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.

Controlling factors for the occurrence of heteroepitaxy of polyethylene on highly oriented isotactic polypropylene

The controlling factors for the epitaxial crystallization of high-density polyethylene (HDPE) on highly oriented isotactic polypropylene (iPP) substrates have been studied in detail by means of transmission electron microscopy and electron diffraction. The results obtained in this work indicate that the crystallization process must be considered in the investigation of epitaxial growth of polymers on polymeric substrates, because of the unique morphological and crystallization characteristics of polymers. Crystallization rate has an important effect on the epitaxial crystallization of polymers. Higher rates result in the formation of thicker epitaxial layers. Isothermal crystallization temperature is another factor affecting epitaxial growth of polymers. Lower temperatures are favorable to epitaxial crystallization of polymers. There exists a critical epitaxial temperature at given experimental conditions, above which no epitaxial growth occurs at all. The influence of crystal dimensions of both the substrates and the deposited polymers on epitaxial growth confirms that secondary nucleation is an important controlling factor for the occurrence of epitaxial crystallization in polymers. The requirement satisfying the secondary nucleation criterion is that the substrate crystal dimension in the matching direction must be greater than the crystal thickness of the deposited polymer. Once the requirement of the secondary nucleation is satisfied, subsequent epitaxial growth is based on the lamellar growth habit of the deposited polymer itself. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.

Impact behavior of phenolphthalein poly(ether sulfone) ultrahigh molecular weight polyethylene blends

This work presents the structure and impact properties of phenolphthalein poly(ether sulfone) blended with ultrahigh molecular weight polyethylene (PES-C/UHMWPE) at different compositions. The addition of UHMWPE can considerably improve the Charpy and Izod impact strength of the blends. The fracture surface is examined to demonstrate the toughening mechanics related to the modified PES-C resin. (C) 1998 John Wiley & Sons, Inc.

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.

Morphology and mechanical properties of PP/HMWPE blends

Mechanical properties and morphology of blends of polypropylene (PP) with high molecular weight polyethylene (HMWPE) prepared by coprecipitation from xylene solution are investigated. Compared to blends of PP with commercial high-density polyethylene (HDPE), the mechanical properties of the blends of PP/HMWPE are much superior to those of PP/HDPE blends. Not only is the tensile strength stronger, but also the elongation at break is much higher than that of the PP/HDPE blends of the same composition. These differences increase with increasing HMWPE and HDPE content. Scanning electron microscopy of the fracture surface resulting from the tensile tests shows that the compatibility in PP/HMWPE blends is much better than that in PP/HDPE blends. This is most likely attributable to the enhanced chain entanglement of HMWPE with the PP in the amorphous phase due to the lower crystallinity, owing to the high molecular weight of the HMWPE, and a much more flexible chain. The thermal behavior and spherulite morphology of both blends are also investigated.

The fabrication and performance of an Ag/AgCl reference electrode in human serum

A simple set of electric circuits was used to assemble a pulse generator. With pulse potentials and under galvanostatical control, a clean silver wire was anodized electrochemically for 0.2-0.5 min in 1.0 moll(-1) HCl with a pulse current density of 20 mA cm(-2), and the pulse wave parameters of t(a)/t(c) = 1 and a cycle of 4 s forming an Ag/AgCl reference electrode. Even though the AgCl layer was consumed during the working period when the Ag/AgCl electrode was used as a cathode, the AgCl layer could be in situ recovered electrochemically in serum used when a reversed potential was applied to the electrode system immediately after the measuring program was finished. The current response curve of the anode indicated that an AgCl layer in high density was basically accomplished during the first 6 pulse cycles in human serum. In order to keep a stable and uniform AgCl layer on the reference electrode after each measuring cycle, the ratio of the recovery time (t(r)) to the working time (t(w)) was measured and the smallest value was obtained at 0.03. The open-circuit potential of the Ag/AgCl electrode with respect to a SCE in 0.1 moll(-1) KCl was monitored over a period of 14 days and the mean value was 40.09 mV vs SCE with a standard deviation of 2.55 mV. The potential of the Ag/AgCl reference electrode did remain constant when the measurements were repeated more than 600 times in undiluted human serum with a standard deviation of 1.89 mV. This study indicated that the Ag/AgCl reference electrode could been rapidly fabricated with a pulse potential and could be used as a reference electrode with long-term stable properties in human serum samples.

