טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMoses Nir
SubjectFabrication and Characterization of Composite Polypropylene
Fibers with Carbon Nanotubes
DepartmentDepartment of Chemical Engineering
Supervisor Professor Yachin Cohen
Full Thesis textFull thesis text - English Version


Abstract

Properties enhancement of polymers by addition of carbon nanotubes (CNT) is a widely investigated field in recent years due to their outstanding mechanical, electrical and thermal characters. Effective utilization of the nanotubes depends on the ability to achieve uniform dispersion of the carbon nanotubes in the polymeric matrix. The overall objective of this work is to investigate a method of multi-walled carbon nanotubes (MWCNT) incorporation into polypropylene (PP) by impregnation of the nanotubes from aqueous dispersion into porous PP beads (reactor product) and to subsequently fabricate and characterize PP/ MWCNT nanocomposite fibers.  In addition, 1,3:2,4-Di(3,4-dimethylbenzylidene)sorbitol (DMDBS), which is an efficient nucleating agent for PP, was added to the PP with MWCNT in order to investigate a possible mutual influence of the CNT and DMDBS on the morphological and physical properties of the composite.PP and MWCNT were mixed in the melt by extrusion, following two methods of preparation: dry-blending up to 1% (w/w) nanotubes loading with PP beads and impregnation of MWCNT from aqueous dispersion into porous PP beads and adsorption of the nanotubes onto the pore surface at content of 0.1% (w/w). Following the melt-blending samples were fabricated by compression molding into plates or by melt spinning of fibers. In order to use the impregnation method, relative high volumes of stable MWCNT aqueous dispersions were formed after sonication, using sodium dodecyl benzenesulfonate (NaDDBS) as dispersing agent. High resolution scanning electron microscopy (HRSEM) images of the plates’ cross-sections revealed that the nanotubes are organized in aggregates that have dimensions on the order of a few microns. Evaluation of the CNT dispersion in PP was done using small angle x ray scattering (SAXS), by calculating a nano-scale dispersion index (NSDI), which is the ratio between the integrated total scattering from a given sample to the expected value, based on its CNT content. The impregnation based samples achieved very high NSDI values (80%) which are ~60% higher than these obtained by dry blending method. The effect of MWCNT and DMDBS on oriented crystallization, long period parameter and mechanical properties was shown to be small.