Showing papers by "South China University of Technology published in 2000"

Rubber toughening in polypropylene: A review

Abstract: The recent advances in the studies of the toughening methods and theories of polypropylene (PP)–elastomer blends are reviewed in the present article. Inclusions are key to toughening PP; they can play the role of agent-induced crazing, cause shear yielding of the matrix around them, and end the propagation of cracks. The major theories interpreting the toughening mechanisms of the blends are: multiple crazing, damage competition theory, shear-yielding theory, microvoids, and cavitation theories. The factors affecting the toughening effect are relatively complicated. Therefore, these theories have been verified only in some cases when they have been applied in relevant conditions. To achieve the objective of better toughening, it is important to improve the uniform distribution of dispersed-phase particle size and suitable filler size, as well as improving the dispersion of the inclusions formed in the matrix; in addition the matrix materials or fillers must be functional with suitable modifier in order to enhance the interfacial adhesion or to improve the interfacial morphological structure between the filler and matrix. However, the exact toughening mechanisms for PP–rubber blends have to be studied further because of complications resulting from the crystallinity of the matrix. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 409–417, 2000

Preparation and characterization of poly(vinyl acetate)-intercalated graphite oxide nanocomposite

Abstract: Graphite oxide, a pseudo-two-dimensional solid in bulk form, was synthesized from natural graphite powder by graphite oxidation with KMnO4 in concentrated H2SO4. Poly(vinyl acetate) intercalated graphite oxide nanocomposite was prepared by an in situ intercalative polymerization reaction, in which an n-octanol–graphite oxide intercalation compound was first obtained, vinyl acetate monomer was then dispersed into the interlayer of the modified graphite oxide, followed by thermally polymerizing the monomer. It was experimentally shown that the c-axis spacing increased to 1.152 nm when poly(vinyl acetate) was intercalated into the interlayer space of the graphite oxide. Thermal analysis and FT-IR spectrometry were also used to characterize the nanocomposite. The extractability of the intercalated poly(vinyl acetate) and the electrical properties of the nanocomposite were evaluated.

Relationship between water absorbency and reaction conditions in aqueous solution polymerization of polyacrylate superabsorbents

Abstract: Polyacrylate superabsorbents were prepared by in situ aqueous solution polymerization in a polyethylene bag, which was submerged in a water bath. The influence of the initiator content, bath temperature, isopropanol content, initial monomer concentration, and crosslinker content (Cc) on water absorbency (Q) were investigated. The temperature change of the monomer mixture during polymerization was also analyzed. Increase of the chain ends in networks resulting from decrease of the molecular weight in free-radical polymerization causes an increase of the water absorbency of superabsorbents and also reduces the crosslinking efficiency. The results are in conformity with the classical network theory. An empirical relation of Q = 2.45 Cc−0.600 was obtained and the validity of Flory's swelling equation was confirmed indirectly. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 808–814, 2000

A study of pyridinium‐type functional polymers. IV. Behavioral features of the antibacterial activity of insoluble pyridinium‐type polymers

Abstract: The antibacterial activity of insoluble pyridinium-type polymers with different structures against Escherichia coli suspended in sterilized and distilled water was investigated by a colony count method. The results show that the antibacterial activity of insoluble pyridinium-type polymers, except for one containing I−, is characterized by an ability to capture bacterial cells in a living state by adsorption or adhesion, with the process of capturing bacterial cells being at least partially irreversible. This feature differs from the antibacterial activity of the corresponding soluble polymers, which is characterized by the ability to kill bacterial cells in water. In addition, insoluble pyridinium-type polymers can also capture dead bacterial cells. This implies that insoluble pyridinium-type polymers possess broad prospects for development in new water treatment techniques and whole-cell immobilization techniques. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 676–684, 2000

Analysis of the structure of lignin-carbohydrate complexes by the specific13C tracer method

