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Process–Structure–Properties in Polymer 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 (10 January 2021) | Viewed by 63255

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Dr. Swee Leong Sing

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Guest Editor

Department of Mechanical Engineering, National University of Singapore, Singapore 117575, Singapore
Interests: additive manufacturing; 3D printing; 3D bioprinting; laser–material interactions; laser-based advanced manufacturing
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Prof. Dr. Wai Yee Yeong

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Guest Editor

Singapore Centre for 3D Printing, School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798, Singapore
Interests: additive manufacturing; 3D printing; 3D bioprinting
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Dear Colleagues,

Additive manufacturing (AM) methods have grown and evolved rapidly in recent years. AM for polymers is an exciting field and has great potential in transformative and translational research in many fields, such as biomedical, aerospace, and even electronics. Current methods for polymer AM include material extrusion, material jetting, vat polymerization, and powder bed fusion.

In this Special Issue, state-of-the-art reviews and current research results, which focus on the process–structure–properties relationships in polymer additive manufacturing, will be reported. This includes but is not limited to assessing the effect of process parameters, post-processing, and characterization techniques. Submissions related to novel applications, designs, processes or characterization methods are also welcomed.

Contributions focused on polymer additive manufacturing in any of the following topics are of particular interest:

Materials, processes and machines;
Process monitoring, modeling, and control;
Design for additive manufacturing;
Development of novel polymers for additive manufacturing;
New applications of polymers additive manufacturing in the industries.

Dr. Swee Leong Sing
Prof. Wai Yee Yeong
Guest Editors

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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

Additive manufacturing
3D printing
Polymers
Mechanical properties
Microstructural analysis
Thermal properties

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Advanced Manufacturing for Polymers in Polymers (24 articles)

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Editorial

Jump to: Research, Review

2 pages, 162 KiB

Open AccessEditorial

Process–Structure–Properties in Polymer Additive Manufacturing

by Swee Leong Sing and Wai Yee Yeong

Polymers 2021, 13(7), 1098; https://doi.org/10.3390/polym13071098 - 30 Mar 2021

Cited by 7 | Viewed by 2437

Abstract

Additive manufacturing (AM) methods have grown and evolved rapidly in recent years [...] Full article

(This article belongs to the Special Issue Process–Structure–Properties in Polymer Additive Manufacturing)

Research

Jump to: Editorial, Review

16 pages, 12297 KiB

Open AccessArticle

Additively Manufactured Parts Made of a Polymer Material Used for the Experimental Verification of a Component of a High-Speed Machine with an Optimised Geometry—Preliminary Research

by Artur Andrearczyk, Bartlomiej Konieczny and Jerzy Sokołowski

Polymers 2021, 13(1), 137; https://doi.org/10.3390/polym13010137 - 31 Dec 2020

Cited by 13 | Viewed by 2829

Abstract

This paper describes a novel method for the experimental validation of numerically optimised turbomachinery components. In the field of additive manufacturing, numerical models still need to be improved, especially with the experimental data. The paper presents the operational characteristics of a compressor wheel, measured during experimental research. The validation process included conducting a computational flow analysis and experimental tests of two compressor wheels: The aluminium wheel and the 3D printed wheel (made of a polymer material). The chosen manufacturing technology and the results obtained made it possible to determine the speed range in which the operation of the tested machine is stable. In addition, dynamic destructive tests were performed on the polymer disc and their results were compared with the results of the strength analysis. The tests were carried out at high rotational speeds (up to 120,000 rpm). The results of the research described above have proven the utility of this technology in the research and development of high-speed turbomachines operating at speeds up to 90,000 rpm. The research results obtained show that the technology used is suitable for multi-variant optimization of the tested machine part. This work has also contributed to the further development of numerical models. Full article

(This article belongs to the Special Issue Process–Structure–Properties in Polymer Additive Manufacturing)

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17 pages, 8313 KiB

Open AccessArticle

Crystallization and Thermal Behaviors of Poly(ethylene terephthalate)/Bisphenols Complexes through Melt Post-Polycondensation

by Shichang Chen, Shangdong Xie, Shanshan Guang, Jianna Bao, Xianming Zhang and Wenxing Chen

