Purpose
This paper aims to investigate the deposited structure and mechanical performance of printed materials obtained during initial development of the Big Area Additive Manufacturing (BAAM) system at Oak Ridge National Laboratory. Issues unique to large-scale polymer deposition are identified and presented to reduce the learning curve for the development of similar systems.
Design/methodology/approach
Although the BAAM’s individual extruded bead is 10-20× larger (∼9 mm) than the typical small-scale systems, the overall characteristics of the deposited material are very similar. This study relates the structure of BAAM materials to the material composition, deposition parameters and resulting mechanical performance.
Findings
Materials investigated during initial trials are suitable for stiffness-limited applications. The strength of printed materials can be significantly reduced by voids and imperfect fusion between layers. Deposited material was found to have voids between adjacent beads and micro-porosity within a given bead. Failure generally occurs at interfaces between adjacent beads and successive layers, indicating imperfect contact area and polymer fusion.
Practical implications
The incorporation of second-phase reinforcement in printed materials can significantly improve stiffness but can result in notable anisotropy that needs to be accounted for in the design of BAAM-printed structures.
Originality/value
This initial evaluation of BAAM-deposited structures and mechanical performance will guide the current research effort for improving interlaminar strength and process control.
The
current severe acute respiratory syndrome coronavirus 2 (SARS-COV-2)
pandemic has highlighted the need for personal protective equipment,
specifically filtering facepiece respirators like N95 masks. While
it is common knowledge that polypropylene (PP) is the industry standard
material for filtration media, trial and error is often required to
identify suitable commercial precursors for filtration media production.
This work aims to identify differences between several commercial
grades of PP and demonstrate the development of N95 filtration media
with the intent that the industry partners can pivot and help address
N95 shortages. Three commercial grades of high melt flow index PP
were melt blown at Oak Ridge National Laboratory and broadly characterized
by several methods including differential scanning calorimetry (DSC),
X-ray diffraction (XRD), and neutron scattering. Despite the apparent
similarities (high melt flow and isotacticity) between PP feedstocks,
the application of corona charging and charge enhancing additives
improve each material to widely varying degrees. From the analysis
performed here, the most differentiating factor appears to be related
to crystallization of the polymer and the resulting electret formation.
Materials with higher crystallization onset temperatures, slower crystallization
rates, and larger number of crystallites form a stronger electret
and are more effective at filtration.
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