Abstract: In the present study the specifically13C-enriched lignin precursors of biosynthesis (i.e., coniferin-[side chainα−13C], coniferin-[side chain-β−13C] and coniferin-[side chain-γ−13C]) were synthesized and administered exogeneously to ginkgo shoots (Ginkgo biloba L.) to obtain13C-enriched lignin-carbohydrate complexes (LCCs). The specifically13C-enriched LCCs were isolated from the newly formed xylem of ginkgo shoots administered with the13C-enriched precursors and degraded by enzymes. Lignin-rich fractions, so called enzyme-degraded LCCs (EDLCCs), were obtained. By determining their13C-NMR spectra, information related to the chemical structure of lignin building units and linkages between phenylpropane units of lignin and carbohydrates were obtained. It was found that these precursors were incorporated in natural lignin successfully. Three lignin-carbohydrates linkages (i.e., ether type, ester type, ketal type) were found at the Cα-position of the side chain of phenylpropane units in ginkgo LCC. No lignin-carbohydrate bond at the Cβ- or Cγ-position of the lignin side chain was observed in the13C-NMR spectra of the13C-enriched LCCs. This fact indicates that a specific13C tracer technique can be useful in NMR study of the chemical structure of LCCs.

Laser remelting of plasma sprayed Al2O3 ceramic coatings and subsequent wear resistance

Abstract: This paper deals with the laser melting of Al2O3 and Al2O3+13wt.%TiO2 ceramic coatings deposited by atmospheric plasma spraying. After laser melting, metastable phase γ-Al2O3 transforms into stable phase α-Al2O3 in Al2O3 coatings, whereas in Al2O3+13wt.%TiO2 coatings besides this phase transformation, TiO2 may react with Al2O3 and transform into TiAl2O5. The melting layer becomes much denser and, hence, its hardness has been greatly developed despite the existence of some cracks. Furthermore, the increase in hardness of the melting layers is almost independent of coating type and generally increases with the laser energy density. However, the coating type has a strong influence on the thickness of the laser melting layers. As to the coatings with the same coating type, the depth of laser melting roughly increases with the laser energy density. Finally, it has been found that the introduction of TiO2 can improve the wear resistance of ceramic coatings, particularly, of the melting layers, although TiO2 reduces the hardness of these ceramic coatings.

Effect of filler content and surface treatment on the tensile properties of glass-bead-filled polypropylene composites

Abstract: The tensile properties of polypropylene (PP) filled with two A-glass beads with the same size, PP/3000 (glass bead surface pretreated with a silane coupling agent) and PP/3000U (no surface pretreatment), have been measured by using an Instron materials testing machine at room temperature, to identify the effects of the filler surface pretreatment and its content on the tensile properties of these composites. The results show that the Young's modulus Ec of the composites increases non-linearly with increasing volume fraction of glass beads ϕf, while the tensile yield strength σyc and tensile stress at break σbc of the composites decrease with an increase of ϕf, in the ϕf range 0–30%. Furthermore, the values of Ec and σbc of the PP/3000 system are somewhat higher than those of the PP/3000U system under the same test conditions, but this is in contrast to the tensile strain at break ebc and tensile fracture energy Ebc, especially at higher ϕf values. Good agreement is shown between the measured tensile strength and the predicted value by using an equation proposed in previous work. In addition, ebc and Ebc reach maximum values at ϕf = 25% for both systems. This indicates that there is a brittle–ductile transition for the composites in tension. © 2000 Society of Chemical Industry

A study of pyridinium-type functional polymers. III. Preparation and characterization of insoluble pyridinium-type polymers

