Uni- and biaxial impact behavior of double-gated nanoclay-reinforced polypropylene injection moldings

摘要

Polypopylene/nanoclay three-dimensional parts wereproduced without intermediate steps by direct injectionmolding to explore the influence of flow features andnanoclay incorporation in their impact performance.The nanocomposite was obtained by direct compoundingof commercial PP with nanoclay masterbatch. Theas-molded morphology was analyzed by X-ray andTEM analyses in terms of skin-core structure andnanoclay particle dispersion. The nanoclay particlesinduced the reduction of b-form spherulites, a knowntoughener. The impact behavior was assessed in tensileand biaxial modes. The PP nanocomposite moldingtoughness was practically unaffected by the processingmelt temperature and flow rate. Conversely thenanoclay presence is influent in the impact performance.Under biaxial stress impact, the regions close toweld lines are tougher than the bulk and the fracturedevelops with main crack paths along the flow directionand the weld line. Cracking along the weld lineresults from less macromolecular interpenetration andchain entanglement, and unfavorable nanoparticle orientation.It seems that a failure mechanism whichinvolves nanoclay delamination and multiple matrixcrazing explains the toughening of PP in the directionswhere the nanoparticle orientation with respect toloading is adequate.