Excellent mechanical properties of carbon nanotubes (CNTs) make them outstanding candidate
reinforcements to enhance mechanical properties of conventional composites. The glass/polyester
composites are widely used in many industries and applications. Improving the mechanical properties of
such composites with addition of CNTs can increase their applications. In this research, multi-walled carbon
nanotube (MWCNT) at different weight ratios (0.05, 0.1, 0.3, 0.5 wt.%) were added to chopped strand mat
(CSM)/Polyester composites. Mechanical stirring with the aid of sonication technique were used to achieve a
good dispersion state of MWCNTs in the polymeric matrix. The specimens were fabricated by the hand layup
method. It is assumed that a high level of dispersion in the preparation stage may lead to better
mechanical properties of the nanocomposite. Scanning electron microscopy (SEM) was employed to
determine the dispersion state of carbon nanotubes in the matrix. Mechanical tests (tensile and flexural) were
performed in order to evaluate the effects of adding MWCNT on CSM/Polyester composites. The results
exhibit improvements in flexural strength while the values of tensile strength do not show significant
changes. Although addition of filler at all above ratios increased the flexural strength, introducing only 0.05
wt.% MWCNT into the CSM/Polyester composites enhanced the flexural strength by 45%. Moreover,
improvements in Young's and flexural moduli were observed.