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
Large-scale extrusion-based 3D printing for highway culvert rehabilitation
A significant problem associated with repairing deteriorating highway culverts is the resultant lowered flow capacity. This can be mitigated by the use of culvert diffusers. Current culvert diffusers are made using fiberglass reinforced thermosetting epoxy polymers, which require custom made molds. This research work explores the use of large-scale 3D printed thermoplastic polymer composite to manufacture culvert diffusers. The research work shows that 3D printing technology reduces the manufacturing time as well as the cost of culvert diffusers. Large-scale 3D printing technology is well-suited for the manufacture of individualized culvert diffusers with unique geometrical designs without the need for molds. 3D printing technology is also capable of using different materials according to environmental requirements. The use of segmental manufacturing in conjunction with large-scale 3D printing enables the manufacturing of culvert diffusers larger than the build envelope of the 3D printer. Different post-processing techniques used for cutting, finishing, and joining the 3D printed segments are discussed.
Investigation and Realization of Watertight FDM Structures Made of Ultem 9085 in Pressurized Systems
Fused Deposition Modeling (FDM) parts generally show a fluid permeability due to their specific and characteristic strand structure. Therefore, an application including contact with water is difficult and limits the areas of application of this Additive Manufacturing (AM) technology. In this paper the aim is to determine the water tightness of FDM manufactured Ultem 9085 structures in a pressurized system using a suitable test setup. Based on the results, optimization approaches such as parameter modification, variation of the specific part thickness and a surface treatment shall identify if a complete tightness can be realized. For the validation of the results, analysis methods such as CT-scans and macroscopic images are used to determine the component surface.
Effect of Carbon Fiber On the Fracture Toughness of Fused Filament Fabricated CF/ABS Composites
This study reports the effect of carbon fiber (CF) on the fracture toughness of 3D printed carbon fiber/ acrylonitrile butadiene styrene (CF/ABS) composites. Chopped carbon fiber was compounded with ABS to prepare CF/ABS filaments containing 0-25 wt.% CF. Compact tension specimens were designed, 3D printed, and tested to measure the composites’ mode-I fracture toughness, KIc. The results showed CF/ABS composites can be made with up to 25 wt.% loading without any drop in their fracture toughness. In fact, ABS’s KIc increased by ~22% with an introduction of 10 wt.% CF. There was a slight drop in KIc, once the CF content was increased to 15 wt.%. Further increase in CF content from 15 to 25 wt.% did not cause any significant change in KIc and it was found to remain similar to that of the neat ABS. The fracture toughness trend with CF content was qualitatively explained in terms of two competing mechanisms, namely increased actual fracture surface area and less perfect interlayer adhesion at the presence of CFs.
Enabling Mechanically Adaptive 4D-Printing with Cellulose Nanocrystals
Additive manufacturing of stimuli-responsive materials is an area of 4D-printing that is continuing to gain interest. Cellulose nanocrystal (CNC) thermoplastic nanocomposites have been demonstrated as a water responsive, mechanically adaptive material that has promise to generate 4D-printed structures. In this study, a 10wt% CNC thermoplastic polyurethane (TPU) nanocomposite is produced through a masterbatching process and printed using fused filament fabrication (FFF). A design of experiments (DOE) was implemented to establish a processing window to highlight the effects of thermal energy input on printed part mechanical adaptivity (dry vs. wet storage modulus). The combination of high temperatures and low speeds result in thermal energies that induce significant degradation of the CNC/TPU network and reduced absolute values of storage moduli, but the mechanical adaptation persisted for all the printed samples.
Characterization of polypropylene/hydrocarbon resin blends for 3D printing
Additive manufacturing (AM) of polyolefins, such as polypropylene (PP), employing filament-based material extrusion (MatEx) has gained significant research interest in recent years. The semicrystalline nature of PP makes it challenging to process using MatEx. The addition of amorphous low molecular weight hydrocarbon resins into PP matrix was found to delay the onset of crystallization of the blends. The slow crystallization behavior, as evident by the increased crystallization half-times, aided the relaxation of residual stresses during MatEx of PP blends that resulted in manufactured parts with reduced warpage. Rheological characterizations were performed on the PP blends revealing the shear-thinning nature. The combined interaction among crystallization rates, timescales, and morphology was found to affect the interlayer welding process during MatEx. Mild thermal annealing of the manufactured parts resulted in mechanical properties which approach that of injection molded parts.
Machine Learning and Data-Driven Additive Manufacturing
Additive manufacturing has emerged as a disruptive digital manufacturing technology. However, its wild adoption in the industry is still impacted by high entry challenges of design for additive manufacturing, limited materials library, processing defects, and inconsistent product quality. Machine learning has recently gained increasing attention in additive manufacturing due to its exceptional data analysis performance, such as classification, regression, and clustering. This paper provides a review of the state-of-the-art machine learning applications in different domains of additive manufacturing.
Effects of Steam Heat and Dry Heat Sterilization Processes on Polylactic Acid with Hydroxyapatite Composite Printed by FFF
3D printing is used for various medical applications, such as the manufacture of guides for surgical operations, custom medical instruments, and low-cost medical applications. In few of these studies that have been performed, the effect of sterilization on these parts has not been considered yet. The fused filament fabrication process (FFF), which is the most widely used today, is used for the making of these guides and instruments. One of the most used materials in the FFF process is polylactic acid (PLA) due to its ease of printing, however, this could be degraded with the sterilization processes by steam heat and dry heat and lose its dimensional accuracy and resistance, something required for medical applications. The purpose of this study is to determine the effects of the steam heat and dry heat sterilization processes on the mixture of PLA and hydroxyapatite (HA) to check whether this mixture can be used in medical applications that are not implantable in the human body. The percentage by weight of hydroxyapatite used is 5%. To study the effect of sterilization processes already mentioned, 3D specimens were printed for flexural, tensile, Shore Hardness and impact mechanical tests. Thermogravimetric analysis (TGA), Differential scanning calorimetry (DSC) and Dynamic mechanical thermal analysis (DMTA) tests were also performed. It is concluded that the blend of PLA and hydroxyapatite increases its resistance to temperature but decreases its mechanical characteristics.
Shear Induced Crystallization Through Altering Polymer Melt Flow Area
A novel additive manufacturing technique has been developed in the Manufacturing Science Laboratory at Lehigh University.The technique utilizes an extrusion based 3D printer, which has the ability to regulate the areaof the polymer flow inside the extrusion head, thus, allowing precise control over shear rate applied to polymer melt. The controlled shear alters the melt rheology, which in turn controls the evolution of crystallinity in the printed parts. The temporal control of shear translates to spatial control of melt rheology. Thus, the localized evolution of molecular orientation and nucleation/crystallization kinetics as well as the mechanical and optical properties can be precisely controlled during the additive manufacturing process. In this research, a semi crystalline poly-lactic acid (PLA)was utilized to validate the developed technique of controlling the shear rate while printing. The confinement will induce shear on the polymer the degree of which can be controlled by the gap between the conical cavity and theconical extruder tip. The analytical modeling results indicate that this strategy can increase the induced shear rate. Preliminary experimental analysis validated an increase incrystallinity percentage up to 16%.
Fiber Orientation Measurements for Large Additive Manufactured Parts Using Optical and SEM Imaging
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
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
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
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
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
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
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
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
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
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
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
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.
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