Melt Spun LLDPE/CNT Nanocomposite Fibers: Effect of CNT and Ultraviolet (UV) Degradation on Mechanical Properties

Polymers are susceptible to degradation when exposed to radiations. These radiations reduce the life span of the polymer products. Many natural and synthetic polymers are attacked by ultraviolet (UV) radiations and products made using these materials may crack or disintegrate, and is a common problem in products exposed to sunlight. Continuous exposure is a more serious problem than intermittent exposure, since attack is dependent on the extent and degree of exposure. Carbon nanotube (CNT) is a good candidate to counter the degradation of polymers. In this study, special fibers of linear low-density polyethylene (LLDPE/CNT) nanocomposite, with good strength, are melt spun using a twin screw extruder with multi mixing elements and a 10 hole-spinneret. These nanocomposite fibers are processed from the melt at 275 degrees C and a mass flow rate of 1.9 g/min. Specially made aligned-carbon nanotubes are used with an average diameter of 30 nm and an average length of 500 mu m. These CNTs are mixed with LLDPE melt in three consecutive mixing stages inside the twin screw extruder. This three stage mixing process produces nanocomposite fibers with well dispersed CNT in the LLDPE matrix. Nanocomposite fibers of pure LLDPE reinforced with 1 wt% of carbon nanotubes were artificially exposed to UV rays for 1000, 3000 and 10,000 minutes. Effect of UV exposure was analyzed by mechanical testing and DSC analysis. The mechanical properties such as yield stress, tensile strength and modulus of LLDPE/CNT were relatively stable for up to 3000 minutes of UV exposure compared to pure LLDPE fibers. There was a significant degradation in mechanical properties of pure LLDPE with increase in UV exposure time. With the addition of CNT to LLDPE, the UV degradation was prevented up to 3000 minutes exposure. Initially, with the addition of CNT the mechanical properties of the nanocomposite fibers decrease, however, upon exposure to UV rays for 10,000 minutes, the yield stress, tensile strength and modulus of 1 wt% LLDPE/CNT were found to be 20%, 79% and 33% higher compared to pure LLDPE fibers, respectively. The CNT based LLDPE nanocomposite has less degradation compared to the pure LLDPE.