Publications

This report documents a cross-site effort to identify and evaluate materials that are suitable replacements for the polyurethanes known as EN-7 and EN-8. EN-7 and EN-8 are commercial formulations that contain free toluene diisocyanate (TDI) and which are used as adhesives and as encapsulants in many weapon applications. TDI is an OSHA-regulated volatile diisocyanate and has been targeted for elimination from future weapons use, prompting the need for a TDI-free replacement material.

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Additive manufacturing (AM) is a relatively new technological advancement that allows for rapid prototyping, development of intricate shapes, and reduction in manufacturing time. The materials of interest for this project are Ultem 1010, ABS M30, FDM Nylon 12, PC, and PPSF. However, little is known regarding the aging behavior of these AM materials. The limited aging study outlined herein was designed to compare the chemical, physical, and mechanical properties of AM parts as they experience accelerated aging at 70 °C for a total of 24 weeks. In general, ABS M30 stood out as it appeared to undergo chemical and physical changes leading to increase in density and an overall more brittle material, making this commonly used material not attractive for long-term use.

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A copolymer of maleic anhydride and styrene is functionalized with Diels–Alder (DA) capable pendant groups to enable the study of this material with different crosslink densities. This constituent is synthesized using commercially available starting materials and relatively simple and uncomplicated chemistries which open the possibility for its use in large-scale applications. The 10%, 25%, 50%, and 100% DA nominal crosslinking based on available pendant furan groups on the polymeric component is investigated. The reaction kinetics are monitored using infrared spectroscopy and rheology. Based on the rheological results, carbon nanotube (CNT) incorporation into the DA matrix is explored in order to determine its effects on the complex modulus of the material. This work is meant as a proof of concept for this DA material with the possibility of its incorporation into other commonly used bulk materials and/or adhesives to allow for an easily reversible product formulation.

The moisture absorption behavior of two fiber reinforced composite materials was evaluated in a unidirectional manner The flat materials were exposed to varying humidity and temperature conditions inside of an environmental chamber in order to determine their effective moisture equilibrium (M m ) and moisture absorption rate (D z ). Two-ply (thin) and four-ply (thick) materials were utilized to obtain M,,, and Dz, respectively. The results obtained from laboratory work were then compared to modeling data to better understand the material properties. Predictions capabilities were built to forecast the maximum moisture content, time required for saturation, and the moisture content at any given humidity and temperature. A case study was included to demonstrate this capability. Also of interest were cubed samples to investigate directionality preferences in water immersion studies. Several coatings were evaluated for their water permeation properties. Further dissemination authorized to the Department of Energy and DOE contractors only; other requests shall be approved by the originating facility or higher DOE programmatic authority.

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A report meant to document the chemistries investigated by the author for covalent surface modification of CNTs. Oxidation, cycloaddition, and radical reactions were explored to determine their success at covalently altering the CNT surface. Characterization through infrared spectroscopy, Raman spectroscopy, and thermo gravimetric analysis was performed in order to determine the success of the chemistries employed. This report is not exhaustive and was performed for CNT surface modification exploration as it pertains to the "Next Gen" project.

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