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Polypropylene blends with polyhedral oligomeric silsesquioxanes (POSS) bearing different alkyl groups were investigated to elucidate the effect of the alkyl group length on the mechanical behavior of the blends. In particular, blends of polypropylene (PP) with either octamethyl-POSS, octaisobutyl-POSS, or isooctyl-POSS were studied. Differential scanning calorimetry evidenced only minor changes in the degree of crystallinity compared to neat PP. Uniaxial tensile tests showed that the incorporation of octamethyl-POSS induces an increase in Young’s modulus and a reduction of the yield strength in comparison with unfilled PP. By contrast, upon the incorporation of octaisobutyl-POSS and isooctyl-POSS, both Young’s modulus and the yield strength were found to decrease by increasing the POSS content. It is suggested that POSS behave as particles having a siliceous hard-core surrounded by a hydrocarbon soft-shell, which limits the stress transfer from the matrix to the core in dependence on the length of the alkyl groups. Finally, the essential work of fracture method was employed to study the fracture behavior of octamethyl-POSS/PP blends, with different POSS contents (0, 3, and 10 wt %)

Abstract. Interactive effects of carbon allotropes on the mechanical reinforcement of polymer nanocomposites were investigated. Carbon nanotubes (CNT) and nano-graphite with high shape anisotropy (nanoG) were melt blended with poly(1,4-cis-isoprene), as the only fillers or in combination with carbon black (CB), measuring the shear modulus at low strain amplitudes for peroxide crosslinked composites. The nanofiller was found to increase the low amplitude storage modulus of the matrix, with or without CB, by a factor depending on nanofiller type and content. This factor, fingerprint of the nanofiller, was higher for CNT than for nanoG. The filler-polymer interfacial area was able to correlate modulus data of composites with CNT, CB and with the hybrid filler system, leading to the construction of a common master curve.

The filler networking process promoted by multiwalled CNTs is studied in neat and CB-filled poly(1,4-cis-isoprene) matrices. TEM analysis, tensile, dynamic-mechanical, and electrical measurements reveal that the CNTs form a filler network at low concentration in neat PI and a continuous hybrid filler network at a lower CNT concentration in the presence of CB, with a remarkable increase of the nonlinear dynamicmechanical behavior of the nanocomposites at low deformation. A synergistic effect between CB and CNTs is demonstrated. The addition of CNTs to the CB-filled PI matrix leads to initial modulus values much larger than those calculated by simple addition of the two initial moduli of the composites containing only CB and only CNTs, respectively

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In this work, melt spinning experiments were tentatively used for the determination of the elongational viscosity of polymer melts at different levels of tensile strain and strain rate. The materials examined were two high-density polyethylene grades for blow moulding with similar number-average molecular mass but different polydispersity index. The data from melt spinning tests were compared with transient extensional viscosity data obtained by uniform isothermal tensile tests, performed by means of an extensional rheometer, as well as with those produced by converging flow tests (Cogswell model). The results showed that for high strain and strain rate levels, the melt spinning experiments provide elongational viscosity data quite close to the transient extensional viscosity values obtained from the tensile tests