Preparation of fully cross-linked CNBR/PP-g-GMA and CNBR/PP/PP-g-GMA thermoplastic elastomers and their morphology, structure and properties

Binary CNBR/PP-g-GMA and ternary CNBR/PP/PP-g-GMA thermoplastic elastomers were prepared by reactive blending carboxy nitrile rubber (CNBR) powder with nanometer dimension and polypropylene functionalized with glycidyl methacrylate (PP-g-GMA). Morphology observation by using an atomic force microscope (AFM) and TEM revealed that the size of CNBR dispersed phase in CNBR/PP-g-GMA binary blends was much smaller than that of the corresponding CNBR/PP binary blends. Thermal behavior of CNBR/PP-g-GMA and CNBR/PP blends was studied by DSC. Comparing with the plain PP-g-GMA, T, of PP-g-GMA in CNBR/PP-g-GMA blends increased about 10degreesC. Both thermodynamic and kinetic effects would influence the crystallization behavior of PP-g-GMA in CNBR/PP-g-GMA blends. At a fixed content of CNBR, the apparent viscosity of the blending system increased with increasing the content of PP-g-GMA. FTIR spectrum verified that the improvement of miscibility of CNBR and PP-g-GMA was originated from the reaction between carboxy end groups of CNBR and epoxy groups of GMA grafted onto PP molecular chains. Comparing with CNBR/PP blends, the tensile strength, stress at 100% strain, and elongation at break of CNBR/PP-g-GMA blends were greatly improved.

Viscous-force-dominated tensile deformation behavior of oriented polyethylene

High-density polyethylene with shish-kebab structure, prepared by a melt extrusion drawing, was employed to investigate the effect of the well-defined lamellar orientation on the deformation characteristics under uniaxial tensile deformation along the drawing direction. This was done by investigating the true stress-true strain dependencies at different strain rates, recovery properties, and stress relaxation measurements. Measurements were complemented by recording in-situ wide-angle X-ray scattering patterns during the deformation process. The oriented samples showed not only a higher modulus, but different from analogous isotropic samples, a homogeneous deformation without necking. The true strain associated with the onset of fibrillation was determined. Because of the preorientation, it is shifted to 0.3, which is below the value 0.6 of the isotropic counterpart. The main finding is a strong enhancement of the Viscous force, as was revealed by stress relaxation experiments; the viscous force takes up 70% of the total stress. The presence of shish-kebabs, i.e., interconnected lamellae in a stack, seems to be responsible for the high viscous force in the oriented samples. The absence of necking has to be ascribed to the high viscous force.

The effect of self-nucleation on structure and properties of iPP

The effects of self-seeding nucleation on the crystallization behavior and properties of polypropylene (iPP) were studied. DSC results indicated that the crystallization temperature of iPP increased obviously after the process of self-seeding nucleation. The results of polarized fight microscopy showed that the spherulite size decreased markedly, as a result, the mechanical properties and the transparency of iPP were all improved.

Homoepitaxial crystallization in films of a thermotropic liquid crystalline chloro-poly(aryl ether ketone)

The homoepitaxial crystallization in the films of a thermotropic liquid crystalline chloro-ply(aryl ether ketone) is studied by transmission electron microscopy (TEM) and electron diffraction (ED). The homoepitaxy takes place in the temperature range 330-320 degreesC, in which a highly-ordered smectic crystalline phase of the copolymer with a single-crystal-like banded structure is formed during the cooling process from the isotropic melt. The homoepitaxial crystallizations with angles of 32 degrees and 122 degrees between the two b axes are the major populations observed, and possess epitaxial contact planes of (100)(I)-(210)(II) and (010)(I)-(210)(II); respectively.

Studies on the morphology transition of micro-crystal growth in polymer films in high vacuum and strong electrostatic field

The morphology of films of isotactic polypropylene poly (3-dodecylthiophene) and iPP/P3DDT blend formed in electrostatic fields has been investigated by using scanning electron microscope. The experiment results show that the micro-crystal morphology of polymer films was strongly dependent on electrostatic fields. It was found that the effect of the electrostatic field led to the formation of dendrite crystals aligned in the field direction, and some branches of P3DDT ruptured. However, the micro-crystals in these films grew into spherulites without electrostatic field,and have no crystal orientation.

The effect of electrostatic field on the micro-crystal morphology of polymer films

The micro-crystal morphology of the films of isotactic polypropylene (iPP), poly(3-dodecylthiophene) (P3DDT) and iPP/P3DDT blend grown in different electrostatic environments has been investigated by using scanning electron microscope. The experimental results show that the micro-crystal morphology of polymer films was strongly dependent on electrostatic field. It was found that the micro-crystal morphology of the films of iPP, P3DDT and iPP/P3DDT blend grown in the electrostatic field was in the form of dendrite crystals, in which main stems were aligned in the field direction, and some branches of P3DDT were ruptured. However, the micro-crystals of the films of iPP, P3DDT and iPP/P3DDT blend have no crystal orientation in the absence of electrostatic field. (C) 2001 Elsevier Science Ltd. All rights reserved.

Epitaxial crystallization of sPP on the (100) lattice plane of HDPE crystals

Crystallization behavior of syndiotactic polypropylene(sPP) on the (100) lattice plane of high-density polyethylene(HDPE) crystals was studied by means of transmission electron microscopy and electron diffraction. The results indicate that sPP crystals can grow epitaxially on the (100) PE lattice plane with their chain directions +/-37 degrees apart from the chain direction of the HDPE substrate. The contact planes are (100) lattice planes for both polymers. This kind of epitaxy is explained in terms of parallel alignment of HDPE chains along the rows formed by the {CH3, CH2,CH3} groups in the (100) lattice plane of the sPP crystals. This implies that in the epitaxial crystallization of sPP with fiber oriented HDPE substrate, not only the (110) but also the (100) HDPE lattice planes can act as the oriented nucleation sites. Furthermore, according to the poor matching between HDPE chains in the (100) lattice plane and the {CH3, CH2, CH3} group rows in the (100) lattice plane of the sPP crystals, it is concluded that the geometric matching is not the only controlling factor for the occurrence of polymer epitaxy.

