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Polymers in Additive Manufacturing

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A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Processing and Engineering".

Deadline for manuscript submissions: closed (20 June 2022) | Viewed by 42382

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Dr. Rafiq Ahmad

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Laboratory of Intelligent Manufacturing, Design and Automation, University of Alberta, Edmonton, AB T6G 2R3, Canada
Interests: hybrid manufacturing; 3D printing of multimaterial polymers and alloys; smart manufacturing; systems design and development; Industry 4.0; polymer processing and manufacturing
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Special Issue Information

Dear Colleagues,

Additive manufacturing (AM), also known as 3D printing, is one of the essential technologies in the fabrication of fully customized complex components and objects. AM solutions are available for several materials, including metals, alloys, ceramics, and polymers. Due to the low cost of fabrication, the use of polymers can vary between cheap substitutes of natural products to high-quality products for many resource-based applications. AM provides a viable manufacturing solution for polymer-based products with reduced fabrication time and cost. In addition the many advantages of using polymers as one of the primary AM material, there are also shortcomings related to the topology, strength, microstructure, bonding, and functionality of polymer-based structures. The particular features, properties, and limitations of polymers in the various AM technologies also varies. The manufacturing and fabrication of components using polymers with sandwich-structured specimens with different material combinations is also a growing research area. For example, using conventional thermoplastics such as poly(lactic acid) (PLA), acrylonitrile butadiene styrene (ABS), and high-impact polystyrene (HIPS) through the filament-based extrusion process can demonstrate improved properties. New advancements in AM also include 4D printing technology, which is simply the fabrication of 3D-printed structures capable of changing with time. Industry 4.0, the fourth revolution of industry, is also playing an important role in new smart ways of polymer-based AM processes.

Recognizing the importance of theory, simulations, and real experimental analysis in understanding the properties of polymer-based products under normal and extreme conditions, this Special Issue of Polymers invites contributions addressing several aspects of polymers fabrication systems, such as the development of new multiscale strategies to address more complicated systems, new ways of design and manufacturing polymer-based structures, design for additive manufacturing (DfAM), new methods of control and monitoring polymer components, new sensing and on-the-fly inspection of polymer AM processes, hybrid sandwich structures modelling and fabrication, simulation methodologies satisfying the fundamental polymer fabrication, new theoretical developments on polymers bonding, new methods for computing self-assembly in polymers, etc. The above list is only indicative and by no means exhaustive; any original theoretical or simulation work or review article on the role of polymer design and fabrication is welcome. We hope that these contributions will address a variety of systems, including new material combinations, new system designs, new manufacturing processes, and new ways of sensing and controlling the AM processes.

Dr. Rafiq Ahmad
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Polymer fabrication
Sandwich structures
Simulation methodologies
Analytical approach to polymer additive manufacturing
Modeling polymer manufacturing
On-the-fly inspection
Design for additive manufacturing (DfAM)

Published Papers (12 papers)

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Research

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16 pages, 2909 KiB

Open AccessArticle

Hot Lithography Vat Photopolymerisation 3D Printing: Vat Temperature vs. Mixture Design

by Farzaneh Sameni, Basar Ozkan, Hanifeh Zarezadeh, Sarah Karmel, Daniel S. Engstrøm and Ehsan Sabet