Studies on the electrical conductivity of carbon black filled polymers

The conductivity mechanism for a carbon black (CB) filled high-density polyethylene (HDPE) compound was investigated in this work. From the experimental results obtained, it can be seen that the relation between electrical current density (J) and applied voltage across the sample (V) coincides with Simmons's equation (i.e., the electrical resistivity of the compound decreases with the applied voltage, especially at the critical voltage). The minimum electrical resistivity occurs near the glass transition temperature (T-g) of HDPE (198 K). It can be concluded that electron tunneling is an important mechanism and a dominant transport process in the HDPE/CB composite. A new model of carbon black dispersion in the matrix was established, and the resistivity was calculated by using percolation and quantum mechanical theories. (C) 1996 John Wiley & Sons, Inc.

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.

MODIFICATION OF PP/HDPE BLENDS BY PP-PE SEQUENTIAL POLYMERIZATION PRODUCT

The morphology and mechanical properties of polypropylene/high-density polyethylene (PP/HDPE) blends in a wide range of compositions modified by a sequential Ziegler-Natta polymerization product (PP-PE) have been investigated. PP-PE contains multiple components such as PP, ethylene-propylene copolymer (EPC), and high molecular weight polyethylene (HMWPE). The effects of PP-PE on the mechanical properties and morphology of the PP/HDPE blends are the aggregative results of all its individual components. Addition of PP-PE to the blends not only improved the tensile strength of the blends, but the elongation at break increased linearly while the moduli were nearly unchanged. Morphological studies show that the adhesion between the two phases in all the blends of different compositions is enhanced and the dispersed domain sizes of the blends are reduced monotonously with the increment of the content of PP-PE. PP-PE has been demonstrated to be a more effective compatibilizer than EPC. Based on these results, it can be concluded that the tensile strength of the blends depends most on the adhesion between the two phases and the elongation at break depends most on the domain size of the dispersed component. (C) 1995 John Wiley & Sons, Inc.

EFFECT OF ETHYLENE-PROPYLENE COPOLYMER WITH RESIDUAL PE CRYSTALLINITY ON MECHANICAL-PROPERTIES AND MORPHOLOGY OF PP/HDPE BLENDS

Morphology and mechanical properties of polypropylene (PP)/high density polyethylene (HDPE) blends modified by ethylene-propylene copolymers (EPC) with residual PE crystallinity were investigated. The EPC showed different interfacial behavior in PP/HDPE blends of different compositions. A 25/75 blend of PP/HDPE (weight ratio) showed improved tensile strength and elongation at break at low EPC content (5 wt %). For the PP/HDPE = 50/50 blend, the presence of the EPC component tended to make the PP dispersed phase structure transform into a cocontinuous one, probably caused by improved viscosity matching of the two components. Both tensile strength and elongation at break were improved at EPC content of 5 wt %. For PP/HDPE 75/25 blends, the much smaller dispersed HDPE phase and significantly improved elongation at break resulted from compatibilization by EPC copolymers. (C) 1995 John Wiley & Sons, Inc.

PLASMA-INDUCED GRAFTING OF STYRENE ONTO NASCENT POLYETHYLENE POWDER

In this paper, the graft copolymers of styrene to nascent linear polyethylene reactor powders were prepared through plasma graft polymerization. The grafting reaction was initiated by the alkyl radicals formed on the surface of nascent polyethylene with plasma treatment as indicated by electron spin resonance spectra. In graft copolymerization by alkyl radicals, the grafting yield increased with either the plasma power or the plasma treatment lime. Compared with ordinary polyethylene powders, nascent polyethylene reactor powders were found to be more easily plasma-grafted. This has been attributed to the greater sensitivity to irradiation in producing reactive centres under the same conditions. High density polyethylene showed almost the same grafting yield as linear low density polyethylene at 50 degrees C. The surface morphology of nascent polyethylene observed by scanning electron microscope before and after the grafting showed that the silk-like fibrils were not destroyed by plasma treatment.