Polymers 2020, 12(12), 3053; https://doi.org/10.3390/polym12123053 - 19 Dec 2020

Cited by 16 | Viewed by 4389

Abstract

Three kinds of modified poly(ethylene terephthalate) (PET) were prepared by solution blending combined with melt post-polycondensation, using 4,4′-thiodiphenol (TDP), 4,4′-oxydiphenol (ODP) and hydroquinone (HQ) as the bisphenols, respectively. The effects of TDP, ODP and HQ on melt post-polycondensation process and crystallization kinetics, melting behaviors, crystallinity and thermal stability of PET/bisphenols complexes were investigated in detail. Excellent chain growth of PET could be achieved by addition of 1 wt% bisphenols, but intrinsic viscosity of modified PET decreased with further bisphenols content. Intermolecular hydrogen bonding between carbonyl groups of PET and hydroxyl groups of bisphenols were verified by Fourier transform infrared spectroscopy. Compare to pure PET, both the crystallization rate and melting temperatures of PET/bisphenols complexes were reduced obviously, suggesting an impeded crystallization and reduced lamellar thickness. Moreover, the structural difference between TDP, ODP and HQ played an important role on crystallization kinetics. It was proposed that the crystallization rate of TDP modified PET was reduced significantly due to the larger amount of rigid benzene ring and larger polarity than that of PET with ODP or HQ. X-ray diffraction results showed that the crystalline structure of PET did not change from the incorporation of bisphenols, but crystallinity of PET decreased with increasing bisphenols content. Thermal stability of modified PET declined slightly, which was hardly affected by the molecular structure of bisphenols. Full article

(This article belongs to the Special Issue Process–Structure–Properties in Polymer Additive Manufacturing)

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12 pages, 2554 KiB

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PVDF-BaTiO₃ Nanocomposite Inkjet Inks with Enhanced β-Phase Crystallinity for Printed Electronics

by Hamed Abdolmaleki and Shweta Agarwala

Polymers 2020, 12(10), 2430; https://doi.org/10.3390/polym12102430 - 21 Oct 2020

Cited by 50 | Viewed by 6114

Abstract

Polyvinylidene difluoride (PVDF) and its copolymers are promising electroactive polymers showing outstanding ferroelectric, piezoelectric, and pyroelectric properties in comparison with other organic materials. They have shown promise for applications in flexible sensors, energy-harvesting transducers, electronic skins, and flexible memories due to their biocompatibility, high chemical stability, bending and stretching abilities. PVDF can crystallize at five different phases of α, β, γ, δ, and ε; however, ferro-, piezo-, and pyroelectric properties of this polymer only originate from polar phases of β and γ. In this research, we reported fabrication of PVDF inkjet inks with enhanced β-phase crystallinity by incorporating barium titanate nanoparticles (BaTiO₃). BaTiO₃ not only acts as a nucleating agent to induce β-phase crystallinity, but it also improves the electric properties of PVDF through synergistic a ferroelectric polarization effect. PVDF-BaTiO₃ nanocomposite inkjet inks with different BaTiO₃ concentrations were prepared by wet ball milling coupled with bath ultrasonication. It was observed that the sample with 5 w% of BaTiO₃ had the highest β-phase crystallinity, while in higher ratios overall crystallinity deteriorated progressively, leading to more amorphous structures. Full article

(This article belongs to the Special Issue Process–Structure–Properties in Polymer Additive Manufacturing)

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23 pages, 2622 KiB

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Helicoidally Arranged Polyacrylonitrile Fiber-Reinforced Strong and Impact-Resistant Thin Polyvinyl Alcohol Film Enabled by Electrospinning-Based Additive Manufacturing

by Rahul Sahay, Komal Agarwal, Anbazhagan Subramani, Nagarajan Raghavan, Arief S. Budiman and Avinash Baji