Polymers 2022, 14(15), 2988; https://doi.org/10.3390/polym14152988 - 23 Jul 2022

Cited by 6 | Viewed by 2244

Abstract

In the vat photopolymerisation 3D printing technique, the properties of the printed parts are highly dependent on the degree of conversion of the monomers. The mechanisms and advantages of vat photopolymerisation at elevated temperatures, or so called “hot lithography”, were investigated in this paper. Two types of photoresins, commercially used as highly accurate castable resins, with different structural and diluent monomers, were employed in this study. Samples were printed at 25 °C, 40 °C, and 55 °C. The results show that hot lithography can significantly enhance the mechanical and dimensional properties of the printed parts and is more effective when there is a diluent with a network T_g close to the print temperature. When processed at 55 °C, Mixture A, which contains a diluent with a network T_g = 53 °C, was more readily impacted by heat compared to Mixture B, whose diluent had a network T_g = 105. As a result, a higher degree of conversion, followed by an increased T_g of the diluents, and improvements in the tensile strength and dimensional stability of the printed parts were observed, which enhanced the outcomes of the prints for the intended application in investment casting of complex components used in the aero and energy sectors. In conclusion, the effectiveness of the hot lithography process is contained by a correlation between the process temperature and the characteristics of the monomers in the mixture. Full article

(This article belongs to the Special Issue Polymers in Additive Manufacturing)

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29 pages, 15318 KiB

Open AccessArticle

Fused-Filament Fabrication of Short Carbon Fiber-Reinforced Polyamide: Parameter Optimization for Improved Performance under Uniaxial Tensile Loading

by Carlos Belei, Jana Joeressen and Sergio T. Amancio-Filho

Polymers 2022, 14(7), 1292; https://doi.org/10.3390/polym14071292 - 23 Mar 2022

Cited by 21 | Viewed by 2764

Abstract

This study intends to contribute to the state of the art of Fused-Filament Fabrication (FFF) of short-fiber-reinforced polyamides by optimizing process parameters to improve the performance of printed parts under uniaxial tensile loading. This was performed using two different approaches: a more traditional 2k full factorial design of experiments (DoE) and multiple polynomial regression using an algorithm implementing machine learning (ML) principles such as train-test split and cross-validation. Evaluated parameters included extrusion and printing bed temperatures, layer height and printing speed. It was concluded that when exposed to new observations, the ML-based model predicted the response with higher accuracy. However, the DoE fared slightly better at predicting observations where higher response values were expected, including the optimal solution, which reached an UTS of 117.1 ± 5.7 MPa. Moreover, there was an important correlation between process parameters and the response. Layer height and printing bed temperatures were considered the most influential parameters, while extrusion temperature and printing speed had a lower influence on the outcome. The general influence of parameters on the response was correlated with the degree of interlayer cohesion, which in turn affected the mechanical performance of the 3D-printed specimens. Full article

(This article belongs to the Special Issue Polymers in Additive Manufacturing)

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17 pages, 6137 KiB

Open AccessArticle

Influence of Extruder’s Nozzle Diameter on the Improvement of Functional Properties of 3D-Printed PLA Products

by Piotr Czyżewski, Dawid Marciniak, Bartosz Nowinka, Michał Borowiak and Marek Bieliński

Polymers 2022, 14(2), 356; https://doi.org/10.3390/polym14020356 - 17 Jan 2022

Cited by 30 | Viewed by 3131

Abstract

The dynamic growth of the use of polymer construction parts manufactured individually and in a small series makes it necessary to improve additive methods in the areas of materials, equipment and processes. By observing selected phenomena occurring during the processing of polymer materials in other production technologies (e.g., extrusion and injection molding), it is possible to obtain solutions that positively affect the final performance properties of the products obtained in additive manufacturing technologies using thermoplastic filament. The aim of this research was to determine the effect of the diameter of the print head nozzle on the spatial structure (path width) and selected mechanical properties of samples produced by the FFF method with PLA material. The obtained results were compared to the samples with a solid structure produced using injection molding technology. In the experiment, the RepRap device for additive manufacturing was used, with the use of nozzles with diameters of 0.2 mm, 0.4 mm, 0.8 mm and 1.2 mm. The test objects were produced with a layer height of 0.2 mm, full filling (100%) and with constant remaining printing parameters. The conducted research allowed us to conclude that the use of layer heights lower than the standard ones gives favorable results for selected mechanical properties. The use of an extruder nozzle diameter of 0.8 mm allows one to obtain a macrostructure with a high degree of interconnection of layers and paths and favorable mechanical properties. The test results can be used in the construction of functional elements that are produced by fused deposition modeling (FDM) and fused filament fabrication (FFF) methods in prototype, unit and small-lot production. Full article

