The effect of clay on the nucleating behavior of 1,3：2,4-bis（3,4-dimethylbenzylidene） sorbitol （DMDBS） in cryatallization of isotactic polypropylene （iPP） was investigated by means of differential scanning calorimetry （DSC）, dynamic rheology and polarized light microscopy （PLM）. It is interesting to note that the incorporation of layered clay nanoparticles into DMDBS-nucleated iPP may induce a synergetic nucleation effect while the DMDBS content is below 0.1 wt%, otherwise it restricts the crystallization rate prominently as the DMDBS content increases up to 0.3 wt%, which has exceeded the content threshold to yield a nucleating agent （NA） network. As shown by dynamic rheological investigations, the clay nanoparticles demonstrate an obstructive effect of disturbing the consistency of DMDBS fibrils network. Moreover, to further demonstrate the importance of NA network formation in the crystallization of iPP, we used another NA named HPN-20e, which can not form network structure at all over the concentration studied, for comparison. In this case, the nucleated-crystallization rate is independent on the addition of clay nanoparticles, as the nucleating mechanism is an individual nuclei manner without NA network forming.
In this study, four hydroxyl-terminated polydimethylsiloxanes （PDMSOH） with different viscosities and hydroxyl contents were used to improve the toughness of polycarbonate （PC） through reactive melt blending. A largely improved toughness of PC has been achieved, and the low temperature toughness of PC/PDMSOH blends could overtake that of PC homopolymer in much higher temperatures （e.g. -10 ~C versus 23 ~C）. Moreover, it was found that the more the hydroxyl content, the less the PDMSOH was needed to reach the highest toughness, suggesting that equivalent molar ratio between the carbonyl group content of PC and the hydroxyl group content of PDMSOH was required for the toughening of PC. Ultraviolet spectrophotometry was used to analyze the possible reaction between PC and PDMSOH. Contact angle was measured to assess the change of interfacial interaction between PC and PDMSOH as change of viscosity and hydroxyl content. The formation of PC-co-PDMSOH copolymer was believed to be the key for the toughening effect. This work gives a profound recommendation of the optimum kind and dosage of PDMSOH which should be used to improve the toughness of PC and will find immediate industrial applications.
The combined effects of stretching and single-walled carbon nanotubes （SWCNTs） on crystalline structure and mechanical properties were systematically investigated in melt-spun polypropylene （PP） fibers prepared at two different draw ratios. The dispersion, alignment of the SWCNT bundles and interfacial crystalline structure in the composite fibers are significantly influenced by the stretching force during the melt spinning. The nanohybrid shish kebab （NHSK） superstructure where extended PP chains and aligned SWCNT bundle as hybrid shish and PP lamellae as kebab has been successfully obtained in the composite fibers prepared at the high draw ratio and the related formation mechanism is discussed based on the results of morphological observations and 2d-SAXS patterns. Large improvement in tensile strength and modulus has been realized at the high draw ratio due to the enhanced orientation and dispersion of SWCNT bundles as well as the formation of NHSK.
