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The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.

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Additive Manufacturing & 3D Printing

Fiber Orientation Measurements for Large Additive Manufactured Parts Using Optical and SEM Imaging
Rifat Ara Nargis | David A. Jack, April 2021

Acrylonitrile Butadiene Styrene (ABS) is widely used in additive manufactured part production due to its widespread availability and ease of manufacturing, but unfortunately its structural and thermal performance limits its use in industrial applications. The addition of fiber reinforcements, specially chopped carbon fiber to the ABS matrix has the potential to enhance its structural performance while simultaneously reducing dimensional variations during thermal changes. The quantification of the fiber orientation in the processed ABS bead is important to understand its correlation to the mechanical and structural properties of the processed thermoplastic. This study presents the sample preparation and acquisition of images of fiber orientation and void measurements through optical and scanning electron microscopy of an additive manufactured bead with 13% by weight carbon fiber reinforced ABS. The images are then analyzed, and the fiber orientation is measured using the method of ellipses. The method of ellipses poses a problem of ambiguity for the direction of fiber orientation. With the SEM images the ambiguity problem can be solved using an electrical shadowing technique and the orientation of the fibers in the ABS matrix can be determined. The results for the orientation from the two methods are contrasted, and a discussion is provided on the impact the fiber orientation has on the final part performance. The results also indicate the presence of voids caused by the deposition process that is unique to the currently employed additive manufacturing process which will hamper the final part performance.

3D Printing Sustainable Biocomposites From Recycled PLA and Micro-Crystalline Cellulose
Akhilesh K. Pal | Erick O. Cisneros-López | Arturo U-Rodriguez | Feng Wu | Manjusri Misra | Deborah F. Mielewski | Alper Kiziltas | Amar K. Mohanty, April 2021

The motivation for this work was to increase the economic life of recycled poly(lactic acid) (rPLA) (30 wt%) by utilizing it with virgin PLA (70 wt%) in the presence of a fiber-based reinforcing filler, micro-crystalline cellulose (MCC) and an epoxy-based chain extender. A conventional melt extrusion technique was used to fabricate the strands with and without MCC and chain extender in the PLA/rPLA blend matrix. It was observed that the complex viscosity of rPLA was improved significantly after the addition of the chain extender, which resolved the issue related to excessive polymer flow during processing and hence made it possible for use in fused deposition modeling (FDM)-based 3D printing. The addition of the chain extender improved the impact strength of 3D the printed PLA/rPLA specimens. The voids in the 3D printed material contributed to the reduced weight of the developed sustainable composites. The modulus and tensile strength of the 3D printed sustainable biocomposites were improved significantly, and impact strength increased by ~10% by reinforcing the blended matrix with 5% of MCC.

Developing Photopolymerizable Acrylate Resin Formulation for Impact Modified 3D Printed Thermosets
Chinmay Saraf | Amy Niu | Alan J. Lesser,, April 2021

This contribution focuses on engineering photopolymerizable acrylate resin formulations for a superior fracture energy absorption of 3D printed acrylate thermosets. Herein, we report a polydimethyl siloxane-based block copolymer as an impact modifier, compatible with the UV curing process, which undergoes reaction induced phase-separation during the 3D printing process to form a rubbery phase sufficient for enhanced impact properties. A systematic investigation of the effect of concentration of the impact modifier on the morphology of rubbery domains and fracture toughness was conducted. Results show that at an optimum concentration of 15 wt.% and particle size of 57 nm, an order of magnitude improvement in the fracture energy release rate is realized. Fractographic analysis of the impact modified thermosets using optical microscopy indicates the presence of significant plastic deformation in an otherwise brittle material. Notably, the engineered acrylate thermosets, at an optimum concentration, exhibit similar improvements in the impact properties irrespective to the print layer thickness and independent of the crack orientation with respect to the printed interphase. Detailed investigation of the failure mechanisms for impact modified thermosets show that the block copolymer diffuses to the interphase during the 3D printing process, resulting in preferential localization of the impact modifier near the print interphase resulting in an isotropic enhancement of the fracture toughness.