(This article belongs to the Special Issue Polymers in Additive Manufacturing)

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14 pages, 3772 KiB

Open AccessArticle

Sandwich Multi-Material 3D-Printed Polymers: Influence of Aging on the Impact and Flexure Resistances

by Ana C. Pinho and Ana P. Piedade

Polymers 2021, 13(22), 4030; https://doi.org/10.3390/polym13224030 - 21 Nov 2021

Cited by 12 | Viewed by 2512

Abstract

With the advances in new materials, equipment, and processes, additive manufacturing (AM) has gained increased importance for producing the final parts that are used in several industrial areas, such as automotive, aeronautics, and health. The constant development of 3D-printing equipment allows for printing multi-material systems as sandwich specimens using, for example, double-nozzle configurations. The present study aimed to compare the mechanical behavior of multi-material specimens that were produced using a double-nozzle 3D printer. The materials that were included in this study were the copolymer acrylonitrile-butadiene-styrene (ABS), high-impact polystyrene (HIPS), poly(methyl methacrylate) (PMMA), and thermoplastic polyurethane (TPU). The configuration of the sandwich structures consisted of a core of TPU and the outer skins made of one of the other three materials. The mechanical behavior was evaluated through three-point bending (3PB) and transverse impact tests and compared with mono-material printed specimens. The effect of aging in artificial saliva was evaluated for all the processed materials. The main conclusion of this study was that the aging process did not significantly alter the mechanical properties for mono-materials, except for PMMA, where the maximum flexural stress decreased. In the sandwich structures, the TPU core had a softening effect, inducing a significant increase in the resilience and resistance to transverse impact. The obtained results are quite promising for applications in biomedical devices, such as protective mouthguards or teeth aligners. In these specific applications, the changes in the mechanical properties with time and with the contact of saliva assume particular importance. Full article

(This article belongs to the Special Issue Polymers in Additive Manufacturing)

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15 pages, 4018 KiB

Open AccessArticle

Utilization of Antibacterial Nanoparticles in Photocurable Additive Manufacturing of Advanced Composites for Improved Public Health

by Christopher Billings, Changjie Cai and Yingtao Liu

Polymers 2021, 13(16), 2616; https://doi.org/10.3390/polym13162616 - 06 Aug 2021

Cited by 12 | Viewed by 2242

Abstract

This paper presents the additive manufacturing and characterization of nanoparticle-reinforced photocurable resin-based nanocomposites with a potential antimicrobial function for improved public health applications. Two types of photocurable resins are reinforced by titanium dioxide (TiO₂) or zinc oxide (ZnO) nanoparticles with average diameters in the 10–30 nm range to provide antimicrobial properties. The developed nanocomposites can be additively manufactured using the digital light processing method with an outstanding surface quality and precise geometrical accuracy. Experimental characterizations are conducted to investigate key mechanical properties of the 3D printed nanocomposites, including Young’s Modulus, tensile strength, and abrasion resistance. Specimens produced were observed to demonstrate the following characteristics during testing. Tensile strength increased by 42.2% at a maximum value of 29.53 MPa. The modulus of elasticity increased by 14.3%, and abrasion resistance increased by 15.8%. The proper dispersion of the nanoparticles within the cured resin is validated by scanning electron images. The wettability and water absorption testing results indicate that the developed nanocomposites have an outstanding water resistance capability. The pairing of digital light processing with these novel nanocomposites allows for the creation of complex composite geometries that are not capable through other manufacturing processes. Therefore, they have the potential for long-term usage to improve general public health with antimicrobial functionality. The pairing of an unmodified photocurable resin with a 1% ZnO concentration demonstrated the most promise for commercial applications. Full article

(This article belongs to the Special Issue Polymers in Additive Manufacturing)

