Evaluation of the Impact Resistance of POM/TPU/CB Three-Phase Nanocomposite for Application in Bumper Bracket

 The effect of carbon black nanoparticles and thermoplastic polyurethane on the tensile strength and impact properties of polyacetal (POM), which is widely used in the application of automotive parts such as bumper brackets, has been investigated. Improving the impact resistance of polyacetal is one of the challenges of automotive industry, which would diminish the car damage in accidents. The incorporation of thermoplastic polyurethane into the polyacetal matrix can create good compatibility and increase its impact resistance. In addition, the presence of carbon block in the polyacetal matrix can simultaneously elevate the tensile strength and impact resistance and increase the UV resistance of polyacetal.

Standard mechanical testing specimens of the POM/CB/TPU nanocomposites, containing 0.42% (by wt) carbon black and different fractions of 2.5, 5 and 7.5 % (by wt) of thermoplastic polyurethane (TPU) were produced through a twin-screw extruder and injection molding. Standard tensile and impact tests were performed to evaluate the mechanical performance of nanocomposites. The morphology of fractured surfaces of impact specimens and the toughening mechanisms were investigated using scanning electron microscopy (SEM). 

The results of tensile test showed that the presence of carbon black nanoparticles increases the Young's modulus and the tensile strength of polyacetal. However, the inclusion of thermoplastic polyurethane into the POM/CB reduced the tensile behavior. The incorporation of a phase with soft segments to the polymeric matrix with hard segments reduces the tensile strength. In addition, the carbon black and the thermoplastic polyurethane increase the elongation-at-break of this three-phase nanocomposite. The results of impact test showed that the presence of carbon black nanoparticles and thermoplastic polyurethane in the polyacetal matrix leads to enhanced impact resistance. Plastic deformation, crazing, fibrillated structure and microvoid were the dominant toughening mechanisms in nanocomposites.