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Melt Spun PET/CNT Nanocomposite Fibers: Effect of CNT and Post Drawing Process on the Mechanical Properties



Carbon nanotubes (CNT) have found profound interest in advanced material composites due to its exceptional properties. With the modulus of elasticity in the range of 1.2 TPa and the strength of 60 GPa, it plays a vital role in strengthening the relatively softer plastics and acts as a good reinforcing element. However, the reinforcing CNT needs to be well distributed in the polymer matrix and to a greater extent is to be well aligned along the longitudinal direction. The issue of CNT distribution can be addressed by using an extruder with good mixing capability, such as a twin screw extruder. The alignment of the CNT in the matrix can be achieved by adopting a suitable processing method, such as a fiber melt spinning process. The high draw ratio of melt spinning process is well known for producing highly oriented polymer molecules and in analogy, it is expected to highly orient the nanotubes. However, considering the fact that the CNT has very low density, it is possible that the CNTs are partially aligned during the melt spinning process. Thus, there is a need to further post process the composite in order to utilize the reinforcing element properties to its maximum extent. In the current study, a co-rotating twin screw extruder with 3 zones of mixing elements was used to produce nanocomposite fibers (PET/CNT) of polyethylene terephthalate (PET) and carbon nanotubes (CNT). The polymer and CNT are fed by two separate feeders. The polymer is fed at the entrance, whereas the CNT is fed at three different positions on the extruder barrel where the mixing zones are located. A constant CNT concentration of 1wt% was considered for the present study. The melt spun fibers were later post drawn in solid state at a speed of 50 mm/min at room temperature. The addition of 1 wt% CNT enhanced the mechanical properties of PET/CNT nanocomposite fibers and this has been discussed in our previous studies. Further, the post drawing of these fibers is expected to have a better alignment of CNT within the matrix. This leads to an increase of 340% in modulus value of the 1wt% PET/CNT nanocomposite fibers. The tensile strength was enhanced by 390% and the yield strength by 85% in comparison to the nanocomposite fibers before drawing. This huge increase in mechanical properties of PET/CNT nanocomposite fibers is attributed to the presence of CNT, its distribution and alignment in the PET matrix as shown in the scanning electron microscope (SEM) images.

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