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16 pages, 5094 KiB

Open AccessFeature PaperArticle

Recycling of Selective Laser Sintering Waste Nylon Powders into Fused Filament Fabrication Parts Reinforced with Mg Particles

by Mohammad Uddin, Daniel Williams and Anton Blencowe

Polymers 2021, 13(13), 2046; https://doi.org/10.3390/polym13132046 - 22 Jun 2021

Cited by 12 | Viewed by 4139

Abstract

This paper presents recycling of selective laser sintering (SLS) waste nylon into printable filaments and parts reinforced with Mg particles. Waste nylon and waste–Mg powder mixture with 2%, 4%, and 8% Mg to nylon were extruded into the filaments. Moisture absorption, differential scanning calorimetry, and melt flow index experiments were conducted to determine the thermal characteristics, while tensile and flexural tests were conducted to evaluate mechanical properties and failure mechanisms. The results were compared with off-the-self (OTS) nylon. Waste powder was found to be extrudable and printable as FFF filament. Waste filament diameter closely matched standard filament size, while exhibiting reduced moisture absorption. High melting and crystallisation temperature for the waste nylon demonstrated a degradation of the plastic during the SLS process. Young’s modulus and ultimate tensile strength for the waste filament increased by 1.6-fold compared to that for OTS, while Mg-composite filament surpassed the waste and OTS. Waste and Mg composite dog bone results showed an increase in strength and stiffness, but the ductility deteriorated. Both flexural strength and modulus for the waste nylon increased by 13% and 26%, respectively, over OTS, and the addition of Mg enhanced flexural strength by up to 5-fold at 8% Mg over the waste. Printed surface topography demonstrated that the waste and Mg composite filaments can print the parts with desired geometric shapes and acceptable surface texture. The findings showed that recycling waste SLS powder into FFF prints would be a viable and useful alternative to disposal, given its abundance. Full article

(This article belongs to the Special Issue Polymers in Additive Manufacturing)

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18 pages, 8044 KiB

Open AccessArticle

On the Mechanical Response of Silicon Dioxide Nanofiller Concentration on Fused Filament Fabrication 3D Printed Isotactic Polypropylene Nanocomposites

by Nectarios Vidakis, Markos Petousis, Emmanouil Velidakis, Lazaros Tzounis, Nikolaos Mountakis, Apostolos Korlos, Peder Erik Fischer-Griffiths and Sotirios Grammatikos

Polymers 2021, 13(12), 2029; https://doi.org/10.3390/polym13122029 - 21 Jun 2021

Cited by 23 | Viewed by 2891

Abstract

Utilization of advanced engineering thermoplastic materials in fused filament fabrication (FFF) 3D printing process is critical in expanding additive manufacturing (AM) applications. Polypropylene (PP) is a widely used thermoplastic material, while silicon dioxide (SiO₂) nanoparticles (NPs), which can be found in many living organisms, are commonly employed as fillers in polymers to improve their mechanical properties and processability. In this work, PP/SiO₂ nanocomposite filaments at various concentrations were developed following a melt mixing extrusion process, and used for FFF 3D printing of specimens’ characterization according to international standards. Tensile, flexural, impact, microhardness, and dynamic mechanical analysis (DMA) tests were conducted to determine the effect of the nanofiller loading on the mechanical and viscoelastic properties of the polymer matrix. Scanning electron microscopy (SEM), Raman spectroscopy and atomic force microscopy (AFM) were performed for microstructural analysis, and finally melt flow index (MFI) tests were conducted to assess the melt rheological properties. An improvement in the mechanical performance was observed for silica loading up to 2.0 wt.%, while 4.0 wt.% was a potential threshold revealing processability challenges. Overall, PP/SiO₂ nanocomposites could be ideal candidates for advanced 3D printing engineering applications towards structural plastic components with enhanced mechanical performance. Full article

(This article belongs to the Special Issue Polymers in Additive Manufacturing)