Polymers 2020, 12(10), 2376; https://doi.org/10.3390/polym12102376 - 15 Oct 2020

Cited by 16 | Viewed by 4097

Abstract

In this study, we demonstrate the use of parallel plate far field electrospinning (pp-FFES) based manufacturing system for the fabrication of polyacrylonitrile (PAN) fiber reinforced polyvinyl alcohol (PVA) strong polymer thin films (PVA SPTF). Parallel plate far field electrospinning (also known as the gap electrospinning) is generally used to produce uniaxially aligned fibers between the two parallel collector plates. In the first step, a disc containing PVA/H₂O solution/bath (matrix material) was placed in between the two parallel plate collectors. Next, a layer of uniaxially aligned sub-micron PAN fibers (filler material) produced by pp-FFES was directly collected/embedded in the PVA/H₂O solution by bringing the fibers in contact with the matrix. Next, the disc containing the matrix solution was rotated at 45° angular offset and then the next layer of the uniaxial fibers was collected/stacked on top of the previous layer with now 45° rotation between the two layers. This process was continued progressively by stacking the layers of uniaxially aligned arrays of fibers at 45° angular offsets, until a periodic pattern was achieved. In total, 13 such layers were laid within the matrix solution to make a helicoidal geometry with three pitches. The results demonstrate that embedding the helicoidal PAN fibers within the PVA enables efficient load transfer during high rate loading such as impact. The fabricated PVA strong polymer thin films with helicoidally arranged PAN fiber reinforcement (PVA SPTF-HA) show specific tensile strength 5 MPa·cm³·g⁻¹ and can sustain specific impact energy (8 ± 0.9) mJ·cm³·g⁻¹, which is superior to that of the pure PVA thin film (PVA TF) and PVA SPTF with randomly oriented PAN fiber reinforcement (PVA SPTF-RO). The novel fabrication methodology enables the further capability to produce even further smaller fibers (sub-micron down to even nanometer scales) and by the virtue of its layer-by-layer processing (in the manner of an additive manufacturing methodology) allowing further modulation of interfacial and inter-fiber adherence with the matrix materials. These parameters allow greater control and tunability of impact performances of the synthetic materials for various applications from army combat wear to sports and biomedical/wearable applications. Full article

(This article belongs to the Special Issue Process–Structure–Properties in Polymer Additive Manufacturing)

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20 pages, 7211 KiB

Open AccessArticle

Novel Method for the Manufacture of Complex CFRP Parts Using FDM-based Molds

by Paul Bere, Calin Neamtu and Razvan Udroiu

Polymers 2020, 12(10), 2220; https://doi.org/10.3390/polym12102220 - 27 Sep 2020

Cited by 30 | Viewed by 4754

Abstract

Fibre-reinforced polymers (FRP) have attracted much interest within many industrial fields where the use of 3D printed molds can provide significant cost and time savings in the production of composite tooling. Within this paper, a novel method for the manufacture of complex-shaped FRP parts has been proposed. This paper features a new design of bike saddle, which was manufactured through the use of molds created by fused deposition modeling (FDM), of which two 3D printable materials were selected, polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS), and these molds were then chemically and thermally treated. The novel bike saddles were fabricated using carbon fiber-reinforced polymer (CFRP), by vacuum bag technology and oven curing, utilizing additive manufactured (AM) molds. Following manufacture the molded parts were subjected to a quality inspection, using non-contact three-dimensional (3D) scanning techniques, where the results were then statistically analyzed. The statistically analyzed results state that the main deviations between the CAD model and the manufactured CFRP parts were within the range of ±1 mm. Additionally, the weight of the upper part of the saddles was found to be 42 grams. The novel method is primarily intended to be used for customized products using CFRPs. Full article

(This article belongs to the Special Issue Process–Structure–Properties in Polymer Additive Manufacturing)

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19 pages, 7186 KiB

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Rheology-Assisted Microstructure Control for Printing Magnetic Composites—Material and Process Development

by Balakrishnan Nagarajan, Martin A.W. Schoen, Simon Trudel, Ahmed Jawad Qureshi and Pierre Mertiny

Polymers 2020, 12(9), 2143; https://doi.org/10.3390/polym12092143 - 20 Sep 2020

Cited by 6 | Viewed by 3369

Abstract

Magnetic composites play a significant role in various electrical and electronic devices. Properties of such magnetic composites depend on the particle microstructural distribution within the polymer matrix. In this study, a methodology to manufacture magnetic composites with isotropic and anisotropic particle distribution was introduced using engineered material formulations and manufacturing methods. An in-house developed material jetting 3D printer with particle alignment capability was utilized to dispense a UV curable resin formulation to the desired computer aided design (CAD) geometry. Formulations engineered using additives enabled controlling the rheological properties and the microstructure at different manufacturing process stages. Incorporating rheological additives rendered the formulation with thixotropic properties suitable for material jetting processes. Particle alignment was accomplished using a magnetic field generated using a pair of permanent magnets. Microstructure control in printed composites was observed to depend on both the developed material formulations and the manufacturing process. The rheological behavior of filler-modified polymers was characterized using rheometry, and the formulation properties were derived using mathematical models. Experimental observations were correlated with the observed mechanical behavior changes in the polymers. It was additionally observed that higher additive content controlled particle aggregation but reduced the degree of particle alignment in polymers. Directionality analysis of optical micrographs was utilized as a tool to quantify the degree of filler orientation in printed composites. Characterization of in-plane and out-of-plane magnetic properties using a superconducting quantum interference device (SQUID) magnetometer exhibited enhanced magnetic characteristics along the direction of field structuring. Results expressed in this fundamental research serve as building blocks to construct magnetic composites through material jetting-based additive manufacturing processes. Full article

