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New Materials and Approaches in Polymer Additive Manufacturing

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Materials Simulation and Design".

Deadline for manuscript submissions: closed (30 June 2021) | Viewed by 29722

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Dr. Nicole Zander

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Guest Editor

Weapons and Materials Research Directorate, United States Army Research Laboratory, Aberdeen Proving Ground, Aberdeen, MD, USA
Interests: material extrusion additive manufacturing; reactive extrusion; polymer processing; melt and electrospinning; biomaterials; surface modification
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Dr. Kevin Hart

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Department of Mechanical Engineering, Milwaukee School of Engineering, S-229 Allen Bradley Hall of Science, 432 E Kilbourn Ave, Milwaukee, WI 53202, USA
Interests: additive manufacturing; polymer composites; multi-functional materials
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Special Issue Information

Dear Colleagues,

The applications of additive manufacturing (AM), or the layer-by-layer building process, are extensive. Pre-production models, end-use automotive parts, art and medical implants are some of the areas in which AM parts are being used. While AM offers many advantages over traditional manufacturing, several disadvantages including slow build rates, poor mechanical properties for plastic parts in particular, and a lack of industry standards for testing and evaluating the limits of the widespread use of the technology. New methods for processing and post-processing and new materials are needed to improve the quality of 3D-printed parts and the range of mechanical properties achievable. This Special Issue focuses on polymer-based additive manufacturing techniques such fused filament fabrication, selective laser sintering, vat polymerization, material jetting and paste extrusion. In particular, it is aimed at publishing cutting-edge original research and review papers on the latest advances in new materials and approaches in polymer additive manufacturing. The topic themes include polymer AM feedstock development, composite and complex feedstocks, multi-material printing, in-situ and post-processing techniques to improve polymer welding/part strength, structure–property relationships, new approaches/technologies for 3D-printing polymers, characterization techniques, and process modeling.

Dr. Nicole Zander
Dr. Kevin Hart
Guest Editors

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Keywords

additive manufacturing
3D printing
polymers
feedstocks
process modeling
technologies

Published Papers (7 papers)

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Research

26 pages, 5544 KiB

Open AccessArticle

Superior Properties through Feedstock Development for Vat Photopolymerization Additive Manufacturing of High-Performance Biobased Feedstocks

by Anthony M. Clay, Joshua R. Mitchell, Zachary R. Boelter and John J. La Scala

Materials 2021, 14(17), 4843; https://doi.org/10.3390/ma14174843 - 26 Aug 2021

Cited by 2 | Viewed by 2431

Abstract

Vat photopolymerization additive manufacturing (Vat AM) technologies have found niche industrial use being able to produce personalized parts in moderate quantity. However, Vat AM lacks in its ability to produce parts of satisfactory thermal and mechanical properties for structural applications. The purpose of this investigation was to develop high-performance resins with glass transition temperatures (Tg) above 200 °C for Vat AM, evaluate the properties of the produced thermosets and establish a structure–property relationship of the thermosets produced. Herein, we have developed SLA-type resins that feature bio-derived monomer hesperetin trimethacrylate (HTM) synthesized from the flavonone hesperetin. Diluents 4-acryloyl morpholine, styrene, 4-methyl styrene and 4-tert butylstyrene (tbutylsty) were photocured with HTM as the monomer and all produced thermosets with Tg values above 200 °C. Investigations of suitable crosslinkers urethane dimethacrylate, the vinyl ester CN 151 and Ebecryl 4859 (Eb4859) showed that each crosslinker displayed different benefits when formulated with HTM as the monomer and tbutylSty as the diluent (HTM:crosslinker:tbutylSty with mass ratio 2:1:2). The crosslinker CN 151 produced the thermoset of greatest onset of thermal decomposition temperature (T₀) of 352 °C. Eb4859 produced the thermoset of highest tensile strength, 19 ± 7 MPa, amongst the set of varied crosslinkers. The formulation featuring UDM (HTM:UDM:tbutysty) offered ease of processing and was seemingly the easiest to print. Investigations of reactive diluent showed that styrene produced the thermoset of the highest extent of cure and the overall highest tensile strength, 25 ± 5 MPa, while tbutylSty produced the thermoset with the greatest Tan-δ Tg, 231 °C. HTM was synthesized, formulated with diluents, crosslinkers and initiators. The HTM resins were then 3D printed to produce thermosets of Tg values greater than 200 °C. The polymer properties were evaluated and a structure–reactivity relationship was discussed. Full article

(This article belongs to the Special Issue New Materials and Approaches in Polymer Additive Manufacturing)

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19 pages, 8550 KiB

Open AccessFeature PaperArticle

Design of Shape Memory Thermoplastic Material Systems for FDM-Type Additive Manufacturing

by Paulina A. Quiñonez, Leticia Ugarte-Sanchez, Diego Bermudez, Paulina Chinolla, Rhyan Dueck, Truman J. Cavender-Word and David A. Roberson