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

Functional biosynthesis of an allophycocyan beta subunit in Escherichia coli

Allophycocyanin is a phycobiliprotein with various biological and pharmacological properties. An expression vector was constructed using CpeS as the bilin lyase for the allophycocyanin beta subunit, resulting in overexpression of a fluorescent allophycocyanin beta-subunit in Escherichia coli. A high-density cell culture was developed using a continuous feeding strategy. After 16 h of culture, the dry cell density reached 21.4 g 1(-1), the expression of the allophycocyanin beta-subunit was 0.86 g l(-1) broth, and the relative chromoprotein yield was 81.4%. The recombinant protein showed spectral features similar to native allophycocyanin, which provide an efficient methodology for large-scale production of this valuable fluorescent protein. (C) 2008, The Society for Biotechnology, Japan. All rights reserved.

Construction and characterization of two bacterial artificial chromosome libraries of Zhikong scallop, Chlamys farreri Jones et Preston, and identification of BAC clones containing the genes involved in its innate immune system

Large-insert bacterial artificial chromosome (BAC) libraries are necessary for advanced genetics and genomics research. To facilitate gene cloning and characterization, genome analysis, and physical mapping of scallop, two BAC libraries were constructed from nuclear DNA of Zhikong scallop, Chlamys farreri Jones et Preston. The libraries were constructed in the BamHI and MboI sites of the vector pECBAC1, respectively. The BamHI library consists of 73,728 clones, and approximately 99% of the clones contain scallop nuclear DNA inserts with an average size of 110 kb, covering 8.0x haploid genome equivalents. Similarly, the MboI library consists of 7680 clones, with an average insert of 145 kb and no insert-empty clones, thus providing a genome coverage of 1.1x. The combined libraries collectively contain a total of 81,408 BAC clones arrayed in 212 384-well microtiter plates, representing 9.1x haploid genome equivalents and having a probability of greater than 99% of discovering at least one positive clone with a single-copy sequence. High-density clone filters prepared from a subset of the two libraries were screened with nine pairs of Overgos designed from the cDNA or DNA sequences of six genes involved in the innate immune system of mollusks. Positive clones were identified for every gene, with an average of 5.3 BAC clones per gene probe. These results suggest that the two scallop BAC libraries provide useful tools for gene cloning, genome physical mapping, and large-scale sequencing in the species.

Settling abalone veliger larvae in a free-swimming microalgal culture

In the current abalone hatchery in China, insufficient diatoms on vertically placed corrugated pvc plates at later stage often could not support the growth of postlarvae up to the stage that they can feed on live macroalgae. As a result, stripping the spats (35 mm) off by anaesthetization and switching the diet from live diatoms to artificial powdered diet in combination has to be performed in most of the abalone farms. This manipulation normally leads to more than 50% mortality. Here we report the direct use of the unicellular green alga Platymonas helgolandica Kylin var. tsingtaoensis as a potential alga to be used to settle the veliger larvae of the Pacific abalone Haliotis discus hannai and to feed the postlarvae. Settlement rate of 2-day-old veliger larvae in mono culture of P helgolandica could be as high as 92% ( +/- 4.2%) on day 10 in small scale trials, higher than that in the selected benthic diatom strain (53.6% +/- 12.7%) when settled in the water in which bacteria propagation was controlled by treatment of 2 ppm of benzylpenicillinum calcium and streptomycin sulfate. Postlarvae fed solely on P. helgolandica or the selected benthic diatom Navicula-2005-A grew at rates of 40.1 ( +/- 1.9) and 45.8 (+/- 13.4) mu m day(-1), respectively, when raised at 22 degrees C until day 50 postfertilization. P. helgolandica was shown to have distinct diurnal settling rhythm characterized with a peak of settled cells in the middle of the night for cell division and a peak of free-swimming cells in the middle of the day. High density of attached P. helgolandica cells on the inner surface of the culture facility in the night fits the nocturnal feeding behavior of the abalone spats. Judged by the promising larvae settling rate, growth and survival rates of the postlarvae fed with this alga, the free-swimming micro-green alga P. helgolandica constitutes a potential species for settling the veliger larvae and for supporting the growth of postlarvae as well. (c) 2006 Published by Elsevier B.V.