(This article belongs to the Special Issue Process–Structure–Properties in Polymer Additive Manufacturing)

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25 pages, 11357 KiB

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Deformation Process of 3D Printed Structures Made from Flexible Material with Different Values of Relative Density

by Paweł Płatek, Kamil Rajkowski, Kamil Cieplak, Marcin Sarzyński, Jerzy Małachowski, Ryszard Woźniak and Jacek Janiszewski

Polymers 2020, 12(9), 2120; https://doi.org/10.3390/polym12092120 - 17 Sep 2020

Cited by 61 | Viewed by 6088

Abstract

The main aim of this article is the analysis of the deformation process of regular cell structures under quasi-static load conditions. The methodology used in the presented investigations included a manufacturability study, strength tests of the base material as well as experimental and numerical compression tests of developed regular cellular structures. A regular honeycomb and four variants with gradually changing topologies of different relative density values have been successfully designed and produced in the TPU-Polyflex flexible thermoplastic polyurethane material using the Fused Filament Fabrication (FFF) 3D printing technique. Based on the results of performed technological studies, the most productive and accurate 3D printing parameters for the thermoplastic polyurethane filament were defined. It has been found that the 3D printed Polyflex material is characterised by a very high flexibility (elongation up to 380%) and a non-linear stress-strain relationship. A detailed analysis of the compression process of the structure specimens revealed that buckling and bending were the main mechanisms responsible for the deformation of developed structures. The Finite Element (FE) method and Ls Dyna software were used to conduct computer simulations reflecting the mechanical response of the structural specimens subjected to a quasi-static compression load. The hyperelastic properties of the TPU material were described with the Simplified Rubber Material (SRM) constitutive model. The proposed FE models, as well as assumed initial boundary conditions, were successfully validated. The results obtained from computer simulations agreed well with the data from the experimental compression tests. A linear relationship was found between the relative density and the maximum strain energy value. Full article

(This article belongs to the Special Issue Process–Structure–Properties in Polymer Additive Manufacturing)

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23 pages, 6143 KiB

Open AccessArticle

System Performance and Process Capability in Additive Manufacturing: Quality Control for Polymer Jetting

by Razvan Udroiu and Ion Cristian Braga

Polymers 2020, 12(6), 1292; https://doi.org/10.3390/polym12061292 - 4 Jun 2020

Cited by 25 | Viewed by 4386

Abstract

Polymer-based additive manufacturing (AM) gathers a great deal of interest with regard to standardization and implementation in mass production. A new methodology for the system and process capabilities analysis in additive manufacturing, using statistical quality tools for production management, is proposed. A large sample of small specimens of circular shape was manufactured of photopolymer resins using polymer jetting (PolyJet) technology. Two critical geometrical features of the specimen were investigated. The variability of the measurement system was determined by Gage repeatability and reproducibility (Gage R&R) methodology. Machine and process capabilities were performed in relation to the defined tolerance limits and the results were analyzed based on the requirements from the statistical process control. The results showed that the EDEN 350 system capability and PolyJet process capability enables obtaining capability indices over 1.67 within the capable tolerance interval of 0.22 mm. Furthermore, PolyJet technology depositing thin layers of resins droplets of 0.016 mm allows for manufacturing in a short time of a high volume of parts for mass production with a tolerance matching the ISO 286 IT9 grade for radial dimension and IT10 grade for linear dimensions on the Z-axis, respectively. Using microscopy analysis some results were explained and validated from the capability study. Full article

(This article belongs to the Special Issue Process–Structure–Properties in Polymer Additive Manufacturing)

