Mechanical Properties of Carbon Nanotube Reinforced Polycarbonate at Cryogenic Temperature
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Mechanical Properties of Carbon Nanotube Reinforced Polycarbonate at Cryogenic Temperature Anita Oliver, Abdallah L. Mbaruku, and Justin Schwartz Department of Mechanical Engineering, FAMU-FSU College of Engineering, 2525 Pottsdamer, Tallahassee, FL, 32310 ABSTRACT Carbon nanotube (CNT) reinforced polymers are of high interest for various industries due to their unique mechanical and electrical properties. Most research has been done at room temperature (RT), but little is known about properties at cryogenic temperature. This paper presents results on CNT-polycarbonate (PC) composites with respect to mechanical properties at 77 K in comparison with RT. CNT-PC composites with 0wt% (neat), 0.1wt%, and 1.0wt% CNTs have been studied. Results imply that the CNT effects are more obvious at low temperature and are seen in the form of serrations in the stress-strain plot. No significant difference has been noticed between the neat and reinforced samples at either temperature. However, it was determined that the strength increases drastically while the elongation decreases at low temperature as compared to RT. SEM images confirm that the samples at low temperature exhibit brittle failure. Additionally, it can be seen that at low temperature the nanotubes align with the direction of tensile force while the nanotubes at RT align with the sample surface. INTRODUCTION The development of polymer-matrix carbon nanotube (CNT) composites has progressed rapidly over the past few years, taking advantage of the mechanical and physical properties of single wall (SW) and multiwall (MW) CNTs. While the literature characterizing CNTs is expanding rapidly [1, 2], there is an absence of data on their cryogenic mechanical properties. This is in part because of the difficulties associated with mechanical measurements on individual tubes compounded with the difficulties associated with cryogenic measurements. Here we report on the effects of low temperature (77 K) on the mechanical properties of composite forms. Specifically, a polycarbonate (PC) matrix is reinforced with multiwalled CNTs. Mechanical testing is performed in a linear tensile testing device [3] with displacement and load transducers calibrated at each measurement temperature as well as a thermocouple for temperature measurement. Fracture surfaces are studied using scanning electron microscopy (SEM) after mechanical testing. SAMPLE PREPARATION Samples used for mechanical testing are prepared by collaborators at Rensselaer Polytechnic Institute [4]. MWNT's are grown via Thermal Chemical Vapor Deposition using a Ferrocene – Xylene system. Typically, these CNTs exhibit an average diameter of ~ 65nm and an average length of ~ 600µm. The CNTs are scraped off of the substrate and melt mixed with the raw PC pellets for 10 minutes at 250°C using a Thermo-Haake twin-screw mixer. The composite is then retrieved from the mixer and chopped into pieces. About 0.7 g of these chopped pieces per sample are compression molded for 10 minutes at 250°C under roughly 4 metric tons. The m
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