Study of an aramid surface reactivity: Modification with a cold plasma or an electron beam followed by a postgrafting reaction

Different modes of activation are described for a postgrafting reaction of acrylic acid on poly(p-phenylene terephthalamid) (PPTA)mitrogen plasma or electron-beam irradiation. Both lead to surface radical formation, and these species are able to initiate grafting. The Functionalization through amino group attachment is characteristic of plasma treatment. Degradation initiated by UV-visible emission of plasma is noticed, leading to the amide clivage. The surface grafting is more important when the PPTA is irradiated with a cold plasma and if water is used as the solvent. The polymer crystallinity degree reduces the grafting of the electron beam-irradiated PPTA even with a high radical concentration. © 1994 John Wiley & Sons, Inc.     

Plasma modification of cellulose derivatives as biomaterials

A film of cellulose acetate was submitted to a cold plasma of tetrafluoromethane or of sulfur hexafluoride. The interactions of these cold plasmas and cellulose acetate lead to a material whose surface has been modified by fluorination. Comparison of CF₄ or SF₆ plasma treatment shows that fluorine atoms provided by each kind of plasma induce degradation and grafting of fluorocarbon radicals on the surface. As a consequence, the surface energy decreases and offers the possibility of a better response of plasma-modified cellulose derivatives used as biomaterials (e.g. hemodialysis membrane).     

Pore microgeometry analysis in low-resistivity sandstone reservoirs

The objective of this work is to analyse the pore microgeometry and its effect on petrophysical properties in six low-resistivity sandstone reservoirs by combining a 2D quantitative petrographic image analysis (PIA) and 3D petrophysical tools. The classic petrophysical tools enable the measurement of different classic reservoir properties such as specific surface area, average pore diameter, pore size distribution, macroporosity and microporosity, capillary pressure versus saturation, pore chamber–pore throat diameter ratio, electrical properties and permeability. The petrographic image analysis quantifies pore microgeometry in more than four orders of magnitude, from submicron to millimeter scale. Chloritic low-resistivity sandstones show dual porosity structure defined as chloritic texture. The pore microgeometrical parameters measured by petrographic image analysis allow one to model different reservoir properties such as capillary pressure, permeability and electrical behaviour. The results obtained in these models show that pore microgeometry plays an important role in the physical properties of low-resistivity sandstone reservoirs.     

Chemical modification of epoxy resins by dialkyl(or aryl) phosphates: Evaluation of fire behavior and thermal stability

The improvement of flame-retardation of thermosetted epoxy–amine resins was attempted by chemically incorporating phosphorus-containing reagents. By reacting 4,4′-diglycidylether of bisphenol A (DGEBA) with dialkyl (or aryl) phosphate, it was possible to chemically modify the epoxy resin and then cure it in the presence of 4,4′-diaminodiphenylsulfone (DDS) to obtain epoxy-amine resin with good flame-retardant and thermal stability behaviors. The quantitative aspect of the addition of dialkyl (or aryl) phosphate onto glycidyle oxiranes was evaluated by elemental analysis of the modified epoxy-amine resins. Flammability and thermal behaviors of modified DGEBA/DDS resins depend on the nature of phosphate groups (the best flame-retardation was observed on resins bearing phenyl phosphate groups) and their concentration in the material. In relation to DGEBA/DDS samples containing additives of the same structure [trialkyl(or aryl) phosphate], cured resins incorporating chemically bonded phosphate groups show a better flame-retardation. On the contrary to the nonomodified DGEBA/DDS [with or without trialkyl (or aryl) phosphate as additive], combustion of modified DGEBA/DDS resins is accompanied by formation of intumescent char. Chemical modification of DGEBA by dialkyl (or aryl) phosphates can be carried out in situ during the curing of epoxy resins without change in the fire behavior. © 1996 John Wiley & Sons, Inc.     

Effect of multi-walled carbon nanotubes on the lamellae morphology of polyamide-6

We show that crystal organization on both micro and nanoscales can be profoundly modified by dispersing carbon nanotubes (CNTs) in polyamide-6 by melt compounding. X-ray diffraction and transmission and scanning electron microscopies all indicate that when CNTs are well dispersed, crystalline spherulites are not present and remarkably crystalline lamellae grow aligning perpendicularly to the surface of the nanotubes. Such an epitaxial growth induced by CNTs during melt processing is particular to polyamide-6 because of crystallographic matching of CNTs and polyamide-6 crystal lattices. Macroscopically this epitaxial nucleation and growth can be detected and quantified by examining the splitting of the exothermic peak in calorimetric (DSC) experiments. Using optical microscopy and image analysis we show that the amount of trans-crystalline epitaxial crystallites increases when CNTs' dispersion quality is improved.     

Mechanical and electrical properties of multi walled carbon nanotube/ABC block terpolymer composites

Composites of multi-walled carbon nanotubes (MWCNTs) in ABC block terpolymer matrices of different compositions are studied. The composites were obtained by dispersion of MWCNTs in poly(styrene-block-butadiene-block-methyl methacrylate) (SBM) in a selective solvent for the M block, followed by solvent evaporation and compression molding. The structures of the MWCNT/SBM composites are investigated by transmission electron microscopy. The processing conditions, i.e. solvent cast or compression molding, induce different non-equilibrium microstructures and the MWCNTs modify the SBM organization only locally. We show that by fixing the processing procedure we are able to obtain samples with reproducible microstructure and properties. The electrical conductivity thresholds of these composites are lower than 1 wt.%. The reinforcing effect of the MWCNTs measured by dynamical mechanical analysis is mainly related to the SBM microstructures of the matrix and to the MWCNT dispersion quality.     

Alkoxylation of epoxidized polyisoprene by opening of oxirane rings with alcohols

Alkoxylation of epoxidized polyisoprene catalyzed by cerium ammonium nitrate (CAN) was achieved under very mild conditions both in melt and in solution. The cleavage of the epoxidized units with alcohols leads to the formation of alkoxyalcohol units and epoxide rearrangement units in the case of 20 and 38 % epoxidized 1,4‐polyisoprenes. For higher percentage of epoxidation (72 %), cyclization of epoxidized units is observed, which dramatically reduces the alcohol grafting percentage onto the polymer chains. The glass transition temperature increase with the percentage of alkoxylation is attributed to both alkoxy and hydroxyl groups formed after the ring opening of the epoxidized units. However, size‐exclusion chromatography analysis of the modified polymers showed a decrease in the number‐average molecular weight and an increase in the weight‐average molecular weight, which can be interpreted as the degradation and crosslinking of the polymer chains, respectively. Copyright © 2004 Society of Chemical Industry     

Modification of isotactic polypropylene by a cold plasma or an electron beam and grafting of the acrylic acid onto these activated polymers

Surface grafting of polymeric materials, such as films and fibers, may improve their reactive surface properties. Polypropylene active sites that should initiate a surface postgrafting can be formed by either nitrogen cold plasma or an electron-beam irradiation. The plasmamodified polymer surface is cross-linked and functionalized with primary amino groups and with oxidized groups, and it is almost not degraded. Electron-beam-modified polypropylene is also functionalized through an aging reaction, emphasized by a high radical concentration. In both cases, active surface films are susceptible to react with monomers in a postgrafting reaction. The grafting yield and rate of acrylic acid were shown to be dependent on the formed amino group concentration: The hydrophilic character of the modified polypropylene surface enhances the acrylic acid approach. The electron-beam treatment leads also to a reactive surface that can initiate a grafting reaction. But its yield and rate are dependent on the radical concentration: radicals formed during the irradiation. © 1994 John Wiley & Sons, Inc.