critical temperatures of PLA, that is, glass-transition, melting, and decomposition temperatures. Moreover, with the introduction of foaming, the specific tensile strength and modulus decreased, whereas the ductility and toughness increased severalfold. The results unveil the feasibility of a novel additive manufacturing technology that offers numerous opportunities toward the manufacturing of specially designed structures including functionally graded foams for a variety of applications.