Synthesis and characterization of low density polyethylene (LDPE) reinforced with functionalized CNTs

A systematic approach was undertaken to increase strength, modulus, and toughness of low density polyethylene (LDPE) filaments through infusion of functionalized CNT and ultra high molecular weight polyethylene (UHMWPE). CNTs were functionalized with OH functional groups using chemical treatment. Functionalized CNTs and UHMWPE were first dry mixed with LDPE, and filaments were then drawn using a melt extrusion process. Loading of UHMWPE varied from 8-10 wt% while that of CNT was at 2-4 wt%. LDPE has been infused first with UHMWPE, and then with both UHMWPE and CNT, and filaments were extruded. Neat LDPE filaments were also extruded as control samples. Individual filaments from each category were tested under tension according to ASTM D3379-75. In addition, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) studies were also conducted to measure changes in thermal and crystalline behavior. Filament tests have revealed that the tensile elongation of LDPE can be increased by about 200% with the addition of 10 wt% UHMWPE. This is however, is accompanied by a loss of about 50% ultimate tensile strength. In the next step, when 2 wt% CNTs and 8 wt% UHMWPE are added, tensile strength of the composite filament is restored to the level of neat LDPE (∼25 MPa) with an increase in modulus by 44% and in ultimate fracture strain by about 60% compared to that of neat LDPE. The source of improvement has been traced as formation of copolymer between LDPE and UHMWPE and strong interfacial interaction between the CNT and the polymers.