Materials 2021, 14(15), 4254; https://doi.org/10.3390/ma14154254 - 30 Jul 2021

Cited by 15 | Viewed by 2538

Abstract

The work presented here describes a paradigm for the design of materials for additive manufacturing platforms based on taking advantage of unique physical properties imparted upon the material by the fabrication process. We sought to further investigate past work with binary shape memory polymer blends, which indicated that phase texturization caused by the fused filament fabrication (FFF) process enhanced shape memory properties. In this work, two multi-constituent shape memory polymer systems were developed where the miscibility parameter was the guide in material selection. A comparison with injection molded specimens was also carried out to further investigate the ability of the FFF process to enable enhanced shape memory characteristics as compared to other manufacturing methods. It was found that blend combinations with more closely matching miscibility parameters were more apt at yielding reliable shape memory polymer systems. However, when miscibility parameters differed, a pathway towards the creation of shape memory polymer systems capable of maintaining more than one temporary shape at a time was potentially realized. Additional aspects related to impact modifying of rigid thermoplastics as well as thermomechanical processing on induced crystallinity are also explored. Overall, this work serves as another example in the advancement of additive manufacturing via materials development. Full article

(This article belongs to the Special Issue New Materials and Approaches in Polymer Additive Manufacturing)

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13 pages, 4535 KiB

Open AccessArticle

Porosity Reducing Processing Stages of Additive Manufactured Molding (AMM) for Closed-Mold Composite Fabrication

by Marquese Pollard, Phong Tran and Tarik Dickens

Materials 2020, 13(23), 5328; https://doi.org/10.3390/ma13235328 - 24 Nov 2020

Cited by 2 | Viewed by 2099

Abstract

This article aims to merge two evolving technologies, namely additive manufacturing and composite manufacturing, to achieve the production of high-quality and low-cost composite structures utilizing additive manufacturing molding technology. This work studied additive manufacturing processing parameters at various processing stages on final printed part performance, specifically how altering featured wall thickness and layer height combine to affect final porosity. Results showed that reducing the layer height yielded a 90% improvement in pristine porosity reduction. Optimal processing parameters were combined and utilized to design and print a closed additive manufacturing molding tool to demonstrate flexible composite manufacturing by fabricating a composite laminate. Non-destructive and destructive methods were used to analyze the composite structures. Compared to the well-established composite manufacturing processes of hand lay-up and vacuum-assisted resin transfer molding methods, additive manufacturing molding composites were shown to have comparable material strength properties. Full article

(This article belongs to the Special Issue New Materials and Approaches in Polymer Additive Manufacturing)

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16 pages, 4781 KiB

Open AccessArticle

Effects of Environmental Temperature and Humidity on the Geometry and Strength of Polycarbonate Specimens Prepared by Fused Filament Fabrication

by Lichen Fang, Yishu Yan, Ojaswi Agarwal, Shengyu Yao, Jonathan E. Seppala and Sung Hoon Kang

Materials 2020, 13(19), 4414; https://doi.org/10.3390/ma13194414 - 3 Oct 2020

Cited by 26 | Viewed by 3571

Abstract

It is widely known that the printing quality of fused filament fabrication (FFF) is heavily affected by environmental temperature and humidity, taking the form of warping and porosity. However, there is little understanding about the quantitative relations between environmental conditions, geometry, and the mechanical properties of printed parts. In this study, we systematically investigated those relations using bisphenol A polycarbonate as a model material system. For the environmental temperature, an in-situ infrared imaging analysis revealed the presence of an up to 5.4 °C/mm thermal gradient when printing using an open-chamber printer and a heated build plate. For the environmental humidity, an analysis of X-ray micro-computed tomography (micro-CT) scans showed an up to 11.7% porosity that was brought by polymer water content absorbed from environmental moisture. Meanwhile, tensile tests showed a mechanical performance loss associated with those defects, but, surprisingly, the transverse direction ductility had the potential to increase at a higher porosity. Furthermore, the experimental results were combined with analytical and parametrical studies to elucidate quantitative relations between environmental conditions and printing quality. Based on the results, quantitative guidelines for the estimation of printing quality based on environmental conditions are provided that would also help users to obtain desired printing results with a better understanding of the effects of environmental conditions. Full article

(This article belongs to the Special Issue New Materials and Approaches in Polymer Additive Manufacturing)

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18 pages, 7777 KiB

Open AccessFeature PaperArticle

Post-Process Effects of Isothermal Annealing and Initially Applied Static Uniaxial Loading on the Ultimate Tensile Strength of Fused Filament Fabrication Parts

by Rhugdhrivya Rane, Akhilesh Kulkarni, Hardikkumar Prajapati, Robert Taylor, Ankur Jain and Victoria Chen