Comparative Study of Filled and Unfilled PLA Produced Via Injection Molding and 3D Printing
Chethan Savandaiah | Bernhard Plank | Julia Maurer | Juergen Lesslhumer | Georg Steinbichler |, April 2021

This study investigates the impact of two different processing methods, Injection molding (IM) and 3D printing (3Dp), on Neat/unfilled polylactic acid (NPLA) and the short carbon fibers (SCFs) filled polylactic acid (SPLA). Furthermore, the resulting processing conditions and its influence on mechanical properties, such as tensile, flexural, notched Charpy impact test, and heat deflection temperature (HDT) along with the process-induced effects, such as fiber length distribution and voids were studied. The process-induced voids were evident in all the computed tomography (CT) scans, 3Dp specimens have higher void volume fraction compared to no visible voids in IM specimens. Similarly, the mechanical test results such as tensile, flexural and notched Charpy impact test follow the trend for 3Dp SPLA and IM SPLA. On the contrary, 3Dp 0° and ±45° NPLA tensile test results are comparable to IM NPLA, whereas 3Dp 0° NPLA has the highest impact resistance compared to injection molded NPLA and SPLA as well as 3Dp SPLA specimens, indicating the annealing effect induced by the heated 3D printing bed along with increased void volume fraction. Furthermore, the HDT study indicates the maximum serviceable temperature of both NPLA and SPLA remained comparable regardless of the processing method. Moreover, the change in fiber length distribution for SPLA injection molded and extruded filament specimens were negligible.

3D Printed Hybrid Composite Structures - Design and Optimization of A Bike Saddle
Alec Redmann, May 2020

As designers and engineers continue to push the boundaries of high performance and lightweight design, the use of complex geometries and composite materials is growing. However, traditional composite manufacturing often requires the use of additional tooling and molds which can significantly increase the cost. In this study, a carbon fiber reinforced composite bike saddle is designed and manufactured to demonstrate a newly developed hybrid composite manufacturing process. Using a 3D printed epoxy to print the final part geometry and co-cure pre-impregnated carbon fiber reinforcement, the bike saddle can be optimized, designed and manufactured in less than 24 hours.

Compressibility In Fused Filament Fabrication
David Kazmer, May 2020

Fused filament fabrication (FFF) is one of the most accessible and flexible additive manufacturing processes. However, it is plagued by consistency issues related to material deposition. The role of compressibility is explored with an instrumented nozzle to relate the observed printing pressure to variations in deposited road widths. Variations in road width are analyzed relative to those predicted using a double domain Tait equation (PVT model) for high impact polystyrene (HIPS). Compressibility was found a critical effect, varying the road widths by up to 50% when accelerating and decelerating. The effect of the speed of transient stress propagation was also investigated but found insignificant.

Design and Evaluation of Bicomponent Core-Sheath Die for 3D Printer Filament Feedstock Co-extrusion
Rebecca Ruckdashel, May 2020

Carbon based or inorganic fillers in 3D filament can enhance properties of 3D printed parts and are attracting considerable interest from academic and industry researchers, such as MarkForge, BASF, ColorFabb, and Graphene 3D Lab. Although 3D-tailored composites have been developed, very little work has been done on the production of advanced 3D filament feedstock for FDM. Work is needed on biomedical application filaments which require (i) high filler or nanoparticle loading, (ii) dimensional accuracy and (iii) superior surface finish. Current FDM filaments rarely exceed filler concentration of 10%, for example, in case of calcium phosphate without sacrificing quality. In this work, a melt-spinning die was designed with 2D FEM flow simulations to minimize interfacial flow instabilities. With the die, a co-axial 3D feedstock filament up to 20% filler concentration was spun. Tensile bars were successfully printed with 15% filler content and had similar tensile properties to neat PLA.

Determination of Physical Properties of Fused Filament Fabrication Parts as Influenced by the Nozzle
Justin Limkaichong, May 2020

A design of experiments using different nozzle diameters with varying road heights and shear rates (based on print speed) was done using lab-made polylactic acid filament. Subsequent tensile testing and calculation was done to obtain the main responses of ultimate engineering stress and tensile modulus. Linear models were made to determine the significance between the different dependent and independent variables. The main results show that larger nozzles, shorter layer heights, and lower shear rates provide stronger, heavier and stiffer fused filament fabrication parts.

