Mechanical Properties of Polyethylene Containing Defunctionalized Single Wall Carbon Nanotubes
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Mechanical Properties of Polyethylene Containing Defunctionalized Single Wall Carbon Nanotubes Meisha L. Shofner1, Haiqing Peng2, Zhenning Gu2, Valery N. Khabashesku2, John L. Margrave2, and Enrique V. Barrera1 1 Department of Mechanical Engineering and Materials Science, Rice University, Houston, TX 77005, U.S.A 2 Department of Chemistry and Center for Nanoscale Science and Technology, Rice University, Houston, TX 77005, U.S.A. ABSTRACT To take advantage of the benefits of chemical functionalization and the desirable properties of unfunctionalized SWNTs, this research studies the effect of removing functional groups from SWNTs dispersed in a polymer matrix. Chemical functionalization of single wall carbon nanotubes (SWNTs) is a method for disrupting rope structure and adding reactive species to the nanotube to improve interfacial bonding and load transfer in composites, but changes to the nanotube hexagon structure caused by chemical modifications are expected to have a detrimental effect on the SWNTs’ intrinsic mechanical properties. Thus, composites containing defunctionalized SWNTs and polyethylene are analyzed to evaluate the effect of functional group removal on the mechanical properties. The mechanical properties are measured using tensile tests. Issues of defects in the SWNT structure, polymer degradation, and changes in the fiber/matrix bonding as a result of functionalization removal are studied using Raman spectroscopy, thermogravimetric analysis, infrared spectroscopy, and dynamic mechanical analysis. INTRODUCTION Single wall carbon nanotubes (SWNTs) are desirable reinforcements for polymer matrix composites because of their exceptional multifunctional properties [1-3]. However, the structure that endows these properties also possesses few defects and causes individual SWNTs to aggregate into larger ordered structures known as ropes. These two features limit bonding and load transfer between SWNTs and host polymer matrices. Chemical functionalization handles both of these issues by creating reactive sites and disrupting the rope structure, and it is expected to reduce the intrinsic SWNT properties by perturbing the structure. This paper uses functionalization as a temporary fiber treatment to aid processing and investigates the subsequent removal of fluorine functional groups on the nanotube sidewall with respect to changes to mechanical properties of a SWNT/high density polyethylene (HDPE) composite. Composites containing purified (P-SWNTs) and fluorinated (F-SWNTs) SWNTs and neat HDPE are processed by conventional polymer processing techniques and heat treated remove the functionalization. Fluorination is used as the functionalization technique because it is capable of producing gram-size quantities of functionalized nanotubes, it is reversible, and it successfully breaks up large ropes [4, 5]. Also, the thermal decomposition pattern of F-SWNTs in polyethylene provides an opportunity for direct bonding between the nanotube and polymer through the evolution of HF formed when liberated fluorine
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