The effect of nanoclays on the nucleation, crystallization, and melting mechanisms of isotactic polypropylene

Abstract

The influence of organomodified nanoclay (montmorillonite) on the crystallization and melting mechanisms of isotactic polypropylene (iPP) was studied. Films of both neat polymer and clay nanocomposites were prepared after molecular weight optimization through melt extrusion. Products exhibited the tactoidlike morphology since no compatibilizers were used. The effect of introduction of nanoclay within the polymer was studied through isothermal crystallization and linear heating. The results indicated that low nanoclay concentrations induce the formation of the β‐crystalline structure, its formation being inhibited with high nanoclay contents. Dynamic nonisothermal bulk crystallization experiments indicated that nanoclays act as nucleating agents of iPP. Isothermal, bulk crystallization studies indicated that the crystallization process (induction time and crystallization kinetics) is proportionally accelerated by the nanoclay presence. There was also an accelerated formation of secondary crystallization when nanoclays were present in high concentrations. POLYM. ENG. SCI., 47:1889–1897, 2007. © 2007 Society of Plastics Engineers

Mechanical performance of double gated injected metallic looking polypropylene parts

“…However, !-phase is occasionally observed during crystallization from melt. It can be obtained mainly by introducing specific nucleating agents in the melt using processing equipment such as extruders [13][14][15] incorporating an appropriate filler in micron and nanometer scale in the melt using internal mixers and extruders [16,17], inducing temperature gradients [18] and by shear forces in controlled flow fields [19][20][21]. A toughness improvement is associated to !-PP, being attributed to the development of a more perfect crystalline structure, with higher continuity of the amorphous phase and more connecting bridges between individual crystallites than a material containing solely "-crystallites [22]; and to the occurrence of a !-" transformation during loading which is accompanied with volume contraction in respect to the related crystallographic densities [23].…”

Solvent‐assisted extrusion of polypropylene/clay nanocomposites

“…It is well-known that the monoclinic form (a) presents a higher modulus, and the trigonal one (b) leads to a higher impact strength. Medellin-Rodriguez et al 23 detected the formation of b-crystalline structures in PP/clay nanocomposites and observed that the a form was the predominant structure, but the low clay concentration induced the formation of bcrystalline structures.…”

“…Flexural modulus tests were determined in an Instron Norwood, MA 4466 universal testing machine according to ASTM D 790. The Izod impact strength was determined at 23 C according to ASTM D 256 in a Resil Impactor Ceast Pianezza, Italy pendulum-type impact tester. The fracture surfaces of the Izod impact tested specimens were studied with scanning electron microscopy (SEM) in a JEOL JSM 6060 microscope operating at 10 kV.…”

Physical gelation process as direct evidence for crystallization behavior of isotactic polypropylene/clay composites

“…Avrami time constants were obtained by curve fitting on DSC experimental data for neat iPP crystallized at different temperatures 24 and iPP samples filled with 2 and 6 wt% of clay. 26 The modified Avrami model is examined to predict experimental crystallinity values of Misra et al's work. 17 Results in Figure 5 indicate that the proposed equation is capable of predicting crystallization behavior of PP clay composites up to 90% relative crystallinity.…”