Development of An Agile, Battlefield Additive Manufacturing Plant For Recycled Pet
Prabhat Krishnaswamy, May 2020

The objective of the overall project is to conduct applied research that will lead to the development of an innovative agile manufacturing plant for onsite fabrication of recycled thermoplastic products at the US military’s forward operating bases (FOBs). The proposed manufacturing plant needs to be contained in 20-foot ISO containers for both shipment and operation. A study by the US Department of Defense (DoD) of base camp waste confirmed that the single largest source of waste plastics is Polyethylene Terephthalate (PET) from water and other beverage bottles. The on-going project to convert waste or reclaimed PET (rPET) to useful products is currently being conducted by Emc2 and the US Army Corps of Engineers and is being supported by the DoD’s Strategic Environmental Research and Development Program (SERDP) as a three year effort starting in June 2018.

Electro-Spun PVP (POLYVINYLPYRROLIDONE) Nanofibers: An Experimental Investigation
Utkarsh, May 2020

Electrospinning is a well-established and straightforward method of manufacturing nanofibers from different materials like polymers, ceramics, and metals. In the current study, Polyvinylpyrrolidone (PVP) nanofibers were produced using the electrospinning process. The process control parameters viz. polymer concentration, voltage, collecting drum rotational speed, flow rate and collecting distance were studied to obtain the minimum fiber diameter for sound absorption applications. The effects of these electrospinning parameters on morphology and diameter of fibers were investigated. The minimum fiber diameter was found to be regulated by two main parameters, i.e. polymer concentration and voltage applied that both had significant effects on fiber morphology. On the other hand, flow rate, rpm, and collecting distance had the least significant effects compared to the other two. This work offers a promising attempt in the open literature to carefully study the effect of electrospinning control parameters in PVP nanofiber fabrication.

Enhancement of Binding Matrix Stiffness In Composite Filament Co-Extrusion Additive Manufacturing
Chethan Savandaiah, May 2020

The Flexural modulus and strength are an intrinsic aspect of parts produced via dual matrix composite filament co-extrusion (CFC) based additive manufacturing. In this research work, the main objective is to optimize thermoplastic’s (TP) flexural properties by reinforcing it with particulate fillers for CFC printed parts. Accordingly, an effort has been made in this respect and neat Polyamide-6 (PA6) and its composite (PA6.CF) was chosen as a binding matrix for CFC flexural specimens. The PA6 binding matrix is reinforced with particulate carbon fibers (PCF). To improve the compatibility between the PCF and matrix, stearyl titanate coupling agent (1.5 wt. %) was utilized. Constraints such as defects and porosity are of critical attributes and play a vital role in defining the mechanical performance of the 3D printed parts. Herein, the printed specimens were subjected to a non-destructive testing method: micro-computed thermography (µ-CT). PA6 and reinforced PA6 specimen revealed similar porosity and defect volume. Furthermore, the three-point bending test results of 3D printed CFC composite with PA6.CF as a binding matrix showed approx. 46% increase in flexural stiffness and 27% increase in flexural strength when compared to CFC specimens printed with neat PA6 as a binding matrix. In addition, the cryo-fractured fractography of carbon composite filament, an epoxy-based thermo-cured continuous carbon fiber, revealed even distribution of carbon fibers with no visible voids.

Investigation of Glass Bubbles iM16K Polyamide 12 Composites for Selective Laser Sintering
James Klett, May 2020

Selective Laser Sintering is an additive manufacturing technique that has been increasingly exploited in small-batch production to supplement traditional polymer processing techniques. Integrating specialized additives with PA12 SLS powder allows for the production of parts with tailored properties. 3MTM Glass Bubbles iM16K offers the possibility to reduce SLS powder cost, reduce part weight, and improve mechanical performance. Both intrinsic and extrinsic properties and their effects on SLS processing have been investigated. Tensile testing revealed the average Young’s modulus could be improved by 30% at 5 wgt% loadings, while maintaining ultimate tensile strength.