Materials 2020, 13(2), 352; https://doi.org/10.3390/ma13020352 - 12 Jan 2020

Cited by 22 | Viewed by 4438

Abstract

Fused filament fabrication (FFF) is one of the most popular additive manufacturing (AM) techniques used to fabricate polymeric structures. However, these polymeric structures suffer from an inherent deficiency of weak inter-laminar tensile strength. Because of this weak inter-laminar strength, these parts fail prematurely and exhibit only a fraction of the mechanical properties of those fabricated using conventional means. In this paper, we study the effect of thermal annealing in the presence of an initially applied static uniaxial load on the ultimate tensile strength of parts fabricated using FFF. Tensile specimens or dogbones were fabricated from an acrylonitrile butadiene styrene (ABS) filament with a glass transition temperature (T_g) of 105 °C; these specimens were then isothermally annealed, post manufacture, in a fixture across a given range of temperatures and static loads. Tensile testing was then performed on these specimens to gauge the effect of the thermal annealing and static loading on inter-laminar tensile strength by measuring the ultimate tensile strength of the specimens. A design of experiments (DOE) approach was followed to calculate the main and interaction effects of the two factors (temperature and static loading) on the ultimate tensile strength, and an analysis of variance was conducted. Cross-sectional images of the specimens were studied to observe the changes in the mesostructure of the specimens that led to the increase in inter-laminar strength of the parts. The results show that temperature plays a dominant role in increasing the ultimate tensile strength and an 89% increase in the average ultimate tensile strength was seen corresponding to an annealing temperature of 160 °C. A change in the mesostructure of the parts is seen, which is characterized by an increase in bond length and void coalescence. These results can be helpful in studying the structural strength of 3D printed parts, and thus could eventually guide the fabrication of components with strength comparable to those of conventional manufacturing techniques. Full article

(This article belongs to the Special Issue New Materials and Approaches in Polymer Additive Manufacturing)

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24 pages, 5935 KiB

Open AccessArticle

Evaluating the Quality Surface Performance of Additive Manufacturing Systems: Methodology and a Material Jetting Case Study

by Razvan Udroiu, Ion Cristian Braga and Anisor Nedelcu

Materials 2019, 12(6), 995; https://doi.org/10.3390/ma12060995 - 26 Mar 2019

Cited by 59 | Viewed by 7083

Abstract

The performance characterization of the manufacturing processes for additive manufacturing (AM) systems is a significant task for their standardization and implementation in the industry. Also, there is a large diversity of materials used in different AM processes. In the present paper, a methodology is proposed to evaluate, in different directions, the performance of an AM process and material characterization in terms of surface quality. This methodology consists of eight steps, based on a new surface inspection artifact and basic artifact orientations. The proposed artifact with several design configurations fits different AM systems sizes and meets the needs of customers. The effects of main factors on the surface roughness of up-facing platens of the artifacts are investigated using the statistical design of experiments. The proposed methodology is validated by a case study focused on PolyJet material jetting technology. Samples are manufactured of photopolymer resins and post-processed. Three factors (i.e., artifact orientation, platen orientation, and finish type) are considered for the investigation. The case study results show that the platen orientation, finish type, and their interaction have a significant influence on the surface roughness (Ra). The best Ra roughness results were obtained for the glossy finish type in the range of 0.5–4 μm. Full article

(This article belongs to the Special Issue New Materials and Approaches in Polymer Additive Manufacturing)

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12 pages, 3486 KiB

Open AccessArticle

Hydrostatic High-Pressure Post-Processing of Specimens Fabricated by DLP, SLA, and FDM: An Alternative for the Sterilization of Polymer-Based Biomedical Devices

by José A. Robles Linares-Alvelais, J. Obedt Figueroa-Cavazos, C. Chuck-Hernandez, Hector R. Siller, Ciro A. Rodríguez and J. Israel Martínez-López

Materials 2018, 11(12), 2540; https://doi.org/10.3390/ma11122540 - 13 Dec 2018

Cited by 23 | Viewed by 6632

Abstract

In this work, we assess the effects of sterilization in materials manufactured using additive manufacturing by employing a sterilization technique used in the food industry. To estimate the feasibility of the hydrostatic high-pressure (HHP) sterilization of biomedical devices, we have evaluated the mechanical properties of specimens produced by commercial 3D printers. Evaluations of the potential advantages and drawbacks of Fused Deposition Modeling (FDM), Digital Light Processing (DLP) technology, and Stereolithography (SLA) were considered for this study due to their widespread availability. Changes in mechanical properties due to the proposed sterilization technique were compared to values derived from the standardized autoclaving methodology. Enhancement of the mechanical properties of samples treated with Hydrostatic high-pressure processing enhanced mechanical properties, with a 30.30% increase in the tensile modulus and a 26.36% increase in the ultimate tensile strength. While traditional autoclaving was shown to systematically reduce the mechanical properties of the materials employed and damages and deformation on the surfaces were observed, HHP offered an alternative for sterilization without employing heat. These results suggest that while forgoing high-temperature for sanitization, HHP processing can be employed to take advantage of the flexibility of additive manufacturing technologies for manufacturing implants, instruments, and other devices. Full article

(This article belongs to the Special Issue New Materials and Approaches in Polymer Additive Manufacturing)

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