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18 pages, 6729 KiB

Open AccessArticle

3D Direct Printing of Silicone Meniscus Implant Using a Novel Heat-Cured Extrusion-Based Printer

by Eric Luis, Houwen Matthew Pan, Swee Leong Sing, Ram Bajpai, Juha Song and Wai Yee Yeong

Polymers 2020, 12(5), 1031; https://doi.org/10.3390/polym12051031 - 1 May 2020

Cited by 47 | Viewed by 6453

Abstract

The first successful direct 3D printing, or additive manufacturing (AM), of heat-cured silicone meniscal implants, using biocompatible and bio-implantable silicone resins is reported. Silicone implants have conventionally been manufactured by indirect silicone casting and molding methods which are expensive and time-consuming. A novel custom-made heat-curing extrusion-based silicone 3D printer which is capable of directly 3D printing medical silicone implants is introduced. The rheological study of silicone resins and the optimization of critical process parameters are described in detail. The surface and cross-sectional morphologies of the printed silicone meniscus implant were also included. A time-lapsed simulation study of the heated silicone resin within the nozzle using computational fluid dynamics (CFD) was done and the results obtained closely resembled real time 3D printing. Solidworks one-convection model simulation, when compared to the on-off model, more closely correlated with the actual probed temperature. Finally, comparative mechanical study between 3D printed and heat-molded meniscus is conducted. The novel 3D printing process opens up the opportunities for rapid 3D printing of various customizable medical silicone implants and devices for patients and fills the current gap in the additive manufacturing industry. Full article

(This article belongs to the Special Issue Process–Structure–Properties in Polymer Additive Manufacturing)

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12 pages, 2923 KiB

Open AccessArticle

Mode I Fracture Toughness of Polyamide and Alumide Samples obtained by Selective Laser Sintering Additive Process

by Dan Ioan Stoia, Liviu Marsavina and Emanoil Linul

Polymers 2020, 12(3), 640; https://doi.org/10.3390/polym12030640 - 11 Mar 2020

Cited by 37 | Viewed by 4517

Abstract

Selective Laser Sintering is a flexible additive manufacturing technology that can be used for the fabrication of high-resolution parts. Alongside the shape and dimension of the parts, the mechanical properties are essential for the majority of applications. Therefore, this paper investigates dimensional accuracy and mode I fracture toughness (K_IC) of Single Edge Notch Bending samples under a Three Point Bending fixture, according to the ASTM D5045-14 standard. The work focuses on the influence of two major aspects of additive manufacturing: material type (Polyamide PA2200 and Alumide) and part orientation in the building environment (orientations of 0°, 45° and 90° are considered). The rest of the controllable parameters remains constant for all samples. The results reveal a direct link between the sample densities and the dimensional accuracy with orientation. The dimensional accuracy of the samples is also material dependent. For both materials, the angular orientation leads to significant anisotropic behavior in terms of K_IC. Moreover, the type of material fundamentally influences the K_IC values and the fracture mode. The obtained results can be used in the development of additive manufactured parts in order to obtain predictable dimensional tolerances and fracture properties. Full article

(This article belongs to the Special Issue Process–Structure–Properties in Polymer Additive Manufacturing)

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Review

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18 pages, 4052 KiB

Open AccessReview

3D Printing of Fibre-Reinforced Thermoplastic Composites Using Fused Filament Fabrication—A Review

by Andrew N. Dickson, Hisham M. Abourayana and Denis P. Dowling

Polymers 2020, 12(10), 2188; https://doi.org/10.3390/polym12102188 - 24 Sep 2020

Cited by 113 | Viewed by 12091

Abstract

Three-dimensional (3D) printing has been successfully applied for the fabrication of polymer components ranging from prototypes to final products. An issue, however, is that the resulting 3D printed parts exhibit inferior mechanical performance to parts fabricated using conventional polymer processing technologies, such as compression moulding. The addition of fibres and other materials into the polymer matrix to form a composite can yield a significant enhancement in the structural strength of printed polymer parts. This review focuses on the enhanced mechanical performance obtained through the printing of fibre-reinforced polymer composites, using the fused filament fabrication (FFF) 3D printing technique. The uses of both short and continuous fibre-reinforced polymer composites are reviewed. Finally, examples of some applications of FFF printed polymer composites using robotic processes are highlighted. Full article

(This article belongs to the Special Issue Process–Structure–Properties in Polymer Additive Manufacturing)

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