Abstract: The copolymers of 4-vinylpyridine (4VP), styrene (St) and divinylbenzene (DVB) with varied compositions, P(4VP-St-DVB), were synthesized by suspension polymerization using 2,2'-azobisisobutyronitrile (AIBN) as an initiator. The insoluble (crosslinked) pyridinium-type polymers in benzyl-pyridinium bromide form, which possess various macromolecular chain compositions, were prepared by the reaction of each P(4VP-St-DVB) with benzyl bromide (BzBr), respectively. By using different halohydrocarbon RX in the quaternization of P(4VP-St-DVB), the insoluble pyridinium-type polymers with various pyridinium group structures were obtained. The structures of P(4VP-St-DVB) and its quaternized product Q-P(4VP-St-DVB) were identified by FTIR. The 4VP content in each copolymer P(4VP-St-DVB) was measured by nonaqueous titration; and the pyridinium group content (C q ) in each Q-P(4VP-St-DVB) sample was determined by means of the back titration manner in argentometry and/or the elemental analysis method, respectively. In addition, the particle structure and the surface morphology of the thus-prepared polymer were observed using SEM. According to a series of experimental results, the preparation and characterization of insoluble pyridinium-type polymers are analyzed and discussed. This work can prepare the ground for a study on the antibacterial activity of insoluble pyridinium-type polymers.

Study of modified polypropylene nonwoven cloth. II. Antibacterial activity of modified polypropylene nonwoven cloths

Abstract: Removal of E. coli from water by modified polypropylene (PP) nonwoven cloths which were prepared through radiation-induced grafting of 4-vinyl pyridine (4-VP) onto PP nonwoven cloths and followed by quaterization was carried out by filtration. The results showed that the content and structure of the pyridinium group on PP nonwoven cloths were important factors to affect their antibacterial activity. The antibacterial activity increased with the number of piled sheets of the used nonwoven cloths and decreased with increase of the viable bacterial cell concentrations in the influent and with filtration rates. The activity detection results found that modified PP nonwoven cloths possessed the ability to capture the bacterial cell alive, and no morphological changes of adhered bacterial cells were observed using SEM; thus, the surfaces of the modified PP nonwoven cloths may not be bactericidal, but bacteriostatic.

Hybrid image coding based on partial fractal mapping

Abstract: The fractal image compression technique models a natural image using a contractive mapping called fractal mapping in the image space. In this paper, we demonstrate that the fractal image coding algorithm is compatible with other image coding methods. In other words, we can encode only part of the image using fractal technique and model the remaining part using other algorithms. According to such an idea, a new mapping in the image space called partial fractal mapping is proposed. Furthermore, a general framework of fractal-based hybrid image coding encoding/decoding systems is presented. The framework provides us with much flexibility for real implementations. Many different hybrid image coding schemes can be derived from it. Finally, a new hybrid image coding scheme is proposed where non-fractal coded regions are used to help the encoding of fractal coded regions. Experiments show that the proposed system performs better than the quadtree-based fractal image coding algorithm and the JPEG image compression standard at high compression ratios larger than 30.

Microstructure evolution of laser clad layers of W–C–Co alloy powders

Abstract: Clad layers using high power carbon dioxide laser and various powder compositions of W, C, Co and WC on carbon steel substrate have been investigated. Microstructures of the clad layers are greatly affected by the processing parameters: powder size; powder type; shielding gas; degree of dilution; and geometry of the clad layer. Clad layers with large WC particles in a eutectic matrix and a high hardness, or with a mostly eutectic structure and low hardness, can be made for applications of cutting tools or wear resistant surfaces, respectively. Microstructure such as: (1) WC, Co 3 W 3 C, and a binary eutectic mixture of Co 3 W 3 C and α-(Fe,Co); (2) Co 3 W 3 C and a binary eutectic mixture of Co 3 W 3 C and α′-(Fe,Co); (3) a binary eutectic mixture of Co 3 W 3 C and α′-(Fe,Co) have been produced in the clad layer.

Trader dynamics in a model market

Abstract: We explore various extensions of Challet and Zhang's Minority Game in an attempt to gain insight into the dynamics underlying financial markets. First we consider a heterogeneous population where individual traders employ differing "time horizons" when making predictions based on historical data. The resulting average winnings per trader is a highly non-linear function of the population's composition. Second, we introduce a threshold confidence level among traders below which they will not trade. This can give rise to large fluctuations in the "volume" of market participants and the resulting market "price".