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13 pages, 3928 KiB

Open AccessArticle

Fused Filament Fabrication Based on Polyhydroxy Ether (Phenoxy) Polymers and Related Properties

by Christian Brauner, Marco Küng, Delal Arslan and Christoph Maurer

Polymers 2021, 13(10), 1549; https://doi.org/10.3390/polym13101549 - 12 May 2021

Cited by 7 | Viewed by 2149

Abstract

This paper describes the first-time application of polyhydroxy ether polymers, so-called phenoxy, to fused filament fabrication (FFF). Phenoxy is an amorphous thermoplastic polymer that is based on the same building blocks as epoxide resins. This similarity creates some unique properties such as dissolution to epoxide systems, which is why phenoxy is used as an additive for toughening. In this study, the processing parameters were characterized, a filament was extruded and applied to FFF printing, and the final mechanical characteristics were determined. The study concludes with a comparison with other standard FFF materials. Full article

(This article belongs to the Special Issue Polymers in Additive Manufacturing)

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28 pages, 126923 KiB

Open AccessArticle

Dual Graded Lattice Structures: Generation Framework and Mechanical Properties Characterization

by Khaled G. Mostafa, Guilherme A. Momesso, Xiuhui Li, David S. Nobes and Ahmed J. Qureshi

Polymers 2021, 13(9), 1528; https://doi.org/10.3390/polym13091528 - 10 May 2021

Cited by 13 | Viewed by 6667

Abstract

Additive manufacturing (AM) enables the production of complex structured parts with tailored properties. Instead of manufacturing parts as fully solid, they can be infilled with lattice structures to optimize mechanical, thermal, and other functional properties. A lattice structure is formed by the repetition of a particular unit cell based on a defined pattern. The unit cell’s geometry, relative density, and size dictate the lattice structure’s properties. Where certain domains of the part require denser infill compared to other domains, the functionally graded lattice structure allows for further part optimization. This manuscript consists of two main sections. In the first section, we discussed the dual graded lattice structure (DGLS) generation framework. This framework can grade both the size and the relative density or porosity of standard and custom unit cells simultaneously as a function of the structure spatial coordinates. Popular benchmark parts from different fields were used to test the framework’s efficiency against different unit cell types and grading equations. In the second part, we investigated the effect of lattice structure dual grading on mechanical properties. It was found that combining both relative density and size grading fine-tunes the compressive strength, modulus of elasticity, absorbed energy, and fracture behavior of the lattice structure. Full article

(This article belongs to the Special Issue Polymers in Additive Manufacturing)

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24 pages, 8988 KiB

Open AccessArticle

A Design for Additive Manufacturing Strategy for Dimensional and Geometrical Quality Improvement of PolyJet-Manufactured Glossy Cylindrical Features

by Natalia Beltrán, Braulio J. Álvarez, David Blanco, Fernando Peña and Pedro Fernández

Polymers 2021, 13(7), 1132; https://doi.org/10.3390/polym13071132 - 02 Apr 2021

Cited by 6 | Viewed by 1952

Abstract

The dimensional and geometrical quality of additively manufactured parts must be increased to match industrial requirements before they can be incorporated to mass production. Such an objective has a great relevance in the case of features of linear size that are affected by dimensional or geometrical tolerances. This work proposes a design for additive manufacturing strategy that uses the re-parameterization of part design to minimize shape deviations from cylindrical geometries. An analysis of shape deviations in the frequency domain is used to define a re-parameterization strategy, imposing a bi-univocal correspondence between verification parameters and design parameters. Then, the significance of variations in the process and design factors upon part quality is analyzed using design of experiments to determine the appropriate extension for modelling form deviation. Finally, local deviations are mapped for design parameters, and a new part design including local compensations is obtained. This strategy has been evaluated upon glossy surfaces manufactured in a Vero™ material by polymer jetting. The results of the proposed example showed a relevant improvement in dimensional quality, as well as a reduction of geometrical deviations, outperforming the results obtained with a conventional scaling compensation. Full article