Reliability Evaluation of Conductive Tracks Integrated Into Additively Manufactured Components
Kaja Schmidt, May 2020

The use of 3D printing technologies enhanced with component placement and electrical interconnect deposition can provide structural electronic systems with higher fabrication freedom. Thermosetting resins that are used as adhesives in electronic packaging processes have the potential to fulfill new requirements coming from this application. Their use as building and conductive materials in additive manufacturing can lead to advantages, especially when selecting the same chemical basis. In this work, an extrusion-based additive manufacturing process was used to process the adhesives. A basic concept is introduced how the integration of electrical components and conductive tracks can be realized with this process-material combination and experimental work on two-dimensional tracks is presented. The developed process and the material selection for 2D-tracks was evaluated electrically as well as mechanically and was supported by highly accelerated life tests to ensure reliable performance. Different aspects of the integration were covered with three experiments that provide an understanding of properties of conductive adhesives printed as a tracks as well as their contacting behavior on SMD components. First design rules are derived from these experiments that can serve as a first step for developing processes for three-dimensional tracks and the procedure of contacting a component within the printing process.

Simulation of a Saxton-Mixer in High-Performance Extruders Using the Immersed Boundary Method
Jochen Kettermann, May 2020

The Immersed Boundary Surface Method(IBS)is a novel and very promising implementation of the Immersed Boundary Method (IBM) for modeling complex, moving processes. In order to validate IBS for the first time in plastics processing, this paper deals with the numerical simulation of a Saxton-mixer in foam-extend (release of OpenFOAM)as a complex application geometry.The Saxton-mixer [1] is well suited for validation because it canstillbe solved using traditional simulationmethods, but is alreadycomplex enough to test andvalidate IBS within a real-worldprocessing environment. For this purpose, body-fitted andIBS simulations are performedin the same wayand their results compared. In addition, the mixing zone is also investigated experimentally in order to evaluate the model qualityof the simulations.The results of both simulation methods are consistent and differ only slightly. Thus, the implementation of IBS is valid. Furthermore, a comparison of the simulation model with experimentsreveals asignificant influence of the rheological flow model. The results of thenon-Newtonian IBS modelare already approaching the experiments well and are therefore promising results for further applicationsof IBSin plastics processing.

The Influence of Laser Power Variation on SLS-printed PA6 Parts and their Long-term Properties
Tobias Heckner, May 2020

In the field of Additive Manufacturing (AM), Selective Laser Sintering (SLS) is well-known as anAM technique to produce partswith comparatively high load capacity. The usage of Polyamide 6 (PA6) materials allowshigher continuous operating temperatures than Polyamide 12 (PA12) materials, which aretypicallyused forSLS. For this work,PA6 SLS specimens were printed with a high temperature SLS industry printer. The samples were aged thermo-oxidatively at different temperatures, tested mechanically and investigated with different analytical methods. The SLS processing of PA6 materials has not beenstudied sufficiently yet. The aim of this study was to deliver first contributions:the laser power energy wasvaried to identify the influence on the mechanical properties of the printed specimens andtheirlong-term properties. In addition, the material structure of the specimens wasinvestigated and the viscosity number (VN) was determined.

Understanding the Limitations of 3D Printed Polymers Through A Staged Screening Protocol
Jessica Hemond, May 2020

Direct printing of polymers has continued to advance with new printing technologies and engineering grade materials allowing actual additive manufacturing versus 3D printing of prototypes. Key developments include the adaptation of digital light processing (DLP) printers as well as improvements to and novel powder-based printing systems. These technologies offer the ability to bring new printed materials to the market. However, simply because a material can be printed does not mean that it will function well. With the number of printing and material advances, the need to understand possible failure modes and incorporate that knowledge into screening testing is critical. This work provides basic consideration and screening methodology to ensure that these possible material failure modes are accounted for.

Expanding the Impact of Polymeric-based 3D Printing Technologies
David A. Roberson | David Espalin | Ryan B. Wicker, June 2015

Over the past two decades, additive manufacturing (AM) technology has become fully ingrained into pop culture, with Do it Yourself (DIY) applications for the home, schools and other locations in addition to industrial applications for the aerospace, automotive, and biomedical industries. While AM can be used to fabricate objects from metals, polymers, and ceramics, polymeric materials are currently the most common. ASTM Standard F2792-12a describes techniques that can convert polymeric materials into useful products: 1) sheet lamination; 2) material extrusion; 3) vat photopolymerization; 4) powder bed fusion (with polymers); 5) binder jetting; and 6) material jetting. The automotive industry was an early adopter of 3D printing of polymeric materials, for example in the early 1990s a Japanese manufacturers used a commercialized vat photopolymerization process (widely known as stereolithography (SL)) to manufacture prototype door panels. More recently, an extrusion-based AM system was used on the International Space Station (ISS) .

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