A novel self-optimizing approach for knowledge acquisition

Abstract: The attribute reduction and rule generation (the attribute value reduction) are two main processes for knowledge acquisition A self-optimizing approach based on a difference comparison table for knowledge acquisition aimed at the above processes was proposed In the attribute reduction process, the conventional logic computation was transferred to a matrix computation along with some added thoughts on the evolution computation used to construct the self-adaptive optimizing algorithm In addition, some sub-algorithms and proofs were presented in detail In the rule generation process, the orderly attribute value reduction algorithm (OAVRA), which simplified the complexity of rule knowledge, was presented The approach provided an effective and efficient method for knowledge acquisition that was supported by the experimentation

Swelling behaviors of polyacrylate superabsorbent in the mixtures of water and hydrophilic solvents

Abstract: The swelling behaviors of polyacrylate superabsorbent in the mixtures of water and hydrophilic solvents, including methanol, ethanol, ethylene glycol, glycerol, acetone, dimethyl formamide, and dimethyl sulfoxide, were investigated. In 20 wt % solvent–water mixture, the superabsorbent with granularity between 40- and 80-mesh could reach swelling equilibrium at 25°C in several hours. It was also found that mixture temperature between 15 and 35°C had little influence on absorbency. Furthermore, the influence of water temperature between 0.5 and 99°C on absorbency was also rather limited when the superabsorbent was swelled by distilled water. The mixture concentration influenced absorbency significantly by changing the solubility parameter of the solvent–water mixture, particularly when the solubility parameter of the solvent–water mixture was 20, whereas the absorbing capacity of the superabsorbent was very low when the solubility parameter was < 17.5. The polarity fraction of solvents did not have any obvious influence on equilibrium absorbency, but not enough polarity fraction might affect the absorbing rate. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1331–1338, 2000

Synthesis and characterization of solid-phase graft copolymer of Polypropylene with styrene and maleic anhydride

Abstract: Polypropylene (PP) was modified by solid-phase graft copolymerization with maleic anhydride (MAH) and styrene (St), using benzoyl peroxide as the initiator and xylene as the interfacial agent. Effects of various factors such as monomer concentration, monomer ratio, initiator concentration on grafting percentage, and acid value were investigated. The graft copolymer was characterized by Fourier transform infrared, pyrolysis gas chromatography—mass spectroscopy, and dynamic mechanical analysis, and the intrinsic viscosity of the extractive from the reaction product was investigated. The results showed that the grafting percentage and acid value of the graft copolymer of PP with two monomers (MAH and St) were considerably higher than those of the graft copolymer of PP with MAH alone. The graft segments were shown to be the copolymer of St and MAH with a substantial molecular weight. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2482–2487, 2000

Blind extraction of singularly mixed source signals

Abstract: This paper introduces a novel technique for sequential blind extraction of singularly mixed sources. First, a neural-network model and an adaptive algorithm for single-source blind extraction are introduced. Next, an extractability analysis is presented for singular mixing matrix, and two sets of necessary and sufficient extractability conditions are derived. The adaptive algorithm and neural-network model for sequential blind extraction are then presented. The stability of the algorithm is discussed. Simulation results are presented to illustrate the validity of the adaptive algorithm and the stability analysis. The proposed algorithm is suitable for the case of nonsingular mixing matrix as well as for singular mixing matrix.

Impact fracture behavior of PP/EPDM/glass bead ternary composites

Abstract: The effects of glass bead filler content and surface treatment of the glass with a silane coupling agent on the room temperature impact fracture behavior of polypropylene (PP)/ethylene-propylene-diene monomer copolymer (EPDM)/glass bead(GB) ternary composites were determined. The volume fraction of EPDM was kept constant at 10%. The impact fracture energy and impact strength of the composites increased with increasing volume fraction of glass beads (Φ g ). Surface pretreatment of the glass beads had an insignificant effect on the impact behavior. For a fixed filler content, the best impact strength was achieved when untreated glass beads and a maleic anhydride modified EPDM were used. The impact strength exhibited a maximum value at Φ g = 15%. Morphology/impact property relationships and an explanation of the toughening mechanisms were developed by comparing the impact properties with scanning electron micrographs of fracture surfaces.