(This article belongs to the Special Issue Polymers in Additive Manufacturing)

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16 pages, 3362 KiB

Open AccessArticle

Multi-Response Optimization of Tensile Creep Behavior of PLA 3D Printed Parts Using Categorical Response Surface Methodology

by Muhammad Waseem, Bashir Salah, Tufail Habib, Waqas Saleem, Muhammad Abas, Razaullah Khan, Usman Ghani and Muftooh Ur Rehman Siddiqi

Polymers 2020, 12(12), 2962; https://doi.org/10.3390/polym12122962 - 11 Dec 2020

Cited by 28 | Viewed by 3945

Abstract

Three-dimensional printed plastic products developed through fused deposition modeling (FDM) endure long-term loading in most of the applications. The tensile creep behavior of such products is one of the imperative benchmarks to ensure dimensional stability under cyclic and dynamic loads. This research dealt with the optimization of the tensile creep behavior of 3D printed parts produced through fused deposition modeling (FDM) using polylactic acid (PLA) material. The geometry of creep test specimens follows the American Society for Testing and Materials (ASTM D2990) standards. Three-dimensional printing is performed on an open-source MakerBot desktop 3D printer. The Response Surface Methodology (RSM) is employed to predict the creep rate and rupture time by undertaking the layer height, infill percentage, and infill pattern type (linear, hexagonal, and diamond) as input process parameters. A total of 39 experimental runs were planned by means of a categorical central composite design. The analysis of variance (ANOVA) results revealed that the most influencing factors for creep rate were layer height, infill percentage, and infill patterns, whereas, for rupture time, infill pattern was found significant. The optimized levels obtained for both responses for hexagonal pattern were 0.1 mm layer height and 100% infill percentage. Some verification tests were performed to evaluate the effectiveness of the adopted RSM technique. The implemented research is believed to be a comprehensive guide for the additive manufacturing users to determine the optimum process parameters of FDM which influence the product creep rate and rupture time. Full article

(This article belongs to the Special Issue Polymers in Additive Manufacturing)

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Review

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33 pages, 8041 KiB

Open AccessReview

Scientometric Analysis and Systematic Review of Multi-Material Additive Manufacturing of Polymers

by Yufan Zheng, Wenkang Zhang, David Moises Baca Lopez and Rafiq Ahmad

Polymers 2021, 13(12), 1957; https://doi.org/10.3390/polym13121957 - 12 Jun 2021

Cited by 32 | Viewed by 5357

Abstract

Multi-material additive manufacturing of polymers has experienced a remarkable increase in interest over the last 20 years. This technology can rapidly design and directly fabricate three-dimensional (3D) parts with multiple materials without complicating manufacturing processes. This research aims to obtain a comprehensive and in-depth understanding of the current state of research and reveal challenges and opportunities for future research in the area. To achieve the goal, this study conducts a scientometric analysis and a systematic review of the global research published from 2000 to 2021 on multi-material additive manufacturing of polymers. In the scientometric analysis, a total of 2512 journal papers from the Scopus database were analyzed by evaluating the number of publications, literature coupling, keyword co-occurrence, authorship, and countries/regions activities. By doing so, the main research frame, articles, and topics of this research field were quantitatively determined. Subsequently, an in-depth systematic review is proposed to provide insight into recent advances in multi-material additive manufacturing of polymers in the aspect of technologies and applications, respectively. From the scientometric analysis, a heavy bias was found towards studying materials in this field but also a lack of focus on developing technologies. The future trend is proposed by the systematic review and is discussed in the directions of interfacial bonding strength, printing efficiency, and microscale/nanoscale multi-material 3D printing. This study contributes by providing knowledge for practitioners and researchers to understand the state of the art of multi-material additive manufacturing of polymers and expose its research needs, which can serve both academia and industry. Full article

(This article belongs to the Special Issue Polymers in Additive Manufacturing)

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