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A high‐density polyethylene (HDPE) masterbatch containing 20.2 wt% multiwalled carbon nanotubes (MWNTs) was melt diluted with neat HDPE using two different methods: a twin screw microcompounder and a single‐screw extruder. The electrical properties of these composites were assessed using bulk electrical conductivity measurements, their mechanical properties were evaluated using tensile tests and dynamic mechanical analysis (DMA), and percent crystallinity was determined by wide angle x‐ray diffraction (WAXD) and differential scanning calorimetry (DSC). A percolation threshold (pc) of 4.5 wt% MWNTs was found in compression‐molded samples. Extruded samples were prepared with nanotube concentrations below and above the compression‐molded percolation threshold (2 and 7 wt% MWNTs) and passed through the extruder twice before entering a low‐shear melt annealing zone. Different melt annealing times were used and their effects on the electrical and mechanical properties of the resulting quench‐cooled composites were evaluated. Results showed that extruded composites were nonconductive, indicating that a conductive nanotube network did not form on the time scale of these experiments. Annealing time also did not affect significantly the mechanical properties of the resulting solid composites. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

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We report the development of a collaborative problem-based laboratory project that is designed for implementation at the end of the general chemistry series or at the beginning of organic chemistry. The objectives of this laboratory project are to separate a mixture of two metabolites, urea and cholesterol, and to determine the percent composition of the components of this mixture. In the first of two laboratory periods, students participate in small group discussions in which differences in polarity, and hence solubility, are addressed and used to devise a procedure for the separation and quantification of the metabolites. Procedures are then discussed as a class and further refined. The second laboratory period is dedicated to performing the separation and completed with melting point determination and collecting infrared (IR) spectra of the separated metabolites. This laboratory project provides a review of general chemistry concepts and an introduction to organic chemistry concepts while allowing students to learn experimental techniques (melting point determination, IR determination, and recrystallization). Students expand their skill set by developing their analytical, critical thinking, presentation, and teamwork skills which, in tandem, create a laboratory environment where students work together to solve problems.