Novel morphology in ring-banded spherulites from single-phase mixtures of poly(epsilon-caprolactone) with poly(styrene-co-acrylonitrile)

Novel morphology of ring-banded spherulites in the surface of poly(epsilon-caprolactone)/poly(styrene-co-acrylonitrile) (PCL/SAN) blends was discovered and studied by SEM and TEM. The ring-banded spherulites separate into those exhibiting a very dark contrast, of relatively regular bundles of lamellae and others appearing with a much brighter intensity, of a coarse and irregular aggregates of lamellae. The origin of the novel morphology is not due to different crystalline structures as in the case of isotactic polypropylene because only one crystal structure exists in PCL/SAN blends. The formation may reflect whether spherulites in PCL/SAN blends are nucleated at the bottom surface or at the top (free) surface.

Epitaxial recrystallization of HDPE-quenched ultrathin films on oriented iPP substrates

The recrystallization behavior of high-density polyethylene (HDPE) on the highly oriented isotactic polypropylene (iPP) substrates at temperatures below the melting temperature of HDPE has been investigated by means of transmission electron microscopy. The results obtained by the bright-field observation and the electron diffraction show that upon annealing the HDPE-quenched films on the oriented iPP substrates at temperatures below 125 degrees C, only a small amount of HDPE recrystallizes on the iPP substrate with [001](HDPE)//[001](iPP), while annealing the HDPE-quenched films at temperatures above 125 degrees C, all of the HDPE crystallites recrystallize epitaxially on the iPP substrate with [001](HDPE)//[101](iPP). (C) 1997 John Wiley & Sons, Inc.

Isothermal crystallization of PP-g-GMA copolymer

The overall isothermal crystallization kinetics for neat polypropylene and grafted polypropylene systems were investigated. The rate constants were corrected assuming the heterogeneous nucleation and three dimensional growth of polypropylene spherulites. A semiempirical equation for the radial growth rate of polypropylene spherulites was developed as a function of temperature, and was used to determine the number of effective nuclei of different temperatures. The number of nuclei in grafted samples was estimated to be 10(2)-10(3) times larger than that of neat polypropylene. (C) 1997 John Wiley & Sons, Inc.

Effect of lamellar thickness on the epitaxial crystallization of PE on oriented iPP films

The effects of lamellar thickness on the epitaxial crystallization of polyethylene on the oriented isotatic polypropylene have been studied by means of transmission electron microscopy. The results obtained from the bright field electron microscopy and electron diffraction show that the epitaxial orientation of the PE crystals on the iPP substrate depends not only on the thickness of the oriented iPP lamellae, but also on the lamellar thickness of PE crystals. No epitaxial orientation relationship between PE crystal and iPP substrate can be found, when the PE crystals are thicker than the lamellar thickness of iPP along the matching direction. This suggests, that the epitaxial nucleation of PE in the PE/iPP epitaxial system is controlled not only by the chain-row matching, but also by a secondary nucleation process.

Growth rates of different polymorphs from interspherulitic boundary profiles

Quantitative data on the crystallization kinetics of polymorphic polymers can be derived from the investigation of gross spherulitic morphology formed in isothermal conditions. Depending on distance between centers, and the time lag between their formation and relative growth rates, various types of boundary lines can be generated by the impinging of two spherical bodies whose radii increase linearly with time, In polymorphic polymers, different types of spherulites often develop simultaneously at different rates from sporadic or predetermined nuclei. In same cases, the so-called growth transformation, in which a nucleus of the fast growing specie is formed at the tip of an advancing lamella of the slower crystal form, provides an alternative mode of nucleation, It is shown that if only one event of growth transformation takes place at the front of a slow growing body, the fast growing spherulite swallows the parent one and the resultant shape of interspherulitic boundary is described by two symmetrical logarithmic spirals whose parameters can be extracted from micrographs taken at the end of crystallization. These concepts are applied to determine the radial growth rate of gamma form spherulites of polypivalolactone in a wide range of temperatures through analysis of the alpha/gamma interspherulitic profiles formed in isothermal conditions and direct measurement of the growth rate of the alpha counterparts at the same temperature.

EPITAXIAL BEHAVIOR OF HDPE ON THE BOUNDARY OF HIGHLY ORIENTED IPP SUBSTRATES

The epitaxial crystallization behavior of high-density polyethylene on the boundary of highly oriented isotactic polypropylene (iPP) substrates has been investigated by means of atomic force microscopy (AFM) and transmission electron microscopy (TEM). The results obtained from AFM and TEM indicate that the epitaxial nucleation of HDPE on the highly oriented iPP substrates occurs earlier than that in the pure HDPE phase, i.e., homogeneous nucleation. Therefore the epitaxially grown HDPE lamellae can grow across the boundary of the iPP substrate into the HDPE spherulitic phase with the epitaxial orientation relationship remaining.

EFFECTS OF CRYSTALLIZATION RATES ON INTERFACE LAYER THICKNESS OF EPITAXIAL HDPE ON ORIENTED IPP

The effect of crystallization rate on the epitaxial interface layer thickness of high-density polyethylene (HDPE) in the epitaxial system with oriented isotactic polypropylene (iPP) has been investigated by electron microscopy. The results of bright-field