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

Abstract

Polypopylene/nanoclay three-dimensional parts were produced without intermediate steps by direct injection molding to explore the influence of flow features and nanoclay incorporation in their impact performance. The nanocomposite was obtained by direct compounding of commercial PP with nanoclay masterbatch. The as-molded morphology was analyzed by X-ray and TEM analyses in terms of skin-core structure and nanoclay particle dispersion. The nanoclay particles induced the reduction of b-form spherulites, a known toughener. The impact behavior was assessed in tensile and biaxial modes. The PP nanocomposite molding toughness was practically unaffected by the processing melt temperature and flow rate. Conversely the nanoclay presence is influent in the impact performance. Under biaxial stress impact, the regions close to weld lines are tougher than the bulk and the fracture develops with main crack paths along the flow direction and the weld line. Cracking along the weld line results from less macromolecular interpenetration and chain entanglement, and unfavorable nanoparticle orientation. It seems that a failure mechanism which involves nanoclay delamination and multiple matrix crazing explains the toughening of PP in the directions where the nanoparticle orientation with respect to loading is adequate. POLYM. ENG. SCI., 53:724-733, 2013. FIG. 7. Depth sensing indentation results. (a) Typical indentation load-penetration depth curves for PP-6 sample in the skin and core. (b) Er and H profiles through the thickness for PP-6 sample. (c) Average values of Er as a function of MB content in the skin and core. (d) Average values of H as a function of MB content in the skin and core. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

Characterization of PP/TPV/MMT Ternary Nanocomposites Produced by Injection Molding

“…In our previous investigations conducted on PP/organoclay nanocomposite moldings – carried out on pieces that included a weld line – we found that nanoclay induces changes in the morphology developed upon processing . It enhances molecular orientation induced by flow increasing the level of crystalline phase orientation in the flow direction.…”

“…[12] In our previous investigations conducted on PP/organoclay nanocomposite moldingscarried out on pieces that included a weld linewe found that nanoclay induces changes in the morphology developed upon processing. [13][14][15] It enhances molecular orientation induced by flow increasing the level of crystalline phase orientation in the flow direction. To find out the influences of the weld lines and of the complex flow upon final properties, fracture toughness was evaluated at different locations of the parts and a spatial distribution of toughness was found.…”

Trends in the multifunctional performance of polyolefin/clay nanocomposite injection moldings

“…In order to reproduce in-service conditions, the impact performance was assessed by means of uniaxial tensile (in-plane) and biaxial flexural (out-of-plane) tests [69] (Figure 6.6). In order to reproduce in-service conditions, the impact performance was assessed by means of uniaxial tensile (in-plane) and biaxial flexural (out-of-plane) tests [69] (Figure 6.6).…”

“…Visual inspection of biaxially impacted samples showed that the orientation of polymer molecules and clay platelets induced by melt flow prevailed, and the weldline was not the determinant of the toughness of the moldings (Figure 6.8). Cracking along the weldline results from less macromolecular interpenetration and chain entanglement, and unfavorable nanoparticle orientation [69]. The same moldings were fractured using mode-I double-edge-notched tensile specimens.…”

Polypropylene/Clay Nanocomposites Produced by Shear Controlled Orientation in Injection Moulding: Deformation and Fracture Properties

“…Manufacturing of PP/ nanoclay composites using conventional injection moulding (CIM) is not an easy task. Mouldings usually displayed poor nanoclay dispersion since the imposed thermomechanical conditions do not generate large enough stress fields to deagglomerate/ exfoliate the clay agglomerates completely [7] and [8]. Besides poor dispersion, the presence of voids and defects in thick specimens is a common feature in many industrial mouldings.…”